GHG BACT Examples
• Next several sections walk through BACT reviews for
GHGs for a number of source categories.
• They are designed to demonstrate the kinds of
technical and policy issues that can arise and how
they can be addressed.
• These examples do not represent guidance on what
an actual BACT review must address and they do not
represent any guidance on what constitutes BACT for
similar sources that undergo an actual
determination.
DRAFT
1
GHG BACT Example:
Municipal Solid Waste Landfill
BACT Example: MSW Landfill
Project: New, large municipal solid waste landfill.
Step 1: Identifying all available controls
•For capture of the landfill gas, the application proposes use of
an active capture system that will be in compliance with the
NSPS that applies to the NMOC emissions
•For control, the following NSPS compliant options are examined:
– Flaring of the gas
– Using gas in on-site internal combustion engines to generate
electricity for sale
– Treating gas for delivery to a natural gas pipeline
DRAFT
3
BACT Example: MSW Landfill (cont’d)
Step 1 (cont’d)
• The permitting authority asked the applicant to
review two additional control measures:
– Collect and control landfill gas earlier in the life of the
landfill than is specified in the NSPS
– A gas turbine to generate power rather than internal
combustion engines
• At this stage, there are two options for gas capture :
– NSPS compliant active capture system
– That system, with earlier initiation of gas collection
DRAFT
4
BACT Example: MSW Landfill (cont’d)
Step 1 (cont’d)
• There are four options for the control of the landfill
gas:
–
–
–
–
Flaring,
Fueling engines,
Fueling a gas turbine, and
Treatment and routing of the gas to a pipeline
DRAFT
5
BACT Example: MSW Landfill (cont’d)
Step 2: Elimination of technically infeasible options
• Applicant demonstrated that the volume of gas
would be inadequate to fuel a commercially available
gas turbine
• Permitting authority reviewed the record
• Accepted elimination of that option from further
consideration
DRAFT
6
BACT Example: MSW Landfill (cont’d)
Step 3: Evaluation and ranking of controls by their
effectiveness
• Applicant used CO2e emissions over the life of the landfill, as
the effectiveness indicator
• Considered combinations of capture systems and controls for
overall effectiveness
• Early capture of gas and conversion of the gas to pipeline
quality for export is the most effective combination, from a
PSD perspective:
– Maximum amount of gas would be captured
– Most of the gas would not be combusted on site
• Flaring and the use of engines are similar in their control
– Reducing methane emissions significantly
– Generating relatively small on-site CO2 emissions
DRAFT
7
BACT Example: MSW Landfill (cont’d)
Step 4: Evaluating the most effective controls
• Analysis of the cost effectiveness, expressed as $/ton of CO2e
reduced over the life of the landfill.
• Applicant found conversion of gas to pipeline quality was not
cost effective. Would more than double the overall cost of the
project since the landfill was far from an existing pipeline.
• NSPS compliant control system with early collection was cost
effective for either the flare or the engines case.
• The flare was more cost effective because revenue from the
sale of power from use of engines would not offset the added
cost of the engines and a power transmission line.
DRAFT
8
BACT Example: MSW Landfill (cont’d)
Step 4 (cont’d)
Any significant energy and environmental impacts to be
considered:
• The application noted a positive environmental impact from
the use of a flare because NOX emissions for a flare would be
lower than those for the engines.
• Public comment identified positive energy and environmental
offsite impacts arising from using landfill gas to generate
electricity which displaces offsite energy generation and
associated emissions.
• Permitting authority determined that this benefit outweighed
the lower NOx emissions and better cost effectiveness of a
flare.
DRAFT
9
BACT Example: MSW Landfill (cont’d)
Step 5: Selecting BACT
Permitting authority determined BACT to be:
• NSPS compliant active collection system with early
installation/operation
• Landfill gas routed to engines and used to generate
electricity
DRAFT
10
BACT Example: MSW Landfill(cont’d)
Step 5 (cont’d)
Permit conditions are:
• CO2e limit on engine emissions, expressed in lbs per kWh,
to be demonstrated in a stack test annually.
