Study On Adsorption Performance And Adsorption Kinetics Of Modified Gases In Modified Coke

Mercury emission control has been paid widespread attention by researchers of all over the world. Sorbent injection is one of the most prospective technologies for mercury emission control in coal-fired flue gas. The key of successful application of the technology is to research and develop low-cost and high efficiency mercury sorbents. Because biomass has the characteristics of abundant reserve, low sulfur and nitrogen content, high ash reactivity, and zero CO2net emission, it is very important to carry out the study on preparation of biomass chars, and their mercury adsorption properties and adsorption dynamics.Four kinds of biomass, named peanut shell (PS), corn stalk (CS), wheat straw (WS) and wood chips (WC) were sleeted. Firstly, the pyrolyzed biomass chars were prepared in a fixed bed pyrolysis/activation experimental facility. Then the pyrolyzed biomass chars were impregnated in solutions of halogenated potassium to obtain the different impregnated biomass chars. Finally, the steam activated biomass chars and all modified biomass chars were prepared through treating the pyrolyzed biomass chars and the impregnated biomass chars by steam activation, respectively. The different kinds of biomass chars were characterized by surface area analyzer, SEM-EDS analyzer, ICP-AES analyzer and FT1R analyzer. The effects of preparation and modification conditions on the physical and chemical characteristics of biomass chars and release of alkali/alkali earth metals and chlorine was demostrated. The results indicated that:(1) Pyrolyzed biomass chars prepared at873K showed the best pore structure and surface chemical structure.(2) During the pyrolysis process of different biomass, sodium is the easiest to release, followed by potassium, and release of calcium and magnesium is the lowest. The release ratio of chlorine bound in the PS is the lowest, however that bound in the WC is the highest.(3) There was no significant improvement on porous structure of the biomass chars after impregnation by KC1, KBr and KI solutions. Instead of physical properties, the surface chemical properties of the biomass chars have been changed apparently after impregnation by KCl, KBr and KI that the number of surface oxygen functional groups and halogen elements (Cl, Br and I) content were increased significantly.(4) Steam activation can improve the surface area and porosity of biomass chars significantly, but also can significantly reduce the halogen elements (Cl, Br and I) content. The mercury adsorption was carried out in a fixed bed adsorber with a quartz tube to study the effects of biomass species, adsorption temperature, superficial velocity, pyrolysis temperature, modification reagents and steam activation on elemental mercury adsorption characteristics. The results indicated that:(1) For biomass chars pyrolyzed from four tested biomass, the adsorption capability of the PS char was the highest, followed by the CS char and WS char, and the adsorption of the WC char was the lowest.(2) The unit mercury adsorption capability of pyrolyzed biomass chars showed the trend of decrease first and increase later with increasing the adsorption temperature.(3) The unit mercury adsorption capability of pyrolyzed biomass chars showed an increase with decreasing the superficial velocity.(4) The biomass chars pyrolyzed at873K showed the best adsorption characteristics.(5) Increasing of mercury adsorption rate and adsorption capability of the KC1, KBr, KI-impregnated biomass chars compared to the pyrolyzed biomass chars indicates that KC1, KBr, KI-impregnated biomass chars have a great promotion on Hg0removal performance. In addition, mercury adsorption capability in a order from strong to weak were KI, KBr, KI-impregnated chars.(6) Steam activation can further improve the adsorption capability based on the impregnated chars, but the effect is not significantly improved. In addition, the mercury adsorption capability of the same biomass is ordered as all modified, impregnated, steam activated, and pyrolyzed biomass chars.Four models including pseudo-first-order model, pseudo-second-order model, Fick’s intra-particle diffusion model and Elovich model were performed to fitting the mercury adsoprion curves. The results showed that all the examined models describe efficiently Hg0adsorption process except the Fick’s intra-particle diffusion model. The mercury adsorption mechanism by biomass char sorbents studied was complex and dominated by external mass transport process, pore diffusion process and chemisorptions process jointly. Chemisorptions was the controlling step of mercury adsorption process of pyrolyzed biomass chars, steam activated biomass chars, and all modified biomass chars, while chemisorptions and external mass transport has an equivalent influence on the mercury adsorption process of impregnated biomass chars.