Reduction of emission from natural gas lean-burn engines for cogeneration

Since this project started in 1996 the emission limits for engines have been tightened and extended to include the emission of UHC. Engine manufacturers and owners of existing engines will therefore look for ways to reduce the emissions. The objectives of this project have been to develop catalysts, strategies and methods to minimise the emissions. The project has investigated the influence of engine parameters on emissions from lean-burn engines and the flue gas conditions and causes of deactivation of catalysts. In Sub-project 1 a number of processes based on catalytic emission reduction have been reviewed. This has been done with respect to existing and to future plants, respectively, based on latest released engines. Fundamentals and test results from catalytic reduction of methane are presented, including possible catalytic toxification. Field test results up to 5000 operation hours are presented for catalysts developed in the project. These show approx. 95-99% CO reduction and 25-85% UHC reduction in the temperature range 415-490 deg. C. Data concerning investment costs and net profits due to loss reduction for the most promising catalytic based technologies are given. Payback time can be as low as three years for the catalytic based solutions. Sub-project 2 concluded that the most efficient non-catalytic method of UHC emission reduction at existing plants was found to be either to install an incineration unit with an efficiency of 95% or to modify or exchange the engine. However, none of the major engine suppliers on the Danish market have yet introduced modification kits to comply with the new UHC emission limits. The effect of adding hydrogen to methane as a fuel for spark ignited engines has been extensively investigated. Tests showed a reduction in UHC of approximately 40%, and an increase in efficiency of approximately three percentage points at the test engine. Adiabatic pre-reforming may be used to convert naturl gas into methane, hydrogen and carbon dioxide and at the same time increase the methane number. The process has been found to be competitive with adding of hydrogen but it is still not economical