- Absorption heat pumps are mostly used to increase the efficiency of boilers and/or combined heat and power plants.
The flue gas from heating plants or combined heat and power plants can be condensed largely irrespectively of the district heating networks’ return temperature.
In biomass boilers, more than 30% of additional usable energy can be extracted from the flue gas, in gas boilers more than 10%.
- Absorption chillers are used to cool buildings or production processes using waste heat which often cannot be fully utilised in summer. Special-purpose machines operated at low temperatures, e.g. flow/return = 70°C/55°C, are particularly suitable for this purpose.
- Absorption heat exchangers are used to actively cool the return flow of a district heating network. They are installed as a transfer station between a warmer primary network and a secondary network with a lower temperature.
This increases the transport capacity of the primary network; with the cold return flow, additional waste heat sources can often be tapped.
Each of the machine types mentioned can also be used in combination: For example, an absorption heat exchanger can be used to increase the line capacity in winter and as a chiller in summer.
Biomass combustion systems
- Absorption heat pumps play a particularly important role in biomass boilers, as the fuel used in large plants usually has a water content of 40 to 55%.
Since absorption machines use heat as the driving energy, this technology allows the moisture contained in the flue gas to be condensed almost completely without noticeably increasing electricity consumption. The output of a biomass furnace operated with wood chips thus increases by more than 30%.
Since the flue gas has a very low moisture content after passing through the condensation plant, the energy requirement for devaporisation is reduced.
Industrial process heating and chilling
- Absorption heat pumps are used to raise waste heat, which would otherwise be lost unused at low temperature levels, to a higher, usable temperature. Because heat is used to drive the heat pump, the electricity consumption is less than 0.5% of the delivered heat.
If low-temperature waste heat is available, directly gas-fired heat pumps can, in effect, be used as a boiler with an efficiency of approx. 160%.
- Category 2 absorption heat pumps provide usable heat at temperature that is higher than the heat pump’s driving heat. This allows, for example, water to be heated to 95°C from otherwise dissipated waste heat at 65°C. About half of the driving heat used is released into the environment as waste heat.
- Absorption chillers are used to cool buildings or production processes using waste heat as driving energy.
In the industrial sector, it often makes sense to use the same unit as a chiller in summer and as a heat pump in winter.
Depending on the mode of operation, the industrial waste heat is drawn from various sources, such as cooling water, waste water, exhaust air or flue gas from production. To ensure successful, economical operation, it is important to optimise the unit for each application scenario, taking into consideration all involved processes.
Combined heat and power generation
Improved combined heat and power (CHP) and trigeneration (CCHP)
In combined heat and power generation, gas engines or other processes are used to simultaneously generate electricity and heat. In the case of trigeneration – the combination of power generation, heat generation and cooling –, the heat is then used as input to an absorption chiller for cooling.
This, in turn, paves the way for two approaches for improving use of absorption machines:
- Used as a chiller, for example, the exhaust gas from a gas engine with a temperature above 400°C can be used to operate a double-stage chiller. Thus the cooling capacity of the same trigeneration plant can be increased by approx. 40% compared to the use of a simple single-stage chiller.
- Used as a heat pump, the exhaust gas from a gas engine can be condensed and the fuel efficiency of the CHP plant increased to more than 100%.