Market and Technology Assessment Natural Gas Compressors

U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Building Technologies Program

December 17, 2014TABLE OF CONTENTS

1. INTRODUCTION

................................ ................................ ................................ .................. 4
1.1 Authority and Background

................................ ................................ .................... 5
1.2 Compressors Under Consideration

................................ ................................ ........ 5 Compressor Types

................................ ................................ ........................... 7 1.2.1 Prime Mover Types

................................ ................................ ......................... 8 1.2.2 Compressor Systems

................................ ................................ ....................... 8 1.2.3
1.3 Equipment Definitions

................................ ................................ .......................... 9 Natural Gas Compressor Package

................................ ................................ ... 9 1.3. 1 Compression Unit

................................ ................................ ............................ 9 1.3.2
Prime Mover

................................ ................................ ................................ .... 9 1.3.3 Reciprocating Natural Gas Compression Unit

................................ ................ 9 1.3.4 Centrifugal Natural Gas Compression Unit

................................ .................. 10 1.3.5 Axial Natural Gas Compression Unit

................................ ............................ 10 1.3.6
1.4 Efficiency Metrics

................................ ................................ ............................... 10 Compressor Unit Efficiency

................................ ................................ .......... 10 1.4.1 Thermal Efficiency

................................ ................................ ........................ 10 1.4.2 Heat Recovery

................................ ................................ ............................... 11 1.4.3 Gas Efficiency

................................ ................................ ............................... 11 1.4.4
1.5 Test Procedures

................................ ................................ ................................ ... 11
1.6 Rulemaking Analyses Process Overview

................................ ............................ 12
2. MARKET AND TECHNOLOGY ASSESSMENT

................................ ............................. 15
2.1 Market Assessment

................................ ................................ ............................. 15 Manufacturers Participating in U.S. Market

................................ ................. 15 2.1.1
Small Businesses

................................ ................................ ........................... 16 2.1.2 Packagers and Installers

................................ ................................ ................ 16 2.1.3
Trade Associations

................................ ................................ ........................ 17 2.1.4 Regulatory Programs

................................ ................................ ..................... 18 2.1.5 Nonregulatory Programs

................................ ................................ ............... 20 2.1.6 Shipments and Value

................................ ................................ ..................... 21 2.1.7
2.2 Technology Assessment

................................ ................................ ...................... 24 Overview of Compressor Technologies

................................ ........................ 24 2.2.1 Compressor Package Efficiency

................................ ................................ ... 31 2.2.2 Compressor Losses

................................ ................................ ........................ 33 2.2.3 Technology Options for Improving Efficiency

................................ ............. 38 2.2.4
3. SCREENING ANALYSIS

................................ ................................ ................................ ... 45
3.1 Te chnological Feasibility

................................ ................................ .................... 45
3.2 Practicability to Manufacture, Install, and Service

................................ ............. 45
3.3 Adverse Impacts on Product or Equipment Utility or Availability

..................... 45
3.4 Adverse Impacts on Health or Safety

................................ ................................ .. 46
LIST OF ITEMS FOR COMMENT

................................ ............................... 47 APPENDIX A

- REFERENCES

................................ ................................ ................................ 51 APPENDIX B

-LIST OF TABLES AND FIGURES

Figure 1.1 Schematic Diagram of a Typical Compressor Package

................................ ................ 7 Table 1.1 Overview of Currently Available Compressor Test Procedures

................................ .. 12 Figure 1.2 Flow Diagram of Standards Rulemaking Process

................................ ...................... 14 Table 2.1 Major Gas Compressor Manufac turers

................................ ................................ ......... 15 Table 2.2 Summary of Natural Gas Sector Compressor Activity

................................ ................. 21 Table 2.3 Annual Compressor Station Compressor Package Shipments by Year

........................ 22 Table 2.4 Annual Compressor Station Compressor Package Shipments by HP Range for 2009 to
2013

................................ ................................ ................................ ................................ ...... 23
Table 2.5 2012 North American Reciprocating Engine Orders

................................ .................... 23 Table 2.6 Typical Performance Ranges

– Reciprocating Compressors 1

................................ ..... 25 Table 2.7 Typical Performance Ranges

– Centrifugal Compressors 1

................................ .......... 26 Table 2.8 Typical Performance Ranges

– Reciprocating Gas Engines 1,14

................................ ... 27
Table 2.9 Typical Performance Ranges

– Gas Turbines 1,14

................................ ......................... 28 Table 2.10 Characteristic Electric Motor Efficiency 14

................................ ................................ 28 Table 2.11 Representative Efficiencies of Various Compressor Technologies 1

.......................... 32 Figure 2.1 Prime Mover Efficiency by Rated Horsepower

................................ ......................... 33LIST OF ACRONYMS

AEC annual energy consumption
AEO Annual Energy Outlook
ANSI American National Standard Institute

API American Petroleum Institute
BLS Bureau of Labor Statistics

BT Building Technologies Program
CAIR Clean Air Interstate Rule
CAMR Clean Air Mercury Rule
CFD computational fluid dynamic
CFR Code of Federal Regulations
CO 2 carbon dioxide
DOE U.S. Department of Energy
DOJ U.S. Department of Justice

EERE Office of Energy Efficiency and Renewable Energy

EIA Energy Information Administration
EISA E nergy Independence and Security Act of 2007

EPA U.S. Environmental Protection Agency
EPCA Energy Policy and Conservation Act

EU European Union
FFC full

- fuel cycle

FR Federal Register
GHG greenhouse gas
GREET Greenhouse Gases, Regulated Emissions, an d Energy Use in Transportation
GRIM Government Regulatory Impact Model

HAP hazardous air pollutant Hg mercury HI Hydraulic Institute

HP horsepower
HVAC heating, ventilating, and air conditioning
ImSET Impact of Sector Energy Technologies
ISO Inte rnational Organization for Standardization kg kilograms
kW kilowatt
LCC life

- cycle cost
MPC manufacturer production cost
MSP manufacturer selling price

MIA manufacturer impact analysis
NIA national impact analysis
NEMS National Energy Modeling System
NES national energy savings
NESHAPs national emissions standards for hazardous air pollutants
NOPR notice of proposed rulemaking
NO X oxides of nitrogen

NPV net present valueOEM original equipment manufacturer
OMB Office of Management and Bud get
PBP payback period

PM particulate matter
R&D research and development

RFI request for information

rpm revolutions per minute
SCC social cost of carbon
SG&A selling, general, and administrative costs
SO 2 sulfur dioxide
TSD technical support d ocument U.S. United States
U.S.C. United States Code
VSD variable speed drive

1. INTRODUCTION

The U.S. Department of Energy (DOE) Appliances and Equipment Standards Program, within the Office of Energy Efficiency and Renewable Energy’s Building Technologies Program (BT), develops and promulgates test procedures and energy conservation standards for certain consumer appliances and commercial and industrial equipment. The process for developing standards involves analysis, public notice an d comment, and consultation with interested parties. Interested parties include manufacturers, consumers, energy conservation and environmental advocates, State and Federal agencies, and any other groups or individuals having an interest in
these standards and test procedures.

To inform its decision making regarding the possibility of developing efficiency standards for new natural gas compressors, DOE issued a request for information, comment, and supporting data about the characteristics, applications an d energy use of gas compressors (RFI). Following up on the RFI, t his Market and Technology Assessment (MTA) document has two primary purposes. The first is to overview the preliminary information that DOE has gathered
from the RFI and other sources concer ning the market for and technology of compressors in advance of a public meeting to be held on December 17, 2014. At this meeting, DOE will invite interested parties to review information in this document, and to discuss the impact of potential
standards t o the industry and to the natio n. The second aim of this MTA document is to describe the legal context as well as some of the procedural and analytical approaches DOE us es in considering potential new energy conservation standards. As such, the document is intended to encourage and facilitate the input of interested parties and serves as the starting point for evaluating energy conservation standards or energy use standards . It is not a definitive statement on any issue to be determined in the rulemaking.

This document is organized in the following manner. Section 1 lays out a number of background issues, including DOE’s statutory authority with respect to compressors, the scope of coverage under consideration, definitions, metrics to describe compressor ef ficiency, test procedures to measure compressor efficiency, and DOE’s rulemaking process. S ection 2describes the market for compressors (section 2.1 ) and the technology related to co mpressor efficiency (section 2.2 ). S ection 3 describes how DOE would evaluate technology options for improving compressor efficiency, including how factors such as safety, reliability, manufacturability, consumer util ity, and other variables would be considered . Appendices A and
B summarize ar eas that DOE plans to seek input , and sources cited in assembling this document.

DOE will maintain information about this rulemaking on its Office of Energy Efficiency and Renewable Energy (EERE) website at: http://www1.eere.energy.gov/buildings/appliance_standards/commercial/commercial_industrial_

compressor s.html

.

1.1 Authority and Background

Title III of the Energy Policy and Conservation Act, 42 U.S.C. § 6291, et seq., (EPCA) sets forth a variety of provisions designed to improve the energy efficiency of products and commercial equipment. (All references to EPCA refer to the statute as amende d through the American Energy Manufacturing Technical Corrections Act (AEMTCA 2012), Pub. L. 112

- 210 (December 18, 2012)). Part C of Title III (42 U.S.C. §§ 6311−6317), which was subsequently re

designated as Part A

– 1 for editorial reasons, establishes an energy conservation program for certain industrial equipment, which includes compressors, the subject of today’s writing. (42
U.S.C. § 6311(2)(B)(i)) Unlike some other types of equipment included in EPCA, the term “compressors” is undefined.

Section 341 of EPCA, 42 U.S.C. § 6312, provides a general statement of purpose to improve the efficiency of a variety of industrial equipment to conserve the energy resources of
the Nation. That provision permits the Secretary of Energy to classify by rule certain e quipment as covered equipment if a determination is made that doing so is necessary to carry out the purposes of Part A

- 1 of EPCA. As a result, DOE is considering extending coverage to compressors used in the natural gas infrastructure, provided such compr essors meet the general EPCA criteria for coverage.

1.2 Compressors Under Consideration

At the time of publication of this document, DOE is exploring the energy savings opportunity associated with natural gas compressors and has not established which, if any,

compressors to consider regulating . DOE is aware that natural gas compressors appear in a wide variety of applications. As noted in the Request for Information (RFI) published on August 5, 2014 (79 FR 25377), DOE believes the transmission and distribution of natural gas to be one of the largest applications for natural gas compressors. As a result, DOE has focused its initial research efforts on natural gas compressor technologies used in the national pipeline
infrastructure for the transmission and distrib ution of natural gas. DOE remains committed to investigating opportunities throughout the natural gas supply chain including the gathering, processing, transmission and storage market segments.Although DOE’s initial efforts have centered around transmis sion and distribution compressor equipment, increased industry focus on shale gas has led to increased installation of compressors used for extraction and process. Compressors used in the upstream, on average, are smaller in physical size and higher in ope rating speed than transmission compressors, and therefore inherently less efficient. More significantly, a sizeable portion of the upstream industry is serviced by contracted compressors that are designed to be versatile, readily available in short
lead ti me, and reliable, but are not necessarily optimally sized for a given installation. Upstream compressors are generally not controlled as well as the larger transmission compressors that have more sophisticated control systems and load control means. Preval ent control methods are inefficient in that they recirculate flow or reduce pressure that has been previously compressed. Most upstream compressors are driven by natural gas engines, which use process gas as fuel, taken from the stream prior to the sales m eter. Accordingly, upst r eam operators and are not incented to be concerned with compression efficiency, per se. Taking these factors into consideration, the upstream and process areas are believed to hold the greatest opportunity for efficiency improvement , especially when new compressors, rather than retrofits, are considered for future regulation. The Department remains committed to investigating opportunities throughout the natural gas supply chain including the gathering, processing, transmission and

st orage market segments.

The Appliances and Equipment Standards Program has the authority to regulate products on the basis of their physical and f unctional product definitions. Whereas there can be a strong correlation between a product’s physical attribut es and the applications in which it is used, once these physical attributes are defined, the standards generally apply to the product regardless of the application in which it is ultimately used. Thus what would distinguish a “covered” gas compressor from one exempt from standards, is not where it is used but the specific physical and functional definition of the covered product. The sections that follow present general technology descriptions of compressors and compressor components. These descriptions are broad and
would be tailored as necessary to regulate equipment when economically justified to do so.

Natural gas compressors have two primary components : the compression unit in which compression actually occurs, and the prime movers, which provide mecha nical power to the compression unit . The compression units are typically reciprocating, centrifugal, or axial, while the prime movers are normally reciprocating gas engines, gas turbines, or electric motors

. Figure

1

. 1 illustrates the schematic diagram of a typical gas turbine

- driven centrifugal compressor gas compression package

. Sections 1.2.1 and 1.2.2 describe the compressor types and the prime

movers most common to natural gas transmission and distribution.Figure 1

. 1 Schematic Diagram of a Typical Compressor Package

Compressor Types 1.2.1

1.2.1.1 Reciprocating

Reciprocating compressors use pistons traveling linearly to compress a trapped volume of gas, which is then allowed to escape using check valves. Reciprocating compressors may be “integral” with or inseparable , i.e. “separable” from their prime mover

. Relative to centrifugal or axial compressors, reciprocating compressors are thought to be more efficient across different output levels but to carry greater maintenance requirements. 1 13 Reciprocating compressors, whether integral or separable, are usually driven by reciprocating gas engines or electric motors.

1.2.1.2 Centrifugal

Centrifugal compressors use rotating impellers to compress gas perpendicula rly to the direction of rotation against a stationary housing. Relative to reciprocating compressors, centrifugal compressors are thought to be less efficient across different output levels, but to offer reduced maintenance requirements. 1 13 Relative to axial compressors, centrifugal compress ors tend to exist in lower flow and higher pressure applications. Centrifugal compressors are usually driven by gas turbines or electric motors.

