Innovative Cleaning and Inspection Plays a Critical Role in Refinery Debottlenecking
Debottlenecking is all about analysing the capacity and time utilization of each piece of equipment and then recognising opportunities for increasing throughput with the least capital expenditure.
Every business owner wants to increase production whilst reducing expenditure and within the oil, gas, petrochemical and energy industries an additional desire – or should we say necessity – is the reduction of CO² emissions.
Within oil refineries debottlenecking is about avoiding emergency critical path situations. It is about identifying problems before they become cause for concern and getting the large, difficult tasks finished so that shutdowns can be shortened. Often these problems are cleaning and inspection related
Debottlenecking presents challenges in various areas and one of those targets the quick, efficient cleaning of heat exchangers and other plant assets. Often regarded as a “traditional” procedure it is crucial that clients source and encourage a more inventive approach to achieve successful de-scaling whether for performance or for integrity inspection especially on the more challenging of exchangers in order to avoid bottlenecking.
For the past twenty years Tube Tech has been working with several of the the worlds largest oil refineries to develop radically innovative cleaning and inspection techniques to assist with de-bottlenecking activities caused by heavily fouled, difficult exchangers or exchangers perceived as “un-cleanable”. The companies’ innovations have included in-situ and even on-line cleaning of heat transfer equipment where previously local contractors had struggled and needed to use cranes and scaffolding to affect a mediocre cleaning result. With this knowledge Tube Tech is able to offer the following advice to engineers tasked with refinery debottlenecking where cleaning is involved.
Debottlenecking to Save Time, Save Money and Reduce Emissions
About 50% of financial losses directly related to fouling within any oil refinery are due to the crude distillation unit (CDU). These crude exchangers regularly suffer from scaling of tubes or tube blockages which thwarts the transfer of heat and substantially reduces overall efficiency and subsequent production throughput.
Such heat exchangers become “baked” with carbon scale with a high percentage blocked causing back pressure and poor delta T’s. As a result these exchangers become critical path simply because cleaning contractors cannot clean to the required IRIS or Eddy Current standards. This eventually leads to a frustrating bottleneck situation and if these crude exchangers cannot be cleaned properly this limits furnace capacity which means a costly cut to the operations flow rate. The loss of throughput multiplied by the profit equates quite simply to loss of plant profits. These costs can be huge and often dominate energy losses as well as having a tremendous impact on the increase in ones CO2 footprint.
100% clean of BP Fin Fans
A number of ACC fin-fans serving the coker unit at a BP refinery in Germany, had become blocked with a material that consisted of an elastic, cured polymer, similar to rubber, like bathroom sealant. The deposit was pliable but tough and resistant to jetting pressures of up to 750 Bar/10kpsi. Once cooled, the deposit tended to harden to a brittle, glass-like consistency. Each unit contained 225 x 10 metre carbon steel tubes, terminated by 328mm-deep header boxes. The reduced efficiency of the ACC fin-fans was estimated to be costing the refinery around $20,000 per day for each unit. These exchangers had become critical path items in the refinery’s shutdown list not only because they could only be taken out for maintenance during a scheduled shutdown but also because previous high pressure jetting contractors who had been given six days to clean had struggled to reach the desired inspection standard. An added complication was that replacement bundles had been delayed and hence the plan to clean these fin fan exchangers was given to Tube Tech very late in the planning stage. I was important to significantly reduce time as well as achieve the correct cleanliness standard. An additional hazard for the cleaning team involving aromatic solvent left behind by a previous chemical cleaning attempt.
The nature and extent of the fouling in the ACCs, which normally handle E3 reformate, was revealed by careful inspection. The fouling to be removed from the tubes varied from a sticky, putty-like substance to crisp brittle restrictions, which included the remains of catalytic (PCA) material.
