BÀI GIẢNG TRANG TRÍ ĐỘNG lực (MARINE PROPULSION PLANT)

CHAPTER I: NOTIONS AND CLASSIFICATION OF MARINE PROPULSION PLANT (Total: 08 periods, Theory: 08 periods, practical: 00 periods) 1.1 Notions of Marine propulsion plant Marine propulsion plant (MPP) is a group that consists of main propulsion plant equipment and other auxiliary propulsion plant equipment to take on the action ability of ship and the life of crews on ship in every sea condition Depending on the ability of working, that group can be divided as follows: 1.1.1 Main propulsion plant equipment Main propulsion plant equipment is a system of equipment that undertake speed and direction of ship They consist of following parts: a Main engine: Main engine generates mechanical energy to turn a ship's propeller In the marine propulsion plant, kinds of following main engine can be used: Steam engine, steam turbine, gas turbine, diesel engine, and “generator – motor” In fact, a diesel engine propulsion plant is mostly used nowadays Besides this, on modern ships newly manufactured with large power, the steam turbine propulsion plants are being developed In the marine propulsion plant, one or more main engine can be used b Propulsion equipment Propulsion equipment transforms mechanical energy of the main engine into thrust force when maneuvering The oldest type of mechanical propulsion for ships is Jet propulsion The Jet propulsion is based on jet principal of water line ejected strongly and fast in a contrary direction of ship It usually consists of an impeller or pump installed inside the hull, which draws water from outside, imposes on it an acceleration, and discharges it astern as a jet at a high velocity This kind of propulsion was used on ships from 1782 In 1801 the first steam ship driven by paddle wheel was appeared, with paddle wheels installed both sides of ship Paddle wheel was used on steamers until about 1850 Two kinds of propulsion equipment above have disadvantages of unwieldy and low efficiency With paddle steamers, the immersion varied with ship displacement, the wheels came out of the water when the ship rolled, so the course will be changed and they were easily damaged due to rough seas The idea to use a screw propeller on ship appears in 1680, but until 1836 the first screw propeller was applied The screw propeller has many advantages over paddle wheel Nowadays, screw propeller was used on all ship with advantage of high efficiency and safe working There are two kinds of screw propeller used in the marine propulsion plant, they are: Non controllable - pitch propeller and controllable - pitch propeller There may be one or more propellers are used in the propulsion plant according to type of ship and the installation of the propulsion plant c Driving equipment It is intermediate equipment to transmit power from a main engine to a screw propeller Driving equipment consists of: Shafting, flanges, split muff coupling, clutch, and reduction gear d Main boiler Its duty is to supply steam (with high pressure and temperature) to steam engine, steam turbine and other auxiliary machinery Main boiler is used only on steam ship e Conveyance equipment They are used to convey working substance to a main engine They consist of steam tube, gas tube 1.1.2 Auxiliary equipment of MPP It supports the main propulsion plant equipment and other operations of a ship Auxiliary equipment consists of: a Generator Its duty is to supply electric energy for the ship to serve many different objects, such as: illuminating, loading and unloading cargoes and all other electric equipment Remember that, there must be at least two generators in the marine propulsion plant Generators can be driven by diesel engines like in the diesel engine propulsion plant In the other hand, in the steam propulsion plant, the generators can be driven by steam engines or steam turbines Besides this, in large power diesel engine propulsion plant, a waste recovery steam turbine can be used to drive the generator b Compressed air system Compressed air system generates and stores compressed air with high pressure for starting and reversing the main engines, starting generator engines, cleaning parts of the engine Besides this, compressed air is also used in remote control and automatic control systems Compressed air system consists of compressors, reservoirs (air tank), non-reversible valves, relief valves, and compressed air pipes c Auxiliary boiler Auxiliary boiler supplyes steam to heat fuel, water, diesel engine (before starting) and cabins In addition, it also serves steam machineries and equipment (such as cargo pumps on tanker ships) 1.1.3 Safety equipment of MPP To undertake the safe operations of the ship in every condition to limit damages due to trouble Safety equipment consists of: a Bilge system Its duty is to suck dryly shaft tunnel, cargo holds and engine room Because bilge water is mixture of water, oil, sludge so it is required to provide with the oily - water separator in the system to separate oil from water before pumping out to sea b Ballast system Its duty is to adjust the balance of the ship c Fire protection system It is easy to happen damages due to fire on the ship especially in the engine room, so protection firing should be specially concerned Fire protection system consists of: Personal fire extinguishings, carbon dioxide cylinders, foam cylinders, water fire extinguishing system, carbon dioxide fire extinguishing system, foam fire extinguishing system d Repairing equipment, store and spare parts for replacing 1.1.4 Equipment for serving the domestic requirement They are equipment to undertake the living requirements