玉米秸桿生物燃料螺旋壓力機設計畢業論文-資料下載頁

　　

【正文】 areas under previous inplan economic system. Lastly, inefficient selfbuilt stoves with heating e?ciency lower than 10% were widely used, resulting in unreasonably higher energy consumption per capita. Families had to send their surplus labor to collect every kind of biomass fuels, at the cost of rural ecology destruction. Rural household energy shortage caused a much higher social cost than personal cost.In most areas, the 1980s marked a major shift away from subsistence farming towards a more mercialized and industrialized rural economy. Township and village industry gradually dominated rural output. More families with higher ine appeared. Increased supply of straw and stalks due to the rapid development of agricultural production resulting from a household responsibility system, made it possible to basically solve the fuel shortage problem. Fig. 3 shows the change of biomass energy consumption between 1989 and 1998, and it reached the climax at the end of 1980s. There was a movement of rural laborers out of agriculture to town and village enterprises (TVEs) or to towns and cities. The trend toward urbanization first decreased and then increased the demand for energy, and also speeded up the need for cleaner and more e?cient sources, indicating a start of rural energy mercialization. With rural living standards increased and the improvement of mercial energy availability, the biomass energy is taking the place of mercial energy, and consequently, the total consumption of straw and stalk and firewood decreased rapidly.. The change of the biomass energy consumption along with timeFrom 1991 to 2000, the annual growth rate of total energy consumption in the rural area was %, while biomass energy consumption decreased at a rate of %. The proportion of consumed biomass energy over the total consumed energy in livelihood decreased from 84 to 55%. The proportion of the consumption of straw and stalk as biofuel over their output decreased from 79 to 37%. The annual consumption of straw and stalk has decreased at a rate of % in recent years. The decrease of using straw and stalk was about 7 Mt. There was an estimated 1400 Mt of straw and stalk that was replaced, or was thrown away or burnt (see Table 2). Owing to the closing of hillsides to livestock grazing and fuel gathering to facilitate forestation, plus the replacement by coal and charcoal, the consumption of firewood dropped from 140 Mtce in 1985 to below 81 Mtce in 2000.. The di?erences of biofuel consumption among di?erent districtsBecause of the big di?erences in natural resources and economies, the energy supply in the rural areas is more dependent on local natural resources that led to a big di?erence in the utilization of biofuel among di?erent places. Table 3 depicts the utilizations of straw and stalk in six main districts and the annual growth rate of related indexes in recent years. As for the usage of straw and stalk as fuel per capita, and the proportion of straw and stalk consumption over daily energy consumption in rural areas, the southern areas are higher than the northern areas while the northeast, north and east are higher than the northwest, southwest and west areas. The proportion of straw and stalk consumption per capita over total energy consumption in the north is higher than that in the south. In the northern areas, especially north China and northwest areas, the change rate of using straw and stalk as life energy is slower than that in the southern areas. The rate of replacement by mercial energy in the southern areas is obviously faster than that in the northern areas. As for the firewood resources, the coverage of forest in the east is larger than the west, and the south is larger than the north.4. The emission of poisonous gases caused by the domestic biofuel consumptionAccording to the consumption of biofuel in China’s rural areas in 2000, Table 4 gives the result after using the conversion standard presented by Streets [10], . the emission factor of SO2 by the burning of straw and stalk and firewood is t/PJ, that of NOx is 91 t/PJ and 45 t/PJ, respectively, and that of CO2 is t/t and t/t, respectively. So, CO2 was Mt, SO2 was 22:9  104t and NOx was 44:3  104t. SO2 accounted for % of the total outflow discharge ( Mt) in China, NOx %. If we take the energy consumption of coal and LGP into consideration [11,12], the emission of CO2 was 902 Mt.Along with the replacement by mercial energy in the rural area, the consumption of straw and stalk and firewood is dropping gradually. But because part of the straw and stalk is burnt in the field, which is nplete bustion, the emission of poisonous gases by each unit of straw and stalk is increasing. Therefore, the dropo? rate of the poisonous gas emission is between 1 and 2%, though the consumption of biofuel decreases at an annual rate of %.If we consider the substitution function of domestic energy, . the dropo? rate of the consumption of biofuel will necessarily lead to an increase mercial energy, we can deduce the outflow discharge of the poisonous gases by meeting the demand for total available heat. Suppose the consumption of biofuel still decreasesTable 4The emission of poisonous gases caused by the domestic biofuel consumptionEnergy consumptionCarbon dioxideSulfur dioxideNitrogen oxides(Mtce/PJ)(Mt)(104 t)(104 t)StrawFirewoodTotalat 3% in the ing years, the demand for total available energy remains constant, half of the available heat of the replaced straw and firewood is provided by LPG, half by coal and charcoal, then the consumption of coal will increase at % annually, LPG at 8–10%, which will eventually lead to an increase in the total emission by burning biofuel after substitution, especially the emission of SO2.5. ConclusionChina has abundant biomass energy resources. In 2000, the annual