NH3/H2O absorption-based cold and electricity combined production cycle

Given the ever-increasing global demand for energy, and the attention being paid to environmental issues and climate change, research is increasingly being carried out into new, more efficient cooling and electricity production technologies based on renewable or recovered sources. In this context, absorption systems are well suited to harnessing low-temperature energy for cold production. The advantage of these machines is that mechanical compression is replaced by thermochemical compression, using heat as the energy source. In addition to the control systems, the main electricity input is for a pump, but this is around 10 to 30 times less than that required for a compressor. Another advantage of absorption machine technology is that it can produce cold using well-known refrigerants such as ammonia or water, which are not harmful to the ozone layer and do not emit greenhouse gases. Absorption cooling systems have until now been niche technologies, but the market is growing with a reduction in their costs, which were halved between 2007 and 2016 according to a European study. Such systems are particularly promising in two areas: the recovery of industrial waste heat, and the use of renewable heat sources, especially in solar air-conditioning where the solar resource is well suited to the cooling requirement.

Although characterized by a low level of technological maturity (TRL 3-4 on a maturity scale of up to 9), the co-production, within the same cycle, of electricity and cooling from a low-temperature thermal source is the subject of numerous studies. Such a system would make it possible to increase the energy efficiency of the overall system and to mutualize certain components. This article focuses on a combined system for parallel production of cooling and electricity from a low-temperature heat source. The study is based on an experimental prototype of a water/ammonia absorption chiller with a thermal power of 10 kW at the generator, in which a turbine is integrated. A 1D model of the turbine, calibrated on CFD (Computational Fluid Dynamics) simulations, is integrated into a validated model of the absorption machine and used to study the interactions between the turbine and the cycle containing it. The constraints imposed by the turbomachine on the cycle are highlighted, and solutions for increasing the system's flexibility are proposed.

The analyses carried out have enabled us to define the cycle's operating range and study its performance. These results, together with feedback from the prototype, will be very important for the future development of a full-scale demonstrator for an application yet to be identified.