Home » Cellulosic Ethanol » Manure Incineration
July 28, 2006
Van Der Geest Dairy, located near Wausau, Wisconsin, has developed a unique technology for manure disposal. The farm has 3,800 cows and uses a flush-barn manure collection system.
Bedding, in the form of dried manure, is produced by burning about half of the manure generated by the herd. To do this, the manure from the dairy is first dried to a low moisture content so that it can either be incinerated or used as bedding. The heat released in the incineration process is what is used to dry the manure to low moisture content.
Initial dewatering of the manure is achieved by pumping the manure across two sidehill screens, one curved surface Houle and one flat panel Agpro. Both have 0.080″ slot widths. The narrower, but taller, Agpro is preferred.
Prior to selecting the sidehills, the farm operated both Integrity roller drum machines and the Accent internally fed rotary drum screen. Sidehills won out because of their high capacity and simplicity.
Solids from the sidehills fall into a pair of KP-16 screw presses. The Vincent press was selected, after a nine-month testing program, over FAN, Manure Monster, and Boldt screw presses. Both Vincent and FAN modified their presses numerous times. Efforts by both companies failed to adequately press the manure without prethickening.
Key features that led to the selection of the Vincent press are as follows:
- The KP-16, with its larger screw diameter, has greater capacity.
- There is ample separation between the gearbox and the inlet hopper seal, assuring long gearbox life.
- Vincent presses are available with standard NEMA motors which are readily available throughout North America.
- The Vincent press has removable covers over the screen, making it convenient to pressure and acid wash the screen.
- The screw of the Vincent press is supported at both ends, at the gearbox and at the cake discharge, which assures the screw-screen alignment that is necessary for long screen life.
The cake from the screw presses is conveyed to a system developed by Energy Unlimited. The key component is a Heil triple pass rotary drum dryer. Here the manure press cake, at 70% moisture content, is dried down to 10%.
Next, the dried manure is separated from the gas stream in a cyclone separator. The solids are blown into a storage bin, from which they a blown into a vertical combustion chamber. The solids are burned in the combustion chamber without the need for auxiliary fuel. The products of combustion (hot gasses) are directed into the dryer drum, where they dry the manure press cake.
An induced draft fan draws the gasses through the dryer and combustion chamber. From the dryer, the gasses go to a covered trench. Filtrate from the sidehill screens and press liquor from the two screw presses flows through this 450′ long trench. Particulate and gas pollutants are captured and oxidized, and aeration is achieved. Another induced draft fan draws the gasses through the trench and pushes them to a smoke stack. A white plume of water vapor is generally visible from the stack.
Water from the trench is directed into a treatment pond. The treated water is used for barn flushing.
About half of the dried manure is used as bedding for the cows, with the other half being used as fuel for the combustion chamber.
This unique system for manure disposal is receiving a great deal of attention from environmental specialists.
Issue 176