氧化锰烟气脱硫的可行性

Trans. Nonferrous Met. Soc. China 23(2013) 3089?

3094

Feasibility of flue-gas desulfurization by manganese oxides

Wan-qi YE, Yun-jiao LI, Long KONG, Miao-miao REN, Qiang HAN

School of Metallurgy and Environment, Central South University, Changsha 410083, China

Received 13 August 2012; accepted 29 November 2012

Abstract: For the purpose of effective and economic desulfurization of flue-gas, the predominance area diagram of the Mn ?S ?O system at different temperatures was constructed based on the thermodynamic data obtained from the literatures. It is seen from this figure that flue-gas desulfurization by manganese oxides is feasible from the thermodynamic point of view. Additionally, the most appropriate temperature range for flue-gas desulfurization is between 600 and 800 K, and the reaction is strongly exothermic to maintain the heat balance. The natural manganese ores encompass large tunnels that exhibit large surface areas and highly chemical activity, which can provide a high enough SO 2 removing efficiency. From the superposition of the diagrams of Mn ?S ?O and Fe ?S ?O systems, it is found that there is a coexistent stability region of MnSO 4 and Fe 2O 3, which provides the possibility of desulfurization by selective sulfation without ferric sulfate forming. A multi-stage desulfurization system has been discussed briefly. Key words: predominance area diagram; desulfurization; manganese oxides; dry FGD processes

1 Introduction

The principal cause of acid rain is generally attributed to the sulfur dioxide (SO 2) emitted from coal

combustion and other industrial processes. Although the

concentration of sulfur dioxide in such gases is small low,

the total quantity is very large [1]. Many methods have

been developed for removing sulfur dioxide from flue gases [2?4]. Data on worldwide flue gas desulfurization (FGD) applications reveal that wet FGD technologies, in particularly wet limestone FGD processes, have been predominantly chosen from other FGD technologies [5] due to their high efficiency (higher than 90%) of the sulfur dioxide absorption and the use of cheap reactant [2]. In those technologies, SO 2-containing flue gases contact with alkaline aqueous slurry which is generally

made from either lime or limestone in absorption towers. Although wet FGD technologies can meet the regulatory requirements for the control of sulfur dioxide emissions, some troublesome problems can’t be ignored. One objection is that the waste products are normally discarded as voluminous liquid slurry in an impoundment and ultimately capped with a clay barrier, which is then covered with topsoil once the slurry is de-watered over time [6]. A still further objection to these processes employing aqueous phase absorption is

that such processes usually necessitate cooling the flue gas to about 55 °C [7], which ultimately has a higher density and leads to settle in the vicinity of the stack. As

a result, local pollution may become worse, even though the quantities of sulfur compounds emitted to the atmosphere are reduced [3]. Dry FGD technologies, in which SO 2-containing flue gases contact with dry sorbents (lime or limestone), are considered to be more suitable for flue gas desulfurization due to their low operating costs, high desulfurization efficiency, and no water consumption. Besides, dry FGD processes are operated at elevated temperature. As a result, the wastes produced by dry FGD processes are easier to dispose than that from wet

FGD processes [5].

Manganese oxides (MnO x ) have received special emphasis as an absorbent for sulfur dioxide recovery.

Both mineral slurry and dry manganese oxides (ores) have been shown to be effective sorbents for sulfur compounds removing [8?11]. In the leaching of manganese ores, sulfur dioxide is shown to be a rapid, effective and sensitive reductant for manganese oxide minerals [8]. However, the formation of dithionate may bring pollution to the follow-up processes [12]. During the absorbing process, the SO 2 in the waste gases reacts

Foundation item: Project (51344006) supported by the National Natural Science Foundation of China

Corresponding author: Yun-jiao LI; Tel: +86-731-88830476; Fax: +86-731-88710171; E-mail: yunjiaoli6601@https://www.wendangku.net/doc/4f14619681.html,

DOI: 10.1016/S1003-6326(13)62838-1