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Thermal Engineering

What is Reverse Brayton Cycle – Brayton Refrigeration Cycle – Definition

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Reverse Brayton cycle, is similar to the ordinary Brayton cycle but it is driven in reverse, via net work input. This cycle is also known as the gas refrigeration cycle or Bell Coleman cycle. Thermal Engineering

Heat Pump – How does it work

Heat Pump - Heating and Air Conditioning
Heat Pump, Refrigerator, Air Conditioner – basic principle of operation

The term heat pump is usually reserved for a device that can heat a house in winter by using an electric motor that does work W to take heat Qcold from the outside at low temperature and delivers heat Qhot to the warmer inside of the house.

The operating principle of refrigerators, air conditioners, and heat pumps is the same and it is just the reverse of a heat engine. In general, a heat pump is a device that transfers heat energy from a heat source to a “heat sink“, but in this case the transfer occurs in the opposite direction of spontaneous heat transfer by absorbing heat from a cold space and releasing it to a warmer one. As diagrammed in the figure, by doing external work W, heat is taken from a low-temperature region (heat source) and a greater amount of heat is exhausted at a higher temperature (heat sink).

The most widely used thermodynamic cycle or method for heating, air-conditioning, refrigerators and heat pumps is the vapor compression cycle. But the Brayton cycle can be also used to drive the heat pumps.

 
What is Heat in Thermodynamics
zeroth-law-of-thermodynamics-heat

See also: Heat in Thermodynamics

While internal energy refers to the total energy of all the molecules within the object, heat is the amount of energy flowing from one body to another spontaneously due to their temperature difference. Heat is a form of energy, but it is energy in transit. Heat is not a property of a system. However, the transfer of energy as heat occurs at the molecular level as a result of a temperature difference.

Consider a block of metal at high temperature, that consists of atoms that are oscillating intensely around their average positions. At low temperatures, the atoms continue to oscillate, but with less intensity. If a hotter block of metal is put in contact with a cooler block, the intensely oscillating atoms at the edge of the hotter block gives off its kinetic energy to the less oscillating atoms at the edge of the cool block. In this case there is energy transfer between these two blocks and heat flows from the hotter to the cooler block by this random vibrations.

In general, when two objects are brought into thermal contact, heat will flow between them until they come into equilibrium with each other.  When a temperature difference does exist heat flows spontaneously from the warmer system to the colder system. Heat transfer occurs by conduction or by thermal radiation. When the flow of heat stops, they are said to be at the same temperature. They are then said to be in thermal equilibrium.

Reverse Brayton Cycle – Brayton Refrigeration Cycle

reverse Brayton cycle - cooling and heat pumps
reverse Brayton cycle

In general, the Brayton cycle describes the workings of a constant-pressure heat engine. Today, modern gas turbine engines and airbreathing jet engines are also a constant-pressure heat engines

A Brayton cycle that is driven in reverse direction is known as the reverse Brayton cycle. Its purpose is to move heat from colder to hotter body, rather than produce work. In compliance with the second law of thermodynamics, heat cannot spontaneously flow from cold system to hot system without external work being performed on the system. Heat can flow from colder to hotter body, but only when forced by an external work. This is exactly what refrigerators and heat pumps accomplish. These are driven by electric motors requiring work from their surroundings to operate. One of possible cycles is a reverse Brayton cycle, which is similar to the ordinary Brayton cycle but it is driven in reverse, via net work input. This cycle is also known as the gas refrigeration cycle or Bell Coleman cycle. This type of cycle is widely used in jet aircrafts for air conditioning systems using air from the engine compressors. It is also widely used in the LNG industry where the largest reverse Brayton cycle is for subcooling LNG using 86 MW of power from a gas turbine-driven compressor and nitrogen refrigerant.

 
References:
Nuclear and Reactor Physics:
  1. J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983).
  2. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.
  3. W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
  4. Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering, Springer; 4th edition, 1994, ISBN: 978-0412985317
  5. W.S.C. Williams. Nuclear and Particle Physics. Clarendon Press; 1 edition, 1991, ISBN: 978-0198520467
  6. Kenneth S. Krane. Introductory Nuclear Physics, 3rd Edition, Wiley, 1987, ISBN: 978-0471805533
  7. G.R.Keepin. Physics of Nuclear Kinetics. Addison-Wesley Pub. Co; 1st edition, 1965
  8. Robert Reed Burn, Introduction to Nuclear Reactor Operation, 1988.
  9. U.S. Department of Energy, Nuclear Physics and Reactor Theory. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.

Advanced Reactor Physics:

  1. K. O. Ott, W. A. Bezella, Introductory Nuclear Reactor Statics, American Nuclear Society, Revised edition (1989), 1989, ISBN: 0-894-48033-2.
  2. K. O. Ott, R. J. Neuhold, Introductory Nuclear Reactor Dynamics, American Nuclear Society, 1985, ISBN: 0-894-48029-4.
  3. D. L. Hetrick, Dynamics of Nuclear Reactors, American Nuclear Society, 1993, ISBN: 0-894-48453-2.
  4. E. E. Lewis, W. F. Miller, Computational Methods of Neutron Transport, American Nuclear Society, 1993, ISBN: 0-894-48452-4.

