HCHP
<&EPA COMBINED HEAT AND
POWER PARTNERSHIP
Catalog of
CHP Technologies
Section 1. Introduction
U.S. Environmental Protection Agency
Combined Heat and Power Partnership
iiCHP
SEPA COMBINED HEAT AND
POWER PARTNERSHIP
September 2014



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Acknowledgments
This Guide was prepared by Ken Darrow, Rick Tidball, James Wang and Anne Hampson at ICF
International, with funding from the U.S. Environmental Protection Agency and the U.S.
Department of Energy.
Catalog ofCHP Technologies

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Section 1. Introduction
Combined heat and power (CHP) is an efficient and clean approach to generating electric power and
useful thermal energy from a single fuel source. CHP places power production at or near the end-user's
site so that the heat released from power production can be used to meet the user's thermal
requirements while the power generated meets all or a portion of the site electricity needs. Applications
with steady demand for electricity and thermal energy are potentially good economic targets for CHP
deployment. Industrial applications particularly in industries with continuous processing and high steam
requirements are very economic and represent a large share of existing CHP capacity today. Commercial
applications such as hospitals, nursing homes, laundries, and hotels with large hot water needs are well
suited for CHP. Institutional applications such as colleges and schools, prisons, and residential and
recreational facilities are also excellent prospects for CHP.
The direct benefits of combined heat and power for facility operators are:
•	Reduced energy related costs - providing direct cost savings.
•	Increased reliability and decreased risk of power outages due to the addition of a separate
power supply.
•	Increased economic competitiveness due to lower cost of operations.
In addition to these direct benefits, the electric industry, electricity customers, and society, in general,
derive benefits from CHP deployment, including:
•	Increased energy efficiency - providing useful energy services to facilities with less primary
energy input.
•	Economic development value - allowing businesses to be more economically competitive on a
global market thereby maintaining local employment and economic health.
•	Reduction in emissions that contribute to global warming - increased efficiency of energy use
allows facilities to achieve the same levels of output or business activity with lower levels of
fossil fuel combustion and reduced emissions of carbon dioxide.
•	Reduced emissions of criteria air pollutants - CHP systems can reduce air emissions of carbon
monoxide (CO), nitrogen oxides (NOx), and Sulfur dioxide (S02) especially when state-of-the-art
CHP equipment replaces outdated and inefficient boilers at the site.
•	Increased reliability and grid support for the utility system and customers as a whole.
•	Resource adequacy - reduced need for regional power plant and transmission and distribution
infrastructure construction.
CHP systems consist of a number of individual components - prime mover (heat engine), generator,
heat recovery, and electrical interconnection - configured into an integrated whole. The type of
equipment that drives the overall system (i.e., the prime mover) typically identifies the CHP system. The
purpose of this guide is to provide CHP stakeholders with a description of the cost and performance of
complete systems powered by prime-mover technologies consisting of:
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Introduction

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1.	Reciprocating internal combustion engines
2.	Combustion turbines
3.	Steam turbines
4.	Microturbines
5.	Fuel cells
In 2008, the EPA CHP Partnership Program published its first catalog of CHP technologies as an online
educational resource for regulatory, policy, permitting, and other interested CHP stakeholders. This CHP
Technology Guide is an update to the 2008 report1. The Guide includes separate, detailed chapters on
each of the five prime movers listed above. These technology chapters include the following
information:
•	Description of common applications
•	Basic technology description
•	Cost and performance characteristics
•	Emissions and emissions control options
•	Future developments
This introduction and overview section provides a discussion of the benefits of CHP technologies, a
summary comparison of the five main prime-mover technology systems, and a discussion of key CHP
benefits. There is also an appendix that provides the formulas for the various performance
measurements used in the Guide.
1.1 Overview of CHP Technologies
The five technologies described in the Guide make up 97 percent of the CHP projects in place today and
99 percent of the total installed CHP electric capacity. Table 1-1 shows the breakdown by each prime
mover technology.