• Compliance with the landfill NSPS design, operating and
recordkeeping requirements
• Earlier trigger for gas capture and use
• Requirement to operate engines under a written O&M
plan to assure combustion efficiency
DRAFT
11
GHG BACT Example:
Natural Gas Fired Boiler
BACT Example: Gas Boiler
Project Scope:
• Existing major source
• New 250 MMBtu/hour natural gas-fired boiler
DRAFT
13
BACT Example: Gas Boiler (cont’d)
Step 1: Identifying all available controls
Permit application lists the following four controls:
• Oxygen Trim Control:
– Inlet air flow adjusted for optimal thermal efficiency
• Economizer:
– Increases thermal efficiency by preheating feedwater
• Blowdown Heat Recovery:
– A heat exchanger transfers some of the heat in the blowdown water to
feedwater for deaeration or preheating
– Increases the boiler’s thermal efficiency
DRAFT
14
BACT Example: Gas Boiler (cont’d)
Step 1 (cont’d)
• Condensate Recovery:
– When hot condensate is returned to the boiler as feedwater, the
thermal efficiency increases
Permitting Authority asks for inclusion of air preheater
DRAFT
15
BACT Example: Gas Boiler (cont’d)
Step 1 (cont’d)
• Public comment asks for consideration of a combined cycle
natural gas-fired turbine
• Applicatant explains that a boiler is necessary for business
purposes:
– Providing process steam (and not electricity) and
– Varying steam demand
• Permitting authority rejects a combined cycle natural gas-fired
turbine for consideration on grounds it would “redefine the
source.”
DRAFT
16
BACT Example: Gas Boiler (cont’d)
Step 2: Eliminating technically infeasible options
• Permitting authority determines that the six controls are
technically feasible; demonstrated or available and applicable
to this type of source
Step 3: Evaluation and ranking of controls by their
effectiveness
• Applicant ranked control measures for the boiler based on
their impact on the thermal efficiency of the boiler (Could
also be based on emissions per unit of steam produced)
DRAFT
17
BACT Example: Gas Boiler (cont’d)
Step 3 (cont’d)
The permit applicant completed the control
effectiveness analysis and found:
• Most effective single measure is oxygen trim control
• Air preheater is no more effective than an economizer in
recovering exhaust heat
• The most effective combination of measures is: oxygen
trim control, an economizer, condensate recovery, and
blowdown heat recovery .
DRAFT
18
BACT Example: Gas Boiler (cont’d)
Step 4: Evaluating the most effective controls
• Permit applicant completed an analysis of the cost
effectiveness:
– Considered both measures and combinations of measures,
– Expressed as $/ton of CO2e reduced
– Given the size and layout of the facility, boiler blowdown heat
recovery was not cost effective
• Next most effective combination of measures was:
– the use of oxygen trim control
– an economizer
– condensate recovery
DRAFT
19
BACT Example: Gas Boiler (cont’d)
Step 4: (cont’d)
• Any significant energy and environmental impacts to be
considered in this step.
• Application identifies recovery and reuse of condensate:
– Reduces the use of feedwater treatment chemicals
– Reduces generation of related waste
– Reduces the amount of water going to wastewater treatment at the
site
DRAFT
20
BACT Example: Gas Boiler (cont’d)
Step 5: Selecting BACT
Permitting authority determined, and the record showed, that
BACT was the combination of:
•
•
•
Oxygen trim control,
An economizer, and
Condensate recovery
DRAFT
21
BACT Example: Gas Boiler (cont’d)
Step 5: (cont’d)
Permit conditions included:
•
•
•
•
•
•
Emission limit: lbs of CO2e per pound of steam produced, 30-day
rolling monthly average
CO2e emissions determined from natural gas use and standard
emission factors
Steam production determined from a gauge
Installation of boiler as described in the application, as a design
standard
Preventive maintenance program for the air to fuel ratio controller
Periodic calibration of gas meter and steam flow analyzer
DRAFT
22
GHG BACT Example:
Petroleum Refinery Hydrogen Plant Addition
BACT Example: Petroleum Refinery
Hydrogen Plant
Project Scope:
• Expand the hydrogen production and hydrotreating
capacity of an existing major source refinery
• For simplicity, analysis addresses the GHG BACT for
the new hydrogen plant that is being added in the
context of a larger project
DRAFT
24
BACT Example: Petroleum Refinery
Hydrogen Plant (cont’d)
DRAFT
25
BACT Example: Petroleum Refinery
Hydrogen Plant (cont’d)
Project Scope (cont’d):
• Proposed project producing hydrogen via the steam methane reforming
(SMR) process. In SMR, methane and steam are reacted via a catalyst to
produce hydrogen and CO. The reaction is endothermic and the necessary
heat is provided in a gas-fired reformer furnace. The CO reacts further
with the steam to generate hydrogen and CO2.
