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What are the different types of reboilers?

Jan. 06, 2025

Chemicals

What Are Reboilers and Their Types?

Heat exchangers are crucial in delivering heat to the base of industrial distillation columns.

Reboilers function as heat exchangers specifically designed to supply heat at the bottom of distillation columns. They convert liquid from the column's base into vapor, which is then cycled back into the column to assist in the distillation separation process. The heat imparted by the reboiler is subsequently withdrawn by the condenser located at the column's top.

Efficient reboiler performance is essential for effective distillation. Conventional distillation systems derive all their vapor from the reboiler, which takes in a liquid stream from the column's bottom and may either partially or wholly vaporize it. Typically, steam is utilized to provide the necessary heat for this vaporization.

Types of Reboilers

Choosing the appropriate reboiler type for a particular application is crucial for its design. While most reboilers follow the shell and tube heat exchanger format, other heating fluids such as hot oil or Dowtherm (TM) can also be employed. In certain conditions, fuel-fired furnaces may serve as reboilers.

The common types of heat exchanger reboilers include:

Kettle Type Reboilers

Kettle reboilers (Image 1) are renowned for their simplicity and reliability. They closely resemble shell and tube heat exchangers. The system may either necessitate liquid pumping from the column's bottom or rely on sufficient liquid head for natural flow into the kettle. In these reboilers, the steam circulates through the tube bundle and exits as condensate while the liquid, known as the bottoms, traverses the shell side. An overflow weir or retaining wall segregates the tube bundle from the reboiler section where the remaining liquid, referred to as the bottoms product, is withdrawn, ensuring the tube bundle is adequately submerged to minimize the presence of low-boiling compounds in the bottoms product.

Thermosyphon Reboilers

Thermosyphon reboilers (Image 2) eliminate the need for pumping the bottom liquid into the reboiler, utilizing natural circulation driven by the density difference between the inlet liquid from the column and the liquid-vapor mixture exiting the reboiler. These reboilers, also known as calandrias, can be more complex than kettle reboilers which demand closer operational supervision. Variants of thermosyphon reboilers include vertical, horizontal, once-through, or recirculating types.

Fired Reboilers

Used in certain cases, fired heaters (Image 3) or furnaces can function as distillation column reboilers. This setup generally requires a pump to cycle column bottoms through heat transfer tubes located in the convection and radiant sections of the furnace. The heat source here can be either fuel oil or fuel gas.

Forced Circulation Reboilers

In forced circulation reboilers (Image 4), a pump facilitates the circulation of the column bottoms liquid through the reboiler. This configuration is valuable when the reboiler must be distanced from the column or when the bottoms product exhibits high viscosity. Additionally, certain fluids sensitive to temperature (like those that can polymerize upon contact with overheated tube surfaces) are managed with high recirculation rates to mitigate tube wall temperatures and avoid fouling.

Understanding the Function of Reboilers in Distillation

A reboiler serves as a pivotal component within any distillation column, providing the necessary heat to convert the liquid feed into vapor. This vapor then ascends through the column towards the condenser, where it is subsequently condensed. The operation of distillation hinges on the varying volatilities and boiling points of substances, underscoring the reboiler's essential function in ensuring a smooth distillation process.

As discussed earlier, reboilers utilize various heating media, including steam and hot oil, to achieve effective heating. Recognizing the various types of reboilers and their applications can greatly enhance understanding within this industrial process.

Types of Reboilers

In the chemical sector, there are primarily three types of reboilers utilized in distillation columns, although kettle-type and thermosyphon reboilers are chiefly employed. Let's explore each type in detail:

1. Internal Reboilers

Internal reboilers, often mounted at the column's base, are recognized for their straightforward design. Also known as stab-in reboilers, they circulate heating media through tube bundles while submerged in liquid at the column's bottom.

2. Kettle Type Reboilers

Commonly called submerged bundle reboilers, kettle-type reboilers enable the process fluid to reside in the shell while steam or hot oil traverses the tubes, heating the liquid around them to vaporize and ascend within the distillation tower. These are frequently utilized within chemical, petrochemical, and polymer sectors.

3. Thermosyphon Reboilers

Thermosyphon reboilers, known for their effectiveness in distillation operations, function like heat exchangers. With no external devices needed for circulation, these reboilers utilize the thermosyphon principle, allowing steam or other heating fluids to efficiently heat the column bottoms.

4. Fired Reboilers

Fired reboilers, also referred to as furnaces, consist of convection and radiant sections. These units mainly serve to preheat fluids utilizing natural gas or fuel oil.

5. Forced Circulation Reboilers

Similar to thermosyphon reboilers, forced circulation reboilers employ pumps for liquid circulation, vital for transferring the column bottoms into the heating zone of the reboiler.

FAQ on Reboilers and Their Types

1. Why is a Reboiler Used in Distillation Columns?

Answer: Reboilers are essential for separating substances in a distillation column by providing the necessary heat to vaporize the bottom liquid.

2. What is the Difference Between a Boiler and a Reboiler?

Answer: While boilers generate steam for electricity, reboilers are designed to heat and vaporize liquids in distillation processes.

3. What is the Difference Between Kettle Reboilers and Thermosyphon Reboilers?

Answer: Kettle-type reboilers require external equipment for forced circulation, while thermosyphon reboilers operate through natural circulation.

Wrapping Up

This article provided a comprehensive overview of reboilers and their **types**. We have discussed various aspects of this fundamental topic in chemical engineering. Should you have any questions or wish to explore specific subjects further, please feel free to reach out through the comment section. Also, let us know if there are other topics you'd like covered, and we'll happily create a detailed article on those as well.

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