1. Section tasks
Dust-laden gas enters the bag dust collector. The dust with large particles and large specific gravity settles down due to the action of gravity and falls into the ash hopper. The gas containing finer dust passes through the filter bag under the action of the deflector and dust is retained. In order to achieve the purpose of purifying the flue gas, the dust concentration of the purified flue gas is ≤ 50mg/m3. Meet environmental requirements.
2. How it works
The gas purification method of the low-pressure pulse bag filter is an external filter type. Dust-laden gas enters the filtration room of each unit through the diversion pipe. Due to the design, the bottom of the filter bag is sufficient and reasonable air flow passes through the proper distance from the vertical distance from the inlet port of the air inlet. Flow and natural flow distribution, to achieve uniform air distribution throughout the filter room, dust particles in dusty gas directly fall into the ash bucket after separation by natural sedimentation, and the rest of the dust under the guidance of the diversion system, with the airflow into the middle box filter area , adsorbed on the outer surface of the filter bag. The filtered clean gas passes through the upper case and the exhaust pipe through the filter bag.
The filter bag adopts compressed air for cleaning and cleaning, and the cleaning mechanism consists of an air bag, a blow pipe and an electromagnetic pulse control valve. A spray tube is installed on the top of the outlet of each row of filter bags in the filter chamber. The injection tube is provided on the lower side of the injection tube at the center of the filter bag. Each pulse tube is provided with a pulse valve and communicates with compressed air. During cleaning, the solenoid valve opens the pulse valve, and the compressed air is sprayed by the cleaning control device (differential pressure or timing, manual control) according to the set program to open the electromagnetic pulse injection. The compressed gas passes each pulse in a very short time and in order. The valve induces air several times the amount of air injected into the filter bag through the nozzle on the blowing pipe to form an air wave. The filter bag generates rapid expansion and impact vibration from the mouth of the bag to the bottom, resulting in a strong cleaning action, shaking the filter Dust on the bag.
3. Process indicators
Soot blowing gas pressure ≥0.3mpa
Smoke outlet dust concentration ≤50mg/m3
Cycle time 60～120min
Flue gas temperature 120～160°C
Running resistance ≤1200pa
Motor current
Smoke humidity
4. System equipment
(1) LCMD-type off-line dedusting and low-pressure pulse bag dust collector body structure frame and box body – structural frame is used to support the dust collector body, ash hopper and ash transport equipment, etc.; the box body includes the upper box body, the middle box body and Ash bucket and so on.
(2) filter bags, cages and flower plates – filter bags and cages constitute the filter system of the dust collector; flower plates are used to support the filter bag assembly and separate the filter chamber (dust containing section) and the clean room, and As a filter platform for the filter bag, the filter bag assembly is loaded from the flower plate.
a. Filter bag
For the entire boiler bag filter, the filter bag is the core component. The quality of the filter material directly affects the dust collection efficiency of the dust collector. The life of the filter bag directly affects the operating cost of the dust collector.
Selection of imported German BWF high-quality Laideng needle felt: PPS/PPS551CS17, polyphenylene sulfide, waterproof and oil-repellent treatment, temperature 190 °C Instant 200 °C, unit weight ≥ 550g/m2.
The filter material is a surface filter type filter material, which completely cleans the dust and reduces the possibility that the dust will be hardened after forming a cloth powder layer on the surface of the filter bag.
b.
The bag cage adopts a round structure. The longitudinal reinforcement and the anti-spread ring of the bag cage are evenly distributed and have sufficient strength and rigidity to prevent damage and deformation (longitudinal bar diameter ≥ φ4, 12 bars, reinforced counter-support ring φ5, spacing 200 , φ158 × 6000), installed at the top of the “η”-shaped cold stamping short tube, used to ensure the vertical bag cage and protect the safety of the filter bag mouth when blowing.
The cage material is made of 20# carbon steel. The cage wire production line is molded once to ensure the straightness and distortion of the cage. The filter bag frame is smooth and burr-free after touch-welding, and there is enough strength to prevent welding and no welding. Welds and leaks.
The bag cage adopts organic spraying technology, which has strong coating, wear-resistance and corrosion resistance, avoids corrosion of the cage surface and filter bag adhesion after the dust collector work for a period of time, ensures smooth bag changing, and at the same time reduces the damage to the bag during the bag replacement process. .
The electromagnetic pulse valve is the key equipment of the cleaning system, and its selection is related to the cost of the dust collector and the cleaning effect. The electromagnetic pulse valve is an imported electromagnetic pulse valve with injection pressure <0.3Mpa, DC24V, φ3″. The diaphragm is durable and its service life is more than 1 million times. It meets the requirements for efficient operation of the pulsed electromagnetic valve and greatly reduces the maintenance workload. .
c. Bypass valve, off-line valve
The bypass device retains a certain distance from the high temperature zone to ensure good operation under long-term high temperature conditions. Each set of dust collector is equipped with multiple sets of bypass valves to meet the passage of flue gas when the bypass protection function of the dust collector is started.
