Optimized CAPEX and OPEX for Acid Gas Removal Units: Design AGR without Sulphur Recovery Processes
Authors: Qassim A S , Mathur A K 
Published: May 2012

Qatar is a small country in the Middle East region. However, it sits on the third-largest proven gas reserve. Efforts to commercialize this gas reserve have resulted in Qatar becoming the world's largest LNG exporter. Currently, Qatar's industrial gas demand is met by lean gas from four sources: the North Field Alfa (NFA) production station complex; Onshore stripped associated gas (SAG) sources, Offshore stripped associated gas (SAG) sources; and the Khuff reservoir.

Qatar Petroleum (QP) needs to meet industrial gas specifications on sulphur contents and environmental regulations and reduce atmospheric emissions. QP has therefore undertaken a project to install new Gas Sweetening Facilities (GSF) including compression, dehydration, sulphur recovery or disposal, and utilities.

Sweetening of sour fuel gas results in production of huge quantities of acid gas. Acid gas is a mixture of Carbon Dioxide and Hydrogen Sulfide which can not be flared or vented due to environmental concerns. Therefore, disposal of this acid gas poses a challenge as we sweeten the fuel gas and drives the selection of process configuration of the new facilities. There are two options available to deal with this acid gas: Processing acid gas through a sulphur recovery plant and producing Sulphur as a by-productRe-injecting the acid gas into the gas reservoir and eliminating environmental emissions

With millions of riyals at stake, QP knows that they need to do everything they can to ensure a successful outcome. Therefore, QP uses a stage-gate process that provides assurance for upper management that shortcuts are not taken and important steps are not missed as a project progresses. When QP decided to undertake a project to sweeten fuel gas from the Khuff gas reservoir, we carried out a feasibility and concept optimization study to look at various options. We focused on capital expenditure (CAPEX) and operating expenditure (OPEX) considerations along with the effect of new facilities on the environment and safety. Other factors that governed the final outcome of the study were online reliability, ease of operation, capability to handle varying feed rates or composition and by-product handling.

This study evaluated various alternatives for what to do with the acid gas produced from the new facility as well as the selection of the project sites. The sites evaluated for the new facilities were Dukhan and Mesaieed as QP already has industrial establishments at these sites. These sites are approximately 100 Kms apart. Dukhan and Mesaieed sites have different features, in terms of available utilities, proximity to the injection well and plant area.

Considering available units and the re-injecting facilities already available within Gas Recycling (RG) Plant in Dukhan, it was finally concluded through a systematic analytical process to install new GSF with acid gas reinjection configuration at Dukhan. Major factors that lead to this decision were: no market for sulphur and high capital and operating expenses for sulphur recovery unit (SRU). Additional advantages of selection of re-injection of acid gas option were environmental and safety.

In this paper we are going to describe four options. The first entails acid gas re-injection. The other three involve installation of a new SRU with or without upgrading existing SRUs. We also present here the approach taken to select the best option taking into account CAPEX, OPEX, the environment and safety aspects.