Refrigeration cycle costs

Substituting the throttle value in a compression refrigeration cycle by a process expander both increases the efficiency of the cycle and allows power recovery. However, this is at the expense of increased capital cost. 

The mixed refrigerant cycle was developed to meet the need for hq-uefying large quantities of natnral gas to minimize transportation costs of this fuel. This cycle resembles the classic cascade cycle in principle and may best be understood by referring to that cycle. In the latter, the natural gas stream after purification is cooled successively by vaporization of propane, ethylene, and methane. Each refrigerant may be vaporized at two or three pressure levels to increase the natnral gas coohng efficiency, but at a cost of considerable increased process complexity. 

Estimate the annual cost of providing refrigeration to a condenser with duty 1.2 MW operating at —5°C. The refrigeration cycle rejects heat to cooling water that is available at 40 °C and has an efficiency of 80% of the Carnot cycle efficiency. The plant operates for 8,000 hours per year and electricity costs 0.06/kWh. 

A high system pressure increases the size, weight, and cost of equipment (Dossat, 1981). A pressure ratio of 10 is considered to be the maximum for a refrigeration cycle (Perry and Chilton, 1973). 

The oil gas market has a strong influence on the price of utilities. A consistent method for estimating the cost of utilities can be developed based on thermo-chemical calculations and typical efficiency of industrial processes, as power plants, boilers, turbines, refrigeration cycles, etc. Each utility can be related to its equivalent fuel value, as indicated by the Table B2 (Douglas, 1988). Once the cost of fuel known, the price of other utilities can be easily determined. Note that the prices in Table B2 are only for illustration purposes. 

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