GB2136554A - Oil burner and a method of effecting combustion therein - Google Patents

Abstract

An oil burner which comprises primary and secondary throats, primary and secondary sleeves 6, 2, primary and secondary swirlers 12, 11, and independent dampers 9, 4 arranged at air passages 8, 3 to primary and secondary sleeves. With such arrangement, the oil burner is enabled to effect stable combustion under very low load for small steam requirement, with the result of much energy saving. <IMAGE>

Description

SPECIFICATION Oil burner and a method of effecting combustion therein This invention relates to an oil burner and to a method of effecting combustion therein.

In the conventional boiler, the number of working burners is increased or decreased according to the variations of load and the quantity of combustion is changed in proportion to the required quantity of steam, and the lowest combustion quantityfor obtaining stable combustion is limited. In marine transportation circles, there is a trend for turbine steamers equipped with a main boilerto be obliged to maintain for a long period of time the so-called "quasi-anchoring" such as standing by in the ocean, during which only a very small quantity of steam (1/60 -1/80 ofthe rated evaporation quantity) is required.

For such small requirement of steam, however, conventional burners cannot provide stable combustion at loads down to the above-mentioned quantity of steam. The present situation is that 1/20 of the rated evaporation quantity is the limitof minimum quantity of steam and therefore excess steam is discharged to no purpose. This not only causes loss offuel but also waste of power because auxiliaries such as fans, pumps, heaters, etc. consume large amounts of power appropriate to their rating even at the time ofthe lowest combustion load.

According to the invention in one aspect there is provided an oil burner comprising a primary sleeve having two air supply ports which are respectively connected to auxiliaries for small capacity and auxiliaries for large capacity, a secondary sleeve with a secondarythroat at the downstream end thereof, said primary sleeve being of divergent shape atthe downstream end thereofto form a primary throat, a primary swirler and a fuel atomizer arranged in said primarythroat, a secondaryswirlerabouttheouter circumference of said primary throat, and independent dampers arranged to control the air supplied into the upstream ends of said primary and secondary sleeves respectively, whereby the air supply to each sleeve can be opened and closed off.

In another aspect the invention provides in a boiler having a plurality of oil burners, at least one of which is a wide-range oil burner comprises a primary sleeve having two air supply ports which are respectively connected to auxiliaries for small capacity and auxiliaries for large capacity, a secondary sleeve with a secondary throat at the downstream end thereof, said primary sleeve being of divergent shape at the downstream end thereof to form a primary throat, a primary swirler and a fuel atomizer arranged in said primarythroat, a secondaryswirleraboutthe outer circumference of said primarythroatand independent dampers control the air supplied into the upstream ends of said primary and secondary sleeves, whereby the air supply to each sleeve can be opened and closed off, a method of effecting combustion in said widerange oil burner or burners whereby atthe time of normal combustion all burners effect combustion underthe same condition but at the same time of very low load combustion auxiliaries are switched over to small capacity, said secondary and primary dampers are closed fully and air is introduced into the primary throatforeffecting stable combustion byonlythe wide-range burner or burners.

The nature and advantages ofthe present invention will be understood more clearlyfrom the following description made with reference to the accompanying drawings, in which: Figure lisa sectional view of a conventional oil burner; Figure 2 is a sectional view of a burner according to the present invention; Figure 3 and Figure 4 are graphs showing the characteristics of the burner according to the present invention; Figure 5 is an embodiment ofthe present invention; and Figure 6 is a system diagram ofthe embodiment shown in Figure 5.

Referring first to Figure 1, in a conventional oil burner, combustion air enter at a and passes through the part b, a flame being formed at a primary swirlerc.

In the case where a plurality of burners are arranged, extinction is effected by stopping the supply of air into a boiler by closing a slide damper e fixed to a slide shaft d. In operation the required quantity of air decreases in proportion to reduction of the quantity of oil supplied for combustion and consequently the air flow rate is also lowered, with the resu It that stable combustion becomes impossible at low oil supply rates. The limit of combustion is 117 to 1110 ofthe rated load combustion and the limit of the lowest quantity of steam is 1115 to 1/20 of the rated evaporation quantity.

Stable combustion is not achieved under conditions lower than the above limits.

Referring nowto Figure 2, an oil burner according to the invention is shown and constitutes one of a plurality of burners in a boiler. This oil burner is provided with a secondary sleeve 2 at the rear of a secondarythroat 1 of a boiler. A primary sleeve 6 is disposed in the secondary sleeve 2 and the airfor combustion is supplied to a passage between the primary sleeve 6 and the secondary sleeve 2through an air intake 3 formed atthe rear of the secondary sleeve 2. A primarythroat7 of divergent shape is connected to the downstream end of the primary throat 6, around which a secondary swirler 11 is disposed. Formed atthe rear or upstream part of the primary sleeve 6 is an air intake 8. Air entering the air intake 8 flows through the primary sleeve 6.The air intakes 3,8 are provided wih slide dampers 4,9 respectively, which are operated by sliding shafts 5,10 respectivelyto open and close the air intakes. Formed atthe upstream end ofthe primary sleeve 6 is a wind box 16, to which a duct 14 is connected which is independent of the air intake 8 and which serves to supplythe small quantities of air under very low load conditions into the primary sleeve 6 via auxiliariesfor small capacity. A damper 15to be opened and closed is provided in the duct 14. A primary swirler 12 and a burner nozzle 13 are provided in the downstream end portion ofthe primary sleeve 6.

