Optimization of Shale Gas Sweetening Process Coupling with Claus Process Based on Energy Synthesis

Abstract

As a sort of emerging unconventional energy, shale gas has extensive market outlook by virtue of its enormous reserves, and concerns for shale gas exploitation and processing have been raised nowadays. Raw shale gas must be processed to achieve certain specifications before it can be transmitted in pipelines or utilized by consumers. Sweetening is a gas conditioning process to decrease the concentration of acid gases such as hydrogen sulfide and carbon dioxide which are not preferred in sales gas in consideration of heating value specification and corrosion prevention. However, the after-treatment of acid gases is not discussed in many research of sweetening process.
In this paper, a flowsheet of shale gas sweetening process is established using Aspen Plus v8.6. Dissolution of light gases and weak electrolyte, absorption of acid gases and reactions in electrolyte solution are considered simultaneously in process modelling. Diethanolamine (DEA) solution is employed as the solvent to separate acid gases from raw shale gas. The optimal feed stage of rich solvent regeneration and reflux ratio of regenerator are analysed to optimize the sweetening flowsheet. A three-stage Claus process is simulated coupling with shale gas sweetening process to convert hydrogen sulfide in acid gas to element sulphur for pollution reduction. A principle is proposed to determine the operating temperature of each Claus reactor which is a decisive parameter on sulfur recovery efficiency and performance of Claus process. Ultimately, the sulfur recovery efficiency of the three-stage Claus process proposed in this paper is 97.35 %. The effectivity of the principle is confirmed by the results reported in literatures. Energy synthesis is then adopted to integrate sweetening process with Claus process in both mass and energy flow. The coupled process provides with more streams than a single sweetening or Claus process, promoting the reasonability of energy utilization. Streams are extracted and matched for heat exchanger network (HEN) synthesis to reduce the energy consumption and total annual cost of the whole process.