Heat exchanger maintenance in a petrochemical plant

Pipe cover before coating.


Perez Mitchell is a Mechanical Maintenance Engineer for Ducor Petrochemicals, a polypropylene (PP) plant in Rotterdam, the Netherlands. He has specialised in rotating equipment for over 27 years. Since starting with Ducor in 2012, Perez now speaks from 10 years of experience about the challenges of working with heat exchangers in petrochemical applications. In this interview, we discuss the importance of heat exchangers in the PP production process, the benefits of a preventative maintenance approach, and the reason for choosing a reliable water treatment provider.

By Ellie Pritchard

Ducor produces approximately 160 Kt of around 45 different grades of polypropylene in small batches for niche markets such as medical, food and beverage, textiles and so on (see box text Ducor Petrochemicals). For petrochemical applications, heat exchangers are used for condensation of solvents and chemicals, the heating and cooling of reactors, production units and intermediate products, the cooling of water and hydrocarbons, and process heat recovery. They are, essentially, vital equipment for such processes.

Preventative maintenance

Perez Mitchell is Mechanical Maintenance Engineer for Ducor Petrochemicals in the Netherlands.

Perez explains that his current role is varied as he is responsible for all mechanical maintenance on site, including piping and civil. “My job is to make the installations in the plant stable; I work together with a reliability engineer and really focus on preventative maintenance.” As an overview of his average day, Perez begins by making sure he is up to speed on all reports from the previous day’s production shift – any concerns are discussed with the appropriate foreman or work preparator where necessary. He also handles administration, attends meetings, speaks with vendors regarding internal and external repairs, and occasionally visits vendors to inspect equipment that is dismantled for repair. But the main aspect of his job is the constant update of 85% of the plant’s 1823 maintenance plans.
Before 2012, Ducor mostly relied upon breakdown maintenance, handling an issue as and when it occurred. In a previous interview with Valve World (October 2021), Perez described it as running from one fi re to the next: “It can be satisfying to ‘extinguish these fi res’. Never a dull moment, as the saying goes. However, it also takes up a lot of your time and energy from more structural tasks.”
In 2012, the company invested in setting up a more cohesive and preventative system based on historical data (maintenance reports, system errors etc.).
“From this system, we receive notifications of what to inspect and when to maintain it. Needless to say, we update the system on a regular basis with actions to be completed and error notifications. If certain errors keep coming back, we conduct a root cause analysis with our colleagues on the production floor. Not only has this approach led to less unplanned downtime, it has also made our work more structured, freeing up time to improve the production capacity of our plant.” Now, Perez says that 80% of his work is preventative, leading to his main responsibility being the updating of 1539 mechanical maintenance plans which require small adjustments every day.
“We always joke that even the cleaning lady will be able to go out and do the job soon because these plans are so detailed, with photos and each individual step planned out, and also special information such as which specific bolts to use. For all of our planned shutdowns we have a lot of companies coming in from outside because our own maintenance and technical departments are small. We always have to hire in some mechanics to work with us for some periods of time, meaning the plans have to be incredibly well maintained for them to use.”

Cover post-coating

Overall production process
Ducor’s feedstock is propylene gas, coming by pipeline and ship and barge. Ducor employs Novolen gas phase technology to polymerize the gas. This proprietary process utilizes one or two identical vertical gas-phase stirred bed reactors (three homopoly-mer reactors and one copolymer reactor). Homopolymers and random copolymers can be manufactured either in a single reactor or in a reactor cascade with two reactors, depending on the required capacity and product range. Alternatively, two reactors can be operated in parallel to achieve higher capacities for a single train plant and to produce bimodal resins. This flexibility in the configuration is better suited to the company’s strategy to produce a high number of various grades. These grades can be obtained by changing the conditions (temperature, pressure and reactants) in the reactor. The end product from the Novolen-process is a polymer powder. This powder is mixed with nitrogen in a purge silo to remove the residual propylene (deactivation of PP-powder) and transferred to storage. Finally, the powder is converted by pressing the gelatinized powder through a matrix (and being cut into pellets).
(Source: Valve World magazine, October 2021)

Reactor gravity condensor.