1.2.1.3 Axial

Axial compressors use rotating vanes to compress gas parallel to the axis of vane
rotation. Relative to r eciprocating compressors, axial compressors are thought to be less efficient across different output levels, but to offer reduced maintenance requirements. 1 13 Relative to centrifugal compressors, axial compressors tend to exist in high fl ow and lower pressure applications. Axial compressors are usually driven by gas turbines or electric motors.Prime Mover Types 1.2.2

INGAA Error! Bookmark not defined. describes the more prevalent types of prime movers drivers) which ar e used in pipeline applications: reciprocating gas engines, gas turbines and
electric motors.

1.2.2.1 Reciprocating Gas Engine

Reciprocating gas engines use pistons to harness ene rgy from combusted gas in a trapped volume, which is then expelled using valves. Relative to gas turbines, reciprocating gas engines are thought to be more efficient across different output levels but to carry greater maintenance requirements. Reciprocatin g gas engines are typically used to drive reciprocating compressors.

1.2.2.2 Gas Turbine

Gas turbines use rotating vanes or impellers to harness energy from a flow of combusted gas. Relative to reciprocating gas engines, gas turbines are thought to be less efficient across different output levels, but to offer reduced maintenance requirements. Gas turbines are typically used to drive centrifugal or axial compressors.

1.2.2.3 Electric Motor

Electric motors use electrical energy to create magnetic fields that rotate a shaft. Electric motor efficiency is less straightforward to compare with that of reciprocating engines or gas turbines, because it requires knowledge of how the electricity was generated. Relative to other prime movers, electric motors offer the greatest efficiency across output levels and the lowest maintenance requirements. Additionally, electric motors generate no on

- site emissions and little acoustic noise, and for those reasons may be preferred in populated areas where sufficient electric power is ava ilable

.

Compressor System s 1.2.3

There may be greater potential for energy savings if the energy conservation standards
addressed compressor s as a system of components. Compressor systems are subject to a variety of inefficiencies, and those inherent in the comp ressor unit are often among the smallest. As a result, addressing other system inefficiencies may offer the greatest opportunity for cost

- effective energy savings.

DOE is considering the following options for regulation depending on how compressor s are de fined and sold:

1. Defining and establishing standards for the compressor unit exclusive of the prime mover. This option would likely involve a metri c such as isentropic efficiency of compression.

2. Defining and establishing stand ards for packages shipped including both a compressor
unit and a prime mover and, potentially, auxiliary equipment.3. Defi ning and establishing design requirements for compressors or compressor packages

, that mandate certain technology be used or avoided.

1.3 E quipment Definitions

The term “compressors” is undefined by EPCA. As part of a Department of Energy Request for Information (RFI) published on August 5, 2014 (79 FR 25377) and related to the air compressors rulemaking , DOE considered a variety of definitio ns for this term in order to help ensure a reasonable level of clarity with respect to the type of equipment that might be regulated. In its ongoing proceeding, DOE offered for comment the several definitions for “ natural gas compressors” to clarify the co verage of any potential test procedure or energy conservation
standard.

However, DOE recognizes that air and natural gas compressors may have considerable technological differences, even when the categories (e.g., “reciprocating) used to describe them

are apparently similar. For the purpose of this assessment, then, reciprocating and centrifugal compressors will be defined per the definitions below :

Natural Gas Compressor Package 1.3.1

A “natural gas compressor package ” is defined to be a set of equipment that is used to increase the pressure of natural gas and includes, but is not limited to, the compression unit, the prime mover , and associated auxiliary hardware including controls, sensors, vents, and measures for safety and maintenance

.

Compression Unit 1.3.2

A “compression unit” is defined to be the assembly that uses mechanical input power to perform physical compression of natural gas. A compression unit is powered by a prime mover. In certain cases (e.g., integral reciproc ating compressors) the compression unit and the prime mover may be part of the same assembly.

Prime Mover 1.3.3

A “prime mover” is defined to be the assembly that consumes electrical energy , thermal energy from natural gas combustion , or another source of input energy in order to supply the mechanical power used for natural gas compression. In certain cases (e.g., integral reciprocating compressors) the compression unit and the prime mover may be part of the same assembly.

Reciprocating Natural Gas Compress ion Un it 1.3.4

A “reciprocating compressor” is defined to be a natural gas compressor that pe r forms compression on an enclosed volume of gas using a piston traveling linearly.Centrifugal Natural Gas Compress ion Unit 1.3.5

A “centrifugal compressor” is a type of natural gas compressor in which the flow enters the compressor in an axial direction (parallel with the axis of rotation) and exits in the radial direction (perpendicular to the axis of rotation). Compression is achieved by first using a rotating
radial imp eller to a ccelerate the gas and impart kinetic energy. Then a stationary diffuser is used
to transform the increased kinetic energy into pressure rise . The diffuser may or may not contain fixed vanes. A centrifugal compressor may contain one or more sets (stages) of alternating impellers and diffusers, and these stages will be located within a static housing.

Axial Natural Gas Compress ion Unit 1.3.6

An “axial compressor” is a type of natural gas compressor in which the flow enters and exits the compressor in an axial direction (parallel with the axis of rotation). Compression is achieved by first using a row of rotating airfoils to accelerate the gas and impart kinetic energy. Then a row of stationary airfoils is used to diffuse the gas and transform the increased kin etic energy into pressure rise . An axial compressor may contain one or more sets (stages) of alternating rotating and stationary airfoils, and these stages will be located within a static housing.

1.4 Efficiency Metrics

To establish a metric that could be used to determine the efficiency of a gas compressor, DOE reviewed currently available metrics used within industry. DOE will continue to research and seek comment on efficiency metrics, along with additional metrics not in this section, with regard to their a pplicability to gas compressors and current use in industry. DOE recognizes that not all of the terms below may have agreed

- upon metrics that would enable standards, but presents them to enable an organized discussion of energy

- saving opportunities.

Compr essor unit efficiency and thermal efficiency are discussed in INGAA’s Interstate Natural Gas Pipeline Efficiency, in relation to compressors and compressor drivers respectively,
and are described as follows.

Compressor Unit Efficiency 1.4.1

As applied to natural gas compressor units, compressor efficiency measures how much energy is expended in compressing the gas compared to how much overall energy is used by the compressor. Inefficient compressors heat the gas more than do efficient compressors while raising it s pressure and thus have lower efficiency values. 2 This relationship may be express ed as isentropic efficiency, a dimensionless parameter reflecting how close a compressor comes to the theoretical physical maximum.

Thermal Efficiency 1.4.2

As applied to a prime mover (engine, turbine or motor) that drives a compressor, thermal efficiency measures how much of the potential energy of an input fuel or electric power is converted into useful energy that can be used to drive a compressor. The maj ority of energy thatis not converted into useful energy is considered “waste heat” in the exhaust

, cooling and lubrication systems. 2

Heat Recovery 1.4.3

Both compressors and prime movers generate waste heat in compression and combustion, respectively. Using waste heat either directly or to generate electrical power may be economical, depending on compressor type and size. Heat recovery is sometimes lumped in compressor unit or prime mover efficiency values. Because the savings materialize remotely, where the heat or generated electrical power is consumed, it may be useful to consider that savings separately.

Gas E fficiency 1.4.4

As applied to a natural gas compr essor or any of its subcomponents, gas efficiency reflects how effective a compressor is at retaining natural gas

. Natural gas may escape in a variety of ways, including through seals or packing, uncombusted

, in the exhaust stream, through valves, or any o ther hardware in the compressor package. DOE is not aware of an established metric to quantify gas efficiency. Logically, it could be represented as the mass flow of gas leaving the equipment divided by the mass flow of gas entering the equipment, discount ing the gas used as fuel. Although not commonly discussed as efficiency, improving this parameter would enable a compressor to deliver more natural gas for a given energy consumption.

A special case of gas loss comes during compressor “blowdown,” when the unit is intentionally depressurized during periods of maintenance or low demand. The pressurized gas may be flared, stored, or simply vented to the atmosphere. The U.S. Department of Transportation , which is responsible for gas pipeline safety, currently requires that compressor emergency shutdown be tested annually, which also entails blowing down the unit. For units frequently blown down a (e.g., peak demand units), aggregate lost gas may be significant.

1.5 Test Procedures

Manufacturers must use a DOE prescr ibed test procedure to establish compliance if any standards are adopted and make representations of energy efficiency for gas compressors. DOE
would also use that verify the performance of covered equipment if standards are established.

Thus, in conjunction with considering setting standards for gas compressors, DOE is also considering whether to develop a test procedure that would be applied to all potentially covered

gas compressors. The test procedure would likely include an efficiency descriptor and the methods necessary to adequately measure the performance of the compressor for the purposes of determining compliance with energy conservation standards.

When establishing or amending test procedures, DOE reviews existing industry test procedures currently used to measure the energy use or energy efficiency of the covered equipment. DOE then considers whether to: (1) adopt a test procedure(s) in its entirety, (2) adopt

a I.e., having undergone blowdown, which is when a compressor intentionally depressurized during periods of maintenance or low demand. Blowdown usually results in a large amount of wasted gas and energy.portions of a test procedure(s) with modification or additions, or (3 ) develop a new test procedure if existing test procedures do not provide necessary energy use or efficiency methods necessary to calculate DOE’s energy use or efficiency metrics. In addition, DOE’s test procedures consider a variety of factors, including ambient test conditions, repeatability and tolerances on test conditions and results, and test equipment calibration and accuracy. Table 1.1
shows a n umber of test procedures that relate to gas compressors for which DOE is considering establishing standards.

Table 1

. 1 Overview of Currently Available Compressor Test Procedures

Test Procedure Origin

API 617 Axial and Centrifugal Compressors

and Expander

- Compressors U.S.

ASME PTC

- 10 Performance test Code on

Compressors and Exhausters U.S.

ASME PTC

- 09 Displacement Compressors,

Vacuum Pumps And Blowers U.S.

ISO1217:2009 Displacement Compressors

– Acceptance Tests International

ISO5389:2005 Turbocompressors

–

Performance test code International

In addition to these test procedures

, DOE is aware of guidelines published by the Gas Machinery R esearch Council and Southwest Research Institute

, which provide s suggested best practices for field testing of reciprocating, and centrifugal compressors 3 4

DOE will review these test procedures, along with additional test procedures that may not
be listed in Table 1.1 . Additionally, DOE will seek comment on the appropriateness of adopting these procedures, either in whole or in part, as a basis for a DOE test procedure. If DOE adopts test procedures for gas co mp ressors, it will seek to align these procedures to the greatest extent practicable with those that are already widely used by industry to limit manufacturer burden s

.

1.6 Rulemaking Analyses Process Overview

While DOE has not yet determined if it will be developing efficiency standards for new natural gas compressors , should it decide to do so, the process that it will follow is described
below

.The analyses conducted in support of a rulemaking ensure that, if standar ds are established, DOE selects standards that achieve the maximum improvement in energy efficiency that is technologically feasible and economically justified and will result in significant energy savings, as required by EPCA. Economic justification inclu des the consideration of the factors set forth in EPCA, which encompass the economic impacts on domestic manufacturers and consumers, national benefits including environmental impacts, issues of consumer utility, and impacts from any lessening of competiti on.

Error! Not a valid bookmark self

- reference. summarizes the analytical components of
the DOE standards

- setting process. The analyses are presented in the center column. Each analysis has a set of key inputs, which are data and information required for the analysis. “Approaches” are the methods that DOE will use to obtain key inputs. The results of each analysis are key outputs, which feed directly i nto the rulemaking. Arrows indicate the flow of information between the various analyses. DOE ensures a consistent approach to its analyses throughout the rulemaking by considering each analysis as a part of the overall standard

- setting
framework.Figure 1

. 2 Flow Diagram of Standards Rulemaking Process2. MARKET AND TECHNOLOG Y ASSESSMENT

The market and technology assessment provides information about the natural gas

compressor industr y and the performance attributes of this equipment. DOE may use this assessment to determine equipment classes and identify potential design options or efficiency levels for each equipment class.

2.1 Market Assessment

DOE’s market assessment identifies and characterizes the manufacturers of gas compressors, estimates market shares and trends, and addresses regulatory and non

- regulatory initiatives intended to improve the energy efficiency or reduce the energy consumptio n of the gas

compressors that DOE may consider regulating

.

The market assessment allows DOE to gather data that can help identify important issues (e.g., potential small business impacts, competitive disruptions, and other factors that may arise
from ena cting standards). For example, market structure data can be used to assess competitive impacts as part of the manufacturer impact analysis.

DOE considers manufacturers, industry organizations, and other interested parties as potential sources of such inf ormation. In addition, DOE is considering examining national market reports or data collected in national energy use surveys, or extrapolating historical compressor sales data from the U.S. Census Bureau. In addition to these sources

, DOE will seek

comment on other sources of data that may help characterize the gas compressor market.

Manufacturers Participating in U

. S

. Market 2.1.1

Nine manufacturers represent the majority of the natural gas compressor market within the scop e of this assessment , and are listed i n Table 2.1

.

Table 2

. 1 Major Gas Compressor Manufacturers

Manufacturer Compressor Types Manufactured Reciprocating Centrifugal Ariel Corporation X Burckhardt Compression b X

Cameron X

Dresser

- Rand Group X X

G E Oil & Gas X X Howden Compressors, Inc

. b X X Neuman & Esser USA, Inc. X

Siemens AG X Solar Turbines, Inc. X

b Burckha rdt and Howden may be less active in the U.S. transmission/storage market and more active in the refining sectors. Because scope is still under consideration, however, they are retained here.Several of the above manufacturers have diverse product offerings within other industries as well as the oil and gas industry

. There is a mix of compressor types available from these
manufacturers

. Several exclusively manufacture reciprocating or centrifugal compressors, while others manufacture both types of equipment.

