Prior to the Rainhill trials of 1829 Henry Booth, treasurer of the Liverpool and Manchester. Railway suggested to George Stephenson, a scheme for a multi-tube ...
DESIGN, FABRICATION AND TESTING OF A STEAM GENERATOR
BY
UBI ATEB PASCHAL, ROWLANDS DAVID OLUSINA, UCHOLA LAWRENCE AND OCHI VICTOR
BEEN A PROJECT SUBMITTED TO THE SCHOOL OF ENGINEERING AND ENGINEERING TECHNOLOGY IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OF BACHELORS OF ENGINEERING IN MECHANICAL ENGINEERING FEDERAL UNIVERSITY OF TECHNOLOGY, MINNA
SUPERVISED BY: PROF. M. S. ABOLARIN
NOVEMBER, 2010
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ABSTRACT This project report discusses the design, fabrication and testing of a steam generator. The steam generator is used to harness the energy liberated as heat in a variety of processes and converts it into a form which is useful for applications in the industry, medicine, agriculture etc. the water tube concept was used for this steam generator and it generates steam at a flowrate of 0.0035m3/s and at a temperature of 509oC. The heat used is typically produced intentionally for the production of steam for industrial or domestic purposes. The first step of steam generation is to transfer the heat gotten from the heat source (fuel) into clean water in the boiler. This is done by having the heat source elevate the temperature in the combustion chamber. This heat produced, heats up the water in the water tube without contaminating it. There are several different geometric schemes for doing this, but the principle remains the same.
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CHAPTER ONE 1.0 INTRODUCTION 1.1 HISTORICAL BACKGROUND Steam is a useful and powerful purveyor of energy. It is referred to as vaporized water. At standard temperature and pressure, pure steam (unmixed with air, but in equilibrium with liquid water) occupies about 1,600 times the volume of an equal mass of liquid water. In the atmosphere, the partial pressure of water is much lower than 1 atm, therefore gaseous water can exist at temperatures much lower than 100°C (212°F). In common speech, Steam most often refers to the white mist that condenses above boiling water as the hot vapor mixes with the cooler air. This mist consists of tiny droplets of liquid water. Pure steam emerges at the base of the spout of a steaming kettle where there is no visible vapor. Steam is said to be saturated if it is in equilibrium with liquid water. It is also said to be superheated if it exist at a temperature higher than its boiling point at a given pressure. For super heating to take place, one of the following two things must occur; either all the liquid water must have evaporated or in the case of steam generators (boilers) the saturated steam must be conveyed out of the steam drum before super heating can occur as steam cannot be super heated in the presence of liquid water. There are three stages of heating to convert liquid water to super heated steam. First, the enthalpy of water, liquid enthalpy or sensible heat, hf (i.e. the heat that can be measured with a thermometer) is raised. Then the latent heat (i.e. the heat that does not raise the temperature of a liquid) is added. After all of the liquid is taken from the steam drum, sensible heat is then added, super heating the steam. (Spirax Sarco website, 2009). 1.2 PROBLEM STATEMENT 6
To design and fabricate a mobile steam generator that (a) is less hazardous (in terms of surface temperature) (b) that can produce steam efficiently and effectively at a relatively low cost. 1.3 JUSTIFICATION Through history mankind has reached beyond the acceptable to pursue a challenge, achieving significant accomplishments and developing new technology. The desire to generate steam in demand sparked this revolution, and technical advances in steam generation allowed it to continue. However, in modern times steam generators (boilers) have had the challenge of immobility, size (requirement of large space for installation and operation) and cost (it is expensive to build). Therefore a system that takes all these limitations into account and provides a way of minimizing them is required. Thus the concept of this steam generator finds its roots. 1.4 OBJECTIVES The objectives of this project are: (a) To develop a system that produces steam efficiently by generating the heat required for the conversion of water to steam and minimize heat loss to the surrounding. (b) To make the system as cost effective as possible. (c) To develop a mobile steam generating plant that is compact and easy to adapt in the existing machinery arrangement. (d) To design a steam generator that is easy to operate.
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1.5
SCOPE AND LIMITATIONS
1.5.1 Scope The steam generator involves the design, fabrication and testing of a water tube boiler used to generate steam for various industrial and domestic applications. It involves cost analysis, modifications and the selection of suitable materials which fulfill the design requirements for the fabrication. It also covers the design description, analysis and calculations as well as the history of steam generation and applications. 1.5.2 Limitations/Constraints The limitations of the design include: (i)
Cost of materials: The most suitable material to be used for the fabrication of the steam generator shell, tank and chimney is stainless steel. However due to the cost of stainless steel, mild steel which also satisfies considerably the design requirement of the steam generator at a lower cost was selected.
(ii)
Cost of material handling: Due to the unavailability of a direct production line for the fabrication of the various parts, movement between factories was made to get the project completed. This increased the material handling cost.
(iii) Unavailability of required machinery for fabrication within the university. (iv) The pressure guage at the outlet of the steam generator needs a return valve to function as required this was not achieved due to cost.
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CHAPTER TWO 2.0
LITERATURE REVIEW Throughout history, mankind has reached beyond the acceptable to pursue a challenge, achieving significant accomplishments and developing new technology. This process is both scientific and creative. Entire civilizations, organizations, and most notably, individuals have succeeded by simply doing what has never been done before. A prime example is the safe and efficient use of steam. One of the most significant series of events shaping today’s world is the industrial revolution that began in the late seventeenth century. The desire to generate steam on demand sparked this revolution, and technical advances in steam generation allowed it to continue. Without these developments, the industrial revolution as we know it would not have taken place. It is therefore appropriate to say that few technologies developed through human ingenuity have done so much to advance mankind as the safe and dependable generation of steam.
2.1
THEORY OF PRODUCING STEAM Water and steam are typically used as heat carriers in heating systems. It is well known that water boils and evaporates at 100°C under atmospheric pressure. By higher pressure, water evaporates at higher temperature - e.g. a pressure of 10 bar equals an evaporation temperature of 184°C. During the evaporation process, pressure and temperature are constant, and a substantial amount of heat is use for bringing the water from liquid to vapor phase. When all the water is evaporated, the steam is called dry saturated. In this condition the steam contains a large amount of latent heat, corresponding to the heat that was led to the process under constant pressure and temperature. So despite temperature and pressure is the same for the liquid and the vapor, the amount of heat
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is much higher in vapor compare to the liquid. This latent heat in the dry saturated steam can efficiently be utilized to different processes requiring heat. (W.M Huitt, 2009). 2.1.1
Steam Saturation Curve The three phases of a particular substance can only coexist in equilibrium at a certain temperature and pressure, and this is known as its triple point. The triple point of H2O, where the three phases of ice, water and steam are in equilibrium, occurs at a temperature of 273.16 K and an absolute pressure of 0.006112 bar. This pressure is very close to a perfect vacuum. If the pressure is reduced further at this temperature, the ice, instead of melting, sublimates directly into steam. (Spirax Sarco website, 2009) As the temperature increases and the water approaches its boiling condition, some molecules attain enough kinetic energy to reach velocities that allow them to momentarily escape from the liquid into the space above the surface, before falling back into the liquid. Further heating causes greater excitation and the number of molecules with enough energy to leave the liquid increases. As the water is heated to its boiling point, bubbles of steam form within it and rise to break through the surface. Considering the molecular structure of liquids and vapours, it is logical that the density of steam is much less than that of water, because the steam molecules are further apart from one another. The space immediately above the water surface thus becomes filled with less dense steam molecules. When the number of molecules leaving the liquid surface is more than those re-entering, the water freely evaporates. At this point it has reached boiling point or its saturation temperature, as it is saturated with heat energy. If the pressure remains constant, adding more heat does not cause the temperature to rise any further but causes the water to form saturated steam. The temperature of the boiling water and saturated steam within the same system is the same, but the heat energy per unit mass is much greater in the steam. At atmospheric pressure the saturation temperature is 100°C. However, if the pressure is increased, 10
this will allow the addition of more heat and an increase in temperature without a change of phase. Therefore, increasing the pressure effectively increases both the enthalpy of water, and the saturation temperature. The relationship between the saturation temperature and the pressure is known as the steam saturation curve. (Spirax Sarco website, 2009)
Figure 2.1: steam saturation curve Source:http://www.spiraxsarco.com/resources/steam-engineering-principles-and-heattransfer/what-is-steam, 12th November, 2009. From figure 2.1, it can be seen that water and steam can coexist at any pressure on this curve, both being at the saturation temperature. Steam at a condition above the saturation curve is known as superheated steam:
Temperature above saturation temperature is called the degree of superheat of the steam.
Water at a condition below the curve is called sub-saturated water.
If the steam is able to flow from the boiler at the same rate that it is produced, the addition of further heat simply increases the rate of production. If the steam is restrained from leaving the boiler, and the heat input rate is maintained, the energy flowing into the boiler will be greater than the energy flowing out. This excess energy raises the pressure, in turn allowing the saturation temperature to rise, as the temperature of saturated steam correlates to its pressure.
