Atmos Burner Chapter 4 2024 PDF

ATMOSPHERIC GAS BURNER Abdul Aziz Bin Adam DPG 40333 FUEL & GAS COMBUSTION Learning Outcomes Describe Explain Describe common type of the performance the component of a atmospheric burner. characteristics of an at...

ATMOSPHERIC GAS BURNER Abdul Aziz Bin Adam DPG 40333 FUEL & GAS COMBUSTION Learning Outcomes Describe Explain Describe common type of the performance the component of a atmospheric burner. characteristics of an atmospheric burner. atmospheric burner. Explain Describe Describe atmospheric burner characteristics and causes of unstable combustion. requirements of a flames. stable flame. Construct Troubleshoot an atmospheric atmospheric burner. burners. Learning Outlines Introduction Types of Atmospheric Burner Performance Characteristic The Components Atmospheric Burner Combustion: An Explanations Stable Flame: The Requirements Un-Stable Flame: The Cause Troubleshooting: Skills 1.0 INTRODUCTION Basically, four overall classifications for gas-fired burners Atmospheric Power Forced and Induced Draft Premix and Pressure Power  Introduction An atmospheric burner is a simple device that requires no fans or electrical supply Designed to burn gaseous fuels efficiently and simple Most common types of burners found in residential and commercial equipment IDEAL BURNER CHARACTERISTICS Blue flame with possibly some yellow Distinct individual flame No blowing or lifting of tips when using pattern flames propane or butane as the fuel Flame heights are No flash-back of burner No lazy flames uniform around the flames burner periphery No offensive odors emanating from the combustion process  2.0 TYPES of ATMOSPHERIC BURNER Atmospheric Burner Common Specialized Atmospheric Burner Atmospheric Burner Pilot Single Port Multi Port Burner Burner Burner Sand Pan Infrared Barber Burner radiant Burner Burner  Common Atmospheric Burner Pilot Burner Single Port Burner Multi Port Burner Pilot Burner The pilot burner is essentially a robust premixed burner unit It designed to provide a stable flame for igniting the gas exiting the flare tip the venturi or mixer It features three main gas jet or orifice components, burner nozzle  Pilot burners Main Functions Function To provide a mount for the To ignite the main burner To heat the thermocouple thermocouple or flame or thermopile generator. thermopile generator This provides the voltage for the Pilotstat power unit.  Pilot burners are categorized according to their ability to premix gas with air. Types of pilot burners: Pilot Burner Aerated pilots Non-aerated pilots Pilot Burner: Aerated Pilot Aerated pilots premix air and gas, and develop a sharp, intense blue flame Relatively stable flame Not too affected by draft and main flame variations Have good thermocouple response Shorter thermocouple life Clogging due to dust and lint especially for burners that are near the floor, such as water heaters  Pilot Burner: Aerated Pilot Incinerating pilot  No primary air intake Give a softer blue flame Pilot Burner: Because their combustion air is solely secondary air, Non-Aerated these pilots are affected by draft and main flame variations. Pilot Do not have the same dust and lint problems as the aerated pilots Promote longer thermocouple life produce less torching (the hard, sharp, hot flame from aerated pilots). Pilot Burner: Non-Aerated Pilot Changes in pilot supply pressure can affect these pilots more than the aerated type Supply pressure the pilot flame will roar, giving a noisy pilot operation and lower thermocouple life. Supply pressure there is insufficient heat, giving low thermocouple output voltage. Pilot Burner: Non-Aerated Pilot  Simple design Inexpensive Single / The mixer tube is simply extended, and gas is burned on the end of the tube Mono-port Burner No burner head This design produces a single large flame. To eliminate yellow tipping when burning natural gas, single port burners need about 50% (or more) primary air. Single / Mono-port Burner Have more flashback Noisier than most other types of burners. The flames on large single port burners also tend to lift. To minimize lifting a flame retention device-a crimped ring-is inserted just inside the lip of the burner port.  Single / Mono-port Burner Types lnshot Upshot burners burners Usually fires horizontally. Air-gas mixture flows through a bend and into a riser tube where it bums Gas bums on the end of the straight vertically. extension of the mixer tube Flame spreader is sometimes A flame spreader is sometimes mounted above the port to spread mounted in front of the burner port the flame to spread the flame (not shown). Multi port Burners Most common atmospheric burner used in appliances Basic components are the same as a mono-port upshot burner with the addition of a multiport burner head When a number of these burners are used together it is referred to as a burner bed.  