Other companies expanded their open pan operations and also erected vacuum plants. The British Soda Company, a subsidiary of the Staveley Iron and Chemical Company of Chesterfield, established their Glacia Vacuum Salt Works at Sandbach in 1919. Here they erected a Kestner triple effect brine evaporator which had been obtained from a wartime glycerine factory and modified for use with brine. This was a forced circulation external calandria type evaporator and the most advanced brine evaporator in the UK at that time.
In the period between the wars small vacuum evaporators of the Mirlees type with internal calandrias were installed by most salt manufacturers. Cerebos at Greatham on Teeside and at their subsidiary the Middlewich Salt Company, Palmer Mann at Sandbach, Charles Moore at Lymm, Mangers at Stafford, New Cheshire at Wincham, and the Salt Union at Stoke Prior. At all these works, open pan salt making was continued alongside the vacuum operation.
Salt Making in the 1930s
By the late 1930s it was becoming apparent that the days of the open pan were numbered. Many of the uses which required open pan salt (and for which vacuum salt was unsuitable) had disappeared due to technical innovation such as refrigeration. Two markets which vacuum salt could not supply were the Salt Cake process and the export of low bulk density factory-filled salt to West Africa, which was still considerable.
In 1937 the Salt Union was taken over by ICI and became the ICI Salt Division. Research started on modifications to the vacuum process that would enable the economic production of a salt that would meet these demands.
One line of research was the application of the Krystal Process for controlled crystallisation which had been developed in Oslo in 1922 but not yet applied to salt making. A pilot plant to examine the process was installed at Winsford before the war and after the war a full scale evaporator body was installed as a fourth effect of the triple effect evaporator at Stoke Prior in Worcestershire. An important advantage of the so-called Krystal or Oslo evaporator was its ability to use the mother liquor brine from a conventional vacuum evaporator and still make pure salt, thereby reducing effluent problems and brine wastage.
The Oslo Evaporator yields salt with spherical crystals known as “granular salt” and this was found to be suitable for use in the Mannheim Furnaces of the salt cake process. When the Stoke Prior Works was eventually closed, the Oslo evaporator body was transferred to Weston Point Works at Runcorn where it was added to the present-day line of Oslo evaporator vessels which form part of the complex evaporator installation at that site.
ICI’s search for a low bulk density vacuum salt studied the growth of crystals with a non-cubic defect or dendritic structure. This work resulted in the trace addition of sodium ferrocyanide (hexacyanoferrate II) in order to produce a low bulk density dendritic salt.
A spin-off from this work was the discovery that levels of as little as 4ppm of this additive was an effective anti-caking agent. This property has eliminated the very real danger from a serious caking of the dry salt when in silos and has enabled dry vacuum salt to be handled in bulk tankers with pneumatic discharge into a customer’s storage silo.
Salt Making in the 1950s
1950’s patents were taken out by both ICI and the Dutch KNZ company and the use of sodium hexacyanoferrate is now standard practice throughout the industry.
These developments enabled ICI’s Salt Division to close down all its Winsford open pan operations by the mid 1950’s.
The immediate post war years saw a gradual decline of open pan operation and the erection of new and second generation vacuum evaporators, as part of a general expansion of the chemical industry. At the Sandbach Palmer Mann works, the 1930’s small Mirlees plant was joined by a similar plant of the same size in about 1950. While also in 1950, the British Soda Company added a much larger internal calandria triple effect Mirlees evaporator to the 1919 external calandria Kestner evaporator. The latter operated for a further three years before final dismantlement.
Cerebos and Palmer Mann were very much food salt suppliers. On the other hand, British Soda’s salt demand was geared to Staveley’s chlorine –caustic soda requirement and chlor-alkali operations dictated plant size at the Murgatroyd Salt and Chemical works, also at Sandbach, which began operations in 1950. The Charles Moore vacuum salt plant at Lymm was owned by the Distillers Company and earmarked for chemicals manufacture, but succumbed in 1950 to subsidence and led eventually to the Distillers’s joint holding in the Murgatroyd Company.
At Stafford a triple effect Oslo evaporator was installed but was to prove less successful than that in use by ICI at Stoke Prior and later that at Weston Point.
Salt Making in the 1970s
All open pan operations in Middlewich had closed down by 1970 and the last major works to close was that of Palmer Mann at Sandbach which ceased operations in 1971.
All Stafford salt making, including that of Cerebos at Greatham and Middlewich and British Soda at Sandbach, ceased in 1969 with the start up of British Salt. The 1960’s saw the closure of many of the small, older vacuum plants and this trend continued in the 1970’s, by which time salt production had consolidated on two major sites . That at Weston Point which represented all the ICI (later Salt Union and now Ineos) operations and the British Salt Works at Middlewich which represented a merger of Cerebos and Amasal Group.
The New Cheshire Salt Works Ltd remained until 2006 as a third vacuum white salt maker at Wincham. Their small, triple effect Svenson evaporator, enabled them to corner the market for high purity special salts not previously viable on the two major plants.
For historical correctness it must be recorded that the last open pan works Cheshire was the remaining operational pan of the of the Lion Salt Works which ceased operation in 1986, now in process of restoration as a working museum and as a monument to the industry.
18th, 19th & 20th Century Salt Making
- Eighteenth Century Salt Making – Inland White Salt
- Eighteenth Century Salt Making – Open Pan Salt Technology
- Nineteenth Century Salt Making – Developments in Salt Making Technology
- Nineteenth Century Salt Making – The Entrepreneurs
- Nineteenth Century Salt Making – Tricks of the Trade
- Salt Making in the 20th Century