CH4 + H2O = CO + 3H2
CO + H2O = CO2 + H2
• The hydrogen is then separated from the CO2 and other impurities. The
application shows that the purification is done using a Pressure Swing
Adsorption Unit. The permit applicant proposes to use the off gas from
that step (containing some hydrogen, CO2, and other gases) as part of the
fuel for the reformer furnace.
DRAFT
26
BACT Example: Petroleum Refinery
Hydrogen Plant (cont’d)
Step 1: Identifying all available controls
• Permit application lists the following control options for GHG emissions:
– Furnace Air/Fuel Control – An oxygen sensor in the furnace exhaust is to be
used to control the air and fuel ratio for optimal efficiency
– Waste Heat Recovery – The overall thermal efficiency is to be optimized
through the recovery of heat from both the furnace exhaust and the process
streams to preheat the furnace combustion air, to preheat the feed to the
furnace and to produce steam for use in the process and elsewhere in the
refinery.
– CO2 Capture and Storage – Capture and compression, transport, and geologic
storage of the CO2. (Some refineries isolate hydrogen reformer CO2 for sale
but that is not a part of this example project.)
• The permitting authority did not require the applicant to consider any
additional control options beyond those in the application, and none were
suggested in public comments.
DRAFT
27
BACT Example: Petroleum Refinery
Hydrogen Plant (cont’d)
Step 2: Eliminating the technically infeasible options
• In this example, the permitting record shows that all
three controls are technically feasible because there
is no evidence that any of these options are not
demonstrated or available to this type of source.
DRAFT
28
BACT Example: Petroleum Refinery
Hydrogen Plant (cont’d)
Step 3: Evaluation and ranking of controls by their
effectiveness
• The applicant ranked control measures for the hydrogen plant based on
the CO2e emissions per unit of hydrogen produced.
• An output-based indicator is a good way to capture the overall effect of
multiple energy efficiency measures used in the design of a complex
process such as this.
• The permit applicant effectiveness analysis included benchmarking data
on the energy efficiency and GHG emissions of recently installed hydrogen
plants.
• Benchmarking data showed that this hydrogen plant would be a lower
emitter (on an output basis) than similar new plants, and the permitting
authority concurred in that determination.
• The applicant determined that the most effective control combination was
one in which all three options (furnace control, heat recovery and CCS)
were included.
DRAFT
29
BACT Example: Petroleum Refinery
Hydrogen Plant (cont’d)
Step 4: Evaluating the most effective controls
• Applicant analysis of the cost effectiveness of measures and
combinations of measures was expressed as $/ton of CO2e
reduced. The applicant also determined the incremental cost
effectiveness.
• The information supplied by the applicant demonstrated that
the transport and sequestration of CO2 would not be cost
effective because the nearest prospective location for
sequestration was more than 500 miles away and there was
not an existing pipeline suitable for CO2 transport between the
refinery and the sequestration location.
DRAFT
30
BACT Example: Petroleum Refinery
Hydrogen Plant (cont’d)
Step 4 (cont’d)
• The cost of transport was significant in comparison to the amount
of CO2 to be sequestered and the cost of the project overall.
• In responding to public comments on the issue, the permitting
authority noted that in circumstances in which a refinery was
located near an oil field that used CO2 injection for enhanced
recovery, the cost calculations for transport and sequestration
would likely be in a range that would not exclude CCS.
