2 Trackmobiles
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SECTION V C
PROCESS DESCRIPTION
SULFURIC ACID
Flow Diagram
Figure ^_ is a simplified process flow sheet for
both the old and new sulfuric acid units, including
combined raw material handling and storage facilities.
Process Description
Molten sulfur is delivered to the plant in 20 ton
tank trucks from the Texas Gulf Sulfur terminal in
Searsport. The hot liquid sulfur is unloaded into
below ground steam heated storage tanks.
Approximately
2,300 tons of raw sulfur is stored in bulk for use in
the event the molten sulfur supply is delayed or discontinued.
Raw sulfur is dumped via payloaders into below ground
sulfur melting pots which are adjacent to the molten
sulfur storage. Molten sulfur is pumped to Sulfur Burners
in both the old and new acid plants via submerged pumps from
the molten sulfur storage tanks.
Air is taken directly from the atmosphere through a
blower and dried in the Air Drying Tower against a counter
current stream of concentrated (66° Be') acid at from 90
to 120.
Air leaves the Drying Tower at slightly above one
atmosphere pressure, with under 30 ppm moisture and enters the Sulfur Burner.
In the Sulfur Burner, molten sulfur is burned to
form sulfur dioxide. The resulting gases contain
approximately 9% SO2, 12% O2, and 79% N2.
Considerable
heat energy is liberated during combustion of sulfur and
the burner product gases are generally about 1650°F.
The burner gas is then cooled to 775°F in a Waste
Heat Boiler which produces 60 psig steam. For temperature control, a by-pass around the Waste Heat Boiler is
provided.
The hot gases then pass through the Hot Gas Filter
where ash is removed, and on to the Converter.
The Converter consists of four layers of vanadium
pentoxide catalyst which facilitates the oxidation of
sulfur dioxide to sulfur trioxide. The reaction is
exothermic and the gas leaves the first catalyst bed
at about 1100°F. and is passed through a second Waste
Heat Boiler where additional steam is produced.
Between the second and third catalyst bed of the
converter additional reaction heat is removed by passing
the gases over steam superheater coils which super heat
the 60 psig steam well above saturation. The gases leave
the Converter at about 8OO F.
In the old acid plant, the converter exit gases are further cooled against ambient air by passing the gases
through a large duct which runs completely around the outside of the acid plant building. In the newer plant, the gases are cooled in an Economizer against incoming boiler feed water, followed by an air cooled Gas Cooler.
The gases then pass into the Absorber where the SO3 combines with dilute sulfuric acid to form concentrated (98-99%) sulfuric acid. Weak acid enters the top of the packed Absorber and the concentrated acid leaves the bottomand joins the Air Drying Tower concentrated effluent acid.
Stack gases, essentially O2, N2 and some sulfur oxides, are vented out the Absorber.
The acid from the Absorber and Air Drying Tower is recirculated through coolers and back into the columns. As the concentration increases due to burner gas absorption, a product acid stream is purged from the recirculating acid.
This product stream (98-99% H2SO4) is then diluted to 66° Be' (93.19% H2SO4) and sent to storage.
Raw Material & Supplies Requirements per ton 100% H2SO4
Sulfur 0.338 tons
Supplies, including Boiler water chemicals 5.8 cents/utilities Requirements
per ton 100% H?SO/
Power 9.2 KWH
\ZTLO
Net Steam produced SddQ lbs.
City Water 356 gal.
Storage & Distrubution
Product sulfuric acid is stored in two tanks
having a total capacity of 4,000 tons acid, 100%
basis. This is equivalent to approximately twenty
days of full production.
One tank (1500 ton capacity)
is adjacent to the plant; the other (2500 ton capacity)
is located about 700 feet away.
From either tank, acid
can be delivered to the superphosphate plant, the
ammonium sulfate plant, the alum plant, or to a tank car
loading station.
Operation
Both plants are operating satisfactorily, showing a
97% conversion of sulfur to sulfuric acid. The older
unit produces continuously at a rate 50% above design;
the newer unit produces continuously at a rate 20% above
design. Purity, concentration and color of the acid is good.
NORMAL SUPERPHOSPHATE
Flow Diagram
A schematic flow sheet for production of superphosphate is shown on Figure 6.
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Process Description
Normal superphosphate is produced by the acidification
of phosphate rock in a batch operated one ton Mixer and a
40 ton Gunite lined Den.
Florida rock (74-76 BPL) is delivered to the plant in
rail hopper cars from the Searsport terminal where ships
are unnloaded. The rock is stored in bulk in several
locations at the plant. Normally, 2000 to 3000 tons of
rock are stored at the plant.
Rock is transported via payloaders to a Bucket Elevator
which feeds two Raymond Roller Mills. The mills are used
alternately to grind the rock (66% + 200 mesh, 90% + 100
mesh) and convey the rock pneumatically to two 112 ton
Ground Rock Silos (225 total tons).
