Comparison of different incinerator technologies
Domestic waste incineration technology started late in China, and has been applied and developed in western developed countries for decades or even hundreds of years. Influenced by the geographical location, industrial technology characteristics and garbage characteristics of various countries, dozens of different garbage incineration processes have been produced at present. According to the relevant requirements of Technical Specification for Domestic Waste Incineration Treatment Engineering (GJJ90—2009) and the reasonable commercial operation needs, the selection of incinerator shall meet the following requirements:
(1) The number of incineration lines and the scale of a single incineration line should be determined according to the processing scale of the incineration plant, the technical maturity of the furnace type and other factors. Four incineration lines.
(2) The selected boilers shall be suitable for super-large, type I and type II waste incineration plants.
Super-large waste incineration plant: the total incineration capacity of the whole plant is more than 2000 tons/day.
Primary waste incineration plant: the total incineration capacity of the whole plant is 1200? 2000 tons/day (including 1200 tons/day);
Secondary waste incineration plant: the total incineration capacity of the whole plant is 600? 1200 tons/day (inclusive).
(3) The garbage shall be fully burned in the incinerator, the burning loss rate of the cinder shall be ≤5%, and the residence time of the flue gas in the secondary combustion chamber shall be not less than 2s at ≥850℃. (Avoid the generation of dioxins)
(4) Within the range of low calorific value and low calorific value of the designed garbage, the designed incineration capacity of the garbage should be ensured, and the requirements for the change of garbage characteristics throughout the year should be met.
(5) The incinerator has overload handling capacity, and the garbage feed should be adjustable.
At present, mainstream incinerators can be divided into mechanical grate incinerator, fluidized bed incinerator and rotary incinerator.
1 mechanical grate incinerator
Mechanical grate belongs to garbage layer burning incinerator. Grate blocks form a furnace, and garbage is constantly turned, stirred and pushed forward through the relative movement between grates. After the primary garbage is put into the hopper, it enters the grate, and under the action of its own gravity and the driving force of the grate, it is continuously loosened, dried and fully burned. The grate is divided into drying zone, burning zone and burnout zone, and the garbage passes through each zone on the grate in turn until it is completely burned out. Combustion-supporting air is introduced from the lower part or side of the grate and fully mixed with garbage to ensure combustion efficiency. During normal operation, the furnace temperature is maintained at 850℃? At 950℃, the heat generated by combustion can maintain the furnace temperature under normal circumstances. When the calorific value of garbage is low, it is necessary to inject fuel oil as auxiliary fuel.
(A) the advantages of mechanical grate furnace
(1) A single boiler has a large capacity. At present, the operating performance of domestic incinerators has reached 800t/d, and the highest can reach1200 t/d. ..
(2) The garbage is evenly distributed in the incinerator and fully burned. During operation, the feeding situation can be adjusted according to the garbage incineration in the furnace.
(3) Under normal circumstances, the residence time of flue gas in the furnace at 850℃ is not less than 2s without adding auxiliary fuel. The dust content in the flue gas is low, which reduces the load of the subsequent flue gas purification system and reduces the operating cost.
(4) The technology is mature, and the running time of the equipment is over 8000 hours/year. ..
(B) the shortcomings of mechanical grate furnace
(1) Because the key components such as moving and stator need to be made of high-temperature alloy steel, the equipment cost is high.
(2) The incinerator is relatively large, which correspondingly increases the floor space.
(3) The garbage needs to be burned continuously, so it is not advisable to start and stop the furnace frequently.
2 fluidized bed incinerator
Different from the layered combustion mode of mechanical grate furnace, fluidized bed incinerator uses fluidization technology to burn garbage. Quartz sand is usually set in the furnace as a heat carrier, also known as bed material. Before garbage incineration, heat the heat carrier in the furnace to above 600℃ to make it flow in boiling state. After the garbage is crushed, it is put into the furnace, and the fluidized garbage is fully mixed with the heat carrier, so that the water in the garbage evaporates and starts to burn after the temperature rises.
