Capital versus energy costs

An increase in solvent loading (F) is beneficial in reducing both energy costs (equation 10.3) and capital costs since it reduces the amount of solvent which must be recirculated for a given output of product. The major units will now be considered in turn. 

For a mild steel centrifugal compressor, 7cc ( UK, current) is given by 

Reciprocating compressor costs follow a similar relationship but according to [14] are about 15% greater than the above range. 

Cost estimation is a risky process but the above result does enable approximate cost calculations to be performed. 

2 Extraction towers. Cost depends on internal diameter, material of construction, internal pressure and method of closure. Some of the correlations in the literature (see [15] for example) present vessel costs as a function of total vessel weight, while others give costs directly in terms of vessel dimensions and material of construction. Over the restricted range of dimensions listed below, the graphical data given in [14] may be represented within 15% by 

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Reflux ratio and minimum number of stages (trays) The design of a fractionating column could be looked upon as a capital cost versus an energy cost trade-off issue, which is basically a function of... 

More details are provided in Figure 3.4a, which illustrates how several design parameters are affected by the variation of the optimization variables and zb- Figure 3.4f shows how annual capital cost and annual energy cost vary with these two variables. Both figures are plotted versus zb for three different values of with fixed Tr = 367 K. 

Economics Power-recoveiy units have no operating costs in essence, the energy is available free. Furthermore, there is no incremental capital cost for energy supply. Incremental installed energy-system costs for a steam-turbine driver and supply system amount to about 800 per kilowatt, and the incremental cost of an electric-motor driver plus supply system is about 80 per kilowatt. By contrast, even the highest-inlet-pressure, largest-flow power-recoveiy machines will seldom have an equipment cost of more than 140 per kilowatt, and costs frequently are as low as 64 per kilowatt. However, at bare driver costs (not including power supply) of 64 to 140 per kilowatt for the power-recovery driver versus about 30 to 80 per Idlowatt for... 

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