Other References:

Diesel Engine – Car Recycling

See also:

Heating and Air Conditioning

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What is Governing of Steam Turbine – Definition

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Governing of steam turbine is the procedure of controlling the flow rate of steam to a steam turbine so as to maintain the speed of the turbine fairly constant irrespective of load on the turbine. Thermal Engineering

Governing of Steam Turbine

Governing of steam turbine is the procedure of controlling the flow rate of steam to a steam turbine so as to maintain the speed of the turbine fairly constant irrespective of load on the turbine. The typical main turbine in nuclear power plants, in which steam expands from pressures about 6 MPa to pressures about 0.008 MPa, operates at speeds about:

  • 3000 RPM for 50 Hz systems for 2-pole generator (or 1500RPM for 4-pole generator),
  • 1800 RPM for 60 Hz systems for 4-pole generator (or 3600 RPM for 2-pole generator).

The variation in load (power output) during the operation of a steam turbine can have a significant impact on its performance and its efficiency. Traditionally, nuclear power plants (NPPs) have been considered as baseload sources of electricity as they rely on a technology with high fixed costs and low variable costs.  However, this simple state of affairs no longer applies in all countries. The share of nuclear power in the national electricity mix of some countries has become so large that the utilities have had to implement or to improve the manoeuvrability capabilities of their power plants in order to be able to adapt electricity supply to daily, seasonal or other variations in power demand. For example, this is the case in France where more than 75% of electricity is generated by NPPs, and where some nuclear reactors operate in load-following mode.

The primary objective in the steam turbine operation is to maintain a constant speed of rotation irrespective of the varying load. This can be achieved by means of governing in a steam turbine. The principal methods of governing which are used in steam turbines are:

  1. Nozzle Governing
    Nozzle Governing. Source: wikipedia.org License: CC BY-SA 3.0

    Throttle governing. The main parts of a simple throttle governing system are the throttle-stop valves and especially control valves between steam generators and main turbine. The primary aim of control valves is to reduce the steam flow rate. Incidental to reducing the mass rate of flow, the steam experiences an increasing pressure drop across the control valve, which is in fact an isenthalpic process. Although throttling is an isenthalpic process, the enthalpy drop available for work in the turbine is reduced, because this causes an increase in vapor quality of outlet steam.

  2. Nozzle governing. In the nozzle control governing, the steam supply from the main valve is divided into two, three, or more lines. The flow rate of steam is regulated by opening and shutting of sets of nozzles rather than regulating its pressure.
  3. Bypass governing. This is generally used for the overload valve which passes the steam directly into the latter stages of steam turbine. During such operation, bypass valves are opened and live steam is introduced into the later stages of the turbine. This generates more energy to satisfy the increased load.
  4. Combination of 2 and 3.
 
References:
Reactor Physics and Thermal Hydraulics:
  1. J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983).
  2. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.
  3. W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
  4. Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering, Springer; 4th edition, 1994, ISBN: 978-0412985317
  5. Todreas Neil E., Kazimi Mujid S. Nuclear Systems Volume I: Thermal Hydraulic Fundamentals, Second Edition. CRC Press; 2 edition, 2012, ISBN: 978-0415802871
  6. Zohuri B., McDaniel P. Thermodynamics in Nuclear Power Plant Systems. Springer; 2015, ISBN: 978-3-319-13419-2
  7. Moran Michal J., Shapiro Howard N. Fundamentals of Engineering Thermodynamics, Fifth Edition, John Wiley & Sons, 2006, ISBN: 978-0-470-03037-0
  8. Kleinstreuer C. Modern Fluid Dynamics. Springer, 2010, ISBN 978-1-4020-8670-0.
  9. U.S. Department of Energy, THERMODYNAMICS, HEAT TRANSFER, AND FLUID FLOW. DOE Fundamentals Handbook, Volume 1, 2 and 3. June 1992.
  10. U.S. NRC. NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition

See also:

Steam Turbine

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What is Turbine Blade – Definition

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Turbine blades are the principal elements that convert pressure energy of working fluid into kinetic energy. Turbine blades are of two basic types. Thermal Engineering

Turbine Blades

Steam TurbineThe most important turbine elements are the turbine blades. They are the principal elements that convert pressure energy of working fluid into kinetic energy. Turbine blades are of two basic types:

  • moving blades
  • fixed blades

In steam turbines, the steam expands through the fixed blade (nozzle), where the pressure potential energy is converted to kinetic energy. The high-velocity steam from fixed nozzles impacts the moving blades, changes its direction and also expands (in case of reaction type blades). The change in its direction and the steam acceleration (in case of reaction type blades) applies a force. The resulting impulse drives the blades forward, causing the rotor to turn. Steam turbine types based on blade geometry and energy conversion process are:

  • impulse turbine
  • reaction turbine

Modern steam turbines frequently employ both reaction and impulse in the same unit, typically varying the degree of reaction and impulse from the blade root to its periphery. The rotor blades are usually designed like an impulse blade at the rot and like a reaction blade at the tip.

