The AN Granules Plant has a capacity of 400 tons/stream day.
Normal operation is 6 days/week with seventh day being utilized for the cleanup and maintenance necessary in this kind of corrosive solids handling operation.
The unit has bulk storage in a humidified enclosed warehouse for 36,000 tons of product.
The original prilling tower was replace which produces and excellent hi-density material for agricultural use.
The flow of 83% NH4N03 to the 85% tank is supplied by the 83% A. N. storage circulating pump, discharging at approximately 40 psig. It flows through a level control valve and into the top of the 85% tank.
The 85% tank is equipped with steam coils. The coils are supplied by 180 lb. steam through a temperature control valve, which controls the temperature on the 85% tank at approximately 250 degrees F.
Since revisions to the solutions plant, and insertion of the Brinks scrubber system, and the acid heater, we are producing 86 to 87% NH4N03, which is fed to the 85% tank. This 85 to 87% A. N. is concentration to a small extent by the returning of fines and oversize from the Sweco to the 85% tank, and the steam coils controlling the temperature at 250 degrees F.
In addition, the 60% weak A. N. solution is also returned to the 85% tank from the #1 scrubber. This, of course, instead of concentrating, weakens the 86 to 87% NH4N03 so that on an average, we still will be leaving the 85% tank at approximately 85% NH4N03 concentration.
There is a steam ejection vent to atmosphere off the 85% tank to remove as much of the exhaust off the tank as possible to prevent condensation back into the 85% tank, and also to keep the steam from flowing back into the Sweco, thus wetting the screens down and plugging them off. (Air evacuationcan be used.)
The LT. is located on the north bottom of the 85% tank, which transmits signal to L.R.C. on panel board, which in turn controls L.C.V. to 85% tank.
There is a screen on the bottom of the tank to prevent fines, or any foreign material from getting into the pumps, since the pumps take suction directly off the bottom of the tank.
There are two 85% pumps. Under normal conditions, we operate with one and maintain the second as a spare. The discharge of the 85% pump flows through a L.C.V. and into the top of the evaporator.
The evaporator is a tube and shell vessel with 250 lb. steam supply for the shell, and hot air and nitrate on the tube side
The 85% NH4N03 enters the top of the evaporator and is distributed to the tubes by weirs forming a nitrate film on the tubes. Hot air enters the bottom of the evaporator (tube side) and counter-flows through the 85%. This, along with the steam on the shell, heats the A. N. at approximately 330 degrees F., boiling out the H20 and concentrating the liquid to 98.5% NH4N03.
The temperature of the A. N. leaving the evaporator depends a great deal on many circumstances, so, you cannot adhere to the 330 degree F. temperature- this is just a guideline.
Instead of trying to control a given temperature, what we really want is to control the temperature at whatever necessary to enable us to operate the plant with a .60 to .65 moisture outlet the pan.
The temperature exit the evaporator is controlled by a T.C.V. which is located on the 250 lb. steam supply to the shell side of the evaporator. The temperature is transmitted to a temperature recorder controller located on the panel board.
The air temperature to the evaporator is approximately 330 degrees F. This is air pulled off the chiller by the booster blower and forced through the air heater. The air heater has 250lb. steam supplied to the shell side, which heats the air on the tube. The air is prevented from flowing into the 99% tank by a liquid seal, caused by the evaporator outlet extending down to 4" off bottom of 99% tank. The hot 99% A. N. flows through this seal and down into the 99% tank.
The 99% tank is a jacketed vessel with 250 lb. steam on the jacket. The jackets are there for the purpose of maintaining the temperature on the 99% tank and to help control moisture. The salting out point of 99.9% NH4N03 is 333 degrees F.
Also, inside the tank is an agitator with two impellers for the mixing of the Nuclo that is added to the 99% tank (1.8- 2% per ton).
There is a steam ejection vent on the tank for the removal of steam and heat to help control moisture and prevent Nuclo chute from pluggage. (Air evacuation can be used).
The pump that delivers the A. N. to the pan takes suction from the submerged suction of the pump in the 99% tank. The suction extends from the top of the tank where the pump is located, to approximately 3 feet in the liquid. The level must be controlled above 55% in the tank because at this level, the pump loses suction.
The pump discharges the A. N. to the inlet pan valve and recycle valve. Part of the A. N. goes to the pan. The remainder of the A. N. goes through the recycle valve and returns to the 99% tank.
The inlet pan valve (melt to pan) is either wide open, or completely closed. Other than opening this valve wide open, or completely closed, there is no control on this valve.
The amount of A. N. (melt) to the pan is determined by the amount the recycle valve to the 99% tank is opened or closed. By closing the recycle valve, the recycle flow is restricted; building a pressure on the discharge of the 99% pump, raising the melt pressure to the pan and causing more melt to be delivered to the pan.
The melt to the pan flows through the inlet valve and into the distribution header, which is in front of the pan and extends the diameter of the pan. From the distribution header, the melt flows through nozzles and is sprayed on the pan.
The nozzle has a vortex located in the back side of the nozzle which causes the melt to swirl and gives a better distribution action to the pan.
The pressure on the nozzles is very important. Too little pressure does not give a good spray, and oversizes are formed because the melt has a tendency to come out in streams rather than spray, and too much melt hits in one spot causing oversize, and not very good product size material. Too high a pressure in turn causes the melt to spray through the bed cover on the pan and causes the pan to have A. N. buildup on it. This causes loss of pan action and as the scrapers break off the buildup, the chunks can cause pluggage on inlet the precooler.
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