NANAIMO CHLOR-ALKALI AND SODIUM CHLORATE PLANTS
The CanadianOxy Chemicals Ltd. Nanaimo plant is situated on Northumberland Channel, adjacent to the Harmac Pulp
Mill of MacMillan Bloedel Ltd. Total acreage of the site is fifteen. Together, both plants employ 40 people.
The plants produce chlorine, caustic soda and sodium
chlorate. Rated capacity is 86 tonnes per day chlorine, 97
tonnes per day caustic soda and 21 tonnes per day sodium
chlorate. These chemicals are used in the bleaching
process of the pulp mill.
CHLOR-ALKALI
The production of chlorine and caustic soda is based on the
following chemical reaction:
Common salt + fresh water + direct current =
Chlorine + caustic soda + hydrogen gas.
Or, in chemical symbols:
2NaCl + 2H 2O + direct current = Cl2 + 2NaOH + H2
Approximate consumption, per day, of the foregoing
components is as follows:
Salt:
Electrical power:
Fresh water:
160 tonnes
11,000 kilowatts
1,000,000 litres
The salt used in the Nanaimo Plant is shipped by sea from Mexico, where it is produced by the sun evaporating sea water
in large lagoons. The raw salt arrives at the plant in barge loads of approximately 8,000 tonnes. The salt is stored and
dissolved on a concrete pad. Purification of the brine produced from this salt is necessary to remove calcium and
magnesium. These impurities are removed by treating with caustic soda and sodium carbonate, allowing the sludge to
settle, then filtering.
Electrical power is supplied by the British Columbia Hydro Power Authority.
Fresh water is obtained from the Harmac water main. Large quantities of sea water from Northumberland Channel are
also used for cooling purposes.
The plant operates on a twenty four hour per day, seven day per week basis.
The Nanaimo plant was built in March 1963, with construction commencing on that date and operation commencing a year
later. Two hundred and fifty men were employed during main construction period. Most equipment and materials were
purchased from B.C. and Canadian suppliers.
CHLOR-ALKALI PROCESS DESCRIPTION
Chlorine and caustic soda (and hydrogen as a by-product) are produced by the electrolysis of Brine. In the Hooker HC-4
and H-2 electrolytic cells, connected in series, brine is decomposed by direct current electricity. Chlorine gas is formed at
the anode (positive [+] electrode) and hydrogen plus caustic soda is formed at the cathode (negative [-] electrode).
Purified brine is heated, saturated with recovered salt and fed to the cells, which are designed to operate at 55,000
amperes. Power for the electrolytic conversion is converted to DC in silicon rectifiers.
The hot and wet chlorine gas is cooled, dried with sulphuric acid and then compressed to 95 psig. It is shipped by pipeline
to the pulp mill. Liquefaction and liquid chlorine storage facilities provide standby capacity to balance mill demand.
The hot hydrogen gas is used to preheat the brine feed to the cells., then burned as fuel in the boiler, which has a capacity
of 44,000 pounds per hour steam.
The caustic soda from the electrolytic cells, along with unreacted salt, remains in solution in the form of a weak liquor
containing 11% NAOH and 16% NaCl. This solution is evaporated and cooled to remove the salt. The concentrated
(50%) caustic soda is pumped to the Harmac mill as a solution in water. The salt removed by the evaporation process is
returned to the cells.
SODIUM CHLORATE
This plant similarly utilizes DC electric current to convert brine to sodium chlorate. The two processes differ in that the
products of electrolysis, chlorine and caustic soda (with by-product hydrogen) are allowed to mix rather than be kept
separate as is the case with the chlor-alkali process.
The plant commenced construction in 1981 and production commenced in July of 1982. The bulk of the production is
trucked to the Harmac pulp mill with a small amount, also trucked, being delivered to Western Pulp in Port Alice.
The production of sodium chlorate is based on the following chemical reaction:
NaCl + 3H 2O + direct current = NaClO 3 + 3H2
Approximate daily consumption for salt is 16 tonnes and for power 5,000 kilowatts.
CHLORATE PROCESS DESCRIPTION
A regulated flow of salt slurry (brine plus solid crystal salt) is fed to a titanium reactor which in turn feeds the electrolytic
cells through which 30,000 ampere direct current is applied. The resulting chlorine and caustic combine to form sodium
hypochlorite which in turn is converted to sodium chlorate by close control of the reaction conditions.
