TOPICAL REPORT NUMBER 3

REVISION NO. 1

SEPTEMBER 1993

Reduction of NOX and SO2

Using Gas Reburning,

Sorbent Injection, and

Integrated Technologies

A report on two projects conducted jointly under

cooperative agreements between:

The U.S. Department of Energy

 and

Energy and Environmental Research Corporation
Reduction of NOX and SO2 Using

Gas Reburning, Sorbent Injection,

and Integrated Technologies

Introduction and Executive Summary ..................................................................................1

Definitions of Technology .......................................................................................................2

Overview Of Two Demonstration Projects At Three Sites .................................................3

Gas Reburning ...................................................................................................................5

Process Benefits .......................................................................................................................6

Reduced Firing Rate ..........................................................................................................7

Flue Gas Recirculation ......................................................................................................7

Overfire Air System ...........................................................................................................8

Boiler Control and Safety Systems ....................................................................................8

Boiler Adaptation ..............................................................................................................8

Integration Of Gas Reburning With Other Technologies ..................................................9

History of Development .........................................................................................................10

Demonstration Beginnings ....................................................................................................10

Legislative & Marketplace Incentives ..................................................................................11

Commercialization .................................................................................................................12

EER’s Marketing Plans .....................................................................................................14

Hennepin: Demonstrating The Potential Of GR-SI On Tangentially-Fired Boilers ........15

Testing Program ...............................................................................................................15

Pretest Modifications ........................................................................................................16

GR-SI Demonstration Data ...................................................................................................16

Lakeside: GR-SI Demonstration On A Cyclone-Fired Boiler ............................................20

Testing Program .............................................. .................................................................20

Pretest Modifications ....................................... ................................................................20

Test Results ...................................................... ................................................................21

Cherokee: Demonstrating GR & Low-NOX Burners On A Wall-Fired Boiler ................22

Testing Program ...............................................................................................................23

Pretest Modifications ........................................................................................................23

Test Results ......................................................................................................................24

Environmental Monitoring ...................................................................................................27

Air Monitoring ..................................................................................................................28

Wastewater Monitoring ....................................................................................................28

Solid Waste & Groundwater Monitoring ..........................................................................29

Health & Safety Monitoring .............................................................................................29 References .................................................................................................................. 31

Cover photo:

Sorbent injection

through boiler wall at

Hennepin Unit No. 1.

TECHNOLOGY
Introduction and

Executive Summary

Coal is America’s most abundant fossil

fuel. Its combustion creates the steam that

produces most of this country’s electricity. The

burning of coal, however, liberates two types

of gases that have been linked to the formation

of acid rain: nitrogen oxides (NOX) and sulfur

dioxide (SO2). With the passage of each

successive piece of clean air legislation over

the past two decades, the electric utility

industry has been made increasingly aware that

it would eventually have to reduce both types

of emissions from existing and new plants, to

environmentally acceptable levels.

With increasing pressures to change

operations on one hand and aging plants with

limited lives and physical space on the other,

the power industry, in conjunction with the

Department of Energy (DOE), has been

exploring and cooperatively developing retrofit emission-control technologies able to

resolve this dilemma. After more than 15

years of experimentation and laboratory

testing, these and other new technologies have

come of age and are now ready for

commercial-scale application.

The Clean Coal Technology Demonstration

Program (also referred to as the CCT Program), is a unique government/industry costshared effort to develop these advanced coalbased technologies. The CCT Program

provides numerous options for addressing a

wide range of energy and environmental issues,

including acid rain, global climate change,

improved energy efficiency, energy security,

and environmental quality. It is intended to

demonstrate a new generation of innovative

coal utilization processes in a series of

full-scale, "showcase" facilities built

throughout the United States. This program

will take the most promising of the advanced

coal-based technologies and move them into

the marketplace by demonstrating their

commercial viability. These demonstrations

are at a scale large enough to provide the

necessary data—design, construction, and

operation—to enable the private sector to

evaluate the commercial potential of each and

to confidently predict each technology's

commercial readiness. The importance of

successfully demonstrating these technologies

has increased significantly since the passage of

the 1990 Clean Air Act Amendments and the

soon-to-follow regulations for the control of

nitrogen oxides.

Gas Reburning, Sorbent Injection and

Integrated Technologies — the subject of this

Topical Report — are one such set of promising innovative developments. In addition to

discussing the technologies involved, this

report will describe two specific projects,

results to date, and the commercial promise of

these processes.

The objectives of Gas Rebuming and

Sorbent Injection were to have a 60% reduction in NOX emissions and a 50% reduction in

SO2 emissions. These objectives have been

achieved at the tangentially-fired boiler at the

Hennepin site of Illinois Power and at the

cyclone-fired boiler operated by City Water,

Light and Power in Springfield, Illinois.

The other project, Gas Reburning and LowNOX Burners, had the goal of a 70% NOX

reduction from the wall-fired boiler operated

by Public Service of Colorado at Denver. In

early preliminary testing, this goal was also

achieved. Energy and Environmental Research

(EER) is now ready to design and install Gas

Reburning and Sorbent Injection systems, and

Gas Reburning-Low NOX Burner systems for

any utility or industrial application. These

technologies are offered with performance and

emission control guarantees.

1
Reduction of NOX and SO2

Using Gas Reburning,

Sorbent Injection, and

Integrated Technologies

Project Participants

Gas Reburning and Sorbent Injection:

Energy and Environmental Research Corp.

U.S. Department of Energy

Gas Research Institute

 Illinois Department of Energy and Natural Resources

 Illinois Power Company

 City Water, Light and Power of Springfield (IL)

 as reburning is an extremely

 flexible technology, adaptable

 to a variety of electric utility

retrofit situations. Used either by itself, or in

combination with other emission-control

Gas Reburning and Low-NOX Burners:

Energy and Environmental Research Corp.

U.S. Department of Energy

Gas Research Institute

Public Service Company of Colorado

Colorado Interstate Gas Company

Electric Power Research Institute

Contacts

Dr. C. Lowell Miller

Associate Deputy Assistant Secretary for

Clean Coal Technology

U.S. Department of Energy

(301) 903-9451

Harry J. Ritz, DOE Project Manager

CT-10

U.S. Department of Energy

Pittsburgh Energy Technology Center

P.O. Box 10940

Pittsburgh, PA 15236

(412) 892-6137

A.D.Jensen

Director of Marketing

Energy and Environmental Research Corp.

P.O. Box 153

Orrville, OH 44667

(216) 682-4007

2

technologies, it can help to significantly reduce

NOX, SO2 and CO2 emissions.

The further development of gas reburning and

its integration with other emission-control

technologies is currently being assisted through

two Clean Coal Technology demonstration

projects. As subsequently detailed in this topical

report, the two demonstration projects include:

(1) a two-plant project where gas reburning is

combined with sorbent injection and applied to a

tangentially-fired boiler and a cyclone-fired

boiler, both burning high-sulfur Illinois coal

(Hennepin and Lakeside, respectively); and (2) a

western, low-sulfur coal-burning plant with a

wall-fired boiler, where gas reburning and lowNOX burners are combined to reduce NOX

emissions (Cherokee). These three boiler types

(tangential, cyclone, and wall-fired) represent

97% of the pre-NSPS boiler population. Each of

the three demonstration facilities has its own set

of retrofit conditions and emission problems,

yet each is a logical candidate for demonstrating gas reburning technology.

Definitions of Technology

Gas Reburning

Gas Reburning (GR) is primarily a NOX

control technology. A small amount of natural

gas (15 to 20% of the total energy input) is

injected in place of coal into the boiler above

the normal combustion zone. This creates an

oxygen-deficient (fuel-rich) zone where the

hydrocarbon radicals from the gas react with

the nitrogen oxides from the coal combustion.

This reaction forms molecular nitrogen, the

same kind of nitrogen that exists naturally in

the atmosphere. Additional air is injected

above the reburn zone, finishing the combustion at a lower temperature and preventing

NOX from forming. Used by itself, gas

reburning has been shown to routinely reduce

NOX emissions by more than 60%.

G
Illinois Power’s Hennepin Unit No. 1

is the demonstration site for the GRSI process on a tangentially-fired

pulverized coal unit.

Sorbent Injection

Sorbent Injection (SI) technology is used to

decrease SO2 in emissions from coal-fired

boilers. A sulfur-absorbing agent, usually lime

or hydrated lime, is blown into the flue gases.

