Return line filtration

Fluid analysis will prove the need for better filtration. The addition of a 3-micron absolute return line filter to supplement the kidney loop filter can solve the problem. 

Low pressure hydraulic filters are typically designed for operating pressures up to 28 bar, with flows up to 1200 1/min. Generally they have a wide application range, particularly for industrial and mobile applications, including high flow tank top and tank top return line filters. Many versions are of the spin-on type and can be provided as dual flow assembly off-line filtration. Core-less low pressure filler elements contain no metal and are designed to minimize waste disposal. 

Such inlet strainers, of course, do not remove any pump-generated contantina-tion, which is then fed directly into the system on the pressure side. Equally, they are not necessary in systems with closed reservoirs, with silt-control filtration on the return line, or where fluid is introduced into the system upstream of the return line filter. Suction line filters are cheap, but do not usually have indicators to show when they are dirty or blocked. 

Sometimes, a continuous filtration system is used to clean the fryer oil. In this process, it is recommended to take out approximately 5% of the fryer oil, filtered through an in-line filter, and returned to the fryer. This system can be good, but in most cases, the flow of oil through the fryer is not uniformly distributed because of various factors. This allows fines to accumulate on the fryer pan at various spots and not be removed by the filter. In other words, a continuous filter of this type is as good as the system s capability to push all the fines through the filter, with minimum accumulation in the fryer. 

A technique of special interest to the pharmaceutical and other industries is FBRM. It is an on-line instrument that can give information on parameters such as particle size , surface area, filtration rate and flocculationSi- It is used in crystallisation, filtration and drying applications. It works by scanning a laser beam in a circular motion over a surface at high speed. Light is back scattered by the particles and picked up by a detector. The duration of time that it takes for the backscattered light to return to the detector is called chord... 

After successful commissioning on water, the filters should operate on brine. Once the filters are in operation, the clarity of the filtered brine should be tested. An on-line turbidimeter, if provided, can be used to verify correct operation and quality before placing the system on stream. The filtrate returns to the feed tank during this time. 

An interesting feature of the Russian process is the two-step method employed for the complete recovery of arsenic from solution waste-streams. In the first step, which is similar to the recovery method used in the Thylox process, the solution is heated to 70°C (158 F), and arsenic sulfide is precipitated by the addition of 75% sulfuric acid. The precipitate is separated from the liquid by filtration, dissolved in aqueous sodium carbonate, and returned to the circulating solution-stream. The clear liquid is then passed to the second step where it is made alkaline with sodium carbonate solution and treated with a solution of ferric sulfate. In this operation the small amount of arsenic remaining in the solution after the first step is fixed and precipitated as ferric arsenite and arsenate. The precipitate is finally removed by filtration, and the filtrate, which contains about 10 to 20 ppm of arsenic, is either discarded or processed for recovery of thiosulfate. Wooden tanks lined with acid-resistant materials are used in both steps of the arsenic-recovery operation. Each tank is sized for a solution residence time of 4 hr and provided with a mechanical agitator. 

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