Oil skimmer removes tramp oil from the washing water of wet scrubber
In die casting plants, the molds are sprayed with a high-temperature release agent to ensure that the cast parts can be removed from the mold without any problems. To avoid odors and health hazards, the resulting vapors are extracted. The contaminated air is fed into a wet scrubber. In the wet scrubber, impurities such as dust particles, release agent vapors and oil droplets are washed out of the air. To do this, the air is passed through a chamber.In this chamber, water constantly trickles through the contaminated air and absorbs the contaminants from the air.
The problem
The contaminated water is fed into a sedimentation tank. The lighter contaminants such as dust particles, oil, grease and separating agents float on the surface of the water. Heavier metal particles settle to the bottom. The cleaned water is pumped back into the wet scrubber. Due to the high dirt load, the washing water had to be changed at very short intervals. When changing the washing water, the container also had to be cleaned manually, which involved a lot of work.
The task
A system was sought to significantly extend the service life of the washing water
Various systems were reviewed and in some cases tested:
1. floating oil extraction
The first attempt was to remove the floating layer, consisting of oil, grease, separating agents and dust, with a floating oil extractor. A height-adjustable funnel, mounted on floats, was used so that the edges of the funnel were just below the surface of the water. A pump was then used to suck up the floating phase. However, as the release agent used in the die casting process was very viscous, the floating contamination was only captured in the immediate area around the funnel.
Release agent floating further away did not reach the funnel at all. In addition, the strongly adhering contaminants accumulated on the floats and the funnel, meaning that the funnel had to be cleaned very frequently. The adhering dirt made the funnel so heavy that it sank. As a result, the pump only pumped water.
2. belt skimmer
A further test with a belt skimmer was also unsuccessful, as only an area of approx. 10 cm around the skimmer was kept free of floating contaminants.
The dirt floating further away did not reach the skimmer at all, as there was no current in the sedimentation tank.
As an experiment, the floating phase was then moved manually to the belt skimmer. The removal rate increased significantly as a result.
However, due to the viscous consistency, the drainage channel became clogged within a very short time.
Solution: FRIESS oil skimmer with oil collector tube
Only a further test with a FRIESS oil skimmer with oil collector was finally successful. The oil collector tube was able to remove the entire floating phase of contaminants. The oil skimmer with oil collector tube consists of the actual oil skimmer with drive and scraper and an oil collector tube, which is connected to form an endless ring.
FRIESS oil skimmer W20
The largest part of the oil collector tube floats on the water surface, while a small part of the oil collector tube is located in the oil skimmer, where it is driven and oil is scraped off. The floating oil and grease mixture initially adheres to the outside of the oil collector tube. The oil collector tube coated with oil is then drawn into the oil skimmer. There the oil and grease is scraped off.
A particular advantage over the other systems tested was that the oil collector tube reaches almost the entire surface of the tank. As the oil collector tube creates a circular movement on the surface of the tank, the floating phase of oil and grease was set in motion despite the high viscosity and was thus driven towards the oil collector tube.
As soon as the oil and grease mixture adheres to the oil collector tube, it is conveyed into the skimmer by the oil collector tube.
As the oil conveyed is highly viscous and very sticky, the oil skimmer was arranged so that the oil and grease can fall vertically downwards from the scrapers into a collection container.
For this purpose, the oil skimmer was mounted outside the actual tank. The oil skimmer is bolted to a mounting bracket that is open at the bottom.
The removed sludge falls through the mounting bracket into an open container located below the oil skimmer. This reliably prevents blockages.
Additionally, cleaning work is no longer necessary.
Summary:
- Effective removal of the oil and grease mixture
- Clogging is reliably avoided
- No more cleaning work required