Rock is then conveyed via Bucket Elevator into a
Weigh Hopper.
Sulfuric acid is delivered from the acid
storage tanks to the Acid Surge Tank and diluted in a lead lined
Acid Dilution Tank to 56°Be'. Heat of dilution is removed by
circulating water through lead coils in the Dilution Tank.
Dilute sulfuric acid at 130°F is pumped to the Acid Feed
Tank and then dropped by gravity into the Mixer along with
the ground rock in a predetermined weight ratio.
The Mixer is a pan type, equipped with paddles for
continued slow agitation of the mix.
During acidulation
noxious fumes of water vapor, hydrogen f1uoride, carbon dioxide and silica dust are removed from the Mixer
by an induced draft blower, and scrubbed in a two
stage wooden Scrubber against cascading sea water.
The sea water flows back into the bay.
When the acidulation is complete, the batch is
dropped from the Mixer into the Den by gravity flow
where the mixture cures and hardens. Subsequent
batches are mixed and dumped into the Den until the
Den has been filled.
After the Den has been filled and the mixture is
allowed to solidify, the Den doors are opened. The
Den is moved along a track in such a manner that the
superphosphate is pushed out and chopped off by large
Excavator blades. The superphosphate breaks easily
and falls into a chute leading to a Bucket Elevator.
From the Elevator, the superphosphate travels via
overhead Belt Conveyor to bulk storage for final curing.
Raw Material & Supplies Requirements
per ton Superphosphate:
* Sulfuric Acid 0.357 tons
* Phosphate Rock 0.586 tons
* Sterox 0.12 lbs.
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Utilities Requirements
per ton Superphosphate
Power 20.3 kwh
City Water 30.3 gal.
Steam 40-^- " -
Storage & Distribution
A total of 15,000 tons of bulk storage space is
available. This must be split between phosphate rock
and normal superphosphate, and occasionally triple
superphosphate which is purchased, stored and shipped
through the plant. The usual peak inventory of normal
superphosphate is about 9,000 tons.
When warehouse space becomes a limiting factor,
the normal superphosphate is reworked through a
Tailing Mill and Screen. This serves to increase the
bulk density, blend the product and increase the
available P2O5 content about 0.5% by releasing moisture
which was trapped during curing in the bulk pile.
Although this procedure improves the product and permits
greater tonnage to be stored, the added handling cost
discourages full time use of this technique.
Normal superphosphate is shipped only as bulk.
Rail cars are loaded at a spot alongside the bulk
warehouse.
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Operation
The normal superphosphate plant produces a
reasonably typical product. Specifications are easily
met, although some problems were recently encountered
when low grade rock was used.
Phosphate rock is tested in the laboratory in
order to select a formulation for the mix. The
formulation varies from rock differences and must be
altered with each new rock shipment. A typical
formulation is as follows:
Per Mix Batch
Ground rock 840 lbs.
Acid, 56° Be' 688 lbs.
Total mix 1528 lbs.
Fume loss shrinkage, 8% 122 lbs.
Batch weight 1406 lbs.
Normally, sixty Mixer batches will fill the Den.
The plant is capable of producing 600 Mixer batches
each day, which is equal to 10 Dens per day. A Den
contains about 42 tons of product. An eight hour
shutdown is needed every week to clean the Den,
Excavator and Conveyors.
The Mixing operation is controlled by operator
experience. By noting the consistency of the mix, the
operator judges when to drop the mixture into the Den.
Occasionally, a particular rock or formulation will
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cause abnormal thickening of the mixture. In such
cases Sterox, a lubricating agent, is added in small
quantities.
AMMONIUM SULFATE
Flow Diagram
A schematic flow sheet for the ammoniiim sulfate
process is shown on Figure ~7 .
Process Description
Ammonium sulfate is produced in crystal form in
a continuous single train atmospheric Neutralizer Crystallizer.
Sulfuric acid (66° Be') is pumped directly from
acid storage into the Neutralizer-Crystallizer.
Ammonia is pumped from Sphere storage directly into
the Neutralizer-Crystallizer.
The resulting exothermic
heat of reaction is removed by allowing the liquor to
boil and steam is vented out the top of the NeutralizerCrystallizer, At one atmosphere pressure, the saturated
liquor boils around 230° F.
Circulation is maintained by continuous overflow of
the liquor into the Overflow Tank and then pumped back
to the top of the Neutralizer-Crystallizer.
Crystals of ammonium sulfate collect in the conical
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lower section of the Neutralizer-Crystallizer and are
drawn off as a slurry by gravity into the Sharpies C-28
Centrifuge. Mother liquor from the Centrifuge is
collected in the Mother Liquor Tank and then pumped to
the Overflow Tank for recycling back to the NeutralizerCrystallizer.
