Adiabatic Pre-Cooling Air Cooled Heat Exchanger (GAS TURBINE & GENERATOR COOLER)
Applications:
- The Adiabatic Air Pre-Cooling System, as the name suggests, is used to pre-cool the ambient air to a temperature required for process cooling
- Adiabatic system removes heat from air by evaporating water in a stream of hot air. In the process of going from liquid to vapor the water cools the air stream by absorbing the latent heat for evaporation from within the air itself leading to cooling of this air to a few degrees above the ambient wet bulb temperature
- Particularly good fit in hot ambient environment where the air temperature is not suitable for process cooling using Air Cooled Heat Exchangers, Chillers and similar equipment that use ambient air for process cooling applications
- Adiabatic Pre-Cooling System finds applications in various industries like Power Generation, Oil & Gas, Data Centers, HVAC, Pharmaceutical, Chemical etc.
- The system comprises of specially designed high-pressure pumps and misting nozzles which break up the water particles to a size below 10 microns leading to instantaneous evaporation and cooling of the air stream
- Air Cooled Heat Exchangers in conjunction with Adiabatic Air Precooling System can achieve process temperatures below the ambient air temperature
- This system can also lead to reduce footprint for the Air Coolers where space is a constraint.
Challenges Encountered:
- The output power & efficiency of Gas Turbines are significantly influenced by higher ambient temperature with higher temperatures leading to notable decline in power output. This issue becomes even more critical during heightened power demand in hot climates during summer months. While the power demand for cooling is higher during this period due to higher ambient temperature, power generated by the turbine reduces due to the higher inlet air temperature to the gas turbine. Thus, cooling of inlet air to the turbine assumes great significance to maintain the power generated in hot arid desert climates and summer months. The lower the air inlet temperature, higher is the density and mass of the air and resultantly the power generated. A reduction of air temperature to the turbine by 1°C results in around 0.6% increase in the power generated
- A greenfield power plant being constructed in the middle east faced these challenges to generate higher power during summer months. The Turbine & Generator cooling system required the cooling water at a temperature much cooled below the ambient air temperature to generate rated power even during the hot months. Typical Air-Cooled Heat Exchanger designs have an approach of 5°C which means the water can be cooled only upto 5°C above the ambient air temperature. With the air temperature reaching 50°C in summer months it meant that the cooling water could only be provided in the turbine & generator at 55°C which would lead to a significant loss of power generated.
Curated/offered Solutions:
- One option was to use conventional chillers to cool the water instead of Air-Cooled Heat Exchangers. However, these chiller systems had very high capital and running costs as well as maintenance cost. A significant portion of the power generated would be required to run the chillers making it unfeasible to use this system.
- Dolphin Heat Transfer stepped in to provide a solution based on Air Cooled Heat exchanger system in conjunction with an Adiabatic Pre-Cooling system to cool the air to 36°C from an ambient temperature of 50°C. This solution resulted in the cooling water being returned to the system at 41°C instead of 55°C resulting in significant cooling efficiency and increase in power generated by cooling inlet air as well as stator windings.
- The adiabatic system is mounted below the air-cooled heat exchanger. It comprises of high-pressure pumps which pressurize the spray water to around 70-100 bar. This water is pushed through special spray nozzles which atomizes the water to a size below 10 microns causing instantaneous evaporation. The latent heat of evaporation is drawn from the air resulting in lowering the air temperature to few degrees above the wet bulb temperature. The system also consists of water treatment module, temperature & humidity sensors and auxiliaries to make the complete package.
- Cooled air is drawn into the tube bundles by the fans. The configuration can be Induced Draft or Forced Draft.
- System operates only when the ambient temperature is above the set temperature to prevent wastage of water. Temperature sensors below the tube bundle monitor the air temperature and cut off the system when the required air temperature is reached.
Benefits /Value proposition:
- The combined Air Cooler + Adiabatic Pre-Cooling system provides process cooling temperatures below ambient air temperature.
- No additional space is required to install the system as the area under the Air Cooler is utilized for this purpose.
- It reduces power consumption and capital costs as well as maintenance costs associated with conventional chillers. Chillers also require additional space for installation, piping and accessories.
- Adiabatic System can be retrofitted on existing Air Coolers.
- Adiabatic System can also reduce the overall foot print of the Air Coolers as size of the cooler can be reduced even when process cooling below ambient temperature is not required.
Uniqueness about the project:
- The solution offered a cost and space effective solution to enhance the power generated by the gas turbine.
- Due to the effectiveness of the solution the Power plant has decided to implement the same solution as a retrofit for the existing Air Coolers in other stations.
- New Greenfield project being implemented with similar Adiabatic System.
