Experimental and mechanism studies on simultaneous desulfurization and denitrification from flue gas using a flue gas circulating fluidized bed

Abstract

The oxidizing highly reactive absorbent was prepared from fly ash, industry lime, and an oxidizing additive M. Experiments of simultaneous desulfurization and denitrification were carried out in a flue gas circulating fluidized bed (CFB). The effects of influencing factors and calcium availability were also investigated on the removal efficiencies of desulfurization and denitrification. Removal efficiencies of 95.5% for SO 2 and 64.8% for NO were obtained respectively under the optimal experimental conditions. The component of the spent absorbent was analyzed with chemical analysis methods. The results indicated that more nitrogen species appeared in the spent absorbent except sulfur species. A scanning electron microscope (SEM) and an accessory X-ray energy spectrometer were used to observe micro-properties of the samples, including fly ash, oxidizing highly reactive absorbent and spent absorbent. The simultaneous removal mechanism of SO 2 and NO based on this absorbent was proposed according to the experimental results.flue gas circulating fluidized bed, simultaneous desulfurization and denitrification, oxidizing highly reactive absorbent, mechanismIn recent years, the interests in combined desulfurization and denitrification from flue gas increased rapidly. Many technologies have been proposed, among which the stage treatment technology is considered to be a mature one. In this traditional technology, a separate NO x control system, e.g., the selective catalytic reduction (SCR) or selective non-catalytic reduction (SNCR), should be installed to the back of the desulfurization equipment. Although it succeeded in combined removal of the SO 2 and NO, it is not easy to achieve wide industrial application because of the large occupying area and high running cost. To reduce the cost of flue gas purification, development of new technologies and equipments of simultaneous flue gas desulfurization and denitrification has become the leading research direction in the air pollution control field. There are many investigations in the world, but most of them have technical and economic defects, and cannot develop to practicable technologies.The technology of flue gas desulfurization with flue gas CFB [1] was firstly proposed by Lurgi Lentjes Bischoff (LLB) Company in Germany and developed rapidly by the comprehensive investigation for the process and the accumulation of engineering practice in the past 20 years. It has achieved increasing commercial application all over the world as it reduced the cost of investment and running to 50%-70% of that for wet process. The large-scale installation of flue gas CFB has been applied in the world and China, however, this technology lacks the ability of simultaneous denitrification.The research results show that the key point for simultaneous desulfurization and denitrification technique in CFB is to oxide NO into NO 2 rapidly in the flue gas, the latter is easily soluble in water. There is less litera-

Simultaneous Removal of SO2 and NO from Flue Gas Using Multicomposite Active Absorbent

“…Here, the circulating flow rate is 3.8 kg/(m 2 s), and the circulation multiple is 85. 10 In flue gas desulfurization technology, an important operational factor, Ca/S, is usually used to evaluate the utilization of the absorbent and serves as a critical technological parameter to determine the added amount of the absorbent. For the simultaneous desulfurization and denitrification from flue gas mentioned in this article, Ca/(S + N) is used instead of Ca/S, and is expressed as the following:…”

“…The reacted and unreacted solid particles of absorbent were collected by a cyclone dust collector and recirculated into the reactor. Here, the circulating flow rate is 3.8 kg/(m 2 s), and the circulation multiple is 85 …”

“…In flue gas desulfurization technology, an important operational factor, Ca/S, is usually used to evaluate the utilization of the absorbent and serves as a critical technological parameter to determine the added amount of the absorbent. For the simultaneous desulfurization and denitrification from flue gas mentioned in this article, Ca/(S + N) is used instead of Ca/S, and is expressed as the following: C a / false( normal S + normal N false) = n 1 / n 2 Here, n 1 and n 2 stand for the molar weights of slaked lime in absorbents and the gas mixture (SO 2 + 1 / 2 NO) in flue gas, respectively. The definition of stoichiometric relationship is based on the feed rate of slaked lime, SO 2 , and NO to the reactor and the expected removal products mainly include CaSO 4 /CaSO 3 and Ca(NO 3 ) 2 /Ca (NO 2 ) 2 in the spent absorbent …”

Simultaneous removal of SO2 and NO by highly reactive absorbent containing calcium hypochlorite

“…On the basis of our previous work [10,12], the highly reactive absorbent containing C was prepared from fly ash, industrial lime, and additive, C. The mixture containing fly ash and industrial lime (in the ratio of 3:1 in weight), and C and water (the water to solids ratio was kept at 20:1) was stirred and digested at 363 K, and dried for 6 h. Thus, the highly reactive absorbent was obtained.…”

“…For the flue gas simultaneous desulfurization and denitrification process mentioned in this article, Ca/(S 1 N) is used instead of Ca/S, and this is expressed as [10]:…”