System and method for treating high-water content domestic waste by recirculating high-temperature flue gas

Abstract

The present invention discloses a system and method for treating domestic garbage with high moisture content by recycling high-temperature flue gas, wherein the treatment system includes a combustion furnace, a flue gas extraction device, a flue gas purification device, a garbage drying device and an air distribution device; a two-stage economizer is arranged in the tail flue of the combustion furnace; the flue gas extraction device includes a flue gas extraction port, a circulating fan and a flue gas duct; the flue gas extraction port is located in the middle of the two-stage economizer; the garbage drying device includes a horizontal flue gas chamber and a vertical drying chamber, and the flue gas duct is connected to the horizontal flue gas chamber and the vertical drying chamber through a control valve; the air distribution device includes a horizontal flue gas chamber air distribution device and a vertical drying chamber flue gas air distribution device. The treatment system and method of the present invention are used to dry garbage entering the furnace with high moisture content to improve the calorific value of the garbage in the incineration stage, improve the combustion condition, and increase the furnace temperature and burnout rate, which is of great significance for the incineration of garbage with high moisture content and garbage in cold areas in the north and rainy areas.

Description

Technical Field

[0001] The invention relates to a system and method for treating domestic garbage with high moisture content by recycling high-temperature flue gas, belonging to the technical field of garbage drying and incineration treatment. Background Art

[0002] Due to my country's unique eating habits and waste recycling methods, the calorific value of garbage entering the incinerator is low. Most of the garbage entering the incinerator is kitchen waste and other low-calorific value waste, and its water content is sometimes very high, so the calorific value of the garbage is low. In order to maintain normal combustion of the garbage entering the furnace, other high-calorific value auxiliary fuels such as coal and fuel oil have to be mixed in. For garbage incineration in northern regions in winter, the situation is even worse. Rainy and snowy weather in winter will increase the moisture content in the garbage, which will be mixed in the garbage in the form of ice cubes, and some northern regions still use coal for heating, which will cause a large amount of slag and ash with no calorific value to be mixed in the domestic garbage entering the furnace, which can easily cause equipment failure.

[0003] The specific impacts of northern winter climate on waste incineration include:

[0004] (1) Due to freezing, the frozen water cannot be removed during the filter pressing process, resulting in a longer drying time in the drying section after the garbage enters the furnace, increasing the length of the drying section, delaying the grate combustion point, shortening the normal combustion and burnout time, and causing incomplete combustion and reduced thermal efficiency. Ice cubes are mixed in the garbage, and after melting, the burning flame in the grate will be extinguished, posing a huge risk to the safe operation of the boiler. Incomplete combustion will also aggravate flue gas pollution.

[0005] (2) In the north, the temperature is below zero in winter. The moisture in the garbage increases the water vapor partial pressure in the flue gas, which increases the flue gas dew point temperature and corrodes the tail heating surface. In order to reduce the corrosion rate, the air used for combustion in the incinerator needs to be preheated with high-quality steam, which reduces the energy utilization efficiency of the waste power plant. For example, for a 500t / d incinerator, the primary air volume is about 6600Nm 3 / h. If the primary air is heated from -15℃ to 20℃, about 2.5-3.5t of steam will be consumed per hour, accounting for one tenth of the total steam volume, and the thermal efficiency loss of the whole plant is obvious; the lower temperature will also lead to a decrease in the fermentation rate of garbage, and it is necessary to pass steam into the fermentation tank, which will further reduce the power generation capacity of the plant.

[0006] (3) The water and ice in garbage affect ignition. The large amount of water vaporizes and absorbs heat, which lowers the temperature of the combustion chamber and increases the ignition heat. As the water content increases, the ignition process is delayed and the combustion rate of volatiles is significantly reduced, that is, the water content affects the precipitation of volatiles in garbage. During garbage incineration, the water content also affects the total amount of dioxins and toxic equivalents. Water activates the active sites of fly ash, promotes the synthesis of dioxins as a whole, and increases the toxic equivalents of dioxin emissions.

