Bio Fouling at a refinery in Dubai removed and stopped
The refinery ISO OCTANE in Dubai, UAE is a rather small refinery. The refinery is not operating constantly, but is used only batch wise. Due to this mode of operation, as well the cooling loop is not running in full capacity all the time. The cooling loop is operated with limited water circulation, if there is no production in the refinery.
During inspection of the cooling water system, there was found heavy fouling, caused mainly by organic material, the so called biofilm caused by biofouling. It was found this fouling is the same in the entire system. A flange or a valve which is closed is a part of the piping system, where there is no water flow. This is called a dead end or a dead leg. These are the critical parts in each water system. A portion where there is no flow of water, is the typical place where corrosion or biofilm will start taking place in a water system. Once there is a biofilm established in a system, the biofilm creates biofouling and in a lot of cases the biofilm will contaminate the whole water system. The problem of such biofilm is they might house bacteria, which might cause MIC, corrosion caused by microorganism.
Adding chemicals or introducing heat is able to solve the problem in the parts of a water system, where water is flowing. In a dead leg adding chemicals or using UV-light is not solving the problem, because the water in this dead end is not circulated, it is mostly local in this flange. So bacteria, algae or biofilm can grow there and are not affected by the chemicals added to the system or by heat.
The common dead leg definition is implicated in the GMP (good manufacturing practice) wording, which says: “Not to have an unused portion greater in length than six times, the diameter of the unused pipe measured from the axis of the pipe in use.”
In the return line of the cooling loop, so called biocide was added in the water to stop the growth of algae. But at the cooling tower heavy growing of algae was found. These algae have been taken by the water from the cooling tower and contaminated the entire system. The biofouling or biofilm is forming a slimy film at the inner surfaces, this film is reducing the heat transfer drastically and so the cooling was not sufficient anymore.
After survey at side, it was decided to install Merus Rings at different strategic locations throughout the cooling water loop, in order to get maximum results, with as little as possible investment from customer side. During the demonstration this open cooling water loop was running with full capacity, in order to get the system cleaned as much as possible.
Exact after 2 month the spots checked before has been opened again. It can be clearly seen, a lot of the existing fouling is removed, and the inner surfaces of the pipes start to get clean.
Even old corrosion spots are slowly started to be removed, the rust is taken downstream and will settle in the sump of the cooling tower.
How long it will take to remove all the corrosion can not be told, this have to be seen over time. The corrosion rate which has been in average 8.5mpy, has lowered in the 2 month to less than 1.5MPY.
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