Design and application of carbide slag desulfurization wastewater treatment system
2016-02-03 09:36:38
Author: Yang Jiajun
Abstract: With the gradual promotion of electricity carbide slag desulfurization, the ways to deal with desulfurization-wastewater that generated faced with great challenges.Because of the highly content of the suspended solids SS, COD and heavy metal in the wastewater generated by carbide slag desulfurization,and the traditional desulfurization wastewater treatment process had been difficult to meet the processing requirements. The optimizing treatment processes after the upgrade added with the electro-flocculation system and activated carbon adsorption system based on the traditional processes that can effectively reduce the indicators of SS, COD, heavy metals, and the removal efficiency of COD and heavy metal of them is above 90% which was fully able to meet the increasingly stringent wastewater emission standards and it was worthy to be promoted .
Keywords: electro-flocculation system; activated carbon adsorption system; efficiency
overview
Carbide slag is the waste residue of of, which are discharged from chemical plant in the production of acetylene, main component is calcium hydroxide and mass fraction can usually reach 60% ~ 80%, and the minor components with the sources of calcium carbide residue and production conditions, vary. The carbide slag wet desulfurization has been as a mature technology of flue gas desulfurization step by step. Electric slag - gypsum wet desulphurization compared with the traditional limestone gypsum wet flue gas desulfurization, has more advantages, but due to the carbide slag impurity elements in complex, in addition to the conventional silicon, iron, aluminum, magnesium, sulfur, phosphorus oxide or hydride, there are still coke, organic phenols and heavy metals impurities, these impurities in the desulfurization slurry accumulation, and ultimately into the desulfurization gypsum, affecting the quality of desulphurization gypsum. To this end, the system shall be promptly removed from the amount of wastewater, guarantee system normal operation, the desulfurization wastewater also don't to traditional limestone - gypsum wet flue gas desulfurization, the main characteristics is suspended solids (SS 15000~23000 mg / L), COD (700 mg / L) and heavy metals (including PB, Cr, as, Hg reached 20 mg / L, Hg maximum up to 40 mg / L) content is extremely high. Therefore, it is necessary to the conventional desulfurization wastewater treatment processes are designed for the upgrading. Otherwise, the water quality is very difficult to discharge standards.
Two, process design:
1) the traditional process:
2）The improved process:
3）Process design
FGD wastewater treatment process consists of the following three parts: FGD wastewater treatment system, chemical dosing system and sludge dewatering system. From the improved process, obviously can see increased electric flocculation system and activated carbon adsorption system, reduce the aeration system and sodium hypochlorite dosing system. Here, since most subsystems are very mature technology, focusing on electric flocculation system and activated carbon adsorption system.
The wastewater desulfurization device produces a weak acid, contain some solids. The chemical and physical treatment, wastewater suspended impurities and heavy metals have been removed, wastewater has been clarified, the treated water standard (an emission standard) after discharge. The wastewater desulfurization unit row to wastewater treatment system, through the following processing steps of single continuous treatment process:
From the FGD system of wastewater cyclone overflow the wastewater into the wastewater treatment system, firstly collected wastewater in the buffer pool, through the buffer pool, to make the system stable operation flow.
And wastewater by a wastewater lift pump, into electrocoagulation device, aluminum, iron and other metal as the anode, in the role of DC, anodic dissolution, Al, Fe ion, after a series of hydrolysis and polymerization and ferrous oxidation process, the development of a several hydroxyl complexes, polynuclear hydroxyl complex even hydroxides, the wastewater in the colloidal impurities and suspended impurities coagulating sedimentation and separation. At the same time, charged contaminant particles in an electric field swimming and some of the charge is electrode and promote its destabilization of coagulation.
Enter the electrocoagulation equipment water electrolysis to generate nascent oxygen and hydrogen, nascent oxygen has strong oxidation, removal in wastewater by organic matter and reduce wastewater COD removal rate generally in more than 90%.
The electrocoagulation treatment of wastewater can achieve the following effect: Cr<0.001, the removal rate is up to 100%. Ni<0.005 maximum removal rate, up to 100%. Zn<0.062 removal rate up to 57%, the rest of the heavy metal ions also have removal efficiency of different degree.
The wastewater treatment method of electrocoagulation after entering, neutralization / reaction / flocculation tank. In the neutralization tank, wastewater pH by adding lime milk between further adjusted to 9~9.5, in this process, most of the remaining heavy metals to form a micro soluble hydroxide precipitated from wastewater.
In the box and not as hydroxide precipitation of heavy metals, in the reaction tank by adding organic sulfur liquid, the residual heavy metals and organic sulfide formation of sparingly soluble compounds, in the form of solid precipitation.
In the flocculation tank, adding flocculant so that the suspended sediment in the water, easy to form large particle flocculation settlement.
To clarify the settling pool, flocs and water are separated, through adding coagulant, accelerate suspended matter and sediment flocculation, improve flocculation effect, the floc settling at the bottom of the pool, sludge concentration is formed under the action of gravity, row to center pool mud collecting tube; sludge through the sludge circulation pump and sludge pump pumping out to clarify water by peripheral pool overflow water tank overflow tank body, pressurized by the pump after entering the activated carbon filter, re entering the next level of pH adjusting box.
