Issue link: https://www.e-digitaleditions.com/i/1277345
11 www.spirofl ow.com valves, which is a problem that can severely impact a facility's operation, effi ciency, and maintenance costs. To make struvite pellets, the company adds magne- sium chloride and, if necessary, sodium hydroxide to a concentrated dewatering stream and feeds it into a fl uidized-bed reactor, in which minute struvite particles begin to form via a controlled chemical precipitation process. The controlled reaction method and retention time cause the struvite particles to layer and grow in diameter, like pearls, until they reach the desired size, which is typically between 1 and 3.5 millimeters. The pellets discharge from the reactor in a water stream that carries them to a dewatering screen. The pellets are then moved through a dryer with a cyclonic dust collec- tor to remove surface moisture and any dust from the pellets. A bucket elevator gently moves the pellets from the dryer to a three-deck classifying screener, which sizes the pellets into four product categories, each of which is conveyed to a dedicated fl exible-fabric storage silo. An operator later discharges pellets from a silo into a palleted bulk bag, which a forklift moves to a storage area prior to transport to a fertilizer distributor. Finding a bag-fi lling system The company successfully completed several fi eld tri- als using a single-reactor installation to treat a small percentage of the wastewater streams at wastewater treatment facilities, ethanol biofuel plants, and food processing plants in the US and Canada. The next year, the company began planning its fi rst full-scale com- mercial operation for the Durham Advanced Waste- water Treatment Facility in Tigard, Ore. Because this multiple-reactor installation would treat 100 percent of the wastewater stream, the company needed to fi nd a cost-effective and effi cient bag-fi lling system to fi ll 40 tons of pellets per month into polyethylene-lined, 1-ton- capacity bulk bags. "When we fi rst started searching for a bag-fi lling sys- tem, we looked at three different equipment suppliers," says Aynul Dharas, Ostara vice president of projects. "We found one supplier's system better suited to our application than the others. Their bag-fi lling system was robust and simple to operate, requiring just one operator. And the system suited what we were trying to achieve — four silos feeding into one chute to fi ll the bags. It also was the best price, which was another im- portant factor for us, so we decided to purchase one for the Oregon facility." This supplier, Spirofl ow Systems, Monroe, N.C., sup- plies standard and custom powder handling equipment, specializing in bulk bag fi llers and dischargers, mechan- ical and pneumatic conveyors, and a wide range of oth- er material handling systems and equipment. After a bulk bag is fi lled, the bag-fi lling system's powered roller conveyor moves it out of the fi lling zone to an indexing roller conveyor.