Wet crystals at about 230°F. are ejected from the
Centrifuge into the rotary type Dryer. Air is drawn through
the Dryer by an induced draft Blower, which discharges
into the Mother Liquor Tank. Fines are thus collected
in the Mother Liquor Tank while the air escapes through
a vent stack.
Leaving the Dryer, the crystals (145°F.) are conveyed
via Bucket Elevator to a vibrating Screen. Oversize
crystals are rarely encountered, and are easily dumped by
hand into the Overflow Tank.
Product crystals travel by gravity through chutes to
waiting plant trucks or to a small St. Regis Bagging unit.
The trucks carry the crystals to bulk storage. The bags
are palletized and carried to the warehouse on fork lift
trucks.
Raw Materials & Supplies Requirements
Per Ton Sulfate 100%
Ammonia 0.265 tons
Sulfuric Acid 0.74 tons
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Utilities Requirements
Per Ton Sulfate, 100%
Power 23.3 kwh
City Water 174 gal.
Steam 150 lbs.
Storage & Distribution
Crystals are stored in bulk and bags in the old
warehouse. Bulk sulfate is loaded by the shipping crews
in the superphosphate plant. Bags bear no label except
contents and analysis. Manufacturers name is omitted.
Multi-ply kraft bags are normally used. Occasionally,
polyethylene bags are used. When necessary, the plant can
bag crystals at a rate of 30 tons per eight hours.
Operation
Neutralizer pH is controlled manually. A new
automatic pH controller is installed but has never worked
properly.
The appearance of the product is poor. The product
crystals are hot and very fine and tend to cake almost
immediately into a solid fused mass. An effort to reduce
this caking by spraying a "Petro Aq" additive onto
the crystal is being tried.
The purity of the crystal is acceptable. Iron contamination
ranges from 15 to 20 ppm.
The demonstrated plant efficiencies for ammonia
and sulfuric acid are 97.2% and 100%, respectively.
--------------------------------
ALUM
Flow Diagram
A schematic flow sheet of the Alvmi process is
shown on Figure ^ .
Process Description
Alum (aluminum sulfate hydrate) is produced batchwise
by the digestion of bauxite ore with sulfuric acid.
Granular bauxite is delivered in bulk to the plant
via trucks from Searsport. The bauxite is stored in the
building in a bulk pile and handled by bulldozers.
Inventory space is available for approximately 6,000 tons
of bauxite.
Bauxite is fed to an Elevator which conveys the
material to an overhead Crude Bauxite Hopper. The
bauxite then drops onto a Belt Conveyor and is conveyed
to the processing area.
Bauxite is then dumped into a second Bucket Elevator
and carried to a Feed Hopper which discharges into a
Raymond Mill where the bauxite is finely ground and
pnevm;iatically conveyed to a Cyclone Separator.
Leaving
the cyclone Separator, a Redler conveyor drags the bauxite
to a large 45 ton Ground Bauxite Storage Bin. The same
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Redler conveyor drags the bauxite into one of two
Dissolver Tanks.
Sulfuric acid (66° Be') is pumped from acid
storage into the Dissolver Tank. The Volume of acid is
measured by level from the top of the Dissolver.
Bauxite is then allowed to enter the Dissolver while
agitating the mix. The quantity of Bauxite is measured
by running time of the Redler conveyor. Some heat is
supplied with steam coils to start the digestion. Once
started, the reaction progresses freely and fumes are
vented through a natural draft stack. The Dissolvers are
constructed of carbon steel, lined with lead and brick.
During digestion the formation of sediment from clays,
calcium, silica, etc, precipitate into a sludge or "mud".
Iron is removed by the addition of sodium bisulfite, which
forms a precipitate iron complex, liberating sulfur oxide
fumes out the stack. Following digestion the sediment is
allowed to settle and alum liquor (38° Be') is decanted off,
filtered and pvunped into one of two Alum Storage Tanks.
The Filters are Adams cartridge type, precoated with
Johns Manville Celite 545 filter aid. Two Filters are
available and alternately switched from service to backwash.
Washing consists of a four step cycle during which the
IS
mud progressively mixed with liquor from previous washes.
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Mud is pumped from the Dissolver into one of four
Mud Tanks and washed with 15° Be', 10° Be', and 7°
Be' liquor, and finally with incoming water. TlS#
mud is then pumped to a collecting pond for disposal.
Liquid is decanted from the pond for reuse when it
reaches about 10° Be'.
Liquor from the first wash (15° Be') is pumped
to the Storage Tanks to adjust the Alum concentration
from 38° Be' to 36° Be'.
Raw Material & Supplies Requirements
Per Ton 100% dry alum
Bauxite 0.340 ton
Sulfuric Acid 0.516 ton
Sodiiom Bisulfite 6 lbs.
Supplies (Jinl4<;:
Utilities Requirements
Per Ton 100% dry alum
Power 16 kwh
City Water 546 gal.
Steam 1430 lbs.
