Experimental Study On The Fuel-nitrogen Transformation And The Alkali/Alkali-earth Metal Ions Catalysis During The Biomass Pyrolysis

In recent years, our country has made great progress in the development and utilization of biomass energy. Direct combustion is the main biomass utilization technology, and with the increasingly stringent environmental requirements, the control of NOx in the process of heat utilization of biomass gradually on the agenda. Pyrolysis is the beginning of the combustion process, and the severe physical and chemical reaction happened in this stage. The transformation behavior of the fuel nitrogen in this stage largely determines the formation of NOx of the oxidation stage. This article chooses straw, wheat straw and poplar chip, the common agroforestry wastes in china, and the transformation characteristic of fuel-nitrogen during the biomass pyrolysis is studied by using a thermo gravimetric analyzer coupled with a Fourier transform infrared(TG-FTIR) spectromete.The experimental results showed that the release curves of four nitrides (NH3, HCN and HNCO, NO) are consistent with the DTG curves, and release less in later stage (>500℃).Different kinds of biomass in the proportion of nitrogen in the form of occurrence are different, which leads to the different release behavior of nitrogen products. NH3and HCN are the main gas nitrides, which can account for more than70%of the four nitrides, and with the increase of the ration of H/N, relative yield of NH3increase, while HCN/NH3ratio decrease. There are81.50%of the fuel nitrogen into char in the process of poplar chip pyrolysis, while the majority of the fuel nitrogen into volatile in the process of straw and straw pyrolysis, and their yields of char-N are29.97%and33.45%respectively. The increase of heating rate is advantageous to the generation of volatile-N, and the yield of char-N is dropped. The pyrolysis reaction activation energy increase when the biomass were washed or pickling, that’s because the catalysis of mineral component in the biomass were weakende, The release peak and quantity of NH3increase obviously after washing and acid pickling, while little influence on HCN release. The release peak and quantity of HNCO and NO increase significantly after the straw, poplar chip are washed and pickling, while little influence on wheat straw. After deashing, char-N production decrease significantly, and pickling is greater than the washing.In order to further investigate how the mineral components in biomass ash influence on nitrogen transformation, this paper choose the alkali/alkali-earth metal K, Ca, Mg, which is the main metal elements in the biomass ash, and we adopt the method of solution impregnation to load the metal chlorides on biomass. The results showed that, K, Ca, Mg can reduce the reaction activation energy of biomass pyrolysis, and the relationship of catalysis degree is K<Ca<Mg. The addition of K, Ca, Mg can greatly improved the yield of char-N during biomass pyrolysis. KCl can inhibit the generation of NH3, HNCO and NO, and contribute to the generation of HCN. CaCl2can inhibit the generation of NH3, HNCO and NO, and had little effect on HCN. MgCl2can inhibit all the four nitrides. The influence degree of the three kinds of metal elements on nitrogen transformation is K<Ca<Mg.