REHABILITATION OF EXISTING FLUID
All heat transfer fluids begin their service life with beneficial characteristics. Attributes such as pump-ability, longevity, range of use, heat transfer efficiency, safety, and low cost of ownership make these fluids the standard in reliable performance for process heating applications.
Unfortunately, these fluids do not last forever. Over time, the properties of all heat transfer fluids will degrade. As the composition of the fluid changes, these changes can easily be measured through fluid chemistry testing. Testing will determine the fluids density, viscosity, thermal conductivity, solids content, acidity, and flash point.
As the physical properties of the fluid diminish, the performance of the heating system and the efficiency of the process will also be reduced accordingly. The primary indicators of fluid degradation and contamination are:
- Solids Formation due to thermal stress and/or oxidation of the fluid.
- Accumulation of Low Boilers due to insufficient venting of the fluid.
- Accumulation of High Boilers due to excessive venting of the fluid.
- Moisture Intrusion due to open expansion tank or exchanger leaks.
- Introduction of Foreign Contaminants due to accidental events or process leaks.
- Degraded Physical Properties due to a lack of partial fluid replacements over time.
Fortunately, when fluid degradation and contamination are detected early enough, in most cases, the fluid can be rehabilitated. When test results show a problem with the fluid, there are several relatively inexpensive maintenance measures available to restore the physical properties of the fluid back to “like-new” conditions. Annual fluid testing is the key to identifying and correcting ordinary age-related fluid degradation issues. Failure to invest in these periodic fluid care maintenance recommendations will eventually lead to the much greater expense of replacing 100% of the fluid in the system.
To avoid replacing the fluid, HEAT has developed a variety of specialized products and services for fluid care and fluid rehabilitation. The following are sample procedures provided to illustrate the most common methods of fluid rehabilitation. Actual procedures are developed for each customer, based on the fluid sample test results along with consultation with the fluid manufacturer.
SAMPLE THERMAL FLUID REHABILITATION PROCEDURES
High-Temperature Filtration: High-temperature filters are designed to continuously remove solids from the fluid while at operating temperature. The filter consists of a pressure vessel housing which contains one or more glass fiber wound filter cartridges. High-temperature filters are highly recommended as an effective method of prolonging the life of your fluid. These filters can be installed on a temporary basis when performing fluid rehabilitation. However, they are best suited for permanent installations on heat transfer systems in a slip-stream configuration. A small percentage (typically 1%) of the system flow rate passes through the filter. High-temperature filters are an excellent way to continuously remove insoluble solids from the fluid.
Low-Temperature Filtration: When heat transfer fluids degrade due to oxidation, the fluid can become very acidic. These acids will react with the heat transfer fluid and form viscous solids (sludge) that at higher operating temperatures can pass through high-temperature filters. When test results show high levels of acidity and presence of high boilers, the fluid rehabilitation plan must also include Low-temperature filtration. This will usually require the entire system to be cooled down to allow the sludge to become viscous enough to be captured by the low-temperature filter elements. To achieve this, the HEAT team will install a flushing and filtration skid into the piping system. This equipment is used to re-circulate the fluid through a large capacity filter housing to catch and remove the heavy sludges and particulates that are suspended in the fluid while at ambient temperature. The flushing skid may also include an onboard electric heater that is then used to raise the fluid temperature up to a maximum of 225 degrees Fahrenheit. We have found that some contaminates are more easily removed at low temperatures and other contaminants are more easily removed at higher temperatures.
Light Ends Venting: Part of the natural aging and degradation process of heat transfer fluids involves the accumulation of low-boiling products in the fluid system. These are naturally occurring volatile components (light-ends) of the heat transfer fluid. Over time and at higher temperatures, the accumulation of these low boilers will lower the flash point and ignition point of the fluid and become a serious safety and fire hazard. Fortunately, this issue can be easily managed with a properly designed and operated inert gas venting package installed on the system expansion tank. Routine fluid testing will indicate when venting should be scheduled. Venting should only be done as part of fluid rehabilitation program or as part of a scheduled fluid care maintenance program. Continuous venting is not an acceptable method of flash point management. This approach will rapidly damage the fluid by removing all the necessary volatile compounds from the heat transfer fluid. In addition, when fluid testing indicates excess moisture in the heat transfer fluid, the expansion tank venting system can also be used to remove moisture from the system.
Vacuum Dehydration: In some cases, when high levels of moisture or other contamination are found in the fluid, vacuum dehydration may be the only way to remove the contamination safely and efficiently. When testing indicates that this step is required, the HEAT team will install and operate this specialized vacuum equipment to properly remove the contaminants and rehabilitate the fluid.
Partial Fluid Changes: One of the most important steps in maintaining the overall health of heat transfer fluid is to drain and replace 5% of the total system volume with virgin fluid every year. This step is also known as “Sweetening”. As part of an annual fluid maintenance program, the 5% sweetening is the best way to fully maintain the original physical properties of the fluid. When sweetening is done as part of a fluid rehabilitation program, the percentage of volume replacement may range from 10% to as much as 25% depending on the condition of the fluid.
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