In order to strengthen the supervision of the operation process of boiler bag filter in desulfurization facilities in thermal power enterprises and improve the operation efficiency of desulfurization facilities, the Ministry of Environmental Protection issued the Notice on the Lead Seal of the Baffle of the bypass flue of desulfurization facilities in thermal power enterprises (Huanban [2065438+00] No.965438+0) on June 20/0. According to the requirements, at the end of September, 20 10, all thermal power plants in Zhejiang Province carried out the first lead seal on the desulfurization bypass baffle. Over the past year or so, the power plant has taken a series of measures to deal with the lead seal problem. The actual opening situation of the bypass after lead sealing and the countermeasures to gradually cancel the bypass are analyzed and discussed.
1, treatment measures of lead seal
1. 1 Modify the bypass opening protection logic.
At the beginning of the request for lead seal, the thermal power plants in Zhejiang Province responded positively. After the demonstration organized by each group and the reference given by each technical unit, the protection logic of the bypass opening is modified at first. Among the common bypass baffle protection interlocks, there are four kinds of interlocks that all thermal power plants unanimously choose to keep. Bypass when the inlet pressure of booster fan exceeds the limit, bypass when GGH stops, bypass when multiple circulating pumps trip, and bypass when booster fan trips. The retention of these four interlocks is mainly based on the protection of desulfurization equipment and the consideration of the safety of flue and baffle. For MFT bypass opening and RB bypass opening, most power plants also choose to keep them, and partially cancel MFT signal to directly trigger the bypass opening. Most factories cancel the bypass when the concentration of imported smoke is higher than the fixed value and the smoke temperature is lower, and a few change to alarm; The interlocking part of the oil gun is cancelled, and some parts are changed to manual judgment to be able to cast or retreat; Some plants still keep putting into operation when the inlet temperature is higher than the fixed value, and some plants change to alarm because of the possibility of flue gas overheating; The interlock of the disappearance of the opening signal of the inlet and outlet baffles is similar, and the power plant also reserves or changes to alarm as appropriate.
When modifying the bypass opening protection logic, besides choosing whether to keep the interlock, the trigger conditions of the interlock are also modified, mainly increasing the delay (such as overtemperature, stall, signal disappearance, etc.). ) and relax the set values (such as pressure, temperature, vibration conditions, etc. ). The most typical is the protection setting value of the inlet pressure of booster fan. After analyzing the design parameters of desulfurization manufacturers and the actual operation of flue and baffle of each furnace, the positive and negative limits are generally relaxed. From the follow-up actual operation effect, there is no adverse effect, and these modifications are still cautious and reasonable.
1.2 Adjust bypass baffle test and GGH off-line flushing cycle.
In order to ensure the reliable opening of the bypass baffle, as a means of inspection, the periodic activity test of the bypass baffle has always been carried out as a routine work, usually once every 1-2 months. Nearly half of the factories have not carried out the periodic test of the bypass baffle after lead sealing, mainly using the unit for mediation or shutdown. In the investigation, it was found that the seal of bypass baffle in some factories was easy to deform. Because it is impossible to control whether the deformation will affect the opening, canceling the regular inspection will bring certain risks. In the power plant with GGH device, when the GGH pressure difference rises to a certain allowable limit and online high-pressure water flushing cannot be relieved, it is necessary to stop desulfurization and carry out offline high-pressure water flushing. Plants with high frequency may be washed 2-3 times every 1 month. After the implementation of lead sealing, the bypass opening is restricted, and the environmental protection department no longer allows the periodic test time of the bypass baffle to be counted as exemption time, so the power plant also controls the frequency of these two bypass openings. At present, some factories have been able to synchronize with the maintenance of units, which is the reason for the selection of equipment itself, or the transformation in recent years. The offline frequency of GGH, which was put into operation earlier, is generally higher, with an average of 1 time in February, which has a great influence on the opening times of baffles and the operation rate.
Modification and optimization of 1.3 equipment
The reliability of equipment is directly related to the normal operation of desulfurization system, and the transformation and optimization of equipment system is an essential link in canceling bypass transition. The transformation and optimization measures mainly include:
(1)GGH heat exchange element is changed to large channel anti-blocking type; Reform GGH soot blower, increase air compressor purging, extend regular off-line flushing cycle as much as possible, and synchronize with unit maintenance. During maintenance, the heat exchange elements are chemically cleaned, and some heat exchange elements can be reserved.
(2) In the factory where the baffle is opened many times due to the negative pressure fluctuation in front of the booster fan, the feed-forward and feedback coefficients are modified by adjusting the combustion conditions, and the flue and baffle pressures are recalculated, thus relaxing the fixed values.
