Application of the second law of thermodynamics to industrial processes

Bruce A. Hedman

doi:10.17918/00007705

An extensive industrial energy data base was developed at the four-digit and sub four-digit Standard Industrial Classification (SIC) level. The data base contains information defining 108 industrial processes which represent the top sixty energy consuming four-digit SIC industries and account for approximately 72 percent of the industrial manufacturing sector energy consumption in the United States. Each process contained in the data base is characterized by a process configuration (i.e., flow diagram) representing a nationally typical plant, and energy and mass balances for each of the unit operations which comprise the process. In all, over 1200 unit operations are included and are defined according to operation type, thermal efficiency, energy use and losses. Additionally, over 6000 process streams are identified and characterized by temperature, pressure, enthalpy, specific heat and if a waste effluent, by environmental contaminant levels. In order to assess the effectiveness of energy utilization in the industrial sector, 27 of the most energy intensive processes contained in the data base were analyzed with an approach based on the Second Law of Thermodynamics. The processes represent various industries including food, pulp and paper, chemicals, petroleum, glass and cement, and metals and account for over 57 percent of the industrial manufacturing sector energy consumption. Unlike the First Law, the Second Law of Thermodynamics distinguishes the quality of energy as well as the quantity and introduces the concepts of available energy-the maximum work that can be derived from a flow or system, and lost work-a measure of the potential work or available energy destroyed by system irreversibilities. By determining the lost work generated by each component (i.e., unit operation) in the processes examined, the true locations and magnitudes of process inefficiencies were identified. Further analysis of the results at this level demonstrated a one-to-one correspondence between lost work and energy, suggesting that lost work is, in fact, the fuel penalty exacted in overcoming process irreversibilities. The lost work contributions of the various process unit operations were aggregated into 37 major generic classifications in order to identify areas of inefficiency common to the processes investigated. The results indicate that energy converter operations (i.e., utility operations such as process steam boilers or on-site power generation) are major sources of process lost work (accounting for over 31 percent of the total), with boilers the single largest contributor (25 percent). Other primary sources of irreversibility in industrial processes include melting and heating furnaces, kilns, rolling and forming operations and petroleum subprocesses such as catalytic reforming and crude distillation. Using the direct relationship established between lost work and energy, the amount of input fuel consumed by the lost work generated in heat exchangers and coolers was estimated to be approximately 318 x 10('12) Btu per year. The development of a unique industrial data base and the subsequent application of lost work analysis to the most energy intensive processes therein represent an initial attempt at a systematic investigation of industrial energy utilization. Results at this stage suggest that certain Second Law techniques may provide additional insight into developing more effective energy use in both existing and new processes.

Application of the second law of thermodynamics to industrial processes

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Application of the second law of thermodynamics to industrial processes

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