RESIDENTIAL AND COMMERCIAL LIGHT OIL BURNERS PART-1 By: William D. Fitzgibbons INTRODUCTION

Transcription

1 Service Application Manual SAM Chapter A Section 12 RESIDENTIAL AND COMMERCIAL LIGHT OIL BURNERS PART-1 By: William D. Fitzgibbons INTRODUCTION The primary objective of this section is to provide the Refrigeration Service Engineer with a working knowledge of the oil fired heat source in Total Comfort... Installation, Service Techniques, and Preventive Maintenance Procedures. While generally applicable, information provided will always be superseded by the burner manufacturer s specifications. All data will be confined to burners of the pressure atomizing type designed to burn #2 Fuel Oil. Although commonly known as residential type burners, advances in both burner design and control components have resulted in manufacture of equipment with rated capacities of in excess of twenty (20) gallons of fuel per hour for commercial and industrial applications. burner components A pressure atomizing burner is usually comprised of the following components as shown in Figure 1. Blast Tube Blower Housing Motor Fuel Pump Blower Wheel Pedestal or Flange Mount End Cone or Choke Ring High Voltage Ignition Transformer Ignition Electrodes Electrode Mount Nozzle Pipe Figure 1 Copyright 1978, 2009, By Refrigeration Service Engineers Society. -1-

2 Delayed Oil Valve (Some Models) Nozzle(s) Air Diffuser Ignition Wires or Bars Pump Drive Couplings Nozzle Adapter Air Volume Controller component location and function Burner Blower Housings are designed for Blower Wheel location above or below center line of Blast Tube, and left or right side motor location resulting in clockwise or counter clockwise rotation of motor, blower, and fuel pump, according to burner manufacturer s design. The blast tube, either an integral part of, or attached to blower housing, houses the firing assembly consisting of nozzle pipe, nozzle(s), electrode mount and electrodes, nozzle adapter, and air diffuser. Burners are available with blast tubes of varying lengths to facilitate proper installation in boilers and furnaces with enclosing panels. The end cone or choke ring is attached to open end of blast tube. According to burner design, the high voltage transformer may be mounted on either side of blower housing or fastened to top of inboard end of housing by a hinge, serving as a cover for the opening providing access to firing assembly. When attached to side of housing, transformer high voltage terminals are accessible from inside housing and are connected to ignition electrodes with cables or preformed bars provided. When transformer is mounted on top of housing, terminals are connected to electrodes with a variety of spring or wiper contactors. High Voltage current is generally 6,000 to 12,000 volts. Extreme caution should be used when checking operation of this component. Figure 2 Typical Nozzle and Electrode Assembly Copyright 1978, 2009, By Refrigeration Service Engineers Society. -2-

