US3003546A - Domestic heating devices - Google Patents

Description

Oct. 10, 1961 w. A, BEACH ETAL DOMESTIC HEATING DEVICES s Sheets-Sheet 1 Filed June 27, 1956 2 3 31:15::E555u5:553525 5 T? 0 Mm? 6 2,) 2 n Ea E :E :EEEE 155111;;

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William A Beach Robert L. Burke Inventors David R. Hogin Paten Attorney Oct. 10, 1961 w. A. BEACH EI'AL 3,003,546

DOMESTIC HEATING DEVICES Filed June 27, 1956 3 Sheets-Sheet 2 FIG.- 3

William A. Beach Robert L. Burke Inventors David R. Hogin Potent florney Oct. 10, 1961 w. A. BEACH ETAL 3,003,546

DOMESTIC HEATING DEVICES Filed June 27, 1956 :s Sheets-Sheet 3 William A. Beach Robert L. Burke Inventors David R. Hogin Patent Attorney 3,003,546. 1C Patented Oct. 10,1961

3,003,546 DOMESTIQ TEEATING DEVICES William A. Beach, Nixon, Robert L. Burke, Fanwood, and David R. Hogin, Berkeley Heights, N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware Filed June 27, 1956, Ser. No. 594,186

2 Claims. (Cl. 158-4) 1 This invention relates to improvementsin heating devices and more particularly relates to design of combustion chambers for use with small capacity high pressure oil burners in heating houses.

The majority of home heating devices using oil as a fuel are of the gun type or high oil pressure, relatively low air pressure type. Conventional high pressure gun burners which have a low oil capacity are inefiicient and give off obnoxious smoke. If excess air is used to reduce smoking, then poorer heat efiiciencies are obtained. These burners normally require from 40% to 150% excess air to give clean combustion. These amounts of excess air reduce the burner efiiciency by about 8% to 25%. If the burners are adjusted to use only the air theoretically needed for complete combustion, they give a very smoky flame. The smoke or soot formed coats the heat exchange surfaces and this further reduces the heat efficiency. Because of the tendency of oil to smoke in domestic heating devices, the heat exchangers have been made with relatively large passageways to avoid clogging and such heat exchangers are much less efiicient than the ones with smaller passageways.

In most cases, oil-fired heating units or devices are oversized, that is, they are larger than the house requires. One of the reasons for this is that the lower capacity oil burners have a greater tendency to smoke than the larger sizes. The relatively large oil burners now in use run for shorter heating periods and have a longer downtime and therefore longer time for standby stack losses, that is, there is more opportunity for stack loss during the longer down periods. These greater downtime stack losses result in a lower seasonal cfiiciency. To reduce these losses, therefore, this invention provides a burner that will operateeificiently at a low firin rate.

It has been discovered that smoke formation in conventional low capacity domestic type heating equipment is related to the nature of the flow of the burning gases in the combustion chamber. Smoke is formed when the burning gases. are in streamline flow. Smoke is not formed when the burning gases are in turbulent flow, provided the burner is designed properly.

,At low oil rates of below about 1.25 gallons per hour, the conventional combustion chambers are too large to give turbulent flow of the gases when no excess air is used. When using the conventional combustion chambers at low oil rates, therefore, the air rate has to be increased beyond that theoretically needed for complete combustion in order to obtain turbulent flow and no smoke, so the etficiency of the heating equipment is reduced. This range of below 1.25 gallons of oil per hour is very important because it is large enough for most modern homes. The average modern home in the New Jersey area, for example, requires only about 0.75 gallon of oil per hour for heating.

It has been found that smoke can be eliminated from combustion gases from high pressure oil burners fired at low oil rates while operating at high efficiency, if turbulent flow is maintained in the combustion chamber, assuming proper atomization of the oil fuel in the air. A test was made using a combustion chamber of substantially the same size as a conventional combustion chamber and using oil at different rates around one' until smoke formed and it was found that at the lower oil rates, more excess air was necessary to prevent smoking, but in all cases the total volume of air introducedinto the combustion chamber was substantially the same and this amount of air resulted in turbulent flow in the combustion chamber. Smoking occurs when the flow of the gases through the combustion chamber is streamline flow as compared to turbulent flow.

The efficiency of high pressure oil burners fired at oil rates (below 1.25 gallons per hour) can be improved by designing the combustion chamber to give turbulent flow with no excess air or little excess air. accomplished by constructing the combustion chamber with a much smaller cross sectional area (normal to the flow of the burning gases) than a conventional com bustion chamber. It also may be accomplished by inserting packing or bafiles into the combustion chamber.