SO2 removal is enhanced by the injection

pattern of the sorbent and by using chemical

additives. The resulting reactions produce dry

non-toxic particles which are collected downstream in either the electrostatic precipitator

after flue gas conditioning or the baghouse. SI

in combination with GR technology has

achieved SO2 removal in the 50-60% range.

Low-NOX Burners

Low-NOX Burners (LNBs) are coal-fired

burners specifically designed to reduce the

formation of nitrogen oxides through the

careful control of the coal/air mixture during

combustion. By causing a more gradual

mixing of the fuel and air, the combustion

flame temperature is lowered, resulting in a

NOX reduction of 30 to 50%, and up to a

70-75% reduction of NOX when used in

combination with GR.

Overview Of Two

Demonstration Projects

At Three Sites

There are two demonstration projects

discussed in this report, each involving the

use of gas reburning in conjunction with a

second type of emission control technology.

The performing organization in both projects

is Energy and Environmental Research

Corporation (EER) of Irvine, California, with

its Engineering Services Group located at

Orrville, Ohio.

The Hennepin/Lakeside Project

The Hennepin/Lakeside Project was

intended to demonstrate the combined use of

gas reburning and sorbent injection to achieve

approximately 60% NOX reduction and 50%

SO2 capture on each of two different boiler

configurations (tangential and cyclone). Both

of these boilers are burning high-sulfur coal.

 Control

CCT Site Firing Technologies

 I Hennepin Tangential GR, GR-SI, SI

 I Lakeside Cyclone GR, GR-SI, SI

 III Cherokee Wall LNB, GR-LNB

3
City Water, Light and Power Company’s

Lakeside Unit 7 is the demonstration

site for GR-Sl technology on a cyclonefired boiler.

4

Gas reburning and sorbent injection can be

conducted independently or in combination.

The total project cost of approximately

$37.5 million is shared 50/50 between DOE

and the project participants, which include:

Energy and Environmental Research Corporation (EER), the Gas Research Institute (GRI),

the State of Illinois, Department of Energy and

Natural Resources, and the two host utilities,

Illinois Power Company and City Water, Light

and Power of Springfield, Illinois.

The Hennepin/Lakeside Project was

selected by DOE in 1986 and was awarded a

cooperative agreement in 1987. Construction

was initiated at Hennepin in May 1989 and

was completed in August 1990 followed by

startup testing. At Lakeside, construction was

initiated in June 1990 and was completed in

May 1993. Operation at Hennepin was begun

in December of 1990 and at Lakeside in May

of 1993. A final report is scheduled for

publication in November of 1994.

The Cherokee Station Project

The Cherokee Station Project, located in

Denver, Colorado, focuses on NOX reduction

only, since ground-level ozone is a major

concern in the Denver area and because the

station’s wall-fired boiler is burning compliance coal. Both gas reburning and low-NOX

burners are used to reduce NOX emissions by

approximately 70%. The total project cost of

about $16.2 million is divided 50/50 between

DOE and the remaining project co-funders: the

Public Service Company of Colorado (the host

utility), the Gas Research Institute, Colorado

Interstate Gas Company, the Electric Power

Research Institute, and EER. The demonstration is located at the 172 MWe Cherokee

Station, Unit No. 3.

The Cherokee Station project was selected

by DOE in December of 1989. Design work

began in 1990 and construction was completed

in April of 1992. Project completion and the

final report are scheduled for December 1994.
Gas Reburning

The need to reduce NOX emissions from coalfired boilers has gained increased attention in

recent years as more is learned about the

environmental impact of nitrogen oxides in the

formation of acid rain, smog, visibility impairment and climatic warming. While about half of

all NOX pollution comes from automobiles and

other types of vehicles, coal-burning boilers

contribute about 25% of the total NOX emitted

nationwide. Thus, there is a significant need to

develop more emission-control technologies for

reducing NOX from power plants. Gas reburning

is one such technology that has been shown to

reduce nitrogen oxides by 60% or more in a

typical coal-fired boiler.

Gas reburning is applicable to all types of

coal-fired boilers. Even though other methods

exist to reduce NOX emissions from boilers,

gas reburning is one of the most cost-effective

reduction methodologies.

Full Scale Gas Reburning Tests

 Gross Capacity Firing

UtiIity Unit (MWe) Configuration

Illinois Power Hennepin 1 80 Tangential

P.S. Colorado Cherokee 3 172 Wall

City Water, Light & Power Lakeside 7 40 Cyclone

Ohio Edison* Niles 108 Cyclone

*This demonstration is not part of the CCT Program.

Public Service of Colorado’s Cherokee

Station Unit No. 3 is the test site for the

GR/Low-NOX Burner technology

demonstration. It burns low-sulfur

western coal. The city of Denver,

Colorado is in the background. 5
Typical GR-SI injector

specifications.

Natural Gas Reburning Controls Emissions

In the 1970s burning natural gas

in a utility boiler was limited. Gas

supplies appeared to be diminishing rapidly, and the government

passed laws restricting the use of

gas in utility boilers. But today, the

position on natural gas use has

changed. As federal price controls

were removed from gas, new

supplies became available, and a

gas surplus developed. Concerns

over acid rain prompted new

attention to gas, which burns

cleanly and emits virtually no SO2.

 NOX emissions from a gas

reburning system are expected to

be about 60% less than those from

a unit fired solely with coal.

The capital cost of retrofitting a

natural gas reburn system on a

500-megawatt boiler is estimated

to be around $30 per kilowatt.

This approximate capital cost

must be adjusted depending on

the boiler configuration and

design requirements.

An industry study examined

the feasibility of using up to 20%

natural gas at the 50 largest SO2

emitting power plants in the

United States. It found that gas

supplies are available and that

nearly 86% of the plants could be

hooked into gas pipelines at a

cost of less than $8 million per

plant.

6

Process Benefits

While being able to significantly reduce

nitrogen oxide emissions from coal-fired

powerplant boilers, gas reburning has the

following additional benefits:

Flexibility—

Gas reburning is applicable to all types of

coal-buming boilers: tangentially-fired,

cyclone-fired, wall-fired, wet bottom, etc.

As detailed in the demonstration project

descriptions, gas reburning is a technology

that can be made to work with, and positively complement, other types of emissioncontrol processes, such as sorbent injection

and low-NOX burners;

Ease of Retrofit—

Gas reburning requires a minimum amount of

new capital equipment to make it work on an

existing coal-fired boiler. Since there is very

little additional space required, gas reburning

can be retrofitted into plants on even the

most physically restricted sites:

Particulate Reduction—

Since natural gas contains no ash, particulate

loading is reduced in direct proportion to the

amount of coal displaced;

SO2 Reduction—

In similar fashion, since natural gas contains

no sulfur, SO2 emissions are reduced in direct

proportion to the amount of coal displacement;

and

 CO2 Reduction—

Since the ratio of hydrogen to carbon is greater

for natural gas than for coal, gas reburning

reduces carbon dioxide (CO2) emissions by

about 6-9% at nominally 15-20% of fuel

substituted by natural gas (CO2 is not normally

considered a pollutant, but it has been identified as a "greenhouse gas" contributing to

climate change).
Reduced Firing Rate

The firing rate of the coal burner is

reduced by simply cutting back on the

amount of coal supplied to the burner.

Their operation at less than maximum

capability is known as burner "turndown."

Burner turndown has several benefits by

itself. Because there is less coal processed

through the plant pulverizers, there is less

fly ash produced, resulting in a reduced load

on the precipitator. Also, since the combustion intensity in the lower furnace regions is

reduced in proportion to the burner turndown, there is a direct beneficial effect on

NOX emissions, and a further reduction in

ash deposition potential.

Flue Gas Recirculation

For gas reburning to be most effective,

the natural gas must be injected into the

furnace and mixed rapidly with the coal’s

combustion products. In smaller boilers,

adequate mixing can normally be achieved by

simply injecting the natural gas at a high

velocity. However, in larger furnaces it is

difficult to obtain adequate mixing through

simple injection, since the amount of gas

supplied is quite small, compared to the total

mass flow passing through the furnace. In

these instances, penetration of the injected

gas can be improved by adding flue gas as a

carrier with minimal oxygen content to

maintain the fuel-rich zone.