3 The blower wheel is usually mounted directly on motor shaft, and is centered in housing. Fuel pump is mounted on side of blower housing directly opposite motor and connected to motor shaft or blower wheel hub by means of flexible coupling(s) provided. Fuel pump nozzle port is connected to nozzle pipe with soft copper tubing, usually1/4 O.D., where pipe projects through blast tube or blower housing wall. Final connections are made with flared or housing compression fittings. (Figure 2) Fuel pumps commonly used are Webster and Sundstrand. Pump function is to transport fuel oil from tank and discharge it to nozzle(s) at proper atomizing pressure. Pumps are available for both clockwise or counter clockwise rotation, and with left and right hand nozzle ports and left or right hand inlet or suction ports to meet the requirements of various burner manufacturers. Pumps are also designed for use with One or Two Pipe fuel transportation systems. Field changes required will be outlined under Adapting Fuel Pumps to One- and Two-Pipe Systems. Ignition Electrodes are steel rods encased in porcelain insulating tubes. One end terminates in a suitable connector for the high voltage cable or bus bar, and the other end which extends several inches or more beyond its insulating tube, is bent slightly in order to obtain the correct distance between opposing tips when electrodes are assembled in mount, which is part of firing assembly. This distance is known as the spark gap, and is generally specified as 3/16. Distance between center of nozzle(s) and electrode tips vertically, and distance between tips and face of nozzle horizontally governed by angle rating of nozzle used, see Figure 2 for details of electrode setting. It is important that porcelain insulators be dry and clean, as carbon deposits, dust or oil film will permit high voltage current to circumvent spark gap and cause ignition failure and safety shutdown of oil burner. nozzle pipe assemby The nozzle pipe assembly, components of which are covered under a previous heading, is constructed to suit the requirements of a specific burner and no two assemblies will be alike in every detail. A typical assembly is shown in Figure 2. Nozzle pipes may be straight or bent in various ways dependent upon the location at which they project through blast tube or blower housing wall for connection to fuel pump nozzle port. No adjustment of components other than spark gap dimension should be made without first consulting burner manufacturers instructions. Changes in flame pattern are sometimes made by moving nozzle pipe forward or backward in slotted attachment hole, in accordance with burner manufacturers instructions. blower wheel The blower wheel forces what is described as primary air through blast tube where diffuser and choke ring create required turbulence and mix air with the oil spray which is ignited by high voltage spark at electrodes, producing the desired flame pattern and complete combustion. Excess primary air will produce a raw, inefficient flame and insufficient primary air conversely will produce a smudgy, smoky flame resulting in excessive sooting of boiler of furnace and inefficient operation. A primary air volume control is provided on inlet side of blower housing. Correct primary air adjustment is indicated by presence of a slight haze over fire, with no evidence of smoke in combustion chamber or heat exchange areas of boiler or furnace. oil burner installation condition of existing heating equipment Before installing an oil burner in an existing boiler or furnace, it is important to investigate the condition of heating equipment to determine whether the plant can be satisfactorily oil-fired in its present condition or whether repairs are required. Particular care should be taken to determine if there are any leaks in heat exchanger of warm air furnace. Warped or cracked fire, ash-pit, and cleaning doors should be repaired or sealed in order that excess air infiltration may be reduced to a minimum. Copyright 1978, 2009, By Refrigeration Service Engineers Society. -3-

4 Overall dimensions of the ash-pit should be checked to establish whether a suitable combustion chamber can be constructed and to determine the length of burner blast tube required. heating requirements and boiler or furnace capicity If there is any indication that heating requirements are in excess of installed boiler or furnace capacity, it is advisable to check the heating load in accordance with the formula established by the American Society of Heating and Ventilating Engineers, as set forth in the A.S.H.V.E. Guide. If boiler or furnace is undersize for the load, excess fuel consumption will result. In addition, an undersized unit may not provide sufficient heat during unusually cold weather, and sluggish operation and unequal heat distribution will be experienced. Ratings of installed heating boilers may be obtained from a pamphlet published by the Heating, Piping, and Air Conditioning Contractors National Association, Net Load Recommendations for Heating Boilers. The ratings published in this pamphlet list the net steam load in square feet of direct standing radiation. In order to obtain the maximum output of boiler, it is necessary to add a suitable factor, approximately one third, for piping and pickup load. The institute of Boiler and Radiator Manufacturers (IBR) and the Steel Boiler Institute (SBI) have established ratings in gallons per hour (GPH) for boilers. These ratings will be indicated on more recent boiler installations. The National Warm Air Heating and Air Conditioning Association has established similar ratings for forced warm air heating furnaces. These ratings will be noted on furnaces of more recent manufacture and may be found in the fourth edition of Technical Code for the Design and Installation of Mechanical Warm Air Heating Systems. Maximum burner efficiency will be realized when a firing rate is selected that is no larger than actually required to carry the heating load, yet large enough to be responsive to the heat demand. Listed in Table 1 are the approximate furnace or boiler loads that can be satisfactorily carried by nozzles of various capacities. Table 1. Maximum Furnace Or Boiler Loads Corresponding To Various Nozzle Capacities NOZZLE CAPACITY OUTPUT MAXIMUM BOILER CAPACITY Oil Input in Gallons per Hour At Furnace Bonnet or Boiler Output in BTU Per hour Equivalent Direct Radiation [EDR]* Steam Gravity Hot water , , , , , , , , , , , , , , , , , ,000 1,040 1, ,000 1,250 2, ,000 1,460 2, ,000 1,667 2, ,000 1,870 3, ,000 2,083 3, ,000 2,500 4, ,000 2,917 4, ,000 3,333 5, ,000 3,753 6, ,000,000 4,167 6, ,200,000 5,000 8, ,400,000 5,833 9, ,600,000 6,667 10, ,800,000 7,500 12, ,000,000 8,333 13,333 Copyright 1978, 2009, By Refrigeration Service Engineers Society. -4-

