Morgantown, W.Va. — 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.