Demonstration Summary and Status Update

Enhancing the Use of Coals by Gas Reburning and Sorbent Injection

Project Status Update

The GR-SI process has achieved 60%

NOX reduction and 50% SO2 reduction

goals on different boiler configurations at

power plants burning high-sulfur

midwestern coal —a tangentially fired

nominally 80-MWe boiler at Illinois Powers

Hennepin Plant in Hennepin, IL, and a

cyclone-fired nominally 40-MWe boiler at

City Water, Light, and Power's Lakeside

Station in Springfield, IL. The Hennepin

project has been completed.

Plant Capacity/Production

Hennepin: tangentially-fired 80 MWe (nominal)

Lakeside: cyclone-fired 40 MWe (nominal)

Project Status/Accomplishments

Permitting and engineering design

efforts were originally completed for three

project sites. In 1990, plans to use the third

site (Bartonville, IL) were suspended.

Construction and operations are

complete at the tangentially-fired boiler at

Hennepin. A matrix of 32 gas reburn tests

were completed, achieving NOX reduction

rates of 60-65%. In one short-term test, a

77% reduction in NOX was achieved.

Evaluation of 20 over-fired air tests

indicated substantial NOX reduction was

achieved at low loads with lesser reductions as load increased. Combined

operational testing of gas reburning and

sorbent injection began in August 1991 with

SO2 reduction in the range of 50-55%. Longterm load following testing, initiated in January

1992, has exceeded project goals of 60% NOX

and 50% SO2 reductions. Operations at

Hennepin were completed January 15, 1993.

At Lakeside, construction and equipment

checkout were completed in May 1993, at

which time start-up activities were initiated.

Project Funding

Total project cost $ 37,588,955 100%

DOE 18,747,816 50%

Participants 18,841,139 50%

Participants

Energy and Environmental Research

Corporation; Gas Research Institute; Illinois

Department of Energy and Natural Resources;

Illinois Power Company; City Water, Light and

Power of Springfield, Illinois.

Project Objective

To demonstrate gas reburning to attain

60% NOx reduction along with sorbent

injection to reduce 50% of the SO2 on two

different boiler configurations: tangentiallyfired and cyclone-fired.

Commercial Application

Gas reburning and sorbent injection is

the unique combination of two technologies.

The commercial application for these

technologies, both separately and combined, extends to both utility companies

and industry in the United States and

abroad. In the United States alone, these

two technologies can be applied to over

900 pre-NSPS utility boilers; additionally

the technologies can be applied to new

utility boilers. With 60% NOX removal and

50% SO2 removal, these technologies have

the potential to extend the life of a boiler or

power plant and also provide a way to use

higher sulfur coals without exceeding

emission limits for NOX and SO2.

Milestone Completion

Phase I–Design and Permitting 5-89

Phase II–Construction, Start-up, and

Shakedown

 Hennepin

 Lakeside

Phase III–Operation, Data Collection,

Reporting and Disposition

 Hennepin

 Lakeside

Project Complete

8-91

5-93

12-93

8-94

12-94

7
Boiler Distribution

in U.S.

 %

Wall-Fired 46

Tangentially-Fired 40

Cyclone-Fired 11

Other 3

Total 100

8

Flue gas is a convenient natural gas

carrier, since it contains only about three

percent oxygen and is readily available from

the combustion process. Normally recirculation of about three percent of this gas is

sufficient. In the case of a gas reburning

application, a typical flue gas recirculation

system includes a low-volume high-pressure

fan, a cyclone dust collector, and ducting to

the injectors. Since flue gas recirculation is

commonly used in many commercial coalfired boilers to control steam temperatures,

its technology is proven. For application in

gas reburning, however, the flow rate of

these systems must be lowered and the

pressure increased.

Correct location, size, and shape of the

gas injectors are important to the success of

the gas reburning process. These parameters

vary with each application and are therefore

determined by site-specific design and

process modeling.

Overfire Air System

The overfire air system supplies the

remaining air required to complete combustion.

The total air supplied to a boiler with gas

reburning is about the same as that supplied for

normal operation. The only difference is due to

the slightly different combustion air requirements for natural gas compared to coal.

The location, size, and shape of the overfire

air ports are important design parameters. For

instance, the air must be injected far enough

downstream from the gas injectors to provide

adequate residence time for the NOX reduction

reactions to occur. At the same time, however,

they must be close enough to assure complete

combustion within the furnace chamber. It is

possible, by varying the design of the gas injectors and overfire air ports, to minimize NOX

emissions without significant reduction of boiler

thermal performance or combustion efficiency.

Retrofitting with gas reburning can

therefore provide an opportunity to improve

the operation of an existing power plant.

Boiler Control and

Safety Systems

Some modifications are required to the

boiler control system in order to implement

gas reburning. These usually involve

changing the fuel and air controls to include

the gas and overfire air streams. Additional

controls are required where flue gas

recirculation is utilized. The overall operation of the boiler, including the control of

steam flow, excess air, steam pressure and

temperature are not affected provided that

adequate excess air control capability exists

on the boiler.

As with these demonstrations it is

necessary to design a Safety System according

to NFPA guidelines to ensure that no added

risks to boiler operation are introduced by the

installation of the gas reburning system. Each

site must be examined individually due to the

presence (or absence) of an existing flame

safety system. The presence of a main fuel

flame in the boiler and boiler load greater than

minimum safe values for reburning must exist.

Boiler Adaptation

Even though each firing configuration

has similar flow pattern characteristics,

existing plants have all been engineered to

achieve specific steam conditions and flow

rates, and to bum specific types of coal. No

two retrofit situations can therefore be

expected to be the same. Generally, however, installing a gas reburning system

within a given type of boiler will require the

following types of changes.
Coal burners must be "turned down" by

about 20% when retrofitting with gas reburning. Although most types of boiler firing

configurations can accommodate this level of

turndown, the effects on the furnace flow

patterns differ. In wall- and cyclone-fired

boilers, turndown can be achieved by removing some burners or cyclones from service, or

by turning them down uniformly. The general

flow patterns in the furnaces remain virtually

unchanged. With a tangentially-fired boiler,

however, turning down the burners can also

change the overall swirl in the furnace. This,

coupled with changes in burner tilt to maintain

steam temperature, can cause changes in the

furnace’s overall flow patterns. When low-NOX

burners are used with gas reburning in wallfired units, burner velocities, swirl, and flame

volume are altered.

Upper furnace conditions are substantially different for wall-, tangentially-, and

cyclone-fired boilers. This means a different

approach must be taken to retrofit each type.

Both numerical and physical flow models

have been developed to determine the

optimal injection location. These models

address both furnace flow patterns and

thermal conditions.

Integration Of Gas

Reburning With Other

Technologies

One overriding advantage of gas reburning

technology is its compatibility with other

emission-control technologies, enabling it to be

integrated into other advanced systems. This

capability significantly expands its potential

role for combination with a wide range of other

applications. Examples include using it in

combination with the following technologies:

SO2 Control Technologies —

Furnace Sorbent Injection, Duct Sorbent

Injection, Wet Scrubbers, Dry Scrubbers, and

Coal Switching;

NOX Control Technologies —

Low-NOX Burners, Selective Non-Catalytic

Reduction (ammonia or urea injection), and

Selective Catalytic Reduction; and

Particulate Control Technologies —

Electrostatic Precipitators and Fabric Filters

(Baghouse).

Gas reburning has been integrated with two

other emission-control technologies (Furnace

Sorbent Injection and Low-NOX Burners) in two

demonstration projects involving all three types

of boiler firing configurations. The two types of

integrated emission-control systems may prove

to be popular, due to their universal benefits

vis-a-vis the specific requirements of the 1990

Clean Air Act Amendments.

One other type of combined system, Gas

Reburning/Low Sulfur Coal Switching, also

seems to be an attractive means of controlling

both NOX and SO2. However, switching to

low-sulfur coal changes a number of combustion dynamics and design parameters.

GR/S1 equipment schematic, Hennepin Unit No. 1.

9
Gas Reburning

Process Factors

• Slightly Fuel-Rich

 (90% theoretical air)

• Reactant Gas Phase

 Residence Time

 (0.3 - 0.5 seconds)

• Furnace Temperature

 (1600-2200 °F)

10

History of Development

The development of gas reburning technology has been underway in various laboratories

for some time. Researchers in the 1970s

included the John Zink Company and Shell

Development Company in the U.S. Subsequent

work was also done by Mitsubishi of Japan,

including commercial scale tests where NOX

reductions greater than 50% were achieved

when oil was used as the reburning fuel. The

California-based firm of Energy and Environmental Research Corporation (EER)

became interested in the potential of gas

reburning and, with support from EPA and

GRI, began extensive bench and pilot-scale

testing in 1981 to characterize the fundamental

process variables. Tests conducted on a 10

million Btu/hr (1 MWe) pilot plant convinced

EER that natural gas is the best fuel for

reburning. These tests also provided valuable

scale-up information needed for the development of commercial applications under

industrial conditions.

