28-08-2014, 12:38 PM
A PROJECT REPORT FOR CHEEMA BOILERS LIMITED Batch 2010-2014 Partially Submitted To Fulfill the Award of Bachelor of Technology in MECHANICAL ENGINEERING for RBIENT HOSHIARPURUnder Punjab Technical University Submitted To: Submitted By: ME (8th) Supervised By: DECLERATION I hereby declare that the project work entitled “BOILERS ” is an authentic record of my own work carried out at “CHEEMA BOILERS LTD.MOHALI” as requirements of Industry Internship project for the award of degree of B.Tech in MECHANICAL ENGINEERING. RAYAT AND BAHRA INSTITUTE OF ENGG. & NAN
A PROJECT REPORT FOR CHEEMA BOILERS LIMITED Batch 2010-2014 Partially Submitted To Fulfill the Award of Bachelor of Technology in MECHANICAL ENGINEERING for RBIENT HOSHIARPURUnder Punjab Technical University Submitted To: Submitted By: ME (8th) Supervised By: DECLERATION I hereby declare that the project work entitled “BOILERS ” is an authentic record of my own work carried out at “CHEEMA BOILERS LTD.MOHALI” as requirements of Industry Internship project for the award of degree of B.Tech in MECHANICAL ENGINEERING. RAYAT AND BAHRA INSTITUTE OF ENGG. & NANO TECHNOLOGY, HOSHIARPUR, (Signature of student)) DATE: Certified that the above statement made by the student is correct to the best of our knowledge and belief. SIG.& SEAL PREFACE Knowledge can be acquired both through formal and informal methods of learning. In making of a professional both these methods play an important role. While classroom instructions, lab activities & reading through study material have a direct impact on the process of learning, practical methods such as observations, discussions, industrial visits & exhibitions etc, but the most important component in professional training comes from the shop floor. It is, therefore, imperative`, an engineering graduate passé through an industrial training program to acquire necessary hands-on experience to qualify him before he gets into the job market. This industrial training is highly conductive for the development of • Confidence • Solid foundation of knowledge and personality • Creativity • Excellence and self-discipline With this point of view, six months of our curriculum have been devoted to Project. It gives an engineer an exposure and insures him to face the actual problems and ground realities faced in the professional world. The experience gained by me in this semester has been prodigious and has given me a feeling of achievements towards my carrier as an upcoming electronics engineer. I have tried to assimilate all the information about my project in this dissertation, which is presented chapter wise in the forthcoming s ACKNOWLEDGEMENT A formal statement of acknowledgment is hardly sufficient to express my gratitude towards the personalities who have helped me to undertake and complete this project. Training in an organization like which is fuelled by the individuals with so much zest and energy, “teaming” up to form a formidable force, was in itself a true learning experience which is going to help me immensely in my career. I hereby convey my thanks to all those who have rendered their valuable help, support and guidance. Firstly I would thank MR. R.K. SINGH for granting me the permission to work as a Trainee in this esteemed company and for providing me all the facilities and helping me to undertake a project “BOILERS” and providing highly valuable technical guidance, constructive criticism and moral support. The acknowledgement would be incomplete if I don’t mention the worthful guidance and unconditional support and cooperation I received from the Officers and staff of Bunker Busting. Lastly, I bow before the almighty with folded hands. Leader in Manufacturing Process Steam & Power Generation Equipment Cheema Boilers Limited, popularly known as CBL is a trusted name in the field of Indian Boiler Industry. It is known for its commitment, competence and compliance. CBL was established in the year 1999 to provide complete solution to steam generation needs. The company's origin in the boiler industry goes back to founding of it's sister concern Cheema Engineering Services (P) Limited engaged in manufacturing of Steam Boilers, Pollution Control equipment, Fluidized Bed Conversion and energy saving devices since 1991. It's visionary Mr. Harjinder Singh Cheema, currently CBL Managing Director along with his three brothers, now CBL Directors started this company with Boiler services and very soon CBL moved to manufacturing of full-fledged Process Boilers. Presently company is manufacturing all types of boiler to meet the requirement of process and power industry. CBL has got its own manufacturing facilities