Figure 5 shows an example of an oil burner according to the present invention, which is used in combination with a conventional oil burner. In Figure 5, A is a conventional oil burner and B is an oil burner according to the present invention. A boiler Bo is provided with a plurality of oil burners at least one of which is of the type shown at B. Awind box 17 common to the burners is connected to a blower 18 so thattheairnecessaryforcombustion atthe predetermined maximum load can be supplied.As shown in Figure 6, oil burners A, B are provided with a fuel supply system Cforfeeding fuel oil, and a steam system D for supplying steam for atomizing the fuel oil. Thesetwo systems C and Dare divided into systems C1, D1 for combustion under normal load and systems C2, D2 respectively for ultra low-load operation.

When burning art a predetermined load using the normal system, fuel oil from an oil tank 19 passes through a filter20, is pressurized by a pump 21, heated bya heater 22, passes th rough anotherfilter23, is regulated quantitatively by an oil regulating valve 24, is supplied to an oil header 25 and finally is supplied uniformly to each burnerforcombustion under the same conditions. The ratio between air and fuel is regulated by the oil regulating valve and a damper 18a provided in the blower 18.

Steam is supplied to a steam header 27, via a pressure regulating valve 26, and then supplied to each oil burnerforatomizing oil.

During this normal working, slide dampers 4,9 are slid to open fullythe air intakes 3,8, wherebythefan 18 for large capacity operation is driven and each apparatus connected to the systems C1, D1 is actuated and thusthefuel oil and steam are supplied butthe systems C2, D2 are closed,togetherwith a blower 28 and the damper 15. When carrying out the ultra-low load combustion, the auxiliaries for large capacity operation are stopped and those for small capacity set in operation, i.e. the systems Cl, Dl are closed down butthe systems C2, D2 are opened and supply fuel and steam to onlythe oil burner B.Atthis time, the blower 18 is stopped, dampers 4,9 ofthe oil burner B are closed by the damper 15 is opened and the air of small quantity is supplied from the fan 28 for low capacity operation into the primary throat via the duct 14 and the wind box 16. In this case, as oil burns only atthe primarythroat ofthe oil burner B, the air passage is appropriately narrow and the required airflow speed can besecured,with the resultthat stable and complete combustion is carried out under u Itra-low load. In the case ofthis ultra-low load combustion, oil from the oil tank 19 is supplied to the oil burner B via a small capacity filter 29, a pump 30, a heater 31 and an oil regulating valve 32.On the other hand, steam (or air) is supplied to the burner B via a pressure regulating valve 33 and an electromagnetic valve 34.

Thus switch-overfrom the normal systemtothe ultra-low load system can be effected easily by the changeover of valve and the change of air passage. In this ultra-low load combustion, ON/OFF (high/low) or proportional control can be applied. The ratio between air and fuel is regulated by the oil regulating valve 32 and the air damper 15.

Figure 3 shows a comparative example ofthe combustion load rates and coefficients of excess air forthe conventional burner and the burner according the the present invention. As is clear from Figure3, againstthecombustion rangeof 100%-15% in the case ofthe conventional burnerA, the burner B has a combustion range of 100% -5% As compared with the conventional burner, a burner as shown in Figure 2 provides safe and complete combustion even forthe ultra-low load combustion, with resultant energy saving.

Claims (3)

1. An oil burner comprising a primarysleeve having two air supply ports which are respectively connectedtoauxiliariesforsmall capacity and au xiliaties for large capacity, a secondary sleeve with a secondarythroat atthe downstream end thereof, said primary sleeve being ofdivergentshapeatthe downstream end thereof to form a primarythroat, a primary swirler and a fuel atomizer arranged in said primarythroat, a secondary swirler aboutthe outer circumference of said primary throat, and independent dampers arranged to control the air supplied into the upstream ends of said primary and secondary sleeves respectively, whereby the air supply to each sleeve can be opened and closed off.

2. In a boiler having a plurality of oil burners, at least one of which is a wide-range oil burnercompris esa primary sleeve having two airsupply portswhich are respectively connected to auxiliaries for small capacity and auxiliariesfor largecapacity,a secondary sleeve with a secondarythroat atthe downstream end thereof, said primary sleeve being of divergent shape atthe downstream end thereofto form a primary throat, a primaryswirlerand afuel atomizer arranged in said primarythroat, a secondary swirler aboutthe outercircumference of said primarythroat and independent dampers to control the air supplied into the upstream ends of said primary and secondary sleeves, wherebythe air supplyto each sleeve can be opened and closed off, a method of effecting combustion in said wide-range oil burner or burners whereby atthetime of normal combustion all burners effect combustion underthe same condition butatthetime of very low load combustion auxiliaries are switched overto small capacity, said secondary and primary dampers are closed fully and air is introduced into the primary throat for effecting stable combustion by only thewide-range burner or burners.

3. An oil burner substantially as hereinbefore described with reference to and as illustrated in Figure 2 of the accompanying drawings.