With the rapid development of China's economy in recent years, the level of urbanization rate is also increasing year by year, the collection, elimination and treatment of urban household waste has become increasingly urgent. Compared with the traditional sanitary landfill, domestic waste incineration is more environmentally friendly, efficient, and has significant economic benefits. According to the "13th Five-Year Plan" issued by the Development and Reform Commission for the construction of harmless treatment facilities for urban household waste, the proportion of waste incineration in the treatment of urban household waste in the country will increase from 31% in 2015 to 54% in 2020. Currently, more and more traditional power companies are focusing on domestic waste incineration power generation projects. Similar to traditional thermal power generation projects, the most critical equipment for domestic waste incineration power generation projects is the waste incinerator (hereinafter referred to as the incinerator), this paper compares several mainstream incinerator technology routes at the current stage, and analyzes the advantages and disadvantages of several types of furnaces, and puts forward suggestions for the selection of furnace types.
Different incinerator technology comparisonLife waste incineration technology in China started late, in the western developed countries have decades or even hundreds of years of application and development. Affected by the geographic location of each country, industrial technology characteristics and the impact of the characteristics of the garbage, the current generation of dozens of different waste incineration treatment process. According to "domestic waste incineration treatment engineering technical specifications" (GJJ90-2009) of the relevant requirements and reasonable commercial operation needs, incinerator selection considerations to meet the following requirements:
(1) the number of incineration lines and the size of a single incineration line should be based on the incineration plant's scale of treatment, the furnace's degree of technological maturity and other factors to determine the appropriate set of 2? 4 incineration line.
(2) the selected boiler should be suitable for extra-large class, class I, class II waste incineration plant.
Extra-large class waste incineration plant: the total incineration capacity of the plant 2000t / d and above.
Type I waste incineration plant: the total incineration capacity of the plant 1200?2000t/d (including 1200t/d);
Type II waste incineration plant: the total incineration capacity of the plant 600?1200t/d (including 600t/d).
(3) garbage in the incinerator should be fully combusted, combustion slag thermal scorching rate of ≤ 5%, secondary combustion chamber flue gas temperature in ≥ 850 ℃ under the conditions of the retention time of not less than 2 s. (to avoid dioxin generation)
(4) in the design of the garbage low calorific value and the lower limit of the low calorific value of the range of the design of the incineration capacity of garbage should be guaranteed, and should be adapted to the whole year the garbage characteristics change throughout the year.
(5) The incinerator has overload capacity, the waste feed should be adjustable.
The current mainstream incinerator type can be divided into mechanical grate incinerator, fluidized bed incinerator, rotary incinerator.
1 Mechanical grate incinerator
Mechanical grate belongs to the garbage layer combustion incinerator, the grate block constitutes the furnace bed, relying on the relative movement of the grate so that the garbage is constantly turning, stirring and pushing forward. Primary garbage into the hopper into the grate, in its own gravity and the grate under the action of the driving force, constantly being turned loose, so that it is dry, in order to fully combustion. The grate is divided into drying area, combustion area and burned out area, and the garbage passes through each area on the grate in turn until it is completely burned out and discharged. The combustion air is introduced from the lower or side of the grate and mixed with the garbage to ensure the combustion efficiency. During normal operation, the furnace temperature is maintained at 850°C?950°C. Generally, the heat from combustion can maintain the furnace temperature, and if the calorific value of the garbage is low, it is necessary to spray fuel oil as auxiliary fuel.
(a) the advantages of mechanical grate furnace
(1) a single furnace with a large capacity, the country has 800t / d incinerator operating performance, the maximum of up to 1200t / d.
(2) garbage in the incinerator is evenly distributed, combustion is sufficient. The feeding situation can be adjusted according to the garbage burning condition in the furnace during operation.
(3)-Generally, without adding auxiliary fuel can make the furnace flue gas temperature at 850C under the condition of retention time of not less than 2 s. The flue gas in the dust content is low, reduce the subsequent flue gas purification system load, reduce the operating cost.
(4)The technology is mature, and the running time of the equipment is more than 8000h/a.
(2) the shortcomings of the mechanical grate furnace
(1) because of the grate activity and fixation of key components such as high-temperature alloy steel manufacturing, so the cost of equipment is higher.
(2) incinerator volume is relatively large, the corresponding increase in floor space.
(3) The garbage needs to be incinerated continuously, and it is not suitable to start and stop the furnace frequently.
2 Fluidized bed incinerator
Different from the mechanical grate furnace layer combustion method, fluidized bed incinerator using fluidization technology for waste incineration. Usually set in the furnace quartz sand as a heat carrier, also known as bed material. In the incineration of garbage, the first furnace heat carrier heated to more than 600 ℃, so that it is boiling flow, garbage crushed into the furnace, fluidized garbage and heat carrier fully mixed, garbage evaporation of water, the temperature rises after the start of combustion.
