@Iluviaporos - I think sometimes they are asking for plant experience more because they need to make sure you are going to be OK working around machinery, rather than because they want you to work directly with the machinery.
Generally they are going to want qualified engineers or mechanics to really work with the equipment. Plant maintenance services are generally quite specialized since anything worth maintaining is going to be really expensive. They don't want their average workers messing around with it.
But, they do want their average workers to be savvy enough that they aren't going to, say, get a finger caught in the machine.
So, even if all you are going to be doing is making sure the gears are properly oiled, or that the rubbish bins nearby are being taken care of, experience is definitely going to be a plus in your application.