No matter what type of heat exchangers or which industries they are being employed in, eventually all of these units will foul. As deposits are building up on the interior walls of heat exchanger tubes, so, too, is an insulating barrier forming on the tube wall that will interfere with heat transfer. While the type of deposits, their tendency to adhere to the tube walls and their insulating value vary depending on the fluids or gases flowing within the tubes, the end result is the same: a loss in productivity. As the heat transfer rate drops, so does the heat exchanger’s efficiency. This loss of efficiency will not only negatively impact the unit’s production capacity, but will also drive up the cost of the final product. To reduce this impact and help keep production flowing at peak efficiency, heat exchanger performance must be monitored. If fouling is identified, the deposits must be removed. Outcomes are always improved when the characteristics of the fouling are determined as soon after performance declines are detected. While high-pressure water cleaning (hydroblasting) has historically been the method of choice for fouling mitigation in industrial markets, the use of mechanical tube cleaners with low-pressure water has been gaining popularity.
Safety
Now more than ever, safety on thejob sitee has become the number one priority of plant management. A commitment to safety has meant that conventional approaches to heat exchanger cleaning are being reconsidered, while new and innovative cleaning methods have been developed. Improvements in cleaning technologies using mechanical tube cleaners and low-pressure water provide for very safe cleaning applications with unprecedented results. Low-pressure water means less pressure and a smaller safety zone.
Figure 1. Low-Pressure Water Footprint, shows a typical safety zone for a low-pressure water application.
Figure 2. High-Pressure Water Footprint shows the larger safety zone required for high-pressure water cleaning of the same heat exchangers.
High-pressure water applications often use from 10,000 to 40,000 or more PSI to remove tube deposits while low-pressure water mechanical methods use under 700 PSI to provide a thorough cleaning.
In addition, low-pressure water mechanical cleaning requires significantly smaller crew sizes than high-pressure water methods. As an added benefit, low-pressure water mechanical cleaning is done in place; it is no longer necessary to dismantle the heat exchanger and move it to a separate work zone for cleaning. This reduces the risk of accident, injury and component damage.
Environmental Impact
When considering the various options available for cleaning heat exchangers, the environmental impact of the various cleaning methods must weigh into the selection process. The amount of secondary waste/wastewater generated by each cleaning method and the ease and cost of disposal of waste is often a concern. One great environmental and economic advantage of the low-pressure water mechanical cleaning methods is water conservation.
Speed
Time really is money for plants in the processing industries. When a unit is down for maintenance, that unit is not generating revenue. Giving consideration to the environmental impact of how a heat exchanger is cleaned is important. However, the reality for many plant managers is that budget constraints will drive the decision-making process on how to clean. Because new and innovative low-pressure water mechanical cleaning applications require far less unit downtime than the high-pressure water approach, it is the cleaning method that is most economically advantageous for industry. The time required for low-pressure water mechanical cleaning can be 70% less than high-pressure water methods. This can mean a unit downtime of hours cleaning with mechanical cleaners versus days with hydroblasting.
HYDROBLASTING VERSUS MECHANICAL TUBE CLEANING
Hydroblasting heat exchanger tubes with 40,000 PSI or more of water pressure has often been the approach plants have taken, however, there are significant limitations associated with this method. When compared to the footprint required for low-pressure water mechanical cleaning methods, the hydroblasting footprint is sizeable. Hydroblasting requires multiple water trucks, cleaning apparatus and pumps on site, as well as a large crew of technicians present to operate the equipment and ensure that the large safety zone is maintained. In addition, the duration of cleaning is lengthy compared to mechanical tube cleaning because water alone is not the best cleaning agent. The environmental impact of using thousands of gallons of water to clean one heat exchanger is a scenario drawing greater scrutiny than ever. In drought-stricken parts of the world where industry and agriculture are bound by strict water usage laws, the water requirements of high-pressure water cleaning have made this approach far less appealing.