Fluidized bed incinerator due to the presence of heat carrier, combustion stability, good adaptability to changes in the garbage, combustion thermal efficiency. The disadvantage is that there are requirements for the particle size of the garbage into the furnace, due to the fluidized bed incinerator using fluidized combustion, so it is difficult to achieve fluidization of the garbage in the larger specific gravity or diameter of the components, to affect the combustion efficiency. Therefore, it is required to sieve out the components with larger specific gravity or diameter before the garbage is fed into the furnace, so it is necessary to install additional high-power garbage crushing device. In addition, because the garbage is burned directly after entering the furnace, in order to improve the combustion efficiency, it is necessary to control the water content of the garbage entering the furnace, and pre-treat the garbage before entering the furnace to reduce the water content. In addition, the fluidized bed boiler maintenance is relatively more, the annual operating time is relatively short, usually only 6000?8000h.
3 Rotary kiln incinerator
Rotary kiln incinerator is a rotatable boiler lined with refractory coating inside the steel cylinder, which is slightly tilted in the direction of the axis. Garbage is put into the boiler 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 end of the furnace. The garbage is gradually dried and burned in the furnace, and is discharged to the slag removal device after combustion. Sometimes, in addition to the rotating cylinder, it is also equipped with front push grate or rear push grate, the front grate is used for drying and the rear grate is used for burning. However, the combustion is not easy to control, the garbage calorific value of low combustion difficulties. Rotary incinerator is more often used in the higher calorific value of industrial solid waste incineration, in the life of the incineration of garbage less application.
Several typical incinerator characteristics are shown in Table 1.
Currently, China's domestic waste incineration power generation projects mainly rely on the municipal health system of urban garbage centralized recycling of garbage from a single source and classification collection of standardized degree is low, which leads to the furnace into the garbage composition is complex, high moisture content and calorific value of instability. Based on this, the mechanical grate furnace is the most suitable for China's garbage characteristics. It not only has a wide feed opening, no need to sort and crush the garbage, but also has sufficient incineration and stable operation. Flue gas purification system import dust concentration is low, reducing the flue gas purification system $ fly ash treatment costs, is the most suitable for China's municipal waste incineration power generation project incinerator type. Fluidized bed incinerator is similar to the traditional coal-fired fluidized bed boiler, with high combustion efficiency and low investment cost. However, it is necessary to sort and treat the garbage entering the furnace. If combined with the project characteristics, in the coal reserves of rich resources in the region can be considered to use fluidized bed incinerator, in the lower price of coal in the area of the appropriate mixing of coal combustion, can improve the economic efficiency of the system.
The main mechanical grate typeMechanical grate furnace according to its design structure and running direction, can be roughly divided into tilted reverse push type (hereinafter referred to as reverse push type) and tilted downward push type (hereinafter referred to as downward push type) of the two categories, the reverse push-type grate is mainly characterized by the forward direction of the grate and the direction of transport of garbage is the opposite direction of the grate, the grate is in operation in the garbage has a better mixing and loosening effect, to ensure that the primary waste in the grate on the opposite direction. Ensure that the primary garbage in the grate continued to get turned, is conducive to the drying of the garbage, improve the combustion efficiency; push type grate is usually with different ways of movement such as reciprocating movement, sliding, tipping, ladder fall, etc., in order to achieve the full combustion of garbage, improve the combustion efficiency of the purpose. At present, the most widely used at home and abroad, several major mechanical grate furnace characteristics compared to Table 2.
Table 2 ? Comparison of the characteristics of several major mechanical grate furnace
1MARTIN reverse push grate furnace
MARTIN (Martin) incinerator developed by the German MARTIN company, has been widely used worldwide, a number of domestic projects are currently used in Japan Mitsubishi company Martin incinerator, see Figure 1. grate for the one-piece tilting reverse push reciprocating grate, fixed grate and movable grate according to a certain level. Grate and movable grate according to a certain angle of inclination (generally 26 °) sequential arrangement, due to tilt and grate counterpropulsion effect, the bottom layer of garbage upward, the upper layer of the downward, forming a continuous turning, stirring, loosening the garbage after rapid drying and full contact with the air in order to achieve efficient combustion efficiency. The combustion air is fed from the bottom of the furnace and blown out from the gap of the grate block, which has a good cooling effect on the grate.
Figure 1 ?MARTIN (Martin) incinerator
Features of the grate:
(1) Counter-push design for high combustion efficiency. The garbage slides upward along the grate surface so that the dry combustion of the newly entered garbage can be completed in a very short time.
(2) The garbage stays in the furnace for a long time, and the residual combustible materials in the burn-out area can be sent back to the combustion area by the counter-push method, which makes the combustion more complete.
(3) The garbage layer is fully stirred and the combustion state is stable.
