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Analysis

Addressing Industrial Needs with a Transnational Pipeline Network

Wed, 01/22/2014 - 15:53

The oil and gas industry is the largest contributor to the state of Tabasco’s GDP. The gas processing complex known as Ciudad PEMEX, which began operations in Macuspana in 1958, chips in with a substantial portion of this income. The nearby urban area, which goes by the same name, is the only city in Mexico created by presidential mandate. The settlement was established to house the workers of PEMEX and opened up with all the necessary services for its inhabitants to live their daily lives. The main activities of Ciudad PEMEX are eliminating pollutants and separating components in wet sour gas through three industrial processes: sour gas sweetening, sulfur recovery, and recovery of liquefiable elements in natural gas such as ethanol, propane, and heavy gases.

In its early days, Ciudad PEMEX had an absorption plant dedicated to processing wet gas produced in the José Colomo, Chilapilla, and Hormiguero fields. This plant no longer exists and Ciudad PEMEX now has four gas sweetening plants, two sulfur plants, and two cryogenic plants. In 2009, a new plant that eliminates nitrogen in cryogenic processes began operations to complement the complex’s downstream capabilities. The sweetening process consists of removing pollutants, mainly hydrogen sulfide and carbon dioxide, from wet sour gas by selectively absorbing contaminants though an aqueous solution. Sour gas, a mixture of hydrogen sulfide and carbon dioxide, is a common byproduct of the sweetening process. For sulfur recovery, this compound is passed through a thermal reactor or combustion chamber, before passing through two catalytic reactors, where it is converted into elemental sulfur. This is stored and transported elsewhere in a liquid state. In cryogenic processing, sweet wet gas coming from plants or directly from the fields is dehydrated and subsequently chilled with cool air from the process and an external mechanical refrigeration system. The cooling procedure and the gas’ high pressure enable the condensation of heavy hydrocarbons, such as ethanol, propane, and butane, which are separated and sent to the demethanizer distillation tower. Natural gas, mainly methane, is obtained after further cooling processes, and is later injected into the national duct system. Nitrogen is an inert gas that lowers the energy value per volume of natural gas and takes up valuable space in pipelines. A nitrogen rejection unit selectively removes nitrogen from natural gas. In the Ciudad PEMEX plant, a portion of the gas from the liquid natural gas recovery procedures in the cryogenic facilities is processed to reduce nitrogen to 1.2% mol. This is done by drastically lowering the temperature of the gas mixture and altering its pressure to a point where the gas’s components are liquefied but nitrogen is not.

In order to take advantage of dry natural gas, a pipeline was built between Ciudad PEMEX and Mexico City to supply Mexico’s central region, while the Yucatan Peninsula region receives gas through the Ciudad PEMEX-Merida pipeline. The price of natural gas in Mexico is currently established by a netback pricing model, affected by international prices. According to this, the price of natural gas is based on the Henry Hub, to which transportation costs from Houston to Los Ramones I are added. Conversely, costs from Los Ramones to distribution nodes, such as Ciudad PEMEX, are subtracted. Being one of the largest natural gas processing hubs in the country, Ciudad PEMEX is one of the most important distribution points in the system.