7 tips for cleaning Texas Towers (VCFEs)
Like many other pieces of heat transfer equipment, the Vertical Combined Feed and Effluent Exchanger (VCFE/Texas Tower) is an unsung hero of many industrial processes and as such tends to be taken for granted.
A VCFE/Texas Tower takes heated product from the process outlet to preheat raw feed inlet, therefore thermal efficiency and throughput on these assets are critical to the process. When running efficiently, Texas Towers reduce the load on fired equipment, thus lowering energy consumption and in turn CO2 emissions.
However, with the detrimental effects of fouling often falling into the ‘out of sight, out of mind’ category, it can be seven to 10 years – sometimes longer, before Texas Towers are cleaned.
They operate for so long that any reduction in efficiency is usually a gradual process which goes largely unnoticed until either throughput or temperature has deteriorated sufficiently to cause very big problems for refineries. Literally.
Texas Towers are probably the tallest shell and tube exchangers, with heights ranging between 18 – 25 metres. They are often very difficult to access, which can present significant safety issues.
Here are our top seven tips to help you ensure your Texas Tower is being cleaned at the right time, by the right contractor.
1. Don’t waste time and money with traditional cleaning techniques
In the case of restricted or no manway, access is required from below. Unblocking or cleaning 25-metres upwards has its own problems when using traditional water jetting or other mechanical means on such small internal diameter tubes, so instead requires a highly specialised approach.
The use of traditional high-pressure water jetting to unblock Texas Tower tubes has proved difficult, if not impossible, on many occasions around the world. There are typically 4000+ tubes within the exchanger and many are designed with 11.7-mm/0.46” internal diameter tubes.
Problems using traditional high-pressure water jetting include:
- Access and operational difficulties
- Danger of hydraulic action when feeding high pressure lances down the small tubes from above
- Lack of water flow to drag water jetting flexible lance up 25-m due to small diameter
- Operators have reported 20 to 50, 12-hour shifts to clean Texas Towers
- Limited success in removing fouling and very often leave tubes blocked
Safety, speed, unblocking and cleanliness are often deemed the most important factors by our clients. See how we successfully improved the performance of a client’s two VCFEs, whilst completing the job in just 5 shifts down from 24 when they were previously cleaned using traditional techniques.
2. Don’t underestimate the level of fouling
In many cases, heat exchangers are designed with a 20%-30% larger surface area than required to allow for fouling, so the calculations set by ASME and TEMA can be unreliable. This means you have to exceed your fouling factors before a warning is released – at which point, the refinery schedules cleaning for the next shutdown, which might be six months down the line, all the while deposit is continuing to build up. This is when it is discovered that instead of being 10% fouled as expected, it can be 30%-40% blocked or severely fouled, making it much harder to clean – and impossible for traditional cleaning methods. We find this is particularly a problem with Texas Towers due to their long run-times.
3. Ensure the VCFE is cleaned every four years
The VCFE is one of a few heat transfer assets that often fall into the “out of sight, out of mind” category, but due to their criticality require cleaning every four years, especially when refineries expand or when there has been process carry-over such as catalyst or oil.
Fouling occurs early on – in our many years of experience, can be seen anywhere between three and 33 years of running.
Even when process assets are sold on the basis that they won’t foul, the law of averages says your asset will foul at some point, so be sure to plan ahead for it.
4. Make sure your cleaning contractor is prepared for unknown fouling characteristics
From our extensive experience of Texas Tower cleaning around the world, we know that gummy and coke-like deposits settle in certain areas of the exchangers. We have attended projects where the accidental carry-over of several cubic metres of light oil was suspected to have burnt off at a high temperature, leaving a hard layer of hydrocarbons of unknown thickness, volume, consistency or location.
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