• Other significant energy and environmental impacts are also
considered in this step. In this case, none were presented in the
application, and the only significant public comment on the issue
was addressed by the permitting authority as noted above.
DRAFT
31
BACT Example: Petroleum Refinery
Hydrogen Plant (cont’d)
Step 5: Selecting BACT
• With the analysis and record complete, the
permitting authority determined that BACT was a
combination of furnace combustion control and
integrated waste heat recovery.
DRAFT
32
BACT Example: Petroleum Refinery
Hydrogen Plant (cont’d)
Step 5 (cont’d)
BACT Permit Limits:
• Emission limit in pounds of CO2e emitted per pound of
hydrogen produced, averaged over rolling 30 day periods.
• CO2e emissions would be determined by metering natural gas
sent to the hydrogen plant. There may need to be an
adjustment for excess fuel gas sent to other parts of the
refinery on a periodic basis. A separate meter and fuel
analysis would be needed to get that credit.
• Hydrogen production would be metered.
• The plant would need to be installed as described in the
application.
• There would need to be a program for calibration and
maintenance of meters and the oxygen trim system.
DRAFT
33
GHG BACT Example:
Coal-Fired Electric Generating Unit
BACT Example: Coal EGU
Project: New greenfield sub-bituminous pulverized
coal-fired boiler and steam turbine electricity
generating facility.
DRAFT
35
Coal EGU – Boiler and Steam Turbine
superheated steam
Multi-stage
Steam
Turbine
Generator
low
pressure
steam
reheated
steam
steam
Steam
Drum
hot boiler
feedwater
extracted
steam
Condenser
Boiler Wall
Watertubes
Reheater
Feedwater
Heater
Superheater
Coal
Silo
Economizer
Burners
cooling water
Cooling
Tower
boiler
feedwater
Air
Pollutant
Emissions
Controls
flue gas
coal
fly ash
Furnace
Chamber
Induced
Draft Fan
Air
Heater
ambient air
coal
bottom
ash
Forced Draft Fan
heated combustion air
Coal
Pulverizer
DRAFT
36
BACT Example: Coal EGU (cont’d)
Step 1: Identifying all available controls
Applicant’s BACT analysis had two elements:
– Efficiency measures, including the design of the boiler and turbine:
• Super critical boiler and turbine design
• Coal drying
• Optimized combustion with continuous control
– CO2 control through CCS.
State requests that the BACT analysis also include:
– Ultra-super critical design
– Integrated Gasification Combined Cycle (IGCC)
– Motor efficiency improvements (to increase net output of electricity
and thereby fuel use)
DRAFT
37
IGCC
DRAFT
38
IGCC with Pre-Combustion CO2 Capture
Step 1 (cont’d)
• Pre-combustion capture of CO2 is an option with coal
gasification. In the gasifier, the coal decomposes in the
presence of oxygen to syngas, a mixture of H2 and carbon
monoxide (CO), along with minor other constituents.
• To enable pre-combustion capture, the syngas is further
processed to convert CO into CO2 while producing additional
H2. A solvent absorption system can then be used to separate
the CO2 from the H2.
DRAFT
39
IGCC with Pre-Combustion CO2 Capture
(continued)
Step 1 (cont’d)
• After CO2 removal, the H2 can be used as a fuel in the
combustion turbine.
• Pre-combustion CO2 capture is less expensive than postcombustion capture. The advantages of this type of system
are the higher CO2 concentration and the lower volume of
syngas to be handled, which result in smaller equipment sizes
and lower capital costs.
DRAFT
40
BACT Example: Coal EGU (cont’d)
• Public comment calls for use of natural gas instead of
coal. While this happened after the BACT
determination and draft permit were out for
comment, it relates to the control measures
considered in Step 1 of the analysis.
• The permitting agency determines this is outside the
scope of BACT, representing a change in basic design
and business purpose.
