CLASSIFICATION OF STEAM POWER PLANTS

Mechanical equipment in Thermal power station.

BOILERECONOMISERTURBINESUPER HEATERAIR PREHEATERCONDENSERClassification of super heaterConvection.Radiation.Combination of convection and radiation.Reheater The function of reheater is similar to the superheater in that it serves to elevate the steam temperature. Primary steam is supplied to the high pressure turbine. After passing through the high pressure turbine, the steam is returned to the steam generator for reheating (in a reheater) after which it is sent to the low pressure turbine. A second reheat cycle may also be provided.

Soot Blowers

The fuel used in thermal power plants causes soot and this is deposited on the boiler tubes, economizer tubes, air pre heaters, etc. This drastically reduces the amount of heat transfer of the heat exchangers. Soot blowers control the formation of soot and reduce its corrosive effects. The types of soot blowers are fixed type, which may be further classified into lane type and mass type depending upon the type of spray and nozzle used.Condenser The use of a condenser in a power plant is to improve the efficiency of the power plant by decreasing the exhaust pressure of the steam below atmosphere. Another advantage of the condenser is that the steam condensed may be recovered to provide a source of good pure feed water to the boiler and reduce the water softening capacity to a considerable extent. A condenser is one of the essential components of a power plant. Functions of Condensers The main purposes of the condenser are to condense the exhaust steam from the turbine for reuse in the cycle and to maximize turbine efficiency by maintaining proper vacuum. As the operating pressure of the condenser is lowered (vacuum is increased), the enthalpy drop of the expanding steam in the turbine will also increase. This will increase the amount of available work from the turbine (electrical output). Cooling TowerThe importance of the cooling tower is felt when the cooling water from the condenser has to be cooled. The cooling water after condensing the steam becomes hot and it has to be cooled as it belongs to a closed system. The Cooling towers do the job of decreasing the temperature of the cooling water after condensing the steam in the condenser.Cooling Towers have one function : Remove heat from the water discharged from the condenser so that the water can be discharged to the river or re-circulated and reused.A cooling tower extracts heat from water by evaporation. In an evaporative cooling tower, a small portion of the water being cooled is allowed to evaporate into a moving air stream to provide significant cooling to the rest of that water stream. Cooling Towers are commonly used to provide lower than ambient water temperatures and are more cost effective and energy efficient than most other alternatives. The smallest cooling towers are structured for only a few litres of water per minute while the largest cooling towers may handle upwards of thousands of litres per minute. The pipes are obviously much larger to accommodate this much water in the larger towers and can range up to 12 inches in diameter.

Advantages of regenerative cycleImprove overall plant efficiency.Protect boiler corrosion. Avoid the thermal stresses due to cold water entering the boiler .Increased the quantity of steam produced by boiler.

Function of economizer To extract a part of heat from the fuel gas coming out of the boiler.To use heat for heating feed water to the boiler. To increases the efficiency of boiler.

The economizer is a feed water heater, deriving heat from the flue gases. The justifiable cost of the economizer depends on the total gain in efficiency. In turn this depends on the flue gas temperature leaving the boiler and the feed water inlet temperature. Air Pre-heater The flue gases coming out of the economizer is used to preheat the air before supplying it to the combustion chamber. An increase in air temperature of 20 degrees can be achieved by this method. The pre heated air is used for combustion and also to dry the crushed coal before pulverizing. Advantages of mechanical handlingHigher reliability.Less labour required.Operation is easy and smooth.Economical for large capacity plant.Losses in transport are minimised.Easily started.

Disadvantages of mechanical handlingNeed continuous maintenance and repair.Capital cost of plant is increased.

Types of BoilersFire Tube BoilerWater Tube BoilerPackaged BoilerFluidized Bed (FBC) BoilerStoker Fired BoilerPulverized Fuel BoilerWaste Heat BoilerThermic Fluid Heater (not a boiler!)What Type of Boilers Are There?17There are different types of boilers based on different fuels and with various capacities. (Questions to audience) What type of boilers do you know of? What kind of boilers do you use in the industry where you work? (Discussion)(Click once and boiler types will appear) We will look closer at the following types of boilers: Fire Tube Boiler, Water Tube Boiler, Packaged Boiler, Fluidized Bed Boiler, Stoker Fired Boiler, Pulverized Fuel Boiler and Waste Heat Boiler.

The boilers can be classified according to the following criteria.According to flow of water and hot gases :(a) Water tube(b) Fire tube.Type of Boilers1. Fire Tube Boiler

Relatively small steam capacities (12,000 kg/hour)Low to medium steam pressures (18 kg/cm2)Operates with oil, gas or solid fuels

19To begin with, we will look at the fire tube boiler:This is generally used for relatively small steam capacities and at low to medium steam pressures. The steam rates for fire tube boilers are up to 12,000 kg/hour with pressures of 18 kg/cm2. Fire tube boilers can operate on oil, gas or solid fuels. The figure illustrates how a fire tube boiler works. The fuel is burned and heats up the water to steam which is turn channeled to the process. Today, most fire tube boiler are in a packaged construction for all fuels.

Type of Boilers2. Water Tube Boiler

Used for high steam demand and pressure requirements Capacity range of 4,500 120,000 kg/hourCombustion efficiency enhanced by induced draft provisionsLower tolerance for water quality and needs water treatment plant20In a water tube boiler, boiler feed water flows through the tubes and enters the boiler drum. The circulated water is heated by the combustion gases and converted into steam at the vapour space in the drum. These boilers are selected when the steam demand as well as steam pressure requirements are high as in the case of process cum power boiler / power boilers. Most modern water boiler tube designs are within the capacity range 4,500 120,000 kg/hour of steam, at very high pressures. Many water tube boilers are of packaged construction if oil and /or gas are to be used as fuel. Solid fuel fired water tube designs are available but packaged designs are less common. The features of water tube boilers are: Forced, induced and balanced draft provisions help to improve combustion efficiency.Less tolerance for water quality calls for water treatment plant.Higher thermal efficiency levels are possible

3. Packaged Boiler

Oil BurnerTo ChimneyComes in complete packageFeaturesHigh heat transferFaster evaporation Good convective heat transferGood combustion efficiencyHigh thermal efficiencyClassified based on number of passes21Does anyone recognize what type of boiler this is? (Click once and name will appear) This is a packaged boiler. More specifically, it is a typical 3 pass, oil fired packaged boiler.The packaged boiler is so called because it comes as a complete package. Once delivered to a site, it requires only the steam, water pipe work, fuel supply and electrical connections to be made to become operational. Package boilers are generally of a shell type with a fire tube design so as to achieve high heat transfer rates by both radiation and convection. The features of packaged boilers are: Small combustion space and high heat release rate resulting in faster evaporation. Large number of small diameter tubes leading to good convective heat transfer. Forced or induced draft systems resulting in good combustion efficiency. Number of passes resulting in better overall heat transfer. Higher thermal efficiency levels compared with other boilers. These boilers are classified based on the number of passes - the number of times the hot combustion gases pass through the boiler. THANK YOU