Maintenance of a platform's Waste Heat Recovery Unit (WHRU) and similar shell and tube heat exchangers can be an extremely dangerous process. It needs to be disconnected, taken off line, and moved to shore for repair. Shell and tube heat exchangers are made of coiled tubes and can become fouled with carbon deposits. The traditional methods for clearing the blockage include bypassing the fouled unit, cutting off bends and cleaning the tubes, then re-welding the U-bends, and complete unit replacement.
The old methods are becoming more outmoded due to advancements in technology. It is inefficient to bypass the unit. Just as it would be less efficient to run your car with 2 cylinders not firing. This inefficiency, of course, also increases operational costs. It is time consuming and costly to cut the U-bends and re-weld them. Sometimes it can be difficult or impossible to get access to reattach them.
Some of these new methods include the ability to clean areas with limited access, and clear deposits from U-bends without ever removing them. This can sometimes be done without even taking the unit offline, and usually takes less time and results in a higher degree of defouling. In fact, many units can be restored to near-factory efficiency. For big refineries, petro-chemical plants, or power plants, this can amount to six figure savings.
The U-bends themselves also retain many deposits, and continue to be a bottleneck to the system. Full replacement carries the cost of completely replacing equipment that, other than the heat exchanger tube fouling, is still in working order. This method also requires the unit be taken offline for the full duration of replacement. obviously this carries a heavy expense and serious loss of production.
Traditional heat exchanger cleaning methods and heat exchanger cleaning equipment have changed very little over the last few decades. Pressure jetting is still the primary means used by many companies, but it is slow, inefficient, and ultimately very costly. Additionally, many companies are skeptical of newer methods, falling back on the "that's the way it's always been done," chain of logic. They are also weary of trying new techniques that are not as "proven" to be effective. Finally, many have long term tube cleaning contracts that do not allow for a change in heat exchanger cleaning technique, unless the contractor were to adopt the new methods.
Newer heat exchanger cleaning equipment and techniques are more technologically advanced, and by extension, require a higher skilled laborer than old style pressure jetting. These new developments include the ability to clean tight radius bends, clean units while keeping them in place, and even while keeping them online. It has also resulted in faster, more efficient cleaning. Many tube bundles can now be cleaned more effectively than with pressure jetting, and jobs that used to take days may now take only a few hours. Difficult to access units are now accessible with these new technologies.
Some of the technology that has been developed includes special nozzles that can be used on tight bends, laser cleaning, and new "smart" metals that respond to changes in density and pressure to prevent damage to the tubes. With these methods, jobs can be finished with less downtime, because cleaning and descaling can be done more quickly. Equipment is also less likely to be damaged in the process. Many of these new processes are safer, create less waste, use no chemicals, and have a significantly reduced environmental impact.
The article was written by Alex Parry who writes about heat exchanger safety at his heat exchanger cleaning equipment site.
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