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5 BACT Analysis

Federal PSD regulations (40 CFR 52.21(j)) require the utilization of BACT to minimize the 

emissions of PSD regulated pollutants from a new major stationary source or major modification 

occurring at an existing major stationary source. For a new major stationary source comprised 

of only new emissions units, BACT shall be applied to each emissions unit that would have the 

potential to emit a regulated PSD pollutant that the new major stationary source is proposed to 

emit in a significant amount. As previously discussed in this permit application, both the 

Developer and Discoverer Americas will be a new major stationary source and each will have 

the potential to emit NOX emissions above the pollutant’s PSD significant threshold. Therefore,

a BACT analysis must be performed for applicable emissions units on the Developer and 

Discoverer Americas that will have the potential to emit NOX.

Based on the definition of OCS source in 40 CFR 55.2, an emissions unit that operates within 

25 miles of an OCS source is not subject to BACT requirements unless the emissions unit is 

attached to the OCS source and has a stationary source aspect.1

 For example, the lifeboats 

and fast rescue boats of the Developer and Discoverer Americas are attached to the drilling

vessels to be available for use in emergency events. When the lifeboats and fast rescue boats 

are used in their intended service (emergency events), they represent mobile sources. 

Therefore, the lifeboat and fast rescue boat engines are not subject to BACT requirements 

under the PSD regulations.

5.1 BACT Analysis Procedure

BACT is defined at 40 CFR 52.21(b)(12) as “an emissions limitation (including a visible emission 

standard) based on the maximum degree of reduction for each pollutant subject to regulation 

under the Act which would be emitted from any proposed major stationary source or major 

modification which the Administrator, on a case-by-case basis, taking into account energy, 

environmental, and economic impacts and other costs, determines is achievable for such 

source or modification through application of production processes or available methods, 

systems, and techniques, including fuel cleaning or treatment or innovative fuel combustion 

techniques for control of such pollutant....”

BACT is evaluated on a pollutant-specific basis for an emissions unit using a procedure that is 

referred to as the “top-down BACT analysis.” The top-down BACT analysis starts with 

consideration of the technology that would achieve the maximum degree of emissions limitation

(lowest emission rate) for an emissions unit and that can be or has been applied to the same 

 1 OCS source means any equipment, activity, or facility which:

(1) Emits or has the potential to emit any air pollutant;

(2) Is regulated or authorized under the Outer Continental Shelf Lands Act (‘‘OCSLA’’) (43 U.S.C. § 1331 et seq.); 

and

(3) Is located on the OCS or in or on waters above the OCS.

This definition shall include vessels only when they are:

(1) Permanently or temporarily attached to the seabed and erected thereon and used for the purpose of exploring, 

developing or producing resources therefrom, within the meaning of section 4(a)(1) of OCSLA (43 U.S.C. § 1331 et 

seq.); or

(2) Physically attached to an OCS facility, in which case only the stationary sources aspects of the vessels will be 

regulated. (40 CFR 55.2)
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type of emissions unit or to a similar type of emissions unit. The top-ranked technology that is 

considered technically available may be eliminated based on costs, economics, environmental

impacts, and/or energy impacts. If the top-ranked technology is not chosen, then the BACT 

analysis proceeds to the next most stringent technology. This analysis continues until a BACT 

conclusion is reached.

The following steps outline the top-down BACT analysis.

Step 1 – Identify All Control Technologies

The first step in the top-down BACT analysis is to define the spectrum of process and/or add-on 

emissions control alternatives potentially applicable to the proposed emissions unit. A review of 

the EPA’s RACT/BACT/LAER Clearinghouse (RBLC) database is usually relied upon to identify 

available BACT control alternatives.

Step 2 – Eliminate Technically Infeasible Options

The second step in the top-down BACT analysis is to evaluate the technical feasibility of the 

alternatives identified in Step 1 and to reject those which are technically infeasible based on 

engineering evaluation or due to chemical or physical principles. The following criteria are 

considered in determining technical feasibility: previous commercial scale demonstrations, 

precedents based on previous permits, and technology transfer from similar emissions units.

Step 3 – Rank Remaining Control Technologies by Control Effectiveness

The third step involves an assessment and documentation of the emissions limit achievable with 

each technically feasible alternative when taking into consideration the specific operating 

constraints of the emissions units undergoing review. After determining what control efficiency 

is achievable with each alternative, the alternatives are rank-ordered into a control hierarchy 

from most to least stringent.

Step 4 – Evaluate Most Effective Control Options and Document Results

The fourth step is to evaluate the costs, economics, environmental impacts, and energy impacts 

of the top or most stringent technique. To reject the top alternative, it must be demonstrated 

that this control alternative is infeasible based on the results of the impacts analysis. If a control 

technology is determined to be infeasible due to costs or adverse energy or environmental 

impacts (including toxic pollutant impacts), the control technology is rejected as BACT and the 

impacts analysis is performed on the next most stringent control alternative.

Step 5 – Select BACT

BACT is identified as the option with the highest control effectiveness that was not eliminated in 

Step 4.

5.2 Summary of BACT Determinations

Below is a summary of the BACT determinations for the applicable emissions units proposed for 

the Developer and Discoverer Americas. For the Developer, the only emissions units having 
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potential NOX emissions are diesel2 (CI) engines. Therefore, the BACT review performed for 

the Developer only addresses diesel engines. Alternatively, the BACT review performed for the 

Discoverer Americas addresses both diesel engines and a diesel-fired heater because the 

drilling vessel is equipped with these two types of NOX generating emissions sources.

5.2.1 Developer and Discoverer Americas Engines

The BACT analyses that we performed for the diesel engines on the Developer and Discoverer 

Americas are presented in engine size groupings. For example, the Developer is equipped with 

eight large (>500 hp) diesel main generator engines and one large diesel emergency generator 

engine, and the Discoverer Americas is equipped with six large diesel main generator engines 

and one large diesel emergency generator engine. The BACT analyses that we performed for 

these large diesel engines are presented under the grouping of “large (>500 hp) diesel 

engines.”

Similarly, the Developer is equipped with two small (≤500 hp) diesel cementing unit engines, 

and the Discoverer Americas is equipped with two small diesel emergency air compressor 

engines. The BACT analyses that we performed for these small diesel engines are presented 

under the grouping of “small (≤500 hp) diesel engines.”

Table 5.1-1 below summarizes the BACT determinations made for the diesel engines installed 

on the Developer and Discoverer Americas.

Table 5.2.1-1

Summary of BACT Determinations for Developer and 

Discoverer Americas Engines

Engine Group Drilling 

Vessel

Number 

of 

Engines

Emissions Unit/

Average 

Annual NOX

Emissions 

Level

Control Technology/

Engine Description (g/kW-hr) Work Practice

Large Developer 8 Main Generator Engines 8.2 40 CFR part 94 Tier 2 

Compliant Design, 

including Turbocharger, 

Aftercooler, High 

Injection Pressure, and 

Low NOX Tuning

(>500 hp) 

Diesel Engines

(GEN-1 thru GEN-8)

Wartsila Model 16V26 A 

(6,651 hp)

Discoverer 

Americas

6 Main Generator Engines 12.1 40 CFR part 94 Tier 1 

Compliant Design, 

including Turbocharger, 

Aftercooler, and High 

Injection Pressure

(GEN-1 thru GEN-6)

STX MAN Model 

14V32/40 (9,387 hp)

Developer 1 Emergency Generator 

Engine

9.2 40 CFR part 94 Tier 1 

Compliant Design, 

including Turbocharger, 

Aftercooler, and 

Electronic Fuel Injection

(EGEN)

Caterpillar Model 3516B 

(2,551 hp)

 2 Marine gas oil, diesel fuel, and distillate fuel oil No. 2 all have very similar properties and are collectively referred to 

as “diesel” in this permit application.
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Engine Group Drilling 

Vessel

Number 

of 

Engines

Emissions Unit/

Average 

Annual NOX

Emissions 

Level

Control Technology/

Engine Description (g/kW-hr) Work Practice

Large

Discoverer 

Americas

1 Emergency Generator 

Engine

9.8 40 CFR part 94 Tier 2 

Compliant Design, 

including Turbocharger, 

Aftercooler, and High 

Injection Pressure

(>500 hp) 

Diesel Engines (EGEN)

STX MAN Model 7L27/38 

(3,097 hp)

Small Developer 2 Cement Unit Engines 7.2 40 CFR part 94 Tier 2 

Compliant Design, 

including Turbocharger, 

Aftercooler, and 

Electronic Fuel Injection

(≤500 hp) 

Diesel Engines (CMU-1 and CMU-2)

Caterpillar Model C15 

(500 hp)

Discoverer 

Americas

2 Emergency Air 

Compressor Engines

7.5 40 CFR part 94 Tier 2 

Compliant Design, 

including Turbocharger 

and Aftercooler (ACOMP-1 and ACOMP2)

Duetz Model F3L912 (50 

hp)

Duetz Model F4L912 (68 

hp)

Noteworthy in light of the OCS source BACT applicability discussion presented at the beginning 

of this section, the direct physical connection of a support vessel (crew boats and OSVs) to the 

Developer or Discoverer Americas would be an unusual event. The typical operation of a 

support vessel is for it to operate under its own power when adjacent to the drilling vessel for 

loading or unloading purposes. The only expected physical connection between the drilling 

vessel and support vessel would be for material transfer hoses such as those that would be 

necessary for the transfer of fuel or drilling mud. Because these types of events are short in 

duration, Statoil believes it is evident that a BACT analysis for support vessels would result in 

determinations that any control technology requirements beyond those with which the specific 

vessel is already equipped would not be cost effective due to the small amount of NOX

emissions reduction that would be achieved during the short time frame that a support vessel 

would be connected to the drilling vessel. Therefore, BACT for support vessels is not discussed 

any further.