Table 1-1. U.S. Installed CHP Sites and Capacity by Prime Mover
Prime Mover
Sites
Share of
Sites
Capacity
(MW)
Share of
Capacity
Reciprocating Engine
2,194
51.9%
2,288
2.7%
Gas Turbine*
667
15.8%
53,320
64.0%
Boiler/Steam Turbine
734
17.4%
26,741
32.1%
Microturbine
355
8.4%
78
0.1%
Fuel Cell
155
3.7%
84
0.1%
Other
121
2.9%
806
1.0%
Total
4,226
100.0%
83,317
100.0%
* includes gas turbine/steam turbine combined cycle
Source: ICF CHP Installation Database, April 2014
1 Catalog of CHP Technologies, U.S. Environmental Protection Agency Combined Heat and Power Partnership Program,
December 2008.
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Introduction

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All of the technologies described convert a chemical fuel into electric power. The energy in the fuel that
is not converted to electricity is released as heat. All of the technologies, except fuel cells, are a class of
technologies known as heat engines. Heat engines combust the fuel to produce heat, and a portion of
that heat is utilized to produce electricity while the remaining heat is exhausted from the process. Fuel
cells convert the energy in the fuel to electricity electrochemically; however, there are still inefficiencies
in the conversion process that produce heat that can be utilized for CHP. Each technology is described in
detail in the individual technology chapters, but a short introduction of each is provided here:
•	Reciprocating engines, as shown above, make up over half of the CHP systems in place, though,
because of the generally smaller system sizes, less than 3 percent of total capacity. The
technology is common place - used in automobiles, trucks, trains, emergency power systems,
portable power systems, farm and garden equipment. Reciprocating engines can range in size
from small hand-held equipment to giant marine engines standing over 5-stories tall and
producing the equivalent power to serve 18,000 homes. The technology has been around for
more than 100 years. The maturity and high production levels make reciprocating engines a low-
cost reliable option. Technology improvements over the last 30 years have allowed this
technology to keep pace with the higher efficiency and lower emissions needs of today's CHP
applications. The exhaust heat characteristics of reciprocating engines make them ideal for
producing hot water.
•	Steam turbine systems represent 32 percent of U.S. installed CHP capacity; however, the
median age of these installations is 45 years old. Today, steam turbines are mainly used for
systems matched to solid fuel boilers, industrial waste heat, or the waste heat from a gas
turbine (making it a combined cycle.) Steam turbines offer a wide array of designs and
complexity to match the desired application and/or performance specifications ranging from
single stage backpressure or condensing turbines for low power ranges to complex multi-stage
turbines for higher power ranges. Steam turbines for utility service may have several pressure
casings and elaborate design features, all designed to maximize the efficiency of the system. For
industrial applications, steam turbines are generally of simpler single casing design and less
complicated for reliability and cost reasons. CHP can be adapted to both utility and industrial
steam turbine designs.
•	Gas turbines, as shown, make up over 60 percent of CHP system capacity. It is the same
technology that is used in jet aircraft and many aeroderivative gas turbines used in stationary
applications are versions of the same engines. Gas turbines can be made in a wide range of sizes
from microturbines (to be described separately) to very large frame turbines used for central
station power generation. For CHP applications, their most economic application range is in sizes
greater than 5 MW with sizes ranging into the hundreds of megawatts. The high temperature
heat from the turbine exhaust can be used to produce high pressure steam, making gas turbine
CHP systems very attractive for process industries.
•	Microturbines, as already indicated, are very small gas turbines. They were developed as
stationary and transportation power sources within the last 30 years. They were originally based
on the truck turbocharger technology that captures the energy in engine exhaust heat to
compress the engine's inlet air. Microturbines are clean-burning, mechanically simple, and very
compact. There were a large number of competing systems under development throughout the
1990s. Today, following a period of market consolidation, there are two manufacturers in the
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Introduction

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U.S. providing commercial systems for CHP use with capacities ranging from 30-250 kW for
single turbine systems with multiple turbine packages available up to 1,000 kW.
