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PAPER NO: CATEGORY:

TP03-01 DRY COOLING

COOLING TECHNOLOGY INSTITUTE
WHY EVERY AIR COOLED STEAM CONDENSER NEEDS A COOLING TOWER
LUC DE BACKER Ph.D. WILLIAM M. WURTZ HAMON DRY COOLING

The studies and conclusions reported in this paper are the results of the author’s own work. CTI has not investigated, and CTI expressly disclaims any duty to investigate, any product, service process,procedure, design, or the like that may be described herein. The appearance of any technical data, editorial material, or advertisement in this publication does not constitute endorsement, warranty, or guarantee by CTI of any product, service process, procedure, design, or the like. CTI does not warranty that the information in this publication is free of errors, and CTI does not necessarily agreewith any statement or opinion in this publication. The user assumes the entire risk of the use of any information in this publication. Copyright 2003. All rights reserved. This paper has been reviewed by members of the Cooling Technology Institute and approved as a valuable contribution to cooling tower literature; and presented by the author at the Annual Conference of CTI.

Presented at the 2003Cooling Technology Institute Annual Conference San Antonio, Texas – February 10-13, 2003

Paper No TP03-01 WHY EVERY AIR COOLED CONDENSER NEEDS A COOLING TOWER By Luc De Backer and William M. Wurtz

ABSTRACT

This technical paper will review the basic types of cooling systems utilized by utility power plants, and explain the reasons why it is advantageous to include a cooling tower in manydry cooling applications. A system where a cooling tower is used in conjunction with an air cooled steam condenser is called a parallel condensing system. This type of system utilizes three traditional types of heat exchangers: a cooling tower, an air cooled steam condenser and a surface condenser. An optimized parallel condensing system reduces both investment costs and operational costs whileusing a minimum amount of water.

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Paper No TP03-01 1. INTRODUCTION In the steam cycle of a power plant, low-pressure water condensed in the steam condenser is pumped to high pressure before it enters the boiler or Heat Recovery Steam Generator (HRSG) where superheated steam is produced. The superheated steam is sent to the steam turbine where the steam expands to low pressureproviding the energy to drive a generator. This low-pressure steam has to be condensed in a condenser in order to complete the steam cycle. The condensation of steam requires a cooling medium. Traditionally, this has been achieved using water from a river, a stream, a pond or seawater. The cold water is pumped through a heat exchanger and the warm water is discharged back to the water source. This iscalled ONCE THROUGH cooling system. A once through system is an open loop system. The need to reduce the vast amount of water requires a closed loop system. Thus the WET COOLING system came into effect, and soon after the DRY COOLING and HYBRID COOLING systems (see Table 1). In a wet cooling system, water is circulated to condense the steam in the same type of heat exchanger that is used in theonce through cooling. The warm water, instead of being rejected to the water source, is cooled in a cooling tower using air as the cooling medium. Only the water carried away due to evaporation, drift and blow-down needs to be replenished by make-up water. Cooling System Once Through Wet Cooling Dry Hybrid Parallel Time period From 1930s From 1950s From 1970s From 1980s From 1990s

Table 1:Evolution of cooling systems used in power plants [R1] 2. WET COOLING SYSTEMS The wet cooling tower system is based on the principle of evaporation. The heated cooling water coming out of the surface condenser is cooled as it flows through a cooling tower, where air is forced through the tower by either mechanical or natural draft. In the United States, the natural draft tower, sometimes also called...