Once on site, cleaning proceeded as planned, with two methods being employed to clean both the headers and tubes of the ACC units. The first method was based on the well-established SafeTrack system, while the second utilised a newly-developed self feeding rigid coiled lance – a hydraulically-driven rotary lance which employs a hydraulically-powered reaming principle with simultaneous pump pressure up to 3500 bar water pressure. The new system applied a high-torque rotary action within the tube, with water to clean the various consistencies of deposit encountered. It is very common for traditional technology to clean the tubes but with the waste ending up in the header boxes, which then basically goes back into the clean tubes when the unit is put back on line! Tube Tech ensured that 100% of deposits were extracted from the header at source.
“Cleaning these important fin-fan units has always been a problem for us, both in getting them cleaned in the time available and to the required eddy current and IRIS inspection standard, using our usual local contractors. This time we had a situation where the decision to clean the units was not made until very late in the planning for the shutdown as our replacements had been delayed,” reported the Shutdown Manager at BP. “As it had been taking six days to clean just one unit and we wanted to clean at least two, we knew we had to look for an alternative service provider and we found Tube Tech. The cleaning went exceptionally well – and so quickly that we were able to get them to clean not just two ACCs, but four. We had been planning to order some new ones, so badly were they blocked, but Tube Tech was able to clean all four to a much higher standard than we have ever seen before, so we have made some really great savings.”
Understand the Debottlenecking Process – Look at Refinery Needs and Wants
It is rare that refineries possess accurate historical data on previous cleaning/inspection activities and what exists is often pitifully inadequate. In their twenty year history Tube Tech have never once found a refinery or petro-chemical plant that could provide archives on how something has been cleaned – i.e. pressures, volumes used, technology applied or any other significant information which could hold the key to improving performance the next time around. Invariably the comments from refinery personnel refer to ‘pressure jetting’ or ‘chemical flushing’ and very little else. A clear and precise information gathering strategy is crucial to understanding the details of the problem – information such as limitations of access, deposit characteristics etc – all of which help contractors to apply the best technology in the most efficient manner. This information reduces the chance of bottlenecking by preparing and understanding a cleaning problem before it occurs, planning for the best cleaning technology which benefits plant performance, reduces the cleaning time, increases energy savings and reduces the CO2 footprint.
Refinery engineers really need to accurately record cleaning activities, ROT HIT values, and heat transfer co-efficient data i.e new operational performance date, performance data prior to cleaning and performance data after cleaning. This information is rarely if ever shared with the contractor or indeed the plant engineers, yet is crucial to motivate contractors and plant personnel alike to deliver best practice. Within their lengthy contract questionnaire Tube Tech request information about the units to be cleaned but also ask for detailed performance information. The reason for the comprehensive questionnaire is to ensure that refinery operators are able to record the increase in performance that a TRUE conscientious specialist cleaning service will provide.
Arabian Texas Tower Clean Reduces Delta
The refinery of one of the world’s largest Arabian oil companies includes a processing stage found in most productive and successful refineries – the Continuous Catalytic Reforming unit or CCR Platformer. Texas towers or V.C.F.E’s (Vertical Combined Feed Exchangers) play a vital part in the platforming stage of the refinery process. Platforming product in its last stage of processing is passed into the Texas Tower to cool it down against cold feed. A VCFE is designed to minimise heat loss, thereby improving fuel consumption of the unit’s furnaces. It is vital that the VCFE operates as efficiently as possible so clearly both tube side and shell side need to be cleaned to the highest possible standard. For traditional high pressure jetting contractors this is no easy task!
The two Texas Towers at this Arabian refinery contain a combined total of 6,200 steel tubes. The tubes are unusually long at 21 metres long, with an internal diameter of 14mm. Tube Tech was contracted to completely unblock and clean between 200 and 300 tubes in each VCFE. The client also stated that a ‘good’ production standard would be quite satisfactory.
As the V.C.F.E’s were opened, it became clear that the client had severely underestimated the level of fouling. Instead of 200-300 blocked tubes, there were almost 3,000 – almost half of the total. Thus the contract risked becoming a classic bottleneck scenario. In the face of high local ambient temperatures, Tube Tech faced a significant challenge to meet the new objective in the time available, particularly as there were to be numerous operational delays that were beyond their control. An early, major obstacle was the lack of suitable scaffolding that was to have been provided by the clients sub contractor.
