The importance of installing a scraper in a settler
posted in Technical Articles by TecnoConverting
I must admit that always surprises me the detail and attention paid on the sizing of lamellar decanters, but in other hand, some don’t give any importance to the sludge extraction system, under construction support structure or even, the anti flotation system. In various previous articles we have already described the importance and the reason why settlers have to be calculated correctly; however, about the scraper, it is very important to keep certain parameters in mind:
When you size a lamellar settler, it´s important to consider much higher solids concentration then in the case of a conventional settler without lamellas. Since a lamellar settler can treat much higher inlet flow than a conventional one with the same. This means that there is higher precipitation of sludge or solids, and is mandatory to install a collection system that removes correctly the solids from the process.
I´ve seen square settlers, for example 10 meters by 10 meters with conical bottom, without any extraction system, or inclusive 50 meters length meters per 10 meters width without sludge extraction system. In time, all this projects had to be adapted with a sludge scraper system to collect the produced sludge.
The experience that allows me to make a list of the typical problems that arise when a sludge scraper is not installed:
– There is high accumulation of sludge on the bottom of the tank and, with time, in time, these solids emerge and come out with the clarified water.
– When there is a sludge extraction sludge, the solids also emerge on outlet clarified water, and interestingly, the amount extracted by the pump is very small. The reason is that the pump removes only the sludge from the near perimeter area, but at any case the further away solids even if the bottom is conical.
– When there is lamellar system without a sludge removal equipment, the problems gets even more complicated: The sludge accumulates in the bottom and slowly rise to lamellar modules until they clog the lamellar system. In this moment the situation gets critical: The under construction structure starts to suffer with the overweight and sometimes collapses. Furthermore, the hydraulic thrust makes the lamella arise and look like they are floating; and if there is no anti flotation system installed the situation gets terrible.
Undoubtedly, our recommendation is always to equip the settler with a good sludge scraper system.For sure we avoid greater problems.
