The Nitrogen-enrichment Of Bio-chars And The Experimental Research On The Removal Of Sulfur Dioxide

The huge emissions of SO₂ and Nitrogen oxides from coal combustion was the main incentive of many air pollution problems such as acid rain, photochemical smog, and secondary particles, which have caused serious threaten to human health and social development. It is urgent to control the emissions of these pollutants. Activated char（carbon） adsorption method gains global concerns because of many benefits such as high removal efficiency, low investment, secondary pollution free, and the potential of integration removal of multiple pollutants. Biomass is a kind of clean and renewable energy which has many advantages such as widely sources, cost saving, near zero CO2 emission and so on. Applied biomass materials into the researchs of adsorbents production and the purification of flue gases will, not only improve the use value of biomass resources but also save the cost of adsorbents, which is very promising for wide application.In this study, three kinds of biomass samples were chosen as the raw materials for the production of carbon-based adsorbents. Pore structure analysis, elemental analysis, and Fourier Transform infrared spectroscopy were used to study and compare these adsorbents. The results showed that, the effect of activation temperature on the changing trends of total yield of different activated bio-chars were different, while these activated bio-chars all retained a total yield higher chan 19%. The pore structure parameters of bio-chars were obviously influenced by the activation temperature, in the studied temperature range of 650 to 850 centigrade, 850 centigrade was the best temperature to gain the optimal pore sturcture for these three activated bio-chars, and the pore structure parameters followed the order of corncob>corn straw>peanut shell. CO2 activation improved the pore structures of bio-chars, and also influenced their surface chemical structures, the kind and amount of surface fuctional groups were decreased with the activation temperature increase. The nitrogen concentrations of the activated bio-chars were all near 1%.In the nitrogen-enrichment study of carbon-based adsorbents, activated bio-chars were used as supports while MEA was used as impregnant, amine impregnation tests were carried out to study the effect of different factors, and finally confirmed a suitable impregnation method and the best precursor for amine impregnation. The results showed that, under the same conditons, methonal plays a better role in amine impregnation when compare with deionized water. For three biomass samples, corncob-based bio-chars present the best nitrogen-enrichment, and the corncob bio-char obtained at 850 centigrade with CO2 activation was chosen as the best precursor.The nitrogen-enriched adsorbents were produced by impregnation with three kinds of organic amines, and their adsorption capacities of SO₂ were tested on a self-bulit fixed-bed reactor. In the studied range（1¹0 wt.%）, the effects of impregnant concentration on adsorption capacities by different amine impregnations were totally different, only MDEA presents the positive effect on the whole, for which showed obviously enhancement on the adsorption ability in a relative high concentration（6¹0 wt.%）. The sample named “10%-MDEA” present the best adsorption capacity of about 153mg/g, which is a huge improvement of up to 170% compared with the precursor. MDEA impregnation successfully imported external N onto the surface of adsorbents, numerous tiny particles distributed inside and outside the pores resulted in the coarse surface. XPS analysis was used to compare the samples during the prcesses of adsorbent production, nitrogen-enhancement, and adsorptions. The adsorption properties were also took into accout to investigate the mechanism of SO₂ removal. SO₂ removal by nitrogen-enriched bio-chars was similar to the CO2 removal by solid amine.In the experimental study of integration removal of sulfur and nitrogen oxides, the effect of different factors on adsorption abilities were as follows: increasing O2 concentration will improve the removal of NO while the SO₂ adsorption fluctuated down. The effect of NO concentration on the removal of SO₂ was firstly increased and then decreased. In the range of 120 to 240 centigrade, higher adsorption temperature obtained lower SO₂ and NO adsorption. The presence of water vapor improved the SO₂ adsorption on the whole, but the removal of NO was only enhanced when the relative humidity（RH） is 15%, in which situation the removal of SO₂ and NO_x were increased at the same time.