Turbine Blade - Impulse and Reaction

steam_turbine_blade_3The efficiency and reliability of a turbine depend on the proper design of the blades. It is therefore necessary for all engineers involved in the turbines engineering to have an overview of the importance and the basic design aspects of the steam turbine blades. Engineering of turbine blades is a multi-disciplinary task. It involves the thermodynamics, aerodynamics, mechanical and material engineering.

For gas turbines, the turbine blades are often the limiting component.  The highest temperature in the cycle occurs at the end of the combustion process, and it is limited by the maximum temperature that the turbine blades can withstand. As usual, metallurgical considerations (about 1700 K) place an upper limits on thermal efficiency. Therefore turbine blades often use exotic materials like superalloys and many different methods of cooling, such as internal air channels, boundary layer cooling, and thermal barrier coatings. The development of superalloys in the 1940s and new processing methods such as vacuum induction melting in the 1950s greatly increased the temperature capability of turbine blades. Modern turbine blades often use nickel-based superalloys that incorporate chromium, cobalt, and rhenium.

Steam turbine blades are not exposed to such high temperatures, but they must withstand an operation with two-phase fluid. High content of water droplets can cause the rapid impingement and erosion of the blades which occurs when condensed water is blasted onto the blades. To prevent this, for example, condensate drains are installed in the steam piping leading to the turbine. Another challenge for engineers is the design of blades of the last stage of LP turbine. These blades must be (due to high specific volume of steam) very long, which induces enormous centrifugal forces during operation. Therefore, turbine blades are subjected to stress from centrifugal force (turbine stages can rotate at tens of thousands of revolutions per minute (RPM), but usually at 1800 RPM) and fluid forces that can cause fracture, yielding, or creep failures.

Turbine Blades – Root, Profile, Shroud

Turbine blades are usually divided into three parts:

  • Root. The root is a constructional feature of turbine blades, which fixes the blade into the turbine rotor.
  • Profile. The profile converts kinetic energy of steam into mechanical energy of the blade.
  • Shroud.  The shroud reduces the vibration of the blade which can be induced by the flowing of high pressure steam through the blades.

Types of Steam Turbines

Steam Turbine - types

Steam turbines may be classified into different categories depending on their construction, working pressures, size and many other parameters. But there are two basic types of steam turbines:

  • impulse turbines
  • reaction turbines.

The main distinction is the manner in which the steam is expanded as it passes through the turbine.

Impulse Turbine and Reaction Turbine

Steam turbine types based on blade geometry and energy conversion process are impulse turbine and reaction turbine.

Steam Turbine - Types of Turbine

 
References:
Reactor Physics and Thermal Hydraulics:
  1. J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983).
  2. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.
  3. W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
  4. Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering, Springer; 4th edition, 1994, ISBN: 978-0412985317
  5. Todreas Neil E., Kazimi Mujid S. Nuclear Systems Volume I: Thermal Hydraulic Fundamentals, Second Edition. CRC Press; 2 edition, 2012, ISBN: 978-0415802871
  6. Zohuri B., McDaniel P. Thermodynamics in Nuclear Power Plant Systems. Springer; 2015, ISBN: 978-3-319-13419-2
  7. Moran Michal J., Shapiro Howard N. Fundamentals of Engineering Thermodynamics, Fifth Edition, John Wiley & Sons, 2006, ISBN: 978-0-470-03037-0
  8. Kleinstreuer C. Modern Fluid Dynamics. Springer, 2010, ISBN 978-1-4020-8670-0.
  9. U.S. Department of Energy, THERMODYNAMICS, HEAT TRANSFER, AND FLUID FLOW. DOE Fundamentals Handbook, Volume 1, 2 and 3. June 1992.
  10. U.S. NRC. NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition

See also:

Steam Turbine

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What is Loss in Steam Turbines – Definition

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Losses in Steam Turbines. The steam turbine is not a perfect heat engine. Energy losses tend to decrease the efficiency and work output of a turbine. Thermal Engineering

Losses in Steam Turbines

The steam turbine is not a perfect heat engine. Energy losses tend to decrease the efficiency and work output of a turbine. This inefficiency can be attributed to the following causes.

  • Residual Velocity Loss. The velocity of the steam that leaves the turbine must have certain absolute value (vex). The energy loss due to absolute exit velocity of steam is proportional to (vex2/2). This type of loss can be reduced by using multistage turbine.
  • Presence of Friction. In real thermodynamic systems or in real heat engines, a part of the overall cycle inefficiency is due to the frictional losses by the individual components (e.g. nozzles or turbine blades)
  • Steam Leakage. The turbine rotor and the casing cannot be perfectly insulated. Some amount of steam leaks from the chamber without doing useful work.
  • Loss Due to Mechanical Friction in Bearings. Each turbine rotor is mounted on two bearings, i.e. there are double bearings between each turbine module.
  • Pressure Losses in Regulating Valves and Steam Lines. There are the main steam line isolation valves (MSIVs), the throttle-stop valves and control valves between steam generators and main turbine. Like pipe friction, the minor losses are roughly proportional to the square of the flow rate. The flow rate in the main steam lines is usually very high. Although throttling is an isenthalpic process, the enthalpy drop available for work in the turbine is reduced, because this causes an increase in vapor quality of outlet steam.
  • Losses Due to Low Quality of Steam. The exhausted steam is at a pressure well below atmospheric and the steam is in a partially condensed state, typically of a quality near 90%. Higher content of water droplets can cause the rapid impingement and erosion of the blades which occurs when condensed water is blasted onto the blades.
  • Radiation Loss. Steam turbine may operate at steady state with inlet conditions of  6 MPa, t = 275.6°. Since it is a large and heavy machine, it must be thermally insulated to avoid any heat loss to the surroundings.
 
