A while ago, a client asked me a very interesting question: did we take the corrected Hazen velocity or corrected upward velocity into account when calculating the properties of lamella clarifiers in our projects.
For certain types of water treatment, a small prefabricated compact clarifier will suffice. The manufacture of these models has evolved over the years. The first clarifiers were made of carbon steel, stainless steel, FRP (fiberglass-reinforced polyester) and had an exterior structure made of carbon steel, before we reached more modern models made of polypropylene with a carbon steel reinforcement structure.
Galvanized carbon steel or even stainless steel (whether Inox 304 or Inox 316) are often considered a better technical option for the supporting structure of lamellar modules instead of pultruded FRP beams and profiles, but this is a common mistake. We have listed below some of the advantages and disadvantages of both materials when used for this specific purpose:
In some facilities, lamella clarifiers need to be covered. This is usually done for aesthetic or practical reasons: they are covered not to be seen or to avoid bad smells. Once the areas likely to generate bad smells have been covered, the gas has to be captured and sent to a gas scrubber (deodorization).
Once, visiting a plant equipped with scrapers, we realized that these were not operating continuously and that the owners decided to stop them every once and a while. When we asked them why, they were not able to give us any technical reason that justified the stopping.
From our experience, we can say that the answer to the question is yes. Scrapers need to be constantly in operation and the example below will leave no doubts as to why it is so.
The torque switch is a component of the scraper that is installed on the control panel to prevent from possible damage due to mechanical over strength.
The function of the torque switch is to constantly monitor the rated current consumed by the electric motor, and when the equipment exceeds the value previously set, it automatically switches off the engine of the scraper.
In several installations circular stainless steel scrapers are usually requesting to incorporate joints between two different metals touching each other, such as stainless steel scraper parts and parts in carbon steel. And the galvanic couple causes the appearance of rust.
We consider it´s interesting to inform some important aspects about the galvanic couple:
Wikipedia’s definition: “A galvanic couple is a corrosive cell that is developed when two different metals are separated by electrolytes. In essence, it is the electrochemical action that is produced by the reaction of two dissimilar metals, given there is a path conducive to electrons and electrolytes. It can be identified by the existence of corrosion at a point located between the two metals”.
We recently visited a facility and realized that there was corrosion problems on the Thomson channels installed.
It is a common situation and truly is a problem: first aesthetic, because it can be seen perfectly by the user causing bad impression; and it ends up being a malfunction, because the channels begin to deteriorate and eventually have to be changed.