Waste incineration power generation

Waste incineration power generation

Waste incineration power generation is the work of introducing, digesting and innovating waste incineration plants and equipment. In recent years, dioxins in the flue gas from municipal solid waste (MSW) incineration are a common concern in the world. Dioxin like highly toxic substances cause great harm to the environment. Effective control of the generation and diffusion of dioxin like substances is directly related to the promotion and application of waste incineration and waste power generation technology. The molecular structure of dioxin is that one or two oxygen atoms connect two benzene rings substituted by chlorine. PCDD (polychloro dibenzo-p-dioxin) is linked by two oxygen atoms, and PCDD (polychloro dibenzo-p-dioxin) is linked by one oxygen atom. The toxicity of 2,3,7,8-pcdd was 160 times higher than that of potassium cyanide.

Working principle of waste incineration power generation:

The sources of dioxins in incinerators are petroleum products and chlorinated plastics, which are precursors of dioxins. The main way of formation is combustion. Domestic waste contains a lot of NaCl, KCl and so on, while the incineration often contains s element, resulting in the pollution. In the presence of oxygen, it reacts with the salt containing Cl to form HCl. HCl reacts with CuO formed by oxidation of Cu. It is found that the most important catalyst for dioxin production is C element (with CO as the standard).

The main advantages of waste incineration power generation are as follows:

The gas controlled pyrolysis incinerator divides the incineration process into two combustion chambers. The temperature of the first combustion chamber is controlled within 700 ℃, so that the garbage can be decomposed at low temperature under the condition of lack of oxygen. At this time, the metal elements such as Cu, Fe and Al will not be oxidized, so some of them will not be produced, which will greatly reduce the amount of dioxin; At the same time, because the production of HCl is affected by the concentration of residual oxygen, the production of HCl will be reduced by anoxic combustion; Moreover, it is difficult to form a large number of compounds in the atmosphere of self reduction. Because the gas controlled incinerator is a solid bed, there will be no smoke and no unburned residual carbon into the secondary combustion chamber. The combustible components in the garbage are decomposed into combustible gases, which are introduced into the second combustion chamber with sufficient oxygen for combustion. The temperature of the second combustion chamber is about 1000 ℃ and the flue length makes the flue gas stay for more than 2S, which ensures the complete decomposition and combustion of dioxin and other toxic organic gases at high temperature. In addition, the catalytic effect of Cu, Ni and Fe particles on the formation of dioxin can be avoided by using bag filter.

Incineration equipment

The MSW incinerator of a MSW incineration power plant is a push forward, multi-stage mechanical grate incinerator made in Canada. The incinerator has been applied to the world's third generation of cap technology, which can effectively reduce the toxic gases generated by incineration.

1. Garbage bin structure

The garbage is transported to the treatment plant by car and then poured into the garbage bin. The newly stored garbage can be put into the furnace for combustion after 3 days. When the garbage is placed in the bin, after fermentation and drainage of leachate, the calorific value of the garbage can be increased, and the garbage can be easily ignited. In the bin, the grab of crane is used to send the garbage to the hopper in front of the furnace.

2. Grate structure

The waste incinerator is a reciprocating, forward pushing, multistage mechanical grate incinerator. The incinerator is composed of a feeder and eight combustion grate units, including two-stage grate in drying section, four stage grate in gasification combustion section and two-stage grate in burnout section. The temperature in the incinerator should be controlled within 700 ℃. The burnt out refuse leaves the incinerator from the last grate and falls into the ash bin.

Feeder and fire door

The feeder pushes the garbage falling into the hopper into the combustion chamber from the front of the fire door through the loading ram. The feeder is only responsible for feeding, does not provide combustion air, and is isolated from the combustion area through the fire door. The fire door remains closed when the feeder is retracted. Closing the fire door can separate the furnace from the outside and maintain the negative pressure in the furnace. At the same time, there are temperature measuring points at the entrance of the combustion chamber. When the garbage temperature of the entrance of the combustion chamber is too high, the electromagnetic valve will control the sprayer sprayed after the fire door to prevent the rubbish from the feeding chute from igniting the garbage in the hopper when the fire door opens.