References:
Reactor Physics and Thermal Hydraulics:
  1. J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983).
  2. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.
  3. W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
  4. Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering, Springer; 4th edition, 1994, ISBN: 978-0412985317
  5. Todreas Neil E., Kazimi Mujid S. Nuclear Systems Volume I: Thermal Hydraulic Fundamentals, Second Edition. CRC Press; 2 edition, 2012, ISBN: 978-0415802871
  6. Zohuri B., McDaniel P. Thermodynamics in Nuclear Power Plant Systems. Springer; 2015, ISBN: 978-3-319-13419-2
  7. Moran Michal J., Shapiro Howard N. Fundamentals of Engineering Thermodynamics, Fifth Edition, John Wiley & Sons, 2006, ISBN: 978-0-470-03037-0
  8. Kleinstreuer C. Modern Fluid Dynamics. Springer, 2010, ISBN 978-1-4020-8670-0.
  9. U.S. Department of Energy, THERMODYNAMICS, HEAT TRANSFER, AND FLUID FLOW. DOE Fundamentals Handbook, Volume 1, 2 and 3. June 1992.
  10. U.S. NRC. NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition

See also:

Steam Turbine

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What is Advantage and Disadvantage of Steam Turbines – Definition

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Advantages and Disadvantages of Steam Turbines. Although approximately 90% of all electricity generation in the world is by use of steam turbines, they have also some disadvantages. Thermal Engineering

Advantages and Disadvantages of Steam Turbines

Advantages

  • Since the steam turbine is a rotary heat engine, it is particularly suited to be used to drive an electrical generator.
  • 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. They are made in a variety of sizes up to 1.5 GW (2,000,000 hp) turbines used to generate electricity.
  • In general, steam contains high amount of enthalpy (espacially in the form of heat of vaporization). This implies lower mass flow rates compared to gas turbines.
  • 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.

Disadvantages

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.
Steam Turbine
Steam Turbine. Source wikipedia.org License: CC BY-SA 3.0
 
References:
Reactor Physics and Thermal Hydraulics:
  1. J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983).
  2. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.
  3. W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
  4. Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering, Springer; 4th edition, 1994, ISBN: 978-0412985317
  5. Todreas Neil E., Kazimi Mujid S. Nuclear Systems Volume I: Thermal Hydraulic Fundamentals, Second Edition. CRC Press; 2 edition, 2012, ISBN: 978-0415802871
  6. Zohuri B., McDaniel P. Thermodynamics in Nuclear Power Plant Systems. Springer; 2015, ISBN: 978-3-319-13419-2
  7. Moran Michal J., Shapiro Howard N. Fundamentals of Engineering Thermodynamics, Fifth Edition, John Wiley & Sons, 2006, ISBN: 978-0-470-03037-0
  8. Kleinstreuer C. Modern Fluid Dynamics. Springer, 2010, ISBN 978-1-4020-8670-0.
  9. U.S. Department of Energy, THERMODYNAMICS, HEAT TRANSFER, AND FLUID FLOW. DOE Fundamentals Handbook, Volume 1, 2 and 3. June 1992.
  10. U.S. NRC. NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition

See also:

Steam Turbine

We hope, this article, Advantage and Disadvantage of Steam Turbines, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about thermal engineering.

What is Classification of Turbines – Steam supply and exhaust conditions – Definition

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Classification of Turbines. Steam turbines may be classified into different categories depending on their purpose and working pressures. Thermal Engineering

Classification of Turbines – steam supply and exhaust conditions

Steam turbines may be classified into different categories depending on their purpose and working pressures. The industrial usage of a turbine influences the initial and final conditions of steam. For any steam turbine to operate, a pressure difference must exist between the steam supply and the exhaust.

This classification includes:

 
Condensing Steam Turbine
Condenser - LP Heaters - Deaerator

Condensing steam turbines are most commonly found in thermal power plants. In a condensing steam turbine, the maximum amount of energy is extracted from the steam, because there is very high enthalpy difference between the initial (e.g. 6MPa; 275°C; x = 1) and final (e.g. 0.008MPa; 41.5°C; x = 0.9) conditions of steam. This is achieved by passing the exhaust steam into a condenser (called a surface condenser), which condenses the exhaust steam from the low-pressure stages of the main turbine (decreases the temperature and pressure of exhausted steam). The exhausted steam is condensed by passing over tubes containing water from the cooling system.

Rankine Cycle - condenser pressure
Decreasing the turbine exhaust pressure increases the net work per cycle but also decreses the vapor quality of outlet steam.

