To ensure smooth and safe operations and avoid unscheduled shutdowns, exceptionally high standards must be employed with every method of cleaning shell and tube heat exchangers. Plant operators or third-party contractors must be prepared to employ multiple techniques for cleaning because one method does not always sufficiently remove every type of residual debris from a bundle or exchanger. The most common types of cleaning are hydroblasting, hydrolancing, abrasive blasting, and both chemical and thermal decomposition. These methods are also used for decommissioning heat exchangers and process equipment for scrap.
This article is Part II of a three-part series that explores the various methods, benefits, challenges and solutions to efficiently and effectively clean heat exchangers, both onsite and off-site. In Part I, we discussed the importance and various benefits of optimal cleaning, as well as how to determine whether heat exchangers should be cleaned onsite or off-site. In Part II, we will discuss the various methods of cleaning heat exchangers. Lastly, in Part III, we will discuss specific safety and environmental issues.
"Off-site cleaning typically involves an automated overhead unit that is stationary and controlled by an operator... in an enclosed room during the entire process, providing the best in safety and environmental protection."
The hydroblasting method is the most efficient way to clean the outside of tube bundles, also known as shell-side cleaning. During this process, the equipment is staged in a dedicated cleaning shop or on a cleaning slab to be cleaned.
Hydroblasting involves high-pressure water systems. Modern equipment configurations today are capable of flowing water to optimum volumes and velocities determined necessary to completely clean a variety of exchanger types.
Off-site cleaning typically involves an automated overhead unit that is stationary and controlled by an operator in a fixed environment. The operator remains in the enclosed room during the entire process providing the best in safety and environmental protection.
Onsite cleaning slabs are open environments. During onsite or field cleaning, the operators use manual hand held blasting guns, trailer units with open control stations, or automated control cabs. These systems can provide a higher level of exposure risks since operators are in the line of fire and are exposed to the hazards of an open slab environment and aerosol drifts.
Hydrolancing is used to clean the tube side or inside of the tubes in a tube bundle. This technique can be completed with flexible or ridged lances. The water cleaning industry has an assortment of cleaning tips and spray patterns available. This type of cleaning method is manipulated by either hand held, open control stations, or enclosed control cabs or rooms.
The main types of hydrolancing include handheld flex, open controlled semi-automated flex, ridged hydrolancing, and fully enclosed automated systems that keep the operator out of the line of fire and harm's way. These methods include single, dual, or multiple lances, and some of these systems can utilize rotation of the lance, or rotation of the tip. The hydrolance tips are designed for flow with cleaning patterns for polishing or cutting. The advantage of multiple tube lancing is that more tubes can be cleaned at the same time. The disadvantage is that operators can only clean as fast as the slowest tube will allow, and the volume of water used per tube will be limited.
Together, these primary methods are the industry standards for cleaning heat exchanger tube bundles. The common process result for onsite or field cleaning is a service clean. The goal during off-site cleaning is to achieve a tube-inspection level of cleaning such as IRIS testing. The disadvantages of hydrocleaning methods are that they require a large water supply and generate large amounts of wastewater. During large turnaround outages, it is often found that the cleaning space required, containment, capture, remediation and disposal of cleaning sludge's and waste water can be more of an undertaking than the cleaning process itself. In these time-sensitive situations, most managers prefer to have the heat exchangers cleaned off-site at dedicated cleaning and repair facilities to avoid any operational delays for repairs and reduce the environmental and safety liabilities at their facilities.
Secondary Cleaning Methods
Abrasive blast cleaning includes many different types of media, which can vary greatly in size and cutting ability. They include sand, slag, dry ice, and glass bead to name a few. Abrasive blasting is used when IRIS inspection cannot be completed after hydrocleaning or for cleaning the various exchanger components. This method is strictly used to clean the inside of the exchanger tubes and not the outside of the bundle. There are both advantages and disadvantages in the cutting power. Although it is efficient, technicians must be especially careful and trained as damage can easily occur.
Another secondary method that is used is chemical cleaning. Technicians typically use chemical solutions based on the product testing, as well as knowledge of the type of material that's being removed. In this method, the chemicals are circulated through the exchangers.
Chemical cleaning is suitable for calcium-fouled or hard water scaled tubes. This process includes soaking, vapor, ultrasonic, and circulation cleaning. Overall, a number of variations of chemical cleaning are available for both onsite and off-site cleaning. However, one of the disadvantages to chemical cleaning is that the product only travels the path of least resistance. Therefore, if plugging issues are discovered in the tubes, it becomes difficult for the chemical solutions to enter the blocked tubes. The spent cleaning solution can also be a challenge, as this cleaning method can produce a large amount of gallons of spent chemicals that must be neutralized and disposed of causing concern for onsite environmental plant managers. Due to these difficulties, chemical cleaning is more effective if it used in conjunction with the hydrocleaning methods.
This process is utilized when traditional hydrocleaning methods are ineffective. The process thermally decomposes product residue while maintaining the operating integrity of the equipment.
Heat exchanger cleaning is most often performed on equipment that will be returned to service. However, equipment that must be cleaned prior to being decommissioned for scrap to eliminate environmental liabilities can be undertaken by using the various primary and secondary cleaning methods discussed.
In conclusion, the method of cleaning should be carefully chosen based on the type of fouling, the speed of the cleaning process, and the level of cleaning required. This ensures proper equipment inspection and maximum efficiency.
In Part III of this series, the author will detail specific safety issues will be discussed.
This article appeared in the September/October 2015 issue of Inspectioneering Journal