Research Papers: Power Engineering

Improving Performance of Refrigerant Cooled Steam Power Plant by Using Cooling Thermal Storage

[+] Author and Article Information
A. S. Hegazy1

Department of Mechanical Engineering, Menoufia University, Shebin Al Kom 11911, Egyptahegazy7@yahoo.com


Present address: P.O. Box 26240, Riyadh 11486, Kingdom of Saudi Arabia.

J. Eng. Gas Turbines Power 131(5), 053002 (Jun 04, 2009) (7 pages) doi:10.1115/1.3078385 History: Received May 19, 2008; Revised January 11, 2009; Published June 04, 2009

It is proposed in the current paper to combine the steam plant with two refrigeration cycles and a cooling storage container. Throughout the time of a day, the steam plant is made to work at full power, where the excess power generated over the electric power demand is used to drive the compressors of the refrigeration cycles. The stored cooling is used for dissipating the heat absorbed by the cooling refrigerant in the steam condenser during the period of peak-loads, while the two refrigeration machines are stopped. In this way, the energy used for driving the refrigeration machine is saved so that the whole power generated by the steam plant is exported to the grid. Energy analyses of the proposed combined system has led to inferring that the net power of the steam plant during the period of exclusive direct cooling of the steam condenser (only the first refrigeration machine is running) is about 70–86% of the whole power generated by the steam plant when the coefficient of performance of the first refrigeration cycle lies in the range of 4–10. Also, it has been found that relatively small coefficients of performance of the first and second cycles, less than 6 and 1.5, respectively, result in low net power of the steam plant over the period of charging the cooling storage container (both refrigeration machines run in unison). In this case, the net plant power amounts to less than 26% of the total generated plant power when the time of storing the cooling is lower than double the time of the peak-loads. This necessitates increasing the storing time to assure reasonable available power to be exported to the grid. Economical analyses of the proposed system have showed that both the capital cost and energy charges are less for the proposed system than that of the steam plant without cooling storage for practically possible operating conditions.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 1

Schematic of the proposed combined system: (a) boiler, (b) steam turbine, (c) steam condenser, (d) boiler feed water pump, (e) generator, (f) refrigerant compressor, (g) motor, (h) refrigerant condenser, (i) throttling valve, (j) evaporator, (k) cooling storage container, (l ) heat exchanger, (m) refrigerant circulating pump, (n), (n′), (o), and (o′) valves, —— water/ steam, – – refrigerant, and – • – electricity

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Figure 2

Direct cooling refrigeration power during the first period

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Figure 3

Net power of the steam plant during peak-loads (third period)

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Figure 4

Effect of storing time interval on the refrigeration machines’ power during the cooling storage period: ——— COPst=1.5, — — — COPst=2.0, ……….. COPst=2.5, and — • — COPst=3.0

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Figure 7

Additional capital cost of plant B per kilowatt of the basic steam plant maximum power: ——— COPdc,1=4.0, — — — COPdc,1=6.0, ……….. COPdc,1=8.0, and — • —COPdc,1=10.0

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Figure 8

Additional energy charges per kilowatt of the basic steam plant maximum power: (a) plant A: ——— COPst=1.5, — — — COPst=2.0, ……. COPst=2.5 — • —, and COPst=3.0 and (b) plant B: —— COPdc,3=4.0, — — — COPdc,3=6.0, ……. COPdc,3=8.0, and — • — COPdc,3=10.0

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Figure 5

Power of the direct cooling compressor during peak-loads (third period)

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Figure 6

Additional capital cost of plant A per kilowatt of the maximum power of the basic steam plant: ——— COPst=1.5, — — — COPst=2.0, ………. COPst=2.5, and — • — COPst=3.0




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