(3) The inlet baffle of booster fan is added to two actuators, and a canopy is added; Increasing the torque of the damper actuator; Replace hoses of all oil pipes; Replace the reliable hydraulic oil pipe to prevent leakage; After the booster fan stops, strengthen dust removal on the hub and blades to ensure the normal vibration of the fan; The reducer of slurry circulating pump is cooled by closed cooling water, with built-in serpentine tube and external lubricating oil cooler to ensure good cooling effect.
(4) Replace the inlet filter screen of the circulating pump, increase the flow and reduce the pump cavitation; The large and small heads at the pump outlet are replaced by stainless steel for corrosion protection; Wear-resistant plate is added to the spray layer of absorption tower, and alloy plate is welded to the middle partition; Stainless steel sheath is added to the easily damaged parts of spray pipe, and inner sleeve is added to the connecting short pipe of absorption tower. Increase the monitoring of spray, thicken the spray layer, support the demister, replace the nozzle, and increase the flushing in the dead zone; The drain tank and pipeline are added at the outlet of the absorption tower to reduce the corrosion of water vapor on the tail flue and the scaling of GGH; After repair, the rubber lining is easy to fall off, which strengthens the quality process control of repair; Modify the flushing logic of demister and increase the flushing frequency of primary demister. Under the premise of ensuring the putting-in-service proactively rate, the inside of the absorption tower should be cleaned regularly.
(5) The scale in the flue is easy to bubble, so it needs to be checked frequently to strengthen the control of the repair quality process; Monitor the chimney corrosion, and timely evaluate and repair the chimney corrosion when the unit is shut down.
(6) Expanding the wastewater treatment system; Add bypass to the triple box; Adding water supply pipe in pulping system; The process water pipe is changed into rubber lining; Online pH meter, the densitometer is replaced, and the measurement on the mother tube is also replaced to ensure the accuracy of detection; The fuse method is used to deal with the cathode spiral fault of electrostatic precipitator online, and the pole wire is replaced in batches when the fault is frequent to ensure the normal operation of the electric field.
2. Statistics and analysis of bypass opening after lead sealing.
We select the period after lead sealing from 20 10,11-2011,and classify the times and reasons of bypass opening in 14 factories in the province. Statistics, and compared with 165438+2009 10-2065438+September 2000. In these two groups of control time, the bypass was opened 436 times before lead sealing and 365,438+08 times after lead sealing, which showed that lead sealing was an environmental force and definitely played a role in limiting bypass opening. The operating rate of nine factories has dropped significantly, some of them have dropped significantly, and four factories have increased, which is not too big.
Among the reasons for opening, there are 19 before lead sealing and 5 after lead sealing. Five items are oxidation air system failure, inlet and outlet baffle failure, abnormal inlet flue gas temperature, external line failure of power grid and tripping of low-voltage desulfurization transformer.
The reasons for opening before lead sealing account for more than 80%, and the top five reasons are GGH fault or off-line cleaning, fluctuation of inlet air pressure of booster fan, booster fan fault, RB or low pressure load of unit and MFT； of boiler; After the lead seal, these five reasons still account for more than 80% of the total. In the ranking, the negative pressure fluctuation of booster fan becomes the last, and the others remain unchanged in turn.
3. Current influence of limited bypass opening.
It can be seen from the modification of the bypass opening logic of Zhejiang Power Plant that the bypass opening of power plant is still in the stage of "opening when it is opened" because most important interlocks are reserved, and the environmental protection department is still understanding it. Therefore, most of the possible impacts caused by the limited bypass opening or cancellation have not been displayed, that is to say, the main engine has not been forced to stop because of the maintenance of desulfurization equipment; When the temperature of boiler MFT, unit RB and inlet flue gas is high, the bypass is also opened, so there is no risk of instability of flue gas system and damage of internal components of absorption tower for the time being. The inlet flue gas temperature is low, with few occurrences and short duration. This year, the sulfur content of coal is generally not very high, and the capacity of bag dust removal system of desulfurization equipment boiler can be buffered. Therefore, in these two cases, each power plant can basically not open the bypass.
In the boiler start-stop stage, three power plants in Zhejiang Province put electrostatic precipitators into operation earlier and put them into use after basic ignition. Most power plants are still gradually put into electric field operation according to the requirements of inlet temperature of electrostatic precipitation, and generally put into desulfurization operation when the unit load is 50%. Zhejiang 4*600MW units (excluding GGH) started the preliminary preparation and scheme demonstration for canceling the bypass as required from the second half of 20 10. Taking 20 1 1 as the transition period, each boiler in the power plant was given 12h as the bypass opening time, including the periodic test of baffles and the abnormal opening time of baffles during the unit grid connection. In view of this requirement, at present, the power plant adopts the synchronous operation of electric dust removal and boiler ignition, and the synchronous operation of desulfurization and unit grid connection (10MW). In order to reduce the abnormality during transportation, increase the storage capacity of slurry for pulping, oxidation, wastewater treatment and accidents, and arrange the maintenance of defective equipment in desulfurization system as far as possible in combination with unit maintenance, and gradually cancel the booster fan. When the unit stops abnormally, try to use sliding parameter operation mode until desulfurization and boiler stop simultaneously. In this way, so far, this year, the power plant only bypasses 1 treatment of oil leakage from the hydraulic pipe of 1 booster fan, and the monthly desulfurization putting-in-service rate is close to 100%.
