ACTIVE LEARNING PROCESS Branch: Electronics & Communication Guided By : Prof. C O Yadav Prepared By : BINI MOL THOMAS 13BEECG069 VISHAL SALVI 13BEECG067 HARSHAL M.H 13BEECG064

Boilers

Objectives 1. Describe the theory, construction, and applications of boilers 2. Describe the common type of boilers 3. Explain how to assess the performance and efficiency of a boiler 4. Describe methods to improve boiler efficiency 5.List energy efficiency opportunities

Objectives Introduction – Purpose? Type of boilers Boiler Assessment Energy efficiency opportunities

Introduction What is a Boiler? Vessel that heats water to become hot water or steam At atmospheric pressure water volume increases 1,600 times Hot water or steam used to transfer heat to a process

Introduction Thermal Equipment/ Boilers BOILER STEAM TO PROCESS EXHAUST GAS VENT STACK DEAERATOR ECO- NOMI- ZER PUMPS Thermal Equipment/ Boilers BOILER VENT BURNER WATER SOURCE BLOW DOWN SEPARATOR FUEL BRINE CHEMICAL FEED SOFTENERS Figure: Schematic overview of a boiler room

What Type of Boilers Are There? Types of Boilers What Type of Boilers Are There? Fire Tube Boiler Water Tube Boiler Packaged Boiler Fluidized Bed (FBC) Boiler Stoker Fired Boiler Pulverized Fuel Boiler Waste Heat Boiler Thermal Equipment/ Boilers

Type of Boilers 1. Fire Tube Boiler Thermal Equipment/ Boilers Relatively small steam capacities (12,000 kg/hour) Low to medium steam pressures (18 kg/cm2) Operates with oil, gas or solid fuels Thermal Equipment/ Boilers (Light Rail Transit Association)

Type of Boilers 2. Water Tube Boiler Thermal Equipment/ Boilers Used for high steam demand and pressure requirements Capacity range of 4,500 – 120,000 kg/hour Combustion efficiency enhanced by induced draft provisions Lower tolerance for water quality and needs water treatment plant Thermal Equipment/ Boilers (Your Dictionary.com)

Type of Boilers 3. Packaged Boiler Thermal Equipment/ Boilers Comes in complete package Features High heat transfer Faster evaporation Good convective heat transfer Good combustion efficiency High thermal efficiency Classified based on number of passes Oil Burner To Chimney Thermal Equipment/ Boilers The packaged boiler is so called because it comes as a complete package. Once delivered to a site, it requires only the steam and water pipe work, fuel supply and electrical connections to be made to become operational. These boilers are classified based on the number of passes - the number of times the hot combustion gases pass through the boiler. More specifically, it is a typical 3 pass, oil fired packaged boiler. This is a packaged boiler. Does anyone recognize what type of boiler this is? (Click once and name will appear) 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. (BIB Cochran, 2003)

4. Fluidized Bed Combustion (FBC) Boiler Type of Boilers 4. Fluidized Bed Combustion (FBC) Boiler Particles (e.g. sand) are suspended in high velocity air stream: bubbling fluidized bed Combustion at 840° – 950° C Fuels: coal, washery rejects, rice husk, bagasse and agricultural wastes Benefits: compactness, fuel flexibility, higher combustion efficiency, reduced SOx & NOx Thermal Equipment/ Boilers The fluidized bed boilers When an evenly distributed air or gas is passed upward through a finely divided bed of solid particles such as sand supported on a fine mesh, the particles are undisturbed at low velocity. As air velocity is gradually increased, a stage is reached when the individual particles are suspended in the air stream – the bed is called “fluidized”. With further increase in air velocity, there is bubble formation, vigorous turbulence, rapid mixing and formation of dense defined bed surface. The bed of solid particles exhibits the properties of a boiling liquid and assumes the appearance of a fluid – “bubbling fluidized bed”. The fuels burnt in these boilers can include coal, washery rejects; rice husk and bagasse (sugar cane wastes) & other agricultural wastes. The fluidized bed boilers have a wide capacity range- 0.5 T/hr to over 100 T/hr. The fluidized bed combustion (FBC) takes place at about 840oC to 950oC. Fluidized bed combustion (FBC) has emerged as a viable alternative and has significant advantages over a conventional firing system and offers multiple benefits: compact boiler design fuel flexibility higher combustion efficiency reduced emission of noxious air pollutants such as SOx (Sulfur oxides) and Nox (Nitrous oxides), both of which contribute to “acid rain”. Three types of FBC boilers are explained on the next slides,

Type of Boilers 5. Stoke Fired Boilers a) Spreader stokers Coal is first burnt in suspension then in coal bed Flexibility to meet load fluctuations Favored in many industrial applications Thermal Equipment/ Boilers

Type of Boilers 5. Stoke Fired Boilers b) Chain-grate or traveling-grate stoker Coal is burnt on moving steel grate Coal gate controls coal feeding rate Uniform coal size for complete combustion Thermal Equipment/ Boilers A type of FBC boiler: This picture illustrates a chain grate or traveling grate stoker. Coal is fed onto one end of a moving steel grate. As the grate moves along the length of the furnace, the coal burns before dropping off at the end as ash. The coal-feed hopper runs along the entire coal-feed end of the furnace. A coal gate is used to control the rate at which coal is fed into the furnace by controlling the thickness of the fuel bed. Coal must be uniform in size as large lumps will not burn out completely by the time they reach the end of the grate. (University of Missouri, 2004)