[0007] If the garbage can be dried before incineration to reduce the moisture content, it can not only reduce the amount of flue gas generated per unit of garbage, but also reduce the flue gas dew point and exhaust loss, improve the combustion conditions, and increase the furnace temperature accordingly; more water-cooled wall heating surfaces can be arranged to save auxiliary fuel and increase the garbage burnout rate. Therefore, in order to improve the combustion conditions, so that the garbage can maintain self-combustion or reduce the coal blending ratio during incineration, it is necessary to dry it and pre-treat it to improve the energy quality. At present, there are many methods for drying domestic garbage before entering the furnace, including adding heaters to increase the temperature of the garbage unloading hall, introducing low-temperature and low-pressure steam to heat the garbage pool, setting up heating air to heat the garbage in the garbage pool, and increasing the number of days for garbage fermentation, but the effect is not ideal. The garbage combustion still has problems such as low heat generation and the inability of the waste heat boiler to produce sufficient steam. When using the technology of increasing the primary air temperature to treat high-water content garbage in the north, whether it is the technical solution of increasing the heating area of ​​the air preheater or adding an air preheater, the investment cost is high and the system changes are large.

[0008] In the existing published patent documents:

[0009] (1) For example, the patent document with publication number CN202993220U, entitled A high-temperature flue gas circulation system for a mechanical grate waste incinerator, recycles the flue gas for use in the grate drying section. The dust in the flue gas will wear the grate furnace. The extracted flue gas temperature is greater than 550°C, and the circulating fan and pipeline must be made of stainless steel, which has a high investment cost. In addition, this method only introduces high-temperature flue gas into the drying section, and does not introduce hot air used in conventional incinerators, which is not suitable for the transformation of existing incinerators.

[0010] (2) Another example is the patent document entitled "A device for recycling low-level waste heat energy from flue gas recirculation in a garbage incinerator" with the authorization publication number CN201396766Y. The device recycles flue gas for air supply in the grate drying section and the grate burnout section. The system structure is complex, and the flue gas recirculation for the burnout section grate does not help reduce the heat loss rate of the incinerator. The extracted flue gas temperature is relatively low, and has limited effect on garbage drying.

[0011] (3) Another example is the patent document with application publication number CN104141958A, entitled Mechanical Waste Incineration Boiler Flue Gas Waste Heat Recycling System and Automated Control Method. The system recycles flue gas for secondary air and grate drying sections. The flue gas temperature of the system is relatively low, and the flue gas volume during the drying process is relatively large, which affects the stability of the furnace. The low-temperature flue gas contains high humidity. If the flue is not well insulated or has air leakage, the circulating flue is prone to condensation. The flue gas contains a high content of acidic gases, which is prone to corroding the pipes and circulating fans. In addition, the circulating flue runs from the tail to the bottom of the incinerator. The flue is too long, with high resistance, making it more prone to corrosion.

[0012] In summary, due to the high furnace temperature, the flue gas drawn out of the furnace has a greater impact on the evaporation amount of the evaporation surface, and the high temperature places high demands on the pipeline and circulating fan, resulting in a high equipment damage rate; the tail flue gas temperature is low, the required flue gas volume is large, and the fan power consumption is high. If a large amount of flue gas after drying enters the furnace again, it will seriously affect the stability of the furnace operation, and the uniformity of garbage drying cannot be guaranteed. Summary of the invention

[0013] Purpose of the invention: In order to solve the problem of high moisture content and low calorific value of domestic waste, the present invention provides a system and method for treating domestic waste with high moisture content by recycling high-temperature flue gas with low manufacturing or modification cost and low energy consumption.