5.2.2 Discoverer Americas Heater

In addition to the diesel engines installed on the Discoverer Americas, the vessel is equipped 

with a cargo heater system that incorporates a diesel-fired heater and a thermal fluid circulation 

loop. The existing diesel-fired heater (Hot Oil Heater (Emission Unit ID HTR)) component of the 

cargo heater system is only operated for testing and maintenance, and it is expected that the 

testing and maintenance operations of the heater will occur for only two hours per year. Based 

on such a limited operating schedule, the potential NOX emissions from the heater are 0.003 

tpy. If any replacement and/or add-on technologies were available to control NOX emissions 

from the heater, the emissions reduction amount would be negligible in consideration of the 
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proposed 0.003 tpy potential NOX emissions rate for the heater. Therefore, any available 

technology would not be cost effective. For example, a NOX control technology capable of 

reducing NOX emissions by 95 percent with an annualized cost of $50 would result in a cost 

effectiveness greater than $20,000 per ton of NOX removed.

Because any replacement and/or add-on NOX emissions control technologies for the Hot Oil 

Heater (Emission Unit ID HTR) would not be cost effective, we have determined that the current 

combustion equipment contained in the heater and proper operation of this equipment represent 

BACT for NOX emissions from the heater. Please note that there is not any further BACT 

determination documentation for the heater in this permit application.

5.3 NOX BACT Analysis for Large (>500 hp) Diesel Engines

In this section, we discuss the top-down BACT analysis conducted for the large (>500 hp) diesel 

engines located on the Developer and Discoverer Americas. In summary, the large diesel 

engines located on the Developer are the eight main generator engines (Emission Unit IDs 

GEN-1 through GEN-8) and the emergency generator engine (Emission Unit ID EGEN). 

Similarly, the large diesel engines located on the Discoverer Americas are the six main 

generator engines (Emission Unit IDs GEN-1 through GEN-6) and the emergency generator 

engine (Emission Unit ID EGEN).

5.3.1 Step 1 – Identify All Control Technologies

NOX will be formed during the combustion reaction of diesel fuel in the large diesel engines

located on the Developer and Discoverer Americas. There are two sources of nitrogen that 

result in NOX emissions during combustion – nitrogen in the combustion air and nitrogen in the 

fuel. Thermal NOX formation occurs by the high temperature thermal dissociation and 

subsequent reaction of combustion air molecular nitrogen (N2) and oxygen (O2), via the wellknown Zeldovich mechanism. Fuel-bound NOX is formed by the direct oxidation of organonitrogen compounds contained in the fuel.

The available control technologies to minimize NOX emissions from diesel engines can be 

characterized by the following two categories: (1) combustion control (in-cylinder controls) and 

(2) post-combustion exhaust treatment (after-treatment). With combustion control or in-cylinder 

control, thermal NOX is reduced by lowering the peak combustion temperature by utilizing 

engine design and calibration parameters such as fuel delivery and valve timing. However, the 

reduced NOX formation provided by in-cylinder control of combustion temperature must be 

balanced with potential negative impacts such as increased emissions of other pollutants (e.g., 

CO, PM, VOC), increased fuel consumption by the engine, and decreased torque output by the 

engine. Post-combustion exhaust treatment relies on the removal of NOX from the exhaust 

stream via chemical reaction technologies.

First, available NOX control technologies for large (>500 hp) diesel engines were determined by 

searching the EPA RBLC using the following search conditions: Process Code 17.110 – Large 

Internal Combustion Engines (>500 HP); Fuel Oil (ASTM #1, 2, includes kerosene, aviation, 

diesel fuel). Table 5.3.1-1 below summarizes the NOx control technologies for large diesel 

engines identified in the RBLC.
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Table 5.3.1-1

EPA RBLC NOX Control Technologies for Large (>500 hp) 

Diesel Engines

Abbreviation Control Technology

Typical Percent 

Reduction

SCR Selective Catalytic Reduction 90%

LND Low NOX Engine Design 50-80%

ITR Ignition Timing Retard 10-50%

IAC Combustion Air Chiller/Intake Air Cooling

HIP High Injection Pressure

WI Water Injection up to 50%

Tier 1 or 2 Tier 1 or Tier 2 Emission Standards per 40 CFR 

part 89 or 40 CFR part 94

30%

- Turbocharger with Aftercooler Varies

GCP Good Combustion Practices -

3

None No controls specified -

The complete RBLC database download for large diesel engines is provided in Appendix D. 

Note that only those determinations made after January 1, 1999, were downloaded because 

older determinations are typically less stringent. The RBLC also listed lean burn and clean fuel 

as NOX control techniques for large diesel engines. However, these techniques do not 

specifically reduce NOX emissions; therefore, they are not discussed further.4

In addition to the large diesel engine NOX emissions controls listed in the RBLC, Statoil

considered the control technologies included in Table 5.3.1-2 below. These control 

technologies were identified by reviewing permit applications and comments on draft permits for 

other OCS sources and reviewing publications on diesel engine emissions control technologies.

Table 5.3.1-2

Other NOX Control Technologies for Diesel Engines

Abbreviation Control Technology

Typical 

Percent 

Reduction

EGR Exhaust Gas Recirculation 40-50%

- EGR with WI Varies

- Engine Replacement (replacing old engine with new)

 3 While good combustion practices can promote efficient combustion and prevent excessive emissions, these 

practices do not necessarily result in NOx emissions reductions for an engine. 4 Clean fuels having a low nitrogen content do reduce NOX produced from fuel-bound nitrogen; however, the amount 

of NOx produced from fuel-bound nitrogen in diesel constitutes a small fraction of the total NOx. Lean burn and air-tofuel ratio control are more related to engine performance than NOX control.
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Abbreviation Control Technology

Typical 

Percent 

Reduction

- Engine Re-Tooling (engine rebuild kits) Varies

- Fuel-Water Emulsions

- Intake Air Humidification

- Engine Derate

- NOX Adsorber (NOX Traps)

LNC/HC-SCR Lean NOX Catalyst/Hydrocarbon SCR

CSNOx CSNOX Emission Abatement System

Except for EGR, specific NOX reduction efficiencies were not identified for the control 

technologies in Table 5.3.1-2. The expected control efficiency for these technologies varies 

based on the level of existing controls in place or the baseline emissions for each particular 

engine. The estimated control efficiencies for technically feasible control technologies are 

included in the evaluation of controls (Step 4) presented later in this section.

5.3.1.1 Selective Catalytic Reduction (SCR)

An SCR system uses catalyst to selectively reduce NOX to elemental nitrogen and water by 

using ammonia as the reducing agent. The ammonia is injected into the exhaust upstream of a 

catalyst bed. The effectiveness of SCR depends on fuel quality and engine duty cycle or load 

fluctuations. Contaminants in the fuel may poison or mask the catalyst surface causing a 

reduction or termination in catalyst activity. Load fluctuations can cause variations in exhaust 

gas temperature and NOX concentration, which can create problems with the effectiveness of 

the SCR system.5

 Exhaust gas temperatures greater than 250 °C are necessary to complete 

the NOX reduction reaction. In marine applications, SCR systems are capable of reducing NOX

emissions more than 90 percent.

6

Anhydrous and aqueous ammonia are regulated as toxic chemicals under the CAA. Therefore, 

SCR systems typically incorporate urea as an intermediate to reduce the risks associated with 

transportation, storage, and handling of ammonia. The urea is then converted to ammonia for 

use as the reducing agent in the SCR system.

5.3.1.2 Low NOX Design (LND)

The RBLC lists LND for several engines, but does not describe the actual NOX combustion 

control technology. It is assumed that these determinations are referring to specific combustion 

chamber designs which provide good mixing of fuel and air before the start of combustion. 

These designs are intrinsic to the particular model of engine associated with each RBLC 

determination for LND.

 5 EPA, AP-42, Section 3.4 - Large Stationary Diesel And All Stationary Dual-fuel Engines, October 1996. 6 EPA, Office of Transportation and Air Quality, Regulatory Impact Analysis: Control of Emissions of Air Pollution from 

Category 3 Marine Diesel Engines (EPA-420-R-09-019), Chapter 4 Technological Feasibility, December 2009.
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5.3.1.3 Ignition Timing Retard (ITR) and Intake Air Coolers (IAC)

ITR reduces NOX emissions in RICE by delaying the injection of fuel in the engine from when 

the chamber is at its smallest to a time when the compression chamber is expanding. The 

larger volume in the compression chamber lowers peak combustion temperature, thus reducing 

thermal NOX formation. Lower peak combustion temperature can also be achieved with charge 

air coolers or IAC, common to turbocharged engines, which reduce the intake manifold 

temperature. The combination of ITR and IAC may reduce NOX by 10 to 50 percent (up to 40 

percent from ITR and an additional 10 percent from IAC).7

5.3.1.4 High Injection Pressure (HIP)

Cooling the flame with ITR and/or IAC reduces NOX at the expense of incomplete combustion, 

resulting in the formation of PM, VOC, and CO emissions and reduced fuel economy.8

 The fuel 

economy penalty can be reduced by increasing injection pressure. HIP can accomplish better 

fuel atomization which leads to better combustion and reduced NOX and PM emissions. ITR 

also has a negative impact by contaminating the lube oil with soot which increases engine wear.

5.3.1.5 Water Injection (WI)

In WI systems, water acts as an inert gas and absorbs heat as it evaporates. Both of these 

factors result in a decrease in the peak combustion temperature, thus reducing thermal NOX

formation by up to 50 percent.9

 The main disadvantage of WI is the large amount of extremely 

pure water required. In general, reduction of NOX by one percent requires up to one percent of 

water in the water-fuel system. In other words, achieving a 50 percent NOX reduction requires 

injecting the engine with as much water as fuel. Another issue with the introduction of water in 

the combustion chamber is the potential for liquid droplets to contact the cylinder surface. In 

this case, there would be an immediate disintegration of the lubrication oil film, damaging the

engine.

