Selection and analysis of flue gas purification in waste incineration power generation

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The normal operation of the flue gas treatment system of waste incineration power plant is very important for the control of secondary pollution, but the specific design of the flue gas treatment syst

Waste incineration power generation is of great significance to realize the recycling, harmlessness and reduction of urban waste. It is also the most effective way to solve the "waste siege" at present. However, the secondary pollution of waste incineration power generation has often become the focus of public attention. In fact, after years of development, the process technology of pollution control of waste incineration power plant has been relatively mature, and there are not too many problems. The key lies in the specific design, project implementation and effective operation management of the project. In order to promote and standardize the construction of domestic waste incineration power plants, the state has successively promulgated some specifications and standards, including technical code for domestic waste incineration treatment engineering (cjj90-2009), evaluation standard for domestic waste incineration plants (cjjt137-2010) and pollution control standard for domestic waste incineration (gb18485-2001), which mainly put forward the requirements of general outline, However, there is not much description of the specific design of the flue gas treatment system of waste incineration power plant, which requires the design unit to summarize and discuss in the actual project design and implementation.
Wet flue gas purification system
The process combination forms adopted by the wet flue gas purification system include: "jet dryer + bag dust collector + primary venturi scrubber + secondary venturi scrubber", "pretreatment scrubber + venturi scrubber + absorber + electric filter", "scrubber + Mixer + flue gas heater". The purification system has the function of purifying particulate pollutants and gas pollutants at the same time, and its purified pollutants removal efficiency is high. It is a widely used flue gas purification system. However, the wet flue gas purification process system is complex, the project investment and operation cost are high, and there is the problem of subsequent wastewater reprocessing. The purified flue gas temperature is very low, not easy to diffuse and easy to form white fog, so the purified flue gas must be heated before discharge.
Current situation of flue gas purification technology
Over the past 30 years, economically developed countries have achieved remarkable results in waste incineration flue gas purification technology through experiments and engineering practice, and formulated emission standards for flue gas pollutants from domestic waste incineration. China's municipal solid waste incineration technology started late. In recent years, some economically developed cities in China have built or are preparing to build domestic waste incineration plants of a certain scale. In order to promote the development of waste incineration technology in China, the State Environmental Protection Administration has promulgated the pollution control standard for domestic waste incineration (gwkb3-2000) on June 1, 2000, and the Ministry of Construction issued the industrial standard technical code for domestic waste incineration treatment engineering (cjj90 2002 j184-2002) on June 3, 2002, which was implemented on September 1, 2002. At present, there are many kinds of incineration flue gas purification processes and equipment in waste incineration treatment plants. There are three commonly used flue gas purification process systems: wet method, semi dry method and dry method. Each purification process has its own characteristics.
Semi dry flue gas purification system
The combined process of semi dry flue gas purification system is: "spray absorption tower + bag filter". Lime absorbers add a certain amount of water to form the lime slurry, which completes the purification of gaseous pollutants in the spray absorption tower in the form of fog. The water in the slurry evaporates at high temperature, and the remaining waste is discharged from the bottom of the spray absorption tower in dry form. Smoke with a large amount of particulate matter is discharged into the bag filter from the spray absorption tower, and the purified flue gas is discharged into the atmosphere through the chimney. The advantage of semi dry flue gas purification system is that the system is simple and there is no need for secondary treatment of reaction products. However, the process system has low removal efficiency of harmful substances, large consumption of absorbent and low utilization rate, and the removal efficiency of purified pollutants is lower than that of wet process.
Dry flue gas purification system
The process combination form adopted by the dry flue gas purification system is: "dry reaction absorption tower + bag filter". The hydrated lime absorbent completes the purification of gaseous pollutants in the dry reaction absorption tower in the form of fog. The flue gas with a large amount of particles is discharged from the dry reaction absorption tower into the bag filter, and the purified flue gas is discharged into the atmosphere through the chimney. The purification efficiency of dry flue gas purification system for pollutants is equivalent to that of wet flue gas purification system. Because the absorbent circulates between the dust collector and the absorption tower, the contact time between the absorbent and flue gas pollutants is prolonged, and the absorbent can be fully utilized. The dry flue gas purification system does not need to carry out secondary treatment of reaction products.