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2.1.2
Enthalpy of Evaporation or Latent Heat (hfg) This is the amount of heat required to change the state of water at its boiling temperature, into steam. It involves no change in the temperature of the steam/water mixture, and all the energy is used to change the state from liquid (water) to vapour (saturated steam). The old term latent heat is based on the fact that although heat was added, there was no change in temperature. However, the accepted term is now enthalpy of evaporation. Like the phase change from ice to water, the process of evaporation is also reversible. The same amount of heat that produced the steam is released back to its surroundings during condensation, when steam meets any surface at a lower temperature. This may be considered as the useful portion of heat in the steam for heating purposes, as it is that portion of the total heat in the steam that is extracted when the steam condenses back to water. The total energy in saturated steam also known as enthalpy of saturated steam or total heat of saturated steam is given by:
hg = hf + hfg Where: hg = Total enthalpy of saturated steam (Total heat) (kJ/kg) hf = Liquid enthalpy (Sensible heat) (kJ/kg) hfg = Enthalpy of evaporation (Latent heat) (kJ/kg) The enthalpy (and other properties) of saturated steam can easily be referenced using the tabulated results of previous experiments, known as steam tables. (Gordon & Yon ,Engineering Thermodynamics 4th edition) 2.1.3 Dryness Fraction Steam with a temperature equal to the boiling point at that pressure is known as dry saturated steam. However, to produce 100% dry steam in an industrial boiler designed to produce saturated
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steam is rarely possible, and the steam will usually contain droplets of water. In practice, because of turbulence and splashing, as bubbles of steam break through the water surface, the steam space contains a mixture of water droplets and steam. Steam produced in any shell-type boiler, where the heat is supplied only to the water and where the steam remains in contact with the water surface, may typically contain around 5% water by mass. If the water content of the steam is 5% by mass, then the steam is said to be 95% dry and has a dryness fraction of 0.95. The actual enthalpy of evaporation of wet steam is the product of the dryness fraction ( ) and the specific enthalpy (hfg) from the steam tables. Wet steam will have lower usable heat energy than dry saturated steam. Actual enthalpy of evaporation = hfgx Therefore: Actual total enthalpy = hf + hfgx Because the specific volume of water is several orders of magnitude lower than that of steam, the droplets of water in wet steam will occupy negligible space. Therefore the specific volume of wet steam will be less than dry steam: Actual specific volume = vgx Where vg is the specific volume of dry saturated steam. (Gordon & Yon , Engineering Thermodynamics 4th edition, pg 174). 2.1.4
Steam Phase Diagram The data provided in the steam tables can also be expressed in a graphical form. Figure 1.2 illustrates the relationship between the enthalpy and temperature of the various states of water and steam; this is known as a phase diagram.
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Figure 2.2: Temperature enthalpy phase diagram Source : Young, Robert: “Timothy Hackworth and the Locomotive”; the Book guild Ltd, Lewes, U.K. (2000) (reprint of 1923 ed.) p.326 From figure 2.2, it can be seen that as water is heated from 0°C to its saturation temperature, its condition follows the saturated water line until it has received all of its liquid enthalpy, h f, (A B).If further heat continues to be added, the water changes phase to a water/vapour mixture and continues to increase in enthalpy while remaining at saturation temperature,hfg, (B - C). As the water/vapour mixture increases in dryness, its condition moves from the saturated liquid line to the saturated vapour line. Therefore at a point exactly halfway between these two states, the dryness fraction ( ) is 0.5. Similarly, on the saturated steam line the steam is 100% dry. Once it has received all of its enthalpy of evaporation, it reaches the saturated steam line. If it continues to be heated after this point, the pressure remains constant but the temperature of the steam will begin to rise as superheat is imparted (C - D).The saturated water and saturated steam lines enclose a region in which a water/vapour mixture exists - wet steam. In the region to the
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left of the saturated water line only water exists, and in the region to the right of the saturated steam line only superheated steam exists. The point at which the saturated water and saturated steam lines meet is known as the critical point. As the pressure increases towards the critical point the enthalpy of evaporation decreases, until it becomes zero at the critical point. This suggests that water changes directly into saturated steam at the critical point. Above the critical point the steam may be considered as a gas. The gaseous state is the most diffuse state in which the molecules have an almost unrestricted motion, and the volume increases without limit as the pressure is reduced. The critical point is the highest temperature at which water can exist. Any compression at constant temperature above the critical point will not produce a phase change. Compression at constant temperature below the critical point however, will result in liquefaction of the vapour as it passes from the superheated region into the wet steam region. The critical point occurs at 374.15°C and 221.2 bar for steam. Above this pressure the steam is termed supercritical and no well-defined boiling point applies. (Young, Robert: “Timothy Hackworth and the Locomotive”; the Book guild Ltd, Lewes, U.K. (2000) (reprint of 1923 ed.) 2.1.5
Water Hammer Water hammer is a liquid shock wave resulting from the sudden starting or stopping of flow. As steam begins to condense due to heat losses in the pipe, the condensate forms droplets on the inside of the walls. As they are swept along in the steam flow, they then merge into a film. The condensate then gravitates towards the bottom of the pipe, where the film begins to increase in thickness. The build up of droplets of condensate along a length of steam pipework can eventually form a slug of water which will be carried at steam velocity along the pipework. This slug of water is dense and incompressible, and when travelling at high velocity, has a considerable amount of kinetic energy. The laws of thermodynamics state that energy cannot be 15
created or destroyed, but simply converted into a different form. When obstructed, perhaps by a bend or tee in the pipe, the kinetic energy of the water is converted into pressure energy and a pressure shock is applied to the obstruction. Water hammer can significantly reduce the life of pipeline ancillaries. In severe cases the fitting may fracture with an almost explosive effect. The consequence may be the loss of live steam at the fracture, creating a hazardous situation. Water hammer is affected by the initial system pressure, the density of the fluid, the speed of sound in the fluid, the elasticity of the fluid and pipe, the change in velocity of the fluid, the diameter and thickness of the pipe, and the valve operating time. 2.1.6
Cavitation This is the formation of vapour bubbles and their subsequent collapse.
2.1.7
Steam Hammer Steam hammer is similar to water hammer except it is for a steam system. Steam hammer is a gaseous shock wave resulting from the sudden starting or stopping of flow. Steam hammer is not as severe as water hammer for three reasons: 1. The compressibility of the steam dampens the shock wave 2. The speed of sound in steam is approximately one third the speed of sound in water. 3. The density of steam is approximately 1600 times less than that of water. The items of concern that deal with steam piping are thermal shock and water slugs (i.e. Condensation in the steam system) as a result of improper warm up.
2.2
CONCEPT OF A STEAM GENERATOR A steam generator is a device used to produce steam by applying heat energy to water. This is done by heating up water to a particular temperature at specific pressure for the purpose of doing work. The primary features of a steam generator include; burners, boilers, fuel tank, chimney,
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pump, Electric panel, pressure Gauge, valves and other control devices (e.g. thermostat, thermometers e.t.c.). Steam generators are used to harness energy used as heat in a wide variety of processes and convert it into a form which is more useful, such as mechanical and electrical energy. The heat used is typically produced intentionally for the production of electricity or is captured as a byproduct of some other industrial process. The heating liquid is directed into many small pipes to increase its surface contact with the water and facilitate rapid heat and steam production. 2.3
STEAM GENERATOR VERSUS STEAM BOILER The steam boiler or steam generator is connected to the consumers through the steam and condensate piping. When the steam is provided to the consumers, it condenses. It can then be returned to the feed water tank, from where it again is pumped to the steam boiler / steam generator. It often happens that the condensate is not fully or partly recycled, and then a make-up of fresh and pre-treated feed water is established. Opposite the principle of the steam boilers, the water in the steam generators evaporates inside the tube winded up into serial connected tube coils. The feed water is heated up to the evaporation temperature and then evaporated. The intensity of the heat, the feed water flow and the size/length of the tube are adapted, so that the water is exactly fully evaporated at the exit of the tube. This ensures a very small water and steam volume (content of the pressure vessel). Thus there are no buffers in a steam generator, and it is temporary overloaded i.e. beyond its nominal steam capacity, a separate buffer tank should be provided (accessories), (www.ttboilers.com, 2009). The advantages using a steam generator compare to conventional steam boilers:
Easy to operate - normally no requirement for boiler authorization
Rapid start-up and establishing full steam pressure 17
2.4
Compact and easy to adapt in the existing machinery arrangement
Price attractive - especially at low steam rates.
STEAM GENERATOR DESIGN Steam generators can be delivered in horizontal execution (with low height), or in vertical execution (occupying limited floor space). Like the steam boilers they are delivered insulated with stainless steel cover sheets and complete with burner, armatures, instrumentation, safeties and a control panel. The steam generators heaters are made with coils made of seamless tubes, where the feed water is preheated and evaporated during the flow through these. The heat is transferred to the water/steam mixture as radiant heat in the combustion chamber to the coils made of steam tubes. (Wikipedia encyclopedia, 2010).
2.5
BASIC FEATURES OF A STEAM GENERATOR
(a) Burner A Burner is the device responsible for:
Proper mixing of fuel and air in the correct proportions, for efficient and complete combustion.
Determining the shape and direction of the flame.
Heat is produced and maintained using burners. Fuel is supplied to the burner in an atomized form and upon ignition, the burner supplies heat to the boilers. The flame is sustained by the constant supply of the fuel. The type of burner used in a steam generator is determined by the type of fuel to be used by the steam generator. An important function of burners is turndown. This is usually expressed as a ratio and is based on the maximum firing rate divided by the minimum controllable firing rate. (Spirax Sarco website, 2009) 18
(b)
Boiler A boiler is a closed vessel in which water or other fluid is heated or vaporized fluid exits the boiler for use in various processes or heating applications. When selecting a boiler the different flame temperatures and combustion characteristics of different fuels should be taking into consideration (i.e. decision on the type of fuel to be used must be made before selecting a boiler). (Spirax Sarco website, 2009) For example:
Oil produces a luminous flame, and a large proportion of the heat is transferred by radiation within the furnace.
