1. What is waste incineration treatment?

Incineration is to burn and burn; in the process of burning, all combustible substances are burned out and turned into ashes.Incineration treatment is the use of high-temperature oxidation to treat domestic waste-the domestic waste is burned at high temperature, so that the combustible waste in the domestic waste is converted into carbon dioxide and water, etc. The ash and slag after incineration are only less than 20% of the original volume of domestic waste, which greatly reduces the amount of solid waste and can also eliminate various pathogens.

2. What is the situation of waste incineration and treatment abroad?

(1) The status quo of incineration treatment in Europe.At present, European countries generally strengthen waste incineration treatment, and the EU's highest waste management decree also clearly supports and encourages energy recovery of waste (mainly incineration).From 1996 to 2007, the amount of landfills in EU member states continued to decrease, while the amount of incineration was on the rise.According to statistics, in 2006, the total population of major European countries was 578 million people, and the total amount of domestic waste generated was about 297 million tons. There were 425 domestic waste incineration power generation (heating) plants, and the waste incineration treatment capacity was about 63.62 million tons, an increase of 20% over 2001.

(2) The status quo of incineration treatment in the United States.In the United States, waste incineration has always occupied a place in the waste treatment system, and the national waste incineration treatment rate in the United States has been about 14%.In 2007, there were a total of 87 waste incineration power generation (heating) plants in the United States, distributed in 26 states, with a total of 220 incinerators, with a total scale of 93,943 tons/day, a total of 28.7 million tons of waste treated, a total installed capacity of 2720MW, and an annual power generation capacity of 17 billion kWh.The incineration capacity of the United States is twice that of China, and it is concentrated in economically developed areas in the northeast.

(3) The status quo of incineration treatment in Japan.In Japan, the amount of waste incineration treatment has always been high. The central incineration plant in Tokyo is only 3.5 kilometers away from the Imperial Palace of Japan; there are 7 waste incineration power plants within 7 kilometers of the Imperial Palace of Japan.

Since the 1960s, Japan has begun to build incineration plants on a large scale. Most of the waste incineration plants that need to be closed after reaching their service life are small waste incineration plants built in the early days, replaced by large-scale waste incineration plants with higher pollution control levels.

In the 1990s, in order to better strengthen the pollution control of waste incineration plants, Japan upgraded waste incineration equipment and flue gas treatment equipment, and incineration still occupies the main position in the treatment of domestic waste.Although the number of waste incineration plants in Japan has decreased, the total amount of incineration treatment has not decreased significantly.

In recent years, the total amount of waste incineration in Japan has decreased slightly, mainly due to the implementation of waste sorting, recycling and reduction, resulting in a decrease in the total amount of waste removal.

In general, Japan's garbage disposal is mainly incineration, garbage sorting and recycling are gradually strengthening, and the amount of landfill treatment is gradually decreasing.

(4) The status quo of incineration treatment in Singapore.Singapore's waste disposal policy is “to develop and maintain sufficient incineration plants to incinerate all incinerable waste, and to develop and maintain sufficient landfills to treat all non-incinerable waste and incinerated ashes.” Singapore implements a waste disposal method of full incineration and landfill of ash.Singapore currently has 4 waste incineration power plants, 1 landfill and 1 supporting offshore transfer station, located in its northern, central, western and southern islands. Except for the earliest Ulubandan incineration power plant, which is 2 kilometers away from residential areas, other treatment plants (sites) are 10 kilometers away from residential areas.The Shimagao landfill mainly landfill the ashes from the incineration of Singapore's four incineration power plants, as well as non-incinerable industrial and construction waste, which is expected to be used until 2045.The Tuas Nan Waste Incineration Power plant has a full-load waste treatment capacity of 3,000 tons/day, which is currently the largest in the world. It produces 981 million kilowatt-hours of electricity annually, accounting for 2%-3% of Singapore's total electricity demand.

      3. What is the current situation of waste incineration and power generation in our country?

Although waste incineration power generation in our country started late, it has developed rapidly. In 1988, Shenzhen established our country's first waste power plant that introduced equipment and technology imported from Mitsubishi Martin, Japan-Shenzhen Municipal Sanitation Comprehensive Treatment Plant (daily treatment of 3×150 tons of waste, installed capacity 4MW).Subsequently, waste incineration power plants in Zhuhai, Shanghai Pudong and Puxi, Ningbo, Hangzhou, Wenzhou, Suzhou, Changzhou, Chongqing, Chengdu, Guangzhou, Fuzhou, Xiamen, Tianjin and Beijing were successively completed and put into operation. In 2010, there were more than 170 waste incineration power generation (heating) plants under construction and under construction across the country.

