Drying and gas or vapor contact with solids – Apparatus – Gravity flow type
Reexamination Certificate
2000-01-13
2001-03-20
Wilson, Pamela (Department: 3749)
Drying and gas or vapor contact with solids
Apparatus
Gravity flow type
C034S168000, C034S177000
Reexamination Certificate
active
06202319
ABSTRACT:
BACKGROUND OF THE INVENTION
(i) Field of the Invention
The present invention relates generally to grain drying equipment. In particular, the present invention relates to a heat exchanger that utilizes the moist hot exhaust air from a grain dryer to pre-heat ambient air prior to entering the blower of the grain dryer.
(ii) Description of the Related Art
Grain dryers are generally well known in the art. A typical prior art grain dryer is shown in FIG.
1
. which is a cut-away view of a single blower and single plenum grain dryer. Most grain dryers in use today utilize this design or variations on it.
Grain dryers of the type shown in
FIG. 1
are known in the prior art and therefore its construction and operation will only be generally described herein. The typical grain dryer is constructed from steel and sheet metal. The major components of a typical grain dryer
11
include: a blower
10
, a top conveying auger
12
, grain columns
14
, an air plenum
16
, inner porous walls
18
, outer porous walls
20
, a lower conveying auger
22
, and an air heater and an air mixing chamber
24
.
A typical grain dryer
11
operates by receiving a supply of wet or moist grain from a separate conveyor (not shown) at a top opening of the dryer and transporting the wet or moist grain across the top of the grain dryer
11
via the top conveying auger
12
. The grain then flows by gravity downward from the top conveying auger
12
, down through the grain columns
14
where it is dried and then to the lower conveying auger
22
. The dried grain is then transported via the lower conveying auger
22
to a bottom opening of the dryer and out of the dryer
11
.
The grain is dried in the grain dryer
11
via the flow of hot dry air through the grain columns
14
. The grain columns
14
are separated from the air plenum
16
by the inner porous walls
18
, are separated from the exterior environment of the grain dryer
11
by the outer porous walls
20
, and are separated from other adjacent grain columns
14
by inner panels
26
. Ambient air is drawn directly from the exterior environment of the dryer and into the grain dryer
11
via the blower
10
. The blower
10
blows the ambient air through a heating chamber
24
where the ambient air is heated as it flows through the heating chamber. The heated air is then blown through an air mixing chamber
24
to ensure that the air is evenly heated. The thoroughly heated and mixed air hen flows into the air plenum
16
. The action of the lower
10
blowing air into the air plenum
16
causes the air pressure in the air plenum
16
to rise to a pressure higher than that of the atmospheric pressure of the exterior environment of the grain dryer
11
. The higher pressure in the air plenum
16
causes the heated air to flow through the inner porous walls
18
of the grain columns and into the columns
14
. The heated air then flows through the grain that is moving downwardly through the grain columns
14
and then out through the outer porous walls
20
to the exterior environment of the grain dryer
11
. When the heated air flows through the grain passing through the grain columns
14
, moisture is extracted from the grain by the heated air and is conveyed to the exterior environment of the grain dryer
11
. Therefore, as the grain flows downwardly through the grain columns
14
and hot air is passed from the air plenum through the inner porous walls
18
, around the grain and through the grain columns
14
and out through the outer porous walls
20
to the exterior environment of the grain dryer
11
, the grain is heated and moisture is removed. The desired moisture content of the grain exiting the grain dryer
11
via the lower conveying auger
22
can be controlled by altering the flow rate of grain leaving the grain dryer
11
which controls the rate that grain passes downwardly through the grain columns or by changing the temperature of the heated air being blown into the air plenum
16
.
A disadvantage of this typical grain dryer
11
is that the moist hot exhaust air leaving the grain columns
14
via the outer porous walls
20
exits to the exterior environment of the grain dryer
11
while it is still at a temperature substantially above that of the ambient air being drawn into the grain dryer
11
. Therefore, significant amounts of energy can be wasted by the exhausting to the exterior environment of the grain dryer
11
moist hot air that is still capable of heating grain and possibly absorbing additional moisture.
Another type of grain dryer is shown in the Noyes et al. U.S. Pat. No. 4,268,971. This grain dryer has both a heating and a cooling mode. This is accomplished by dividing the typical single air plenum into two vertically separated chambers. The grain is heated and moisture is removed in the upper half of the dryer by blowing heated air through the upper chamber of the plenum, through the inner porous walls of the upper half of the grain dryer, around the grain and through the grain columns and out through the outer porous walls of the upper half of the dryer. The grain is cooled in the lower portions of the grain columns by the blower drawing ambient air through the outer porous walls of the lower half of the grain dryer, around the hot grain and through the grain column and through the inner porous walls of the lower half of the grain dryer and into the lower chamber of the air plenum. This cooling air, which is now partially heated and containing moisture removed from the grain, is then drawn from the lower chamber of the air plenum into the blower and mixed with ambient intake air being drawn into the grain dryer to be heated and used to dry grain. This grain dryer also includes a structure for recycling the moist hot exhaust air exiting the grain drying section of the grain dryer along with partially heated air from grain cooling. The moist hot exhaust air is directed to the intake of the blower. The moist hot exhaust air is mixed with the ambient air and with the partially heated air from the second chamber of the air plenum that was utilized to cool the grain. Thereby, the air entering the heater is significantly warmer than that of the ambient air and requires less energy input from the heater section to effectuate the drying of the grain. A significant disadvantage of this grain dryer is that the moist hot exhaust air that is being mixed with the ambient air and with the partially heated air from the lower chamber of the air plenum has a high moisture content. The high moisture content is a direct result of the heating of and moisture extraction from the grain. Since moist hot exhaust air already has a higher moisture content, its additional moisture holding capability is less than that of the cooler and dryer ambient air. Likewise, the partially heated air from grain cooling also has an elevated moisture content above that of the ambient air. Therefore, while requiring less energy input to obtain a desired air temperature, the moisture removing capability of the heated air being used to dry grain is reduced. Therefore, the grain flow rate through the dryer will need to be reduced or the amount of air flowing through the grain dryer will need to be increased to compensate for the reduced moisture holding capacity of the heated air resulting in limited overall savings of energy or time, and possibly reducing grain throughput.
Some grain dryers utilize two blowers in conjunction with a two plenum grain dryer. These grain dryers also have a heating mode and a cooling mode. One blower is connected with a heating element in order to blow heated air into the upper heating air plenum and through the grain column to heat the grain and remove moisture. The other blower is utilized in conjunction with a lower cooling air plenum. The cooling mode takes ambient air and blows it into the cool air plenum and through the lower half of the grain column, thereby cooling the heated grain.
Heat recovery systems are available on these dual fan/dual plenum grain dryers. These heat recovery systems typically direct the air exiting the cooling portio
Howell & Haferkamp LC
Wilson Pamela
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