at Kurali 25 kms from Chandigarh, near Ropar and Corporate Office at Mohali, (Chandigarh). In last 8 years of operation, the company has established its name in Boiler Industry with internal core competency in Engineering, Manufacturing and Project commissioning. A dedicated and multi-skilled manpower has taken this company to a new height of business excellence. Its operation facilities, technology, manpower competency and customer base are expanding every year, which has resulted in doubling the company's turnover year over year. Company has already drawn an ambitious short and long term plan to meet growing demand of energy in India and abroad. CBL is/are already exporting to Asian and European countries. Welding process: • Welding is a process of joining two or more pieces of the same or dissimilar materials to achieve complete coalescence. • One of the most cost-effective methods of joining metal components. • Suitable for any thickness. • Versatile, being applicable to a wide range of component shapes and sizes. Types of welding • Shielded Metal Arc Welding (SMAW) • Submerged Arc Welding (SAW) • Gas Metal Arc Welding (GMAW ) • - MIG , MAG • Gas Tungsten Arc Welding (GTAW / TIG) SMAW….SHIELDED METAL ARC WELDING SUBMERGED ARC WELDING GAS METAL ARC WELDING GAS TUNGSTEN ARC WELDING PARTS OF AN ELECTRODE CORE ROD FLUX COATING STUB COMMONLY USED ELECTRODES 6010 6011 6012 6013 7014 7024 7018 AWS classification of electrodes E 70XX E :- Electrode 70 :- Tensile Strength in Ksi X :- Welding Position: 1 = All Position, 2 = Flat & Horizontal Fillet X :- Composition of Coating Wire electrode An electrode that is in the form of a wire. Wire electrodes are more productive than stick electrodes because they do not require frequent changing. The welding position is important in the selection of the proper wire diameter; as a general rule smaller size wires are used for overhead & vertical position. Shielding gases Argon (Ar) Inert gas Low heat and giving minimum penetration Argon costs less than Helium but more than Carbon Dioxide Use whenever a completely inert shielding gas is required without the need for deep penetration. Helium (He) Completely inert gas Maximum heat input and weld penetration Most expensive option (of the three) Carbon Dioxide (CO2) A compound which is not fully inert. The cheapest option (of the three) Cannot be used on non-ferrous alloys. 1.INTRODUCTION OF BOILERS A steam generator or boiler is , usually , a closed vessel made of steel. Its function is to transfer the heat produced by the combustion of fuel to water , the ultimately to generate the steam. The steam produced may be supplied. 1. To an external combustion engine 2. At low pressure for industrial process work in cotton mills , sugar factories, breweries etc. 3. For producing hot water , which can be used for heating installation at much lower pressure. A boiler is an enclosed vessel that provides a means for combustion heat to be transferred to water until it becomes heated water or steam. The hot water or steam under pressure is then usable for transferring the heat to a process. Water is a useful and inexpensive medium for transferring heat to a process. When water at atmospheric pressure is boiled into steam its volume increases about 1,600 times, producing a force that is almost as explosive as gunpowder. This causes the boiler to be an equipment that must be treated with utmost care. The boiler system comprises of: a feed water system, steam system and fuel system. The feed water system provides water to the boiler and regulates it automatically to meet the steam demand. Various valves provide access for maintenance and repair. The steam system collects and controls the steam produced in the boiler. Steam is directed through a piping system to the point of use. Throughout the system, steam pressure is regulated using valves and checked with steam pressure gauges. The fuel system includes all equipment used to provide fuel to generate the necessary heat. The equipment required in the fuel system depends on the type of fuel used in the system. The water supplied to the boiler that is converted into steam is called feed water. The two sources of feed water are: (1) Condensate or condensed steam returned from the processes and (2) Makeup water (treated raw water) which must come from outside the boiler room and plant processes. For higher boiler efficiencies, an economizer preheats the feed water using the waste heat in the flue gas. 2.TYPE OF BOILERS This section describes the various types of boilers: Fire tube boiler, Water tube boiler, Packaged boiler, Fluidized bed combustion boiler, Stoker fired boiler, Pulverized fuel