5.3.1.6 Tier 1 or Tier 2 Emission Standards per 40 CFR Part 89 or 40 CFR Part 94 

(Tier 1 or 2)

In November 1999, EPA signed the final rule that established Tier 2 standards for 

manufacturers of Category 1 and Category 2 marine engines. Category 1 and Category 2 

marine diesel engines typically range in size from about 700 to 11,000 hp. In January 2003, 

EPA established Tier 1 emission standards for manufacturers of Category 3 marine engines 

(typically 3,000 to 100,000 hp). These Tier 1 standards went into effect in 2003 and became 

retroactive for vessels built from 2000 to 2002. The Tier 1 standards for Category 3 marine 

engines rely on engine-based technologies to reduce emissions. Tier 2 emission standards for 

Category 3 marine engines went into effect in 2011.

The main generator and emergency generator engines located on the Developer and the main 

generator and emergency generator engines located on the Discoverer Americas are marine 

engines subject to exhaust NOX emission standards under 40 CFR part 94. The following is a 

 7 Khair, Magdi K, DieselNet Technology Guide, Engine Design for NOx Control, May 2002. 8 DieselNet Technology Guide, Engine Design for Low Emissions, March 2003. 9 EPA, Office of Transportation and Air Quality, Regulatory Impact Analysis: Control of Emissions of Air Pollution from 

Category 3 Marine Diesel Engines (EPA-420-R-09-019), Chapter 4 – Technological Feasibility, December 2009.
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summary of the 40 CFR part 94 NOX emission standards that apply to the large diesel engines 

located on the Developer and Discoverer Americas.

• Developer main generator engines – Tier 1 NOX exhaust emission standard of 

11.5 g/kW-hr (based on a maximum engine speed of 900 rpm)

10

• Developer emergency generator engine – Tier 1 NOX exhaust emission standard of 

10.0 g/kW-hr (based on a maximum engine speed of 1800 rpm)

• Discoverer Americas main generator engines – Tier 1 NOX exhaust emission standard of 

12.1 g/kW-hr (based on maximum engine speed of 720 rpm)

• Discoverer Americas emergency generator engine – Tier 2 NOX exhaust emission 

standard of 9.8 g/kW-hr.

5.3.1.7 Turbocharger with Aftercooler

A charge air compression system (turbocharger) is used to increase the power output of a 

diesel engine while reducing fuel consumption. A turbocharger on a diesel engine works as 

follows: the engine’s exhaust gas is used to drive a turbine that is mechanically linked to a 

compressor, which increases the charge air to the engine. The increase in air to the engine 

cylinder requires additional fuel, which results in higher power output combined with better fuel 

consumption. By itself, a turbocharger does not reduce NOX emissions. However, the addition 

of an aftercooler system to reduce the charge air temperature after it has been compressed by 

the turbocharger compressor results in a decrease in the engine cylinder temperature during 

combustion, which results in a decrease in thermal NOX emissions.11

As indicated in Table 5.2.1-1 earlier in this section, each of the large diesel engines on the 

Developer and Discoverer Americas is equipped with a turbocharger and aftercooler.

5.3.1.8 Exhaust Gas Recirculation (EGR)

Although not listed in the RBLC, EGR is a newer diesel engine NOX combustion control 

technology that is becoming commercially available. EGR is a method by which a portion of the 

engine’s exhaust gas is returned to its combustion chambers via the combustion air inlet system 

in order to reduce thermal NOX formation. In general, the most important factor contributing to 

the NOX reduction effect of EGR is a decrease in the peak combustion temperature, which 

decrease results from the heat absorption and reduced oxygen content of the returned inert 

exhaust gas. Potential issues associated with EGR include increased PM, VOC, and CO 

emissions, decreased fuel economy, and increased engine wear and durability issues. EGR is 

capable of NOX reductions from 40 to 50 percent.

 10 Note that the Developer main generator engines have been certified to comply with the 40 CFR part 94 Tier 2 NOX

emission standard that is applicable to similar sized engines with a model year starting in 2007. The Tier 2 standard 

is 9.8 g/kW-hr. 11 EPA, Office of Mobile Sources, Final Regulatory Impact Analysis: Control of Emissions from Marine Diesel Engines

(EPA-420-R-99-026), Chapter 3 Technological Feasibility, November 1999.
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5.3.1.9 Engine Replacement and Cam Shaft Cylinder Kits

Other NOX emissions control alternatives for the large diesel engines located on the Developer

and Discoverer Americas include engine replacement and the installation of cam shaft cylinder 

re-engineering kits for certain older engines. Engine replacement is not a specific control 

technology, but replacing an older engine with a new engine meeting current NOX emission 

standards can result in lower emissions. To be a feasible option, the replacement engine would 

have to be capable of performing the duties required of the existing engine under the same 

operation conditions.

Clean Cam Technology Systems, LLC (CCTS) offers retrofit cam shaft re-engineering kits for 

certain diesel engines. The kits reduce NOX emissions by increasing the volume of the residual 

exhaust gas that remains in the combustion chamber after the power stroke. The residual 

exhaust gases reduce the peak combustion temperature, which results in lower thermal NOX

emissions.

5.3.1.10 Fuel-Water Emulsions

The use of a fuel-water emulsion in a diesel engine results in NOX emissions reductions based 

on the same principles discussed above for a WI system. Specifically, the water in a fuel-water

emulsion vaporizes in the engine cylinder and increases fuel dispersion, which results in more 

efficient combustion. Additionally, the water vapor absorbs heat during the combustion process, 

resulting in a decrease in the peak combustion temperature, which reduces thermal NOX

formation by up to 50 percent. One limitation in the use of a fuel-water emulsion in an existing 

engine is the fuel delivery capacity of the engine’s fuel injection system. The fuel injection 

system of an existing engine would not be expected to be designed to handle the increased 

fuel-water emulsion volume. Therefore, such an engine would effectively be derated.

5.3.1.11 Intake Air Humidification

Relying on effects similar to a WI system and the use of a fuel-water emulsion, intake air 

humidification systems use a water spray chamber to humidify the hot charge air to the engine 

before the air enters the engine cylinder. The water in the air acts as an inert gas and absorbs 

heat, which result in a decrease in the peak combustion temperature, thus reducing thermal 

NOX formation. Seawater could potentially be used in the intake air humidification system, but 

the long term effects of using seawater in an engine are unknown. However, it would be 

expected that using seawater in an intake air humidification system would present technical 

difficulties for the system itself, and the corrosion potential presented by the seawater would 

likely be incompatible with the large diesel engines on the drilling vessels. 

5.3.1.12 Engine Derate

Although not listed in the RBLC, an engine can be derated by restricting the engine’s operating 

rate to a level below its rated capacity. Derating an engine reduces its operating temperature 

and could result in lower NOX formation rates. However, the reduction in engine operating 

temperature could also result in higher CO and VOC emissions.
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5.3.1.13 NOX Adsorbers

NOX adsorbers represent an emerging technology that adsorb and store NOX under lean burn 

conditions. With this technology, NOX is adsorbed by a chemical, typically a barium salt or 

other elemental salt. The adsorbent is coated onto a honeycomb monolith or the inside surface 

of the exhaust duct. Periodically, the NOX adsorbent becomes saturated and must be 

regenerated. Regeneration is commonly completed by operating the engine in a fuel rich mode 

for a brief period of time to facilitate the release of NOX in the form of nitrogen or ammonia. 

Sulfur dioxide in the engine exhaust will poison the adsorber chemical, which makes fuel sulfur 

content an important factor for NOX adsorber feasibility.12

5.3.1.14 Lean NOX Catalyst (LNC)/Hydrocarbon SCR (HC-SCR)

Lean NOX catalyst (LNC) systems, also known as hydrocarbon SCR (HC-SCR) systems, 

represent another emerging technology in the area of NOx emissions reduction systems. LNC 

systems use an advanced catalyst to capture and store NOX. The catalyst is regenerated 

during short periods when excess hydrocarbon in the exhaust removes the stored NOX and 

reduces it to nitrogen and water. The hydrocarbon in the exhaust can be either unburned fuel 

from the engine or additional fuel added to the exhaust gases through injection. This system 

has the advantage that no additional reducing agent, such as the ammonia or urea required for 

an SCR system, is necessary. Excess hydrocarbon emissions (i.e., “hydrocarbon slip”) from the 

LNC system are addressed by locating a diesel particulate filter or diesel oxidation catalyst 

downstream of the LNC system. Similar to SCR systems, LNC systems operate best at 

consistent high loads and are not amenable to long periods of engine idle or load shifts.

5.3.1.15 CSNOx Emission Abatement System

CSNOxTM is an emission control technology developed by Ecospec to remove sulfur dioxide, 

NOX, and carbon dioxide from the exhaust stream of an engine or boiler. CSNOx systems treat 

the combustion exhaust gas by passing it through a spray tower having two stages. During 

product testing CSNOx was capable of NOX removal efficiencies between 42 and 66 percent.

5.3.1.16 Good Combustion Practices (GCP)

As previously noted, although good combustion practices (GCP) can promote efficient 

combustion and prevent excessive emissions, these practices do not necessarily result in NOX

emissions reductions for an engine. In regard to large diesel engines, GCP can consist of:

• Training operations personnel on the signs of improper engine operation, including 

visible plumes, and instructing these personnel to report such signs to maintenance 

personnel;

• Having at least one full-time equipment maintenance specialist onboard the drilling 

vessel at all times during drilling activities;

• A weekly inspection of all the engines by the maintenance specialist or his designee to 

evaluate the engines for proper general operation;

 12 Nelson, Bradley, EC/R Incorporated, Alternative Control Techniques Document: Stationary Diesel Engines, EPA 

Contract No. EP-D-07-019, March 5, 2010.
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• Following maintenance procedure schedules recommended by the manufacturer and 

having a copy of the schedules available on the drilling vessel; and

• Having available a maintenance manual provided by the manufacturer for each engine 

on the drilling vessel.

5.3.1.17 Utilizing a “Newer” Drilling Vessel

Statoil has appropriately defined the OCS source in this permit application to include two 

operating scenarios, Operating Scenario 1 (Developer) and Operating Scenario 2 (Discoverer 

Americas). While the overall NOX emissions for Operating Scenario 2 are less than those 

proposed under Operating Scenario 1, Statoil does not consider use of the Developer in place 

of the Discoverer Americas as a candidate control technology, which is consistent with EPA’s 

BACT guidance where permit applicants are not generally required to fundamentally redefine 

the source to which a BACT analysis is applied.

