Process/plant Optimization Specialreport

Energy is the largest variable operating cost after raw materials for most of the process industries and its efficient use is key to sustaining profitable operation. Natural gas is the most common incremental fossil fuel and its general increase in price and in price volatility over the past few years are well known with most experts projecting these trends to continue in the future. Table 1 gives typical specific energy usage (Btu/t product) for common processes1 and the value of a 10% energy reduction in terms of increased financial operating margin at an energy price of $7 per million Btu (mBtu). This value is a significant portion of the total operating margin for most of these processes. In addition to the direct energy price, it seems likely that the US will eventually adopt some regulations regarding greenhousegas emissions. If the regulations in other countries are a guide, these may take the form of a “cap and trade” on CO2 emissions. This will place an increased value on energy reductions since these reductions can be used to offset increases in other areas or can be sold under a cap-and-trade system. If the CO2 reductions are valued at $20/ton, which is at the low range of recent prices in Europe, then reductions in natural gas or equivalent light hydrocarbon fuel usage would have an additional value of approximately $1.3/MBtu. This would add roughly 20% to the value of the energy savings above. To identify energy savings it is important to understand how energy is normally used. In larger process sites energy distribution can be quite complex (Fig. 1). External purchased energy can be