boiler, Waste heat boiler Thermic fluid heater. Water Tube Boiler In 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 possibleMost 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 . Simple Diagram of Water Tube Boiler POWERPAC BOILERS CAPACITY 10 TPH - 150 TPH PRESSURE 10.54 KG/CM2 TO 87 KG/CM2 FUEL RICE HUSK, COAL, LIGNITE, REJECTS, CHAR ETC. STEAM TEMP UPTO 515°C QUANTITY MANUFACTURED 125 NOS HYPAC BOILER CAPACITY 1 TPH - 12 TPH PRESSURE 10.54 KG/CM2 TO 25 KG/CM2 FUEL RICE HUSK, COAL, PETCOKE, LIGNITE ETC. QUANTITY MANUFACTURED 285 NOS F.D. FAN Forced Draft (FD) fans purpose is to provide a positive pressure to a system. This basic concept is used in a wide variety of industries but the term FD Fans is most often found in the boiler industry. Fans for boilers force ambient air into the boiler, typically through a preheater to increase overall boiler efficiency. Inlet or outlet dampers are used to control and maintain the system pressure. Typical fan arrangements are 3SI or 3DI which utilize a wheel center hung on the shaft with integral inlet boxes. CLOSED IMPELLER A closed impeller has side walls on both sides of the impeller such that the pumped fluid must flow between the side walls from the outer circumference of the suction opening to the vane tips. With an open impeller, only the pump housing constrains the fluid from leaving the impeller before reaching the vane tips. A semi-open impeller has a side wall on one side of the impeller, but is open to the pump housing on the other side. AIR PRE HEATER…… An air preheater (APH) is a general term to describe any device designed to heat air before another process (for example,combustion in a boiler) with the primary objective of increasing the thermal efficiency of the process. They may be used alone or to replace a recuperative heat system or to replace a steam coil. In particular, this article describes the combustion air preheaters used in large boilers found in thermal power stationsproducing electric power from e.g. fossil fuels, biomass or waste.[1][2][3][4][5] The purpose of the air preheater is to recover the heat from the boiler flue gas which increases the thermal efficiency of the boiler by reducing the useful heat lost in the flue gas. As a consequence, the flue gases are also conveyed to the flue gas stack (or chimney) at a lower temperature, allowing simplified design of the conveyance system and the flue gas stack. It also allows control over the temperature of gases leaving the stack DUCTING Ducting is a path provided to the flow of flue gases inside the boiler. Our wide range of Ducting & Hoppers used for Boiler & Chimneys & Other related equipments.It is fabricated as per the specifications of our clients. These are incorporated with M.S. Plates.Sheets, Structural and widely used in Any Industry. CHAMBER Micro combustion chambers are the devices in which combustion happens at a very small volume, due to which surface to volume ratio increases which plays a vital role in stabilizing the flame. The term combustion chamber is also used to refer to an additional space between the firebox and boiler in a steam locomotive. This space is used to allow further combustion of the fuel, providing greater heat to the boiler. Large steam locomotives usually have a combustion chamber in the boiler to allow the use of shorter firetubes. This is because: • Long firetubes have a theoretical advantage in providing a large heating surface but, beyond a certain length, this is subject to diminishing returns. • Very long firetubes are prone to sagging in the middle WATER WALL PANEL Water Wall Panels are used in modern day Boilers in place of Steam Generating Tubes to reduce heat loss due to their gas tight nature and reduce insulation costs. We fabricate Water Wall Panels using automatic Fin to tubes welding machines and large Tube Panel Benders to achieve desired shape of panels which can have Swaged Ends, Stub Welded to Headers. We supply Panels with integrated manhole openings in the panels. We have fabricated panels made of Rifle Bore Tubes of Size 50.8 mm OD x 5.6 Mm MWT conforming to SA- 210 Gr. C in Lengths of upto 24 mtrs. X max.28 tubes (2 mtrs. wide) with Straightness within a tolerance of + / - 3mm. CYCLONE to take advantage of coal grades not suitable for pulverized coal combustion, cyclone furnaces feed coal in a spiral manner into a combustion chamber for maximum combustion efficiency. A typical cyclone combustor During coal combustion in a furnace, volatile components burn without much difficulty. Fuel carbon “char” particles (heavier, less volatile coal constituents) require much higher temperatures and a continuing supply of