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Devaporizer & turbo-feed pump for motor ships
Why Devaporizers ?
If the de-aerator cannot be vented to atmosphere or to a gland condenser satisfactorily, a devaporizer (Figure 1) is connected to the vapour outlet condensing the vapour vented with the non-condensable gases and cooling these gases before they are discharged.
Figure 1:Sectional view of devaporizer
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.
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 2:Turbo feed pump
During normal running, a multi-plate restriction orifice allows feed water from the first stage impeller discharge to flow through a two-way non-return valve and a strainer to the bearings. A relief valve is incorporated. A secondary supply of lubricating water is introduced through the two way non-return valve from an outside source such as the main condensate extraction pumps, to protect the bearings from damage during starting, stopping, or stand-by periods of duty.
Figure 3:lubricating-water-system
Figure 3 shows the arrangement of the lubricating water system. The overspeed trip is triggered by a spring loaded unbalanced bolt mounted in the shaft between the two journals.
Summarized below various circulating systems for motorships, some of the basic procedure of heat exchangers & control of temperatures:
- Sea water circulation-systems
The usual arrangement for motorships has been to have sea-water circulation of coolers for lubricating oil, piston cooling, jacket water, charge air, turbo-charger oil (if there are sleeve type bearings) and fuel valve cooling, plus direct sea-water cooling for air compressors and evaporators....
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Shell and tube heat exchangers for engine cooling water and lubricating oil cooling
Shell and tube heat exchangers for engine cooling water and lubricating oil cooling have traditionally been circulated with sea water. The sea water is in contact with the inside of the tubes, tube plates and water boxes....
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Plate type heat exchanger
The obvious feature of plate type heat exchangers, is that they are easily opened for cleaning. The major advantage over tube type coolers, is that their higher efficiency is reflected in a smaller size for the same cooling capacity....
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Details of charged air cooler
The charge air coolers fitted to reduce the temperature of air after the turbo-charger and before entry to the diesel engine cylinder, are provided with fins on the heat transfer surfaces to compensate for the relatively poor heat transfer properties of air....
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Maintenance of heat exchangers
The only attention that marine heat exchangers should require is to ensure that the heat transfer surfaces should remain substantially clean and flow passage generally clear of obstructions. Indcation that fouling has occured is given by a progressive increase in the temperature difference between the two fluids, and change of pressure....
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Central cooling system & Scoop arrangement for motorships
The corrosion and other problems associated with salt water circulation systems can be minimized by using it for cooling central coolers through which fresh water from a closed general cooling circuit is passed. The salt water passes through only one set of pumps, valves and filters and a short length of piping.....
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Circulating systems for steamships
The main sea-water circulating system for a ship with main propulsion by steam turbine is similar to that of a motorship with a central cooling system. The difference is that the sea water passes through a ....
- Closed feed system and feed heating for motor ships
To ensure trouble-free operation of water-tube boilers the feed water must be of high quality with a minimal solid content and an absence of dissolved gases. Solids are deposited on the inside surfaces of steam generating tubes,....
- Marine condenser assembly
A condenser is a vessel in which a vapour is deprived of its latent heat of vaporization and so is changed to its liquid state, usually by cooling at constant pressure. In surface condensers, steam enters at an upper level, passes over tubes in which cold sea water circulates, falls as water to the bottom and is removed by a pump (or flows to a feed tank)....
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Three stage air ejector with internal diffusers
A steam-jet ejector may be used to withdraw air and dissolved gases from the condenser. In each stage of the steam-jet ejector, high pressure steam is expanded in a convergent/divergent nozzle. ...
- Pressure governor for motor ships
The main feature of the governor is that if the pump loses suction the steam ports are opened wide, allowing the pump to accelerate rapidly to the speed at which the emergency trip acts....
- Liquid ring pump- Nash rotary liquid ring pumps
Nash rotary liquid ring pumps, in association with atmospheric air ejectors, may be used instead of diffuser-type steam ejectors and are arranged as shown...
- The Weir electro-feeder - a multi-stage centrifugal pump
A multi-stage centrifugal pump mounted on a common baseplate with its electric motor. The number of stages may vary from two to fourteen depending upon the capacity of the pump and the required discharge pressure....
- Feed water heaters for motor ships
Surface or direct contact feed heaters, play an important part in the recovery of latent heat from exhaust steam. Direct contact feed heaters are also known as de-aerators....
- Devaporizer & turbo-feed pump
If the de-aerator cannot be vented to atmosphere or to a gland condenser satisfactorily, a devaporizer is connected to the vapour outlet condensing the vapour vented with the non-condensable gases and cooling these gases before they are discharged. ...
- Typical de-aerator & Cascade trays
Normally, the de-aerator is mounted directly on a storage tank, into which the de-aerated water falls, to be withdrawn through a bottom connection by a pump or by gravity. The tank usually has a capacity....
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