JPH0155910B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating dust, acidic or alkaline waste discharged from a coal-fired power plant in a non-polluting manner, and in particular for the removal of incinerated ash, desulfurization, etc. This invention relates to a method for effectively removing suspended solids from wastewater generated during the process.

BACKGROUND ART In thermal power plants, especially coal-fired power plants, large amounts of clinker and fly ash are produced by combustion of pulverized coal and fine grained coal, and their disposal has become a problem. A water jet is preferred for discharging and transporting clinker accumulated in the slag tank at the bottom of the furnace.
In addition, sealing water is required to seal the slag tank and the bottom of the furnace. On the other hand, the debris collected by dust collectors such as electrostatic precipitators is micron-sized, as is called fly debris, and is easily blown up, requiring careful handling, and the amount of emissions is large.

As an example, showing these amounts for a boiler unit for a 700MW class coal-fired power plant, clinker is
10T/h, fly ash 80T/h, clinker transport water 300T/h, fly ash humidification water 15-20T/h. In addition, the wastewater discharged from the cooling tower of the desulfurization equipment is a strong acid with a pH of 1 to 2, and the amount discharged is
18 T/h, and the wastewater from Shitukuna, which concentrates CaSO ₄ (gypsum) produced when SO ₂ and SO ₃ in exhaust gas are treated with CaO, is an alkaline liquid with a pH of 9.0 to 9.5.

As mentioned above, large amounts of fly ash and clinker are discharged from coal-fired power plants, and from the desulfurization process, a sulfuric acid solution containing highly concentrated hydrochloric acid and hydrofluoric acid is produced by the spray water used to cool the exhaust gas, and CaSO is produced by the reaction with CaO. _Four
Due to the treatment and transportation of
It requires a water flow of 350T/h. Some of these wastes are used as valuable materials, but some wastewater and
Both fly ash and clinker must be neutralized before being discharged to prevent secondary pollution. Sludge is generated during the neutralization of wastewater, but in order to remove the sludge and clinker contained in the water used for removing the sludge and clinker, a vast settling pond is required. If a small settling tank or the like is used, a large amount of expensive flocculant must be used.

An object of the present invention is to provide an apparatus that can effectively and inexpensively remove suspended solids contained in water used in discharging sludge, clinker, etc., and can effectively reuse this water.

In short, this invention provides a wastewater treatment tank 2 that receives a portion of fly ash collected from the exhaust gas of a coal-fired boiler, acidic cooling water W ₁ after cooling the exhaust gas in the pre-desulfurization stage, and alkaline liquid W ₂ generated during the desulfurization process.
a fly ash processing system having a mixer 15 for mixing the supernatant liquid of 9 and the collected fly ash;
A mixture of slag, which is crushed particles of lumpy high-temperature coal ash that has fallen into the water in the slag tank 1a at the bottom of the boiler, and circulating treated water, sludge from the wastewater treatment tank 29, and supernatant liquid are supplied from a pipe 59 with a valve 60. Treated water has a treatment system for a powder-containing liquid having a dehydrator 38, a sedimentation tank 39 that receives the supernatant liquid from the dehydrator 38, wastewater containing powdered coal from a coal storage yard 53, and the supernatant liquid from a wastewater treatment tank 29. A recovery system, a sealing system that receives the supernatant liquid from the wastewater treatment tank 29 and seals the upper end of the slag tank, and a circulation tank 40 that receives the liquid from the sedimentation tank 39 and circulates and uses the treated water via a pump 41. The method is characterized by a treated water circulation system that supplies the pump 33 and a method for treating effluent from a coal-fired power plant, which separates powder and granules discharged from the boiler from the treated water, and circulates and uses the separated treated water. shall be.

An embodiment of the present invention will be described below with reference to the drawings.