DOE does not have empirical data on the market s hares of particular manufacturers

. However, based on information from the 2014 Compression Technology Sourcing Supplement.,
DOE believes that the nine companies in Table 2.1 supply over 95 % of new compressors likely to be used in compressor stations

. c

Small Businesses 2.1.2

Natural gas compressors are primarily supplied by large manufacturers, and DOE is not aware of any manufacturers of natural gas compressors that qualify as a small business

.

The Small Business Administration (SBA) defines a small business for “Air and Gas Compressor Manufactur ing” as a company with 500 or fewer employees

. The number of employees in a small business is rolled up with the total employees of the parent company; it does not represent the division manufacturing natural gas compressors. SBA lists small business
size standards for industries as they are described in the North American Industry Classification System (NAICS). For natural gas compressors, the size standard is matched to NAICS code 333912, Air and Gas Compressor Manufacturing. d

Packagers and Installers 2.1.3

Nat ural gas compressors are most often custom designed for a specific application, and are inherently large and expensive machines. Due to these barriers there are no known pure assemblers e of natural gas compressors, and manufacturers are often heavily invol ved in the selection and design of equipment. In certain cases, “packagers” or “integrators” may design and fabricate compressor packages, purchasing a (either standard or custom) compressor and a driver and then combing them with other equipment and auxil iaries into a packaged system. Some packagers also install the equipment.

Typically an engineering firm or the owner of a pipeline or compressor station will

spec ify the technical requirements of the compressor to be installed on a project. Depending on contractual agreements the engineering firm or compressor station owner will purchase the compressor, and then typically the OEM or EPC (engineering, procurement, and construction)

contract or will install the compressor. The owner of the compressor station will be responsible for operating the compressor

.

c Compressors stations use reciprocating and centrifugal compres sors, usually rated above 1,000 hp.

d See https://www.sba.gov/content/north

- american

- industry

- classification

- system

- codes

- and

- small

business

- size

- standards

.
e I.e., businesses offering the service of assembly aloneTrade Associations 2.1.4

To gain insight into the natural gas compressor industry, DOE researched various associations within the industry

. Due to the large number of stakeholders in the natural gas industry, no t all the trade associations researched have members who manufacture natural gas compressors, as some focus on areas closely related to natural gas compressors such as natural gas pipeline operation.

2.1.4.1 Gas Compressor Association

The Gas Compressor Association (GCA) represents companies that manufacture, lease, and service natural gas compressors. GCA is organized into six committees

-- education, environmental, health and safety, membership, program and expo, and statistics

. f A m a jority of the nine manufacturers identified in this report are members

.

The environmental and statistics committee are the most relevant to this market assessment. The environmental committee educates GCA members on upcoming regulations that may affect t he membership, as well as facilitates communication between members on compliance challenges. The statistics committee provides guidance for the collection and publication of natural gas compression industry specific data for members. Data are compiled

a nd published by an independent third

- party, and members use these data for various purposes

– e.g. business expansion efforts.

2.1.4.2 Gas Machinery Research Council

The Gas Machinery Research Council (GMRC) was established as a subsidiary of the
Southern Gas Asso ciation in 1952 as a not

- for

- profit research corporation to provide member companies and industry with the benefits of research directed towards reliability and cost effectiveness of the design construction and operation of mechanical and fluid systems

, in cluding natural gas compressors. A m ajority of the nine manufacturers identified in this report are
members g

GMRC research includes pipeline and compressor technology projects

, which currently include, noise mitigation/suppression, piping stiffness, mecha nical vibration issues, predicting power cost of reciprocating compressors, and the performance impact of acoustical impedance on centrifugal compressors. Research is published as technical papers and is available to
members and to the public for a fee.

2.1.4.3 I nterstate Natural Gas Association of America

The Interstate Natural Gas Association of America (INGAA) is a trade organization that advocates regulatory and legislative positions of importance to the natural gas pipeline industry
in North America. Membersh ip consists of pipeline operators who operate approximately 200,000 miles of natural gas pipelines, which is a majority of the interstate pipeline
infrastructure

. h

f See http://www.gascompressor.org/

g See http://www.gmrc.org/

h See http://www.ingaa.org/In 1990 INGAA established INGAA Foundation Inc. which has more than 150 members consisting of natural gas pipeline companies, construction companies, engineering firms, IT service providers, and other companies that provide goods and services to the natural gas pipeline industry

. Five of the nine major manufacturers listed in this assessment are members of
the INGAA Foundation

. The INGAA Foundation facilitates the safe, efficient, reliable and environmentally responsible design, construction, operation and maintenance of the North American natural gas transmission system through activities such a s analysis, and providing a forum for dialogue and collaboration

.

2.1.4.4 American Petroleum Institute

American Petroleum Institute (API) represents all aspects of the American oil and gas industry including production, refinement, distribution, and suppliers. Th eir mission is to influence public policy in support of a strong U

. S

. oil and gas industry. They carry out this mission through work in advocacy, research, statistics, standards, certification and education i

.

API has two standards j that cover the minimum requirements and test procedures for different types of compressors which are listed below:

• API 617, Axial and Centrifugal Compressors and Expander

- Compressors for Petroleum, Chemical and Gas Industry Services

.

• API 618, Reciprocating Compressors for Petroleum, Chemical and Gas Industry
Services. k

2.1.4.5 Gas Processors Association

Gas Processors Association (GPA) represents the “midstream” pipeline industry

, which is primarily composed of pipelines, and storage of natural gas. Its m embers operate approximat ely 190,000 miles of natural gas pipeline

, which is over half of the total pipeline mileage in the contiguous Unite d States. GPA provides membership with several services

, including working with legislators for a safe and viable industry, providing forums to develop standards, conduct ing research, educat ing the workforce, and improv ing safety. Although none of the major manufacturers of natural gas compressors are members of GPA, the membership is often the purchasers ( and ultimately the users ) of natural gas compressors

. l

Regulatory Programs 2.1.5

There are currently no Federal energy conservation standards for natural gas compressors. However

, the following sections detail regulations that may impact selection, construction, and operation of natural gas compre ssors. There are additional regulations regarding areas such as pricing, safety, historic and environmental preservation, and transparency

i See http://www.api.org/
j Which were adopted by American National Standards Institute (ANSI)

k This specification does not cover performance testing, but mate rial testing, hydrostatic testing and other forms of mechanical testing, critical to the integrity and reliability of the compressor and system.

l See https://www.gpaglobal.org/that are not detailed in this assessment as they have a significantly lesser effect on the manufacture, sale or oper ation of a natural gas compressor than the regulations detailed below

.

2.1.5.1 Clean Air Act

Various portions of the Clean Air Act (CAA) (42 U.S.C. § 7401 , et seq .) may apply to the construction and operation of natural gas compressors

, including the New Source Review (NSR) program, Prevention of Significant Deterioration (PSD), and permitting under Title V of the
CAA

. 5

The NSR program and PSD apply to both new construction and major modifications of existing industrial facilities

. The NSR program applies to “non

- attainment” areas (i.e., areas that do not comply with National Ambient Air Quality Standards), and PSD requirements apply to “attainment” areas (i.e., areas that comply with National Ambient Air Quality Standards)

. In
either ca se, a pre

- construction review of emissions and proposed control measures is conducted for any “major sources” of pollutants that exceed certain thresholds.

Title V of the CAA also applies to “major sources” of air pollutants and requires them to
obtain o perating permits, which are usually issued by state authorities

. Permitting requirements vary based on the amount and type of pollutant.

Additionally the construction of a natural gas compressor facility may be reviewed by a State Implementation Plan (SI P), which is a plan for CAA compliance.

For natural gas compressor stations, requirements of the CAA are usually focused on emissions from the prime mover of a natural gas compressor, as it is typically the largest source
of emissions at the station

. Dif ferent natural gas compressors and associated prime movers will require different levels of pollution mitigation for compliance with the CAA

. Therefore compliance strategies, and associated costs, for natural gas compressor technologies are
considered when selecting equipment

.

2.1.5.2 FERC

The Natural Gas Act (NGA) was the first federal regulation of the natural gas industry

a nd was enacted in 1938. I n 1977

, the Department of Energy Organization Act created the Federal Energy Regulatory Commission (FERC) , which uses much of the authority from the
NGA

. 5

In 1986 FERC Order 436 restructured the natural gas pipeline industry into transportation only busines ses

. Prior to this order pipelines transported and sold natural ga s to customers. 5

In 1992 FERC Order 636 required pipelines to provide “ equal in quality ” transportation services regardless of the customer

. Part of this order also encourages the use of natural gas market centers, and imposed new rate designs which were intended to promo te competition. 5

Additional FERC Orders have further changed rights to capacity agreements, and pricing structures, such as encourag ing peak/off

- peak rate structures

, which has ultimately increasedcompetition among pipelines. This increased competition provides an incentive to increase pipeline efficiency, which in part is driven by natural gas compressor efficiency

. 2

2.1.5.3 NEPA

The National Environmental Policy Act (NEPA) of 1969 (42 U.S.C. § 4331 ET SEQ.) requires federal agencies to conduct an Environmental Impact Statement (EIS) for any proposed
action

. FERC was designated as the lead agency for compliance with NEPA by the Energy Policy Act of 2005, which amended the NGA

. 5

FERC reviews proposed natural gas pipeline projects

, which often i nclude natural gas compressor statio n construction or modification. Part of this review includes evaluating alternative options that may hav e a lower environmental impact. However, alternative options may be eliminated from consideration due to various fac tors such as high cost and not meeting
the operational requirements of the proposed pipeline project.

2.1.5.4 U.S. Department of Transportation

The U.S. Department of Transportation ’s Pipeline and Hazardous Materials Safety Administration (PHMSA) has oversight aut hority over the safety of the natural gas pipeline
infrastructure m . PHMSA’s responsibilities were expanded by the Pipeline Safety Improvement Act of 2002 to include requiring pipeline operators to have integrity management programs for “High Consequence Ar eas”, qualification programs for employees who perform sensitive tasks, publicly available pipeline maps and operator contact information

. Other congressional acts have also changed the responsibilities of PHMSA

. Other PHMSA rules and regulations are based on consensus standards and focus on areas such as manufacturing, shipping of pipe material, construction techniques, operating procedures, emer gency response, and abandonment. 5

Nonregulatory Programs 2.1.6

The EPA Natural Gas STAR program is a voluntary partnership that encourages members, oil and gas companies involved in all sectors of the industry, to improve efficiency and
reduce methane emissions

. According to Gas STAR, the transmission and storage sector, where natural gas pipeline compressors are used, accounts for 27% of the industry’s methane
emissions.

Since 1993 the 26 partners in the transmission sector have reduced a cumulative 255.9
Bcf of methane emissions, including 10 Bcf of methane emissions in 2012

. According to Gas STAR data, the top methane reduction technologies used in 2012 were pipeline pump

- down n techniques, use of turbines at compressor station, and installing electric compresso rs

. 6

m See http://www.phmsa.dot.gov/

n The term “pump

- down” refers to lowering the pressure of a pipeline section before performing maintenance in order to minimize or eliminate venting gas to the atmosphereShipments and Value 2.1.7

There are over 300,000 miles 7 of natural gas transmission pipeline in the United States and more than 1,700 compressor stations maintaining pressure on it

. 8 Typically there are multiple compressors at one compressor station, estimated to be abo ut four compressors per
station. 7 A recent EPA white paper estimates that industry operates approximately 7,235 natural

gas

- fir ed reciprocating engines, and 725 natural gas

- fired combustion turbines at compressor
stations. 8 ). The EPA report did not have an estimate for el ectric motors, because it was focused

on on

- site emissions, but a 2010 INGAA publication had an estimate of 200 electric motors in operation to drive compressors

. 2 Compressor stations may have motors for other purposes (e.g., pumps, ventilation, etc.) but the primary drivers in these estimates are driving natural gas

compressors

.

Natural gas compressor s are commonly used in many natural gas industry segments

. Table 2.2 presents EPA estimates for the number of reciprocating and centrifugal compressor s in use in several segments.

Table 2

. 2 Summary of Natural Gas Sector Compressor Activity o

Industry Segment Active Compressor
Units

Production Reciprocating 36,066 Processing Reciprocating 5,624 Centrifugal 906

Transmission Reciprocating 7,235 Centrifugal 725 Storage Reciprocating 1,012 Centrifugal 99 LNG Storage Reciprocating 270 Centrifugal 64 LNG Import Terminal Reciprocating 37 Centrifugal 7 Source: EPA, 2014, Table 3

- 9.

Expansion of the natural gas infrastructure has required construction of additional compressor stations

. From 1996 to 2006 154 compressor stations were added, a 15% rise in the

o These figures do not include rotary screw compressors, of which there are several thousand active. However, they tend to be used in gathering and refrigeration, and not transmission or distribution.total number of stations in service. During this same period, a total of 3.5 million horsepower of compressor capacity was added , which is a 26% i ncrease in installed horsepower. 7

Compressor capacity is usually determined by project requirements, and in 2004 reciprocating gas engines in operation averaged 1,700 horsepower while gas turbines were
lar ger, averag ed 6,600 horsepower. 9

Annual shipments of natural gas compressors were estimated by analyzing completed natural gas pipeline projects in EIA’s Natural Gas Pipeline Project Spreadsheet

. 8 Associated FERC Docket numbers were used to look up information regarding the projects, such as environmental impact assessments, and determine data for each new compressor installed. Projects that were under state authority were left out due to insuffic ient data, and represented 8% of all projects from the EIA spreadsheet for the years estimates were available . Therefore

, the actual total shipments of natural gas compressors are likely larger than the estimates shown
below. T hese estimates are only for compressors at compressor stations and do not include other areas of gas compressor use such as storage, and field compressors for gathering systems.

Annual shipment estimates for natural gas compressor packages installed at compressor
stations from 200 9 to 2013 are shown in Table 2.3 . During this five year period estimates
indicate that natural

- gas

- fueled reciprocating compressors had the highest market share

– totaling 45% of shipments

. Natural

- gas

- fueled centrifugal com pressors were estimated to have the next highest market share with 40%

. Electric motors driven centrifugal compressors compose the smallest amount of shipments during this period of 16%.

