Having knowledge of “Types of Reboiler in Distillation Column” is must for all the chemical engineer and process engineer as well all those who are working in chemical, distillery and refinery. I am going to cover basic to advanced-level information with you. I have around 15 years of experience, and over the years, I have designed many distillation columns and different types of reboilers. Based on my experience, I will cover the essential information that everyone should have. I hope you will love this article.
Today, we are going to cover what a reboiler is and why it is needed. After that, we’ll discuss the parts of a reboiler, types of reboilers (including Kettle, Thermosyphon, and Forced Circulation Reboilers), reboiler selection, frequently asked questions in technical interviews, and, lastly, I’ll share my pro tips to help you ace interviews and effectively select and design reboilers.
Table of Contents
What is Reboiler? why we use reboiler?
A reboiler is a heat exchanger used to boil the mixture or crude feed in a distillation column. It is typically located beneath the distillation column. The feed enters the reboiler, where the fluid is boiled, and the vaporized fluid then rises into the distillation column for separation. In short, a reboiler is a heat exchanger used to boil the fluid, which is essential for separation.
As we know, distillation is a unit operation that involves only physical changes. If you’re not familiar with this concept, check out the article on ‘Unit Operation And Unit Process | Difference Between ‘.
Components of reboiler
The components of reboilers actually depend on the types of reboilers we are going to use. However, I have tried to cover the key and common components that will be applicable for some types of reboilers. It is not necessary that the following components are applicable for all reboilers.
- Shell
- Tube Bundle
- Inlet and Outlet Connections
- Heating flow Connection
- Vapor Outlet
- Liquid Drain or Overflow
- Baffles for heat transfer
- Thermal Insulation for saving the energy
- Control Valves tor auto control
- Safety Devices to avoid any HSSE issue.
- Instrumentation and Sensors for the detection of temperature , level, pressure etc.
Types of Reboiler In Distillation Column
Based on the available books and my knowledge, the common types of reboilers are as follows.
- Thermosyphon Reboiler
- Forced Circulation Reboiler
- Kettle Type Reboiler (Kettle Reboiler)
- Fired tube Reboiler
Let’s discuss it in short. I will come up with a separate article on each type, where I will try to cover all information about it from construction to design to operations. Once I cover it, I will try to link it here as well.
Thermosyphon Reboiler
Thermosyphon Reboiler or natural circulation reboiler is rarely used reboiler in industry. We can design it vertical or horizontal based on process requirement.
Working
Liquid enters the tube bundle, and the heating fluid heats it according to the process requirements. Due to the heating, the temperature rises, which decreases the density of the fluid. As the density decreases, the fluid flows upward, and this is how circulation happens.
Advantages and Disadvantages
The main advantage is that it saves energy; we don’t need a pump to recirculate it. The key disadvantage is that it requires careful installation.
Types of Thermosyphon Reboiler
Following are the two types of it.
Vertical Thermosyphon Reboiler
Following is the example of vertical type.
Horizontal Thermosyphon Reboiler
Following is the example of Horizontal type.
Forced Circulation Reboiler
As you can see in following image in forced circulation reboiler we need a pump to circulate the fluid.
Working
We send the flow to the tube bundle using a pump. This fluid is then heated by a heating fluid, which may be steam or high-temperature oil. In this way, the fluid gets heated or converted into vapor, which then goes to the column, and the warm fluid is sent back to the tube bundle.
Advantages and Disadvantages
The main advantage is that we can use it for viscous liquids, which is not possible in the case of a thermosyphon reboiler. However, the disadvantage is that it requires high energy due to the addition of a pump. It also needs a high capital expenditure because of the pump.
Kettle Type Reboiler
Kettle type is the most commonly used reboiler in the industry, especially in chemical and refinery applications. It normally contains a vessel with a tube bundle inside it. You can see the image of it below.
Working
The tube bundle inside the kettle heats the fluid, which is inside the kettle. The boiled vapors then go to the column for separation.
Advantages and Disadvantages
The main advantage of it is that it provides space to avoid surges, but the main disadvantage is that it requires high costs and more space as well.
Fired tube Reboiler
It is type of reboiler where we use flame or fire to heat fluid or to boil the fluid. Following image is best example of it.
Reboiler Selection
Reboiler Selection is the key skill that every chemical engineer should have. so i am goin to covers some factors that are important for reboiler selection.
Following are the factors
Process Requirements
- Heat duty
- Fluid properties (viscosity, fouling tendencies, boiling point, heat transfer characteristics)
Type of Reboiler
- Kettle
- Thermosyphon
- Forced circulation
- Once-through
- Fired tube
- Operational Conditions
- Pressure and temperature ranges
- Liquid and vapor flow rates
2. Energy Efficiency
- Heat transfer efficiency
- Utilization of available heat sources
3. Space and Layout
- Installation space requirements
- Horizontal vs. vertical space considerations
4. Maintenance and Reliability
- Maintenance requirements
- Ease of serviceability
5. Cost Considerations
- Capital expenditures (CAPEX)
- Operational expenditures (OPEX)
6. Regulatory Compliance
- Industry standards and regulations
Problems in Reboiler
Let’s discuss the problems in a reboiler. The following are common problems that may occur due to different reasons, and you need to take precautions during the design phase. I have written some problems below. these are as per my experience only.
Excessive Heating
Excess heating means we are providing excessive heat to the reboiler as per the operational requirements. Suppose the operational demand is 500 kcal per hour, but we are supplying more than that. This results in overheating or sends a higher amount of vapor to the column than designed.
Low Heating
Low heating means supplying low energy as per process requirements. Suppose, based on material balance and energy balance, our required energy is 500 kcal per hour, but we are supplying only 400 kcal per hour. Another reason could be that we are supplying a lower temperature than the process requirement.
Excess Circulation
It mean getting the excess flow as per operation requirement, this may be due to change in feed flow rate, lower heating or may excess heating, separation issues in column.
Low Circulation
Low circulation is nothing but a lower flow rate than the operational requirements. This may be due to low heating issues, overheating issues, changes in feed composition, changes in feed temperature, or separation issues in the column.
Surging
Surging is nothing but high level variation in fluid flow that may be different reasons like, Changes in feed composition, Poorly designed flow paths, Impact on Separation Efficiency.
Solidifying the Fluid
Solidification of material is also a common problem that may occur due to different reasons, like if the crude inside the reboiler gets concentrated and at the same time the heating temperature is also low, which is below the melting point of the crude inside the kettle.
Frequently Asked Questions on
The following are some common questions I have covered based on Google searches or as per the candidates’ requirements. For your questions, please feel free to ask.
What is reboiler in distillation column?
A reboiler in a distillation column is a heat exchanger that plays the role of boiling the fluid, which is a key step for distillation. The reboiler provides the vapor of the fluid to the column, which is important for separation.
What is Difference Between Thermosyphon and Kettle Reboiler?
Thermosyphon works on the principle of density difference or natural buoyancy effect, while in the kettle, the liquid is boiled in the kettle with the help of a heating tube bundle.
Pro Tips on Reboiler for Interview on Types of Reboiler
Try to understand the steps that are important for the design and selection of it. I have some material for it; you can comment below so I can share it with you. Work on the working principle of each type of reboiler.
Conclusion
A reboiler in a distillation column boils the fluid, which then goes to the column for separation. It is a heat exchanger that boils the fluid. The key types are kettle-type reboilers, thermosyphon reboilers, forced circulation reboilers, and fire tube reboilers.
I hope you enjoyed the article ‘Types of Reboilers in Distillation Columns.’ Please comment below.
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