Zhao Hongwen
(Inner Mongolia Huadian Bao Hair Electric Co., Ltd., Baotou, Inner Mongolia 014013)
Abstract: The flue gas heat exchanger of the desulfurization system is frequently blocked, which seriously affects the normal operation of the desulfurization system and becomes a major problem affecting the utilization rate of the desulfurization system. The cause of the blockage of the flue gas heat exchanger (GGH) was analyzed and a solution was proposed.
Key words: flue gas heat exchanger; plugging; defogger; soot blower
CLC number: X 701. 3 Document code: B Article ID: 1674-1951 (2010) 05-0071-03
introduction
After the desulfurization system of Inner Mongolia Huadian Baotou Electric Co., Ltd. was put into production, the flue gas heat exchanger (GGH) was frequently blocked, resulting in an increase in the current of the booster fan, and the desulfurization system was often shut down. In order to solve this problem, Inner Mongolia Huadian Bao Hair Electric Co., Ltd. has carried out technical transformation of GGH. The GGH heat storage sheet was changed from the DNS type to the Bakdur straight-through type, and the high-pressure water pump was changed from 10 MPa to 150 MPa. After the operation, the GGH blockage has improved, but it has not achieved the intended purpose. GGH plugging is a system problem, and the related equipment is electric dust removal equipment, absorption tower defogger, GGH itself and its cleaning mechanism.
1 electric dust removal equipment
The effect of electrostatic precipitator on GGH is reflected in the export dust content. The relevant regulations stipulate that the mass concentration of GGH inlet dust should be lower than 150mg/m3. If it is higher than 250mg/m3, the desulfurization system should be stopped. The high dust-receiving rate at the outlet of the electrostatic precipitator means that the flue gas reaching the GGH has more ash, and the ash hits the GGH regenerative surface (with moisture), which will react with the gypsum above to form a relatively hard acidified scale. Object. There are two reasons for the increase in dust content at the exit of the ESP equipment.
1.1 Electrostatic precipitator body status
There are fewer people in the new large-scale power plants with auxiliary machine maintenance management experience. Therefore, the maintenance management of the electric dust removal equipment is at the edge. The size of each equipment is not within the scope of maintenance, causing internal defects to accumulate, affecting The dust-containing rate at the outlet of the electrostatic precipitator is more common in the case where the mass concentration of the outlet dust is greater than 300 mg/m3. It is recommended that all equipment be treated fairly in terms of equipment management to improve the health of important auxiliary machines. The quality concentration of dust from the export of electric dust removal equipment of Huadian Baotou Electric Co., Ltd. was about 300mg/m3. In 2008 and 2009, the electric dust removal equipment was separately tendered, and the quality of overhaul was strictly managed, which produced good results and was quite long after overhaul. The mass concentration of dust is about 150 mg/m3 for a period of time. However, due to the special characteristics of the operation of the electric dust removal equipment—the vibration drive parts are operated in the dust, the anode and cathode plates are subjected to vibrating and hammering for many years, and the operation cannot be checked during the operation, it is necessary to maintain the electric dust removal in an efficient state for a long time. The electric dust removal must be repaired in a timely manner, and the inspection level can be determined according to the situation.
1.2 Electrostatic precipitator operation adjustment
The setting of the electric dust removal control system is relatively simple, and the adjustment of the rapping system and the duty ratio (or the thermal power rate) cannot be linked with the load and the coal quality, nor can it be adjusted correspondingly with the electric field exit. The parameters were manually adjusted by the operator, causing an artificial increase in the dust content of the outlet. The technical management department should take the lead and contact the manufacturer for program optimization. The electric dust removal parameter should automatically track the change of coal ash content, and also automatically track according to the combustion situation (such as the amount of smoke). If the electric field of the electric precipitator is faulty, the electric field parameter can be manually adjusted to act as the first electric field corresponding to the second electric field, and so on, to improve the dust removal efficiency.
2 absorption tower defogger
The main components of GGH scale are gypsum and limestone, and calcium sulfite (see Table 1). These substances are all from the absorption tower, which means that the amount of smoke carried away from the design value. If the smoke brings out less of these substances, the scaling should be reversed.
