MARINE AUXILIARIES

Figure 7.4 Shell and tube heat exchanger Ref: www.machineryspace.com

 They are arranged for either 1. a single pass of cooling liquid or 2. a double pass of cooling liquid (Fig 7.4)  The tube bundle has baffles fitted which serve to direct the liquid to be cooled up and down over the tubes as it passes along the cooler.  The joint arrangements at the tube plate ends are different. At the fixed end, gaskets are fitted between either side of the tube plate and the shell and end cover.  At the other end, the tube plate is free to move with seals fitted either side of a safety expansion ring.  Should either liquid leak past the seal it will pass out of the cooler and be visible.  There will be no intermixing or contamination.

• In a single pass heat exchanger, the fluid goes into one end of a tube and out the other.

• In the two pass type the fluid enters and exit on the same side. Baffles can be installed to guide the flow through the shell sides.

Shell and tube heat exchanger



Baffles are installed on the shell side to give a higher heat- transfer rate due to increased turbulence and to support the tubes thus reducing the chance of damage due to vibration. There are a number of different baffle types, which support the tubes and promote flow across the tubes. Figure 5 shows the following baffle arrangements: • Single Segmental (this is the most common), • Double Segmental (this is used to obtain a lower shellside velocity and pressure drop), • Disc and Doughnut.

Shell flanges. Header Provision for thermal expansion: Leakage- tell-tale holes is provided in the retainer ring fitted between the Header and the Shell flanges.

Shell flanges.





The end covers are removed to give access to the tubes for cleaning. 1. Clean the end covers. 2. Check for tube leakages. 3. Cleaning the tubes by using the special tool. 4. To clean heat transfer surfaces (conducting surfaces) for satisfactory cooling operation. 5. The main problem with sea water cooling is fouling of the surfaces, that is the presence of marine plant and animal growth.

CLEANING PROCESS Cleaning cold fluid side (s w) • Algae slimes – mechanical cleaning or flushing through with copper sulphate solution • Marine growth – Mechanical cleaning or chlorination • Scales – soft scale by mechanical cleaning but for hard scales require circulation of an acid declare usually sulphuric acid, hydrochloric acid or citric acid in addition of inhibitors which protect the metal surface. Neutralizing solution be circulated after descaling like sodium carbonate or hydrazine. • Silt, sand, rust etc. – mechanical cleaning 21

CLEANING TOOLS 22



 Tube leakage can result from corrosion. This can be checked for, or identified, by having the shell side of the cooler circulated while the cooling water is shut off and the end covers removed.  Any seepage into the tubes will indicate the leak.  It is also possible to introduce fluorescent dyes into the shell-side liquid: any seepage / leak will show under an ultraviolet light as a bright green glow.  Leaking tubes can be temporarily plugged at each end or removed and replaced with a new tube.

25

26

• Tubes- Aluminum brass, cupro-nickel • Tube plates – Cast Naval brass • Casing and water boxes(end cover) – Cast iron, gunmetal • Baffles – Cooper, rolled naval brass 27

1. The Plate heat exchanger (PHE) consists of a series of thin, corrugated alloy plates, which are gasketed and compressed together in a carbon steel frame to create an arrangement of parallel flow channels. 2. Ports at each corner of the plates act as the headers and the gaskets direct the fluid flow as well as provide the primary seal for the system. 3. One fluid travels in the odd numbered channels and the second in the even.



Figure 7.5 Plate-type heat exchanger: (a) construction, (b) operation

31





• The plate-type heat exchanger is made up of a number of pressed plates surrounded by seals and held together in a frame. • The inlet and outlet branches for each liquid are attached to one end plate. • The arrangement of seals between the plates provides passage ways between adjacent plates for the cooling liquid and the hot liquid. • The plates have various designs of corrugations to aid heat transfer and provide support for the large, flat surface. • A double seal arrangement is provided at each branch point with a drain hole to detect leakage and prevent intermixing or contamination.

Seals around the ports are so arranged that one fluid flows in alternate passages between plates and the second fluid in the intervening passages, usually in opposite directions. The plate corrugations promote turbulence (Figure) in the flow of both fluids and so encourage efficient heat transfer. Turbulence as opposed to smooth flow causes more of the liquid passing between the plates to come into contact with them. It also breaks up the boundary layer of liquid which tends to adhere to the metal and act as a heat barrier when flow is slow. Into contact with them. It also breaks up the boundary layer of liquid which tends to adhere to the metal and act as a heat barrier when flow is slow. The corrugations make the plates stiff so permitting the use of thin material. They additionally increase plate area, both of these factors also contribute to heat exchange efficiency.

The plates must be visually examined to detect the faulty point. The joints between the plates can present problems in service, or on assembly of the cooler after maintenance. If coolers are out of use for a long period, such as during surveys or major overhauls, the sea water side should be drained, flushed through or washed with fresh water, and left to dry until required for service.

1. The control of the temperature of coolers is usually controlled by adjusting the cooling liquid outlet valve. 2. The inlet valve must be left open to ensure a constant pressure within the cooler. By regulating the INLET valve will cause a pressure reducing within the cooler and this could lead to aeration (produce air in the system). 3. The collecting of air within the cooler will cause reducing the cooling effect.