Storage & Distribution
Alum is stored in two tanks holding approximately
100 tons of dry alum as a 50% concentrate. Alum is
pumped directly into rubber lined railroad tank cars
at a loading station and track scale at the plant.
Operation
Each batch made in the Dissolver Tank produces
30 tons of dry alum. About 45 batches per month are
produced. A limiting factor is the time required to
convey bauxite into a Dissolver. While the Redler
conveyor is being used for this service, the Raymond
mill cannot be used to grind bauxite.
Digestion is controlled by titrating grab sample
for free acid. This is done by the operators. Sodium
bisulfite consumpjrtion will vary with the quality of
bauxite. A normal charge for each batch ranges from
100 to 175 lbs., depending on the iron content of previous
alum batches. Iron should not exceed 0.01% in the
product alum.
Settling time of the mud is facilitated by adding
about four pounds of American Cyanamid "Superfloc" to
a batch. This is a floculating agent and is used only
for stubborn batches.
Occasionally, the Redler conveyor will breakdown
during digestion. If the delay for repairs is extended
over five or six hours, the batch in progress tends to
become passive. The reaction will not continue upon
addition of more bauxite and the batch must be sewered.
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AMMONIA
Flow Diagram
Process flow sheets for syn gas preparation,
purification, and the synthesis and storage sections
are shown on Figures ^_ , lO_, and j_/_, respectively.
Process Description
Ammonia is produced continuously in accordance
C
with the following basi^ process steps:
Air Separation
Partial Oxidation
Shift Conversion
Carbon Dioxide Removal
Nitrogen Wash Purification
Compression
Synthesis
Oxygen is provided for the partial oxidation of
oil from a 108 T/D O2 (100% basis) medium pressure Air
Products air separation plant. Air is compressed in
four stages to about 600 psi and passed through the
Ammonia Aqua Wash Tower where CO2 is absorbed in a
counter current stream of weak aqua ammonia. The air
then passes through a Caustic Wash Tower where remaining
traces of CO2 are removed. The air is then cooled to
about 40°F in the Prechiller and passed through a
Dryer to remove moisture.
The Air Plant utilizes Regenerators to cool the
imcoming air and remove the last trace of water vapor
=============================================
and CO2 in the air. The Regenerators are switched
every eight hours. Leaving the Air Separation Plant
are 95% oxygen and 99.9% N2 streams, plus an impure
nitrogen stream which is vented. Oxygen is preheated
with steam in the Oxygen Preheater and sent to the
partial oxidation Texaco Generators.
Oil is delivered in tank trucks and pumped in the
main Oil Storage Tank which serves the boiler house as
well as the ammonia plant. From the Oil Storage Tank,
Bunker "C" grade oil is pumped through a Heater and into
the Oil Flash Tank. Oil for fuel service is also pumped
directly to the burners on the Vaporizers and Preheaters.
The partial oxidation section consists of three
separate trains. Condensate is pumped through the oil
fired Vaporizers where high pressure steam is produced.
The steam is further heated in the No. 1 and No. 2
Preheaters and joins the process oil stream passing
through the Preheaters. The No. 3 Preheater has been taken
out of service recently as a process modification. The
effect of this modification is being studied on the No. 3
partial oxidation train.
Leaving the Preheaters, the oil-stream mixture enters
the Texaco Generator where the oil is combined with 95%
oxvgen to produce a stream of essentially CO, CO2, and
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H2, plus minor amounts of H2S, COS, and N2. The gases
leave the combustion chamber at about 2500°F. and are
rapidly quenched with water. The quench water is
cooled and passed through a large sand filter bed where
soot is removed, followed by a two stage pond decantation
clarifying step.
The exit gases from the quench section are passed
through a series of Peabody and Pease-Anthony type
scrubbers and into the Carbon Scrubbing Tower where
carbon is removed from the gases with a counter current
stream of water. Sooty water is purged from the system
and serves as quench water for the Texaco Generators.
Leaving the Carbon Scrubber, the gases are heated
against First Stage Shift Converter exit gases, mixed
with steam, and passed into the First Stage Shift
Converters. The First Stage Shift Converters are two
parallel vessels containing three beds each of Girdler
catalyst which promotes the conversion of carbon monoxide into
carbon dioxide and hydrogen.
Following heat exchange with the incoming gas, the gas
stream is then cooled first in the MEA Reboiler, then in
the Contact Gas Cooler by saturating the gas with water.
The gases leave the Contact Gas Cooler and pass directly
into the First Stage CO2 Absorber where carbon dioxide is
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absorbed in a counter current stream of 15% MEA.
The gases are then heated in a second Shift Exchanger
and flow into the Second Stage Shift Converter where the
remaining carbon monoxide is converted to hydrogen and carbon
dioxide.
Following exchange with incoming gases, the gases
are further cooled in the second MEA Reboiler and then
enter the Second Stage CO2 Absorber where remaining carbon
dioxide absorbed in a counter current stream of 15% MEA.
