liquid from the channel 28 of the shaft 22 to the pipe are needed the pipe s carrying the washing liquid to a proper nozzle system located further away from the shaft and the pipes at the same time acting as supports for the nozzle system u2014 or of a solution where one or more nozzles are arranged in direct connection with the feeder means 24 and by means of the nozzle s both the walls and the ceiling of the tower or either one of them may be kept clean the nozzle arrangement mentioned above may e g be a larger chamber located at the end of one or more pipe s delivering washing liquid several nozzles having been fastened at the walls of the chamber u2014 or one or more transversal pipe s provided with one or more nozzles the pipe s having been fastened to one or more pipe s at its their opposite end s with regard to the shaft 22 or in proximity thereof as a further embodiment of the invention an apparatus may be devised where in connection with the top of the tower regardless of whether the tower is provided with a ceiling or a cover or whether the tower is open at the top there is arranged a feeding and washing device which is either continuously or intermittently rotating this device may preferably but not necessarily consist of e g a vertical pipe located in the middle of the tower the bottom of the pipe being.