Having seen the report on the China Clay Dries in Par by @Janedoe I finally managed to drive down to Cornwall to have a look. Although large parts of its innards have been ripped there is still quite a lot to see and I spent a happy four to five hours exploring the site.
This time I tried to understand what I saw and to put everything into context. This report is heavily indebted to a 2018 report by @TerminalDecline and any inaccuracies are due to my lack of knowledge
Nevertheless I hope you enjoy it...
The production of English porcelain (china) began in 1745 in Cornwall when the apothecary William Cookworthy discovered china clay (also known as kaolin) deposits at Tregonning Hill. Rouhgly 20 years later, in 1768 he patented a method to turn the clay into fine porcelain and established the Plymouth Porcelain Factory. Other potteries in the UK followed suite and started to use china clay from Cornwall. By the early nineteenth century the kaolin industry had become big business. The deposits around St Austell had emerged as the largest in the world, and china clay was being used in many other products such as paper, paint and rubber goods. Throughout the 19th century thousands of men were employed, with harsh working conditions, either spraying the walls of open pits with high-pressure hoses to remove the clay, or processing and transporting the material, which was exported to all corners of the globe. Before World War I, about 70 china clay producers were operating in Cornwall and the competition was cut throat. By 1910 production was nearly one million tons a year, 75% of which was either exported to North America or Europe.
1) China Clay Dries from the back
In 1919 the three largest china clay producers, namely the West of England China Clay Company (established 1849), Martyn Brothers (established 1849) and North Cornwall China Clays (established 1908), merged into English China Clays (EEC). At that time these three companies accounted for about 50% of the total china clay output. In 1932 ECC acquired its rivals John Lovering and HD Pochin and by the end of the 1960s ECC was producing around 2.5m tons of china clay a year. In 1999 ECC was bought by the French company Imetal (which was founded in 1880 by the Rothschild family). Imetal was later renamed into Imerys, now a multinational company that specialises in the production and processing of industrial minerals.
Unlike tin or copper, china clay did not require deep mining and was retrieved using open cast mining. The walls of the open pits were blasted with water cannons in order to separate the soft clay from the granite. As late as the 1970s, the run-off would enter the local rivers, eventually ending up in St Austell Bay, turning the whole sea white For each ton of clay extracted, there were five tons of waste. The waste or slag was taken and dumped back on the land, in long hills or in large conical structures. These large white hills were soon referred to as the Cornish Alps or Pyramids and rapidly changed the local skyline. Finally the good wet clay was recovered and laid out in massive long low buildings, known as pan-kilns. With a chimney at each end, heat was run along a underfloor flue system and the clay above would slowly dried out. There are around 100 pan-kilns in the St. Austell area, in varying conditions with a few others around Bodmin Moor and Penwith. However, this approach took months and new, more efficient methods for drying the clay were required in order to increase production.
Two of these methods can be seen at the china clay dries in Par. The first method, introduced in 1911 was the filter press (shown in the two pictures below) which was the first meaningful way of speeding up the clay drying process to be invented.
2) Filter Presses
3) Filter Presses
4) Filter Presses
A filter press (see image below) consists of a feed head and a follow head which stood either side of a bank of press plates. The follow head and the plates are hung from a steel joist above, which is supported by the feed head and the bulk head, and the whole press assembly is supported on a pair of steel joists below. A filter cloth is affixed to each of the press plates. Each press plate has a hole in the middle, allowing clay slurry to pass through. Clarified water leaves the press through a small tube at the bottom of each plate. During operation, the press is closed tight by pushing the follow head onto the press plates. The valve is then opened allowing clay being pumped at pressure to enter the feed head and the press. The slurry fills the gap between each pair of plates. A pressure gauge on the feed head gives an indication of current pumping pressure - after 1-2 hours, the gauge will begin to increase, indicating that the press has reached capacity. The feed is shut off, the follow head is retracted, and the plates are separated one by one. The solid cake has a habit of sticking to the filter cloth, therefore it usually has to be freed by hand. A good press operator will be able to judge when it is the right time to shut off the press - shutting it off too early will result in wet cakes, shutting it off too late risks equipment damage and dangerous pressure leaks.
