Performance evaluation of a steam generation system using a novel semi-open heat pump for waste heat recovery in dyeing industry

In order to reduce the steam cost of dyeing industries, a steam generation system with a novel semi-open heat pump is proposed in this paper. It can recover the heat of high temperature wastewater and steam condensate simultaneously. With the use of natural refrigerant, water that is the same medium as the steam, part of the compressed steam out of the heat pump compressor can be compressed continuously by another compressor to reach the usage requirement of dyeing processes, making the steam generation system more concise. Besides, high efficiency contact condenser and water-injected twin screw steam compressor are used for the energy efficiency enhancement. Mathematic models are established and solved for the performance evaluation of the whole steam generation system. Firstly, influence of the heat pump design parameters is analyzed for performance optimization. Afterwards, performance comparison is carried out between the new steam generation system and a conventional steam generation system using heat pump with R245fa. Finally, the economic benefits by using the steam generation system in a dyeing process are discussed. Results show that the proposed system always outperforms the conventional system in thermal and economic performances. Optimal evaporation temperature exits to obtain the maximum economic benefits. With the use of novel semi-open heat pump, specific power consumption for steam generation can be as low as 188 kW h/t. By recovering the heat of 1 t/h waste water at 85 degrees C, the new system can generate 0.064 t saturated steam (150 degrees C) and about $1.02 economic benefit can be yielded, demonstrating its great development and application value.