Dewatering of paint sludge with centrifuges

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90 % cost reduction combined with a positive environmental impact

Wet absorption systems are the standard method to catch and discharge overspray from paint booths. For dewatering of its paint sludge a Polish paint shop purchased a cleaning centrifuge from Rösler. With sizable cost savings this investment paid for itself within the first year of operation. At the same time the dewatering of the paint sludge by centrifuge saves resources and is more eco-friendly

In 1996 the painting job shop Hannex, located in Ordzin, Poland, started with the manual wet painting of components for household appliances. Since then the company has developed into a sophisticated operation with modern work places for manual paint applications as well as several fully automatic painting lines equipped with 6-axis robots and computer controlled paint supply systems. The company is coating metal, plastic and glass components with solvent- and water-based wet paint materials. Krzysztof Iwanicki, general manager at Hannex, explains: „Besides the household appliance industry our customers also include automobile companies and their suppliers around the world.

A focus on costs and the environment
To ensure top quality and cost efficiency, the company utilizes the latest paint application technologies from renowned suppliers. This helps reduce overspray but does not prevent it completely. The catching of the paint mist takes place with the classic Venturi wet absorption method. This uses atomized water to pick up the excess paint particles in the paint booth and discharge the paint/water mixture into three collecting tanks with a total volume of ten cubic meters. To maintain the stability of the process water various chemicals had to be added for controlling the pH value, for defoaming and for protection against bacteria infestation. The addition of coagulants and flocculants made sure that the paint particles were separated from the water and floated to the surface. The resulting sludge was then removed from the surface and pushed into a separate container with a sludge scraper. Subsequently, it was disposed of. On average about 4 tons of sludge and dirty water accumulated per week. The professional disposal of this waste material was not only extremely expensive, but under environmental aspects the resulting high consumption of fresh water was not very eco-friendly. Last-but-not least, this paint sludge disposal system also caused an unpleasant odor, a real nuisance for the employees. Krzysztof Iwanicki continues: „These disadvantages had annoyed me for quite some time. Therefore, I became very interested in paint sludge dewatering with a cleaning centrifuge and was grateful to Filip Kapela, the representative of Rösler OberflĂ€chentechnik in Poland, informing me about this possibility in 2016”. After this first information a joint visit at the headquarters of the equipment manufacturer was arranged. During his visit Krzysztof Iwanicki was able to acquaint himself with the working principle and the performance characteristics of centrifugal filters for paint sludge dewatering. The general manager remembers: „I immediately specified my requirements and subsequently decided to purchase a centrifuge RZ 120 M-V”.

Efficient separation of solids and water from the paint sludge
The semi-automatic cleaning centrifuge can handle a volume of 120 liters per minute. A feed pump continuously feeds the process water into the centrifuge drum, rotating at a speed of 2,750 RPM. The high rotational speed ensures not only an excellent performance in terms of throughput, but it also ensures that very small and light-weight particles are deposited on the drum wall as solid sludge with a residual water content of 20 to 30 %. This represents a significant improvement over the sludge scraper with the residual water content of the sludge amounting of more than 80 %. Once the sludge load in the drum has reached about 22 kg, the sludge can be easily removed by simply extracting the sludge basket out of the drum and dumping the sludge into a waste container.

Alternatively, in fully automatic centrifuges the sludge can be removed from the centrifuge drum with a stationary peeling knife. During the separation cycle this peeling knife is positioned in the center of the drum. For sludge peeling mode the knife moves slowly towards the drum wall by way of a pneumatically activated linear guide. The peeled out sludge falls into a container placed below the centrifuge drum. This peeling knife arrangement prevents any additional load on the bearings of the rotating drum. After completion of the peeling cycle the drum is automatically rinsed out for removal of any residual sludge deposits, which, during the subsequent cleaning cycle could cause an imbalance with the risk of premature bearing failure.
The cleaned process water, now free of paint particles, is fed back into the process with a special water collection tube.

Quick amortization combined with high cost savings
Because of its small footprint Hannex decided to purchase a semi-automatic centrifuge. The RZ 120 M-V is equipped with sophisticated controls and a process water and clear water tank. It is not only easy to operate and maintain, but because of its placement on a movable base, it can be easily utilized at the different collecting tanks. Krzysztof Iwanicki explains: „The centrifugal cleaning process is so effective that we no longer need any coagulants and flocculants for supporting the separation of the paint particles from the water. We could also eliminate all the other chemicals for stabilizing the process water in the collecting tanks. As a matter of fact, we are only using chlorine for disinfecting the reclaimed water coming out of the centrifuge in crystal clear condition”.
But the savings by no longer having to use chemicals are not the only reason for the substantial cost reduction. Because of the drastically decreased residual water content the amount of paint sludge that must be disposed of has become a lot smaller. And finally, a lot less fresh water is required for the collection of the overspray paint mist. Krzysztof Iwanicki concludes: „The centrifuge has been in operation since 2016. It amortized itself already within the first year. And we could reduce the operating costs for paint sludge removal by roughly 70 %. Beginning with the second year of operation our annual cost savings increased to 89 %”.
Besides the sizable cost reduction Krzysztof Iwanicki is also very pleased with the much lower consumption of resources and the positive effect on the environment. This undeniable success prompted him to purchase a second centrifuge for cleaning the water that is used for the general cleaning of the paint booths at Hannex.