FIRED HEATERS .ppt
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This document provides information on fired heaters, including methods of heat transfer, combustion, types of fired heaters, furnace parts, problems that can occur, and introduces several heaters at a refinery. It discusses the three main methods of heat transfer as conduction, convection, and radiation. Fired heaters use combustion of fuel to generate heat that is transferred to process fluids through tubes. Box and cylindrical designs are described. Key furnace parts and issues like overfiring, vibration, and inefficiency are outlined. Example heaters at the refinery include crude, vacuum, visbreaker, and hydrotreating unit heaters.
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FIRED HEATERS .ppt
- 1. FIRED HEATERS Presented By: ABDUL NASIR AZIZ
- 2. METHODS OF HEAT TRANSFER Conduction Convection Radiation Heat is a form of energy. Heat may be transferred in three different ways and all three methods are encountered in the furnace / Fired heaters.
- 3. Conduction Conduction is the transfer of energy through matter from particle to particle. It is the transfer and distribution of heat energy from atom to atom within a substance. Conduction is most effective in solids-but it can happen in fluids. Flow of heat through or across a conductor. The transmission of heat through and by means of matter unaccompanied by any obvious motion in matter.
- 4. Convection Convection is the transfer of heat by the actual movement of the warmed matter. Convection is the transfer of heat energy in a fluid by movement of currents. Convection may be natural or forced. Convection may be natural or forced. In heat transfer by convection there is movement of a mass i.e. a collection of molecule of the hot matter from the warm vicinity to a colder area.
- 5. Radiation Transfer of heat by waves. Radiant heat travels in waves in the same manner as light, the difference being that we can see light where as we can only feel heat.
- 6. Combustion The rapid chemical combination of oxygen with combustible elements of a fuel resulting in the production of heat. The three essential requirements for combustion are: 1. A supply of oxygen. 2. Fuel in a combustible form. 3. A source of heat.
- 7. Combustion Chemical Reactions Carbon Burning: (1) C carbon + + ½ O2 Oxygen CO Carbon Monoxide + + Heat (incomplete) Heat (incomplete) (2) CO carbon Monoxide + + ½ O2 Oxygen CO2 Carbon Dioxide + + Heat Heat C carbon + + O2 Oxygen CO2 Carbon Dioxide + + Heat Heat Hydrogen Burning: 2H2 Hydrogen + + O2 Oxygen = 2H2O Water Vapor + + Heat Heat Methane Burning: CH4 Natural Gas + + 2O2 Oxygen = CO2 Carbon Dioxide + + 2H2O + heat Water vapor + heat
- 8. Fired Heater/Furnace A fired heater is a direct-fired heat exchanger that uses the hot gases of combustion to raise the temperature of a feed flowing through coils of tubes aligned throughout the heater. Depending on the use, these are also called furnaces or process heaters. Some heaters simply deliver the feed at a predetermined temperature to the next stage of the reaction process; others perform reactions on the feed while it travels through the tubes. Fired heaters are used throughout hydrocarbon and chemical processing industries such as refineries, gas plants, petrochemicals, chemicals and synthetics, ammonia and fertilizer plants. Most of the unit operations require one or more fired heaters as start-up heater, fired reboiler, cracking furnace, process heater, process heater vaporizer, crude oil heater or reformer furnace.
- 9. Types of Fired Heaters The purpose of a furnace is to raise the temperature of a process fluid. This is achieved by burning a fuel to generate heat, then using the mechanisms of heat transfer to pass this heat into the process fluid. Most commonly used furnace types are 1. Box type furnaces 2. Cylindrical furnaces
- 10. Box Type Furnace
- 11. A box type heater is in which the tubes are horizontal. The zone of highest heat density is the “Radiant Section". The heat pickup in the radiant tubes is mainly by direct radiation from the heating flame. The zone of lower heat density is the “Convection Section“. This heat pickup in the convection section is obtained from the Combustion Gases/ Flue Gases primarily by convection. Box Type Furnace
- 13. Cylindrical Furnace Vertical heaters are either cylindrical or rectangular. They may have radiant section only or convection and radiant sections. The radiant section tubes will usually be vertical, but some cylindrical heaters have helical coils. The convection section can be either vertical of horizontal
- 14. Combustion Air Supply Combustion air can be supplied by either way: Forced Draft Natural Draft Induced Draft Balanced Draft
- 15. Forced Draft It is achieved by installing an inlet fan. A higher air velocity through the air register can be obtained, which brings about a better mixing of the air and fuel in the burner throat. One of its disadvantages is that when used on furnaces with low stacks, a positive pressure can be caused in the furnace, which could be dangerous. Combustion Air Supply
- 16. Combustion Air Supply Natural Draft This is brought about by the difference in weight of gases in a chimney and the weight of a similar column of air outside the chimney. The draught available is proportional to the height of the chimney and the difference between the specific gravity of air and that of the flue gases, which depends mainly on their temperature.
