TECH SPECIAL...... Lessons learned in commercial scale-up of new chemical processes (4)

Lessons learned in commercial scale-up of new chemical processes (4)

Sequential vs. parallel engineering

Ideally, all of the information needed to commit to a pilot plant, demo plant or commercial plant is known when the decision is made. Sometimes, this is not the case. Some part(s) of the process are not as well defined. However, pressures caused by the market’s window of opportunity, fund shortages or other factors make it necessary to commit to the start of design.

The risk associated with this situation can be mitigated when prior art can be relied upon to develop a design. More than one solution is often feasible, and each solution must be developed, cost-estimated, technically assessed and risk-ranked. The most common approach is to rank all options based on a team assessment after one or more brainstorming sessions, and then develop and cost out the first (or best team-assessed) option.

The evaluation is ended if the first option is found to be technically and economically feasible. If it is not, then the next option is assessed, and so on. This process can be termed “sequential engineering.” The risk with the sequential approach is extended time. In “parallel engineering,” more than one option is examined concurrently, cost-estimated and technically assessed. The risk with the parallel approach is waste of labor if the first option turns out to be acceptable.

It is important to remember that these activities are being performed while a task force of tens to hundreds of engineers and designers are spending money developing design for other parts of the process. The author favors the parallel approach, as it limits the time to solution at a limited increase in engineering cost. Process engineers with front-end engineering and design (FEED) experience are comfortable with either approach. Unfortunately, other engineering disciplines and project management often favor the sequential approach, as they are asked to focus on one task at a time.

Backup option

Engineers are often faced with choosing between multiple options, none of which can be ruled out. As an example, multiple vendors may have equipment components that appear to be technically suitable for a certain step in the process. Unfortunately, very large quantities of material are needed to test each unit on a continuous basis under actual conditions, which requires commitment to a large-capacity, expensive demo plant.

This cost may not be justifiable if the only reason is to produce the required quantity of material for such a test. In this situation, it is feasible to select the top two options, design the unit based on the first, and allow flexibility in the design to replace the system with the second option. Obviously, this process will require a shutdown and added costs. A team of experts and engineers are used to select the top two options.

CONTINUES

Jazayeri, B., Reacxion http://www.hydrocarbonprocessing.com/magazine/2016/october-2016/process-control-and-instrumentation/lessons-learned-in-commercial-scale-up-of-new-chemical-processes