Exhaust gas from the coal-fired boiler 1 passes through a dust collector (electrostatic precipitator) 2 and a conduit 3 to a desulfurization device (not shown) where it is desulfurized and then discharged to the outside of the system. On the other hand, fly ash collected by the electrostatic precipitator 2 is pneumatically transported through a pipe line 13 using pressurized air from a blower 12 and supplied to a silo 14. The appropriate amount is pipe 5
0 to the mixer 15, and the spray nozzle pipe 15
After being humidified and kneaded with the spray water of step a, the mixture is transported by truck 16 to a predetermined location and is either dumped or used effectively (for example, added to cement). In addition to being discharged through this pipe 50, the fly ash flows into a pipe 47 and mixes it with the supernatant liquid extracted from the wastewater treatment tank 29 via pipes 31 and 32.
After being kneaded in , the alkaline liquid is supplied to the wastewater treatment tank 29 as an alkaline liquid. A part of the cooling water (strong acid liquid with a pH of about 1 to 2) that is circulated and used in the exhaust gas temperature reduction process before desulfurization is extracted and supplied to the wastewater treatment tank 29 as the liquid to be treated _W1 , where it is used as the alkaline liquid in the fly ash. It is neutralized by mixing with In this case, an alkaline liquid W ₂ containing CaSO ₄ produced during the desulfurization process may be added. The sludge accumulated in the wastewater treatment equipment during this neutralization process has a high liquid content and cannot be disposed of as it is, so it reaches the water jet conveyor 37 via the pipe 52, and the water flowing from the pump 33 into the pipe 35 causes the water to flow. The water is transported and flows into the dehydrator 38. In the water level control operation of the wastewater treatment tank 29, when the water level is high, the water is sent to the dehydrator 38 equipped with the valve 60, as well as water for sealing the clinker hopper 1a and cooling the exhaust gas from the pipe line 30. Into the water held in the slag tank 1a formed at the bottom of the boiler, high-temperature lumpy coal ash, usually called clinker, falls from the water reactor and is crushed into particles several millimeters in size by the impact of rapid cooling, resulting in black particles called slag. It becomes glassy clinker grains. This clinker grain (hereinafter simply referred to as slag) reaches a water jet conveyor 36, and is supplied to a dehydrator 38 by the water flow in a pipe 34 in the same way as the sludge. The clinker and sludge supplied to the dehydrator 38 are dehydrated and then discharged and transported to a predetermined location by the truck 16a. The supernatant liquid in the dehydrator 38 is sent to a sedimentation tank 39, where suspended solids are sedimented. On the other hand, in the coal storage yard 53, water _W3 is sprayed to prevent spontaneous combustion of the coal, and water containing fine particles of coal such as pulverized coal (hereinafter collectively referred to as pulverized coal) flows into the side ditch 54 and flows into the pipe 55. is discharged by
A part of the water containing this pulverized coal flows into a pipe 56 branching from the pipe 55, and flows into the settling tank 39 via this pipe. In this case, a mixer 57 is arranged in the conduit 56, and a conduit 58 branched from the conduit 31
The supernatant liquid in the wastewater treatment device 29 is introduced by
A supernatant liquid may be added to the water containing the pulverized coal in the mixer 57 to prevent the pulverized coal from settling. The pulverized coal that has flowed into the sedimentation tank 39 acts as a coagulant and causes suspended matter in the waste water supplied from the dehydrator 38 to coagulate and settle. The aggregated suspended matter is discharged to the outside, and the purified water is sent to the circulation tank 4.
0, part of it passes through the pump 41 and reaches the pipe line 24, where it is used together with the supernatant liquid of the wastewater treatment device 29 in the pipe line 30 as replenishment water for exhaust gas cooling, and the rest is sent through the pipe line 42 to the upstream side of the pump 33. The water is introduced into the pipe 36 and added to the make-up water from outside the plant, and is used without waste as a replenishment water for clinker and sludge transportation. A portion of the supernatant liquid in the wastewater treatment tank 29 is added to the clinker hop seal water conduit 61 via a conduit 62 as part of the seal water.

By carrying out this invention, the pulverized coal in the waste water produced during the process of preventing coal ignition, which is discharged as an unnecessary substance within the system, is used as a flocculant, so suspended matter can be removed inexpensively and effectively. The treated water can be recycled and used, which has the effect of significantly reducing the cost of water at power plants.

[Brief explanation of drawings]

FIG. 1 is a waste treatment system diagram for carrying out the method according to the present invention. 1... Coal-fired boiler, 1a... Slug tank, 29... Wastewater treatment equipment, 39... Sedimentation tank,
56... Pipe line for introducing waste water containing pulverized coal, 58... Pipe line for introducing supernatant liquid.

Claims (1)

[Scope of Claims] 1. Wastewater treatment that receives a portion of fly ash collected from the exhaust gas of a coal-fired boiler, acidic cooling water W ₁ after cooling the exhaust gas in the pre-desulfurization stage, and alkaline liquid W ₂ generated during the desulfurization process. A fly ash processing system having a mixer 15 that mixes the supernatant liquid of the tank 29 and the collected fly ash; a mixture of slag, which is crushed particles of lumpy high-temperature coal ash that has fallen into the water in the slag tank 1a at the bottom of the boiler, and circulating liquid; A treatment system for a powder-containing liquid having a dehydrator 38 that receives sludge from a wastewater treatment tank 29 and a supernatant liquid from a pipe 59 with a valve 60; a treated water recovery system having a sedimentation tank 39 that receives the supply of wastewater containing wastewater and the supernatant liquid of the wastewater treatment tank 29; a seal system that receives the supply of the supernatant liquid of the wastewater treatment tank 29 and seals the upper end of the slag tank;
A treated water circulation system that supplies the liquid in the circulation tank 40 to which the liquid of No. 9 is supplied via the pump 41 to the pump 33 that circulates and uses the treated water; A method for treating effluent from a coal-fired power plant, characterized by recycling separated treated water.