Heat Exchangers and Their Types
Heat Exchangers and Their Types
Heat exchanger is an important and expensive item of equipment that is used in almost every industry (oil and petrochemical, sugar, food, pharmaceutical and power industry).
About Heat Exchangers
Heat exchangers are similar to pumps and vessels in that they are widely used in most process plants. The control of heat within any facility is an important part of plant operation, whether by direct application (e.g., in a furnace) or by heat interchange (e.g., in a shell and tube exchanger).
The principal application of a heat exchanger is to maintain a heat balance through the addition or removal of heat by exchange with outside sources or between streams of two different oper ating temperatures. This chapter highlights the general layout requirements for heat exchangers. It also identifies the information required by the plant layout designer to locate, elevate, operate, and maintain the most common ex- exchangers and to position the piping and controls associated with these items.
The most common applications for heat exchangers are
- Cooler-Cools process streams by transferring heat to cooling water, atmosphere, and other media.
- Exchanger- Exchanges heat from a hot to a cold process stream.
- Reboiler-Boils process liquid in the tower bottoms using steam, hot oil, or a hot process stream as the heating medium. Heater- Heats a process stream by condensing steam.
- Condenser- Condenses vapours by transferring heat to cooling water, atmospheric air, or other media.
- Chiller-Cools a process stream to very low temper atures by evaporating a refrigerant.
Types of Heat Exchangers
Heat exchangers can be categorized based on:
- Flow configuration (parallel, counter, crossflow)
- Construction design
- Number of fluid streams
- Nature of heat exchange process (direct or indirect)
The most common types of Heat Exchangers are
Shell and Tube Heat Exchanger
- The shell and tube heat exchanger is the most common type, consisting of a series of tubes enclosed within a cylindrical shell
- One fluid flows through the tubes, while another flows outside the tubes but inside the shell.
- Applications: Power plants, Refineries, Chemical processing
- Advantages
- High-pressure and temperature capability
- Easy to clean and maintain
Plate Heat Exchanger
- A heat exchanger is a small heat exchanger in which two fluids flow independently down adjacent corrugated channels while thin corrugated plates are placed in contact with one another.
- For ease of inspection and cleaning, the stacked plates can be closed using clamping gaskets, brazing (often copper brazed stainless steel), or welding (stainless steel, copper, titanium).
- The first method is the most popular.
- They are used in Low pressure and temperature single phase heating and cooling when fluids are not hazardous, a high pressure drop can be tolerated and alloys are required for the fluids being handled.
- Disadvantages
- Gaskets limit operating pressures and temperatures & require good maintenance
- Typical maximum design pressures are 150-250 psig
- Poor ability to handle solids – due to close internal clearances
- High pressure drop
- Not suitable for hazardous materials
Double pipe heat exchangers
- The most basic kind of heat exchanger is the double pipe kind.
- Two sections of pipe, one within the other, are used to construct them.
- While the second fluid passes through the annulus between the pipes, the first fluid passes through the inner pipe.
- Both co-current and counter-current flow are possible inside twin pipe heat exchangers.
Air-cooled heat exchangers
- Air-cooled heat exchangers cool and condense using ambient air.
- Usually, they are employed in areas with limited cooling water supplies.
- When the heat exchanger output temperature is at least 20 degrees Fahrenheit higher than the maximum anticipated ambient air temperature, air-cooled heat exchangers are often utilized.
- They can be made at temperatures that are closer to the surface, but they are frequently more costly than a cooling tower and water-cooled exchanger combined.
- Because of their size, poor air-size heat transfer coefficients, and structural and electrical requirements, air-cooled exchangers are more costly than water-cooled exchangers.
- Large plot areas are also necessary for air cooler exchangers, which also need to be built to withstand seasonal and daily variations in air temperature.
- Applications
- Oil and gas sector
- Petrochemical industries
- Power generation
- Advantages
- Eliminates water usage
- Lower operating costs in dry regions
Spiral Plate Heat Exchangers
- Two metal plates are twisted around one another to create spiral plate heat exchangers.
- While the second process fluid stream enters the exchanger from the outside and flows inward, the first stream enters in the center and flows outward.
- This produces a flow that is nearly countercurrent.
