The consequences of heat exchanger tube fouling in petroleum refinery process units can be far-reaching and severe, and 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 effects of fouling are certain. The resulting reduction in heat transfer will have an impact on production capacity, which will impact the cost of production and the final product.
To reduce the impact of tube fouling, heat exchanger performance should be monitored for indications of declining heat transfer. Good oversight will enable early identification of fouling characteristics, and awareness of effective cleaning options will inform plant personnel of when and how to proceed with maintenance.
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, playing a role in air pollution and global CO2 emissions. Increasingly, plant process engineers are seeing the value of unit maintenance not only in financial terms, but also in environmental. Water conservation is an additional benefit of low-pressure water mechanical cleaning methods.
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.
In recent decades, conventional approaches to heat exchanger cleaning have improved so much that tubes are often returned to as-new condition. Results are important, but heat exchanger cleaning should be a safe proposition for the plant, and this requires labor force and component safety be given the highest priority. Lowpressure water means less pressure and a smaller safety zone on-site.
Figure 1 shows a typical safety zone for a low-pressure water mechanical tube cleaning application, while Figure 2 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. The high-pressure water footprint is sizable. Multiple water trucks and apparatus arrive on-site, numerous technicians must be present to ensure 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.
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. This reduces the risk of accident, injury and component damage, and eliminates the financial and labor costs associated with heat exchanger disassembly and reassembly.
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 tanks. 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.
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, but when units are closely monitored and cleaned, fouling processes are reversed and production capacity is restored.
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