Masters Theses

Date of Award

6-1986

Degree Type

Thesis

Degree Name

Master of Science

Major

Chemical Engineering

Major Professor

John H. Holmes

Committee Members

Carl Thomas, William Johnson

Abstract

The purpose of this study is to evaluate the application of heat pump systems to a distillation train. A heat pump removes energy from a low temperature source and provides energy at a higher temperature through the addition of compressor work. A Rankine cycle heat pump consists of an evaporator, condenser, throttling device, trim-cooler, innercooler, and a working fluid.

The economic feasibility of a heat pump system is affected by five major variables. The heat pump system is favored by high reboiler heat duties as the benefits grow faster than the costs of the heat pump system. The heat pump system is favored by heat duty ratios, condenser heat duty to reboiler heat duty, near the no trim-exchanger point. Increases in condenser temperature bring a slight reduction in the required utility ratios above the no trim-exchanger heat duty ratio point and a slight increase below it. The heat pump system is favored by low temperature differences.

The utility ratio (natural gas to electricity on a $/million BTU basis) was used as a measure of economic performance. A required utility ratio was determined and compared to the actual utility ratio. If the actual utility ratio in effect or projected is higher then the heat pump is favored.

For a specific case analysis, an example column was chosen and several options were considered. These options were compared to a conventional reboiler and condenser system on the basis of the additional investment required and the return on that investment. The example column was an extractive distillation column used in an ethanol water separation distillation train. Of the options considered, the use of the column overhead fluid as the heat pump working fluid was the most promising. It resulted in a favorable return on investment of 44 percent. The use of a steam driven compressor showed promise, but failed to achieve a favorable return on investment.

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