Converting Waste Heat into Environmentally Friendly Cooling for Industry & Commerce
Production companies are often characterised by their high and constant electricity requirements. It is important to meet these in an economically, ecologically, and technically optimum manner. At the same time the main requirement in many of these companies is for high-temperature process heat (in the form of steam). However, space heating for heating purposes (hot water) is subject to strong seasonal fluctuations and the annual thermal base load often encompasses the provision of hot water for functional and cleaning purposes only. As a result, the electricity and heat demand is often partially decoupled and an economical use of heat can – especially during the height of summer – pose a challenge for combined generation methods. Absorption chillers can be used to convert excess heat into chilled air for air conditioning purposes or for use in production processes. Combined heat, power, and cooling technology can therefore increase the annual utilisation quota for the entire energy production process and is therefore eligible for federal government subsidies in the form of targeted bonus programmes.
Integrating the CHP plant in the energy supply system
The cold from absorption chillers is a substitute for energy from traditional chiller units such as compression refrigeration systems. The annual energy requirement for these machines is reduced. However, the economic benefit of the absorption chiller is not so much derived from direct cost savings for power, but rather from an improvement in thermal energy utilization. The heat demand is increased and the minimum demand in summer is evened out. The downstream installation of an absorption chiller unit is fundamentally capable of increasing the usable volume of heat from the CHP system. The fuel utilization level increases. Any partial load phases of the CHP plant through the lack of significant heat demand in summer can be avoided, or it is even possible to integrate a CHP system with a higher maximum output into the overall system design right from the outset. The overall smoothing of the annual heat demand as well as the increased electricity volume produced in house further improve the system's cost effectiveness.
The absorption chiller
As a general term, the word 'sorption' describes the processes that result in the enrichment of a substance within a given phase (absorption), or to a boundary surface/interface between two phases (adsorption). The absorption chiller, a compact, ready-for-connection unit, is located, for example, in a separate container in the immediate vicinity of the block-type thermal power station. The salt lithium bromide is usually used as absorption medium for refrigeration systems. The coolant is water.
Rather than a mechanical compressor like the ones used in compression refrigeration systems, absorption chillers operate on the basis of a so-called thermal compressor. Thus, the absorption chiller unit has no moving parts and is therefore not subject to any significant wear and tear. The coolant is compressed through absorption and decompressed through desorption. The system exploits the temperature dependency of the physical solubility of two substances. The unrestricted solubility of each of the substances in the other and in any mixed ration of the two substances is therefore an indispensable prerequisite. Other system components as well as the basic thermodynamic principles are largely identical in both absorption chillers and compression refrigeration systems.
The functionality of the thermal compressor requires a substance pairing consisting of coolant and sorption or solution media. The coolant evaporated within the evaporator as a result of the heat absorbed from the refrigeration medium is absorbed in the absorber via the concentrated sorption medium. The solution heat that this releases is dissipated with the aid of cooling water, as otherwise the coolant's absorption capacity would fall dramatically. A solution medium pump then pumps the solution, now enriched with the coolant, into the generator (also known as the extractor) in which heat from an external source (for example, from a CHP system) is added. As a result of the coolant's lower boiling point compared with that of the sorption medium, the coolant is boiled off through the added heat. The resulting refrigerant vapour is channelled to the condenser and follows the familiar route through the cooling circuit. What remains is the solution, enriched with sorption medium and depleted of coolant, which can then be resprayed over the refrigerant vapour within the absorber. Usually there is also a thermal exchange between the refrigerant depleted and refrigerant enriched solution, which results in an energy saving and therefore contributes to an improved efficiency level.
Absorption cooling from GETEC heat & power GmbH
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