Landfill or open dumping takes up a lot of land, and the harmful components in garbage cause serious pollution to the atmosphere, soil and water source, which not only destroys the ecological environment, but also seriously harms human health.
Composting needs to sort out the garbage, which requires higher organic matter content. Compost cannot be reduced, and it also takes up a lot of land.
Incineration treatment is to burn garbage in an incinerator to release heat energy, and the waste heat can be recovered for heating or power generation. The flue gas is discharged after purification, and a small amount of residual residue is discharged for landfill or other purposes. Incineration technology has the characteristics of large capacity, good reduction, complete harmlessness and heat energy recovery. Therefore, incineration treatment of domestic waste is an effective treatment method of harmlessness, reduction and resource utilization. This garbage disposal technology is widely used all over the world. The most scientific and reasonable way of garbage disposal is to sort out the garbage, recycle the useful things that can be recycled, and incinerate the garbage that cannot be recycled.
First, garbage incineration technology
1. Waste incineration conditions
Garbage incineration must meet certain conditions:
Garbage should have a certain calorific value. When the calorific value of garbage is lower than or equal to 3350 kJ/kg (800 kcal/kg), coal blending or oil burning should be used to assist combustion. It is generally believed that the combustion effect of garbage with low calorific value >: 5000kJ/kg( 1200kcal/kg) is good. The low calorific value of municipal solid waste is between 3350 and 8374 kJ /kg (800-2000 kcal/kg). The water content in garbage is ≤ 50%; Garbage has heterogeneity and variability. Garbage changes greatly in different regions and seasons, which brings certain difficulties to garbage incineration.
2. Waste incineration technology
There are three kinds of garbage incineration technologies at home and abroad: stratified combustion technology, fluidized bed combustion technology and rotary combustion technology (also known as rotary kiln).
(1) stratified combustion technology
Stratified combustion technology is relatively mature, and some countries adopt this combustion technology. In order to make the combustion process of garbage stable, grate is the key to stratified combustion. Garbage passes through three areas on the grate: preheating and drying area, main combustion area and burnout area. The garbage catches fire on the grate, and the heat comes not only from the radiation above and the convection of flue gas, but also from the inside of the garbage layer. Under the special action of the grate, the garbage that has caught fire on the grate makes the garbage layer turn and stir strongly, and it is pushed down continuously, so that the bottom of the garbage begins to catch fire. The continuous turning and stirring makes the garbage layer loose, which enhances the air permeability and is helpful for the ignition and combustion of the garbage. The design of furnace arch shape should consider the flue gas flow field, which is beneficial to the thermal radiation of hot flue gas to new garbage, preheating and drying and the combustion of garbage in incineration area. The air distribution design should ensure the best air distribution on the garbage layer on the grate and make rational use of primary air and secondary air.
(2) Fluidized bed combustion technology
Fluidized bed combustion technology has been developed and matured. Because of its high heat intensity, it is more suitable for burning fuel with low calorific value and high moisture. At the same time, due to the large heat storage in the furnace, there is basically no need to support combustion when burning garbage. In order to ensure the full fluidization of the garbage in the furnace, there are strict requirements on the size of the garbage in the furnace, and a series of screening and crushing treatments are needed to make the garbage uniform in size and state. Generally, it is crushed to 15cm, and then sent to a fluidized bed for combustion. The bed material is quartz sand, and the air distribution plate is usually designed as an inverted cone structure with an L-shaped cover. The combustion temperature in the bed is controlled at 800-900℃, the cross-sectional velocity of cold air flow is 2m/s, and the cross-sectional velocity of hot air flow is 3-4m/s ... The primary air is sent to the fluidized bed through the hood and the secondary air is sent from the upper part of the fluidized bed. Fuel is used to preheat the material bed, and when the temperature of the material bed reaches about 600℃, it is put into garbage incineration. The start-up and combustion process characteristics of this boiler are similar to those of ordinary fluidized bed boilers.
(3) Rotary combustion technology
The combustion equipment of rotary incinerator is mainly slow-rotating rotary kiln, and its inner wall can be built with refractory bricks or tubular water wall to protect the drum. The rotary kiln has a diameter of 4-6m and a length of 10-20m, which is determined according to the amount of garbage burned and placed obliquely. At present, the garbage disposal capacity of each building can reach 300t/d (diameter 4m, length 14m). Rotary kilns used to be mainly used to treat toxic and harmful hospital garbage and chemical waste. When the cylinder rolls, the garbage is brought from the lower part of the cylinder to the upper part of the cylinder through the slow rotation of the cylinder of the furnace body and the high-temperature resistant copying plate on the inner wall, and then falls by the weight of the garbage. Because the garbage rolls in the cylinder, it can fully contact with the air and burn completely. The garbage is fed from one end of the drum, dried by hot flue gas and burned after reaching the ignition temperature. When the drum rolls, the garbage rolls and slides down until the ash is discharged from the outlet of the drum.
When the water content of garbage is too large, a first-stage grate can be added at the end of the cylinder to meet the combustion, and the flue gas discharged from the cylinder passes through a vertical combustion chamber (secondary combustion chamber). The secondary air is sent to the burnout chamber, where the combustible components in the flue gas are fully burned. The temperature of the secondary combustion chamber is generally 1000- 1200℃.
Compared with other combustion methods, rotary kiln type garbage combustion device has lower cost and less auxiliary power consumption, but it is difficult to burn garbage with calorific value less than 5000kJ/kg and high water content.
