1 DIESEL, GAS TURBINE AND COMBINED CYCLE POWER PLANTS
UNIT II DIESEL, GAS TURBINE AND COMBINED CYCLE POWER PLANTS
2 Power plant engineering Diesel power plant
INTRODUCTION: A generating station in which diesel engine is used as the prime mover for the generation of electrical energy is known as diesel power station Diesel power plants produce power in the range of 2 to 50 MW. They are used as standby sets for continuity of supply such as hospitals, telephone exchanges, radio stations, cinema theatres and industries. They are suitable for mobile power generation and widely used in railways , submarine & ships.
3 Applications of diesel power plant
They are used as central station for small or medium power supplies. They can be used as stand-by plants to hydro-electric power plants and steam power plants for emergency services. They can be used as peak load plants in combinations with thermal or hydro-plants. They are quite suitable for mobile power generation and are widely used in transportation systems such as automobiles, railways, air planes and ships. Now-a-days power cut has become a regular feature for industries. The only solution to tide over this difficulty is to install diesel generating sets.
5 DIESEL ENGINE power plant
6 FIELD OF USE The diesel electric power-plants are chiefly used in the fields mentioned below. 1. Peak load plant: The diesel plants are used in combination with thermal or hydro-plants as peak load plants. This plant is particularly preferable as peak load plant as it can be started quickly and it has no standby losses as in the case of thermal plants where boilers always must be kept hot. 2. Mobile plants: Mobile diesel plants mounted on skids or trailers can be used for temporary or emergency purposes such as for supplying power to large civil engineering works for supplementing electricity supply systems that are temporarily short of power. 3. Stand-by Units: This can be used as a standby unit to supply part load when required. For example, this can be used with hydro-plant as stand-by unit. If the water available is not sufficient due to reduced rainfall, a diesel station supply power in parallel with hydro-station. The use is made temporarily till the water is available to take the full load.
7 4. Emergency plant: The plants used for emergency purposes are at to standby units, normally idle but are used where power interruption would mean financial loss or danger in key industrial processes, tunnel lighting and operating rooms of hospitals. They are also used for telecommunication and water supply under emergency conditions. 5. Nursery station: When the diesel plant is used to supply the power to a small town in the absence of main grid and which can be moved to another area which needs power on a small scale when the main grid is available is known as "Nursery Station". The main grid cannot extend to every corner of the country till there is enough load. Many times the extension of grid is not possible due to the constructional difficulties as in Assam. Diesel unit of small capacity can be installed to supply the load to a small town during the process of development and it can be removed to another required place till the main grid for tapping the power is available. 6. Starting stations: The diesel units are used to run the auxiliaries for starting the large steam plants. 7. Central stations: This can be used as central station where the capacity required is small (5 to 10 MW). The limit is generally decided by the cost of the plant and local conditions regarding the availability of fuel and water, space requirements and non-availability of the grid. Small supply units for commercial purposes and public utilities e.g. cinema hall, hospital and municipalities are commonly used in practice.
8 Diesel power plants in INDIA
As on July 31, 2013, and as per the Central Electricity Authority the total installed capacity of Diesel based power plants in India is 1, MW. Normally the diesel based power plants are either operated from remote locations or operated to cater peak load demands. Here is some list of presently operating plants. SOURCE: Wikipedia.
9 List of diesel power plants in INDIA
10 Layout of Diesel Power Plant
13 Essential elements of Diesel Power Plant
Engine System Starting System Lubrication System Fuel System Air filter and Supercharge Cooling System Exhaust System Governing System
14 Engine system ENGINE: This is the main component of the plant which develops required power. The engine is generally directly coupled to the generator Generally classified as two stroke engine and four stroke engines.
16 Engine and Air intake system
This is the main component of the plant which develops the required power. The electrical generator is usually direct coupled to the engine. Air intake system- The air intake system conveys fresh air through pipes or ducts to (i) air intake manifold of 4 stroke engine (ii) The scavenging pump inlet of a two stroke engine (iii) The supercharger inlet of a supercharged engine.
