Marine Ship Steam Engineering 2022 -1.pptx

Marine steam engg

1. MARINE STEAM ENGINEERING Objective of the course To develop knowledge on various types of steam machinery – construction & operation wise Safeties to be followed while handling steam equipments on board

2. Steam Engines UNIT 1 ( 2 HRS) Steam Engines Rankine cycle & modified rankine cycle. Comparison between steam reciprocating engine & steam turbine Why steam reciprocating engines could not survive Basic problems on rankine cycle with superheating & subcooling

3. Steam engines Rankine cycle & modified rankine cycle: The  rankine cycle  is a model used to predict the performance of steam turbine systems. It was also used to study the performance of reciprocating steam engines. Rankine cycle  is an idealized thermodynamic  cycle  of a heat engine that converts heat into mechanical work while undergoing phase change.

4. Rankine cycle & modified rankine cycle Rankine cycle is a mechanical cycle which is used to convert the pressure energy of steam into mechanical energy using turbines. In a rankine cycle the components used are the turbine, condenser, pump and the boiler. Water is heated up in the boiler and converted to super heated steam and sent to the turbine. The exhaust from the turbine is converted to liquid in the condenser and is pumped back to the boiler for heating up again.

5. Rankine cycle & modified rankine cycle A modified rankine cycle is used to increase the efficiency of the same rankine cycle by either reheat or using regenerative cycle . In the reheat cycle the exhaust from the high pressure turbine i.e, the first stage turbine is reheated using a re heater and sent back to the low pressure turbine i.e the second stage turbine. This in turn increases the efficiency of the cycle. In a regenerative cycle the exhaust from the condenser is heated to an optimum level by a part of super heated steam that has been separated before entering the turbine.

6. Rankine cycle components The components of simple Rankine cycle are - Boiler Steam Turbine Condenser Pump Apart form above 4, various equipment's like superheater, economiser, air preheater, steam separator etc are used.

7. Rankine cycle components (fig 1)

8. Rankine cycle P-V diagram (fig 2)

9. Rankine cycle Heat energy is supplied to the system via a boiler where the working fluid (typically water) is converted to a high pressure gaseous state (steam) in order to turn a turbine. After passing over the turbine the fluid is allowed to condense back into a liquid state as waste heat energy is rejected before being returned to the boiler, completing the cycle.

10. Steps in the Rankine Cycle Pump:  Compression of the fluid to high pressure using a pump (this takes work) ( Figure 2:  Steps 3 to 4) Boiler:  The compressed fluid is heated to the final temperature (which is at boiling point), therefore, a phase change occurs—from liquid to vapour. ( Figure 2:  Steps 4 to 1)

11. Steps in the Rankine Cycle Turbine:  Expansion of the vapour in the turbine. ( Figure 2:  Steps 1 to 2) Condenser:  Condensation of the vapour in the condenser (where the waste heat goes to the final heat sink (the atmosphere or a large body of water (ex. lake or river). ( Figure 2:  Steps 2 to 3)

12. Ideal rankine cycle

13. Rankine cycle Friction losses throughout the system are often neglected for the purpose of simplifying calculations as such losses are usually much less significant than thermodynamic losses, especially in larger systems. The ability of a rankine engine to harness energy depends on the relative temperature difference between the heat source and heat sink. The greater the differential, the more mechanical power can be efficiently extracted out of heat energy.

14. Rankine cycle The efficiency of the Rankine cycle is limited by the high heat of vaporization by the fluid. The fluid must be cycled through and reused constantly, therefore, water is the most practical fluid for this cycle. This is  not  why many power plants are located near a body of water—that's for the waste heat.

15. Rankine cycle As the water condenses in the condenser, waste heat is given off in the form of water vapour—which can be seen billowing from a plant's cooling towers. This waste heat is necessary in any thermodynamic cycle. Due to this condensation step, the pressure at the turbine outlet is lowered. This means the pump requires less work to compress the water—resulting in higher overall efficiencies.

16. Rankine cycle diagram ( T-s )

17. The four processes in the Rankine cycle Process 1–2 : The working fluid is pumped from low to high pressure. As the fluid is a liquid at this stage, the pump requires little input energy. Process 1-2 is [Isentropic compression]. Process 2–3 : The high-pressure liquid enters a boiler, where it is heated at constant pressure by an external heat source to become a dry saturated vapour. Process 2-3 is [Constant pressure heat addition in boiler].

18. The four processes in the Rankine cycle Process 3–4 : The dry saturated vapour expands through a turbine, generating power. This decreases the temperature and pressure of the vapour, and some condensation may occur. Process 3-4 is [Isentropic expansion]. Process 4–1 : The wet vapour then enters a condenser, where it is condensed at a constant pressure to become a saturated liquid. Process 4-1 is [Constant pressure heat rejection in condenser].

