Info

2,086

2,086

4,588

8,760

Fig. 30-28 Loads by Hours and Electric Rate Periods.

Fig. 30-28 Loads by Hours and Electric Rate Periods.

Fig. 30-29 Percent Power vs. Percent Load for Electric Drive Options.

$30,000 for cycling control is recovered in 1.45 years.

Figure 30-32 shows a similar analysis for the gas-fired reciprocating engine-driven system with the compressor operating in speed control through much of the operating range and modulation control under low load. The fuel required to drive the system is listed in the table and is supplied at a cost of $4.50/Mcf, independent of time of use.

The total cubic feet (CF) of gas requirement is tabulated for each annual block of operating hours. Annual operating costs are determined using a gas cost equivalent to $4.50/Mcf. The annual O&M cost, based on $3.80 per equivalent full-load hour (EFLH), is calculated as $21,584. Figure 30-33 shows the simple payback on the incremental investment in the reciprocating engine system versus the two electric compressor system options. A comparison of the engine option with the cycling control option shows that the additional incremental investment in the engine-driven system of $130,000 versus the cycling control system is returned in 2.24 years.

Example 2

This example is based on a lower-cost electric rate, summarized in Figure 30-34.

A first pass screening calculation revealed that under the lower electric rate, the reciprocating engine-driven air compressor could not be economically applied without benefit of heat recovery. Comparing Figure 30-35 (electric-driven unit with modulation) and Figure 30-36 (electric-driven unit with cycling control), the electric-driven unit featuring cycling control would be a likely choice.

Figure 30-37 considers the reciprocating engine system with heat recovery. Listed natural gas consumption is based on the fuel-chargeable-to-power (FCP) as developed in Chapter 2, assuming heat recovery equivalent to 40% of engine fuel energy input. Displaced boiler efficiency is assumed to be 83% and gas cost is $4.50/Mcf. The O&M rate is increased to $4.20 per EFLH to reflect additional

Load

Electric Drive

Capacity

Modulation % Power consumed

Cycling % Power Consumed

100%

100%

100%

90%

97%

93%

80%

92%

85%

70%

88%

78%

60%

84%

70%

50%

80%

60%

40%

76%

52%

30%

72%

44%

20%

68%

36%

10%

64%

28%

Fig. 30-29 Percent Power vs. Percent Load for Electric Drive Options.

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