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Semelhante a summer intern ppt 2015
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summer intern ppt 2015
- 1. 1 Summer Internship 2015 inSummer Internship 2015 in Piramal Glass LTDPiramal Glass LTD KOSAMBA, SURAT GUJRATKOSAMBA, SURAT GUJRAT Glass furnaceGlass furnace EfficiencyEfficiency Presentation from the “MAHENDRA KUMAR BAIRWA” Department of Ceramic Engineering INDIAN INSTITUTE OF TECHNOLOGY (BANARAS HINDU UNIVERSITY)
- 2. 2 Training Agenda: Glass melting Glass Manufacturing Processes Introduction of furnace Assessment of furnaces Energy efficiency opportunities
- 4. 4 Mixed Raw Melting Furnace Glass Forming Annealing Packing Storage Finishing Operations Fig.- Schematic for glass manufacturing process . Inspection and testing
- 5. 5 Training Agenda: Glass melting Glass Manufacturing Processes Introduction of furnace Assessment of furnaces Energy efficiency opportunities
- 6. 7 Introduction of furnace Furnace Components (The Carbon Trust) Furnace chamber: constructed of insulating materials Hearth: support or carry the steel. Consists of refractory materials Burners: raise or maintain chamber temperature Chimney: remove combustion gases Charging & discharging doors for loading & unloading stock Charging & discharging doors for loading & unloading stock
- 7. 8
- 8. 9 Introduction of furnace Refractory lining of a furnace arc Aluminium zirconium silica refractories used in the furnace Refractory walls of a furnace interior with burner blocks In the 55TPD Furnace what are the Refractories Used in the furnace?Used in the furnace?
- 9. 10 Training Agenda: GlassTraining Agenda: Glass meltingmelting Glass Manufacturing Processes Introduction of furnace Assessment of furnaces Energy efficiency opportunities
- 10. 11 Assessment of Furnaces Heat Losses Affecting Furnace Performance FURNACE Fluegas Moistureinfuel Openingsinfurnace Furnacesurface/skin Otherlosses Heat input Heat in stock Hydrogeninfuel FURNACE Fluegas Moistureinfuel Openingsinfurnace Furnacesurface/skin Otherlosses Heat input Heat in stock Hydrogeninfuel
- 11. 12 Heat Losses in Industrial Heating Furnaces
- 12. 13 Assessment of Furnaces Parameters to be measured Location of measurement Instrument required Required Value Furnace soaking zone temperature (reheating furnaces) Soaking zone and side wall Pt/Pt-Rh thermocouple with indicator and recorder 1200-1300o C Flue gas temperature In duct near the discharge end, and entry to recuperator Chrome Alummel Thermocouple with indicator 700o C max. Flue gas temperature After recuperator Hg in steel thermometer 300o C (max) Furnace hearth pressure in the heating zone Near charging end and side wall over the hearth Low pressure ring gauge +0.1 mm of Wc Oxygen in flue gas In duct near the discharge end Fuel efficiency monitor for oxygen and temperature 5% O2 Billet temperature Portable Infrared pyrometer or optical pyrometer - Instruments to Assess Furnace Performance
- 13. 14 Assessment of Furnaces Direct Method Thermal efficiency of furnace = Heat in the stock / Heat in fuel consumed for heating the stock Heat in the stock Q: Q = m x Cp (t1 – t2) Calculating Furnace Performance Q = Quantity of heat of stock in kCal m = Weight of the stock in kg Cp= Mean specific heat of stock in kCal/kg oC t1 = Final temperature of stock in oC t2 = Initial temperature of the stock before it enters the furnace in oC
- 14. 15 Assessment of Furnaces Direct Method - example Heat in the stock Q = ◦ m x Cp (t1 – t2) ◦ 6000 kg X 0.12 X (1340 – 40) ◦ 936000 kCal Efficiency = ◦ (heat input / heat output) x 100 ◦ [936000 / (368 x 10000) x 100 = 25.43% Heat loss = 100% - 25% = 75% Calculating Furnace Performance m = Weight of the stock = 6000 kg Cp= Mean specific heat of stock = 0.12 kCal/kg oC t1 = Final temperature of stock = 1340 oC t2 = Initial temperature of the stock = 40 oC Calorific value of oil = 10000 kCal/kg Fuel consumption = 368 kg/hr
- 15. 16 Assessment of Furnaces Indirect Method Heat losses a) Flue gas loss = 57.29 % b) Loss due to moisture in fuel = 1.36 % c) Loss due to H2 in fuel = 9.13 % d) Loss due to openings in furnace = 5.56 % e) Loss through furnace skin = 2.64 % Total losses = 75.98 % Furnace efficiency = ◦ Heat supply minus total heat loss ◦ 100% – 76% = 24% Calculating Furnace Performance
