【正文】 ng to these characteristics, we should be in the gasification process as much as possible to raise the temperature and gas residence time, to reduce the tar yield and types of produce in order to achieve control of tar in the gasification to reduce the difficulty of gas purification.2. Catalytic cracking of biomass tar(1)The principle of tar catalytic cracking Take various measures to control the tar generated in the biomass gasification process, but in fact, the tar content of gas is still far beyond the extent of the application allows, so the tar in the gas processing, efficient use of gas essential process, which the catalytic cracking of tar is the most effective and advanced way. Simple washing or filtering approach, but the tar separated from the gas, and waste emissions, a waste of the energy of the tar itself, will produce large amounts of pollution. Tar paralysis tar deposition as a permanent gas, and gas being used. So not only reduce the tar content, and use of energy in the tar. Paralysis requires high temperature (1000℃～1200℃), so the more difficult. The catalytic cracking catalyst, tar paralysis temperature is greatly reduced (about 750℃～900℃), and improve the efficiency of paralysis, tar cracking in a very short period of time more than 99%. The chemical formula describes the transformation process of paralysis. But no matter what the ingredients, the end product of paralysis and gasification gas position, tar cracking did not significantly affect the quality of gasification gas, but the increase in the number. Tar copies of most of the water vapor in the paralysis process have a key role, because it and some tar were the reaction of CO and H2 gas, they are reducing the production of carbon black, but also improves the yield of gas . For example, naphthalene, catalytic cracking, the following reaction occurs:C10H8+10H2O222。10CO+14H2 C10H8+20H2O222。10CO2+24H2 C10H8+10H2O222。2CO+4CO2+6H2+4CH4Therefore, the water vapor is very conducive to the tar cracking and bustible gases.(2)The characteristics and selection of the catalyst Biomass tar catalytic cracking principle with oil catalytic cracking similar, so the choice of catalyst can be inspired from the oil industry. However, due to the tar catalytic cracking of valueadded, low cost requirements have actual meaning. In addition to the catalyst for the use of the oil industry, but also large number of studies of lowcost materials such as limestone, quartz sand and dolomite, and other natural products.The large number of experiments shows that a lot of material has a catalytic tar cracking。 typical materials which are better to have application prospects, charcoal, dolomite, nickelbased catalysts, their properties are listed in Table 1. We can see from the above three typical catalytic results, the best of the nickelbased catalyst at 750℃, a high rate of cracking, and other materials paralysis at 750℃, the effect is not ideal, but because of the more expensive nickelbased catalyst, high cost, difficult to apply general biomass gasification technology, it can only be used in the gas need refined or synthetic gasoline process. The catalytic effect of the charcoal is in fact the next downdraft gasified had a significant effect, but because of the charcoal in the cracked tar at the same time participate in the reaction, so consumption (up ) at 1000℃, the largescale biomass charcoal as a catalyst in gasification is unrealistic, but the charcoal catalytic effect on the gasifies design and small gasifies some guidance. Dolomite (dolomite) is so far to study the largest and most successful catalyst, although the position of dolomite around a slight change, but has a catalytic effect, the general dolomite and CaCO3 / MgCO3 and a is better. The main advantage of the dolomite as tar cracking catalyst is a high catalytic efficiency, low cost, and therefore has a good practical value.(3) The process conditions of tar catalytic cracking Tar catalytic cracking lift requires a suitable catalyst, but also there must be strict conditions. And other catalytic processes, the most important factors affect the catalytic effect of temperature and contact time, so the process conditions is used to determine the requirements in this regard. Dolomite, the following example, analysis of the characteristics of these conditions:Temperature: at the right temperature of any catalytic process must be carried out, dolomite on tar cracking in a high rate of cracking above 800℃, the desired effect of temperature and biomass gas can be obtained at 900℃ of temperature are similar, so relatively easy to achieve, one of the main reason for this is also widely used dolomite.Contact: tar and catalyst contact time is another important factor determining the catalytic effect. As the contact time is again gas stay time and the catalyst specific surface area determined, so the gas stay time and dolomite, and particle size of catalytic cracking process conditions. Under the same conditions, the gas residence time is the longer, the better cleavage. Requirements are different for different means of contact, the gas residence time, for example, at 800℃, the dp187。5mm fixed bed, gas residence time of the general requirements about , while the dp187。 fluidized bed, gas residence time of only . The smaller the diameter of the same dolomite, the better the catalytic effect , but the particle diameter is too small, fixedbed, too much resistance, while the fly ash of the bed is too serious loss, so the dolomite diameter of an appropriate range, the general dp is as well. 參考文獻[1][M].北京:中國電力出版社,2008.[2][M].北京:中國水利水電出版社,2007.[3]于國強、[M].北京:中國電力出版社,2009.[4]張長森、[R].安徽農業(yè)科學2010.