The fouling in heat exchangers is a commom issue in many companies and the resulting cleaning efforts is a common task.
Usually the product is on one side of the heat exchanger, for example a fluid or a gas with a certain temperature. This product is brought to a different temperature level by the fluid on the other side. The product is either cooled with cooling water or heated with a hot liquid or steam. To check the actual condition inside the heat exchanger, Delta T or Delta P can be used. To calculate the u-factor or the heat transfer coefficient is another option. If the temperature or pressure changes, this is an indicator of flow resistance, reduced velocity within the tubes and the beginning of fouling.
The fouling factor
The fouling factor is an indication of how strongly a machine tends to foul. The fouling factor number one is the character of the liquid itself. This means that impurities dissolved or suspended in the fluid will form incrustations on the heat transfer surfaces.
Furthermore, the type of heat exchanger, if it is a plate type or a shell-and-tube type heat exchanger. The resistance against the fluid flow, the velocity and temperature of the fluid are more factors.
Fouling and incrustations impede heat transfer, or in other words, the fouling impedes the heating or cooling performance of the heat exchanger. The thicker and harder the deposits are, the less heat is transferred. As soon as fouling has started, the surfaces are no longer clean and new incrustations form more easily and quickly. Corrosion or Biomass can influence the fouling factor also.
It can be said that the higher the fouling factor, the more likely it is that the fouling in tubular or plate heat exchangers or boilers will start. And the heat transfer, the exchange of thermal energy, will be negatively impaired.
The waterside of the heat exchanger
On this page we concentrate on the cooling water side in a heat exchanger. This is one of the main applications for the Merus-Ring and comes up in almost every project. There are also cases where we deal with the product side, for instance crude oil. But these are very specific cases individual engineered for each customer, because no two products are alike.
In open cooling water systems, deposits – the result of fouling – form depending on the amount of total dissolved solids (TDS) in the water. A rather clean river water, causing less fouling, then a seawater with several thousands of TDS. As higher the TDS, as more calcium carbonate or other minerals are settling on tubes and surfaces.
Is the cooling system closed, rust and corrosion due to aggressive substances in the water is found.
As the waterside is exposed to various external influences biofilm can form easily and fast. Biofouling occurs where algae or bacteria enters the cycle with the water and settles at the rough pipe walls (due to deposits and corrosion).
Heat exchangers with these deposits need to be cleaned regularly. Therefore the heat exchanger is opened and its parts are cleaned manually, often with chemical cleaning agents. For a big tube bundle heat exchanger this means a production stop for several days.
How does Merus stop and avoid the heat exchanger fouling?
We are able to reduce existing deposits and in many cases we bring down the fouling rate and stop fouling completely. The heat transfer remains stable.
The Merus Ring is installed upstream the heat exchanger. In critical applications it might be required direct at the inlet of the exchanger. Are both sides affected by fouling, two Merus Rings are needed at both inlets.
If the cooling loop consists of several heat exchangers it is in most cases not necessary to install one Ring ahead of each heat exchanger. It is sufficient to install the Merus Rings in selected areas.
After the installation deposits, which substance is soluble in the liquid, are solved and don’t settle anymore. In case of water, minerals often become deposits. The Merus technology has the effect of a higher solubility of these minerals in the water. This effect is not limited to watery liquids. On the product side also oily liquids, crude oil or chemicals can be treated. To which degree the solution is applicable to other liquids has to be decided or tested individually.
The astonishing result of the water treatment is that the heat exchanger is nearly self cleaning after the installation of a Merus Ring. Numerous cases and customers prove that after some weeks nearly blocked heat exchangers were clean again – without chemical or manual cleaning.
The Merus Ring does both – removing existing deposits and stopping new deposition. Therefore fouling is stopped.