The current operation mode of power plant is a good practice in Zhejiang Province, and its effect and influence still exist. The first is the risk of low temperature corrosion. When the unit is connected to the grid, the flue gas temperature is not high. At this time, the outlet flue gas temperature must be low when desulfurization is put into operation. Looking up the historical curve, it is found that when the unit was just connected to the grid (10MW), the flue gas temperature at the desulfurization outlet of the power plant was generally around 30 degrees. When the unit load rises, it often takes about 2 hours for the outlet flue gas temperature to rise above 45 degrees (normal flue gas temperature at desulfurization outlet). During this period, there is a risk of low temperature and high humidity corrosion in the flue of the facility. The power plant uses chimneys of two boilers, which further increases the corrosion risk of chimneys. When the unit is overhauled, repairing the chimney anticorrosion layer has become a routine work. Although the electrostatic precipitator is put into use when lifting the furnace, its effect of removing pulverized coal is poor, and unburned carbon, including oil droplets when oil is still needed for poor ignition, still inevitably enters the slurry. According to the power plant, after this operation mode is adopted, it is common that the slurry in the absorption tower turns black (overflows), which sometimes leads to blind spots, so it is necessary to increase wastewater discharge. If measures are taken to increase wastewater discharge, it will take about half a month to completely replace the slurry caused by 1 shutdown, which will have a certain impact on gypsum dehydration and quality. If the unit is started and stopped frequently, the dilution and buffering capacity of gypsum dehydration system will decrease, which is more harmful.
Different power plants have different ways to deal with whether the oil gun needs bypass when it is running. Half of the power plants open baffles under oil load, the other half open baffles under oil load, and the other half can't open them basically. In order to reduce the impact, on the one hand, the power plant should communicate with high places as much as possible, and strive for a stable load above the oil load, that is, no oil injection; On the other hand, even if you inject oil, you should put as few oil guns as possible and use them intermittently. At present, the influence of oil injection on desulfurization slurry is mainly manifested in the foaming and overflow of slurry (defoaming agent is added regularly in some power plants), and the surface of slurry is a little black, but it has little effect on slurry reaction, dehydration and gypsum quality in the tower.
4, cancel the bypass countermeasures
At present, most desulfurization units put into operation in 20 1 1 year are designed with bypass, and the environmental protection department recently proposed that desulfurization bypass will be put on the agenda from 20 12. Judging from the current situation of desulfurization bypass in Zhejiang power plant, it is very difficult and stressful to completely cancel the bypass in a short time. Because there is still a lack of mature and perfect operation experience after the silent plugging of the bypass of the old unit. Once the bypass flue is cancelled or temporarily blocked, the desulfurization device and the main engine will become a series system, which must be started and stopped synchronously. Therefore, we must fully consider the particularity of bypass operation, put forward targeted countermeasures, and improve the operation reliability of bypass furnace and desulfurization system.
4. 1 evaluation of desulfurization facilities
It is suggested that a comprehensive and detailed evaluation should be carried out before the bypass of pulse dust collector in existing desulfurization facilities is cancelled. The evaluation content should include coal quality fluctuation, desulfurization equipment reliability, unit operation reliability, bypass opening statistical analysis, etc. Through evaluation, the main factors and weights that restrict the cancellation of power plant bypass are found out, so as to gradually transform, expand and optimize in the transition period according to the priority, and make the bypass opening level gradually close to cancellation. Priority can also be given to the implementation plant that cancels the bypass: the unit without GGH and canceling the operation of booster fan is the first implementation object to cancel the bypass; Second, there is no GGH unit. Because there are no facilities with such high resistance, it is relatively easy to expand the induced draft fan and cancel the booster fan. This is also the most difficult unit to realize with GGH and booster fan. When the GGH pressure difference can be controlled at a stable level for a long time, the expansion of the induced draft fan and the cancellation of the booster fan can be considered in combination with the denitrification transformation.