5 * Includes net direct standing radiation, plus one-third allowance for piping and pickup load, plus domestic hot-water load. Equivalent Direct Radiation (EDR) for domestic hot water: Steam Systems 1.5 tank storage capacity in gallons Hot-Water systems 2.0 tank storage capacity in gallons size and location of oil storage tank inside tank If space is available in basement, an inside fuel storage tank is generally used because it is less expensive than an outside tank installation. Customary size is 275 gallon capacity, usually of the vertical-oval type, measuring 26 inches in width, 42 inches in height, and 67 inches in length. A check should be made to determine if a tank this size can be brought into basement through doors and passageways. Oil storage tanks located inside buildings shall not exceed 275 gallon, individual capacity, or 550 gallon, aggregate capacity, unless installed in a specially designed fireproof enclosure in compliance with local regulations. A tank should be located so that it is not less than seven (7) feet in a horizontal direction from any fire or flame. It is necessary also, to place an inside tank in a location permitting compliance with local regulations regarding fill and vent piping. The 275 gallon tank should be supported on 1-1/4 12 pipe legs terminating in 1-1/4 floor flanges. After leveling, flanges should be anchored in cement to prevent movement. outside tank Where available basement space is at a minimum or if storage capacity in excess of 550 gallons is required, the oil tank will usually be placed outside of building and buried below ground. Rules of the National Board of Fire Underwriters (Pamphlet #31) should be followed in locating and installing underground fuel storage tanks. Outside underground tanks should be buried with an earth cover of not less than two (2) feet, or covered by not less than one (1) foot of earth, on top of which has been placed a concrete slab not less than 4 thick. When installing an outside tank it is advisable to first check location of sewer, gas, and water mains entering building. The tank should be located with ample clearance between tank and these pipes in case any of them have to be replaced or serviced in the future. tank piping fill pipe Basement installed tanks require a 2 diameter fill pipe which should terminate outside basement wall at least 5 from any window or building opening. Fill pipe should rise at least 12 above horizontal run outside building and terminate in a tamper proof cap. An indirect fill pipe from outside tank should have double swing joints at both tank and building, and fill pipe emptying directly into tank vertically should terminate not less than 12 above grade to prevent any flood water from seeping into tank. A flush with grade type of fill may be approved if enclosed in water-tight well. When an indirect fill pipe is installed, it is advisable to install a tee fitting at tank and run a combination emergency fill and tank cleaning medium to grade level, capped with watertight fitting. Size of fill pipe for outside tanks will be governed by local regulations based on tank capacity, never less than 2, however. Copyright 1978, 2009, By Refrigeration Service Engineers Society. -5-