5. Air remaining in a cooler will considerably reduce the cooling effect. 6. Vents are provided in the highest points of coolers which should be opened on first filling and whenever there is air in the cooler. 7. Vertical mounting of single pass coolers will ensure automatic venting. 8. Positioning the inlet cooling water branch facing downwards and the outlet branch upwards will achieve automatic venting with horizontally mounted coolers. 9. Drain plugs are also fitted at the lowest point in coolers to ensure a complete dry out of cooler.

1) Main Engine Jacket Water System: – Main propulsion plant consists of different sub system for running of main engine like lube oil system, jacket water system (open or closed system), fuel system etc. – While generating energy all these systems gets heated up and the temperatures are controlled by the use of heat exchanger in the system. – Heat exchangers normally used in main propulsion system are – Shell and tube type and plate type heat exchanger.

2) Auxiliary Power Generation System: – Auxiliary power generation system is similar to the main propulsion system, except that the power is generated in terms of output. – Shell and tube type, plate type and plate fin type heat exchanger are generally used 3) Starting Air System: – High pressure air is produced in the compressor which is further cooled in inter-cooler, which acts as a heat exchanger – Shell and tube type exchanger is popularly used for this purpose. 4) Fuel injection system: – For proper atomization, fuel is heated up in a heater with heating medium as steam. Shell and tube type heater is used for this purpose.

5) Refrigeration System and A/C System: – In refrigeration system, for meat room, fish room and vegetable room, evaporator acts as phase change heat exchanger. – Shell and tube type unit is used for condenser unit in refrigeration system and A/C System 7) Fresh Water System: – For generating fresh water, sea water condenser and jacket water evaporator is used. Both are types of heat exchangers. – Shell and tube type and plate type heat exchangers are normally used for this.

DIFFERENTIAL EXPANSION IN COOLERS Example of u-tube cooler design Differential Thermal Expansion Since fluid in the shell is at a different temperature than the fluid in the tubes, there are corresponding differences in expansion of shell and tubes. Some provision must be made in design to compensate for this difference in thermal expansion. 1. “U”-Tube Design In the “U” -tube exchanger, the shape of the tubes takes care of differential expansion. As the name implies, the tubes have a “hairpin” shape, with both ends of the tube fastened to one tubesheet. This “U” bend design allows each tube to expand and contract independently.

Cont’ 2. Floating Head Designs This type meets the expansion problem by having one stationary tubesheet, and one free to move - “float” - back and forth as the tubes expand and contract under the influence of temperature changes.



Cont’ 3. Fixed Tubesheet Design The fixed tubesheet heat exchanger employs straight tubes secured at both ends into tubesheets, which are welded to the shell. When a thermal expansion problem exists, an expansion joint is incorporated in the shell. This permits the shell to expand and contract.

Leakage Dectection Leakage- tell-tale holes is provided in the retainer ring fitted between the header and the Shell flanges.

Operational of Heat Exchangers/Coolers Temperature control of coolers is usually achieved by adjusting the cooling liquid outlet valve. The inlet valve is left open and this ensures a constant pressure within the cooler. This is particularly important with sea water cooling where reducing pressure could lead to aeration or the collecting of air within the cooler. Air remaining in a cooler will considerably reduce the cooling effect. Vents are provided in the highest points of coolers which should be opened on first filling and occasionally afterwards. Vertical mounting of single pass coolers will ensure automatic venting. Positioning the inlet cooling water branch facing downwards and the outlet branch upwards will achieve automatic venting with horizontally mounted coolers. Drain plugs are also fitted at the lowest point in coolers.



Malaysian Institute of Marine Engineering Technology (MIMET) Marine Auxiliaries / WAS / Jan 2021

Fresh water production from sea water for domestic and auxiliary purposes is an essential requirement aboard ships. A considerable amount of fresh water is consumed in a ship. The crew consumes an average 100 liter/head/day. In a steam ship (a ship whose main propulsion unit is steam turbine or a ship which is a large tanker having steam turbine driven cargo oil pumps) the consumption for the boiler can be as high as 30 tonnes/day. Sufficient potable water may be taken on in port to meet crew and passenger requirement. But the quality of this water will be too poor for use in water tube boilers and for filling expansion tanks. It is common practice to take on only a minimum supply of potable water and make up the rest by distillation of sea water. Malaysian Institute of Marine Engineering Technology (MIMET) Marine Auxiliaries / WAS / Jan 2021

Malaysian Institute of Marine Engineering Technology (MIMET) Marine Auxiliaries / WAS / Jan 2021

Malaysian Institute of Marine Engineering Technology (MIMET) Marine Auxiliaries / WAS / Jan 2021

Malaysian Institute of Marine Engineering Technology (MIMET) Marine Auxiliaries / WAS / Jan 2021

Malaysian Institute of Marine Engineering Technology (MIMET) Marine Auxiliaries / WAS / Jan 2021

Malaysian Institute of Marine Engineering Technology (MIMET) Marine Auxiliaries / WAS / Jan 2021

Malaysian Institute of Marine Engineering Technology (MIMET) Marine Auxiliaries / WAS / Jan 2021

Malaysian Institute of Marine Engineering Technology (MIMET) Marine Auxiliaries / WAS / Jan 2021

Malaysian Institute of Marine Engineering Technology (MIMET) Marine Auxiliaries / WAS / Jan 2021