Table 2

. 3 Annual Compressor Station Compressor Package Shipments by Year

Primary Driver Fuel Natural Gas Natural Gas Electric Compressor Technology Reciprocating Centrifugal Centrifugal

Annual Shipments 2009 42 28 6

2010 34 23 4

2011 7 21 10

2012 16 12 9

2013 5 8 7

Cumulative Market Share 45% 40% 16%

The data showed a wide range of compressor horsepower ratings, from the smallest reciprocating unit of just over 1,000 hp to a large electric motor

- driven 42,000 hp unit. Natural

gas

- fueled reciprocating compressors were the smallest with an average of 4,880 hp, and no units were more than 8,180 hp. Natural gas centrifugal units covered the largest range of sizes from 1,600 hp to 30,000 hp, with an averag e size of 12,022 hp

. Electric motor driven centrifugal compressors tended to be the largest units and on average were 16,203 hp. Estimated shipments for various horsepower ranges are shown in Table 2.4

.Table 2

. 4 Annua l Compressor Station Compressor Package Shipments by HP Range for
2009 to 2013

Primary Driver Fuel Natural Gas Natural Gas Electric Compressor Technology Reciprocating Centrifugal Centrifugal

Shipments by Horsepower Ranges 1,000

- 2,500 20 2 3
2,501

- 5,000 57 7 1
5,001

- 7,500 2 9 2
7,501

- 10,000 25 7 7
10,001

- 15,000 0 41 7
15,001

- 20,000 0 17 4
20,001

- 30,000 0 9 9
30,001

- 50,000 0 0 3 Average Horsepower 4,880 12,022 16,203

An additional data point for shipment estimates is the 2013 Mechanical Drive Order Survey published by COMPRESSORtech2. It uses annual surveys of manufacturers to show orders for mechanical drive equipment for the gas compressor marketplace received in 2012. In that year, 14 orders were received in North America for gas turbines used with centrifugal compressors. The turbines ranged from 40,230 to 80,461 hp (60.1 to 120 MW). These may include units larger than those used in natural gas transmission. Orders f or Reciprocating engines during this time are shown in Table 2.5 . The data provided global orders by fuel type and geographic region. The global perce nt age of engines fueled by natural gas was used to estimate
the orders for natural gas engines in North America. The equipment orders in Table 2.5 are greater than the estimates provided in Table 2

. 4 for several reasons. First, they include orders in Canada and Mexico, while estimates from EIA projects are only with in the United States. Second, they include all applications of gas compressors including gathering, transmission, storage, and distribution while EIA data only has compressors located a compressor stations which is a subset of all natural gas compressors in use (12)

.

Table 2

. 5 2012 North American Reciprocating Engine Orders

Output Range Global Percent
Natural Gas North America Orders (hp) (MW) Total Estimated Natural Gas
670 to 1,341 0.5 to 1.00 2% 2,307 40
1,342 to 2,682 1.01 to 2.00 24% 1,374 332
2,683 to 4,694 2.01 to 3.50 22% 128 28

Growth of the natural gas pipeline infrastructure is expected to continue

. An INGAA publication had a projected expansion of an additional 4.38 million horsepower of pipeline compressors from 2014 to 2035

. Additionally , DOE estimates that there will be 8.40 million horsepower of compressors on gathering pipelines during this time frame

. 102.2 Technology Assessment

The technology assessment focuses on understanding how energy is used by natural gas

compressor s and what potential technology changes to the design and construction of these

compressor s would improve their energy efficiency. Measures that improve the ener gy efficiency of the equipment are called “technology options.” These measures are based on existing technologies, as well as working prototypes. In consultation with interested parties, DOE will develop a list of technology options to consider in this rul emaking. Initially, this list will include all those options that may improve energy efficiency, in cluding a max

- tech design. DOE will consider each of these technology options against four screening criteria, as discussed in section
3 . Technology options that pass all the screening criteria are called “design o ptions” and are analyzed in later analyse s not within scope of this document.

To develop the list of technology options that could improve the efficiency of the

compressor s for which DOE is considering regulating , DOE is reviewing manufacturer catalogs, recent trade publications, and technical journals. DOE also intends to consult with interested parties to gather information on compressor designs and applications.

Overview of Compressor Technologies 2.2.1

Natural gas compressors consist of two main components: the compressor, in which the natural gas is actually compressed, and the prime move r, or the compressor driver. As noted in
Section 1.2 , there are several different equipment types for each component, and a natural gas compressor can be designed using multiple different combinations of components depending upon its specific application a nd performance requirements. The following is a description of the different individual equipment types for both components.

2.2.1.1 Compressors

The two major compressor types used in the transmission and distribution (T&D) of natural gas are reciprocating and d ynamic. Dynamic compressors used in natural gas T&D can be further divided into centrifugal and axial compressors

.

Reciprocating Compressors

Reciprocating compressors are positive displacement devices, i.e., devices that add pressure by compressing the ga s through mechanical displacement, typically with a cylinder

piston c ombination

. 2 The number and size of the cylinders used can be changed to mee t the required compression ratio and throughput. As such, reciprocating compressors provide the greatest flexibility in operating range for both discharge pressure and flow capacity.

Higher discharge pressures can only be achieved using multiple

- staging. The number of stages is determined by the overall compression ratio, as the compression ratio per stage is generally limited by the discharge temperature and usually does not exceed four . Multi

- stage units are able to reach higher pressures by utilizing in tercooling between stages to maintain the
gas temperatu re within safe operating limits. 11Reciprocating compressors are typically driven by natural

- gas powered reciprocating engines or electric motors and vary from fractional to more than 20,000 horsepower (hp) per
unit

. 11 In addition, reciprocating compressors are normally divided into separate categories based on the designed operating speed, slow (~200

- 400 rotations per minute (rpm)), medium (~500

- 900 rpm), and high (~900

- 1 8 00 rpm). Slow speed compressors generally come as an integrated package with the driver and are the most efficient compressor type, maintaining a higher efficiency over a wider bandwidth of operating pressure and gas flow conditions. Slow speed compressors were also the predominant equipment type used in transmission and distribution for
decades. 2 However, in recent years, the indus try has begun to use high speed reciprocating compressors. While less efficient than other compressors , high speed compressors provide four to five times the power and run at two to three times the speed as slower compressors of the
same size. 12 As such, hi gher speed compressors are able to compress more gas and achieve higher throughputs using smaller units, resulting in significantly reduced installation costs that outweigh the increase in energy costs caused by using less efficient units

. 2 The typical performance ranges for reciprocating compressors can be seen below:

Table 2

. 6 Typical Performance Ran ges

– Reciprocating Compressors 2

Isentropic Efficiency (Percent) Inlet Flow (cfm) Discharge Pressure (psig)

Slow

- speed Reciprocating 80

- 92

0

- 2,500 3

- 80,000 Medium

- speed Reciprocating 75

- 90 High

- s peed Reciprocating 70

- 82

According to INGAA 2 , reciprocating compressors are more effective when used in situations with high and varying pressure ratios (i.e., when the ratio of discharge to suction pressure varies substantially) and lo w overall flow; CAGI lists the advantages of using a reciprocating compressor over other compressor types : 11

• Greater flexibility in capacity and pressure range.

• Higher compressor efficiency and lower power cost.

• Capability of delivering higher pressures.

• Capability of handling smaller volumes.

• Less sensitive to changes in gas composition and density.

Dynamic Compressors

Dynamic compressors are ma chines in which air or gas is compressed by the mechanical action of rotating vanes or impellers imparting velocity and pressure to the air or gas. There are two major types of dynamic compressors, axial and centrifugal

. 11

Centrifugal Compressors

The centrifugal compressor is one of the simplest machines available for gas compression. Unlike a reciprocating compressor, which uses positive displacement, thecentrifugal compressor is a continuous flow machine in which one or more rotating impellers a dd energy to the gas. The gas flow enters at the eye of the impeller and is discharged from the impeller tip at increased velocity and pressure. The gas flow then enters a diffuser where most of its remaining kinetic energy is converted to pressure rise

. C entrifugal compressors have a more limited operating range than reciprocating compressors but are able to operate at significantly higher flow rates. For centrifugal compressors, the maximum discharge pressure achievable using a single

- stage unit is limite d by the impeller’s strength. In cases where the pressure requirement exceeds that strength, centrifugal compressors may be mult i

- staged

. 11 The t ypical performance ranges for centrifugal compressors can be seen below:

Table 2

. 7 Typical Performance Ranges

– Centrifugal Compressors 2

Size (hp) Efficiency (Percent) Inlet Flow (cfm) Discharge Pressure (psig)

1,000

- 30,000 75

- 88 100

- 200,000 3

- 10,000

Centrifugal compressors are normally driven by gas turbines or electric motors and have
a similar capacity range to reciprocating compressors. Unlike reciprocating compressors, centrifugal compressors develop pressure within the unit, independent of the load, resulting in constant discharge pressures over a considerable range of flows. 11 As such, centrifugal compressors are more effective in situations with low/medium, relatively constant pressure ratios
and h igh, mildly variable flow rates. 2 Other advantages of using centrifugal compressors are listed by CAGI 11 as follows:

• Lower installed first cost where pressure and volume conditions are favorable.

• Lower maintenance expense.

• Greater continuity of service and dependability.

• Less operating attention required.

• Greater volume capacit y per unit of plot area.

• Adaptability to high

- speed low

- maintenance

- cost drivers.

Axial compressors

Axial compressors are also continuous flow machines in which one or more rotating series of blades set along a common shaft continuously add energy to the gas. However in an axial compressor, the gas flow enters and is discharged at increased pressure and velocity along the axis of the main shaft. Axial compressors are only capable of delivering low discharge pressures, less than 100 psig, which falls we ll outside the range of normal pipeline operations (900

- 1750 psig). As such, they are rarely used in tran smission and distribution.

2.2.1.2 Compressor Prime Movers

Three primary types of prime movers (drivers) are used in pipeline applications: reciprocating gas e ngines, gas turbines, and electric motors. 2 Compressor selection usually dictates the choice of the prime mover. Gas engines are generally limited to driving reciprocating

compressors , while gas turbines generally drive centrifugal compressors. Electric motors , on the other hand, may be used with either compressor technology, but pipeline companies have begunusing electric motors (possibly for reaso ns outlined later in section 2.2.1.2 ) to power centrifugal compressors on a more widespread basis than reciprocating compressors

. 2

Reciprocating Gas E ngine s

The natural gas engine driver is currently the most common driver used in the oil and gas industry. 11 Reciprocating gas engines are similar to reciprocating compressors, using a cylinder

piston combination, but gas engine cylinders are filled with natural gas that is ignited and
combusted to caus e the piston to move. Gas engines are also divided into separate categories by speed, with the categories generally corresponding to those used for compressors, and are always combined with a compressor of corresponding speed

. 2

Slow

- speed compressors and gas engines normally come in an integrated package where the engine uses a common crankshaft to drive both the compressor and power cylinders. Medium and high speed engines come in separa ble package s and are connected to the compressor either directly or using a flexible coupling or, in smaller sizes, a belt

- drive. Gas engines are also further divided by size into two different groups, small and large horsepower. Small horsepower engines are generally used for oil field services such as gas gathering, gas injection, and small gas processing plants. Large horsepower units are used in process plants, main line gas transmission, gas injection, and la rge ga s plants. 11

Table 2

. 8 Typical Performance Ranges

– Reciprocating Gas Engines 2
, 11

Speed Range (rpm) Size (hp) Efficiency (percen t) Small Large Slow speed engine 0

- 600 25

- 800 800

- 7000 30

- 43 Medium speed engine 600

- 900 5

- 400 400

- 3600 32

- 46 High speed engine 900

- 2100 5

- 400 400

- 3600 32

- 43

While modern gas engines are quite efficient, they do have power limitations, and can have high vibration issues that affect reliability. Also, certain components may require frequent maintenance, and the engine units require significant amounts of spare p arts and service

contracts

. Error! Bookmark not defined.

Gas turbines

A gas turbine engine operates by drawing ambient a ir into an axial or centrifugal “high pressure compressor”, where work is performed and the pressure and density of the air inc reased. The high pressure air exits the compressor to a combustor, where it is mixed with natural gas and ignited. The high pressure exhaust from the combustion process is exhausted into the “high

pressure turbine ,” where it is expanded and used to drive t he “high pressure compressor.” After passing through the “high pressure compressor,” the combusted air is expanded through a separate “low pressure turbine,” which used to drive external loads, such as a natural gas compression unit. Gas turbines tend to have poor efficiency at low loads, and so are most economically used in compressor stations with high volumes of gas flow

. 11 As with most otherte chnologies discussed here, gas turbines can be separated based on their size and power output capacity.

Table 2

. 9 Typical Performance Ranges

– Gas Turbines 2
, 11

Size (hp) Power Output (MW) Efficiency (percent)

Small 600

- 6,000 0.5

- 5 24

- 31

Medium 6,000

- 25,000 5

- 20 27

- 36 Large 25,000

- 70,000 20

- 50 29

- 40

Electric motors

Electric motors are the most widely used compressor drivers when considering air and process compressor applications, but they are the least commonly used driver for natural gas transmission and distribution, for two primary reasons:

1. Natural gas compressors must be able to operate at variable speeds, so most electric motors will require variable frequency drives, which significantly increase the initial purchase and maintena nce costs.
2. Electric motors of the size used in natural gas applications require a reliable source of electric power supply, which is frequently not available and is costly to install.

Despite these issues, electric motors are being used more frequently t han before due to environmental considerations, because they do not have any (local) emissions. 11 There are three major types of electric motors, i nduction, synchronous, and direct current (DC). Synchronous motors are the most commonly used motor type for compressor applications, because it is the most efficient of the three. However, DC motors are becoming more popular because they do not require a variable frequency drive to operate at different speeds, reducing operating cost.