of all ship's crews They consist of light system, ventilation and air conditioner system, provision refrigerator system, fresh water system, washing water sytem and so on 1.1.5 Deck's equipment They consist of steering gear, mooring winches, cargo winches, life equipment (life boats, life rafts an so on ) 1.2 Classification of Marine Propulsion Plant Depending on the kind of working substance used in the main engine, the marine propulsion plant can be classified by two main types They are steam propulsion plant and diesel propulsion plant Besides these, nuclear propulsion plant can also be used To combine main kinds of propulsion plant with driving modes, we have many different kinds of propulsion plant 1.2.1 Steam propulsion plant It is a kind of propulsion plant in which, generating process of mechanical power is the process of using heat energy when burning fuel to generate steam in a main boiler, and then steam expands and generates power in a steam engine or a steam turbine In the steam propulsion plant, the main propulsion plant equipment is group of boiler and steam engine or boiler and steam turbine In 1807, the first time the steam ship Klecmong with power of 18 horses - power appeared on a river of South America Although the ship had small power and low speed but this event had a great significance in the ship building industry With improvement of science and technology, ship building industry manufactured many steam engines with power up to thousand horses - power In the whole of 19 century, all of ships used the direct driving steam engine propulsion plant Nevertheless, steam engine has still many disadvantages This type of engine has small power, low efficiency, weight and dimension is big, so cannot satisfy the high requirements of sea transport In about years of 80 of 19 century, a Swedish engineer Guntavdo Laval made a first steam turbine with power of horses - power, speed of 25000 rpm But until 1896 steam turbine applied to drive screw propeller and the steam turbine propulsion plant came In this period, all of steam turbines were used to drive directly screw propellers, so working conditions of turbine and propeller were contradicted each other If revolution of turbine is high then its power is large, efficiency is high and weight, dimension can be reduced In the othe hand, if turbine and propeller working together then thrust efficiency of propeller is decreased because revolution of turbine is excessively higher than optimum working revolution of propeller Therefore, in direct driving steam turbine propulsion plant, turbine has large dimension and low efficiency To operate effectively power of steam turbine, it is required to provide intermediate equipment to reduce revolution of turbine to optimum revolution range of propeller From 1910, multi - stages mechanical gears box was applied on board and the indirect driving steam turbine propulsion plant was appeared Besides this, turbine was also used to drive screw propeller in the electric driving steam turbine propulsion plant In beginning period of 20 century, because steam engine was still used, the combinative steam engine - steam turbine propulsion plant was used to decrease a loss of heat due to unperfected expansion of steam in steam engine 1.2.2 Diesel engine propulsion plant In 1903, the first diesel engine vessel was used in the world It is named "Vandan" and made in Russia Although came latter, the diesel engine propulsion plant had fast improved and popularly applied because it has many advantages Diesel engines have high heat efficiency, low specific fuel consumption, their dimension and weight are smaller than steam engines, and range of power is large Up to now, diesel engines were used on board by three kinds of: Direct driving diesel engine propulsion plant, indirect driving diesel engine propulsion plant and special driving diesel engine propulsion plant In the direct driving diesel engine propulsion plant, direction and revolution of propeller are the same with main engine This kind of propulsion plant is generally applied on tanker ships, general cargo ship Main engine is kind of low - speed diesel engine, direct reversing The most common is low - speed diesel engine, two - stroke with cross head and used heavy fuel oil The direct driving diesel engine propulsion plants have disadvantages that their weight and dimension are large so they are not suitable for ships with small displacement, limited height of engine room In that case, it is necessary to provide with indirect driving diesel engine propulsion plant to drive propeller In the indirect driving diesel engine propulsion plant, a main engine is generally kind of high and medium speed diesel engine, non- - reversible Its revolution is much higher than propeller In this kind of propulsion plant, two or more main engines can be installed together to drive propeller In the other hand, only one main engine can be used to drive two or more propellers in some cases Besides of shafting, clutch and gears box should be provided between main engine and propeller The indirect driving diesel engine propulsion plants are commonly used on passenger ships, container ships, and naval ships In comparison with the direct driving diesel engine propulsion plant, this kind of propulsion plan is more complex and lower transmission efficiency Special driving diesel engine propulsion plants are electric driving diesel engine propulsion plant and diesel engine propulsion plant with controllable - pitch propeller The same as the indirect driving diesel engine propulsion plant, a main engine is kind of high and medium speed diesel