Sorbent injection has been undergoing

development since the mid 1970s with funding

from EPA, DOE, EPRI and several commercial firms. Most of the work has focused on

identifying the process parameters which

optimize sulfur capture. Work has also been

done on determining the impacts of the sorbent

injection process on the overall performance of

boilers, and on finding methods to reduce these

impacts. This work included laboratory scale

reactivity tests; bench scale process design

development tests that focused on time/

temperature history and sorbent reactivity

effects; large pilot-scale testing that focused on

impacts of firing system design; and combustion model development programs. A number

of field evaluations have been completed and

additional efforts are in progress. EER has

participated both directly and indirectly in most

of this development work.

In the last 10 years, a number of test programs for sorbent injection have been carried

Demonstration Beginnings

The next logical step toward commercialization of gas reburning and integrated

technologies is to apply the existing knowledge

and experience gained at the bench and pilotplant level to a commercial operating plant.

The technology needs to be demonstrated as

being technically sound and economically

competitive. DOE’s Clean Coal Technology

Demonstration Program is providing the

means to accomplish that end.

EER’s Gas Reburning-Sorbent Injection

(GR-SI) proposal was chosen for funding in

DOE CCT-1. Initially intended to be installed

at three different sites with three different

boiler configurations, this project was subsequently cut back to only two host sites in

Illinois. The May 1989, CCT-III solicitation

resulted in funding of EER’s second gas

reburning demonstration project: an integrated GR/Low-NOX Burner project on a

wall-fired boiler at the Cherokee Station of

Public Service of Colorado near Denver,

Colorado.

Work on these two projects is well

underway. When completed, they will provide

a comprehensive data base for use in the

development of additional applications to other

commercial plants. These two projects will

also provide the much needed validation of the

processes involved and the design methodologies employed. They will demonstrate to the

utility industry that viable technologies do

exist to reduce NOX and SO2 emissions to the

levels required by the Clean Air Act Amendments of 1990, without having undue economic or operational impacts.

out on boilers ranging from 15 to 600 MW,

using a variety of coals. The Clean Coal Technology Program has several of these sorbent

injection projects. These projects, however, all

focused on optimizing sorbent injection by itself.

None involved gas reburning.
Legislative &

Marketplace Incentives

Gas reburning can be applied commercially to meet specific NOX control requirements in a cost-effective manner. Gas

reburning also controls SO2 by displacing

part of the coal which contains sulfur. In

addition, sorbent injection, integrated with

gas reburning, provides enhanced SO2

control. Therefore, both SO2 and NOX

control regulations are important to the

deployment of gas reburning and integrated

technologies.

Titles I and IV of the 1990 revisions to the

Clean Air Act are intended to mitigate NOX in

ozone non-attainment areas and acid rain,

respectively. They include NOX and SO2

control provisions which could be met by gas

reburning and integrated technologies.

Title IV – Acid Rain Mitigation

Title IV is intended to reduce both NOX and

SO2 so as to mitigate acid rain. The top 100

SO2 sources are required to moderate SO2

emissions and implement NOX controls in

Phase I (starting in January 1995). In Phase II

(starting in January, 2000) all sources are

required to have both NOX and more stringent

SO2 controls.

Title IV controls SO2 via a system of

emission allowances. Each allowance authorizes the bearer to emit one ton of SO2. The

EPA will distribute the allowances based on

the plant’s total annual heat input in the mid

1980s multiplied by an emission factor (2.5lb./

Demonstration Study and Status Update

Evaluation of Gas Reburning and Low-NOX Burners on a Wall-Fired Boiler

Plant Capacity/Production

Public Service of Colorado Cherokee

Station, Unit No. 3 — 172 MWe

Project Status/Accomplishments

Phase 1, Design and Permitting, began on

October 13, 1990 and was essentially

completed in September of 1991. Work

completed in Phase I included permitting

activities, engineering design, drawings and

process specifications and ordering of long

lead time items.

Phase 11, Construction and Startup, began

on June 13, 1991 with demolition and the removal of an abandoned electrostatic precipitator. The construction phase of the project

proceeded through the remainder of 1991 and

was concluded on April 24, 1992. Startup was

completed with only minor problems on June

30,1992.

Phase III of the project began after

maintenance work was performed on Unit

#3's pulverizers during the summer of 1992.

Phase III work completed to date includes

complete checkout of the Continuous

Emissions Monitoring System (CEMS) and

the Boiler Performance Monitoring System

(BPMS), a baseline test with the Low NOX

Burners and parametric optimization tests.

The optimization testing was completed in

April 1993. Results of the optimization tests

indicate that NOX reduction of 70% from

baseline values were achieved at full load.

Long Term Testing has started and is

planned to continue for a twelve month

period. In preliminary startup tests a 70%

NOX reduction was achieved.

Project Funding

Total project cost $16,194,172 100%

U.S. DOE: 8,097,085 50%

Other Participants: 8,097,087 50%

Participants

Energy and Environmental Research

Corporation, Public Service Company of

Colorado, Gas Research Institute, Colorado

Interstate Gas Company, Electric Power

Research Institute, U.S. Department of

Energy.

Project Objective

To attain a 70% decrease in the emissions

of NOX from an existing wall-fired utility boiler

firing low-sulfur coal using both gas reburning

and low-NOX burners.

Commercial Application

Gas reburning in combination with lowNOX burners is applicable to wall-fired boilers.

The technology can be used in new and preNSPS wall-fired boilers. Specific features of

this technology that increase its potential for

commercialization are as follows:

• Can be retrofitted readily to existing plants

• Reduces emissions by more than 70%

• Has the potential to improve boiler operability

• Has the potential to reduce the cost of

 electricity

• Consists of commercially available

 components

• Requires minimal space

Milestone Completion

Phase I—Design and Permitting 9-91

Phase II—Construction, Start-up, and

Shakedown

Phase III—Operation, Data Collection,

Reporting and Disposition

Project Complete

 6-92

 9-94

 12-94

11
106

 Btu for Phase I and 1.2 lb/106 Btu

SO2 and NOX emissions in the United

States, showing that NOX emissions

have generally held constant from

1973 to 1991 at 18-20 million tons per

year. Sources: DOE/FE0193P and

EPA-450-R-92-001

Phase II). New plants receive no allowances.

The SO2 emission allowances may be sold

or bought. Decisions will be made to install so

2 controls or to buy allowances based on the

commodity costs of SO2 allowances ($/ton of

SO2 emitted)

The SO2 control provided by gas reburning

and integrated technologies will free additional

allowances which may be sold at current market

values.

Title IV requires existing units to be retrofitted to reduce NOX emissions to preliminary

emission limits of 0.45 and 0.50 lb/106

 Btu for

tangentially- and wall-fired units, respectively.

Gas reburning demonstrations have satisfied

these NOX limits readily on a routine basis. Environmental Protection Agency will define

limits for cyclones, wet bottom furnaces and

cell burner furnaces by 1997. Compliance may

be achieved by meeting these limits on an annual average basis by any means, or by applying "Low NOX Burner Technology." This term

will be specifically defined by EPA in late

1993 and is expected to include conventional

low NOX burners and possibly overfire air ports

which are an integral part of gas reburning.

Title I — Ozone Non-Attainment Area

NOX Mitigation

Atmospheric ozone is produced in part by

reactions involving NOX. Title I requires NOX

emissions to be reduced so as to bring areas

with high ozone into compliance with ambient

air quality standards. The EPA has defined the

specific areas of the country with ambient

ozone concentrations exceeding the standards

as ozone non-attainment areas.

In some cases, NOX sources outside of nonattainment areas may be transported into the

areas by prevailing winds, thus contributing to

the high ozone levels in the area. In such cases,

the contributing areas and non-attainment areas

may be combined into Transport Regions. All

sources within the Transport Regions are then

subject to NOX control. There is potential for

most of the United States east of the Mississippi

River to be included in such Transport Regions.

For plants within ozone non-attainment

areas or transport regions, compliance with the

Title IV NOX requirements may be a moot

point. The additional NOX reductions required

by Title I will necessitate more effective

controls than the Low NOX Burner Technology

of Title IV.

Gas reburning and integrated technologies

are excellent candidates for meeting these

combined Title I and Title IV requirements.