17 Air filter and supercharger
Air filter is used to remove the dust from the air which is taken by the engine. The supercharger is used to increase the pressure of the air supplied.
18 Air intake system Air is first drawn through a filter to catch dirt or particles that may cause excessive wear in cylinders. Filters may be of following types: Dry type (paper, cloth, felt, glass wool etc) Wet type (oil impingement type, oil bath type where oil helps to catch particles) Following precautions should be taken while designing air intake systems
19 Following precautions should be taken while designing air intake systems
Air intake should be located outside the engine room. Air intake should not be located in confined places to avoid undesirable acoustic vibrations. Pressure drop in the air intake line should minimum to avoid engine starvationbe Air filters should be accessible for periodic cleaning. In some cases a muffler may be introduced to prevent engine noise from reaching outside air.
20 Air intake system The air required for the combustion of fuel inside the diesel engine cylinder is drawn through the air filter. The purpose of the filter is to remove dust from the incoming air. dry filter- may be made of felt , wood or cloth. wet filter- oil bath is used.
21 Fuel supply system Fuel from the storage tank is pumped through a filter into a smaller tank called all day tank . this tank supplies the daily requirements of the diesel engine.
22 Starting system The function of this system is to start the engine from cold by supplying compressed air at about 17 bar supplied from an air tank is admitted to a few cylinders making them work like reciprocating air motors to run the engine shaft. Fuel is admitted to the remaining cylinders and ignited in the normal way causing the engine to start.
23 Lubrication system It includes the oil pumps, oil tanks, filters, coolers and connecting pipes. The purpose of the lubrication system is to reduce the wear of the engine moving parts Part of the cylinder such as piston , shafts , valves must be lubricated. The lubricant is cooled before recirculation. Lubrication also helps to cool the engine
24 The following are the important functions of a lubrication system
LUBRICATION: To keep parts sliding freely past each other, reducing friction and wear. COOLING: To keep surfaces cool by taking away part of the heat caused by friction. CLEANING: To keep the bearings and piston rings clean. SEALING: To form a good seal B/W the piston rings and cylinder walls. REDUCING NOISE: to reduce the noise of the engine by absorbing vibration.
26 Fuel system It includes the storage tank, fuel pump, fuel transfer pump, strainers and heater. Pump draws diesel from storage tank to day tank through the filter The day tank is usually placed high so that diesel flows to engine under gravity. Diesel is filtered before being injected into the engine by the fuel injection pump. strainers
27 The fuel injection system performs the following functions
Filter the fuel Meter the correct quantity of the fuel to be injected Time the injection process Regulate the fuel supply Secure fine atomization of fuel oil Distribute the atomized fuel properly in the combustion chamber Oil is atomized either by blast or pressure jet. In pressure jet atomization oil is forced to flow through spray nozzles at pressure above 100 bar. It is known as solid injection
28 Classification of solid injection systems
Common rail injection system: The system is named after the shared high-pressure (100 to 200 bars)reservoir (common rail) that supplies all the cylinders with fuel. With conventional diesel injection systems, the fuel pressure has to be generated individually for each injection. With the common rail system, however, pressure generation and injection are separate, meaning that the fuel is constantly available at the required pressure for injection. Individual pump injection system: Distributor system:
31 Individual pump Injection System
32 Individual pump Injection System
The schematic is shown in fig. An individual pump or pump cylinder connects directly to each fuel nozzle. Metering and injection timing controlled by individual pumps. Nozzle contains a delivery valve actuated by the fuel pressure.
34 Distributor System The schematic is shown here.
The fuel is metered at a central point. A pump meters, pressurizes and times the fuel injection. Fuel is distributed to cylinders in correct firing order by cam operated poppet valves which admit fuel to nozzles.
