Wastewater treatment system design – MgO FGD technology
1. Flue Gas Desulfurization Technology Overview
Magnesium desulfurization technology around the world have a lot of application performance, which has been applied in 13 of the more than 100 projects. Taiwan’s power plant is 95% of magnesium oxide, the United States, Germany and other places have been applied, China has started to promote, and has been applied in a few areas. Calcium magnesium desulfurization desulfurization relative terms, to avoid a series of problems simplified wet exist, such as pipe blockage, low flue gas temperature, flue gas with water and the presence of secondary water pollution; the process maturity only inferior calcium method, simple structure, small footprint, adequate sources of raw materials, low cost, good safety performance, dramatically reducing the amount of investment, and to reduce secondary pollution, desulfurizer recycling, reduce the desulfurization costs, overall economic efficiency has been greatly improved.
Power plant (2x225MW) flue gas desulfurization unit renovation project (FGD) using magnesium oxide wet FGD technology, process system consists of desulfurizer slurry preparation systems, flue gas systems, SO2 absorption system, the desulfurization tower evacuation system, magnesium sulfite dewatering system , process water systems, wastewater treatment systems, Utility and instrument air system components. Basic use of closed-circuit water circulation throughout the FGD way, wastewater, mainly from the desulfurization tower desulfurization process, water slurry within the desulfurization apparatus in the process of continuous cycle, will be enriched in heavy metal elements and F-, C1-, on the one hand to accelerate the corrosion of desulfurization equipment, other On the one hand affect the quality of desulfurization by-products, therefore, desulfurization unit to emit a certain amount of waste water with high salt obvious feature, its heavy metal ions, ion, ss excessive levels, while the pH value does not meet emissions standards, the need for targeted treatment.
(This article is only for flue gas desulphurization renovation project wastewater treatment system design brief.)
2. Design of water and water quality
According to the information provided in a power plant in Shandong, the desulfurization unit total displacement of 144t / d, an average displacement of 6t / h, continuous emission, this device is designed treatment capacity of 8t / h.
Water desulfurization waste water: temperature 49 ℃, pH2-3, suspended solids 5900mg / L, SO42- <10000mg / L, C1-10000mg / L, F-1000mg / L.
3. Design Principles
Mature and reliable coagulation sedimentation process technology to ensure the indicators of treated water up to the national “Integrated Wastewater Discharge Standard” GB8978-1996 platoon level standards; sewage treatment facilities to have a small footprint, the project investment, running low energy consumption, low processing costs, suitable for power plant renovation project; the design should take full account of ancillary equipment vibration, noise and other measures to prevent secondary pollution.
4. Process
The slurry discharged from the desulfurization tower solids content of 15%, the main ingredient is solid magnesium sulfite. Discharge slurry must be dewatered before they can be further processed to give the desired products. In this project, including dewatering dewatering system supply tank, dehydration supply pump, centrifugal dewatering machine, dryer, and other related equipment.
Desulfurization tower desulfurization slurry is pumped through a slurry discharge people dehydration supply tank, byproducts of desulfurization and then concentrated by centrifugation after dewatering screw conveyer transported to a hot air dryer, dryer outlet moisture content of about 10 percent of byproducts artesian people one-product storage warehouse. The whole process of entering the wastewater treatment system produces, after discharge. The project desulfurization wastewater treatment process: neutralization, sedimentation, flocculation, clarification.
And: Acidic waste generated increased from flue gas desulfurization cyclone separator and waste pump into the box, and the box set pH adjustment system, by controlling the dosage and frequency valve means for controlling milk of lime to maintain the wastewater and in the case of pH (8.8-9.0), where a large number of raw wastewater of heavy metal ions (such as Zn2 +, Mg2 +, etc.) are in the form of hydroxide precipitation, the energy in the waste water and mixing tank, a stirring motor set.
Settlement: neutralization tank waste water gravity flow sedimentation tank, where a large number of Mg and other heavy metal wastewater with very fine precipitated hydroxides and complexes form from wastewater. Meanwhile, in order to ensure that other trace heavy metal ions in wastewater precipitated in the settling tank dosage organic sulfur compounds, so that other heavy metal ions and sulfur ions reaction of insoluble metal sulfides. Since the formation of hydroxides and fine metal sulfide particles in the waste water is not easy to settle, so by adding iron complex formation of fine particles in the waste water floc. Mixed evenly, Shen
Drop box set stirring motor, waste water into the flocculation tank by gravity.
Flocculation: flocculation tank dosing flocculant (PAM), stirring to form a larger fine alum floc ensure clarifier can complete solid-liquid separation. Flocculation tank set stirring motor.
Clarification: the flocculation tank to the waste water in the clarification tank liquid separation, since the waste water is very small (5m3 / n), to clarify the box is easy to install and maintain the vertical flow sedimentation tank, stable and reliable, while saving a machinery and equipment (rotary scraping machine). Clarification is formed under the action of gravity and concentrated concentrated sludge, concentrated sludge discharged by sludge screw sludge, water flows into the tank from the surrounding water triangular weir. Clarifier sludge concentration meter is installed, timing detection mud.
Since the wastewater pH higher (8.8-9.0), and therefore the water tank is installed stirring motor, and is equipped with pH adjustment systems, pH adjustment system controls the metering pump HC1 set plus, in order to ensure the water quality in the tank discharge (pH = 6-9), the effluent discharged by the health and rinse water desulfurization island.
5. Process System Design
Flue gas desulfurization project wastewater treatment system design is divided into three parts, namely: wastewater treatment systems, sludge dewatering systems, chemical dosing system.