[0014] Technical solution:

[0015] A system for treating domestic garbage with high moisture content by recycling high-temperature flue gas, comprising a combustion furnace, a flue gas extraction device, a flue gas purification device, a garbage drying device and an air distribution device; a two-stage economizer is arranged in the tail flue of the combustion furnace; the flue gas extraction device comprises a flue gas extraction port, a circulating fan and a flue gas duct; characterized in that: the flue gas extraction port is located in the middle of the two-stage economizer; the garbage drying device comprises a horizontal flue gas chamber and a vertical drying chamber, and the flue gas duct is connected to the horizontal flue gas chamber and the vertical drying chamber respectively through a control valve; the air distribution device comprises a horizontal flue gas chamber air distribution device and a vertical drying chamber smoke air distribution device, the horizontal flue gas chamber air distribution device is arranged in the horizontal flue gas chamber, and the vertical drying chamber smoke air distribution device is arranged in the vertical drying chamber; a hot air drying wind inlet is also arranged in the vertical drying chamber.

[0016] The treatment system and method of the present invention extracts and removes the high-temperature flue gas between the two-stage economizers and sends it to the horizontal flue gas plenum at the bottom of the garbage feeding port and the vertical drying plenum at the bottom of the grate drying section, and combines it with the original hot air drying wind of the incinerator to dry the high-moisture content entering the furnace and improve the calorific value of the garbage entering the incineration section. The high-temperature flue gas drying wind flow direction of the vertical drying plenum is perpendicular to the grate drying section, and the high-temperature flue gas drying wind flow direction of the horizontal flue gas plenum is parallel to the grate drying section, so that the flue gas dries the wet garbage from two directions to avoid the phenomenon of uneven garbage drying.

[0017] High-temperature flue gas is extracted from the middle of the two-stage economizer. Electric valves are installed at the inlet and outlet of the flue duct. When the moisture content of the garbage is greater than a certain threshold, the electric valves are opened through the automatic control system, and the high-temperature flue gas is extracted and sent into the vertical drying air chamber and the horizontal flue gas air chamber of the waste incinerator grate furnace; the circulation fan adopts frequency conversion regulation, and the amount of extracted flue gas can be adjusted according to the moisture content of the garbage; a cyclone separator is arranged in front of the circulation fan, a discharge valve is arranged at the lower end of the separator, and a pneumatic conveying device is arranged below the discharge valve to separate the fly ash in the high-temperature flue gas and send the fly ash into the ash bunker; in order to achieve more efficient drying, this system adopts an automatic measurement and control system. A flue gas flow meter and a thermometer are installed on the flue duct, etc., for flue gas flow measurement, flue gas temperature measurement, circulation fan speed regulation, regulating air plate angle regulation, flue duct electric valve switching, etc.

[0018] Specifically, the present invention extracts flue gas (about 300 - 400 °C) from the two-stage economizer of the waste heat boiler, and after dust removal by the cyclone separator, it is transported to the vertical drying air chamber and the horizontal flue gas air chamber through the high-temperature fan; the vertical drying air chamber is connected to the high-temperature flue gas drying air and the original hot air drying air of the incinerator; the horizontal flue gas air chamber is connected to the high-temperature flue gas drying air. The horizontal flue gas air chamber is located at the bottom of the garbage feeding port, is as wide as the furnace chamber, and the flowing direction of the flue gas at the outlet of the air distribution holes is parallel to the drying section of the grate.

[0019] To ensure that the moisture content of the garbage entering the incineration section of the grate furnace is stable within a certain range, 3 to 6 regulating air plates are arranged in the vertical drying air chamber. The size of the regulating air plates fits the wall surface of the drying air chamber. The size and deflection angle of the air distribution holes in the horizontal flue gas air chamber are adjustable; according to the change of the moisture content of the garbage, the deflection angle and the size of the air distribution holes are changed, so as to change the distribution of the hot flue gas in the drying section of the grate, and try to ensure that the change of the moisture content of the garbage entering the incineration section is not large, thereby improving the combustion stability of the furnace chamber.