19. Rankine cycle components operations Water is converted to steam in the boiler which gives very high pressure and temperature steam. This steam is expanded in a steam turbine (steam runs the turbine) which in turn rotates generator. The steam, after expansion, comes out of turbine and passes through condenser. Work of condenser is to remove out the latent heat of vaporisation so that steam will convert into water. This water is now pumped back to boiler where it is heated again and further process are repeated.

20. Rankine cycle components operations Rankine cycle is a power producing cycle and widely used in steam based power plants. The main principle of rankine cycle is to produce a high pressure and temperature steam which strikes rotates steam turbine by striking the blade of the turbine and ultimately turbine rotates with high speed and the turbine is coupled with generator which converts the mechanical energy to electrical energy.

21. Real Rankine cycle (non-ideal)

22. Real Rankine cycle (non-ideal) In a real power-plant cycle (the name "Rankine" cycle is used only for the ideal cycle), the compression by the pump and the expansion in the turbine are not isentropic. In other words, these processes are non-reversible and entropy is increased during the two processes. This somewhat increases the power required by the pump and decreases the power generated by the turbine.

23. Real Rankine cycle (non-ideal) The efficiency of the steam turbine will be limited by water-droplet formation. As the water condenses, water droplets hit the turbine blades at high speed causing pitting and erosion, gradually decreasing the life of turbine blades and efficiency of the turbine. The easiest way to overcome this problem is by superheating the steam. 

24. Rankine cycle with reheat

25. Rankine cycle with reheat

26. Rankine cycle with reheat The purpose of a reheating cycle is to remove the moisture carried by the steam at the final stages of the expansion process. In this variation, two turbines work in series . The first accepts vapour from the boiler at high pressure. After the vapour has passed through the first turbine, it re-enters the boiler and is reheated before passing through a second, lower-pressure, turbine. The reheat temperatures are very close or equal to the inlet temperatures, whereas the optimal reheat pressure needed is only one fourth of the original boiler pressure

27. Rankine cycle with reheat This prevents the vapour from condensing during its expansion and thereby reducing the damage in the turbine blades and improves the efficiency of the cycle, because more of the heat flow into the cycle occurs at higher temperature. Today, double reheating is commonly used in power plants that operate under supercritical pressure.

28. Regenerative Rankine cycle

29. Regenerative Rankine cycle

30. Regenerative Rankine cycle

31. Regenerative Rankine cycle 1-2: Boiler - heat added at constant pressure 2-3: High-Pressure Turbine (HP) - isentropic expansion. 3-4,5: Splitter - stream 3 is split into streams 4 and 5. 5-6: Low-Pressure Turbine (LP)- isentropic expansion. 6-7: Condenser - heat rejected at constant pressure. 7-8: Pump #1 - isentropic compression. 8-9: Feedwater Heater (FWH) - temperature increases by mixing. 4-9: Feedwater Heater (FWH) - temperature decreases by mixing. 9-1: Pump #2- isentropic Compression

32. Regenerative Rankine cycle After emerging from the condenser (possibly as a subcooled liquid) the working fluid is heated by steam tapped from the hot portion of the cycle. This cycle is commonly used in real power stations. Regeneration increases the cycle heat input temperature by eliminating the addition of heat from the boiler at the relatively low feedwater temperatures that would exist without regenerative feedwater heating. This improves the efficiency of the cycle, as more of the heat flow into the cycle occurs at higher temperature .

33. Regenerative Rankine cycle Regeneration is an attempt to reduce the irreversibility associated with transferring heat from the high-temperature reservoir to the subcooled liquid that leaves the pump in an ordinary Rankine Cycle. There is a very large difference between the temperature of the hot reservoir the temperature of the pump effluent. So, it is wasteful to feed such cold liquid to the boiler.

34. Regenerative Rankine cycle In a regeneration cycle, two turbines are used and a portion of the effluent from the high pressure turbine is used to “preheat” or “regenerate” the boiler feed The device in which the boiler feed stream is preheated is called a Feedwater Heater. The feedwater heater shown here is called an OPEN feedwater heater because the condenser effluent is pumped up to the same pressure as the high-pressure turbine effluent and they are allowed to MIX or combine into one stream.

35. Steam reciprocating engine & Steam turbine In a reciprocating steam engine, of piston and cylinder type,  steam  under pressure is admitted into the cylinder by a valve mechanism. As the  steam  expands, it pushes the piston, which is usually connected to a crank on a flywheel to produce rotary motion. A  steam turbine  is a device that extracts thermal energy from pressurized  steam  and uses it to do mechanical work on a rotating output shaft.

36. Working of steam engines A steam engine works when water is heated to an invisible vapour known as steam. The volume of water expands as it turns to steam inside the boiler, creating a high pressure. The expansion of steam pushes the pistons that connect to the driving wheels that operate the locomotive.

