Prospects for biomass energy application technologies

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Abstract: This paper outlines the current status of research and development on biomass energy application technologies both domestically and internationally. Based on China’s actual conditions, it discusses the prospects for further research and development, as well as several issues that should be given attention in future work. Keywords: biomass, energy, gasification, liquefaction, pelleting, fuel 1. Introduction Biomass energy is the earliest form of energy to be used directly by humans since the invention of fire. With the development of human civilization, research and development on the use of biomass energy have experienced many setbacks. Eventually, people came to realize the limitations of fossil fuels such as oil, coal, and natural gas. Meanwhile, the unrestrained use of these fossil fuels has led to a significant increase in the emission of waste substances such as CO2, dust, and SO2, thereby polluting the environment and causing severe consequences for the planet on which humanity depends for survival. Biomass energy, which comes from nature’s gifts, produces almost no pollution; its resources are renewable and will not run out. It also plays an important role in protecting and improving the ecological environment, making it one of the ideal renewable energies. The development of technologies for the utilization of biomass energy aims to convert forest logging and wood processing residues, as well as agricultural and forestry residues such as straw and wheat straw, into high-quality energy sources through physical or chemical processes. This approach helps to improve thermal efficiency, reduce the use of fossil fuels, protect the environment, and promote sustainable development. Since the energy crisis triggered by the Middle East wars in the 1970s, research on the development and utilization of biomass has attracted even more attention. Developed countries such as the United States, Sweden, Austria, Canada, Japan, the United Kingdom, and New Zealand, as well as developing countries like India, the Philippines, and Brazil, have all revised their energy policies and invested substantial human resources and funds in the research and development of biomass energy. The research and development of biomass energy in our country started relatively late. With economic development, attention began to be paid to research on the utilization of biomass energy. Starting from the 1980s, research and development in this area were included in key research programs, with substantial financial and human resources invested in them. A professional R&D team has been established, a number of high-level research achievements have been obtained, and China’s biomass energy industry has taken initial shape. 2. Current status of research and development in biomass energy application technologies 2.1 Overview of foreign research and development In developed countries, research and development efforts in biomass energy are mainly focused on gasification, liquefaction, pyrolysis, solidification, and direct combustion. Biomass gasification is a process in which organic materials are converted into combustible gases under high temperatures using a partial oxidation method. The generated gas can be used directly as fuel in engines, boilers, household stoves, and other applications. The application of gasification technology reached its peak during World War II. With increasing interest in the development and utilization of biomass energy, research on the application of gasification technology has once again attracted attention. The main current applications of research are gasification for power generation, methanol synthesis, and steam production. Austria has successfully implemented a regional heating system based on the combustion of wood residues; currently, there are 80–90 regional heating stations with capacities of 1,000–2,000 kW, which supply 10×109 MJ of energy per year. In Canada, 12 laboratories and universities are conducting research on biomass gasification technology. In August 1998, the rapid pyrolysis technology and equipment for biomass in a circulating fluidized bed, applied for by Freel, Barry A., were released. Sweden and Denmark are implementing plans to use biomass for combined heat and power generation, thereby enabling biomass energy to meet heating needs while supplying high-quality electricity. In 1999, 26% of the energy used for district heating and cogeneration in Sweden came from biomass. The United States is at the forefront of the world in terms of the use of biomass energy. It is reported that there are currently over 350 biomass power plants in the U.S., mainly located in pulp and paper processing facilities as well as other forestry product processing plants, most of which are situated in suburban areas. With an installed capacity of 7,000 MW, it creates around 66,000 jobs. According to predictions by relevant scientists, by 2010 the capacity for biomass power generation will reach 13,000 MW; at that time, 4,000,000 acres of energy crops and biomass residues will be used as raw materials for gasification-based power generation, thereby creating more than 170,000 jobs and contributing positively to the development of rural economies. Fluidized bed gasification technology boasts uniform gas-solid contact within the bed, a large reaction area, uniform reaction temperature, and high gasification efficiency per unit area. Advantages such as a lower reaction temperature compared to fixed beds have made it a topic of interest for scientists since 1975. These include circulating fluidized beds, pressurized fluidized beds, and conventional fluidized beds. The Center for New and Renewable Energy at Anna University in India has recently developed a fluidized-bed gasification system for research purposes, using agricultural residues such as rice husks and sugarcane bagasse; a pilot-scale fluidized-bed system has been set up, with the generated gas being used to power diesel generators. In 1995, the University of Hawaii and the University of Vermont in the