Consider Modular Pilot-Plant Construction

Modular construction hasn't gained the role it deserves for pilot plants. Our experience at ExxonMobil Research and Engineering shows that building pilot plants in one central facility whenever possible for shipment and installation around the world makes a lot of sense.

The approach is based on building units in sections that readily can be transported by road, rail or sea depending on the final destination. Road transportation is most common and also most restrictive. Larger modules are possible but become significantly more costly and impose more limitations on routes available. Standard road-transportable sizes are more than adequate for most pilot plants and even small-scale demonstration units. You simply design the modules to be smaller or to come apart for shipment.

Modular construction isn't a new idea; the petrochemical industry has used it for decades. However, it's often just considered for avoiding onsite construction in inhospitable or inaccessible locations like the North Sea or in areas with inadequate infrastructure. In these cases, it may be the only practical option. However, the approach offers many benefits for projects that don't suffer from these obvious handicaps.

Compelling Advantages
Modular construction allows most pilot plants to be fabricated in a controlled environment, typically a shop specializing in modular or pilot-plant and laboratory unit construction. Shop construction always is more efficient than field construction because it can eliminate or at least minimize many inefficiencies and variables affecting productivity.

The work area usually is enclosed and protected from the weather. The room around the construction area generally is more open for access from all sides and is organized for greater efficiency. Section fabrication, layout and assembly often can take place on large worktables. Scaffolding or rolling platforms can surround larger components to reduce inefficient ladder use. Cranes and hoists -- permanent or temporary -- may be on hand to move and place larger equipment. Welding equipment or outlets are readily available.

Temporary construction power is easier to provide and usually already conveniently distributed around the work area. Specialty tools can be justified due to repeated use and result in significant cost savings. Stock rooms, equipment bins and similar materials storage can be set up nearby in a convenient location.

A Good Turn

Figure 1. Laying a modular pilot plant on its side may overcome height restrictions for shipping.

Operating restrictions such as permits, black-out times and access limitations are eliminated -- and with them, the time spent obtaining permits and clearances, accommodating operational needs, keeping traffic corridors open, relocating tools or equipment as operations require and a host of similar issues.

Shop construction also promotes a steady crew size. Field construction often involves obtaining new craft workers, training them in procedures and practices, and then releasing them at project end, losing all accrued orientation and experience. Shop construction frequently can be scheduled to keep the crews for longer periods -- thereby eliminating repeated training and learning curves.

The approach also increases quality because the shop conditions promote better work. Climate control ensures components aren't assembled in high humidity or bad weather that may result in internal corrosion, water or dirt damage. The proximity of specialty equipment allows better quality construction. Inspections usually are easier and more routine.

Our experience indicates that shop fabrication is 20%–50% more efficient than similar field construction. This is particularly true when onsite work would involve cramped spaces, such as laboratory hoods, or exterior locations exposed to weather.

Safety also benefits from the more organized and efficient approach to construction. It helps eliminate potentially unsafe field expedients and shortcuts. The more-open access typical of shop construction reduces ergonomic-related injuries because bending, stretching and contorted positions can be avoided through proper unit placement in the shop. The lack of hazardous materials decreases potential for worker exposure, fires, explosions or spills.

But Resistance Remains
Given these advantages why do companies still resist modular construction?

First there's a perception that units constructed offsite won't fit in their intended location. Horror stories abound, although upon investigation many appear to be more urban legends -- or at least classic cases of lack of adequate planning -- than truly relevant examples.

Modular construction does require more upfront design. You must determine how the unit can be moved into place, not just how to build it in place. This often creates problems because low beams, intruding piping or wiring, undersized doors and a host of similar problems arise. Yet, as anyone who's ever moved into a house knows, these issues almost always have viable solutions.

Modules can be made in sections and easily reassembled in place. You can temporarily remove or permanently enlarge doors. Walls often can be opened by detaching panels or even removing and replacing masonry. You can make modules to rig through roofs or upper walls. Existing site piping and wiring frequently -- with planning and advance notice -- can be economically rerouted or temporarily taken out and reinstalled. Such efforts can add to cost but usually are offset by savings modular construction can deliver.