Most renewable fuels contain nitrogen, which will convert to ammonia during gasification. This ammonia will form NOx emission during gas combustion in biomass gasification power plants, where hot gas cleanup is used. Hence, the objective of this research is to develop the two main technologies for ammonia removal in gasification plants. These are SCO (Selective Catalytic Oxidation) and nickel catalyst technologies. The research will be carried out by the European consortium consisting of research institute, three universities and three industrial partners. Fundamental laboratory studies together with testing in real gasification gases using bench-and pilot-scale gasifiers and slipstreams in commercial plants are used to produce the information needed to evaluate the technical and economic feasibility of studied technologies.
1)Better SCO catalysts were found than originally was expected. Metal/alumina catalysts with varying properties were prepared and their applicability for the SCO process was characterized. The most promising catalyst identified was Cu/alumina. In addition, a ZrO2 catalyst was found to be suitable for simultaneous tar and ammonia decomposition giving relatively high conversions for the both impurities. The SCO process was also tested in real gasification gas atmospheres. The results indicated that the ZrO2 catalyst activity with real gases is comparable to lab scale results.
2)Feasible operating window for nickel catalysts was identified. These catalysts were tested in product gas lines of small-scale gasifiers. Reactor model for nickel monolith was developed so that the effects of various operation conditions and the behaviour of the monolith could be studied. The most important operational parameters that affected achievable ammonia and tar conversions were studied. These include air partitioning within gasifier/catalytic reformer system, H2O/C ratio and catalyst inlet temperature. The monolith catalyst was more challenging to operate than was foreseen. However, narrow operating window was successfully found, where over 90% ammonia conversions could be achieved.
3)Comparison of the SCO and nickel-monolith systems to filtering only and wet cleaning methods were made for a case where an atmospheric-pressure CFB gasifier is connected to an existing coal/peat-fired boiler. The evaluation indicated that from economical point of view all the studied catalytic gas cleaning concepts were very close to each other. Thus, the selection can be fully based on technical feasibility and on the required level of gas cleaning. All catalytic gas cleaning concepts are naturally more expensive than the reference case based on filtration only.
4)Directly applicable results were obtained from the CFD studies considering the Lahti Kymijarvi Power Plant (WP3). These modelling studies gave valuable information about the means that could be applied to minimize NOx-emissions from the plant. It also improved understanding of where, why, and how NOx is formed in the boiler. This information can be used in the design of new plants and modifications of similar boilers elsewhere.
Funding SchemeCSC - Cost-sharing contracts
20500 Turku / Abo
48601 Karhula /Kotka