Dairy producers can use Rotary Drums to separate solids from the manure stream for a variety of reasons, including regulatory compliance, nutrient management, ease of manure application, or to produce flume or sand separation make-up water.
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Rotary Drums are used for a variety of applications, including food processing and manure thickening and separation. Some of the other applications include dairy manure separation for nutrient management, thickening manure pre-digestion, food processing, and debris and tramp material removal.
Rotary Drums separate manure into two components: a thicker portion of concentrated manure solids, and a less concentrated liquid portion.
Liquid-solid separation using a Rotary Drum is a simple process, widely used across many industries. Some of these industries include wastewater, dairy, and food processing.
Several key components make up a rotary drum separator. The cylindrical drum containing the screen sections is where separation occurs. It usually has blank portions at each end that allow it to rest and rotate on trunnion wheels. These wheels rest on bearings, which are isolated from the process material. Power from the motor is transmitted to the drum through a banded belt system, which provides the rotational movement of the drum. This rotational movement of the drum is necessary to continually introduce clean screen to the liquid and advance material through the drum. The belt drive system keeps the drum rotating while providing some safety if the drum is overloaded. A support frame and shielding provide a means to support the drum and drive system, while also containing the liquids and solids and directing them to the appropriate location. Safety is also accomplished by these shields.
Liquid containing the materials needing separated is pumped into the inlet feed section of the rotary screen. A large portion of the liquid and fine particles pass through the screen, while materials larger than the screen openings are captured on the screen. The combined rotational movement of the screen and internal flighting push the material from the inlet section to the discharge. As the material moves to the discharge, it begins to tumble, releasing liquid along the way. The dewatered material discharges from the end opposite the feed end and is either processed further or conveyed to a storage location.
The Rotary Drum's unique modular design can be engineered to meet the specific manure separation requirements of most dairy operations, including those with existing Sand Separation Systems. Extensive testing has proven that McLanahan Rotary Drums will remove up to 35 percent of the total solids based on the manure's total solids and screen selection. They improve water quality for use in sand separation, flush flume supply and land applications. Designed for safe and simple operation, Rotary Drums are totally enclosed for safe and clean operation. The internally fed rotary screen includes an automated, high-pressure, clean-in-place system that keeps it operating at peak performance. The drum rests on four heavy-duty trunnion wheels. The one-piece wheel and shaft design is supported by triple-shielded bearings. Unlike other trunnion systems, this one is designed in a way that the bearings do not operate within the path of the manure, ensuring they will have a long service life. A centralized remote grease bank allows for quick greasing of the bearings. Months of testing and years of operational experience has proven that the McLanahan Rotary Drum Separator is one of the most efficient and cost-effective machines to remove manure solids and clean up process water.
Processing rate is based on the screen opening size and material being processed. This chart shows processing rates for dairy manure.
The standard clean-in-place system uses a high-pressure boost pump to provide water pressure higher than tap pressure for small periods of time throughout the run cycle. This chart shows the average flow rate used during the operating cycle.
Separating dairy manure is not simply a particle size differentiation process. It looks more like a thickening process where a mixture of liquid, large and small fibers are captured on the screen, which usually involves about a 1% reduction of total solids in the manure liquid. If the feed total solids is 8%, the liquid exiting the drum will be about 7% total solids.
This is a good question and one that we get asked a lot. The answer to it really depends on what you are trying to accomplish.
A screen with openings 1/8” and larger is considered a coarse screen and is used to primarily remove the larger manure particles. This screen would be used if you’re trying to keep some material out of your lagoon, or maybe you’re looking to make some green bedding and you’re also using a Roll Press. In either case, this screen would remove the larger particles, but the overall capture of fibers would be relatively low, most likely less than 20%. If you’re looking to remove as much material as possible to create clean process water, we would recommend the 18 mesh screen. This has the smallest openings for our standard screen offering and also produces the cleanest process water. The overall removal of fibers with this screen could be as high as 45%. This 18 mesh screen is also a great option if a high removal rate is necessary before putting the manure through a nutrient separation system. Roll Presses are often used to dewater the thickened material coming off the Rotary Screen. If an 18 mesh screen is used, the Roll Press will have more difficulty dewatering the material due to the large amount of fine fibers that are present.
Feel free to contact our Engineering Department if you still have questions about selecting the appropriate screen for your Rotary Drum.
Rotary Drums are used for a variety of applications, including food processing and manure thickening and separation.
