Dry cooling systems

Van Der Walt, N. T., L. A. West, T. J. Sheef and D. Kubal. "The Design and Operation of a Dry Cooling System for a 200 MW Turbo-Generator at Grootvlei Power Station - South Africa," paper presented at the IX World Energy Conference, Detroit, Ml, (1974). 

Figure 4.23 Schematic of advanced dry cooling system proposed by McHale et a I. [1].

The magnitude of the heat rejection of large modern power generating plants is so great that the problem of potential environmental effects due to dry cooling systems must be studied. The plumes from both natural-draft and mechanical-draft towers designed for 1000-MW plants of several representative types are examined with respect to... 

There are dry cooling systems, in which the heat transferred is dissipated directly into the atmosphere using a dry cooling tower, and wet cooling systems, which use a variety of heat-rejecting devices in their water circuits such as ... 

Dry cooling systems can be direct, where the medium to be cooled (such as steam) is condensed in cooling coils without benefit of a condenser, or indirect types, where a condenser is used. 

Small dry cooling systems are commonplace today all over the world for various light duties, such as localized air conditioning, while larger systems are used in arid areas, often for electricity generation. Dry cooling systems, by their definition, do not need water they are more flexible in their siting requirements than wet systems and are less expensive to maintain. However, they are not as thermally efficient, and therefore are more expensive to own and operate for a comparable heat load. 

Kress Indirect Dry Cooling System, Bethlehem Steel s Coke Plant Demonstration at Sparrows Point, Maryland... 

The designers of AHTR identify high efficiency of energy conversion and advanced non-electric applications as major factors contributing to the effective resource utilization, minimized waste and reduced environmental impacts. Specifically, the reduced water consumption and the improved land use are mentioned, which could result from a dry cooling system considered for this concept. 

Reduced penalty for higher heat rejection temperatures. The capital costs of dry cooling systems can be reduced by rejecting heat at a higher temperature but with the penalty of lower plant efficiency. That penalty becomes smaller as the peak temperature of the power cycle increases. For the AHTR Brayton cycle with a minimum helium temperature of 35°C, the losses in efficiency for a 10°C rise in the compressor inlet temperature were calculated to be 1.5, 1.3, and 1.1%, respectively, for AHTR peak coolant temperatures of 705, 800, and 1000°C. 

The high efficiency of the power cycle with low rates of heat rejection is a consequence of the power cycle approximating an ideal Carnot cycle, where heat is inputted at one high temperature and rejected at one low temperature. Figure XXVI-5 also shows that the heat is rejected over a temperature range and thus matches the needs of dry cooling systems. 

Ba.cteria., A wide variety of bacteria can colonize cooling systems. Spherical, rod-shaped, spiral, and filamentous forms are common. Some produce spores to survive adverse environmental conditions such as dry periods or high temperatures. Both aerobic bacteria (which thrive in oxygenated waters) and anaerobic bacteria (which are inhibited or killed by oxygen) can be found in cooling systems. 

In summer the ventilation air has to be dehumidified to keep the required comfort and to prevent from condensation at cold ceilings. The air dehumidification is done by a liquid desiccant dehumidification and cooling system, sketched in Figure 271. Warm and humid outside air is cooled and dried in a special dehumidifier by a concentrated Lithium Chloride salt solution (LiCl-H20) before it is blown into the atrium of the building. From there several air handling units draw the air into the offices and provide additional cooling on demand. 

Snowman, J. W. Replacement of conventional refrigeration systems in freeze-drying by liquid nitrogen cooled systems. PDA Asian Symposium, p. 329-345, Tokyo, 1994 Copyright 1994 PDA, Inc. Bethesda, Maryland, USA... 

These agents are effective on small spill fires. If there is risk of re-ignition from embers or hot surfaces, these ignition sources should be quenched or cooled with water and secured with foam, or the source of fuel should be shut off before attempting extinguishment. An example of a dry chemical system is shown in Figure 7-36. 

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