Performance assessment of boilers,steam system,insulation & refractories


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Performance assessment of boilers,steam,insulation and refractories.

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  • A boileris an enclosed vessel that provides a means for combustion heat to be transferred to water until it becomes heated water or steam.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 hot water or steam under pressure is then usable for transferring the heat to a process.
  • There are different types of boilers based on different fuels and with various capacities. (Questions to audience) What type of boilers do you know of? What kind of boilers do you use in the industry where you work? (Discussion)(Click once and boiler types will appear) We will look closer at the following types of boilers: Fire Tube Boiler, Water Tube Boiler, Packaged Boiler, Fluidized Bed Boiler, Stoker Fired Boiler, Pulverized Fuel Boiler and Waste Heat Boiler.
  • To begin with, we will look at the fire tube boiler:This is generally used for relatively small steam capacities and at low to medium steam pressures. The steam rates for fire tube boilers are up to 12,000 kg/hour with pressures of 18 kg/cm2. Fire tube boilers can operate on oil, gas or solid fuels. The figure illustrates how a fire tube boiler works. The fuel is burned and heats up the water to steam which is turn channeled to the process. Today, most fire tube boiler are in a packaged construction for all fuels.
  • We will now look at 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 different methods to assess boiler efficiency. (Click once) They are direct and indirect method.(Click once) In the direct method, the energy gain of the working fluid, that is the water and steam, is compared to the energy content of the boiler fuel.(Click once) In the indirect method, the efficiency is calculated as the difference between the losses and energy input.We will start with looking at the methodology of the direct method of calculating boiler efficiency.
  • The direct method of determining boiler efficiency is also known as the “input-output” method. This is because it only needs the useful output, which is steam, and the heat input, which is fuel, in order to evaluate the efficiency. The efficiency is evaluated by using this formula where hg is the enthalpy of saturated steam and hf is the enthalpy of feed water.(Click once) The parameters to be monitored for the calculation of boiler efficiency through the direct method are: Quantity of steam generated per hour; the quantity of fuel used per hour; the working pressure and superheat temperature if any; the temperature of feed water; the type of fuel and gross calorific value, GVC, of the fuel.
  • Now, we will look at the indirect method. This is also referred to as the heat loss method. The boiler efficiency can be calculated by subtracting the heat loss fractions from 100 as shown here. The principle losses that occur in a boiler are due to: Dry flue gas; evaporation of water and evaporation of moisture in fuel; moisture present in combustion air; unburnt fuel in fly ash; unburnt fuel in bottom ash, radiation and other unaccounted losses.
  • The data that is required to calculate boiler efficiency according to the indirect method include: Ultimate analysis of fuel in terms of H2, O2, S, C, moisture content and ash content. Percentage of oxygen or CO2 in the flue gas; flue gas temperature; ambient temperature and humidity of air; as well as GCV of fuel. In case of solid fuels, the percentage combustible in ash and GCV of ash.
  • A better understanding of the properties of steam may be achieved by understanding the general molecular and atomic structure of matter and applying this knowledge to ice, water and steamA molecule is the smallest amount of any element or compound substance still possessing all the chemical properties of that substance which can exist. Molecules are made up of even smaller particles called atoms, which define the basic elements such as hydrogen and oxygenOne such compound is represented by the chemical formula H2O, having molecules made up of two atoms of hydrogen and one atom of oxygen.Most mineral substances can exist in the three physical states (solid, liquid and vapour), which are referred to as phases. In the case of H2O, the terms ice, water and steam are used to denote the three phases respectively.