Heat exchanger maintenance

Under Dutch government regulations, the plant is audited a couple of times each year to ensure it can still hold the permit to produce polypropylene. Each aspect of its running must be carefully documented, alerting the local government where necessary, such as in the case of gas flaring. From heat exchangers to vessels to piping – all equipment needs a specific programme.
For the polypropylene process, heat exchangers are essential for regulating the temperature of the main ingredient: propylene gas. The process also requires heat exchangers for the cooling of mechanical lubrication oil.
“We have a complete shutdown every 6 years, the next coming in 2024, and we do all inspections during this time,” Perez explains. “For some heat exchangers, however, we’ll need more frequent inspections due to wearing down of material or fouling.”
Ducor uses shell and tube heat exchangers (both loose and fixed tubes) and plate heat exchangers in a wide range of sizes. The propylene gas and lubricant oils are “clean”, the heat exchangers at Ducor do not necessarily suffer from chemical issues but instead the main issues arise from the water/coolant side, such as ageing, corrosion, scaling, and leaking tubes. The service vendor opts to plug tubes where necessary, but the end result is almost always re-tubing a bundle.
“Cleaning is also a part of the scope, of course,” says Perez. “We first clean the heat exchanger and then we do the incurrent inspection to see if the thickness of the pipe is still good enough.”
One way in which Ducor improved the longevity of its heat transfer equipment is the use of coatings. In particular, the company uses a glass fibre solution provided by Brent OCC called Brebaflake – an epoxy novolak vinylester glass flake coating. “This is a really good solution for us; we use this coating for cooling water applications like pumps. We can apply it even to damaged heat exchangers, meaning the cover, casing, etc… everything but the tubes, basically. When you build up the layers of this Brebaflake, it is a very solid material but quite brittle.”
Perez explains that the coating also makes cleaning easier, as it reduces fouling: “It’s a great preventative and protective solution.”

Water contamination

In 2012, Ducor suffered a major issue with its cooling water in which an iron-oxidising bacteria destroyed vast amounts of equipment.
“A large amount of coolers, pipes, and heat exchangers were seriously damaged by this bacteria; it was eaten away, which is very scary to think about” says Perez.
“The valves and tubes were a disaster and we had a complete shutdown of 6 weeks; we had to do a lot of re-tubing and all the companies here in the Botlek area of Rotterdam were working full time with us to assist with re-tubing and coating.”
“I would always advise for other maintenance engineers to pay special attention to their water treatment provider, because it is so important and really devastating if it goes wrong,” Perez cautions. “The new company we use has a container with acid metering pumps and other devices to make sure nothing goes undetected. Every four weeks, someone from the company comes to check the pumps and make sure everything works well, and if it isn’t then he reports it. It is a big reassurance to use a company you trust for something as vital as this, so I definitely encourage others in our industry to pay special attention to this. Our next step is online monitoring and we’re at this moment in an advanced stage.”

Ducor Petrochemicals
Ducor’s history dates back to 1978 when ICI (Imperial Chemical Industries) built a PP/PE production plant in Rotterdam, the Netherlands. Over the years, the plant has changed owners several times. Before Ducor entered the scene, the Belgian carpet producer DOMO produced granulates here for its products. As the carpet market experienced difficult times, the plant was acquired in 2011 by the Israeli BAZAN Group (oil refining, petrochemicals).
Its subsidiary, Ducor Petrochemicals, produces polypropylene granules (PP) and the sale of polyethylene products for various applications. Examples include food packaging materials, detergent caps, McFlurry plastic cups, flower boxes and litter boxes, as well as textiles, auto parts and healthcare products. The company mainly supplies the above polymers as granules, but also in powder form (non-pelletized resin). Being a relatively small company, unlike many of its competitors, Ducor specializes in (customized) grades in relatively low batch sizes.
(Source: Valve World magazine, October 2021)

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