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The consequences of heat exchanger tube fouling for process units can be far-reaching and severe. Fouled heat exchanger tubes have a negative impact on the heat transfer and production capacity of the petroleum refinery process units in which they reside. As a result, the expense of additional fuel and unit downtime can be a tremendous cost to plants and operators. It is an unfortunate reality that heat exchangers of every type are prone to fouling. While the nature and severity of the fouling process will vary depending on the fluid or gas flowing within the tubes, the detrimental effects of fouling are certain. The reduction in heat transfer that results from fouling will have an impact on production capacity, and this will impact the cost of production and the final product. To reduce this impact, heat exchanger performance must be monitored, and early identification of tube fouling characteristics is essential to determine when and how to proceed with maintenance.
Today, the availability of safe and highly effective low-pressure water mechanical cleaning technologies allow plants to resolve maintenance issues with minimal imposition and expense. The first response for the industry is the Conco TruFit® mechanical tube cleaner, the industry standard for mechanical cleaners. TruFit cleaners are manufactured to the exact specifications of your heat exchanger and have cleaned more than 150 million heat exchangers tubes worldwide.
Environmental Impact
No discussion of the best way to clean a heat exchanger should proceed without a consideration of environmental impact. Like most unit equipment, clean heat exchangers simply work better. Poorly performing heat exchangers use more fuel and this plays a role in global CO2 emissions. Consequently, conscientious plant process engineers are increasingly seeing the value of unit maintenance not just in financial terms, but also as a moral imperative. Another obvious environmental advantage to low-pressure water cleaning methods is water conservation. Typical low-pressure water cleaning of 5,000 tubes will require approximately 8,750 gallons of water versus 193,500 gallons of water in a typical high-pressure water application of the same size unit. On average, low-pressure mechanical cleaning uses 97% less water than traditional high-pressure methods, and that equates to reduced water consumption and protection of nearby aquifers from contaminated wastewater. Table 1 illustrates the significant disparity in water consumption between cleaning methods. Less water being used on site means less to clean up or to reclaim in the post-cleaning phase.
Table 1. Water consumption
Conco Native - June 2018
Giving consideration to the environmental impact of any cleaning system is a best practice, but the reality is that for many plants and operators, budget constraints will drive decision-making on how to clean the heat exchanger. For most plants, time really is money. Because low-pressure cleaning applications require far less unit downtime, it is also the cleaning method that is economically advantageous. Heat exchangers are cleaned where they reside, in place and intact. There is no time wasted and no associated labor costs to disassemble, to move the heat exchanger to a separate cleaning pad, and then to reassemble. The time expenditure for a low-pressure water mechanical cleaning is approximately 70% less than when using high-pressure water—often hours versus days with the TruFit mechanical tube cleaning system. The mechanical cleaners are propelled through the heat exchanger tubes at 20 feet cleaned per second. Figure 1 demonstrates the typical duration of low-pressure water versus high-pressure water applications and the time expenditure associated with getting your process back on-line and producing faster. Time is Money
Figure 1.
Conco Native - June 2018
Low-Pressure Mechanical Cleaning: Innovative…and safe
In recent decades, conventional approaches to heat exchanger cleaning have been improved upon, and innovative methods have been developed to improve outcomes. Heat exchanger cleaning should be a safe proposition for the plant, and labor force and component safety are vital to consider when choosing how to clean. Low-pressure water means less pressure and a smaller safety zone on site. Figure 2 shows a typical safety zone for a low-pressure water mechanical tube cleaning application, while Figure 3 shows the larger safety zone required for a high-pressure water application. High-pressure water cleaning applications have been a common method for cleaning heat exchangers, but there are significant trade-offs associated with this approach. The high-pressure water footprint is sizable. Multiple water trucks and apparatus arrive on site, numerous technicians must be present to ensure that the large safety zone is maintained, duration of cleaning is lengthy, and the environmental impact of using thousands of gallons of water to clean one heat exchanger is a proposition that invites scrutiny. In drought-prone parts of the world, where industry and agriculture are bound by strict water usage restrictions that can come with penalties, the water requirements of high-pressure water cleaning have made this approach unattractive.
Figure 2.
Conco Native - June 2018
Figure 3.
Conco Native - June 2018
High-pressure water applications use 10,000-50,000 PSI. Low-pressure mechanical cleanings use a maximum of 600 PSI, and require significantly smaller crew sizes than high-pressure applications. With low-pressure cleaning, it is no longer necessary to dismantle the heat exchanger and move it to a separate work zone, so cleaning is done in place. This reduces the risk of accident, injury and component damage, and eliminates the financial and labor costs associated with heat exchanger disassembly and reassembly.
Low-pressure water cleaning systems such as TruFit mechanical tube cleaners, Hydrodrill, and the Excaliber pneumatic flex drive system often provide a superior clean to high-pressure methods. In addition to heat exchangers, low-pressure water cleaning methods effectively clean oil/water separators, reactors, drain lines, piping, air-cooled fin fan units and tank cleaning. Low-pressure mechanical methods are effective at cleaning the most tenacious fouling conditions: chemical fouling, calcium carbonate, asphalt, baked-on hard deposits, acrylic, high-density polyethylene, iron oxide, particulate and biological fouling. Tubes cleaned with low-pressure water are usually ready for Eddy Current or other non-destructive testing and require no additional cleaning or preparation. The anecdotal record speaks to the immediate recovery of production capacity and heat transfer in the aftermath of low-pressure mechanical cleaning, and these results are achieved safely and quickly.