Multi-port Burners Distribute flames to provide Purpose good heat transfer to the heat exchanger. Spread the flames so they can be reached by secondary air. Provide stable blue flames.  Multi-port Burners Types Drilled Drilled Slotted Ribbon port pipe port port. Multiport : Drilled port Burner Iron castings made. Forms Segments of Single / Multiple Star Wheel Concentric Rings Rectangular Rings Bars Characteristics Some cast iron drilled port burners have a small raised boss for each port. These bosses give a greater port length (which reduces flashback) and a better opportunity for secondary air to surround the flame jet. The cast sections also provide open areas for proper air distribution. To overcome the small turn down on such low mixture pressures, these burners in large capacity are frequently divided into units such as the separate rings in concentric ring burners-with individual mixers. Smaller drill sizes distribute flames more evenly, Ports should be no larger than a No. 29 drill. To avoid plugging, they should be no smaller than a No. 42. Uses These burners spread the heat at a low intensity over a relatively large area. They are used for relatively low temperature operations such as heating small solution tanks cooking kettles candy furnaces stove top ovens broiler burners. Multiport : Drilled Pipe Burner Made from standard pipe with either one row of holes on top two rows at 30 degrees each side of vertical Used where a long narrow heat band is required, as in large solution tanks.  Multiport : Drilled Pipe Burner Critical Measurement Port size Total port area Ratio of port area to cross-section Total length Distance from mixer to first port Multiport : Slotted port Burner The sawed slots instead.of drilled holes in the pipe The slots must be kept quite narrow which makes them subject to clogging. Length of the slot causes warping in hot locations. Frequently used in oven and broiler burners and in some industrial applications. Multiport : Ribbon port Burner Similar to the drilled pipe burner Rather then drill, Combustion ports are lengthwise slots that have an assembly of crimped and straight metal strips pressed into them  Spaces created by the crimped metal provide the individual ports Continuous flame is produced instead of individual jets Characteristic Because of the solid flame, the slot width must be narrow enough to allow secondary air to reach the center of the flame. As a rule, the continuous flame is generally shorter for the same Btu release of heat than the drilled pipe burner. Ribbon burners are widely used on: Large bakery ovens solder pots on can machinery Use textile singeing shrinking machines  Specialized Atmospheric Burner Sand Pan Burner Infrared radiant Burner Barber Burner Specialized Atmospheric Burner Not all atmospheric burners operate the same way. Some burners use no primary air and produce luminous flames for special effects, While others have no open flame. Still other burners have special designs to deal with very high flow velocities. Specialized Atmospheric Burner – SAND PAN Designed to be installed in an existing masonry fireplace A pipe burner is mounted in a sheet metal pan and covered with a layer of fine sand The burner ports are located at the bottom of the pipe so the natural gas filters through the sand where it is ignited with a pilot flame. As a result, these units are designed for burning natural gas only and not the heavier-than-air LP- gases. Specialized Atmospheric Burner – SAND PAN Gas is burned without a source of primary air, the flames produced tend to bum a luminous yellow color similar to the flames of a wood fire Commonly uses small pieces of mineral fiber material on the surface of the sand. These heat up and glow like the coals of a solid fuel fire. Specialized Atmospheric Burner INFRARED RADIENT Common type is surface combustion burner The radiating surface of the burner is a porous refractory material such as ceramic or stainless steel with small drilled or formed ports or a metal screen The air-gas mixture passes through the burner face material and bums on the surface, which then becomes the radiation source Specialized Atmospheric Burner INFRARED RADIENT An infrared burner needs about 100 % primary air and is designed to have a hot, glowing burner surface. Therefore, the flame must bum close to the burner surface with a high temperature. Major drawback is low surface-heat input loading is required because of the high primary air requirements. This condition limits the heat