6 vent pipe Vent piping for basement or buried oil tanks should not be smaller than 1 1/4 diameter, and shall terminate outside of building at a point not less than 2 feet, measured vertically and horizontally from any window or other building opening. Top of vent pipe must have a return bend or approved vent cap and should extend above grade high enough to prevent being obstructed by either snow or ice. Most communities have specific regulations governing vent pipe height, however, 8 feet above grade is generally accepted. Whether connected to a basement or outside tank the vent pipe should pitch downward toward tank throughout its entire length. A Ventalarm is a must in basement tank installations and is recommended on outside tanks for added safety and convenience in filling. suction and return piping One pipe system function satisfactorily in basement tank installations generally, however, two pipe systems are recommended on all installations, as with this arrangement the fuel pump will purge itself of air automatically and, under emergency conditions, the return line may be used as a suction line. When an outside tank is installed below burner, a two pipe system is mandatory. Changes required in burner pump assembly for One and Two Pipe systems application will be covered in subsequent paragraphs. Most communities permit use of soft copper tubing for suction and return piping between tank and burner using #2 fuel oil, with connections made with flare type fittings. In most basement tank installations, 3/8 OD tubing is satisfactory for both suction and return lines, and 1/2 OD tubing may be used when outside tank is not more than 50 feet from burner. Both suction and return lines should extend to within 3 inches of tank bottom, using slip fittings in tank tappings. A check valve should be installed in suction line at outside tank and tubing should pitch upwards from tank to building wall. Tubing should be formed into loop at tank to allow for minor settling. Some localities require gate valves in suction line both inside and outside of building wall. Installer should familiarize himself with all local regulations before starting installation. Hand valves should never be installed in return line, a return line valve accidentally closed could result in pump breakage and disastrous fire hazard conditions. A variety of fuel oil gauges are available for both basement and outside tank installations and one should be installed, following manufacturer s recommendations. A typical basement tank installation is shown in Figure 3 and an outside tank installation is covered in Figure 4. Figure 3 Typical inside tank installation Copyright 1978, 2009, By Refrigeration Service Engineers Society. -6-

7 Copyright 1978, 2009, By Refrigeration Service Engineers Society. -7-

8 Figure 4 Typical outside tank installation figure 8- One And Two Pipe Changeover-Witout extra parts adapting pumps to one or two pipe fuel supply systems Two most widely used Fuel Units (pumps) are... Sundstrand and Webster. Field changes to adapt these Fuel Units to One or Two Pipe systems are as follows: Sundstrand, Model J and H, Two Pipe System, remove 3/8 pipe plug from return line port. Insert 1/8 socket head pipe plug (provided with unit) into tapping in return port opening, using 3/16 Allen Wrench, and draw up tight. Connect return line to tank to return port. For One Pipe System the 1/8 pipe plug must be removed and return port plugged. Figure 5 shows details. Webster all 6000 and 8000 Series units as Figure 6 indicates Letter P is stamped on pump body adjacent to suction strainer housing cover. Suction strainer housing cover has symbols S1 and S2 stamped on top at opposite sides. When S1 symbol is over P stamped on pump body, unit is adapted for One Pipe System. To reverse as required, remove four screws holding suction strainer housing cover, making sure not to damage gasket. Remove small guide stud from underside of cover with small screwdriver and replace on opposite edge of cover. Replace cover with required symbol (S1 or S2) over P stamping. Return port is plugged for One Pipe System. Webster, type 1R and 2R units illustrated in Figure 7. No special tools are required to change these units from One to Two Pipe Systems. Simply insert a small screwdriver into inlet opening on side marked RET and draw 1/4 by-pass screw tight for Two Pipe System. For One Pipe System, unscrew by-pass screw three (3) complete turns and plug return port, reference Figure 8. Copyright 1978, 2009, By Refrigeration Service Engineers Society. -8-