Combustion grate

The eight stage combustion grate is divided into two-stage drying grate, four stage gasification grate and two-stage burnout grate. There is a hydraulic impulse drive device under each grate. The 8-stage pushing device (pushing bed) pushes the garbage in a certain order, so that the garbage entering the incinerator is pushed to the next grate by the pushing bed matched with each grate. There are evenly distributed holes on the grate, which are used to spray primary air for combustion. The primary air for combustion is supplied by the primary air pipe under the grate. During the pushing process of the grate, the garbage is heated by the heat radiation from the burner and the furnace, as well as the primary air. The moisture evaporates rapidly and ignites.

Burner arrangement

There are two main burners in the first combustion chamber, as shown in Fig. 2, 17 and 18. There is a temperature measuring point above the combustion grate in the incinerator. When the incinerator is started and the combustion temperature is lower than the requirements, the burner 17 is fed with oil to support combustion. Burner 18 is located at the outlet of the furnace and is used to supplement the unburned garbage. The air required for burner is provided by a common combustion fan of four incinerators, and the air required for burner combustion is the clean air inhaled by the atmosphere. When the combustion fan fails or the air supply is insufficient, part of the air supply from the forced draft fan is taken by the bypass (as shown in Fig. 26) to supply the burner.

3. Second chamber flue

The main part of the second combustion chamber is cylindrical flue, and there is no flue gas dead angle caused by pipes. The purpose of setting the second combustion chamber is to make the flue gas stay for more than 2S under the condition of 120 ~ 130% of the theoretical air volume and about 1000 ℃, so as to decompose the harmful gas in the furnace. There is an auxiliary burner at the inlet of the second combustion chamber. When the system detects that the flue gas temperature at the outlet of the second combustion chamber is less than a certain value, it will ignite for supplementary combustion. The secondary air enters the secondary combustion chamber at the inlet of the secondary combustion chamber. The second combustion chamber has two upper and lower outlets leading to the waste heat boiler, and there is a hydraulically driven baffle in front of the two outlets to control the entrance of flue gas.

4. Ventilation system

Each incinerator is equipped with a forced draft fan. The fan inhales air from the garbage pool, and also inhales the gas leaked from the lower part of the pusher bed of the first combustion chamber to the outside of the incinerator. This arrangement of air supply source is to ensure that the garbage bin is in a micro negative pressure state and avoid the gas leakage of the garbage bin. The supply air enters into the waste heat boiler, passes through the two-stage air preheater of the waste heat boiler, and then enters into a large mixing header (as shown in Fig. 21), and then enters into the first combustion chamber and the second combustion chamber of the incinerator as the primary and secondary air respectively. The header can also accept the return air from the bypass of the waste heat boiler. The primary air leaving the header is further divided into two pipes: pipe 1 is connected to three air pipes to supply air to 1 ~ 3 grate; Another pipe 2 is connected to five air pipes to supply air to 4 ~ 8 grate. The primary air supplied to the grate can dry the garbage, cool the grate and supply the air for combustion. The air volume regulating valve on pipeline 1 should be adjusted according to the temperature of the incinerator inlet. The air volume regulating valve on pipeline 2 should be adjusted according to the temperature and oxygen content of the incinerator furnace. The air volume of the furnace should be 70 ~ 80% of the theoretical air volume. The secondary air enters the secondary combustion chamber through the pipeline. The secondary air supply is 120 ~ 130% of the theoretical air supply.

5. Ash discharge system

The ash discharged from the incinerator falls into the ash tank. The layout direction of two parallel ash tanks is perpendicular to that of incinerator, and the ash tanks of four incinerators are connected horizontally. The ash separator driven by hydraulic pressure (as shown in fig.223) chooses to drop the ash into an ash tank. An ash conveyor belt is arranged at the bottom of the ash tank to transport the ash discharged from four incinerators to the ash tank. A certain water level is required in the ash tank to submerge the ash.

6. Flue gas treatment equipment

After the flue gas is discharged by the waste heat boiler, it first enters the semi-dry scrubber, in which the atomizer is used to spray the cooked stone mortar from the top of the tower into the tower to neutralize with the acid gas in the flue gas, which can effectively remove HCl, HF and other gases. There is an activated carbon nozzle on the outlet pipe of the scrubber, and the activated carbon is used to adsorb dioxins / furans in the flue gas. After the flue gas enters the bag filter, the particles and heavy metals in the flue gas are adsorbed and removed. Finally, the flue gas is discharged into the atmosphere from the chimney.