Emission control technology in waste incineration power generation

Release time:

2022-08-09

In the process of incineration and power generation, the tail gas generated by domestic waste is usually treated to reduce the tail gas emission. However, there are not only corresponding solid partic

1. Causes of acid gas formation in domestic waste incineration power plant

Biochemical waste contains a large amount of organic waste, such as tea residue, melon and fruit peel and core, eggshell, solid food, and waste fruits, vegetable leaves, fish and shrimp produced in aquatic products market and fruit and vegetable market. These substances contain protein, so there will be amino acids, that is, n element. At the same time, some proteins also contain s element. During the incineration process, the tail gas will contain NOx and SO2. In addition, HCl and other gases will be produced during the incineration of waste plastics in domestic waste. In order to effectively control acid gas, it is necessary to first understand the causes of acid gas.

(1) Causes of SO2. High temperature is an important condition for producing SO2, because domestic waste contains sulfur, which will react with oxygen to produce SO2. SO2 will seriously affect the ecological environment, and its discharge in the environment will make the rainwater in the surrounding area acidic, that is, acid rain, which will seriously damage the growth of surrounding plants and houses and buildings. At the same time, under specific conditions, hydrogen sulfide will undergo a series of oxidation reactions to produce SO2, as shown in formula (1).

2H2S+3O2＝2SO2+2H2O

S+O2+＝SO2

CL2+H2O+SO2＝SO2+2HCl

CXHYOZ+O2→CO2+H2O+SO2 （1）

(2) Causes of HCl. In the incineration of domestic waste, the organic matter contained in the waste will contain chlorine, which will form HCl after incineration. Its formula: hyclo + H2O2 → incomplete combustion. In addition, domestic waste contains inorganic substances, and its internal chlorine element will be affected by external high temperature to produce a series of chemical reactions, and then generate HCl. The reaction formula is as follows (2).

2NaCL+4SiO2+Al2O3+H2O＝2HCl+Na2(SiO2)4 Al2O3

2NaCL+nSiO2++H2O＝2HCl+Na2(SiO2)n

(n = 2 or 4)

2NaCL+SiO2+0.05•O2+H2O＝Na2SO4+2HCl（2）

HCl will seriously affect the surrounding environment, because the gas can dissolve in water, causing acidification of water body, stimulating human respiratory tract and threatening human health.

(3) Causes of NOx generation. Because domestic waste contains a large amount of organic matter, and there is nitrogen in the organic matter. During waste incineration, nitrogen will react with oxygen to produce a large amount of NOx. These NOx will not only form acid rain, but also cause human discomfort and threaten human health. The NOx generation reaction is formula (3).

CxHyNz+O2＝CO2+H2O+NOx （3）

2. Domestic waste incineration technology

Under the policy constraints of basically realizing the "zero landfill" of primary domestic waste in 2023, incineration will dominate for a long time and is the absolute main means to solve the garbage siege. The main tone of actively promoting the combination of garbage classification and incineration in China will last for decades without major adjustment. Garbage incineration and power generation will become the main harmless treatment method of garbage in the future. On the other hand, the newly announced policies on the decline of state subsidies and waste classification will have an important and far-reaching impact on the waste incineration power generation industry. The new policy will force the market to make optimization and Reform in technology and management, and improve the profitability of waste power generation enterprises through technological progress, improving waste treatment charging policies and improving enterprise operation and maintenance level.

Domestic waste incineration power generation technology mainly includes three links: waste collection, incineration power generation and tail gas treatment. Among them, the garbage collection link is mainly to collect and transfer municipal garbage from various regions; The incineration power generation link is to unload and store the domestic waste, then remove the leachate through reasonable fermentation technology, and retain the combustible waste as the incineration power generation material. At the same time, effective measures will be taken to deal with tail gas during incineration. During incineration, the boiler tail gas pipeline is the main way of tail gas emission. The tail gas is discharged into the purification system first, and then discharged into the air environment after tail gas purification treatment, so as to reduce tail gas pollution. The discharged tail gas contains not only dust and solid particles, but also a variety of acid gases, such as NO2, SO2, HCl, etc.

3. Acid gas control measures

3.1 wet acid removal technology

The wet acid removal technology is generally used to completely remove the particles in the tail gas through the bag filter, and then transported to the wet smoke washing tower. Firstly, after the tail gas enters the tower, the temperature of the tail gas is gradually reduced by spraying liquid. When the saturation temperature is reached, the tail gas is chemically reacted with the alkaline absorption liquid distributed in the gap of the filler below to make it absorb acid gas.

