Liquid purification or separation – Processes – Separating
Reexamination Certificate
2001-03-30
2004-08-10
Popovics, Robert James (Department: 1724)
Liquid purification or separation
Processes
Separating
C210S772000, C210S803000, C210S409000
Reexamination Certificate
active
06773612
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a separator and, more particularly, to a sloped screen separator that removes solids from a manure slurry.
2. Description of the Related Art
When waste, such as manure, is washed away with a stream of flush water, a waste or manure slurry is formed. In agriculture, enclosed animal areas are commonly flushed with water. For example, in the dairy industry, the alleys in a freestall barn are typically flushed twice a day with water to clean the manure from the alleys.
The treatment of manure slurry is a difficult and on-going problem in many agricultural settings. One approach to treating manure slurry is to fill large settling pits or lagoons with the slurry. Gravity then pulls the larger solids to the bottom. The surface water, which contains fewer solids, is typically pumped to another lagoon, where the process is repeated. The surface water of the last lagoon is then pumped out to irrigate agricultural lands, such as alfalfa fields, or used again to flush accumulated manure from animal areas.
This approach, while relatively straightforward, has a number of drawbacks. One drawback is that the accumulated solids in the lagoons have to be periodically removed at a significant expense. Another drawback is that the longer the manure stays in suspension within the slurry, the more nutrients transfer from the solids to the water.
This loads the water with very high levels of nitrogen, phosphorous, and salts. A high loading, in turn, limits the amount of irrigation that can be performed, or requires the addition of fresh water to change the loading of the water. A further problem is that a significant amount of gas, such as ammonia and sulfer, escapes from the slurry in a lagoon, thereby contributing to air pollution.
A common modification to this approach is to run the manure slurry through a separator to remove as many solids from the slurry as possible. By removing solids from the slurry, fewer solids are deposited in the lagoons. Reducing the amount of solids that are deposited into a lagoon increases the useful life of the lagoon, reduces the loading of the water (because solids are removed from the water), and reduces air pollution. One type of separator is a sloped screen separator.
FIG. 1
shows a cut-away perspective view that illustrates a conventional sloped-screen separator
100
, while
FIG. 2
shows a side view of separator
100
. As shown in
FIGS. 1-2
, separator
100
has a back wall
110
, and first and second side walls
112
and
114
that are connected to back wall
110
. Side walls
112
and
114
, in turn, have openings
116
and
118
.
In addition, separator
100
has a top panel
120
that is connected to the top ends of side walls
112
and
114
, and a lower panel
122
that is connected to the bottom ends of back wall
110
and side walls
112
and
114
. Lower panel
122
, in turn, has an opening
124
.
Separator
100
also has a ledge
130
that is connected to side walls
112
and
114
, and a trough
132
that is connected to back wall
110
, side walls
112
, and ledge
130
. Trough
132
has a bottom side
134
, and an opening
136
formed in bottom side
134
. Separator
100
further includes a baffle
140
that is connected to side walls
112
and
114
over the longitudinal center of trough
132
.
As further shown in
FIGS. 1-2
, separator
100
has a front edge
142
that is connected to side walls
112
and
114
and lower panel
122
, and a sloped screen
144
that is connected to side walls
112
arid
114
, ledge
130
, and front edge
142
. Sloped screen
144
typically has slotted or circular openings
146
of 1.5 mm (approximately 0.060 of an inch).
In operation, manure slurry is pumped into trough
132
through opening
136
. Baffle
140
spreads the incoming slurry so that the slurry flows evenly over the edge of ledge
130
onto sloped screen
144
. The slurry flows through screen
144
, with screen
144
extracting the larger solids from the slurry.
Gravity pulls the larger solids extracted by screen
144
down the face of screen
144
. The solids accumulate at the bottom of screen
144
, and eventually fall off of front edge
142
where the solids are collected as stackable manure. In the dairy industry, stackable manure has a moisture content of roughly 75-80%.
One problem with separator
100
is that separator
100
is relatively inefficient. Experimental results indicate that separator
100
removes, at best, approximately 16% of the solids in the slurry. Thus, even though separator
100
removes solids from the slurry, large amounts of solids continue to be added to the lagoons.
Screens with smaller openings are not utilized because the solids in the slurry plug the openings. When the openings in the screen become plugged, all the slurry pumped into opening
136
of trough
132
runs down the face of screen
144
and falls off of front edge
142
, causing slurry to be pumped into the work yard. The resulting clean up can be a significant expense. Thus, due to plugging, screens with openings equal to or less than 1 mm (approximately 0.040 of an inch) are considered to be unworkable.
With separator
100
, the slurry falls through screen
144
and is collected by lower panel
122
. The slurry then flows out opening
124
where the slurry is gravity fed to a lagoon. The flow of slurry into opening
124
creates a suction. If openings
116
and
118
were absent or closed, the suction would pull air through screen
144
. The flow of air through screen
144
, however, pulls and holds solids to screen
144
, thereby plugging the openings
146
. Thus, openings
116
and
118
provide an air intake route that eliminates the suction across screen
144
so that larger solids can fall down the face of screen
144
.
Screen
144
is also subject to plugging from hot summertime conditions. When the available slurry has been pumped through separator
100
, solids to varying degrees remain on the face of screen
144
. In hot summertime conditions, the solids quickly dry. When the slurry is again pumped into separator
100
, the initial slurry runs down the face of screen
144
and falls off front edge
142
until the moisture in the slurry unplugs the openings
146
.
One approach to preventing summertime conditions from plugging screen
144
is to mist the face of screen
144
when slurry is no longer being pumped into separator
100
. This can be accomplished by placing a water line with a number of mist heads across the front of screen
144
.
When the water line is connected to a water source under pressure, such as 2.46 kilograms per square centimeter (approximately 35 pounds per square inch) to 3.87 kilograms per square centimeter (approximately 55 pounds per square inch), the mist heads output mist in the range of 2.65 liters per hour (approximately 0.7 gallons per hour) to 4.9 liters per hour (approximately 1.3 gallons per hour). The level of misting should not cause solids to move down or sheet down the face of screen
144
.
Thus, although sloped screen separators reduce the volume of solids that are deposited into the holding lagoons, there is a need for a separator that removes more solids from the manure slurry.
SUMMARY OF THE INVENTION
The present invention provides a sloped screen separator. The sloped screen separator of the present invention includes an input compartment that has an input opening and an output ledge. A manure slurry is pumped into the input compartment through the input opening, and flows out over the output ledge. The separator also includes a sloped screen that is connected to the output ledge of the input compartment. The sloped screen has a plurality of screen openings that each have a size that ranges from a lower size to an upper size. The lower size is greater than a size that requires shaking before the manure slurry will fall through the screen openings. The upper size is equal to or less than 1 mm. The manure slurry flows out over the output ledge onto the sloped screen when the manure slurry is pumped into the input com
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