Efficient solid settling due to equidistant chevron-shaped tubes GEA 2H TUBEdek® lamella settlers at WEFTEC 2014 in New Orleans
01. August 2014 GEA Heat Exchangers will present a unique tube settler product, the GEA 2H TUBEdek®, at stand 2939 at WEFTEC 2014 in New Orleans.
Settling of solids is considered to be one of the most important processes in water and wastewater treatment. Many pollutants in water are related to solids, which can be removed by gravity in a sedimentation process. It is likewise considered good practice either to convert other soluble pollutants to settleable biosolids or to flocculate them chemically. A high-rate lamella sedimentation process is subsequently employed to remove the solids from the water.
The outstanding performance of GEA 2H TUBEdek® lamella settlers has been demonstrated in more than 1000 wastewater or potable-water plants worldwide – some of them serving populations of more than 500,000 with potable water. The largest wastewater treatment plant equipped by GEA Heat Exchangers is in Mexico City, which treats 650 MGD.
Unlike other tube-settler products, the GEA 2H TUBEdek® lamella settler combines equidistant settling with chevron-shaped channels – product properties that enable highly efficient effects.
In 1904, sanitary engineering pioneer Allen Hazen of the Lawrence Experiment Station (in Massachusetts) proposed that sedimentation performance is a function of basin surface area and is independent of detention time. Hazen’s fundamental settling laws have been used until now for sedimentation tank design. Hazen’s Law likewise demonstrates that additional planes below the water level increase settling performance by shortening the settling path of a particle toward the bottom – and consequently act as additional basin surfaces.
Hazen’s Law applies only to equidistant settling planes such as parallel plate settlers and the GEA TUBEdek® series. It applies wherever the maximum settling path of a particle is uniform between the settling planes. Triangular or hexagonal channels do not relate to Hazen’s Law, with the result that their performance is inferior, even when they provide greater surface area.
These findings are significant and their related phenomena can be observed in practice.
For example: At a paper mill in Brazil, several settling tanks for biosolids are operated in parallel. All process lines are operated under virtually identical conditions. The only difference is that one tank operates with equidistant tubes from GEA Heat Exchangers, whereas the other tanks are equipped with triangular multidistant channels.
The GEA settlers exhibited the expected performance; however, the conventional triangular design failed to withhold the entire solids load and some solids clouds were detectable above the settlers.
In the triangular settler, some of the channels were totally blocked because the sludge was stuck in the lower triangular section, which results in clogging of entire channels or in heavy sludge deposit in the acute angles of the triangular channels.
In contrast, the chevron shape allows the sludge to travel in the direction of the center line of the channel, where it slides downward and exits the settler toward the bottom.
GEA lamella settlers are produced by profile extrusion followed by thermal welding block assembly, a production method that allows almost any customized block sizes. The blocks are self-supporting, rigid, and approved for inspection foot traffic.
GEA Heat Exchangers holds NSF certification, which authorizes application of these systems in potable-water plants.
From September 27 to October 1, 2014, at a fair stand shared with GEA Westfalia Separators, GEA Heat Exchangers will present lamella separators and fill media for treatment of potable water and wastewater.
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