37. Working of steam turbines A steam turbine works by using a heat source (gas, coal, nuclear, solar) to heat water to extremely high temperatures until it is converted into steam. The turbines are connected to a generator with an axle, which in turn produces energy via a magnetic field that produces an electric current.

38. Steam reciprocating engine & Steam turbine A  steam engine  can be either a reciprocating or a turbine type: Reciprocating means the hot  steam  moves a piston up and down, which is connected to a crank-shaft to produce the rotary motion.  Turbine  means that instead of pistons, the  steam  pushes against the blades of a "fan", causing direct rotary motion.

39. Use of steam engine & steam turbine Steam engines are still used in certain areas of the world and in antique locomotives. However, steam power is still heavily used around the world in various applications. Many modern electrical plants use steam generated by burning coal to produce electricity. Steam turbines are found everywhere on the planet and are used to turn generators and make electricity or create propulsion for ships, airplanes, missiles. They convert heat energy in the form of vaporized water into motion using pressure on spinning blades.

40. Advantages of steam turbine over steam engine Thermal efficiency of a steam turbine is usually higher than that of a reciprocating engine. Very high power-to-weight ratio , compared to reciprocating engines. Fewer moving parts than reciprocating engines.  Steam turbines are suitable for large thermal power plants.

41. Advantages of steam turbine over steam engine In general, turbine moves in one direction only, with far less vibration than a reciprocating engine. Steam turbines have greater reliability , particularly in applications where sustained high power output is required.

42. Disadvantages of steam turbine over steam engine Although approximately 90% of all electricity generation in the world is by use of steam turbines, they have also some disadvantages. Relatively high overnight cost . Steam turbines are less efficient than reciprocating engines at part load operation . They have longer startup than gas turbines and surely than reciprocating engines. Less responsive to changes in power demand compared with gas turbines and with reciprocating engines.

43. Why steam reciprocating engines could not survive ??? Diesels replaced steam locomotives because that's what they did - they are more efficient because they cost less money to run. They take too long to get started and build pressure in the boiler to drive the pistons. They are generally less powerful than an internal combustion engine (lower cylinder pressures = less torque) and more bulky/heavy. Depletion of possible fuels causing pollution.

44. Rankine cycle diagram

45. Basic problems on rankine cycle with superheating & subcooling

46. Layout of plant UNIT 2 ( 2 HRS) Layout of plant General lay out of plant and description of a modern geared steam turbine installation including auxiliaries in modern steam ships. Details of scoop system and fitting of astern turbine

47. General layout of turbine power plant

48. General layout of turbine power plant Steam power plant normally has the following equipments: Steam generator or boiler containing water. Major power unit will be a turbine or engine to use heat energy of steam to perform work. Condenser to cool the exhaust steam from the turbine. Pumping arrangement to pump water to the boiler.

49. General layout of turbine power plant General layout of thermal power plant consists of 4 main circuits. They are: 1. Cooling Water Circuit 2. Feed Water and Steam Flow Circuit 3. Air and Gas Circuit 4. Coal and Ash Circuit

50. Cooling Water Circuit 1. This circuit has a cooling tower, cooling water pump(s) and circulating water pump. The amount of cooling water required to condense the steam is significantly large which is taken from lake, sea or river. 2. Cooling water is taken from the upper side of river, it is passed through the condenser & after cooling the exhaust steam, it is discharged to lower side of the river. Such method of cooling water supply is feasible if sufficient cooling water is accessible through the year. This method is identified as open system.

51. Cooling Water Circuit 3. If sufficient water is not available, then the water coming out of the condenser is chilled in a cooling pond or cooling tower. Coolant is recirculated back to the condenser. There will be a small loss of water during circulation & cooling. 4. To compensate for the evaporative loss, water is constantly circulated. As the cooling water coming out of condenser is cooled over with water from the cooling tower, then the system is identified as closed system.

52. Cooling Water Circuit 5. As the water coming out of the condenser is discharged to the river downward side frankly, the system is identified as open system. Open system is inexpensive than the closed system provide sufficient water is accessible during the year.

53. Feed water and Steam Flow Circuit 1. This circuit has feed heaters, boiler, turbine and boiler feed pump. Steam produced in boiler is fed to steam prime mover to increase the power. Steam coming out of prime mover is reduced in the condenser and then fed to boiler with the help of pump. 2. Condensate is heated in feed heaters using the steam tapped from different points of turbine. Feed heaters might be of mix kind or indirect heating form.

54. Feed water and Steam Flow Circuit 3. Some of the steam and water is lost passing through unusual components of system, thus feed water is supplied from an external source to balance this loss. 4. Feed water supplied from the external source is passed through the purifying plant to decrease the dissolve salts to a suitable level. The purification is required to reduce the scaling of boiler tubes.