[0020] According to the different moisture content W of the garbage entering the furnace, there are the following three working modes for the air supply in the drying section of the grate for reference:

[0021] Working mode 1: When W < 50%, turn on the hot air drying air in the vertical drying air chamber, and turn off the high-temperature flue gas in the horizontal flue gas air chamber and the high-temperature flue gas drying air in the vertical drying air chamber.

[0022] Working mode 2: When 50% < W < 58%, turn on the hot air drying air and the high-temperature flue gas drying air in the vertical drying air chamber, and turn off the high-temperature flue gas drying air in the horizontal flue gas air chamber.

[0023] Working mode 3: When 58% < W, turn on all the hot air drying air in the vertical drying air chamber, the high-temperature flue gas drying air in the vertical drying air chamber, and the high-temperature flue gas drying air in the horizontal flue gas air chamber.

[0024] The present invention utilizes medium-high temperature flue gas recycling to treat domestic waste with high moisture content. The high-temperature flue gas between the two-stage economizer is extracted to dry the domestic waste with high moisture content. Compared with the waste drying outside the furnace, the system is relatively simple and does not require additional equipment. Compared with increasing the temperature of the waste unloading hall / increasing the fermentation time, the method can effectively control the moisture content of the waste entering the incineration section of the incinerator. Compared with increasing the primary air temperature, the method does not require additional heating surfaces of the air preheater. The system requires low investment and is flexible in operation. The circulating flue gas can be turned on when the moisture content is high and turned off when the moisture content is low. The response time is short and the speed is fast.

[0025] Beneficial effects:

[0026] (1) The sampling port for extracting flue gas is placed between the two-stage economizer, mainly to balance the amount of extracted flue gas, the flue gas temperature and the impact on the operation of the incinerator. The temperature of the flue gas extracted at this position is reasonable, between 300~400℃, and has the advantages of moderate flow and moderate temperature; relatively speaking, the furnace flue gas temperature is high, which requires high equipment, while the tail flue gas temperature is low and the amount of extracted flue gas is large. Therefore, this patent places the flue gas extraction port between the two-stage economizer. Extracting flue gas. Compared with extracting tail flue gas, this system requires a small amount of dry flue gas, a small fan power, a small flue gas humidity, no low-temperature corrosion, and a fast drying rate; compared with extracting higher temperature flue gas, the circulating flue gas duct and fan of this system do not need to be made of stainless steel, but carbon steel can be used, with low investment cost.

[0027] (2) A cyclone separator is added to the circulating flue to reduce the wear of the circulating flue gas on the grate furnace and circulating fan, thereby improving the reliability and economy of the system; a combination of vertical drying and horizontal drying is adopted to make the garbage drying process more reasonable, avoiding the uneven phenomenon caused by unidirectional flue gas drying, and providing flexible adjustment, which can better ensure that the water content of the garbage entering the grate incineration section is reduced to a certain range.

[0028] (3) Using flue gas recirculation to treat high-water content domestic waste is beneficial to improving pollutant emissions in the high-temperature area of ​​the incinerator and reducing NO in the combustion products. x content, achieving low NO x Combustion; The water vapor generated during the drying process enters the furnace and undergoes a gasification reaction to generate water gas, which improves the incineration efficiency while reducing the amount of fly ash generated.

[0029] (4) This system is suitable for the modification of existing waste incineration plants to incinerate high-moisture waste. There is no need to change the grate structure of the waste incinerator or increase the length of the grate drying section. The drying system can switch working modes according to the moisture content of the waste, which is more in line with actual production needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a system diagram of the present invention;

[0031] Figure 2 This is the structural diagram of the horizontal flue gas chamber;

[0032] Figure 3 This is the structural diagram of the vertical drying air chamber;

