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

NOx Emissions Report
To assess the NOx emissions impacts of potential CHP applications within the HGB
commercial and institutional building sector, the base case (non-CHP) was modeled in
BCHP for each prototypical building type and compared to the corresponding CHP cases.
The BCHP model output includes calculations of the on-site NOx emissions and the
amount of electricity supplied by the utility grid. On-site emissions were calculated based
on each building cluster’s general building characteristics and energy demands while the
off-site NOx emissions were estimated from eGRID. The assumptions used to calculate
the NOx impacts are summarized in Table 2-2.
Table 2-2: NOx Emissions Assumptions
Source
NOx
Production
Unit
Commercial Boilers a 0.074 lbs per MMBtu
Reciprocating Engine Generator (< 2 MW) b 0.14 lbs per MWh
Microturbine c 0.036 lbs per MMBtu
Combustion Turbine (< 10 MW) c 0.167 lbs per MMBtu
Combustion Turbine (> 10 MW) c 0.099 lbs per MMBtu
Reciprocating Engine Generator (> 3MW) c 0.039 lbs per MMBtu
ERCOT Grid Electricity d Notes:
1.07 lbs per MWh
a) EPA report #AP-42 which assumes 50% of boilers are uncontrolled and 50% are controlled
b) Assumes NOx controls are implemented to meet current HGB standard permit level, including
value of thermal energy captured.
c) EPA CHP Emissions Calculator v1.1
d) EPA eGRID for ERCOT (2007)
In calculating off-site NOx emissions from utility generated electricity, a 7% factor is
used to account for transmission and distribution losses. NOx impacts were calculated
with respect to ERCOT-only utilities in the eight county HGB region. Generally, NOx
production rate assumptions for prime movers used in commercial CHP systems were
derived from the default values provided in the EPA CHP Emissions Calculator tool and
those provided in the BCHP model, although CHP systems were forced to meet an
emissions level of 0.14 lbs/MWh established in the standard permit. To establish the
regional NOx impact, the total NOx emissions change for each building prototype and
CHP case were multiplied by the actual number of existing buildings corresponding to
the specific prototype.
2.4.1 CHP Operating Strategies
While CHP systems provide a number of benefits to host facilities, including for example
improved power reliability, the decision to adopt CHP is most often based upon purely
economic considerations. Acceptable payback periods ranging between 3-10 years are
common, although institutional building owners are thought to have the longest time
horizon. As a result of the short payback periods, the CHP design and operating strategy
most likely to be implemented in commercial and institutional buildings is “Case 3:
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