• Fuel cells use an electrochemical or battery-like process to convert the chemical energy of
hydrogen into water and electricity. In CHP applications, heat is generally recovered in the form
of hot water or low-pressure steam (<30 psig) and the quality of heat is dependent on the type
of fuel cell and its operating temperature. Fuel cells use hydrogen, which can be obtained from
natural gas, coal gas, methanol, and other hydrocarbon fuels. Fuel cells are characterized by the
type of electrochemical process utilized, and there are several competing types, phosphoric acid
(PAFC), proton exchange membrane (PEMFC), molten carbonate (MCFC), solid oxide (SOFC), and
alkaline (AFC). PAFC systems are commercially available in two sizes, 200 kW and 400 kW, and
two MCFC systems are commercially available, 300 kW and 1200 kW. Fuel cell capital costs
remain high due to low-volume custom production methods, but they remain in demand for
CHP applications because of their low air emissions, low-noise, and generous market subsidies.
Table 1-2 and Table 1-3 provide a summary of the key cost and performance characteristics of the CHP
technologies discussed in the CHP Technology Guide.
Table 1-2. Summary of CHP Technology Advantages and Disadvantages
CHP system
Advantages
Disadvantages
Available sizes
Spark ignition
(SI)
reciprocating
engine
•	High power efficiency with part-
load operational flexibility.
•	Fast start-up.
•	Relatively low investment cost.
•	Has good load following capability.
•	Can be overhauled on site with
normal operators.
•	Operate on low-pressure gas.
•	High maintenance costs.
•	Limited to lower temperature
cogeneration applications.
•	Relatively high air emissions.
•	Must be cooled even if recovered
heat is not used.
•	High levels of low frequency noise.
1 kW to 10
MW in DG
applications
Compression
ignition (CI)
reciprocating
engine (dual
fuel pilot
ignition)
High speed
(1,200 RPM)
<4MW
< 80 MW for
Low speed (60-
275 RPM)
Steam turbine
•	High overall efficiency - steam to
power.
•	Can be mated to boilers firing a
variety of gaseous, liquid or solid
fuels.
•	Ability to meet more than one site
heat grade requirement.
•	Long working life and high
reliability.
•	Power to heat ratio can be varied.
•	Slow start up.
•	Very low power to heat ratio.
•	Requires a boiler or other steam
source.
50 kW to
several
hundred MWs
Gas turbine
•	High reliability.
•	Low emissions.
•	High grade heat available.
•	No cooling required.
•	Require high pressure gas or in-
house gas compressor.
•	Poor efficiency at low loading.
•	Output falls as ambient
temperature rises.
500 kW to 300
MW
Microturbine
•	Small number of moving parts.
•	Compact size and light weight.
•	Low emissions.
•	No cooling required.
•	High costs.
•	Relatively low mechanical
efficiency.
•	Limited to lower temperature
cogeneration applications.
30 kW to 250
kW with
multiple unit
packages up to
1,000 kW
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Table 1-2. Summary of CHP Technology Advantages and Disadvantages
CHP system
Advantages
Disadvantages
Available sizes
Fuel cells
•	Low emissions and low noise.
•	High efficiency over load range.
•	Modular design.
•	High costs.
•	Low durability and power density.
•	Fuels requiring processing unless
pure hydrogen is used.
5 kW to 2 MW
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Table 1-3. Comparison of CHP Technology Sizin
Cost, and Performance Parameters
Technology
Recip. Engine
Steam Turbine
Gas Turbine
Microturbine
Fuel Cell
Electric efficiency (HHV)
27-41%
5-40+%2
24-36%
22-28%
30-63%
Overall CHP efficiency (HHV)
77-80%
near 80%
66-71%
63-70%
55-80%
Effective electrical efficiency
75-80%
75-77%
50-62%
49-57%
55-80%
Typical capacity (MW.)