4.2 Fuel quality is the primary guarantee.
Coal quality is the primary factor, and the worst coal type should be taken into account through statistical analysis. Among them, ash and sulfur are the main factors, the former affects the dust removal effect of electrostatic precipitator, and the latter affects the desulfurization ability of the whole system. In addition, the ignition difficulty caused by coal quality will affect the effect of micro-oil and plasma ignition, and poor combustion will lead to the abnormal operation of the boiler and bring MFT and other effects. Therefore, if the bypass operation is cancelled, the requirements for coal quality and stability will be improved. The purchase of low-sulfur coal and the mixed combustion of high-sulfur and low-sulfur coal are still the primary tasks to ensure the normal operation of desulfurization system from the source. In addition, burning coal with high volatile content as starting coal as much as possible in the cold start-up stage of the boiler will not only help to shorten the start-up process of the boiler, but also reduce the ignition difficulty and a series of effects on the desulfurization unit caused by consuming a lot of olefin oil.
4.3 Countermeasures for boiler operation and desulfurization operation
During the operation of electrostatic precipitator, in order to reduce the pollution of unburned oily carbon particles to the slurry system of absorption tower, before the boiler starts, especially before the cold start, it is best to put the electrostatic precipitator ash hopper heating, insulation column sleeve heating and discharge electrode insulation chamber heating into operation 24 hours in advance, so as to ensure that the electrostatic precipitator and dry ash removal system are put into operation before ignition, and the absorption tower circulating pump is put into operation. In the ignition start-up stage of boiler, in order to prevent some unburned oil and carbon particles from secondary combustion when they pass through electrostatic precipitator with flue gas, the secondary voltage of each electric field of electrostatic precipitator should be controlled between corona initial voltage and flashover voltage, and the secondary current value should be appropriately limited. In the process of operation, closely monitor the flue gas concentration at the outlet of electrostatic precipitator, and consider implementing the transformation of electric bag precipitator or bag precipitator when necessary, in which the bag precipitator and the framework of the precipitator are well utilized to further improve the dust removal efficiency.
In order to prevent the flue gas at the inlet of the desulfurization absorption tower from overheating and protect the internal components, rubber lining or scale lining of the absorption tower, the demister should be equipped with an emergency spray desuperheating device, and ensure that the spray desuperheating device can be put into operation reliably. During the operation of desulfurization unit, the main operating parameters of desulfurization system and the changes of inlet and outlet temperatures of absorption tower should be closely monitored. In the shutdown stage, all circulating pumps can only be stopped when the flue gas temperature at the inlet and outlet of the absorption tower drops below the allowable temperature limit and the safety is ensured. For the emergency sprinkler system, it is also very important to strengthen equipment maintenance in the daily operation process, set up automatic replenishment for the high-level water tank, and often confirm the water level. The system power supply is connected to the security power supply, and the spray test is carried out regularly to ensure that it can act in time.
During boiler adjustment and desulfurization adjustment, the combustion stability of the boiler should be ensured, the air leakage of the air preheater should be controlled, and the flue gas parameters should not seriously deviate from the design conditions. At the stage of boiler ignition start-up, low-load fuel injection or sudden increase of sulfur content in coal, the operating parameters of desulfurization system should be closely monitored, and the laboratory analysis of slurry quality in absorption tower should be strengthened. Once a large number of overflow and foam appear in the absorption tower, the pH value can not be effectively improved and stabilized, the slurry quality becomes worse, and gypsum dehydration is difficult. The influence can be eliminated by replacing the slurry. Strictly monitor the operating conditions of desulfurization system, strengthen the monitoring of absorbent, process water and steam quality, improve the reliability and stability of on-line instruments, strengthen the chemical supervision of desulfurization system and make it a system form, analyze the chemical analysis of each medium of desulfurization system regularly and irregularly, and pay close attention to and analyze the oil content of slurry in absorption tower during the cold start-up or low-load stable combustion stage of boiler, so as to provide scientific basis for slurry replacement and spray washing of demister.
To improve the maintenance level, in the daily operation practice, it is necessary to strengthen the maintenance and management level of desulfurization systems and equipment, form a strict management system, pay full attention to various defects and fault points of desulfurization systems, analyze and deal with problems in time when they are found, and avoid forming hidden dangers. When necessary, the key equipment of desulfurization system, including chimney, should be included in the maintenance and management of main equipment. Focus on checking the erosion, wear and corrosion of pipeline container system and rotating parts, the scaling and blockage of GGH and demister, and the corrosion and leakage of tail flue and chimney, so as to truly check the desulfurization system at each station to nip in the bud.
4.4 Communicate with the environmental protection department
If the bypass of desulfurization device in thermal power plant is cancelled, I am afraid it will bring some influence to the production and operation of power plant. Power generation groups and power plants should actively communicate with environmental protection departments at all levels, let them know the current situation of bypass opening and the impact of bypass cancellation through analysis, strive for a reasonable transition period, complete necessary transformation and optimization, and make bypass cancellation safe and reliable.