2SITY-2000 reverse push grate furnace
SITY-2000 type incinerator developed by the French Alstom company, the overall structure of the grate and the MARTIN grate is similar to the section of the combustion section of the grate and added a section of the grate, so that the entire grate is divided into two sections, respectively, using two sets of hydraulic transmission device drive, see Figure 2. Grate and grate sheet are downward sloping, the downward angle of the grate is 24 °. The movable grate piece and the fixed grate piece are stepped longitudinal interaction configuration. Garbage slides downward by gravity on the grate, and the bottom layer of garbage is pushed to the upper layer by the reverse movement of the movable grate piece to achieve the stirring effect. At present, Chongqing Sanfeng Kavanta Environmental Industry Co., Ltd. has introduced this technology and produced the furnace independently.
Figure 2 ?SITY-2000 incinerator
Features of the grate:
(1)Improved Martin furnace, combustion efficiency is higher, suitable for China's garbage with high moisture and low calorific value;
(2)Good incineration performance, the rate of unburned ash of ash 0.7% ?2%, the content of fly ash in the flue gas < 3g/m3;
(3)Stable combustion state during operation, efficient cooling of the grate air;
(4)Low investment and maintenance costs.
3SEGHERS type multi-stage grate furnace
SEGHERS (SIGHERS) grate furnace is developed by the Belgian company SEGHERS by different grate unit composed of push reciprocating ladder type multi-stage grate furnace. Each standard grate unit has three forms: sliding, tilting and fixed, see Figure 3, Figure 4. grate *** divided into five segments, consisting of four standard grate units and a longer unterminated combustion grate unit, each segment has its own hydraulic regulator, and combustion air can be adjusted according to the combustion of garbage in the grate on the multi-segment. The movement direction of the garbage on the grate is the same as the movement direction of the grate, and the garbage is fully tipped and stirred by the multi-segment fall to improve the combustion efficiency of the boiler.
Figure 3 SEGHERS incinerator (1)
Figure 4 SEGHERS incinerator (2)
Each section of SEGHERS grate furnace has not only the function of reciprocating movement, but also the function of tipping. 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 Environmental Protection Co., Ltd. has introduced this technology and produced the furnace independently.
Features of the grate:
(1)High combustion efficiency, adapted to a wide range of calorific value changes in the combustion of garbage, the load change range of 70%?110%;
(2)Horizontal garbage conveying and vertical churning, blasting independent of each other's movement, independent control of each part of the system combustion conditions are easy to control and adjust. Especially adapted to China's low calorific value, high moisture content of the garbage;
(3) each combustion section by a different blower separate air supply, strong adjustability. Horizontal air supply instead of vertical air supply is used to reduce the air leakage rate of the grate gap.
4TAKUMA-SN Grate Furnace
TAKUMA-SN Grate Furnace is a downward-pushing step-type reciprocating shaking grate developed by TAKUMA Co., Ltd. and is composed of a feeding device, a drying section, a combustion section, and a combustion section grate, which is shown in Fig. 5, wherein the drying grate is designed to be inclined, and the combustion and combustion grates are all horizontally arranged. . Both can effectively convey the garbage, and at the same time reduce the overall height of the incinerator. Along the garbage forward direction alternately set the fixed section and movable section, the garbage is pushed forward while stirring. In order to effectively carry out the garbage turning and stirring, there is a drop between the grates, so that the combustible components in the garbage and the combustion air are in full contact with the complete combustion.
Figure 5 TAKUMA-SN incinerator
The drying grate is designed with a tilt angle of 8°, with a drop of 650 mm between the drying grate and the combustion grate, and a drop of 500 mm between the combustion grate and the ash grate. Four drive units are used: one in the drying stage, two in the combustion stage and one in the burnout stage. By adjusting the speed of each independent drive unit, the thickness of the garbage and ash layer can be controlled. The garbage is lifted upward at an inclination of 25° every time it advances, and the garbage is repeatedly turned over and stirred to make the garbage burn efficiently.
The characteristics of this incinerator can be fully utilized due to Japan's mature waste separation system and the high calorific value of waste. According to the actual use of the completed projects in China, its low calorific value of China, high moisture content of the waste adaptability is not very satisfactory, winter furnace temperature sometimes does not reach the design value.
Conclusion? Discussion
Domestic waste incineration for power generation is in line with the national implementation of sustainable development strategy, is the future direction of development of solid waste treatment in large and medium-sized cities in China. Among them, the mechanical grate incinerator technology is perfect and reliable, large incineration capacity, strong adaptability to garbage, convenient operation and maintenance, more suitable for China's garbage with low calorific value and high moisture content, and it is the first choice for the domestic garbage incineration power generation project in large and medium-sized cities.SEGHERS grate, SITY-2000 type grate technology, can realize good garbage churning, with good grate The SEGHERS grate and SITY-2000 grate technology can realize good stirring of garbage, and with good grate air outlet mode and high primary air pressure, it can ensure the full combustion of garbage on the grate and maximize the combustion efficiency. And both have been introduced by the domestic company production, there are a number of successful operation cases, whether it is the initial investment or later operation and maintenance costs have obvious advantages.