- 17. Induced Draft In some installations, due to low stack considerations or because the flue gases meet a high resistance to their flow through the stack. To overcome this problem a fan or blower is located between the furnace outlet and stack inlet. Combustion Air Supply
- 18. Balanced Draft In some furnace systems both forced and induced fans are installed. This gives precise control over the combustion / heating process taking place. Combustion Air Supply
- 19. Furnace Parts Walls The walls of the furnace are fastened to a steel construction. The inside of the wall is provided with steel plating against which the insulation material and the heat resistant stone is built up. The stones are held in place by stay bolts. The heat resistant stone is interrupted at various levels to facilitate expansion.
- 20. Furnace Parts Refractory Lining Refractories are construction materials for use at high temperatures, and must be resistant and sufficiently strong at the required temperature. In the oil industry Refractories are mainly used in heaters, which may be either oil or gas fires, in the following conditions : Oxidizing atmosphere. Neutral or acidic gases. Temperatures up to 1500°C. Temperature variations for process control.
- 21. Furnace Parts Tubes These carry the feed through the furnace. Continuous flow through the tubes is arranged by welding the tubes in the “U” type formation. This type of formation permits thermal expansion. Headers are fitted by expanding tube ends against the header opening. The tubes can be arranged in two distinct ways either in parallel or in series.
- 22. Furnace Parts Burners The heat of combustion is provided by burners where proper air fuel ratio is adjusted. The air being supplied is divided into three parts; Primary air which is mixed with the fuel before the point of ignition. Secondary air, which is admitted separately to complete the combustion of volatiles. Tertiary air, which is used to control the flame temperature (Hence controlling the production of NOx).
- 23. Furnace Parts Burner Gun This is a metallic tube supplied with a burner tip, which allows the fuel gas or atomized fuel oil to enter the combustion zone. The position of the burner in relation to the throat is critical and misalignment can lead to firing problems.
- 24. Air Register This usually consists of a cylindrical, flat, box like construction, normally fitted with vanes, which can be adjusted. The task of the air register is to introduce the combustion air into the combustion space. The primary air is supplied around the burner gun tip. It provides air to start the combustion process, acting as a cooling agent and preventing carbonization on the gun itself. The secondary air has a rotating movement, which ensures good mixing and flame formation.
- 25. Burner Throat This is the refractory lined hole in the furnace wall or floor where ignition takes place. The throat consists of a fire resistant brick that can withstand very high temperatures. The throat serves to start the burning off with the air register. They both also help to regulate the form or shape of the flame. Therefore the dimensions of the throat are critical in furnace design to ensure that the flame produced misses the throat lip.
- 26. Soot Blowing In some heaters the convection section contains tubes with extended surface in the form of either fins. Extended surface tubes are used to increase the convection heat transfer area at low capital cost. Because of the tendency of extended surface tubes to foul when burning heavy oils, sootblowers are usually installed.
- 27. Sootblowers employ high pressure steam to clean the tube outer surfaces of soot and other foreign material. Sootblowers may be either automatic electric motor operated by a pushbutton at grade, or manual requiring operation from a platform located at the convection bank level. Generally heaters are supplied with sootblowing facilities in the convection section although tubes may not be of the extended surface type. Soot Blowing
- 28. Decoking The internal cleaning of tubes and fittings may be accomplished by several methods. One is to circulate gas oil through the coil after the heater has been shutdown but before the coils are steamed and water washed and prior to the opening and start of inspection work.This method is effective if deposits in the coil are such that they will be softened or dissolved by gas oil.
- 29. When tubes are coked or contain hard deposit, other methods may be used, such as steam air decoking mechanical cleaning for coke deposits chemical cleaning for salt deposits. Chemical cleaning and steam air decoking are preferable as they tend to clean the tube to bare metal. The chemical cleaning process requires circulation of an inhibited acid through the coil until all deposits have been softened and removed. This is usually followed by water washing to flush all deposits from the coil. Decoking
- 30. Steam-Air Decoking Steam air decoking process consists of the use of steam, air and heat to remove the coke. The mechanics of decoking are: Shrinking and cracking the coke loose by heating tubes from outside while steam blows coke from the coil. Chemical reaction of hot coke with steam. Chemical reaction of coke and oxygen in air.