As with any major international cleaning project, 20 years of experience has taught Tube Tech to mobilise several different cleaning solutions to a client’s site to cover as many unforeseen operational eventualities. This meant that the lack of scaffolding did not prevent the clean from going ahead, thanks to the companies’ inherent forward thinking and its ability to deploy a second and third, fall-back system.
The heavy gum and coke blockages found in approximately 30% of the heat exchanger tubes required an unusual system modification as Tube Tech’s bespoke and very unique 25m long vertical drilling rig intended for this type of blockage could not be deployed due to the absence of suitable scaffolding. With normal high pressure jetting processes, any gum jetted out tends to solidify behind jetting nozzles and can trap the lance, which means it can become irretrievable. In one of the VCFE’s, Tube Tech found three tubes containing metallic blockages from previous contractors’ including broken flexible and rigid lances, drills and cleaning tips.
“Rarely do we encounter such a wide variety of tube deposits. We found literally everything – from coke-like substances to rubbery chewing gum-like full-length blockages,” recalls Martin Byford, Tube Tech General Manager.
Incredibly, apart from the three blocked tubes, all the others were successfully unblocked and cleaned and even more surprising all within five days and nights. With intensive dedication and working in 40 Deg C heat, the Tube Tech teams were able to clean both V.C.F.E’s to inspection standard, well in excess of the production standard requested.
“Following the Tube Tech clean of the VCFE’s, the heat transfer between the exchangers’ tubes and shell increased dramatically, thereby reducing the delta T between ROT and HIT. This is shown by the drop in temperature on the ‘after’ plot. The cleaning therefore led to hotter feed going to the downstream heater inlet,” reported the clients Site Engineer.
Challenging Convention Reduces Time, Cost and Emissions
Questioning conventional practices and long standing beliefs is another way in which individual refineries can successfully debottleneck. The slavish use of common cleaning methods means that many refineries find themselves replacing expensive equipment as the conventional cleaning techniques cannot provide the increase in performance required. Even when effective many conventional cleaning methods often require that the equipment is removed to a cleaning bay for cleaning and if not moved then has to be offline while cleaned.
Fast Flare Line Clean Online
The specialist consultancy arm of one of the world’s largest refinery companies approached Tube Tech to perform a “fast clean” operation – namely from 10 days to 5 on a fouled refinery flare line in Germany, as a plant shutdown was imminent. Tube Tech visited the site, reviewed the task and confirmed not only their ability to reduce the shutdown time by half but also felt strongly that the clean could even be completed whilst on-line believing that “just because no one had done it before did not mean it could not be done”.
The Germany-based facility of this global oil company refines crude oil and produces a variety of hydrocarbon products, including ethylene, propylene, benzene, toluene, xylenes, and methanol. Combustible waste gases from all processes/plants are offloaded into a single flare line for burn-off.
Back pressure had been building up in the 250-metre refinery flare line, as resistance to flow increased, due to the line being restricted approximately 40% overall by pyrophoric and sulphurous sludge deposition. The client’s own inspections suggested there were substantial sections of the pipeline badly restricted by this soft, mud-like sludge. Taking the flare line off-line for cleaning meant that the entire refinery complex would have to shut down, the operational and cost implications of which would be substantial, as any refinery operator will know. The client hoped therefore to limit any such impact by cleaning during a plant shutdown. The risk of cleaning the flare during a shutdown with thousands of workers on site would have had its own logistical problems.
Having surveyed the flare line, recorded the visit with digital images, isometrics and inspection records. Tube Tech was the only contractor to suggest hi-tech high pressure jetting the flare line whilst on-line. If this could be achieved, while addressing all safety issues, it would be a world first for Tube Tech and the oil industry. The flare line clean could then be taken out of the shutdown and safely completed at the client’s convenience.