DRAFT
41
BACT Example: Coal EGU (cont’d)
Step 2: Elimination of technically infeasible options
• All options are considered by the permitting
authority to be available and technically feasible:
–
–
–
–
–
–
Ultra-supercritical boiler and turbine design
Integrated Gasification Combined Cycle
Coal drying
Combustion control
Variable speed motors
CCS
DRAFT
42
BACT Example: Coal EGU (cont’d)
Step 3: Evaluation and ranking of controls by their
effectiveness
• Applicant proposes to rank measures based on emissions
per unit of fuel used
• State requires that options be ranked by CO2 emissions on
a “net” output basis.
• Most effective combination is either ultra-supercritial with
CCS or IGCC with CCS. Coal drying and efficient motors
included in both instances.
DRAFT
43
BACT Example: Coal EGU (cont’d)
Step 4: Evaluating the most effective controls
• CCS dismissed for both designs based on excessive costs,
siting issues, and parasitic electricity load
• In the absence of CCS, IGCC shown to not superior to ultrasupercritical design
• Ultra-supercritical chosen as BACT: cost-effective, no
adverse collateral impacts
• All energy efficiency measure also required
• Permitting agency documents conclusion with supporting
documentation for the record
DRAFT
44
BACT Example: Coal EGU (cont’d)
Step 5: Selecting BACT
BACT is determined to be:
• A ultra-supercritical boiler design w/ high efficiency steam
turbine,
• Control of boiler air fuel ratio,
• Coal drier using low grade/waste heat
• High efficiency variable speed motors for electric drives
DRAFT
45
BACT Example: Coal EGU (cont’d)
Step 5 (cont’d)
Enforceable permit conditions are:
• Annual limit in tons of CO2 per net MWh; rolling 12 month
totals
• O&M plan addressing combustion controls, steam turbine
efficiency and electrical motors
DRAFT
46
GHG BACT Example:
Cement Plant
BACT Example: Cement Plant
Project Scope:
• A new cement kiln is proposed. The product is finished cement for
local markets. Cement is produced from raw materials such as
limestone, chalk, shale, clay, and sands which are quarried, crushed,
ground, and blended to the correct chemical composition.
• The raw material is fed into a large rotary kiln (cylindrical furnace)
which rotates while the contents are heated to extremely high
temperatures. The high temperature causes the raw material to
react and form a hard nodular material called “clinker”. Clinker is
cooled and ground with gypsum and other additives to produce
portland cement.
• CO2 is emitted due to both the decomposition of the limestone and
the combustion of fuel in the kiln.
DRAFT
48
BACT Example: Cement Plant (cont’d)
DRAFT
49
BACT Example: Cement Plant (cont’d)
Step 1: Identify all available controls
• This BACT analysis has four elements: process
technology/energy efficiency, fuel choice, product
specification and CO2 removal and storage.
Process Technology/Energy Efficiency
• Applicant proposes to use a preheater/precalciner design,
which is more efficient that older designs that have less heat
recovery.
DRAFT
50
BACT Example: Cement Plant (cont’d)
Process Technology/Energy Efficiency (Cont’d)
• Applicant presents the following features of the PH/PC design
that improve thermal efficiency and reduce emissions of CO2
related to on-site fuel use.
– Modern cement manufacturing facilities incorporate multi-stage
preheaters prior to the kiln. A five stage preheater is proposed.
– Grate coolers are used to cool the clinker. The grate cooler is integral
to heat recovery from the clinker and higher thermal efficiency. A
reciprocating grate cooler, which is the design with the greatest fuel
use benefit, is proposed.
– Computerized/automated control system is proposed to optimized
fuel combustion conditions.
DRAFT
51
BACT Example: Cement Plant (cont’d)
Process Technology/Energy Efficiency (Cont’d)
– Kiln seals reduce heat loss. The applicant presents information
on the effectiveness and longevity of the kiln seals and proposes
a maintenance plan for the kiln seals.
– Significant heat loss can occur through the kiln shell and proper
insulation keeps these losses to a minimum. The applicant
presents the alternative refractory that were considered and
demonstrates that the most effective was chosen.
• The applicant presents data on the energy use per ton of
clinker that has been achieved at recently built kilns as a
demonstration that the proposed design constitutes
BACT for the thermal efficiency aspect of the new kiln.
