Minimization of life cycle CO2 emissions in steam and power plants

A methodology is presented to minimize life cycle CO2 emissions through the selection of the operating conditions of a steam and power generation plant. The battery limits of the utility plant are extended to include CO2 emissions of: (1) extraction and transport of natural gas burned in its boilers, (2) generation of imported electricity by nuclear, hydroelectric and thermoelectric plants and (3) exploration, extraction and transport of natural gas, oil, coal and uranium consumed by thermoelectric and nuclear plants. The operating conditions of the utility plant are selected optimally to minimize the life cycle CO2 emissions. There are continuous operating conditions such as temperature and pressure of the high, medium and low pressure steam headers and binary operating conditions to represent discrete decisions to select optional pumps drivers between electrical motors and steam turbines or whether some equipment is on or off. A Mixed Integer Nonlinear Programming problem is formulated and solved in GAMS. Significant reductions in life cycle CO2 emissions, natural gas consumption and operating cost are achieved simultaneously in the steam and power generation system of an ethylene plant. This is an important tool to support a decision making process to reduce CO2 emissions in a key industrial sector.