POWDER GAME TWO SIMULATOR
But when you come down in mass flow, the fine and the course particles meet at the outlet and they re-blend.Sandbox – Physics Simulator is a Point-and-Click, Arcade, Object-Simulation, and Single-player video game offered by Eggae True Love. If you have a silo that predominantly discharges from the center, you’ll get the fine powder first, then the course material, and the blend is lost. So how you discharge from a vessel is important. “The finer powders move to the center in a vessel, and the course powders roll off to the periphery. So, when goes to fill this mix into packets, some of the packets get a lot of sugar, some get a lot of citric acid, some get a lot of vitamins because of particle separation,” Maynard explains. “The powders can separate by size, shape, or density. Separation will occur if there is funnel flow. But those drink mixes, along with other products that start as mixed powders, like vitamins, will only discharge fully mixed if the hopper is working in mass flow. One of the fastest-growing segments of powder processing is packeted drink mixes, where different types of powder are mixed-sweetener, flavoring, nutritional/functional granules, etc.-and dispensed into packets through a hopper. “An operator can only realize about 10% to 20% of a hopper’s capacity if there is ratholing.”
I don’t care how much you hit the side of a hopper with a sledgehammer, you’re not going to break a rathole-that material is stuck and stagnant,” says Maynard. It can only flow down through itself in narrow tunnels, overcoming its own cohesion to open up this vertical channel. “Ratholing is fundamentally due to the particles not flowing along the walls of the hopper and being stagnant. Ratholing doesn’t happen with mass flow-only funnel flow, according to Maynard.
Ratholing-named because the vertical tunnels that form within stagnant material resemble rat burrows-happens when powder sticks together due to environmental humidity or moisture being present, and on an industrial scale can be a costly problem.
Poor powder and bulk solids handling-which includes environmental factors in a processing facility-can affect production costs, time to market, and worker safety, says Eric Maynard, vice president at Jenike & Johanson. “If you shake it, guess what happens? Even less chance of flow because you’re just packing the material in tighter with nowhere to go,” he says, adding that an easy way to see bridging in action is at a hotel breakfast buffet, where the cereal dispensers stop working because flakes or puffs, for example, are interlocking and bridging together over the discharge area. Maynard says applying a sledgehammer or having a vibrating hopper to shake the material loose doesn’t work when bridging occurs. The Roman aqueducts, for example, use bridging to hold those arches in place.” Big rocks or material of different sizes literally form an obstruction over an outlet, and they lock together. “Some materials don’t like to flow, they don’t like pressure, and they tend to interlock,” Maynard says. Not all powder and bulk solid jams are created equal, so Maynard detailed the most common obstacles in a hopper that everyone in the industry should be able to identify, and why that material ends up blocking the discharge of product. All because they were trying to get sticky material out of the hopper.” They can get tennis elbow or a hurt shoulder from using a sledgehammer,” Maynard explains, “or, as was the case with a project I worked on years ago in West Virginia, one operator accidentally hit another operator in the head with a sledgehammer. “I’ve been involved in projects over my nearly three decades of doing this, where an operator was injured.
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