Onsite construction is used to build or expand most process plants. Whether the project is done in-house or outsourced, the sequence of work is similar: design, facility construction and modification, and process or system construction and installation.
However, a growing number of companies today are turning to turnkey, automated, skid-mounted systems and modules. The systems may offer a host of advantages, reducing overall costs and project timeframes, when compared to onsite construction.
Keeping, and using, secrets
For instance, when I worked for a skid builder from 1986 to 1991, the company had developed a patented software system to perform closed-loop control of sulfur trioxide injected into the exhaust stack of coal-burning power plants. The only way we allowed customers to get this technology was via purchase of skid-mounted units.
Other skid builders have similar stories. "We have over 60 years of experience providing spray systems for virtually every industry. Our understanding of spray applications led us to develop patent-pending control system software specifically for spray applications," says Bill Kohley, the vice president of Wheaton, Ill.-based AutoJet Technologies.
Although many industries use spray systems, these systems are a specialized niche and are generally not a primary plant process. So they are ideal for outsourcing to a skid builder. "Our engineers spend a lot of time in customer plants, and they continually see problems like overspray of expensive coatings, misting, and product rejects. Most customers do not have the background in spray technology to develop effective spray system software," adds Kohley.
Mobile Process Technology (MPT), Memphis, Tenn., has similar reasons for offering its advanced separation technologies on skids. MPT's advanced separation technologies (Fig. 1) provide waste-stream elimination, resource recovery, and remediation to the chemical, petrochemical, polymer, pharmaceutical, and general manufacturing industries.
Figure 1: Delivery & Pick-Up
Mobile Process Technology's proprietary separation technologies provide waste-stream elimination, resource recovery and remediation to many industries. The skid-mounted units often are leased to customers.
Offsite offers benefits, but requires up-front planning
Labor efficiency is another benefit of off-site construction. Operating plants introduce a host of inefficiencies including security gate check-in, compliance with union work rules, work-permit procurement, and coordination with plant operations and other crafts. This means that a craftman's 8-hr day at an operating industrial plant typically translates into no more than six hours of productive time at the actual work site.
Not only can off-site craftsmen devote more hours to actual work, they are often more efficient because they work on the same types of systems every day. "Skid-builder personnel are extremely efficient because they are always building similar equipment," says Flemming Larsen, automation project manager for Novo Nordisk Engineering (NNE) in Copenhagen. "Skid builders often use an assembly-line approach to manufacturing, which is much faster and less expensive than on-site custom and one-off construction."
NNE designs and builds pharmaceutical plants, and uses pre-built skids and modules whenever possible (Fig. 2). When skids are used in new construction projects, overall construction time can be greatly reduced. "Buildings and utilities can be constructed while skids are being built instead of waiting until the building is ready for occupancy and then starting construction," adds Larsen. "On a recent project, this trimmed the schedule from 32-36 months to 18 months."
Figure 2: Parallel Processing
Novo Nordisk Engineering designs skids and modules in pharmaceutical plant construction whenever possible. A recent project schedule was trimmed from 36 months to 18 months because module-building was done in parallel with facility building.
Reliance on skid builders also reduces on-site interference among different processes and systems. "When construction takes place on-site, it is often necessary to construct separate systems in a more sequential fashion as compared to off-site skidded systems, which can all be built at the same time," adds Larsen.
When processes must be added to existing plants, skid-mounted systems are often the only good answer. Houston-based Hutchison-Hayes' centrifuge skids (Fig. 3) are often purchased for installation on operating oil-production platforms. "The very nature of this business environment dictates that the equipment have an efficient skid-mounted modular design in order to be integrated into the drilling system with as little effort as possible," observes Gary Hensley, executive vice president of Hutchison-Hayes.