Bled steam feed water heating

Fig. 7.7. (a) Overall efficiency of CCGT plant with feed water heating by bled steam and single pressure steam raising (after Rufli (9)). (b) Overall efficiency of CCGT plant with feed water heating with bled steam and dual... 

Kehlhofer explains that the pre-heating loop must be designed so that the heat extracted is. sufficient to raise the temperature of the feed water flow from condenser temperature T to Ta (see Fig. 7.6). The available heat increases with live steam pressure Ipf), for selected 7 b(= Ta) and given gas turbine conditions, but the heat required to preheat the feed water is set by (Ta — T. ). The live steam pressure is thus determined from the heat balance in the pre-heater if the heating of the feed water by bled steam is to be avoided but the optimum (low) live steam pressure may not be achievable because of the requirement. set by this heat balance. 

Feedwater heaters are used to increase the efficiency of steam power plants. A particular heater is used to preheat 10 kg/s of boiler feed water from 20°C to 188°C at a pressure of 1200 kPa by mixing it with saturated steam bled from a turbine at 1200 kPa, as shown in Fig. P4.76. Although insulated, the heater loses heat at the rate of 50 J per gram of exiting mixture. What fraction of the exit stream is steam ... 

Condensate is pumped out of the main condenser hotwell, which is at sub-atmospheric pressure, by the condensate pumps. The water passes through the low-pressure feedwater heaters, whieh heat it using steam bled from the low-pressure turbine eylinders the largest and last low-pressure heater is incorporated into the de-aerator tank, which also removes dissolved air from the feed water and, by virtue of its substantial volume, acts as a reservoir of feed water equivalent to several minutes supply at full delivery flow. 

The steam turbine of AHWR is designed for a steam quality of 99.75%. During normal operation or in a bypass mode of operation the steam from the turbine exhaust is condensed in a condenser, which rejects the heat to seawater. The condensate is heated in heat exchangers by the moderator system. The feed water temperature is finally raised to 403 K through LP (low pressure) heaters and de-aerators using the steam bled from the turbine. The feed water pumps then pump the feed water into the steam drum where it mixes with the water separated from steam-water mixture. 

In the continuous production of nylon 6, similar reaction conditions are used. In one process, a mixture of molten caprolactam, water and acetic acid is pumped continuously to a reactor operating at about 260°C. The feed slowly traverses through the reactor whilst steam is bled off so as to maintain atmospheric pressure. Residence time is 18—20 hours. The product is stripped of low molecular weight material by heating in vacuo and then directly spun into fibre... 

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