The proof is in the performance
In a comparison of TruFit mechanical tube cleaners versus high-pressure water cleaning of 1,000 heat exchanger tubes, the low-pressure TruFit method used a total of 1,750 gallons of water. The high-pressure hydroblast method required 560,608 gallons of water. This large disparity in water usage despite the superior cleaning results of the low-pressure method is in part explained by the differing mechanics of the two methods. The TruFit mechanical cleaning method pumps water for only the three seconds it takes for the mechanical cleaner to be propelled through the tube. The water flow is then stopped. The Hydroblast method pumps water 70% of the time the system is operating which explains the dramatic difference in water use. See Figure 4 for a comparison of tubes cleaned with low-pressure mechanical cleaners and high-pressure water.
Figure 4.
Conco Native - June 2018
Sulfur Recovery Units-Reboiler
Historically, sulfur recovery units have been difficult to clean. This is due to the proximity of the heat exchanger to the boiler, and because the boiler operates at very high temperatures, it requires ceramic ferrules on the tube ends and refractory brick and mortar on one tube sheet. In this environment, deposits can be up to one-half inch thick and coke-like in nature.
The conventional approach to sulfur recovery unit cleaning is to pull the heat exchanger out of the boiler, move it to a pad, and blast it with high-pressure water for several days. This approach requires disassembly of the boiler drum, and removal and replacement of the refractory and ferrules. The results of this cleaning protocol are often mediocre, and afterward, the tubes are typically not clean enough for non-destructive testing.
The most innovative and effective approach to cleaning sulfur recovery units is liquid nitrogen cleaning. Nitrolance™ liquid nitrogen cleaning technology utilizes three basic mechanisms of action on the fouling deposit: mechanical pressure, super-cooling and thermal/volumetric expansion. This technology can be used at locations where the use of water is not an option and enables unit tubes to be cleaned to a level that supports remote field and Eddy Current inspections. Liquid nitrogen cleaning is highly effective. See Figure 5 for a comparison of before and after cleaning with Nitrolance technology. Post-cleaning fouling residue is completely dry and easily collected and disposed of. The environmental benefits of liquid nitrogen cleaning are in keeping with today’s efforts to conserve water, and because there is no liquid waste, concerns about wastewater contamination are eliminated. The post-cleaning phase requires the simple removal of drums of dry waste. There is zero transportation time and expense, and no expense associated with the rebuilding of components. Compared to typical hydroblast applications where cleaning can take an average of 12 days, cleaning applications with liquid nitrogen take an average of two days.
Figure 5. NitroLance Cleaning Results
Conco Native - June 2018
Fin Fan Exchangers
In the external fins of these air-cooled exchangers, dust and debris can settle, while the inside diameter of the unit tubes become jammed with sludge. The conventional cleaning response to this scenario is the use of a fire hose, foam or hand-held lance. These methods are not particularly effective and, worse, often result in damaged fins, reduced airflow and sludge that. The sludge is dumped back into the internal headers, perpetuating the cycle of clogged tubes and poor performance.
FinTech™ACC technology is a game-changing automated cleaning system that cleans fins with a low operating pressure that prevents any bending of fin blades. The FinTech is computer controlled and uses a water jet carriage system that moves at a consistent speed across the bundle. The consistency of the speed and water flow results in a uniform and consistent clean. The water jets can be manipulated to match the geometry and features of the fin network, optimizing the washing effect and protecting the fins from damage. The focused array of water jets distributes water deep into the bundle, and the water used in this technology contains no additives so there is no need to collect and dispose of wastewater. What’s more, the FinTech system is safe for the operator and the components, no scaffolding is required, and it is applicable in both horizontal and vertical applications. It is recommended to follow a FinTech cleaning with mechanical tube cleaners and a Tube Bridge to access the inner diameter of the tubes. This will prevent sludge and other contaminants from entering the header system. See Figure 6 for a representation of the Tube Bridge component. The benefits of FinTech technology are fast and thorough cleaning with no damage to fins and safe, effective cleaning of the tubes and Tube Bridge without contaminating the process stream.
Figure 6. Tube Bridge
Conco Native - June 2018
Catalytic Reactor Vessels/Exchangers
These complex vessels can have over 7,000 tubes that become plugged with catalyst, mixing springs and rings, and in the past have taken weeks to clean. They are often tall units, 40 feet high or more, and must be cleaned from the top. The challenges associated with cleaning this type of unit often means that by the time maintenance occurs, tubes can be badly clogged. The conventional cleaning practice has been to remove the top of the exchanger, a scaffold is erected, several trucks work for upwards of 10 days, leaving behind tubes that are still constructed and tubes with lances that became wedged and bound in the catalyst. This is an expensive, lengthy and less effective cleaning protocol.
A better solution applies a combination of Hydrodrill™ and TruFit technologies to successfully unplug and clean all tubes in the exchanger. Hydrodrill technology uses low-pressure water with a pneumatic motor to safely drill through all blockages, removing broken and embedded lances from prior cleaning attempts. The results of this safe and powerful cleaning approach are numerous. The efficiency of the HydroDrill means faster, better results with a significantly smaller workforce. The HydroDrill is safe, requires a much smaller safety zone, and one-fourth of the labor force which means fewer workers are exposed to risk. Because Hydrodrill and TruFit technologies result in cleaner tubes, use a fraction of the water of other methods, and require a smaller labor force, they are the next generation solution.
There is no better time for plants to respond to the unique challenges of today’s petroleum production environment. Heat exchangers have substantial fouling problems that cost industry billions of dollars in lost production capacity. This isn’t just bad for business; it’s harming our environment by contributing to global CO2 emissions. To improve the performance of fouled heat exchangers, operators must first understand the nature of the fouling and then commit to better stewardship through maintenance. Low-pressure water mechanical heat exchanger tube cleaning methods combine with innovative technologies like hydrodrilling and liquid nitrogen to offer a next-generation toolkit of highly effective and responsive heat exchanger cleaning.
For more information, please visit http://conco.net/ or call (800) 345-3476.