input rate that can be used with a given burner size. In other words, a large surface area is needed to get the desired input rate. As a result, the venturi is larger than other atmospheric burners. Specialized Atmospheric Burner INFRARED RADIENT Specialized Atmospheric Burner BARBER BURNER Capable of high input in a small combustion space Often used under gas fired appliances such as Chinese Woks and deep fryers The circular or rectangular manifold supplies many small burners with gas Each of these small burners has an orifice and fixed primary air opening Because the velocity through the burners is very high, and would normally cause liftoff, the burners are angled so that the stream of gas-air mixture from one burner intersects the next and slows its velocity Specialized Atmospheric Burner BARBER BURNER This stabilizes the flame, even though it is far from the burner ports at maximum input. This type of burner can provide a wide turndown because of the way it handles flow velocity at high inputs. Specialized Atmospheric Burner BARBER BURNER Performance Characteristic Atmospheric burners are designed to Provide complete combustion Stable flames Quiet operation  Complete Rapid carry combustion over of flames Quiet Immediate operation ignition 3.0 PERFORMANCE CHARACTERISTIC Uniform Stables flame heating Wide turndown ratio  Must capably mixing gas and air together so the fuel completely burned. Complete combustion Not produce carbon monoxide or other harmful by-products. Rapid carry over of flames When ignited, flame front must pass smoothly and rapidly over the burner surface. For multi-port burner, the flame front should not delay as it moves from port to port. All ports must ignite. Quiet operation Burners ignite quietly either at ignition or during the run cycle. Burner shutdown also be smooth and quiet, not creating an extinction pop.  A burner fired at its designed input with correct air adjustment should produce a stable flame. The flames stay close to the burner ports Stables flame The flames not lift off the burner. No burner “flashback”. Flashback occurs when the flame front moves back through a burner nozzle, and sometimes back to the air-gas mixing point. Uniform heating A burner must provide uniform heating across its surface. Uneven heating causes excessive stress on heat exchangers and boiler tubes. Wide turndown ratio Turndown ratio – or turndown rate – is the range of inputs satisfactory combustion. Many burners operate at a fixed input. Others, such as range-top burners, must vary their input from high to low. A turndown ratio of 5 to 1 means the burner input can vary from 20% to 100% of rated input and still maintain stable flames at the burner ports.  Components of an Atmospheric Burner  Components of Atmospheric Gas Burner  Components of an Atmospheric Burner Orifice Primary air shutters The fuel is discharged to the burner The air shutter adjusts the size of the through the orifice cap, spud or other primary air inlet(s). device. Some burners have a fixed primary air The orifice is not part of the burner, but inlet and are designed for gas at a it is such a vital part of the burner system specific gas pressure. that it is included in the discussion of Most burners, however, have an burners. adjustable air shutter to adjust the primary air flow.  Venturi The venture is a short tube with a constricted, throat-like passage. This passage increases the velocity and lowers the pressure of a gas passing through it. Most atmospheric burners are Components of necked down to a venture throat. an Atmospheric Burner Mixing tube The mixing tube is the portion of the mixer that lies between the venture and the burner head. The gas and primary air mix together as they move along this tube.  Components of an Atmospheric Burner Burner head Burner ports The burner head uniformly distributed The burner port is an orifice, or opening, the air-gas mixture to the burner ports. that does three things, Its size and shape can be tailored to fit an Discharges the air-gas mixture for appliance combustion chamber and to ignition. provide even heat release to heat Distribute flames to provide an even transfer surfaces. heat transfer to heat exchanger. Spreads the flames so they can be reached by secondary air.  