What are the different types of reboilers?

Heat exchangers typically used to provide heat to the bottom of industrial distillation columns

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Reboilers are heat exchangers typically used to provide heat to the bottom of industrial distillation columns. They boil the liquid from the bottom of a distillation column to generate vapors which are returned to the column to drive the distillation separation. The heat supplied to the column by the reboiler at the bottom of the column is removed by the condenser at the top of the column.

Proper reboiler operation is vital to effective distillation. In a typical classical distillation column, all the vapor driving the separation comes from the reboiler. The reboiler receives a liquid stream from the column bottom and may partially or completely vaporize that stream. Steam usually provides the heat required for the vaporization.

Types of reboilers

The most critical element of reboiler design is the selection of the proper type of reboiler for a specific service. Most reboilers are of the shell and tube heat exchanger type and normally steam is used as the heat source in such reboilers. However, other heat transfer fluids like hot oil or Dowtherm (TM) may be used. Fuel-fired furnaces may also be used as reboilers in some cases.

Commonly used heat exchanger type reboilers are:

Kettle Type reboilers

Kettle reboilers (Image 1) are very simple and reliable. they are similar to shell and tube type heat exchangers. They may require pumping of the column bottoms liquid into the kettle, or there may be sufficient liquid head to deliver the liquid into the reboiler. In this reboiler type, steam flows through the tube bundle and exits as condensate. The liquid from the bottom of the tower, commonly called the bottoms, flows through the shell side. There is a retaining wall or overflow weir separating the tube bundle from the reboiler section where the residual reboiled liquid (called the bottoms product) is withdrawn, so that the tube bundle is kept covered with liquid and reduce the amount of low-boiling compounds in the bottoms product.

Thermosyphon reboilers

Thermosyphon reboilers (Image 2) do not require pumping of the column bottoms liquid into the reboiler. Natural circulation is obtained by using the density difference between the reboiler inlet column bottoms liquid and the reboiler outlet liquid-vapor mixture to provide sufficient liquid head to deliver the tower bottoms into the reboiler. Thermosyphon reboilers (also known as calandrias) are more complex than kettle reboilers and require more attention from the plant operators. There are many types of thermosyphon reboilers including vertical, horizontal, once-through or recirculating.

Fired reboiler

Fired heaters (Image 3), also known as furnaces, may be used as a distillation column reboiler. A pump is required to circulate the column bottoms through the heat transfer tubes in the furnace's convection and radiant sections. The heat source for the fired heater reboiler may be either fuel gas or fuel oil.

Forced circulation reboilers

A forced circulation reboiler (Image 4) uses a pump to circulate the column bottoms liquid through the reboilers. This is useful if the reboiler must be located far from the column, or if the bottoms product is extremely viscous.

Some fluids are temperature sensitive such as those subject to polymerization by contact with high temperature heat transfer tube walls. High liquid recirculation rates are used to reduce tube wall temperatures, thereby reducing polymerization on the tube and associated fouling.

See also

Further reading

The reboiler is an essential part of any distillation column. In this article, we are going to learn what are reboiler and what are the types of reboiler and the use of reboiler in industries.

In the previous article, we discussed are distillation process in which we had discussed the working of distillation.

To generate vapor of the substance, we need to heat the column feed material and in the column. To heat the column feed, the equipment used is a reboiler. Different types of heating media are used in the reboiler. Hence reboiler plays an important role in distillation process.

Before we get into the tutorial about what are distillation columns, let us learn what are reboiler in a distillation column.

What are reboiler in a distillation column?

A reboiler is a heat exchanger that is used to heat the feed of the distillation column and convert the liquid into vapor. Then this vapor goes from the top of the column into the condenser which is then condensed and this is how distillation works.

As the whole distillation operation works on the relative volatilities and boiling point of the substance, the reboiler plays an important role in the proper distillation process.

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In a reboiler, different types of heating media are used such as steam, MEG (methyl ethyl glycol), hot oil, and many more. Steam reboiler in which steam is used to heat the liquid is commonly used in the process.

