Investigation on the Cause of the SO2 Generation during Hot Gas Desulfurization (HGD) Process

In the integrated gasification combined cycle (IGCC) process, the sulfur compounds present in coal are converted to hydrogen sulfide (H2S) when the coal is gasified. Due to its harmful effects on sorbent/solvent and environmental regulations, H2S needs to be removed from the product gas stream. To simulate the H2S removal process, desulfurization was carried out using a dry sorbent as a fluidizing material within a bubbling, high-temperature fluidized bed reactor. The ZnO-based sorbent showed not only an excellent capacity of H2S removal but also long-term stability. However, unexpected SO2 gas at a concentration of several hundred ppm was detected during the desulfurization reaction. Thus, we determined that there is an unknown source that supplies oxygen to ZnS, and identified the oxygen supplier through three possibilities: oxygen by reactant (fresh sorbent, ZnO), byproduct (ZnSO4), and product (H2O). From the experiment results, we found that the H2O produced from the reaction reacts with ZnS, resulting in SO2 gas being generated during desulfurization. The unknown oxygen source during desulfurization was deduced to be oxygen from H2O produced during desulfurization. That is, the oxygen from produced H2O reacts with ZnS, leading to SO2 generation at high temperature.

Influence Rules of Texture on the Stability of High Temperature Coal Gas Desulfurization Sorbent

Pulverizing problem, low mechanical strength and poor wear resistance of desulfurization sorbent limit the further development and industrialization of hot coal gas desulfurization technology. The present paper highlighted on the recent progress of hot gas desulfurization researches and gave a fully detailed introduction on physical parameters that reflect the texture of desulfurizer: specific surface area, pore volume, pore size and its distribution, porosity, fractal dimension and so on. Different from the traditional physical parameters, fractal dimension, as a comprehensive physical parameter describing a fractal structure, reflects the regularity degree of a porous structure. With the increase of sorbent fractal dimension, the complexity of pore spatial geometrical features increases, and the porosity and average diameter for pore decrease. The specific surface area also increased consequentially with the increase of micro-pore. Besides, this paper also investigated the proper texture of desulfurization sorbent that is favorable for desulfurization process on the basis of desulfurization mechanism for fuel gas.

The Recovery of Sulfur Resource during Regeneration Process for the Hot Gas Desulfurization Sorbent

Recovery of sulfur source is an important goal of industrialization regeneration for hot coal gas desulfurization sorbent. The different sulfide forms of sulfur produced in regeneration atmosphere and the method for recovering of sulfur source are discussed in this paper. The regeneration exhausted gas of high temperature desulfurization sorbent mainly has several forms of sulfides: sulfur dioxide, hydrosulfide and elemental sulfur, sulfide form and regeneration atmosphere have a direct relationship. Recovering sulfur dioxide utilize the reduction of CO or ammonia, and recovering hydrosulfide use selective catalytic oxidation which is the desulfurization method for achieve prospects of industrialization, but there is catalyst poisoning in these methods. We point out that the direct recovery of elemental sulfur from different forms of sulfide will be the focus of future research.

The Performance of Regeneration for Modified Semi-Coke Supported (Fe, Zn, ce) Sorbents

In this study, the regeneration behavior of modified semi-coke supported (Fe, Zn, Ce) sorbents were investigated using a fixed bed reactor. The effects of the regeneration temperature, space velocity and oxygen concentration have been considered in order to obtain suitable regeneration conditions. The most suitable regeneration conditions were obtained including 650°C regeneration temperature, 4vol.% of oxygen content and 4000h-1 of space velocity. Typical properties of the sorbents before and after regeneration were characterized using XRD and BET methods. Then the sorbents were tested 3 cycle experiments of desulfurization and regeneration for the purpose of duration test. The breakthrough curves changed slightly and the sulfur capacity only decreased 14.2%, it proved that the sorbents had good regenerability, which implied that the sorbents could be used for hot gas desulfurization.

Regeneration of Iron Oxide Sorbent Used for Hot Gas Desulfurization

Iron oxide sorbent was prepared from red mud and the regeneration behaviors were investigated in a fixed bed reactor. Regeneration parameters including temperature and concentration of oxygen have been considered in order to obtain a suitable regeneration condition. XRD and SEM techniques were used to characterize the fresh and regenerated sorbents. The experimental results show that the sulfided sorbent could be regenerated efficiently using a gas composition of 2% O2-15% H2O- balance N2, at the temperature of 700 °C.

Study on Sorbents Used for Hot Gas Desulfurization

This paper highlights currently excellent metal oxides used for hot gas desulfurization (HGD). Due to the different desulfurization properties, iron oxide and calcium oxide based sorbents are normally used for primary desulfurization while zinc oxide, copper oxide and manganese oxide based sorbents are often devoted to fine desulfurization. However, pure sorbents inevitably have some limitations and so, mixed oxides combining the properties of various metals like zinc ferrite and zinc titanate which get extensive concern are also introduced in this paper.