oxygen. Cyclone furnaces are able to provide a thorough mixing of coal particles and air with sufficient turbulence to provide fresh air to surfaces of the coal particles. Cyclone furnaces were originally designed to take advantage of four things 1. Lower fuel preparation time and costs 2. Smaller more compact furnaces 3. Less fly ash and convective pass slagging 4. Flexibility in fuel types Operation[edit] A cyclone furnace consists of a horizontal cylindrical barrel attached through the side of a boiler furnace. The cyclone barrel is constructed with water cooled, tangential oriented, tube construction. Inside the cyclone barrel are short, densely spaced, pin studs welded to the outside of the tubes. The studs are coated with a refractory material, usually silicaor aluminium based, that allows the cyclone to operate at a high enough temperature to keep the slag in a molten state and allow removal through the tap. Crushed coal and a small amount of primary air enter from the front of the cyclone into the burner. In the main cyclone burner, secondary air is introduced tangentially, causing a circulating gas flow pattern. The products, flue gas and un-combusted fuel, then leave the burner and pass over the boiler tubes. Tertiary air is then released further downstream to complete combustion of the remaining fuel, greatly reducing NOx formation. A layer of molten slag coats the burner and flows through traps at the bottom of the burners, reducing the amount of slag that would otherwise form on the boiler tubes. I.D. FAN Induced Draft (ID) fans are used to create a vacuum or negative air pressure in a system or stack. Our centrifugal blowers are used to maintain elevated ventilation, resulting in increased system efficiency. Twin City Fan can also supply extractor fans, which are typically heavy duty construction to handle particulate in the airstream. In the boiler industry ID Fans are often used in conjunction with FD fans to maintain system pressure which is slightly lower than ambient. HYPAC BOILER * Water cum smoke tube boilers * Capacity - 2 ton to 12 tones * Easily takes the variation of load fluctuations * Burn agriculture residue and other high volume low density fuels * Can be equipped with fluidized bed, moving and stationery grate furnace * Four side water wall design available. WORKING.. FIRST , fresh air is introduced into boiler with the help of fd fan, which takes fresh air from the atmosphere and sends it to the aph. In aph, this fresh air comes in contact with flue gases coming from the chamber and thus gets heated and then goes to combustion chamber In combustion chamber, this air pass through nozzles and comes in contact with fuel and thus ignition occurs in the chamber and this chamber is surrounded by water wall panel and thus water gets heated and this water is send tu the steam chamber where it can be utilized and the flue gases coming out of chamber are sent to cyclone where ash particles are removed. And then it is sent to the aph where this is utilized for heating of the fresh air coming from fd fan and thun finally sent outside to chimney by id fan ,this is the working of hypac boiler. Energy saving devices used in large scale boilers Economiser Superheater stud marking evaporator ECONOMISER In boilers, economizers are heat exchange devices that heat fluids, usually water, up to but not normally beyond the boiling point of that fluid. Economizers are so named because they can make use of the enthalpy in fluid streams that are hot, but not hot enough to be used in a boiler, thereby recovering more useful enthalpy and improving the boiler's efficiency. They are a device fitted to a boiler which saves energy by using the exhaust gases from the boiler to preheat the cold water used to fill it (the feed water). Energy heat recovery with condensing economizer.[clarification needed] The boiler room is a huge energy guzzler. It consists of thermal fluid boilers or steam boiler, with exhaust gases through a common chimney. An indirect contact or contact condensing economizer will recover the residual heat from the combustion products. A series of dampers, an efficient control system, as well as a ventilator, allow all or part of the combustion products to pass through the economizer, depending on the demand for make-up water and/or process water. The temperature of the gases can be lowered from 200°C to 10°C,[citation needed] while preheating the process water from 8°C to 80°C. On average over the year,[clarification needed] boiler combustion efficiency has risen from 80% to more than 95%. The efficiency of heat produced is directly linked to boiler efficiency. The percentage of excess air and the temperature of the combustion products are two key variables in evaluating this efficiency. The combustion of natural gas needs a certain quantity of air in order to be complete, so the burners need a flow of excess air in order to operate. Combustion produces water steam, and the quantity depends on the amount of natural gas burned. Also, the evaluation of the dew point depends on the excess air. Natural gas has different combustion efficiency curves linked to the temperature of the gases and the excess air. For example, if the gases[clarification needed] are chilled to 38°C and there is 15% excess air, then the efficiency will be 94%.