Utilities are crucial for industries as not all chemical reactions take place at ambient temperature or atmospheric temperature. To fulfill the required temperature to the chemical reaction and for other purposes in the chemical plants utilities are required. These utilities contribute to achieving required chemical temperature i.e. high or low temperature for chemical processes. Apart from VAM, a cooling tower is also used to decrease the temperature of cooling water. Previously we had discussed Types of cooling tower in which we had include working of the cooling tower. 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
- Hot water
- Cooling water
- Chilling water
- 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 an 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, the temperature of the system also get increases.
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 produces chilled water by the use of stem but yes it is possible. These 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 compartments of vapor absorption chiller are
These two main components are subdivided into again two parts as below.
#1 Low-pressure side
#2 High-pressure side
Working material in vapor absorption chiller
- Refrigerant – DM Water (Demineralized 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
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
The absorbent of the 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 the presence of oxygen but as the absorption chiller is a vacuum vessel where almost no oxygen is present it hence it will not harm the MOC of the 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 is given in detail.
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.
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
In meant time you can check out Cooling Tower efficiency calculation
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 the concentrated solution
The hot concentrated solution, which had now regained its strong affinity for absorbing more refrigerant returns back to the absorber.
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 circulates through the condenser to moving the heat from the refrigerant vapour. This vapour is condensed into a liquid refrigerant where it passed through pressure reducing valve into an evaporator, which operated under a 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
- As it is a simple heat exchanger working at different pressure it is relatively cheaper and reliable, also it requires very little maintenance and operating cost.
- It works on environment-friendly refrigerant on the place of CFC which has an adverse effect on the ozone layer
- As there are no moving parts which makes it free of noise and vibration.
- All the operations are fully automated hence it requires very little human intervention and make the process easy
Get a master grip on industrial safety …!!!
This was the detailed article on vapor absorption chiller working (VAM) and hope you had understood 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 the comment section, we will help with your confusion. We had cover various chemical engineering topics such as what is deaerator and types of it. Not only that, we had also cover industrial safety-related article like the Fire triangle. Do read those and if you want us to cover any specific topic then notify us using the comment section.