vapour absorption machine

Vapour absorption machine working with flow diagram

vapour absorption machine
Vapour absorption chiller

Utilities are crucial for industries as not all chemical reactions takes place at ambient temperature or atmospheric temperature. To fulfil the required temperature to the chemical reaction and for other purposes in the chemical plants utilities are required. These utilities contribute to achieve high or low temperature for chemical process. In this article we will learn working of Vapour absorption machine / working of Vapour absorption chiller in detail.

Different types of utilities are required to run industries and common utilities are listed below

  1. Steam
  2. Hot water
  3. Cooling water
  4. Chilling water
  5. Brine
  6. Electricity and many more

Different utilities are used as per temperature requirement and today in this article, we will learn how to produce chilled water using absorption chiller i.e also know as VAM chiller machine.

Before we learn and understand the working of Vapor absorption machine we need to refresh Gas law i.e. Gay-Lussac’s Law which is  also known as The Pressure Temperature Law.

This law states that the pressure of a given amount of gas held at constant volume is directly proportional to the Kelvin temperature.

Pressure ∝ Temperature

Explanation- This means if the pressure of the system increase, temperature of the system also get increase.


What is Vapor absorption machine?

Vapor absorption machine (VAM) also known as vapor absorption chiller is to produce chilled water using heat source such as a steam hot water and fuel gas. this sounds weird i.e it produce chilled water by the use of stem but yes it is possible. This is the simplest possible words in which VAM can be described.

In Vapor absorption machine there  are mainly two compartments and other four sub compartments

The main two compartment of vapor absorption chiller are

  1. low pressure side
  2. High pressure side

These two main components are subdivided into again two parts as below.

#1 Low pressure side
1) Evaporator
2) Absorber

#2 High pressure side
1) Generator
2) Condenser

Working material in vapor absorption chiller

  • Refrigerant – DM Water (Demineralize water)
  • Absorbent (Salt) – Lithium bromide (LiBr)

Refrigerant: – Refrigerant of vapor absorption machine is pure (distilled) water. The refrigerant water flow in a closed loop and is recirculated.

Water boiling is change the different pressure and different temperature

For example

1. Sea level
Temperature 100 °C
Pressure 760 mmHg

2. High altitude Everest top
Temperature 70 °C
Pressure 525 mmHg

3. Under vacuum
Temperature 3.7 °C
Pressure 6 mmHg

Absorbent

Absorbent of vapor absorption machine is Lithium bromide (LiBr). LiBr is a highly water attractive chemicals which means it has a great affinity towards water. The higher is the concentration and the lower its temperature, the stronger is the absorption power. LiBr is a nontoxic aqueous solution, but very corrosive in presence of oxygen. LiBr has a corrosive action to metals in presence oxygen but as the absorption chiller is a vacuum vessel were almost no oxygen is present it it hence it will not harm the MOC of machine.

The chemical details of LiBNr are as follows

  • Chemical Formula: Li Br
  • Molecular Weight: 86.856
  • Component: Li = 7.99% / Br = 92.01%
  • Specific Gravity: 3.464 at 25°C )
  • Melting Point: 549°C
  • Boiling Point: 1,265°C
    Read more details on LiBr at Lithium bromide wikipedia page

How does the Vapor absorption machine works

Description of main parts of lithium bromide absorption chiller are given in detail.

vapor absorption machine thermax
vapor absorption machine flow diagram / lithium bromide absorption chiller

Low pressure side

1. Evaporator

The evaporator function is to cools the water flowing through a coil. The evaporator is maintained under vacuum of around 6 mmHg to which the refrigerant water boils at around 4 °C
Water as the refrigerant enters the evaporators at a very low pressure and temperature. since very low pressure is maintained inside the evaporator. This water refrigerant absorbed the heat from the substance to be chilled and gets fully evaporated it then enters the absorber.

2. Absorber

The absorber function is to maintain the pressure of the evaporator in the vacuum by absorbing the refrigerant vapor evaporated in the evaporator

A concentrated solution of lithium bromide is available in the absorber since water is highly soluble in lithium bromide solution then converted in dilute LiBr formed. This solution is pumped to the generator

Inmeant time you can

High pressure side

1. Generator

The generator function is to enrich the LiBr solution to its original concentration. As the lithium bromide solution is depleted, the effect to absorb the refrigerant vapor reduces. The dilute solution to LiBr absorbent flow to the generator to regain its concentration. It is a vessel, where the diluted solution of absorbent is heated by steam hot water or direct gas. The diluted solution releases the refrigerant vapor and becomes concentrated solution

The hot concentrated solution, which had now regained its strong affinity for absorbing more refrigerant returns back to the absorber.

2. Condenser

The condenser function is to refrigerant vapor that are released from the generator are cooled and liquefied.

The hot refrigerant vapour leaving the regenerator flows through eliminators or separator to the condenser the cooling water from a cooling tower circulate through the condenser to moving the heat from the refrigerant vapour. This vapour is condensed into liquid refrigerant where it passed thorough pressure reducing valve into evaporator, which operated under vacuum.

This cycle is repeated continuously lithium bromide on the other hand leaved the generator and re-enters the absorber for absorbing water refrigerant.

Advantages of vapour absorption chiller

  1. As it is simple heat exchanger working at different pressure it is relatively cheaper and reliable, also it requires very less maintenance and operating cost.
  2. It works on environment friendly refrigerant on the place of CFC which has adverse effect on ozone layer
  3. As there is no moving parts which makes it free for noise and vibration.
  4. All the operations are fully automated hence it requires very less human intervention and make the process easy

Get a master grip on industrial safety …!!!

Wrapping Up

This was the detailed article on vapour absorption chiller working (VAM) and hope you had understand the working of vapor absorption machine which is also known as lithium bromide absorption chiller. If you have any doubt regarding vapour absorption system the feel free to use comment section, we will help with your confusion. For more such chemical engineering content pay a regular visit.

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