9 Figure 7 Copyright 1978, 2009, By Refrigeration Service Engineers Society. -9-

10 . No special tools or extra parts are needed to change Webster Service-Saver Fuel-units from a one to two-pipe system. Simply insert a screw driver into the inlet opening on the side marked RET, tighten the 1/4 screw and attach the return line for a two-pipe system. When one pipe system is used, plug is inserted in bottom chamber and 1/4 screw is unscrewed three complete turns. fuel units, ajusting nozzle pressure Sundstrand Fuel Units Pressure adjusting screw is located under cap opposite nozzle port. To adjust pressure, stop burner and remove 1/8 plug adjacent to return port. Insert 150# gauge in tapping and restart burner. Remove cap from pressure regulator screw and turn in or out with small screwdriver to obtain standard 100# pressure. Stop burner and replace 1/8 plug and cap. A small container should be kept handy to collect residual oil discharged during disassembly and assembly operations. Webster Series 6000 and 8000 Fuel Units Nozzle pressure adjustment medium is an Allen Screw located under small slotted head screw centered in top of pressure regulator cover. To adjust, stop burner, remove slotted head screw and 1/4 plug in side of regulator body and insert 150# pressure gauge in 1/4 tapping. Restart burner and turn Allen Screw in or out until nominal nozzle pressure of 100# is obtained. Stop burner and replace 1/4 plug and slotted head screw, making sure that small gasket under screw head is intact. Webster Series 1R and 2R Fuel Units Nozzle pressure adjustment medium is screw under cap opposite nozzle port. To adjust, stop burner and remove adjusting screw cap and pipe plug nearest nozzle port. Insert 150# pressure gauge in pipe tapping. Restart burner and turn pressure adjusting screw in or out to obtain nominal 100# nozzle pressure. Stop burner and replace pipe plug and adjusting screw cap. combustion chamber or firebox The Combustion Chamber or Firebox is a most important requisite to efficient Oil Fired System operation. It is, as the name implies, a chamber or box in which combustion takes place. The burner blast tube is inserted in opening left in front wall of chamber to Copyright 1978, 2009, By Refrigeration Service Engineers Society. -10-

11 a minimum of 1/4 from inside face of wall. Many furnaces and boilers of recent manufacture incorporate factory installed combustion chambers with provision for either specific or universal oil burner installation. Older heating plants require on the job combustion chamber construction. Combustion chambers may be constructed of hard fire brick or soft insulating brick capable of withstanding temperatures of from 2,600 F to 3,000 F. More recently, however, combustion chambers are being prefabricated of stainless steel or in sectional units of preformed refractory material in an assortment of shapes and sizes. Sections are assembled in furnace or boiler and joints sealed with suitable high temperature cement. Space Age Technology has also made available several forms of blanket type high temperature insulating material in sheets or preformed, which may be used to reline an inefficient existing combustion chamber or construct a new one. This material, produced under a variety of trade names, may be cut with a scissors and formed like fiberglass. When subjected to high temperatures it hardens and becomes self supporting. Joints in all combustion chambers (bottom, sides, and around blast tube of burner) must be sealed to prevent infiltration of air other than that supplied by burner blower. Figure 9 shows cutaway view of typical field constructed combustion chamber. Combustion chamber top is open to allow hot gasses to circulate through passages of boiler or furnace and effect required heat exchange. Any space between outer surfaces of chamber and boiler or furnace must be filled with loose insulating wool or pellets. If floor of chamber is laid on concrete floor at least 1 of dry asbestos, block insulation, or hollow tile should first be laid on floor to guard against buckling of concrete floor due to excessive heat transfer. Combustion chambers are sized for input of boiler or furnace in Btu s, as converted to gallons of fuel oil burned per hour, and shaped to fit the physical dimensions of the boiler or furnace. Shape of combustion chamber also dictates angle of nozzle to be used in burner. See Table 2 for chamber size and nozzle data. 80 Sq. In. Per Gal. 90 Sq. In. Per Gal. 100 Sq. In. Per Gal. Nozzle Size GHP Sq. Inch Area Combustion Chamber Table II Combustion Chamber Data Dia. Round Combustion Chamber Inches Square Combustion Chamber Inches Rectangular Combustion Chamber Inches Wth. Lgth. Height From Nozzle to Floor Inches / / /2 10-1/2 11-3/ / /2 11-1/ /8 12-5/8 14-1/ / /4 14-1/ / /2 15-1/2 17-1/ / /4 17-1/ / / / /4 21-1/ /2 23-1/ / /2 24-1/ / /2 25-1/ / /2 26-1/ / /4 27-1/ /4 28-1/ /4 29-1/ / /4 31-3/ / /4 33-1/ / /2 34-1/ /2 37-1/ /4 38-3/4 Round Combustion Chambers usually / /4 41-1/4 42-1/2 42-1/2 not used in these sizes / Sq. Ft. of Steam Rad. (Approx.) The above data applies to the majority of conventional pressure atomizing burners. There are some models of burners that will require a different height from floor to nozzle. Consult your burner manufacturer. You will note the absence, in Table II, of a dimension from center of nozzle to top of combustion chamber. This dimension should always be twice that of nozzle center to floor of chamber. The reason for twice as much refractory above the nozzle as below is that all combustion should take place in the presence of red hot refractory. Above the combustion chamber there should be no flame, only completely burned gases. In no case should combustion chamber walls extend more than three or four inches higher than boiler water leg (bottom of water filled section). To do so reduces effective heating surface of boiler. When dimension from center of nozzle to top of chamber requires chamber walls to be extended beyond this height, the use of twin nozzles is recommended, for example, Copyright 1978, 2009, By Refrigeration Service Engineers Society. -11-

