Aqueous parts washer cleaning processes have become mainstream ever since ozone depleting solvents have been legislated out of use. However, the expenditure could be high when operating in a batch process, i.e. ending when the cleaning solution has been exhausted by accumulated oils and soils. The nature of this batch cleaning process results in both high cleaner replacement costs and the incremental costs of oily waste disposal. This disposal problem also applies to “biodegradable” cleaners, since discharge to drain is prohibited once they are contaminated with waste oils.
Membrane UF is a cleaner recycling solution that can significantly reduce the operational cost of aqueous parts washers. As illustrated in adjacent figure, the membrane acts as a barrier to the free floating and emulsified oil phases, but passes the free detergent and water.
Once designed into a system as shown in the process and Instrumentation Diagram below, the membrane continuously traps the oily and soiled phases in the working tank while recycling regenerated cleaner back to the parts washer sump. By performing a mass balance on the oil contents within the wash tank, time-dependent oil concentration profiles can be obtained. As an example, low steady state oil levels can be maintained by filtering as little as half the washer volume per day. This indicates that relatively small, economical filtration systems can be used for recycling and achieve a significant improvement in washer performance. The implications of this example are significant. Recycling systems will have a great impact on process cost and part quality. By regenerating the cleaning fluid, savings are realized through reductions in the consumption of cleaner and the disposal of spent cleaner. To further reduce the disposal volume of oily waste, the contents in the working tank shown below can be batched down intermittently. System payback based on these savings typically is achieved in less than a year.
Additionally, since the recycling systems allow parts washers to operate at low steady state oil levels as shown in the adjacent figure, parts are consistently cleaned to a higher level. Consequently, secondary surface finishing operations (e.g. painting, electroplating, etc.) produce higher quality parts that lower rework rates. These benefits can result in even greater cost savings than those realized by minimizing cleaner usage and disposal rates. FSI’s WRS Wastewater Recycling System is ideal for aqueous cleaner recycling application.