Liquor flow through the elctrolytic cells is maintained at a high circulation rate by taking advantage of the hydrogen gas lift
effect. Riser pipes carry the mixture of liquor and hydrogen gas from the cells to the degasifiers where hydrogen is
separated from the liquor and the liquor returned to the reactor, then back to the electrolytic cells.
The liquor is circulated in the foregoing manner until the desired sodium chlorate strength is achieved (620 grams per litre).
Being a continuous process, once liquor strength is achieved a small stream is continuously transferred from the reactor,
treated to remove undesirable sodium hypochlorite and stored hot at 60°C. Product solution is transported in stainless steel
tanker truck to our two customers.
The hydrogen gas, separated from the liquor in the degasifier, is cooled passed through caustic scrubbers to remove any
traces of chlorine gas, compressed and burned as fuel in the boiler.
MAY 1985
Diagram of the Hooker HC-4 Cl2 production electrochemical cell
Schematic Flow Chart of the Chlorine and NaOH production facility
Schematic of the operation of a typical membrane Chlor-alkali cell
Chlorate recirculation cell
Schematic Flow Chart of the Chlorate Plant Operation
Ammonium Perchlorate: Rocket Fuel
Perchloric acid synthesis
One important practical application of the instability of chlorine compounds, in this case of the chlorate anion, is to the preparation of
perchloric acid. The reactions are done in two separate steps, under different conditons(!):
4 KClO3 → 3KClO4 + KCl
2 KClO4 + H2SO4 → 2HClO4(l) + K2SO4
basic
acidic
And the pure liquid perchloric acid is distilled off from the high-boiling sulfuric acid. Perchloric acid has chlorine in its highest
oxidation state, +7. It is a strong oxidizer, and contact of HClO4 with even a small amount of organic matter can result in an explosion.
Ammonium perchlorate
Although perchloric acid is a very powerful oxidizer, by itself it is quite stable. It only becomes reactive when in the presence of
oxidizable compounds. When, however, the oxidizing perchlorate anion is mixed with an oxidizable cation one gets, well, rocket fuel.
Ammonium perchlorate contains both components of an autoredox reaction, and is hence explosive. However, it is remarkably stable in
the absence of a detonator. It is the most common fuel for solid state rockets, and its application has developed from occasional use in
JATO (Jet-assisted take-off) booster rockets for overloaded military aircraft to missiles such as those carried by nuclear submarines,
and for peaceful uses to the propulsion system for the space shuttle. In rocket fuel, aluminum is added to balance the electron demand
(create a complementary redox reaction), since perchlorate has more oxidizing potential than ammonium has reducing potential. The
controlled oxidation of aluminum powder by NH4ClO4 in the solid-fuel booster rockets of the space shuttle is enhanced by certain
additives. In this reaction, both the NH4+ ions and the Al are oxidized by the perchlorate anion. The booster is composed of cylindrical
sections about 2 m in diameter and 1 m high. The segments are filled with a concentric ring of the the two reagents mixed in a resin
binder (this mixture sets to a pasty solid) at the factory and then are shipped to the lauch site where the segments are assembled. This
saves hugely on shipping costs.
In the photo the large central tank under the shuttle proper can be seen, flanked by the twin solid-fuel booster rockets. The central tank
contains conventional l. O2 and H2 fuel for the shuttle’s main engine.
Richard Feynman gave the United States a lesson in how science is done when he used a simple experiment to uncover the reason for
the disastrous explosion of the Space Shuttle, Challenger. The Challenger was launched on Tues-day, January 28, 1986. The day was
unusually cold for Florida—the temperature at the time of launch was 29 °F. The world watched in horror when, after a minute or so of
flight, the shuttle and its rockets exploded in a fireball, killing everyone onboard. To understand the reason for the explosion and the
importance of Feynman’s experiment, recall something of the design of the shuttle. The main engine is fueled by liquid hydrogen and
oxygen, which are contained in the large tank strapped onto the belly of the shuttle. The hydrogen and oxygen combine to give water,
and the energy this reaction produces provides the thrust to boost the shuttle into orbit. To provide additional thrust at the time of
launch, however, solid-fuel booster rockets are strapped on each side of the shuttle. The solid-fuel rockets are made in sections, and
the sections are shipped from the factory to the Kennedy Space Center where they are joined to make the completed booster rocket.
The joint between the sections was designed so that hot gases from the burning solid fuel would not leak through the walls of the
rocket. Part of the design to close the joint, and yet make it somewhat flexible, included a thin O-ring made of a special rubber (Figure 7).