The Developer and the Discoverer Americas are dynamically-positioned drilling vessels, which 

are considered leading edge technology in the deep waters where Statoil intends to explore. To 

execute the drilling program within the time frame of the lease, Statoil is proposing to permit 

both of these drilling vessels to allow flexibility in securing a vessel to initiate drilling activities.

5.3.2 Step 2 – Eliminate Technically Infeasible Options

In the below table, we have summarized the NOX emissions control options that are not 

technically feasible for the large diesel engines located on the Developer and Discoverer 

Americas.

Table 5.3.2-1

BACT Options Determined to be Technically Infeasible for 

Large (>500 hp) Diesel Engines

Drilling 

Vessel

Number of 

Engines

Emissions Unit/

Engine Description

Technically Infeasible

Control Technology/

Work Practice

Developer 8 Main Generator Engines

(GEN-1 thru GEN-8)

Wartsila Model 16V26 A 

(6,651 hp)

• Exhaust Gas Recirculation (EGR)

• Water Injection (WI)

• Fuel-Water Emulsion

• Intake Air Humidification

• Cam Shaft Cylinder Kits (Re-tooling)

• Engine Derate

• NOX Adsorbers

• Lean NOX Catalyst (LNC)/Hydrocarbon SCR 

(HC SCR)

• CSNOx Emission Abatement System

• Low NOX Design (LND)/Engine Replacement

Discoverer 

Americas

6 Main Generator Engines

(GEN-1 thru GEN-6)

STX MAN Model 14V32/40 

(9,387 hp)

• EGR

• WI

• Fuel-Water Emulsion

• Intake Air Humidification

• Cam Shaft Cylinder Kits (Re-tooling)
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BACT Analysis 5-13 ENVIRON

Drilling 

Vessel

Number of 

Engines

Emissions Unit/

Engine Description

Technically Infeasible

Control Technology/

Work Practice

• Engine Derate

• NOX Adsorbers

• LNC/HC SCR

• CSNOx Emission Abatement System

• Selective Catalytic Reduction (SCR)

Developer 1 Emergency Generator Engine

(EGEN)

Caterpillar Model 3516B 

(2,551 hp)

• EGR

• WI

• Fuel-Water Emulsion

• Intake Air Humidification

• Cam Shaft Cylinder Kits (Re-tooling)

• Engine Derate

• NOX Adsorbers

• LNC/HC SCR

• CSNOx Emission Abatement System

Discoverer 

Americas

1 Emergency Generator Engine

(EGEN)

STX MAN Model 7L27/38 

(3,097 hp)

• EGR

• WI

• Fuel-Water Emulsion

• Intake Air Humidification

• Cam Shaft Cylinder Kits (Re-tooling)

• Engine Derate

• NOX Adsorbers

• LNC/HC SCR

• CSNOx Emission Abatement System

• LND/Engine Replacement

In the following, we outline why the above technologies have been determined to be technically 

infeasible.

5.3.2.1 Exhaust Gas Recirculation (EGR)

EGR is a relatively new control technology that has primarily been applied to smaller high speed 

diesel engines such as those in cars or trucks, not to large, medium bore, medium speed 

engines used in marine applications. Exhaust gas that is recirculated back into the cylinders of 

the engine adds wear-inducing contaminants (e.g., soot) and causes an increase in engine oil 

acidity, which can result in engine inefficiency and an increase in engine wear. Due to the 

limited application (if any) of EGR on engines such as the large diesel engines located on the 

Developer or Discoverer Americas and the noted technical issues associated with its general 

application, we have determined that it is not technically feasible to retrofit the existing large 

diesel engines on the Developer or Discoverer Americas with EGR.

5.3.2.2 Water Injection/Fuel-Water Emulsions/Intake Air Humidification

Water injection is considered technically infeasible for the large diesel engines due to engine 

retrofit incompatibility, excessive fresh water (non-salt water) requirements, and limited space 

availability on the vessels, which availability would be necessary to store the fresh water to be 

used in the system. Furthermore, water injection introduces the potential for engine damage. 
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BACT Analysis 5-14 ENVIRON

The use of water injection can lead to cold corrosion of engine components and damage to

turbochargers and charge air coolers.13 In consideration of the individual technical infeasibility 

determinations reach for EGR and water injection, the combination of EGR and water injection 

is also considered technically infeasible.

Fuel-water emulsion is considered technically infeasible due to engine design and fuel injection 

system limitations; excessive fresh water (non-salt water) requirements; limited space 

availability on the vessels, which availability would be necessary to store the fresh water to be 

used in the fuel-water emulsion; and concerns about circulating the fuel-water emulsion into fuel 

storage tanks on the drilling vessels. Furthermore, the technology has only been installed on 

heavy fuel oil burning engines that typically operate at steady-state loads, whereas the drilling 

vessel engines under consideration burn diesel fuel at variable loads.

Intake air humidification is considered technically infeasible due to limited available space on 

the drilling vessels, which would be necessary for heat exchanger and water storage

components of an intake air humidification system. Large volumes of water are required to 

produce enough water vapor for an intake air humidification system. Typically, an intake air 

humidification system requires twice the amount of water compared to water injection or fuelwater emulsion systems. Additionally, heat required to vaporize the water is provided by the hot 

compressed air after the engine turbocharger, which at low engine loads may not provide 

enough heat to properly operate the system. For these reasons, intake air humidification is not 

considered technically feasible.

5.3.2.3 Cam Shaft Retrofits

Clean Cam Technology Systems, LLC (CCTS) cam shaft retrofit kits are only available for twostroke Detroit Diesel engines, model series 71 and 92.14 None of the large diesel engines 

proposed in this permit application are two-stroke engines. Therefore, this technology is not 

feasible for the engines.

5.3.2.4 Engine Derate

Derating the large diesel engines on the Developer and Discoverer Americas would likely result 

in lower NOX emissions, but the reduction in available power for these engines would cause a 

safety risk for each drilling vessel because the diminished power availability would potentially 

reduce the vessel’s ability to maintain correct positioning during storms and loop current events. 

Based on the safety risks associated with derating the large diesel engines on the drilling 

vessels, this technology is not feasible.

5.3.2.5 NOX Adsorbers

The development of NOX adsorber systems for diesel engines is ongoing, with NOX adsorbers 

currently available for on-road gasoline and diesel passenger vehicle engines. NOX adsorber 

systems are considered technically infeasible because they are not currently available for large 

marine diesel engines.

 13 Per communication with Quentin Stewart with Wartsila on July 6, 2012. 14 Per communication with Don Fairchild with CCTS on June 29, 2012.
Outer Continental Shelf Title V and PSD Permit Application

BACT Analysis 5-15 ENVIRON

5.3.2.6 Lean NOX Catalyst (LNC)/Hydrocarbon SCR (HC SCR)

While LNC systems have performed well in some retrofit applications, these systems have 

primarily been used in on-road diesel applications. It has also been installed on diesel engines 

used in backhoes, graders, and wheel loaders. However, neither the LNC nor the HC SCR

technology is commercially available for large marine engines.133

 Since these technologies are 

not currently available for large marine engines, they are considered technically infeasible 

options for the engines.

5.3.2.7 CSNOx Emission Abatement System

CSNOxTM technology is currently in the demonstration stages of product development and has 

not been installed or tested on an engine with varying loads similar to the main generator and 

emergency generator engines. Since CSNOx technology is not currently available for use on 

the large diesel engines located on the Developer and Discoverer Americas, it is not considered 

technically feasible for our application.

5.3.2.8 Low NOX Design (LND)/Engine Replacement for Developer Main 

Generator Engines and Discoverer Americas Emergency Generator 

Engine

LND typically means the latest engine design features that minimize NOX emissions generation 

in an engine, and these features are intrinsic to a particular engine. Therefore, LND changes to 

an existing engine essentially represent the replacement of the engine with an engine that has 

been designed and constructed with the latest LND features.

Engine replacement is not technically feasible for the main generator engines aboard the 

Developer because these engines meet the currently effective 40 CFR part 94 Tier 2 NOX

emission standard. Although the Developer main generator engines were manufactured prior to 

the Tier 2 emission standards applicability date (2007+ model year applicability date for engines 

the size of the main generator engines), emission certification testing (see Appendix B for the 

certification summary for the engines) demonstrates that the engines comply with the Tier 2 

NOX emission standard that would apply to the engines. Therefore, Tier 2 compliant 

replacement engines would not be required to limit NOX emissions to a level lower than that 

achieved by the current Developer main generator engines.

Similarly, engine replacement is not technically feasible for the emergency generator engine 

aboard the Discoverer Americas because the engine meets the currently effective 40 CFR part 

94 Tier 2 NOX emission standard that is applicable to the engine. Therefore, a Tier 2 compliant 

replacement engine would not be required to limit NOX emissions to a level lower than that 

achieved by the current Discoverer Americas emergency generator engine.

5.3.2.9 Selective Catalytic Reduction (SCR) for Discoverer Americas Main 

Generator Engines

An SCR system is designed in consideration of unit-specific operations and exhaust stream 

characteristics. For example, an emissions unit’s exhaust stream temperature is an important 

variable in regard to the design and operation of an SCR system because the stream’s 
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BACT Analysis 5-16 ENVIRON

temperature influences the specific type of catalyst that must be chosen for the system to 

ensure optimum NOX reduction. Therefore, if the temperature of the exhaust gas is below the 

optimum operating window of the selected catalyst, then the NOX reduction efficiency of the 

SCR system will decrease and the quantity of reducing agent emitted to the atmosphere (“slip”) 

or available for undesirable side reactions will increase. Conversely, if the temperature of the 

exhaust gas is above the optimum operating window of the catalyst, then the reducing agent 

can be oxidized and generate additional NOX. Due to the large load variation demanded by 

operations on drilling vessels, the main generator engines aboard the vessels do not operate at

a steady load for long periods of time, which results in inconsistent exhaust gas temperatures 

for the engines. Because the engines will not operate under uninterrupted steady loads, the 

NOX reduction efficiency of an SCR system would likely be considerably less than 90 percent. 