The carbon dioxide rich MEA is recovered in a Regenerator
where heat supplied by the hot gases and steam in the
Reboilers is used to separate the carbon dioxide from the
MEA. Carbon dioxide and water vapor exit the Regenerator
and pass through the Acid Gas Condenser where reflux
condensate is recovered and returned to the Regenerator.
The acid gas, which is essentially carbon dioxide plus
some sulfides, is sent to the main plant boilers where
the objectional odorous sulfides are burned and vented out
the boiler stack.
From the Second Stage Absorber the gas, essentially
H2, passes through the Carbon Scrubber where any remaining
carbon dioxide is removed in a counter current stream of
weak caustic. The hydrogen is then cooled against flashing
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ammonia in the Hydrogen Chiller.
Leaving the Hydrogen Chiller, the hydrogen gas
enters the Nitrogen Wash Unit where the hydrogen is
scrubbed in a stream of cold liquidified nitrogen to
absorb and remove any remaining last tract of contaminant
carbon dioxide and carbon monoxide. Refrigeration for the
Nitrogen Wash is supplied by the Air Plant.
From the Nitrogen Wash, the pure hydrogen stream
enters the Methanator, which serves as a guard to any
remaining traces of oxygen to water or carbon monoxide to
methane in order to insure against synthesis catalyst
poisoning.
Pure nitrogen from the air plant then joins the
purified hydrogen stream in a 3:1 ratio of hydrogen to
nitrogen and is cooled in the Syn Gas Cooler.
The Syn gas mixture is then compressed to 4500 psi
in three stages of the main compressor and sent to the
synthesis loop. The ammonia synthesis loop consists of a
circulating stream of H2, N2, and NH3 which pass through
the Ammonia Converter where H2 and N2 are combined to
form ammonia in the presence of 24,000 lbs, of Topsoe
KM-1 and KM-2 catalyst. The synthesis gases leave the
Converter and pass through an air cooled condenser where
ammonia is condensed. The vapors are recycled to the
====================================
synthesis loop via the Compressor, the ammonia is
collected in a series of pressure let-down vessels.
Raw Materials & Supplies Requirements
Per ton ammonia
Oil, Bunker "C" 6.23 bbl
Oil, #2 fuel 0.13 bbl
Caustic (liquid NaOH) 0.605 lbs.
Shift Catalyst 55.4<:
MEA 0.442 gal.
Ammonia 0.003 ton
Utility Requirements
Per ton ammonia
Power 1300 kwh
Steam 12,860 lb.
Salt Water 15,000 gal.
City Water 400 gal.
Cooling Water 25,000 gal.
Storage and Distribution
Ammonia is stored in a 30 ton pressure bullet for
delivery to the nitric acid, ammonium nitrate and solution
plants. The main ammonia inventory is stored in two 2000
ton Horton spheres, which are refrigerated with three small
compressors totaling only 97 HP. This is inadequate
compression during warm weather.
Refrigeration grade ammonia is filtered and stored in
a 50 ton pressure bullet.
Aqua ammonia is made and stored in a 25,000 gallon
pressure bullet (30 tons NH3).
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All ammonia shipments are by rail. Tank car loading
facilities (scale and dock) are available to fill one car
at a time.
Operation
Although designed to produce 125 T/D the ammonia
plant has never met this rate, in spite of a raft of
changes made in the plant. In the past ten years, the
process scheme has been altered substantially in such
units as carbon scrubbing, CO2 removal, and partial
oxidation, with only moderate rewards.
Partial oxidation thermal efficiency is in the
range of 82%, which is reasonable for the oil fired
Texaco Process.
Corrosion of the MEA system continues to plague the
operation.
NITRIC ACID
Flow Diagram
A simplified process flow sheet is shown on Figure ix.
Process Description
Nitric acid is produced in a high pressure unit
designed to make 59% HNO3 on a continuous basis from the
oxidation of ammonia.
Air is passed through a screen and water scrubber and
compressed to 25 psig in the First Stage Compressor.
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The hot (280OF) compressed gas then passes through the
Intercooler where moisture is condensed and removed in
the Separator, The air then enters the Second Stage
Centrifugal Compressor at 80° F. and discharges at 110
psig, 470°F.
The compressed air stream is then split, and 85% of
the flow enters the Air Preheater where heat is exchanged with
hot burner gases. For temperature control, a by-pass around
the Air Preheater is provided. The air exits the Air
Preheated at about 580° F. and enters the ammonia-air
Mixer.
Anhydrous liquid ammonia from the ammonia plant
pressure bullet storage enters the steam heated Ammonia
Vaporizer followed by the Ammonia Superheater. Leaving
the Superheater at 210° F the ammonia gas is filtered and
joins the air stream in the Mixer. Ammonia and air are
blended in the Mixer to a composition of 9.5% NH3 by volume.
