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In general, organic thermal fluid heat transfer systems offer one of the safest and most cost-efficient options for factories that require process heating. When operated and maintained properly, they will provide reliable performance for many decades. 

Unfortunately, when maintenance budgets are slashed and routine maintenance is deferred, damage occurring to the fluid will compound and eventually cause damage to the entire heat transfer system on thermal fluid systems. The fact that these systems are so reliable, makes it is easy to forget the enormous difference between LOW Maintenance and NO Maintenance. Each year of deferred maintenance increases safety risks and the risk of unplanned and extended shutdowns, sometimes lasting 6-12 months. 

Once thermal fluid undergoes severe oxidation and/or severe thermal degradation, it will no longer have the physical properties necessary to provide a safe and reliable operation for your process. Degraded fluid will produce solid particles and high viscosity sludge that will stick to the inside surfaces of the entire piping system, including process vessel jackets and heat exchanger surfaces. These byproducts of degradation will continually increase to the point where they cause damage, and eventually cause the heater to fail. This type of unplanned shutdown typically results in a plant being shut down while waiting for a new heating system to be fabricated and installed. 

Once a thermal fluid system has reached the point of severe degradation, simply changing the fluid does not solve the problem: the internal surfaces of the entire system are covered with thick sludge and carbon deposits. Even if the old fluid can be drained out of the system, the sludge and coke deposits will remain behind on the inside surfaces of the piping. 

If a sludge filled system is not cleaned and is simply re-filled with a new fluid, the situation will actually become worse: the new fluid will act as a solvent and cause much of the sludge and solids to break free from the pipe surfaces, thereby contaminating the new fluid with a slurry of entrained solids and high viscosity liquids.  

HEAT has performed many Decontaminations of sludge-fouled heat transfer systems. In each case, a customized cleaning procedure was developed based on fluid test results and detailed physical inspections of the system. The cleaning techniques ultimately used in any cleaning procedure will vary depending upon the degree of contamination found within each major component of the system. 

In each case, HEAT will work with your fluid manufacturer to determine the most appropriate procedure.   

The following is an example of cleaning procedure outline. This procedure does not cover all situations and is provided to illustrate some of the potential complexities of cleaning a severely degraded system. 


1. System Cleaner Additive & Filtration: First, a system cleaner is added to the fluid. These additives are typically a mild solvent-based cleaner that will begin the process of breaking down the solids and sludge in the system piping and jackets. The HEAT service team will travel to the customer site and will drain off drain off between 2 to 5% of the total system volume (depending on the severity level of the fouling) and replace this volume with the system cleaner additive. At this time, the HEAT service team will also install high-temperature side stream filtration units at key locations in the system. The cleaner is designed to work slowly over several weeks or months and allow the customer to continue operating their normal process at normal temperature. As the cleaner works to dissolve fouling in the system, the side stream filters will collect this debris from the fluid. The cleaner additive is typically installed 2 to 8 weeks prior to the date of a planned system shutdown to perform the full flushing and cleaning of the system.   

2. Hot Draining of Fluid: In the next step, the HEAT team returns to the site to drain and remove as much of the existing fluid from the system as possible. First, the heater is turned off and the bulk fluid temperature is cooled down to between 150°-200°F before initiating the hot draining process. In many cases, when dealing with severely degraded fluid, the viscosity is too high at ambient fluid temperatures to allow for proper draining of the system. The primary circulating pumps are typically run for as long as possible to maintain as many solids in suspension as possible during the draining process. Pressurized air or nitrogen may also be used to push the fluid from sections that do not have adequate drainage. Any low piping runs that do not have drains will require the breaking of flange connections to allow trapped fluid to drain into catch basins for transfer to the disposal containers. In some cases, the fluid manufacturer will agree to accept this contaminated fluid back for reconditioning and credit against the purchase of new fluid. Otherwise, this contaminated fluid must be disposed of by the customer. 