A suitable oil burner similar to conventional oil burn-- ers of the high pressure oil burner type is used wherein the nozzle is selected to supply oil at any rate below 1.25 gallons of oil per hour. The burner is supplied with a fan to supply the theoretical amount of air for combustion of the oil or slightly more than the theoretical amount. The oil is atomized in passing through the oil nozzle and thoroughly mixed with the air in conventional manner to obtain exceedingly good mixing which is also important in preventing smoke formation.

According to the present invention, home oil heating devices are designed so that they do not produce smoke when using little or no excess air. Two important mixing zones have been found for conventional high pressure gun burners. One of these mixing zones is the immediate area surrounding the air and oil injection system. The other of these mixing zones is the combustion chamber. By proper sizing of the combustion chamber in relation to the oil feed rate to the burner, clean burning.

at low air rates is obtained.

In the drawing:

FIG. 1 represents apartial vertical cross-section of one form of an oil heating device; 1

'FIG. 2 represents a partial enlarged cross-sectional view of the oil burner;

FIG. 3 represents a diagrammatic elevational view of another form of heating device in which the burner is at the top of the heating device;

FIG. 4 represents a vertical crosssectional view of or blower section 16 (not shown in detail but of conventional design). The main portion of oil line 14 is arranged centrally of blast tube 15 and exteudslongitudinally therethrough to leave a space 17 for the passage of air from blower section 16 to the combustion chamber presently to be described. The outlet end of the oilline 14 is provided with a nozzle 18 for atomizing the oil for admixture with the air introduced by the fan or blower section 216. Blast tube "15 is preferably provided adjacent its outlet end with internal vanes 19 which are helical vanes to give the air introduced from blower section 16 a swirling motion. In this way good mixing of the atomized oil and air is obtained. The burner 12 is provided with an air orifice member 20 having a central opening 21 arranged adjacent the outlet end of blast This may be.

3 tube beyond-the nozzle 18 of the oil line 14. Electrodes 22 are diagrammatically shown in FIG. 1 for igniting the oil-air mixtureiutroduced into the combustion chamber 23.

As shown in FIG. 1, the outlet end of blast tube 15 is securely attached to horizontally arranged portion 24 of the, combustion chamber 23 in any suitable manner. The combustion chamber 23 has a vertical portion 25 and an open outlet end 26 arranged substantially centrally in the lower portion of the heating device or furnace 10. The combustion chamber 23 may be circular, square or rectangular or other shape in cross section and as shown in FIG. 1 the combustion chamber is substantially square. The combustion chambers of the present invention are preferably of uniform cross sectional area. The space or region 27 around the combustion-chamber 23 in the lower portion of the furnace 10 may be left open so heat is radiated from the combustion chamber to the heat transfer surfaces 28 shown at the top, bottom and side walls of the furnace shell 10. For a hot water heater the heat exchange surfaces contain water as shown.

The upper portion of the furnace or boiler 10 is provided with off-set baffies 29 and 36 in order to cause the combustion gases to take a circuitous path through the boiler. The combustion gases leave the furnace 10 through stack 32. Baffles 29 and comprise heat exchange elements. Other arrangements of heat exchange devices may be provided in the furnace 10.

Referring now to FIG. 3, the furnace or shell 46 is shown as a vertically arranged cylindrical member with the burner 48 arranged at the top of the furnace 46 and having the outlet end of its blast tube 49 directed downwardly into furnace 46. The burner 48 is provided with a conventional fan or blower section 52 (not shown in detail) and oil line 54 provided with outlet nozzle 56. The outlet end of blast tube 49 extends a short distance into the furnace 46. Forming an extension of burner 48 is a combustion chamber 58 which is shown as a vertical chamber which may be circular, rectangular or any other shape in cross section and which extends downwardly from the top of the furnace. The lower end of the combustion chamber 58 has an outlet 62 spaced a distance above the floor of furnace 46 for the combustion gases leaving the combustion chamber. A vertical bailie 64 is provided inside the furnace 46 which extends upwardly from the bottom of the furnace to near the top of the combustion chamber 58 but spaced therefrom as shown at 64'. Baffle 64 is substantially parallel to combustion chamber 58 and extends across the furnace or shell 46 to form two separate compartments at the bottom of the shell 46. The combustion gases from the outlet end 62 of combustion chamber 58 pass upwardly in the shell 46 to the left of baffle 64 in FIG. 3, then over the top of bafile 64 through space 64' and then down in the shell to the right of battle 64 through space 66 to the bottom outlet 68 leading to a stack (not shown). Any conventional heat exchange surfaces may be provided in the lower portion of the furnace or boiler housing 46 and in the space 72 between the combustion chamber 58 and the adjacent side wall of the furnace 46. The baflle 64 may be provided with heat exchange fluid.

