Introduction
Overview of Chemical Industry Energy Use
Chemicals manufacture is the second largest energy-consuming enterprise in U.S. industry, accounting for over 6.5 quadrillion Btus (quads) of feedstock and process energy use in 2002, or nearly a third of industrial energy use [ACC 2003]. More than half of the energy used by the chemical industry is used as feedstocks (Figure 1). The other half is primarily used to provide heat, cooling, and power to manufacturing processes, with a small amount used for conditioning and lighting buildings.
CoalFuel Oil/LPG Natural Gas 1901 TBtu Electricity 525 TBtu Coal 271 TBtu Other 426 TBtu 58 TBtu Heavy Liquids 1132 TBtu NGL/LPG 1497 TBtu Natural Gas 680 TBtu 32 TBtu 3342 TBtu
Figure 1. Energy Use in the U.S. Chemical Industry, 2002 [ACC 2003]
The chemical industry has achieved significant energy efficiency gains since the 1970s, precipitated by the Middle East oil crises and resulting pressures on energy supply. Between 1974 and 1990, fuel and power consumed per unit output in the industry has decreased by nearly 40% (see Figure 2). However, as Figure 2 illustrates, efficiency improvements have not been as impressive since the early 1990s, and have remained relatively flat over the last five years. Further improvements in energy efficiency will be necessary for the industry to maintain a competitive edge.
The chemical industry’s dependence on energy for raw materials as well as fuel and power makes it particularly vulnerable to fluctuations in energy price. High fuel and feedstock prices can have a profound effect on chemical processing, which typically requires large amounts of energy to convert raw materials into useful chemical products. Recent spikes in natural gas price, for example, caused temporary plant shutdowns of gas-based *****ing facilities in some regions of the country. Petroleum and natural gas price increases continue to create price uncertainties in commodity chemical markets, and are a key driver for olefins pricing [CMR 2004].
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Chemical Industry U.S. Industry Figure 2. Energy Intensity in U.S. Chemical Industry [ACC 2003]
As energy prices continue to rise and supplies become more volatile, chemical companies are increasingly looking toward energy efficiency as a way to reduce production costs and improve their competitive edge. The challenge for today’s chemical manufacturers is to effectively focus their resources on improving the equipment and processes that will produce the greatest benefits in energy use, productivity, and yield.
Objectives of the Analysis
At the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (DOE/EERE), the Industrial Technologies Program (ITP) is supporting research and development to improve the energy efficiency and environmental performance of processes used in many of the basic materials industries. ITP’s Chemicals and Allied Processes (CAP) subprogram works specifically with the chemicals, petroleum refining, and forest products industries to accelerate the development of advanced, energy-efficient technologies. Projects are cost-shared by industry and typically involve high-risk, pre-competitive research that individual companies could not fund independently. In many cases, the research has national rather than local benefits, i.e., chemical companies across the nation can potentially reap the energy and economics benefits of research.
To guide research decision-making and ensure that Federal funds are spent effectively, ITP needs to know which manufacturing processes are the most energy-intensive and least efficient. To gain knowledge of process inefficiencies in chemicals manufacture, the ITP CAP program commissioned a “bandwidth” study to analyze the highest energy-consuming chemical processes. The objectives of the study were to
• identify and quantify the inefficiencies of existing technologies and processes in selected chemicals manufacture;
• pinpoint the location of energy losses;
• calculate the recoverable energies for each process; and
• examine energy losses in major unit operations that are common across the chemicals selected.
The advantage of this study is the use of “exergy” analysis as a tool for pinpointing inefficiencies. Prior analyses have focused only on energy and ignored the quality of energy and the degradation of energy quality. Exergy analysis goes a step further to evaluate the quality of the energy lost, and distinguishes between recoverable and non-recoverable energy. A description of the unique characteristics and benefits of exergy analysis and the results of the study comprise the remainder of this report.