.005-10
0.5-several hundred
MW
0.5-300
0.03-0.25
200-2.8 commercial CHP
Typical power to heat ratio
0.5-1.2
0.07-0.1
0.6-1.1
0.5-0.7
1-2
Part-load
ok
ok
poor
ok
good
CHP Installed costs ($/kWe)
1,500-2,900
$670-1,100
1,200-3,300
(5-40 MW)
2,500-4,300
5,000-6,500
Non-fuel O&M costs ($/kWhe)
0.009-0.025
0.006 to 0.01
0.009-0.013
0.009-.013
0.032-0.038
Availability
96-98%
near 100%
93-96%
98-99%
>95%
Hours to overhauls
30,000-60,000
>50,000
25,000-50,000
40,000-80,000
32,000-64,000
Start-up time
10 sec
1hr-1 day
10 min -1 hr
60 sec
3 hrs - 2 days
Fuel pressure (psig)
1-75
n/a
100-500
(compressor)
50-140
(compressor)
0.5-45
Fuels
natural gas, biogas,
LPG, sour gas,
industrial waste gas,
manufactured gas
all
natural gas, synthetic
gas, landfill gas, and
fuel oils
natural gas, sour gas,
liquid fuels
hydrogen, natural gas,
propane, methanol
Uses for thermal output
space heating, hot
water, cooling, LP
steam
process steam, district
heating, hot water,
chilled water
heat, hot water, LP-HP
steam
hot water, chiller,
heating
hot water, LP-HP steam
Power Density (kW/m2)
35-50
>100
20-500
5-70
5-20
NOx (Ib/MMBtu)
(not including SCR)
0.013 rich burn 3-way
cat.
0.17 lean burn
Gas 0.1-.2 Wood 0.2-.5
Coal 0.3-1.2
0.036-0.05
0.015-0.036
0.0025-.0040
NOx (lb/MWhTotal0utPut)
(not including SCR)
0.06 rich burn 3-way
cat.
0.8 lean burn
Gas 0.4-0.8
Wood 0.9-1.4
Coal 1.2-5.0.
0.17-0.25
0.08-0.20
0.011-0.016
Power efficiencies at the low end are for small backpressure turbines with boiler and for large supercritical condensing steam turbines for power generation at the high end.
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Key comparisons shown in Table 1-3 are described in more detail below:
•	Electric efficiency varies by technology and by size with larger systems of a given technology
generally more efficient than smaller systems. There is overlap in efficiency ranges among the
five technology classes, but, in general, the highest electric efficiencies are achieved by fuel
cells, followed by large reciprocating engines, simple cycle gas turbines, microturbines, and then
steam turbines. The highest electric efficiencies are achievable by large gas turbines operating in
combined cycle with steam turbines that convert additional heat into electricity.
•	Overall CHP efficiency is more uniform across technology types. One of the key features of CHP
is that inefficiencies in electricity generation increase the amount of heat that can be utilized for
thermal processes. Therefore, the combined electric and thermal energy efficiency remains in a
range of 65-80 percent. The overall efficiency is dependent on the quality of the heat delivered.
Gas turbines that deliver high pressure steam for process use have lower overall efficiencies
than microturbines, reciprocating engines, and fuel cells that are assumed, in this comparison,
to deliver hot water.
•	Installed capital costs include the equipment (prime mover, heat recovery and cooling systems,
fuel system, controls, electrical, and interconnect) installation, project management,
engineering, and interest during construction for a simple installation with minimal need for site
preparation or additional utilities. The costs are for an average U.S. location; high cost areas
would cost more. The lowest unit capital costs are for the established mature technologies
(reciprocating engines, gas turbines, steam turbines) and the highest costs are for the two small
capacity, newer technologies (microturbines and fuel cells.) Also, larger capacity CHP systems
within a given technology class have lower installed costs than smaller capacity systems.
•	Non-fuel O&M costs include routine inspections, scheduled overhauls, preventive maintenance,
and operating labor. As with capital costs, there is a strong trend for unit O&M costs to decline
as systems get larger. Among technology classes gas turbines and microturbines have lower
O&M costs than comparably sized reciprocating engines. Fuel cells have shown high O&M costs
in practice, due in large part to the need for periodic replacement of the expensive stack
assembly.
•	Start-up times for the five CHP technologies described in this Guide can vary significantly.
Reciprocating engines have the fastest start-up capability, which allows for timely resumption of
the system following a maintenance procedure. In peaking or emergency power applications,
reciprocating engines can most quickly supply electricity on demand. Microturbines and gas
turbines have a somewhat longer start-up time to "spool-up" the turbine to operating speed.
Heat recovery considerations may constrain start-up times for these systems. Steam turbines,
on the other hand, require long warm-up periods in order to obtain reliable service and prevent
excessive thermal expansion, stress and wear. Fuel cells also have relatively long start-up times
(especially for those systems using a high temperature electrolyte.). The longer start-up times
for steam turbines and fuel cells make them less attractive for start-stop or load following
operation.
