Absorption chillers are a group of heat-chillers. This is their big advantage over the compressor chillers as to drive the absorption of the units, the cheaper low-potential heat energy rather than more valuable electricity.
Especially effective is their use where there are heat sources in the form of secondary energy, ie Waste in the form of steam, hot water, combustion gases and the heat of chemical reactions, etc.
It is through absorption chillers and heat pumps the fullest possible use of energy resources, reduce thermal pollution, ie to solve the most urgent problems of energy.
The process of removing heat from objects in absorption cooling units is carried out essentially in the same way as in compression refrigerating machines. The only difference - in ways to increase the pressure of the working agent. Here, it is improved by a so-called thermochemical compressor, which uses an exothermic reaction absorbance (absorption) and endothermic reactions separation.
The most common machines are running on a binary solution consisting of absorbent (absorber) and refrigerant.
Basic requirements for such solutions:
a) the ability to mix in any proportion (vzaimorastvoryatsya). Limited solubility of the refrigerant in the absorbent leads to limited opportunities in the implementation cycles;
b) a higher normal boiling point as compared with the absorbent refrigerant. Reducing the difference in normal boiling point entails rectification refrigerant, ie complicates the scheme and introduces additional thermodynamic losses.
Solution with a high content of the refrigerant in the absorbent called strong, with less - weak. With respect to the water when it is used as a refrigerant, and conversely sometimes taken. It is necessary to pay attention to when using the calculations to various help and methodical literature.
Currently widely adopted such mixtures:
a) water-ammonia solution (H2O + NH3), whose components have
The following normal boiling temperature: t0 = 100 ° C and tNH3 = -33 ° C, and the difference between these temperatures is Ats = 133 degrees. Here the water - absorbent ammonia - refrigerant;
b) a solution of lithium bromide (LiBr + H2O), with a boiling point:
tLiBr = 1312 ° C and tS * 2 ° = 100 C. The temperature difference Ats = 1212 degrees. Here, lithium bromide - absorbent, water - refrigerant.
Absorption chillers are continuous and batch.
Chillers continuous contain all the devices required for continuous operation. They can be single-stage, two-stage, absorption and resorption and combined.
MDC are used in single stage if the parameters of the heating medium are sufficient to obtain the desired temperature in the evaporator.
Two-stage XM - using a heating medium or low potential for lower temperatures in the evaporator.
In the absorption and resorption car capacitor replaced absorber, which is called rezorberom. In this rezorber cooling water is heated to higher temperatures and can be used in heating systems.
In combined refrigerating machines in one of the steps of the compressor can be used.
In a batch chiller absorber and a generator are combined in one apparatus. Dates absorption and generation (evaporation) are shifted in time. In an industry as such chillers are used.
Typical sources of irreversible losses in the absorption machine are as follows:
- Impossibility to increase the boiling point of any solution in the generator due to the balance of pressures therein, and the capacitor;
- Incomplete process vapor absorption in the absorber due to the finite time of contact of steam and the final solution and the heat transfer surface;
- Need for steam distillation to increase its concentration before it is fed to the condenser.
The last remark applies to machines running on binary solutions where small difference between the normal boiling point of the refrigerant and absorbent (eg, water-ammonia solution).