چەكلەی رانکین بۆ دیزاینەکانی پاشکەشکردنی ئاودا و چەكلەی رانکین بۆ جەمێرکاری
Rankine Cycle bi Closed Feed Water Heaters
Closed feed water heaters li ser bikin di Rankine cycle da hewce benefits û di hemû modern power plants de bêt ser hatîn. Closed feed water heater indirect mode of heat transfer bîrkar dike, yani extracted steam an jî bleed steam ji turbine di shell and tube heat exchanger di feed water re heat bide. Ji ber ku steam û water directly mix nedin, steam û water circuits her du pressure yên din ne. Closed feed water heater di cycle de T-s diagram e wekhe şoşê dibaxtar di Fig:1 de.
Theoretically or ideally heat transfer in closed feed water heater should be in such a way that the temperature of the feed water should be increased to that of the saturation temperature of the extraction steam (heating the feed water).
Lê di actual plant operation de maximum temperature ên feed water bibêje ye dengir ye saturation-temperature ên steam. Serbestî ye ku few degrees temperature gradient effective and efficient heat transfer ji bo bibe.
Condensate or condense steam ji heater shell da next heater (low- pressure) di cycle de an jî sometimes condenser.
Open û Closed Feed Water Heaters an derbas bike
Open û closed feed water heaters an derbas bike:
Open feed water heater |
Closed feed water heater |
Open û simple |
More complex in design |
Good heat transfer characteristics |
Less effective heat transfer |
Direct mixing extraction steam and feed water temperature in a pressure vessel |
In-direct mixing feed water and steam in a shell and tube type heat exchanger. |
Pump is required to transfer the water into next stage in the cycle. |
Closed feed water pumps don’t require pump and can operate with the pressure difference between the various heaters in the cycle. |
Requires more area |
Requires less area |
Less expansive |
More expensive |
Hemû modern day power plants open û closed feed water heaters combination bikin thermal efficiency ên cycle maximize bike.
Cogeneration Phenomenon
Engineering thermodynamics looks at converting the valuable form of energy (heat) to work. In power plants, this is done by transferring it to the working fluid called water. So the purpose is to avoid the wastage of heat of steam in the steam turbine condensers. This is possible if find the means to use the low-pressure steam going into the condenser.
Cogeneration is the concept of utilizing the heat of the steam for a useful purpose, rather than wasting it (currently wasted in the condensers).
Cogeneration means Combined Heat and Power (CHP) that is the generation of heat and power simultaneously for the industry requiring process heating steam. In cogeneration plant, both heat-and-power are judiciously utilized so the efficiency of it can be as high as 90% or more. Co-generation offers energy savings.
Cogeneration offers the reduction in wasting of large amount of steam and the same can be utilized in many devices in the form of heat. Most of the industries like paper and pulp, chemical, textile and fiber and cement are depending upon co-generation plant for process heating steam. Process heat steam requirement in above industries are in the order of 4 to 5 kg/cm2 at temperature around 150 to 180oC.
Paper, chemical and textile industries require both electric power and process steam to accomplish their objective. So this requirement can be easily meet through by installing cogeneration power plant.
Temperature in inside the boiler is of the order of 800oC to 900oC and the energy is transferred to the water to produce steam of pressure 105 bar and temperature around 535oC for co-generation power plants. Steam at these parameters are considered as of very good quality source of energy and is thus first utilized in steam turbine for producing power and the turbine exhaust (low quality energy) is used to meet the requirement of process steam.
Cogeneration plant is known for meeting the requirement of power while meeting the process steam requirement of Industrial processes.
Ideal steam-turbine co-generation is shown in the figure 2 above. Let us say that the process heat requirement Qp is at 5.0 Kg/cm2 at around 100 KW. In order to meet the process steam requirement at 5.0 Kg/cm2 steam is expanded in the turbine till the pressure of the steam drop to 5.0 Kg/cm2 and thus produces the power around 20 KW.
The condensate from process heater is recycled backed to boiler for cyclic operation. Pump work required to raise the pressure of the feed the water in the cycle is considered as small so not considered.
All energy transferred to the working fluid in the boiler is used either in steam turbine or in process plant, thus utilization factor of the cogeneration plant is:
Where,
Qout Heat rejected in the.
Thus in the absence of the condenser the heat utilization factor of the cogeneration plant is 100%.
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