Kryos Energy Inc.

Brooklyn Union Gas Co.

Stephen J Markbreiter

Irving Weiss

Hans P Schorr

Daniel J Dessanti

The cryogenic treatment of landfill gas removes troublesome compounds that cause severe corrosion of combustion engines in which the gas is used as fuel. It involves compressing the gas to an elevated pressure and isenthalpically expanding the gas to chill the gas to a temperature below -20 .degree. F. The compressed gas is first cooled to eliminate moisture as condensate. Methanol is injected into the gas so that it can be deeply chilled without forming ice with residual moisture in the gas. An aqueous methanol condensate containing troublesome compounds forms in, and is removed from, the deeply chilled gas before it is expanded to provide refrigeration for chilling the gas. By adding water to the aqueous methanol, the troublesome compounds lose solubility in diluted methanol and form a supernatant layer that can be separated for disposal. The diluted methanol can be recycled.

Cryogenic treatment of landfill gas to remove troublesome compounds

Cogeneration of electricity and liquid carbon dioxide is conducted by combusting methane-rich gas to power a gas turbine and a steam turbine; each turbine drives an electric generator. Carbon dioxide is separated from the combustion products by an amine absorption system to which heat for releasing absorbed carbon dioxide is supplied by steam drawn from the steam turbine. Some of that steam is used to produce refrigeration with an ammonia absorption refrigeration unit. The refrigeration is applied to the separated carbon dioxide to liquefy it. Fractionation to yield purified liquid carbon dioxide is easily achieved and saleable refrigeration is another optional product of cogeneration.

Cogeneration of electricity and liquid carbon dioxide by combustion of

Conventional liquified natural gas (LNG) plants are designed to eliminate moisture and up to 1.0% by volume of carbon dioxide (CO.sub.2) present in gas delivered by pipelines. Pipelines can no longer be expected to supply gas with such a low CO.sub.2 content. The invention pretreates gas with as much as 1.5% to 3.5% by volume of CO.sub.2 so that it becomes acceptable to LNG plants. The pretreatment involves scrubbing natural gas with cold methanol at a temperature below -30.degree. F. and flashing absorbed CO.sub.2 from methanol withdrawn from the scrubber by passing it through a pressure-reducing valve, followed by two successive warming flashings of CO.sub.2. Then, the methanol can be recycled to the scrubber. Required refrigeration is supplied to the methanol entering or leaving the scrubber.

Natural gas pretreatment prior to liquefaction

Cogeneration of electricity and saleable refrigeration is achieved by passing pipeline gas with added methanol through a turbo-expander coupled to an electrical generator so that moisture in the gas forms an aqueous methanol condensate separable from the cold, expanded gas. The condensate is distilled to separate discard water from recycle methanol. After recovering refrigeration therefrom, the expanded gas is warmed to a temperature above 32.degree. F. by adding all the required heat as reboiler heat for the distillation and passing the expanded gas in heat exchange with distilled methanol vapor which is liquefied and used partly as reflux and partly as recycle methanol.

Cogeneration of electricity and refrigeration by work-expanding pipeline

Land-fill and other gases containing principally methane and carbon dioxide have been separated into high BTU fuel gas and discard carbon dioxide containing appreciable methane. Such discard gas can now be simply fractionated into high-purity liquid carbon dioxide with recoveries in excess of 80% while using a single refrigerant at a single low temperature to satisfy all refrigeration requirements of fractionation. This novel fractionation is ideally combined with the process of separating land-fill gas into high BTU fuel gas because then the methane and carbon dioxide are recovered completely as two valuable products, high BTU fuel gas and pure liquid carbon dioxide.

Liquid carbon dioxide recovery from gas mixtures with methane

The high pressure of pipeline gas is reduced to the low pressure of a distribution system with simultaneous generation of refrigeration by passing the gas through two successive centrifugal compressors driven by two turbo-expanders in which the compressed gas is expanded to successively lower pressures. Refrigeration is recovered from the gas as it leaves each turbo-expander. Methanol is injected into the pipeline gas before it is expanded to prevent ice formation. Aqueous methanol condensate separated from the expanded gas is distilled for the recovery and reuse of methanol.

Pipeline gas pressure reduction with refrigeration generation

Methane-containing gases with an appreciable content of carbon dioxide are scrubbed with cold methanol to remove the bulk of the carbon dioxide in a simple system comprising a single gas-liquid contact column and featuring regeneration of the methanol containing carbon dioxide solely by multiple-stage flashing. Land-fill gases containing methane and carbon dioxide as the principal components can be economically processed in such a system to yield methane-rich fuel gases.

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Edison, NJ, United States of America

Stephen J Markbreiter