What is process heating and cooling in heat exchanger?
Process Heating and Cooling refers to the use of a heat exchanger to raise or lower the temperature of a fluid (a liquid or gas) to a specific, required value for a subsequent industrial step, reaction, or storage condition. It is the most common and direct application of heat exchangers across all industries
The core principle is always the same: a process fluid (the stream you need to heat or cool) exchanges heat with a service fluid (the utility stream providing or absorbing the heat).
1. Process Heating
This involves adding thermal energy to a process fluid to increase its temperature.
- Goal: To bring a material to the optimal temperature for a chemical reaction, distillation, sterilization, or other processing step.
- How it works: The cold process fluid is routed through one side of the heat exchanger. A hot service fluid flows on the other side, transferring its heat across a solid barrier (like metal plates or tubes) to the process fluid.
- Common Service Fluids (Heat Sources):
- Steam: The most common source. It transfers a large amount of latent heat as it condenses.
- Hot Water or Thermal Oil: Used for lower temperature requirements.
- Hot Process Stream: Another fluid from elsewhere in the plant that needs cooling itself (this is efficient heat recovery).
- Combustion Gases: Directly from a furnace or flame.
Real-World Example: Pre-heating Crude Oil
In an oil refinery, thick, viscous crude oil must be heated before it enters the large distillation column where it will be separated into fractions like gasoline, diesel, and kerosene.
- Process Fluid: Cold crude oil.
- Service Fluid: A hot, already-processed stream from the distillation column (like gas oil).
- Why? The heat exchanger, often called a “crude pre-heat train” recovers heat from the hot product, saving enormous energy. It also ensures the crude is at the perfect temperature for effective separation.
2. Process Cooling
This involves removing thermal energy from a process fluid to decrease its temperature.
- Goal: To stop a chemical reaction, condense a vapor into a liquid, prepare a product for storage, or protect downstream equipment from heat damage.
- How it works: The hot process fluid is routed through one side of the heat exchanger. A cold service fluid flows on the other side, absorbing the waste heat from the process fluid.
- Common Service Fluids (Heat Sinks):
- Cooling Water: From a cooling tower or river. This is the most common coolant.
- Air: Used in air-cooled heat exchangers (fin-fans), especially in areas where water is scarce.
- Refrigerant: Used when very low temperatures are required.
- Cold Process Stream: Another fluid from elsewhere in the plant that needs heating.
Real-World Example: Cooling Reactor Effluent
A chemical reactor produces a new compound through a highly exothermic (heat-releasing) reaction. The output stream is extremely hot.
- Process Fluid: Hot product from the reactor.
- Service Fluid: Cooling water.
- Why? The heat exchanger, often called a “reactor effluent cooler,” quickly lowers the temperature to stop the reaction at the desired point, prevent product degradation, and make the stream safe for handling and storage.
The Dual Role: Heat Recovery
The most efficient industrial processes combine heating and cooling into a single step for maximum energy conservation. This is done with a Heat Recovery Heat Exchanger.
Real-World Example: Feed Effluent Exchanger
This is a classic example in oil refineries and chemical plants.
- Process Fluid (that needs heating): Cold “feed” about to enter a reactor.
- Service Fluid (that needs cooling): Hot “effluent” leaving the reactor.
- How it works: The cold feed and hot effluent are routed through a large shell and tube heat exchanger. The hot effluent heats up the cold feed, while simultaneously the cold feed cools down the hot effluent.
- Benefit: This drastically reduces the plant’s energy needs. The furnace that further heats the feed uses much less fuel, and the cooler that further cools the effluent uses much less water or electricity.
Summary in a Table
| Aspect | Process Heating | Process Cooling |
| Primary Goal | Increase temperature of a process fluid | Decrease temperature of a process fluid |
| Energy Flow | Heat is added to the process | Heat is removed from the process |
| Role of Service Fluid | Provides heat (e.g., Steam, Hot Oil) | Absorbs heat (e.g., Cooling Water, Air) |
| Common Industrial Need | Starting reactions, distillation, evaporation | Stopping reactions, condensation, storage |