DRAFT
52
BACT Example: Cement Plant (cont’d)
Step 1 (cont’d)
Fuel Choice
• Applicant proposes to use a combination of coal as the
primary fuel and wood wastes (when they are available).
• Applicant presents data showing that other solid fuels (tires,
waste plastics) do not represent a reduction in CO2 emissions
at the kiln.
• Permitting Authority agrees.
DRAFT
53
BACT Example: Cement Plant (cont’d)
Step 1 (cont’d)
Product Composition
• Applicant does not address product composition in the initial
application.
• To the extent that one can make a finished product, meeting
all of its quality requirements with less clinker, the finished
product will be less energy intensive and the emissions of CO2
per unit of product will be reduced. Fly ash from coal
combustion can be used in a blended cement. However, the
use of fly ash may be limited by product quality requirements
and fly ash characteristics.
DRAFT
54
BACT Example: Cement Plant (cont’d)
Step 1 (cont’d)
Product Composition
• With that in mind, the agency asks the applicant to consider
maximum use of fly ash and other additives as blending
materials with consideration of the markets to be served.
• Applicant presents information on product specifications in
the anticipated markets and indicates that up to 5% fly ash
from a nearby coal fired utility could be used in some of their
product. A CO2 reduction in terms of CO2 per ton of finished
cement due to fly ash use is noted.
• This alternative is accepted for further review by the
permitting authority.
DRAFT
55
BACT Example: Cement Plant (cont’d)
Step 1 (cont’d)
CO2 Capture/Removal and Storage
• Applicant presents information on two means of capture and
control: conventional Carbon Capture and Storage and the
Calera process.
• The Calera process uses a wet scrubber to capture CO2
emissions and chemically convert the captured CO2 to
carbonates. Carbonate minerals can then be precipitated
from the solution, dried, and used to make blended cement
or other building materials.
DRAFT
56
BACT Example: Cement Plant (cont’d)
Step 2: Eliminating technically infeasible options
Fuel Choice
• During the public comment, use of natural gas in place of coal
is raised.
• The applicant points out that it is technically feasible to use
gas, with an increase in NOx emissions. However, there is no
natural gas supply infrastructure with sufficient capacity in the
area.
• The costs of getting gas delivered and used are addressed and
the applicant presents data showing it will not be cost
effective. The permitting authority agrees.
DRAFT
57
BACT Example: Cement Plant (cont’d)
Step 2 (cont’d)
Product Composition
• Applicant present data showing that use of more fly ash will
not allow them to meet product specifications.
• Applicant also presents data on the availability of other
product blend materials showing that they can adversely
affect product quality and there is no identifiable long term
supply.
• As a result, the assessment is limited to 5% fly ash in 80% of
the product, averaged over 12 months.
DRAFT
58
BACT Example: Cement Plant (cont’d)
Step 2 (cont’d)
CCS
• The applicant points out that the Calera process is still under
development and not commercially available. The applicant
also notes that once it is commercial, issues of markets for the
by-product and cost would need to be considered. Lastly the
applicant points out that the nature of the Calera process and
its products would be a change to their fundamental business
purpose.
• The applicant notes that the capture and purification of CO2
from a cement kiln is understudy and is not commercially
available.
• The application indicates that CCS is not commercially
available or technically feasible and should be dismissed. The
agency concurs.
DRAFT
59
BACT Example: Cement Plant (cont’d)
Step 3: Evaluating and ranking controls for their
effectiveness
• The measures were ranked based on CO2 emitted per ton
of clinker. (Cement kiln performance benchmarking data is
presented on this basis.)
• At the agency’s request the ranking also was done based
on CO2 emitted per ton of finished cement. This change
allowed the analysis to capture the impact that fly ash
addition could have on emissions.
DRAFT
60
BACT Example: Cement Plant (cont’d)
Step 4: Evaluating the most effective controls
The use of the high efficiency kiln design and the use of
fly ash in the product were both found to be cost
effective on the basis of dollars per ton of CO2
eliminated.