5) Feed head of a filter press
The second method for speeding up the drying process, the Buell dryer, was introduced to the china clay industry by the English China Clays company in 1944 just after WW2. The dryer itself is composed of a large upright cylindrical chamber, inside of which are 25 to 30 layers of trays or "hearths". Indirectly heated air from an oil-fired (latterly natural gas-fired) furnace or steam heater is distributed throughout the dryer by a series of fans and ducts. At the centre of the dryer is a rotating column, to which the trays are attached and positioned radially within the dryer. Material enters the top of the dryer and lands on one of the top trays. As the central column rotates, fixed arms push the material off the tray, dropping it down onto the one below it. Gradually the material works its way down through the dryer in this manner, and after 45 minutes clay exits the bottom of the dryer onto conveyor belts.
6) Buell Drier
7) Mechanism below Buell Drier
Before the advent of stringent health and safety rules the steam from the dryers, including the dust, was simply exhausted to the atmosphere. Dryers spat out enormous volumes of clay dust, to an extent that almost everything within a 100 yard radius of a dryer was dusted in clay. Eventually, like most industries, the clay companies were forced by law to start reducing dust emissions from their drying plants and one way to do this was the large-scale introduction of wet scrubbers. The steam from the dryer enters the base of a large cylindrical vessel, and passes through a fine mist of china clay slurry. Clay dust particles suspended in the steam get caught in the mist of clay slurry. The slurry drains out at the bottom, while the "scrubbed" steam leaves through the stack. The clay slurry is then pumped to the filter presses. Wet scrubbing had the side effect of pre-heating the clay slurry as well as slightly reducing it's moisture content. This in turn slightly reduced the moisture content of the resulting filter cake, and consequently made drying marginally more efficient.
8) Wet Scrubber
Finally, after the drying process was completed, the dried china clay was stored in the linhay before it was removed from the dries either by ship from the Par Docks.
9) Linhay
And two more pictures...
Thank you very much for looking. Hope you liked it...
This time I tried to understand what I saw and to put everything into context. This report is heavily indebted to a 2018 report by @TerminalDecline and any inaccuracies are due to my lack of knowledge
Nevertheless I hope you enjoy it...The production of English porcelain (china) began in 1745 in Cornwall when the apothecary William Cookworthy discovered china clay (also known as kaolin) deposits at Tregonning Hill. Rouhgly 20 years later, in 1768 he patented a method to turn the clay into fine porcelain and established the Plymouth Porcelain Factory. Other potteries in the UK followed suite and started to use china clay from Cornwall. By the early nineteenth century the kaolin industry had become big business. The deposits around St Austell had emerged as the largest in the world, and china clay was being used in many other products such as paper, paint and rubber goods. Throughout the 19th century thousands of men were employed, with harsh working conditions, either spraying the walls of open pits with high-pressure hoses to remove the clay, or processing and transporting the material, which was exported to all corners of the globe. Before World War I, about 70 china clay producers were operating in Cornwall and the competition was cut throat. By 1910 production was nearly one million tons a year, 75% of which was either exported to North America or Europe.
1) China Clay Dries from the back
In 1919 the three largest china clay producers, namely the West of England China Clay Company (established 1849), Martyn Brothers (established 1849) and North Cornwall China Clays (established 1908), merged into English China Clays (EEC). At that time these three companies accounted for about 50% of the total china clay output. In 1932 ECC acquired its rivals John Lovering and HD Pochin and by the end of the 1960s ECC was producing around 2.5m tons of china clay a year. In 1999 ECC was bought by the French company Imetal (which was founded in 1880 by the Rothschild family). Imetal was later renamed into Imerys, now a multinational company that specialises in the production and processing of industrial minerals.
