tailieunhanh - Intro to Marine Engineering 2E Episode 5

Tham khảo tài liệu 'intro to marine engineering 2e episode 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | ỉ 10 Feed systems feeder . This is a multi-stage centrifugal pump driven by a constantspeed electric motor. The number of stages is determined by the feed quantity and discharge pressure. Steam turbine-driven feed pumps are usual with high-pressure watertube boiler installations. A typical turbo-feed pump is shown in Figure . The two-stage horizontal centrifugal pump is driven by an impulse turbine the complete assembly being fitted into a common casing. The turbine is supplied with steam directly from the boiler and exhausts into a back-pressure line which can be used for feed heating. The pump bearings are lubricated by filtered water which is tapped off from the first-stage impeller. The feed discharge pressure is maintained by a governor and overspeed protection trips are also provided. High-pressure feed heater The high-pressure feed heater is a heat exchanger of the shell and tube type which further heats the feed water before entry to the boiler. Further heat may be added to the feedwater without its becoming steam since its pressure has now been raised by the feed pump. The incoming feedwater circulates through U-tubes with the heating steam passing over the outside of the tubes. Diaphragm plates serve to support the tubes and direct the steam through the heater. A steam trap ensures that all the heating steam is condensed before it leaves the heater. Bled steam from the turbine will be used for heating. Operation and maintenance During operation the feed system must maintain a balance between feed input and steam output together with a normal water level in the boiler. The control system used is described in Chapter 15. The condenser sea water boxes are protected by sacrificial mild steel plates which must be renewed regularly. The tube plates should be examined at the same time to ensure no erosion has taken place as a result of too high a circulating water speed. Any leaking tubes will cause feedwater contamination and where this is suspected the .