engine, nonreversible Advantage of the special driving diesel engine propulsion plant is very flexible However, it has disadvantages: system is complex, transmission efficiency is low So it commonly used for flexible ships such as: workshop ships, naval ships, passenger ships, fishing ships, rescue ships and so on 1.2.3 Other types Besides the main types of marine propulsion plant as mentioned above, some others are known as gas turbine propulsion plant and nuclear propulsion plant Gas turbines differ from steam turbines in that gas rather steams is used to turn shaft These have also become more suitable for use in ships Many naval ships are powered by gas turbine and several container ships are also fitted with them Nuclear propulsion plant is commonly used on naval ships, especially submarines But this form of power will be used more in merchant ships when oil fuels become rarely Nuclear propulsion plant uses the energy released by the decay of radioactive fuel to generate steam, and the steam is used to turn a shaft via a turbine in the conventional way 1.3 Technical characteristics of Marine propulsion plant In a marine propulsion plant, the characteristics of the main engine have a direct effect on technique of operation, methods of design and installation systems and equipment in the engine room According to the type of main engines, nowadays there are two main types of propulsion plant, they are diesel engine propulsion plant and steam propulsion plant (with main engine is steam turbine) 1.3.1 Technical characteristics of diesel engine propulsion plant - In the diesel engine propulsion plant, working substance is combustion product of air - fuel mixing formed in engine combustion chamber - Thermal efficiency is high while specific fuel consumption is low - Output is not continuously generated It should be provided with air and gas distributors suitable for suction and exhaust cycles of the main engine - When working, diesel engines generate reciprocating forces and inertia moments These inertia forces and moments vibrate body of engine and ship's hull The balance of a diesel engine is depended on weight of the engine moving parts, number of cylinders and suitable arrangement of cranks - Engine parts withstand also the forces that vary cyclically These characteristics limit an increase in power and revolution of main engine - Immediate pressures and tempretures in the engine combustion chamber are very high; the engine parts have to work in high temperature and friction condition so the longevity of diesel engines are reduced - Moving rule of the pistons independ on direction of crank shaft so rotation direction of diesel engines can be easily reversed by change work order of starting mechanism In the diesel engine propulsion plant, reversing equipment can be installed on the engine to reverse directly rotation of the engine or installed on shafting to reverse direction of propeller shaft - In light load conditions, diesel engines are not working economically and stably - It is flexible because of short time for starting - Heat energy, which goes out of engine with gas together, is high; if waste heat recovery equipment is used in the diesel engine propulsion plant then its efficiency is raised 1.3.2 Technical characteristics of steam turbine propulsion plant - Working substance is high-pressure steam generated in main boiler - Output is continuous: it is the most important advantage of turbines It permits raise revolution of turbines, therefore can increase power, efficiency and reduce weight, dimension of turbines Nowadays, the modern turbines have revolution up to 15000 (rpm) or more - Working substance flows continuously through the turbine so rotating moment, heat and mechanical load in the parts of engine are stable Therefore, turbine has a high longevity - All moving parts of turbine are installed on a rotor, rotated with the same certain direction and speed It permits to reduce mechanical losses, raise efficiency of turbine When working, turbine doesn't generate inertia forces - Output of turbine depends on only parameters and amount of steam that flow through turbine So turbine can generate a large power - Turbine direction is determined by direction of steam, which acts on blades wheel of turbine With a certain blade wheel, turbine cannot reverse its self To reverse direction of ship, it should be provided with astern turbine So it increases power loss of system Nowadays, that problem has been solved with using intermediate driving or controllable - pitch propeller - Turbine's revolution is much higher than optimum range of propeller's revolution, so turbine cannot directly drive propeller Therefore, it should be provided with reducing gears in the system In fact, the steam turbine propulsion plant is only installed on ships with a big displacement - Gas temperature in boiler combustion chamber is limited by heat durability of material Cycle temperature is low; boiler and transmission pipes have heat losses so efficiency of propulsion plant is low Nowadays, efficiency of the steam turbine propulsion plant is about 22 ÷ 26% while it is about 35 ÷ 40% with the diesel propulsion plant - Boiler has been burning continuously, its temperature and pressure is very high High pressure and temperature steam flows continuously inside transmission pipes It may cause danger to operators when emergency happens - It requires having a high quality of water in the system - It takes a long time to prepare for starting the system, so it is not flexible 1.4 Interaction between Hull and Propeller 1.4.1 Resistance of ship When sailing, all resistance act on the ships and