Table 2

. 10 Characteristic Electric Motor Efficiency 11

Efficiency (percent)

Induction 85

- 95 Synchronous 93

- 97

Direct Current 85

- 95

2.2.1.3 Compressor Selection Factors

Determining which compressor is technologically appropriate for an application requires consideration of several factors. Among them are pressure, flow, location, and demand profile.
The discussion that follows identifies issues that DOE will likely consider in its sc reening analysis

, described in section 3. Areas of concern include: technological feasibility; p racticability

to m anufacture, install, and service; a dverse impacts on product utility or product availability to consumers, and; a dverse impacts on health or s afety . S election factors based on solely economic criteria (such as first cost) are considered elsewhere in the rulemaking analysis.Pressure

The natural gas distribution network operates at a wide range of pressure levels. Because different compressor te chnologies are physically more efficient at different pressure levels, they may be more attractive to operators at different points on the grid. In general, reciprocating compressors offer the greatest single

- unit pressure rise capability, followed by cent rifugal compressors, and then by axial compressors.

Making generalization more difficult is the practice of staging, or putting compressors in series to multiply the pressure rise of each unit. Centrifugal compressors are regularly strung together (“compressor chain”) to achieve higher net pressure ratios than could be practically achieved by each unit alone. In certain cases, centrifugal compressors may be retrofit ted with modified impellers if an operator expects prevailing pressure levels to be d ifferent than those anticipated when the unit was installed. This may improve overall pipeline efficiency.

Reciprocating compressors can be similarly operated in series to achieve greater overall pressure rises. Some products are built modularly, so that an operator whose desired pressure level changes can retrofit the unit to do exactly this. Additionally, certain reciprocating compressors are capable of changing pressure ratio by varying effective displacement, commonly by modifying the head end of the c ylinder. This changes the ratio of swept to unswept volume

– the primary determinant of flow rate in reciprocating compressors.

One subtlety inherent in discussing pressure is the differen ce between pressure ratio and absolute output pressure. Energy cons umption is driven more by pressure ratio, which reflects how much work the compressor performs on a gas. All compressors within the scope of this discussion, however, operate relative to a roughly constant ambient pressure, which may drive secondary design specifications. For example, a compressor operating at high pressure may need to be constructed more durably than one at lower pressure to withstand the negative (relatively) pressure of the atmosphere, even if both units are imparting identical pressure rises to the natural

gas.

Output Flow

Gas flow requirements strongly influence compressor selection. For a given power level, lower pressure rise implies greater output flow. As with pressure , certain technologies operate more efficiently at different flow rates.

Complicating the consideration is the ability to operate compressor units in parallel, which linearly multiplies output flow. In some cases, operators may opt to employ smaller units in parallel when a larger unit may be more efficient at full load, both to create redundancy in the
event of failure of one unit and so that the station may operate more efficiently at reduced load
levels by switching off one unit or the other . In In that case, one or more compressors may be
turned off until ne eded.

A special case of paralleling compressors comes with hybrid stations, when compressor units of different types may be operated together so that the station exhibits relative benefits of each technology. For example, a high

- reliability centrifugal co mpressor may be paired with areciprocating compressor with a flatter efficiency/load characteristic. In that case, the centrifugal unit would be used to meet base load demand, and the reciprocating would be used to trim up or down in response to time

- loca lized demand variations.

Reciprocating compressors are capable of changing flow by varying the effective displacement, commonly accomplished by adding clearance volume to the head end of a cylinder or to the crank/frame end of a cylinder, deactivating one end of a cylinder, or with various combinations of these methods applied to cylinder operating in parallel

.

Reliability and Maintenance

In infrastructure a pplications, reliability is para mount. Ope rators are incentivized by regulation and by finances to ensure that compressor stations are always able to meet end

- user demand

.

There is interplay with location and environment. Temperature, humidity, and prevailing weather patterns may further increas e the important of reliability. Certain locations in the network may also have less inherent redundancy and, therefore, require added reliability. Additionally, remote locations with lower service latency may also justify greater weighting of reliability a mong selection criteria.

Conceptually separate from reliability, or “unplanned maintenance,” is scheduled
maintenance intervals. M aintenance carries a cost that is a primarily consideration in equipment
selection.

In general, centrifugal and axial compre ssors are thought to require more frequent service than reciprocating, although the degree and expense of the maintenance may be still lower than that of reciprocating compressors

. 13

In some cases, there may be an interplay between maintenance and efficien cy. Certain types of seals and packing may be more efficient in terms of friction and gas leakage. But if they require more frequent maintenance (planned or unplanned) for example, the overall impact to operational efficiency may be less obvious.

Location and Environment

Compressor selection may be influenced by environmental factors, such as temperature, humidity, altitude, and weather patterns. Beyond those, location requires several other
considerations.

Proximity to population may set limits on emissio ns, or on acoustic noise created by the compressor that would be less important for remote stations. Proximity to electrical power, and the ability to sell cogenerated electricity to the grid, is foremost in evaluating the suitability of
electric motors as prime movers and impl ementing heat recovery (see section 2.2.4.3 ) technology . B ecause population centers tend to be less tolera nt of emissions and acoustic noise and because they tend to have greater availability of electrical service, electric motors are more commonly found closer to metropolitan areas.Security and resistance to damage is an important consideration in compressor station planning. This damage may be accidental (e.g., from construction) or intentional (e.g., terrorism).
Securit y, however, may be less important when selecting specific compressor technologies compared to the design of the overall station.

A nother loc ation

- driven consideration in compressor selection may be physical space occupied by the unit. Dresser

- Rand suggests that reciprocating compressors may occupy roughly triple the volume occupied by a centrifugal compressor. Because compressor stations tend to be located well outside of cities, however, space may be at less of a premium. 13

Demand Profile

Demand profile refers to the pressure and flow o utputs expected of a compressor as a function of time. All compressors see some variation in pressure and flow requirements, much of it driven by daily and seasonal demand patterns

Compressor Package Efficiency 2.2.2

It is difficult to assign operational efficiency values to compressor technologies without knowledge of the compressor’s unique application. However, DOE outlines some representative values of prime mover efficiency, compressor unit efficiency, and overall package efficiency (sometimes inclusive of heat recovery) in Table 2.11

. For the purposes of the table, “LSR”
means “low

- speed reciprocating” and ref ers to speeds of 200

- 400 rpm, “MSR” means “medium

speed reciprocating” and refers to speeds of 500

- 900 rpm, “HSR” means “high

- speed reciprocating” and refers to speeds of 900

- 1200 rpm, “SEM” means “synchronous electric motor,” “SGT” means “small gas turbin e” and refers to outputs below 6700 HP, “MGT” means “medium gas turbine” and refers to outputs between 6700 and 26800 HP, and “LGT” means “large gas turbine” and refers to outputs above 26800 HP. “SCC” means “small capacity centrifugal,” “MCC” means “mediu m capacity centrifugal,” and “LCC” means “large capacity centrifugal.” Electric motor efficiency contains embedded assumptions about the generation source and correspondingly vary based on the generati on technology. Efficiency of the electric

m otor, itself , can exceed 95%, depending on power factor

. 14 One factor not reflected in this table is efficiency across loading levels.

Thr ee observations emerge from these data. F irst

, the efficiency advantage enjoyed by
low

- speed reciprocating compressor units may be partially offset by the slightly lower efficiency of their prime movers, though this may not hold in all cases. Second, the relative advantage of reciprocating compressors in certain cases may be diminished at higher power levels, where centrifugal compre ssor efficiency rises. The third observation is that adding heat recovery capability to compressors , generally only considered economic when applied to large

compressors, appears to yield the highest overall combined efficiencies.

Table 2.11 displays characteristic efficiency values for various compressor package combinations, two with heat recovery.Figure 2

. 1 plots prime mover efficiency as a function of horsepower based on publicly available catalog data for both reciprocating and centrifugal/turbine drivers

.

Table 2

. 11 Representative Efficiencies of Various Compressor Technologies 2

Compressor Unit Prime Mover Heat Recovery CU Efficiency (%) PM Efficiency (%) Combined Efficiency (%)

LSR LSR None 80

- 92 30

- 43 24

- 40

LSR SEM No ne 80

- 92 25

- 46 20

- 42

MSR MSR No ne 75

- 90 32

- 46 24

- 39

HSR HSR No ne 70

- 82 32

- 43 22

- 35

SCC SGT None 75

- 88 24

- 31 18

- 27

MCC MGT None 75

- 88 27

- 36 20

- 32

LCC LGT None 80

- 88 29

- 40 23

- 35

LCC LGT Organic Rankine 80

- 88 33

- 47 26

- 41

LCC LGT Steam Rankine 80

- 88 34

- 55 26

- 48

LCC SEM None 80

- 88 25

- 46 20

- 40Figure 2

. 1 Prime Mover Efficiency by Rated Horsepower 15

Compressor Losses 2.2.3

C ompressor efficiency is affected by many design elements

. The discussion that follows describes the major sources of losses which contribute to reduce a compressor ’s efficiency. Th e following description s for both reciprocating and dynamic compressors pref ace the discussion of technology options that can improve compressor efficiency

– see section 2.2.4. Major sources
and mechanisms of losses are discussed primarily as they apply to reciprocating and centrifugal

compressors.

2.2.3.1 Reciprocating Compressor Losses

Valve Losses

Of all components, valves play perhaps the largest role in determining compressor efficiency and reliability. Because valves are small relative to the overall cylinder, they impede exhaust and intake flow. Additionally, valves are passive chec k valves. They do not open and close with perfect crispness, which leads to lost gas during the actuation interval (i.e., when the 0% 10% 20% 30% 40% 50% 60%

0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000Efficiency (Lower Heating Value)

Rated Horsepower 

## Prime Mover Efficiency (Lower Heating Value) vs. Rated Horsepower

Reciprocating

Centrifugalvalves are opened and closed) . Finally, valves may not seat crisply when closed, but ring or flutter and allow small amounts of gas to pass them. 16

Passage Losses

Although valves are typically the smallest diameter orifice in the flow pathway, the flow restriction of the cylinder itself can also contribute almost as much to total pressure drop. When the piston is at top dead cent er, the gas has only the clearance volume in which to flow. That clearance volume is typically small relative to the cylinder swept volume. In addition to the
valves themselves, the pressure losses associated with the hardware needed to support and

actuate the valves is not negligible. Finally, another flow restriction results from the location of the valves which are positioned on the swept volume of the cylinders (as opposed to on the unswept end) 16 and are often partially masked by the piston while they are flowing gas.

Pulsation Losses

As gas is drawn into and expelled from the compression chamber, pressure waves are
created in the intake and exhaust manifolds. Th e se waves, and their harmonics, are reflected by the geometry of the manifold and eventually return to the valve. Depending on when the valve

opens next , the propagating wave can aid or hinder the intake or expulsion of gas. For exampl e, the high pressure wave created by the compressor discharge will reflect and return to the cylinder exhaust valve. If the pressure peaks when the exhaust valve opens, the prime mover will work harder to expel gas (or expel less gas for the same work). Co nversely, if the exhaust valve opening coincides with the arrival of a pressure trough, the gas will more easily flow out. 16

The dampening of pul sation s , which must be done to control time

- variant pressure forces to safe levels on compressor manifolds, piping and pressure vessels in both the intake (suction) and exhaust (discharge) segments of the reciprocating compressor system, cause pressure los ses that must be overcome by the compressor. Dampening is typically accomplished with
combinations of expansion bottles, choke tubes, choke

- volume filters, and orifice plates, all of which create static and dynamic pressure dr op

. The dynamic pressure loss is a more significant factor on the higher speed reciprocating compressors that are prevalent today.

Heat Transfer Losses

C ompressors are not perfect adiabatic devices

, and in practice heat transfer occurs. As the compressor operates and rises in temperatu re, heat is conducted through the body and into the suction passage. Cool gas entering the passage begins to draw heat from the passage wall, reducing gas density and compromising efficiency. This process continues as the gas is drawn into the cylinder, wh ere it is further heated by the relatively warmer discharge end of the cylinder
which is also heated by the frequent outflow of hot, pressurized gas. 16

Leakage Losses

Reciprocating compressors use seals to physically separate the high

- pressure area from the atmosphere. How tightly the seals and rings should hug the shaft and piston is an engineering challenge. Too tight, and the shaft will experience more friction. Too lose, and gas more quicklyleaks. In addition, valves do not seat instantaneously or perfectly and, therefore, permit some escape of gas. When gas leaks, whatever energy was used to compress it also disappears

. Furthermore, capacity is reduced by the amoun t of compressed gas that leaked instead of making its way into the outgoing pipeline section.

On the suction side, there is a further penalty. In addition to the capacity

- reduction effect just mentioned, gas leaking through the suction port will be hotte r than the gas it finds on the other side. As the cool gas heats, it loses density and becomes more difficult to compress. The compressor, then, must perform more work for lower output.

Leakage around piston rings is straightforward in a single

- acting sch eme, where the gas is merely wasted. In a double

- acting compressor, the piston function s similarly to a valve in that it seals off high

- pressure from low

- pressure . Leaking gas

, there fore, drops pressure in the high side (where it is desired), boosts pressu re in the low side (where it is not desired ), and also creates the undesirable heat transfer present in the case of the suction valve. Compressor capacity falls, required work rises, and efficiency is negatively affected.

Flow Control Losses

Reciprocating compressor flow is frequently controlled by suction pressure throttling, especially in upstream applications, but also in transmission stations. In this case the pressure into the compressor cylinder is intentionally reduced by a throttling valve. This re duces the density and therefore the flow rate of the cylinder. Depending on the cylinder compression (pressure) ratio, throttling may decrease or increase the required compression power, but it always reduces the efficiency.