•	Availability indicates the amount of time a unit can be used for electricity and/or steam
production. Availability generally depends on the operational conditions of the unit.
Measurements of systems in the field have shown that availabilities for gas turbines, steam
turbines, and reciprocating engines are typically 95 percent and higher. Early fuel cell and
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Introduction

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microturbine installations experienced availability problems; however, commercial units put in
service today should also show availabilities over 95 percent.
1.2 CHP Efficiency Compared to Separate Heat and Power
Many of the benefits of CHP stem from the relatively high efficiency of CHP systems compared to other
systems. Because CHP systems simultaneously produce electricity and useful thermal energy, CHP
efficiency is measured and expressed in a number of different ways.3 A brief discussion of these
measures is provided below, while Appendix A provides a more detailed discussion.
The efficiency of electricity generation in power-only systems is determined by the relationship between
net electrical output and the amount of fuel used for the power generation. Heat rate, the term often
used to express efficiency in such power generation systems, is represented in terms of Btus of fuel
consumed per kWh of electricity generated. However, CHP plants produce useful heat as well as
electricity. In CHP systems, the total CHP efficiency seeks to capture the energy content of both
electricity and usable steam and is the net electrical output plus the net useful thermal output of the
CHP system divided by the fuel consumed in the production of electricity and steam. While total CHP
efficiency provides a measure for capturing the energy content of electricity and steam produced it does
not adequately reflect the fact that electricity and steam have different qualities. The quality and value
of electrical output is higher relative to heat output and is evidenced by the fact that electricity can be
transmitted over long distances and can be converted to other forms of energy. To account for these
differences in quality, the Public Utilities Regulatory Policies Act of 1978 (PURPA) discounts half of the
thermal energy in its calculation of the efficiency standard (EffFERC). The EFFferc is represented as the
ratio of net electric output plus half of the net thermal output to the total fuel used in the CHP system.
Another definition of CHP efficiency is effective electrical efficiency, also known as fuel utilization
effectiveness (FUE). This measure expresses CHP efficiency as the ratio of net electrical output to net
fuel consumption, where net fuel consumption excludes the portion of fuel that goes to producing
useful heat output. FUE captures the value of both the electrical and thermal outputs of CHP plants and
it specifically measures the efficiency of generating power through the incremental fuel consumption of
the CHP system.
EPA considers fuel savings as the appropriate term to use when discussing CHP benefits relative to
separate heat and power (SHP) operations. Fuel savings compares the fuel used by the CHP system to a
separate heat and power system (i.e. boiler and electric-only generation). Positive values represent fuel
savings while negative values indicate that the CHP system in question is using more fuel than separate
heat and power generation.
Figure 1-1 shows the efficiency advantage of CHP compared with conventional central station power
generation and onsite boilers. When considering both thermal and electrical processes together, CHP
typically requires only % the primary energy separate heat and power systems require. CHP systems
3 Measures of efficiency are denoted either as lower heating value (LHV) or higher heating value (HHV). HHV includes the heat
of condensation of the water vapor in the products. Unless otherwise noted, all efficiency measures in this section are reported
on an HHV basis.
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Introduction

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utilize less fuel than separate heat and power generation, resulting for the same level of output,
resulting in fewer emissions.
Figure 1-1: CHP versus Separate Heat and Power (SHP) Production4
Conventional
Generation
Power Station Fuel
(U.S. Fossil Mix)
91 Units Fuel

56 Units Fuel
IL
Power Plant
EFFICIENCY:
33%
EFFICIENCY:
80%
Boiler Fuel
Electricity
Heat
' 30 ~
Units
Electricity
45
Units
Steam
Combined Heat and Power
5 MW Natural Gas
Combustion Turbine
and Heat Recovery Boiler
Electricity
Combined
Heat
& Power
(CHP)

Heat
51% ...OVERALL EFFICIENCY... 75%
Another important concept related to CHP efficiency is the power-to-heat ratio. The power-to-heat
ratio indicates the proportion of power (electrical or mechanical energy) to heat energy (steam or hot
water) produced in the CHP system. Because the efficiencies of power generation and steam generation
are likely to be considerably different, the power-to-heat ratio has an important bearing on how the
total CHP system efficiency might compare to that of a separate power-and-heat system. Figure 1-2
illustrates this point. The figure shows how the overall efficiency might change under alternate power-
to-heat ratios for a separate power-and-heat system and a CHP system.