- 16. 17 Training Agenda: Glass melting Glass Manufacturing Processes Introduction Assessment of furnaces Energy efficiency opportunities
- 18. 19 Energy Efficiency Opportunities: Importance of excess air ◦ Too much: reduced flame temp, furnace temp, heating rate ◦ Too little: unburnt in flue gases, scale losses Indication of excess air: actual air / theoretical combustion air Optimizing excess air ◦ Control air infiltration ◦ Maintain pressure of combustion air ◦ Ensure high fuel quality ◦ Monitor excess air 1. Complete Combustion with Minimum Excess Air
- 19. 20 Energy Efficiency Opportunities: When using burners Flame should not touch or be obstructed No intersecting flames from different burners Burner in small furnace should face upwards but not hit roof More burners with less capacity (not one big burner) in large furnaces Burner with long flame to improve uniform heating in small furnace 2. Proper Heat Distribution
- 20. 21 Energy Efficiency Opportunities: Operating at too high temperature: heat loss, oxidation, decarbonisation, refractory stress Automatic controls eliminate human error Slab Reheating furnaces 1200o C Rolling Mill furnaces 1200o C Bar furnace for Sheet Mill 800o C Bogie type annealing furnaces 650o C –750o C 3. Operate at Optimum Furnace Temperature
- 21. 22 Energy Efficiency Opportunities: Heat loss through openings ◦ Direct radiation through openings ◦ Combustion gases leaking through the openings ◦ Biggest loss: air infiltration into the furnace Energy saving measures ◦ Keep opening small ◦ Seal openings ◦ Open furnace doors less frequent and shorter 4. Reduce Heat Loss from Furnace Openings
- 22. 23 Energy Efficiency Opportunities: Negative pressure in furnace: air infiltration Maintain slight positive pressure Not too high pressure difference: air ex-filtration Heat loss only about 1% if furnace pressure is controlled properly! 5. Correct Amount of Furnace Draft
- 23. 24 Energy Efficiency Opportunities Optimum load ◦ Under loading: lower efficiency ◦ Overloading: load not heated to right temp Optimum load arrangement ◦ Load receives maximum radiation ◦ Hot gases are efficiently circulated ◦ Stock not placed in burner path, blocking flue system, close to openings Optimum residence time ◦ Coordination between personnel ◦ Planning at design and installation stage 6. Optimum Capacity Utilization
- 24. 25 Energy Efficiency Opportunities: Charge/Load pre-heating ◦ Reduced fuel needed to heat them in furnace Pre-heating of combustion air ◦ Applied to compact industrial furnaces ◦ Equipment used: recuperator, self-recuperative burner ◦ Up to 30% energy savings Heat source for other processes ◦ Install waste heat boiler to produce steam ◦ Heating in other equipment (with care!) 7. Waste Heat Recovery from Flue Gases
- 25. 26 Energy Efficiency Opportunities: Choosing appropriate refractories Increasing wall thickness Installing insulation bricks (= lower conductivity) Planning furnace operating times ◦ 24 hrs in 3 days: 100% heat in refractories lost ◦ 8 hrs/day for 3 days: 55% heat lost 8. Minimum Furnace Skin Loss
- 26. 27 Energy Efficiency Opportunities: High emissivity coatings Long life at temp up to 1350 Most important benefits ◦ Rapid efficient heat transfer ◦ Uniform heating and extended refractory life ◦ Emissivity stays constant Energy savings: 8 – 20% 9. Use of Ceramic Coatings
- 27. 28 Energy Efficiency Opportunities: Selection criteria Type of furnace Type of metal charge Presence of slag Area of application Working temperatures Extent of abrasion and impact 10. Selecting the Right Refractory • Structural load of furnace • Stress due to temp gradient & fluctuations • Chemical compatibility • Heat transfer & fuel conservation • Costs
- 28. 29 Summer Internship in 2015Summer Internship in 2015 Piramal Glass LTDPiramal Glass LTD KOSAMBA, SURAT GUJRATKOSAMBA, SURAT GUJRAT Glass furnaceGlass furnace EfficiencyEfficiency THANK YOUTHANK YOU FOR YOUR ATTENTIONFOR YOUR ATTENTION
Notas do Editor