35 Cooling system The cooling system consists of a water source, pump and cooling towers. The pump circulates water through cylinder and head jacket. The water takes away heat form the engine and it becomes hot. The hot water is cooled by cooling towers and re circulated for cooling. The cooling water is treated with 3 ppm Calgon to control the scaling in the different parts of the system and it is also chlorinated once per shift upto 6 ppm to prevent algae growth which would cause the rapid tube fouling. For inhibiting corrosion, 300 ppm of sodium chromate is also added. Generally, the quantity of cooling, water required is 35 to 60 litres per kW per hour.
36 Cooling system The temperature of the hot gases inside the cylinder may be as high as 2750 c . If there is no external cooling, the cylinder walls and piston will tend to assume the average temp. of the gases. Cooling is necessary because: To avoid deterioration or burning of lubricating oil. The strength of the materials used for various engine parts decreases with increase in temperature. Local thermal stress can develop due to uneven expansion of various parts. Increase in pre-ignition and knocking Due to high cylinder head temp. the volumetric efficiency and hence power O/P of the engine are reduced.
38 Elements of cooling system
39 There are two methods of cooling I.C. engines:
1.Air cooling. 2. Liquid cooling
40 Air cooling : In this method, heat is carried away by the air flowing over and around the cylinder. Fins are added on the cylinder which provide additional mass of material for conduction as well as additional area for convection and radiative modes of heat transfer
41 Liquid cooling In this method, the cylinder walls and head are provided with jackets through which the cooling liquid can circulate. The heat is transferred from the cylinder walls to the liquid by convection and conduction. The liquid gets heated during its passage through the cooling jackets and is itself cooled by means of an air cooled radiator system.
42 Types of Water Cooling System
Thermo Siphon System In this system the circulation of water is due to difference in temperature (i.e. difference in densities) of water. So in this system pump is not required but water is circulated because of density difference only.
43 Pump Circulation System
In this system circulation of water is obtained by a pump. This pump is driven by means of engine output shaft through V-belts.
45 Exhaust system The exhaust gases coming out of the engine is very noisy. In order to reduce the noise a silencer is used.
46 Exhaust system This includes the silencers and connecting ducts.
The exhaust gases coming out of the engine is very noisy. silencer (muffler) is provide to reduce the noise.
47 Exhaust system Exhaust pipe leading out of the building should be short in length with minimum number of bends to provide as low a pressure loss as possible. Flexible tubings may be added in exhaust pipe to take care of misalignments and expansion/contraction and also to isolate the system from engine vibrations.
48 Exhaust system Each engine should have its independent exhaust system.
Where possible, exhaust heat recovery should be made to improve plant thermal efficiency. E.g., air heating, low pressure steam generation in diesel-steam power plant etc
49 Governing system The function of the governing system is to maintain the speed of the engine This is done generally by varying fuel supply to the engine according to load. It is achieved with use of governors.
