The Development of Vacuum Evaporation in the UK
The critical parameter in the brine evaporation process is the fuel to salt ratio. In other words, the production of the maximum tonnage of salt for the minimum expenditure on coal. This was the aim with Furnival’s patent pan and a logical development of the machine pan type process was the adoption of multi-effect vacuum evaporation.
This was a process which had been used in sugar refineries since 1812 and was first applied to salt making in North America in 1880’s. There is a record of a pilot plant trial at Shirleywich Saltworks near Stafford in the 1880’s but the UK’s first commercial multi-effect evaporator to be used with brine was installed by James Hargreaves in 1901 at the Electrolytic Alkali Works at Cledford, Middlewich.[See Brine Electrolysis] Technical details of the James Hargreaves evaporator are lost and hence it has been missed from the histories of the industry in which the Salt Union’s Winsford Vacuum Plant of 1905 is claimed as the first in the UK. This plant was purchased from the Manistee Company in the United States; the then world leaders in the technology. With the expertise derived from this plant the Salt Union engaged the Mirlees Watson Company of Glasgow to construct a second very large evaporator alongside the Manchester Ship Canal at Weston Point, Runcorn where production started in 1911.
The superheated steam from the boilers was at too high a pressure and temperature for the brine evaporation and was first used to generate electrical power and it was the low pressure ‘pass-out’ steam from the turbines that was fed to the first effect of the evaporator. The Mersey Power Company Limited was formed to distribute and sell this surplus electricity. The Salt Union already had an open pan saltworks at Weston Point which had been established in 1884 by the Mersey Salt and Brine Company following the construction of a brine pipeline (the Marbury pipe) from Northwich. This preceded the formation of the Salt Union.