生物质能源转换新技术及其应用

New Biomass Conversion Technologies and their Applications

为了利用生物质能源资源生产新形态能源,几十年来世界各国都投入了大量资金和科技人员研究开发高效率的生物质能源转换新技术。以流化床为基础的燃烧技术、气化技术和快速裂化技术相继问世,并逐渐被应用于生物质原料发电、供热、生产交通车辆用生物柴油或汽油和化学药品等行业。利用生物质原料燃烧技术供热和发电比较广泛;气化技术在欧美国家的应用也不断扩大范围和规模,在发展中国家也有一定程度的应用;而在发展中国家,有关生物质原料快速裂化技术的试验和应用情况的文献不多。

In the pursuit of new technologies for the clean, convenient and cheap conversion of biomass into energy, several countries have, over the past few decades, made considerable investment in research and development. Fluidised bed combustion, gasification and pyrolysis technologies have been developed and utilised to varying degrees for heat production, electricity generation and to produce biofuels and chemicals. Traditional technologies of combustion in a grated boiler or cyclone boiler suffered from very low conversion efficiency of biomass to heat (26%). The fluidised bed system enables more complete combustion of fuel providing greater conversion efficiency, but requires considerable energy input for the air flow required to maintain the bed and fuel in suspension. For such systems to operate economically it is necessary to obtain both heat and electricity outputs (combined heat and power CHP), with the potential for conversion efficiencies of over 80%. Fluidised bed CHP systems are in use in USA and Europe, capable of utilising a variety of low density biomass fuels such as wood, straw and crop residues with water contents of up to 25%, usually in mixture with coal and peat in order to minimise problems of slag fouling.Gasification, which involves conversion of biomass fuel to a combustible gas (syngas) is becoming inc-reasingly widespread in industrial processes and for electricity generation. In conjunction with CHP, a total energy conversion efficiency of 75% is obtained from gasification of biomass, or 90% with a fluidised bed gasifier. In remote rural areas, as in much of China and many developing countries, electricity from the grid is not available and prices of traditional fossil fuels are high. There is often an abundance of biomass from crop and forest residues, which cannot be efficiently used to supply domestic energy needs. Small gasifiers with small scale CHP units have been developed for use in such remote locations, with installed capacities between 1 KW and 10 MW, and conversion efficiencies of 35%～45%. The stratified downdraft gasifier system has improved the quality of syngas produced, enabling it to be used with a gas turbine for electricity generation. A ‘micro-biomass’ generator developed in the USA (Free Piston Stirling Generator) allows small scale production of heat and electricity with high efficiency (overall 85%), utilising a wide range of biomass types, but this fuel must be supplied in a finely-ground state. Such systems have great flexibility of use, being especially suited to remote rural locations (e.g. China, India), providing electricity for domestic use where no grid source is available, at a user scale from a few households to a whole village. The potential social benefits from such a local supply of electicity (e.g. for food storage and communications), are great. Future increases in conversion efficiency of gasifiers may come from the use of metal alloy catalysts and hydrolytic enzymes. Conversion of biomass by pyrolysis has the advantage that the major product (pyrolytic oil - PO) can be stored and transported, so that its production can be separated both in space and time from the generation of electricity or heat. The production of PO can take place in remote areas where biomass is abundant and at low or negative cost (where the fuel is a waste material) and then transported to industrial or residential sites. Pyrolysis can also give rise to chemicals with high added value for use by, e.g. the food, pharmaceutical and textile industries, or as insecticides and herbicides. In USA, Canada, Sweden and Finland successful applications of Pyrolysis technology with CHP produce heat and electricity for domestic use as well as fermentable sugars for the production of ethanol, with high efficiency (e.g. 45% using the Integrated Pyrocycling Combined Process). Heat for the pyrolysis process is supplied by the system itself, requiring no external source of energy. Biomass fuel for pyrolysis needs to be dried to avoid water contaminating the PO product and the fuel must be