The off-line valve (or the bypass channel of the precipitator is arranged in the middle of the air inlet and outlet ducts, which is built-in), the bypass valve and the off-line valve adopt the pneumatic quick-opening gland type, O-type bidirectional sealing groove, and the sealing ring adopts acid and alkali resistance. High temperature resistant fluororubber, general temperature resistance up to 200 degrees, service life of at least 2 years.
The two valves adopt simple and reliable linear motion, avoiding the trouble caused by high rotation failure rate; the valve action is set to guide the slide rails and the drive valve is equipped with one per room, so that the dust remover has off-line cleaning and off-line maintenance functions.
Poppet and bypass valves are thin plate constructions. The two valves are controlled by the cylinder. The main components of the valve cylinder are imported products. The voltage level of the two-position five-way solenoid valve is 24v. The entire valve structure is simple, reliable, fast opening and closing speed, can achieve zero leakage when closed, through the PLC can control one or more simultaneous work, close one or more compartments for off-line cleaning, off-line maintenance. When the poppet valve and the manual switching valve are closed, it can ensure that the chamber is completely off-line, and the single-warehouse inspection under the working condition of the dust collector is realized (the manual switching valve can also be used for adjusting the air intake amount), and the limiting device on the poppet valve is realized. Allows operators to detect their operating conditions in a timely manner.
5. Operating points
Bag filter operation can be divided into trial operation and daily operation. First of all, during the test run, a single part of the system must be inspected, then adapted for operation, and a partial performance test must be performed. In the daily operation, the necessary inspections should be carried out, especially the performance of the bag filter. Pay attention to the impact of changes in host equipment load on the performance of the filter. After the machine is started, it is necessary to pay close attention to the working conditions of the bag filter and make a good record.
Commissioning: In the commissioning of the new bag filter, special attention should be paid to checking the following points:
(1) Fan rotation direction, rotation speed, bearing vibration and temperature.
(2) Whether the processing air volume and the pressure and temperature of each test point are consistent with the design.
(3) The installation condition of the filter bag is determined by whether the bag is dropped, loosened or worn after use.
(4) It should be noted whether there is condensation in the bag room and whether the ash discharge system is unblocked. Prevents blockages and corrosion from occurring. Accumulation of dust can affect the production of the mainframe.
(5) Adjustment of cleaning cycle and cleaning time. This work is an important factor in the dust collection performance and operating conditions. If the cleaning time is too long, the attached dust layer will be washed off and become the cause of leakage and damage of the filter bag. If the cleaning time is too short, the dust on the filter bag has not been cleared, and the filtering operation will resume. This will quickly restore the resistance and gradually increase it, ultimately affecting its use.
(6) The interval between cleanings of two ashes is called the ash cleaning cycle. Generally, it is desired that the cleaning cycle be as long as possible so that the precipitator can operate under economical resistance conditions. Therefore, we must carefully study the nature of dust, dust concentration, etc., and according to different cleaning methods to determine the cleaning cycle and time, and adjust the test run to achieve better cleaning parameters.
(7) At the beginning of operation, some unexpected situations often occur. For example, abnormal temperature, pressure, moisture, etc. will damage the new device. Rapid changes in the gas temperature will cause the fan shaft to deform, causing an imbalance, and vibration will occur during operation. Once the operation is stopped, the temperature drops sharply, and when it is restarted, vibration occurs again. It is best to use different types of fans depending on the gas temperature. The quality of the equipment commissioning will directly affect whether it can be put into normal operation. If improper handling is performed, the bag filter may soon lose its effectiveness. Therefore, the commissioning of the equipment must be careful and careful.
6. Daily operation
In the daily operation of the bag filter, due to certain changes in the operating conditions, or some failures, it will affect the normal operation of the equipment and work performance. It is necessary to carry out regular inspections and appropriate adjustments in order to extend the filter. The life of the bag reduces power consumption and recycles useful materials. The issues that should be noted are:
(1) Operation record
Each ventilation and dust removal system must be installed and equipped with the necessary test instruments. In daily operation, it must be measured regularly and accurately recorded. This can be based on the system pressure difference, inlet and outlet gas temperature, main motor voltage The value and change of the current, etc. are used to judge, and the fault is promptly discharged to ensure its normal operation.
The problems found through records are: the working conditions of the dust removal mechanism, the working conditions of the filter bag (damage, paste bags, jams, etc.), and changes in the air volume of the system.
(2) Fluid resistance
The pressure difference can be used to determine the operating conditions: if the pressure difference increases, it means that the filter bag is clogged, the water vapor on the filter bag is condensing, the cleaning mechanism is ineffective, the dust accumulation in the ash hopper is too large, the filter bag is blocked, and the gas flow increases. A decrease in the pressure difference means that the filter bag has been broken or loosened, the intake side duct is blocked, or the valve is closed. There are leaks between the cabinets or sub-chambers, and fan speeds slow down.