The goal of maintaining the lowest practical turbine exhaust pressure is a primary reason for including the condenser in a thermal power plant. The condenser provides a vacuum that maximizes the energy extracted from the steam, resulting in a significant increase in net work and thermal efficiency. But also this parameter (condenser pressure) has its engineering limits:

  • Decreasing the turbine exhaust pressure decreases the vapor quality (or dryness fraction). At some point the expansion must be ended to avoid damages that could be caused to blades of steam turbine by low quality steam.
  • Decreasing the turbine exhaust pressure significantly increases the specific volume of exhausted steam, which requires huge blades in last rows of low-pressure stage of the steam turbine.

In a typical condensing steam turbine, the exhausted steam condenses in the condenser and it is at a pressure well below atmospheric (absolute pressure of 0.008 MPa, which corresponds to 41.5°C). This steam is in a partially condensed state (point F), typically of a quality near 90%. Note that, the pressure inside the condenser is also dependent on the ambient atmospheric conditions:

  • air temperature, pressure and humidity in case of cooling into the atmosphere
  • water temperature and the flow rate in case of cooling into a river or sea

An increase in the ambient temperature causes a proportional increase in pressure of exhausted steam (ΔT = 14°C is usually a constant) hence the thermal efficiency of the power conversion system decreases. In other words, the electrical output of a power plant may vary with ambient conditions, while the thermal power remains constant.

The pressure inside condenser is given by the ambient air temperature (i.e. temperature of water in the cooling system) and by steam ejectors or vacuum pumps, which pull the gases (non-condensibles) from the surface condenser and eject them to the atmosphere.

The lowest feasible condenser pressure is the saturation pressure corresponding to the ambient temperature (e.g. absolute pressure of 0.008 MPa, which corresponds to 41.5°C). Note that, there is always a temperature difference between (around ΔT = 14°C) the condenser temperature and the ambient temperature, which originates from finite size and efficiency of condensers.

Back-pressure Steam Turbine
Back-pressure steam turbine - schema
Back-pressure steam turbine – schema

Back-pressure steam turbines or non-condensing turbines are most widely used for process steam applications. Steam is a principle energy source for many industrial processes. The popularity of process steam as an energy source stems from its many advantages, which include:

  • high heat capacity,
  • transportability
  • low toxicity

The process steam can be produced by back-pressure steam turbines, which also generates mechanical work (or electrical energy).  Back-pressure turbines expand the live steam supplied by the boiler to the pressure at which the steam is required for the process. The exhaust pressure is controlled by a regulating valve to suit the needs of the process steam pressure. Back-pressure turbines are commonly found at refineries, district heating units, pulp and paper plants, and desalination facilities where large amounts of low pressure process steam are needed. The electric power generated by the back-pressure turbine is directly proportional to the amount of process steam required.

Reheat Steam Turbine
Rankine cycle - reheat - superheat
Rankine cycle with reheat and superheat the low-pressure stage

Reheat turbines are also used almost exclusively in thermal power plants. All turbines, that have high-pressure turbine and low-pressure turbines use a steam reheat between these stages. Reheat allows to deliver more of the heat at a temperature close to the peak of the cycle (i.e. thermal efficiency increases). This requires the addition of another type of heat exchanger called a reheater.  The use of the reheater involves splitting the turbine, i.e. use of a multistage turbine with a reheater.  It was observed that more than two stages of reheating are unnecessary, since the next stage increases the cycle efficiency only half as much as the preceding stage.

High pressure and low pressure stages of the turbine are usually on the same shaft to drive a common generator, but they have separate cases. With a reheater, the flow is extracted after a partial expansion (point D), run back through the heat exchanger to heat it back up to the peak temperature (point E), and then passed to the low-pressure turbine. The expansion is then completed in the low-pressure turbine from point E to point F.

The steam must be reheated or superheated in order to avoid damages that could be caused to blades of steam turbine by low quality steam. High content of water droplets can cause the rapid impingement and erosion of the blades which occurs when condensed water is blasted onto the blades. To prevent this, condensate drains are installed in the steam piping leading to the turbine. The reheater heats the steam (point D) and then the steam is directed to the low-pressure stage of steam turbine, where expands (point E to F). The exhausted steam is at a pressure well below atmospheric, and, as can be seen from the picture, the steam is in a partially condensed state (point F), typically of a quality near 90%, but it is much higher vapor quality, than that it would be without reheat. Accordingly, superheating also tends to alleviate the problem of low vapor quality at the turbine exhaust.

Wet Steam Turbine - Expansion

Turbine with Steam Extraction
Extraction type turbines are common in all applications. In some applications, when required, steam can be extracted from turbine before steam flowing through the last stage, named extraction turbine. As in back-pressure turbines, extracted steam can be used for many industrial processes or it can be used to improve the efficiency of thermodynamic cycle. The second case is usually known as the heat regeneration.

Almost all large steam turbines use the heat regeneration (i.e. they are extraction turbines), since it reduces the amount of fuel that must be added in the boiler. The reduction in the heat added can be done by transferring heat (partially expanded steam) from certain sections of the steam turbine, which is normally well above the ambient temperature, to the feedwater. Note that, most of energy contained in the steam is in the form of latent heat of vaporization. Extraction flows may be controlled with a valve, or left uncontrolled.

For example, most of nuclear power plants operates a single-shaft turbine-generator that consists of one multi-stage HP turbine with 3 or 4 self-regulating extraction lines and three parallel multi-stage LP turbines with 3 or 4 self-regulating extraction lines.