The NH3-Air gas mixture passes into the catalyst zone
of the Converter where ammonia and oxygen combine catalytically
to form nitrogen oxides. The catalyst consists of 135 troy
ounces of platinum-rhodium alloy gauze. From the Converter
the burner gas is cooled first in the Converter Gas Precooler
against tail gas, followed by the Tail Gas Heater, and finally
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to about 750° F in the previously noted Air Preheater.
Leaving the Air Preheater, the burner gases pass
through the Catalyst Filter to remove catalyst dust and
are then cooled to 280 F in the air cooled Acid Gas
Cooler, followed by the Acid Condenser. From the Condenser,
the acid gas mixture at 100°F flows into a Separator where
50% acid is collected and fed to the Absorber on the
eighth tray. Gases from the Separator are fed to the
second tray of the Absorber.
The Absorber consists of a tower packed with 38
trays. The upper trays have serpentine cooling coils.
Heat is generated by the reaction of nitrogen oxides and
water to form nitric acid. This heat is removed by
circulating cooling water through the tray coils.
Condensate is fed to the top tray of the Absorber.
The remaining 15% of the compressed air flow is
cooled in the Bleach Air cooler to 170OF. and fed to the
bottom of the Absorber.
Product acid at from 58% to 59% HNO3 is withdrawn from
the bottom of the Absorber. Tail gas which is essentially
nitrogen and oxygen leaves the top of the Absorber, passes
through a Demister, and is heated in the Converter Gas
Precooler to 540°F and then in the Tail Gas Heater. A
portion of the hot tail gas is used to drive the First
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stage Air Compressor via the Tail Gas Turbine. The
tail gases leave the plant through the acid plant
stack.
Raw Materials and Supplies Requirements
Per ton 100% acid
Ammonia 0.290 tons
Catalyst 0.0097 troy ounces
Supplies 9.5<:
Utility Requirements
Per ton 100% acid
Power 11 kwh
Steam 4066 lbs.
City Water 87 gal.
Cooling Water 44,000 gal.
Salt Water 24,000 gal.
Storage & Distribution
The nitric acid storage tank has a capacity of
500 tons acid, 100% basis, which is equal to about one
week of production. Acid is used solely for the manufacture
of ammonium nitrate.
Operation
Burner efficiency is very good, averaging 95 + %.
Absorber effifiiency is also very good as evidenced by tail
gas losses of only 0.1% nitrogen oxides. Overall, plant
efficiency of ammonia to acid averages 93%.
The stack color is comparabld to more expensive plants utilizking catalytic
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disposal of the oxides in tail gases.
A spare supply of catalyst equal to two replacement
charges plus some new catalyst is maintained at all
times. The Catalyst Filter is changed every three months.
The plant is plagued by a very delicate air compression
system. The first stage operates extremely close to surge
conditions. Any minor upset or dip in the second stage will
cause a drastic surge in the first stage axial compressor.
This can cause severe damage and, on one occasion in the
past, blew a turbine through the compressor room roof.
The air compression system limits production. The
absorption and heat exchange hardware was designed to
handle 120 T/D, while the air compressors were sized to
provide air for 60 T/D.
AMMONIUM NITRATE
Flow Diagram
Figure 13 is a schematic flow diagram of the ammonium
nitrate process.
Process Description
Nitric acid is pumped from storage directly into the
Neutralizer. Ammonia flow from the ammonia storage pressure
bullet, plus ammonia from the Stripper in the Ammonia Plant,
is controlled by pH of the Neutralizer stack.
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The Neutralizer operates at atmospheric pressure
and heat of reaction is released through steam in the
Neutralizer stack. Ammonium nitrate liquor of 84%
concentration is produced in the Neutralizer.
The 85% liquor is pumped to the Evaporator which
operates at 21 inches of mercury vacuum. Overhead vapors
are condensed. The Evaporator product concentration is 94%
ammonium nitrate.
Raw Materials & Supply Requirements per ton AN
Aimmonia
Nitric Acid, 100%
Supplies
Utility Requirements
Power 17kwh
Steam 148 lbs
Salt Water 2160 gal
Storage & Distribution
Ammonium nitrate is stored as 84% liquor in an
1800 ton (100% basis) tank equipped with circulation
heaters. The tank is heavily insulated. Only a small
surge capacity of 94% ammonium nitrate is stored. All
ammonium nitrate is consumed in solutions manufacture.
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Operation
The ammonium nitrate plant is relatively simple
to operate.
The plant efficiency is 97.5% on ammonia,
and 98.1% on acid.
The Neutralizer capacity is considerable larger than
the demand, psssible by an additional 100 T/D. However,
the Evaporator is currently being run at its maximun
capacity for 94% concentration.
SOLUTIONS
Flow Diagram
A schematic process flow sheet of the solutions plant
is shown on Figure 14*.