  • Steam today is an integral and essential part of modern technology. Without it, our food, textile, chemical, medical, power, heating and transport industries could not exist or perform as they do. Steam provides a means of transporting controllable amounts of energy from a central, automated boiler house, where it can be efficiently and economically generated, to the point of use. Therefore as steam moves around a plant it can equally be considered to be the transport and provision of energy. For many reasons, steam is one of the most widely used commodities for conveying heat energy. Its use is popular throughout industry for a broad range of tasks from mechanical power production to space heating and process applications. Reasons for using steam include:Steam is efficient and economic to generateSteam can easily and cost effectively be distributed to the point of useSteam is easy to controlEnergy is easily transferred to the processThe modern steam plant is easy to manageSteam is flexibleThe alternatives to steam include water and thermal fluids such as high temperature oil. Each method has its advantages and
  • An understanding of the basic steam circuit or ‘steam and condensate loop’ is requiredNote to the trainer: a detailed description is in the chapter. Below are the summarized points onlyAs steam condenses in a process, flow is induced in the supply pipe. The steam generated in the boiler must be conveyed through main pipes, or 'steam mains‘ and then smaller branch pipes. Heat is transferred from the steam to the pipe, so the pipe work will begin to transfer heat to the air.Steam on contact with the cooler pipes will begin to condense immediately. On start-up of the system, the condensing rate will be at its maximum and is commonly called the ‘starting load’. Once the pipe work has warmed up, the condensing rate is minimal and commonly called the ‘running load’.The resulting condensation (condensate) falls to the bottom of the pipe and will then have to be drained from various strategic points in the steam main.When the valve on the steam pipe serving an item of steam using plant is opened, steam flowing from the distribution system enters the plant and again comes in contact with cooler surfaces. The steam then transfers its energy in warming up an equipment and product (starting load), and, when up to temperature, continues to transfer heat to the process (running load).There is now a continuous supply of steam from the boiler. More water (and fuel to heat this water) is supplied to the boiler to make up for the water which has previously been evaporated into steam. The condensate formed in both the steam distribution pipework and in the process equipment is a convenient supply of useable hot boiler feedwater.
  • Pipe material: Pipes for steam systems are commonly manufactured from carbon steel to ANSI B 16.9 Al06. The same material may be used for condensate lines, although copper tubing is preferred in some industries. For high temperature superheated steam mains, additional alloying elements, such as chromium and molybdenum, are included to improve tensile strength and creep resistance at high temperatures. Typically, pipes are supplied in 6-meter lengths.Pipeline sizing: The objective of the steam distribution system is to supply steam at the correct pressure to the point of use. Pipeline sizing is an important factor.Oversized pipework means:Pipes, valves, fittings, etc. will be more expensive than necessary.Higher installation costs will be incurred, including support work, insulation, etc.For steam pipes a greater volume of condensate will be formed due to the greater heat loss. This in turn means that either more steam trapping is required or wet steam is delivered to the point of use.Undersized pipework means:A lower pressure may only be available at the point of use. This may hinder equipment performance due to only lower pressure steam being available.There is a risk of steam starvation.There is a greater risk of erosion, water hammer and noise due to the inherent increase in steam velocity.The required pipeline size can be calculated based on pressure drop and velocity. Note to the trainer: if time allow you can use the chapter to explain how each of these calculation methods work
  • A filter used in a steam system typically consists of a sintered stainless steel filter element.Filters are used to remove smaller particles than strainers, for example, in the following applications:When there is direct injection of steam into a process, which may cause contamination of the product. Example: In the food industry, and for the sterilization of process equipment in the pharmaceutical industry.Where dirty steam may cause rejection of a product or process batch due to staining or visible particle retention. Example: Sterilizers and paper/board machines.Where minimal particle emission is required from steam humidifiers. Example: Humidifiers used in a “clean” environment.For the reduction of the steam water content, ensuring a dry, saturated supply.
