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3. The Ethylene and Petrochemical Industry This chapter reflects an in-depth analysis of a part of one of the energy-intensive sub-sectors: the petrochemical. In the petrochemical industry mostly relatively simple organic chemicals are produced such as ethylene, propylene and benzene. These chemicals (some through intermediates, e.g. mono vinyl chloride or styrene) form the building blocks for many products such as plastics, resins, fibers, detergents, etc. The single most energy-consuming step in the petrochemical industry is the steam cracking of hydrocarbon feedstocks to produce ethylene, propylene, butadiene and aromatics (benzene, toluene and xylenes). Recent estimates of global energy consumption for the production of ethylene and co-products are not available. In 1990 energy consumption was estimated to be about 1 EJ (or 950 TBtu, excluding feedstock energy consumption), with ethylene production amounting to 50 Million tonnes (WEC, 1995). By 1997, global ethylene production had risen to 70Mt/a (O&GJ, 1998). The U.S. is currently the world’s largest ethylene producer, accounting for about 28% of world capacity (Rhodes, 1997). In section 3.1 we first discuss the major process used to produce ethylene and its co-products, followed by a discussion of the U.S. petrochemical industry (section 3.2) and its energy consumption and intensity (section 3.3). 3.2. Process Description In the cracking process, hydrocarbon feedstocks are preheated in the convection section to 650°C (using fuel gas and waste heat), mixed with steam and cracked in the radiant section at a temperature of about 850°C (Worrell et al., 1994). Subsequently, the gas mixture is rapidly cooled to 400°C (or quenched) to stop the reaction, during which process high pressure steam is produced. Injection of water further decreases the temperature to about 40-50°C and a condensate, rich in aromatics, is formed. The liquid fraction is extracted, while the gaseous fraction is fed to a series of low temperature, high pressure distillation columns. The fractionation sequence varies from plant to plant (Zeppenfeld et al., 1993). Figure 3 shows a typical arrangement. Feedstocks used in steam cracking are ethane, LPG, naphtha, gas oils (GOs) and sometimes coal- derived feedstocks. Many of the installations used today can handle different (if not all) types of feedstock (Chemfacts, 1991). The choice for a particular feedstock, together with processing conditions (heat, pressure, steam dilution rate) will determine the yield of ethylene, propylene and other co-products in steam cracking. Table 7 shows how product yield varies with feedstock type (Chauvel and Lefevbre, 1989). 7 1PDF Image | Energy use and energy intensity
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