Process Description
Nitrogen solutions can be produced containing any
ccmbination of ammonia, ammonitmi nitrate and urea, although
a variety of nitrogen solution grades are generally not
produced.
The principle types made are:
Vap. Press. Salting
Type @ 104° F Temp.
440(22-66-6) 17 psig 140F
450(25-69-0) 22 psig 1°F
Both types are sold as fertilizer manufacturing solutions.
Very little, if any, direct application nitrogen solutions
are produced. The processing equipment consists of a
single train batch operated mixing system for all NH^
and AN bearing solutions and a single train system for
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mixing urea and water- The urea containing solutions
are produced in two steps.
To produce a solution containing only NH3 and AN,
water is first loaded into the Mixing Tank and weighed.
The Mixing Tank is a 13,000 gaL stainless steel pressure
vessel set on a scale. Circulation is started around the
Mixing Tank through a Mixer and Cooler. Ammonia and AN
are fed to the Mixer and heat of reaction is removed as
the solution circulates through the cooler.
Ammonia is
weighed and fed to the Mixer from the Ammonia Weight Tank,
a 20 ton pressure vessel set on a scale. Concentrated 94% AN
is pumped from the surge tank to the Mixer. The amount of AN
used is determined by difference between the final solution
weight and the water and ammonia weights. The solution is
then circulated, analyzed, inhibited with ammonium thiocyanate
and pumped to storage.
Urea bearing solutions are blended from a stock ammonia
and ammonium nitrate solution; and urea syrup. Urea is delivered to the plant both in bags and as bulk, although bagged
urea is preferred.
The urea is conveyed on a Belt Conveyor
from the storage building into the Urea Syrup Tcink where
a 35% urea-water solution is prepared. Heat of solution is
added through coils inserted in the Urea Syrup Tank. The
urea syrup is then added to the stock solution in the Urea
Solution Mix Tank.
The solution in the Urea Solution Mix
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Tank is then circulated, analyzed and pumped directly
into tank cars.
Raw Material & Supplies Requirements
Per ton Per ton
450 N 440 N
Ammonia 0.254 tons 0.223 tons
Ammonium Nitrate 0.708 tons 0.677 tons
Urea - 0.062 tons
Airanonivmi Thiocyanate 3 lbs. - .,
Supplies 1.6<: 1.6*
Utilities Requirements
Per ton solution
Power 6.8kwh
City Water 7.4 gal.
Cooling Water 1980 gal.
Salt Water 1080 gal.
Steam 24 lbs.
Storage and Distribution
Urea bearing solutions (440 N) are loaded directly
from production into tank cars. No storage is available
for this solution type.
The 450 N type is is stored in two 450,000 gallon steel
tanks lined with Lithcote. The tanks are held at one
atmosphere pressure, have no insulation, and breath through
a small water scrubbing column to remove ammonia vapors. A
total of 4000 tons of solution can be stored. To avoid salting
out in Winter, the tanks are equipped with a circulating
line and a steam Heater. However, the Heater is rarely
needed. The tank lining is in need of repair.
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Operation
No difficulty is encountered meeting solution
specifications. Data on raw material consumption is
fairly inaccurate, however, the yield of nitrogen from
urea, ammonia and ammonium nitrate appears to range
from 95 to 100%.
Advantage is taken of the cold weather in Maine by
storing pressure solutions in non-pressure tanks. In
late Stammer, a solution containing about 21% NH3 and 71%
AN is prepared and loaded into storage.
This solution is
compatable with warm weather, having a fairly low vapor
pressure (7 psig @ 100°F) and a high salting temperature
(62°F).
As cooler weather develops, the solution
concentration in the tanks is gradually adjusted to one
having a lower salting temperature and higher vapor
pressure. This is done by preparing solutions of higher
ammonia content. The higher vapor pressure is not a
significant factor because the solution is stored quite
cold during the Winter. By the end of the inventory season,
the stored solution has reached the 450 N type concentration
and is ready for shipment.
UTILITIES
Flow Diagrams
Power distribution is shown on block diagram Figure 15.
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Process Description
Steam is supplied from three sources as follows:
Main Boilers
Stand-by Boiler
Sulfuric Acid Waste Heat Boilers
A 140,000 Ibs/hr Erie City main steam boiler
produces 420 psig steam superheated to 750°F.
Boiler
feed water is demineralized to zero ppm. The steam
purity is less than one ppm solids. Betz chemicals are
used for treatment. The boiler is started up on No.2
grade fuel oil and then operates continuously on Bunker
"C" fuel oil. Boiler feed water make-up ranges from 25 - 30%,
while blowdown is less than 3%. The make-up is fairly
high because condensate is exported to the solutions and
nitric acid plants for process use.
The stand-by boiler is a small 5000 Ib/hr. oil fired
unit, and is used sparingly.
The Sulfuric acid boilers were described above.
