Study Of Novel Absorption Refrigeration And Heat Pump Systems For Highly-efficient Industrial Waste Heat Recovery

Absorption system is an important way to recover industrial waste heat,but the traditional single-effect absorption system has two major drawbacks:the first is that the efficiency of single-effect system is relatively low and is hard to adapt to variable working conditions,and the second one is that its ability to lift the temperature is limited by its thermodynamic construction.These drawbacks limit the utilization of traditional single-effect absorption system in industrial waste heat recovery.To solve these problems,this paper analyzes the performance of absorption cycles from working pairs and cycle construction,and proposes novel concepts for the high-efficient recovery of industrial waste heat.For the first drawback,this paper suggests the use of GAX absorption refrigeration cycle.Typically,the GAX absorption refrigeration cycle uses ammonia-water as working pair,and has issues of rectification,toxicity,and instability under high pressure.Moreover,the latent heat and heat/mass transfer performance of ammonia is weaker than water.However,the water based working pair LiBr-water solution has crystallization risk,so it could not be used by GAX absorption refrigeration system.In this case,we propose to use ionic liquid as the absorbent,which avoids the crystallization risk,rectification and instability issues.In this paper,the NRTL model is used to build the thermodynamic models of ionic liquid based working pairs,and the performance of GAX absorption refrigeration cycle is calculated.The results show that the GAX cycle with[DMIM][DMP]-H₂O can reach COP of 1.02 in the case of high generation temperature.The COP is increased by 27.5%comparing with the COP of 0.8 for the single-effect cycle,and exhibits more stable performance compared to the absorption cycle using the LiBr–water working pair.For the second drawback,the conventional absorption heat pump can effectively lift the temperature of waste heat,however the temperature lift is limited by the waste heat temperature and it can only be driven by thermal energy.Compression heat pump can be driven by the more widely available electrical energy to lift the waste heat temperature,but it has small temperature lift and is not suitable for high temperature working conditions.For example,the commonly used refrigerants R134a is unstable under high temperature and un-efficient under large temperature lift.If we use refrigerants suitable for high temperature working conditions such as water,technical problems of coexistence of negative pressure and positive pressure must be solved.To solve the above problems,this paper proposes the novel concept of compression-absorption heat pump cycle.The proposed cycles combine the compression heat pump cycle and the absorption heat pump cycle through different heat-coupling methods.The cycles achieve high temperature output and large temperature lift driven by electrical energy.Thermodynamic models are built to evaluate the proposed cycles.R134a and LiBr-water are used as the refrigerant of compression heat pump cycle and working pair of absorption heat pump cycle,respectively.When the waste heat with temperature of 30⁴0°C is increased to more than 100°C by the large temperature rising cycle?compression-absorption heat pump I?,the system COP can reach 2.0 or more,which is about 50%higher than that of the compression heat pump.When the high output temperature cycle?compression–absorption heat pump III?is used to recycle waste heat with temperature of 55⁷0°C,the system COP can reach 2.0 or more,and the efficiency is slightly higher than the compression heat pump,while the temperature rise can be much larger than that of the compression heat pump.