4 In this example of a typical CHP system, to produce 75 units of useful energy, the conventional generation or separate heat
and power systems use 147 units of energy—91 for electricity production and 56 to produce heat—resulting in an overall
efficiency of 51 percent. However, the CHP system needs only 100 units of energy to produce the 75 units of useful energy from
a single fuel source, resulting in a total system efficiency of 75 percent.
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Figure 1-2: Equivalent Separate Heat and Power Efficiency


—
~ • % •, ¦
\ t

		 .



1 1 1 1 1
SHP assumes 35.7percent efficient electric and 80 percent efficient thermal generation
CHP overall thermal and electric efficiencies are higher than corresponding efficiencies for SHP across
the range of power-to-heat ratios. However, as shown the SHP efficiency varies as a function of how
much of the lower efficiency electricity is supplied versus the higher efficiency thermal energy. At very
low power-to-heat ratios, as is typical for steam turbine systems, CHP is above the SHP line, but only by
a few percentage points. As electric efficiencies of the CHP systems get higher (and corresponding p/h
ratios increase), the relative improvement of CHP compared to SHP increases dramatically.
1.3 Emissions
In addition to cost savings, CHP technologies offer significantly lower emissions rates compared to
separate heat and power systems. The primary pollutants from gas turbines are oxides of nitrogen
(NOx), carbon monoxide (CO), and volatile organic compounds (VOCs) (unburned, non-methane
hydrocarbons). Other pollutants such as oxides of sulfur (SOx) and particulate matter (PM) are primarily
dependent on the fuel used. Similarly, emissions of carbon dioxide are also dependent on the fuel used.
Many gas turbines burning gaseous fuels (mainly natural gas) feature lean premixed burners (also called
dry low-NOx burners) that produce NOx emissions ranging between 0.17 to 0.25 Ibs/MWh5 with no post-
combustion emissions control. Typically commercially available gas turbines have CO emissions rates
ranging between 0.23 Ibs/MWh and 0.28 Ibs/MWh. Selective catalytic reduction (SCR) or catalytic
combustion can further help to reduce NOx emissions by 80 percent to 90 percent from the gas turbine
5 The NOx emissions reported in this section in Ib/MWh are based on the total electric and thermal energy provided by the CHP
system in MWh.
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exhaust and carbon-monoxide oxidation catalysts can help to reduce CO by approximately 90 percent.
Many gas turbines sited in locales with stringent emission regulations use SCR after-treatment to
achieve extremely low NOx emissions.
Microturbines have the potential for low emissions. All microturbines operating on gaseous fuels feature
lean premixed (dry low NOx, or DLN) combustor technology. The primary pollutants from microturbines
include NOx, CO, and unburned hydrocarbons. They also produce a negligible amount of S02.
Microturbines are designed to achieve low emissions at full load and emissions are often higher when
operating at part load. Typical NOx emissions for microturbine systems range between 4 ppmv and 9
ppmv or 0.08 Ibs/MWh and 0.20 Ibs/MWh. Additional NOx emissions removal from catalytic combustion
in microturbines is unlikely to be pursued in the near term because of the dry low NOx technology and
the low turbine inlet temperature. CO emissions rates for microturbines typically range between 0.06
Ibs/MWh and 0.54 Ibs/MWh.
Exhaust emissions are the primary environmental concern with reciprocating engines. The primary
pollutants from reciprocating engines are NOx, CO, and VOCs. Other pollutants such as SOx and PM are
primarily dependent on the fuel used. The sulfur content of the fuel determines emissions of sulfur
compounds, primarily S02. NOx emissions from small "rich burn" reciprocating engines with integral 3-
way catalyst exhaust treatment can be as low as 0.06 Ibs/MWh. Larger lean burn engines have values of
around 0.8 Ibs/MWh without any exhaust treatment; however, these engines can utilize SCR for NOx
reduction.
