Combustible components of biomass gases mainly contain hydrogen, carbon monoxide and methane. They could be used for combustion and providing heat for power plant or for driv­ing pyrolysis. Biomass gases can also be used for drying instead of flue gas (Yuan et al., 2005). Thus, it is a convenient method for self-sufficiency. When the biomass gases can be used for drying agriculture and forestry products, it does not rigidly require the purity of exhaust gases after combustion. With air, the gases can be burned in all kinds of fireboxes continually and the equipment does not require cleaning and transportation long distance, and simply gives a short payback time. Compared to burning directly for heat, the efficiency is higher and it is valuable for small-scale companies and private business. Besides, biomass gasification gas can be used for drying of wood, grain, tobacco and tea directly at the same time.

4.3.4 Biomass gasification power generation

In recent years, biomass power generation technology research has progressed significantly in China. Experts predict that it will be mature in 2010 to 2020. The development direction of biomass power generation is combining cycle power generation (BIGCC) with advanced gas turbine power generation.

Biomass gasification power generation needs the following components: combustible gas is formed in a gasifier; the gas is purified and then burned in an internal combustion engine or combusted in a gas turbine to drive the generator to generate power. China has a good biomass gasification foundation, in the early nineteenth century; with charcoal gasification furnace gas, many cities in China used gas as a fuel for cars and other vehicles. In the energy shortage in the 1950s, China developed technology for rural irrigation and drainage machinery to provide power through firewood gasification furnaces, which has formed a series of product prototypes. Biomass gasification technology in the 1980s had more rapid development. In 1981 the first rice husk gasification power generation device was designed by Jiangsu Provincial Grain Bureau and a machine factory. This resulted in a 160 kW, downdraft gasifier with a Diesel Engine in Jiangsu. Later it was developed into a series of low heat value gas generators of 60, 160 and 200 kW

The Tenth Five Year’s Research Project of China is ‘160 kW fluidized bed biomass gasification generator technology industrialization research’, and a demonstration unit was built in grain processing factories in Anhui Lianhe Rice Industry Co., Ltd. Using straw, such as wheat straw and soft rice shell etc. as raw materials, with gas calorific value changing from 5200 kJ/m3 to 5800 kJ/m3, with tar content was less than 20 mg/m3, the unit has already been put into operation and gained obvious economic benefits. In Anhui Lianhe Rice Industry Co., Ltd, a set of 400 kW biomass gasification generators were established. Since then, more and more biomass gasification generators have been built in China.

In the 20th century, the Academy of Sciences Guangzhou Energy Institute has studied the circulating fluidized bed of biomass gasification power generation technology. They had a lot of achievements and experience in development and commercialization. In 1991, the first circulating fluidized bed gasification device with diameter of 400 mm, height of 4 m, and feeding quantity 200-300 kg/h has been successfully developed by the Chinese Academy of Sciences Guangzhou Institute of Energy Development in Zhanjiang City, By making use of the wood powder waste, factory products convert into fuel gas as the fuel of boilers, and coal co-firing, each year replacing more than 3000 tonnes of coal. It obtained apparent social benefit and economic benefit. In 1998, the first circulating fluidized bed gasification device and internal combustion engine generator set, 1000 kW power rice husk gasification and power generation units in Fujian run successfully. Subsequently, in Hainan, a 1000 kW biomass demonstration power plant has run successfully for more than 3 years, and has promoted the foundation of more than 20 sets.

Below are some case studies of biomass power plant projects in China.

Case 1

A demonstration construction project of 2 x 12 MW biomass power plant in QuYang city of Shanxi Province, is a renewable energy project through combusting straw directly in the boiler generation. It is an effective way to implement the law of the People’s Republic on renewable energy and the law of the People’s Republic on saving energy, which is in accordance with the renewable energy management regulations and other related policies. Implementation of the project sets an example for effective utilization of renewable resources and the development of biomass power plant in the city and province.

