Patent GB-1408807-A (GB)
Title: Thermally operating apparatus
IPC: F01K25/06
Filed: 1973-08-21
Abstract: 1408807 Boilers ORMAT TURBINES (1965) Ltd 21 Aug 1973 [20 Sept 1972] 39628/73 Heading F4A [Also in Division F1] A heat transfer apparatus includes a pair of heat exchangers connected in a closed system containing a heat transfer fluid made up of a mixture of at least two fluids having different boiling points, a starting fluid that is the fluid having the lower boiling point having a freezing point lower than the freezing point of the operating fluid. The application of heat to the first of the heat exchangers 21 converts liquid therein to vapour which flows into the second heat exchanger 23 from which heat is extracted for converting the vapour therein to a liquid at a temperature and pressure lower than in the first heat exchanger. The apparatus comprises means to feed liquid from the second heat exchanger into the first heat exchanger and means 33 for trapping liquid starting fluid as it is produced by the second heat exchanger during the initial application of heat to the first heat exchanger and for preventing the return of the trapped liquid starting fluid to the first heat exchanger as long as sufficient heat is applied thereto whereby the operating fluid circulates around the system after the starting fluid is trapped. In the plant shown the operating fluid, e.g. ortho-dichlorobenzene is vaporized in a boiler 21 and delivered to a turbine 22 which expands the vapour driving an electric generator 24 which furnishes power to an electrical load 25. Condenser 23 condenses the exhaust vapour at a temperature which is a predetermined increment above the ambient temperature which may be lower than the freezing point of the operating fluid. The condenser is designed to hold the liquid at a temperature which is above its freezing point. The condenser liquid may pass by gravity through the bearings 27 and by reason of the hydrostatic head in the vertical pipe 28 the liquid may pass through the non-return valve 29 and into the boiler 21. When the power plant is on stand-by all the liquid in the system will be drained into the boiler 21. The contents of the boiler will be the operating fluid and a starting fluid which may be methyl alcohol. The initial application of heat to the boiler 21 will cause the starting fluid to boil off and pass into the turbine and condenser. The starting fluid will have little effect on driving the turbine with the result that the bearings 27 will be lubricated well before rotation occurs. More important the various components of the power plant will be heated to a level that will prevent freezing of the condensed operating fluid when the latter begins to boil off and circulate in the plant. In a modification, associated with the vapour side of the condenser is a distillation column designed to condense the starting fluid contained in the main condenser and cause the starting fluid to be collected in a tank which is connected to the boiler by means of a non-return valve. The arrangement is designed so that during colder weather feedback of starting fluid will occur. It is possible to control the feedback by means of a valve between the distillation column and the starting fluid tank. It is stated that the operating fluid may be water and the starting fluid may be methyl alcohol. The starting fluid may be methyl cyclohexane.