12 two seven gallon nozzles mounted in horizontal adapter instead of fourteen gallon nozzle. When this is done chamber height need only be that required for a seven gallon nozzle. It should be noted however that all chamber walls should protect a minimum of three inches of the boiler water leg from direct flame. Whether a boiler is round or square it is recommended that a round combustion chamber be used whenever possible. Figure 10 shows how, in a round chamber, gases can sweep back and continue mixing with atomized oil for more complete combustion. Figure 11 shows how, in a square cornered firebox, air strikes back wall, goes right and left and strikes other walls. This air travels up each corner of firebox, reduces gas temperatures and results in lower CO 2 readings, indicating low efficiency. From these illustrations it can be seen that when a square or rectangular chamber must be used, square corners must be eliminated, as shown in Figure 12. When combustion gas travel is up through the back sections of boiler, the rear wall of combustion chamber should be of corbel or throwback construction to cause gases to sweep back towards the boiler door, effecting greater heat exchange in forward sections before leaving boiler. Figure 12 also shows a side view of corbel construction. It cannot be overemphasized that whether the combustion chamber be round, square, or rectangular, all space between its walls and boiler or furnace must be filled with loose insulation fill and a sealing cap of refractory cement placed over top of walls and trowelled into all crevices and section configurations. Space between burner blast tube and opening in front wall of chamber must be sealed with asbestos rope or refractory cement. mounting burner If heating plant is prepackaged, burner will either be mounted at factory or provision made for flange mounting with mounting holes pre-drilled and tapped for easy assembly. When installation is made in previously coal fired boiler or furnace, burner is usually floor mounted. Copyright 1978, 2009, By Refrigeration Service Engineers Society. -12-

13 Pedestal mounts generally permit height adjustment adequate for centering of burner blast tube in opening left in front wall of combustion chamber. When this is possible, burner base may be anchored directly to concrete floor. When additional height from floor is required, burner base should be supported at the correct height by pieces of unused firebrick or other non-inflammable material and short lengths of 3/8 threaded rod with lower end bent at 90 x 1 suspended from base anchoring holes with nut and washer above base. A simple wooden form with inside measurement several inches larger than burner base is then placed in position and filled with Portland cement or Sakrete mix to the level of burner base. When concrete base has set, anchor nuts may be tightened securely. Burner should be centered with relation to side walls of chamber and centerline of nozzle should be correct height from chamber floor. Burner blast tube should pitch slightly (max. 1/16 over its length) towards combustion chamber to prevent oil leaking from any firing assembly malfunction from flowing back to blower housing and on basement floor. Copyright 1978, 2009, By Refrigeration Service Engineers Society. -13-