What is meant by Indirect Dry Cooling Tower?
An Indirect Dry Cooling Tower is a system that uses two separate fluid loops to reject heat. The process fluid is first cooled by water in a conventional heat exchanger, and then that water is itself cooled by air in a dry cooling tower. The key concept is the word “indirect”—the primary hot fluid (e.g., turbine exhaust steam) never goes to the cooling tower itself. It is isolated from the tower by an intermediate heat exchanger
How It Works: The Two-Loop System
This system decouples the process cooling from the heat rejection to the atmosphere. Here’s a step-by-step breakdown, using a power plant as the example:
Loop 1: Steam Condensation Loop (The “Indirect” Part)
- Steam Inlet: Exhaust steam from the turbine flows into a traditional surface condenser (a shell-and-tube heat exchanger), just like in a plant with a wet cooling tower.
- Heat Transfer: Inside this condenser, the steam transfers its heat to a separate, closed loop of cool water. This causes the steam to condense back into water (condensate).
- Return to Boiler: The condensate is pumped directly back to the boiler to be reused. This loop is now complete.
At this point, the primary cycle is finished. The heat from the steam has been transferred to the water in the second loop.
Loop 2: Cooling Water Loop (The “Dry Cooling” Part)
- Warm Water to Tower: The water in the secondary loop, now warmed up by absorbing the steam’s heat, is pumped to the dry cooling tower.
- Dry Cooling: Inside the tower, this warm water flows through bundles of finned tubes (the heat exchangers). Ambient air is blown across these tubes by fans (mechanical draft) or drawn through by buoyancy (natural draft).
- Heat Rejection: The heat from the water is transferred through the tube walls to the air, cooling the water down significantly—again, purely through sensible heat transfer, with no evaporation.
- Return to Condenser: The cooled water is pumped back to the surface condenser to absorb more heat from the steam, completing the second loop.