Welcome to our comprehensive guide on heaters in power plants!
🌟 Types of Heaters in Power Plants
Power plants mainly use feedwater heaters which are categorized into two types based on how the steam interacts with the water:
1. Open Feedwater Heater
- Steam mixes directly with the feedwater.
- Simple in design but requires careful pressure matching.
2. Closed Feedwater Heater
- Steam does not mix with feedwater.
- Shell-and-tube type construction.
- Steam condenses outside the tubes, heating the water inside.
- Non-condensable gases are vented out.
Note: All heaters except the Deaerator are closed type heaters.
🔥 Types Based on Pressure Levels
Low Pressure Heater (LP Heater)
- Located between the condensate pump and the boiler feed pump.
- Typically extracts steam from the low-pressure turbine.
High Pressure Heater (HP Heater)
- Placed downstream of the boiler feed pump.
- Utilizes steam from the high or intermediate pressure turbine.
📐 Orientation of Heaters
Horizontal Heaters:
- Occupies more floor space.
- Easy level control and floor-mounted.
- Most common type.
Vertical Heaters:
- Less control area for liquid level management.
- Challenging installation and maintenance.
- Save floor space.
🛠 Major Connections in Closed Feedwater Heaters
- Feedwater Inlet Line
- Feedwater Outlet Line
- Extraction Steam Inlet
- Drip Inlet from Higher Heater
- Drip Outlet
- Air Evacuation Line
- Safety Valve Vent
🔥 Heat Transfer Zones
Each closed feedwater heater consists of distinct heat exchange zones:
Desuperheating Zone:
- Reduces the superheat from the incoming steam.
Condensing Zone:
- Condenses steam completely.
- Non-condensable gases are vented.
Subcooling (Drain Cooling) Zone:
- Cools the condensate below the saturation temperature by heat exchange with incoming feedwater.
Each zone is carefully designed and analyzed separately for optimum performance.
📊 Heater Performance Indicators
Two key performance parameters are used to monitor and diagnose the condition of feedwater heaters:
Terminal Temperature Difference (TTD)
- TTD = Saturation temperature of steam (Ts) – Feedwater outlet temperature (To)
- A rising TTD indicates reduced heat transfer.
- 1°C deviation in TTD leads to ~1.8 kcal/kWh heat rate loss.
Drain Cooler Approach (DCA)
- DCA = Drain outlet temperature (Tdo) – Feedwater inlet temperature (Ti)
- Higher DCA shows insufficient subcooling of drains.
- 1°C deviation in DCA leads to ~0.25 kcal/kWh heat rate loss.
🚨 Impact of Deviations
- High heater levels = reduced heat transfer and high TTD.
- Low heater levels = high DCA.
- Proper control of both is essential to maintain thermal efficiency.
🧪 Monitoring Parameters
For efficient heater operation, monitor the following:
- Heater shell-side pressure
- Feedwater inlet/outlet temperatures
- Drip outlet temperature
- Shell-side drip level
- Regularly calculate TTD and DCA
📈 Heater and Steam Flow Arrangements
- Drips from heaters either flow to the next lower-pressure heater or are pumped forward.
- Alternate drip paths to the condenser are provided in case of high-high level conditions.
- Bypass valves are used to bypass heaters when needed, especially during abnormal conditions.
🙏 Conclusion
Heaters in power plants are indispensable for maximizing efficiency, protecting equipment, and ensuring a smooth power generation process. Proper design, operation, and monitoring of feedwater heaters contribute significantly to reducing fuel costs and environmental impact.
By understanding the types, heat transfer zones, and performance parameters like TTD and DCA, engineers can ensure the long-term reliability and efficiency of the plant.
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