Investigation On Flue Gas Desulfurizatio And Denitration By Biomass Chars

Sulfur dioxide and nitrogen oxide are the primary air pollutants from combustion resources, and it draws a wide attention around the world about how to control their emissions economically and efficiently. Currently, there have been many desulfurization and denitrification methods. Among them the activated carbon method is widely noticed because of its feasibility of reducing sulfur dioxide and nitrogen oxide simultaneously and of sorbent regeneration. But the high cost makes it difficult for activated carbon to meet the requirement of widely ustilization. So the researchers are looking for new sorbents with low cost and high adsorption efficiency. In order to use the biomass energy efficiently, we propose a new technology that combines the use of biomass energy and the use of the biomass products for the control of pollutants from coal combustion, in which the biomass char is used as a sorbent. In this thesis, the capacity of biomass char to adsorb sulfur dioxide and nitrogen oxide of flue gas are studied.In the present work, eight kinds of biomass fuels are employed. Different pyrolysis temperatures (400℃,500℃,600℃,850℃),heating rates (fast,slow) and reaction times (10 minutes,20 minutes,30minutes) are taken to study the effects of the pyrolysis conditions on the char adsorption ability. In order to characterize the properties of the chars, Scanning Electron Microscopy (SEM) is used to observe the morphology, and Fourier Transform Infrared Spectrometer (FTIR) is used to get the surface chemical characteristics, and nitrogen adsorption method and mercury porosimetry are used to measure the special surface area and pore-size distribution. The adsorption experiments are carried out on a self-designed small-scale test facility to study the efficiencies of using biomass chars to adorb SO2 and NO speparately and simultaneously. In the experiments, the concentrations of the SO2 and NO are measured using a flue gas analyzer. Additionally, the adsorption capacities of biomass char and activated carbon are compared. At last the effects of some factors on the biomass char adsorption efficiency are discussed.The observation of Scanning Electron Microscopy shows that, after pyrolysis, the coarseness of biomass char surface is enhanced, and both the special surface area and the porosity of the char increase. There are adsorption peaks of silicon dioxide,oxalic acid root,carbonic acid root,hydroxy root,methyl,methylene on the FTIR curves. The carbonization degree of the char is enhanced and the surface function groups are reduced as the pyrolysis temperature increases.The nitrogen adsorption method is applied to measure the mesopores and micropores of the chars while the mercury porosimetry used to measure the macropores and part of mesopores. The results show that, the special surface area of the chars obtained by nitrogen adsotption varies from 0.1 m2/g to 400 m2/g, while those measured by mercury porosimetry vary relatively less from from 10 to 60 m2/g. The micropores of the chars distribute mainly in the range of 0.8-1.5nm and 1.8-3.5nm, and the mesopores and macropores distribute mainly in the range of 10-60nm and 60-600nm. The pyrolysis temperature affects the special surface area obviously. Commonly, the surface area increases as the temperature increases and as the pyrolysis time extends. The pyrolysis condition has a considerable effect on the micropore-size distribution while a relatilvey smaller effect on the macropore-size distribution.The adsorption experiments show that the biomass chars have a certain adsorption capacity for sulfur dioxide and nitrous oxide. The capability of the chars for sulfur dioxide adsorption is better than that for nitrous oxide. The adsorption efficency of nitrous oxide is low when there is only nitrous oxide in the flue gas but is improved when the sulfur dioxide also exists. The flue gas temperature has an effect on the adsorption efficiency. The adsorption efficiency is higher when the flue gas temperature is lower, but is lower when the temperature is above 100℃. Activated carbon has better adsorption capacity than biomass chars. Summarising the experimental results of this study, the best pyrolysis condition is fast pyrolysis at 500℃to 600℃with 10 minutes pyrolysis time.