– Other environmental issues were identified with efforts to
commit to the use of alternative waste as fuels. However,
alternative fuels had not shown a clear CO2 emissions
reduction potential for the site emissions.
DRAFT
61
BACT Example: Cement Plant (cont’d)
Step 5: Selecting BACT
• In this example, BACT is the use of the PH/PC design
with all of the efficiency improvements proposed by
the applicant.
• Additionally, the applicant is to use 5% fly ash in the
cement blend whenever the product specification
allows for its use.
DRAFT
62
BACT Example: Cement Plant (cont’d)
Step 5 (continued)
Enforceable Permit Conditions
• The kiln is to meet a 365 day rolling annual average limit on tons of
CO2 emitted per ton of clinker produced.
• CO2 determined with a CEMS.
• A maintenance plan for insulation and kiln seal is also required.
• An O&M for the process optimization controls, including instrument
calibration and maintenance is required.
• Records of fly ash use in product required. If annual average fly ash
addition is less than 5%, the company needs to justify its lower use
based on product quality concerns or client restrictions.
DRAFT
63
GHG BACT Example:
Natural Gas Compressor Station Expansion
BACT Example:
Natural Gas Compressor Station
Project : Applicant is proposing to install two
reciprocating compressors with reciprocating gas-fired
engine drivers at an existing natural gas pipeline
compressor station.
DRAFT
65
BACT Example:
Natural Gas Compressor Station (cont’d)
Step 1: Identifying all available controls
• Applicant includes the following elements in the initial
BACT determination:
– Air/fuel ratio controllers to minimize methane emissions from
the reciprocating engines
– Periodic inspection and maintenance of the compressor rod
packing to determine when to replace packing
– Use of low-bleed gas-driven pneumatic controllers to reduce
methane venting
– Installation of a new flare and periodic inspection and
maintenance of that flare, which will handle natural gas
emissions during upsets and malfunctions
DRAFT
66
BACT Example:
Natural Gas Compressor Station (cont’d)
Step 1 (cont’d)
• Permitting authority asks that the applicant consider a gas
turbine with a centrifugal compressor in place of the
reciprocating engines because the site already has a turbine
and a turbine will have lower GHG emissions.
• Permitting authority suggests that pneumatic controllers
could be driven by instrument air instead of natural gas with
lower emissions.
• During the public comment period, someone asks that electric
drive be considered.
DRAFT
67
BACT Example:
Natural Gas Compressor Station (cont’d)
Step 1 (cont’d)
• Applicant plans to use the existing condensate tanks.
Permitting authority determines this is a change in the
method of operation of those tanks and requires that they go
through BACT.
• The permitting authority asks that the BACT review address
the installation of vapor recovery on the existing tanks even
though they are not going to be physically modified. Vapor
recovery could also be applied to compressor rod packing.
DRAFT
68
BACT Example:
Natural Gas Compressor Station (cont’d)
Step 1 (cont’d)
• At this point there are eight control measures under
consideration:
–
–
–
–
–
–
–
–
Air/fuel ratio controller on the reciprocating engines
Use of a turbine instead of the reciprocating engines
Periodic inspection and maintenance of compressor rod packing
Use of low-bleed gas-driven pneumatic controllers
Use of instrument air to drive pneumatic controllers
Use of a high efficiency flare for upset emissions control
Vapor recovery unit for condensate tanks and rod packing
Use of electrical drive instead of a gas based drive
DRAFT
69
BACT Example:
Natural Gas Compressor Station (cont’d)
Step 2: Eliminating technically infeasible options
• The applicant provides evidence that electrical service does
not exist in the vicinity of the compressor station and that the
use of electrical drives, vapor recovery unit, and air
compressors (for instrument air) using offsite power
generation is not feasible. Further onsite power generation
will not reduce GHG emissions.
• The applicant indicates that the site needs enhanced ability
to handle load swings and a turbine is not suitable for that
purpose.
• Permitting authority agrees that electric drive and instrument
air are not feasible and that a turbine drive will not meet the
project purpose.