United States carried out work on fluidized-bed gasification for power generation, with funding from the Department of Energy. The University of Hawaii developed a pilot-scale pressure gasification system capable of handling a biomass flow rate of 100 T/d; by 1997, the design, construction, and trial operation were completed, achieving the intended production capacity. The University of Vermont has established a gasification industrial facility with a production capacity of 200 T/d and a power generation capacity of 50 MW. It has now entered the normal operation phase. The research and development of direct combustion and solidification technologies for biomass focus primarily on the design of specialized combustion equipment and the application of biomass pellets. Currently, the technologies that have been developed include specialized steam boilers for burning waste from forestry product processing plants (such as bark from paper mills and scraps from furniture factories). Almost all foreign paper mills have specialized equipment for handling such waste. Due to the varied shapes of biomass, its low bulk density and loose structure pose significant difficulties in transportation, storage, and use, thereby affecting the utilization of biomass. Therefore, research and development on biomass molding technology began in the 1940s. The molding technologies that have been successfully developed can be mainly divided into three categories based on the shape of the molded products: the spiral extrusion technology developed in Japan for producing rod-shaped molded products, the piston extrusion technology developed in European countries for creating cylindrical block-shaped molded products, and the internal pressure drum granular molding technology and equipment developed in the United States. The annual production of pelletized fuel in the United States reaches 800,000 tons. Formed fuel is used in two areas: first, it is further carbonized to produce charcoal sticks or blocks, which serve as charcoal for household use or as raw material for industrial applications ； Secondly, it is burned directly as fuel for use in households or as heating fuel in warm rooms. Countries such as Japan, the United States, and Canada have developed specialized stoves. In North America, over 500,000 households use these specialized stoves as heating devices. . Biomass energy is subjected to normal chemical processing to produce liquid fuels such as ethanol, methanol, and liquefied oil ； It is a popular area of research. Using biological fermentation or acid hydrolysis techniques, biomass is converted into ethanol under certain conditions for use in automobiles and other industries. Canada’s production of ethanol from wooden raw materials amounts to 170,000 tons. Belgium produces over 32,000 tons of ethanol each year using sugarcane as a raw material. The United States generates around 4.5 million tons of ethanol annually from agricultural and forestry biomass as well as corn, with plans to have renewable biomass capable of producing approximately 53 million tons of ethanol by 2010. Another liquefaction conversion technique for biomass energy involves crushing and pre-treating the biomass, and then, in a reaction vessel with or without a catalyst, converting it into liquid fuel through chemical reactions. The United States, New Zealand, Japan, Germany, and Canada** have all carried out research and development work; the calorific value of the liquefied oil is around 3.5×104 KJ/kg, and the yield obtained by liquefying wood-based materials is over 50% of the weight of the dry raw material. The EU organization funded three projects to produce liquefied oil from biomass using rapid pyrolysis technology; a pilot scale of 100 kg/hr has been achieved, with plans to further expand it for commercial production. The yield of the liquefied oil produced by this technique is 70%, and its low calorific value is 1.7×104 KJ/kg. Research on catalytic gasification of biomass aims to reduce the activation energy of the gasification reaction, modify the thermal treatment process of biomass, break down the tar resulting from gasification into small-molecule combustible gases, increase the yield of gas, and improve gas pyrolysis ； At the same time, the gasification temperature is reduced, the gasification rate is increased, and the composition of the biomass gas is adjusted in order to further process it into methanol or synthetic ammonia. Researchers in developed countries such as Europe and the United States have carried out extensive research and development in catalytic gasification. Their studies cover aspects such as catalyst selection, optimization of gasification conditions, and the suitability of gasification reaction devices, and these technologies have already been applied in industrial production facilities. 2.2 Domestic research and development: Research on application technologies for biomass energy in China has received significant attention from ** and scientific researchers since the 1980s. Research and development efforts are primarily carried out in gasification, solidification, pyrolysis, and liquefaction. Research on biomass gasification technology has developed rapidly in China, and it is applied in areas such as centralized gas supply, heating, and power generation. The Institute of Forest Chemical Industry under the Chinese Academy of Forestry began researching and developing upward-absorption type gasification furnaces for centralized heating and gas supply in the 1980s; these furnaces were put into industrial use in Heilongjiang and Fujian provinces, with a maximum production capacity of 6.3×106 kJ/hr. A gasification system has been built that uses shredded branch material for gasification to produce household gas for residents’ use. Recently, in Jiangsu Province, a centralized gas supply system has been developed using straw and wheat straw as raw materials, along with an internal circulation fluidized bed gasification system, to produce gas with a calorific value close to that of medium-grade gas for use by rural residents; the calorific value of this gas is approximately 8000 KJ/NM3. The heat efficiency of gasification exceeds 70/%. The Shandong Provincial Energy Research Institute has developed a downward-flow gasification furnace. It is mainly used for the gasification of agricultural waste such as straw. It has been well promoted and applied in areas where rural residents live in concentrated communities, and has reached an industrial scale. The Guangzhou Energy Research Institute has developed a system that uses wood chips and wood powder as raw materials, along with external circulation fluidized bed gasification technology, to produce wood gas for use as a heat source for drying and for power generation; a gasification power generation system with a capacity of 180 KW has already been built. In addition, institutions such as the Beijing Agricultural Machinery Research Institute and Zhejiang University have also carried out research and development work on biomass gasification technology.  