Unlike tin or copper, china clay did not require deep mining and was retrieved using open cast mining. The walls of the open pits were blasted with water cannons in order to separate the soft clay from the granite. As late as the 1970s, the run-off would enter the local rivers, eventually ending up in St Austell Bay, turning the whole sea white For each ton of clay extracted, there were five tons of waste. The waste or slag was taken and dumped back on the land, in long hills or in large conical structures. These large white hills were soon referred to as the Cornish Alps or Pyramids and rapidly changed the local skyline. Finally the good wet clay was recovered and laid out in massive long low buildings, known as pan-kilns. With a chimney at each end, heat was run along a underfloor flue system and the clay above would slowly dried out. There are around 100 pan-kilns in the St. Austell area, in varying conditions with a few others around Bodmin Moor and Penwith. However, this approach took months and new, more efficient methods for drying the clay were required in order to increase production.
Two of these methods can be seen at the china clay dries in Par. The first method, introduced in 1911 was the filter press (shown in the two pictures below) which was the first meaningful way of speeding up the clay drying process to be invented.
2) Filter Presses
3) Filter Presses
4) Filter Presses
A filter press (see image below) consists of a feed head and a follow head which stood either side of a bank of press plates. The follow head and the plates are hung from a steel joist above, which is supported by the feed head and the bulk head, and the whole press assembly is supported on a pair of steel joists below. A filter cloth is affixed to each of the press plates. Each press plate has a hole in the middle, allowing clay slurry to pass through. Clarified water leaves the press through a small tube at the bottom of each plate. During operation, the press is closed tight by pushing the follow head onto the press plates. The valve is then opened allowing clay being pumped at pressure to enter the feed head and the press. The slurry fills the gap between each pair of plates. A pressure gauge on the feed head gives an indication of current pumping pressure - after 1-2 hours, the gauge will begin to increase, indicating that the press has reached capacity. The feed is shut off, the follow head is retracted, and the plates are separated one by one. The solid cake has a habit of sticking to the filter cloth, therefore it usually has to be freed by hand. A good press operator will be able to judge when it is the right time to shut off the press - shutting it off too early will result in wet cakes, shutting it off too late risks equipment damage and dangerous pressure leaks.
5) Feed head of a filter press
The second method for speeding up the drying process, the Buell dryer, was introduced to the china clay industry by the English China Clays company in 1944 just after WW2. The dryer itself is composed of a large upright cylindrical chamber, inside of which are 25 to 30 layers of trays or "hearths". Indirectly heated air from an oil-fired (latterly natural gas-fired) furnace or steam heater is distributed throughout the dryer by a series of fans and ducts. At the centre of the dryer is a rotating column, to which the trays are attached and positioned radially within the dryer. Material enters the top of the dryer and lands on one of the top trays. As the central column rotates, fixed arms push the material off the tray, dropping it down onto the one below it. Gradually the material works its way down through the dryer in this manner, and after 45 minutes clay exits the bottom of the dryer onto conveyor belts.
6) Buell Drier
7) Mechanism below Buell Drier
Before the advent of stringent health and safety rules the steam from the dryers, including the dust, was simply exhausted to the atmosphere. Dryers spat out enormous volumes of clay dust, to an extent that almost everything within a 100 yard radius of a dryer was dusted in clay. Eventually, like most industries, the clay companies were forced by law to start reducing dust emissions from their drying plants and one way to do this was the large-scale introduction of wet scrubbers. The steam from the dryer enters the base of a large cylindrical vessel, and passes through a fine mist of china clay slurry. Clay dust particles suspended in the steam get caught in the mist of clay slurry. The slurry drains out at the bottom, while the "scrubbed" steam leaves through the stack. The clay slurry is then pumped to the filter presses. Wet scrubbing had the side effect of pre-heating the clay slurry as well as slightly reducing it's moisture content. This in turn slightly reduced the moisture content of the resulting filter cake, and consequently made drying marginally more efficient.
8) Wet Scrubber
Finally, after the drying process was completed, the dried china clay was stored in the linhay before it was removed from the dries either by ship from the Par Docks.
9) Linhay
And two more pictures...
Thank you very much for looking. Hope you liked it...
