In an effort to increase the energy efficiency and reduce environmental emissions from refineries, the Commerce City Refinery of Ultramar Diamond Shamrock, the Office of Industrial Technologies at the U.S. Department of Energy and a team of contractors have collaborated to implement a novel project. A waste heat fired Absorption Refrigeration Unit (ARU) was designed, fabricated, installed and is currently completing a one year field test at the oil refinery in Denver, Colorado. Data is being gathered to document the performance and compare to the predictions. The ARU is designed to provide refrigeration for two process streams at the refinery while being powered by waste heat from a third process stream. The refrigeration benefits the refinery by recovering salable product and increasing the capacity of the process units with no additional electrical demand. The constraints to be satisfied by the ARU design were very stringent: low temperature waste heat; very low refrigeration temperature; limited plot space; geographically separated streams; and very limited cooling water. In order to satisfy all these constraints and to make the economics more favorable, several new concepts were developed and incorporated in the ARU. This paper describes the various cycles considered and the qualitative and quantitative considerations involved in screening the cycles. The parametric analysis and optimization of the most promising cycle is presented.

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Boiler "short cycling" occurs when an oversized boiler quickly satisfies process or space heating demands, and then shuts down until heat is again required. Process heating demands can change over time. Boilers may have been oversized for additions or expansions that never occurred. Installing energy conservation or heat recovery measures may also reduce the heat demand. As a result, a facility may have multiple boilers, each rated at several times the maximum expected load.

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