- 31. Steam and air services are permanently connected to the heater. The heater outlet line incorporates a swing elbow which, during the decoking operation, is disconnected from the outlet line and connected to the decoking header. Coke is carried by this header to the drum or sump. In some instances it may requested by the Process Department or Client that the decoking manifold is connected to allow for reverse flow during the decoking. Steam-Air Decoking
- 32. Snuffing Steam Snuffing is the action of smothering a fire by using steam. As steam is inert and will not burn, it replaces the air around the fire causing it to suffocate. Typically steam is used on pump glands or furnace fires. Snuffing steam connections are supplied generally in the combustion chamber. The control point or snuffing steam manifold is generally located at least 15 meters away from the heater, is supplied by a live steam header and is ready for instantaneous use. Smothering lines should be free from low pockets and should be so arranged as to have all drains grouped near the manifold.
- 33. Burner Assembly
- 34. Burner
- 35. Furnace Problems Over firing After burning Vibration Impingement High skin temperature Inefficiency
- 36. Over Firing The excess air value for a furnace approached the theoretical air value. Then carbon monoxide is formed due to incomplete combustion. This condition is quite often induced during changes in operating conditions e.g. increasing unit throughputs, or raising process temperatures.
- 37. After Burning Any un-burnt gas will burn higher up in the radiant cell or in the convection cell or even further up in the stack. In any case where there is oxygen available from other burners or furnaces and at a temperature not too low for ignition to occur. Sometimes, after burning is indicated by a high flue gas temperature at the furnace outlet. If an increase in air flow decreases skin temperature then after burning is taking place. Serious melting away of refractory or damage to the convection bank can result.
- 38. Vibration It is usually caused by a local air shortage on one or more burners. A pulsating effect normally occurs, as the flame in the burner with the air shortage tries to snatch air from its adjacent burners. It may be prevented by ensuring that symmetrical firing is taking place (equal fuel/air distribution). Although if the vibration persists it is possible that some gas guns have uneven perforations or clearances.
- 39. Impingement The contacting of any flame in the radiant cell with the furnace tubes can produce serious damage. This condition can have a number of causes, a high burner load in a narrow furnace for example. Other possible causes include incorrect register operation, coke formation on the burner throat or loose brick / coke deposits fouling the air register obviously the condition should never knowingly be allowed to persist. Therefore remedial action should always be taken once the condition is observed.
- 40. High Skin Temperatures In some areas in the furnace high skin temperatures are caused by high heat fluxes. Although skin temperature is also dependant, of course, on the rate at which the process streams which are being heated can keep the tube wall cool. Normally the higher the velocity of the process fluid through the tubes the faster it can take away heat from the tube wall. If vaporization takes place and the tube wall becomes “dry”, the skin temperature rises rapidly. Also a thin layer of coke, deposited on the inside wall of the tube, will restrict the rate at which the process fluid can take heat away and high skin temperatures will result. The maximum skin temperature allowable on a tube is dependent on the tube material and the reason for limitation i.e. scaling, internal or external corrosion.
- 41. Inefficiency The efficiency of a furnace can be defined as the fraction of heat in the fuel supplied which is transferred to the process fluid (or to steam). The heat which is not transferred to the process fluid or stream is lost to the atmosphere by radiation from the furnace walls (normally between 3 to 6%) and through stack losses. The operator has no control over radiation losses as such but can have considerable influence over stack loss. Stack loss is the heat, which is lost up the chimney in the form of hot furnace gases. The amount of heat which is lost in this way is dependent on the flue gas quantity and temperature.
