Heat Pump System Research For Printing And Dyeing Industry Wastewater Heat Reuse

China has the largest printing and dyeing industry in the world, while relatedresearches on heat recovery of printing and dyeing wastewater are still remain in apreliminary stage. Waste heat recovery of printing and dyeing wastewater with theapplication of wastewater source heat pump in production process, is a more practicalway. For the wastewater source heat pump systems, the efficiency of heat recovery nowstill stay at low standards and the economy benefits are far from ideal. These situationsare caused by a series of reasons, including the insufficient analysis of wastewaterqualities, thermal properties as well as energy flux characteristics. The optimizedmatches between heat pumps and heat requirements are also seldom employed,meanwhile excessive expectations for the payback times are quite universal.In this study, practical conclusions were given based on surveys in the printing anddyeing field and theoretical calculations of cases, including the energy fluxcharacteristics of an entire printing and dyeing process. Further, the quantity andtemperature characteristics of wastewater were also investigated. The relationshipamong process water temperature, river water temperature and the heat requirementfeatures of different dyeing processes were discussed. In addition, an optimal designwas proposed with the most economy match among waste heat, heat requirement andheat pump systems.Coupon corrosion tests were conducted in this study to analyze the corrosion effectof wastewater on different metal materials, with wastewater samples from severalwastewater treatment factories. Components and particle size analysis of wastewaterwere conducted in laboratory to investigate the mechanism of blockage in heat pumps.Electrochemical workstation was used to determine the rate of corrosion. These workswere aimed to provide a theoretical background for the prevention of blockage, theselection of heat exchangers materials, as well as the selection of wastewater heatsource position. The water quality of wastewater which adopted by the printing anddyeing factory was also analyzed in this study.A novel type of anti-blockage plate heat exchanger was chosen to solve the blockageof printing and dyeing wastewater heat exchanger, based on the water quality ofwastewater sampled at the inlet to the urban wastewater network. Experiments indicated that the anti-blockage heat exchangers shown obvious anti-blockage advantages andprovided high heat transfer efficiency.In summary, prior to the application of heat pumps to facilitate the heat recovery ofprinting and dyeing wastewater, position of heat source should be chosen at the outlet ofprocessed wastewater from wastewater factories. The temperature range of water fromoutlet and used for heat pump usage should be controlled at45~60℃. Besides,optimized usage of off-peak electricity can further bring considerable economic benefitsfor printing and dyeing enterprises.