With
funding from the National Energy Technology Laboratory (NETL),
researchers at Kansas State University (KSU) are developing emissions
control and monitoring technologies that can be applied to engines used
in natural-gas-gathering systems. This alternative to engine replacement
would provide the U.S. natural gas industry with a more efficient way
to upgrade existing engines while mitigating greenhouse gases.
Thousands
of reciprocating engines are now in service in the
natural-gas-gathering industry. These engines are used to produce
electricity for a leasehold, compress and re-inject natural gas for
increased oil production, or compress natural gas so that it can be
delivered to local gathering systems that feed ultimately into gas
transmission pipelines. As the engines age, it is possible that most
would need to be replaced in order to meet new federal EPA emissions
regulations. Since engine replacement would be cost prohibitive to the
industry, KSU is designing and testing retrofit technologies that can be
installed on existing engines for a fraction of the cost.
Extensive
field tests performed by KSU and their research partners—Innovative
Environmental Solutions, El Paso Corporation, Pipeline Research Council
International Inc., and Enginuity—have provided valuable insight into
controlling emissions from gas-gathering engines. Currently available
non-selective catalytic reduction (NSCR) systems were shown to
simultaneously control both nitrogen oxides (NOx) and carbon monoxide
(CO), but only within a very small operating window, and not on a
consistent basis.
KSU
is developing models that will be used to improve NSCR performance and
to determine enhanced, reliable environmental control strategies.
Studying the possible impacts of new EPA National Ambient Air Quality
Standards and NOx levels on small-engine emissions, KSU researchers
found that current emission compliance measures are based on plume
models that were developed for larger emission sources. KSU’s
four-stroke cycle engine model and exhaust gas oxygen (EGO) sensor model
will better predict emissions from small engines. Important
developments and findings to date include the following:
- The
EGO sensor model includes a simplified methane combustion mechanism and
a newly developed kinetic model for CO formation and oxidation.
- Output
from the EGO sensor model is comparable to experimental engine data and
confirms that sensor output not only depends on the oxygen
concentration, but also on the CO and hydrogen levels.
- A
“lean shift” has been detected when methane is present in the exhaust
emissions, creating a higher output voltage from the sensor; this is due
to the extra reducing species present that compete with the oxygen for
the catalytic surface reactions.
- A modified reaction scheme has been used in the EGO model in order to optimize calculation time.
- Results
of CO kinetics and emissions from the four-stroke cycle engine model
are consistent with previous field tests. The model incorporates engine
speed and inlet conditions in addition to trapped equivalence ratio.
The
updated KSU models take into account small-engine characteristics and
preferred catalytic conditions. Once validated, the models can be used
in field engine control boards that can help meet new EPA emission
standards by replacing outdated air fuel controllers.