- TO THE TRAINER This PowerPoint presentation can be used to train people about the basics of furnaces and refractories. The information on the slides is the minimum information that should be explained. The trainer notes for each slide provide more detailed information, but it is up to the trainer to decide if and how much of this information is presented also. Additional materials that can be used for the training session are available on www.energyefficiencyasia.org under “Energy Equipment” and include: Textbook chapter on this energy equipment that forms the basis of this PowerPoint presentation but has more detailed information Quiz – ten multiple choice questions that trainees can answer after the training session Workshop exercise – a practical calculation related to this equipment Option checklist – a list of the most important options to improve energy efficiency of this equipment Company case studies – participants of past courses have given the feedback that they would like to hear about options implemented at companies for each energy equipment. More than 200 examples are available from 44 companies in the cement, steel, chemicals, ceramics and pulp & paper sectors
- A furnace is an equipment used to melt metals for casting or to heat materials to change their shape (e.g. rolling, forging) or properties (heat treatment). Since flue gases from the fuel come in direct contact with the materials, the type of fuel chosen is important. For example, some materials will not tolerate Sulphur in the fuel, in which case you can use light diesel oil. Solid fuels generate particulate matter, which will interfere the materials placed inside the furnace, therefore coal is not often used as fuel. Furnace ideally should heat as much of material as possible to a uniform temperature with the least possible fuel and labor. The key to efficient furnace operation lies in complete combustion of fuel with minimum excess air. Furnaces operate with relatively low efficiencies (as low as 7 percent) compared to other combustion equipment such as the boiler (with efficiencies higher than 90 percent. This is caused by the high operating temperatures in the furnace. For example, a furnace heating materials to 1200 oC will emit exhaust gases at 1200 oC or more, which results in significant heat losses through the chimney.
- All furnaces have the following components as shown in the figure: Refractory chamber constructed of insulating materials to retain heat at high operating temperatures. Hearth to support or carry the steel, which consists of refractory materials supported by a steel structure, part of which is water-cooled. Burners that use liquid or gaseous fuels to raise and maintain the temperature in the chamber. Coal or electricity can be used in reheating furnaces. Chimney to remove combustion exhaust gases from the chamber Charging and discharging doors through which the chamber is loaded and unloaded. Loading and unloading equipment include roller tables, conveyors, charging machines and furnace pushers
- Ideally, all heat added to the furnaces should be used to heat the load or stock. In practice, however, a lot of heat is lost in several ways as shown in the figure. These furnace heat losses include: Flue gas losses: part of the heat remains in the combustion gases inside the furnace. This loss is also called waste-gas loss or stack loss. Loss from moisture in fuel: fuel usually contains some moisture and some of the heat is used to evaporate the moisture inside the furnace Loss due to hydrogen in fuel which results in the formation of water Loss through openings in the furnace: radiation loss occurs when there are openings in the furnace enclosure and these losses can be significant, especially for furnaces operating at temperatures above 540°C. A second loss is through air infiltration because the draft of furnace stacks/chimneys cause a negative pressure inside the furnace, drawing in air through leaks or cracks or when ever the furnace doors are opened. Furnace skin / surface losses, also called wall losses: while temperatures inside the furnace are high, heat is conducted through the roof, floor and walls and emitted to the ambient air once it reaches the furnace skin or surface. Other losses: there are several other ways in which heat is lost from a furnace, although quantifying these is often difficult, for example, losses due to formation of scales.