Tube Tech offered to demonstrate their ideas on a full-scale mock-up of key sections of the flare line at its UK operations centre. The client’s consultants came to the UK, and witnessed a successful on-line trial, which demonstrated multiple fail-safes. Tube Tech’s bespoke method coped with potentially high temperatures and pressures inside the flare line and prevented oxygen and spark ingress and the escape of toxic gases. The major technical difficulty was to design access via 25mm valve ports located at intervals along the length of the flare line.
All systems devised for the project were trialed on the life-sized mock-up. Mechanical orbital cleaning heads and pulsed high-pressure hydro jetting lances, designed to be heat and scratch resistant when fed into the small 25mm entry points, were utilized. Locating the deposits and establishing their level and density before cleaning was carried out by TracerCo, using gamma ray-based inspection during and after cleaning. Intrinsically-safe inspection equipment was used by Tube Tech using a novel high pressure / temperature sealing technology through the 25mm ports to take digital images before and after cleaning.
The objective was to reduce the deposition level within the flare line by removing as much sludge as possible, to level the remaining deposit and achieve an 80% cleanliness level in order to reduce back-pressure. Even though some entry points turned out to be corroded shut or obstructed by weld intrusion, Tube Tech’s ‘design-on-the-run’ reputation came to bear and equipment was modified to accommodate this unforeseen additional challenge.
With cleaning underway, some very good reports came back from the inspectors and in just five days the cleaning standard had been achieved.
“Based on the client’s sample analysis, we came prepared for soft, mud-like deposition. Actual samples found during removal were concrete-like lumps, commonly known as ‘sulphurcrete’ and not just sludge! We were, however, still able to wash loose concretion downstream to an interceptor tank. Whilst our objective had been achieved, we offered to return with appropriate equipment and a further guarantee to this time remove all the remaining sulphur concretion at some future date,” reports Mike Watson, Technical and Managing Director, Tube Tech International Ltd. “This was the first time an on-line clean of a flare line had been accomplished. We have already developed an even more powerful system, to tackle any future unexpected deposits and even longer and larger flare lines, just in case another similar opportunity presents itself anywhere in the world. A considerable digital video archive of information and knowledge was built up during the exercise, which means we can repeat the exercise any time in the future.”
By challenging convention Tube Tech were able to avert a total refinery shutdown thereby providing huge financial savings for the refinery.
It Is About Working With the Right People
Successfully debottlenecking a refinery involves working with specialists. Refinery operators and engineers need to be asking contractors the right questions which will include:-
- Have you experience in refinery debottlenecking?
- What inventive methods do you employ?
- Can you provide evidence of your experience?
- How will you approach our debottlenecking problem?
- Do you understand how this particular activity will affect the rest of our plant?
- Who will be on the team that comes to my plant?
Heat exchangers need to be cleaned out regularly. In practice, maintenance schemes for heat exchangers are based on legislation, which means that inspection and clean out is required every two to four years. However, it is likely that some heat exchangers should be cleaned more regular, because the savings achieved by thermal efficiencies and increased production capability will rapidly outweigh the extra costs of a cleaning exercise. Quite often large amounts of time and money are spent on unnecessary inspections of heat exchangers brought about by doubt caused by heavily scaled tubes that could harbour under scale corrosion. Tube scale is often so hard that no inspection tool can provide a suitable reading or even be pushed down a tube.: Solution?….Clean it with the right technology at the right time. It is clear and evident that a cost-effective clean-out strategy is needed for heat exchangers in a train.
Forming a debottlenecking plan for cleaning activities can pay dividends. For example: Separating out and prioritising exchangers which are a) critical path, b) difficult to clean c) Those that never seem to be cleaned effectively in the time allowed and finally d) those that are removed to a cleaning bay. Finding the best practice solution for each selection should make debottlenecking cleaning activities run more smoothly instead of simply using the same tool for all.
“We stand by our creed that ‘Failure is not an option’ and will continue to invent and develop cleaning systems to assist refineries with their debottlenecking exercises whether emergency critical path or not,” concludes Mike Watson.