Gas reburning alone can achieve over 60%

NOX control. In addition, if less NOX control is

required initially (for Title IV compliance),

less gas can be cofired, further reducing cost. If

more NOX control is required, the gas reburning

system can be upgraded with Low NOX Burners

or to Advanced Gas Reburning.

Commercialization

EER is now ready to design gas reburning

and sorbent injection systems for virtually any

utility boiler application. Accordingly, EER is

now offering these technologies commercially

with performance and emission control

guarantees.

The potential commercial applications of the

emissions-control technologies involved in both

demonstration projects, while similar, are nevertheless different enough to discuss separately.

GR-SI

(Hennepin & Lakeside Projects)

The commercial market potential for gas

reburning and sorbent injection, either

separately or combined, includes both utility

and industrial applications in the U.S. and

abroad. In combination, these two technologies can be retrofitted to over 900 pre-NSPS

utility boilers in the U.S. alone. They can

also be applied to new boilers. Their use

could enable the use of higher sulfur coals

without exceeding emission limits of NOX

and SO2.

Millions of Metric Tons

12
Economic Considerations

Since gas reburning and integrated technologies can meet or

exceed the NOX control requirements of both Title I or Title IV of

the 1990 Amendments to the

Clean Air Act, economic considerations are a key issue affecting

technology development. Application of gas reburning and integrated technologies requires

modifications to existing power

plant equipment. As a result its

capital costs and operating costs

depend on site-specific factors.

Some factors affecting the cost of

these gas reburning technologies

are:

• gas availability at site

• coal-gas cost differential

• sulfur dioxide removal requirements

• value of SO2 allowances

The emission control costs for

gas reburning and integrated

technologies as applied to a nominal 500 MWe power station with a

capacity factor of 65%, a SO2

emission level of 6.0 lb/106 Btu and

a $1.00/106

 Btu coal to gas cost

differential are shown below in the

table.

The operating cost of gas

reburning is dominated by the differential cost between coal and

gas. For the subject sites of this report, the gas-coal cost differential

ranges from $1.00 to $1.50/106

Btu, corresponding to 90-95% of

the total operating cost. For gas

reburning-sorbent injection, the

cost of the sorbent influences costs

particularly for high sulfur coals

Nominal Performance and Costs

of Gas Reburning and Integrated Technologies

requiring substantial amounts

of sorbent. Typical capital and

operating costs for gas

reburning technologies is

shown in the figure below as a

function of the coal to gas cost

differential.

The capital cost component corresponds to 0.7 to 2.0

mills/kwhr for the various

systems, independent of the

coal-gas cost differential. The

operating cost increases

linearly with the coal to gas

cost differential.

Capital and operating costs

presented here are application specific; consequently the

data presented here serve to

indicate economic trends.

13
GR-Low-NOX Burners

(Cherokee Station)

Gas reburning in combination with lowNOX burners is applicable to wall-fired

utility boilers, both pre-NSPS and new. The

addition of the low NOX burner enhances

the commercialization potential of this

combined technology.

Gas Pricing

and Availability

Current forecasts show

excellent gas reserves and

stable prices compared to

previous projections. Gas is

now increasingly a market

commodity not so different

from coal. Gas users can

negotiate directly with producers and transporters under a

variety of contractual arrangements and options ranging

from spot pricing to long-term/

price-certain contracts for

natural gas supply.

EER’s

Marketing Plans

EER has been closely involved in the

commercial development of both sorbent

injection technology (since the mid-1970s)

and gas reburning systems (since 1981). It is

also a pioneer in the integration of these two

technologies, and is the first organization to

combine gas reburning with low-NOX

burners. This long and accomplished track

record in the development of NOX and SO2

control systems, coupled with the sponsorship and involvement in the three integrated

GR demonstration projects featured in this

report, gives EER the necessary experience

and the technical know-how to market these

technologies.

According to recent reports, the marketplace demand for such easily retrofitted,

integrated emission control systems is quite

large, ranging from 25% to 80% of the coalfired utility boilers in the U.S., depending

primarily on the gas-coal cost differential.

The most likely candidates for gas

reburn/sorbent injection retrofits would be

utility boilers with the following characteristics:

• Currently burning medium- to high-sulfur

coal,

• Have at least 10 but less than 20 years of

remaining useful life,

• Restricted or cramped sites, and

• Ready access to a natural gas supply.

Commercialization of this technology

will largely depend upon the technical

expertise and demonstration experience

gained from this program. This information

will permit the analysis and design of

customized gas reburning and integrated

technology retrofit systems to suit the

specific needs of all potential customers — a

capability absolutely critical to the successful implementation of these technologies.

14
Hennepin:

Demonstrating The

Potential Of GR-SI On

Tangentially-Fired

Boilers

The GR-SI testing and demonstration

program recently completed at Illinois

Power’s Hennepin Generating Station, Unit

#1 is one-half of a larger project intended to

show the ability of EER’s integrated gas

reburning and sorbent injection process to

reduce NOX emissions by 60% and SO2 by

50%.

Testing Program

The objectives of the test program were: (1)

to optimize the operation of the GR-SI system,

(2) to show that the performance goals have

been achieved, (3) to quantify the costs and

operational impacts of the GR-SI process, (4)

to build a data base for use in subsequent GRSI applications, and (5) to provide sufficient

operating hours to determine the long-term

effects of GR-SI operation.

Testing began with baseline operation

(without GR-SI) for 50 days to gather baseline

NOX and SO2 emission data. Gas reburning was

then optimized, followed by the optimization of

the sorbent injection process. A 12-month,

long-term demonstration of GR-SI using the

baseline coal as primary fuel was concluded in

October 1992.

In addition to emission data, operation and

maintenance costs for the GR-SI system were

monitored, along with all maintenance costs

associated with boiler operation. Data were

also collected for optimization of the percentage of gas heat input, zone stoichiometries, gas

injection velocity, sorbent mass flow rate,

sorbent injection velocity and configuration,

and boiler operation parameters.

To be able to monitor the emissions and

performance data, a Boiler Performance

Monitoring System (BPMS) was developed

and installed at Hennepin. This automated,

real-time system enables EER to continuous

monitor emissions, heat absorption trends,

stoichiometric calculations, and boiler

performance. It also provides immediate

information on fuel mass flow rates, steam

rates, temperatures, and pressures. Manual

sampling was done of particulate flow at the

ESP inlet and outlet to determine the effect of

sorbent injection on ESP performance. N2O

was measured at the stack breeching. To be

able to characterize the furnace flow field, infurnace temperatures were measured, both

before and after installation of the GR-SI

system.

Extensive testing of boiler tube thickness

was conducted before, during, and after the

program to determine the effects of GR-SI on

tube wear. Tests on promoted sorbents were

also run at the end of the program.

 Hennepin

 Operating Hours

Hours

Baseline 860

Gas Reburning (GR) 397

Sorbent Injection (SI) 115

GR-Sl 757

Total 2,129

Main process gas supply.

15
Pretest Modifications

To retrofit the Hennepin plant with a

GR-SI test system, modifications for SI

were required in four areas: the sorbent receiving and storage area, boiler piping, ash

disposal, and the electrostatic precipitator.

For GR, natural gas injection nozzles were

installed at the four comers of the boiler,

directly above the primary combustion zone.

To improve the penetration of natural gas

mixing in the furnace, an 18-inch-diameter

duct was installed to recycle flue gas from

the duct between the economizer and air

heater. The flue gas was then directed

through a particulate removal device, a

recirculation fan and delivered to the gas

reburning nozzles for injection with the

natural gas.

Overfire air ducts were also installed at

each comer of the boiler, directly above the

reburning zone. These air ducts also serve

as ports for the lower level sorbent injectors.

A second sorbent injection elevation with a

six nozzle configuration was installed in the

upper furnace.

Site-specific auxiliary systems associated

with ash collection from sorbent injection include a flue gas humidification system between the air heater and ESP, and a CO2 injection system to control pH of the spent sorbent

before being discharged to the ash pond.

Hennepin Short-Term HCI-HF Data

Natural gas: 19% of the total heat input

Calcium/sulfur molar ratio: 1.66

% Reduction Final lb/106

 Btu

HCI 63-86 (9.3 - 25) X 10-3

HF 95-99.7 (1.6 - 19) X 10-5

GR-SI

Demonstration Data

At this stage of project evaluation, test

results are available from the Hennepin

tangentially-fired boiler GR-SI demonstration.