Because of the existence of heat carrier, fluidized bed incinerator has stable combustion, good adaptability to garbage change and high combustion heat efficiency. Its disadvantage is that there is a requirement for the particle size of garbage into the furnace. Because the fluidized bed incinerator adopts fluidized combustion mode, it is difficult to fluidize the components with large specific gravity or diameter in garbage, which affects the combustion efficiency. Therefore, it is required to screen out the components with large specific gravity or diameter before the garbage enters the furnace, so it is necessary to increase the high-power garbage crushing device. In addition, since the garbage is directly burned after entering the furnace, in order to improve the combustion efficiency, it is necessary to control the moisture content of the garbage entering the furnace, and pretreat the garbage before entering the furnace to reduce the moisture content. In addition, the fluidized bed boiler maintenance is relatively more, and the annual operation time is relatively short, usually only 6000? 8,000 hours
3 rotary kiln incinerator
Rotary kiln incinerator is a rotatable boiler, and the steel cylinder is lined with refractory paint and slightly inclined along the axis. The garbage is fed from the upper part of the boiler, and the furnace body rotates slowly, so that the garbage is constantly turned over and moved to the furnace head. The garbage is gradually dried and burned in the furnace, and then discharged to the slag removal device. Sometimes, in addition to the rotating drum, there are forward-pushing grates or backward-pushing grates. The front grate is used for drying and the rear grate is used for burning out. However, its combustion is not easy to control, and it is difficult to burn when the calorific value of garbage is low. Rotary incinerators are mostly used to incinerate industrial solid waste with high calorific value, but less used in domestic waste incineration.
See table 1 for the characteristics of several typical incinerators.
At present, the garbage source of domestic waste incineration power generation projects in China mainly depends on the centralized recycling of urban garbage by municipal sanitation system. The source channel of garbage is single, and the standardization of classified collection is low, which leads to complex composition, high moisture content and unstable calorific value of garbage entering the furnace. Based on this, the mechanical grate furnace is most suitable for the characteristics of garbage in China. It not only has a wide inlet, but also does not need to classify and crush the garbage, so the garbage is burned fully and runs stably. The imported dust concentration of flue gas purification system is low, which reduces the treatment cost of USD fly ash, and it is the most suitable incinerator for China municipal solid waste incineration power generation project. The fluidized bed incinerator is similar to the traditional coal-fired fluidized bed boiler, with high combustion efficiency and low investment cost. However, the garbage must be sorted and treated, and then sent to the furnace. If combined with the characteristics of the project, fluidized bed incinerator can be considered in areas with rich coal reserves and resources, and proper coal mixing in areas with low coal prices can improve the economic benefits of the system.
Main types of mechanical grate furnaces
According to its design structure and running direction, mechanical grate furnaces can be roughly divided into two categories: inclined reverse push type (hereinafter referred to as reverse push type) and inclined forward push type (hereinafter referred to as forward push type). The main feature of the reverse-pushing grate is that the moving direction of the grate is opposite to the conveying direction of the garbage. During operation, the grate has a good stirring and loosening effect on the garbage, which ensures that the primary garbage can be continuously turned over on the grate, which is beneficial to the drying of the garbage and improves the combustion efficiency. Flat-push grates usually cooperate with different motion modes, such as reciprocating motion, sliding, overturning, step descending, etc. To achieve the purpose of fully burning garbage and improving combustion efficiency. At present, the characteristics of several main mechanical grate furnaces widely used at home and abroad are compared in Table 2.
Table 2? Comparison of characteristics of several main mechanical grate furnaces
1 Martin type reverse push grate furnace
Martin Incinerator is developed by German Martin Company and widely used in the world. At present, many domestic projects use Martin incinerator produced by Mitsubishi Corporation of Japan, as shown in figure 1. The grate is an integral inclined reverse reciprocating grate, and the fixed grate and the movable grate are arranged in turn according to a certain inclination angle (generally 26). Due to the inclination and reverse push of the grate, the bottom garbage goes up and the upper garbage goes down, constantly turning and stirring. After loosening the soil, the garbage quickly dries and fully contacts with the air to achieve high combustion efficiency. Combustion air is fed from the bottom of the furnace and blown out from the gap of the grate, which has a good cooling effect on the grate.
Figure 1? Martin incinerator
Characteristics of grate:
(1) reverse design, high combustion efficiency. The garbage slides upward along the surface of the grate, so that the newly added garbage can be dried and burned in a short time.
(2) The garbage stays in the furnace for a long time, and the residual combustible materials in the burnt-out area can be sent back to the combustion area by backward pushing, so that the combustion is more complete.
(3) The garbage layer is fully stirred and the combustion state is stable.
2SITY-2000 reverse grate furnace
SITY—2000 incinerator was developed by Alstom Company of France. The overall structure of the grate is similar to Martin grate, and another grate is added in the combustion section, so that the whole grate is divided into two sections, which are driven by two sets of hydraulic transmission devices respectively, as shown in Figure 2. The grate and grate pieces are inclined downward, and the downward inclination of the grate is 24. The movable grate plates and the fixed grate plates are arranged alternately in a stepped longitudinal direction. The garbage slides down on the grate by gravity, and the garbage at the bottom is pushed to the upper layer by the reverse movement of the movable grate, thus achieving the effect of stirring. At present, Chongqing Sanfeng Kawanta Environmental Industry Co., Ltd. has introduced this technology furnace type and produced it independently.