Referring now to FIG. 4 an arrangement similar to that shown in FIG. 1 is set forth but in this form of the invention there is a different arrangement of the burner. In this modification the oil burner 82 provided with a blower section 84, oil line 86, blast tube 87, and nozzle 88 are arranged to extend into the lower portion of the furnace housing 90. Diagrammatically shown are helical vanes 92 arranged behind or upstream of the nozzle 88 for giving the introduced air a swirling movement for admixture with the atomized oil. The outlet from the burner is arranged in the bottom of a vertically arranged combustion chamber 94 having an outlet 96 at its upper end arranged some distance below the roof of housing 90. The combustion chamber may be rectangular, square or circular in cross section or any other shape but is preferably circular in cross section. The furnace is pro vided with a stack 98. Any conventional or suitable heat exchange surfaces or devices (not shown) may be provided in the upper portion 192 of the furnace or boiler housing $0. If desired, additional heat exchange surfaces or devices may be supplied to the wall around space 15min the lower portion of the furnace housing 90 around the combustion chamber 94 similar to those shown-in FIG. 1.

The burners in FIGS. 3 and 4 are also provided with air orifice members like the one illustrated in FIG. 2 at 20.

In order to determine how efiiciently domestic 'oil burners were operating, an intensive testing program was carried out ona large number of house heating furnaces. In each instance, the stack temperature was measured and the combustion gases analyzed for CO to get the running-or operating efiiciency which is the usual measure of heat-recovered from the flue or combustion gas during burner operation. Also the smoke was measured, using a Bacharach instrument. Finally, the burner tubing was taken apart and the actual gallons per hour of oil that the burner was firing were measured. It was found'that there was a large excess of air necessary to prevent excessive smoking and hence that low efliciency was being obtained. 'The most important factor causing low system efiiciency was oversizing the oil burner,

that is, installing an oil burner that is larger than the house requires. These larger burners also run for shorter periods so that they have a longer time for standby stack losses.

"Ihe conventional oil burner is in the range of about 1 gallon per hour of oil'feed or more, whereas the testing program done in connection with the present invention showed that .oil rates of less than about 0.8 gallon per hour would be sufficient for the greatest number of homes tested. In these tests it was found that the average stack temperature was about 670 F. and there was about 8% CO in the stack gases. The running efiiciency was about 72%. One way to increase the runningefficiency is to lower the stack temperature with more heat exchange or reduce the firing rate, and the other way is to cut down on the air and increase the percent CO However, the amount of air cannot be reduced because the burners are already smoking and the average ran between about 3% and 5 smoke number on the Bacharach scale.

Testing was .done on a number of different burners and combustion chamber combinations to relate smoke level with percent CO The test was started with excess air-and a low percent CO and. here there was zero smoke (Bacharach). Then, closing the air shutter on the bumer, a point was reached where smoke formation started. Closing the air shutter further increased smoke rapidly up to the top of the smoke scale. With different burnercombustion chamber combinations, the same sort of re lation was found, except that the smoke started at different CO levels. One burner-combustion chamber was fired .at different firing rates and it was found that smoking started at different CO levels, but the unexpected and surprising .fact was, that in each case the burner started to smoke when the total air flow got down to exactly thesame volume in all the oil rates tested with this burner-combustion chamber combination.

Theconclusion was reached that the flow in the combustion chamber was turbulent and the oil droplets "and .air weremixing rapidly. It was determined that to avoid smoking in :oil burners it was necessary to have a Reynolds number above about 1400. From this work it was realized that the combustion chamber area is important, that is, the cross sectional area of the combustion chamber taken at right angles to the path of the flame from the .oil burner. It is, of course, also important to have a sufiicient length of combustion chamber to provide time for burning. For the low rates below about 1.25 gallons of oil per hour, it was found that the conventional combustion chamber was too large in cross sectional area to give a Reynolds number above about 1400, unless excess air was used and then the efficiency decreased. In all cases the Reynolds numbers are about the same and this shows that the point at which smoking starts is tied up with the critical transition point from turbulent to streamline flow.