Gas recycling is the process of taking a side stream off the discharge line from the compressor and, after cooling the gas, connects it back to the compressor suction. The amount of gas recycle is controlled by a recycle valve. This process controls the flow from a unit o r station, however it is extremely inefficient as almost all of the work input in compressing the recycled gas is wasted energy. Gas recycling is common on process compressor applications, but less prevalent in transmission applications.

2.2.3.2 Dynamic Compressor Losses

The key aerodynamic components in the centrifugal compressor are the inlet, inlet guide vane, impeller, diffuser, return channel, volute, and sidestream. 17 All new energy enters the compressor via the impeller, making it the heart of the system

. 18 Th e impeller is the rotating
component that applies torque, accelerates the gas and imparts kinetic energy in the way of velocity and potential energy in the form of pressure. The inlet inducer is a section of the impeller that transforms axial flow at the inlet to radial flow

. Inlet guide vanes direct the flow to the inducer at the right rotor inlet angle

.

The diffusers are the second most important aerodynamic component in a compressor. 17
As g as leaves the rotor it enters the diffuser at an angle that depends on the rotor’s geometry and velocity . The primary purpose of the diffuser is to convert kinetic energy into more potential energy and to effi ciently increase the static pressure. 18 Centrifugal compressor diffusers can bevaned on vaneless. 17 A vaneless diffuser is generally a simple flow channel with parallel walls
and without a means to guide the flow

. In contrast, v aned diffusers are designed to guide the gas
flow to achieve specific operating conditions

. 18 Vane design involves balancing efficiency with operational flexibility. Vaneless diffusers general ly exhibit a wi der range of operating flows whereas vaned diffusers allow a compressor to reach hig her levels of peak efficiency. 17

S uperior aerodynamic designs are the key to reducing losses in centrifugal compressor s

. Three

- dimensional Computational Fluid Dynamics (CFD) codes are the most rigorous analytical techniques that can be used to calculate the flow through aerodynamic components such as impellers and d iffusers. One important aspect in this process is the correct simulation of the
various losses. 19

The estimation of centrifugal compressor performance and of the potential benefit of design improvements necessitates a rigorous examination of the various types of losses that exist within a compressor. These losses are typically expressed in terms of a reduction in total

pressure. 18 Botha and Moolman categorized the primary sources of loss in centrifugal

compressors , divid ing loss mechanisms into two main groups, (1) internal loss mechanisms and (2) parasitic loss mechanisms. Internal loss mechanisms are associated with losses emanating
from the main flow through the compressor, which impacts both the efficiency and the pressure
ratio that can be achieved by the compressor. Internal losses include the incidence loss at impeller entry, impeller flow losses (i.e. the blade loading loss, skin friction los s and clearance loss) and the mixing loss at the impeller exit. The main parasitic losses include the (1 ) disc friction loss, (2) recirculation loss and (3) leakage loss. 19

Internal Loss Mechanisms

The details of the impeller geometry or shape are crucial to achieving good efficiency.
One such f actor is the blade leading edge angles or, more specifically, the blade leading edge
incidence. Incidence is defined as the difference between the relative flow angle of the gas as it approaches the rotating impeller blade and the impeller blade angle

. The incidence loss occurs when the relative fluid flow angle of the fluid entering the impeller deviates from the actual blade inlet angle. This means that the fluid has to change direction immediately, resulting in a significant loss in energy. 19

Three groups of losses result from fluid movement over the impeller. The blade loading loss results from the momentum loss due to boundary

- layer build

- up on the blade surfaces 19
causing the flowing fluid to experience a smaller exit area. 18 The skin friction l oss is the loss experienced due to the adhesive forces between the channel surfaces and the fluid. The channel surfaces are those surfaces created by the hub, blades and shroud. Clearance losses arise from the need to allow free rotation by means of a fini te clearance between the impeller and the stationary casing. Typically fluid will leak through this gap (between the blade tip and casing) from the higher pressure on the pressure side of the blade to the lower pressure on the suction side of the
blade. Th is mixing of the two fluid flows results in the formation of a loss

- inducing small vortex on the suction side (low pressure region) of the impeller vane outer tip. 19

After the flow has left the impeller, the primary (flow proceeding directly from the impeller) and secondary (flow traveling along the direction of the housing, having separatedfrom the impeller at an earlier point in time) flows mix, but not with perfect smoothness

, resulting in lost energy referred to as the “ mixing loss ” . In a centrifugal compressor impeller this is traditionally called slip, as it appears that the flow field has slipped against the direction of rotation from the pressure to the suction side. Whether the compressor has a vaned diffuser or not, there is always a vaneless space directly following the impeller where the flow is diffused.. As a result of friction and other factors, a loss, referred to as the vaneless diffuser loss, is experienced. 19 Compressors featuring v aned diffusers will also experience v aned diffuser l osses , which occur as a result of skin friction and incidence losses due to the vanes. 18

Parasitic Losses

Disc friction is a major source of parasitic loss. D isc friction loss in a centrifugal compressor is caused by the friction in the gas flowing in the gap between the impeller bac k wall and the casing wall. Other major parasitic losses include: the losses in the seals, the bearings, and the gear box . Often, these losses and disc friction are referred to collectively as “ external loss. ” 18

Another type of parasitic loss is recirculation. Recirculation losses occur as the flow turns around after leaving the impeller and recirculates back into the impeller section. 19 Some of the flow exiting the impeller leaks through the clearance gaps and seals to the lower pressure regions
of the compre ssor, causing the l eakage loss. 19

Botha and Moolman simulated losses over a typical mass flow range. They found the mixing and the vaneless diffuser losses dominati ng the internal losses. These losses were followed in importance by skin friction, clearance and leakage losses. 19

Flow Control Losses

Centrifugal compressor operation is characterized by an operating map that has a minimum permissible flow rate at each speed and head or pressure ratio combination in order to avoid operating the compressor in surge. Surge is an unstable flow phenomenon that damages the compressor internal components. Surge is most commonly avoided in centrifugal compressors, b y recycling gas when the flow rate is nearing the minimum safe level. Gas recycling is the process of taking a side stream off the discharge line from the compressor and, after cooling the gas, connect ing it back to the compressor suction. The amount of gas recycle is controlled by a recycle valve. This process is extremely inefficient as almost all of the work input in compressing the recycled gas is wasted energy.

Centrifugal compressor flow may also be controlled by suction pressure throttling

. In this case the pressure into the compressor cylinder is intentionally reduced by a throttling valve. This reduces the density and therefore the flow rate of the compressor

. T hrottling increases the head required from the compressor for a given flow rate and therefore reduces the efficiency.Technology Options for Improving Efficiency 2.2.4

Compressor efficiency can be increased by improving the technology used in the design and manufacturing process es

. Based on its preliminary review, DOE identified the follo wing technology options as having the potential to improve compressor efficiency

.

2.2.4.1 Improving Compressor Unit Efficiency

Valves (Reciprocating Compressors)

Reciprocating compressors rely upon a closed chamber to perform compression, but then must somehow exp el the gas and intake new gas in order to repeat the process. Normally, this is done using valves. As the gas traverses the valve, however, it encounters flow resistance that causes pressure loss and requires the prime mover to work harder than if the valv es were not required. Furthermore, valves are normally held closed using springs, which require energy to open. Finally, valves in practice do not open and close instantaneously and crisply, but may “bounce” and allow some gas to slip past what would ideal ly be a tight seal. Simple enlarging valves would seem to enhance flow. However, a practical limit is set by the fraction of the cylinder that can be dedicated to valves. Additionally, larger valves would tend to grow in mass, and exhibit larger losses in actuation and ringing. 16

A number of efforts exis t to improve valve performance. For example, Zahroof Valves claims to offer a 20% increase in valve efficiency (by allowing gas to flow with fewer changes of direction) and 10% reduction in compressor input power

. 20 If so, it would suggest that valves account for a significant fraction of compressor power lo ss. However, t hese figures may pertain to retrofit applications on older units with valves less efficient than those on modern equipment

.

Multistaging (All Technologies)

Although the objective of a compressor is to introduce pressure rise into a gas,

accom panying temperature rise is inherent, even if the machine adds no heat energy. In practice, all compressors add some amount of heat energy. From that comes the practice of describing compressor efficiency relative to an ideal unit that adds no heat energy to the gas (i.e., an isentropic compressor) . As compression is performed, each incremental bit of heat energy causes the rest of the compression process to become less efficient

– the prime mover must work harder to overcome it. As a result, compression pr ocess efficiency could be enhanced by pausing midway, removing heat energy, and then completing the process.

This is essentially what occurs in multistage compression units, which are commonly intercooled ( i.e. , discard heat before the second compressor i nlet). With intercooling, a compression process becomes mathematically closer to the physical ideal. The addition of two or

more stages , each intercooled, is already a common practice used to increase compressor efficiency . Without mentioning cost, however , the marginal benefit to doing so declines because of the inherently lower efficiency of smaller compressors and because each stage introduces new pumping losses as gas is routed from one stage to the next. 16In practice, adding additional compressors where not required by other aspects of an application may add cost, complexity, and maintenance that could deter an operator from opting
for multistage units.

Pressure Wave Optimization (Reciprocating Only)

As gas is drawn into and expelled from the compression chamber, pressure waves are created in the intake and exhaust manifolds. Those waves, and their harmonics, are reflected by the geometr y of the manifold and eventually return to the valve. Depending on when the valve next opens, the propagating wave can aid or hinder the intake or expulsion of gas. For example, the high pressure wave created by the compressor discharge will reflect and re turn to the cylinder exhaust valve. If the pressure peaks when the exhaust valve opens, the prime mover will work harder to expel gas (or expel less gas for the same work). Conversely, if the exhaust valve opening coincides with the arrival of a pressure t rough, the gas will more easily flow out. 16

Complicating the design of such a system is geometric complexity of the manifolds, varying intake an d exhaust pressures (that alter wave velocity), and variation in compressor speed w hich alters the time between valve openings. To address these factors , some groups have
introduc ed actively

- tuned manifolds that can vary their natural frequencies in respon se.

Press ure wave optimization can lower pipeline energy costs by over 20%, 21 though it is unclear how much of that savings is in the compressor, itself . Additionally, it is unclear whether that figure applies to retrofits only, or whether new compressors would also see benefits from the technology.

Operating Speed (Reciprocating)

Reciprocating compressors are designed to operate at a range of speeds, usually described as crankshaft revolutions per minute (rpm). Although high

- speed (roughly, above 900 rpm) reciprocating compressors can be smaller for a given power output ( and may have an accompanying lower installed cost ) , some sources suggest that it may come at a cost to efficiency. 13

One reason for this is increased pumping losses. If faster, smaller units have correspondingly smaller valves, gas flow will be restricted. Compounding that effect is the fact that gas must enter and leave the cylinder more quickly, and flow at higher velocities. Because fluid flow resistance rises on the order of velocity squared, even a modest increase in gas velocity may increase pumping losses significantly. CAGI suggests that the valve l osses alone may rise 20% relative to slower units, though it acknowledges that value may be imprecise

. 11

Beyond pumping losses, higher

- speed unit s may be more prone to vibration issues, and require that additional balancing measures be added to mitigate that vibration. In certain cases, these measures may come at the expense of efficiency. 13

Variable Vane Geometry (Centrifugal)One limitation of centrifugal compressors relative to reciprocat ing units is reduced
tolerance of off

- speed operation. At low flow rates, compressors can “surge,” wherein pressure from the discharge causes flow to reverse, which can damage the unit. Additionally, a compressor at the upper limit of its flow capability can “choke,” and be unable to draw enough gas to function. Normally, large compressors like those used in pipeline applications contain equipment to prevent damage to the unit. However, off

- speed operation, even short of choke or

surge, can result in inefficient gas flow.

One technology th at has been developed to overcome this limitation is variable vanes. Vanes can be installed on either the inlet or the exhaust side of the compressor impeller , and serve to change the angle of gas flow so that it can be more efficiently handled by the impe ller
and/or the diffuser . However, the angle at which peak efficiency is reached varies according to flow rate. Variable vane geometry allows that angle to be adjusted in step with compressor
output; so that efficiency is boosted across the unit’s operatin g range. 17

Variable vane geometry does not necessarily improve peak efficiency of the unit (and may slightly decrease it). As a result, it may no t be useful or economically justifiable for those
units operating at a fixed speed for a base load p capacity.

Dry Gas Shaft Seals (Centrifugal)

Shaft seals in centrifugal compressors separate the high

- pressure volume of the unit from
the ambient. Seals mus t be tight enough to prevent gas leakage, but freely spinning to avoid harming compressor efficiency. Historically, most seals used oil as a lubricant and seala nt. However, such seals require an oil circulating apparatus to remove gas that had dissolved in to the
oil and re

- inject the oil into the seal. In contrast, dry gas seals replace oil with a high

- pressure chamber of air or inert gas that resists the outflow of high

- pressure natural gas from the compression chamber. Such seals are thought to carry reduced maintenance requirements in addition to reducing gas loss. In addition, they may bolster efficiency by exerting less drag on the spinning impeller. 22

Intelligent Flow Control Systems (Reciprocating)

Reciprocating compressor flow can be controlled e fficiently through the use of various
hardware devices that automatically adjust clearance volume , adjust valve behavior, or deactivate ends of individual compressor cylinders. The operation of these devices in
combinations one or more cylinders as pressur e, temperature and speed conditions change must
be done so as to optimize the efficiency, while simultaneously keep ing the compressor operating within safe limits of rod load, pin reversal, power, volumetric efficiency, etc. This requires
efficient “unload ing” hard ware and smart control systems in order to effective ly manage the efficiency and safety of the compressor at all operating conditions. A number of hardware devices and at least one smart control are available for application to reciprocating compr essors. Th is technology is applicable to upstream, transmission, storage and process reciprocating compressors of all sizes. It is more widely used in pipeline applications than elsewhere, being

p Here, “base load” refers to the portion of consumer demand that varies little with time.rather uncommon in the upstream applications where inefficien t suction throttling and recycle operation is prevalent.