Biomass solidification technology in our country began in the mid-1980s and has now reached industrial-scale production. Currently, there are dozens of factories in China that use wood chips as raw material to produce rod-shaped charcoal. Screw extrusion molding machines are available in single-head and double-head versions; the single-head machine has a production capacity of 120 Kg/hr, while the double-head machine achieves a production capacity of 200 Kg/hr. In 1990, the Institute of Forestry Chemistry under the Chinese Academy of Forestry collaborated with the Donghai Grain Machinery Factory in Jiangsu Province to research, develop, and produce two types of rod-shaped formers: single-head and double-head. In 1998, it partnered with the Jiangsu Zhengchang Group to develop an internal-pressure drum-type pelletizer, with a production capacity of 250–300 kg/hr. The pellets produced by this machine are particularly suitable for use in households or as heating fuel. Nanjing Pingya Heating Equipment Co., Ltd. introduced heating appliances suitable for home use from the United States, and through domestic adaptation and development, has now established a production scale. Biological fermentation gas production technology has been industrialized in China, and the technology has become increasingly mature; the main raw materials used are animal manure and high-concentration organic wastewater. A centralized biogas supply system has also been established in Shanghai. Shenyang Agricultural University has introduced a set of fluidized bed rapid pyrolysis testing equipment from abroad to research and develop liquefied oil technologies, as well as conduct experiments on producing ethanol using fermentation techniques. In addition, the Institute of Forest Chemistry under the Chinese Academy of Forestry has conducted research on biomass catalytic gasification technology. East China University of Science and Technology has also carried out experimental research on the production of ethanol through the acid hydrolysis of biomass, but industrial-scale production has not yet been achieved. 3. Prospects for the application of biomass energy technology in China. Biomass energy is an important source of energy; it is estimated that by the next century, 40% of the world’s energy consumption will come from biomass energy. In China, 70% of the energy used in rural areas comes from biomass. The country possesses abundant biomass energy resources – the total amount of agricultural waste in rural areas alone amounts to over 600 million tons per year. With economic development, the improvement of people’s living standards, and growing awareness of environmental protection, the rational and efficient utilization of biomass energy will inevitably receive increasing attention. Therefore, it is of great significance to utilize biomass energy scientifically and to strengthen research on its application technologies. At present, China has a group of scientific and technical personnel who have been engaged in research and development of biomass conversion technologies for a long time. A research and development system for biomass energy with Chinese characteristics has taken initial shape, and extensive theoretical and practical research has been conducted on biomass conversion and utilization technologies. A number of high-quality research results have been achieved, and some of these technologies have been industrialized, laying a solid foundation for further research and development in the future. Considering the current status of research and development in biomass energy utilization technologies abroad, as well as China’s existing technical level and practical conditions, I believe that the application of biomass energy technologies in China will develop primarily in the following areas. 3.1 High-efficiency direct combustion technologies and equipment: China has a population of over 1.2 billion, the vast majority of whom live in rural areas and small towns. The main way in which energy is used for household purposes remains direct combustion. Residual materials such as straws and rice straw, which are loose-form materials, serve as the primary source of energy for rural residents. Developing efficient burners to improve thermal efficiency remains an important issue that needs to be addressed. The rapid growth of township enterprises has not only driven the development of the rural economy but also accelerated the consumption of fossil fuels, especially coal. Therefore, the development and modification of coal-using equipment in these enterprises (such as boilers), as well as the use of biomass to replace coal, should occupy an important place in future research and development efforts. After crushing and grading loose agricultural and forestry residues to shape them into standardized fuels, and with the development of specialized technologies and equipment, this approach holds great market potential in China. The promotion of pelletized fuels for use in households and heating rooms will be a key focus in the research and development of biomass-based fuel pellets. 