Really great photos and nice report.
With my Chemical Engineer's hat on though, for your own sake please
don't enter plant units like the rotary drier: technically, they're classified as confined spaces and there's a good reason why there's a whole swathe of HSE legislation governing entry (
https://www.hse.gov.uk/confinedspace/).
Bottom line: confined spaces can harbour low oxygen / toxic atmospheres and they continue to kill a number of people every year, even in this day and age. I was very close to someone who died in exactly those circumstances. Unless you're 100% sure that there's a safe atmosphere (i.e. have Drager tested or have reliable, calibrated, gas monitoring with you),
please don't enter!! Confined spaces also extend to any area in which a hazardous atmosphere can accumulate - for example depressions below ground level (pipe trenches / bunds / etc. ), even if they are open to the sky.
I don't want to detract from your report - I no longer work in industry (ex ICI down the road at Runcorn) and it's great to see places like this that I heard about, that we relied upon on our site, but never got to work at - but neither do I want others reading it to think that it's OK to unwittingly expose themselves to significant hazard levels. Please keep safe.