The following findings are conclusive:

• Gas reburning performance is unaffected

by injection of the regular hydrated lime.

• SO2 emissions reduction of up to 57%

has been achieved during short-term

testing by injecting hydrated lime with a

Ca/S molar ratio of 2 through the upper

injection configuration at full load.

Eighteen percent of the SO2 reduction is

attributable to the replacement of coal

with sulfur-free natural gas. The

remaining 39% reduction is due to the

effectiveness of the fine hydrated lime

that is injected into the top of the boiler.

Long-term testing has also shown that

the 50% SO2 reduction goal can be

obtained at a molar Ca/S ratio of 1.75;

and

 • So far, there have been no observed

adverse effects to boiler performance:

ash deposition and fireside corrosion

have not increased, and neither has

boiler-wall deposition.

Other encouraging results include:

successful start-ups of the retrofitted plant

and long-term operation of the GR-SI

system; and close correlation between the

pilot-scale and predicted results.

Achievement of 60% and 50% reductions in NOX and SO2 is a commercial

reality. Routine day-to-day operation of the

Hennepin GR-SI system by plant personnel

resulted in NOX/SO2 emissions reduction of

67% and 53%, respectively. Hydrogen

chloride (HCl) and hydrogen fluoride (HF)

combustion products were also removed.

ESP Performance

Emissions of particulate matter during

16
Gas Reburning Demonstration Data

A substantial body of data has been

obtained from the Hennepin Gas

Reburning installation after operation for

1,150 hours (including GR and GR-SI

operating hours). This includes parametric optimization tests as well as long term

data. The operations at Hennepin were

completed in January 1993. Illinois Power

intends to retain the gas reburning

system for future NOX control.

The parametric tests evaluated the

effects of Gas Reburning process

variables over the boiler operating range.

Once during parametric testing under

optimum conditions, NOX emissions were

reduced by as much as 77% from the

baseline coal fired level. These data were

analyzed to select conditions which

produced the best balance of performance for commercial operation. NOX

emission data were obtained under these

conditions as a function of the gas firing

rate in parametric and long-term tests

(under comparable conditions). Baseline

uncontrolled emissions firing 100% coal (no

gas) were 0.75 lb/106

 Btu before installation

of the Gas Reburning system. Gas

Reburning with the design amount of gas

firing (118%) reduced NOX emissions by

60% to 70% down to 0.23 to 0.30 lb/106

 Btu.

The gas injection rate can be used as an

adjustable parameter to control NOX

emissions to meet a range of requirements.

Even with only 10% gas firing, NOX emissions are reduced by 55% to 0.34 lb/106

 Btu.

The cost effectiveness of gas is high.

Following the parametric tests, long-term

tests were conducted under normal commercial service conditions. This was a

particularly severe test since the unit is

cycled daily. NOX emissions were measured

as a function of time (no tests in May or

June 1992). NOX emissions were reduced

by an average of 67.3% to 0.245 lb/106 Btu.

Average Hennepin Long-Term GR-SI Data

Natural gas: 18% of the total heat input

Calcium/sulfur molar ratio: 1.75

% Reduction Final lb/106

 Btu

SO2 52.6 2.51

NOX 67.3 0.245

The effect of Gas Reburning on

durability of the unit was also evaluated

during the long-term test. Since the

Reburning zone operates under oxygen

deficient conditions, there was concern

that tube wastage might be accelerated in

this area due to the presence of reduced

sulfur species or fluctuating oxidizing and

reducing conditions. Accordingly, extensive durability evaluations were conducted

throughout the test program including both

baseline and GR-SI operating periods.

The measurements included direct

inspection, ultrasonic tube thickness

measurements and destructive testing of

tube sections. The results of these tests

have confirmed no measurable increase

in tube wastage rates occurred due to

Gas Reburning or Sorbent Injection. Gas

Reburning is a demonstrated process and

is ready now for commercial use.

Long-Term GR-S1 Performance at Hennepin

Average NOX Reduction 67.3%; Average NOX 0.245 lb/MMBtu

Average SO2 Reduction 52.6%; Average SO2 2.51 lb/MMBtu

17
Advanced

Gas Reburning

Advanced Gas Reburning is a synergistic combination of Gas

Reburning and Selective Non-Catalytic Reduction (SNCR). In this

case, Gas Reburning uses only 10% of the boiler fuel as natural gas

and SNCR uses urea, ammonia or other proprietary nitrogen compounds. NOX reductions achieved in pilot plant testing were 82% to

83% based on a nitrogen agent to NOX molar ratio of 1.5:1.

A Comparison of Gas Reburning (GR)

and Its Advanced Technology

Process

GR

Status Gas Urea NOX Reduction

Com. 18% - 60-75%

Advanced GR Pilot 10% Yes 82-83%

Effect of SO2 credit on NOX control

cost (with spent sorbent-ash

sluice neutralization)

GR-SI operation with flue gas humidification have been limited to essentially the

levels of baseline operation without humidification. Full load (70 MWe) baseline

particulate emissions ranged from 0.018 to

0.035 lb/106

 Btu, corresponding to ESP

collection efficiencies of 99.6 to 99.8%.

These results compared to full load GR-SI

particulate emissions of 0.015 to 0.025 lb/

106 Btu, corresponding to ESP collection

efficiencies of 99.8 to 99.9%. The particulate emissions decreased with decreasing

ESP flue gas temperature due to flue gas

cooling by humidification.

Boiler Efficiency and Heat Transfer

The boiler efficiency decreased slightly

(less than 2%) during GR and GR-SI

operations, compared to the baseline

operation.

GR and GR-SI also impacted the heat

transfer profile. GR results in increased heat

absorption in the secondary and reheat superheaters, a decrease in the furnace heat absorption, and no change in the heat absorption by

the primary superheater or economizer. GR-SI

results in reduced heat absorption in the furnace, secondary and reheat superheaters, and

an increase in the primary superheater and

economizer heat absorption.

18

SO2 Credit ($/Ton)
Boiler Tubes

Ultrasonic tube thickness measurements

were taken at approximately 4,000 points in

the boiler during each of the three tests:

1988 (prior to GR-SI retrofit), 1990 (prior to

GR-SI operation), and 1992 (after GR-SI

operation). The results indicate that wall

thicknesses measured in 1992 were, in many

cases, larger than 1988 and 1990 measurements. In some cases the wall thickness

reductions between 1990 and 1992 were

preceded by an apparent increase from 1988

to 1990. In only a few sections, was there a

consistent reduction in wall thickness from

1988 to 1992. In those areas, the tube wall

life would still be expected to last beyond

the year 2023, the expected life of the unit.

Several areas showed that significant tube

wall wear had already occurred at the time

of the earliest measurements (1988).

Chimney Inspection

The chimney was inspected before and

after GR-SI testing, in April 1990 and

October 1992. Internal and external examinations of the chimney were conducted for

changes in wear rate and deposition of

particulate matter. The inspections showed

no increase in the internal wear (mortar) but

increased deposition of particulate matter

throughout the chimney. Illinois Power has

indicated that this is not of concern.

Promoted Sorbents

In addition to the regular hydrated lime

(HL), three sorbents promoted with

proprietary additives were also tested at

Hennepin.

Promoted sorbents have better performance and lower SO2 control costs than the

hydrated lime. PromiSORBTM A also

contributes some NOX reduction.

PromiSORBTM B provides significant

improvement in the cost of SO2 emission

control. PromiSORBTM is a commercial

product offered by a joint venture between

EER Corporation and Petroleos de Venezuela. Similarly, higher surface area hydrated

lime (HSAHL), as developed by the State of

Illinois Geological Survey, has better

performance and lower costs.

PROMISOXTM PROCESS

Sorbents Tested at Hennepin

Hydrated High Surface

Lime (HL) Area HSAHL PromiSORBTM A PromiSORBTM B

$/ton sorbent 74 89 89 93

 delivered

Ca/S Molar Ratio 1.75 1.71 1.75 1.75

Ca utilization, % 24 35 33 39

Sorbent cost, $/ton 380 310 330 290

 SO2 removed* *Actual costs will depend on site specific factors

19
Lakeside: GR-SI

Demonstration On A

Cyclone-Fired Boiler

This City Water, Light, and Power generating unit (Lakeside Station) in Springfield,

Illinois, is the second half of a two-site project

to demonstrate the ability of EER’s integrated

GR-SI retrofit process to reduce NOX and SO2

emissions. The Lakeside Unit #7 is a cyclonefired, 40 MWe boiler that bums high-sulfur

Illinois coal.