Emissions from steam turbines depend on the fuel used in the boiler or other steam sources, boiler
furnace combustion section design, operation, and exhaust cleanup systems. Boiler emissions include
NOx, SOx, PM, and CO. Typical boiler emissions rates for NOx range between 0.3 Ibs/MMBtu and 1.24
Ibs/MMBtu for coal, 0.2 Ibs/MMBtu and 0.5 Ibs/MMBtu for wood, and 0.1 Ibs/MMBtu and 0.2
Ibs/MMBtu for natural gas. Uncontrolled CO emissions rates range between 0.02 Ibs/MMBtu and 0.7
Ibs/MMBtu for coal, approximately 0.06 Ibs/MMBtu for wood, and 0.08 Ibs/MMBtu for natural gas. A
variety of commercially available combustion and post-combustion NOx reduction techniques exist with
selective catalytic reductions achieving reductions as high as 90 percent.
Fuel cell systems have inherently low emissions profiles because the primary power generation process
does not involve combustion. The fuel processing subsystem is the only significant source of emissions
as it converts fuel into hydrogen and a low energy hydrogen exhaust stream. The hydrogen exhaust
stream is combusted in the fuel processor to provide heat, achieving emissions signatures of less than
0.019 Ibs/MWh of CO, less than 0.016 Ibs/MWh of NOx and negligible SOx without any after-treatment
for emissions. Fuel cells are not expected to require any emissions control devices to meet current and
projected regulations.
Other pollutants such as SOx and PM are primarily dependent on the fuel used. CHP technologies that
could use fuels other than natural gas, including reciprocating engines and steam turbines, could also
incur other emissions from its fuel choice. For example, the sulfur content of the fuel determines
emissions of sulfur compounds, primarily S02.
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SO2 emissions from steam turbines depend largely on the sulfur content of the fuel used in the
combustion process. S02 comprises about 95 percent of the emitted sulfur and the remaining 5 percent
is emitted as sulfur tri-oxide (S03). Flue gas desulphurization (FGD) is the most commonly used post-
combustion S02 removal technology and is applicable to a broad range of different uses. FGD can
provide up to 95 percent S02 removal.
C02 emissions result from the use the fossil fuel-based CHP technologies. The amount of C02 emitted in
any of the CHP technologies discussed above depends on the fuel carbon content and the system
efficiency. The fuel carbon content of natural gas is 34 lbs carbon/MMBtu; oil is 48 lbs of carbon/MMBtu
and ash-free coal is 66 lbs of carbon/MMBtu
1.4 Comparison of Water Usage for CHP compared to SHP
Water is critical in all stages of energy production, from drilling for oil and gas to electricity production.
As water supply levels are being challenged by continuing and severe droughts, especially in the
Southeast and Western regions of the U.S., as well as increasing demand and regulations, water
requirements and usage are becoming important considerations in energy production.
According to the U.S. Geological Survey (USGS), thermoelectric power, which uses water for cooling
steam turbines, accounts for the largest share of water withdrawal in the U.S., at 49 percent in 2005
(latest year data are available). Table 1-4 shows the water consumption (gai/MWh) by SHP technology
and cooling technology.
Table 1-4: Water Consumption by SHP Technology, Cooling Technology6

Cooling Technologies - Water Consumption (gal/MWh)
Open-
Loop
Closed-Loop
Reservoir
Closed-
Loop
Cooling
Tower
Hybrid
Cooling
Air-Cooling
Fuel Technology
Thermal
Coal
300
385
(±115)
480
between
60
(±10)
Nuclear
400
625
(±225)
720
between
60
(±10)
Natural Gas Combustion
Turbine
negligible
negligible
negligible
negligible
negligible
Natural Gas Combined-
Cycle
100
130*
(±20)
180
between
60*
(±10)
Integrated Gasification
Combined-Cycle
not used
not used
350'
(±100)
between
60
(±10)
Concentrated Solar
Power
not used
not used
840
(±80)
between
80'
(±10)
Non-
Thermal
Wind
none
none
none
none
none
Photovoltaic Solar
none
none
none
none
none
Estimated based on withdrawal and consumption ratios
6 Stillwell, Ashlynn S., et al, Energy-Water Nexus in Texas. The University of Texas at Austin and Environmental Defense Fund,
April 2009.