55. Air and Gas Circuit 1. This circuit has air pre-heater, air filter, dust collector and chimney. Air from the atmosphere enters the air preheater through a forced or induced draught fan or by using both. Dust as of the air is removed by means of using air filter prior entering the combustion chamber. 2. Exhaust gases passes through the economiser where heat exchange occurs with the feed water and enters air preheater where heat exchange occurs with air. Then exhaust gases goes to the atmosphere through the chimney.

56. Coal and Ash Circuit 1. This circuit has ash storage, coal storage, coal handling and ash handling systems. Handling system consists of screw conveyors, belt conveyors and so on. 2. Coal arrives at storage yard is used as per requirement. Ash from combustion of coal is collected at the back of the boiler is detached to ash storage yard during ash handling operation.

57. General lay out of plant in modern steam ships Working principle of steam power plant Working fluid cycle steam power plant is a closed cycle, which uses the same fluid repeatedly. Water is filled into the boiler to fill the entire surface area of heat transfer. In the boiler, water is heated by the hot gases of combustion fuel with air so that turned into vapour phase. Steam produced by boiler with pressure and temperature are directed to do work on the turbine to produce mechanical power in the form of rotation.

58. General lay out of plant in modern steam ships The steam comes out of the turbine and then flows into the condenser to be cooled with cooling water. Condensate water is then used again as boiler feed water. Thus the cycle goes on and repeats. Rotation of turbine is used to turn a generator that is coupled directly to the turbine. So when the turbine rotates, the generator output terminals generate electricity. Although working fluid cycle is a closed cycle, but the amount of water in the cycle would decrease. The reduction is due to the leakage of water either intentional or unintentional

59. Details of scoop system A scoop is designed to supply sea-water circulation through the central coolers while the vessel is underway. It may be installed instead of a conventional sea-water circulating pump. The scoop imposes some extra drag on the hull so that the power for sea-water circulation is supplied from the main propulsion instead of from the generators and electrical system.

60. Details of scoop system

61. Details of scoop system Economic advantages are claimed for a correctly designed scoop but the arrangement is viable only for a simple straight through flow as for central coolers or the large condenser of a steam ship. The electrically driven pump is used only for manoeuvring or slow speeds. It is of smaller capacity than would be required for an ordinary circulating pump.

62. Details of scoop system

63. Details of scoop system Small axial flow circulating pumps have been installed in conjunction with some scoop arrangements, with the idea that at speed, the pump impeller would be idle and provide very little resistance to the scoop flow. The axial flow pump, intended for slow speed and manoeuvring, suffered from thrust problems when idling in a number of installations.

64. Astern turbine The steam turbine has until recently been the first choice for very large power marine propulsion units. Its advantages of little or no vibration, low weight, minimal space requirements and low maintenance costs are considerable. Furthermore a turbine can be provided for any power rating likely to be required for marine propulsion. However, the higher specific fuel consumption when compared with a diesel engine offsets these advantages, although refinements such as reheat have narrowed the gap.

65. Astern turbine Marine steam turbine engines have largely been replaced by the more economical marine two stroke diesel engine, mainly for commercial reasons as the diesel engine is much more economical. There are still a few about turbines, running like clockwork(continuous operation) along with reliability, little maintenance and high speed- pushing large cruisers and battleships along at forty knots.

66. Astern turbine For marine applications, the cross compound double reduction steam turbine was a popular choice because it was more compact, taking up less space in the ships engine-room. It also had the advantage of a built-in astern turbine giving easier astern movement, with up to 50% astern output power as that of the ahead turbine.

67. Cross compound double reduction steam turbine

68. Cross compound double reduction steam turbine The propulsion machinery consists of a high-pressure and a low-pressure turbine coupled to a double reduction gear which drives a single screw. The turbines are arranged side by side and are connected by a steam crossunder pipe in an arrangement known as "cross-compound." Such an arrangement permits each turbine to operate at the speed best suited to the existing steam conditions.

69. Cross compound double reduction steam turbine Because turbines operate most efficiently at high speeds and propellers at low speeds, a reduction gear is used to couple the two to produce efficient propeller rpm. In a cross-compound turbine, the total available energy in the steam is divided almost equally between the two turbines when operating at full load, so that each performs nearly the same amount of work.

70. Cross compound double reduction steam turbine The high pressure and low pressure turbines are really separate turbines having their own drive shafts, which are coupled to a double reduction gearbox that decreases their revolutions from several thousand to about 100 RPM, the normal operating propeller shaft speed. The high pressure turbine rotor also has several rows of blades that are used as an astern turbine, which enables the ship to manoeuvre when arriving or departing ports.