OCR Text |
Show best economics among the processes presented in their respective categories. The fired gas turbine yields slightly superior economics because of the larger scale, and heat recovery in the gas turbine cycle. The carbon dioxide/methane reforming process is more efficient than the steam reforming process where the latent heat of vaporization is lost. ENERGY EFFICIENCY Over 90% of the energy input to the glass melting processes is accounted for by the natural gas, electric boost, and the energy required to produce the oxygen. An analyses of these inputs also serves as an excellent proxy for the relative operating costs of these processes. Table 1 shows these inputs for the air-fuel process and the three oxy-fuel processes chosen. To calculate the total energy used for melting it is necessary to select a conversion factor for adding the electric boost input in kilowatts and the oxygen input (also converted to kilowatts) to the natural gas input measured in Btus. The conversion factor of 10,000 Btu/KW is used to roughly reflect the energy it takes to produce electricity. This gives a more realistic representation of the energy consumption (than using 3414 Btu/KW) and incorporates the fact that electricity is a finer and more expensive form of energy. It is seen that all of the oxy-fuel processes offer energy savings relative to the air-fuel process ranging between 20% and 24%. The raw material preheating scheme is most efficient, consuming only 4 MMBtu per ton of glass. This is no surprise based on earlier discussions of the merits of providing recovered heat directly to the batch and cullet. CAPITAL COSTS AND OVERAll ECONOMICS By adding the capital related costs to the operating costs essentially reflected by the energy inputs presented above, a complete picture of the relative economics of these glass melting processes is obtained. Table 2 provides this information. The analysis does not include costs of labor and raw materials since these will be the same for all four processes. The costs associated with the natural gas, electric and oxygen input are added to provide the unit operating cost. The cost of miscellaneous inputs (including NH3, cooling water etc.) is included with the electricity costs. The total operating costs for the oxy-fuel processes do not exceed those of the air fuel process by more than 9% and in one case (gas turbine) are actually lower. The unit capital costs of the oxy--fuel processes are much lower than the air-fuel process because of the significant savings realized through the elimination or downsizing of the pollution control equipment. The carbon dioxide/methane reforming process offers the maximum savings (52%) because of the relative simplicity of the equipment. Even the gas turbine, most expensive of the oxy-fuel processes, offers an estimated capital savings of 19%. - 11 - |