Second, the development of waste incineration technology abroad
The method of garbage incineration was put forward as early as 190 1 Americans. At first, the main task was to reduce the volume of garbage, but it was not widely used because the smoke produced by garbage combustion could not be controlled at that time. In the 1960s, with the progress of flue gas treatment technology, this method of incinerating garbage was popularized and developed in Europe.
The earliest garbage power station in Japan was built in Osaka in 1965. At present, there are about 3000 garbage incinerators and 13 1 garbage power station with a total installed capacity of 650MW. By the year 2000, the garbage power generation capacity will reach 2000 MW. There are 8 garbage power plants, with daily garbage handling capacity exceeding 1000t/d (the highest is 1800t/d). The largest garbage power plant was built in 1995, with a power generation capacity of 24MW. In order to prevent the corrosion of boiler tubes, Japan's early garbage power plants used low parameters, and the power generation efficiency was low, only 10%- 15%, and now it is seeking to increase it to 30%.
The waste incineration plants in the United States have developed rapidly, with 400 incinerators built in 1990, and the incineration rate reached 18%, which increased to 40% in 2000. The garbage power generation in the United States has reached 2000MW. Recently, a garbage power station is under construction, with a daily garbage disposal capacity of 2,000 tons/day, steam temperature of 430-450℃ and power generation capacity of 85MW.
Britain's largest garbage power station is located in London, with five rolling grate boilers, which handle 400,000 tons of garbage every year.
There are more than 300 waste incineration boilers in France, which can handle 40% of municipal waste, and there are 4 Martin boilers in Paris, which can handle 450t/d of waste every day.
Germany has the most efficient garbage power generation technology in the world, and 1998 has 75 garbage incineration boilers.
The waste incineration rate in Singapore reached 100%, and a 2700 t/d waste power station was built in 1986.
Third, develop domestic waste incineration technology and waste power generation.
In recent ten years, many units in China have studied waste incineration technology and developed waste power generation equipment. Some introduce foreign advanced technology, and some develop their own, all of which are in the initial stage.
Factory A introduced foreign MHI company's waste boiler technology, and jointly produced a 150t/d waste boiler, which was installed in Shenzhen. In July, 1997, the relevant national ministries and commissions conducted a special appraisal. The main body of the waste incineration boiler is designed by MHI, and the structural design is completed by Factory A, and finally confirmed by MHI. The grate adopts MHI- Martin feedback grate, and the grate and important combustion automatic control device are provided by MHI.
The first domestic 75t/d waste incineration boiler designed and manufactured by Factory B has been debugged and perfected, and it has been running stably in the near future. This boiler is installed in Shunde City, Guangdong Province. The plant's 3×200t/d garbage boiler was installed in Zhuhai and put into operation on 1999. Factory B of this furnace system adopts the design technology of Temporlla furnace body in the United States, adopts the grate of Detroit company in the United States, and all the power generation equipment and auxiliary machines are made in China.
Factory C adopted the CAO (Controlled Air Oxidation) waste incineration system developed by Canada Ruiwei Environmental Protection Co., Ltd., designed and manufactured a waste heat furnace with a daily processing capacity of 3× 100t/d, which was put into operation at the end of 1999.
The Institute of Engineering Physics of China Academy of Sciences undertook the National Eighth Five-Year Plan project, and developed a demonstration project of 100t/d fluidized bed waste incinerator, which was installed in Shangzhuang, Haidian District, Beijing, and has been put into operation. Mudanjiang Institute of New Technology undertook the development of "Automatic Burning Reciprocating Grate Device" in the Eighth Five-Year Plan project, and completed the test of 50t/d daily self-ignition garbage incinerator.
Garbage power generation projects built and under construction in some large and medium-sized cities in China include:
A 3x 150t/d garbage power plant has been built in Shenzhen. 1 and unit 2 are Mitsubishi-Martin grate incinerators imported from Japan, and unit 3 is 150t/d Martin grate incinerator jointly operated by Hangzhou and Mitsubishi, and the three units generate 4000kW of electricity.
A 3×200t/d incinerator has been built in Zhuhai and put into operation on 1999.
In 2000, Beijing plans to build a large-scale modern garbage power station with a daily garbage disposal capacity of 1272t/d and imported equipment. The whole project cost is 7100000 yuan.
Shanghai imported French equipment and built two 1000t/d garbage power stations with 8500kW generators in Pudong, with an investment of 670 million yuan.
Fourth, the development prospect and direction of garbage power generation in China.
China is a developing country. After the reform and opening up, cities have developed rapidly, but the urban infrastructure construction in China is weak, and urban garbage has become one of the urban environmental pollution sources. In order to beautify the city, improve the environment, benefit mankind, make the urban ecosystem virtuous circle, and coordinate the development of environment and social economy. Therefore, the treatment of urban garbage has become one of the increasingly urgent tasks in urban infrastructure construction. China has a large population and a small population. Incineration for power generation or heating is the most promising method for harmless, reducing and recycling municipal solid waste, which is more suitable for China's national conditions. At present, some domestic cities have adopted foreign technology or domestic independent research and development technology to build and are building a number of garbage power plants, which have begun to achieve some good social benefits. With the implementation of the national environmental protection policy and the acceleration of urban infrastructure construction, garbage power generation will develop rapidly in China and will surely become a promising industry in China.
We should learn from foreign advanced technology and combine our national conditions to develop advanced waste incineration technology suitable for our national conditions. Judging from the technical level and processing capacity of domestic mechanical power generation manufacturing industry, it is fully capable of realizing the localization of waste incineration technology and waste power generation equipment.