US3430610A - Steam raising boilers and process for improving thermal efficiencies of such boilers - Google Patents

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March 4,1969 w HALUWELL ETAL 3,430,610

STEAM RAISING BOILERS AND PROCESS FOR IMPROVING THERMAL EFFICIENCIES OF SUCH BOILERS Filed Jan. 10, 1967 Sheet of 5 12, n FL 11 m ct March 4, 1969 w, uw ETAL 3,430,610

STEAM RAISING BOILERS AND PROCESS FOR IMPROVING THERMAL EFFICIENCIES OF SUCH BOILERS Filed Jan. 10, 1967 I Sheet 2 of 5 Fig.3.

March 4, 1969 W. HALLIWELL ETAL STEAM RAISING BOILERS AND PROCESS FOR IMPROVING THERMAL EFFICIENCIES OF SUCH BOILERS Filed Jan. 10, 1967 Sheet 3 of3 5 Fig.4.

United States Patent STEAM RAISING BOILERS AND PROCESS FOR IMPROVING THERMAL EFFICIENCIES OF SUCH BOILERS Walter Halliwell, Bolton, and Frank Pitts, Kersal, England, assignors to Magnesium Elektron Limited, Swinton, Manchester, England Filed Jan. 10, 1967, Ser. No. 608,407 Claims priority, application Great Britain, June 3, 1966,

24,873/ 66 U.S. Cl. 122-479 7 Claims Int. Cl. F22g /00 ABSTRACT OF THE DISCLOSURE Disclosure This invention relates to stream raising boilers and a process for improving the thermal efficiencies of steam raising boilers and, in particular, of oil-fired boilers in which superheat temperature cannot be achieved or can only be achieved at the expense of introducing excessive amounts of air into the combustion zone.

It is commonplace to convert to oil-firing boilers which have been designed for operation on solid or pulverised fuel or on gas and it is then frequently impracticable, without major and costly reconstruction of the boiler, in particular of the combustion chamber, to attain the maximum superheat temperature which the construction of the boiler tubes would permit without increasing the proportion of excess air used with consequent loss of thermal efiiciency. It is known to overcome this difficulty by constructing refractory walls within the combustion chamber to shroud part of the wall tubes thereby reducing absorption of heat in the combustion chamber and increase it in the superheaters. Another way of avoiding the need to use high proportions of excess air is to recirculate the cool combustion gases through the combustion chamber. In either case high costs of installation and maintenance are involved.

In the course of introducing particulate magnesium into boiler combustion chambersfor the purpose of controlling formation of sulphur trioxide it has been observed that, under certain conditions, magnesium is deposited on the wall-tubes of the boiler and that this phenomenon is associated with a rise in superheat temperature although the excess air content of the combustion gases remain constant.

The object of this invention is to achieve a controlled increase in superheat temperature without a simultaneous increase in excess air, or of permitting a reduction in excess air without reduction in superheat temperature.

According to this invention magnesium in the form of particles which will pass a sieve and will be retained on a 100 B5. sieve are injected into the boiler combustion chamber in a direction making an angle between 30 below the horizontal and 60 above the horizontal and in a plane (as seen in plan view) making an angle between 45 and 135 with the direction in which the fuel is injected, in such manner that a heat-reflecting layer of magnesium oxide is maintained on the surface of a predetermined section of the combustion chamber wall-tubes. The oil may be injected from a plurality of ice fuel injection nozzles or burners in opposite directions or in the same direction while the magnesium may be injected in opposite directions across the fuel streams. The position or each position of injection of magnesium in the combustion chamber wall may be located between the levels of the lowest and of the highest banks of fuel injection nozzles or burners. Magnesium may be injected at more than one position but in the case of each injection position the angles referred to are applied in relation to the direction of fuel injection nearest to the position of magnesium injection. The velocity with which the magnesium particles are injected and the size of the particles are preferably so chosen in relation to the combustion chamber dimensions and the gas flow existing within the chamber that combustion of the particles is substantially complete before the burning particles have fallen to a level below the lowest bank of oil burners and that no substantial proportion of the particles is carried out of the combustion chamber before combustion of the particles is complete.

The effect of this method of controlling the injection of magnesium particles is to produce a white deposit of heat-reflecting magnesium oxide on that area of the walltubes lying between the plane of the lowest bank of oil burners and a plane situated below the position at which the combustion gases leave the combustion chamber and enter the superheaters or reheaters. The height of the band covered by magnesium oxide is varied according to the desired increase in superheat temperature and/or reduction in excess air and can be controlled by varying the velocity and angles of injection of the magnesium within the limits specified. The increase of superheat temperature and/or reduction in excess air can also be varied by varying the reflectivity of the magnesium oxide coating which is controlled by varying the rate at which magnesium is injected. To achieve maximum economy, the velocity and angles of magnesium injection are varied by trial until the rate of magnesium injection is the minimum consistent with the desired improvement in thermal efiiciency.

The invention is illustrated by way of example in the accompanying diagrammatic drawings, wherein:

FIGURE 1 is a vertical section of an oil-fired boiler constructed in accordance with the invention;

FIGURE 2 is a horizontal section on the plane 2-2 on FIGURE 1;

FIGURE 3 is a vertical sectional view of another form of boiler;

FIGURE 4 is a sectional view on line 4-4 on FIG- URE 3; and

FIGURE 5 is a sectional view on the line 5-5 on FIGURE 4.

