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Anhydrous Ammonia
General Description
All plumbing components have a certain amount of restriction.
These restrictions cause a pressure drop which allows some
of the anhydrous ammonia to partially vaporize as it flows
from the tank. The amount and density of the vapor can
vary greatly, therefore vapor cannot be accurately measured.
The purpose of the NH3500 system is to condense the vapor
back into a liquid which can be accurately measured and
controlled.
The system uses standard plumbing from the nurse tank.
Material from the applicator’s brake-a-way coupler hose
enters the NH3500’s shut-off valve through a strainer and
flow into the heat exchanger’s “hot “ side. The “hot” side
is high pressure (slightly less than tank pressure). Liquid
anhydrous ammonia from the hot chamber flows through
the stainless steel flowmeter and into the stainless steel
servo valve.
The pressure changes from high to low at the servo valve
butterfly. “Low pressure” is between 10 and 60 PSI (.7 to .41
bar) depending on application rates and temperature. The
majority of the liquid from the servo valve continues on to
the manifold and out to the applicator knives.
A small outlet on the low pressure side of the servo allows
some of the liquid (5-10% of total NH
) to enter the heat
exchanger’s “cold” side. The “cold” side is very low pressure
(ideally atmospheric)). This liquid vaporizes at nearly -28° F
(-33° C). The thermal connection between the two chambers
of the heat exchanger cools the incoming anhydrous
ammonia below its dew point.
This condenses all vapors on the high pressure side of the
system and provides the flowmeter with 100% liquid which
can be accurately measured and controlled
The material used for the refrigeration process is completely
vaporized by the time it leaves the cold side of the heat
exchanger The vapor is directed to four special vapor tubes
attached behind standard liquid tubes and injected into
the soil This material has already been measured by the
flowmeter and therefore all material incorporated into the
soil registers ion the monitor
When the unit is turned off the small amount of liquid in the
heat exchanger will begin to spin In vapor form the pound
or two of liquid may register as much as 25 lbs (11kg) on
the monitor This condition is eliminated by using of a Hold
Cutout Module The Hold Cutout Module is installed at the
plumbing unit six pin connector and prohibits any flowmeter
pulses from reaching the console when the electric shutoff is
in the OFF position
Pre-Installation
Make certain that your application is within the capabilities
of the system Under ideal conditions the NH3500 system is
capable of 6000 lbs (2727 kg) of NH
per hour (83 lbs/3.7 kg
“N” per minute) maximum and 600 lbs. (273 kg) NH
per hour
(8.2 lbs./3.7 kg “N” per minute). When operating conditions
are less than ideal the system’s minimum capacity may
increase and its maximum capacity my decrease
To calculate your application in lbs⁄kg of “N” per minute
apply the following formula to your operation
“N” FLOW RATE = SPEED x WIDTH x SPRAY RATE ⁄ CONSTANT
* English width is feet, constant 496 and Metric width is in
meters, constant 600.
Go through the equation twice, first using your maximum
lbs/kg per area and maximum speed, and then using your
maximum lbs/kg per area and minimum speed. If your
maximum is over 82 lbs. (37 kg) of “N” per minute, you
must lower your speed or application rate or both. If your
minimum in under 8.2 lbs. (3.7 kg) “N” per minute, you must
raise your speed or application rate or both. Figures based
on 45° F/4.5° C and high capacity plumbing fittings.
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