affect to the ships’ movement are determined as follow: R = RN + RK (KG) Where: - RN (KG): Resistance of water acts on ship's hull - RK (KG): Resistance of air affects on floatage of ship a Resistance of water Resistance, which is generated when a ship moves on water surface, depends on ship's speed, roughness of wetted surface, form and structure of ship's hull Resistance of water is performed by: R N = RS + R H + R M (KG) Where: - RS : Wave - making resistance - RH : Form resistance - RM : Frictional resistance * Wave - making resistance is made due to wave when a ship moves on water surface RS = C S ρV Ω (KG) With: - CS : Wave - making resistance coefficient - ρ: Kinetic viscosity of water (KGs2/m4) Seawater: ρ = 104.8 Fresh water: ρ = 102 - V: Ship's speed (m/s) - Ω: Area of wetted surface (m2) * Form resistance is generated due to form and outside structure of ship's hull when a ship moves on water surface: ρV Ω RH = C H (KG) CH: Form resistance coefficient: * Frictional resistance Frictional resistance is generated due to roughness of ship's hull It is determined by: RM = C M ρV Ω (KG) CM is frictional resistance coefficient Reynolds calculated it: CM = 0.455 lgRe (Re Reynolds number) b Resistance of air Besides the resistance of water, air also generates resistance when a ship moves Resistance of air is generated by air affecting on ship's floatage Resistance of air depends on form and section area of ship's floatage, ship's speed, direction and speed of the wind Resistance of air is performed by: ρ K VG FC RK = C K (KG) Where: - CK: Air resistance coefficient, it depends on floatage structure form of a ship: All of ship's floatage have a form of a pyramid: CK = 0.4 ÷ 0.5 A part of ship's floatage have a form of a pyramid: CK = 0.6 ÷ 0.7 Ship’s floatage have a form of a arc: CK = 0.7 ÷ 0.8 Ship’s floatage have a flat form: CK = 0.8 ÷ 1.0 - ρK: Density of air, ρK = 0.125 (KGs2/m4) - FC: Transverse projected area of floatage (m2) - VG: Relative speed of the wind (m/s) VG = V + W + 2V W cos α (m/s) V- Ship's speed (m/s) W- Absolute speed of the wind (m/s) α - Angle is formed by direction of the ship and the wind 1.4.2 Relationship between main engine power and resistance of ship's hull We consider that effective thrust force (generated by propeller when a ship moves) is T (KG), in balance moving condition, we have: T=R (KG) To maintain ship's speed at V (m/s) with resistance R (KG), necessary power can be determined: NK = TV 75 or NK = RV 75 (hp) In fact, ship's hull has an effect on thrust force of propeller That effect can be performed as hull efficiency ηH : ηH = NK NP Where: - NK : Necessary power to maintain ship's speed at V (m/s), with resistance R (KG) - NP : Thrust power of propeller It is performed: 10 NP = TP V P 75 (hp) VP - Advance speed of propeller (m/s) TP - Thrust force of propeller (KG) In fact, the propeller is now working in water, which has been disturbed by the passage of the hull, and in general the water around the stern has acquired a forward motion in the same direction as the ship This forward-moving water is called the wake, and one of the results of the wake influence is that the propeller's speed is not the same with speed of the ship The difference between ship and propeller's speed is called wake speed VW VW = V − V P (m/s) According to Froude expression, wake coefficient w is defined as a ratio between wake speed and propeller's speed: w= VW VP or w= V − VP VP However, Froude expression is used only in older published data, particularly British According to Taylor definition, wake coefficient w is the ratio between wake speed and ship's speed: w= VW V or w= V − VP V - For one propeller-ship: w = 0.5 δ - 0.1 - For two propellers-ship: w = 0.5 δ - 0.16 (δ: Fat coefficient of the ship) Then, propeller's speed is that: VP = V(1-w) (m/s) When a ship's hull is towed, there is an area of high pressure over the stern, which has a resultant forward component reducing the total resistance However, with a self- propeller hull, the pressure over some of this area is reduced by the action of the propeller in accelerating the water flowing into it, the forward component is reduced, the resistance is increased and so also the necessary thrust force to propel the ship Therefore, when propeller working to propel the ship only T (KG) overcome resistance R of ship and component (TP - T)(KG) overcome augment of resistance when accelerating the water TP − T = t is called thrust-deduction fraction The thrust-deduction fraction t is determined TP by practical formula of Kenvil: Ratio: t = C1w C1: coefficient depends on rudder structure characteristic C1 = 0.5 ÷ 1.05 We can perform: TP (1 − t ) = T (KG) Then: 11 TP = T 1− t or TP = R 1− t (KG) Now, use determined values on formula of hull efficiency: TV NK TV RV ηH = = 75 = = R N P T PV P T PV P V (1 − W ) 1− t 75 And: ηH = 1− t 1− w Thrust power of propeller: NP = NK ηH or NP = RV 75η H (hp) Then, power on propeller hub: N CV = NP ηP (hp) With ηP is efficiency of propeller, for: - Non-controllable pitch propeller: ηP = 0.6 ÷ 0.75 - Controllable - pitch propeller: ηP = 0.58 ÷ 0.65 When driving propeller, a part power output of a main engine is lost to overcome friction resistance on shaft bearings, clutch, and reducing gears box So the power of a main engine depends on also shafting efficiency ηtr : Ne = N CV RV = η tr 75η H η Pη tr (hp) Shafting efficiency depends on characteristics of propulsion plant: - Direct driving propulsion plant: ηtr = 0.95 ÷ 0.98 - For indirect driving propulsion plant, shafting efficiency ηtr still depends on efficiency of clutch and reducing gears box and its value