The equipment that affects the carrying capacity in the absorption tower is a defogger. The regulations stipulate that the carrying amount of the flue gas must be less than 75mg/m3 when leaving the defogger. In fact, the carrying amount far exceeds the design value. The increased carrying capacity indicates that the defogger does not work well. The defogger specification specifies that the effective range of the defogger is 35% ~ 100% load. This shows that if the defogger is operated at less than 35% load and higher than 100% load, the design efficiency cannot be achieved, that is, the problem of poor defogging effect and large slurry volume occurs.
2.1 Low flow rate operation
In order to save electricity, some units open the bypass system so that the amount of flue gas passing through the booster fan is less than 35% of the designed smoke. At this time, the flue gas flow rate is not within the effective range of the demister operation, and the flue gas pair The collision amount of the demister plate surface is reduced, so that some flue gas floats out of the defogger and does not reach the defogging effect, and finally the water content in the flue gas at the exit of the demister is increased, and the slurry in the water is also taken out of the absorption tower. GGH. On the other hand, high-speed flue gas has a self-cleaning effect on GGH, and this effect can be considered weakened or absent when the flue gas volume is less than 35%. Then the slurry in the mist adheres to the heat storage surface, and by the heating of the high-temperature smoke, the dust in the smoke and the acidic substance in the smoke rapidly deposit a deposit which is difficult to clean.
Huadian Bao Hair Co., Ltd. GGH technical inspection 1 month later to check the heat storage surface, found that there is a thin layer of hard scaling, which is caused by the above reasons. Therefore, the required parameters of the equipment manual should be taken very seriously, and random changes can cause unimaginable consequences.
2.2 High flow rate operation
Some data show that there is a serious shortage of design capacity in domestic power plant desulfurization systems. In the early stage of design, it is not wrong to refer to the design of the flue gas of the boiler. However, it is not considered that the coal burned by the power plant is not a design coal type, and the amount of flue gas is very high. The desulfurization system of Huadian Baotou Electric Co., Ltd. has a 20% larger flue gas volume than the designed flue gas during high load operation.
At high load, the GGH has a significant increase in water volume due to the smoke exceeding the design value (a corrosion hole has appeared in the GGH net flue gas outlet, and a large amount of water is sprayed from the hole), which causes the GGH differential pressure to rise. As the amount of flue gas increases, the amount of slurry in the flue gas will exceed the design value; at the same time, the flue gas flow rate will cause the flue gas flow rate to exceed the design value of the demisters (Huadian Bao Hair Co., Ltd. designed to be 4. 5m/s). The droplets collected on the surface of the demister will be taken away by the high-speed flue gas. The defogger can not effectively remove the droplets in the flue gas, causing the flue gas to bring water and the amount of pulp to increase, and the downstream GGH bears the brunt. Become a victim. The mist eliminator has two layouts, vertical and horizontal. Vertical arrangement, the design of the flue gas flow rate does not exceed 4. 5m / s; horizontal arrangement, the design flue gas flow rate can reach 6m / s.
The most common is the vertical arrangement (vertical flue gas flow direction), if you want to retrofit you can add a level of horizontal placement at the exit level flue. According to the data, the latest vertical demister flow rate can reach up to 6.5m / s, so you can also add a high-speed vertical defogger. If there is a 2-stage mist eliminator, the first level focuses on low-fluid gas flow rate (such as flow rate below 4m/s), and the second-level considers high-flow flue gas, and the design flow rate can reach 5m/s or more. A 3-stage mist eliminator is the best.
2.3 defogger flushing water
If there is a problem with the defogger flushing water, the demister will be partially blocked, and the flow rate of the flow passage will increase, resulting in poor defogging effect. The problem caused by this cause is the same as in Article 2.
(1) Flushing procedure. Flushing is essential to maintain efficient operation of the mist eliminator, and flushing should be carried out in strict accordance with the regulations. Flushing can clean the surface of the demister. The side effect is that the rinse water will be carried away by the flue gas. Therefore, the procedures must be strictly implemented, and the flushing timing should be adjusted in time according to the shutdown inspection situation.
(2) Flush water pressure. In order to keep the demister clean, flushing water is the only means to ensure proper water pressure. Huadian Baotou Electric Co., Ltd. defogger flushing water requires a nozzle pressure of 0. 2MPa, but there is no pressure gauge at the end of the flushing water pipe, the flushing pressure cannot be adjusted according to the meter, and there is no way to increase the pressure gauge on the steel-plastic composite pipe. . In order to solve this problem, the operating personnel observe the flushing effect of the flushing water during the shutdown, determine the relationship between the valve opening degree and the flushing water pressure, and then adjust the flushing water pressure according to the valve opening degree and the defogger water pump outlet pressure. The inspection results show that the transformation effect is very good.
