Municipal Solid Garbage Incineration and Electricity Power Generation System
A Introduction of Incineration System Technology
1. Garbage acceptance
Municipal waste is transported into the factory by a special garbage truck, and then automatically weighed by a truck scale, and then enters the unloading hall of the joint factory (the weighbridge room has the functions of weighing, metering, transmission, printing, and data processing). The garbage bin is a large cement pit with anti-seepage and anti-corrosion, with a filtrate drainage ditch in the middle. There are two garbage pits, which can store garbage disposal capacity for 10-15 days in total. The incinerator is arranged in the middle position. On both sides of the incinerator, garbage pits, garbage unloading platforms and sorting equipment are set up respectively. The garbage unloading platform adopts an outdoor type with gates. The garbage discharge channel is close to the garbage storage pit. The garbage truck dumps garbage into the garbage pit from the outside. At the same time, an air curtain is set at the garbage door to prevent the odor from leaking. The unloading platform is equipped with a dedicated garbage transport truck entrance and exit. The two unloading halls are each equipped with 3 garbage truck unloading doors. There are traffic lights in the lobby and the crane control room to indicate the status of the door opening and closing. The platform has enough area to meet the driving, U-turn and unloading of the largest garbage transfer vehicle without affecting the operations of other vehicles. In order for the garbage truck driver to accurately aim the garbage at the garbage door and unload the garbage into the garbage pool without causing the truck to turn into the garbage bin, there is a white zebra crossing sign in front of each door, and a car stop is set near the door. Set up water hydrants to clean the ground around the garbage unloading platform, maintain the slope of the ground and set up drainage ditches in the direction of the garbage storage pit to collect and discharge sewage, and send it to the collection tank together with the leachate collected in the garbage storage pit. The section of the garbage storage pit is shown in the figure.
Schematic diagram of garbage storage pit (single side)
1.2 Garbage storage
Garbage is easy to ferment when piled up in the garbage bin, and the design should enable the garbage leachate to be discharged smoothly to ensure that the garbage can be received normally in the event of equipment accidents or maintenance. The side wall above the garbage pool is equipped with an incinerator primary fan suction port to make the garbage warehouse in a negative pressure state to prevent the accumulation of odor and methane gas, and extract the odor from the pool as the combustion-supporting air for the incinerator. At the same time, an accident fan is installed on the upper part of the garbage storage pit, and the outlet of the accident fan is directly connected to the chimney through a bypass. In the case of plant shutdown for maintenance or emergency accidents, the gas in the garbage storage pit is discharged through the 15m-high emergency chimney. Atmosphere, to avoid the free overflow of odor. At the same time, it meets the requirements of fire protection, explosion-proof and flame-proof. A reliable garbage leachate collection system is installed in the garbage pool, and the collection and treatment capacity of garbage leachate is designed according to the garbage volume 5%. The bottom of the garbage bin has a slope of not less than 2% in the width direction and at both ends, and the slope faces the garbage door. The side wall of the garbage bin is equipped with a grid door, so that the garbage leachate flows through the grid to the leachate ditch, and then flows into the leachate collection tank. After the garbage leachate in the leachate pool is pumped out by the pump, it is filtered into the buffer tank. Then the pump is sprayed into the incinerator for incineration, which completely solves the difficult problem of garbage leachate treatment. In order to prevent the infestation of mosquitoes and bacteria, a liquid medicine spraying device is set up. The device is composed of a liquid medicine storage tank, a spray pump and a hose. The liquid medicine is regularly sprayed into the garbage pool for sterilization according to seasonal changes.
2. Garbage feeding system
2.1. Brief description
One orange flap grab crane is set above each garbage pool. The crane has a lifting capacity of 5t, and the rail top elevation is 19.5m. The crane is equipped with a weighing device, and has sub-system measurement, pre-alarm, overload protection, anti-sway, anti-tilt, self-positioning, anti-collision and other functions. It can record and can In the crane control room, display statistics and record the various parameters of the feeding. The crane is equipped with manual operating system and automatic operating system switching port. The crane can be used for charging the incinerator and mixing, dumping, transporting, stirring the garbage, etc., and stacking them in the predetermined area in order to ensure the uniform and stable combustion of the components of the garbage into the furnace. The incinerator is equipped with 5 garbage inlets, which are evenly distributed in the incinerator for a week. Each garbage inlet corresponds to a two-stage screw feeder, and the garbage is fed into the furnace in the order of "grab → garbage hopper → first-stage screw feeder → second-stage screw feeder → incinerator".
