Method and device for achieving desulfurization wastewater zero discharging with full flue gas

Abstract

The invention discloses a method and device for achieving desulfurization wastewater zero discharging with full flue gas. The method includes the steps that desulfurization wastewater discharged froma coal-fired power plant slurry dewatering system is directly fed into a bypass bubble tower in front of a desulfurizing tower, and then is subjected to reducing concentration with hot flue gas in front of the desulfurizing tower; desulfurization wastewater concentrated water is fed into three connection tanks for charging treatment; settled supernatant liquid is fed into a wastewater tank to be buffered and stored; part of waste heat flue gas is led out behind an electrostatic dust collector and is further pressurized through a high-pressure fan to be fed into an inlet of a Venturi atomizingtube; the desulfurization wastewater stored in the wastewater tank is led into the Venturi tube through negative pressure at a pipe opening of the Venturi tube, high-speed airflow at the throat position of the Venturi tube can impact and atomize the led-in desulfurization wastewater, and meanwhile the waste heat flue gas and liquid drops are subjected to forceful heat transfer so that the pre-evaporation effect on the liquid drops can be achieved; and solid evaporated products are captured by the follow-up electrostatic dust collector or a bag-type dust remover, and therefore low-cost zero discharging of the desulfurization wastewater can be realized.

Description

technical field [0001] The invention belongs to the field of industrial wastewater treatment, and in particular relates to a method and a device for realizing zero discharge of desulfurization wastewater by using all flue gas. Background technique [0002] Limestone / gypsum wet desulfurization process, as the mainstream desulfurization technology in coal-fired power plants, has the advantages of high desulfurization efficiency, mature technology, stable operation and convenient maintenance. However, in order to maintain stable and reliable operation of the slurry circulation system, a certain amount of desulfurization wastewater needs to be discharged regularly . The "Guidelines for Feasible Technologies for Pollution Prevention and Control in Thermal Power Plants" officially implemented in June 2017 clearly stated that, in addition to desulfurization wastewater, all types of wastewater after treatment can basically achieve "multiple uses of one water, cascade utilization", a...

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Problems solved by technology

However, the desulfurization wastewater is the terminal wastewater of the power plant, which is affected by many factors, and it is greatly affected by the working conditions and coal types; the pH is between 4.5-6.5, it is weakly acidic, and the content of chloride ions is high; the gypsum particles, silicon dioxide, iron The content of suspended solids with aluminum compounds as the main component is high, which may easily cause fouling of the membrane filtration device; the content of total dissolved solids is high, and the range of variation is large, generally 30000-60000 mg / L, and the content of hardness ions such as Ca2+ and Mg2+ is high , Mercury, lead, arsenic and other heavy metal pollutants exceed the standard

The traditional physical and chemical desulfurization wastewater treatment methods commonly used at present can only remove most of the heavy metal ions, but cannot remove the highly mobile chloride ions

[0003] Aiming at the status quo of desulfurization wastewater with complex water quality and its difficulty in treatment, the Chinese patent No. 201710054360.3 discloses a wastewater concentration system and method based on liquid column evaporation using flue gas waste heat. The desulfurization wastewater is sprayed into the In the evaporation tower, the waste heat of the flue gas in front of the desulfurization tower is used to concentrate the desulfurization wastewater. A demister is arranged at the outlet of the evaporation tower to remove the liquid droplets in the flue gas. The purpose of desulfurization wastewater concentration reduction, but this method increases the corrosion of the existing flue; the Chinese patent No. 201010179796.3 discloses a thermal power plant wet flue gas desulfurization wastewater spray evaporation treatment method, the desulfurization wastewater is directly in the power plant Spray evaporation in the flue before the dust collector to achieve zero discharge of desulfurization wastewater, but this method directly sprays the desulfurization wastewater without reduction treatment into the main flue before the electrostatic precipitator, which increases the corrosion risk of the electrostatic precipitator; the patent number is The Chinese patent of 201510275955.2 discloses a zero-discharge process and system for desulfurization wastewater. It uses chemical softening and microfiltration membrane for pretreatment, adopts nanofiltration and reverse osmosis separation, freezes and crystallizes sodium sulfate decahydrate with a purity of more than 99%, evaporates Crystallization of sodium chloride with a purity of 98% also provides a zero-discharge system that can reuse desulfurization wastewater, but the system is lengthy, the processing steps are cumbersome, and the investment and operating costs are high; the Chinese patent No. 201611008084.9 discloses A system and method for the comprehensive treatment of desulfurization wastewater concentration and flue gas drying. After the desulfurization wastewater is treated by a traditional triple box, it is concentrated by an evaporator. The concentrated wastewater is evaporated and crystallized by the heat of the flue gas in the bypass flue, and the air flows through the dust removal. Then it is discharged from the chimney, but this method directly uses the high-temperature flue gas in front of the air preheater to evaporate the desulfurization wastewater, and the subsequent solid evaporated product is collected by a cyclone dust collector instead of being captured by an electrostatic precipitator and mixed into the fly ash. It not only increases the energy consumption of desulfurization wastewater evaporation, but also its solid evaporated product needs to be treated as hazardous solid waste due to the enrichment of heavy metals and other pollutants

The Chinese patent No. 201610031262.3 discloses a method and device for treating desulfurization wastewater by using flue gas waste heat. The desulfurization wastewater discharged from the slurry dehydration system is directly sprayed into the concentration system transformed from the main flue before the wet desulfurization absorption tower. In this method, the effluent from the concentration system is directly sent to the main flue in front of the electrostatic precipitator for atomization and evaporation. However, the desulfurization wastewater in this method is not treated by three-box dosing. There are more calcium, magnesium and heavy metal ions in the water, and the water quality is poor. Not only Increase the risk of corrosion and fouling of the main flue before the electrostatic precipitator, and increase the risk of clogging of the mechanical atomization or medium atomization method used

[0004] Treating desulfurization wastewater by evaporation and crystallization, in order to achieve higher salt separation requirements, often requires high energy consumption and high economic costs; compared with flue evaporation, on the one hand, the bypass evaporation tower brings relatively high costs to the power plant. Large investment, on the other hand, brings pressure on land use for power plants that occupy a tight area for their equipment

However, the low treatment capacity of desulfurization wastewater in flue evaporation and the inability to completely evaporate dryness under low load limit the development of flue evaporation technology for desulfurization wastewater. 90~120℃) for reduction and concentration, and then use the waste heat of the flue gas before electrostatic precipitator (about 120℃) for atomization and evaporation to dryness. The cascade utilization of the waste heat of the flue gas in the power plant realizes desulfurization while reducing the investment of the power plant Zero discharge of waste water

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