  • Performance assessment of boilers,steam system,insulation & refractories

    2. 2. What is a Boiler ?  Vessel that heats water to become hot water or steam.  At atmospheric pressure water volume increases 1,600 times.  Hot water or steam used to transfer heat to a process. PERFORMANCE ASSESSMENT OF BOILERS
    3. 3. TYPES OF BOILERS  Water Tube Boiler  Packaged Boiler  Fluidized Bed (FBC) Boiler  Fire Tube Boiler  Stoker Fired Boiler  Pulverized Fuel Boiler  Waste Heat Boiler
    4. 4. FIRE TUBE BOILER  Relatively small steam capacities (12,000 kg/hour)  Low to medium steam pressures (18 kg/cm2)  Operates with oil, gas or solid fuels
    5. 5. ASSESSMENT OF A BOILER Boiler Efficiency : Thermal efficiency: % of (heat) energy input that is effectively useful in the generated steam. BOILER EFFICENCY CALCULATION 1) DIRECT METHOD: 2) INDIRECT METHOD: The energy gain of the working fluid (water and steam) is compared with the energy content of the boiler fuel The efficiency is the different between losses and energy input
    6. 6. BOILER EFFICIENCY : DIRECT METHOD Boiler efficiency ( ) = Heat Input Heat Output x 100 = Q x (hg – hf) Q x GCV x 100 hg -the enthalpy of saturated steam in kcal/kg of steam hf -the enthalpy of feed water in kcal/kg of water Parameters to be monitored: - 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
    7. 7. BOILER EFFICIENCY : INDIRECT METHOD Efficiency of boiler ( ) = 100 – (i+ii+iii+iv+v+vi+vii) Principle losses: i. Dry flue gas ii. Evaporation of water formed due to H2 in fuel iii. Evaporation of moisture in fuel iv. Moisture present in combustion air v. Unburnt fuel in fly ash vi. Unburnt fuel in bottom ash vii. Radiation and other unaccounted losses
    8. 8. Contd….. Required calculation data • Ultimate analysis of fuel (H2, O2, S, C, moisture content, ash content) • % oxygen or CO2 in the flue gas • Fuel gas temperature in C (Tf) • Ambient temperature in C (Ta) and humidity of air in kg/kg of dry air • GCV of fuel in kcal/kg • % combustible in ash (in case of solid fuels) • GCV of ash in kcal/kg (in case of solid fuels)
    9. 9. PERFORMANCE ASSESSMENT OF INSULATION What is Insulation? Insulation, or more correctly thermal insulation , is a general term used to describe products that reduce heat loss or heat gain by providing a barrier between areas that are significantly different in temperature.
    10. 10.  It make your home warmer in winter and also helps keep it cooler in summer.  Air is a poor conductor of heat, so the tiny pockets of air trapped in insulation minimise the amount of heat which can pass between the inside and outside of your house. HOW INSULATION WORKS?
    11. 11. Building insulation refers broadly to any object in a building used as insulation for any purpose.While the majority of insulation in buildings is for (1)thermal purposes, the term also applies to (2) acoustic insulation, (3) fire insulation, and (4)impact insulation. Thermal insulation can refer to material used to reduce the rate of heat transfer or the methods and processes used to reduce heat transfer. Heat or thermal conduction is the spontaneous transfer of thermal energy through matter to equalize temperature differences. It is also described as heat energy transferred from one material to another by direct contact.
    12. 12. DIFFERENT KINDS OF MATERIAL USED IN INSULATION The different materials used in the Insulation process are:  Glass mineral wool (glasswool)  Rock mineral wool (stone mineral wool)  Rigid foam  Sheep wool
    13. 13. TYPES OF INSULATION  Structural Insulated Panel  Sprayed Foam  Concrete  Blanket batts and roll  Foam board  Loose fill-in and blow-in  Reflective  Fibre Insulation
    14. 14. STRUCTURAL INSULATED PANEL Structural insulated panels (SIPs), also called stressed-skin walls, use the same concept as in foam-core external doors, but extend the concept to the entire house. They can be used for ceilings, floors, walls, and roofs. The panels usually consist of plywood, OSB, sandwich ed around a core of expanded polystyrene, polyurethane , polyisocyanurate, compr essed wheat straw, or epoxy.
    15. 15. Insulated Concrete Forms ICFs are hollow, light- weight "stay in place" forms made of two Expanded Polystyrene (EPS) panels which are connected by polypropylene webs. During construction, the forms are stacked to the desired height then filled with concrete making stable, durable and sustainable walls.
    16. 16. Oriented strand board, (OSB) or Sterling board (UK), is an engineered wood product formed by layering strands (flakes) of wood in specific orientations
    17. 17. Loose Fill Cellulose is 100% natural and 75-85% of it is made from recycled newsprint. a. Fibrous Type – from mineral wool rock, glass wool, slag wool or vegetable fiber usually of wood fiber. b. Granular Insulation from expanded minerals like perlite, vermiculite or ground vegetable matter.
    18. 18. Sound Insulation (Soundproofing) is any means of reducing the intensity of sound with respect to a specified source and receptor. Soundproofing affects sound in two different ways: noise reduction and noise absorption.