Gas produces a transparent blue flame, and a lower proportion of heat is transferred by radiation within the furnace.
The objectives of a boiler are:
To release the energy in the fuel as efficiently as possible.
To transfer the released energy to the water, and to generate steam as efficiently as possible.
To separate the steam from the water ready for export to the plant, where the energy can be transferred to the process as efficiently as possible. (Spirax Sarco website, 2009)
A number of different boiler types have been developed to suit the various steam applications. Boilers are of various types which include: Cochran boiler, Hydronic boilers, Benson boilers (supercritical steam generators).Babcock and Wilcox boilers, fire tube boilers, water tube boilers e.t.c. (c)
Boiler turndown: The turndown rate is not simply a matter of forcing differing amounts of fuel into a boiler, it is increasingly important from an economic and legislative perspective that the
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burner provides efficient and proper combustion, and satisfies increasingly stringent emission regulations over its entire operating range. (Spirax Sarco website, 2009) Types of burners include: Oil burners, pressure jet burners, Gas burners, rotary cup burners, dual fuel burners. 2.6
STEAM AS A RESOURCE In 200 B.C., a Greek named Hero designed a simple machine that used steam as a power source. He began with a cauldron of water, placed above an open fire. As the fire heated the cauldron, the cauldron shell transferred the heat to the water. When the water reached the boiling point of 212oF (100oC), it changed form and turned into steam. The steam passed through two pipes into a hollow sphere, which was pivoted at both sides. As the steam escaped through two tubes attached to the sphere, each bent at an angle, the sphere moved, rotating on its axis. Hero, a mathematician and scientist, labeled the device aeolipile, meaning rotary steam engine.
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Although the invention was only a novelty and he made no suggestion for its use, the idea of generating steam to do useful work was born. Even today, the basic idea has remained to generate heat, transfer the heat to water, and produce steam. Intimately related to steam generation is the steam turbine, a device that changes the energy of steam into mechanical work. In the early 1600s, an Italian named Giovanni Branca produced a unique invention (Image shown in figure 2.3). He first produced steam, based on Hero’s aeolipile. By channeling the steam to a wheel that rotated, the steam pressure caused the wheel to turn. Thus began the development of the steam turbine. The primary use of steam turbines today is for electric power production. In one of the most complex systems ever designed by mankind, superheated high pressure steam is produced in a boiler and channeled to turbine-generators to produce electricity.
Figure 2.3: the picture of Giovanni Branca’s steam turbine Source: Wikipedia encyclopedia, 2010 2.7
DEVELOPMENT FROM STEAM ENGINES Thomas Savery (1650-1715) Thomas Savery was an English military engineer and inventor who in 1698 patented the first crude steam engine, based on Denis Papin's Digester or pressure cooker of 1679. 21
Thomas Savery had been working on solving the problem of pumping water out of coal mines, his machine consisted of a closed vessel filled with water into which steam under pressure was introduced. This forced the water upwards and out of the mine shaft. Then a cold water sprinkler was used to condense the steam. This created a vacuum which sucked more water out of the mine shaft through a bottom valve. The image of Savery’s crude steam engine is shown in figure 2.4. Thomas Savery later worked with Thomas Newcomen on the atmospheric steam engine. Among Savery's other inventions was an odometer for ships, a device that measured distance traveled. (About.com: Inventors, 2009)
Figure 242: picture of Thomas Savery crude steam engine Source: (About.com: Inventors, 2009) Thomas Newcomen (1663-1729) Thomas Newcomen was an English blacksmith, who invented the atmospheric steam engine, an improvement over Thomas Slavery's previous design.
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The Newcomen steam engine used the force of atmospheric pressure to do the work. Thomas Newcomen's engine pumped steam into a cylinder. The steam was then condensed by cold water which created a vacuum on the inside of the cylinder. The resulting atmospheric pressure operated a piston, creating downward strokes. In Newcomen's engine the intensity of pressure was not limited by the pressure of the steam, unlike what Thomas Savery had patented in 1698. In 1712, Thomas Newcomen together with John Calley built their first engine on top of a water filled mine shaft and used it to pump water out of the mine. The image of Newcomen’s steam engine is shown in figure 2.5. The Newcomen engine was the predecessor to the Watt engine and it was one of the most interesting pieces of technology developed during the 1700's. (About.com: Inventors, 2009)
Figure 2.5: picture of Newcomen’s steam engine Source: (About.com: Inventors, 2009) James Watt (1736-1819) James Watt was a Scottish inventor and mechanical engineer, born in Greenock, who was renowned for his improvements of the steam engine. In 1765, James Watt while working for the
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University of Glasgow was assigned the task of repairing a Newcomen engine, which was deemed inefficient but the best steam engine of its time. That started the inventor to work on several improvements to Newcomen's design. Most notable was Watt's 1769 patent for a separate condenser connected to a cylinder by a valve. Unlike Newcomen's engine, Watt's design had a condenser that could be cool while the cylinder was hot. Watt's engine soon became the dominant design for all modern steam engines and helped bring about the Industrial Revolution. Figure 2.6 shows the picture of James Watt Steam engine.
Figure 2.6: picture of James Watt Steam Engine Source: (About.com: Inventors, 2009) A unit of power called the Watt was named after James Watt. The Watt symbol is W and it is equal to 1/746 of a horsepower, or one Volt times one Amp. (About.com: Inventors, 2009) 2.8 2.8.1
DEVELOPMENT OF BOILER TYPES Fire-tube boiler
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Haycock and wagon top boilers For the first Newcomen engine of 1712, the boiler was little more than large brewer’s kettle installed beneath the power cylinder. Because the engine’s power was derived from the vacuum produced by condensation of the steam, the requirement was for large volumes of steam at very low pressure hardly more than 1 psi (6.9 kPa) The whole boiler was set into brickwork which retained some heat. A voluminous coal fire was lit on a grate beneath the slightly dished pan which gave a very small heating surface; there was therefore a great deal of heat wasted up the chimney. In later models, notably by John Smeaton, heating surface was considerably increased by making the gases heat the boiler sides, passing through a flue. Smeaton further lengthened the path of the gases by means of a spiral labyrinth flue beneath the boiler. These under-fired boilers were used in various forms throughout the 18th Century. Some were of round section (haycock). A longer version on a rectangular plan was developed around 1775 by Boulton and Watt (wagon top boiler). This is what is today known as a three-pass boiler, the fire heating the underside, the gases then passing through a central square-section tubular flue and finally around the boiler sides. Figure 2.7 shows the picture a fire tube boiler
Figure 2.7: a fire tube boiler
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Source: Wikipedia encyclopedia, 2010 Cylindrical fire-tube boiler An early proponent of the cylindrical form, was the American engineer, Oliver Evans who rightly recognised that the cylindrical form was the best from the point of view of mechanical resistance and towards the end of the 18th Century began to incorporate it into his projects. Probably inspired by the writings on Leupold’s “high-pressure” engine scheme that appeared in encyclopaedic works from 1725, Evans favoured “strong steam” i.e. non condensing engines in which the steam pressure alone drove the piston and was then exhausted to atmosphere. The advantage of strong steam as he saw it was that more work could be done by smaller volumes of steam; this enabled all the components to be reduced in size and engines could be adapted to transport and small installations. To this end he developed a long cylindrical wrought iron horizontal boiler into which was incorporated a single fire tube, at one end of which was placed the fire grate. The gas flow was then reversed into a passage or flue beneath the boiler barrel, then divided to return through side flues to join again at the chimney (Columbian engine boiler). Evans incorporated his cylindrical boiler into several engines, both stationary and mobile. Due to space and weight considerations the latter were one-pass exhausting directly from fire tube to chimney. Another proponent of “strong steam” at that time was the Cornishman, Richard Trevithick. His boilers worked at 40-50 psi (276-345 kPa) and were at first of hemispherical then cylindrical form. From 1804 onwards Trevithick produced a small two-pass or return flue boiler for semi-portable and locomotive engines. The Cornish boiler developed around 1812 by Richard Trevithick was both stronger and more efficient than the simple boilers which preceded it. It consisted of a cylindrical water tank around 27 feet (8.2 m) long and 7 feet (2.1 m) in diameter, and had a coal fire grate placed at one end of a single cylindrical tube about three feet
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wide which passed longitudinally inside the tank. The fire was tended from one end and the hot gases from it travelled along the tube and out of the other end, to be circulated back along flues running along the outside then a third time beneath the boiler barrel before being expelled into a chimney. This was later improved upon by another 3-pass boiler, the Lancashire boiler which had a pair of furnaces in separate tubes side-by-side. This was an important improvement since each furnace could be stoked at different times, allowing one to be cleaned while the other was operating. Railway locomotive boilers were usually of the 1-pass type, although in early days, 2pass "return flue" boilers were common, especially with locomotives built by Timothy Hackworth. 2.8.2
Multi-tube boilers A significant step forward came in France in 1828 when Marc Seguin devised a two-pass boiler of which the second pass was formed by a bundle of multiple tubes. A similar design with natural induction used for marine purposes was the popular “Scotch” marine boiler. Prior to the Rainhill trials of 1829 Henry Booth, treasurer of the Liverpool and Manchester Railway suggested to George Stephenson, a scheme for a multi-tube one-pass horizontal boiler made up of two units: a firebox surrounded by water spaces and a boiler barrel consisting of two telescopic rings inside which were mounted 25 copper tubes; the tube bundle occupied much of the water space in the barrel and vastly improved heat transfer. Old George immediately communicated the scheme to his son Robert and this was the boiler used on Stephenson’s Rocket, outright winner of the trial. The design was and formed the basis for all subsequent Stephensonian-built locomotives, being immediately taken up by other constructors; this pattern of fire-tube boiler has been built ever since.
