Great Plains NH3 Safety - Manual (Page 29)

2013-07-15 Table of Contents Index 407-551M
Great Plains Manufacturing, Inc. Table of Contents Index 25
Anhydrous Application
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Anhydrous ammonia is 82% Nitrogen, the highest of any
fertilizer. The compound NH
3
is normally a gas at
ambient temperatures. It is retained in the soil only by
chemical reactions and physical mechanisms, primarily
reactions with soil moisture.
Consult with your agronomist about optimal application
timing, rate and depth, based on proposed crop, soil
temperature, soil moisture content and ambient
temperature. Non-optimal applications can result in NH
3
loss to the atmosphere, soil drying, and undesired long
term changes in soil pH.
Weather Extremes
Cold Weather Low Flow
Catastrophic Release Hazard:
Do not take measures to boost pressure in cold weather.
Ad hoc boosting could create risk of line rupture or tank
explosion. The Great Plains system is designed for vapor
pressure and gravity delivery only.
Vapor pressure changes with ambient temperature (see
table at right). In colder weather, there may be
insufficient pressure for higher application rates. The
Raven AccuFlow™ Installation and Operation manual
has a temperature-rate-speed chart.
Hot Weather Venting
Unexpected Release Hazard:
Avoid hot weather, or be extra vigilant about remaining
upwind of the tank relief valve (
, page 21). In extremely hot
weather, the tank pressure relief valve will periodically vent
NH
3
when the vapor pressure exceeds 250 psi. Tank
temperatures above 116
°F (47°C) cause venting.
Direct sun on the tank, or parking the tank in a hot shed,
could result in relief venting well below an actual ambient
temperature of 116
°F.
Avoid Dead Calm
The wind is your friend. Normal anhydrous ammonia
operations involve small releases of NH
3
vapor.
Accidents, malfunctions and serious operator errors can
result in releases of liquid NH
3
, which turns into a rapidly
expanding gas cloud. You need to be “up wind” of all
potential releases, and that is only possible if there is at
least a breeze to carry the fumes away from you.
NH
3
Temperature and Pressure Relationship
Anhydrous Ammonia Exposure Hazard:
Keep the nurse tank cool. Stay up-wind of relief valves.
Check the tank pressure gauge. In hot weather, ammonia vapor
releases can occur at a relief valve.
Normally, over-pressure releases occur at the nurse tank relief
valve (
, page 21). It is designed to operate at a lower
pressure than other (hydrostatic) relief valves in the system.
However, with operating valves closed, trapped NH
3
could
activate hydrostatic relief valves anywhere in the system.
Lower Operating Limit:
A manifold pressure of at least 10 psi is required for the
AccuFlow™ to operate correctly. If the static pressure prior to
operation is not much above that, it may fall below this limit
when NH
3
begins to flow.
Degrees F (C) Pressure (psi)
-28
°F (-33°C)
0 psi
0
°F (-18°C)
16 psi
32
°F (0°C)
48 psi
60
°F (16°C)
93 psi
100 °F (38°C) 197 psi
116 °F (47°C) 250 psi
A80
A80