Growing rates of manure produced from large dairies have increased concern for
the environmental quality of nearby streams and watersheds. Typically the manure from
the freestalls on these dairies is flushed with water to a mechanical separator. Here,
flushed dairy biomass (DB) is parted into separated solids and separated liquid. The
separated liquid is discharged into lagoons for treatment and eventual land application.
This thesis proposes thermodynamic models for firing DB in small scale boiler
systems that would eliminate land application and lagoons, which are being claimed to
be the source of nutrient leaching and overloading.
Fuel analysis of flushed DB from a dairy in central Texas show that it contains
93%moisture (%M), 3%ash (%A), and 4%combustibles (%Cb), while separated DB
solids contain 81%M, 2%A, and 17%Cb. The dry, ash-free higher heating value of DB
is approximately 20,000 kJ/kg. Using dry, ash-free results, computations can be made
over ranges of %M and %A. For example, DB containing 70%M requires 9.74%Cb to
vaporize all moisture and produce gaseous products of combustion at 373 K, but requires
17.82%Cb to burn in a regenerative combustor with a flame temperature of 1200 K. Separated solids that are pressed in an auger to 70%M (3%A and 27%Cb) can
burn at 1200 K with exhaust temperatures of up to 1130 K and a minimum required heat
exchanger effectiveness of 15%. Pressed solids can thus be fired in a boiler, where the
remaining separated liquid can be used as feed water. The pressed solids only can
release about 30% of the heat required to vaporize the remaining unclean feed water.
However, pressed DB solids can be blended with drier fuels to vaporize almost all the
unclean water. The low quality steam produced from the unclean water can be used in
thermal processes on the farm.
A similar system can be developed for vacuumed DB without the need to
vaporize unclean feed water. As for large dairies with anaerobic digester systems
already installed, directly firing the produced biogas in a small scale boiler system may
be another way to similarly vaporize the remaining effluent.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/4844 |
| Date | 25 April 2007 |
| Creators | Carlin, Nicholas Thomas |
| Contributors | Annamalai, Kalyan |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | 1463829 bytes, electronic, application/pdf, born digital |
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