Understanding the Two-Stage Steam Absorption Chiller: Efficient Cooling with Water and Lithium Bromide

 Two Stage Steam Absorption Chillers

In this blog let us explore the basics of fascinating world of two-stage steam absorption chillers, which utilize water as the refrigerant and lithium bromide as the absorbent to achieve remarkable cooling efficiency. Learn how this cutting-edge refrigeration technology operates through a continuous cycle divided into six crucial steps. From solution pumps and heat exchangers to condensers and absorbers, understand the intricate process of creating an extreme vacuum that drives the refrigeration effect. Discover the benefits of this green technology and its superiority over conventional systems in terms of efficiency and operational simplicity. Ideal for anyone interested in HVAC systems, energy efficiency, and sustainable cooling solutions.

How it works ?:-  Steam Machines

Remarkably efficient two stage absorption refrigeration cycle uses water as the refrigerant and lithium bromide as the absorbent.

It is the strong affinity these two substances have for each other that makes the cycle work. The entire process occurs in hermetic vessels in almost complete vacuum.

The large diagram above indicates the complete chilling cycle.

The six steps are detailed below, with "corresponding numbers in the diagram to show where each step takes place.

Two stage absorption chilling cycle is continuous; however for the sake of clarity and simplicity, is divided into six steps.

 

  

1. Solution Pump/Heat Exchangers

A dilute solution (58.3%) of lithium bromide and water descends from the Absorber to the Solution Pump. This flow of dilute solution is split into two streams and pumped through heat exchangers to the First-Stage Generator and to the Second-Stage Generator.

Exclusive two-way split of solution flow virtually eliminates the possibility of crystallization (solidification) by allowing the unit to operate at much lower solution concentration and temperatures than series flow systems.

 

2. First-Stage Generator

 An outside steam source heats dilute lithium bromide (58.3%) coming from the Solution Pump/Heat Exchangers.

This produces hot refrigerant vapor which is sent to the Second-Stage Generator, leaving a concentrated solution (63.8%) that is returned to the Heat Exchangers.

 

3.Second-Stage Generator

The energy source for the production of refrigerant vapor in the Second Stage Generator is the hot refrigerant vapor produced by the First-Stage

This is the heart of York's remarkably efficient two-stage absorption effect. The refrigerant vapor produced in the First Stage Generator is increased by 40 % at no additional expense of fuel. The result is much higher than in conventional systems.

 

This additional refrigerant vapor (dotted arrows) is produced when dilute solution foam the Heat exchanger is heated by refrigerant “vapor from the First- Stage Generator,

The additional concentrated solution (light grey) that results is returned to the Heat Exchanger. The refrigerant vapor from the First-Stage Generator condenses into liquid (dark grey) giving up its heat, and continues to the Condenser.

 

 4. Condenser

Refrigerant from two sources - (1) liquid (dark grey) resulting from the condensing of vapor produced in the First-Stage Generator and (2) vapor (dotted arrows) produced by the Second-Stage Generator - enters the Condenser. The refrigerant vapor is condensed into liquid and the refrigerant liquid is cooled. The refrigerant liquids are combined and cooled by condenser water. The liquid then flows down to the Evaporator.

 

5.Evaporator

 Refrigerant liquid from the Condenser passes through a metering valve and flows down to the Refrigerant Pump. where is pumped up to the top of the Evaporator. Here the liquid is Sprayed out as a fine mist over the Evaporator tubes. Due to the extreme vacuum (6mm Hg) in Evaporator, some of the refrigerant liquid vaporizes, creating the refrigerant effect. (This vacuum is created by hygroscopic action the strong affinity lithium bromide has for water -in the Absorber directly below.)

 

The refrigerant effect cools returning system chilled water in the Evaporator tubes. The refrigerant liquid /vapor picks up the heat of returning chilled water, cooling it from 54° F to 44° F. The chilled water is then supplied back to the system.

 

 6. Absorber

As refrigerant liquid/vapor descends to the Absorber from the Evaporator, concentrated solution (62.7%) coming from the Heat Exchanger is sprayed out into the flow of descending refrigerant. The hygroscopic action between lithium bromide and water - and the related changes in concentration and temperature -result in the creation of an extreme vacuum in the Evaporator directly above. The dissolving of the lithium bromide in water gives off heat. which is removed by condenser water entering from the Cooling tower at 85° F and leaving for the Condenser at92° F (black dotted lines). The resultant dilute lithium bromide solution collects in the bottom of the Absorber. where it flows down to the Solution Pump.

  The chilling cycle is now completed and begins again at Step 1

 

Thanks for reading!