- Furnace efficiency is calculated after subtracting the various heat losses. In order to find out furnace efficiency using the indirect method, various parameters must be measured, such as hourly furnace oil consumption, material output, excess air quantity, temperature of flue gas, temperature of furnace at various zones, and others. Date for some of these parameters can be obtained from production records while others must be measured with special monitoring instruments. This table lists the instruments that are needed to measure these parameters. For example. The flue gas temperature is measured with a Hg in steel thermometer if the temperature is up to 300 oC, but with a thermocouple if the temperature is high than this. The session “Monitoring Equipment” explains different monitoring instruments in more detail
- A furnace’s efficiency increases when the percentage of heat that is transferred to the stock or load inside the furnace increases. The efficiency of the furnace can be calculated in two ways, similar to that of the boiler: direct method and indirect method. Direct method The efficiency of a furnace can be determined by measuring the amount heat absorbed by the stock and dividing this by the total amount of fuel consumed. Thermal efficiency of the furnace =Heat in the stock / Heat in the fuel consumed for heating the stock The quantity of heat (Q) that will be transferred to stock can be calculated with this equation: Q = m x Cp (t1 – t2) Where, Q = Quantity of heat of stock in kCal m = Weight of the stock in kg Cp= Mean specific heat of stock in kCal/kg oC t1 = Final temperature of stock in oC t2 = Initial temperature of the stock before it enters the furnace in oC
- The heat input is 400 liters per hour. The specific gravity of fuel is used to convert this into kg. Therefore: 400 l/hr. x 0.92 kg/l = 368 kg/hr. The heat output is calculated as follows: = m x Cp x ΔT = 6000 kg x 0.12 x (1340 – 40) = 936000 kCal The efficiency is: = (heat input / heat output) x 100 = [(936000 / (368 x 10000)] x 100 = 25.43 percent The approximate heat loss is 100% – 25% = 75%
- The furnace efficiency can also be determined through the indirect method, similar to the evaluation of boiler efficiency. The principle is simple: the heat losses are subtracted from the heat supplied to the furnace. (Note that a detailed methodology to calculate each individual heat loss is provided in the chapter) Adding the losses a to f up gives the total losses: Flue gas loss = 57.29 % Loss due to moisture in fuel = 1.36 % Loss due to H2 in fuel= 9.13 % Loss due to openings in furnace= 5.56 % Loss through furnace skin = 2.64 % Total losses = 75.98 % (Click once) The furnace efficiency calculated through the indirect method = 100 – 75.98 = 24.02%
- Typical energy efficiency measures for an industry with furnace are: Complete combustion with minimum excess air Proper heat distribution Operation at the optimum furnace temperature Reducing heat losses from furnace openings Maintaining correct amount of furnace draft Optimum capacity utilization Waste heat recovery from the flue gases Minimize furnace skin losses Use of ceramic coatings Selecting the right refractories
- The amount of heat lost in the flue gases (stack losses) depends on the amount of excess air. Too much excess air will reduce flame temperature, furnace temperature and heating rate. Too little excess air will result in an increase in unburnt components in flue gases that are carried away through the stack and it also causes more scale losses. The air ratio (= actual air amount / theoretical combustion air amount) gives an indication of excess air. If a reheating furnace is not equipped with an automatic air/fuel ratio controller, it is necessary to periodically take a sample of gas in the furnace and measure its oxygen contents with a gas analyzer. (Click once) Optimizing combustion air is the most attractive and economical measure for energy conservation. Potential savings are higher when the temperature of the furnace is high. To obtain complete combustion of fuel with the minimum amount of air, it is necessary to control air infiltration, maintain pressure of combustion air, fuel quality and monitor the amount excess air.
- A furnace should be designed to ensure that within a given time the stock is heated uniformly to a desired temperature with the minimum amount of fuel. Where burners are used to fire the furnace, the following should be ensured for proper heat distribution: The flame should not touch or be obstructed by any solid object. Obstruction causes the fuel particles to de-atomize, which affects combustion and causes black smoke. If the flame impinges on the stock scale losses will increase. If the flame impinges on refractories, products from incomplete combustion can settle and react with the refractory constituents at high temperatures. The flames of different burners should stay clear of each other, as intersecting flames cause incomplete combustion. It is also desirable to stagger burners on opposite sides. The burner flame has a tendency to travel freely in the combustion space just above the material. For this reason, the axis of the burner in small furnaces is never placed parallel to the hearth but always at an upward angle, but the flame should not hit the roof. Large burners produce longer flames, which may be difficult to contain within the furnace walls. More burners of less capacity ensure a better heat distribution inside the furnace and also increase the furnace life. In small furnaces that use furnace oil, a burner with a long flame with a golden yellow color improves uniform heating. But the flame should not be too long, because heat is lost of the flame reaches the chimney or the furnace doors.