DRAFT
70
BACT Example:
Natural Gas Compressor Station (cont’d)
Step 3: Evaluation and ranking of controls by their
effectiveness
• Applicant ranks the measures and combination of
measures based on CO2e emitted per hour, at full
load
• The most effective combination is:
– Air/fuel ratio controller on the reciprocating engines
– Periodic inspection (monitoring) and maintenance of compressor rod
packing
– Use of low-bleed gas-driven pneumatic controllers
– Use of a high efficiency flare for upset emissions control
– Vapor recovery unit for condensate tanks and rod packing
DRAFT
71
BACT Example:
Natural Gas Compressor Station (cont’d)
Step 4: Evaluating the most effective controls
Applicant agrees to the most effective combination. No
significant energy, economical or environmental
impacts were identified by the applicant, the agency or
the public.
DRAFT
72
BACT Example:
Natural Gas Compressor Station (cont’d)
Step 5: Selecting BACT
BACT is determined to be:
• Air/fuel ratio controller on the reciprocating engine
• Periodic inspection (monitoring) and maintenance of
compressor rod packing to determine when packing
replacement is needed
• Low-bleed pneumatic controllers in place of high-bleed
controllers
• Use of a high efficiency flare for vapor control and for upset
emissions control
• Vapor from condensate tanks and rod packing vents routed to
flare
DRAFT
73
BACT Example:
Natural Gas Compressor Station (cont’d)
Step 5 (cont’d)
Permit conditions include:
• A monthly limit on GHG emissions (CO2e) per horsepower
hour, including both methane and CO2 emissions, for the
engines
• Equipment requirements for the engine air/fuel controls, the
compressor rod packing, the flare, and the vapor control
system
• Development and implementation of a preventive
maintenance plan for these control measures including leak
detection and repair
DRAFT
74
GHG BACT Example:
Gas Turbine Electric Generating Unit
BACT Example: Gas Turbine
Project: Construction of a new 500 MW natural gasfired combined cycle power plant with two combustion
turbines, heat recovery steam generators with
supplemental firing and steam turbines.
DRAFT
76
BACT Example: Gas Turbine(cont’d)
Step 1: Identifying all available controls
• Applicant identifies two measures for consideration:
– High thermal efficiency system design.
– Carbon capture and storage.
• Public comment calls for non-fossil electricity generation,
but the air agency determines that this is redefining the
source and beyond the BACT review.
• Permitting authority (PA) notes that benchmarking data
for recent projects show higher thermal efficiencies than
the proposed design. PA asks for further consideration of
alternative designs, including other turbines and varying
ratios of gas turbine and steam turbine power
generation.
DRAFT
77
BACT Example: Gas Turbine (cont’d)
Step 2: Eliminating technically infeasible options
• Applicant presents information indicating that CCS is
not commercially available for gas turbine systems
and that an appropriate sequestration site in the
area is not demonstrated.
• Permitting Authority agrees CCS is not technically
feasible.
DRAFT
78
BACT Example: Gas Turbine (cont’d)
Step 3: Evaluation and ranking of controls by their
effectiveness
• Comparison of technologies is based on CO2e per
MWh.
• Analysis shows that an alternative gas turbine will
provide higher overall efficiency
• Analysis shows that varying the steam to gas power
generation ratio will not improve efficiency of the
range of anticipated operating conditions.
DRAFT
79
BACT Example: Gas Turbine (cont’d)
Step 4: Evaluating the most effective controls
• With a commitment to a higher efficiency gas turbine design
and the dismissal of CCS as technically infeasible, no further
analysis of cost and collateral impacts is done.
Step 5: Selecting BACT
• Significant issues were encountered in trying to convert the
high efficiency design into an emissions limit that accounts for
differing operating conditions, ambient conditions and system
degradation over its useful life.
DRAFT
80
BACT Example: Gas Turbine (cont’d)
Step 5: (cont’d)
• Resulted in the following BACT conditions:
– Mass emission limits for GHGs: hourly, daily and annual
averaging periods.
– Additional efficiency limit in Btu/kWh, demonstrated in an
annual compliance test
DRAFT
81