is about 0.86 ÷ 0.96 In fact, the power of a main engine Ne determined above equals to only 85% its designed power 1.5 Requirements of Marine Propulsion Plant To operate the ship safely and economically, a marine propulsion plant has to satisfy the general requirements as follow: - The transformation of energy is optimum - Equipment are simple - It is safe and trustful - Dimension and weight are small - Longevity is high - Cost must be low 12 In fact, to meet all these requirements together is very difficult To simplify it, we study the following requirements; 1.5.1 Requirement about the power of marine propulsion plant according to propeller and hull characteristics Suppose NK (hp) is the necessary power to maintain ship's speed at V (m/s), with total resistance R (m/s), then; RV 75 NK = (hp) According to result of 1.4, thrust power of propeller is that: NP = NK ηH (hp) The power on propeller hub: NP RV = η P 75η H η P N CV = (hp) Power of the main engine: Ne = N CV RV = η tr 75η H η Pη tr (hp) Power of the main engine depends on type, functions and displacement of the ship If the ships have the same displacement, but functions and types are different then their powers are also different Therefore, definition "relative power" is used: α= Ne D (hp/T - displacement) With D: Displacement of ship(T) Or: α= N CV η tr D (hp/T - displacement) The power on the propeller hub NCV is determined according to 1.4 However, to simplify the power on the propeller hub can be calculated by Naval formula: N CV = V D Cw (hp) Where: - V: Ship's speed (knot/h) - D: Displacement (T) - Cw: Naval coefficient Finally: α= V3 ⋅3 C wη tr D (hp/T - displacement) 13 - The seawater contains many scale components, so it is easy to precipitate the scale on the cooling surfaces Because of this, heat exchange ability is reduced and parts of the engine cooled by the sea water are easily cracked - Because sea water contains many scale and salt, it will cause erosion and electrolytic corrosion - The temperature of the sea water going out of the engine is very low (It is limited to about 45 ÷ 50o C) this lead to: + Thermal stress of the cylinders, cylinder covers and piston crowns are very high + Temperature at the end of compression stroke is low, so combustion process is not perfect + Waste energy for cooling water is high + The operators cannot reuse the thermal energy of the cooling water, so propulsion efficiency is reduced - Effect of the cooling depends on the environment condition that the ship is operating 63 To auxiliary machineries Figure 5.8: Open cooling system 1- High sea chest 2- Low sea chest 3- Strainer 4- Cooling seawater pump 5- Lubricating oil cooler 6- Three-way valve 5.4.3.2 The closed cooling system Feature Figure 5.10 illustrates a closed cooling system In the closed cooling system, both fresh and sea water are used The fresh water is pumped to cool the engine (such as cylinders, cylinder covers ) and other auxiliary machineries such as the air compressors The fresh water going out of the engine with high temperature returns to the suction pipe of the fresh water pump and then, it is cooled in the fresh water cooler before it is pumped to the engine again and that makes a closed circuit The sea water is taken into the ship to cool the fresh water, the lubricating oil, the supercharged air and other machinery and then it is discharged overboard The temperature of the fresh water can be regulated by a thermostatic control valve Steam or air bubble generated in the system will go up to the expansion tank The fresh water in the system will be replenished from the expansion tank to the suction pipe of the fresh water pump Advantages 64 - Reduce waste energy for cooling water - Reduce rust, scale on the cooling surfaces of the engine - Due to high quality of the fresh water (in comparison with sea water), the engine can be operated with high temperature of the cooling water (60 ÷ 85oC) This reduces thermal stress of the cylinders and piston crowns In addition, the thermal energy of the cooling water can be reused so the efficiency of the propulsion plant will be increased - The cooling water temperature can be automatically regulated - Effect of the cooling mostly does not depend on the environment condition Disadvantages - The system is complex and expensive - a large amount of fresh water is stored on board, so transportation ability of the ship is reduced 65 Expansion tank C.FW pump htr f.w clr l.o clr Air clr C.SW pump To auxiliary machineries Figure 5.10: Closed cooling system 5.4.3.3 Main components of the cooling system There are following main components in the cooling system: Sea chests Cooling fresh water pumps Cooling sea water pumps Expansion tank Thermostatic control valve Fresh water cooler Strainers 66 Pipe line and fitting Indicators (thermometer, pressure gauges, level indicator ) 5.5 Compressed Air System 5.5.1 Function of the compressed air system The compressed air system supplies compressed air to carry out different purposes: - To start and reverse the main engine - To start the diesel generators - To supply compressed air for the remote control system and other automatic control equipment - To supply compressed air for air whistle (air horn) - To clean sea chest - To clean and dry parts of machinery when repairing, tighten and loosen bolts and nuts 5.5.2 Requirements of compressed air system 5.5.2.1 Main air compressor - If main engine is started by compressed air, then there must be at least two air compressors in the system and each of them can be able to supply air to both reservoirs However, when cylinders of the main diesel is arranged air charging