- 42. Introduction to MCR Heaters DESCRIPTION TAG NO. Crude Heater 100 – H1 Vacuum Heater 110 – H1 Visbreaker Heater 130 - H1 A/B/C Diesel – Max Process Unit Heaters 284 – H1 284 – H2 284 – H50A/B Naphtha Hydrotreating Unit Heater 200 – H1 Platforming Unit Heaters 300 – H1 300 – H2 300 – H3 Sulphur Recovery Unit Heaters 820 – H1/2 820 – H3/4 820 – H50/51
- 43. Crude Heater 100-H1 SPECIFICATIONS ITEM NO. 100 - H1 SERVICE CRUDE HEATER TYPE Vertical Box DUTY MMkcal/hr 53.44 HEATER COIL 8 PASSES DESIGN TEMP. oC 487/372 DESIGN PRESS. kg/cm2G 15.5 / FV NO. OF BURNERS 24
- 44. Vacuum Heater 110-H1 SPECIFICATIONS ITEM NO. 110 - H1 SERVICE VACUUM HEATER TYPE CYLINDRICAL DUTY MMkcal/hr 13.88 HEATER COIL 6 PASSES DESIGN TEMP. oC 574/398 DESIGN PRESS. kg/cm2G 10.5 / FV NO. OF BURNERS 08
- 45. Visbreaker Heaters 130- H1A/B/C SPECIFICATIONS ITEM NO. 130 - H1 A/B/C SERVICE VISBREAKER HEATER TYPE CABIN DUTY MMkcal/hr 9.72 HEATER COIL 1 PASS DESIGN TEMP. oC 593 DESIGN PRESS. kg/cm2G 62.4 ELASTIC DESIGN PRESS. kg/cm2G 38.7 (RUPTURE) NO. OF BURNERS 08
- 46. Reactor Heater 284-H1 SPECIFICATIONS ITEM NO. 284 - H1 SERVICE REACTOR HEATER TYPE CYLINDRICAL DUTY MMkcal/hr 6.6 HEATER COIL 2 PASSES DESIGN TEMP. oC 603 DESIGN PRESS. kg/cm2G 86.5 RUPTURE DESIGN PRESS. kg/cm2G 103 ELASTIC NO. OF BURNERS 06
- 47. Product Fractionator's Heater 284-H2 SPECIFICATIONS ITEM NO. 284 - H2 SERVICE PRODUCT FRACTIONATOR FEED HEATER TYPE VERTICAL BOX DUTY MMkcal/hr 26.51 HEATER COIL 4 PASSES DESIGN TEMP. oC 445 DESIGN PRESS. kg/cm2G 18.2 NO. OF BURNERS 12
- 48. Thermal Cracker Heater 284-H50A/B SPECIFICATIONS ITEM NO. 284 - H50 A/B SERVICE THERMAL CRACKER HEATER TYPE UOP CABIN DUTY MMkcal/hr 17.67 HEATER COIL 2 PASSES DESIGN TEMP. oC (I/O) 586/608 DESIGN PRESS. kg/cm2G 39.38 RUPTURE IN DESIGN PRESS. kg/cm2G 28.41 RUPTURE OUT DESIGN PRESS. kg/cm2G 70 ELASTIC NO. OF BURNERS 15
- 49. Charge Heater 200-H1 SPECIFICATIONS ITEM NO. 200 - H1 SERVICE CHARGE HEATER TYPE CYLINDRICAL DUTY MMkcal/hr 4.4 HEATER COIL 4 PASSES DESIGN TEMP. oC 397 DESIGN PRESS. kg/cm2G 59 NO. OF BURNERS 03
- 50. Plat forming Unit Heaters 300-H1/H2/H3
- 51. Sulphur Recovery Unit Heaters SPECIFICATIONS ITEM NO. 820 - H1 820 - H2 SERVICE REACTION FURNACE BURNER REACTION FURNACE SIZE mm mm 1900×5200 DUTY MMkcal/hr 1.46 DESIGN TEMP. oC 343 oC 343 DESIGN PRESS. kg/cm2G 3.5 kg/cm2G 3.5 NO. OF BURNERS 01 01
- 52. Incinerator Burner( 820-H3 ) / Incinerator ( 820-H4 ) SPECIFICATIONS ITEM NO. 820 - H3 820 - H4 SERVICE INCINRATOR BURNER INCINRATOR SIZE mm mm 1600×4500 DUTY MMkcal/hr 3.646 DESIGN TEMP. oC 343 oC 343 DESIGN PRESS. kg/cm2G 0.12 kg/cm2G 0.12 NO. OF BURNERS 01 01
- 53. SCOT Line Heater Burner (820-H51) / SCOT Line Heater (820- H52) SPECIFICATIONS ITEM NO. 820 - H51 820 - H52 SERVICE SCOT LINE HEATER BURNER SCOT LINE HEATER SIZE mm mm 700×2500 DUTY MMkcal/hr 0.768 DESIGN TEMP. oC 343 oC 343 DESIGN PRESS. kg/cm2G 3.5 kg/cm2G 3.5 01 01