Presentation on Steam Power Plants R.C.Chaturvedi Dept. of Mechanical Engineering

Thermodynamic Cycle Steam Power Plant operates on Thermodynamic Cycle in which heat energy released by burning fuel is taken up by water which works as the working fluid. Water is converted into Steam as it receives heat in a boiler. The Steam then expands in a turbine producing mechanical work which is then converted into electrical energy through a generator. The exhaust steam from the turbine is then condensed in a condenser and condensate thereafter pumped to the boiler where it again receives heat and the cycle is repeated. This Thermodynamic Cycle is known as Rankine Cycle. Rankine Cycle

Steam Conditions at Point 1 represents Saturated steam Steam Conditions at Point 1’ represents Unsaturated steam Steam Conditions at Point 1’’ represents Superheated steam

Rankine Cycle Efficiency The Cycle efficiency is improved by : Increasing Boiler Pressure Superheating of Steam Reducing Condenser Pressure

Steam Power Plant The Steam Power Plant comprises the steam generating equipment and the prime-movers. In the boiler/steam generators steam is produced and then utilized to drive the turbines which are coupled to generators to get electricity.

Layout of a Steam Power Plant

Typical Utility Cycle Layout H.P.H. = High pressure heater D. C. = Drain cooler I.P.H. = Intermediate pressure heater T. = Trap L.P.H. = Low pressure heater S. = Surge tank D.H. = De-aerating heater S. T. = Storage tank

Layout of Steam Power Plant The Layout of Steam Power Plant comprises the following for circuits: Coal and Ash Air and Gas Feed Water and Steam flow Cooling Water

Coal and Ash Circuit Coal arrives at the Storage Yard and after necessary handling, passes into the furnace through the feeding device. The components are: Wagon trippler Coal Handling Plant Coal Mill Ash resulting from combustion of coal collects to the back of the boiler and is removed to the ash storage yard, through Ash Handling Equipment.

Outline of Coal handing Equipment

Mechanical Handling System Outline of ash disposal equipment Mechanical Handling System

Air and Gas Circuit Air is taken from atmosphere through the action of a Forced or Induced Draught Fan and passes on to the furnace through Air Preheater, where it has been heated by the heat of flue gases which pass to the Chimney via the Air preheater. The flue gases after passing around boiler tubes and superheater Reheated tubes in the furnace pass through economizers, air preheater and a dust catching device or precipitator before being exhausted to the atmosphere.

Feed Water and Steam Power Circuit In the feed Water and Steam Circuit Condensate leaving the condenser is heated in the following sequence: First through a closed type Low Pressure Feed Water Heaters by drawing steam from low pressure extracted point of the Steam Turbine. Thereafter through a open type Deaerator by drawing Steam from medium pressure extraction point of the steam turbine. If then passes through closed type High Pressure Heater by drawing Steam from High Pressure extraction point of the Steam Turbine.

Feed Water and Steam Flow Circuit (Contd……) In the boiler drum and tubes, feed water circulates due to the difference between the density of water in the lower temperature and the higher temperature sections of the boiler. Wet steam from the drum is further heated up in the Super heater before being supplied to the Steam Turbine. After expanding in high pressure turbine steam is taken to the Reheater and brought to its original superheat before being passes to the Intermediate pressure Turbine. The exhaust from the IP turbine is then passed through Low Pressure Turbine. From there it is exhausted through the condenser into the hot wet. A part of steam and water is lost while passing through different stages and this is compensated by supplying additional feed water from Water Treatment Plant.

Cooling Water Circuit The cooling water supply to the condenser helps in maintaining a low pressure in it. The water may be taken from a natural source such as rivers, lake or sea or the same water may be cooled and circulated over again through a cooling towers.

Boiler The Boilers used in electric-power generating plants are called Utility Boilers. They can be either sub critical or super critical units. The sub critical boilers are water tube-drum type and are normally operate at between 130 and 180 bar steam pressure. The supercritical boilers are drumless once-through type and operate at 240 bar pressure or higher. Majority of the utility boilers are of the 170-180 bar water tube-drum variety, which produce superheated steam at about 540-560 deg C with on or two stages of reheating.

Combined circulatory pump Once through (or Monotype) Boiler Loeffler Boiler Benson Boiler Combined circulatory pump

Velox Boiler

Economiser

Tubular type air preheater

Storage Type Air preheater

Cyclone separator Basic elements of electrostatic precipitators. Typical fractional efficiencies of dust collectors.

Ball and race Mill

Plan of Furnace with tangential firing

Steam Turbines The steam Turbine is a prime-mover in which the potential energy of the Steam is transformed into Kinetic energy, and later in it turn is transformed into the mechanical energy of rotation of the turbine shaft.

Closed feed water heaters

Tray Type Open Heater

Reheating of Steam In order to limit the quality of Steam at turbine exhaust , reheating of Seam has to be adopted. All the Steam after partial expansion in the turbine is brought back to the boiler, reheated by Combustion gases and then feed back to the turbine for further expansion.

Regenerative Feed Water Heating In the Rankine Cycle the condensate which is fairly at low temperature mixes with hot boiling water and thus results in decrease of cycle efficiency. Therefore, the feed water from the hot well of condenser is heated by drawing steam from turbine after expansion and thus improves the cycle efficiency. This heating method is called regenerative feed water heating.