[citation needed] The condensing economizer can thus recover the sensible and latent heat in the steam condensate contained in the flue gases for the process. The economizer is made of an aluminium and stainless steel alloy.[citation needed] The gases pass through the cylinder and the water through the finned tubes. It condenses about 11% of the water contained in the gases STUD MARKING Stud marking is done in boiler tubes. There is advantage of stud marking that due to stud marking, surface area got increased and due to inc. in surface area, more area is available for heat exchange and that’s why more heat is transferred to the water. EVAPORATOR Early boilers used seawater directly, but this gave problems with the build-up of brine and scale.[3] For efficiency, as well as conserving feedwater, marine engines have usually been condensing engines. By 1865, the use of an improved surface condenser permitted the use of fresh water feed,[4] as the additional feedwater now required was only the small amount required to make up for losses, rather than the total passed through the boiler. Despite this, a large warship could still require up to 100 tons of fresh water makeup to the feedwater system, when under full power.[5] Attention was also paid to de-aereating feedwater, to further reduce boiler corrosion.[4] The distillation system for boiler feedwater at this time was usually termed an evaporator, partly to distinguish it from a separate system or distiller used for drinking water. Separate systems were often used, especially in early systems, owing to the problem of contamination from oily lubricants in the feedwater system and because of the greatly different capacities required in larger ships. In time, the two functions became combined and the two terms were applied to the separate components of the system. SUPER HEATER Superheater : It is integral part of boiler and is placed in the path of hot flue gases from the furnace.The heat recovered from the flue gases is used in superheating the steam before entering into the turbine (i.e.,prime mover).Its main purpose is to increase the temperature of saturated steam without raising its pressure. Following are the advatages of using economizer. 1.There is an increase in efficiency of the steam power plant. 2.Erosion of turbine blade is minimized (or) even eliminated. 3.Steam consumption of the prim-mover is reduced. 4.Condensation loss in the pipes is reduced. 5.It removes entrained water particles from the steam conveyed to the steam turbines and increases the temperature of saturated steam. Whatever type of boiler is used, steam will leave the water at its surface and pass into the steam space. Steam formed above the water surface in a shell boiler is always saturated and cannot become superheated in the boiler shell, as it is constantly in contact with the water surface. If superheated steam is required, the saturated steam must pass through a superheater. This is simply a heat exchanger where additional heat is added to the saturated steam. In water-tube boilers, the superheater may be an additional pendant suspended in the furnace area where the hot gases will provide the degree of superheat required.In other cases, for example in CHP schemes where the gas turbine exhaust gases are relatively cool, a separately fired superheater may be needed to provide the additional heat. If accurate control of the degree of superheat is required, as would be the case if the steam is to be used to drive turbines, then an attemperator (desuperheater) is fitted. This is a device installed after the superheater, which injects water into the superheated steam to reduce its temperature. BOILER FITTINGS AND ACCESSORIES • Safety valve: It is used to relieve pressure and prevent possible explosion of a boiler. • Water level indicators: They show the operator the level of fluid in the boiler, also known as a sight glass, water gauge or water column is provided. • Bottom blowdown valves: They provide a means for removing solid particulates