Some myths about mechanical cleaning
Because it has long been the only option when unit cleaning becomes unavoidable, the true cost of mechanical cleaning has been overlooked.
MARCELLO FERRARA and CRISTINA FERRARA
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Mechanical cleaning has been used since the inception of the oil and gas industry. Since that distant beginning, many developments have been achieved in the industry, but basically the principle of equipment cleaning remains the same: mechanical removal of deposits. This article addresses a technology for cleaning equipment without opening it up and without proceeding to mechanical removal of deposits.
The key in evaluating the technology is having a mind shift over current practices and focusing on the value rather than simply the cost. Evaluating the global cost connected with mechanical cleaning is of paramount importance for driving change. The oil and gas industry is striving for profit recovery. Rethinking myths can be an easy and painless alternative to cost cutting.
Conventional mechanical cleaning
We will hereinafter refer to heat exchangers as a template for any equipment. Today’s technology for cleaning heat exchangers comprises at least 20 operations, from flushing the system to removing, transporting, cleaning and pressure testing, to finally restoring the equipment to the process. All of these operations have their related costs and carry a hazard.
On top of the operational costs (the bidding paid costs) are the refiner’s organisational costs in terms of:
• Awarding (bid organisation, evaluation and award)
• Control during execution.
Following equipment downtime, the huge cost of production loss has to be added to these operational and organisational costs.
Because of continuous improvements in process safety and environmental performances, many problems associated with mechanical cleaning are now only acceptable when there is no other choice.
Consider the continuous technical effort and investment the hydrocarbon processing industry makes in limiting airborne emissions – for instance, investments and revamps for the purpose of limiting volatile organic compounds (valve substitution, flange insulation, double seals on pumps, double seals on tanks, and so on) – and then see what happens during hydroblasting.
Consider also the continuous effort in the hydrocarbon processing industry to improve safety in operations and to reduce waste generation. Mechanical cleaning was until now the only available technology for cleaning heat exchangers and process equipment, which is why myths have been created and operators take them for granted as unavoidable (see Figure 1).
The average perception of mechanical cleaning is simply the cleaning cost or even the cost of hydroblasting alone. In reality, the cost of mechanical cleaning is more than 30 times the cost paid to the mechanical cleaning company.
Consider preheat train cleaning in a major turnaround. Nobody will argue about the cost of spare parts; it is mandatory to replace gaskets and bolts after extraction and cleaning of bundles, but the cost can be very significant. By considering a 40 heat exchanger preheat train, this can easily be more than $200000 and this could be easy to recover. What if this cost can be saved simply by not opening the bundles?
More importantly, at current refining margins, an average 100000 b/d refinery can make a profit in the range of $2 million/day. Saving seven days of downtime can represent a minimum value of $14 million. It is worth thinking about how to debunk myths.
The following account of ‘myths’ is not a criticism of the current way of thinking, but a hint as to new ways for improvement. By focusing on value and achievable optimisations, the reader might find ways of reducing losses as an alternative to cost cutting.
Working by tradition
Many operators are keen to work according to tradition and are reluctant to change. They have been instructed to do so by colleagues, according to company policy, or by following the history of the site.
But if you look at the developments implemented over time, and at the number of patents granted for the oil and gas industry, you may be surprised by how innovative this industry is – probably the most innovative industry on the planet.
Because mechanical cleaning has been the only cleaning technology available to the oil and gas industry for many years, all of the budget, turnaround and operational activity related to cleaning has been designed according to mechanical cleaning. The industry has become so used to mechanical cleaning, considering it ‘unavoidable’, that any evaluation has been made by taking as a reference its cost of execution, taking for granted all of the other related costs.
Working according to tradition is of course a choice that any individual or company can make; the question is how cost effective is this compared with new approaches and is it worth taking the ‘risk’ of trying something new? The answer must be driven by a risk/benefit analysis.
The myth of ‘100% cleaning’
Mechanical cleaning is considered by the industry as the standard operation which achieves the maximum allowable cleaning. Therefore 100% cleaning is achieved after mechanical cleaning. But does the oil and gas industry need 100% cleaning of equipment? With conventional mechanical cleaning, the answer is obviously yes.
Everyone in the oil and gas industry knows, however, that after any mechanical cleaning, fouling deposition will start again. Fouling indeed depends on the process, not on the cleaning method and/or the equipment design.
It is very common after mechanical cleaning, depending on the process, for about 10-30% of efficiency to be lost after a few days of run. For example, in a CDU, the furnace inlet temperature may decrease by 3-5°C within one month from start-up, depending on the processed feed. Figure 2 illustrates a real case for a vacuum unit, which speaks for itself.
In a conventional situation, the unit is allowed to run in a non-â€¨optimal state, provided the feed rate is not impacted. While the unit is running in a non-optimal state, money is being lost. To date, such losses are much more sustainable than a cleaning shutdown because the industry has mechanical cleaning in mind. No operator can even think of a production loss of, say, 14-21 days for the sake of recovering performance.
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