The activated carbon filter pressure vessel is a pressure vessel filled with coarse sand cushion and high quality activated carbon. It is the work done by the carbon bed. Carbon bed composed of activated carbon particles have many micro pores and large specific surface area, has a strong physical adsorption capacity. The water through the carbon bed, water pollutant adsorbed by activated carbon effectively. In addition on the surface of the activated carbon non crystalline part has some oxygen tube to groups, through the carbon bed water pollutants by activated carbon adsorption, thus further deep removal in wastewater Harmonia, odor, SS and Hg, Pb, CD, Zn, Fe, Mn, chromium and other heavy metals, removal of arsenic from water, sulfide, chlorine and other high molecular compound.
Out of the active carbon filter in the clarification of water inflow pH adjusting box, continuous measurement of the pH value of the water discharge, when the pH value is too high, to the waste water into hydrochloric acid, regulating pH value reached standard back to the water storage pool, which can be.
3.1 electric flocculation system
Standard electric flocculation equipment consists of flow regulating device, electrolytic reactor, separation device, power supply and control system, as shown in figure 1. The flow control device used to measure and adjust the water flow into the Xu Ning electric device; electrolysis reactor is composed of a set of metal electrode plate, in the case of electricity generation electrolytic metal hydroxide flocs and hydrogen to produce Xu Ning flotation separation device; for waste water pollutants by flotation separation with Xu Ning place, its essence is an air floating sedimentation tank, containing slag and mud scraping device, in order to achieve the slag water separation (mud); power supply power supply device of electrolytic reaction, provide direct current for electro Xu Ning process, in order to complete the electrolytic reaction; the main function of the control device is a complete set of electric device coordination, Xu Ning stable and automatic operation.
1- flow control device; 2- electrolysis reactor; 3- separation device; 4- power supply; 5- control system
Figure 1 standard electrocoagulation equipment construction
The use of high efficient electrolytic flocculation electric flocculation technology, high activity group of flocculation generated very strong adsorption, has a good removal effect for non soluble organic polymer. At the same time, and the electric float and electrochemical oxidation combined, can further improve the organic matter removal rate, especially for difficult biochemical degradation of organic matter, by using strong oxidation cut chemical bond, improve organic matter can be biochemical, combined with biochemical treatment method can in order to achieve the purpose of fully biodegradable COD removal rate generally in about 90%, enough to ensure that the limit value of the COD of the treatment of desulfurization waste water to achieve "sewage comprehensive discharge standard of GB8978-1996 level emissions standards requirements is less than or equal to 100, while the traditional combination process of pre aeration and sodium hypochlorite dosing system, removal efficiency is only 30%, simply can not meet the discharge standard.
Electric flocculation technology because of its high efficiency of flocculation, to achieve the water of colloidal particles and impurity particles can be very good adsorption and flocculation, tiny particles so that the water of aggregated into larger floc, the floc formed more than adding flocculant formation of floc, more compact, thus conducive to settlement interception is separated from the water. Electric flocculation effluent of sedimentation, filtration technology can effluent turbidity control below 3 NTU. If the turbidity of raw water is very high >100NTU, it only need simple change operation parameters can reach and low turbidity water the same flocculation treatment. Electric flocculation technology for the removal of turbidity, suspended solids rate can reach more than 90%. For carbide slag desulfurization wastewater up to 15000~23000 mg / L concentration of SS, after only about 200mg / with to precipitate the subsequent dosing flocculation and clarification tank, but also can further reduce the index of SS.
Electric flocculation technology in the course of the power on reaction the generation of OH - ions in water, the combination of iron and manganese ions to form insoluble precipitates, with sand filtration equipment can be effective removal of heavy metal ions in water, the removal rate can reach 80% - 95%. For the removal of chromium ions, due to Cr6+ toxicity, to restore the low toxicity of Cr3+, Cr3+ and OH- by neutralization precipitation to remove. Electrocoagulation electrolysis produces two valent Fe2+ as a reducing agent, Cr6+ water can be fully transformed into low valence Cr3+, combined with the reaction of OH-, precipitation separation material removal. Electrocoagulation for the chromium ion removal rate can reach more than 90%
3.2 activated carbon adsorption filtration system
The traditional wastewater treatment process, wastewater by clarifier precipitation filtration after adjusting the pH value, then discharged directly, which suspended SS often exceed the standard, do not meet the 70mg/L emission limit requirements. This activated carbon absorber can be as the last barrier. Due to the activated carbon, the adsorption efficiency and even far less than 70mg / L emission limits.
Activated carbon adsorption systems by the adsorption unit, including a activated carbon adsorber, 2 sets of feed water pump, anti flushing unit and local control cabinet and a corresponding pipeline (including pressure gauge, the pulsation damper), pipe fittings, valves, pipe cables, cables and other accessories.
The main technical parameters:
Working pressure: 0.05MPa~0.6MPa
Working temperature: 5 to 40 DEG C
Mode of operation: manual or automatic control
Simplified material: Q235 rubber lining
Three, conclusion
With China's increasing attention to environmental protection, desulfurization wastewater emission targets is more and more strict, the desulfurization waste water quality generally must achieve "sewage comprehensive discharge standard of GB8978-1996 level emissions standards, the traditional wastewater treatment process has been unable to meet the requirements, especially for carbide slag desulfurization wastewater is even more so. After optimization of wastewater treatment process, in its unique philosophy and advantages for high concentration of suspended solid SS, high COD concentration, high concentration of heavy metals, and the current in the developed countries has run a successful case, it is worth to promote domestic.
reference
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