Chun Yen Lin

Date of Graduation

1977

Document Type

Dissertation

Degree Type

PhD

Department

Civil and Environmental Engineering

Committee Chair

D.G. Nichols

Committee Co-Chair

C.Y. Wen

Committee Member

W. Squire

Committee Member

J.T. Sears

Committee Member

H.V.S. GangaRao

Abstract

This study examines the available work energy for coal conversion processes as derived from the second law of thermodynamics. The concept of available work energy can provide the relationship between operating conditions and useful energy recovery; while the total energy based on the first law of thermodynamics can establish the relationship between quantities of heat and work energy. The concept of total energy recovery and the available work energy loss is applied to each of the process units in various coal conversion processes. The coal conversion processes which were studied include those which produce synthetic crude oil, pipeline gas, methanol and/or electricity. The preliminary conceptual design of the coal conversion processes is investigated in order to estimate the unit production cost of the various products. Some discussions of altering the operating conditions in order to increase the available work energy recovery are presented in this study. About 15% of available work energy in the feed coal is lost in the coal pyrolysis step, and 12% is lost in the COED char gasification. Oxygen consumption in the COED pyrolysis represents about 1% loss in the available work energy associated with the feed coal. A 5% increase in carbon utilization amounts to a reduction of approximately 4% of the available work energy loss in the gasification process based on the available work energy of the feed coal. The second law efficiency of the combustion process studied here will increase 3% if the combustion temperature is increased from 2000°F (1367 K) to 2600°F (1700 K). In the steam turbine power generation process, the steam boiler has the most available work energy loss. Use of the reheat process with 2400 psia/1000°F/1000°F [16.5 (MN/m²) / 811 K / 811 K] has the second law efficiency of 47%, while the process with 600 psia/1000°F [4.1 (MN/m²) / 811 K] has the second law efficiency of 40%. In the production of synthetic crude oil and methanol, the second law efficiency of the overall process is 57%, while that for the synthetic crude oil and pipeline gas production is 53%. Low-Btu gas production has the second law efficiency of 68%. All these coal conversion processes are designated on a self energy-sustaining basis. Thus, it has been found that process analysis based upon considerations derived from the second law of thermodynamics can be used to achieve an understanding of the process variables, process units, and process schemes which provide more desirable characteristics.

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