Now, that we have learned what are reboiler and which are utilities used in the reboiler, let's move forward and learn what are the different types of reboiler.

Types of reboiler

Three types of reboilers are used in the chemical industry in a distillation column but the majorly there are only two types, kettle-type reboiler, and thermosyphon reboiler. Let's proceed with the post and learn all the types of reboiler in detail along with the figures

1. Internal Reboilers

Internal reboiler are the simplest type of reboiler in which is mounted in the distillation tower itself in the bottom. They are also known as Stab-in reboiler.

As shown in the figure, In the internal boilers, heating media is circulated in the tube bundles. Internal boilers are submerged in a pool of liquid in the bottom of the distillation column and heating media (usually steam) is passed into the tube of the reboiler from the top and condensate is out from the bottom. The steam then flows inside the tube, heat the column bottom liquid and converts it in vapor and liquid mixture.

In this way, internal reboiler are used into the column to perform heating and distillation process is continued.

2. Kettle type reboiler

A kettle reboiler is also known as a 'submerged bundle reboiler. In a kettle-type reboiler, the process fluid that is needed to be heated remains in the shell while the heating utility such as steam or hot oil circulates in the tube.

The utility passed in the tubes of kettle reboiler, heat the liquid coved the tubes and the liquid converted into vapor goes to the top of the distillation tower.

These types of reboiler are widely used in the chemical, petrochemical, and polymer industries. These are not only used in a distillation column but also in a circulation tower where we can use brine to reduce temperature.

The only disadvantages of the kettle-type reboiler is scaling and deposition of salts or other solid material in the kettle.

3. Thermosyphon reboiler

Thermosyphon reboiler are a widely used type of reboiler in distillation column. Thermosyphon reboiler are similar to heat exchangers. As shown in the figure, the distillation column bottom is connected to the bottom of the thermosyphon reboiler.

In these reboilers, Steam or other heating media such as hot oil or MEG is circulated in the tubes of the reboiler which then heat the column bottom liquid.

The reason why these Thermosyphon reboiler are widely used it, that they don't require any external equipment for circulation. Here the working principle is the thermosyphon effect.

Thermosyphon reboiler are of two types based on reboiler orientation, vertical Thermosyphon and vertical Thermosyphon reboiler.

4. Fired reboiler

Fired reboilers are also known as a furnace which is used with the distillation column. This reboiler is divided into two sections, the convection section and the radiant section. In the bottom of the furnace, the heat source is there which is fired using natural gas, or fuel oil. The main purpose of a fired reboiler is to preheat the fluid or process.

In a fired reboiler, the pump is used to circulate the fluid in the reboiler from the top of the furnace which is then heated in the reboiler.

5. Forced circulation reboilers

Forced circulation reboiler working is similar to the thermosyphon reboiler but the only difference is, that pumps are used. In this type of reboiler, liquid from the bottom of the distillation column goes into the pump suction and discharges into the reboiler inlet. Hence pump is used to circulate the distillation bottom liquid into the reboiler bottom and in this way, it is heated and converted in to vapour liquid mixture.

FAQ (What are reboiler and types of reboilers)

1. Why reboiler is used in the distillation column?

Ans ' The distillation column is used for separating components or substances and it requires heat. Reboiler is a type of heat exchanger that provides heat to the column bottom liquid and generates vapor.

2. What is the difference between boiler and reboiler?

Ans ' Boilers are used to generate steam in for the generation of electricity and reboilers are used to reboil the distillation column bottom liquid using steam or other heating media.

3. What is the difference between kettle reboiler and a thermosyphon reboiler?

Ans ' In kettle-type reboiler, external equipment is used i.e. pump to perform force circulation whereas in a thermosyphon reboiler, the thermosiphon effect is used to perform natural circulation.

Wrapping Up

This was the detailed information on what is reboiler and what are the types of reboiler. We had coved various chemical engineering aricle which will help you to learn more concepts. If you have any doubt on this topic, feel free to use the comment section. Also if you want us to cover any topic, do let us know in the comment, and we will surely make a detailed article on that.

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