The high pressure feedwater heaters are usually heated by extraction steam from the high pressure turbine, HP, whereas the low-pressure feedwater heaters are usually heated by extraction steam from the low pressure turbine, LP. Both are usually self-regulating. It means that the greater the flow of feedwater the greater the rate of heat absorption from the steam and the greater the flow of extraction steam.

Steam turbine of typical 3000MWth PWR
Schema of a steam turbine of a typical 3000MWth PWR.
 
References:
Reactor Physics and Thermal Hydraulics:
  1. J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983).
  2. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.
  3. W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
  4. Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering, Springer; 4th edition, 1994, ISBN: 978-0412985317
  5. Todreas Neil E., Kazimi Mujid S. Nuclear Systems Volume I: Thermal Hydraulic Fundamentals, Second Edition. CRC Press; 2 edition, 2012, ISBN: 978-0415802871
  6. Zohuri B., McDaniel P. Thermodynamics in Nuclear Power Plant Systems. Springer; 2015, ISBN: 978-3-319-13419-2
  7. Moran Michal J., Shapiro Howard N. Fundamentals of Engineering Thermodynamics, Fifth Edition, John Wiley & Sons, 2006, ISBN: 978-0-470-03037-0
  8. Kleinstreuer C. Modern Fluid Dynamics. Springer, 2010, ISBN 978-1-4020-8670-0.
  9. U.S. Department of Energy, THERMODYNAMICS, HEAT TRANSFER, AND FLUID FLOW. DOE Fundamentals Handbook, Volume 1, 2 and 3. June 1992.
  10. U.S. NRC. NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition

See also:

Steam Turbine

We hope, this article, Classification of Turbines – Steam supply and exhaust conditions, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about thermal engineering.

What is Reheat Steam Turbine – Definition

by
Reheat steam turbines are also used almost exclusively in thermal power plants. This requires the addition of another type of heat exchanger called a reheater. Thermal Engineering

Classification of Turbines – steam supply and exhaust conditions

Steam turbines may be classified into different categories depending on their purpose and working pressures. The industrial usage of a turbine influences the initial and final conditions of steam. For any steam turbine to operate, a pressure difference must exist between the steam supply and the exhaust.

This classification includes:

Reheat Steam Turbine

Rankine cycle - reheat - superheat
Rankine cycle with reheat and superheat the low-pressure stage

Reheat turbines are also used almost exclusively in thermal power plants. All turbines, that have high-pressure turbine and low-pressure turbines use a steam reheat between these stages. Reheat allows to deliver more of the heat at a temperature close to the peak of the cycle (i.e. thermal efficiency increases). This requires the addition of another type of heat exchanger called a reheater.  The use of the reheater involves splitting the turbine, i.e. use of a multistage turbine with a reheater.  It was observed that more than two stages of reheating are unnecessary, since the next stage increases the cycle efficiency only half as much as the preceding stage.

High pressure and low pressure stages of the turbine are usually on the same shaft to drive a common generator, but they have separate cases. With a reheater (moisture separator-reheater – MSR), the flow is extracted after a partial expansion (point D), run back through the heat exchanger to heat it back up to the peak temperature (point E), and then passed to the low-pressure turbine. The expansion is then completed in the low-pressure turbine from point E to point F.

The steam must be reheated or superheated in order to avoid damages that could be caused to blades of steam turbine by low quality steam. High content of water droplets can cause the rapid impingement and erosion of the blades which occurs when condensed water is blasted onto the blades. To prevent this, condensate drains are installed in the steam piping leading to the turbine. The reheater heats the steam (point D) and then the steam is directed to the low-pressure stage of steam turbine, where expands (point E to F). The exhausted steam is at a pressure well below atmospheric, and, as can be seen from the picture, the steam is in a partially condensed state (point F), typically of a quality near 90%, but it is much higher vapor quality, than that it would be without reheat. Accordingly, superheating also tends to alleviate the problem of low vapor quality at the turbine exhaust.

Wet Steam Turbine - Expansion

 
References:
Reactor Physics and Thermal Hydraulics:
  1. J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983).
  2. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.
  3. W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
  4. Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering, Springer; 4th edition, 1994, ISBN: 978-0412985317
  5. Todreas Neil E., Kazimi Mujid S. Nuclear Systems Volume I: Thermal Hydraulic Fundamentals, Second Edition. CRC Press; 2 edition, 2012, ISBN: 978-0415802871
  6. Zohuri B., McDaniel P. Thermodynamics in Nuclear Power Plant Systems. Springer; 2015, ISBN: 978-3-319-13419-2
  7. Moran Michal J., Shapiro Howard N. Fundamentals of Engineering Thermodynamics, Fifth Edition, John Wiley & Sons, 2006, ISBN: 978-0-470-03037-0
  8. Kleinstreuer C. Modern Fluid Dynamics. Springer, 2010, ISBN 978-1-4020-8670-0.
  9. U.S. Department of Energy, THERMODYNAMICS, HEAT TRANSFER, AND FLUID FLOW. DOE Fundamentals Handbook, Volume 1, 2 and 3. June 1992.
  10. U.S. NRC. NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition

See also:

Steam Turbine

We hope, this article, Reheat Steam Turbine, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about thermal engineering.