that condense and lie on the bottom of a boiler. As the name implies, this valve is usually located directly on the bottom of the boiler, and is occasionally opened to use the pressure in the boiler to push these particulates out. • Continuous blowdown valve: This allows a small quantity of water to escape continuously. Its purpose is to prevent the water in the boiler becoming saturated with dissolved salts. Saturation would lead to foaming and cause water droplets to be carried over with the steam - a condition known as priming. Blowdown is also often used to monitor the chemistry of the boiler water. • Flash Tank: High pressure blowdown enters this vessel where the steam can 'flash' safely and be used in a low-pressure system or be vented to atmosphere while the ambient pressure blowdown flows to drain. • Automatic Blowdown/Continuous Heat Recovery System: This system allows the boiler to blowdown only when makeup water is flowing to the boiler, thereby transferring the maximum amount of heat possible from the blowdown to the makeup water. No flash tank is generally needed as the blowdown discharged is close to the temperature of the makeup water. • Hand holes: They are steel plates installed in openings in "header" to allow for inspections & installation of tubes and inspection of internal surfaces. • Steam drum internals, A series of screen, scrubber & cans (cyclone separators). • Low- water cutoff: It is a mechanical means (usually a float switch) that is used to turn off the burner or shut off fuel to the boiler to prevent it from running once the water goes below a certain point. If a boiler is "dry-fired" (burned without water in it) it can cause rupture or catastrophic failure. • Surface blowdown line: It provides a means for removing foam or other lightweight non-condensible substances that tend to float on top of the water inside the boiler. • Circulating pump: It is designed to circulate water back to the boiler after it has expelled some of its heat. • Feedwater check valve or clack valve: A non-return stop valve in the feedwater line. This may be fitted to the side of the boiler, just below the water level, or to the top of the boiler. • Top feed: A check valve (clack valve) in the feedwater line, mounted on top of the boiler. It is intended to reduce the nuisance of limescale. It does not prevent limescale formation but causes the limescale to be precipitated in a powdery form which is easily washed out of the boiler. • OTHER STEAM PARTS Steam accessories • Main steam stop valve: • Steam traps: • Main steam stop/Check valve: It is used on multiple boiler installations. Combustion accessories • Fuel oil system: • Gas system: • Coal system: • Soot blower Other essential items • Pressure gauges: • Feed pumps: • Fusible plug: • Inspectors test pressure gauge attachment: • Name plate: • Registration plate: ASSESSMENT OF A BOILER This section describes the Performance evaluation of boilers (through the direct and indirect method including examples for efficiency calculations), boiler blow down, and boiler water treatment. 3.1 Performance Evaluation of a Boiler The performance parameters of a boiler, like efficiency and evaporation ratio, reduces with time due to poor combustion, heat transfer surface fouling and poor operation and maintenance. Even for a new boiler, reasons such as deteriorating fuel quality and water quality can result in poor boiler performance. A heat balance helps us to identify avoidable and unavoidable heat losses. Boiler efficiency tests help us to find out the deviation of boiler efficiency from the best efficiency and target problem area for corrective action. 3.1.1 Heat balance The combustion process in a boiler can be described in the form of an energy flow diagram. This shows graphically how the input energy from the fuel is transformed into the various useful energy flows and into heat and energy loss flows. The thickness of the arrows indicates the amount of energy contained in the respective flows. A heat balance is an attempt to balance the total energy entering a boiler against that leaving the boiler in different forms. The following figure illustrates the different losses occurring for generating steam. The energy losses can be divided in unavoidable and avoidable losses. 