6. Pulverized Fuel Boiler Type of Boilers 6. Pulverized Fuel Boiler Pulverized coal powder blown with combustion air into boiler through burner nozzles Thermal Equipment/ Boilers Combustion temperature at 1300 -1700 °C Benefits: varying coal quality coal, quick response to load changes and high pre-heat air temperatures A type of FBC boiler: Pulverized Fuel Boiler One of the most popular systems for firing pulverized coal is the tangential firing using four burners corner to corner to create a fireball at the center of the furnace. This is shown in the figure. The coal is pulverized to a fine powder until less than 2% of the coal is +300 micro meter and 70-75% is below 75 microns for bituminous coal. The pulverized coal is then blown with part of the combustion air into the boiler plant through a series of burner nozzles. The combustion takes place at temperatures ranging between 1300-1700 degrees Celsius depending mainly on the coal grade. The particle residence time in the boiler is typically 2 to 5 seconds and the particles have to be small enough to be completely combusted during this time period This system has many advantages : ability to fire varying quality of coal quick responses to changes in load use of high pre-heat air temperatures etc. Tangential firing

Independence Steam Electric Station - Newark, AR Operation: Unit 1 - January 1983/Unit 2 - December 1984 Fuel: Low-sulfur coal mined near Gillette, Wyoming Capability: 1,678 megawatts

Type of Boilers 7. Waste Heat Boiler Thermal Equipment/ Boilers Used when waste heat available at medium/high temp Auxiliary fuel burners used if steam demand is more than the waste heat can generate Used in heat recovery from exhaust gases from gas turbines and diesel engines Thermal Equipment/ Boilers Agriculture and Agri-Food Canada, 2001

Assessment of a Boiler 1. Boiler performance Causes of poor boiler performance Poor combustion Heat transfer surface fouling Poor operation and maintenance Deteriorating fuel and water quality Heat balance: identify heat losses Boiler efficiency: determine deviation from best efficiency Thermal Equipment/ Boilers

Assessment of a Boiler Heat Balance Thermal Equipment/ Boilers An energy flow diagram describes geographically how energy is transformed from fuel into useful energy, heat and losses Thermal Equipment/ Boilers Stochiometric Excess Air Un burnt FUEL INPUT STEAM OUTPUT Stack Gas Ash and Un-burnt parts of Fuel in Ash Blow Down Convection & Radiation

Assessment of a Boiler Heat Balance Thermal Equipment/ Boilers Balancing total energy entering a boiler against the energy that leaves the boiler in different forms Thermal Equipment/ Boilers 12.7 % BOILER Heat loss due to dry flue gas 8.1 % Heat loss due to steam in fuel gas 100.0 % 1.7 % Heat loss due to moisture in fuel A Heat balance is an attempt to balance the total energy that enters a boiler against the energy that leaves it. This figure illustrates the different typical losses that occurs while generating steam. (Question) Does anyone have any suggestions of what the two major heat losses are? (Discussion) (Click once and answer reveals) They are dry fly gas that represents a heat loss of 12.7% and heat loss as a result of steam in the flue gas of 8.1%. (Click once for other heat losses to appear) Other heat losses are due to moisture in the fuel and in the air, as well as unburnts in residue and radiation. (Click once) This leaves 73.8% of heat that goes to steam generation. Fuel 0.3 % Heat loss due to moisture in air 2.4 % Heat loss due to unburnts in residue 1.0 % Heat loss due to radiation & other unaccounted loss 73.8 % 73.8 % Heat in Steam

Assessment of a Boiler Heat Balance Thermal Equipment/ Boilers Goal: improve energy efficiency by reducing avoidable losses Avoidable losses include: Stack gas losses (excess air, stack gas temperature) Losses by unburnt fuel Blow down losses Condensate losses Convection and radiation Thermal Equipment/ Boilers The goal of a Cleaner Production and/or energy assessment must be to reduce the avoidable losses, i.e. to improve energy efficiency. The following losses can be avoided or reduced: Stack gas losses: Excess air (reduce to the necessary minimum which depends from burner technology, operation, operation (i.e. control) and maintenance) and Stack gas temperature (reduce by optimizing maintenance (cleaning), load; better burner and boiler technology). Losses by unburnt fuel in stack and ash (optimize operation and maintenance; better technology of burner). Blow down losses (treat fresh feed water, recycle condensate) Condensate losses (recover the largest possible amount of condensate) Convection and radiation losses (reduced by better insulation of the boiler).

Assessment of a Boiler 1. Boiler Efficiency Thermal Equipment/ Boilers Thermal efficiency: % of (heat) energy input that is effectively useful in the generated steam Thermal Equipment/ Boilers

Boiler efficiency () = hf /hg Assessment of a Boiler Boiler Efficiency: Direct Method Boiler efficiency () = hf /hg Heat Input * 100% Heat Output Thermal Equipment/ Boilers

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