- It is important to operate the furnace at its optimum temperature. Operating temperatures of various furnaces are given in the table. Operating at too high temperatures causes heat loss, excessive oxidation, de-carbonization and stress on refractories. Automatic control of the furnace temperature is preferred to avoid human error.
- Heat can be lost through openings by direct radiation through openings in the furnace, such as the charging innless, extracting outlet and the peephole in the wall or ceiling. due to pressure differences between the inside of the furnace and the ambient environment causing combustion gases to leak through the openings. But most heat is lost if outside air infiltrates into the furnace, because in addition to heat loss this also causes uneven temperatures inside the furnace and stock and can even lead to oxidization of billets. (Click once) Measures to reduce the heat loss include It is therefore important to keep the openings as small as possible and to seal them. Opening the furnace doors less frequent and for the shortest time period as possible.
- In addition to the options mentioned on the previous slide, proper management of the pressure difference between the inside and outside of the furnace is important to minimize heat loss and adverse impacts on products. Tests conducted on seemingly airtight furnaces have shown air infiltration up to 40 percent. To avoid this, slight positive pressure should be maintained inside the furnace. But the pressure difference should not be too high because this will cause ex-filtration. While this is less of a problem than infiltration, it can still result in flames reaching out of the furnace, overheating of refractories leading to reduced brick life, increased furnace maintenance, and burnout of ducts and equipment. Heat loss through opening is about 1 percent of the total quantity of heat generated in the furnace, if furnace pressure is controlled properly.
- One of the most vital factors affecting the furnace efficiency is the load. This includes the amount of material placed in the furnace, the arrangement inside the furnace and the residence time inside the furnace. a) Optimum load If the furnace is under loaded the proportion of total heat available that will be taken up by the load is smaller, resulting in a lower efficiency. Overloading can lead to the load not heated to the right temperature within a given period of time. There is a particular load at which the furnace will operate at maximum thermal efficiency, i.e. where the amount of fuel per kg of material is lowest. This load is generally obtained by recording the weight of material of each charge, the time it takes to reach the right temperature, and the amount of fuel used. The furnace should be loaded to the optimum load at all times, although in practice this may not always be possible (Click once) b) Optimum arrangement of the load The loading of materials on the furnace hearth should be arranged so that It receives the maximum amount of radiation from the hot surfaces of the heating chambers and flames Hot gases are efficiently circulated around the heat receiving surfaces of the materials Stock is not placed in the following position: (a)In the direct path of the burners or where flame impingement is likely to occur, (b) In an area that is likely to cause a blockage or restriction of the flue system of the furnace (c) Close to any door openings where cold spots are likely to develop (Click once) c) Optimum residence time of the load Fuel consumption is kept at a minimum and product quality is best if the load only remains inside the furnace until it has the required physical and metallurgical properties. Sometimes the charge and production schedule does not correspond with the capacity of the furnace. This results in fuel wastage and sometimes in reduced product quality. Coordination between the furnace operator, production and planning personnel is therefore essential. Optimum utilization of furnace can be planned at design stage, by selecting the size and type (batch, continuous) that best matches the production schedule.
