Feed-Gas Treatment Design for the Pearl GTL Project

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper IPTC 10682, "Sustained Development in the Pearl GTL Treating Design," by H. Grootjans, Shell Global Solutions Intl. B.V., prepared for the 2005 International Petroleum Technology Conference, Doha, Qatar, 21–23 November. Feed gas for Shell's gas-to-liquids (GTL) project in Qatar must be treated to meet the stringent contaminant specifications for a modern GTL process. This gas that contains hydrogen sulfide (H2S), carbon dioxide (CO2), several mercaptan species, and carbonyl sulfide (COS) requires a series of treatment processes. These processes must be selected and integrated to provide a cost-effective treating complex that removes contaminants in an environmentally friendly way. The full-length paper details the process selection method, indicating the process options available and the environmental benefits achieved. Introduction The Pearl GTL project in Ras Laffan, Qatar, will consist of two trains that together will produce 140,000 B/D of middle distillates and base oils from natural gas using Shell GTL technology. In addition, the plant will produce significant quantities of condensate and liquefied petroleum gas (LPG). Startup of the project is targeted for late 2009. Feed gas is supplied from the North field. Before this sour feed gas can be processed in the downstream GTL units, it must be treated for deep contaminant removal to meet stringent specifications. Gas produced from the North field contains a range of sulfur components, such as H2S, COS, and several mercaptan species. The gas also contains CO2 and traces of mercury. Deep removal of all sulfur-containing components will be required as well as full removal of mercury. CO2 must be partly removed, and the gas will need to be dried to avoid freezing in the ethane- and LPG-extraction units. Because of the wide range of contaminants and deep level of removal required, it is not possible to treat the feed gas in a single unit. Fig. 1 shows an overall block scheme of the treating units. Process Selection For optimal treating-complex design, process selection for the individual units must be made on the basis of an integrated approach that considers interactions between units. Optimal process determination must consider the following.CO2 and sulfur dioxide emissions.Treating-unit operability over a range of feed gases.Treating-unit capital cost.Operating costs. The full-length paper details the background of two key-process selection decisions. The selection of these two processes was done in parallel to account for interactions between the two processes.