Experimental Study On Increasing Mercury Removal Performance Of FeMnO_x By Non-Thermal Plasma

Mercury emissions from coal-fired power plants have gained more and more attention.At present,activated carbon injection technology is considered to be one of the most effective for post-combustion mercury removal,which is based on the great specific surface area and rich pore structure of activated carbon.However,the activated carbon adsorb mercury through physical adsorption,and the adsorption capacity depends on many factors,like temperature of flue gas,residence time,mercury concentration and flue gas composition and so on.At the same time,activated carbon injection will increase the amount of carbon in the fly ash,which affect the use of fly ash as a by-product.Therefore,severals researchers have shifted their research focus to find out a recyclable and effective non-carbon based adsorbent.For these reasons,a recyclable sorbent was prepared and then treated by non-thermal plasma to increase the mercury removal performance and stability.Besides,the effects of adsorption temperature,non-thermal plasma treatment conditions and different flue gas components on mercury adsorption removal were also studied.Furthermore,the stability of mercury adsorbed on sorbents were also studied using the toxicity characteriastic leaching procedure?TCLP?,which provided an effective and reliable means for the post-treatment of mercury removal sorbents.In this paper,a recyclable sorbent FeMnO_x was prepared and then treated by non-thermal plasma.It was characterized by specific surface test?BET?,transmission electron microscopy?TEM?,X-ray diffraction?XRD?,Raman spectroscopy,H_2-programmed temperature reduction(H_2-TPR)and X-ray photoelectron spectroscopy?XPS?and so on.The results showed that the non-thermal plasma treatment has no obvious effect on the specific surface area,pore size,pore volume and surface microstructure of the sorbent.Whereas,XPS tests showed that non-thermal plasma treatment increased the content of lattice oxygen and high valence of manganese compounds of sorbents FeMnO_x.Then,the mercury removal performance of sorbents before and after plasma treatment was investigated.The results showed that the non-thermal plasma treatment greatly improved the mercury removal efficiency of the sorbent FeMnO_x and increased with the increasing treatment time,ttreatment voltage and O₂ content.And the optimum adsorption temperature of the treated sorbent by non-thermal plasma was 80-130 °C,which was very close to the temperature of the actual sorbents injection.In addition,in the simulated flue gas atmosphere,during the whole adsorption experiment?30 minutes?,the mercury removal efficiency was maintained at more than 75%.NO,SO₂ and H2 O inhibited mercury adsorption,while O₂ and HCl promoted mercury removal.Meanwhile,non-thermal plasma treatment greatly improved regeneration performance.Finally,Hg-TPD and XPS analysis showed that the high-valent manganese and lattice oxygen in the adsorbent played a significant role in the process of mercury removal.High valence of manganese oxides and lattice oxygen were consumed during mercury adsorption,while non-thermal plasma treatment could replenish it and increase mercury removal regeneration performance better than without non-thermal plasma treatment.The mercury stability of the used sorbents can affect the methods of post treatment.The results of toxicity characteristic leaching procedure showed that mercury adsorbed on the sorbents FM-1-30 had good stability,and the Hg concentration of the filtrate was only 15.13 ?g/L,which did not exceed the maximum mercury leaching?0.2 mg/L?defined by EPA.Besides,in the great acid environment,the leaching rate of Hg increased.In addition,the leaching rate of Hg increased with the increase of solid-liquid ratio and leaching time.The XPS results of the FM-1-L showed that the Mn and Fe contents in the adsorbent had not obviously decrease.That is to say,Mn and Fe ions in the adsorbent were not leached out.In summary,the combination of magnetic separation,thermal regeneration and plasma treatment makes FeMnO_x an efficient,economical,promising and environmentally friendly sorbent.