51 ADVANTAGES AND DISADVANTAGES OF DIESEL POWER PLANT
Simple design & layout of plant Occupies less space & is compact Can be started quickly and picks up load in a short time Requires less water for cooling Thermal efficiency better that of Steam Power Plant of same size No ash handling problem Less operating and supervising work is required DISADVANTAGES-> High running charges due to costly price of Diesel Generates small amount of power Cost of lubrication very high Maintenance charges are generally high Noise problem Capacity is restricted. Cannot be of very big size
52 Gas Turbine Power Plant
9 November 2018 Gas Turbine Power Plant
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54 Gas turbine power plant
9 November 2018 Gas turbine power plant Working principle : Air is compressed(squeezed) to high pressure by a compressor. Then fuel and compressed air are mixed in a combustion chamber and ignited. Hot gases are given off, which spin the turbine wheels. 9 November 2018
57 Energy Flow Diagram
58 Gas turbine power plant
9 November 2018 Gas turbine power plant Description: Gas turbines burn fuels such as oil, nature gas and pulverized(powdered) coal. Gas turbines have three main parts: Air compressor ii) Combustion chamber iii) Turbine 9 November 2018
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60 Basic Components Compressor Combustion Chamber Turbine
Draws in air & compresses it Combustion Chamber Fuel pumped in and ignited to burn with compressed air Turbine Hot gases converted to work Can drive compressor & external load Air is drawn into the front of the compressor. Each succeeding stage is smaller increasing velocity (recall Bernoullis equation). Between each rotating stage is a stationary stage or stator. The stator partially converts the high velocity to pressure and directs the air to the next set of rotating blades. The rotor imparts velocity to the air (like a fan). Each stage consists of a rotor and stator and results in a pressure increase. Air exits the compressor and enters the diffuser. Suddenly, the air moves from a narrow passage into a wide area. By bernoulli, the air loses velocity and expands in volume and increases pressure. Now, the air is slow moving and high pressure, usually about 19:1. Fuel is injected here and the mixture is ignited by a spark. The spark causes a rapid increase in the volume of the air an combustion gases (at constant pressure). The combustion mixture goes rearward to a nozzle which directs the gas onto the turbine blades and accelerates the gases. The gases are now high velocity, high temperature, low pressure and are used to turn the turbine. The kinetic and thermal energy of the gases are transferred the turbine blades. The turbine is multistaged to remove as much of the energy from the gas as possible.
61 Basic Components Compressor Combustion Chamber Turbine
Draws in air & compresses it Combustion Chamber Fuel pumped in and ignited to burn with compressed air Turbine Hot gases converted to work Can drive compressor & external load
62 Basic Components Compressor Combustion Chamber Turbine
Draws in air & compresses it Combustion Chamber Fuel pumped in and ignited to burn with compressed air Turbine Hot gases converted to work Can drive compressor & external load
63 Compressor Supplies high pressure air for combustion process
Compressor types Radial/centrifugal flow compressor Axial flow compressor
64 Compressor Radial/centrifugal flow Axial flow
Adv: simple design, good for low compression ratios (5:1) Disadvantage: Difficult to stage, less efficient Axial flow Good for high compression ratios (20:1) - Most commonly used Radial flow or centrifugal compressor- compressor draws in the entering air at the hub of the impeller and accelerates it radially outward by centrifugal force through the impeller. Reasonably efficient for high pressure ratios developed in a single stage. Axial flow- Rotor has fixed blades which force the air rearward much like an aircraft propeller. The stator directs the air rearward to the next stage. Very much like a turbine used in reverse. Used in multistage arrangements and pressure ratios increase with the number of stages.
65 Compressor Controlling Load on Compressor Compressor Stall
To ensure maximum efficiency and allow for flexibility, compressor can be split into HP & LP sections Vane control: inlet vanes/nozzle angles can be varied to control air flow Compressor Stall Interruption of air flow due to turbulence
66 Use of Compressed Air Primary Air (30%) Secondary Air (65%)
Passes directly to combustor for combustion process Secondary Air (65%) Passes through holes in perforated inner shell & mixes with combustion gases Film Cooling Air (5%) Insulates/cools turbine blades
67 Combustion Chambers Where air & fuel are mixed, ignited, and burned
Spark plugs used to ignite fuel Types Can: for small, centrifugal compressors Annular: for larger, axial compressors (LM 2500) Can-annular: for really large turbines
68 Can Type- Individual liners and cases mounted around the engine each with its own fuel nozzle.
69 Annular type- Liner consists of an undivided circular shroud extending all the way around the outside of the turbine shaft housing. The dome of the liner has small slots and holes to admit primary air. There are also holes in the dome for the fuel nozzles to extend through into the combustion area. The combustion space is formed by the inner and outer liners. The inner liner prevents flame from contacting the turbine shaft housing.
70 Can-annular type- Designed to deal with split spool compressor
Can-annular type- Designed to deal with split spool compressor. Individual cans are placed inside an annular case. Combines the strength of annular design with the convenience of maintenance of the can. Also keeps high temperatures in the inner can.
