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Marine Machinery 7 E Part 2

Tham khảo tài liệu 'marine machinery 7 e part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 30 Main propulsion services and heat exchangers Figure 1.25 Package feed system for tanker 1. Extraction pumps 2. Steam jet air ejectors 3. L.P. heater and drain cooler 4. De-aerator 5. Flash chamber 6. De-aerated water storage tank Main propulsion services and heat exchangers 3 Figure 1.26 Typical de-aerator Weir Pumps Ltd it will be apparent that de-aerators of this type must be installed at such a height in the engine room that the pressure head at the extraction or feed pump suction is greater than that corresponding to the water temperature. The maintenance required is the control of corrosion the cleaning of the nozzles the renewal of those showing signs of erosion which will seriously impair the efficiency the overhaul of fittings and the maintenance of the safety valve. Devaporizers If the de-aerator cannot be vented to atmosphere or to a gland condenser satisfactorily a devaporizer Figure 1.27 is connected to the vapour outlet condensing the vapour vented with the non-condensable gases and cooling these gases before they are discharged. In the process the feed water is raised slightly in temperature. In design and construction devaporizers are similar to the other small heat exchangers working at moderate pressures. Leaving the devaporizer the feed water enters the de-aerator header. 32 Main propulsion services and heat exchangers Figure 1.27 Sectional view of devaporizer Weir Pumps Ltd Weir multi stage turbo-feed pump The water tube boiler with its low storage capacity in relation to its steaming capability demands a steady supply of pure feed water. The robust and reliable turbine driven centrifugal pump is ideal for use as a water tube boiler feed pump. Additionally its uncontaminated exhaust can be used for feed heating and this improves cycle efficiency. The successful development of water lubricated bearings and their use in the Weir turbo-feed pump permitted the turbine and pump to be close-coupled in a very compact unit Figure 1.28 . During normal