Crop stalks (CSS) is a rich, clean, renewable and sustainable energy. Its development and utilization can not only reduce the sulfur dioxide emissions, solve the energy related problems of environmental pollution, and promote sustainable economic and social development, but also improve the coal-dominant energy structure and layout gradually in the province. The imple­mentation of 2 x 12 MW biomass power plant demonstration project in QuYang city of Shanxi province, provide electricity safeguard for local power for local enterprise development, realize the economic and reasonable utilization of local abandoned straw, increase the farmers’ income and improve the planting industry benefit; increase the fiscal revenue and local employment opportunities, and promote the development of the local economy. Using waste heat for central heating could save energy consumption, reduce environmental pollution and improve the quality of the urban life in many aspects.

With mature technologies, the demonstration project biomass power plant in QuYang city of Shanxi province has reliable economic benefit and significant social, ecological and environmen­tal benefits. The scale of the project is 2 x 12 MW, matching 2 x 75 t/h biomass (straw) circulating fluidized bed boiler. The total investment is 181.29 million Yuan; static investment is 172.38 mil­lion Yuan. With an annual consumption of 180,000 tonnes, the annual power generation is about 150 x 106 kWh/y at full load operation. With a price of 0.51651 Yuan/kWh (including taxes), the annual income is 78.96 million Yuan, while with a price of0.44188 Yuan/kWh (not including tax), the annual income is 67.55 million Yuan. As a by-product, the annual output of chemical fertilizer is 9000 tonnes, increasing a value of 4.5 million Yuan. Using waste heat can create considerable income.

Using straw can solve three problems: energy shortage, environment protection, and addition to farmers’ incomes. If 180,000 tonnes of straw are burnt in a year, it can save about 90,000 tonnes of standard coal, reduce sulfur dioxide emissions by 900 tonnes, smoke and dust emissions by 600 tonnes. If the price of straw is 60 Yuan per tonne, the project increases local farmers’ income by more than 1000 Yuan per year.

Case 2

In Lishui city of Zhejiang province, an effective utilization of biomass gasification power of 10 MW has been built. Lishui city has a bamboo forest area of 1333.4 million m2, occupying 15.6% of the area in Zhejiang province, which is a good resource base for developing biomass power. In this project, the produced gas is directly used in a gas engine for generating power. The single-machine capacity of the electric generator is 1000 kW and the project has a total of 10 units. As a by-product, the carbon product is 80 tonnes, the bamboo vinegar fluid product is 27 tonnes, and the wood tar product is 8 tonnes every day.

This project has a 10 MW generator production with a recovery bamboo charcoal and a bamboo vinegar fluid device. Its main components are raw material field, conveying system, bunker, drying, biomass gasifier, gas cooling and purification devise, vinegar recycling equipment, carbon powder collection devices, gas generating sets, condensed water device and pipelines connecting the workshop etc.

The project’s total investment is 110 million Yuan, of which the main equipment cost is 50 million Yuan, the cost of the carbon processing equipment is 2 million Yuan, the cost of electric Internet system is 10 million Yuan, the cost of land and building construction is 20 million Yuan, the technological cost is 7.5 million Yuan, the cost of the earlier stage is 5.5 million Yuan, the current fund is 15 millionYuan. After operating, the project income is 133.728 millionYuan, after tax is 18.2216 millionYuan.

Case 3

The project of biomass gasification power in Qing Yuan city of Zhejiang province, with an investment of 110 millionYuan, is one of the first biomass gasification power projects of the east China area, which is invested in by the China Forest Energy Corporation.

The poly-generation technology, using the principle of carbon, gas, liquid and hot water are produced during the biomass processing simultaneously. The combustible gas is injected into the generator power, and hot water will be used for heating, bamboo vinegar and bamboo charcoal are collected respectively for comprehensive utilization. This biomass gasification power generation technology is realizing straw and forest tree remains high efficiency and high added value using, which is in international leading level.

The biomass gasification power project consumes remains of bamboo processing and logging

80,0 tonnes to 100,000 tonnes, generating 72 million kWh power per year, producing 24,000 tonnes of bamboo charcoal, 8000 tonnes of bamboo vinegar fluid, and providing 3000 jobs, achieving an output of more than 130 million Yuan/year.