71 Turbines Consists of one or more stages designed to develop rotational energy Uses sets of nozzles & blades Turbines, like compressors, consist of stator and rotor elements. Stators prepare the mass flow for harnessing of power through the turbine rotor. The nozzles take the high pressure, high-energy mixture and give it velocity for driving the rotor. Also deflects the gases to a specific angle in the direction of the turbine wheel rotation. Rotors consist of a shaft and bladed wheel. Turbine operates at high speed
72 Gas turbine power plant…
9 November 2018 Gas turbine power plant… Applications of gas turbine: drive pumps, compressors and high speed cars. aircraft and ships. Power generation (used for peak load and as stand-by unit). 9 November 2018
73 OPEN CYCLE GAS TURBINE POWER PLANTAND ITS CHARACTERISTICS
Gas turbines usually operate on an open cycle Air at ambient conditions is drawn into the compressor, where its temperature and pressure are raised. The high pressure air proceeds into the combustion chamber, where the fuel is burned at constant pressure. The high-temperature gases then enter the turbine where they expand to atmospheric pressure while producing power output. Some of the output power is used to drive the compressor. The exhaust gases leaving the turbine are thrown out (not re-circulated), causing the cycle to be classified as an open cycle
74 CLOSED CYCLE GAS TURBINE POWER PLANT AND ITS CHARACTERISTICS
The compression and expansion processes remain the same, but the combustion process is replaced by a constant-pressure heat addition process from an external source. The exhaust process is replaced by a constant- pressure heat rejection process to the ambient air.
75 Closed cycle gas turbine power plant
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76 Advantages of gas turbine power plant
9 November 2018 Advantages of gas turbine power plant Storage of fuel requires less area and handling is easy. The cost of maintenance is less. It is simple in construction. There is no need for boiler, condenser and other accessories as in the case of steam power plants. Cheaper fuel such as kerosene , paraffin, benzene and powdered coal can be used which are cheaper than petrol and diesel. Gas turbine plants can be used in water scarcity areas. Less pollution and less water is required. 9 November 2018
77 Disadvantages of gas turbine power plant
66% of the power developed is used to drive the compressor. Therefore the gas turbine unit has a low thermal efficiency. The running speed of gas turbine is in the range of (40,000 to 100,000 rpm) and the operating temperature is as high as 1100 – 12600C. For this reason special metals and alloys have to be used for the various parts of the turbine. High frequency noise from the compressor is objectionable. 9 November 2018
78 Methods of Improvement of Thermal Efficiency of Open Cycle Gas Turbine Plant
1. Intercooling 2. Reheating 3. Regeneration
79 Intercooling A compressor utilizes the major percentage of power developed by the gas turbine. The work required by the compressor can be reduced by compressing the air in two stages and incorporation a intercooler between the two.
80 1-2’: LP compression 2’-3: Intercooling 3-4’: H.P. compression 4’-5: C.C. Combustion chamber(heating) 5-6’: T(Turbine) -Expansion
81 Work Ratio is increased
Thermal efficiency decreases but it increases at high pressure ratio.
82 Reheating The output of gas turbine can be improved by expanding the gasses in two stages with a reheater between the two. The H.P. turbine drives the compressor and the LP turbine provides useful power output.
83 T-s diagram for closed loop cycle turbine
1-2’: Compression 2’-3: C.C (heating) 3’-4’: Turbine(Expansion) 4’-5: Reheater(heating) 5-6’: Turbine(Expansion)
84 Net Work output increases.
Thermal Efficiency Decreases.
85 Regeneration The exhaust gasses from the turbine carry a large quantity of heat with them since their temperature is far above the ambient temperature. They can be used to heat air coming from the compressor there by reducing the mass of fuel supplied in the combustion chamber.