Process introduction of flue gas treatment system
Taking a waste incineration power plant project in the South as an example, the domestic waste incineration capacity of the project is 2250t / D (750t / D) × The 3 line is a large-scale waste incineration plant. The flue gas treatment system adopts semi dry method (rotary spray deacidification + activated carbon injection + cloth bag dedusting) flue gas purification process. According to each waste incineration line, a flue gas purification device is arranged. The main operation process includes: quicklime, hydrated lime, activated carbon loading process, lime slurry manufacturing and transportation process, fly ash collection and transportation process. Transportation and spraying process of activated carbon and hydrated lime, transportation and operation process of ammonia, etc.
Analysis and improvement of design problems of flue gas treatment system
The design of the project places most of the flue gas purification workshop indoors and is divided into reaction tower area, dust collector area, pulping room area, ash reservoir area, fan area, chimney area and ammonia tank area, which can basically meet the functional requirements. When the project entered the construction, commissioning and operation stage, some detailed problems related to the design were found and the design was modified.
Bag filter
The manual regulating valve of bag air inlet is inconvenient to control. Improvement measures: replace with automatic regulating valve.
Individual ash hoppers of the dust collector will accumulate ash. Cause: when the ash unloading valve is switched to manual operation, the silo wall vibrator in the control system cannot be interlocked with the operation of the ash unloading valve, and DCS cannot manually start the vibrator, resulting in no operation of the silo wall ash cleaning device. Improvement measures: the vibrator is interlocked with the ash cleaning of the bin; Manual operation control of silo wall vibrator is added on DCS.
The position of the ash hole of the ash hopper of the dust collector is unreasonable, and the ash can not be cleaned by using the ash hole at the 4m platform. Improvement measures: adjust the position of ash hole to adapt to the platform.
Reaction tower
There is no installation platform at the top of the reaction tower, and the platform cannot be connected with the step plate of the flue gas distributor. There is no step plate around the rotary atomizer, so it is impossible to disassemble the connecting pipes and cables on the atomizer. It is difficult to disassemble the atomizer during operation. Improvement measures: set up a small maintenance platform inside the distributor and connect with the top platform.
The atomizing wheel at the top of the reaction tower protects the water flow switch. When the flow exceeds the maximum working flow or the water contains impurities, the switch will be stuck. If the switch is stuck in the open state and the fault cannot be identified, the fault can be judged only by closing the manual regulating valve on site. However, after closing the regulating valve, it cannot be reopened to the required flow. Improvement measures: add a flow switch with flow display.
The gravity flap valve at the bottom of the reaction tower is not well sealed and the discharge is faulty. Improvement measures: replace the star rotary blanking valve, or consider using double-layer gravity flap valve.
The installation position of some valves of the rotary atomizer at the top of the reaction tower is high, resulting in inconvenient operation and maintenance. Improvement measures: add a small platform that can be used for maintenance.
The size of the hoist used for the maintenance of the reaction tower is too large; The lifting limit height is close to the maintenance support of atomizer + the height of atomizer; The maintenance support roller is too deformed and the support is unstable; The top platform is narrow, and the roller is easy to be damaged when changing direction. Improvement measures: select a smaller lifting weight for the maintenance hoist and reduce the size of the hoist; All supports use movable roller supports. The roller should find the roller of appropriate specification, and select smaller size to increase strength.
Fly ash conveying and ash silo system
The bucket elevator of the fly ash conveying system has no heat tracing system, which is easy to produce condensation and lead to caking and blockage. Improvement measures: install heat tracing system.
The chain manhole of the bucket elevator is high and there is no operation and maintenance platform. Improvement measures: move the position of the manhole to 1.5m of the bucket elevator.
The ash silo is set outdoors and no external maintenance structure has been added for a long time. Rainwater will penetrate into the waterproof layer of the ash silo and conveyor, affect the thermal insulation effect and lead to agglomeration of fly ash. Improvement measures: design and construct the enclosure measures of ash silo.
(4) The setting of high material level gauge of ash silo is unreasonable and can not reflect the full material situation in time. Improvement measures: when it is installed on the top, it should be moved to the side of the blanking port of the top bucket elevator, and the length of the anti rotation level gauge should be lengthened.
