Investigation of Continuous Gas Engine CHP Operation on Biomass Producer Gas

About 2000 hours of gas engine operation with producer gas from biomass as fuel has been conducted on the gasification combined heat and power (CHP) demonstration and research plant, named "Viking" at the Technical University of Denmark. The plant and engine have been operated continuously and unmanned for five test periods of approximately 400 hours each. Two different control approaches have been applied and investigated: one where the flow rate of the producer gas is fixed and the engine operates with varying excess of air due to variation in gas composition and a second where the excess of air in the exhaust gas is fixed and the flow rate of produced gas from the gasifier is varying. It was seen that the optimal control approach regarding the gasifier operation resulted in engine operation with significant variation of the NO x emissions Producer gas properties and contaminations have been investigated. No detectable tar content was observed, and this was confirmed by three different measuring methods. Likewise, no particles were detected in the gas. Considerable amounts of ammonia were measured in the produced gas. An analysis of engine operation at varying load has been carried out. Standard emissions, load and efficiency have been measured at varying operating conditions ranging from 90% to 50% load. Relatively high emission of unburned CO was seen at all operating conditions when compared to the current regulation for CO emissions. Measurements of the emission of poly cyclic aromatic hydrocarbons (PAH) showed that there were no detectable PAH in exhaust gas from the engine when it is operated on producer gas. The emissions of aldehydes were measured to be significantly lower for producer gas operation than for natural gas. The engine heads have been removed several times in order to inspect the internal parts for formation of deposits, wear and corrosion, and no significant built up has been seen. Frequent oil analysis has been conducted and no significant degeneration has been seen.