86 Regenerative Cycle has more efficiency than simple cycle at lower pressure ratio.
Above certain pressure ratio limit, the efficiency of cycle drops since in that case regenerator will cool the compressed sir instead of heating it
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88 COMBINED POWER CYCLES 9 November 2018
89 TYPES Gas Turbine-Steam Turbine Power Plant
MHD-Thermionic Steam Power Plant Thermo Electric-Steam Power Plant MHD-Steam Power Plant Nuclear-Steam Combined Power Plant MHD-Gas Turbine Power Plant 9 November 2018
90 GAS TURBINE-STEAM TURBINE POWER PLANT
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91 GAS TURBINE-STEAM TURBINE POWER PLANT
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92 MHD-THERMIONIC STEAM POWER PLANT
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93 THERMO ELECTRIC-STEAM POWER PLANT
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95 Combined Cycle Power Plant
The Combined Cycle Power Plant or combined cycle gas turbine, a gas turbine generator generates electricity and waste heat is used to make steam to generate additional electricity via a steam turbine.
96 A Combined Cycle Power Plant produces high power outputs at high efficiencies (up to 55%) and with low emissions. In a Conventional power plant we are getting 33% electricity only and remaining 67% as waste. By using combined cycle power plant we are getting 68% electricity.
98 Inner Workings of a Combined-Cycle Power Plant
A combined-cycle power plant uses both a gas and a steam turbine together to produce up to 50 percent more electricity from the same fuel than a traditional simple-cycle plant. The waste heat from the gas turbine is routed to the nearby steam turbine, which generates extra power.
99 Fig: A Combined Cycle Power Plant
100 How a Combined-Cycle Power Plant Produces Electricity
Gas turbine burns fuel: The fast-spinning turbine drives a generator that converts a portion of the spinning energy into electricity. Heat recovery system captures exhaust: The HRSG creates steam from the gas turbine exhaust heat and delivers it to the steam turbine.
101 Steam turbine delivers additional electricity:
The steam turbine sends its energy to the generator drive shaft, where it is converted into additional electricity.
102 Advantages of Combined Cycle Power Plant
The efficiency of the combined cycle plant is better or higher than the turbine cycle or steam cycle plant. The efficiency of combined cycle power plant will be of the order of about 45 to 50%. fewer moving parts and less vibration than a reciprocating engine very low toxic emissions runs on a wide variety of fuels high operating speeds
103 Disadvantages of Combined Cycle Power Plant
Higher cost longer start-up less responsive to power demands shrill whining noise.
104 INTERGRATED GASIFICATION COMBINED CYCLE (IGCC)
105 Content Overview IGCC Process Future development Conclusions
106 Overview INTEGRATED GASIFICATION COMBINED CYCLE GASIFICATION
PRODUCE SYNGAS COMBINED CYCLE POWER GENERATION LOW EMISSION HIGH EFFICIENCY
110 IGCC for Municipal Solid Waste
111 GASIFIER TYPES Manufacturer Gasifier type Application ConocoPhillips
Coal- water slurry feed, Oxygen blown, refractory lined gasifier wide range of coal General Electric Energy (GE) Coal-water slurry feed, O2 blown, refractory lined gasifier bituminous coal, pet- coke or blend of pet coke with low rank coal Kellog Brown and Root (KBR) dry feed, air blown transport reactor low rank coal Mitsubishi Heavy Industry (MHI) dry feed, air blown Shell dry feed, coal is crushed, dried and fed into gasifier, oxygen blown, waterwall in gasifier wide variety of feedstock
112 Kellog Brown and Root (KBR)
113 FUTURE DEVELOPMENT Improve gasifier performance
Improve gas turbine efficiency Improve the heat exchanger system Reducing cost of air separation unit or switch to air blown process as Japan did Optimize energy saving in IGCC Improve control of the integrated system
114 CONCLUSION Promising technology in early development
Substitute for current coal fired power plant Need more R&D to make it more competitive Prospect of zero emission from coal