4. Can domestic waste be burned?Can it be burned thoroughly?

First of all, we must explain what is the calorific value: the heat released when the fuel per unit mass (or volume) is completely burned, that is, the heat released by the complete combustion of 1 kilogram (or 1 cubic meter) of a certain solid (gas) fuel is called the calorific value of the fuel.

With the continuous development of our national economy and the continuous improvement of people's living standards, the calorific value of daily domestic waste has been continuously increased.The current calorific value level is equivalent to 1/4 of ordinary coal, and the specific data calorific value is about 4200 kJ/kg. During the stable combustion process, it is completely possible to burn without adding auxiliary fuels such as coal, oil or natural gas. Nowadays, domestic mechanical grate furnaces are relatively mature and can completely incinerate domestic waste. The residue after incineration is a dense and non-corrupt sterile substance.

5. What are the benefits of incineration?How much electricity can a ton of domestic waste generate?How much carbon dioxide emissions can be reduced?

Waste incineration treatment has the advantages of “reduction, resource-based, and harmless”, and the incineration treatment facility occupies a relatively large area, the waste is stabilized rapidly, the reduction effect is obvious, the odor control of domestic waste is relatively easy, and the waste heat from incineration can be used. While treating domestic waste safely, harmlessly and efficiently, it can also use the waste heat generated by its incineration for power generation (heating) utilization, which meets the requirements of the circular economy and is currently a widely respected domestic and international waste treatment technology.

The use of waste heat generated by the incineration of domestic waste to generate electricity can supply power to the power grid every year, realize waste resource utilization, and save non-renewable resources-coal, natural gas or fuel oil, reducing carbon dioxide emissions.It is estimated that the domestic grate furnace domestic waste incineration power plant has an online power of about 250-350 kw.h/t, each ton of domestic waste incineration for power generation can save 81-114 kg of standard coal and reduce 202-283 kg of carbon dioxide.

      6. What kind of city is suitable for waste incineration treatment?

With the acceleration of urbanization in our country and the improvement of people's living standards, the scale of cities is getting bigger and the urban population is getting bigger and bigger, which has led to the continuous increase in the production of municipal solid waste, and the urban waste siege crisis is becoming more and more serious.Landfill and composting treatment can no longer fully meet the demand, and composting has a greater negative impact on the soil. Most landfills are already about to be filled and landfill sites must be re-selected. Due to the shortage of land and environmental requirements, waste incineration power generation (heating) technology is developed in different cities according to the actual situation, and the harmless treatment of waste is even more urgent.

According to the needs of economic development and the actual situation, areas with low GDP tend to continue to adopt landfill methods, but only if there is enough land for landfill waste.In more developed areas and cities, with the continuous increase of the urban population, incineration treatment is suitable because it can save land resources and carry out harmless treatment.

7. What are the main incineration treatment technologies?

There are two main mainstream waste incineration treatment technologies: one is mechanical grate furnace technology and the other is circulating fluidized bed technology.

According to our country's relevant technical policies, “Waste incineration should currently adopt mature technologies based on grate furnaces, and other furnace-type incinerators should be used cautiously.It is forbidden to use incinerators that cannot meet the control standards. ” Mechanical grate furnace technology should be the mainstream technology for domestic waste incineration and treatment.Characteristics of mechanical grate furnace technology: long application history and mature technology.Garbage does not need to be pretreated, the failure rate is low, the annual running time is long, and the processing capacity is large.There is no need to add auxiliary fuel during the stable combustion process, and the amount of fly ash produced is small. It has extensive performance abroad and at home. The vast majority of the global waste incineration treatment industry adopts this technology.

Circulating fluidized bed technology: The application time in the field of waste incineration treatment is relatively short, and it is still in the technical exploration period.At present, the domestic circulating fluidized bed needs to consume non-renewable coal when it is running, and there are certain requirements for the particle size of the coal block. The coal block must be processed and broken before it can be fed into the furnace by the coal feeding equipment.At the same time, due to its technical characteristics, the circulating fluidized bed needs to sort and crush the waste before the waste is incinerated. During the pretreatment and transportation process in the plant, it is easy to cause the leakage of sewage and odor, causing secondary pollution to the environment.The technology is more adaptable in incineration treatment such as waste-derived fuels (RDF) and sludge, and the addition of coal cannot exceed 30%.

      8. How to use the heat energy of incineration?

There are a large number of combustibles in domestic waste. Domestic waste is used instead of coal as fuel to burn, emit heat and generate steam in an incinerator, which can generate electricity, combined heat and power or direct heating.The use of incineration to generate electricity (heating) for domestic waste not only treats domestic waste, but also saves the country's non-renewable resources-coal or fuel oil, and at the same time makes up for the lack of electricity in our country.

