The process for extraction of oil from shale was patented in the UK in 1694: British Crown Patent No. 330 covered "a way to extract and make great quantityes of pitch, tarr, and oyle out of a sort of stone." However, it was not until the mid 1800s that commercial extraction on any great scale began. The impetus was the demand for lamp-oil, which began to outstrip the production of the whaling industry. Shale-oil production was only economically viable for a short period because crude oil, discovered in Pennsylvania in 1859, was cheaper.
The traditional process of mining the shale and extracting it in a retort and condenser remains much the same today as when there was active shale processing at Kimmeridge. The process is known as "pyrolysis" or destructive distillation. The shale is heated in a retort to about 500ºC at which point the waxy hydrocarbon, known as kerogen, vapourises. When condensed, the oil is dark brown, heavy and slow flowing. It is also difficult, smelly and expensive to refine.
Nowadays, some shale-oil is produced by heating the raw material in situ below ground and pumping the resulting oil in much the same way as crude oil is extracted. With crude oil extraction becoming more expensive, there is renewed interest in oil shale and plans are supposedly afoot to exploit several large deposits. But to return to the nineteenth century extraction processes, on which the model will be based:
This view of a large Scottish shale-oil works of the same period shows some architecture. As well as the retort-house there are large holding tanks. I suspect that's why in real life the extraction process was carried out at Wareham: there's really no room at Kimmeridge for this sort of set-up. But, we can assume that in a smaller setup (self-contained on the wharf) there's a small holding tank inside and the stuff emerges already in the shipping barrels. In at least one period, Wanostrocht used oil-shale lumps to provide the heat as well. Although it was smelly, the shale was used locally for heating and was known as "Kimmeridge Coal". This gives two options for modelling the process: either use coke for heating the retort or shale itself, depending on the required complexity.
None of the technical information told me what a retort-house at Kimmeridge would have looked like even if there had been one there. However, I found a small old one for sale, and in fact it just looks like any other industrial building. The retorts are inside. It is, however, quite interesting, has a rather sweet small chimney doubling as a clock and it'll form the basis for my outline design.
I wrote that back in 2001, when I was expecting to use just one level of the retort house. It's still an interesting structure but I'll need to add a second story and rearrange the various elements to fit my new cunning plan. However, there are plenty of prototypes around the area with a ground floor of stone (stops the furnace burning the walls, of course) and a lighter upper story of shiplap wood. So elements of this building will remain the focus for the new layout.