Helium: Its Extraction and Purification

Abstract

Abstract This paper discusses the extraction of helium from natural gas as practiced in existing helium plants. There are various sources of helium but natural gas is currently the only commercial source. Several phases of the helium extraction process, such as refrigeration systems and methods of carbon dioxide and water removal, are similar to those in natural gas processing. It is concluded that in cryogenic processes, solid desiccants are more suited than glycol for water removal, and that with proper plant design, natural gas containing small amounts of carbon dioxide can be processed cryogenically. Discussed are (1) the relationship of processing pressure to the recovery method and equipment sizing, various methods of developing required refrigeration for the cryogenic process and the design, utilization and metallurgy of such items as compressor, heat exchangers, control valves, fractionating towers, dehydrators and insulation. Helium purification is examined as to methods of removing hydrogen, nitrogen and methane from the helium stream. Included are noncryogenic methods of purifying helium. Introduction The role of helium has shifted in recent years from its well known use as a lifting gas to many new, exciting and possibly more important applications. The quantity of helium used for lifting purposes has fallen behind that used for such other present-day purposes as pressurization, shielded arc welding, controlled atmosphere and research. Helium is valuable because as a gas it is odorless, tasteless, nontoxic, nonflammable, inert and light. As a liquid it is valuable because of its very low boiling point of -452F at atmospheric pressure. Because of these unique properties, it has other small but important uses such as purging, leak detection, cryogenics, chromatography and heat transfer. Small concentrations of helium can be found in air and in certain minerals, and it was recovered from these sources for some early experimental work; but because of the very low concentrations, these are not considered to be commercial sources. When helium was discovered in natural gas, all commercial recovery efforts quickly shifted to this new and exciting source. Some pioneer plants were built in the United States and Canada to extract helium from natural gas during World War I. These early plants, built before the advance of technology and under a wartime emergency atmosphere, were small and of uncertain design. From 1921 to 1925 the Linde Co. operated such a plant for the U. S. Navy near Fort Worth, Tex. In 1925 operation of this plant was assumed by U. S. Bureau of Mines. Great advances in technology resulted from the pioneering effort in the Fort Worth plant, contributing heavily to the establishment of an economically feasible method for extracting helium from natural gas by a low-temperature liquefaction process. This new technology was used in the late 1920's when USBM erected a helium extraction plant near Amarillo, Tex., to process natural gas from the Cliffside field. At this time the plant at Fort Worth was closed down. During World War II, USBM built four additional helium extraction plants and enlarged the one at Amarillo to provide helium for wartime use. These plants were built under extreme emergency conditions when time was not available to experiment with different designs; therefore, they were all quite similar to the Amarillo plant. In 1959 the government put its latest plant on stream at Keyes, Okla. This plant featured larger units and increased efficiency in helium recovery. In the early 1960's the government started its farsighted conservation efforts for helium that resulted in construction of five new helium plants by private companies. JPT P. 341ˆ