[0033] In the attached figure: 1-evaporator; 2-superheater; 3-economizer; 4-cyclone separator; 5-circulating fan; 6-vertical drying air chamber; 7-combustion air chamber; 8-burnout air chamber; 9-grate drying section; 10-grate combustion section; 11-grate burnout section; 12-ash room; 13-pusher; 14-horizontal flue gas air chamber; 15-furnace; 16-lower hopper; 3-1 flue gas extraction port; 6-1 hot air valve; 6-2 high-temperature flue gas valve; 6-3 regulating air plate; 14-1 air distribution hole; 14-2 high-temperature flue gas valve. DETAILED DESCRIPTION

[0034] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0035] The present invention discloses a system and method for treating domestic waste with high water content by recycling high-temperature flue gas. Figure 1 ,

[0036] The treatment system includes a flue gas extraction device, a flue gas purification device, a garbage drying device and an air distribution device, etc.; the flue gas extraction device includes a flue gas extraction port 3-1 located between the two-stage economizer, a circulating fan 5 and a flue gas duct, etc.; the flue gas purification device is a high-temperature cyclone dust collector 4; the garbage drying device includes a horizontal flue gas plenum 14 and a vertical drying plenum 6; the air distribution device includes a horizontal flue gas plenum air distribution hole 14-1 and a vertical drying plenum air plate 6-3.

[0037] Firstly, the high-temperature flue gas between the two-stage economizers of economizer 3 is extracted into the insulation pipe by the high-temperature circulation fan 5 through the flue gas extraction port 3-1. Before the flue gas is sent into the vertical drying air chamber 6 and the horizontal flue gas air chamber 14, the fly ash carried by the flue gas is removed by the cyclone separator 4, and the fly ash directly enters the ash room 12; the high-temperature flue gas drying wind and the hot air drying wind are adjusted in direction by the regulating wind plate 6-3 in the vertical drying air chamber 6; the garbage entering the furnace enters the pusher 13 through the lower hopper 16 and is subjected to convection drying by the high-temperature flue gas drying wind in the lateral horizontal flue gas air chamber 14.

[0038] Specifically, for garbage with different moisture contents W, the grate drying section has the following three working modes for reference:

[0039] Working mode 1: When W < 50%, the hot air drying air in the vertical drying air chamber 6 is turned on, and the high-temperature flue gas drying air in the horizontal flue gas air chamber 14 and the high-temperature flue gas drying air in the vertical drying air chamber 6 are turned off. The high-temperature flue gas valves 6-2 and 14-2 are closed, and the hot air valve 6-1 is opened. The original hot air drying air in the incinerator is sent into the drying air chamber 6. At this time, the moisture content of the garbage entering the furnace is relatively low, and the moisture content requirement of the incineration section can be met under the radiation in the furnace and the drying of the hot air.

[0040] Working mode 2: When 50% < W < 58%, the hot air drying air and the high-temperature flue gas drying air in the vertical drying air chamber 6 are turned on, and the horizontal flue gas air chamber 14 is turned off. Since the water content further increases, the drying demand cannot be met only by the hot air drying air. At this time, in order to reduce the moisture content, on the basis of working mode 1, the high-temperature flue gas drying air in the vertical drying air chamber 6 is turned on. First, the high-temperature flue gas in the middle of the two-stage economizer of the economizer 3 is extracted by the circulating fan 5 through the flue gas extraction port 3-1 into the heat preservation pipeline. The high-temperature flue gas valve 14-2 is closed, and the high-temperature flue gas valve 6-2 and the hot air valve 6-1 are opened. The hot air drying air and the high-temperature flue gas drying air are sent into the drying air chamber 6. The circulating air volume of the high-temperature flue gas can be adjusted accordingly by adjusting the rotation speed of the circulating fan 5.