In view of the harsh environment in the garbage pool, the operation of the grab crane is remotely controlled by the driver in the cab, which is set at an elevation of 18m. The operator can conveniently observe the conditions in the garbage storage pit. The operator is equipped with a display on the upper front and connected with the camera device above the feeding hopper to make it conducive to operation. The crane adopts automatic control, which can reduce the labor of the operator, and it can also be switched to manual control. The grab crane is equipped with a metering device, which transmits the amount of garbage loaded to the control room for recording. The cab and the central control room are arranged separately, and the central control room is located on the 9.5m level, which is convenient for controlling all equipment.
2.2. Selection of main equipment
The grab bucket crane grabs garbage volume, garbage bulk density (0.35/m3), grab volume (2.5m3). There are 10 feeding hoppers in the vertical incinerator, and each 5 feeding hoppers need a grab and servo. In this design, two orange-leaf grab cranes can meet the requirements. The crane specifications are as follows:
φ1200 level one screw feeder: 10 sets
φ1000 two-stage screw feeder: 10 sets
3. Combustion system
3.1. Waste incineration process
See the attached drawings for the waste incineration process.
3.2. Combustion system
3.2.1. Air supply system of incinerator
The incinerator adopts a unique bottom air (primary air) and bottom side air (secondary air) mixed air (tertiary air) system to enable the waste to achieve high-efficiency "3T" technical combustion, that is, time-flue gas at high temperature Lower residence time> 5s, higher than 2s specified by the national standard; temperature-furnace temperature can reach 1000ºC, and the flue gas outlet temperature can be controlled above 850ºC to ensure the full combustion of garbage and effectively prevent the formation of dioxins. ; Turbulent-12 tangential air ducts are added above the combustion layer to generate turbulent flow of the furnace gas, and the stirring flow is uniform. The combustion rate of the vertical waste incinerator can reach more than 95%.
Primary air system: coordinated cone-shaped distributing technology to solve the problem of distributing garbage in the furnace at high temperature. The air required for combustion in the incinerator is fed from the bottom of the furnace and passed through the cone-shaped grate at the bottom of the furnace (the upper edge is regularly arranged with ventilation holes along the circumference) ) Drain to the slag layer to diffuse, on the one hand to cool the slag, on the other hand to increase the air temperature, the temperature of the air entering the combustion chamber from the slag layer is 400-500ºC, so the garbage burns quickly and completely in the furnace.
Unique bottom side air technology: Roots blower is used for air intake, and there are more than 100 holes on the inner wall of the furnace jacket for ventilation, so that the slag can be more fully cooled. The combustion zone of the incinerator is equipped with 3 tangential air inlets to stir the flue gas of the combustion zone to achieve the goal of uniform combustion, more complete combustion and energy saving.
3.2.2. The combustion process in the furnace
The furnace uses a new type of refractory brick technology that does not adhere to the residue. There is no heating surface such as steam or water in the furnace. Therefore, the combustion temperature in the furnace is higher than that of the traditional waste incinerator, and the heat storage capacity is stronger and more stable, which is beneficial to curb dioxins. The formation of English. According to the characteristics of the waste incineration process, when the temperature is between 250 ºC and 650 ºC, "dioxin" will be produced, and 300 ºC is the most dangerous temperature area. The temperature of this system is set to 900 ºC (national The requirement is ≥850ºC), and when the temperature is lower than this temperature, automatic fuel injection will be carried out to increase the temperature of the flue gas outlet. The automatic fuel injection device is in standby state and does not work under normal conditions. The current operating case shows that the gas outlet temperature has reached 936 ºC by relying on garbage self-incineration without adopting any measures to refuel, coal, electricity, etc.
A heat accumulator is installed in the upper part of the furnace combustion zone, which is made of dense-hole heat accumulating bricks, which has large heat storage capacity. When the combustion intensity in the furnace increases and the furnace temperature rises, the heat accumulator absorbs heat; when the combustion intensity in the furnace decreases and the furnace temperature decreases, the heat accumulator releases heat into the flue gas, which can effectively control the temperature of the flue gas. Maintain the temperature above 850°C to ensure the control of dioxin generation and the stable operation of the waste heat boiler.
3.2.3. Flue gas system process
The residence time of the flue gas at high temperature is controlled to be greater than 3s, which effectively reduces the generation of harmful substances such as dioxins. When the incinerator is operating in the rated state, the outlet flue gas temperature is greater than 850°C. Each incinerator corresponds to a flue gas outlet. The flue gas contains a relatively large amount of fly ash. After the flue gas exits the incinerator, it enters two first-stage cyclones tangentially, and the flue gas after the two-stage cyclone dust removal is combined into one Entering the vertical waste heat boiler can effectively prevent pipe blockage in the waste heat boiler and reduce the frequency of purging and maintenance. The particles separated by the first-stage cyclone dust collector are larger, and they are sent back to the screw feeder by pipes and enter the furnace to continue burning. After the waste heat is used, the flue gas temperature is about 250ºC, and it enters the bag filter for further dust removal, so that the content of particulate matter in the flue gas is minimized and meets the national standard emission requirements. The trace fine particles collected by the bag filter generally cannot continue to burn, and the flue gas is discharged from the bag After the dust collector comes out, it enters the washing tower, and the detergent is a specially prepared attapulgite solution. Removal of SO2 and HCl and other acid gases and peculiar smells in the flue gas. The flue gas has completely reached the emission requirements set higher than the national standard at this step. The flue gas at the outlet of the desulfurization tower has a large moisture content, and the flue gas at the outlet enters a high level after passing through the induced draft fan. The arranged pool is washed twice, and the more purified chimney is discharged into the atmosphere. It should be pointed out that the flue gas treatment effect of this project can meet the emission standards of relevant regulations.
