PHE Fouling and Scaling

- Cause of Fouling

No matter what material the plate is, after operating several years, the efficeincy of PHE will go down, the reason mostly is due to fouling, if you let it be, corrugation and leak will happen eventually.

There are always varies soluble or insoluble suspended particles within cooling water, such as calcium carbonate, sulfate, etc.. If the dissolved concentrations exceed a certain level, they will adhere to the surface of plates, and form an insulating layer on the surface of the board, which reduce the attenuation transfer between the two fluids.
As the thickness of the material increases, the performance of the PHE will decrease over time, resulting in too small product size and reduced process.

- Comparision of Fouling Resistance Capability Between S&THE and PHE

Figure1-S&T-GPHE-Comparision

In Figure 1, we compare the efficiency, space, weight, and cleaning time of gasketed plate heat exchangers and shell-and-tube heat exchangers. It can be seen that the plate heat exchanger has superior performance compared to the shell-and-tube heat exchanger, far exceeding 3-5 times.

Unlike shell and tube heat exchanger, there is a high degree of turbulence in the plate heat exchanger, which improves the sediment removal rate and actually makes the plate heat exchanger less prone to fouling. In addition, compared to most shell and tube heat exchanger designs, the velocity distribution in the plate heat exchanger is more uniform, which eliminate low-speed areas that are particularly prone to fouling.

Figuire2-Fouling-Resistance-Comparision

Figure 2 shows the comparison between the fouling resistance of the cooling water in the plate heat exchanger and the fouling resistance on the tube side of the shell-and-tube heat exchanger at the same speed. A significant difference in pollution resistance can be seen. The fouling resistance inside the plate heat exchanger is much lower than the fouling resistance inside the shell and tube heat exchanger.

- Minimizing Fouling

There are 4 ways we to reduce the fouling inside the plate heat exchanger:
-Appropriate heat exchanger plate design;
-Correct selection of plate type combination of plate heat exchanger;
-Mechanical or chemical cleaning;
-Plate heat exchanger surface coating.

 

in order to reduce fouling, it is very important to understand the mechanism of sediment accumulation and the influence of operating conditions on the deposition rate first.

- Description of scale status of some marine working conditions

Lubricating oil cooler (plate or tube heat exchanger)
This heat exchanger device is under lubricating oil and cooling water conditions. Due to the high temperature of the lubricating oil, most of the cases are water-cooled side scale after a period of use. But some of them are due to the quality of the lubricant used and the long maintenance cycle, thus forming oil scale on the hot side. The heat exchanger needs to be dissembled for cleaning when the flow channel is about to jam. The plates should be combined with agents for soak and scaling during the cleaning process.
Both plate heat exchanger and tube heat exchanger can perform non-disassembled internal cycle cleaning with internal circulation device and special agent within reasonable maintenance time. The premise is that the internal scaling of the heat exchanger unit is evaluated.
Central cooler (currently mostly plate structure)
This device is mostly used for sea water and fresh water heat exchange conditions. The plate will have a certain scaling without maintenance for a long time. There will be a certain marine microbial attachment and accumulation on the seawater side of the heat exchanger. In severe cases, the heat exchanger should be removed and soaked with portable container device and special agent.
In this condition, it can perform non-disassembled internal cycle cleaning with internal circulation device and special agent. The premise is that the internal scaling of the heat exchanger device is evaluated and an appropriate dose is added.
This working condition is mostly limescale, which need to use weak acidic agent when the limescale is heavy.
Water generator (mostly plate heat exchanger)
This device is mostly used for sea water and fresh water heat exchange condition. This condition is a high temperature service, and the cooling side is easy to scale, which belongs to the regular maintenance station.
In this condition, it can perform non-disassembled internal cycle cleaning with internal circulation device and special agent. The premise is that the internal scale situation and cycle of the heat exchange device should be evaluated regularly for best results.
This working condition is mostly limescale, which need to use weak acidic agent when the limescale is heavy.

Marine boiler
The boiler will form scale inside after long term use, which can can use the circulation device and with the agent for cleaning and maintenance work.
Fuel oil system
Most ocean shippers use heavy diesel as fuel. Heavy diesel oil has more impurities and high viscosity. The fuel system should also be regularly maintained and cleaned to run the system smoothly.
The key maintenance parts are pipeline, fuel pump and oil distributor.
Most ships have a short maintenance time. Marine heat exchanger is mostly titanium material, and cleaning agents can consider products with high scaling force and high efficiency.
The ship parking terminal will have requirements for sewage discharge, that is beneficial to choose green products.