SEPTEMBER 2019 COVER STORY
From brine to bag: the salt production process
STEP ONE: Extraction
Located about three miles from the Middlewich facility, the Warmingham
Brinefields contain extensive salt reserves. At a depth of 180m to 500m below
the surface, salt deposited over 300 million years ago – when Cheshire was in the tropics –
sits between layers of rock.
The salt is extracted using sustainable solution mining techniques, whereby the salt is
converted to brine, which is then pumped across town to the main salt plant. This is a long
process, explains Crabb: “If we drill a new borehole today, we’d be two or three years from it
being in a position to produce salt we could use.”
Over time, the extraction of salt forms large cavities that can be up to 100m wide. Many
of British Salt’s old production cavities are in use for storing natural gas, providing the UK
with gas storage used to help balance gas supplies. As much as 95% of all water used at the
Middlewich site is recycled and sent back to collect more salt.
STEP TWO: Purification
Once the brine is pumped to the main plant it goes through a multiple-stage
purification process, removing the impurities that are naturally present in the
salt deposits. The brine is purified through a series of settlement tanks and reaction vessels.
Three stages of purification remove magnesium, sulphate and calcium carbonate
impurities. The quality of brine is constantly monitored via an advanced analysis and
monitoring system, to produce the highest purity final salt and ensure efficient operations.
Extracted impurities are returned to the brine field in a mature cavity. The purified brine is
then either used in the next stage of production, the evaporation process, or is available
for purchase for use as a finished product.
STEP THREE: Evaporation
The purified brine undergoes a final filtration before being passed into the
first of six evaporation vessels. The brine is boiled under vacuum, a process
which is highly energy efficient. The heat used in this evaporation process is generated
from the on-site combined heat and power (CHP) plant, and the steam is ultimately
re-used in the process, ensuring nothing is wasted. The salt crystals, which form as the
brine is evaporated, are separated from the brine in clarifying vessels and then, finally,
using centrifuge technology.
The salt produced at this stage is Undried Vacuum (UV) salt, which is used as a product
in its own right or which can be dried further to form Pure Dried Vacuum (PDV) salt.
STEP FOUR: Drying, Grading & Storage
The UV salt is then mixed with hot air inside fluidised dryers. The smallest salt
crystals are extracted from the air in the dryers and transferred to the compaction
plant. The remaining dried salt is then graded through a series of screens, which separates
the salt crystals based on their particle size to form Fine 50, Fine 60 and Tanker Fine and
Tanker Coarse products. Any remaining salt crystals are packaged as standard PDV salt.
STEP FIVE: Compacted Products
The smallest salt crystals and salt dust are transferred to a compaction plant.
This material is compacted into a water softening range known as Aquasol
and Granulite. Block salt is produced through the compaction of salt and is available as a
popular water softening product.
STEP SIX: Packaging
Once the product is ready for market, it’s then packaged on-site. British Salt’s
plant has two high speed packing lines. This line can package up to 1500 sealed
bags of product per hour, compared to just 400 on the previous ones.
the roost, with the company struggling to attract
anyone new. “The old guard are great, and we
really appreciate their loyalty, but it can create
something of a glass ceiling for people coming
through the ranks below,” says Crabb. “On top of
that, our retention levels have always been good,
but we’ve long struggled to attract anyone new.”
To combat this, British Salt has engaged
in what Crabb calls a “covert and overt talent
development programme”. Despite appearances,
Middlewich is a relatively advanced site, especially
with the new boiler and packing line. This means
the skills Crabb and the team need to attract
will be vastly different to those needed even 15
years ago. “We’ve restarted our apprenticeship
programme, focusing on electrical engineers
in particular as the factory of the future will be
based on control systems,” Crabb explains. “Our
new boiler plant will have a continuous emissions
monitoring system on it, for instance. Fine-tuning
that will need a certain IT skill base.”
Attracting new blood is a significant challenge
for the site. Why would someone taking their
first steps into manufacturing want to work at a
50-year-old factory using equipment that Crabb
admits “was state-of-the-art in 1969 but hasn’t
been upgraded since”? The hook is to be part of
transforming the site, says Crabb. “Even the new
packing line will be obsolete in five years, so we
need skills that are able to adapt. We are a legacy
site with legacy assets but with lots of heritage
and brand power and the opportunity to bring
the factory into the 21st century.”
This blend of history and technology, it
is hoped, will see British Salt attract a new
generation of workers into the industry. And
once they’ve joined, the brightest and best can
pick a path to further development, whether in
leadership or more technical skills. On top of
this, the company organises regular ‘job swaps’,
where new staff spend time working in other
departments. “We recently sent one of our
mechanical fitters to work in the brine fields,”
says Crabb. “There was a bit of scepticism about
it, but he’s loving it. We also send operators
and technicians out to the factories where
our newest equipment is being made. A team
has recently got back from Italy, for example.