3.3, incinerator slag discharge
The incinerator slag is discharged from the annular gap between the bottom of the furnace and the cone-shaped grate with a width of 40-60mm. After the bottom wind flows upward to cool the slag, the slag is hard and brittle when it is discharged. The bottom edge of the furnace is equipped with static jaws, and the bottom edge of the conical grate is equipped with movable jaws. The jaws are made of wear-resistant manganese steel. The larger pieces of slag are squeezed by the jaws, and then fall down. The inverted cone-shaped slag hopper at the bottom of the furnace is discharged from the slag pipe to a slag pit of -5.7m in the factory building. The slag is discharged to a horizontal belt arranged at 0m by a bucket elevator, and then sent to the slag bin. Since the primary air at the bottom of the furnace is fed by the above-mentioned inverted cone-shaped slag hopper, in order to avoid leakage of the primary air, a material seal with a height of about 3m is set in the slag discharge pipe.
3.4. Waste liquid and odor burning
The waste storage pit filtrate returns to the filtrate collection tank. After the garbage leachate in the leachate pool is pumped out by the pump, it is filtered into the buffer tank, and then sprayed into the incinerator with the pump for incineration. The side wall above the garbage pool is equipped with an incinerator primary fan suction port to make the garbage warehouse in a negative pressure state to prevent the accumulation of odor and methane gas, and extract the odor from the pool as the combustion-supporting air for the incinerator. At the same time, an accident fan is installed on the upper part of the garbage storage pit, and the outlet of the accident fan is directly connected to the chimney through a bypass. In the case of a plant shutdown for maintenance or emergency accidents, the gas in the garbage storage pit is discharged into the atmosphere through the 70m high chimney , To avoid the free overflow of odor. At the same time, it meets the requirements of fire protection, explosion-proof and flame-proof.
4. Waste heat boiler system
The waste heat boiler is a vertical boiler specially made for this project. The flue gas flows through the following heating surfaces of the waste heat boiler: superheater, evaporator, and economizer. The tube bundles of the superheater and the economizer are cleaned by an effective dust removal device. In order to avoid low-temperature corrosion of the heating surface pipes, the flue gas temperature at the outlet of the economizer is reduced to about 180°C. The waste heat boiler steams 25 tons per hour, the temperature is 226ºC, the pressure is 2.4mpa, and it can be equipped with 9mw steam turbine and supporting power generation equipment.
It should be noted that the flue gas temperature at the outlet of the incinerator is high, and the flue gas sent to the cyclone dust collector and the waste heat boiler should be lined with refractory bricks. Moreover, the conveying distance is relatively long, and the outside of the flue should be insulated to reduce the temperature drop along the way and improve the thermal efficiency of the waste heat boiler.
The total length of the flue gas passage in the new vertical waste heat boiler used this time is about 9m, and the flue gas flow rate is greater than 10m/s. Therefore, it can be seen that the flue gas can completely pass through the waste heat boiler within 1s and the flue gas will drop to about 180°C. , The inlet temperature of the new waste heat boiler is about 850ºC, and the outlet temperature is about 180ºC. Therefore, it can be calculated that the cooling rate of the waste heat boiler is 680ºC/s, which meets the requirement that the flue gas cooling rate must be 500 ºC/s ~1 000 ºC/s , It can completely destroy the conditions for regenerating dioxin and avoid the synthesis of dioxin.
5. Flue gas purification system
After the flue gas is discharged from the incinerator, dioxin will be significantly synthesized after passing through the cooling section. 200 ºC ~ 500 ºC is the most active temperature range for the reaction, and the maximum synthesis rate appears around 300 ºC. Shortening the residence time of the flue gas in this range can significantly reduce the generation of dioxins.
The average cooling rate of the flue gas is a key inhibitory factor. Generally, the flue gas cooling rate in the domestic waste incinerator is within the range of 100 ºC/s~200 ºC/s, and the dioxin concentration at the outlet of the corresponding furnace is generally 5 ng 1-TEQ/m3. To achieve the standard of less than 0.1 ng1-TEQ/m3, the flue gas cooling rate must be 500 ºC/s ~1000 ºC/s.