3. Refill with Flushing Fluid or Sacrificial Fluid: Once the system has been thoroughly drained, the HEAT team will then refill the system with either a specialized “flushing fluid” or with a “sacrificial load” of the new replacement fluid. This fluid will perform most of the work in cleaning out the heat transfer system. Flushing fluids are designed to aggressively cut through the sludge and hard coke deposits sticking to the inside surfaces of the piping system. In some cases, flushing fluid cannot be used when it is determined that flushing fluid residue would be incompatible with the new heat transfer fluid. In these cases, a sacrificial load of the new heat transfer fluid is used for flushing and filtering operations. Most new heat transfer fluids have sufficient solvent properties to provide effective cleaning when used in place of a flushing fluid. After flushing and draining, this sacrificial fluid is typically returned to the manufacturer for re-processing and a credit against the purchase price of the final new fluid. 

flushing filtration skid cut out

4. Low-Temperature Flushing & Filtration: Prior to filling the system with the flushing fluid, the HEAT team will also install a low temperature, high-capacity flushing, and filtration skid. This equipment will be used to re-circulate the flushing fluids at high velocity through the system. This low-temperature, high-capacity filter housing will be used to catch and remove most of the heavy sludges and particulates that are dissolved and become suspended in the flushing fluid while at ambient temperature. The flushing skid also includes an onboard electric heater that is then used to raise the flushing fluid temperature up to a maximum of 225°F. We have found that some contaminants are more easily dissolved and removed at low temperatures and other contaminants are more easily dissolved and removed at higher temperatures. 

5. High Temperature Filtration: After the low-temperature filtration of the flushing fluid is completed and the low-temperature filters are no longer catching contaminants, the flushing skid will be isolated from the heat transfer system. At this point, the system’s primary circulating pumps and heater are activated to bring the flushing fluid temperature up to 350°F. This is done to achieve the flushing fluids maximum solvent characteristics. Upon reaching the higher flushing fluid temperature, the HEAT team will then utilize our high-temperature filters (originally installed for use with the system cleaner additive) to remove the remaining higher temperature contaminants from the fluid. The high-temperature filtration will continue for at least 24 hours.

6. Draining the Flushing Fluid: After filtration is complete, the heater is turned off and the system is cooled down to ambient temperature. It is important to drain as much of the flushing fluid from the system as possible to remove all traces of contamination and prevent interactions with the new virgin heat transfer fluid. Pressurized air or nitrogen may also be used to push the fluid from sections that do not have adequate drainage. Any low piping runs that do not have drains will require the breaking of flange connections to allow trapped fluid to drain into catch basins for transfer to the disposal containers. In most cases, the fluid manufacturer will accept this contaminated flushing fluid back for reconditioning and credit against the purchase of the new fluid.  

7. Visual Inspections & Manual Cleaning: Once the system has been fully drained, it is best to perform a visual inspection on the entire piping system. Sample sections of piping should be removed, and access ports opened for visual inspection to ensure that sludge and fouling has been removed from the system. Key components such as control valves should be removed and taken to the maintenance shop for final cleaning by hand and inspection before being returned to service. 

8. Refill with Virgin Fluid: The system is now ready to be re-filled with the new heat transfer fluid. After circulation of the virgin fluid has been achieved, a sample should be taken for testing. Even after extensive cleaning procedures, it is still likely that the new fluid will pick up additional particulates and moisture from the piping system. 

vacuum dehydration machine blue

9. Polishing Filtration: While the new fluid is still at a low temperature, the flushing and filtration skid will be brought back into service for a final polish filtration of the new heat transfer fluid using beta 1000 filter cartridges. This step will ensure that both the system and the fluid are in “like-new” condition.

10. Vacuum Dehydration: If moisture is shown in the final fluid sample test, then a final vacuum dehydration step may be required to remove the water prior to system heat up to operating temperature and system return to normal operations. 

The above procedure is provided only as an illustration of one potential plan. Each contamination case must be analyzed to determine the best course of action. For example, in cases where process products have leaked into the heat transfer fluid, a dedicated temperature-controlled kidney loop system may be required to achieve removal through filtration at specific temperatures where the product will be captured and not pass through the filters. Other cases may require dedicated kidney loop filtration of heater coils or expansion tanks to address specific types of contamination removal.  

Contact our experts to begin developing a plan to get your system back to peak efficiency. 

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