Cogenerative, Direct Exhaust Integration of Gas Turbines in Ethylene Production

Within the past few years, gas turbines have been integrated into several new world-class ethylene production plants, for the first time using the exhaust as a source of preheated combustible oxygen for the cracking furnaces. The economic inducements and technical impact of such integration on the process are discussed. The general ethylene cracking and recovery process is described, and the various ways of integrating gas turbines are compared, culminating in the current leading designs. Means of providing ambient air backup to protect furnace operation from gas turbine trips are discussed. Furnace group sizing and oxygen demand for the major feedstocks, including naphtha and ethane/propane, are compared with the current range of oxygen and power available from single and dual gas turbines on the world market. Methods of partial integration, where gas turbine integration of the entire ethylene plant would produce more power than can be economically utilized or consume more premium fuel than available, are discussed. Fuel savings relative to ambient air operation are parametrized with percent exhaust oxygen and exhaust temperature. Aeroderivative and industrial gas turbine types are compared. Comparative economics with another means of gas turbine cogeneration, that of auxiliary boiler replacement with a combined cycle in a central utility, are presented.