Additionally, the exhaust gas temperature variability would make it difficult to control slip 

emissions from an SCR system.

There are several technical, environmental, and safety concerns associated with the operation 

of an SCR system. According to EPA’s Tier 2 BACT/LAER Memorandum15, a refiner reported 

that catalyst plugging problems for an SCR system installed on a process heater at its facility 

have prevented the system from operating at its expected NOX reduction efficiency. The 

following are several steps that can be taken to reduce the potential for plugging and corrosion: 

(1) operate with the lowest ammonia injection levels needed to achieve the desired control 

performance, (2) reduce the level of sulfur in the fuel (3) ensure proper mixing of the flue gas 

and the ammonia to eliminate cold surfaces for ammonium salts to condense, and (4) operate at 

temperatures above the dew point of the ammonium salt. While proper design considerations 

and the incorporation of sophisticated process control into an SCR system can provide means 

to manage these conditions, the expansiveness of the operating window required for the main 

generator engines and the dynamic operation of the engines are expected to limit the overall 

effectiveness of an SCR system. Moreover, if necessary, additional operating costs and engine 

emissions would be required to operate electric heaters that would provide supplemental heat to 

the SCR system to ensure that it operated above the dew point of ammonium salts that could 

potentially form in the system. A technical complication that is relatively unique to drilling 

vessels is the consideration that must be given to weight and space constraints for these 

vessels. Drilling vessels must stay within overall weight and weight distribution limits to ensure 

they meet stability and buoyancy requirements required for safety purposes. In addition, most 

drilling vessels have been designed and constructed to maximize space utilization, and extra 

space is often times not readily available for changes to existing equipment components. These 

overall weight and space constraints limit the use of add-on emissions controls such as an SCR 

system. If emissions controls are added to a vessel, then the weight and positioning of the 

additional equipment affects the vessel’s weight bearing capacity for other purposes, which can 

result in costs to resolve and/or limit certain activities that are integral to the function of the 

drilling vessel. Additionally, such added weight may require structural modifications (e.g.,

additional load bearing structures). Moreover, the effect of these weight-related changes, as 

well as the effects on power availability due to the addition of emissions controls to certain 

engines, may require approval by various government and classification organizations (e.g., 

 15 EPA Memorandum, BACT and LAER for Emissions of Nitrogen Oxides and Volatile Organic Compounds at Tier 

2/Gasoline Sulfur Refinery Project, January 19, 2001.
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BACT Analysis 5-17 ENVIRON

United States Bureau of Safety and Environmental Enforcement, United States Coast Guard, 

American Bureau of Shipping).

Environmentally speaking, SCR systems generally operate with a molar ammonia-to-NOX ratio 

greater than that required by the reduction chemical reaction in order to achieve optimal NOX

reduction efficiencies. This operational condition is referred to as ammonia slip and it results in 

the emission of odorous ammonia into the atmosphere. Ammonia is not only odorous, but it can 

react in the atmosphere to generate fine particulate matter that scatters light and results in 

regional visibility problems. Furthermore, the formation of ammonium salts can cause visible 

plumes and elevated opacity readings from the stack of the emissions unit. Besides the noted 

air quality environmental concerns associated with an SCR system, some of the depleted 

catalysts from these systems may be considered hazardous wastes and therefore require 

comprehensive management procedures and precautions, as well as expensive disposal 

mechanisms. Lastly, although urea would likely be used in any SCR system for the main 

generator engines because it is less toxic than anhydrous ammonia and aqueous ammonia, the 

transportation, storage, and handling of urea, particularly in a marine environment, would still 

require safety and environmental considerations and management practices.

The Discoverer Americas is equipped with six identical main generator engines. Each of the 

engines is an STX MAN 14V32/40 with a maximum power rating of 7,000 kW (9,387 hp). The 

Discoverer Americas does not require the simultaneous operation of all six engines, as 

represented by Statoil’s proposed average and maximum hourly permit bases for the engines. 

The proposed annual average permit basis for the engines is the operation of three of the six

engines at 35 percent engine rating; and the proposed maximum hourly permit basis is the 

operation of four engines at 80 percent engine rating. An SCR system was not part of the initial 

design for the Discoverer Americas, and the drilling vessel is not currently equipped with an

SCR system.

In addition to the space requirements for the SCR reactor(s) and associated equipment, a large 

stainless steel urea storage tank would need to be installed on the drilling vessel to supply the

SCR system with reducing agent. Based on typical main generator engine operations, a new

18,500 gallon (70 m3

) urea storage tank would be required to operate the SCR equipment under 

normal operating conditions for approximately two weeks. The new stainless steel tank (~3 m 

diameter x ~10 m length) would be roughly the same size and weight as one of the main 

generator engines. Space limitations on the vessel would not allow the SCR equipment, 

specifically the urea storage tank, to be installed in the engine room without removing one of the

main generator engines (engine room layout drawing included in Appendix D).

The removal of an engine would significantly reduce the available power for the drilling vessel.

A reduction in available power for the drilling vessel would cause a safety risk and potentially 

reduce the vessel’s ability to maintain correct positioning during storms and loop current events. 

Based on the space constraints on the Discoverer Americas and the safety risks associated with 

removing one of its main engines to incorporate SCR system equipment, we have determined 

that SCR is not feasible for the main generator engines located on the drilling vessel.
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BACT Analysis 5-18 ENVIRON

5.3.3 Step 3 – Rank Remaining Control Technologies by Control Effectiveness

The following technologies represent those considered to be technically feasible for the main 

generator and emergency generator engines on the Developer and Discoverer Americas. The 

technologies are listed from the highest to lowest potential NOX emissions control.

• Selective Catalytic Reduction (SCR) – Up to 90% NOX emissions reduction

o Developer Main Generator Engines

o Developer Emergency Generator Engine

o Discoverer Americas Emergency Generator Engine

• Engine Replacement/40 CFR part 94 Tier 2 Emission Standards – Up to 20% NOX

emissions reduction

o Discoverer Americas Main Generator Engines

• Engine Replacement/40 CFR part 94 Tier 3 Emission Standards – Up to 37% NOX

emissions reduction

o Developer Emergency Generator Engine

• 40 CFR part 94 Tier 1 Compliant Design – Baseline emissions

o Discoverer Americas Main Generator Engines

o Developer Emergency Generator Engine

• 40 CFR part 94 Tier 2 Compliant Design – Baseline emissions

o Developer Main Generator Engines

o Discoverer Americas Emergency Generator Engine

5.3.4 Step 4 – Evaluate Most Effective Control Options and Document Results

Below we evaluate the cost effectiveness for the NOx emissions control technologies 

determined to be technically feasible for the large (>500 hp) diesel engines located on the 

Developer and Discoverer Americas. For a particular NOX emissions control technique, the 

cost effectiveness was determined by dividing the technique’s annualized costs by the NOX

emissions reduction resulting from the control technique. Please see Appendix D for the 

detailed costs and cost effectiveness calculations performed as part of this BACT review.

5.3.4.1 Selective Catalytic Reduction (SCR) for Developer Main Generator 

Engines

The Developer is equipped with eight identical main generator diesel engines. Each of the 

engines is a Wartsila 16V26A with a maximum power rating of 4,960 kW (6,651 hp). The 
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BACT Analysis 5-19 ENVIRON

Developer does not require the simultaneous operation of all eight engines, as represented by 

Statoil’s proposed average and maximum hourly permit bases for the engines. The proposed 

annual average permit basis for the engines is the operation of three of the eight engines at 

60 percent engine rating; and the proposed maximum hourly permit basis is the operation of five

engines at 60 percent engine rating. An SCR system was not part of the initial design for the 

Developer, and the drilling vessel is not currently equipped with an SCR system.

Similar to the technical difficulties discussed above for the Discoverer Americas main generator 

engines, Statoil and Wartsila have concerns about the space requirements necessary to install 

SCR equipment and a related urea storage tank on the Developer to control NOX emissions 

from the vessel’s main generator engines. Wartsila estimated urea usage of 4,000 liters per day 

for normal engine operating conditions, which would require a new 15,000 gallon stainless steel 

storage tank to allow SCR operation over a two week period. This new stainless steel tank (~3

m diameter x ~8 m length) would be roughly the same size and weight as one of the main 

generator engines. Additional space to install new equipment on the Developer is extremely 

limited without having to remove existing equipment. Although vessel space limitations likely 

make the installation of SCR equipment technically infeasible, we have performed the following 

SCR cost effectiveness analysis to demonstrate that SCR is not cost effective for the Developer

main generator engines.

The installation of one SCR system to treat the combined exhaust gases from the eight main 

generator engines on the Developer is not believed to be less costly than an individual SCR 

system for each engine because one large SCR system would be expected to require extensive 

structural modifications to the vessel when compared to eight smaller SCR systems. 

Additionally, a single SCR system would introduce process control and NOX emissions control 

technical difficulties. Moreover, a single SCR system would not provide any backup or spare 

SCR capacity, which would require the cessation of main generator engine operation during 

SCR system maintenance or malfunction events. Likewise, the installation of only two or three 

SCR systems would likely not result in cost savings versus the installation of eight SCR systems 

because the two or three systems would be larger than the eight systems in order to provide for 

comparable NOX emissions control across the potential operating ranges of the engines and to 

provide some amount of backup or spare SCR system capacity during system maintenance or 

malfunction events. Furthermore, similar to one large SCR system, two or three SCR systems 

would result in complications in regard to process control requirements and the maintenance of 

high levels of NOX emissions control over the varying engine loads and corresponding 

fluctuations in mixed exhaust stream characteristics.