From the beginning Feynman and others thought that a possible cause of the Challenger explosion was that the solid fuel had burned
through the wall of the booster rocket and then burned into the tank holding the liquid hydrogen, thus exploding the hydrogen. But
how did this happen? When the shuttle is launched and the solid fuel begins to burn, the walls of the rocket casing move slightly
outward. If this movement caused a joint between sections to open, the fuel would burn through the joint. But the O-rings were
supposed to prevent this. Based on information from engineers involved in the design of the solid rocket boosters, one hypothesis to
explain the accident was that, due to the unusually cold weather, the rubber O-rings had not expanded properly, and flame burned
through the joint. To prove this point, Feynman did a dramatic—but very simple—experiment. During a public hearing Feynman took a
sample of the rubber O-ring, held it tightly in a C-clamp, and put it into a glass of ice water. Everyone could make the qualitative
observation that the rubber did not spring back to its original shape! The poor resilience of the rubber at low temperatures doomed the
Challenger. It should be noted that the manufacturer’s instructions contained clear warnings about the limitations of this rubber,
which must be able to withstand extremely high temperatures and pressures. The compromis that was made with this material was that
it should be used above 15°C only, perfectly reasonable except when Florida gets an unusually cold winter.
More trouble with ammonium perchlorate: the Henderson, Nevada explosion.
Although NH4ClO4 is relatively stable, as perchlorates go, it can be ignited. In 1987, a fire of unknown origin broke out at a
large ammonium perchlorate manufacturing plant in Henderson, Nevada. Ammonium perchlorate is an oxidizer in solid rocket propellant.
The plant was owned by PEPCON. The fire quickly got out of control, and eventually led to the detonation of thousands of pounds of
the chemical stored at the site. The detonation demolished the plant and its shock wave caused significant property damage in nearby
Las Vegas. Two people died in the blast, an amazingly small number given the severity of the explosion.
The following are some more pictures showing an aerial view of the plant location after the explosion and its location in the Las Vegas
area. The ring road around the site is clearly visible, but the plant itself was blown clear away!
More recently the same company had another fatal accident, and the following story provides more detail on the original 1988
explosion.
“Plant safety inspected once
By Glenn Puit and Keith Rogers, Review-Journal (Las Vegas, Nevada)
Officials, speaking in the wake of a deadly chemical explosion, say they are not required to check factories.
The American Pacific Co. chemical plant where a man died Wednesday in an explosion of a rocket fuel component had been
inspected by Utah safety officials only once, in 1991, shortly after it opened.
Officials with Las Vegas-based American Pacific would not discuss safety guidelines at their Western Electrochemical Co. plant, 14
miles northwest of Cedar City. The business relocated to southwestern Utah after a series of massive blasts involving the same
material, ammonium perchlorate, leveled the company's operations near Henderson on May 4, 1988.
"We certainly can't go and sit on their doorstep every day," said Robert Dreman, a safety health manager for Utah's Occupational
Safety and Health Division.
Dreman said the state safety division is not legally required to conduct random inspections of businesses. Instead, inspectors
respond when there is a serious accident, a report is filed warning of imminent danger, or a series of incidents leads the agency to
schedule inspections. He also said Western Electrochemical adheres to its own safety policies, which he described as stringent.
"They (Western Electrochemical) can refuse us entry, so we are kind of between a rock and a hard place," Dreman said. "We have
to work with any employer."
Ammonium perchlorate is an oxidizing ingredient that enhances ignition of solid fuels in rocket and missile engines.
In 1988, at American Pacific's plant near Henderson -- Pacific Engineering & Production Co. of Nevada, or PEPCON -- a series of
colossal explosions left two dead, injured 300 and caused $75 million in damage. Clark County fire investigators blamed the blasts on
welders, cramped storage, messy conditions and wind. Company officials disputed those contentions.
Shortly after that, the company moved the operation to Iron County, Utah, and renamed it Western Electrochemical. On
Wednesday, a smaller explosion ripped through a building at the plant, killing Daniel Baldeck, 44, of Cedar City. A co-worker, Ron
Meachum, 44, was burned over 50 percent of his body and remained in critical condition Thursday at the University of Utah Medical
Center.
The safety division's investigation into Wednesday's explosion is continuing. Preliminary reports indicate it may have occurred
while a dust collector was being cleaned.”