Trimming the fat
Maximizing throughput from a glycol plant in Singapore

Thorough understanding of process technology and tight control of operating parameters can be key to extracting maximum output and efficiency from chemical plants. This has been demonstrated on a monopropylene glycol (MPG) plant in Singapore, leading to a significant capacity increase at a time of high demand.

The debottlenecking of the MPG plant at the Seraya Chemicals complex was driven by a business need for additional capacity to satisfy rising customer demand. High boiling point and low toxicity have led to increasing use of MPG as an environment-friendly coolant for vehicle engines, and MPG is also used in a growing number of pharmaceutical and food applications.
Faced with this expanding market, a combined team from Seraya’s engineering, process technology and operations groups addressed how to expand capacity in the shortest time and at the lowest cost.

Optimum conditions
“One of our technologists, Chao-Yuan Kho, knew the MPG unit like the back of his hand,” said Larry June, Process Technology manager. “He had an idea for
streamlining the reaction process, redesigning the distillation columns and tightening the operating window to really squeeze out every last bit of ‘design fat’ from the unit.”
Kho’s theory was tested with extensive computer simulation and reaction modeling before the project was given the green light. “Theoretically we knew it could work, but there’s always an element of engineering judgment involved in making
final design decisions,” says June. One of the keys to the streamlined reaction process was running the unit within a narrow range of temperatures and concentrations. “There’s a window of operability where, if you can create the right conditions, you can really boost the throughput of feed to the reactor—but it’s like threading a needle.”
The engineering and construction
teams had a window of just 10 days in which to implement the design and engineering work. “It was important that, at a time when there was a lot of pressure from the business to continue producing, the project could be completed with minimal downtime,” explains project manager Keng-Lum Low. “We also scheduled the shutdown to coincide with a seasonal dip in demand.”
Short timescale
The short timescale meant that the scope of the work was continually refined during the project planning and execution. “We were continually evaluating the detail of the design and engineering because we were using a lot of pre-fabricated parts and couldn’t afford to have anything not work or not fit properly once the unit was down. We had to get everything right first time,” Low explains. Low’s team worked closely with contractors and suppliers before and during the work to ensure that the materials and expertise required were available when they were needed. “We tried to anticipate every conceivable situation so
there would be no surprises,” he adds.
Design and equipment changes to the plant included running two special high-pressure feed pumps in parallel, installing a new reboiler and various internal modifications to the distillation columns.
The debottlenecking was carried out with minimal capital expenditure for a project of this type. The result, following a flawless startup and exemplary safety record, was a capacity increase of around 25 percent. The project also took just eight days to complete, two less than planned.
Process technologist Lorel Chow was
responsible for evaluating any impact of
design changes on the process requirements. “Lorel was continually checking
every piece of work to make sure that it
would not create a bottleneck in the process that would have severely affected the success of the project,” says Keng-Lum. “She made a number of timely interventions.”
The plant’s programmable logic controller was also reprogrammed to safeguard the unit within the new operating window. Despite the tight operating parameters there was no impact on the safety and reliability of the unit. “What we have done is still well within the thermal and mechanical design limits,” says Larry June. “The safeguarding measures have also been verified by our Chemicals Technology group based in Amsterdam.”
Future prospects
Product quality was also virtually unaffected. “We have sacrificed some aspects of the reaction conversion but it’s in the parts per million range and does not appear to have any negative impact on the purity of the MPG,” says June. The Seraya plant is governed by Good Manufacturing Practices for all consumer-grade chemicals. The additional capacity is key to meeting existing customers’ needs and developing new markets. “This project is another demonstration of our manufacturing team’s technical capability. The additional capacity will support our existing customers in the Americas, Middle East and Asia, and also go towards pre-marketing in China to set the stage for the upcoming Nanhai chemical complex,” says Olivier Thorel, global business manager for PO and Urethanes. Nanhai, which is due for completion in 2005, includes a 60,000 t/y MPG plant. Further refinement of the process employed at Seraya could
lead to additional capacity. “There are still minor bottlenecks in the process preventing us from reaping the full benefit of this process modification,” says June. “We’re working to identify the bottlenecks and we’re hoping we can realize an additional five percent capacity increase.”