Zero-discharge desulfurization wastewater treatment via membrane and crystallization
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Solution Overview
Problem
Current zero discharge technologies for desulfurization wastewater in power plants generate significant amounts of sludge and mixed salt, which are costly to dispose of and lack resource utilization, failing to achieve real zero discharge and increasing operating costs.
Innovation Solution
A sequential process involving pretreatment, membrane treatment, and evaporative crystallization to separate and recycle sludge and salt components, achieving industrial-grade purity and reducing disposal costs through the recycling of by-products.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If membrane concentration is adopted after pretreatment to reduce evaporation load, then evaporation amount is reduced, but sludge and mixed salt are produced as by-products that can only be treated as solid waste
Solution Approach 1:
The patent recovers valuable substances from the by-products: magnesium hydroxide is recovered for use in desulfurization, calcium carbonate is recovered for construction materials, and sodium chloride is recovered for industrial salt production. This transforms waste disposal into resource recovery, resolving the contradiction between reducing evaporation load and managing solid waste by-products.
Solution Approach 2:
The patent converts harmful solid waste by-products into beneficial resources. The sludge containing magnesium and calcium is transformed into useful chemicals for desulfurization and construction, while mixed salt is converted into sellable industrial salt. This principle resolves the contradiction by turning the harmful effect of by-product generation into a beneficial resource recovery process.
2Ease of manufacture
If mixed sludge is subjected to pressure filtration and landfill, then sludge disposal is achieved, but disposal costs increase significantly and resources are not used rationally
Solution Approach 1:
Instead of discarding sludge through landfill, the patent recovers valuable magnesium and calcium components for industrial use. The magnesium hydroxide is used in desulfurization processes, calcium carbonate is used for construction materials, and associated salts are recovered as industrial salt. This resolves the contradiction by transforming a disposal problem into a resource recovery opportunity.
Solution Approach 2:
The patent converts the harmful effect of sludge accumulation and landfill costs into a beneficial resource recovery process. By extracting and utilizing valuable components from sludge, the system transforms waste management into a profit-generating activity, resolving the contradiction between ease of disposal and resource utilization.
3Ease of manufacture
If mixed salt is taken as solid waste for landfill, then salt disposal is achieved, but landfill costs increase and certain environmental risks remain
Solution Approach 1:
The patent recovers sodium chloride from the mixed salt by-products and processes it into high-purity industrial salt that can be sold and utilized. This eliminates the need for landfilling salt waste, resolving the contradiction between easy disposal and environmental risks by creating a valuable recovered product.
Solution Approach 2:
The patent converts the harmful effect of salt waste landfilling into a beneficial resource recovery process. By purifying and recovering sodium chloride for industrial use, the system eliminates landfill costs and environmental risks while creating a sellable product, thus resolving the contradiction between disposal ease and harm reduction.
4Object-affected harmful factors
If zero liquid discharge is achieved through conventional methods, then wastewater discharge problem is solved, but large amounts of solid waste are generated that require costly landfilling
Solution Approach 1:
The patent implements comprehensive resource recovery from all by-products: magnesium hydroxide for desulfurization, calcium carbonate for construction, and sodium chloride for industrial salt production. This resolves the contradiction by transforming solid waste generation into resource recovery, achieving zero discharge while eliminating waste disposal needs.
Solution Approach 2:
The patent converts the harmful effect of solid waste generation into a beneficial resource recovery process. By systematically recovering and utilizing valuable components from sludge and mixed salt, the system transforms waste management into a profit-generating activity, resolving the contradiction between solving wastewater discharge and minimizing solid waste.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The process enables real zero discharge by recycling by-products, reducing disposal costs, and achieving significant environmental benefits by utilizing industrial-grade magnesium hydroxide and calcium carbonate, while minimizing landfill risks and operational costs.
Implementation Method 1
lime milk is added to a first-stage reaction tank, the pH value is adjusted to 8-9 under stirring conditions, iron, zinc, lead, nickel and chromium are produced into hydroxide precipitate, fluoride ions are produced into CaF2 precipitate, and silicon is produced into CaSiO3 precipitate
Implementation Method 2
an appropriate amount of organic sulfur is added to make mercury and copper produce sulfide precipitate
Implementation Method 3
an appropriate amount of coagulant and coagulant aid is added to form easily separated large particle precipitate
Implementation Method 4
sodium hydroxide is added to the second-stage reaction tank, the pH value is adjusted to 12.0 to 12.5 under stirring conditions, magnesium ions are reacted to produce magnesium hydroxide, magnesium hydroxide is precipitated
Implementation Method 5
sodium carbonate is added to the third-stage reaction tank, calcium ions are reacted under stirring conditions to produce calcium carbonate, calcium carbonate is precipitated
Implementation Method 6
the incoming wastewater is first filtered by ultrafiltration to filter out nanometer suspended matters, colloid, microparticles, bacteria and virus macromolecular substances in the wastewater
Implementation Method 7
clear water enters a pH adjustment tank, a certain amount of hydrochloric acid is added, the pH is adjusted to 5.5, and the wastewater is pumped to a nanofiltration membrane separation system; after the desulfurization wastewater is subjected to nanofiltration, sulfate-rich concentrated solution returns to a desulfurization tower
Implementation Method 8
the precipitated penetrating liquid with the sulfate content being lower than 1000 mg/L is pumped for reverse osmosis; after the nanofiltration penetrating liquid is concentrated by reverse osmosis
Implementation Method 9
the MVR evaporative crystallization system adopts a forced circulation heater, the feed liquid is continuously evaporated and concentrated, sodium chloride is subjected to supersaturated crystallization
Implementation Method 10
the MVR evaporative crystallization system adopts a forced circulation heater, the feed liquid is continuously evaporated and concentrated
Implementation Method 11
sodium chloride is subjected to supersaturated crystallization, is thickened, centrifuged, dried, packed and palletized
Implementation Method 12
sodium chloride is subjected to supersaturated crystallization, is thickened, centrifuged, dried, packed and palletized
Implementation Method 13
sodium chloride is subjected to supersaturated crystallization, is thickened, centrifuged, dried, packed and palletized
Data Source
AI summary
A zero discharge process for separating sludge and salt from desulfurization wastewater includes a pretreatment process, a membrane treatment process and an evaporative crystallization process; in the pretreatment process, the desulfurization wastewater enters a raw water tank, an aeration fan introduces compressed air into the raw water tank, and the wastewater is lifted to first-stage reaction and clarification by a raw water pump; in the membrane treatment process, the incoming wastewater is first filtered by ultrafiltration, then enters a pH adjustment tank, and is pumped into a nanofiltration membrane separation system and a reverse osmosis membrane separation system; in the evaporative crystallization process, the incoming wastewater is first subjected to two-stage preheating, then enters a degasser, and finally enters an evaporative concentration system and a crystallization system.