Feed Water Treatment for Steam Power plant MOHD ABDUL JABBAR POWER PLANT ENGINEERING IV YEAR I SEMESTER MECHANICAL ENGINEERING DEPARTMENT

CORROSION FEED WATER TREATMENT Introduction: In steam power plant water is one of the most important raw material. water used for steam power plant contains impurities which must be treated before use. Classification of impurities in water: Visible impurities Microbiological growth: Presence of micro organism as they produce clogging troubles.

b. Turbidity and sediments: turbidity is the suspended insoluble matter and sediments are the coarse particles which settle down in stationary water. 2. Dissolved gases Carbon dioxide b. oxygen c. nitrogen d. methane e.Hydrogen sulphide. 3. Minerals and salts. a. Iron and manganese b. sodium and potassium salts c. fluorides d. silica. 4. Minerals acids: It may results in the chemical reaction with the boiler material.

5. Hardness: the salts of calcium, magnesium and sulphates etc forms a hard surface which resists heat transfer and clogs the passage in pipes. Presence of these salts is known as hardness. Troubles caused by the impurities in water: Scale formation Corrosion Carry over and Embrittlement

Methods of feed water treatment: Mechanical treatment Sedimentation b. coagulation c. Filteration d. Interior painting 2. Thermal treatment a.Deaeration b. distillation by evaporators 3.Chemical treatment a. Cold-lime soda softening process b. Hot-lime soda softening process c. Lime- phosphate d. Ion exchange process ( sodium zeolite / hydrogen zeolite process )

4. Demineralization 5.Blow down pH value of water: pH value of water is the logarithm of the reciprocal of hydrogen ion concentration. It is number from 0 to 14 with 7 indicating neutral water. pH value of water is determine by a pH meter.

COOLING TOWERS AND HEAT REJECTION In power plant the hot water from condenser is cooled in cooling tower, so the is can be reused in condenser for condensation of steam. In cooling tower the hot water is made to trickle down drop by drop and it comes contact with the air moving in opposite direction. As a result some water is evaporated and is taken away by air. In evaporation the heat is taken away from the water which results cooling of water.

Factors affecting cooling of water in cooling tower: 1.Temperature of air 2. temperature of water 3.Humidity of air 4. Velocity of air entering in tower 5. Size and height of the tower 6. Degree of uniformity in descending water 7. Arrangement of plates in tower.

Classification of cooling tower according to construction material: Timber Concrete (ferro concrete , multideck concrete hyperbolic) Steel duct type. Types of cooling towers: Natural draught cooling tower Mechanical draught cooling tower Forced draught cooling tower Induced draught cooling tower

Natural draught cooling tower

Hyperbolic concrete natural cooling tower

Natural draught cooling tower

Forced draught cooling tower

Forced draught cooling tower

Induced draft cooling tower

Induced draught tower

Induced draught

Maintenance of cooling towers The fan ,motor housing etc should be inspected regularly Motor bearing should be greased to avoid noises and vibrations The water spraying nozzles should be inspected regularly for clogging The circulating water should be tested for hardness to avoid scale formation and corrosion.

Draught system Introduction: The small pressure difference which causes a flow of gas to take place is termed as “Draught” The function of the draught is to force air to the fire and carry away the gaseous products of combustion. In a boiler furnace proper combustion take place only when sufficient quantity of air is supplied.

Classification of Draught

Natural draught

Natural draught

Forced draught

Induced draught

Balanced draught

Steam jet draught The boiler produces steam. If we utilize, a small portion of the pressurized steam for producing draught in a boiler system then we call the draught as steam jet draught. As the steam, causes the draught, generated in the boiler itself, there will be no need for extra electric power to run draught fans. No demand for additional electricity for running the draught fans hence reducing the cost of the system.

Construction of the system is simple and easy to maintain Construction of the system is simple and easy to maintain. Thus, maintenance cost is also low. In steam jet draught system a small portion of generated steam exhausts through a nozzle and the kinetic energy of the jet of high-velocity steam drags the air or flue gases in the boiler system. The stream jet draught in two types. One is natural stream jet draught, and another is force steam jet draught.

Forced Stream Jet Draught: In forced stream jet draught, we feed a portion of the stream produced in the boiler to the entry point of the furnace through diffusion pipe. Due to the kinetic energy of steam, there will be a draught at the entry point because of which fresh air gets dragged to the grate and then to the economiser then to preheater then ultimately to the chimney.

Forced steam jet draught

Natural Steam Jet Draught In natural steam Jet draught, we fit the steam nozzle in a smoke box attached to the bottom portion of the stack. The steam forcefully enters in the smoke box due to which flue gases created in the furnace get dragged in the smoke box because of the resultant draught created the kinetic energy of the steam jet. This process of creating draught in this way is called natural jet steam draught.

Natural steam jet draught

Advantages Steam jet draught is simple, economical and occupies very little space or occupies no space. But draught is only possible after steam gets produced which is the main disadvantage of steam Jet draught.

Draught losses The frictional resistance offered by the flues and gas passages to the flow of flues gases. Loss near the bends in the circuit. Loss due to friction head in equipments like grate, economizer, super heater etc. Loss due to imparting velocity to the flue gases.

Advantages of Mechanical draught Easy control of combustion and evaporation Increase in evaporative power of a boiler Improvement in the plant efficiency Reduced chimney height Capability of consuming low grade fuel Prevention of smoke The fuel burning capacity of grate is high then natural draught.