Figure 2? SITY-2000 incinerator
Characteristics of grate:
(1) The improved Martin furnace has higher combustion efficiency and is suitable for the characteristics of high moisture and low calorific value of garbage in China.
(2) Good incineration performance, with unburned ash rate of 0.7%? 2%, the content of fly ash in flue gas is less than 3g/m3;
(3) the combustion state is stable during operation, and the exhaust air cooling efficiency of the furnace is high;
(4) Low investment and maintenance costs.
Three-stage multi-stage grate furnace
SEGHERS (segars) grate furnace is a forward reciprocating stepped multi-stage grate furnace composed of different grate units developed by SEGHERS Company in Belgium. Each standard grid unit has three forms: sliding, rotating and fixing, as shown in Figures 3 and 4. The grate * * * is divided into five sections, consisting of four standard grate units and 1 long unfinished grate units. Each section has its own hydraulic regulating mechanism, and the combustion-supporting air can also be adjusted in multiple sections according to the combustion of garbage on the grate. The moving direction of the garbage on the grate is the same as that of the grate. Through multi-stage falling, the garbage is fully overturned and stirred, thus improving the combustion efficiency of the boiler.
Fig. 3 segars incinerator (1)
Fig. 4 segars incinerator (2)
Each grate of Segues grate furnace not only has the function of reciprocating motion, but also has the function of overturning. The sliding grate pushes the garbage forward and determines the thickness and residence time of the garbage layer, while the swinging grate plays the role of stirring the garbage layer. At present, Shenzhen Energy and Environmental Protection Co., Ltd. has introduced this technology furnace type and carried out independent production.
Grille features:
(1) has high combustion efficiency, and is suitable for garbage combustion with a wide range of calorific value, with a load change range of 70%? 1 10%;
(2) Horizontal garbage conveying, vertical mixing and air blowing move independently of each other, and each part is independently controlled, so the combustion condition of the system is easy to control and adjust. Especially suitable for garbage with low calorific value and high moisture in China;
(3) Each combustion section is supplied with air by different blowers, with strong adjustability. Using horizontal air supply instead of vertical air supply to reduce the air leakage rate of grate joints.
4 Ta-Sn alloy grate furnace
Takuma-SN grate is a stepping reciprocating rocking grate developed by Tan Xiong Co., Ltd., which consists of feeding device, drying section, burning section and burnout section, as shown in Figure 5. Among them, the drying furnace row is designed to be inclined, and the combustion and incinerator rows are arranged horizontally, which can not only effectively transport garbage, but also reduce the overall height of the incinerator. The fixed section and the movable section are alternately arranged along the forward direction of the garbage, and the garbage is pushed forward while being stirred. In order to effectively turn and stir the garbage, there are gaps between the grates, so that the combustible components in the garbage can fully contact with the combustion-supporting air and burn completely.
Fig. 5 TAKUMA-SN incinerator
The design inclination angle of drying furnace row is 8, there is a gap of 650 mm between drying furnace row and burning furnace row, and there is a gap of 500 mm between burning furnace row and burnt grate. Four driving units are adopted: one in the drying stage, two in the combustion stage and one in the burnout stage. By adjusting the speed of each independent driving unit, the thickness of garbage and ash layer can be controlled. Every time the garbage is pushed forward, it will be lifted along the inclination angle of 25 degrees, and it will be repeatedly turned and stirred to make the garbage burn efficiently.
Due to the mature garbage sorting system and high calorific value of garbage in Japan, the characteristics of this incinerator can be fully exerted. According to the actual use of domestic completed projects, the adaptability of low calorific value and high moisture content garbage in China is not very satisfactory, and sometimes the furnace temperature can not reach the design value in winter.
Knot? discuss
Domestic waste incineration power generation conforms to the national sustainable development strategy and is the development direction of solid waste treatment in large and medium-sized cities in China in the future. Among them, the mechanical grate incinerator has perfect technology, large incineration capacity, strong adaptability to garbage and convenient operation and maintenance, which is more suitable for the characteristics of low calorific value and high moisture content of garbage in China, and is the first choice for domestic garbage incineration power generation projects in large and medium-sized cities. Segs grate and SITY—2000 grate technology can realize the good mixing of garbage, and cooperate with the good exhaust mode and high primary air pressure of the furnace to ensure the full combustion of garbage on the grate and maximize the combustion efficiency. And both of them have been introduced into production by domestic companies, and there are many successful cases of operation, which have obvious advantages in both early investment and late operation and maintenance costs.