The operational flexibility required for the main generator engines makes it difficult to determine 

the cost effectiveness for any one of the eight engines because assuming a greater proportion 

of the potential emissions under the emissions cap occurs at one or two engines results in a 

lower cost effectiveness value for that engine or those two engines, but the cost effectiveness 

values for the remaining engines increase significantly. One could conduct numerous 

combinations of emissions/cost effectiveness analyses for the eight engines, but these 

evaluations rely on emission rate limits for each engine, which runs counter to the proposed 

emissions cap permit basis for the engines. Statoil believes the most accurate cost

effectiveness determination for the engines is based on the total NOX emissions reduction that 
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BACT Analysis 5-20 ENVIRON

would occur for the eight engines when each is equipped with an SCR system and the total cost 

that would be associated with the installation and operation of the eight SCR systems. This 

analysis results in a cost effectiveness of $17,203/ton, which we do not believe to be cost 

effective. Below we discuss the details of this cost effectiveness determination.

The estimated total capital cost for the installation of an SCR system on a main generator 

engine aboard the Developer is $3,500,000. Based on a 10-year life for an SCR system and 

the utilization of a 7 percent annual interest rate, the annualized cost for an SCR system for a 

main generator engine on the Developer would be $563,143. There are several noteworthy 

components of this annualized cost determination. First, the SCR system cost estimate used in 

this analysis is conservative because we did not include the costs associated with continuous 

emissions monitoring system (CEMS) equipment, engineering and supervision, contractor fees, 

project contingency, and the fuel penalty associated with operating electric heaters. Second, as 

pointed out, we have assumed that an SCR system installed on a Developer main generator 

engine would have a life of 10 years. In the more typical stationary source owner or operator 

circumstances, an engine and SCR system could be assigned a useful life more representative 

of the true useful life of the equipment. A 10-year useful life has been assigned for this cost 

effectiveness analysis because this time period represents a realistic estimate of the longest 

continuous period Statoil would likely lease the Developer. Drilling vessel leases are typically 

issued for periods of one to two years with an option to renew once for an additional year. This 

is done to allow both the lessee and lessor to take advantage of changing market conditions. 

Leasing the same drilling vessel for additional years of service beyond the first option (i.e., after 

three years) requires negotiation of a new lease agreement. Therefore, the use of a 10-year 

useful life actually represents a conservative basis for determining the SCR system cost 

effectiveness for the Developer under a Statoil lease.

Third, if Statoil were to install SCR systems on the drilling vessel, Maersk would require a 

financial commitment from Statoil to remove the systems at the end of the Statoil-Maersk lease 

agreement. Maersk has expressed that the SCR systems would be requested to be removed 

from the vessel because the systems would not be required by other lessees of the vessel, and 

Maersk and future lessees would not want to operate and maintain the otherwise unnecessary 

equipment. Therefore, because any SCR system installed on the main generator engines of the 

vessel would be required to be removed at the end of the Statoil-Maersk lease agreement, 

Statoil has included the cost to conduct this removal activity in the cost effectiveness analysis. 

Fourth, we have included retrofit costs in this BACT cost analysis. The Developer is an existing 

drilling vessel that was not designed with sufficient space or accessibility for SCR system 

installation. Therefore, a considerable portion of the indirect costs used in this analysis is the 

costs associated with downtime of the vessel for the installation and removal of the SCR 

systems under consideration. As described by EPA,

16 the cost associated with lost production 

for an existing source due to the installation of an emissions control device is a component of 

the indirect installation costs for a control device installation project. In this case, Statoil leases 

the drilling vessels for exploration activities and is obligated to pay a certain lease rate whether 

the drilling vessel is actively drilling or not. To install and remove the SCR systems, the drilling 

 16 EPA Pollution Control Cost Manual, Sixth Edition, Chapter 2 - Cost Estimation: Concepts and Methodology, 

January 2002 (EPA/452/B-02-001), pp. 2-28-2-30. 
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BACT Analysis 5-21 ENVIRON

vessel would be down for several days to allow sufficient time for equipment installation and

removal and associated commissioning. The lease rate for the Developer is approximately 

$500,000 per day. We have estimated that 20 days would be required for the installation of the 

SCR systems and associated commissioning, while 10 days would be required for the removal 

of the SCR systems and the installation of the original vessel equipment. Statoil believes the 

start-up cost based on the non-recoverable lease rate of the Developer is justified under the 

procedures and guidance provided by EPA. Lastly, Statoil has assumed that SCR system 

installation and removal activities would be able to occur at sea, which may not be realistic, but 

this assumption eliminates additional lease days to travel to and from a port.

Now that we have presented the annualized cost, the final component of this BACT cost 

effectiveness analysis is to determine the NOX emissions reduction that would result from the 

installation of the SCR system. We have conservatively estimated that an SCR system would 

reduce NOX emissions from a main generator engine by 75 percent, even though we expect

that it will be difficult to maintain this level of reduction at consistently varying engine loads. This 

efficiency is based on the difference between a baseline NOX emission factor of 8.2 g/kW-hr 

(see Section 3.2.1 for the basis of this value) for the main generator engines and a post-SCR 

system emission factor of 2.0 g/kW-hr, which was provided by an SCR system vendor.

To determine the main generator engine-SCR system cost effectiveness, we divided the 

estimated annualized cost of $563,143 by 32.74 tpy, which is the amount of NOX emissions 

reduction estimated to be achieved by a 75 percent efficient SCR system. The resulting value is 

approximately $17,200/ton, which we do not believe to be cost effective. Therefore, we do not 

believe that SCR is cost effective for the main generator engines located on the Developer. 

Please see Appendix D for the cost effectiveness calculations and supporting SCR equipment 

and operating cost information and data.

5.3.4.2 Selective Catalytic Reduction (SCR) for Developer Emergency Generator 

Engine

The Developer is equipped with one emergency generator engine (Emergency Generator 

Engine (Emissions Unit ID EGEN)) that will be operated during planned maintenance and

testing checks or in the event of an emergency. The engine maintenance and testing checks

are generally brief and typically involve the engine operating under low load scenarios. During 

the maintenance and testing events, the engine’s exhaust temperature is unlikely to reach the 

minimum temperature needed for an SCR catalyst to function properly, which would likely result 

in the need to install an electric heater to heat the exhaust to a sufficient temperature. The 

proposed potential NOX emissions from normal maintenance and testing of the emergency 

generator engine and the expected emergency use of the engine based on past operations are

0.76 tpy. Although there are serious technical difficulties related to operating an SCR system on 

engines that operate less than an hour at low loads, we have performed the following SCR cost 

effectiveness analysis to demonstrate that SCR is not cost effective for the Developer

emergency generator engine.

The estimated total capital cost for the installation of an SCR system on the emergency

generator engine aboard the Developer is $250,220. Based on a 10-year life for an SCR 
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BACT Analysis 5-22 ENVIRON

system and the utilization of a 7 percent annual interest rate, the annualized cost for an SCR 

system for the emergency generator engine on the Developer would be $40,879. Note that 

Statoil did not include CEMS costs or the costs associated with the required downtime for the 

Developer for the installation and removal of an SCR system on the emergency generator 

engine. As previously described, Statoil would be responsible to pay the lease rate for the 

drilling vessel during the time period that would be required to install and remove the SCR 

system from the emergency generator engine even though the drilling vessel would not be able 

to conduct drilling operations during this time period. Therefore, the annualized cost used in this 

analysis is a conservative estimate.

Now that we have presented the annualized cost, the final component of this BACT cost 

effectiveness analysis is to determine the NOX emissions reduction that would result from the 

installation of the SCR system. The NOX emissions control efficiency for the SCR system is 

assumed to be 90 percent based on information provided by an SCR vendor. Therefore, the 

SCR system would be expected to reduce NOX emissions from the emergency generator 

engine by 0.68 tpy.

To determine the emergency generator engine-SCR system cost effectiveness, we divided the 

estimated annualized cost of $40,879 by 0.68 tpy, which is the amount of NOX emissions 

reduction estimated to be achieved by a 90 percent efficient SCR system. The resulting value is 

approximately $60,000/ton, which we do not believe to be cost effective. Therefore, we do not 

believe that SCR is cost effective for the emergency generator engine located on the Developer.

Please see Appendix D for the cost effectiveness calculations and supporting SCR equipment 

and operating cost information and data.

5.3.4.3 Selective Catalytic Reduction (SCR) for Discoverer Americas Emergency 

Generator Engine

The Discoverer Americas is equipped with one emergency generator engine (Emergency 

Generator Engine (Emissions Unit ID EGEN)) that will be operated during planed maintenance 

and testing checks or in the event of an emergency. The maintenance and testing checks are 

generally brief and typically involve the engine operating under low load scenarios. During the 

maintenance and testing events, the engine’s exhaust temperature is unlikely to reach the 

minimum temperature needed for an SCR catalyst to function properly, which would likely result 

in the need to install an electric heater to heat the exhaust to a sufficient temperature. The 

proposed potential NOX emissions from normal maintenance and testing of the emergency 

generator engine on the Discoverer Americas are 1.03 tpy. Although there are serious technical 

difficulties related to operating an SCR system on engines that operate less than an hour at low 

loads, we have performed the following SCR cost effectiveness analysis to demonstrate that 

SCR is not cost effective for the Discoverer Americas emergency generator engine.

The estimated total capital cost for the installation of an SCR system on the emergency

generator engine aboard the Discoverer Americas is $250,220. Note that we used the capital 

and annual costs estimated for the installation of an SCR system on the Developer emergency 

generator engine for this engine. We believe this assumption is conservative because the 

Discoverer Americas emergency generator engine is rated 20 percent higher than the 
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BACT Analysis 5-23 ENVIRON

Developer emergency generator engine. Based on a 10-year life for an SCR system and the 

utilization of a 7 percent annual interest rate, the annualized cost for an SCR system for the 

emergency generator engine on the Discoverer Americas would be $40,879. Note that Statoil 

did not include CEMS costs or the costs associated with the required downtime for the 

Discoverer Americas for the installation and removal of an SCR system on the emergency 

generator engine. As previously described, Statoil would be responsible to pay the lease rate 

for the drilling vessel during the time period that would be required to install and remove the 

SCR system from the emergency generator engine even though the drilling vessel would not be 

able to conduct drilling operations during this time period. Therefore, the annualized cost used 

in this analysis is a conservative estimate.