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The role of CHP technologies could be critical in water issues, as CHP systems, particularly reciprocating
engine, combustion turbine, microturbines, and fuel cells, use almost negligible amounts of water. A
boiler/steam turbine CHP system water consumption would be similar to the SHP technology shown in
Table 1-4.
1.5 Outlook
In the last twenty years, there has been substantial improvement in gas turbine technology with respect
to power, efficiency, durability, emissions, and time/cost to market. These improvements have been the
combined results of collaborative research efforts by private industry, universities, and the federal
government. Public-private partnerships such as the DOE Advanced Turbine Systems Program and the
Next Generation Turbine program have advanced gas turbine technology. Current collaborative research
is focusing on both large gas turbines and those applicable for distributed generation. Large gas turbine
research is focused on improving the efficiency of combined cycle plants to 65 percent (LHV), reducing
emission even further, and integrating gas turbines with clean coal gasification and carbon capture. The
focus for smaller gas turbines is on improving performance, enhancing fuel flexibility, reducing
emissions, reducing life cycle costs, and integration with improved thermal utilization technologies.
Continued development of aeroderivative gas turbines for civilian and military propulsion will provide
carryover benefits to stationary applications. Long-term research includes the development of hybrid
gas turbine fuel cell technology that is capable of 70 percent (LHV) electric efficiency.
Microturbine manufacturers are continuing to develop products with higher electrical efficiencies.
Working cooperatively with the Department of Energy, Capstone is developing a 250 kW model with a
target efficiency of 35 percent (gross output, LHV) and a 370 kW model with a projected 42 percent
efficiency. The C250 will feature an advanced aerodynamic compressor design, engine sealing
improvements, improved generator design with longer life magnet, and enhanced cooling. The project
will use a modified Capstone C200 turbocompressor assembly as the low-pressure section of a two shaft
turbine. This low-pressure section will have an electrical output of 250 kW. A new high-temperature,
high-pressure turbocompressor assembly will increase the electrical output to 370 kW. Product
development in microturbines over the years has been to achieve efficiency and cost reductions by
increasing the capacity of the products. Starting with original products in the 30-50 kW range,
microturbine manufacturers have developed and are continuing to develop increasingly larger products
that compete more directly with larger reciprocating gas engines and even small simple cycle gas
turbines.
Public-private partnerships such as the DOE Advanced Reciprocating Engine System (ARES) funded by
DOE and the Advanced Reciprocating Internal Combustion Engine (ARICE) program funded by the
California Energy Commission have focused attention on the development of the next generation
reciprocating engine. The original goals of the ARES program were to achieve 50 percent brake thermal
efficiency (LHV), NOx emissions to less than 1 g/bhp-hr (0.3 Ib/MWh), and maintenance costs of
$0.01/kWh, all while maintaining cost competitiveness. The development focus under ARES includes:
•	Combustion chamber design
•	Friction reduction
•	Combustion of dilute mixtures
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Introduction

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•	Turbocompounding
•	Modified or alternative engine cycles
•	Exhaust energy retention
•	Exhaust after-treatment - improving SCR and TWC operation and proving the operation of Lean
NOx catalyst (LNC)
•	Water injection
•	High power density
•	Multiple source ignition
The U.S. DOE funds collaborative research and development toward the development of improved ultra-
supercritical (USC) steam turbines capable of efficiencies of 55-60 percent that are based on boiler tube
materials that can withstand pressures of up to 5,000 psi and temperatures of 1,400 °F. To achieve these
goals, work is ongoing in materials, internal design and construction, steam valve development, and
design of high pressure casings. A prototype is targeted for commercial testing by 2025. Research is also
underway to restore and improve the performance of existing steam turbines in the field through such
measures as improved combustion systems for boilers, heat transfer and aerodynamics to improve
turbine blade life and performance, and improved materials to permit longer life and higher operating
temperatures for more efficient systems.
The focus on emerging markets such as waste heat recovery and biomass-fueled power and CHP plants
is stimulating the demand for small and medium steam turbines. Technology and product development
for these markets should bring about future improvements in steam turbine efficiency, longevity, and
cost. This could be particularly true for systems below 500 kW that are used in developmental small
biomass systems and in waste-heat-to-power systems designed to operate in place of pressure
reduction valves in commercial and industrial steam systems operating at multiple pressures.
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