What is Extraction Turbine – Turbine with Steam Extraction – Definition

by
Extraction turbines are common in all applications. In some applications, when required, steam can be extracted from turbine before steam flowing through the last stage, named extraction turbine. Thermal Engineering

Classification of Turbines – steam supply and exhaust conditions

Steam turbines may be classified into different categories depending on their purpose and working pressures. The industrial usage of a turbine influences the initial and final conditions of steam. For any steam turbine to operate, a pressure difference must exist between the steam supply and the exhaust.

This classification includes:

Extraction Turbine – Turbine with Steam Extraction

Extraction type turbines are common in all applications. In some applications, when required, steam can be extracted from turbine before steam flowing through the last stage, named extraction turbine. As in back-pressure turbines, extracted steam can be used for many industrial processes or it can be used to improve the efficiency of thermodynamic cycle. The second case is usually known as the heat regeneration.

Almost all large steam turbines use the heat regeneration (i.e. they are extraction turbines), since it reduces the amount of fuel that must be added in the boiler. The reduction in the heat added can be done by transferring heat (partially expanded steam) from certain sections of the steam turbine, which is normally well above the ambient temperature, to the feedwater. Note that, most of energy contained in the steam is in the form of latent heat of vaporization. Extraction flows may be controlled with a valve, or left uncontrolled.

For example, most of nuclear power plants operates a single-shaft turbine-generator that consists of one multi-stage HP turbine with 3 or 4 self-regulating extraction lines and three parallel multi-stage LP turbines with 3 or 4 self-regulating extraction lines.

The high pressure feedwater heaters are usually heated by extraction steam from the high pressure turbine, HP, whereas the low-pressure feedwater heaters are usually heated by extraction steam from the low pressure turbine, LP. Both are usually self-regulating. It means that the greater the flow of feedwater the greater the rate of heat absorption from the steam and the greater the flow of extraction steam.

Steam turbine of typical 3000MWth PWR
Schema of a steam turbine of a typical 3000MWth PWR.
 
References:
Reactor Physics and Thermal Hydraulics:
  1. J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983).
  2. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.
  3. W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
  4. Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering, Springer; 4th edition, 1994, ISBN: 978-0412985317
  5. Todreas Neil E., Kazimi Mujid S. Nuclear Systems Volume I: Thermal Hydraulic Fundamentals, Second Edition. CRC Press; 2 edition, 2012, ISBN: 978-0415802871
  6. Zohuri B., McDaniel P. Thermodynamics in Nuclear Power Plant Systems. Springer; 2015, ISBN: 978-3-319-13419-2
  7. Moran Michal J., Shapiro Howard N. Fundamentals of Engineering Thermodynamics, Fifth Edition, John Wiley & Sons, 2006, ISBN: 978-0-470-03037-0
  8. Kleinstreuer C. Modern Fluid Dynamics. Springer, 2010, ISBN 978-1-4020-8670-0.
  9. U.S. Department of Energy, THERMODYNAMICS, HEAT TRANSFER, AND FLUID FLOW. DOE Fundamentals Handbook, Volume 1, 2 and 3. June 1992.
  10. U.S. NRC. NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition

See also:

Steam Turbine

We hope, this article, Extraction Turbine – Turbine with Steam Extraction, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about thermal engineering.

What is Back-pressure Steam Turbine – Process Steam – Definition

by
Back-pressure Steam Turbine – Process Steam. Back-pressure turbines or non-condensing turbines are most widely used for process steam applications. Thermal Engineering

Classification of Turbines – steam supply and exhaust conditions

Steam turbines may be classified into different categories depending on their purpose and working pressures. The industrial usage of a turbine influences the initial and final conditions of steam. For any steam turbine to operate, a pressure difference must exist between the steam supply and the exhaust.

This classification includes:

Back-pressure Steam Turbine

Back-pressure steam turbine - schema
Back-pressure steam turbine – schema

Back-pressure steam turbines or non-condensing turbines are most widely used for process steam applications. Steam is a principle energy source for many industrial processes. The popularity of process steam as an energy source stems from its many advantages, which include:

  • high heat capacity,
  • transportability
  • low toxicity

The process steam can be produced by back-pressure steam turbines, which also generates mechanical work (or electrical energy).  Back-pressure turbines expand the live steam supplied by the boiler to the pressure at which the steam is required for the process. The exhaust pressure is controlled by a regulating valve to suit the needs of the process steam pressure. Back-pressure turbines are commonly found at refineries, district heating units, pulp and paper plants, and desalination facilities where large amounts of low pressure process steam are needed. The electric power generated by the back-pressure turbine is directly proportional to the amount of process steam required.