2.8.3
Water-tube Boilers
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Combined heat and power (CHP) plant Water-tube boilers differ from shell type boilers in that the water is circulated inside the tubes, with the heat source surrounding them, because the tube diameter is significantly smaller, much higher pressures can be tolerated for the same stress. Water-tube boilers are used in power station applications that require:
A high steam output (up to 500 kg/s).
High pressure steam (up to 160 bar).
Superheated steam (up to 550°C).
However, water-tube boilers are also manufactured in sizes to compete with shell boilers. Small water-tube boilers may be manufactured and assembled into a single unit, just like packaged shell boilers, whereas large units are usually manufactured in sections for assembly on site. However, when the pressure in the water-tube boiler is increased, the difference between the densities of the water and saturated steam falls, consequently less circulation occurs. To keep the same level of steam output at higher design pressures, the distance between the lower drum and the steam drum must be increased, or some means of forced circulation must be introduced. Figure 2.8 shows the picture of a Babcock and Wilcox water tube boiler.
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Figure 2.8: Babcock and Wilcox water tube boiler with longitudinal steam drum Source: Wikipedia encyclopedia, 2010 Water-tube boiler sections The energy from the heat source may be extracted as either radiant or convection and conduction. (a)
The furnace or radiant section: This is an open area accommodating the flame(s) from the burner(s). If the flames were allowed to come into contact with the boiler tubes, serious erosion and finally tube failure would occur. The walls of the furnace section are lined with finned tubes called membrane panels, which are designed to absorb the radiant heat from the flame.
(b)
Convection section: This part is designed to absorb the heat from the hot gases by conduction and convection. Large boilers may have several tube banks (also called pendants) in series, in order to gain maximum energy from the hot gases. Alternative water-tube boiler layouts The following layouts work on the same principles as other water-tube boilers, and are available with capacities from 5000 kg/h to 180000 kg/h.
(a)
Longitudinal drum boiler: The longitudinal drum boiler was the original type of water-tube boiler that operated on the thermo-siphon principle. Cooler feed water is fed into a drum, which is placed longitudinally above the heat source. The cooler water falls down a rear circulation header into several inclined heated tubes. As the water temperature increases as it passes up through the inclined tubes, it boils and its density decreases, therefore circulating hot water and steam up the inclined tubes into the front circulation header which feeds back to the drum. In the drum, the steam bubbles separate from the water and the steam can be taken off. Typical capacities for longitudinal drum boilers range from 2250 kg/h to 36000 kg/h.
29
(b)
Cross drum boiler: The cross drum boiler is a variant of the longitudinal drum boiler in that the drum is placed cross ways to the heat source. The cross drum operates on the same principle as the longitudinal drum except that it achieves a more uniform temperature across the drum. However it does risk damage due to faulty circulation at high steam loads; if the upper tubes become dry, they can overheat and eventually fail. The cross drum boiler also has the added advantage of being able to serve a larger number of inclined tubes due to its cross ways position. Typical capacities for a cross drum boiler range from 700 kg/ h to 240000 kg/h. Advantages of water-tube boilers:
They have small water content, and therefore respond rapidly to load change and heat input.
The small diameter tubes and steam drum mean that much higher steam pressures can be tolerated, and up to 160 bar may be used in power stations.
The design may include many burners in any of the walls, giving horizontal, or vertical firing options, and the facility of control of temperature in various parts of the boiler. This is particularly important if the boiler has an integral superheater, and the temperature of the superheated steam needs to be controlled. Disadvantages of water-tube boilers:
They are not as simple to make in the packaged form as shell boilers, which mean that more work is required on site.
The option of multiple burners may give flexibility, but the 30 or more burners used in power stations means that complex control systems are necessary.
2.8.4
Bent tube or Stirling boiler
30
A further development of the water-tube boiler is the bent tube or Stirling boiler. Again this operates on the principle of the temperature and density of water, but utilises four drums in the following configuration. Cooler feedwater enters the left upper drum, where it falls due to greater density, towards the lower, or water drum. The water within the water drum, and the connecting pipes to the other two upper drums, are heated, and the steam bubbles produced rise into the upper drums where the steam is then taken off. The bent tube or Stirling boiler allows for a large surface heat transfer area, as well as promoting natural water circulation. Figure 2.9 shows a Stirling water tube boiler with four cross-drums.
Figure 2.9: Stirling water tube boiler with four cross-drums Source: Wikipedia encyclopedia, 2010 2.9
STRUCTURAL RESISTANCE The 1712 boiler was assembled from riveted copper plates with a domed top made of lead in the first examples. Later boilers were made of small wrought iron plates riveted together. The problem was producing big enough plates, so that even pressures of around 50 psi (344.7 kPa) were not absolutely safe, nor was the cast iron hemispherical boiler initially used by Richard Trevithick. This construction with small plates persisted until the 1820s, when larger plates
31
became feasible and could be rolled into a cylindrical form with just one butt-jointed seam reinforced by a gusset; (Timothy Hackworth's Sans Pareil) 11 of 1849 had a longitudinal welded seam. Welded construction for locomotive boilers was extremely slow to take hold. Once-through monotubular water tube boilers as used by Doble, Lamont and Pritchard are capable of withstanding considerable pressure and of releasing it without danger of explosions. These Inventions lead to the development of boilers/steam generators which are used extensively for domestic and industrial applications. (Wikipedia encyclopedia, 2009).
32
2.10 FUNCTIONS AND USES OF A STEAM GENERATOR The main application of steam can be roughly divided into heating/humidifying applications and motive/drive applications as shown in figure 2.10.
Figure 2.10: Distribution of various types of steam Source: http://www.tlv.com/global/TI/steam-theory/types-of-steam.html, 12th Nov, 2009. However the general uses of steam generators includes: 1. Steam is used for energy storage, which is introduced and extracted by heat transfer, usually through pipes. Steam is a capacious reservoir for thermal energy because of water’s high heat of vaporizations. 2. Steam is used in the generation of electricity. In most countries, about 86% of electric power is produced using steam as the working fluid. 3. In cogeneration steam is typically condensed at the end of its expansion cycle and returned to the boiler for reuse. However in cogeneration, Steam is piped into buildings to provide heat energy after it is used in the electricity generator cycle.
33
4. Steam is used for sterilization. Autoclaves, which use steam under pressure is used in microbiology laboratories and similar environments for sterilization. 5. Steam is used in agriculture for soil sterilization to avoid the use of harmful chemical agents and increase the soil health. 6. Steam is also used for domestic purposes like cooking of vegetables, steam cleaning of fabrics and carpet and heating of buildings. 7. In industries, a steam engine uses the expansion of steam in order to drive a piston or a turbine to perform mechanical work. In each case, water is heated in a boiler and the steam carries the energy to the target object (i.e. the point of application).
Figure 2.11: Type of steam generator used in a Coal-fired Power Plant Source: Milton Beychok, 2009 Figure 2.11 gives an illustration of the system and mode of operation of a steam generator used in a coal fired power plant. The source of heat energy is pulverized coal which is supplied to the
34
boiler through a coal air mixer. The superheated steam produced is used to drive a turbine for the production of electricity. (Milton Beychok, 2009).
35
CHAPTER THREE 3.0
DESIGN ANALYSIS, CALCULATIONS AND MATERIAL SELECTION
3.1
DESIGN ANALYSIS
3.1.1 Mode of Operation With the fuel (diesel) in the tank, the switch on the panel is turned on to power the burner. The pressure pump is then turned on to pump the water from its source via a hose into the steam pipe in the combustion chamber of the boiler. As the water flows through the coils of the steam pipe, the flame from the burner heats up the water in the steam pipe coils converting the water to steam before it gets to the outlet. The pressure gauge connected to the outlet reads the pressure value of the steam. The valve at the outlet is then turned on to expel the steam for use. The fumes in the combustion chamber is been expelled through the chimney simultaneously as the steam is expelled. A thermostat in the panel regulates the temperature of the boiler. When the heat in the boiler exceeds the required temperature, the burner trips off and if the temperature required is too low to produce the desired heating effect, the burner turns on. 3.1.2 Features of the Steam Generator, their uses and method of Fabrication (i) Chimney: the chimney is that component/feature which serves as a tunnel for expelling the burnt gases which is a product of combustion. The chimney is fabricated using mild steel and is bolted together (as shown in fig 3.1). The height of the chimney is 1230mm above the level of its fixture and 1970mm above normal ground level. It has a thickness of 2mm. This height is chosen because some gases which are denser than air would be inhaled if it is not made above the height of an average person. Figure 3.1 shows the AUTOCAD drawing of the chimney.
36
Figure 3.1: Chimney and the chimney cap Source: Self (ii) Fuel Tank: the fuel tank is the enclosure which stores the fuel and supplies it for combustion. The type of fuel used for the steam generator is diesel. The fuel tank is fabricated using mild steel. The type of joining process used in its fabrication is welding. The dimension of the fuel tank is given by 750 × 400 ×160mm. The volume of the tank is 0.048m3(48litres). Figure 3.2 shows the AUTOCAD drawing of the fuel tank.
37
Figure 3.2: Fuel tank Source: Self (iii) Castor wheels (Tyres): the tyres are attached below the frame of the steam generator to aid its mobility. The rear tyres are fixed while the front tyres are not fixed (i.e. can rotate at 3600 about their pivot). Figure 3.3 shows a picture of a castor wheel.