valves, then these valves can be considered as a compressor driven by main engine One of these compressor is driven by other engine which is not main engine Total capacity of compressors must be enough to supply fresh air into reservoirs at necessary pressure for starting main engine in time of an hour - Depending on pressure of air used in the system, the air compressors with one stage or multiple stages are equipped The purpose of using the multiple-stage air compressors is to increase compression work and reduce compressed air temperature at the end of compression stroke 5.5.2.2 Emergency air compressor If the engine, which drive main compressors mention above started by compressed air, then an emergency air compressor which driven by independent mechanical energy must be equipped This compressor need not compressed air for its starting Capacity of emergency air compressor must be enough for starting the engine driving main compressors For this purpose, a small reservoir can be arranged 5.5.2.3 Safety valve arrangement There must be safety valve on compressors to avoid 10% over maximum working pressure in the cylinder There must be a pressure relief device in the jacket cooling water of cylinder to prevent leakage of compressed air into cooling system 5.5.2.4 Compressed air pipe Provision shall be made to reduce to a minimum the entry of lubricating oil into the compressed air system and to drain this system; 67 All discharge pipe from starting air compressor shall lead directly to air receivers, and all starting pipe from the air receivers to main or auxiliary engine shall be entirely separate from the compressor discharge pipe system; The starting pipe which leads from reservoir to main engine must be separated to air charging pipe from main air compressor The main starting air arrangement for main propulsion internal combustion engines shall be adequately protected against the effect of backfiring and internal explosion in the starting air pipe - Unwelding high-pressure pipes and zinc galvanized are used in the system - Air pressure in the system depends on different duties: For starting engines: P = 18 ÷ 30 KG/cm2 For the control system and other purposes: P = - 11 KG/cm2 5.5.2.5 Air reservoir - There must be at least two main air reservoirs for the system - Total capacity of the main air reservoir must be enough to start continuously main engine without charging air into the reservoirs with following conditions: - For direct reversing the main diesel engine, capacity of air reservoirs must be enough for at least twelve times of starting of the engine Z=12C Here: Z is amount of starting time of each engine C is constant and depends on: C=1 for the ship with one propeller and main engine drive directly propeller shaft C=1.5 for twin screw ship with two main engine or one propeller ship with two main engine that drive indirectly propeller shaft C=1/2 for indirect reversing engine and variable pitch propeller There must be an emergency air reservoir and its capacity must be enough for six times of starting of the diesel generators - Besides the charge and supply valve, the air reservoirs must be provided with safety valve, pressure gauge, drain valve; a manhole for inspecting and repairing must also be installed In some ships, the air reservoirs can be provided with pressure switch to control the start and stop of the air compressors - Hydraulic test must be carried out before using or after working period of the air reservoirs Ptest=1.5Pmax - Inside inspection Hydraulic test years/time 10 years/time or when the class required 68 Figure 5.13: Reservoir 5.5.3- The typical compressed air system Figure 5.14 illustrates a compressed air system 69 No.2 Air tank No.1 Air tank M/e No.1 main Air comp Reducing valve No.2 main Air comp DRYER Contrl aIR Serv air No.1 d/g No.2 d/g Emer D/g EMER AIR COMP EMER AIR TANK Figure 5.14: Compressed air system 70 5.6 Ballast system 5.6.1 Function of ballast system Its function is to increase stability for the ship; it ensures the balance for the ship in every condition The ballast system is used when the ship is sailing in light load condition, loading and unloading of cargoes, or in some special cases To aft peak tk No.1 p No.2 p To Fore Peak tk Over board pump No.1 s No.2 s To other system Figure 5.16: Ballast system 5.6.2 Requirements of ballast system All of the ship must be equipped a ballast system which is able to pump water in and out of any ballast tank in every condition The ballast system must be equipped with suitable protecting devices such as Non return valve, stop valve There must be opening and closing indicator of these valves to avoid sea water flowing into ballast tanks or from one to the another A blind flange or bending pipe must be equipped in the ballast system or hold bilge system when cargo hold is arranged to contain ballast water A blind flange or bending pipe must be equipped when a tank is used to store fuel or ballast water 5.6.3 Components of ballast system 5.6.3.1 Ballast tanks - The ballast tanks are used to store water for purpose of adjusting the balance of the ship - The ballast tanks can be fore peak, aft peak, double bottom or side tank In some cases cargo holes is used as ballast tanks In the aft arrangement, ballast tank normally is placed in the center and near to stern area of the ship The tank of two sides can be either side tank or wing tank 71 - Capacity of tanks depends on displacement of the ship Each tank is provided with a valve, vent pipe, sounding hole, manhole for checking and cleaning In the big ship, ballast and hold bilge pipe are positioned in a tunnel along the keel of