Study On Preparing Coal Based Activated Carbon By Non-pitch Agglomerant And It Used In Flue Gas Desulfurization

China is the country with the largest coal consumption in the world; the sulfur dioxide emissions from thermal power plants have caused great pollution to the environment. In all desulfurization processes, due to the advantages of high desulfurizing activity, easy-generation and no secondary pollution, activated carbon desulfurization technology has been widely studied and applied. At present, in the process of the formed activated carbon preparation, the binder is the most important factor which determines the comprehensive performance, it is usually known that the activated carbon prepared in the market with asphalt and tar as binder has high mechanical strength, but also has some disadvantages, for example, low desulfurization efficiency, heavy pollution in preparation and high cost. Our study uses the non-asphalt binder NPA and Taixi Coal as main raw materials, successfully developed a new type of activated carbon NPAC for flue gas desulfurization, through comparison with conventional activated carbon with asphalt as binder, it can be got following conclusions:1. Non pitch agglomerant (NPA) is a high quality binder prepared by activated carbon, the NPA additive is favor to form the secondary basic pore of coal-based activated carbon, which promoted to increase the number of pores and specific surface area, the total surface area of NPAC is of higher72.2%than PAC, and the micropore area is higher196%, the average pore size decreases from3.53nm to2nm, which devotes to the more developed pore structures.2. By high temperature carbonization and activation, the graphite-like structure of (002) and (10) peak in NPAC and PAC structure are strengthened,this is mainly due to the forming of more stable crystalline structure and skeleton carbon structure by the presence of binder in the process of carbonization and activation, the aromatic and degree of graphitization increasing at last. Wherein the diffraction peak intensity NPAC is maximum, the degree of graphitization is stronger, which is the reason for the highest mechanical strength.3、To some extent, the content ratio of the active carbon has changed through high temperate steam activation. At the same conditions of high temperate steam activation, the disintegration appeared at the groups of the coal surface, and the surface element area of oxygen, nitrogen and sulfur were decreased. The concentration of oxygen and O/C on the NPAC and PAC surface has been reduced. But when the number of oxygen atoms on the coal surface is reduced, the interaction between electron donor and election acceptor of the delocalized π electron on a plane layer of carbon atoms has been enhanced. Cπ is the primary source of alkali of the active carbon surface. The concentration of π-π*on the aromatic ring is proportional to the desulfurization capacity of the activated carbon. The sulfur capacity of NPAC and PAC are22.98mg/g and30.71mg/g respectively, which are corresponding to10.89%and7.25%of the concentration of surface π-π*, and the its relation equation is y=1.85x+10.26.4、With the increase of the addition amount of NPA and molding pressure, it increases the combination surface of coal particles and the binder, the clearance between the particles and feedstock has decreased, the structure is more compact, the mechanical strength enhances;the formation of secondary base hole is much abundant, After it was activated,the activated effective pore increased,sulfur content increases, but It clogs the hole due to excessive dosage, the sulfur content is lower, molding pressure is peaked and declined caused by rebound over the General Assembly, the mechanical strength is reduced.When the content of NPA binder increased from11%to11%,the mechanical strength of the active carbon from82.63%to89.79%,the NPAC sulfur content from17.53mg/g to32.68mg/g, then continued to increase the binder, the sulfur capacity of the active carbon reduces and the mechanical strength increases slowly. The molding pressure increases from40kN to300kN, NPAC mechanical strength from68.13%to91.41%, sulfur content from6.86mg/g to31.53mg/g, when the molding pressure continues to increase, the pressure comes to the peak and declines, NPAC mechanical strength and sulfur capacity are reduced.5、With the increase of carbonization temperature, crystallite structure of the NPAC becomes stable, the degree of graphitization increases, mechanical strength improves, but the carbonization reaction is reduced, which is not conducive to the activation of reaming or the increase of the specific surface area and leading to decline in sulfur content. With the increasing of the carbonization time:the mechanical strength of activated carbon changes little; as a result of the degassing or the rearrangement of the structure,there forms plenty of active sites and basic holes on the carbon surface which sulfur capacity have increased.6、Activation conditions have great impact on the development of the secondary basic holes of NPAC. With increments of activation temperature, activation time and activation agent flow, the mechanical strength of NPAC reduces gradually, while its sulfur capacity firstly increases and then decreases. At the highest point in sulfur capacity, if continue to increase the activation dynamics, it will lead to that the reaction rate proceeds faster, carbon of hole wall is consumed in excess, the effective holes and sulfur capacity reduce.7、Optimized conditions for NPAC preparation are as follows:15%for addition amount,200kN for forming pressure,1.0mL/min for water vapor flow,880℃for activation temperature and150min for activation time.8、Both of water regeneration and heat regeneration methods can make the inactivated NPAC recovered certain desulfurization activity. Water regeneration method can improve the desulfurization activity of NPAC by prolonging the regeneration time and increasing the regeneration temperature. Heat regeneration method can make the desulfurization ability of NPAC recovered greatly, regeneration temperature between330℃and450℃is proved to be beneficial to the desorption reactions; the temperature range is conducive to the sulfate reduction and the release of SO2. The NPAC samples have abundant pore size distribution near lnm before and after regeneration, while in comparison, it has more abundant hole at lnm before regeneration than that after regeneration. In the heating process of regeneration, sulfuric acid stored in the NPAC pore structure will react with center activated carbon around microporous and consume part of the carbon, causing the generation of new holes at2nm in the regenerated samples.