Figure 3.3: Castor Wheel Source: self (iv) Burner: the burner provides the required heat through flame when it is put on. The Air-Fuel ratio can be adjusted as desired from the burner panel. The burner has two electrical wires which are connected to the panel and two hose which is fixed to the fuel tank. One of the hose which is connected close to the base of the tank serves as the inlet through which the fuel required to be
38
burnt enters the burner while the second hose which is connected closer to the top of the fuel tank serves as the return hose through which gases or excess fuel returns to the fuel tank. The product name and model of the burner used is Elco Econom 2000. Some of the features of the burner (Elco Econom 2000) includes: Support plate of components removable for maintenance, adjustment of air on pressure side, 2800 rpm motor, single – phase power supply 230v/50Hz/3A, flame control by removable photo resistive cell, removable protective hood, power of 60 to 350 kW, fully automated blown-air burners, low level noise and the element and internal parts are easily accessible without prior removal of the fuel piping, simply by turning round the support plate of the components. Figure 3.4 shows the picture of the burner.
Figure 3.4: Elco Econom 2000 Burner Source: Self (v) Pressure gauge: the pressure gauge is located at the steam pipe outlet. It is used to measure the pressure at which the steam flows out of the boiler. It is calibrated from 0 to 4 bars. It aids in the investigation of the steam flow characteristics (flow rate, volume, etc). Figure 3.5 shows a schematic diagram of a pressure guage.
39
Figure 3.5: a schematic diagram of a pressure guage Source: DOE fundamentals handbook; instrumentation & control, volume 1 & 2. (vi) Outer Shell: the outer shell serves as housing for the inner shell and the coiled steam pipe. It is made of mild steel. It is cylindrical in shape having a diameter of 380mm, height of 800mm, and a thickness of 2mm. It comprises of coils and an inner shell. With laggings located in between the outer and inner shells. It is covered at both ends with shell covers (dome shaped plates). The method of fabrication involved rolling of a flat mild steel sheet of 1194 X 800mm. After the rolling operation was carried out; the ends of the rolled mild steel sheet were tacked and then, welded. The shell covers were then attached to the ends of the cylinder and welded. Openings (cutout) were then made for the chimney steam pipe inlet and outlet. Figure 3.6 shows the AUTOCAD drawing of the outer shell.
40
Figure 3.6: a wireframe model of the outer shell Source: Self (vii) Inner shell: the material used for the inner shell is mild steel. It is cylindrical in shape having a diameter of 330mm, height of 650mm and a thickness of 2mm. It comprises of coils to form the boiler. It is covered at both ends with shell covers. The coils are tacked to the body of the inner shell using small mild steel pieces. The inner shell serves as the combustion chamber. The method of fabrication involves rolling of a flat mild steel sheet of 1068 X 650mm. After the rolling operation was carried out, the ends of the rolled mild steel sheet were tacked and welded. The shell covers were then attached to the ends of the rolled mild steel sheet and welded. Openings (cutouts) were made for the chimney, steam pipe outlet and inlet. Figure 3.7 shows the AUTOCAD drawing of the inner shell.
Figure 3.7: a wireframe model of the inner shell Source: Self (viii) Shell covers: they are used to cover the internal and external shell respectively. They are made of mild steel and are dome shaped. The larger shell covers have a diameter of 380mm, a thickness of 2mm and a depth of 330mm. The smaller shell covers have diameter of 330mm, a thickness of 2mm and a depth of 39mm.
41
They are fabricated through presswork using a disher (die). At one of the ends of the cylinder circular openings are made on the shell covers through which the burner nozzles fit-in into the combustion chamber. The shell covers are welded to their respective cylinders. Figure 3.8 shows the AUTOCAD drawings of the shell covers.
330
(a)
(b) Figure 3.8: (a) orthographic representation of the inner shell cover (b) orthographic representation of the outer shell cover Source: Self (ix) Steam pipe: The steam pipe serves as the passage and an enclosure where the water passes and transforms to steam on the application of heat (i.e. the water passed from the input hose goes through the steam pipe forming vapour and then steam as it proceeds through the steam pipe, to give out steam from the outlet hose). The steam pipe is made of alloy steel usually with a composition 2.25%Cr; 1%Mo and 0.16–0.29% carbon. It is popularly known as steam steel pipe. It has a thickness of 6mm with an internal and external diameter of 25mm and 19mm
42
respectively. The entire length of the steam pipe used is 11000mm (11m). The coil diameter is 260mm measured from the external surface. The steam pipes were shaped to the coil-liked shape through cold-working by placing it in a cylindrical die to form the required shape. The steam pipes were cut to a length of 810mm (approximately 0.8m) before they are coiled. The individual coils were then joined together through welding at the required joints. The coiled steam pipes are layed horizontally in the inner cylindrical shell. Figure 3.9 shows the picture of a section of the steam pipe coiling.
Figure 3.9: Steam Pipe Coiling Source: Self (x) Pressure pump: the pressure pump used is katcher 201. The pressure pump is used to pump the water at the required pressure to the steam pipe through a hose. The pump used delivers a maximum pressure of 100 bars. The pump is detachable and consists of the following features:
The start/stop knob for its operation.
Two openings for the inlet and outlet.
A wire for the power source.
A hose (Dirt blaster lance) for expelling dirt and impurities in the water.
This pressure pump offers up to 100bar maximum pressure with 360 litres per hour. Its universal motor has a power rating of 1600 watt. The K201 is supplied with a dirt blaster lance, which increases the machines performance by 50% and is ideal for removing moss and algae from patios and walls. The machines detergent suction tube enables detergent to be applied via the
43
machines low-pressure nozzle to aid cleaning results. Figure 3.10 shows the picture of a pressure pump.
Figure 3.10: Karcher 201 Pressure Pump Source: Self (xi) Electrical Control Panel: all electrical interactions and connectivity are sourced to the panel. The panel consists of the series of parts on the board for electrical wirings and interaction. Also incorporated on the panel is a digital thermometer which senses and displays the temperature in the combustion chamber. A thermostat is also incorporated in the combustion chamber to detect and trip off the burner if a temperature of about 550oC is reached during dry boiling conditions (i.e. when the generator is in operation with no water fed in through the steam pipe). Figure 3.11 shows the picture of the digital panel. Digital Display
Digital Indicator
Sensor
Figure 3.11: Digital Panel Source: Self
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(xii) Steam generator Handle: the material used for the steam generator handle is mild steel. The handle is used to aid easy movement and mobility of the steam generator within the factory complex. It is fabricated through bending using the bending machine. It was then welded to the fuel tank. (xiii) Rockwool: It is also known as stone wool. It serves as the material used for thermal insulation in the steam generator (to minimize heat loss). Stone wool is a furnace product of molten rock at a temperature of about 1600 °C, through which a stream of air or steam is blown. More advanced production techniques are based on spinning molten rock on high speed spinning wheels somewhat like the process used to prepare cotton candy. The final product is a mass of fine, intertwined fibres with a typical diameter of 6 to 10 micrometers. Mineral wool may contain a binder, often food grade starch, and an oil to reduce dusting. Figure 3.12 shows the picture of rock wool insulation.
Figure 3.12: Rockwool Source: Wikipedia encyclopedia, 2010 (ix) Angled Iron (bar): the angled bars are provided to serve as support for the shells. It is positioned between the outer shell and the fuel tank. It is made of mild steel and one end of the
45
bar is cut to a chordal shape corresponding to the radius of the outer shell to allow the outer shell to sit conveniently on the angled bars. 3.1.3
Design Considerations The major objective of the system (steam generator) is to be able to generate the heat required for the conversion of water to steam and minimize heat loss to the surrounding and dispose of the exhaust fumes after utilization. The design requirements for the steam generating plant include:
The air-fuel ratio should be sufficient enough to supply the required heat during combustion for the conversion of water to steam.
Pressure pump to pump water into the stem pipe in the boiler.
The digital panel should provide the temperature at various instant during the system operation.
The fuel level indicator should provide an approximate volume of fuel in the fuel tank.