Now that we have presented the annualized cost, the final component of this BACT cost 

effectiveness analysis is to determine the NOX emissions reduction that would result from the 

installation of the SCR system. The NOX emissions control efficiency for the SCR system is 

assumed to be 90 percent based on information provided by an SCR vendor. Therefore, the 

SCR system would be expected to reduce NOX emissions from the emergency generator 

engine by 0.92 tpy.

To determine the emergency generator engine-SCR system cost effectiveness, we divided the 

estimated annualized cost of $40,879 by 0.92 tpy, which is the amount of NOX emissions 

reduction estimated to be achieved by a 90 percent efficient SCR system. The resulting value is 

approximately $44,400/ton, which we do not believe to be cost effective. Therefore, we do not 

believe that SCR is cost effective for the emergency generator engine located on the Discoverer 

Americas.

Please see Appendix D for the cost effectiveness calculations and supporting SCR equipment 

and operating cost information and data.

5.3.4.4 Engine Replacement/Tier 2 Emission Standards for Discoverer Americas

Main Generator Engines

While engine replacement is not a specific control technology, replacing an older engine with a 

new engine meeting current NOX emission standards could result in lower NOX emissions. A 

new (2011-2015 model year) replacement engine with the same power rating and cylinder 

displacement size as the existing Discoverer Americas main generator engines would be 

manufactured to meet 40 CFR part 1042 Tier 2 emission standards for Category 3 Engines. 

The installation of a 40 CFR part 1042 Tier 2 compliant replacement engine would result in a 

NOX emissions control efficiency of approximately 20 percent. This percent reduction was 

determined by comparing the baseline NOX emission factor for the existing 40 CFR part 94 Tier 

1 compliant main generator engine, 9.2 g/kW-hr, to the 40 CFR part 1042 Tier 2 emission 

standard, 9.7 g/kW-hr, that would be required for a new replacement engine having the same 

power rating, engine speed (in rpm), and cylinder displacement size as the existing main

generator engines.

Similar to the discussion above for SCR on the Developer main generator engines, the 

operational flexibility necessary for the main generator engines makes it difficult to determine 

the cost effectiveness for any one of the eight engines. Statoil has conducted the cost 
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BACT Analysis 5-24 ENVIRON

effectiveness analysis for the main engine replacement based on three engines operating at 

35 percent load and five engines on standby. Statoil conservatively estimates the total capital 

cost for replacement of the eight Discoverer Americas main generator engines to be $6,250,000 

per engine. This cost estimate only includes the cost associated with rig downtine associated 

with removing the existing engines and installing eight new main generator engines. Statoil 

conservatively estimates that the replacement of all eight main engine would take 100 days at a 

daily lease rate of $500,000 per day. Please note the total capital cost estimate does not 

include the actual engine cost or any other costs associated with the replacing the engines.

As previously described, Statoil would be responsible to pay the lease rate for the drilling vessel 

during the time period that would be required to remove the existing main generator engines

and install a replacement engine even though the drilling vessel would not be able to conduct 

drilling operations during this time period. Therefore, this total capital cost is a conservative 

estimate. Based on a 10-year life for the replacement engine and the utilization of a 7 percent 

annual interest rate, the annualized cost for one replacement main generator engine on the 

Discoverer Americas would be $889,859.

Now that we have presented the annualized cost, the final component of this BACT cost 

effectiveness analysis is to determine the NOX emissions reduction that would result from the 

replacement of the existing main generator engine with a lower NOX emitting replacement 

engine. We have estimated that the installation of a 40 CFR part 1042 Tier 2 compliant 

replacement engine would result in a total NOX emissions reduction of 83 tpy (10.37 tpy per 

engine) relative to the existing engines.

To determine the replacement main generator engines cost effectiveness, we divided the 

estimated annualized cost of $889,859 by 10.37 tpy, which is the amount of NOX emissions 

reduction estimated to be achieved by one replacement engine. The resulting value is 

approximately $85,821/ton, which we do not believe to be cost effective. Therefore, we do not 

believe that engine replacement is cost effective for the main generator engines located on the 

Discoverer Americas.

Please see Appendix D for the cost effectiveness calculations and supporting engine 

replacement equipment and operating cost information and data.

5.3.4.5 Engine Replacement/Tier 3 Emission Standards for Developer

Emergency Generator Engine

While engine replacement is not a specific control technology, replacing an older engine with a 

new engine meeting current NOX emission standards could result in lower NOX emissions. A 

new (2012 model year+) replacement engine with the same power rating and cylinder 

displacement size as the existing Developer emergency generator engine would be 

manufactured to meet 40 CFR part 1042 Tier 3 emission standards. The installation of a 40 

CFR part 1042 Tier 3 compliant replacement engine would result in a NOX emissions control 

efficiency of approximately 37 percent. This percent reduction was determined by comparing 

the baseline NOX emission factor for the existing 40 CFR part 94 Tier 1 compliant emergency 

generator engine, 9.2 g/kW-hr, to the 40 CFR part 1042 Tier 3 emission standard, 5.8 g/kW-hr, 
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BACT Analysis 5-25 ENVIRON

that would be required for a new replacement engine having the same power rating and cylinder 

displacement size as the existing emergency generator engine.

The estimated total capital cost for the installation of a replacement emergency generator 

engine on the Developer is $84,755. This total capital cost does not include the costs 

associated with the required downtime for the Developer for the removal of the existing 

emergency generator engine and the installation of a replacement engine. As previously 

described, Statoil would be responsible to pay the lease rate for the drilling vessel during the 

time period that would be required to remove the existing emergency generator engine and 

install a replacement engine even though the drilling vessel would not be able to conduct drilling 

operations during this time period. Therefore, this total capital cost is a conservative estimate. 

Based on a 10-year life for the replacement engine and the utilization of a 7 percent annual 

interest rate, the annualized cost for a replacement emergency generator engine on the 

Developer would be $40,879.

Now that we have presented the annualized cost, the final component of this BACT cost 

effectiveness analysis is to determine the NOX emissions reduction that would result from the 

replacement of the existing emergency generator engine with a lower NOX emitting replacement 

engine. We have estimated that the installation of a 40 CFR part 1042 Tier 3 compliant 

replacement engine would result in a NOX emissions control efficiency of 37 percent, as 

described above. Therefore, the replacement emergency generator engine would be expected 

to reduce NOX emissions by 0.28 tpy relative to the existing engine.

To determine the replacement emergency generator engine cost effectiveness, we divided the 

estimated annualized cost of $12,067 by 0.28 tpy, which is the amount of NOX emissions 

reduction estimated to be achieved by the replacement engine. The resulting value is 

approximately $43,407/ton, which we do not believe to be cost effective. Therefore, we do not 

believe that engine replacement is cost effective for the emergency generator engine located on 

the Developer.

Please see Appendix D for the cost effectiveness calculations and supporting engine 

replacement equipment and operating cost information and data.

5.3.4.6 Tier 1 Emission Standards for Discoverer Americas Main Generator 

Engines and Developer Emergency Generator Engine

The emergency generator engine on the Developer and the main generator engines on the 

Discoverer Americas are equipped with 40 CFR part 94 Tier 1 compliant technology (e.g., 

turbocharger, aftercooler, high injection pressure), which represents the only remaining 

technically feasible technology for the engines. Because these engines are already equipped 

with Tier 1 compliant technology, no cost effectiveness determinations are necessary for the 

technology.
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5.3.4.7 Tier 2 Emission Standards for Developer Main Generator Engines and 

Discoverer Americas Emergency Generator Engine

The main generator engines on the Developer and the emergency generator engine on the 

Discoverer Americas are equipped with 40 CFR part 94 Tier 2 compliant technology (e.g., 

turbocharger, aftercooler, high injection pressure), which represents the only remaining 

technically feasible technology for the engines. Because these engines are already equipped 

with Tier 2 compliant technology, no cost effectiveness determinations are necessary for the 

technology.

5.3.5 Step 5 – Select BACT

With SCR and engine replacement eliminated, the following table summarizes the BACT 

determinations made for the large (>500 hp) diesel engines on the Developer and Discoverer 

Americas.

Table 5.3.5-1

Summary of BACT Determinations for Developer and 

Discoverer Americas Large (>500 hp) Diesel Engines

Drilling 

Vessel

Number 

of 

Engines

Emissions Unit/

Engine Description

Average 

Annual NOX

Emissions 

Level

(g/kW-hr)

Control Technology/

Work Practice

Developer 8 Main Generator Engines

(GEN-1 thru GEN-8)

Wartsila Model 16V26 A (6,651 

hp)

8.2 40 CFR part 94 Tier 2 

Compliant Design, including 

Turbocharger, Aftercooler, 

High Injection Pressure, and 

Low NOX Tuning

Discoverer 

Americas

6 Main Generator Engines

(GEN-1 thru GEN-6)

STX MAN Model 14V32/40 

(9,387 hp)

12.1 40 CFR part 94 Tier 1 

Compliant Design, including 

Turbocharger, Aftercooler, and 

High Injection Pressure

Developer 1 Emergency Generator Engine

(EGEN)

Caterpillar Model 3516B (2,551 

hp)

9.2 40 CFR part 94 Tier 1 

Compliant Design, including 

Turbocharger, Aftercooler, and 

Electronic Fuel Injection

Discoverer 

Americas

1 Emergency Generator Engine

(EGEN)

STX MAN Model 7L27/38 

(3,097 hp)

9.8 40 CFR part 94 Tier 2 

Compliant Design, including 

Turbocharger, Aftercooler, and 

High Injection Pressure

5.4 NOX BACT Analysis for Small (≤ 500 hp) Diesel Engines

In this section, we discuss the top-down BACT analysis conducted for the small (≤500 hp) diesel 

engines located on the Developer and Discoverer Americas. The small diesel engines located 

on the Developer are the two cement unit engines (Emissions Unit IDs CMU-1 and CMU-2). 