Project Status

The retrofitting at Lakeside was begun in

mid-1990, and was completed in early 1993.

Start-up and baseline operation of the GR-SI

began in the May of 1993. All demonstration

operation and testing is scheduled for completion in August of 1994. The date of the final

report on this project is scheduled for November of 1994.

Natural gas injectors being installed at

Lakeside. Flanged piping is for connecting

recirculated flue gas lines.

20

This specific testing program has the same

five objectives as the overall GR-SI demonstration program: (1) to optimize the operation

of the GR-SI system, (2) to demonstrate that the

performance goals can be achieved, (3) to

quantify the costs and operational impacts of

the GR-SI process, (4) to establish a data base

for use in future GR-SI applications, and (5) to

provide sufficient operating hours to determine

the long-term effects of GR-SI operation.

Testing began with baseline operation

(without GR-SI) in order to gather baseline

NOX and SO2 emission data. Once this baseline

testing was completed, the gas reburn portion

of the process was optimized. This was

followed by the optimization of the sorbent

injection system in the presence of ideal GR

conditions.

A 12-month demonstration of GR-SI is

underway using baseline coal. During this

operational demonstration, continuous

monitoring of NOX and SO2 emissions is being

conducted. In addition, all operating and

boiler/system maintenance data is being

recorded.

As at Hennepin, the impact of GR-SI on

boiler tube thickness will be extensively tested

before, during, and after the test program to

determine if there is any wall erosion or tube

deterioration. Additional tests, including

alternate sorbents, will also be carried out

within the program. Upon completion of this

demonstration testing, a final report will be

published. All test results will be reported to

DOE, GRI, and the Illinois Department of

Energy and Natural Resources, the three major

co-funders of the project.

Testing Program

Pretest Modifications

The following physical modifications

were required to retrofit the Lakeside #7
boiler and related equipment with the GR-SI

emission reduction system. The principal

boiler changes included the through-thewall installation of an array of natural gas/

flue gas recirculation nozzles, an overfire air

duct and nozzles, sorbent injection nozzles,

and test ports. To improve the penetration of

the natural gas into the furnace, a flue gas

recirculation fan was installed, with appropriate ductwork, to provide flue gas as a

transport medium. The sorbent is delivered

to the various sorbent injection nozzles

through a pneumatically-operated system of

flexible hoses from the newly constructed

sorbent storage facility. To enhance the

penetration of the sorbent into the boiler, a

125 HP sorbent injection fan was installed to

pull air from the boiler room for delivery to

the sorbent injection nozzles.

Related construction activities included:

the construction of a cylindrical sorbent

storage silo, able to hold a five-day supply

(325 tons) of hydrated lime, and all related

sorbent handling equipment and unloading

facilities; a dry ash handling facility for

short-term storage of the GR-SI ash byproduct before shipment to a landfill; and

the installation of a natural gas supply line

to the plant, including a pressure-reducing

station and meter.

Test Results

GR-SI operation of the Lakeside unit has

just begun. The initial GR tests show that the

60% NOX reduction goal has been achieved.

Initial SI tests similarly indicate that the 50%

SO2 reduction goal for GR-SI operation will be

achieved. GR-SI-process flow diagram.

21
Cherokee:

Demonstrating GR &

Low-NOX Burners On A

Wall-Fired Boiler

This project is intended to demonstrate

the ability of an integrated gas reburning, lowNOX burner process to significantly reduce

NOX emissions. It has been installed on the

Public Service Company of Colorado’s Cherokee Station, Unit #3, which is a 172 MWe,

low-sulfur coal-burning, wall-fired boiler.

Developed by EER, this process uses natural gas as a reburn fuel (up to 20% of total

fuel input). The gas is fired above the main

coal combustion zone in the boiler, creating a

slightly fuel-rich zone. NOX moving upward

from the lower region of the furnace is

"reburned" in this zone and converted to

atmospheric nitrogen.

GR-LNB System Schematic at Cherokee

22

Low-NOX burners installed in the coal

combustion zone retard the production of NOX

by staging the burning process to carefully

control the coal/air mixture. When LNBs are

used synergistically with GR, a projected 70%

reduction in NOX emissions is attainable.

Project Status

This project was awarded in October of

1990. Design of the Cherokee retrofit began

immediately, including the design, arrangement, and sizing of the system’s components;

placement of component orders; and the

selection of contractors. The design process

was completed in mid-1991.

Construction began immediately afterward

and was completed in April of 1992. Baseline

operation of the GR system was delayed while

the plant rebuilt its coal pulverizers. Optimization testing began in November 1992. The

long-term operation phase began in April

1993. Initial test results have achieved the

project goal of a 70% reduction in NOX

emissions at a controlled excess air level.
Testing Program

The objectives of the GR-LNB testing

program are: (1) to optimize the operation of

the GR-LNB process, (2) to demonstrate that

the performance goal (>70% NOX reduction) is

achievable, (3) to quantify the costs and

operational impacts of the GR-LNB process,

and (4) to build a data base and the know-how

for use in subsequent GR-LNB applications.

Pretest Modifications

The major LNB retrofit item was the replacement of the 16 front-wall burners with

Foster Wheeler Internal Fuel Staging lowNOX burners. The remaining portions of the

fuel system required only minor modifications.

Placing a GR system on this boiler

involved the installation of three subsystems:

Diagram of a low-NOX

burner.

(EER's FlamemastEERTM Type

4AFW Low NOX Burner is shown)

(1) the natural gas metering and distribution

system; (2) the flue gas reinjection system; and

(3) the overfire air system. The first of these

subsystems delivers natural gas to the upper

furnace reburning area. The flue gas reinjection

subsystem helps ensure good natural gas

penetration into and dispersion throughout the

furnace. The overfire air subsystem is above

the natural gas injection zone and assists in

achieving complete combustion.

Initial construction work involved the

removal of an obsolete electrostatic precipitator to make room for the overfire air and flue

gas reinjection fans, motors, ductwork, and

supporting structures. Next, natural gas

injectors and overfire air nozzles were installed

in the furnace walls. Since portions of the

furnace wall tubing had to be removed, the

boiler was shut down for about two months.

During this outage, most of the work on the

natural gas subsystem was completed, and much

of the overfire air and flue gas recirculation

system work, at and adjacent to the boiler, was

also completed. Simultaneous with this mechanical work was the installation of all electrical,

instrumentation, and system controls.

23
Cherokee gas reburning low-NOX burner

model.

24

Similar to the other GR demonstration systems installed, the Cherokee unit’s overfire air

is taken from the boiler, downstream from the

air heater. It is then routed around the boiler to

an overfire air fan, boosted in pressure, and

routed back to the boiler. The flue gas

reinjection subsystem takes flue gas leaving

the air heater, routes it to a multiclone and

recirculation fan, boosts its pressure, and then

routes it back to the boil

Test Results

Extensive parametric tests of gas

reburning have been completed at Cherokee.

NOX emissions can be shown as a function

of stoichiometry. For the baseline and low

NOX burner tests, which involve a single

combustion zone, the overall stoichiometry

is employed. For GR, the stoichiometry

refers to the Gas Reburning Zone. The

minimum NOX emission with GR-LNB

measured to date was 0.20 lb/106

 Btu. This

was found at a Reburning Zone stoichiometry of 88% of theoretical air and a gas

firing rate of 20%. This NOX level corresponds to a reduction of 72% from the

baseline level and 60% from the low NOX

burner level. The one-year long-term test is

currently in progress.

In general, the NOX emission is reduced

with increasing gas feed up to about the 20%

input level.

For baseline, LNB, and GR-LNB, the

NOX emission increases with increasing load.

The increase in NOX with increasing load is

more moderate with GR-LNB than that with

baseline or LNB.

Long-term demonstration of the Cherokee

Unit’s GR-LNB system has just begun. The

initial demonstration results obtained at

constant or varied loads in the first three

months agreed with parametric test results.
Flow diagram, gas reburning and low-NOX

burners on a wall-fired boiler.

The mounting shroud for the low-NOX burner is

being checked during installation in the boiler

wall at Cherokee Unit No. 3.

