Characteristics and simple classification of wastewater from thermal power plants
Sewage from thermal power plants includes industrial cooling water drainage, acid and alkali regeneration wastewater from chemical water treatment systems, filter backwash wastewater, boiler cleaning wastewater, coal transport washing and dust removal wastewater, oily wastewater, and cooling tower wastewater.
Because there are many kinds of industrial sewage, the types, contents and discharge capacity of pollutants in various kinds of sewage are not fixed, so the composition of industrial sewage is quite complex.
The main pollutants are: suspended matter, oil, organic matter and sulfide, etc.
The same kind of wastewater can be reused by the same wastewater treatment process.
Therefore, whether the classification of wastewater is reasonable is the key to the comprehensive utilization of wastewater.
According to the characteristics of waste water in thermal power plant and the purpose of treatment and reuse, waste water in thermal power plant is divided into the following categories:
- Low-salt wastewater. Such as the boiler boiler drainage, thermal system drainage water, industrial water system drainage, filter backwash water, domestic sewage and so on.
- High salinity wastewater. Such as reverse osmosis concentrated drainage, ion exchange equipment regeneration wastewater, circulating water drainage and so on.
- Simple treatment of reusable wastewater. Including coal-containing wastewater, ash washing and slagging wastewater.
- Poor waste water that cannot be reused.
For example: desulfurization wastewater, chemical cleaning wastewater, air preheater flushing wastewater, GGH flushing wastewater, etc. are treated as coal yard spray water or ash unloading and humidification.
Analysis of Substances in Thermal Power Plant Wastewater Needing Special Treatment
- Acid and alkali wastewater
Acid and alkali wastewater is mainly produced by regeneration of ion exchange demineralization equipment of boiler make-up water treatment system, backwashing of prefilter for condensate polishing treatment and regeneration of high-speed mixed bed.
The characteristic of this kind of wastewater is that the pH value does not meet the discharge or reuse requirements, and the main component of the wastewater is inorganic salt, such as chloride ion, etc. the discharge amount of this kind of wastewater is relatively small.
The acid and alkali wastewater is discharged to the acid and alkali wastewater pond through the waste liquid drainage ditch, and the pH value is adjusted by adding acid and alkali to make it meet the standard and reuse.
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- Treatment of oily wastewater
There are many ways to treat oily wastewater. This paper introduces one of them – air flotation separation technology.
Air flotation separation technology is to inject air into the water in the form of micro bubbles, so that the micro bubbles adhere to the oil particles suspended in the water, and float up because its density is less than the water, forming the scum layer to separate from the water.
The key to the quality of effluent water is the size, density and uniformity of fine bubbles. The bubble generation device has been determined during the equipment selection, and can not be changed basically.
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- Phosphorus treatment
There are two necessary processes to deal with phosphorus in water.
One is to transform the water-soluble phosphorus into the solid substance of phosphorus-containing elements which is insoluble in water by chemical or physical methods, and the other is to filter these solid substances out of sewage.
- Treatment of COD, suspended solids and other pollutants in wastewater of thermal power plants
The suspended solids in the waste water produced by thermal power plants are mainly coal powder, ash and dust. These suspended particles have a large ratio, a small specific surface area, and their mass concentration usually changes greatly. The treatment effect by filtration or air flotation is not ideal, but by coagulation sedimentation method, it can achieve the ideal effect.
Development trend of comprehensive treatment of power plant wastewater
- Shunt management
Make waste water resource.
For the power plant water, because of the way of using water, different water quality also has great differences. On the one hand, the drainage with good water quality does not need to be treated. It can be used for the next level system with low water quality requirements to achieve the purpose of water saving.
On the other hand, for the drainage with serious pollution, corresponding treatment facilities are added according to its water quality characteristics to make it reach the water quality index of a certain system and reuse the wastewater, which can not only reduce the load of wastewater treatment facilities, improve the treatment effect, but also greatly reduce the operation cost.
- Establish and perfect zero discharge system of waste water in thermal power plant
Zero discharge system of waste water in thermal power plant is a model of water saving and waste water reduction. It can use the increasingly tense water resources to a large extent and reduce the total water consumption of the power plant, so as to effectively alleviate the problems caused by the shortage of water resources in thermal power plant.
Domestic sewage and industrial wastewater are used for Ash Flushing, flushing, fire fighting, greening and spraying after treatment.
After the advanced treatment of domestic sewage, it is used as the make-up water of circulating water. Optimize and balance the water quantity and quality of waste water in thermal power plant as a whole, make rational use of it and realize zero discharge of waste water.
In the research and development of power plant wastewater treatment technology, the scientific research department should focus on solving the technical problems such as scaling of ash water closed-circuit circulating system, pH value of ash water exceeding the standard, ash water used as supplementary water of circulating cooling system and domestic sewage used as supplementary water of ash water closed-circuit circulating.