Steam
from the acid Waste Heat:Boilers is distributed among
the older plants, ie., ammonium sulfate, alumi and
superphosphate. This distribution is not metered or charged
into the production cost of these plants.
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Electrical power for all plant sections is generated
in a 7500 kw turbogenerator. The turbine drive operates
from superheated steam from the main boilers in 14 stages.
The steam discharges at 28" Hg, 100° F. Some 60 psig,
450° F steam is bled from the third stage for process
distribution, and occasionally low pressure surplus steam
is fed to the sixth stage. The design generator power
factor is 0.8. The actual generator power factor is
0.96 to 1.00. Condensate from the acid plant turbine
joins the turbogenerator discharge at the surface condenser.
The surface condenser is cooled with circulating slat water.
It is proposed that by the Fall of 1967, the ammonia
plant will be shut down. This will eliminate the need for
power generating facilities, including both the 7500 kw
turbogenerator and 140,000 pph high pressure steam boiler.
However, since a small portion of the steam and power
is also distributed to other operating units not retired,
it will be necessary to provide utility services equal to
sustaining the operating units. This will involve uprating
the power transformer station, and incorporating a small
(40,000 pph) auxiliary steam boiler into the existing
steam distribution system.
There are three water systems in the plant. City
water from a nearby lake is used for sanitary purposes.
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some cooling requirements, and for process make-up water.
A chromate inhibited closed circuit cooling water
system serves the newer plants. The circulating cooling
water is cooled with salt water pumped from the bay.
Salt water is also used for cooling service in the
power plant, ammonia plant, nitric acid plant, and ammonium
nitrate plant. The salt water temperature ranges from
30° F to 64° F from Winter to Summer.
All salt water used
is on a once-through basis, and returns to the bay in
surface ditches.
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AMMONIA STORAGE
Flow Diagram
Process Description
It is proposed that by the Fall of 1966, ammonia
raw material will be supplied the NCI plant from a
10,000 ton low temperature.atmospheric storage terminal.
The ammonia will be brought to the plant in Grace ships
from Trinidad. The existing ammonia manufacturing
facilities will be retired.
Anhydrous ammonia is delivered to the terminal in
9,000 ton cargos from W. R. Grace & Company atmospheric
ammonia tankers. Ammonia is then delivered from the
terminal to the Hortonsphere storage of the Northern
Chemical Industries plant. The ammonia tanker is
unloaded in sixteen hours. The terminal is capable
of delivering ammonia to the plant at a rate of 410
tons per day.
Refrigeration for the terminal is integrated with
the plant sphere refrigeration in such a manner that
normal vapor boil-off from the terminal is delivered
to the spheres. During tanker unloading, the short
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term high: vapor boil-off is vented and burned. When
unloading, about 26 tons of ammonia vapor are lost,
accounting for only 0.3% of the cargo. During normal
holding of the terminal, about 4^ tons per day of
vapor are sent to the spheres.
Liquid anhydrous ammonia, saturated at one atmosphere, is pumped via a by-pass line from the pumps
into the filling line at the dock to precool the
piping. Ammonia from the tanker is then pumped into
the storage tank via the ship pumps. As the liquid
enters the tank, all of the energy which it has picked
up in the unloading operation results in evaporation
of a part of the liquid.
During filling, the excess vapors formed by the
flashing liquid, plus the vapor displaced by the liquid
are allowed to escape through a pressure relief system
to a vent stack equipped with a flare to destroy the
vapors. Ignition is maintained by bleeding^propane
into the vent gas stream.
During holding, all of the energy picked up from
external sources results in evaporation of a part of
the liquid ammonia stored in the tank. The ammonia
vapor formed is withdrawn from the tank by the small
holding compressor.
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Ammonia vapors at one atmosphere are compressed
by the holding compressor to 56 psig. The compressor
automatically loads and unloads to maintain the tank
at 0,5 psig. Leaving the compressors, the hot ammonia
vapors are cooled to saturation by contact with liquid
ammonia in the flash tank. The flash tank is located
adjacent to the NCI plant storage spheres, and the
pressure of the fiish tank is equalized with the
operating sphere pressure of 56 psig.
Liquid ammonia for Cooling flows by gravity from
the spheres to the flash tank on level control. The
hot superheated ammonia gas enters the flash tank
through a dip pipe beneath the liquid level. The
resulting saturated vapors flow into the sphere vapor
space to join the existing sphere refrigeration system,
or to pass directly into the plant for processing.
Liquid anhydrous ammonia is pumped from the storage
terminal to the heater. The heater provides the energy
necessary to raise the liquid ammonia temperature up
to that of the NCI storage spheres. Steam is provided
to the heater from NCI at 150 psig, saturated. Leaving
the heater, the liquid ammonia flows into the spheres.
Ammonia is delivered from the NCI spheres to all sections
of the plant via existing hardware.
