By David McKee
As economies of scale in grain industry operations have grown in significance, so have the sizes of the average grain storage bin. The larger storage bins have amplified the costs and hazards associated with the regularly scheduled bin clean outs that occur in every well-managed operation.
Sending valuable employees into a grain bin to setup, adjust, operate or trouble shoot faulty discharge equipment is a major safety nightmare for managers. Having these valued employees attack towering piles or broad thick carpets of grain with shovels is an equal horror from a personnel cost and morale standpoint.
A typical maize storage bin with a 70-foot (21.3-meter) diameter and three discharge outlets will have a residual pile of 38,000 bushels (965 tonnes) after gravity flow has stopped. A good manager will avoid sending employees into the enclosed bin to face a pile of grain that risks engulfing them.
Bin entry also poses health risks to employees. Dust levels in the bin can be very high, and the grain dust may contain relatively high concentrations of pesticides, herbicides and other toxins. Recent studies show higher and higher incidents of black lung disease due to exposure in large storage bins during clean out.
Recent advances in clean out systems now have made possible grain bin clean out without personnel entry. One technology leader has been Laidig Systems, Inc. which got its start in the commercial feed and grain industry by offering robust auger-type bottom unloaders that made possible the storage of soybean meal in large concrete or steel silos. The company then adapted its high-powered bottom reclaim technology to grain applications with its CleanSweep system, operating at several grain processing plants.
The Laidig unloaders are engineered to start at the push of a button under full load, and to advance the reclaim auger with continuous undercutting of the material. The pile is cut from underneath to create mass flow, eliminating the bridging problems that normally occur with such cohesive, tough-to-handle materials as soybean meal and other meal type products.
A powerful industrial bin clean out system constitutes a major capital investment for a grain processing facility. Therefore the benefits must be carefully assessed. One benefit too large to quantify is the reduction in liability for health and safety risks.
It is much easier to put a value to grain storage losses. As much as 20% of the grain in a flat bottom bin remains after free flow has stopped. Depending on the aeration system and the moisture content at intake, this grain could become moldy within a couple of months. Payback can be quick when facilities can avoid wasting 10,000 to 40,000 bushels (250 to 1,000 tonnes) of grain.
Improved grain quality is the main benefit of more frequent bin clean out, according to the feed division director of a large poultry integrator in the northeastern U.S. He explained that the Laidig CleanSweep "allows us to keep our corn inventory much closer to first-in, first-out. We are now able to clean our bin every four to six weeks. In a typical operation, a bin gets cleaned out only three to four times per year. We can keep our feed inventory fresher."
A high-capacity automated discharge system can eliminate much of the down time that normally occurs during routine clean outs. Another plant manager using CleanSweep reports that the bin is emptied now in six hours, whereas it had previously taken 60 hours with a combination of shovel conveying and hand clean out.
Convenience is as much a factor as safety, as the bin clean out system starts up while still buried in the grain. There is no need to remove grain covering the motor, drop power cords, get confined space entry permits or do other set up requiring personnel time and entry into the bin before turning it on.
With light duty equipment, the reclaim auger cuts up to the edge of the pile. But bridging may also occur, causing the auger arm to dig down under the pile and requiring the system to be backed out of the pile and restarted.
Alternatively, if the grain pile eventually collapses, lighter-weight bin sweeps can be immobilized, and require digging out by workers in the bin.
At one pet food facility that installed the CleanSweep in early 2002, the facility engineer said automated clean out takes the grain level down to only an inch on the bottom of the bin. "Now we don’t have to do any shoveling, and the clean out hazard to workers was eliminated," he said. "CleanSweep compared to the old light duty set up is similar to the difference between a man with a shovel and one with an automated backhoe — it is night and day."
The payback period to recover the cost of the CleanSweep was calculated at less than three years, the engineer said. This has all come from manpower savings at clean out time.
The CleanSweep now comes in two models. The smaller Model CS210 is for bins up to 70 feet (21.3 meters) in diameter. It offers an auger delivery rate of up to 75 cubic feet per minute. The reclaim auger has a diameter of 14 inches and is powered by a hydraulic reclaim drive of 15hp.
The larger unit is the CS510 and is intended for bin diameters up to 110 feet. The reclaim auger has a diameter of 28 inches and can deliver up to 250 CFM. The hydraulic reclaim drive is 50hp.
Both models have an adjustable reclaim auger rotation of 10 to 80 rpm, and nominal sweep advances of 8 to 24 inches per hour.
David McKee is a consultant for the grain based industries. He can be reached by E-mail at email@example.com.