The conventional burner was further modified to use asmaller air opening. The conventional burner end air opening was about 1.88 inches (internal diameter) whereas in the modified burner, the end air opening was about 0.75 inch (internal diameter) when using the conventional oil nozzle pressure of about 100 lbs. per square inch.

According to the present'invention, it is necessary to have the combustion chambers designed for turbulent flow and at the low oil firing rates of between about 0.5 and 0.8 gallon per hour, smaller combustion chambers than are generally standard in the field must be used. Better mixing at the inlet of the combustion chamber is also important and two burner design features which must be taken into consideration are (1) smaller burner and air openings than conventional to give higher combustion air velocity, and (2) higher oil nozzle pressure when using conventional air openings. With the lower capacity oil burners and closer sizing, the oil burner will run longer when it operates and this will reduce standby stack losses substantially. V

The following data show that burning gases in a combustion zone must be turbulent for clean combustion and the Reynolds number must be above about 1400 for the conventional typeof burner using oil at a nozzle pressure of about 100 lbs./in. The combustion chamber of the modified burner of the present invention had a cross sectional area (norm-a1 to the flow of burning gases) of about 15 square inches and had an air orifice member 20 provided with an opening of about 0.75 inch (internal diameter) and the spray angle of the oil nozzle was about 30. The oil rate was maintained atrabout 0.53 gallon per hour. The oil nozzle was about 0.5 inch behind the air orifice member having the 0.75 inch opening.

The oil pressure was about 100 lbs./in. at the nozzle and the amount of air was such as to give a velocity of about 70 feet per second of air flowing through the air opening and past the oil nozzle. Compressed air was used instead of the fan on the oil burner in amount equal to that which would be supplied by the fan or blower on Table 1 Bacharaeh Excess Air, Combustion CO2, Vol. Percent Smoke Vol. Percent Chamber Number Temp, F.

0 Less than 1.-.. 2, 550 0 do 2, 600 0 do 2, 600

Changing the cross sectional area of the combustion chamber with constant oil feed rates produces eifects given in the following Table 2.

Table 2 Minimum Requirement For Clean Burning Oil Feed Combustion Length of Rate, Chamber Combustion I g.p.h. Area in sq. Chamber CO2, Excess Combustion inches 1 (inches) Vol. Air, Chamber, Percent Vol. Reynolds Percent N o.

l Normal to direction of fiow of combustion gases.

The data in Table 2 show that with a large conventional combustion chamber and small oil feed rate, a large amount of excess air is needed to produce clean burning and to give a Reynolds number above about 1400. However, with this large excess of air, the efliciency is poor. With the smallest combustion chamber of 15 square inches the combustion was most efiicient with no excess air and formation of 15 /2 vol. percent C0 which means that the theoretical amount of air necessary for complete combustion was used with the production of no smoke. Although a 15 square inch combustion chamber is small, itgives the highest efificiency. The cross sectional area may be increased to about 25 square inches and use some excess air and still give better heating efiiciency than conventional oil burners and combustion chambers while producing clean smokeless burning.-

Details of construction and operation of the burner are not shown in the drawing as conventional apparatus is here relied upon. A suitable oil pump (not shown) is used for supplying oil under pressure such that the nozzle pressure of the oil will be between about 75 and 200 pounds per square inch (p.s.i.). The oil nozzle 88 is selected to atomize the oil into extremely fine. oil particles. The air supplied by the blower section of the burner is provided to supply air at a velocity of between about 50 and 90 feet per second throughan air orifice member 20. V

The burner in a home heating unit will of course be under control of one or more room thermostats and will operate intermittently. The combustible mixture from the burner is ignited in any suitable manner as by a spark produced from electrodes diagrammatically shown at 22. Preferably, when the burner is to be started, means are provided for first actuating the fan or blower before the oil pump is started so that the oil will be properly atomized by the air stream when the oil pump forces oil under pressure through the oil nozzle and also it is preferred to have the oil pump stop first before the air blower is stooped to avoid smoking.