(3) Security
Baghouse dust collectors should pay special attention to measures to prevent combustion, explosions and fire accidents. When dealing with combustion or high-temperature gases, incomplete combustion of dust, sparks, burning and explosive gases, etc. often enter the system, and some of the dusts have the property of spontaneous ignition or charging, and most of the materials of the filter materials are All of them are flammable and frictionally prone to accumulate static electricity. Under such operating conditions, there are hazards of burning and explosion accidents. The consequences of such accidents are often very serious. Fire prevention and explosion protection measures should be well considered, such as:
a. Install a combustion chamber or Mars trap in front of the precipitator to completely burn unburned dust and gas or trap the planet.
b. Take measures to prevent the accumulation of static electricity. Each part is grounded with a conductive material or conductive fibers are added during the manufacture of filter media.
c. Prevent the accumulation or accumulation of dust, so as to avoid spontaneous combustion and explosion of dust.
d. Before entering the bag room or pipeline inspection or overhaul, be sure to ventilate and prevent CO poisoning.
(4) Precautions for stopping work
Before the bag filter is stopped, in addition to the need for thorough cleaning, attention should also be paid to the following issues:
a. Moisture condensation often occurs in the bag room. This is caused by the presence of moisture-containing gas, especially the gas produced by the combustion. Therefore, before the system is cooled, the moisture-containing gas is discharged and the dry air is completely replaced. That is, after the process equipment stops running, the exhaust fan of the bag filter should be operated for a period of time before it stops operating.
b. During long-term shutdown, pay attention to the cleaning and rust-prevention work of the fan to prevent dust and rain from entering the bearing (note that the motor is protected against moisture). Before the operation is stopped, the dust in the ash hopper should be removed. Ash removal mechanism and drive part should be sufficient.
c. During the shutdown of the bag filter, regular short-time operation (air running) is the best maintenance method to ensure the normal operation of the dust removal system.
(5) Always check the operation of the control valve, pulse valve, and timer. The malfunction of the pulse valve rubber diaphragm is a common fault, which directly affects the cleaning effect. The device is of the external filter type. The inner frame of the bag is used to check whether the parts of the fixed filter bag are loose and whether the tension of the filter bag is appropriate. The support frame is smooth to prevent abrasion of the filter bag. Ash is cleaned with compressed air. Therefore, it is required to remove oil mist and water droplets, and the oil-water separator must be cleaned frequently to prevent malfunction of the moving mechanism and plugging of the filter bag.
Prevent condensation. In use, it is necessary to prevent the gas from cooling in the bag room to below the dew point, especially when bag filters are used under negative pressure. Because the shell often leaks air, so that the bag room gas temperature is lower than the dew point, the filter bag will be damp, resulting in dust is not loose, but sticky to the filter bag, the fabric hole blocked, resulting in clear Ash failure, so that the filter pressure drop is too large, can not continue to run, and some produce a paste bag can not dust. To prevent condensation, the temperature of the gas must be kept above the dew point of 25 to 35°C above the deduster and its system (such as the kiln mill’s dew point temperature of 58°C and the operating temperature should be above 90°C). Ensure the good use of filter bags. The measures are as follows:
a. Add raw material sheds. In the production of cement, the raw materials, fuels, and mixed materials have different water contents. If they are placed in a fixed pile, preventing rain can greatly reduce the moisture content of the materials. This is an effective measure to reduce the moisture content of materials. Cement plants in the south of China are relatively common. However, some of the material piles are too small and others are not. Therefore, the use of bag filter has caused certain difficulties.
b. Reduce air leakage. The air leakage of the gap in the dust collector body should be controlled below 3.5%. In the precipitator system, the leakage of process equipment such as the closed unloading valve of the discharge port of the ball mill, the leakage of the closed ash valve under the precipitator, and the flange connection of the pipeline, etc., are often ignored by the maintenance managers. , Increased unnecessary air leakage, deteriorated the bag filter operating conditions.
c. Dust-laden gas should be evenly distributed in the dust collector to prevent eddy currents at the corners from causing the amount of gas passing through here to reduce the formation of localized low temperatures and cause condensation problems.
d. Do a good job of insulation and rain protection in various places such as dust collectors and pipelines. It has been proved that good insulation measures can make the difference between inlet and outlet temperatures of the bag filter very small. This is an effective measure to prevent condensation.
e. Take appropriate warming measures. If far-infrared electric heaters, electric heaters are installed in the dust collector, or additional radiators are installed in the bag room, the temperature of the host’s smoke can be appropriately increased.
f. Strengthen the temperature monitoring of the dust collector and dust removal system so as to grasp the conditions of use of the bag filter and prevent condensation.
Prevent dust reduction efficiency
(1) Block the air leakage, in particular, block the air leakage from the dust outlet of the dust collector. Because there is a large amount of slowly falling dust in the ash hopper of the dust collector, the reverse flow upward leakage air current causes the secondary flying of the falling dust again and again, so that the dust leakage in the dust removal device can double the dust concentration in the dust collector. Above the dust concentration of the intake air, the working conditions of the bag filter are deteriorated and the dust collection efficiency of the bag filter is affected.
(2) Prevent air flow inside the dust collector from short-circuiting. Because dust gas has a high concentration of dust (eg, 20 g/m3), even if only 1% short circuit escapes, it will exceed the emission standards. Dust-laden gas escapes directly from certain gaps without the filter bag, and this is not allowed to happen.