Heat Exchanger In Pharmaceuticals

Heat Exchanger

The water system is playing a crucial role in the pharmaceutical industry's development. Water for injection is one of the prerequisites of the sterile dosage form in the manufacturing industry. The heat exchanger is equipment that maintains the temperature of WFI in WFI system flow. There are multiple usages of the heat exchanger. The name itself tells that it exchanges the heat of the medium.

As above said, for the Pharmaceutical Industry, Water System has a crucial role. Without developing water, the medicine could not get manufactured. For liquid dosage forms, the water treatment for the generation of water for pharmaceutical use is mandatory. It is not like that, the source water collected from the well, or corporation is directly used for the production of medicines. Before usage of water for medicinal purposes, the water is treated to generate purified water and water for injection. Both the water has their separate specification and standards.

A typical tube and shell-type Heat Exchanger

This was a brief intro to the water requirement in pharma. Now we will come directly to the topic of heat exchangers used in the water system. We shall start this with the definition of the heat exchanger.

The heat exchanger is equipment, used to transfer heat between two or more fluids.

Heat exchangers are used in both processes of cooling and heating. These fluids are separated by a solid wall to prevent mixing (Shell and tubes). They are widely used in space heating, refrigeration, air conditioning, power stations, chemical plants, petrochemical plants, petroleum refineries, natural-gas processing, sewage treatment, and in the pharmaceutical industry for WFI maintenance.

The classic example of a heat exchanger is circulating fluid known as engine coolant flows through radiator coils and air flows to the coils, which cools the coolant and heats the incoming air. An example is HVAC System. In most cases, in the pharma company, the heat exchanger is installed to maintain the temperature of water in a controlled state. The heat exchanger assembly is small but the purpose of the equipment is big.

Normally heat exchanger has an external cylindrical body, tubes for WFI circulation, inlet, and outlet for utility supply and return. The mechanism of the heat exchanger is as simple as its design.

Heat exchanger Operation Principle:

The heat exchanger operates by a heat transfer mechanism. There are two types of heat transfer mechanisms are used by heat exchangers

1. Single-phase heat transfer 
2. Two-phase heat transfer.

In single-phase heat exchangers, the fluids do not undergo any phase change throughout the heat transfer process. It means, both the warmer and cooler fluids remain in the same state of matter at which they entered the heat exchanger. For example, in water-to-water heat transfer applications, the warmer water loses heat which is then transferred to the cooler water, and neither changes to a gas or solid. One more example is geothermal gaseous (boiler steam) to water heat transfer. In this process, boiler steam losses its heat, and water increase the heat.

On the other hand, in two-phase heat exchangers, fluids experience a phase change during the heat transfer process. The phase change can occur in either or both of the fluids involved, resulting in a change from a liquid to a gas or a gas to a liquid. Some of the types of two-phase heat exchangers available include boilers, condensers, and evaporators.

Types of Heat Exchanger:

1. Double Tube Heat Exchangers: Double tube heat exchangers use what is known as a tube within a tube structure.
2. Shell and Tube Heat Exchangers:
3. Tube in Tube Heat Exchangers:
4. Plate Heat Exchangers:

So, in this post, I am going to explain the tube and shell type, heat exchanger.

Tube and Shell Type Heat Exchanger:

The tube and shell heat exchanger is commonly used to transfer the heat of one medium to another. Refer to the below diagram for a better understanding.

The main constituents of this type of heat exchanger are the tube, shell, front-rear end headers, and baffles or fins. There are several variations of shell-and-tube exchangers available; the differences lie in the arrangement of flow configurations and details of construction.

Shell and tube heat exchangers are typically used for high-pressure applications (with pressures greater than 30 bar and temperatures greater than 260 °C). This is because the shell and tube heat exchangers are robust due to their shape.

Several thermal design features must be considered when designing the tubes in the shell and tube heat exchangers.

Parts of Heat Exchanger:

1. Outer shell for heat exchanger: 

This is nothing but the outer body of the heat exchanger. In the pharmaceutical industry, all the parts need to be made of SS316L for contact parts and other parts can be made up of SS304. Inside the outer shell, the tubes, fins or baffles, supporting and/or tube separating discs are constructed.

2. Baffles or fins for heat exchanger: 

The baffles are used to support the tubes, give direction to fluid flow to tubes in an approximately natural manner, and maximize the turbulence of the shell fluid. There are many various kinds of baffles. The choice of baffle form, spacing, and geometry depends on the allowable flow rate of the drop in shell-side force. In application to cool air with shell-and-tube technology, fins can be added on the tubes to increase heat transfer area on the airside and create a tubes & fins configuration.

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3. Tubes and Tube support disc for heat exchanger: 

Shell and tube heat exchangers consist of a series of tubes that contain fluid that must be either heated or cooled. A second fluid runs over the tubes that are being heated or cooled so that it can either provide the heat or absorb the required heat. A set of tubes is called the tube bundle and can be made up of several types of tubes: plain, longitudinally finned, etc. Typically, the ends of each tube are connected to flanges. The tubes may be straight or bent in the shape of a U that is called U-tubes.

4. Inlet for utility point for heat exchanger:

The utility point must be either heated gas or liquid which can transfer its heat towards fewer heated fluid that is running from the tubes. This process is more robust, if the baffles, fins are provided to the heat exchanger.

5. Outlet for utility point for heat exchanger: 

After heating and transferring the heat, the medium can come from the outlet point.

6. Fluid inlet for heat exchanger:

This is the point from where the fluid to be heated is introduced.

7. Fluid outlet for heat exchanger: 

After heat transfer, the fluid is collected from the outlet point.

Flow Configuration of Heat Exchanger:

Benefits of the Heat Exchanger:

Typically, the heat exchanger is introduced to heat the fluid to the required temperature. The design of the shell and tube heat exchanger is simple but it required a geothermal gas as the heating medium. For e.g. boiler steam, warm water supply.

The heat exchanger can also be used as the reverse. For e.g. to reduce the temperature of the fluid. This is typically required in the HVAC system.

References:

https://en.wikipedia.org/wiki/Heat_exchanger

https://www.thomasnet.com/articles/process-equipment/understanding-heat-exchangers/