Gas works?
inputs coal, produces tar as a waste.
essentially treat as a power station, that produces no power, but in inside cities as opposed to outside (making getting the coal in interesting)
need something to use the tar, or dispose of it.
Smokeless Fuels plant
again takes coal in, no specific output, inless you want to sell the resulting product in small shops
Also have an idea for an acetate works (chemical works) chain, but its big, and until I can draw at least the buildings I'm keeping quiet.