As a result of the investigations carried out in connection with the present invention it was found that most home heating devices using oil burner of the gun type were over-sized, inefiicient and produced smoke which was not due to the oil fuel quality. Most types showed a Bacharach smoke number of between about 3 /2 and 5. As above mentioned average stack temperature was 670 and the average percent CO by volume was 8%. Most of the homes could be provided with oil gun burners burning only between about 0.5 and 0.8 gallon per hour and having a combustion chamber of a much smaller cross sectional area (normal to the burning gases) than in the conventional heating units used for home heating to produce more efiicient and economical operation with clean burning of the oil. The combustion chamber is constructed so that the gases undergoing combustion are in turbulent flow and have a Reynolds number greater than about 1400. The most economical size of combustion chamber for burning about 0.6 gallon of oil per hour at a pressure of about psi. in an oil burner having a high pressure nozzle was one having a cross sectional area (normal to the flow of burning gases) of about 15 square inches and a length of about 58 sgonawea 7: inches. This cross sectional; area for the combustion chamber for rates of oil flow between.-about.0.5- and..0.8. gallon per hour may bebetween about 15 and 30 square inches andfthe-length should be at least 35 inches.

In the modified burner. theair'ropening-ofa' conventionaloilburnerwas reduced .in.size tCLhaVCJUJ internal diameter between about.0.75' and 1.50 inches and this gave .good mixing with the atomized .fuel and no smoke when substantially to 3% excess air wasobtained in the an ain-blower connectedtosaidblast tube at :said; inlet end' thereof. to discharge air.:for :theusupportof. combustionthrough said tube.-to.be. thoroughly; mixedwith. oil. discharged. from.said.-.nozzleapparatus adjacent said.

nozzle apparatus..only, said blower being rated to supply substantially the.theoretical.amount of air needed for the support. of: combustion. without. producing smoke, (5.), means within said. blast tubetor. igniting said oil mixed with-.said: air, (6), a; combustionchamber extendfluer. or combustion gases, when using: oil at 100,p.s.i... 1 ing from said outlet end of said blast. tube to receive from the burner nozzle. When the internal diameter." ofthe end cone was increased to about 2.10inches, smoking was obtained. when .usingoilat. 100 .p .s.i., .over the range of 0 to 200% excess air, but when the oil presamixture. of:.oil.- and: air. issuing-, from said: central opening; of. said.orifice..member, said combustion chamber havinganiimperforate wall, an outlet end, and. auniform cross sectionalrarea (atiright. angles to. the. direction. of

sure;.was.increased to. 15.0..p.s.i .noz.zle pressure,smoking 15, flow of: said: mixture of oil; and. air. issuing thercinto stopped at excess air :and cleanburning was;obtained..

'Iheefliciency ofthe oil burnersat present is;limited.. bythe smallamount ofjheat exchange:;surface;andthia; can. bedmprovedv by adding more:.heat: exchange; surheating units, the heat exchangers.- haverherctofore. been. built with 1 /2. or 2. inch;.passages;;to be sure that'the. passages would not plug up. with..soot.. This ..typ.e.-of. heat exchanger. is much less efficient thanonewithssmaller pas.-

through saidorifiee member) of. about square inches to give a Reynolds number of said mixture in said com-.

bustiomchamber greater. than .about. 1400. for turbulent flowof.said.mixtur.e. in saidchamber to, obtain substan-- facer. Because-ofthe.tendencyforoiltosmokeiuhome;v 2 tially complete-combustion.with.substantially no: excess' air, and. (7) ashelhmemberwherein said .outlet end of.

said .combustion chamber is located.

2. A heatinggunit.accordingjo. claim.1. inwhich said nozzle. apparatus isradaptedto discharge oil at a rate sages, and witha smoke-free oil. burner, the:.heat.:exof about 0.6 gallon per .hour,vand:said.combustion .chamchangers should. bedesigned-.with. smaller. passages,; say. about V2. an inch.to.1 inch... Soot depoaitedonheat: 6X-.- change-surfaces. reducestheir efficiency' and. this .can. be: avoided. by using the. present invention and.having,--a;- smoke-free combustion.

Whatis. claimed is:

1. A heating unitfor house heating service including: (1) an. air blast. tube.havingan.in1et:.end...and an outlet end,. (2) an orifice. member having a'icentral. opening iof.

about 0.75 of an inch diameterlocatediacrossthe-outlet end of said blast tube, (3) a.- nozzle apparatus located. rearwardly of said member and withinsaidblast tubeessentially coaxially therewithwherefromoil for com-.- bustion. is discharged through said .central. openingofsaid orificemember, said nozzle. apparatusbeing oi the: high.- 40:

oil-pressure-atomizing type rated to discharge .oil at'be.-- low about 0.8 gallonper. hour when suppliedwith. oil ata pressure of about pounds.-.per.-square inch, (4') her. is. about :58 incheslong.

References Citediin' the :file of this patent UNITED STATESBATENTS

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