A major North American brewer recently sought an improved process for handling the dry grain dust that is a by-product of the brewing process - with a goal of transforming this costly waste stream into a profit stream by converting it into a marketable secondary product. With a Moyno High Solids Pumping System, the brewer was able to achieve this goal.
The Situation
In the beer-brewing process, dry hops and grains are injected into the brew tanks, creating a significant amount of dust. Each brew tank is ventilated, using a ventilation system that exhausts through a bag filter to capture airborne solids.
Disposing of the dust is a costly process. It is stored in a silo, then loaded into trucks for transportation to a landfill. Filling the trucks from the silos once again generated a significant amount of dust which, since at this point there was no ventilation system, spewed everywhere. In addition, dry grain dust poses an explosion hazard.
The brewer attempted to wet down the dust solids to minimize dust spread, but the positive displacement pump technology required excessive amounts of water to get the solids to pump. Since freight cost is based on weight, shipping the excessive water become very expensive. Another solution was needed.
The Solution
The best option was to convert the dry dust to a saleable by-product. Spent grain -- the moist solids from the cooked grains after the brewing process -- is the main such by-product, marketed as animal feed. If the dust could be moistened to the right consistency, it could be metered into the spent grain stream, thereby allowing the dust solids to be sold for a profit. Moistening the dust would also diminish its explosive nature. So mixing the grain dust solids into the spent grain was the best option.
The brewery needed a viable option to take the dry dust solids from the silo, economically convert it into a viscous paste, and then combine it at a low ratio with the spent grain stream located 70 ft away. Realizing that the current pump technology was not feasible, the company''s engineers decided to try the Moyno® 2000HS -- High Solids Pumping System.
With an integral twin-screw auger feeder and specially designed progressing cavity pump, the Moyno 2000 HS System efficiently handles high solids, semidry material. The self-cleaning twin-screw feeder easily provides a constant, pressurized feed rate into the Moyno® G4 Progressing Cavity Pump elements, which provides a steady, non-pulsing flow for significantly lower operating pressures. The resulting 100% pump cavity fill rate enhances overall system performance and cost efficiency. The twin-screw feeder also eliminates the need for a feed pump or extended augers common to lengthy, competitive, open-throat progressing cavity pumps.
How the System Works
Most positive displacement pump manufacturers claim they can pump a product as long as they can get it into the elements. Since the only thing a pump element can do is pull a vacuum, atmospheric pressure is required to push the product. The maximum benefit of atmosphere is 14.7 psi minus the pump''s Net Positive Suction Head Required (NPSHR). This available inlet pressure is extremely limited considering that super viscous materials have high line losses and there are numerous unknowns in trying to predict if a product will bridge or rat hole. Atmospheric pressure alone is not enough to get the material into the pump; in this case the brewer needed to water the solids down significantly. Due to limitations on the suction side of the pump, innovative and sophisticated means are needed to get non-flowable products into the pump elements.
The Moyno TSF has a wide surge zone and a pressure tube section that is capable of generating a positive stuffing pressure. Depending on viscosity, the TSF can generate up to 30 psi stuffing pressure into the G4 pump elements. The suction side of the Moyno G4 pump is specially designed for high viscosity. The pump inlet has a wide sweep radius, and the pump''s universal joint is located outside the product flow path, allowing for an unobstructed feed into the element. The rotor''s patented auger gives the viscous product a final boost into the elements.
The significant stuffing pressure of the TSF, together with the G4 inlet design, provides excellent fill efficiencies to the pump elements on viscous, non-flowable products. The Moyno G4 pump is designed to generate the required discharge pressure, up to 1,000 psi, to move the viscous material through the discharge piping. The flexibility in geometry of the twin screw feeder and the Moyno progressive cavity pumping principle allows the pump system to be easily modified. With this flexibility, the Moyno 2000 HS pump system can be designed to fit any application, instead of trying to force the application to fit the pump.
The twin-screw feeder length and hopper size offered considerable flexibility for surge capacity. Since the auger screws worked in an intermeshing action, the brewer considered whether the twin-screw feeder could also be used as a mixer, thereby saving large capital requirements for a high viscosity mixing tank.
The Moyno 2000 HS system was set up as a batch-type sequence. Water was injected through multiple spray nozzles into the twin-screw feeder. The dry solids grain dust was added to the twin-screw feeder hopper at a controlled speed through a rotary valve.
By running the twin-screw feeder of the 2000 HS system in reverse, the intermeshing augers continuously rolled the solids over and over, thereby effectively mixing the solids with a controlled amount of water. To automate the system, feeder RPMs and drive torque were monitored. Solids or water were added to the mixture until a set torque was achieved, indicating the paste had sufficient consistency.
After mixing, the directional rotation of the twin-screw feeder was reversed and it began stuffing the viscous paste into the suction housing of the pump. A pressure sensor at the inlet of the pump sensed the stuffing pressure. Once the suction pressure achieved the setpoint, the pump was energized and the grain dust paste was metered into the spent grain stream.
During operation, the twin-screw feeder speed could also be controlled off the suction pressure sensor to maintain a constant and positive stuffing pressure. A level sensor monitored the twin-screw feeder hopper fill level as the twin-screw feeder hopper was pumped down to low level. The augers were then reversed; water and solids were added for the next batch. Typical batch cycle time was less than 20 minutes.
The Conclusion
After startup, Moyno upgraded the twin-screw feeder shafts from packing to mechanical seals to better handle the light viscosity during the initial water phase of the batch sequence. Except for this conversion, the system has been in operation for two years with no spare parts used. The brewer estimated the payback period for the project was approximately 7-9 months.
The Moyno® HS system proved to be a robust and reliable solution for pumping the highly viscous grain paste. Not only did the brewer find a practical, effective solution for its dry grain dust issue, but it also turned a costly waste into a revenue stream. For moving high solids content, the Moyno® 2000 HS System is a cost-effective alternative to expensive, high-maintenance piston pumps, conveyors, and other types of positive displacement pumps.