Debottlenecking Takes A Broader View

Modeling is gaining a greater role in improving throughput and energy efficiency.

By Seán Ottewell, Editor at Large

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UniSim also has helped with new controls and procedures at Porvoo. In one case, after a steam loss caused a plant shutdown, the simulator was used to develop a mitigation practice to allow operations to be maintained if the same thing happened again. Similarly, UniSim has served to test and optimize a new fuel-gas lineup and controls -- allowing a flawless hot cutover.

Honeywell also is seeing a rise in demand for debottlenecking procedures associated with less traditional technologies such as shale oil extraction.

"In Alberta, for example, there is a lot of growth in steam-assisted gravity drainage. A lot of new plants are being constructed there with a potential need for debottlenecking in water treatment, oil handling and steam generation. Such processes are very heat integrated, presenting good opportunities for process and capital cost optimization. But this is a very industry-specific, localized example," explains Pete Henderson, product manager for the simulation business.

A less-localized example of increasing demand is in power generation, particularly for new clean coal technologies. "A lot of these essentially involve the gasification of coal and are becoming more like chemical facilities themselves. There are some different unit operations involved in gasification, some peculiarities, for example, coal crushing and gasification equipment. You also have to consider the hardness of the coal, its particle characteristics; these are fundamental things. So UniSim has to move, too," notes de Jonge.

A urea-granulation debottlenecking project illustrates another new area. Here, the company used a third-party simulation package but transferred the operating conditions from a UniSim design. "It's a very extensible product, which makes it very customizable," adds Henderson.

EXPANDING DEBOTTLENECKING EFFORTS
Process Systems Enterprise (PSE), London, U.K., also is benefiting from broader work in debottlenecking.

One key business area is purified terephthalic acid (PTA) production, where its flagship gProms high-fidelity predictive modeling platform is at the heart of debottlenecking activities.

"We are doing work with a lot of PTA manufacturers on a range of different options -- on one level adjusting concentrations of feedstock, on a second level redesigning internal configurations of, for example, feed locations, during shutdown. Depending on the price of paraxylene and acetic acid feedstocks, these can yield $2–4 million/yr in reduced feedstock costs," says Mark Matzopoulos, chief operating officer and marketing director. The payback period typically is 6–12 months, depending on whether the project requires capital expenditure.

A recent success has come from its work with Spain's Repsol, which is working on a new hydrogen peroxide to propylene oxide (HPPO) process to compete against those being developed by other manufacturers.

"We have been carrying out model-based optimization of the reactor and separation sections. The key here is the complex multi-tubular reactor, which is difficult to design to give uniform performance across the tube bundle (Figure 2) -- it is also very difficult to model. Poor design leads to unwanted side reactions and the potential for hot spots. So we constructed a flowsheet that included a high-fidelity multi-tubular reactor model and a separation section with many columns, and performed a rigorous economic optimization that maximized annual profit as the objective function," explains Matzopoulos, who adds that PSE specializes in reactor optimization of all kinds.

This model involved 49 decision variables, which is way beyond what anyone has done before, he claims. It included, for example: reactor design decisions such as tube diameter, pitch and quantity; distillation column operating decisions such as reflux ratios and pressures; intermediate stream purities; and configuration decisions such as number of trays.

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