Research On The Drying Characteristics And Technology Of Printing And Dyeing Sludge

Printing and dyeing wastewater must be treated by physical-chemical and biological method to satisfy the emission control regulations. In this process, much printing and dyeing sludge was produced. The output of printing and dyeing sludge has close correlation with water quality of printing and dyeing wastewater and its treatment technics. With the development of printing and dyeing industry, the output of printing and dyeing sludge become larger and larger. The moisture of printing and dyeing sludge is very high, so the treatment of printing and dyeing sludge is very difficult. Then the treatment of printing and dyeing sludge has become a problem which feaze printing and dyeing corporation. On the one hand, torrefaction can reduce the cubage of printing and dyeing sludge, on the other hand, it make good preparation for resourceful utilization of printing and dyeing sludge. So torrefaction is a effective method to solve the problem of printing and dyeing sludge.Static drying characteristics of two kinds of typical printing and dyeing sludge were studied besed on the research of their physical and chemical characteristics. The drying curve and dying rate curve of two kinds of printing and dyeing sludge was made in this article. The results show that, printing and dyeing sludge drying process include three periods: preheating period, constant rate drying period and the falling rate drying period. Constant rate drying period is the primary period in the drying process, which has highest drying rate and largest evaporation amount. Drying tempreture and particle size and the sourece of printing and dyeing sludge have influence on drying time and drying rate. The higher the drying temperature and the smaller the particles of sludge, the shorter time be needed to dry to a certain moisture content and the higher drying rate in constant rate drying stage. With the drying tempreture increased and the size of sludge particle decreased, the critical moisture content of sludge increse, and constant rate drying period become shorter. Reducing the sludge particle size and increasing the surface area of sludge is more beneficial for sludge drying process.In this article, the printing and dyeing sludge need to be dryed to moisture content of 30%. Then the drying technology of printing and dyeing sludge was explored and researched. First, the drying effect and energy consumption of drying by paddle-dryer were researched at different operation mode: the continuous feeding mode , the intermittent feeding mode and. Drying of printing and dyeing sludge by paddle-dryer is feasible, the evaporation rate of water can reach 12.5Kg/m2·h and the vapor consumption is 1.4～1.5Kg/KgH2O. But the continuous feeding operation mode and intermittent feeding operation mode both have some flaws. In dry sludge backmixing operation mode, when mixing ratio is 2.5:1(mass ration of dry sludge and wet sludge), printing and dyeing sludge can be dryed to the moisture content of 30%, but energy consumption is higher. On this basis, combining the advantages of plate-dryer, a combined drying technology of printing and dyeing sludge was formed: In continuous feeding operation mode, First ,the dry sludge(moisture content of 30%) and wet sludge(moisture content of 83%) were mixed at mixing ratio of 1:1 (mass ratio) and dryed in a Paddle-Dryer. Then the sludge which come from paddle-dryer was transported into a improved plate-dryer and be dryed to predetermind target(moisture content of 30%) by the boiler flue gas. Experiment results show that: combined drying technology is stable and reliable for drying of printing and dyeing sludge, and the heat of steam and boiler flue gas both were made full use of. The moisture content of discage of the conbined drying technology can maintain at 30%. The discahrge were sludge particles with diameter at 2-8mm. It can reduce dust pollution and the difficulty to collect dry sludge. The integrated energy cost of conbined drying technology is 164.1 yuan/t (wet sludge). The combined technology is very meaningful to be popularizated and applicated.