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Few plants, especially older ones, have unused space where a new process system can be installed while the old one is still running. Existing facilities are often "trapped" by the way their plant matured from mostly manual handling and processing to partial automation.
Equipment layout tends to spread out over time, simply because existing equipment is in place and rearranging it can be expensive and disruptive. Thus, there is design pressure to locate new equipment remotely in order not to disrupt existing production while a process is upgraded. As the plant layout evolves, delivering or conveying materials becomes more complex. Longer runs, torturous paths and tight spaces all constrain the selection of materials handling, which expands the project cost and complexity by requiring materials to be moved a longer distance.
This push on scope and cost is often a compounded cost. For example, an existing plant has process Step A, Step B and Step C located in reasonably close proximity. Moving Step B away requires conveyance from A to B, and from B back to C-conveyance, times two.
For most production plants, serious process improvement means a planned outage of sufficient duration to allow for on-site dismantling, the installation of new equipment, power and control wiring, testing, and troubleshooting. However, many small- and medium-sized plants or processes may have an alternative to site-built systems. Pre-engineered, pre-built processing systems can minimize the interruption of production while reducing the total cost of an upgrade.
Skid-mounted wet systems are common in chemical processing because pumps and valves for liquids are usually relatively small. Pre-built systems are much less common in industries where dry materials are processed, in part because the associated equipment tends to be physically larger. Yet for many plants, the modular design of dry processes is the path to success for a process upgrade or even new process installations.
HeadroomVertical space is often not well used in older plants where manual labor was the norm, with good reason. The operator is safest and most productive on the floor, and raw materials mostly come to the process at floor level. In addition, maintenance at floor level is easier and requires no expenditure on access equipment.
That underused headroom might be put to effective and efficient use, however, even in a plant with only 10 or 12 ft of height available. With careful planning, vertical space can be used to reduce the process footprint and still provide functional access for inspection and service. A vertical design that takes advantage of gravity flow reduces or eliminates the need for conveyors.
FootprintCombining available headroom with a small footprint yields several process advantages for dry product processing. Shorter chutes can be steeper for dependable gravity flow. Shorter conveyors require a bit less power and-more importantly-perform better. A short screw conveyor needs no hanger bearing, and a short vacuum conveyor can operate at high vacuum and low velocity.
Few dry processing systems will fit on a single skid, but a skidded module can serve as the anchor for a compact system. Figure 1 shows the anchor module for a compact system design. This skid contains the major process equipment, including feeders, crushers, screeners, pulverizer, packaging and the process control panel.
This fully automatic system can replace decades-old equipment, where cumbersome portable conveyors were tried in an attempt to relieve the operators from feeding the process equipment via scoop and bucket. Careful design of the new system allows the anchor skid to enter the existing process room without modifying the 8-ft-high door, yet service access is maintained to all components.
Figure 2 shows the same system fully installed. The several items located off the skid need only to be reconnected to the conduit in place on the skid. After a quick check of the direction of rotation, the system is ready to process, having already been fully tested at the factory.
The same discipline can be used for larger systems. Modular process towers with modular decks and a handrail can speed installation. If the site allows passage of large assemblies, smaller towers may even be delivered with some of the process equipment already in place on the deck modules.
Figure 3 shows a powder production system that was erected adjacent to an existing calciner, in the space previously used to store barrels of powder waiting to be calcined. This compact design actually increased the availability of floor space by eliminating four batch ball mills and the space for in-process drums. Mechanical installation was accomplished in a few days, with wiring/piping taking a few days more.
Operators no longer handle the coarse material directly; material is now dumped and fed automatically. Coarse crushing, tertiary crushing, screening, pulverizing, air classification, and conveyance to the calciner are all done automatically and continuously. The operators are relieved from crude manual labor, the plant is cleaner, the finished product is more uniform, and throughput is higher.
Pros and ConsModular design has some perceived disadvantages. Because many of the field functions are moved to the fabrication shop, the equipment cost seems higher; however, installation costs are almost always much lower. The modular approach can also be limited by process size and site constraints. Fully pre-built systems are limited in throughput, but modular systems are valid for all but very large process requirements.
If the only access to the location for the new equipment is through a very narrow path or by elevator, pre-building may not be cost effective. In addition, modular design can result in reduced access for inspection and maintenance. However, careful design can accommodate the inevitable need to inspect, service or remove equipment.
Advantages of modular design and construction include:
- Minimized length and size of conveyors, floor space, and headroom
- Reduced length of dust collection branches
- Offsite primary testing of the process and controls
- Lower onsite installation costs
- Shorter installation and system startup time
For more information, contact Applicon Co. Inc. at 450 N. Somerset Ave., Indianapolis, IN 46222; call (317) 635-7843; fax (317) 635-7853; email firstname.lastname@example.org; or visit www.appliconco.com.