- Flue gases carry 35 to 55 percent of the heat input to the furnace with them through the chimney. The higher the amount of excess air and flue gas temperature, the higher the amount of waste heat that is available. However, the primary objective should be to minimize the amount of waste heat generated through energy conservation measures. Waste heat recovery should only be considered when further energy conservation is not possible or practical. Waste heat in flue gases can be recovered for preheating of the charge (stock, load), preheating of combustion air or for other processes as described below. a) Charge pre-heating When raw materials are preheated by exhaust gases before being placed in a heating furnace, the amount of fuel necessary to heat them in the furnace is reduced. Since raw materials are usually at room temperature, they can be heated sufficiently using high-temperature flue gases to noticeably reduce the fuel consumption rate. (Click once) b) Preheating of combustion air For a long time, fuel gases were only use for preheating of combustion air for large boilers, metal-heating furnaces and high-temperature kilns. But preheating using heat from flue gases is now also applied to compact boilers and compact industrial furnaces. A variety of equipment is available to recover waste heat. External recuperates are most common, but other techniques are also used, such as self-recuperative burners. For example, a modern recuperate use furnace exhaust gas of 1000°C can preheat the combustion air to over 500 oC, which results in energy savings of up to 30 percent compared with using cold combustion air entering the furnace. (note: this equipment is further explained in the chapter “Waste Heat Recovery”) Since the volume of combustion air increases when it is preheated, it is necessary to consider this when modifying air-duct diameters and blowers. It should be noted that preheating of combustion gases from high-density oils with a high Sulphur content, could cause clogging with dust or sulphides, corrosion or increases in nitrogen oxides. (Click once) c) Utilizing waste heat as a heat source for other processes The temperature of furnace exhaust gas can be as high as 400- 600 °C, even after heat has been recovered from it for preheating the charge or combustion air. One possibility is to install a waste heat boiler to produce steam or hot water from this heat, especially when large quantities steam or hot water are needed in a plant. Sometimes exhaust gas heat can be used for heating purposes in other equipment, but only if the heat quantity, temperature range, operation time etc. are suitable for this. Fuel consumption can be greatly reduced. One existing example is the use of exhaust gas from a quenching furnace as a heat source in a tempering furnace.
- About 30 to 40 percent of the fuel used in intermittent or continuous furnaces is used to make up for heat lost through the furnace skin/surface or walls. The extent of wall losses depend on: Emissivity of wall Thermal conductivity of refractories Wall thickness Whether the furnace is operated continuously or intermittently There are several ways to minimize heat loss through the furnace skin: Choosing the appropriate refractory materials Increasing the wall thickness Installing insulating bricks. Outside wall temperatures and heat losses of a composite wall are much lower for a wall of firebrick and insulation brick compared to a wall of the same thickness that consists only of refractory bricks. The reason is that insulating bricks have a much lower conductivity. Planning operating times of furnaces. For most small furnaces, the operating periods alternate with the idle periods. When the furnaces are turn off, heat that was absorbed by the refractories during operation gradually dissipates through radiation and convection from the cold face and through air flowing through the furnace. When the furnace is turned on again, additional fuel is needed to heat up the refractories again. If a furnace is operated continuously for 24 hours in three days, practically all the heat stored in the refractories is lost. But if the furnace is operated 8 hours per day all the heat stored in the refractories is not dissipated. For a furnace with a firebrick wall of 350 mm thickness, it is estimated that during the 16 hours that the furnace is turned off, only 55 percent of the heat stored in the refractories is dissipated from the cold surface. Careful planning of the furnace operation schedule can therefore reduce heat loss and save fuel.
- We already discussed high emissivity coatings earlier, but we now summarize the main points from an energy conservation perspective. Ceramic coatings in the furnace chamber promote rapid and efficient transfer of heat, uniform heating and extended life of refractories. The emissivity of conventional refractories decreases with increase in temperature whereas for ceramic coatings it increases slightly. This outstanding property has been exploited by using ceramic coatings in hot face insulation. Ceramic coatings are high emissivity coatings and a have a long life at temperatures up to 1350oC. Energy savings of the order of 8-20 percent have been reported depending on the type of furnace and operating conditions.
- We discussed the different types of refractories earlier. But despite the advantages of some refractories over others, it is important to select the right refractory for the specific application. The selection of refractories aims to maximize the performance of the furnace, kiln or boiler. Furnace manufacturers or users should consider the following points in the selection of a refractory: Type of furnace Type of metal charge Presence of slag Area of application Working temperatures Extent of abrasion and impact Structural load of the furnace Stress due to temperature gradient in the structures and temperature fluctuations Chemical compatibility to the furnace environment Heat transfer and fuel conservation Cost considerations