46
Figure 3.13: A 2D representation of the steam generator Source: Self The Figure 3.13 shows the AUTOCAD drawing of the steam generator and its components. The direction of the arrows shows the direction of movement of the item concerned. 3.1.4 Specifications
Burner Specification Name: Elco Econom 2000 Speed of motor: 2800 rpm, single – phase power supply 230v/50Hz/3A Power Rating: 60 to 350 kW
Pressure Pump Name and Model: Karcher 201 Maximum Pressure: 100 bar Volumetric flow rate: 310 litres per hour flow Motor Power: 1600 Watts
Fuel Tank Dimension: 750 × 400 ×160mm Volume: 48 litres
Chimney Dimension: 120 × 250 × 1230mm
Steam Pipe Number of turns of the steam pipe (coiling): 12 Length: 11000mm Thickness: 6mm 47
Internal diameter: 19mm Volume of fluid in the steam pipe: 3.5 litres (0.0035m3)
3.2
Flow rate: 0.0035m3/s
Voltage Rating: 220/240V
CALCULATIONS
3.2.1 Formulae and Equations Flow rate (Q): this defined as the quantity of a liquid flowing per second through a section of a pipe or channel. It is generally denoted by Q. mathematically, it is expressed as; Q = Area × Velocity Q = AV or Q = Volume per unit time = Where, A = Cross-sectional area of the pipe V = Average velocity of the fluid V
= Volume of the liquid flow through the pipe
In the design of the steam generator, the flow rate is gotten as: Q=
V t
But v = volume of liquid flowing through the pipe = πr2h Where, r = internal radius of the steam pipe h = length of the steam pipe Heat loss during conduction and convection (q) 48
V t
𝒅𝑸 𝒅𝒕
For steady heat transfer
𝒒𝒌 = - KA
𝒅𝑻 𝒅𝒓
𝒅𝑸 𝒅𝒕
=
𝒕𝒆𝒎𝒑𝒆𝒓𝒂𝒕𝒖𝒓𝒆 𝒅𝒊𝒇𝒇𝒆𝒓𝒆𝒏𝒄𝒆 𝒓𝒆𝒔𝒊𝒔𝒕𝒂𝒏𝒄𝒆
= 𝒒𝒌 which is a constant. The rate of heat conduction is given by:
................................................................................................................ (equation 1)
where K = thermal conductivity A = area (for a cylinder, A = 2πrl) Considering a hollow cylinder as shown in figure 3.14 Where ri = inner radius ro = outer radius Ti = internal temperature
ri
ro
To = external temperature
𝑞𝑘 dr = -KAdT Figure 3.14
𝑞𝑘 dr = -2πrlKdT 𝑟 𝑑𝑟
𝑞𝑘 ∫𝑟 𝑜 𝑖
𝑇
= -2πlK∫𝑇 𝑜 𝑑𝑇 𝑟 𝑖
𝑟
𝑞𝑘 In 𝑜 = -2πlK(To - Ti) 𝑟𝑖 𝑟
𝑞𝑘 In 𝑜= 2πlK(Ti -To) 𝑟𝑖
𝑞𝑘 =
2𝜋𝑙𝐾(𝑇𝑖 −𝑇𝑜 ) 𝑟 𝐼𝑛 𝑜 𝑟𝑖
=
𝑇𝑖 −𝑇𝑜 1 𝑟 𝐼𝑛 𝑜 2𝜋𝑙𝐾 𝑟𝑖
49
1
𝑟𝑜
Where 2𝜋𝑙𝐾 𝐼𝑛
𝑟𝑖
represents the resistance.
To find the heat loss of the concentric cylinders taking into consideration the insulation used, we solve as follows making reference to the cylindrical section of the shells as shown in figure 3.15 Where ri = radius of the inner shell r1 = ri + thickness of the insulation material r2 = radius of the outer shell
r2
T1 = temperature at the surface of the inner shell
r1 T2 = temperature at the surface of the rockwool insulation
ri
T3 = temperature at the surface of the outer shell To = temperature of the surrounding
Figure 3.15 For the inner part, the heat transfer is through convection and is given by:
𝑞𝑐 = hiAi(Ti – T1) =
=
𝑇𝑖 – 𝑇1 1 2𝜋𝑟𝑖 𝑙ℎ𝑖
𝑇𝑖 – 𝑇1 1 ℎ𝑖 𝐴𝑖
……………………………………………………………………equation 2
After the inner section the heat is transferred via conduction and is given by;
𝑞𝑘1 =
𝑞𝑘2 =
𝑇1 – 𝑇2 1 𝑟 𝐼𝑛 1 2𝜋𝑙𝐾1 𝑟𝑖
𝑇2 – 𝑇3 1 𝑟 𝐼𝑛 2 2𝜋𝑙𝐾2 𝑟1
………………………………………….…….………………equation 3
……………………………………………………….............equation 4
the final heat transfer on the outside is through convection and is given by;
50
𝑞𝑐 = hoAo(T3– To) =
=
𝑇3 – 𝑇𝑜
𝑇3 – 𝑇𝑜 1 ℎ𝑜 𝐴 𝑜
…………………………………………………...………………………equation 5
1 2𝜋𝑟2 𝑙ℎ𝑜
Making the temperature difference the subject of the formula in equations 2 to 5 gives: 𝑞
Ti – T1 = 2𝜋𝑟𝑐𝑙ℎ ………………………………………………………………...equation 6 𝑖
T1 – T2 = T2 – T3 =
𝑖
𝑟 𝑞𝑘1 𝐼𝑛 1 𝑟𝑖
2𝜋𝑙𝐾1 𝑟 𝑞𝑘2 𝐼𝑛 2 𝑟1
2𝜋𝑙𝐾2 𝑞
T3 – To = 2𝜋𝑟 𝑐𝑙ℎ 2
……………………………………………………………...equation 7
……………………………………………………………...equation 8 ……………………………………….……………………...equation 9
𝑜
Therefore the heat transfer from Ti to To is computed as follows:
Ti – To = (Ti – T1) + (T1 – T2) + (T2 – T3) + (T3 – To) From equations 6 to 9; 𝑞𝑐
Ti – To = 2𝜋𝑟 𝑙ℎ + 𝑖
𝑖
𝑟 𝑞𝑘1 𝐼𝑛 1 𝑟𝑖
2𝜋𝑙𝐾1
+
𝑟 𝑞𝑘2 𝐼𝑛 2 𝑟1
2𝜋𝑙𝐾2
For a steady heat transfer, 𝑞𝑐 = 𝑞𝑘1 =𝑞𝑘2 = q Therefore, 𝑟 𝐼𝑛 1
1
𝑟𝑖
𝑟 𝐼𝑛 2
1
𝑟1 Ti – To = q( 2𝜋𝑟 𝑙ℎ + 2𝜋𝑙𝐾 + 2𝜋𝑙𝐾 + 2𝜋𝑟 𝑙ℎ ) 𝑖
q=
𝑖
1
2
𝑇𝑖 – 𝑇𝑜 𝑟 𝑟 𝐼𝑛 1 𝐼𝑛 2 𝑟𝑖 1 1 𝑟1 + + + 2𝜋𝑟𝑖 𝑙ℎ𝑖 2𝜋𝑙𝐾1 2𝜋𝑙𝐾2 2𝜋𝑟2 𝑙ℎ𝑜
Temperature at the surface of the outer shell (T3) 51
2
𝑜
𝑞
+ 2𝜋𝑟 𝑐𝑙ℎ 2
𝑜
To find the temperature at the outermost surface (i.e. the surface of the outer shell), equation 4 or 5 is used and T3 is made the subject of the formula. This means that when the steam generator is in operation, the temperature at the surface of the outer shell is given by the value of T3. Insulation thickness (t) When insulation is added to the inner shell, the outer surface will decrease in temperature and at the same time the surface area for convective heat dissipated will be increased. It is therefore possible that some optimum thickness of insulation exist due to this opposition effect. Considering figure 3.16 Where Ti = inner surface temperature
r
To = temperature of surrounding air
R
ho = convection at the outer boundary r – R = thickness of insulation
Figure 3.16 the heat loss per unit length of the cylindrical shell through the insulation is given as: 𝑞 𝑙
=
=
𝑇𝑖 – 𝑇𝑜
𝑟 𝑅 2𝜋𝐾
𝐼𝑛
+
1 2𝜋ℎ𝑟
2𝜋(𝑇𝑖 – 𝑇𝑜 ) 1 𝑟 1 𝐼𝑛 + 𝐾 𝑅 ℎ𝑟
An optimum value of the heat loss may be found by setting the first derivative of to r to be zero. 𝜕
𝑞
i.e. 𝜕𝑟 ( 𝑙 ) = 0 let u = 2𝜋(Ti – To)
52
𝑞 𝑙
with respect
𝑑𝑢 𝑑𝑟
=0 1
Let v = 𝐾 𝐼𝑛 𝑑V 𝑑𝑟 𝜕 𝜕𝑟
=
𝑞
(𝑙 ) =
1 𝐾𝑟 1 𝐾
𝑟 𝑅
1
+
ℎ𝑟
1
≡ 𝐾 𝐼𝑛 𝑟 −
1 𝐾
1
𝐼𝑛 𝑅 + ℎ𝑟
1
− ℎ𝑟 2
( 𝐼𝑛
𝑟 1 1 1 + )0−2𝜋(𝑇𝑖 – 𝑇𝑜 )× − 2 𝑅 ℎ𝑟 𝐾𝑟 ℎ𝑟 1 𝑟 1 ( 𝐼𝑛 + )2 𝐾 𝑅 ℎ𝑟
=0
By cross multiplication, we have: −2𝜋(𝑇𝑖 – 𝑇𝑜 ) ×
1 1 − 2=0 𝐾𝑟 ℎ𝑟
Dividing through by -2𝜋(Ti – To), we have that: 1 1 − 2=0 𝐾𝑟 ℎ𝑟 1 1 = 2 𝐾𝑟 ℎ𝑟 𝐾𝑟 = ℎ𝑟 2 Dividing through by r; 𝐾 = ℎ𝑟
and
𝑟=
𝐾 ℎ
= 𝑟𝑐
Where 𝑟𝑐 denotes the critical radius which is the optimum thickness to minimize heat loss. Enthalpy of Vapour enthalpy of vapour = x hg Steam Quality X=
ℎ𝑔 − ℎ𝑓 ℎ𝑓𝑔
Moisture Content Moisture content = m = (1 - x) Combustion Analysis 53
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame. Fuels of interest often include organic compounds (especially hydrocarbons) in the gas, liquid or solid phase. The fuel used for combustion in the steam generator is diesel. It is known that Diesel fuel is not a single compound, but rather a mixture of hydrocarbons. The "average" is C12H23. Diesel goes from C10H20 to C15H28. General the combustion formula is given as:
And can also be expressed as Fuel + Air
Heat + Water + Carbon dioxide + Nitrogen
The chemical equation for the complete combustion of Diesel fuel would then be: 4C12H23 + 71O2
48CO2 + 46H2O + heat
However it is Impossible to get the complete combustion of Diesel fuel, what comes out the exhaust is a widely varying mixture of substances from elemental carbon to potentially unburned fuel. The reasons why diesel was chosen instead of kerosene includes the following:
The cost of maintaining and using a diesel operated burner is lower
Diesel is economical and burns slower than kerosene due it its higher density
Ideally, diesel is less expensive than kerosene because it is gotten below kerosene.