Efficient Pulsation Control (Reciprocating)

The GMRC and other sources have develop ed technologies that reduce or eliminate the pressure drop and efficiency losses associated with pulsation control. These involve technologies such as pulsation attenuation networks, tunable side branch absorbers and virtual orifices that cancel pulsation waves, rather than dampen them. Other technologies that have emerged are methods of dynamically changing the pulsat ion dampening orifice size as operating conditions change, which has the potential to optimize the trade

- off between pulsation control and efficiency. All of these technologies are in the early stages of practical application in the field.

2.2.4.2 Improving Prime Mover Efficiency

Turbocharging (Reciprocating)

Turbochargers use smaller centrifugal compressors and turbines to enhance power output of reciprocating compressors. The turbine is installed in the exhaust stream and extracts energy from the flow, while the compressor pre

- compresses ambient air before it enters the power cylinder. In addition to increasing unit power density, turbocharging may increase engine efficiency by utilizing heat that would be otherwise wasted. 23 Conceptually, turbocharging is a
form o f heat recovery, though it is listed outside of that section because the recovered energy is fed directly into the engine.

Turbocharging may also buffer a compressor against reduced efficiency on hot days,
when the less

- dense ambient air diminishes the ou tput power of the engine.

High er Speed (Reciprocating)

In contrast to high

- speed reciprocating compressors, high

- speed reciprocating engines

may tend to be more efficient than their low

- speed and centrifugal counterparts. 13 Less clear is whether this is inherent in the operating principles, or whether it is a result of manufacturers focusing on improving efficiency in high

- speed units, whic h may carry greater appeal to customers for their (generally) lower cost. Nonetheless, Table 2.11 suggests that, at least at small capacities, high

- an d medium

- speed engine efficiency may exceed that of low

- speed engine technology

.

Air/Fuel Controls (All Technologies)

One operating parameter for combustion engines is the air/fuel ratio . In general, low ratios produce more power for a given compressor siz e, but are less fuel efficient. Additionally, which ratio is optimum may vary based on the heat content of the fuel gas, which can differ significantly based on the gas origin. Adding air/fuel controls and exhaust sensors can enable
compressors to operate more efficiently across different operating conditions. Rich

- burn, high

speed reciprocating engines, in particular, may see the greatest benefit from such controls. 24Advanced Ignition Systems (Reciprocating)

Reciprocating engines rely on an ignition source to initiate combustion. Certain ignition strategies may offer the ability to accelerate combustion and ignite higher air/fuel ratios than would be possible with traditional ignition strategies. In general, higher air/fuel ratios offer reduced fuel consump tion (and NOx production), perhaps as much as 3%. 25

Inlet Air Cooling ( Gas Turbine )

Higher ambient air temperatures reduce density of the air being ingested by a gas turbine, in turn diminishing power output and efficiency. 9 Various inlet air cooling strategies have been developed for mitigating that effect, and keeping a turbine closer to its efficient operating point, including fogging, evap oration, vapor compression heat pumping, and (less commonly) adsorption. In addition to maintaining efficient operation in a turbine in service, inlet air cooling may enable specification of a smaller compressor. Instead of meeting peak demand with pure

co mpressor capacity (and, in turn, operating off

- design on colder days), turbine inlet cooling may be able to efficiently make up the difference in power output. 26

2.2.4.3 Heat Recovery (Centrifugal and Reciprocating)

Both compressor units and prime movers alike expe l waste heat while operating

. Depending on the grade of the heat and location of the compressor, it may be economical to use waste heat directly or to generate electrical power. A variety of working fluids can be used for heat recovery cycles, including st eam, pentane, and supercritical carbon dioxide. q

Heat recovery capability can be designed into compressor stations, or added later without disrupting compressor station function. INGAA suggests that heat recovery is more viable for large compressor statio ns with high annual load factors, and estimates that between 500 and 600 MW of generation capacity would be possible. 9 Both centrifugal and recipr ocating compressors can be used with heat recovery. However, centrifugal compressor packages are usually more economically attractive , as they are often paired with gas turbines, which typically have a higher exhaust temperature

.

The savings potential can be considerable. One compressor station in Louisiana recovered 4.6 MW of electrical energy, which represented over 25% of the turbine’s rated

power. 9 As a point of reference, operators may realize a 3

- year investment payback if able to sell generated electricity at 5 cents/kWh. 27

Currently, a company called ORMAT claims to be the only provider of energy recovery systems on gas pipeline compressor s. r However, other technologies that are heat

- source neutral could, in theory, be deployed in similar applications. Echogen Power Systems offers a heat recovery system using supercritical carbon dioxide, claimed to be suitable for a range of power and temp erature levels that would include most natural gas compressors. 28

q Here, “supercritical” refers to a realm of pressure and temperature wherein gases and liquids cease to be distinct and, therefore, no boiling or condensing can occur. This property can save energy in certain applications.

r See Ormat Technologies, Inc

.Although electrical power generation from waste heat requires certain temperature levels to be practically efficient, it is possible to use lower

- grade heat for space heating, water heating, or various industrial processes that require it. Although straightforward to implement, direct heat use requires that there be a demand for the heat, which usually correlates to human population. Because many compressor stations (particularly larger ones, where heat recovery is more practical) are located away from population centers, direct heat use may not be commonly implemented on natural gas compressors.

2.2.4.4 Improving Gas Efficiency

Almost all compressors lose some fraction of the natural gas they process to the atmosphere. Although not directly measured in most efficiency metrics for compressors and prime movers, lost natural gas can be viewed as a form of inefficiency. When gas is l ost, the energy used to compress and transport that gas is lost alongside it. In 1992, compressor station emissions accounted for 16% of natural gas emissions of the oil and gas industry, which, itself, accounted for 14% of global anthropogenic emissions. 29

Reduce Blowdown Frequency

Whether blowdown meaningfully contribute s to a compressor’s annual lost gas total depends directly on how frequently blowdown occurs. EPA suggests that for a typical transmission compressor (reciprocating), a blowdown roughly every two weeks would jettison a volume of gas equivalent to what is lo st via rod packing s annually. 29 Blowdown normally occurs when a compressor is unneeded and switched off and when maintenance is required. Although the former event is largely a function of network factors external to the compressor, reducing the need for maintenance could contribute to gas efficiency by shrinking blowdown frequency.

Dresser

- Rand suggests that motors offer the longest intervals betwe en overhaul, followed by reciprocating compressors and then centrifugals. 13 With respect to unscheduled maintenance, however, centrifugal unit s out perform reciprocating units. 13 Service intervals and unscheduled maintenance may both be improved by using modern valves t , magnetic bearings u , and sensors that monitor vibration patterns and exhaust for signs of impending failure. v

When compressors are stopped but not required to blow down for maintenance, it is possible to maintain pressure until the unit is needed again. Reciprocating compressors in particular exhibit greater losses when stopped, but static sealing devices may be engaged to mitigate this loss. 29 To a lesser degree, centrifugal compressors also lose gas when stopped.

Blowdown Gas Recovery

Eliminating blowdown s altogether is likely infeasible. However, it is possible to attempt

to reco ver the gas blown down, either for storage until the compressor goes online or for

s “Rod packing” is the material surrounding a piston rod in a reciprocating compressor that prevents gas from escaping around the rod.

t See Zahroof Valves

.
u See http://www.waukbearing.com/uploads/NAM_Canned_Magnetics_Case_Study_US_bleed.pdf

.
v See http://www.altronic

- llc.com/detonation

- sensor

- monitoring.shtml

.reinjection into the incoming pipeline. Some sources suggest payback from implementation of such technology may fall between 1 and 3 years. 30

Low

- emission Rod Packing (Recipr ocating)

Various rod packing technologies exist to reduce gas leakage along the shaft of a reciprocating compressor. 31 Normally, the seals and rings are made from advanced materials, f or example, carbon

- impregnated T eflon in place of bronze. 32 One manufactur er claims to have developed an oil

- flooded system that virtually eliminates packing leakage, and to have successfully demonstrated this system at several sites in Europe successfully for 30,000 operating hours. 33

Dry Shaft Seals (Centrifugal)

Shaft seals in centrifugal compressors separate the high

- pressure volume of the unit from
the ambient atmospheric pressure

. Seals must be tight enough to prevent gas leakage, but freely spinning to avoid harming compressor efficiency. Historically, most seals used oil as a lubricant and sealant. However, such seals required an oil circulating apparatus to remove gas that had
di ssolved into the oil and re

- inject the oil into the seal. In contrast, dry gas seals replace oil with a high

- pressure chamber of air or inert gas that resists the outflow of high

- pressure natural gas from the compression chamber. Such seals are thought to carry reduced maintenance requirements in addition to reducing gas loss. 16 22 Therefore, compressors with dry gas seals may need to be less frequently blown down for maintenance.

Non

- seal Leak Sources

In addition to seal leakage, natural gas compressors emit uncombusted gas from other

compres sor componentry, including compressor isolation valves, pressure relief valves, valve stems, pump seals, and other connections and fittings. Nearly any joint, improperly installed or maintained, is a gas leak candidate. EPA suggests that these sources, in aggregate, may exceed seals in overall volume of leaked gas. 29

Hermetic Sealing

Instead of replacing various compressor componentry with improved versions that leak less, some manufacturers offer outright hermetic sealing. This practice is common on small (non

natural gas) compressors found (e.g.) in consumer appliances, but is not widespread for pipeline applications. MAN Diesel & Turbo w and Dresse r

- Rand x

, however, advertise hermetic sealing with an electric motor prime mover specifically for pipeline applications, and claims the package produces no emissions whatsoever.

w See http://turbomachinery.man.eu/products/compressors/pipeline

- compressors

x See http://www.dresser

- rand.com/products/turbo/datum/datumc.php2.2.4.5 Auxiliary Technologies for Improving Compressor Efficiency

Fan and Pump Variab le Frequency Drives

Compressors and prime movers often employ auxiliary hardware such as cooling fans and oil pumps to operate. Depending on operating conditions, including temperature, humidity, and load, demand for these auxiliary services may vary. Powe r fans and pumps with variable speed motors that can match output to demand may offer energy savings relative to lower

- cost single

- speed electric motors.

3. SCREENING ANALYSIS

The purpose of the screening analysis is to screen out technology options that DOE will not consider in its potential energy conservation standard rulemaking for natural gas

compressor s. At the outset, DOE develops a list of technology options for consider ation through its own research and in consultation with interested parties. Development of the list is based on the technologies described in section 2.2 . The identified candidate technology options encompass all those technologies that may improve energy efficiency.

DOE then reviews each technology option considering the following four criteria, as provided in sections 4(a)(4) and 5(b) of Procedur es, Interpretations, and Policies for Consideration of New or Revised Energy Conservation Standards for Consumer Products (see 10 CFR Part 430, Subpart C, Appendix A):

3.1 Technological F easibility

DOE does not further consider technologies that are not incorporated in commercially available equipment or in working prototypes.

3.2 Practicability to M anufacture, I nstall, and S ervice

If DOE determines that the adoption of a particular technology at the mass production level for a given type of equipment, along with that technology’s reliable installation and servicing , cannot be achieved on the scale necessary to serve the relevant market by the time of the effective date of the standard, DOE does not consider that technology further.

3.3 Adverse I mpacts on P roduct or E quipment U tility or A vailability

If DOE determines that a technology will have a significant adverse impact on the utility of the equipment to significant subgroups of consumers, or result in the unavailability of any covered equipment type with perfor mance characteristics (including reliability), features, size, capacities, and volumes that are substantially the same as equipment generally available in the United States at the time, it does not consider that technology further.3.4 Adverse I mpacts on H ealt h or S afety

If DOE determines that a technology will have significant adverse impacts on health or safety, it does not consider that technology further.

DOE will fully document the reasons for eliminating any technology options during the screening analys is an d solicit stakeholder comment.LIST OF ITEMS FOR COMMENT APPENDIX A

-

Item 3

- 1 Given the breadth of application of natural gas compressors, DOE requests comment on where potential cost

- effective energy savings lie. Often, these exist
where market forces do not incentivize the purchase of efficient equipment.

Item 3

- 2 DOE requests comment on the scope of coverage specifically whether a gas compressor energy conservation standard should be inclusive or exclusive of the prime mover.

Item 4

- 1 DOE requests comment about test procedures that may be suitable for assessment of energy consumption in natural gas compressors. In addition to specifying which and how physical parameters must be measured, such a procedure should specify the conditions under which the measurements are taken and interpreted.

Item 4

- 2 DOE requests comment about whether the test procedures in ISO 1217:2009 and ISO 5389:2005, which address the testing of displacement and turbo compressors, respectively, would be appropriate for rating gas compressors. DOE also requests information about other applicable test procedures it should consider along with any deficiencies or issues that should be addressed prior to prescribing test procedure requirements to measure energy consumption.

Item 5

- 1 DO E is seeking both present and historical shipments data (specifically from

2003

- 2013) for gas compressors, with further breakdowns, where available, including, but not limited to, equipment type (both compression principle and driver type), equipment size, and application. DOE is also interested in comments regarding how gas compressors are manufactured and shipped as original equipment from the manufacturer, for example, as a package (i.e., with both compressor and prime mover), or as a separate component, or both.

Item 5

- 2 DOE requests shipment information on upstream and gathering natural gas compressors, and how their numbers compare to those of natural gas compressors in other applications.

Item 5

- 3 DOE seeks comment on how an energy conservation standa rd for gas compressors might impact future equipment shipments.Item 5

- 4 DOE is seeking comment about the types of equipment used in gas compressors. Specifically, DOE is interested in information regarding the compression principles (e.g., positive

- displacement or dynamic compressors) and primary driver types (e.g., natural gas or steam turbines or electric motors) used in gas compressors, as well as what design, construction, and performance characteristics would be attributed to each type. DOE is also interested in information regarding the compression principles and driver types used in gas compressors based on application type.