Atmospheric Burner Combustion: An Explanations Combustion process through an atmospheric burner: Starting at the venture and ending at the burner ports. FUEL SUPPLY VENTURI MIXING TUBE BURNER PORT  Venturi A venturi (at point B) sucks primary air into the burner and thoroughly mixes the air and gas before ignition. There are changes of element occur Pressure Changes The venture on a burner is always a negative pressure in relation to the air surrounding the burner. Due to the negative pressure, atmospheric air is sucked in and mixed with the high velocity gas flow. Velocity Changes Bernoulli’s Theorem, When velocities increase, the pressure decreases When velocities decrease, the pressure increases Flow Velocities Flow velocities is the rate at which the gas-air mixture leaves the burner port. Flow velocity can be modified either by altering the gas flow or the primary air supply. Adjusting method; By increasing the rate of gas flow through orifice, By widening the primary air opening Distribution of flow velocity Friction of the port walls slows down the flow velocity until it reaches zero at the port walls. Flame Speed Flame speed is the speed at which a flame moves through a fuel-air mixture. Burning velocity Rate of flame Flame speed propagation Ignition velocity Flammability Limits Flame Speed and Limits of Flammability Decrease or increase the percentage of the gas-air mixture, the flame speed decreases or increase correspondingly Methods of Measuring Flame Speed Bunsen burner flame and One-inch diameter tube the graphed result. test. Flame speed of different gases (calculated using Bunsen method)  Type of gas Test method Gas-air ratio employed Factors Influence the Measurement of Flame Speed Relation of the flames to Size and energy- shape of the absorbing container sinks Temperature of the mixture  Combustion at the Port At some distance above the Since flow velocity is highest After the gas-air mixture burner port, the flow at the port centerline, the leaves the burner port, it velocity equals burning flame stabilizes the furthest slows down. speed, and the flame from the burner port around stabilizes at that point. the centerline. The flame also stabilizes at For this reason, the inner lower points near the burner flame assumes its typical wall, where flow velocities conical shape fall off. Stable Flame: The Requirements Characteristix Quality Requirement Definition: “A stable flame is a flame that does not waver, lift off the burner, or flashback into the mixing tube” Qualities of a Stable Flame Outer Mantle Outer Cone A stable atmospheric Bunsen burner flame has several color Inner Cone zones. Unburned mixture gas + primary air Inner cone Outer cone Outer mantle Thin blue cone on the Darker bule cone, outer Colorless mantle that burner tip. The inner cone cone that surrounds the surrounds the outer cone. marks the first step in the inner cone. This is where Since burning is usually burning process where gas the secondary air diffuses completed at the outer is burned to form products into the flame. cone, there are almost no such as aldehydes, If enough secondary air is unburned gases at the alcohols, carbon monoxide present, and other outer mantle. and hydrogen. conditions are favorable, This nearly invisible mantle The velocity of the products from the inner only glows because of the unburned gas-air mixture cone are completely combustion products' high forms the shape of the burned here, yielding the temperature. inner cone final products: carbon dioxide and water vapor. Requirements of a Stable Flame Must maintain a fine balance between the flame speed and the flow velocity. Adjusting the primary air supply or the gas flow rates will change the flame speed and flow velocities. Parameter Primary Air Gas Supply Supply Primary Air Supply The primary air supply sets the flame characteristics. Adjustments to the air supply will cause the flame to change shape and color. Air increase Percentage of primary air increases, the flame sharpens, and thinner cone gets smaller Adjustment of the primary air creates a 10% gas-air mixture (NG), maximum flame speed is reached Beyond this point, although adding more primary air increases flow velocity, the flame speed slows down proportionately. The flame start to lift off the burner port. Further increase of primary air supply  complete flame liftoff. Air decrease Burning speed decreases, since more secondary air is required to complete combustion. The flame gets longer and burning speed slows down If further reduced, yellow tips appear in the flames. The flames will become completely yellow if all primary air is shut off. Gas Supply Amount of gas-air mixture passing through a port-called "port loading“ Burner port-loading is expressed as the number of Btus per square inch of port-area Port loading can be changed by altering either the orifice size or the gas pressure (manifold pressure) Un-Stable Flame: The Cause If any condition changes the balance between the flow velocity and the flame speed, unstable flames are created. Unstable flames are unacceptable on an atmospheric burner as they cause incomplete combustion or delayed ignition Lift-Off Unstable Flames Flashbac Other k Flashback Flashback is a condition in which the inner cone is inverted. It extends into the port, rather than above it. If a combustible mixture is left in the burner head, it may ignite very dangerous for the operator as well as for the equipment. If burning continues in the burner head, incomplete combustion occurs as well as soothing of the burner.  