 
References:
Reactor Physics and Thermal Hydraulics:
  1. J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983).
  2. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.
  3. W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
  4. Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering, Springer; 4th edition, 1994, ISBN: 978-0412985317
  5. Todreas Neil E., Kazimi Mujid S. Nuclear Systems Volume I: Thermal Hydraulic Fundamentals, Second Edition. CRC Press; 2 edition, 2012, ISBN: 978-0415802871
  6. Zohuri B., McDaniel P. Thermodynamics in Nuclear Power Plant Systems. Springer; 2015, ISBN: 978-3-319-13419-2
  7. Moran Michal J., Shapiro Howard N. Fundamentals of Engineering Thermodynamics, Fifth Edition, John Wiley & Sons, 2006, ISBN: 978-0-470-03037-0
  8. Kleinstreuer C. Modern Fluid Dynamics. Springer, 2010, ISBN 978-1-4020-8670-0.
  9. U.S. Department of Energy, THERMODYNAMICS, HEAT TRANSFER, AND FLUID FLOW. DOE Fundamentals Handbook, Volume 1, 2 and 3. June 1992.
  10. U.S. NRC. NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition

See also:

Steam Turbine

We hope, this article, Back-pressure Steam Turbine – Process Steam, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about thermal engineering.

What is Condensing Steam Turbine – Definition

by
Condensing steam turbines are most commonly found in thermal power plants. In a condensing steam turbine, the maximum amount of energy is extracted from the steam. Thermal Engineering

Classification of Turbines – steam supply and exhaust conditions

Steam turbines may be classified into different categories depending on their purpose and working pressures. The industrial usage of a turbine influences the initial and final conditions of steam. For any steam turbine to operate, a pressure difference must exist between the steam supply and the exhaust. This classification includes:

Condensing Steam Turbine

Condenser - LP Heaters - Deaerator

Condensing steam turbines are most commonly found in thermal power plants. In a condensing steam turbine, the maximum amount of energy is extracted from the steam, because there is very high enthalpy difference between the initial (e.g. 6MPa; 275°C; x = 1) and final (e.g. 0.008MPa; 41.5°C; x = 0.9) conditions of steam. This is achieved by passing the exhaust steam into a condenser (called a surface condenser), which condenses the exhaust steam from the low-pressure stages of the main turbine (decreases the temperature and pressure of exhausted steam). The exhausted steam is condensed by passing over tubes containing water from the cooling system.

Rankine Cycle - condenser pressure
Decreasing the turbine exhaust pressure increases the net work per cycle but also decreses the vapor quality of outlet steam.

The goal of maintaining the lowest practical turbine exhaust pressure is a primary reason for including the condenser in a thermal power plant. The condenser provides a vacuum that maximizes the energy extracted from the steam, resulting in a significant increase in net work and thermal efficiency. But also this parameter (condenser pressure) has its engineering limits:

  • Decreasing the turbine exhaust pressure decreases the vapor quality (or dryness fraction). At some point the expansion must be ended to avoid damages that could be caused to blades of steam turbine by low quality steam.
  • Decreasing the turbine exhaust pressure significantly increases the specific volume of exhausted steam, which requires huge blades in last rows of low-pressure stage of the steam turbine.

In a typical condensing steam turbine, the exhausted steam condenses in the condenser and it is at a pressure well below atmospheric (absolute pressure of 0.008 MPa, which corresponds to 41.5°C). This steam is in a partially condensed state (point F), typically of a quality near 90%. Note that, the pressure inside the condenser is also dependent on the ambient atmospheric conditions:

  • air temperature, pressure and humidity in case of cooling into the atmosphere
  • water temperature and the flow rate in case of cooling into a river or sea

An increase in the ambient temperature causes a proportional increase in pressure of exhausted steam (ΔT = 14°C is usually a constant) hence the thermal efficiency of the power conversion system decreases. In other words, the electrical output of a power plant may vary with ambient conditions, while the thermal power remains constant.

The pressure inside condenser is given by the ambient air temperature (i.e. temperature of water in the cooling system) and by steam ejectors or vacuum pumps, which pull the gases (non-condensibles) from the surface condenser and eject them to the atmosphere.

The lowest feasible condenser pressure is the saturation pressure corresponding to the ambient temperature (e.g. absolute pressure of 0.008 MPa, which corresponds to 41.5°C). Note that, there is always a temperature difference between (around ΔT = 14°C) the condenser temperature and the ambient temperature, which originates from finite size and efficiency of condensers.

 
References:
Reactor Physics and Thermal Hydraulics:
  1. J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983).
  2. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.
  3. W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
  4. Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering, Springer; 4th edition, 1994, ISBN: 978-0412985317
  5. Todreas Neil E., Kazimi Mujid S. Nuclear Systems Volume I: Thermal Hydraulic Fundamentals, Second Edition. CRC Press; 2 edition, 2012, ISBN: 978-0415802871
  6. Zohuri B., McDaniel P. Thermodynamics in Nuclear Power Plant Systems. Springer; 2015, ISBN: 978-3-319-13419-2
  7. Moran Michal J., Shapiro Howard N. Fundamentals of Engineering Thermodynamics, Fifth Edition, John Wiley & Sons, 2006, ISBN: 978-0-470-03037-0
  8. Kleinstreuer C. Modern Fluid Dynamics. Springer, 2010, ISBN 978-1-4020-8670-0.
  9. U.S. Department of Energy, THERMODYNAMICS, HEAT TRANSFER, AND FLUID FLOW. DOE Fundamentals Handbook, Volume 1, 2 and 3. June 1992.
  10. U.S. NRC. NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition

See also:

Steam Turbine

We hope, this article, Condensing Steam Turbine, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about thermal engineering.