Pulping and dry jet system
During the use of the slurry vibrating screen of the pulping system, the discharge connecting hose is easy to vibrate and crack, resulting in leakage. Improvement measures: the connection between the vibrating screen and the slurry storage tank shall be changed into the form of funnel, and the hose shall be inserted into the funnel without hard connection, so as to avoid leakage caused by continuous vibration pulling the hose.
The quicklime silo is blocked at the star valve during the first blanking. The reason may be that the feeding time is long and the materials are squeezed into blocks by moisture. Improvement measures: increase the ash poke hole of quicklime bin and choose star valve with access door.
The pulping workshop has no perfect sewage discharge facilities, and the lime slurry slag pool has no ponding recovery equipment, resulting in nowhere to go for sewage and waste slurry, polluting the workshop environment. Improvement measures: the cleaning drainage ditch shall be set in the pulping room, the sewage shall be discharged in time, and the slag pool shall be cleaned regularly.
The position of the low material level meter of hydrated lime is too low. When the material level is low, only 2.2m3 is left, and the net weight is about 2T. In addition, the material distribution at the bottom of the bin is uneven. When the low material level alarm is given, there is basically no material. Improvement measures: add a low material level at about 10m3, and keep the original low material level as low material level.
When the amount of hydrated lime entering the site exceeds the capacity, the full warehouse information can not be fed back in time for the reagent loading personnel. Improvement measures: add full warehouse on-site alarm reminder.
Activated carbon, hydrated lime and lime slurry transmission pipelines are not equipped with segmented flanges. If the pipeline is blocked, it cannot be cleaned. Improvement measures: add segmented flanges at the spray outlet, spray and pipe elbow, which are convenient for operation.
There is no maintenance platform and access door at the flue of dry powder nozzle. Improvement measures: add maintenance platform and access door.
The exhaust pipe at the outlet of the exhaust fan of the lime slurry slurry tank is directly evacuated, which may cause dust pollution. Improvement measures for connecting the exhaust pipe to the workshop.
The slurry outlet of the slurry storage tank is not provided with a manual valve, which is inconvenient for the maintenance of the control valve. Improvement measures: increase the switching interlock of slurry pump in the program; A manual valve is added in front of the electric valve.
The hose connection joint of compressed air pipe on the top of activated carbon and quicklime silo is damaged. Improvement measures: pay attention to the pressure grade when purchasing the steel pipe, steel pipe flange and joint.
The densitometer of pulping tank often gives false alarm, which is very low 1.03 ~ 1.05 / very high 1.5 +. Cause: the densitometer is installed in the cylinder diaphragm of the pulping tank, where the slurry fluidity is poor, the lime on the probe rod is scaling, and the range selection of the densitometer is too wide. Improvement measures: clean the densitometer regularly, and consider narrowing the measuring range (1 ~ 1.5kg / m3) to reduce the error during replacement and selection.
SNCR system
Ammonia leakage during ammonia feeding. The ammonia feeding port is too high, and the ammonia in the feeding pipe cannot be completely removed. Improvement measures: reduce the installation height of the feed inlet of ammonia pump, and set a special feed joint at the feed inlet.
Other issues
There is no outlet pipe at the safety exhaust port of flue gas compressed air storage tank, which is easy to cause personal injury during startup. Improvement measures: the air storage tank shall avoid the personnel passage, and a safety valve shall be set on the top of the air outlet pipe.
On site ash silo and lime silo are not equipped with fluidizing air device, so it is impossible to effectively remove ash in case of ash discharge failure. Improvement measures: add fluidization device.
Concluding remarks
There are many forms of flue gas purification process, which are mainly divided into wet method, semi dry method and dry method, and each has its advantages and disadvantages. Due to the high purification efficiency of pollutants and high utilization rate of absorbent of the dry flue gas purification system, there is no need for secondary treatment of reaction products, so the dry flue gas purification process system is preferred in the design. The emission concentration of flue gas pollutants purified by the dry flue gas purification process system meets the relevant emission standards.
(some articles on this website are collected from the Internet, such as infringement contact deletion)