Fresh water generator
Since feed water losses occur in all steam power plants , fresh water ( fresh water ) must be replenished. Either you carry fresh water in tanks or you are forced to produce feed water from seawater . For sensitive high-pressure steam systems, even the fresh water carried along cannot be used without further ado, it must therefore be treated. The extraction of the feed water from sea water or the treatment of the fresh water takes place in evaporators.
The submersible evaporator consists of a cylinder , which is heated by coils that are immersed in seawater. Part of the sea water evaporates, the resulting steam is sucked off by the condenser and condensed there, added to the old feed water or passed through a special preheater into collecting cells. Exhaust steam from the auxiliary machines or, in the case of increased evaporation operation, bleed steam from the steam engine or steam turbine was used for heating. The steamships have largely disappeared in the meantime, and motor ships are heated by the cooling water from the high-temperature cooling water system. The submerged tube evaporator then works at a negative pressure of around 0.1 bar.
The vacuum evaporator is the most widely used feed water generator today. Depending on the size of the system, it is possible to produce up to 50 tons of fresh water (water quantities are always given in tons on a seagoing vessel) with a salt content of less than four milligrams per liter from seawater per day. The system consists of the evaporator with its heating tube bundle, a liquid separator, the vapor condenser, the distillate cooler, the lye pump, the distillate pump, the radiator system for suction and the salt measuring system.
The heating steam flows through the heating tube bundle at a pressure of around 0.7 bar and a temperature of around 90 degrees Celsius and is discharged as condensate via the condensate pot to the condenser. The seawater that is evaporated first passes the distillate cooler, then the cooling pipes in the vapor condenser, flows through the radiator condenser as cooling water and then enters the evaporator. The sea water evaporates after it has flowed through the aforementioned facilities as cooling water and has been heated almost to the evaporation temperature. There is a vacuum of 99 percent in the evaporator. The vapor generated flows through the liquid separator to the vapor condenser and from there is sucked off as distillate by the distillate pump. It flows through the distillate cooler. It then flows into the distillate tank under the control of the salt measuring system. A heater, operated with a motive steam of 12 bar, ensures the negative pressure in the evaporator. About 33 percent of the seawater flow rate is converted into distillate. The remaining 67 percent is pumped overboard by the drain pump through the drain regulator.
Compact evaporator systems that work according to the same principle are installed in today's motor ships. The cooling water heat from the main engine is used for heating.