**1. Introduction**

The primary purpose of the steam condenser in a steam plant is to convert the turbine exhaust steam into water for reuse in the boiler and to create and maintain vacuum at the turbine exhaust. This is achieved by cold water circulation through tube bundles and condensing the steam on their outer surfaces. Referable to the large reduction in the specific volume on changing from steam to condensate, a vacuum is formed within the condenser. Getting to this vacuum continuously as minimum as possible is very important for the steam plant to attain the highest possible power from the turbine. A rise in the condenser pressure can be produced due to the existence of air, ammonia, and other noncondensable gases [1]. This rise in pressure in the condenser results in lowering the useful turbine power and in turn the plant efficiency degenerates [2–5].

The presence of air lowers the partial pressure of steam and therefore brings down the saturation temperature of steam, which leads to increasing evaporation enthalpy (latent heat), and therefore, more cooling water will be required in the condenser. In addition, this gives rise to increasing condensate subcooling, which is undesirable because it means that the excess heat removed for this purpose serves no useful process and entails providing additional boiler firing [6]. Thus, continuous removal of the air and noncondensable gases from the condenser is very critical for maintaining the plant efficiency possibly high. Beside this task, the air extraction system prevents air blanketing of condenser tubing that could dramatically reduce the heat transfer and stop the condensing process. Also, it reduces the condensatedissolved oxygen levels that could lead to corrosion of boiler tubing.

studied in detail in [14–19]. The results of these studies showed significant rise in net power as well as efficiency of the steam plant. However, for realizing this combined system, a relatively huge VCRS is required, which leads to material increase of the combined system cost. In the current study, a relatively small VCRS is required as it serves to cool only the air contained in the air cooler of steam plant condenser. This leads to lessening the temperature of the air and water vapor mixture in the air cooler, resulting in condensing some of the water vapor. Hence, the mass flow rate of the air and water vapor mixture extracted from the steam condenser is decreased and consequently the power consumed by the vacuum pump lessens. Meanwhile, water vapor leaving the steam condenser and lost to the surroundings is reduced. In general, this contributes to contracting both the power consumed in the auxiliary systems of the steam plant and the steam consumption.

*Air Cooling in Steam Plant Condenser Using Refrigeration System for Improving Vacuum Pump…*

The steam plant condenser is typically a shell and tubes heat exchanger. **Figure 1**

depicts a section through a steam plant condenser. The steam leaving the plant turbine enters the condenser at its top with temperature *T*ci and flows around the outer surface of the cooling tubes in which cooling water is circulated. Heat is transferred from the steam into the cooling water where steam condenses and the condensate is extracted out of the condenser at the bottom with temperature *T*ce. A segment of the condenser (called air cooler) is shielded for cooling the air associated with the condensate and leaked from the environment. This segment is possibly located near the inlet of cooling water, and the number of the cooling tubes is increased in it, so that the air associated with some water vapor collected in this section is cooled to a temperature *T*vpi, which is lower than that of the condensate. This will lead to decreasing the mass rate of water vapor, the air pulled by the vacuum pump connected to this segment. As a result, the energy used up by the vacuum pump for extracting the air and its accompanying water vapor to the environment are decreased. In the current study, it is suggested to circulate chilled

**2. Conception of the modified steam plant condenser**

*DOI: http://dx.doi.org/10.5772/intechopen.83787*

**Figure 1.**

**225**

*A schematic section through steam plant condenser.*

The air and noncondensables are extracted from the bottom of the condenser, where the temperature is the lowest, by using vacuum pump. The air and noncondensables sucked by the vacuum pump contain a relatively big amount of noncondensed steam; each kilogram of air can contain more than 2 kg of water vapor [7]. This results in increasing the parasitic work of the pump. In condenser design, it is considered reducing the subcooling of the condensate possibly to the lowest degree to minimize heat removal. For reducing the amount of steam mixed with the air sucked by the air pump, the steam condenser has a portion of tubes near the air pump suction screened off and the condenser tubes in this portion contain the coldest water, and the number of cooling tubes is increased. Hence, the temperature of the air drops below that of the outlet condensate, and more steam associated with the air is condensed so that the mass flow rate of the air and steam mixture drawn by the air pump is reduced and, in turn the power of the dry pump is lowered.

The air extraction system (vacuum pump) can be centrifugal compressor, steam jet ejector air ejector, or water ring pump [8, 9]. A hybrid system of these components is preferred as they offer several advantages toward minimizing venting equipment size and save parasitic consumption [7]. The power required for operating these equipment sorts is dependent on both the rates of air and the noncondensables and noncondensed steam sucked by the vacuum pump. The temperature decrease of the air in the condenser air cooler is limited when the normal cooling water is used. For obtaining considerable drop in air temperature it is proposed in this work to modify the condenser by incorporating a refrigeration system into the condenser. This system is utilized to chill the cooling water, which is used for cooling the air in the condenser rather than the normal cooling water. Of course the use of the refrigerant directly to cool the air exploiting the air cooler as an evaporator for the refrigeration system and circulating the cold liquid refrigerant of this system through the tubes of the air cooler will be more efficient than using the chilled water. However, this configuration calls for redesigning the air cooler to be adapted for receiving and evaporating the refrigerant, which will be expensive for already existing power plants. The latest configuration can be taken into consideration for the design of the new plants.

The concept of using dry ammonia for cooling steam plant condenser is described in Ref. [10]. This concept states that the condenser cooling water is replaced by liquid ammonia, which evaporates as it acquires heat from the condensing steam. The heat of condensation absorbed by the ammonia is rejected in an air cooled condenser of a refrigeration machine into the surrounding atmosphere. This concept was tested and well documented [11–17], with the participation of several major equipment vendors (Baltimore Air Coil, the Trane Company, Curtiss-Wright, CB&I, and Union Carbide). In addition, the concept of using vapor compression refrigeration system (VCRS) combined with steam plant condenser was

*Air Cooling in Steam Plant Condenser Using Refrigeration System for Improving Vacuum Pump… DOI: http://dx.doi.org/10.5772/intechopen.83787*

studied in detail in [14–19]. The results of these studies showed significant rise in net power as well as efficiency of the steam plant. However, for realizing this combined system, a relatively huge VCRS is required, which leads to material increase of the combined system cost. In the current study, a relatively small VCRS is required as it serves to cool only the air contained in the air cooler of steam plant condenser. This leads to lessening the temperature of the air and water vapor mixture in the air cooler, resulting in condensing some of the water vapor. Hence, the mass flow rate of the air and water vapor mixture extracted from the steam condenser is decreased and consequently the power consumed by the vacuum pump lessens. Meanwhile, water vapor leaving the steam condenser and lost to the surroundings is reduced. In general, this contributes to contracting both the power consumed in the auxiliary systems of the steam plant and the steam consumption.