    19. 19. PERFORMANCE ASSESSMENT OF STEAM SYSTEM What is steam?  Molecule: smallest of any compound  Water = H2O ◦ two hydrogen atoms (H) ◦ one oxygen atom (O) Three physical states : ◦ solid: ice ◦ liquid: water ◦ vapour: steam
    20. 20. Why do we use steam?  Transport and provision of energy  Benefits: •Efficient and economic to generate •Easy to distribute •Easy to control •Easily transferred to the process •Steam plant easy to manage •Flexible Steam saturation curve:
    21. 21. Typical steam circuit
    22. 22. MOST IMPORTANT COMPONENTS 1. Pipes 2. Drain points 3. Branch lines 4. Strainers 5. Filters 6. Separators 7. Steam traps 8. Air vents 9. Condensate recovery system 10. Insulation
    23. 23. Pipe material: carbon steel or copper Correct pipeline sizing is important Size calculation: pressure drop or velocity  Ensures that condensate can reach steam trap  Consideration must be give to • Design • Location • Distance between drain points • Diameter of drain pipe PIPES: DRAIN POINTS: BRANCH LINES: Take steam away from steam main Shorter than steam mains Pressure drop no problem if branch line < 10 m
    24. 24. STRAINERS: Y-Type strainers  Handles high pressures  Lower dirt holding capacity: more cleaning needed FILTERS  Consists of sintered stainless steel filter element  Remove smallest particles – Direct steam injection – e.g. food industry – Dirty stream may cause product rejection – e.g. paper machines – Minimal particle emission required from steam humidifiers – Reduction of steam water content
    25. 25. SEPARATOR  Separators remove suspended water droplets from steam  Water in steam causes problems o Water is barrier to heat transfer o Erosion of valve seals and fittings and corrosion STEAM TRAPS Selection depends on steam trap’s ability to oVent air at start-up oRemove condensate but not steam oMaximize plant performance: dry steam AIR VENTS : Effect of air on heat transfer
    26. 26. CONDENSATE RECOVERY SYSTEM  What is condensate – Distilled water with heat content – Discharged from steam plant and equipment through steam traps  Condensate recovery for – Reuse in boiler feed tank, desecrator or as hot process water – Heat recovery through heat exchanger INSULATION  Insulator: low thermal conductor that keeps heat confined within or outside a system  Benefits: Reduced fuel consumption Better process control Corrosion prevention Fire protection of equipment
    27. 27. PERFORMANCE ASSESSMENT OF REFRACTORIES What are the refractories?  Any material can be described as a refractory, if it can withstand the action of abrasive corrosive solids, liquids or gases at high temperature.  A good refractory lining inside a furnace can help life of a blast furnace from 4-5 yrs or 10-15 yr. Classification Refractories can be classified -on the basis of chemical composition -method of manufacture -according to their refractoriness.
    28. 28.  Acidic refractories These are used in areas where slag and atmosphere are acidic. They are stable to acids but attacked by alkalis. e.g. fire clay, silica, Quartz, Zirconia.  Basic refractories These are used on areas where slags and atmosphere are basic, stable to alkaline materials but reacts with acids. e.g. Magnesia , Alumina, Dolomite. On the basis of chemical composition • Neutral refractories These are used in areas where the atmosphere is either acidic or basic and are chemically stable to both acids and bases. e.g. Chromate, Carbide, Mullite.
    29. 29. Based on refractoriness  Low heat duty refractories For low temperature environment i.e. 1520 —1630 ºC  Medium heat duty refractories For temperature ranging from 1630—1670 ºC  High heat duty refractories For temperature ranging from 1670—1730 ºC  Super duty refractories For temperature above 1730 ºC
    30. 30.  Transportation of Raw material  Grinding  Pre-Treatment Calcination Stabilizer addition  Mixing Bonding material Wet Mixing (14-20% water) Semi plastic Dry Mixing ( < 5% water)  Moulding Hand Moulding (Wet Mixed) Machine Moulding (Dry and Semi wet Mixed)  Drying Avoids high shrinkage and gives strength. Make refractories safe for handling.  Firing Removes water of Hydration, 30% Shrinkage in Volume MANUFACTURING STEPS
    31. 31. SELECTION OF REFRACTORIES  Area of application  Working temperatures  Extent of abrasion and impact  Stress due to temperature gradient  Heat transfer and fuel conservation  Cost consideration APPLICATIONS Refractories are meant to sustain at high temperature so the very common applications are Used in furnaces such as blast furnac and coke oven.  Used in boilers.  Mostly used in cement industry in Preheater Rotary Kiln Burner pipe