Cement Kiln suggestion
First let me start by saying this game is kickass!
May I suggest that the cement kiln be changed from fire fuel to wind / water fuelled using the windmill or water wheel as power source, this to me seems more logical, additionally you could have an upgrade that allows for power with motor to take over vs the wind / water as you progress with the addition of it being faster with electric motor.
Thanks for your consideration.
I like this idea, you could link it with mechanics and add a primitive crank style power generator. Like the small sized hand turned generators that Edison would have used to show off light bulbs, but wind or water turned. A little copper for conduction, some iron for the case and a wood handle/crank