Vapour absorption machine working with flow diagram

Today, we are going to learn what a vapour absorption machine, also known as vam chiller, is in detail along with a flow diagram.

Utilities are crucial for industries as not all chemical reactions occur at ambient or atmospheric temperatures. To fulfill the required temperature for the chemical reaction and for other purposes in the chemical plants, utilities are required.

These utilities contribute to achieving the required chemical temperature i.e. high or low temperature for chemical processes. Apart from VAM chiller, a cooling tower is also used to decrease the cooling water temperature.

Previously we had discussed Types of cooling towers in which we included the 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

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 requirements and today in this article, we will learn how to produce chilled water using an absorption chiller i.e also known as VAM chiller machine.

Before we learn and understand the workings of a 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 increases, the temperature of the system also increases.

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What is Vapor absorption machine?

A vapor absorption machine (VAM) also known as a vapor absorption chiller, produces chilled water using a heat source such as steam hot water and fuel gas. It works using the absorption refrigeration cycle, where refrigerant (water) evaporates to cool, is absorbed by lithium bromide (LiBr) in the absorber, and then separated using heat in the generator.

This sounds weird, i.e., it produces chilled water by using a stem, but yes, it is possible.

What are the types of VAM Chiller

• Single-Effect : Use low-temperature heat sources like hot water or steam;
• Double-Effect : Operate with medium-to-high-temperature heat sources; higher efficiency (COP ~1.2-1.4).
• Triple-Effect : Use very high-temperature sources; highest efficiency (COP ~1.8-2.0);
• Hot Water-Fired: Use hot water as the heat source; ideal for waste heat recovery.
• Steam-Fired: Operate with steam; suitable for industrial setups.
• Direct-Fired: Burn fuel directly; standalone and flexible.
• Exhaust Gas-Fired: Utilize waste heat from engines or turbines; for co-generation systems.
• Hybrid Chillers: Combine heat sources for optimized energy use.

This consists of mainly two compartments and four other sub-compartments

The main two compartments of the 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 (Demineralized water)
• Absorbent (Salt) – Lithium bromide (LiBr)

Refrigerant: The refrigerant of the vapor absorption machine is pure (distilled) water, flows in a closed loop and is recirculated in the compartments.

Water boiling changes the different pressure and 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

The absorbent of the vapor absorption machine is Lithium bromide (LiBr). LiBr is a highly water-attractive chemical 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 the 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 work?

A description of the main parts of the lithium bromide absorption chiller is given in detail. This is a single stage.

Low-pressure side

1. Evaporator

The evaporator’s function is to cool the water flowing through a coil. The evaporator is maintained under a 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 absorbs the heat from the substance to be chilled and gets fully evaporated it then enters the absorber.

2. Absorber

The absorber function maintains 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 into dilute LiBr formed. This solution is pumped into the generator.

In the meantime, you can check out Cooling Tower efficiency calculation

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 of absorbing 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 returned back to the absorber.

2. Condenser

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

The hot refrigerant vapor leaving the regenerator flows through eliminators or separators to the condenser the cooling water from a cooling tower circulates through the condenser to move the heat from the refrigerant vapor. This vapour is condensed into a liquid refrigerant where it passes through a pressure pressure-reducing valve into an evaporator, which operates under a vacuum.

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

Advantages of vapor absorption chiller

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

FAQ (Vapour absorption machine)

Wrapping Up

This was a detailed article on vapor absorption chiller working (VAM). I hope you have understood the workings of a vapor absorption machine, also known as a lithium bromide absorption chiller. If you have any doubts regarding this, feel free to use the comment section; we will help with your confusion. If you want us to cover any specific topic, then notify us using the comment section.