9. What exhaust gases are produced by incineration treatment?How to control?

The standard of flue gas control system for domestic waste incineration is far stricter than that of coal-fired boilers, fuel-fired boilers, and coking furnaces.

The exhaust gas emitted by the domestic waste incineration power generation (heating) plant mainly comes from the flue gas generated by the incinerator. The main pollutants contained are dust, hydrogen chloride (HCl), sulfur dioxide (SO2), nitrogen oxides (NOX), carbon monoxide (CO), hydrogen fluoride (HF), organic pollutants, dioxins and heavy metals.The computer control system realizes a high degree of automation of waste incineration, thermal energy utilization, flue gas treatment and other processes, so that the incineration system operates under rated operating conditions, so that the concentration of raw emissions is minimized.Before the flue gas is treated by the flue gas purification system and discharged into the atmosphere through the chimney, an on-line flue gas monitor is used to continuously monitor the flue gas emission indicators of each incineration line to ensure that the waste incineration power generation (heating) plant's flue gas is discharged up to standard.

10. What kind of waste residue is produced by incineration treatment?How to deal with it?

Slag: Domestic waste is incinerated at high temperature in an incinerator, so that the various components of domestic waste are thoroughly oxidized, decomposed and passivated to become slag. The composition is mainly glass, metal and various inorganic substances.

Slag is mainly the residue after the combustion of domestic waste. The amount produced depends on the composition of the waste. Its main components are manganese oxide (MnO), silica (SiO2), calcium oxide (CaO), aluminum oxide (Al2O3), iron oxide (Fe2O3), scrap metal, and a small amount of unburned organic matter. According to the “Domestic Waste Incineration Pollution Control Standard” (GB18485-2001) stipulates: "The slag after incineration shall be treated as general solid waste."The slag generated by waste incineration is treated harmlessly at high temperature, and then separated from scrap metals such as scrap steel and iron by magnetic separation, and the slag is comprehensively utilized. It can be used as a paving cushion, a material for the covering layer of a landfill, and a material for the production of burn-free bricks. The comprehensive utilization rate of slag can reach 98%, and the parts that cannot be comprehensively utilized are sent to landfills for landfill.

Fly ash: The dust (fly ash) collected by the flue gas purification system contains harmful substances such as dioxins and heavy metals. According to the “Domestic Waste Incineration Pollution Control Standard” (GB18485-2001), "Dust removal fly ash shall be treated as hazardous waste."

Fly ash is hazardous waste and must be collected separately. It must not be mixed with domestic waste, incineration residues, etc., nor with other hazardous waste.The fly ash from the incineration of domestic waste shall not be stored for a long time at the place of origin, shall not be simply disposed of, and shall not be discharged.The place where the fly ash from the incineration of domestic waste is produced must undergo the necessary stabilization and curing treatment, and it can only be transported after the stabilization and curing treatment. Special means of transportation are required for transportation.It is transported to the fly ash storage warehouse by airtight collection and transportation, and after passing the leaching toxicity test, it is sent to the landfill for landfill.

11. What are the dioxins produced by waste incineration?

Dioxins are actually an abbreviation for dioxins. It refers not to a single substance, but to two categories of 210 compounds containing many similar substances or isomers with similar structure and properties. This kind of substance is very stable, has a high melting point, is extremely difficult to dissolve in water, can be dissolved in most organic solvents, is colorless, odorless, and severely toxic fat-soluble substances, so it is very easy to accumulate in living organisms.Dioxins are pollutants produced during combustion. The dioxins emitted by open-air incineration of garbage or spontaneous combustion of garbage in landfills are many times that emitted by modern incineration of the same amount of garbage; regenerated non-ferrous metals, steelmaking, iron ore incineration, coking, cremation of human remains, cast iron production, cement production, pulp and paper making (chlorine-containing bleaching process is the main process of forming dioxins) and other industries have also produced a large number of dioxins; there are also automobile exhaust, cigarettes, barbecues, fireworks, forest fires and volcanic eruptions in nature, etc. Can produce dioxins, in fact, dioxins are not far from us. Far away.At present, the dioxins present in our environment mainly come from metallurgy, coking, petrochemical and other industries.

12. Why are there dioxins in the flue gas of waste incineration?

In the process of incineration of domestic waste, the production pathways of dioxins include the following aspects：

(1) Domestic waste itself contains trace amounts of dioxins. Due to the thermal stability of dioxins, although most of them can be decomposed by high-temperature combustion, some will still be discharged with the flue gas after combustion.

(2) During the combustion process, dioxins are generated from chlorine-containing precursor substances. The precursor substances include polyvinyl chloride (which is a commonly used plastic), pentachlorophenol (which is a mildew-proof preservative commonly used in textiles, leather products, wood, weaving pastes and printing pastes), etc. During combustion, the precursor molecules will generate dioxins through rearrangement, free radical condensation, dechlorination or other molecular reactions. Most of these dioxins are decomposed by high temperature combustion.