Newer cleaning systems utilizing mechanical tube cleaners operate at far lower water pressures than hydroblasting. A typical water pressure for a low-pressure application is under 700 PSI compared to the average range of 10,000 to 40,000 PSI used in hydroblasting. Also, the cleaning components of these mechanical systems are smaller, more specialized and require fewer technicians than high-pressure water methods. Fewer crew members mean less unit congestion, lowering the safety risk for the labor force and the equipment being cleaned. Additionally, the environmental impact of mechanical cleaning with low-pressure water is far less than with high-pressure water methods. Mechanical cleaning uses an average of 90% less water than hydroblasting, and this dramatic reduction in water consumption equates to 90% less contaminated wastewater to be contained and treated. It also means less exposure to contaminated wastewater for personnel and nearby aquifers.
Figure 3. HPW vs. LPW Charts, compares the crew size, safety footprint, wastewater generated and water pressure requirements for hydroblasting versus mechanical tube cleaning of 21 heat exchangers.
HPW vs. LPW Charts, cleaning 21 heat exchangers using hydroblasters at 20,000 PSI generated 48,000 gallons of wastewater while the mechanical tube cleaning method at 500 PSI generated only 5,000 gallons of wastewater.
Figure 4. HPW vs. LPW Wastewater
This large disparity in water use despite the superior cleaning results of the low-pressure method is in part explained by the differing mechanics of the two methods.
The Hydroblast method pumps water 70% of the time the system is operating, dramatically driving up water consumption and creating vast quantities of wastewater. The mechanical tube cleaner shooting method pumps water for only the three seconds it takes for the mechanical cleaner to be propelled through the tube. The flow is then stopped, conserving water.
The three types of low-pressure water mechanical tube cleaning systems: tube shooting, brushing and drilling. Depending on the type of deposit and the extent of the fouling, these systems are often used in combination to provide superior cleaning compared to hydroblasting.
Figure 5. HPW vs. LPW Cleaning Results
Low-pressure water mechanical tube cleaning is effective at removing the most tenacious deposits including:
- Particulate and biological fouling
- Calcium-Carbonate
- Asphalt
- Baked-on hard deposits
- Acrylic
- High-density polyethylene
- Iron oxide and others
Tubes cleaned with low-pressure water mechanical cleaners are ready for Eddy Current or other non-destructive testing and require no additional cleaning or preparation. Once brought back online, these units will show an immediate recovery of production capacity and heat transfer. Through low-pressure mechanical cleaning, these results are achieved safely, quickly and efficiently.
Tube shooting methods, such as with Conco’s TruFit™ system, utilize a mechanical tube cleaner that is propelled through a tube using low-pressure water at under 700 PSI.
Figure 6. Tube Shooting. Mechanical tube cleaners are available in a variety of sizes, materials, and configurations
Figure 7. Mechanical Tube Cleaners
The best mechanical tube cleaners to use are ones custom engineered to match the interior diameter of the tubes to be cleaned, the tube materials and the types of deposits. Typical configurations include mechanical tube cleaners with spring tension metal blades and stainless steel wire brushes. Special application mechanical tube cleaners are also available such as the Cal-Buster™.
Figure 7d. Calcium Cutter, equipped with “glass-cutter wheels” to score and break apart Calcium-Carbonate deposits or U-Tube Cleaners
Figure 7e. U-Tube Cleaner, designed to navigate and thoroughly clean the bends of U-Tube units. While low-pressure water is used to propel the mechanical tube cleaner down the length of the tube, it also serves to flush out the deposits as they are loosened
Fouled heat exchanger tubes cost processing industries billions of dollars in lost production, capacity and revenue. While traditional high-pressure water methods can be used to mitigate tube fouling, the large crew sizes, huge footprints, high volume of waste water and lengthy time required to thoroughly clean a heat exchanger are causing many plant managers to reconsider their maintenance strategies. Low-pressure water mechanical cleaning methods featuring small crew sizes, small footprints, low volumes of waste water and short cleaning times offer a next generation tool kit of highly effective and responsive cleaning for any plant that operates heat exchangers.
For more information on how low-pressure water mechanical cleaning can help your plant, call Conco Services Corp. at 800-345-3476, visit www.conco.net or email Tim Meyer tmeyer@conco.net
