Sulfur combustion as a source of energy: Reaction mechanism development and process simulation

Abstract

Acid gas found in crude natural gas, is separated from natural gas and processed in Claus process to produce sulfur. Elemental sulfur combustion is traditionally used to generate SO2 to produce sulfuric acid that is consumed in chemical industries, but is now also being considered as an energy vector for power generation. H2S, SO2 and sulfur are the main components for this research. Claus process has high efficiency for acid gas with high H2S content, but when H2S content is below 50%, co-combustion of fuel gas (methane) together with lean acid gas is required to sustain combustion in the furnace that significantly enhances the operating cost of sulfur production along with increasing CO/CO2 emission. Using the Claus process as a base, two novel processes are designed that are highly efficient for sulfur production from lean acid gas. Both the processes initiate with sulfur combustion, which is typically seen only in sulfuric acid plants. In the first process, sulfur combustion generates SO2 that is mixed with acid gas and is sent to catalytic reactors for sulfur recovery, thus avoiding the requirement of acid gas combustion. In the second process, SO2 from sulfur combustion at high-temperature is mixed with acid gas in the furnace for sulfur production. The remaining gas is sent to the catalytic reactors for further sulfur recovery. For various feed compositions, the two processes together with the Claus process were optimized by minimizing the emissions of H2S and SO2 in the tail gas. For acid gas feeds with H2S content varying from 10-65%, sulfur recovery efficiency in the first process varied within a small range of 98.3- 98.5%, while for the second process, it varied between 96.8-98.6%. In comparison, the optimized Claus process efficiency remained between 96-98.2% that was nearly 2% lower than the first process for the lean acid gas feeds. The suggested processes reduce CO and SO2 emissions from the stacks of sulfur recovery units. Overall, process 1 resulted in a steady SRE for all H2S concentrations, but process 2 works better for H2S concentrations above 45%. This research includes a detailed reaction mechanism, developed and validated with data from lab-scale and industrial plant studies. The reaction mechanism is used to conduct sulfur furnace simulations, where the effects of feed air/sulfur ratio and oxygen enrichment of air stream on furnace temperature and the concentrations of SO2, SO3, and O2 are investigated. The dominant reaction pathways involved in sulfur combustion, particularly for the production of SO2 and SO3, are identified. It was found that the feed air/sulfur ratio monitors the furnace temperature, and can be used to obtain the desired O2/SO2 ratio at the furnace exit for the optimal operation of catalytic converter (for SO2 oxidation to SO3) that follows the furnace in the sulfuric acid plant. Moreover, high oxygen enrichment above 35% (while maintaining the desired O2/SO2 ratio at the furnace exit) significantly increased the furnace capacity through reduced total gas flow (thus decreasing blower energy requirement and equipment size). The developed reaction mechanism provides a method to obtain optimized furnace parameters to achieve high efficiency and reduced costs in sulfuric acid plants.

Date of Award	Jul 2021
Original language	American English