The small diesel engines located on the Discoverer Americas are the two emergency air 

compressor engines (Emissions Unit IDs ACOMP-1 and ACOMP-2).
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BACT Analysis 5-27 ENVIRON

5.4.1 Step 1 – Identify All Control Technologies

Available NOX control technologies for small (≤500 hp) diesel engines were determined by 

searching the EPA RBLC using the following search conditions: Process Code 17.210 – Small 

Internal Combustion Engines (≤500 HP); Fuel Oil (ASTM #1, 2, includes kerosene, aviation, 

diesel fuel). Table 5.3-1 below summarizes the NOx control technologies for large diesel 

engines identified in the RBLC.

Table 5.4.1-1

EPA RBLC NOX Control Technologies for Small (≤500 hp) 

Diesel Engines

Abbreviation Control Technology

Typical Percent 

Reduction

ITR Ignition Timing Retard 10-50%

IAC Combustion Air Chiller/Intake Air Cooling

Tier 1 or 2 Tier 1 or Tier 2 Emission Standards per 40 CFR part 

89 or 40 CFR part 94

30%

- Turbocharger with Aftercooler Varies

GCP Good Combustion Practices -

None No controls specified -

The complete RBLC database download for small diesel engines is provided in Appendix D. 

Note that only those determinations made after January 1, 1999, were downloaded because 

older determinations are typically less stringent. The RBLC also listed lean burn and clean fuel 

as NOX control techniques for small diesel engines. However, these techniques do not 

specifically reduce NOX emissions; therefore, they are not discussed further.

The RBLC database does not indicate that SCR technology has been installed on engines rated 

at 500 hp or less. This suggests that SCR has not previously been deemed as BACT for this 

engine category due to technical infeasibility and/or energy, environmental, or economic 

impacts. as previously discussed in Section 5.2. The same holds true for small engines ≤ 500 

hp and SCR is not discussed further in this section.

In addition to the small diesel engine NOX emissions controls listed in the RBLC, Statoil 

considered the control technologies included in Table 5.4.1-2 below. These control 

technologies were identified by reviewing permit applications and comments on draft permits for 

other OCS sources and reviewing publications on diesel engine emissions control technologies.

Table 5.4.1-2

Other NOX Control Technologies for Diesel Engines

Abbreviation Control Technology

Typical 

Percent 

Reduction

EGR Exhaust Gas Recirculation 40-50%
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Abbreviation Control Technology

Typical 

Percent 

Reduction

- EGR with Water Injection (WI) Varies

- Engine Replacement (replacing old engine with new)

- Engine Re-Tooling (engine rebuild kits)

- Fuel-Water Emulsions

- Intake Air Humidification

- Engine Derate

- NOX Adsorber (NOX Traps)

LNC/HC-SCR Lean NOX Catalyst/Hydrocarbon SCR

CSNOx CSNOX Emission Abatement System

Except for EGR, specific NOX reduction efficiencies were not identified for the control 

technologies in Table 5.4.1-2. The expected control efficiency for these technologies varies 

based on the level of existing controls in place or the baseline emissions for each particular 

engine. The estimated control efficiencies for technically feasible control technologies are 

included in the evaluation of controls (Step 4) presented later in this section.

Because the list of NOX emissions control technologies for small diesel engines does not 

include any technologies that were not reviewed in Step 1 of the large diesel engine BACT 

analysis in Section 5.3.1, please refer to that section of the permit application for a detailed 

description of the potential NOX emissions control technologies for small diesel engines.

5.4.2 Step 2 – Eliminate Technically Infeasible Options

The following control options are considered technically infeasible for all of the small diesel 

engines located on the Developer or Discoverer Americas unless otherwise noted.

• Exhaust Gas Recirculation (EGR)

• Engine Replacement

• Water Injection (WI)

• Fuel-Water Emulsion

• Intake Air Humidification

• Cam Shaft Cylinder Kits (Re-tooling)

• Engine Derate

• NOX Adsorbers

• Lean NOX Catalyst (LNC)/Hydrocarbon SCR (HC SCR)
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BACT Analysis 5-29 ENVIRON

• CSNOx Emission Abatement System

The following outlines why the above technologies have been determined to be infeasible for 

small diesel engines located on the Developer and Discoverer Americas.

5.4.2.1 Exhaust Gas Recirculation (EGR)

EGR is a relatively new control technology that has primarily been applied to smaller high speed 

diesel engines such as those in cars or trucks. Exhaust gas that is recirculated back into the 

cylinders of the engine adds wear-inducing contaminants (e.g., soot) and causes an increase in 

engine oil acidity, which can result in engine inefficiency and an increase in engine wear. Due 

to the limited application (if any) of EGR on marine engines such as the small diesel engines 

located on the Developer or Discoverer Americas and the noted technical issues associated 

with its general application, we have determined that it is not technically feasible to retrofit the 

existing small diesel engines on the Developer or Discoverer Americas with EGR.

5.4.2.2 Engine Replacement

Engine replacement is not technically feasible for the small engines located on the Developer

and Discoverer Americas because the engines are relatively new and comply with the stringent

40 CFR part 94 Tier 2 NOX emission standards. Therefore, a new small diesel engine would 

likely have the same NOX emissions characteristics as the existing small diesel engines on the 

Developer and Discoverer Americas, resulting in relatively none to limited NOX emissions 

control.

5.4.2.3 Water Injection, Fuel-Water Emulsions, and Intake Air Humidification

Water injection, fuel-water emulsion, and intake air humidification are considered technically 

infeasible due to engine retrofit incompatibility, the excessive fresh water (non-salt water)

requirements, and limited space availability on the vessels, which availability would be 

necessary to store the fresh water to be used in these systems. Furthermore, water injection 

introduces the potential for engine damage. The use of water injection can lead to cold 

corrosion of engine components and damage to turbochargers and charge air coolers.

In consideration of the individual technical infeasibility determinations reach for EGR and water 

injection, the combination of EGR and water injection is also considered technically infeasible.

5.4.2.4 Cam Shaft Retrofits

Clean Cam Technology Systems, LLC (CCTS) cam shaft retrofit kits are only available for twostroke Detroit Diesel engines, model series 71 and 92. None of the small diesel engines 

proposed in this application are two-stroke engines. Therefore, this technology is not feasible

for the engines.

5.4.2.5 Engine Derate

Derating the small diesel engines on the Developer and Discoverer Americas would likely result 

in lower NOX emissions, but the reduction in available power for these engines would cause 

operational complications on the drilling vessels because the services (cement unit and air 

compression operations) provided by the engines must be achievable at rates corresponding to 
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BACT Analysis 5-30 ENVIRON

the engines’ rated capacities. The cement operations on a drilling vessel are critical to safe 

drilling operations, and derating the cement unit engines could potentially result in scenarios 

where safe drilling operations would be comprised due to insufficient cement unit operating 

rates. Similarly, the emergency air compressor engines located on the Discoverer Americas

represent “emergency” operations, and derating these engines would potentially compromise 

critical drilling vessel operations that could lead to damage to vessel equipment or result in 

unsafe vessel operations. Based on the safety risks associated with derating the small diesel 

engines on the drilling vessels, this technology is not feasible.

5.4.2.6 NOX Adsorbers

The development of NOX adsorber systems for diesel engines is ongoing, with NOX adsorbers 

currently available for on-road gasoline and diesel passenger vehicle engines. NOX adsorber 

systems are considered technically infeasible because they are not currently available for small

marine engines.133

5.4.2.7 Lean NOX Catalyst (LNC)/Hydrocarbon SCR (HC SCR)

While LNC systems have performed well in some retrofit applications, these systems have 

primarily been used in on-road diesel applications. It has also been installed on diesel engines 

used in backhoes, graders, and wheel loaders. However, neither the LNC nor the HC SCR

technology is commercially available for marine engines. Since these technologies are not 

currently available for marine engines, they are considered technically infeasible options for the 

engines.

5.4.2.8 CSNOx Emission Abatement System

CSNOxTM technology is currently in the demonstration stages of product development and has 

not been installed or tested on an engine similar to the cement unit engines or emergency air 

compressor engines. Since CSNOx technology is not currently available for use on the small 

marine diesel engines located on the Developer and Discoverer Americas, it is not considered 

technically feasible for our application.

5.4.3 Step 3 – Rank Remaining Control Technologies by Control Effectiveness

40 CFR part 94 Tier 2 compliant engine design, including turbocharger, aftercooler, and/or

electronic fuel injection technologies, is essentially the only remaining NOX emissions control 

technology remaining for the small diesel engines located on the Developer and Discoverer 

Americas. We have determined that 40 CFR part 94 Tier 2 compliant engine design, including 

charge air cooling and ignition control design and operations, is technically feasible for the small 

diesel engines on the drilling vessels.

5.4.4 Step 4 – Evaluate Most Effective Control Options and Document Results

The small diesel engines on the Developer and Discoverer Americas are equipped with Tier 2

compliant technology, which represents the only remaining technically feasible technology for 

the engines. Because these engines are already equipped with Tier 2 compliant technology, no 

cost effectiveness determinations are necessary for the technology.
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5.4.5 Step 5 – Select BACT

Based on the above analysis, the following table summarizes the BACT determinations made 

for the small (≤500 hp) diesel engines on the Developer and Discoverer Americas.

Table 5.4.5-1

Summary of BACT Determinations for Small (≤500 hp) Diesel 

Engines on the Developer and Discoverer Americas

Drilling 

Vessel

Number 

of 

Engines

Emissions Unit/

Engine Description

Average 

Annual NOX

Emissions 

Level

(g/kW-hr)

Control Technology/

Work Practice

Developer 2 Cement Unit Engines

(CMU-1 and CMU-2)

Caterpillar Model C15 (500 hp)

7.2 40 CFR part 94 Tier 2 

Compliant Design, including 

Turbocharger, Aftercooler, and 

Electronic Fuel Injection

Discoverer 

Americas

2 Emergency Air Compressor 

Engines

(ACOMP-1 and ACOMP-2)

Duetz Model F3L912 (50 hp)

Duetz Model F4L912 (68 hp)

7.5 40 CFR part 94 Tier 2 

Compliant Design, including 

Turbocharger and Aftercooler