6. Flue gas washing process
Waste incinerator flue gas contains harmful gases such as SO2, HCl, and a large amount of smoke. In order to avoid secondary pollution, the flue gas must be purified. This design adopts advanced multi-component toxic waste gas treatment technology (vertical incineration technology) to remove acid gases such as SO2 and HCl in the flue gas. In order to ensure that harmful substances such as dioxins and heavy metals meet the emission standards, the technology includes auxiliary purification measures that add activated carbon attapulgite adsorption.
The basic principle of vertical incineration technology is that the absorbent CaO is soaked and digested by water to generate Ca(OH)2, and then react with acid gases such as SO2 and HCl in the flue gas, as well as the adsorption characteristics of the attapulgite solution to achieve Deacidification purpose.
The flue gas purification tower is a reactor made of 316L stainless steel. Built-in advanced packing. The sieve trays and circular bubble cap trays are washed with a special attapulgite solution and adsorbed to achieve the purpose of flue gas purification.
The hot flue gas and the mixed powder material exchange heat and mass transfer and the following chemical reactions occur:
Ca(OH)2+2HCl=CaCl2+2H2O
Ca(OH)2+SO2=CaSO3+H2O
Ca(OH)2+SO3=CaSO4+H2O
The automatic control of the deacidification process mainly includes: SO2 emission concentration control-adjust the absorbent feed volume according to the SO2 content in the flue gas;
The quicklime and activated carbon attapulgite are respectively sent to the absorbent silo and activated carbon silo of the flue gas purification system by a special vehicle provided by the outsourcing agency, and then sent to the washing tower by quantitative weighing and conveying equipment.
The total lime consumption of this project is 0.038t/h (calculated based on 80% CaO purity). Each system is equipped with a lime silo, which is fed independently, and the volume of the silo is guaranteed for 15 days. The lime digester and the hybrid humidifier are continuous operations, and the process is controlled according to the flue gas temperature and SO2 concentration produced by the boiler.
The maximum total consumption of activated carbon attapulgite in this project is 0.75kg/h. Each system is equipped with an activated carbon silo, which is fed independently. The volume of the silo is guaranteed for 15 days. The addition of activated carbon is a continuous operation, and the amount of activated carbon added is controlled by the frequency conversion screw feeder. The adjustment signal is given according to the boiler load adjustment and the change of the dioxin monitoring data, and the step adjustment is implemented. In order to ensure that the activated carbon is added at a uniform speed, the activated carbon attapulgite receiver is equipped with a special blower to loosen the activated carbon.
7. Bag dust collector
Introducing new bag technology, this design adopts a low-pressure jet pulse bag filter with bypass to collect the smoke and dust in the flue gas. The filter bag is made of acid-proof, water-resistant and corrosion-resistant filter. It has the characteristics of good acid and alkali resistance, strong ash cleaning and regeneration ability, high filtration efficiency, long-lasting operation, low resistance and good hydrophobicity. It has a long service life and can be recycled.
The pulse controller works according to the continuously monitored filter bag resistance, and the pulse controller controls the pulse valve to blow. The compressed air passes through the pulse valves in a very short time sequence and is sprayed into the filter bag through the nozzle on the blowing pipe. The vibration and the reverse airflow generated by the expansion of the filter bag force the dust attached to the outer surface of the filter bag Fall out of the filter bag and fall into the ash bucket.
The compressed air required for dust removal by the bag filter is supplied by its own air compressor station. Because the bag filter has a good trapping effect on small particles, it has a high removal efficiency for the dry salt products and activated carbon powder produced during the desulfurization process. Especially after adopting the anti-acid Leighton filter, it is more suitable for occasions with strict control of acidic substances. The removal rate of SO2 in this flue gas purification system is greater than 90%, the removal rate of HCl is about 95%, and the purification rate of dust More than 99.99% can ensure that the flue gas emission meets the requirements of the national emission standard "Pollution Control Standard for Municipal Solid Waste Incineration".
The flue gas at the outlet of the waste heat boiler must be discharged after a series of treatments. The process is: high temperature flue gas of incinerator → first-stage cyclone dust collector → second-stage gravity sedimentation → waste heat boiler (heat conversion) → washing tower (secondary cyclone dust collector, integrated with the washing tower) → bag filter → flue gas washing Tower → induced draft fan → clean water spray pool → chimney. Dust particles are removed by the dust collector, acidic substances are removed by the neutralization reaction of the scrubber, and the toxic and harmful substances that do not react with the acid are mainly removed by activated carbon adsorption. After the flue gas is purified, it is close to the EU flue gas emission standards. Only slight water vapor can be seen at the chimney discharge port. The flue gas temperature is 45-55°C, which completely subverts the bad impression left by the public from the previous waste incineration.
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