3.2.2 Application of formulas and equations `Flowrate (Q): Q = π × 0.012 × 11 = 0.0035m3 (3.5 litres)
54
The cross-sectional area of the steam pipe sis given by: A=
A=
πD2 4 π × 0.0192 4
= 0.0003 m2 The mass flow rate of the water can be calculated as follows: Mass = density × volume Mass = 1000 × 0.0035 = 3.5Kg Where the density of water is 1000kg/m3 The volume flow rate (Q), mass flow rate (ṁ) and velocity (V) are as calculated for various instant is shown in table 4.1.
55
Volume, V
Flow rate, Q
Velocity ,v
Mass flow
(m/s) = Q/A
rate, ṁ (kg/s)
Area A (m2)
Time, t (s) (m3)
(m3/s) =V/t
0
0.0035
__
__
__
__
1
0.0035
0.0035
0.0003
11.6667
3.5000
5
0.0035
0.0007
0.0003
2.3333
0.7000
10
0.0035
0.0004
0.0003
1.3333
0.3500
15
0.0035
0.0002
0.0003
0.6667
0.2333
60
0.0035
0.0001
0.0003
0.3333
0.05830
Table 3.1: Shows the relationship between the flow rate, volume, velocity and time. Insulation thickness (t) It is known that 𝑟𝑐 =
𝐾 ℎ
K of rock wool = 0.04w/mk h of surrounding air = 7.9w/mk (for air to mild steel to air ) Therefore: 𝑟𝑐 =
0.04 7.9
𝑟𝑐 = 0.005𝑚 From the analysis the critical radius (rc) is 0.005m. However, the insulation thickness of the rock wool is 0.05m which is above the critical radius so as to adequately enhance the minimization of heat loss. Temperature at the surface of the outer shell (T3) From www.engineersedge.com/engineering;
56
The thermal conductivity of mild steel is between 26 - 37.5 BTU/(hr.ft.oF) Taking the average thus; 26 + 37.5 = 31.75 𝐵𝑇𝑈/(ℎ𝑟. 𝑓𝑡. F) 2 But 1 BTU/(hr.ft.oF) = 1.731 w/mk Therefore K2 = 1.731 x 31.75 K2 = 54.96w/mk For T3
q=
𝑇𝑖 – 𝑇𝑜 𝑟1 𝑟 𝐼𝑛 𝐼𝑛 2 𝑟𝑖 1 1 𝑟1 + + + 2𝜋𝑟𝑖𝑙1ℎ𝑖 2𝜋𝑙1𝐾1 2𝜋𝑙2𝐾2 2𝜋𝑟2 𝑙2ℎ𝑜
where l1= 0.65m
k1= 0.04w/mk
l2= 0.8m
k2= 54.9w/mk
ri= 0.33m
Ti= 509oC
r1= 0.38m
To= 27oC
r2= 0.382m
hi= ho = 7.9w/m2k
q=
q= q=
509 – 27 0.38 𝐼𝑛 0.33
0.382 𝐼𝑛 1 1 0.38 + + + 2𝜋(0.33)(0.65)(7.9) 2𝜋(0.65)(0.04) 2𝜋(0.8)(54.9) 2𝜋(0.382)(0.8)(7.9)
482 0.0939+ 0.8636+ 0+ 0.0659 482 1.0234
57
q = 470.98𝑊𝑎𝑡𝑡𝑠 To obtain the values for the temperatures T1, T2 and T3 the following is considered; For T1,
q=
q=
𝑇𝑖 – 𝑇1 1 2𝜋𝑟𝑖 𝑙1ℎ𝑖
509 – 𝑇1 1 2𝜋(0.33)(0.65)(7.9)
but q= 470.98 Watts Therefore; 470.98=
470.98=
509 – 𝑇1 1 2𝜋(0.33)(0.65)(7.9)
509 – 𝑇1 0.0939
(470.98 x 0.0939)= 509 – T1 T1= 509-(470.98 x 0.0939) T1= 509 – 44.2250 T1= 464.77oC For T2
q=
q=
𝑇1 – 𝑇2
𝑟 𝐼𝑛 1 𝑟𝑖 2𝜋𝑙1𝐾1
464.77 – 𝑇2 0.38 0.33 2𝜋(0.65)(0.04) 𝐼𝑛
but q= 470.98 Watts therefore 58
470.98 =
470.98 =
464.77 – 𝑇2 0.38 0.33 2𝜋(0.65)(0.04) 𝐼𝑛
464.77 – 𝑇2 0.8636
(470.98 x 0.8636)= 464.77 – T2 T2= 464.77 – (470.98 x 0.8636) T2= 464.77 – 406.74 T2= 58.03oC For T3
q=
q=
𝑇1 – 𝑇3
𝑟 𝐼𝑛 2 𝑟1 2𝜋𝑙1𝐾1
58.03 – 𝑇3 0.382 0.38 2𝜋(0.8)(54.9) 𝐼𝑛
but q= 470.98 Watts therefore 470.98 =
470.98 =
58.03 – 𝑇3 0.38 0.33 2𝜋(0.65)(0.04) 𝐼𝑛
58.03 – 𝑇3 0
(470.98 x 0)= 58.03– T3 T3= 58.03 – (470.98 x 0) T3= 58.03 – 0 T3= 58oC
59
Steam Quality From steam tables, at T= 300oC, P= 85.81bar, hf= 1344.01 KJ/Kg, hfg= 1404.9, hg= 2748.9KJ/Kg. But, hf + xhfg= hg 2748.9= 1344.01 + 1401.9x 2748.9 – 1344.01= 1404.9x 1404.89
x= 1404.9 = 0.9999 therefore x= dryness fraction= 0.9999 and the steam efficiency is 99.99% Moisture Content Moisture content = m = (1 - x) = 1-0.9999 =0.0001 = 0.01% Actual Enthalpy of Steam From the superheated steam table, at 1.5 bar and a temperature range of 500oC to 550oC the enthalpy of steam at 509oC can be found by interpolation. T (oC)
h (KJ/Kg)
500
3595
509
X
550
3704
Table 3.2 : table of values gotten from the superheated steam table 60
T−T1 h−h1
=
T2 −T1 h2 −h1
509−500 h−3595 9 h−3595
=
=
550−500 3704−3595 50
109
9 × 109 = 50 (h – 3595) 981 50
= h – 3595
h = 3614.62 KJ/Kg Enthalpy of Vapour Enthalpy of vapour = hg But actual enthalpy of vapour = x hg = 0.9999 × 3614.62 = 3614.26KJ/Kg 3.3
MATERIAL SELECTION Successful performance efficiency and profitability of an engineering project depends ultimately on the choice of materials used. The materials selected were based on the following design requirement. (a) Shells, tank and chimney
High thermal conductivity
Malleability
Heat resistance at elevated temperatures
Resistance to corrosion
Weldability
61
Low cost
(b) Coiled water tube
High thermal conductivity
Malleability
Heat resistance at elevated temperatures
Resistance to corrosion
Weldability
Low cost
(c) Insulation Material
Low thermal conductivity
Durability
During the screening process the material that did not meet the above criteria were eliminated. The materials that meet the above criteria includes: cast iron, stainless steel and mild steel for components listed in (a) above, rock wool (stone wool) and ceramic fibre wool for the thermal insulation material, and brass, copper and alloy steel for the coiled water tube. After ranking, the materials that best satisfy the design requirement is mild steel (0.15 – 0.46%C) for the components listed in (a) above, rock wool for the thermal insulation based on the requirement and from table 4.1, and a low alloy steel containing 2.25Cr and 1Mo (popularly known as steam pipe) for the coiled water tube. The presence of chromium gives it the required strength, hardenability and corrosion resistance, while molybdenum increases the creep resistance at elevated temperatures and red hardness.