(3) When the combustion is insufficient, too much unburned material is produced in the flue gas. At a temperature of 300-500℃, the decomposed dioxins after high temperature combustion encounter an appropriate amount of catalyst substances (mainly heavy metals, especially copper) will be regenerated.

13. Can the production of dioxins in waste incineration be controlled?

Although incineration may produce dioxins, as long as the combustion conditions are controlled, such as allowing the smoke to stay in the furnace for a longer time, the production of dioxins can be greatly reduced.

(1) Choose an incinerator that meets the national standard "Domestic Waste Incineration Pollution Control Standard" (GB18485-2001) to control the combustion temperature and ensure that the residence time of the flue gas in the area where the combustion chamber temperature reaches above 850℃ is not less than 2 seconds, so that the secondary combustion gas forms a swirl, making the combustion more complete and adequate, and the dioxins are fully decomposed.Studies have shown that the production of dioxins has a lot to do with the concentration of carbon monoxide.Adjust the volume and ratio of the first and second air during operation, and strengthen the disturbance through the second air to make the garbage combustion more adequate, thereby controlling the content of carbon monoxide in the flue gas and the production of dioxins.

(2) When the flue gas temperature drops to the range of 300~500℃, a small amount of decomposed dioxins will be regenerated. Therefore, the design considers minimizing the cross-sectional area of the tail of the waste heat boiler and increasing the flow rate of the flue gas to reduce the residence time of the flue gas from high temperature to low temperature to reduce the regeneration of dioxins.

14. Can dioxin emissions be controlled?

First, an activated carbon inlet device is arranged on the flue of the flue gas purification system to spray activated carbon with a specific surface area greater than 700m2/g into the flue gas to adsorb dioxins.At the same time, in the bag dust collector, when the flue gas passes through the filter layer formed by particulate matter, the remaining trace amounts of dioxins in the dust-containing flue gas can still be filtered and adsorbed by the unreacted Ca (OH) 2 or CaO powder, activated carbon powder, etc. in the filter layer. The powder layer composed of powder, activated carbon powder, etc. is further purified.

The second is to choose a high-efficiency cloth bag dust collector and use a high-efficiency filter material to filter and collect the fly ash with dioxins, and stabilize it with ”chelating agent + cement + water".

15. Does the waste incineration treatment plant smell?How to control the stench?

The decay and decomposition of organic matter in domestic waste will inevitably produce stench pollution.The source of stench pollution mainly comes from the raw garbage entering the factory. During the unloading process of the garbage truck and the garbage dump in the garbage storage pit, the stench gas is emitted. Its main components are hydrogen sulfide (H2S), ammonia (NH3) and so on.

In order to control the stench generated by the incineration plant, the following measures can be taken：

(1) The garbage itself is smelly, so it is not ruled out that there is a smelly smell along the transportation route. In this regard, it is mainly the use of airtight, automatic loading and unloading structure of the transport vehicle to transport the garbage, to minimize the odor overflow.；

(2) After the garbage truck enters the workshop, it will dump the garbage into the garbage pit through the discharge.The garbage discharge door is electric lifting type and is controlled by a special person. After the transport vehicle completes the discharge, it is closed in time to make the garbage pit airtight.

(3) An air curtain is set up at the main entrance of the garbage discharge hall to prevent odor from escaping.

(4) The garbage pit is airtight, and the suction outlet of the fan is set above the garbage pit, so that the garbage pit and the discharge hall are in a negative pressure state, which can not only effectively control the escape of odor, but also at the same time the stench gas is used as combustion air to lead to the incinerator, the stench gas decomposes at high temperature in the incinerator, and the odor can be removed.In order to avoid the escape of odor, the garbage pit plant is a closed plant.

(5) Plant a certain number of tall trees around the factory area to reduce the impact.

(6) In order to prevent the pollution of the surrounding environment by the odor of the garbage pit during the maintenance of the whole plant, the odor in the pit is purified by the activated carbon exhaust gas purifier and discharged outdoors.Regularly detect the odor concentration at the outlet of the purifier. When the odor outlet concentration reaches the national standard control limit, replace the activated carbon in the purifier in time, and the waste activated carbon will be mixed with domestic waste into the incinerator for high-temperature incineration treatment.

(7) The leachate treatment system is a closed structure with a trachea at the top, and the biogas and odor generated are introduced into the garbage storage pit through the trachea and exhaust fan.(Prepared by experts organized by the Department of Science and Technology of the China Association for Science and Technology and the Chinese Society of Environmental Sciences)