ship, so that it is easy for checking and repairing 5.6.3 Ballast pump A centrifugal pump, which has high capacity, is normally used in the ballast system Capacity of the pump must be enough to pump in or out completely these tanks in loading or discharging cargo time To increase ability of drying up ballast water tank, a vacuum pump or ejector sometime is provided 5.6.3.3 Valves and pipe line - There must be one valve for each ballast tank With ballast tanks arranged at the bottom of the ship, there must be mechanism to open remotely ballast valves of these tanks from upper deck or convenient place 5.7 Bilge system 5.7.1 Function of bilge system The bilge system is used to: - Dry up bilge water in the engine room, separate oil from bilge water and discharge cleaned water out to the sea - Store and treat dirty oil in engine room Dry up water in cargo holes, tanks in the ship and discharge it out to the sea Mixture of water and oil in the engine room is called "bilge water" The bilge water is formed due to leakage of oil and water from systems, equipment, stern tube, and cleaning cargo holds 5.7.2 Cargo hold bilge 5.7.2.1 General requirements There must be bilge pipe for any cargo hold or confined spaces and the system can pump out completely all theses places The bilge pipe for cargo holes, engine room, and shaft tunnel must separate to the others which is not dry up pipe There must be enough thickness of bilge pipe which go through double bottom tanks, deep tanks or fuel tanks The pipe that go through the double bottom tank, wing tank can be damaged due to going a ground or collision That needs to provide a non return valve near the suction end or stop valve which can be closed from an easy reaching position 5.7.2.2 Bilge pump There must be at least two bilge pump on the ship which is mechanical independent driven and connected to main bilge line However, with length of ship less than 90m, one of the bilge pumps can be driven by main engine The ballast pump, cleaning pump, and general service pump which is mechanical independent driven can be used as bilge pump but satisfy the condition of its suitable connection to main bilge line Capacity of bilge pump is calculated as follow: Q= 5.66d2 x10-3 (m3/h) d; inside diameter of main bilge pipe (in the table given by class) 72 Type of bilge pump: the pump mention above must be self priming pump type Some time eductor can be used as bilge pump but driving water for this eductor must be supply from two pumps 5.7.3 Engine room bilge system 5.7.3.1.General requirement + Oil content control and monitoring equipment There must be oily water separator on the ship of displacement between from 400 to 10000 tones to ensure that the mixture of water and oil after going out this device has content oil smaller than 15ppm There must be alarm and auto stop discharging device when content of oil over 15ppm on the ship which have displacement of over 10000 deadweight tone + Bilge tanks All the ship of displacement of over 400 tones must be equipped one or more tanks which has enough capacity to store the untreated bilge oil This tank must be design so that it is easy for cleaning and discharging to reception facilities The system has some of following tanks: Bilge water tank, bilge separator oil tank, waste oil tank, sludge tank Volume of these tanks is designed depending on kind and size of ship It is also met requirements of the class 5.7.3.2 Bilge pump A piston pump or screw pump (snake pump) is normally used in the engine room bilge system For the vessel having deadweight of 10000 M/T or more, this pump must be automatically stopped when oil content in bilge water after going out oily water separator is over 15 ppm To obtain good operation, a sludge pump should be fitted to transfer sludge oil and bilge pump if for bilge water 5.7.3.3 Oily water separator A content below 15 ppm of oil in discharge water is required for this oily water separator An alarm device must be equipped to notify duty engineer when oil content is over 15 ppm 5.7.3.4 Valves and pipe line Non-return valves shall be arranged in suction line near the tanks in the bilge system For the ship having deadweight less than 10000 M/T, a three way valve actuated automatically when oil content is over 15 ppm 5.7.4 The typical bilge system Figure 5.18 is an illustration of a bilge system 73 To overboard Solenoid valve B.W oil Monitor device Oily water separator To incinerator Bilge pump To shore connection W.O.T B.W B.W.T S.W valve B.S.O.T B.S.O T Sludge.Tk B.W Figure 5.18: Bilge system 74 CÁC ĐỀ THI THAM KHẢO PHIẾU THI HẾT MÔN Số: 01 Môn học: TRANG TRÍ ĐỘNG LỰC TÀU THỦY Hệ: Ðại học quy CHỮ KÝ: Trưởng môn State concept & functions of Main propulsion plant equipments of Marine propulsion plant? Describe structure, operation & transmission efficiency of hydraulic clutch? (Given figure 13) Học sinh không tẩy, xóa, làm bẩn phiếu thi PHIẾU THI HẾT MÔN Số: 02 Môn học: TRANG TRÍ ĐỘNG LỰC TÀU THỦY Hệ: Đại học quy CHỮ KÝ: Trưởng môn State concept & functions of Auxiliary equipments of Marine propulsion plant? Describe structure, operation of hydraulic speed reducer? (Given figure 14) Học sinh không tẩy, xóa, làm bẩn phiếu thi 75 PHIẾU THI HẾT MÔN Số: 03 Môn học: TRANG TRÍ ĐỘNG LỰC TÀU THỦY Hệ: Đại học quy CHỮ KÝ: Trưởng môn State concept & functions of Safety equipments of Marine propulsion plant? State about disc friction clutch: (Given figure 15) - Explain structure? - Working process? - Advantage & disadvantage? Học sinh không tẩy, xóa, làm bẩn phiếu thi PHIẾU THI HẾT MÔN Số: 04 Môn học: TRANG TRÍ ĐỘNG LỰC TÀU THỦY Hệ: Đại học quy CHỮ KÝ: Trưởng môn State concept & functions of Main propulsion plant equipments of Marine propulsion plant? 