Condensate polishing is a special way of water treatment in large capacity and high parameter generator set. Its main purpose is to remove metal corrosion products and trace dissolved salts in condensate. The normal operation of condensate polishing system is of practical significance to ensure the water and steam quality of the unit, shorten the start-up time of the new unit, improve the protection ability of condenser leakage, and extend the pickling cycle of the unit.
Condensate polishing usually adopts the following three ways: in vitro regeneration deep mixed bed; Powder resin filter; Tubular filter and deep mixed bed. Xisaishan Power Generation Co., Ltd. chose powder resin filter.
Powder resin filtration technology
Powder resin filtration technology is to use powder resin as covering medium to precoat the filter element of precision filter. It is used to replace the melting ionic substances, remove the suspended solid particles, organic matter, colloidal silicon and other colloidal substances.
Powder resin filter system
Made by USF Lite, or idreco, Italy, it is a pressure pipe body made of a layer of thick stainless steel and a detachable tube plate clamped between the two halves of the working groove. The tubesheet is drilled with holes to fix the filter element.
It is manufactured by grave techno lgies. Its structure is that the bottom tube sheet is fixed, and the filter element joint protrudes into the inlet and outlet pressure ventilation system. The filter element is connected to the joint engraved with thread or guide rod, and is installed in place through the top grid.
According to material and structure, common filter elements are divided into polypropylene stainless steel filter element, polypropylene melt blown filter element and folding polypropylene filter element.
Powder resin for condensate polishing
The resin powder used in the filter system of condensate polishing powder system is completely transformed in the resin powder factory with high purity and high dosage of regenerant. Its characteristics are: low impurity; The particle size is uniform; High regeneration degree; Compared with the homogeneous resin, the surface activity is higher.
Because resin does not need regeneration, only filters, film laying boxes, auxiliary boxes, air tanks and other equipment are required, so the area of the resin is small, the investment in infrastructure is low and the operation is simple.
The unit quality of the work exchange capacity is large. When the working exchange capacity of traditional granular resin reaches the failure point, it is only 20% – 50% of the theoretical exchange capacity; When the working exchange capacity of powder resin reaches the failure point, the exchange capacity of the resin reaches 60% – 95% of the theoretical exchange capacity.
It can effectively remove organic matter and colloidal silicon. The removal rate of organic and colloidal substances by ion exchange resin is very limited, while the powder resin filtration technology has the dual characteristics of filtration and desalination. The removal rate of colloidal silicon can reach 99% under suitable pH condition; However, colloidal silicon can not be removed in deep mixed bed.
It can effectively remove the corrosion products of thermal system. Under the suitable pH condition, the removal rate of iron impurity is more than 95%. The removal rate of iron oxide in deep mixed bed is 90% for Fe2O4; Fe2O3 and FeO are only 50%.
High operating costs. Because the powder resin can not be reused, the operation cost is high. At present, there are no manufacturers producing powder resin in China. The resin powder, especially the anion tree fat powder, is very easy to fail in the air, and the storage period is required to be half a year.
The total exchange capacity of resin is low, and the leakage resistance of condenser is poor. The total exchange capacity of the powder resin filter is less than 1% of the deep mixed bed, so the deep mixed bed can more effectively resist the leakage of the condenser.
It has high requirements for the tightness of the unit. The highly regenerated oxyhydrogen resin powder is easily polluted by carbon dioxide in the atmosphere or water exposed to the atmosphere, which shortens the operation cycle.
The requirements for resin properties are more strict. Powder resin does not have the ability to wash residues, so all powder resins must meet the technical conditions in order to reduce the invasion of pollutants.
Application of powder resin technology in condensate polishing
The biggest weakness of the powder resin is that the total exchange capacity is low and the leakage capacity of the condenser is poor. Therefore, the technology has certain regional limitations. For the areas with high salt content in the circulating water, it is better to choose the deep mixed bed. In the condensate polishing process, the selection of powder resin filter should ensure the following conditions: ensure the quality of make-up water; The leakage of condenser should be avoided as far as possible, and titanium tube or stainless steel tube should be selected as condenser tube; The circulating water quality of the unit is good and the salt content is low; The vacuum tightness of the unit system is good.
Economic comparison between powder resin and deep mixed bed
Taking a 600 MW drum boiler unit as an example, the initial test cost and 20-year operation cost of the two systems are compared. Assuming that there is no condenser leakage, no resin cross contamination and no other abnormal phenomena, the powder resin system can save 1.145829 million US dollars compared with the deep electric layer concrete bed system.
For condensate polishing system, deep mixed bed system or powder resin system are technically feasible, and each system has its own advantages. Therefore, in the selection of condensate polishing system, the system scheme should be selected according to the actual situation of power plant and comprehensive factors.