3.2 Intensive comprehensive development and utilization: Biomass energy, especially firewood, is not only an excellent source of energy but can also be used to produce chemical raw materials such as charcoal, activated carbon, and wood vinegar. The establishment of a large number of fast-growing timber and fuel production bases provides abundant raw materials for the industrialized and comprehensive utilization of wood-based energy. As our economy continues to develop, it has facilitated the gradual migration of rural residents living in scattered areas to towns and cities, thereby creating practical possibilities for centralized gas supply and improved energy efficiency. In the future, energy plants should be established based on the number of people living in concentrated areas, to chemically convert biomass energy. The gases produced are collected and purified before being delivered to residents’ homes as fuel, thereby improving thermal efficiency and the standard of living for residents. The intensive and integrated utilization of this biomass energy can not only address the energy needs of residents, but also generate significant economic benefits through the production of chemical products in factories, while also providing employment opportunities for the surplus labor force in rural areas. Therefore, from the perspectives of the ecological environment and energy utilization, establishing energy-wood bases and implementing integrated forestry-energy projects represent a practical direction for development. Rural areas have abundant straw resources, and a large amount of this straw is discarded or burned directly in the fields, which not only results in significant waste of biomass energy but also causes serious air pollution. Therefore, the efficient conversion using renewable biomass energy holds good prospects for development in the future. 3.3 Innovative and efficient utilization of biomass energy: With the rapid advancement of science and technology, the development of biomass energy will rely on innovative technologies to achieve further progress. The research and development of new biomass energy technologies, such as studies on efficient and low-cost conversion methods using biotechnology, rapid liquefaction at atmospheric pressure to produce liquefied oil, research on catalytic chemical conversion techniques, as well as biomass energy conversion equipment like fluidized bed technology, are among the key areas of focus. Breakthroughs in these areas will **promote the development and application of biomass energy. 3.4 Development and utilization of municipal solid waste: The amount of household waste is increasing at a rapid rate of 8% to 10% per year. There is great potential for industrialized utilization of waste to generate electricity, provide heat through incineration, or produce gas for use by residents. 3.5 Development of energy crops: Efforts should be made to develop various plants that can produce \"green oil\", such as oil palm and Euphorbiaceae plants, in order to provide abundant and high-quality resources for the use of biomass energy. 4. Recommendations 4.1 The research and development of biomass energy application technologies are currently focused on ecological and environmental protection aspects; in the medium to long term, they will help address the issue of limited resources. Therefore, the social benefits of developing and utilizing biomass energy far outweigh its economic benefits. At the current stage of development, **policy support and financial backing are required. Relevant policies should be formulated to encourage and support enterprises in investing in biomass energy development projects. 4.2 China possesses abundant biomass resources, but given its large population, the per capita amount of these resources is relatively low. Therefore, in terms of the development direction of biomass application technologies, it is necessary to take into account China’s decentralized energy system in order to meet the growing energy needs of rural areas, towns, and villages. The focus should be on meeting the energy requirements for residential use, thereby reducing reliance on fossil fuels, especially coal. In rural areas with more developed economic conditions, wood gasification systems should be widely promoted. Promote pelletized fuel and specialized heating boilers in cities to replace coal-fired heaters and small boilers. 4.3 Strengthen basic and applied research. Fundamental theoretical and applied research on catalytic degradation, direct and indirect liquefaction mechanisms in the chemical conversion of biomass energy, genes for high biomass energy production and their patterns of variability, as well as the \"hybridization\" of biotransformation microorganisms. **In planning scientific research projects, it is important to leave some room for the development of research on biomass energy applications. 4.4 China has developed 5.4 million hectares of fuelwood forests, with an annual growth volume of around 180 million tons; it is planned to expand the area of such forests to 8.6 million hectares by 2010. At the same time, there is a large amount of economic fruit peels developed in mountainous areas. By utilizing these forestry resources to establish energy plants, these biomasses are pyrolyzed; the resulting gas is used as household gas, while the solid charcoal produced through pyrolysis is further processed into activated carbon for use as a chemical product, thereby generating economic benefits. It not only resolves the issue of energy shortages in some rural areas but also creates job opportunities for rural laborers, thereby promoting the development of rural areas in mountainous regions. In the initial stage, select an appropriate location to establish a demonstration energy plant system for the comprehensive utilization of biomass through the integration of forestry and energy, and then promote its widespread use. 4.5 Strengthen international exchanges and cooperation in biomass, introduce advanced foreign technologies and equipment for biomass applications, accelerate the development and utilization of biomass in China, and establish a structural framework for the development and utilization of biomass energy that suits China’s national conditions.