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). - 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).4 3.1.2 Boiler efficiency Thermal efficiency of a boiler is defined as “the percentage of (heat) energy input that is effectively useful in the generated steam.” There are two methods of assessing boiler efficiency: ? The Direct Method: the energy gain of the working fluid (water and steam) is compared with the energy content of the boiler fuel ? The Indirect Method: the efficiency is the difference between the losses and the energy Input 3.1.3 Direct method of determining boiler efficiency Methodology This is also known as ‘input-output method’ due to the fact that it needs only the useful output (steam) and the heat input (i.e. fuel) for evaluating the efficiency. This efficiency can be evaluated using the formula: Parameters to be monitored for the calculation of boiler efficiency by direct method are: ? Quantity of steam generated per hour (Q) in kg/hr. ? Quantity of fuel used per hour (q) in kg/hr. ? The working pressure (in kg/cm2(g)) and superheat temperature (oC), if any ? The temperature of feed water (oC) ? Type of fuel and gross calorific value of the fuel (GCV) in kcal/kg of fuel And where ? hg – Enthalpy of saturated steam in kcal/kg of steam ? hf – Enthalpy of feed water in kcal/kg of water Advantages of direct method ? Plant workers can evaluate quickly the efficiency of boilers ? Requires few parameters for computation Heat Output 3.2 Boiler Blow Down When water is boiled and steam is generated, any dissolved solids contained in the water remain in the boiler. If more solids are put in with the feed water, they will concentrate and may eventually reach a level where their solubility in the water is exceeded and they deposit from the solution. Above a certain level of concentration, these solids encourage foaming and cause carryover of water into the steam. The deposits also lead to scale formation inside the boiler, resulting in localized overheating and finally causing boiler tube failure. It is therefore necessary to control the level of concentration of the solids in suspension and dissolved in the boiled water. This is achieved by the process of 'blowing down', where a certain volume of water is blown off and is automatically replaced by feed water – thus maintaining the optimum level of total dissolved solids (TDS) in the boiler water and removing those solids that have fallen out of solution and which tend to settle on the internal surfaces of the boiler. Blow down is necessary to protect the surfaces of the heat exchanger in the boiler. However, blow down can be a significant source of heat loss, if improperly carried out. Since it is tedious and time consuming to measure TDS in a boiler water system, conductivity measurement is used for monitoring the overall TDS present in the boiler. A rise in conductivity indicates a rise in the "contamination" of the boiler water. 3.3 Boiler Feed Water Treatment Producing quality steam on demand depends on properly managed water treatment to control steam purity, deposits and corrosion. A boiler is the sump of the boiler system. It ultimately receives all of the pre-boiler contaminants. Boiler performance, efficiency, and service life are direct products of selecting and controlling feed water used in the boiler. When feed water enters the boiler, the elevated temperatures and pressures cause the components of water to behave differently. Most of the components in the feed water are soluble. However, under heat and pressure most of the soluble components come out of solution as particulate solids, sometimes in crystallized forms and other times as amorphous particles. When solubility of a specific component in water is exceeded, scale or deposits develop. The boiler water must be sufficiently free of deposit forming solids to allow rapid and efficient heat transfer and it must not be corrosive to the boiler metal. Deposit control is explain first, followed by the two major types of boiler water treatment: internal water treatment and external water treatment De-aeration In de-aeration, dissolved gases, such as oxygen and carbon dioxide, are expelled by preheating the feed water before it enters the boiler. All natural waters contain dissolved gases in solution. Certain gases, such as carbon dioxide and oxygen, greatly increase corrosion. When heated in boiler systems, carbon dioxide (CO2) and oxygen (O2) are released as gases and combine with water (H2O) to form carbonic acid, (H2CO3). Removal of oxygen, carbon dioxide and other non-condensable gases from boiler feed water is vital to boiler equipment longevity as well as safety of operation. Carbonic acid corrodes metal reducing the life of equipment and piping. It also dissolves iron (Fe) which when returned to the boiler precipitates and causes scaling on the boiler and tubes. This scale not only contributes to reducing the life of the equipment but also increases the amount of energy needed to achieve heat transfer. De-aeration can be done by mechanical de-A