3.2 dry acid removal technology

Using dry acid removal technology, quicklime powder is usually sprayed in the absorption tower, so that the quicklime powder can contact with acid gas in a large area, so as to absorb acid gas and obtain good acid removal effect. However, this method often has low acid removal efficiency. In application, the removal rate of HCl is about 60%, and the removal rate of SO2 is only about 30%. In order to effectively improve the efficiency of acid removal, it is necessary to appropriately increase the amount of absorbent in application.

3.3 semi dry acid removal technology

Using the semi dry acid removal technology, mainly under the application of high-efficiency atomizer, spray cooked stone mortar into the absorption tower, which can be sprayed downward from the top of the tower or upward from the bottom of the tower, so as to make the sprayed cooked stone mortar contact with the tail gas in a large area and efficiently absorb the solid particles and acid gas in the tail gas. Semi dry acid removal technology has good atomization effect in application, and the tail gas can be in relatively full contact with the absorption liquid, which not only helps to reduce the temperature of the tail gas, but also can effectively absorb the acid gas and remove the solid particles distributed therein. After the cooked stone mortar is sprayed, the water contained in it will be evaporated to reduce the amount of wastewater. In the application of semi dry acid removal technology, the device involved is relatively simple, the amount of wastewater generated is relatively small, the operation cost is not high, and good acid removal effect can be obtained. Semi dry acid removal technology has a high acid gas removal rate. When combined with cloth bag, the hydrogen chloride removal rate can exceed 90%.

3.4 low nitrogen combustion technology

At present, foreign low nitrogen combustion technology is relatively mature, especially the air staged combustion technology has high utility. Many developed countries have also successively developed low NOx burners. In this regard, China pays more attention to the control measures with small application investment and convenient installation and transformation. In recent years, a variety of low nitrogen burners have been developed, such as Tsinghua radial concentrated nitrogen and low NOx burner and Harbin Institute of technology radial concentrated nitrogen and low NOx burner, which have achieved remarkable results in application. Low NOx burners in the application stage include low NOx precombustion chamber burner, mixing promotion burner, separated flame burner, self recirculation burner, etc. The air staged combustion technology is mainly divided into one or even multiple stages. Add some air in the combustion area to make the excess air coefficient a < 1, create a fuel rich area and synchronously create a reducing atmosphere, so as to inhibit the generation of NOx and reduce the generated NOx at the same time. After that, add enough air to the rear combustion area to make a > 1 and create a lean fuel area to improve combustion efficiency.

3.5 flue gas denitration technology

At present, in the process of waste incineration power generation, due to the application of low nitrogen combustion technology and "3T" technology, the secondary pollutants in incineration treatment are effectively controlled. At the same time, SNCR technology can use ammonia as reaction reducing agent and establish an efficient and automatic in furnace denitration system in the incinerator, which can reduce NOx emission again and make the final emission meet relevant standards. In addition to SNCR, conventional flue gas denitration technologies include SCR. At the same time, various industries have also developed some new flue gas denitration technologies, such as activated carbon adsorption method, liquid absorption method, microbial method, electron beam method, etc. Although the relevant technologies are not mature at present, the prospect of technology application is still good.

3.6 new acid removal process

In addition to the above technologies, new acid removal processes such as NHD removal process and low-temperature methanol washing process can also be applied. The NHD removal process belongs to a new purification process with low energy consumption. The main components used are mixed with polyethylene glycol dimethyl ether, which has low volatility and low vapor pressure, and the solvent does not need washing and recovery. Its essence is to absorb the acid gas by physical method; Low temperature methanol washing process is a physical absorption method, which can continuously reduce the circulation volume during the continuous increase of operating pressure, and can remove HCl, SO2, no and other acid gases. The flue gas treatment system of domestic waste incineration plant is the combination of multiple technologies. Through practical research, it is found that the combined use of dry and semi dry deacidification technology can remove more than 90% of SO2 and 99% of HCl.

epilogue

In order to make full use of domestic waste, waste incineration power plants need to pay close attention to taking effective technical measures to treat acid gas, reduce relevant gas emissions, alleviate the huge pressure of domestic waste faced by cities and promote the development of environmental protection.

(this article quotes "China electric power industry", if the infringement contact is deleted)

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