Item 5

- 5 DOE is also seeking comment about how gas compressors are sized (e.g., by brake horsepower, input/outpu t pressure, or delivered gas volume) and the general sizes of gas compressors based on both equipment and application type.

Item 5

- 6 DOE requests input on ways to characterize gas compressor sizing and selection practices for different equipment and end us e applications.

Item 5

- 7 DOE requests comment on the degree of gas compressor oversizing that is prevalent under current industry practices. Specifically, the degree to which this oversizing may be a factor for different end

- use applications.

Item 5

- 8 Are gas compressors marketed and sold on the basis of efficiency? Do certain customers tend to purchase certain compressor types or efficiency levels? What makes compressors more or less efficient?

Item 5

- 9 DOE seeks information on any voluntary efforts by ma nufacturers that are already in place to improve the energy efficiency of gas compressors and what type of voluntary efforts to improve efficiency, if any, are likely to occur in the near

future.

Item 5

- 10 DOE requests comment on how compressors are market ed, sold, shipped, and assembled, and on the various distribution channels through which gas compressors pass through from the manufacturer to the final end

- user.

Item 5

- 11 DOE seeks comment on the different agents involved in the sale and installation

of a typical gas compressor for each distribution channel.

Item 5

- 12 DOE seeks comment on the share of industry shipments for each different distribution channel, and any differences in gas compressor design that may apply.

Item 5

- 13 DOE seeks comment of wha t consumer populations would be disproportionately

affected if DOE were to adopt new energy conservation standards.Item 6

- 1 DOE is aware that an important application of gas compressors is in the transportation, production, and processing of natural gas. DOE seeks comment on other major applications (e.g., injection, withdrawal, lifting, or filling) in which gas compressors are used.

Item 6

- 2 DOE also seeks information regarding any particular characteristics or features that are unique to each of these d ifferent applications.

Item 6

- 3 DOE seeks input on gas leakage by equipment type, and on data that may help characterize the amount of leakage by specific source.

Item 6

- 4 DOE seeks input on technologies available to reduce gas leakage, including the

cost effectiveness and applicability of each.

Item 6

- 5 DOE requests specific comment on compressor blowdown, including estimated leak volume, technologies able to reduce blowdown frequency and capture the gas

blown down.

Item 6

- 6 DOE seeks comment regarding th e typical energy use of gas compressors broken down by, where available, application type, equipment type, and equipment size.

Item 6

- 7 DOE seeks recommendations on sources of data, or analysis methods that would provide demand profiles for gas compressors and their end

- use applications. Further, DOE seeks comment on what gas compressor design features would affect their typical demand profile.

Item 6

- 8 DOE seeks recommendation s on sources of data or analysis on the fraction of time, in hours, per year that gas compressors spend at off

- design (efficiencies other than the specified design point) operation under normal operating

conditions.

Item 6

- 9 DOE seeks comment on the types, and rate of adoption

, of different control

systems that are employed to adjust a gas compressor’s output to meet end

- use application demands during off

- design operation.

Item 6

- 10 DOE is interested in information about the typical range in efficiency levels of gas compressors broken down by equipment type and size, and why the range exists. For example, do more efficient compressors incorporate particular design

features?

Item 6

- 11 DOE seeks comment about how gas compressor efficiency is likely to change

over time in the absence of standards.

Item 6

- 12 DOE is interested in what opportunities, if any, for improving gas compressor energy efficiency are possible.Item 6

- 13 DOE requests comment about any compressor features that represent usefulness to the user, such as pressure, flow, fuel type, physical size, p ortability, serviceability, emissions, and acoustic noise, and on applications in which particular forms of utility may be especially important. Additionally, how would an effort to increase energy efficiency of a compressor affect these features?

Item 6

- 14 DOE seeks comment about whether installation costs for gas compressors ch ange with higher efficiency equipment. If so, DOE seeks comment about the reasons
for, and the amount of

, such an increase.

Item 6

- 15 DOE seeks comment about whether maintenance c o sts for gas compressors change with higher efficiency equipment. If so, DOE seeks comment about the
reasons for, and the amount of

, such a change.

Item 6

- 16 DOE seeks comment about whether repair costs for gas compressors changes with higher efficiency equ ipment. If so, DOE seeks comment about the reasons for, and the amount of such a change.

Item 6

- 17 DOE recognizes that gas compressors can have a very long mechanical lifetime (hours of operation). While many factors contribute to equipment lifetimes, DOE seeks data about the mechanical lifetimes for gas compressors under typical operating conditions. Further, DOE seeks comment about whether d ifferences in equipment design or capacity would affect gas compressor lifetimes.

Item 6

- 18 DOE seeks recommendations o n sources of data or analysis methods correlating gas compressor maintenance and repair with gas compressor lifetime and efficiency.

Item 7

- 1 DOE is interested in how effi ciency improvements would impact equipment performance, features, ut ility or safety.REFERENCES APPENDIX B

-

1 Interst ate Natural Gas Association of America. Interstate Natural Gas Pipeline Efficiency . 2010. Interstate Natural Gas Association of America: Washington, DC. http://www.ingaa.org/File.aspx?id=10929

2 Interstate Natural Gas Association of America. Interstate Natural Gas Pipeline Efficiency . 2010. Interstate Natural Gas Association of America: Washington, DC. http://www.ingaa.org/File.aspx?id=10929

3 Wilcox, Melissa, Klaus Brun, Ph.D. Guideline for Field Testing of Reciprocating Compressor Performance

. 2009. Gas Machinery Research Council: Dallas, TX. https://www.gmrc.org/documents/ GuidelineforFieldTestingofReciprocatingCompressorPerformance .p df

4 Brun, Klaus, Ph.D., Marybeth G. Nored. Guideline for Field Testing of Gas T urbine and C entrifugal Compressor Performance . 2006. Gas Machinery Research Council: Dallas, TX. https://www.gmrc.org/documents/GuidelineforFieldTestingofCentrifugals.pdf

5 Interstate Natural Gas Association of America. Interstate Natural Gas Pipeline Desk Reference. 2009.

Interstate Natu ral Gas Association of America: Washington, DC. http://www.ingaa.org/File.aspx?id=6070

6 Environmental Protection Agency. Reduce Your Methane Emissions. 2014. Environmental Protection Agency: Washington, DC. http://www.epa.gov/gasstar/index.html

7 Energy Information Administration. About U.S. Natural Gas Pipelines

– Transporting Natural Gas

. 2007. Energy Information Administration, Office of Oil and Gas: Wash ington, DC. http://www.eia.gov/pub/oil_gas/natural_gas/analysis_publications/ngpipeline/fullversi

o n.pdf

8 U.S. Environmental Protection Agency Office of Air Quality Planning and Standards. Oil and Natural Gas Sector Compressors . 2014. Environmental Protect ion Agency: Washington, DC. http://www.epa.gov/airquality/oilandgas/2014papers/20140415compressors.pdf

9 Hedman, Bruce. Waste Energy Recovery Opportunities for Interstate Natural Gas Pipelines. 2008. Interstate Natural Gas Association of America: Washingto n, DC. http://www.ingaa.org/File.aspx?id=6210

10 ICF International. North American Midstream Infrastructure through 2035: Capitalizing on Our Energy
Abundance . 2014. INGAA Foundation: Washington, DC. http://www.ingaa.org/file.aspx?id=21498

11 Compressed Air and Gas Institute. Compressed Air and Gas Handbook, Ch. 7

– Gas and Processes. 2013. Compressed Air and Gas Institute: Cleveland, OH. http://www.cagi.org/education/handbook.aspx#

12 Deffenbaugh, Danny, Klaus Brun, Ph.D., Ralph Harris, Ph.D., J. Pete Harrell , Robert McKee, J. Jeffrey Moore, Ph.D., Steven Svedeman, Anthony Smalley, Ph.D., Eugene Broerman, Robert Hart, Marybeth Nored, Ryan Gernentz, and Shane Siebenaler. Advanced Reciprocating Compression Technology (ARCT) . 2005. Southwest Research Institute: S an Antonio, TX. http://www.netl.doe.gov/File%20Library/Research/Oil

- Gas/Natural%20Gas/NT42269_FG093005.pdf13 Potter, Randy. Don’t Retire... ReHire! The use of Integral Slow Speed Engines as Horsepower Expansion . 2005. Dresser

- Rand: Houston, TX. https://www.d resser

- rand.com/techpapers/tp141.pdf

14 WEG Electric Corp. Synchronous Motors. 2014. WEG Electric Corp: Sao Paolo, BR. http://ecatalog.weg.net/files/wegnet/WEG

- synchronous

- motors

- technical

- article

- english.PDF

15 General Electric. Gas Compression & Mechanical Drive Products . 2014. General Electric. Fairfield, CT. https://www.ge

- distributedpower.com/products/gas

- compression

- mechanical

- drive

,

Solar Turbine. Gas Turbine Packages . 2014. Solar Turbines: San Diego, CA. https://mysolar.cat.com/cda/layout?m=35881&x=7

Caterpillar Oil & Gas. Engines for Gas Compression . 2014. Caterpillar Oil & Gas: Peoria, IL. https://catoilandgas .cat.com/products/engines

16 Hanlon, Paul. Compressor Handbook. 2001. McGraw Hill: New York, NY. http://www.apvgn.pt/documentacao/compressor_handbook_hanlon.pdf

17 Dresser

- Rand. Engineer’s Notebook . 2014. Dresser

- Rand: Houston, TX. http://www.dresser

rand.com/ insights/winter10

- 11/insights_Winter10

- 11 _EngNotebook.pdf

18 Boyce, Mehenvan P., Ph.D. Principles of Operation and Performance Estimation of Centrifigual Compressors. 1993. Texas A&M Engineering Experiment Station Turbomachinery Laboratory: College Station, TX. http://turbolab.tamu.edu/proc/turboproc/T22/T22161

- 177.pdf

19 Botha, Barend, Adriaan Moolman. Determining the Impact of the Different Losses on Centrifugal Compressor Design. 2005. South African Institution of Mechanical Engineering: Cape Town , South
Africa. http://www.saimeche.org.za/resource/collection/1A689269

- FE0A

- 4DC1

- B1EC

5ABFF5534 FC1/Botha_and_Moolman

- 2005_11__600_dpi_

- _2005__21_3___23

- 31.pdf

20 Zahroof Valves, Inc. Compressor Valves

– Redefined . 2014. Zahroof Valves, Inc.: Houston, TX. http://zahroofvalves.com/

21 Slater, DJ. PAN Technology Ready for Field Test. In Compressortech 2

. 2014. Waukesha, WI, June. Compressortech 2 . Pp. 72

- 74. http://www.ct2

- digital.com/ct2/june_2014?sub_id=4IIMGiTXujSb&folio=72#pg77

22 Dresser

- Rand. Dry Gas Seals

. 2014. Dresser

- Rand: Houston, TX. http://www.dresser

rand.com/literature/turbo/85189

- DryGasSeals.pdf

23 EPA Office of Air Quality Planning and Standards. Compilation of Air Pollutant Emission Factors, Volume I: Stationary Point and Area Sources. 2000. Environmental Protection Agency: Research Triangle Park, NC. http://www.epa.gov/ttnchie1/ap42/ch03/final/c03s02.pdf , Page 2

24 EPA. Install Automated Air/Fuel Ratio Controls. 201 2. Environmental Protection Agency: Washington,
DC. http://epa.gov/gasstar/documents/auto

- air

- fuel

- ratio.pdf

25 Altronic, Inc. High Pressure Fuel Injection System for Large Gas Engines and Integral Compressors

. 2004. Altronic, Inc.: Girard. OH. http://www.altronicinc.com/pdf/engine

- controls/form

- HyperFuel

- 11

- 04.pdf

26 Forsyth, John. Gas Turbine Inlet Air Chilling for LNG. 2013. Gas Technology Institute: Des Plaines, IL.
ht tp://www.gastechnology.org/Training/Documents/LNG17

- proceedings/Mach

- 4

- John_Forsyth.pdf27 Engle, David. From Waste Heat to Power: Closed

- loop, organic Rankine

- cycle plants are adding multimegawatts

– without additional fuel. In Distributed Energy, the Jour nal for Onsite Power
Solutions. 2008. Forester Media: Santa Barbara, CA. http://www.ormat.com/research/papers/waste

- heat

- power

28 Persichilli, Alex Kacludis, Edward Zdankiewicz , and Timothy Held. Supercritical CO 2 Power Cycle Developments and Commercialization: Why sCO 2 can Displace Steam. 2012. Echogen Power Systems LLC: Akron, OH. http://www.echogen.com/documents/why

- sco2

- can

- displace

- steam.pdf

29 Southern Research Institute. Greenhouse Gas (GHG) Verification Guideline Series: Natural Gas Compressor Leak Mitigation Technologies. 1999. Environmental Protection Agency: Washington, DC. http://www.epa.gov/etv/pubs/03_v p_mitigation.pdf

30 EPA. Redesign Blowdown Systems and Alter ESD Practices. 2004. Environmental Protection Agency: Washington, DC. https://www.globalmethane.org/documents/m2mtool/docs/redesignblowdownsystems.pdf

31 T.F. Hudgins. Compressor Emission Control s. 2008. T.F. Hudgins: Houston, TX. http://www.tfhudgins.com/files/comm_id_21/EmissionsControl_SalesSheet.pdf

32 EPA. Reducing Methane Emissions from Compressor Rod Packing Systems. 2006. Environmental Protection Agency: Washington, DC. http://www.epa.gov/g asstar/documents/ll_rodpack.pdf

33 Lindner

- Silwester, T. Consider true

- zero

- emission packing for reciprocating compressors. 2014. Hoerbiger Kompressortechnik Holding GmbH: Vienna, Austria. http://www.hydrocarbonprocessing.com/Article/3394995/Consider

- true

- z ero

- emission

- packing

- for

reciprocating

- compressors.html