Reduced flow velocity Faster Overheated burning burner gases During Underfired ignition burner Leaking Extinction burner pop Remedies for Flashback Lifting Flames Caused when the flow velocities of the gas-air mixture from the ports is greater than the burning speed Lifting flames can be very dangerous. Because the flame cones rupture, the gases do not burn completely, and they produce aldehydes and carbon monoxide. These by-products of incomplete combustion are toxic. Due to the incomplete combustion, all of the heat content of the gas may not be released in the appliance, causing a drop in efficiency  Shallow ports Faster Cold burning burner gases Increased Overfired flow burner velocity Lower Excessive burning gas speed pressure Excessive primary air Remedies for Flashback  Other Unstable Flames Yellow Tips Waving Flame indicate a problem with the primary air Occur when the flame is pushed off the intake burner by excessive air movement due to caused by glowing carbon particles in the drafts or cracked heat exchangers flames can usually be eliminated by increasing primary air. Other Unstable Flames Floating Flames a "lazy" flame with undefined cones, reaching for air and rolling in the combustion chamber This flame usually indicates incomplete combustion. Flame Rollout Flames rolling out of the combustion chamber when the burner is turned on indicates flame rollout  Complete combusti on Wide Rapid turndown carry over ratio of flames Performance Characteristic Uniform Quiet heating operation Stables Immediat flame e ignition Complete combustion burner must be capable of mixing gas and air together  fuel is completely burned. NO carbon monoxide or other harmful by-products produced. Rapid carry over of flames When ignited, the gas burner flame front must pass smoothly and rapidly over the burner surface. In the case of a multi-port burner, the flame front should not delay as it moves from port to port. All ports must ignite. Quiet operation Burners must ignite quietly either at ignition or during the run cycle. Burner shut-down should also be smooth and quiet, not creating an extinction pop Immediate ignition There should be no delay in burner ignition Stables flame Designed input with correct air adjustment should produce a stable flame. The flames should stay close to the burner ports NO lift off flame NO flash-back flame Uniform heating A burner must provide uniform heating across its surface. Uneven heating causes excessive stress on heat exchangers and boiler tubes. Wide turndown ratio Turndown ratio – or turndown rate – is the range of inputs satisfactory combustion. Many burners operate at a fixed input. Others, such as range-top burners, must vary their input from high to low. A turndown ratio of 5 to 1 means the burner input can vary from 20% to 100% of rated input and still maintain stable flames at the burner ports.  The fuel is discharged to the burner through the orifice cap, spud or other device. The orifice is not part of the burner, but it is such a vital part of the burner system that it is included in the discussion of burners. Orifice The air shutter adjusts the size of the primary air inlet(s). Some burners have a fixed primary air inlet and are designed for particular gas at a specific gas pressure. Primary air Most burners, however, have an adjustable air shutter to adjust the primary air shutters flow The venture is a short tube with a constricted, throat-like passage. This passage increases the velocity and lowers the pressure of a gas passing through it. Venturi Most atmospheric burners are necked down to a venture throat.  The mixing tube is the portion of the mixer that lies between the venture and the burner head. The gas and primary air mix together as they move along this tube Mixing tube The burner head uniformly distributed the air-gas mixture to the burner ports. Its size and shape can be tailored to fit an appliance combustion Burner head chamber and to provide even heat release to heat transfer surfaces. The burner port is an orifice, or opening, that does three things, Discharges the air-gas mixture for ignition. Distribute flames to provide an even heat transfer to heat exchanger. Burner ports Spreads the flames so they can be reached by secondary air