Low Grade Heat Recovery from Process Streams for Power Generation

Abstract

Methods are described for generating electrical power from low grade heat sources from refining and petrochemical processes, including overhead vapors from vapor-liquid contacting apparatuses such as distillation columns, absorbers, strippers, quenching towers, scrubbers, etc. In many cases, these overhead vapors exit the apparatuses at a temperature from about 90° C. (194° F.) to about 175° C. (347° F.). Rather than rejecting the low temperature heat contained in these vapors to cooling air and / or cooling water, the vapors may instead be used to evaporate an organic working fluid. The vapors of the working fluid may then be sent to a turbine to drive a generator or other load.

Description

FIELD OF THE INVENTION[0001]The invention relates to apparatuses and methods for generating power from low grade heat sources including refinery and petrochemical process streams. A representative stream is an overhead vapor from a distillation column, such as a product fractionation column of a hydrocracking process.DESCRIPTION OF RELATED ART[0002]Sources of low grade heat are prevalent in refining, petrochemical, and other industrial applications. For example, low grade heat is estimated to account for 20-30% of the overall energy in a refinery. Low grade heat is normally considered waste heat and treated accordingly. This is due to the relatively low (although often well above ambient) temperatures of low grade heat sources that render them unsuitable for feed preheating, generation of pressurized steam, distillation column reboiling, and generally any other practical use involving heat exchange. As a result, the heat content of such low grade heat sources, though significant, is...

AI Technical Summary

Benefits of technology

[0009]Also, if two or more sources of low grade heat are available (e.g., from different vapor-liquid contacting apparatuses, from heat exchangers operating in series or in parallel, or from other processing equipment), their low grade heat may be consolidated by transfer to a common, intermediate heat transfer medium (e.g., water). The intermediate heat transfer medium may then be used to evaporate the working fluid of the ORC to generate power, for example, from a single turbine. In this manner of consolidating sources of low grade heat, the ORC can be sized to realize greater efficiencies and economies of scale. Moreover, such a consolidated operation improves flexibility in design and plot space planning, since the requirement for close proximity of the turbine to the low grade heat source(s) is relaxed.

Problems solved by technology

This is due to the relatively low (although often well above ambient) temperatures of low grade heat sources that render them unsuitable for feed preheating, generation of pressurized steam, distillation column reboiling, and generally any other practical use involving heat exchange.

As a result, the heat content of such low grade heat sources, though significant, is rejected, for example to the atmosphere using air cooling.

Generally, overhead product such as overhead vapors from distillation columns or other types of vapor-liquid contacting apparatuses are cooled by indirect heat exchange with air (e.g., using an air cooled exchanger) and / or cooling water (e.g., using a trim condenser), since the residual heat in the overhead streams is not considered of sufficient value for recovery of energy in an economical manner.

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