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March 2010 |
All The Rice Stuff |
 GyraMax™ Gyratory Sifter Rice hulls are a valuable byproduct of the rice milling process. Burner fuel is one of the primary uses for rice hulls. In March 2008 a food producer in Arkansas came to SWECO expressing a desire to replace some old competitive gyratory sifter units. These units were being used to screen rice hulls. Because the hulls are so light it takes a lot of screen area to do a good job of screening. The customer had four parallel flow screeners in their screen room. Each sifter consisted of two parallel fed decks, each deck being 40”x120” (102 cm x 305 cm). So each machine provided a total of 67 ft2 (6.2 m2) of screen area. But over the years the machines had become maintenance nightmares. The gear drives required frequent overhauls, and screen changes were very time consuming. To access the bottom deck one had to remove the cover, lift out the top screen frames, lift out the intermediate pan and then finally lift out the bottom screen frames. |
SWECO offered a better way. After extensive testing in the Florence lab we demonstrated to the customer that we could handle their entire flow of rice hulls with only two GyraMax units. Each GyraMax would be a parallel flow model. But unlike the four competitive machines they were replacing, the GyraMax’s would not have complicated gear drives. It was also determined that the GyraMax would have to be shipped “knocked down,” as it would have to be lifted piece-meal to the fifth floor through a hoist way with minimal clearance. Screen changes were still a sticking point, though, as there wouldn’t be enough room in the installation at either end of a GyraMax for replacement of screens. SWECO offered to design and supply three-piece screens to overcome that difficulty. As a first step the customer decided to buy one GyraMax to replace two of the four competitive machines. Perhaps the biggest challenge was that we had to mate up to all existing feed and discharge pipes. Not an easy task! The customer provided CAD drawings of the area. Then the SWECO rep made a thorough |
analysis of the layout to confirm the accuracy of the dimensions and provided SWECO designers with digital pictures of the existing installation. After a few iterations of approval drawings everyone felt comfortable that the design was a workable one. In the meantime, several screen configurations were evaluated and tested before one was chosen for the project. In February, 2009, we delivered the GyraMax unit to the customer. The unit was lifted into place, re-assembled, and installed. Everything lined up perfectly. The machine performed flawlessly in handling the rate and producing efficient separations. The customer was so pleased that they have placed an order for a second GyraMax to replace the last two competitive units. Rice hulls are effectively separated by the SWECO GyraMax
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 Treating Your Wastewater Industrial wastewater discharge is heavily regulated in North America and around the world, enforced with surcharges, fines, and the threat of permit rejections. Some manufacturers are modifying their production processes to produce the minimum wastewater possible, thereby reducing the volume and/or severity of treatment required downstream. But, at the end of the day, there remains a significant amount of industrial wastewater that cannot be discharged "as is". Furthermore, in many plants the wastewater is circulated and re-circulated in other areas of the facility. There may be equipment in place to remove coarse materials, but a significant amount of solids can remain in the circulating water volume. If the solids are abrasive, the result can be expensive as instruments, pumps, right angle pipe elbows, nozzles, etc., can experience severe erosion over a brief period of time. Some plants shut down for one month each year to repair this erosion damage as well as other annual PM work. Eliminating erosion damage, or at least reducing the erosion damage, could limit plant "down-time" and increase productivity. The measures required to treat industrial wastewater are as varied as the industries themselves. Oil, grease, emulsion, complex organic chemicals, biodegradable organics, heavy metals, acids and alkalis are but a few of the undesirable wastewater contents that industrial manufacturers must eliminate or reduce in order to remain in business. Chemical and mechanical methods are commonly employed to remediate wastewater streams, and often both methods are required to attain acceptable discharge clarity. |
For our purposes, we will focus on the mechanical method, primarily the use of decanter centrifuges. As shown in the diagram below, the centrifuge is fed to the right of the machine. The heavy phase (solids) is almost immediately g-forced to the outside of the chamber where it is conveyed to the right, up the Beach, and out the solids discharge ports. The liquid, which is collecting closer to the centrifuge centerline, travels to the left where it is finally discharged through the liquid weirs, and returned to the process, or to the water authority. The difference in speed between the bowl (outer vessel) and the conveyor (helical interior scroll) can be adjusted to optimize the separation result. A high differential speed removes the solids quickly and is often used when the solids are very dense and plentiful, which helps to avoid packing the machine with solids and forcing a shut-down. A low differential speed is used when the specific gravity is low and cake dryness is difficult to achieve. Liquid discharge weirs and pump feed volume can also be adjusted to maximize the performance of the centrifuge. Decanters are currently in use at steel plants where they separate grit, slag, and other heavy solids from water waste streams. Due to the extreme abrasive characteristics of the feed stock, the centrifuges are fitted with sintered tungsten carbide wear protection, and monitored often for wear. Down-time for centrifuge re-conditioning is minimized by keeping a spare rotating assembly (bowl and conveyor unit) on site. When required, the rotating assemblies are swapped out, the repair of the worn-out rotating assembly is performed, and the reconditioned rotating assembly is returned to the site. The centrifuges produce a cake |
 which is transportable, and an effluent which, while not crystal clear in appearance, is essentially free of the abrasive components of the feed stock. The cost benefits of the separation include; re-use of the water, reduced solids disposal cost, and reduced instrument, pump and piping repairs (annually). Plastic re-cyclers consume an enormous volume of water per day. The water is mainly used to clean the raw incoming plastic stock material, which varies from load to load and from plant to plant. Some plants accept everything under the sun; plastic bottles of all sorts, plastic pallets, plastic park benches, trash bins, etc. Other recycling plants are more selective about what they will treat. With the stock material comes varying amounts of un-consumed milk, soda, and other food residue, as well as labels, dirt and unidentifiable substances. Similar in nature to municipal waste dewatering, the liquid/solids separation often requires the addition of coagulant and polymer. The economic drivers for implementation of waste clean-up systems are the regulatory limits which local/regional water authorities place on BOD and water discharge volumes. As with steel manufacturing, the main benefit of cleaning WESP (Wet Electro Static Precipitators) flush lines is to reduce maintenance costs. WESP’s are used to clean smoke discharge from boilers used for power generation. The fuel source from the boilers can be coal, wood, or other flammables. When the fuel source is dirty, such as when wood bark is used, the cost benefits in centrifuging the flush water are extremely attractive. ROI can be realized within one year. |
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Removing solid contaminants from industrial wastewater quite often is an overwhelming undertaking full of surcharges and fees. There are several types of equipment that can help you with this process, and with the proper equipment and the appropriate knowledge you may be able to eliminate a lot of those costs. | |
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Avalanche™ Separator The dual screen design of the Avalanche Separator effectively increases active screen area by up to 67%. The design is simple: a standard diameter frame is modified to accommodate a standard screen on the bottom with an additional, slightly smaller screen above. Material fed to the top screen either passes through the screen or discharges off the side to be rescreened by the lower screen. All particles that pass through either screen are collected and discharged on the bottom |
 SWECO Avalanche Separator spout. The remaining oversized particles are discharged off the bottom screen. The Avalanche frame requires only a 4-inch increase in height over a standard frame with the same footprint. Because of the full 360° discharge off the top screen, a smooth, unobstructed flow is created allowing full benefit of the increased screening area. This |
results in higher flow capacities and standard discharge spouts. The Avalanche is particularly beneficial in dry applications requiring high capacity scalping as well as high efficiency dedusting. |
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