Design and Debugging of Powder Resin Covering Filter in Air Cooling Unit

[Abstract] The 2×600MW direct air cooling unit condensate water treatment system of the second phase expansion project of Shanxi Datong No. 2 Power Plant adopts the design of powder resin covering filter. It is necessary to set up a condensate polishing system for the air-cooling unit, which has many advantages over the yang-negative system. The system consists of a condensate pump, a powder resin covering filter, a cleaning device, a wastewater collection and discharge system, and a compressed air system. The results of the use of the powder resin covering filter indicate that the effluent quality meets the design requirements.
[Key words] Direct air-cooled fine powder resin application The second phase expansion project of Shanxi Datong No. 2 Power Plant was used to construct a 2×600MW direct air-cooling unit. The designed condensate capacity of the unit is 1285t/(h·set), the large value of zui is 1333t/(h·set), and the condensate polishing treatment uses a powder resin to cover the filter system. The system flow is: condensate pump water → powder resin covering filter → low pressure heater. The system is designed for medium voltage operation with 100% bypass. The condensate polishing system is set according to the unit system and is respectively arranged in the steam turbine room of 2 units.
1 Design of powder resin covering filter system 1.1 Composition and operation process of powder resin covering filter system The condensed water of 2 units is all processed, and the finishing equipment of each unit is set according to 3×50% of the amount of condensed water, that is, each The unit is equipped with 3 sets of 1700mm diameter covered filters, 2 sets of operation, and 1 set of spare. Each unit is equipped with a set of membranes, blasting membranes, cleaning facilities and wastewater collection and discharge and compressed air systems. The precision processing control system is designed in three modes: fully automatic, semi-automatic and manual operation. In the fully automatic operation mode, the system is executed according to the following procedure: filling (only occurs when the system is first started or restored) → pre-coating (semi-automatic operation) → holding → filtering operation → backwashing trigger condition judgment → backwashing/filling → Pre-coated for use. In manual mode, the system's equipment and valves are operated manually. Each filter is equipped with 345 filter elements. The filter element adopts HGCOLD-R polypropylene melt-blown filter element of American PALL Company. The filter element size is 57.15mm×1524mm, which guarantees the service life is more than 6 years. The process flow of the condensate polishing system is shown in Figure 1.