2.State about cone friction clutch: (Given figure 16) - Explain structure? - Working process? - Advantage & disadvantage? Học sinh không tẩy, xóa, làm bẩn phiếu thi 76 PHIẾU THI HẾT MÔN Số: 05 Môn học: TRANG TRÍ ĐỘNG LỰC TÀU THỦY Hệ: Ðại học quy CHỮ KÝ: Trưởng môn State concept & functions of Auxiliary equipments of Marine propulsion plant? State about air actuated friction clutch: (Given figure 17) - Explain structure? - Working process? - Advantage & disadvantage? Học sinh không tẩy, xóa, làm bẩn phiếu thi PHIẾU THI HẾT MÔN Số: 06 Môn học: TRANG TRÍ ĐỘNG LỰC TÀU THỦY Hệ: Ðại học quy CHỮ KÝ: Trưởng môn How to classify Marine propulsion plant? State about single - stage reduction gear: (Given figure 18) - Explain structure? - Principle of operation? - Advantage? - Build formula of transmission ratio? Học sinh không tẩy, xóa, làm bẩn phiếu thi 77 [...]... weight of propulsion plant is increased then the cargoes transportation and the independent working ability of the ship is reduced So application methods to reduce the weight of propulsion plant are necessary In fact, the ships have the same displacement but speed and power are varied, so then the weight of propulsion plant is varied In the other hand, with the same power but the weight of propulsion. .. main engine (kg/hp.h) And then: gM = g e N e t g e N e = V t V (kg/knot) 1.5.3 Requirements of propulsion plant for independent working ability of the ship a Requirement about the weight of propulsion plant Total weight or displacement of the ship consists of four main components: - Weight of hull - Weight of propulsion plant - Weight of needments (fuel, lubricating oil, water, provision, stores and spares)... the speed, the larger power is 1.5.2 Requirement about economical norm of marine propulsion plant The economical norm in operating of marine propulsion plant is estimated by amount of fuel consumption of a main engine on one knot of itinerary: gM = B V t (kg/knot) Where: - V: Speed of the ship (knot/h) - t: Working time of propulsion plant (h) - B: The fuel consumption of main engine in the working time... saturated coefficient of the engine room: The number of horsepower (hp) of the propulsion plant on unit of the engine room area KS = ∑N e (hp/m2) S - Volume saturated coefficient of the engine room: The number of horsepower of the propulsion plant in unit of the engine room space KV = ∑N e (hp/m3) V Where: - ∑Ne: Total power of the propulsion plant (hp) - S: Total area of the engine room floors (m2) - V:... the propulsion plant, the times on voyage, operation area of the ship to raise the transportation ability The fuel stored can be calculated according to the fuel consumption in all times of an independent voyage: ∑B = ∑N e g tb t (kg) Where: - ∑B: Amount of the fuel consumption in all times of the voyage (kg) - ∑Ne: Total power of the propulsion plant - gtb: Average specific fuel consumption of the propulsion. .. propulsion plant (hp) - S: Total area of the engine room floors (m2) - V: Total volume of the engine room space (m3) c Requirement about the needments of the propulsion plant Needments stored on the ship to permit her running in a certain time For the marine propulsion plant, main needment is fuel The more amount of fuel stored on the ship, the higher the independent working ability is However, weight of the... the weight of propulsion plant is varied In the other hand, with the same power but the weight of propulsion plant is also varied when type of propulsion plant is different Therefore, the definition of "relative weight" is used: K1 = W D With W is total weight of propulsion plant (kg/T - displacement) (kg) b Requirement about dimension of the engine room Almost machinery is installed in the engine room... ships when revolution of main engine is about 85 ÷ 300 rpm - In a direct driving propulsion plant, the main engine is a kind of low-speed, large power, direct reversing diesel engine The most common is low-speed; two- strokes cycle diesel engine with crosshead 3.2.2 Advantages - Driving efficiency is high A direct driving propulsion plant with short shafting will have a driving efficiency of about 97... reversing direction of the ship This can be done by the multi-stage reduction gear and therefore, the flexibility of the propulsion plant and longevity of the main engine will be increased - Two or more main engines can be used to drive only one propeller, thus increases the flexibility of the propulsion plant and the main engines can be effectively operated in every operating condition (even when light load)... propeller - There are two times of energy transformation 3.4.1.2 Electric driving diagram This is the simplest illustration of the direct current electric driving propulsion plant 6 1 M 2 + _ - 4 G 3 5 ME + - Figure 3.1 Direct current electric driving propulsion plant 1- Electric Motor 2- Excited coil of the motor 3- Excited coil of the generator 4- Generator 5- Main engine 6- Rheostat Generator (4) is driven ... and diesel propulsion plant Besides these, nuclear propulsion plant can also be used To combine main kinds of propulsion plant with driving modes, we have many different kinds of propulsion plant... driving diesel engine propulsion plant, indirect driving diesel engine propulsion plant and special driving diesel engine propulsion plant In the direct driving diesel engine propulsion plant, direction... engine propulsion plants are electric driving diesel engine propulsion plant and diesel engine propulsion plant with controllable - pitch propeller The same as the indirect driving diesel engine propulsion