| Wet flue gas desulfurization(WFGD)is one the most mature desulfurization technology in the world at present,its high efficiency,low operating cost and the average desulfurization efficiency are above 90%,so it is widely used in coal-fired power plants and catalytic cracking of the flue gas treatment.Compared with the traditional limestone/gypsum method,Sodium alkali FGD has the advantages of lower equipment failure rate,higher desulfurization efficiency,less water consumption system,etc.Meanwhile win the widespread high praise.Main ingredients of Sodium alkali desulfurization wastewater is Na2SO4 which is different from CaSO4 produced by the traditional limestone/gypsum method,it is easily soluble in the water to form inorganic salt desulfurization wastewater and it contains more than 1% of the inorganic material belongs to the high salinity wastewater.Direct emissions of such wastewater will not only make the surrounding soil and water salinity increased and the environment damaged,but also waste the resources of Na2SO4.The object of this study was the sodium alkali FGD wastewater of a thermal power plant,it was decided to adopt evaporation concentration method to concentrate processing after analyzing the physical and chemical properties of wastewater.Then,the concentrates was dealt by freezing crystallization,the salt which obtained by separated can be used as product and hypothermic water can be recycled in the desulfurization system.Combined with the characteristic of high salt content of the desulfurization wastewater and the comparative analysis of several high salinity wastewater treatment technologies in such aspects as investment operation cost,technical maturity and environmentally friendly,the mechanical vapor recompression(MVR)evaporation technology was adopted as its characteristic of high efficiency and energy saving.Therefore,the wastewater treatment system was designed based on MVR system in this article,equipment selection and the simulated wastewater treatment parameters were simply analyzed taking the desulfurization wastewater as the research object.Firstly,the selection of parts were analyzed on the basis of wastewater treatment process design system,falling-film evaporator,plate heat exchanger,roots mechanical vapor compression air blower and DTB crystallizer were choosed after comparing eventually.Then the mathematical modeling method was used to establish the system of material and energy balance equation,the effect of various parameters on the performance of the system was analyzed by using the control variable method,such as the effect of evaporation pressure,the compression ratio of compressor,the material enrichment ratio and cooling crystallizer on investment operation cost and performance of the system.By analyzing the relative curve between the factors and the performances and taking the investment costs and operating expenses of the system into account,the optimum operating conditions of the system were obtained.The optimum operating conditions were as following: the evaporation pressure was at 70 ~ 80 kPa,the compressor compression ratio from 1.6 to 2.2 was appropriate.And the concentrate can be returned to the evaporator repeatedly to achieve the desired concentration in the case of less investment cost and maintaining the enrichment ratio constant.In this paper,the operation cost of MVR system was compared with the triple effect evaporation system under the specific process operating conditions.The MVR system could save nearly 1.105 million of operating expenses annually compared with the triple effect evaporation system under the condition that the amount of the wastewater treatment was 3000 kg/h.Accordingly,the energy saving effect of the MVR system relative to the triple effect evaporation system was remarkable,and the MVR system is more accord with the requirement of economic development. |
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