In normal operation, the powder ion exchange resin is pre-coated on the outer surface of the filter cartridge to form a layer of resin filter. When the condensate is filtered, the solid particles in the water are intercepted, and the dissolved ions are exchanged and removed by the resin filter layer, so that the effluent reaches the design requirement. As the filtration and ion exchange proceed, the filter layer is gradually clogged and the resin layer loses its ion exchange capacity and fails. When the conductivity of the effluent, the value of the silica, the pressure difference between the inlet and outlet of the filter or the filtration time reach the set value, the filter fails to exit the operation and the membrane is cleaned. The cleaning is pressurized with compressed air to remove the resin film cake and discharged to the wastewater treatment system through a discharge valve.
When the filter outlet flow rate drops to 96.7m3/h, in order to prevent the filter from falling off, the program will automatically open and hold the pump outlet valve, and start to keep the pump, the filter is kept, and the pre-coated powder ion exchange resin layer is maintained. On the outer surface of the filter element.
1.2 Backwashing of the filter When the filter operating parameter is close to the backwash alarm setting value, the system issues an alarm message that “the filter operation index is close to the backwash setting value, please prepare the spare filter in advance”. In the following cases, the filter issues an alarm requiring backwash: (1) the chemical index (conductivity or silica) of the effluent exceeds the set value; (2) the pressure difference between the inlet and outlet of the filter reaches the set value; The filter running time reaches the set value; (4) The operator manually starts the backwashing program through the man-machine interface.
In addition to the above (2) case, the filter differential pressure reaches the set value and the backwashing process is started directly. After the other parameters reach the set value, the system continues to run for 3 hours. During the period, the backup filter should be pre-coated and put on the line. If the backup filter is not put online within 3 hours, the system will automatically start the backwashing process.
1.3 The necessity of setting the condensate polishing system for the air-cooling unit Although there is no condenser in the unit, there is no problem that the circulating cooling water leaks polluted water supply in the wet cooling unit, but the surface area of ​​the water vapor system of the unit is much larger than that of the wet cooling unit. When the load changes greatly, a large amount of corrosion products fall off, resulting in deterioration of the quality of the condensed water. Secondly, since the air-cooling system is in a negative pressure state, it is inevitable that air leaks into the air to dissolve the CO2 in the air into the condensed water. Due to the higher pH of the system, CO2 is mainly present in the form of bicarbonate, causing corrosion of the entire water vapor system. In addition, boiler feed water will also increase the salt content of the condensate and affect the water vapor quality. Therefore, it is necessary for the unit to set up a condensate polishing system.
1.4 Advantages of powder resin covering filter The unit has a high operating temperature due to condensed water (usually above 60 ° C, and Zui is as high as 85 ° C). At present, there are two types of systems in the country, one is powder resin covering filter system; The first is the Yangyin bed system. The function of the unit to set the condensate polishing is different from that of the wet cooling unit, which is to remove corrosion products and salt from the condensed water. Since the impurities in the condensed water are mainly corrosion products, affecting the quality of the water vapor, removing the corrosion products in the water is the main task of the fine treatment. For this reason, the powder resin-covered filter system has the following advantages over the yang-Yang-bed system:
(1) When the unit is started after the initial or after the shutdown, the system usually contains a large amount of iron and corrosion products. In order to shorten the startup time of the unit, if the solar separation system is put into operation, the resin will be polluted and consume a large amount of Acid and alkali regeneration, resulting in greater waste. Covering the filter system, since the powder resin is used once, it does not need to consume acid or alkali. When the content of corrosion products is large, only the fiber powder can be used for filtering purposes, and the consumption is small, and the running cost is low.
(2) The condensate water quality is good when the unit is in normal operation. The separation system has a large amount of resin, a long running time, and repeated regeneration. Due to the high temperature of the condensed water, the resin will degrade after a certain period of time, which affects the quality of the water vapor. The powder resin covering filter system has a small amount of resin, short running time and one-time use, and has little influence on water vapor quality.
(3) When the condensed water temperature is high and the fine treatment is withdrawn from operation, the powder resin covering filter system is 100% bypassed, and the split bed system can only bypass the negative bed, and the sun bed continues to operate. Since only the sun bed is running, the system effluent is acidic, and a large amount of ammonia is required to prevent corrosion. The large amount of ammonia added shortens the operating cycle of the sun bed, increases the number of regenerations, and so on, increases operating costs, and brings about a large amount of acid and alkali emissions.
(4) The powder resin covering filter system has strong mechanical retention and adsorption filtration, and can effectively remove corrosion products and solid impurities in the condensed water. The exchange capacity of the ion exchange resin can be fully utilized, and the ion exchange speed is fast. Since the powder resin particles are fine, the same resin surface area is much larger than that of the conventional ion exchange resin, and therefore, although only one layer is used, the use requirements can be satisfied. Since there is no need to set up an acid or alkali regeneration system, the wastewater discharge is small and neutral or weakly alkaline. The single device of the system has large output, small footprint and easy layout. The process system is simple, easy to operate, and easy to implement unattended.
1.5 Filter output, structure, filter flow, filming, operating cycle and differential pressure design The original design of the 600MW unit of the plant has a large condensate volume of 1333t / h, the rated condensate volume of 1285t / h. During the construction process, the amount of large condensate modified to zui was 1580.25 t/h, and the rated condensed water volume was 1527.89 t/h, which was about 20% higher than the original design. Obviously, the original design covering filter can not meet the requirements of 100% condensate treatment, so that the bypass door always maintains 10% opening when the unit is running at full load. Therefore, it is recommended to strengthen the cooperation with the steam turbine plant during the design, so that the capacity of the finishing treatment can meet the operation requirements of the unit.
The structure of the powder resin covering filter is generally divided into two types: a large flange ring group and upper and lower manhole doors. The structure of the large flange ring group is relatively strict, and it is convenient to disassemble the filter element, which is convenient for the filter core to be repaired, but the space for lifting the upper cover of the large flange ring group is required. The manhole door type is difficult to repair and find leaks, but it is easy to arrange, and there is no need to reserve a high maintenance space.
The design parameter filter flow rate is related to the number of filter elements, filter specifications and operating pressure difference. The filter element has a small flow rate, a large number of filter elements, and a large filter diameter; the filter element has a large flow rate, the number of filter elements is small, and the operating pressure difference is increased, which is not conducive to the service life of the filter element. The normal flow rate of the filter element of the power plant is 6.88m3/(m2·h), and the flow rate of Zui Datong is 7.1m3/(m2·h). For economical and safe operation, it is recommended that the normal flow rate of the filter element should be 7m3/(m2·h). The number of filter elements in the power plant is 345, calculated according to the normal flow rate of the filter element of 7m3/(m2·h) and the rated outlet flow of the condensate pump of 1527.89t/h. The number of filter elements (treated by 3×50%) should be 404.
From the practice of the power plant, in the stage of load commissioning, the proportion of anion resin is increased, and the expected effect is not obtained, but the pressure difference between the initial operation of the filter is increased. It is recommended that the 168h full load trial and trial production stage, the paving ratio can only use the resin resin of cation resin: anion resin = 1:1; the proportion of fiber powder can be appropriately increased during the trial operation with load. When there are more corrosion products in the condensed water, only the fiber powder can be run.
The normal operating cycle is now set at 504h, but the effluent quality is still very good. Although the filter pressure difference exceeds the set value of the normal operating pressure difference given by the manufacturer, it is far from the set value of the failed pressure difference, indicating that the powder resin has the ability to filter and exchange. Therefore, it is recommended to modify the set value of the operation cycle to reduce the number of membranes per unit area from 1.06kg/m2 to 0.97kg/m2, and the “continuous operation time 504h” is only used as an auxiliary condition for manual judgment of failure. When the running time reaches 504h, if the effluent water quality is still good and the pressure difference is not large, it can continue to operate to improve its economy.
According to the experience of the power plant, the amount of powder resin in the first year can be considered as 4t/set, and fiber powder can be considered as 0.25t/set.

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