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Material
Temperature
Glass wool
230 - 250˚C
Stone wool (rock wool)
700 - 850˚C
Ceramic fibre wool
1200˚C
Table 3.3: The heat the ranked thermal insulation materials can withstand Source: http://en.wikipedia.org/wiki/mineral_wool Adequate information about the past record of usage and effects of these materials on the design requirement has proven its reliability. 3.4
COST ANALYSIS
3.4.1
Material Cost S/N
MATERIAL DESCRIPTION
Quantity Unit Price (N)
Amount (N)
1
Pressure Pump
1
25, 000
25, 000
2
Burner
1
45, 000
45, 000
3
Pressure Gauge
1
2, 500
2, 500
4
Rockwool Insulation (Lagging)
volume
5, 000
5, 000
5
Tyre (Castor wheel)
4
1, 750
7, 000
6
Steam Pipe
4
2, 550
10, 200
7
Pressure Hose
1
1, 000
1,000
length
1,000
1,000
2
7, 500
15, 000
Short 8
Mild steel pipe
9
Mild steel sheet metal (2mm thickness)
63
10
Digital panel and thermostat
1
20, 000
20, 000
11
Gasket
5
300
1,500
12
Painting /finishing
___
7,000
7,000
TOTAL
140, 200
Table 3.4: table showing the material cost of the components 3.4.2
Materials Handling Transportation of materials = N20, 000
3.4.3
Other Cost According to Johnson (1992), “… the labour cost is 20% of the material cost and overhead cost is 10% of material cost…” Therefore; Labour cost = 0.2 x Material cost = 0.2 x 140, 200 = N28, 040.00 Overhead cost = 0.1 x Material cost = 0.1 x 140, 200 = N14, 020.00 Total cost = Material cost + Labour cost + Overhead cost + Materials handling cost = 140, 200 + 28, 040 + 14, 020 + 20, 000 = N202, 260.00
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CHAPTER FOUR 4.0
FABRICATION AND TESTING
4.1
FABRICATION The components of the steam generator and its method of fabrication form the basis of the fabrication and assembly. After each component was fabricated as described in item 3.1.2 of chapter three, the individual components were assembled. The method of assembly is described as follows: The two angle bars which were cut to give the chordal shape of the outer shell were welded to the fuel tank and the outer shell. The castor wheels were welded to the base of the fuel tank and the steam pipe was welded to the inner surface of the inner shell by means of small rods which held the steam pipe firmly in position at the centre of the inner shell. The chimney cap was welded to the upper section of the chimney using flat bars as the support and the sections of the chimney were bolted firmly with the gasket fitted between the layers of the chimney. The burner’s nozzle was fixed to the combustion chamber with bolts and welded supports and the handle was welded to the sides of the fuel tank. An electrical panel (digital panel) was bolted to the handle and electrical connections were made between the burner, the temperature sensor and the panel. Finishing operations (body filling, chrome spraying of the cylinder and painting of other components) was carried out. A pressure guage was fixed and screwed to the outlet of the steam pipe. The assembled components are shown in figure 4.1.
65
Figure 4.1 3D model of the assembly Source: self 4.1.1 Instrumentation (a)
Temperature: A Digital thermometer is installed on the panel with a thermal sensor connected to the combustion chamber to measure the temperature in degree Celsius.
(b)
Fuel level indicator: it shows the volume of fuel in the tank in litres. It is calibrated from 0 to 48 litres.
(c)
Pressure Guage: it measures the pressure at which steam flows out of the steam generator.
4.1.2 Maintenance The following maintenance tasks are to be observed regularly in the cause of the usage and operation of the steam generator:
66
(a)
Chemical cleaning: Water treatment is necessary to aid in the removal of oxygen in the feed water and prevents corrosion. The addition of an oxygen scavenging chemical (Sodium Sulphide, hydrazine or Tannin) will remove oxygen in the feed water and prevent corrosion (Spirax Sarco website, 2009). The chemical cleaning process for a steam generator removes pollutant and impurities that impedes the transfer of heat within the generator that may result in system failure. Hot alkaline chemical cleaning can also be used to remove oil, grease and other protective coatings that were necessary during the fabrication of the steam generator but will act as pollutants and impurities during operation (Chris Passas, 2009).
(b)
Flushing with water: Residual pollutant and impurities from the fabrication of the steam generator include metal scales, welding slag, oil and dirt. Chemical cleaning removes metal scale and corrosives, but flushing the steam generator with water can remove simpler debris such as dirt and sand.
(c)
Cleaning of the combustion chamber: At regular intervals depending on the usage (Precisely after about 100 hours of usage), the steam generator’s combustion chamber should be cleaned to remove sooths and clogging in the combustion chamber. To do this, the burner and the chimney are disassembled from the steam generator and a wire brush is passed through the openings to clean the sooth. A blower or air compressor is then used to blow out the sooth from the combustion chamber.
(d)
Cleaning of the Components: The steam generator component should always be clean and free of dust and dirt. A clean moist cotton material should be used to clean the surfaces of the components on a regular basis.
Major Maintenance of Furnace and Boiler 67
i.
Check the connections of the vent pipe and chimney: Part of the venting system may have deteriorated over time and thus may result in the deterioration of the system over time. Chimney problems can be expensive to repair and may help justify installing new heating equipment that would not use the existing chimney.
ii.
Check the physical integrity of the heat exchanger: This refers to observing to see if there are leakages in the steam pipe. Leaking boilers and heat exchangers are easy to spot.
iii.
Adjust blower control and supply - air temperature: The controls on the boiler and burner should be adjusted to provide optimum water and air temperature settings for both efficiency and comfort any other alternative would consequently result in operational hazards.
iv.
If consideration is to be made on retrofitting or replacing the existing system, a combustion efficiency test should be carried out by a qualified technician on the existing system.
4.1.3 Safety According to Murphy’s Law, anything that can fail, would fail and at the worst possible time. During the design and fabrication stage of the steam generator, the failure concept has been brought to a minimum taking Murphy’s Law into consideration. The following safety procedures were observed in the design and fabrication of the steam generator as well as safety during its operation. i.
A thermostat is incorporated in the design to sense and trip of the supply of fuel and air when the critical temperature is attained. This was incorporated to prevent boiler explosion during dry boiling conditions were no water is supplied to the boiler.
ii.
The chimney was constructed in such a way that it is above an average person’s height to prevent inhaling of the exhaust gases during its operation.
68
iii.
A caution symbol is painted on the outer shell of the boiler to indicate danger of burning due to its surface temperature.
iv.
The rear castor wheels are provided with stoppers to prevent drifting away or movement of the steam generator during operation.
v.
The burner contains a sensor which prevents the ignition of the burner when there is no supply of fuel to it. Other safety measures to be carried out regularly upon operation include:
Check the combustion chamber for cracks and fractures as these can pose as a serious danger during operation.
Test for carbon monoxide (CO) and remedy it if found.
Remove dirt, soot or corrosion from the burner and boiler.
Check the system temperature and panel reading on the panel to ensure that it is operational so as to enable the monitoring of the temperature of the system.
Check the fuel input and flame characteristics and adjust if necessary.
The outlet valve should be kept opened when water is been pumped through the pressure pump during its operation and closed after its usage.
69
4.1.4 Troubleshooting Table 4.1: Faults related to boiler firing S/N Faults
Causes
Remedy
(i) Faulty from main supply. (ii) Faulty fuse. 1
Burner fails to start
(iii)Fault in contaminated control circuit.
Check for the possible fault and rectify
(iv) Fault in base terminal connection.
(i) Cold oil
2
Motor starts but burner fails to light
(ii) Faulty thermostat (iii)Dirty electrode (iv) Loose connection (v) Faulty oil pump
(i) Check the (ii) Check the thermostat if it need changing (iii)Clean the electrode with sandpaper (iv) Check the pump
(i) Insufficient air or too much fuel
3
Burner producing smoking flame
(ii) Low oil temperature (iii)Dirty boiler tube/chamber
Check and repair the possible causes
(iv) Chimney damper partly closed Table 4.2: Faults related to boiler pumps S/N Faults 1
No water being delivered
Causes
(i) Speed may be too 70
Remedy (i) Check if water motor
slow
is directly across the
(ii) Discharge head too high
line and receiving full voltage. (ii) Check operation to see that pipe friction, suction and discharge head are as specified
(i) Piping may be plunged/ blocked 2
Not enough pressure
(ii) Impeller may be plunged (iii)Impeller may be
(i) Inspect impeller and piping suction strainer (ii) Repair or Replace
damaged
3
Pump works for a while and then looses suction
(i) There may be leakage
(i) Inspect suction line
in the suction line
and tighten lose
(ii) Water seal may be
connections
plunged out of
(ii) Inspect line and
position (iii)Air (water bubbles) may be found in liquid
4.2
position of seal (iii)Vent suction back to source of supply
TESTING The steam generator upon testing yielded steam as required at a flowrate of 0.0035m3/s when the generator was fired. The following parameters were also gotten after testing the steam generator. Fuel level after 30mins of operation: approximately 3.6 litres was left out of 4 litres. Temperature of the combustion chamber during operation: 509oC Pressure guage reading during the discharge of steam: 1.5 bar 71
Time taken to suck in 20litres of water: 236 seconds (4 mins 33 seconds) Pre-heating time before steam production: 2 minutes 30 seconds
72
CHAPTER FIVE 5.0
CONCLUSION AND RECOMMENDATION
5.1
CONCLUSION This project presented a successful design, fabrication and testing of the steam generator. The burner used produced sufficient heat at a temperature of 509oC to convert water into pure steam. The steam is delivered at a pressure of 1.5bar with a flow rate of 0.0035m3/s. The efficiency of the boiler obtained is 99.99% at 300oC and tends towards 100% at 509oC.
5.2
RECOMMENDATION The following are the recommendations:
An alternative source of flue gas expulsion.
When cost is not a constraint stainless steel should be used as it posses better material property requirements that mild steel.
An emergency stop should be provided.
73
REFERENCE Abubakar Zakari (June 2010), “Design and Fabrication of Water Heating System for Food Drinks
and
Pharmaceutical
Industries
using
local
material”,
PGD/MECH/2007/517 Mechanical Engineering Department FUT Minna. Gordon and Yon, Engineering Thermodynamics, 4th Edition www.about.com www.engineersedge.com www.engineeringtoolbox.com www.en.wikipedia.org www.spiraxsarco.com www.tlv.com www.ttboilers.com Young, Robert (1923) “Timothy Hackworth and the locomotive”, the book guild Ltd, Lewes, U.K. (2000) (reprint of 1923 edition)
74
APPENDICES APPENDIX A
APPENDIX B
75
MODEL VIEWS OF THE STEAM GENERATOR AND ITS COMPONENTS
76
77
78
79
80
