NOx Emissions Impacts from Widespread Deployment of CHP in ...

NOx Emissions Report
meet a facility’s thermal needs first. In these cases, CHP systems can be thought of as a
“boiler that also produces electricity.”
Table 1-2: Existing CHP Capacity in Texas by Industry
Industry
Share of
Existing
Capacity
Chemicals 66%
Refining 22%
Paper 4%
Manufacturing 4%
Commercial 2%
Food 1%
Other Industrial
Source: Hedman, 2005
1%
1.4 NOx Impacts of CHP
The dramatic efficiency gains achievable with CHP systems result in an overall decrease
in NOx emissions. A comparison of NOx emissions from four different power generating
options is shown in Figure 1-3, where NOx emissions from a natural gas turbine CHP
plant are shown to be more than an order of magnitude lower than that produced by a
utility coal boiler. CHP systems produce the same level of NOx emissions as a combined
cycle gas turbine (CCGT), the utility industry’s most efficient power plant option. 9
The high overall efficiency achieved by CHP systems translates into NOx emission
reductions in two ways:
1. On-site NOx Impacts – CHP systems provide some or all of a facility’s thermal
energy needs, thereby reducing the need to operate conventional boiler systems.
As a result, on-site boilers are used much less frequently and NOx boiler
emissions are thereby reduced or eliminated. In addition, the combustion of
natural gas to operate the CHP system increases NOx emissions. With CHP
adoption, NOx emissions at the facility site will increase.
2. Off-site NOx Impacts – CHP systems provide some or all of a facility’s electrical
energy needs. In addition, some electrical loads can be shifted from electrical
service to thermal service, further reducing total consumption of electricity. As a
result, the amount of electricity sourced from the power grid is reduced. CHP
systems produce less NOx than central station generators because:
• CHP systems do not create any transmission and distribution losses. These
losses, which can amount to 7-10% of total electricity produced at a
9 See the presentation by Austin Energy regarding NOx comparisons to their Dell Children’s Hospital
project at http://files.harc.edu/Sites/GulfCoastCHP/News/CHPEmissions2006/BusinessCaseForCHP.pdf.
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