25
NOX Data from Cherokee Unit 3

26
Environmental

Monitoring

As required by EER’s cooperative agreements with DOE for both demonstration

projects (Hennepin/Lakeside and Cherokee),

environmental monitoring will be conducted

during the course of each project at all three

sites to ensure process acceptability. As

detailed in the Environmental Monitoring Plan

(EMP) submitted for both projects, this

monitoring will be used to develop a data base

for the assessment of the environmental

performances of the technologies used (i.e.,

gas reburning, sorbent injection, LNBs, and

their respective integrated applications). It will

also be used for the replication of any of these

technologies, independent of specific site

characteristics.

Specific monitoring described in both

EMPs includes: air, wastewater, solid waste,

groundwater, and health and safety conditions.

Also described is all additional monitoring

required for specific state and local regulations. All EMP testing and measurements

utilize standard EPA methods and procedures

as applicable.

Environmental monitoring flow chart

27
Shaped boiler tubes, part of the over-fire air

and gas reburn system, were welded into

the boiler wall at Cherokee Station.

28

Air Monitoring

The air monitoring plans for both

demonstration projects include specifications for point-source emissions, fugitive

dust emissions, and ambient air concentrations. Both demonstrations closely monitor

flue gas NOX, SO2, CO, CO2, and O2 continuously. Measurements of particulate

loading and particle size are also included.

Samples are being collected at both the inlet

and outlet sides of the precipitators or

baghouse.

Compliance monitoring of point-source

emissions is conducted for SO2, opacity, and

particulate loading. Supplemental monitoring is also being done for particulates

(including particle size distribution), SO2,

NOX, and CO. Substances monitored are

regulated by the various state air permitting

requirements, or are criteria pollutants under

the National Ambient Air Quality Standards.

CO2 and O2 are also monitored to help in the

data interpretation of SO2, NOX, and CO

levels.

The hazardous air pollutants, hydrochloric acid (HCl) and hydrofluoric acid (HF), in

flue gas have been monitored for the GR-SI

demonstration project, in which HCl and HF

are theoretically expected to be captured by

the sorbent used. This expectation has been

verified at Hennepin and will be tested at

Lakeside as well.

Wastewater

Monitoring

On two of the demonstration sites, large

quantities of sorbent chemicals are being

injected into the boilers. The test program is
performing more sampling and analyses of

wastewater to ensure adequate data for

future applications. This compliance with

supplemental monitoring requirements will

primarily be concerned with the measurement of calcium-sulfur compounds, and pH

levels in the groundwater.

Solid Waste &

Groundwater Monitoring

The EMP for the Hennepin and Lakeside

project addresses the increased volume of

ash generated, and the changed chemical and

physical characteristics of this ash as a result

of the sorbent used. It also discusses the

need for ongoing groundwater monitoring in

the vicinity of the two ash disposal sites after

completion of the operational phases of

these projects.

Health & Safety Monitoring

Each of the utility companies involved

has a health and safety program in place

which ensures safe working conditions at

their individual plants. Each has extensive

training programs in safety procedures,

hazardous conditions, and identification of

all hazardous materials their workers

normally encounter. EER also determines

total suspended particulate concentrations

and noise levels in work areas according to

the environmental monitoring plan.

GR-LNB Operations Control Center

29
Isothermal flow model of the Hennepin

tangentially-fired boiler. Test results were

used to locate gas, overfire air and

sorbent injection ports.

30
References

Reports

"Comprehensive Report to Congress on the

Clean Coal Technology Program: Enhancing

the Use of Coals by Gas Reburning and

Sorbent Injection." (Energy and Environmental

Research Corporation). Report No. DOE/FE0085. U.S. Department of Energy. April 1987.

"Comprehensive Report to Congress on the

Clean Coal Technology Program: Evaluation

of Gas Reburning and Low-NOX Burners on a

Wall-Fired Boiler." (Energy and Environmental Research Corporation). Report No. DOE/

FE-0204P. U.S. Department of Energy.

September 1990.

Papers

Engelhardt, D.A., Rooney, H.V., Payne, R.,

and Ritz, H.J., "Gas Reburning-Sorbent

Injection for Acid Rain Precursor Emission

Control-System Design/Construction/

Operating Constraints," 1992 International

Joint Power Generation Conference, Atlanta,

Georgia, October 1992.

Folsom, B.A., and Browning-Sletten, M.,

"Evaluation of Gas Reburning and Low NOX

Burners on a Wall Fired Boiler," presented at

the ASME International Joint Power Generation Conference, Boston, Massachusetts

(October 21-25, 1990).

Bartok, W., et al., "Field Evaluation of

Combined NOX/SO2 Control via Gas Reburning-Sorbent Injection for Coal-Fired

Utility Boilers," Fourth Symposium on

Integrated Environmental Control, Washington, DC, March 1988.

Bartok, W., May, T.J., and Krueger, M.S.,

"Application of Gas Reburning-Sorbent

Injection Technology for Control of NOX and

SO2 Emissions," EPRI-EPA Joint Symposium

on Stationary Combustion NOX Control, March

1991.

Folsom, B.A., Hong, C.C., Sommer, T.M., and

Pratapas, J.M., "Reducing Stack Emissions by

Gas Firing in Coal-Designed Boilers — Field

Evaluation Results," presented at the EPRI/

EPA 1993 Joint Symposium on Stationary

Combustion NOX Control, Miami Beach,

Florida (May 24-27, 1993).

Hong, C.C., Opatmy, J.C., Sanyal, A.,

Sommer, T.M., and Folsom, B.A., "HCl-HF

Removal by Sorbent Injection in a Pulverized

Coal Fired Utility Boiler Furnace," International Joint Power Generation Conference and

Exhibition, Kansas City, Missouri (October

17-21,1993).

Keen, R.T., Hong, C.C., Opatmy, J.C.,

Sommer, T.M., Folsom, B.A., Payne, R., Ritz,

H.J., and Pratapas, J.M., "Gas ReburningSorbent Injection Demonstration Results,"

1993 EPR1/EPA/DOE SO2 Control Symposium, Boston, Massachusetts (August 24-27,

1993).

31

Angello, L.C., Engelhardt, D.A., Folsom, B.A.,

Opatmy, J.C., Sommer, T.M., and Ritz, H.J.,

"Gas Reburning-Sorbent Injection Demonstration Results," presented at the U.S. Department

of Energy First Annual Clean Coal Technology Conference, Cleveland, Ohio (September

22-24, 1992).
To Receive

Additional Information

To be placed on the Department of Energy’s distribution

list for future information on

the Clean Coal Technology

Program and the demonstraation projects it is financing,

contact:

Mr. George Lynch

FE-22

U.S. Department of Energy

Washington, DC 20585

(301) 903-9434

Preparation and printing of this document

conforms to the general funding provisions

of a cooperative agreement between Energy

and Environmental Research Corp., and the

U.S. Department of Energy. The funding

contribution of the industrial participant

permitted inclusion of multicolored artwork

and photographs at no additional expense

to the U.S. Government.

32

Kokkinos, A., "Reburning for Cyclone Boiler

Retrofit NOX Control," EPRI Journal, pp. 36-

38, December 1992.

Lewis, R.D., "Close Coupled Gas Reburn:

Application to a Tangentially Fired Boiler,"

presented at the EPRI/EPA 1993 Joint

Symposium on Stationary Combustion NOX

Control, Miami Beach, Florida (May 1993).

Opatrny, J.C., et al., "Operating Experience

with a Gas Reburning-Sorbent Injection

System for Acid Rain Precursor Emission

Control for Utility Boilers," ASME International Joint Power Generation Conference,

San Diego, California, October 1991.

Sanyal, A., Sommer, T.M., Hong, C.C.,

Folsom, B.A., Payne, R., and Seeker, W.R.,

"Advanced NOX Control Technologies,"

Power-Gen Europe ’93, Paris, France (May

25-27, 1993).

Sanyal, A., Sommer, T.M., Hong, C.C.,

Folsom, B.A., and Payne, R., "Low-NOX

Burners and Gas Reburning — an Integrated

Advanced NOX Reduction Technology," The

Institute of Energy/International Symposium

on Combustion and Emissions Control,

University of Wales, United Kingdom

(September 21-22, 1993).

Sommer, T.M., Hong, C.C., Moser, H.M., and

Ritz, H.J., "Integrating Gas Reburning with

Low NOX Burners," presented at the U.S.

Department of Energy First Annual Clean Coal

Technology Conference, Cleveland, Ohio

(September 22-24, 1992).

Wu, K.T., et al., "Development and Application of a Gas Reburning Process Model for the

Design of Boiler NOX Reductions," 1991

International Joint Power Generation Conference, San Diego, California, October 1991.