Control of sulfur- and nitrogen-containing component formation as a basis for ecological optimization of coal gasification

Abstract

Gasification of low-grade coal characterized by high ash content and elevated sulfur content is considered an effective approach for improving the environmental performance of coal-based energy systems by transferring the formation of hazardous components to a controlled stage of producer gas generation. At the same time, analysis of recent studies shows that most works are focused on the influence of individual process parameters or on a limited set of impurities, while the issue of integrated control of sulfur- and nitrogen-containing species formation remains insufficiently addressed.

The aim of this study is to establish the formation patterns of sulfur- and nitrogen-containing components in producer gas during coal gasification and to substantiate the possibility of controlling their formation by varying key process parameters.

It is shown that the composition of producer gas is governed by the redox conditions of the process, which are determined by the oxygen content in the oxidizer and the oxidizer-to-fuel ratio. An increase in oxygen content leads to a rise in sulfur-containing species concentrations (H₂S up to 0,32 %, S₂ up to 0,16 %, SO₂ up to 0,12 %), while the content of reactive nitrogen-containing species decreases and the NO concentration remains low. Hydrogen sulfide is identified as the dominant sulfur carrier (95-98 %), which determines the requirements for subsequent gas cleaning processes.

It is demonstrated that temperature defines the transformation pathways of sulfur species. In the range of 1873-2073 K, the maximum H₂S formation is observed (up to 0,4), while further temperature increase leads to a shift toward oxidized forms (SO and SO₂ up to 0,24-0,25 %). It is established that at oxidizer ratios α>0,32, a controlled transition from reducing to oxidizing conditions occurs, accompanied by a decrease in H₂S and an increase in SO and SO₂ concentrations. At low temperatures, the formation of HCN, NH₃, and CS₂ is observed, which disappear at higher temperatures, indicating additional possibilities for composition control.

The obtained results demonstrate that targeted variation of temperature, oxygen content, and oxidizer ratio enables controlled formation of producer gas composition and limitation of environmentally hazardous components without changing the fundamental process scheme. Thus, parametric control of the gasification process can be considered an effective tool for ecological optimization of coal thermochemical conversion.