The Repsol gas man in Tortosa parks his wagon by the rowing club,down by the river (where else) opposite the police station.You will need a gas certificate which means you will have to get a  registerd gas fitter to check and install your gas appliance.He will then issue you a certificate and you take this to  the gas shop opposite the gas man.He then registers you and you will be asked back the following day,if you're lucky,to pick up your cylinder.You could,if you choose to,is borrow a friends certificate.(Not my suggestion but the gas mans,after I'd registered of course......)Cost about 20 - 25 euros for a first full cylinder,you then exchange the empties for fulls for about 12 euros.
The only person that can speak English is a man in the repsol office in Tarragona.