[0041] Working mode 3: When 58% < W, the hot air drying air and the high-temperature flue gas drying air in the vertical drying air chamber 6 are turned on, and the horizontal flue gas air chamber 14 is turned on. At this time, the moisture content of the garbage entering the furnace has exceeded the drying capacity of the vertical drying air chamber 6. To meet the drying demand, the horizontal flue gas air chamber 14 is turned on at this time for horizontal drying, which improves the drying capacity and the drying uniformity. First, the high-temperature flue gas in the middle of the two-stage economizer of the economizer 3 is extracted by the circulating fan 5 through the flue gas extraction port 3-1 into the heat preservation pipeline. The high-temperature flue gas valves 14-2, 6-2, and the hot air valve 6-1 are all opened. The hot air drying air and the high-temperature flue gas drying air are sent into the drying air chamber 6, and the high-temperature flue gas drying air is sent into the horizontal flue gas air chamber 14. The amount of high-temperature flue gas entering the vertical drying air chamber 6 and the horizontal flue gas air chamber 14 can be adjusted accordingly by adjusting the rotation speed of the circulating fan 5, the opening degree of the high-temperature flue gas valve 6-2, and the opening degree of the high-temperature flue gas valve 14-2.

[0042] The above elaboration of the specific implementation manner of the present invention is for the convenience of those skilled in the relevant art to understand and apply the present invention, and does not limit the protection scope of the present invention; based on the principles and technical solutions described in the present invention, the modifications and improvements made by those skilled in the art without creative labor should be within the protection scope of the present invention.

Claims

1. A method for treating high-water content domestic waste by recycling high-temperature flue gas, characterized in that: The system for treating high-moisture domestic waste by using high-temperature flue gas recirculation is used to treat high-moisture domestic waste; the system for treating high-moisture domestic waste by using high-temperature flue gas recirculation includes a combustion furnace, a flue gas extraction device, a flue gas purification device, a waste drying device and a gas distribution device; two-stage economizers are arranged in the tail flue of the combustion furnace; the flue gas extraction device includes a flue gas extraction port, a circulation fan and a flue gas pipeline; it is characterized in that: the flue gas extraction port is located in the middle of the two-stage economizers; the waste drying device includes a horizontal flue gas air chamber and a vertical drying air chamber, and the flue gas pipeline is respectively communicated with the horizontal flue gas air chamber and the vertical drying air chamber through control valves; the gas distribution device includes a horizontal flue gas air chamber gas distribution device and a vertical drying air chamber flue gas distribution device, the horizontal flue gas air chamber gas distribution device is arranged in the horizontal flue gas air chamber, and the vertical drying air chamber flue gas distribution device is arranged in the vertical drying air chamber; a hot air drying air inlet is further arranged in the vertical drying air chamber; the temperature of the flue gas extracted by the flue gas extraction port is 300-400°C; the treatment method is as follows: According to the moisture content W of the waste entering the furnace, control the waste drying device to dry according to the following ventilation modes: Mode 1: When W < 50%, turn on the hot air drying air of the vertical drying air chamber, and turn off the high-temperature flue gas drying air of the horizontal flue gas air chamber and the high-temperature flue gas drying air of the vertical drying air chamber; Mode 2: When 50% < W < 58%, turn on the hot air drying air of the vertical drying air chamber and the high-temperature flue gas drying air of the vertical drying air chamber, and turn off the high-temperature flue gas drying air of the horizontal flue gas air chamber; Mode 3: When W > 58%, turn on the hot air drying air of the vertical drying air chamber, the high-temperature flue gas drying air of the vertical drying air chamber, and the high-temperature flue gas drying air of the horizontal flue gas air chamber.

2. The method according to claim 1, characterized in that: The flue gas purification device is a high-temperature cyclone dust collector.

3. The method according to claim 1, characterized in that: The horizontal flue gas air chamber gas distribution device is a gas distribution hole located on the gas distribution plate.

4. The method according to claim 3, characterized in that: The size and deflection angle of the gas distribution hole are adjustable.

5. The method according to claim 1, characterized in that: The vertical drying air chamber flue gas distribution device is 3-6 adjustable air plates vertically installed in the vertical drying air chamber, and the deflection angle of the adjustable air plates in the vertical direction is adjustable.

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