(3) Inspection of the flushing water pipe. When the defogger flushing water pipe is in operation, pipe breakage or other problems may occur. In the inspection state, the defogger water pipe must be included in the mandatory inspection items to ensure a good flushing effect under running conditions.
2.4 The differential pressure of the mist eliminator cannot be observed, and the blockage situation is unknown. Many absorption towers have not designed the demister differential pressure gauge. There is no way to judge whether the defogger is blocked or not, and it can not be processed in time to affect the effect of the defogger. If possible, increase the pressure detection equipment.
3 GGH self-inspection
GGH was checked during shutdown, and it was found that a large amount of yellow mud-like things on the original flue gas side were covered with support beams. From the dead side of the original flue side, there was also deposited dust. It can be seen that the management of the electric dedusting equipment needs to be improved. local.
GGH soot blowing methods include compressed air, high pressure water, steam soot, and acetylene guns. Huadian Bao Hair Electric Co., Ltd. has three types of soot blowing methods: compressed air, online high pressure water and offline low pressure water. Compressed air is often blown every shift; the online high-pressure water is flushed when the GGH differential pressure rises to 150% of the design value; the low-pressure water is flushed with the online high-pressure water in an off-line mode, and a high-pressure water anti-blocking device is added to the pipeline arrangement. According to the design method, the heat storage surface should be very clean, but this is not the case.
The GGH regenerative surface was remodeled from December 2008 to June 2009. There was no manual flushing. In this respect, the effect is still very good. However, the scaling of the heat storage surface is very obvious. This phenomenon is analyzed and the following six reasons are summarized:
(1) Compressed air supply is not normal, and the amount of gas used for desulfurization is relatively large. Because gas is used elsewhere, the value of the desulfurization system is often required to stop purging.
(2) The compressed air supply pressure is 0. 6~0. 7MPa, compared with the 1. 0MPa required by the GGH manufacturer. A separate compressor should be designed for the desulfurization system. The outlet pressure is above 1.0 MP, and the gas capacity meets the requirements of two units at the same time uninterrupted purge.
(3) Online high-pressure water is cleaned when the GGH differential pressure reaches 150% of the design value, but from the actual situation, the flushing effect at this time is very poor. Purging according to the differential pressure is not suitable. It should be cleaned regularly and flushed in combination with the differential pressure. If the electric dust removal has an electric field exit or a rapping abnormality, high-pressure water flushing should be performed in time.
(4) GGH differential pressure rises. If the high-pressure water can not be washed, the high-pressure water nozzle should be inspected immediately. Even if the high-pressure water nozzle is equipped with reverse purge air, the blockage is very frequent and serious.
(5) Whether the method of soot blowing uses high pressure water or steam, it should be selected according to the blockage of GGH. According to the situation of Huadian Bao Hair Electric Co., Ltd., steam should be used to blow ash. When high temperature and high pressure steam passes between the heat storage surfaces, it will heat the surrounding smoke, causing the flue gas to expand and vibrate the surface, resulting in two functions of purging and vibration. It can be used to purge the plugs that have just adhered, and it can also loosen the scale. From some power plants that use steam purges, the effect of steam purge is significant even at temperatures slightly below design values.
(6) During the daily inspection, it was found that the off-line cleaning effect was better. If the plant has downtime, high pressure water flushing should be arranged. Soak it in low pressure water for more than 6 hours (intermittent flushing), then rinse with high pressure water. If time permits, repeat it.
4 Conclusion
The blockage of GGH is an inevitable process. The most effective work is to delay the speed of scaling and ensure that GGH regenerators work well during the service life cycle, achieving stable operation and saving energy. The cause of the blockage of GGH should be carefully analyzed, and the inspection should be carried out in time to deal with the problems detected in combination with large and small repairs. The author hopes that these experiences accumulated in daily work can provide ideas for solving the GGH blockage problem.
About the author: Zhao Hongwen (1971-), male, Shaanxi Minnan, engineer, engaged in the work of desulfurization operation of power plants.