A combustion chamber 10 is connected at its upper end by channel 8 to superheaters and/or reheaters 9. The chamber 10 is formed by four walls 11, 12, 13, 14 and around all the walls are the usual water tubes 16. Oil burner nozzles 17, 18 extend through the walls into the chamber 10 at an angle of to the plane of the wall in plan (FIGURE 2) so as to inject oil into the furnace in opposite directions. These nozzles in this example are in four banks (FIGURE 1). Magnesium injection tubes or nozzles 20, 21, 22, 23 extend through the walls 11, 13 at an angle of 45 to the vertical, their outer ends being lowermost, and at 70 to the walls 11, 13 in plan and 20, 21 being at to nozzles 22, 23.

The magnesium oxide coating is produced on all four walls 11, 12, 13, 14 between a plane indicated by broken line 25 in FIGURE 1 between the lower two banks of oil burner nozzles 17 and a plane indicated by the broken line 26 which is below channel 8 through which the combustion gases leave the chamber 10.

In FIGURES 3, 4 and 5 the superheaters and reheaters 9 are above the chamber 10, the burner nozzles 17 enter the wall 14 in three banks, and the magnesium injection nozzle 20 enters the wall 11 at right angles (in plan) to the burner nozzles 17 and a similar nozzle 21 enters the wall 13 opposite to the nozzle 20 at the same angle to the vertical as in FIGURE 1.

Thus nozzles 20, 21 are directed oppositely to each other from opposite walls of the chamber 10. Nozzle 20 is at right angles (in plan) to nozzles 17, and nozzle 21 is at 75 to nozzles 17. Nozzles 20, 21 are at 60 to the vertical. The injection of the magnesium may be effected by means of the apparatus disclosed in our co-pending patent application No. 22,963 of 1964.

Example Magnesium in the form of solid granules was injected at the rate of 3 lb. per hour into the combustion cham ber of a boiler consuming 12 tons of crude residual fuel oil per hour. Before commencing injection of magnesium the boiler was operating with 7% excess air to produce superheated steam at a temperature of 517 C., although the boiler had been designed to operate at a superheat temperature of 525 C., using only 5% excess of air over the stoichiometrical amount required for combustion of the fuel. After varying the particle size of the magnesium granules and the rate, velocity and angle of their injection it was found that injection of 3 lb. per hour of magnesium granules of mean Stokes diameter /32" with a velocity of 150 feet per second in a direction at an angle above the horizontal of 30 and at right angles to the direction of injection of the fuel produced an increase of 8 C. in superheat temperature, thus attaining the maximum for which the boiler was designed, this increase being achieved whilst operating with 5% excess air, a reduction of about 30% compared with the boiler performance without magnesium injection.

Under these conditions, the heat-reflecting band of magnesium oxide extended for a height of about 20 feet from a position about 3 feet above the lowest bank of oil burners to about 6 feet below the channel leading to the superheaters.

We claim:

1. In combination with an oil-fired steam raising boiler having a combustion chamber, water tubes lining the combustion chamber, a superheater, the water tubes being in fluid communication with said superheater, burner means for firing said chamber and magnesium injection means for introducing magnesium into said chamber, the process for regulating the steam temperature of the boiler which comprises the steps of injecting fuel in a generally horizontal direction into the combustion chamber of said boiler, injecting magnesium particles which pass a sieve and are retained on a 100 B.S. sieve into said combustion chamber in a direction to form an angle of between 30 below and 60 above a horizontal plane through said chamber and in a direction to form an angle of between 45 and with the direction in which the fuel is injected, thereby to form on the surface of a predetermined section of the combustion chamber walls a heat-reflecting layer of magnesium oxide.

2. The process of claim 1 wherein several banks of fuel injection nozzles are provided, further comprising the step of vertically positioning the magnesium injection nozzles in said chamber between the lowest and highest bank of fuel injection nozzles.

3. The process of claim 1 further including the step of varying the velocity of injection and the size of the magnesium, particles in relation to the combustion chamber so that combustion of the particles is substantially complete before the burning particles have fallen to a level below the lowest bank of burners so that no substantial proportion of the particles reach the superheater.

4. The process of claim 1 wherein the injection of magnesium particles is at a rate of 3 pounds per hour at a velocity of feet per second at right angles to the direction of injection of the fuel.

5. In combination with an oil-fired steam raising boiler having a combustion chamber, water tubes lining the combustion chamber, a superheater, the water tubes being in fluid communication with said superheater, the improvement comprising a plurality of fuel injection nozzles entering said chamber in a generally horizontal direction and means for injecting magnesium particles into said combustion chamber in the region of said injection nozzles, said magnesium injecting means comprising a plurality of injection nozzles arranged at an angle of between 30 below and 60 above a horizontal plane through said boiler and in vertical planes making angles between 45 and 135 with said fuel nozzles, whereby injection of said magnesium particles into said chamber forms on the surface of a predetermined section of the combustion chamber walls a heat-reflecting layer of magnesium oxide.

6. The combination of claim 5 wherein several vertically spaced banks of fuel injection nozzles are provided, said magnesium injecting nozzles being located and directed in said chamber to produce a layer of magnesium oxide on said chamber walls between the levels of the lowest and highest banks of fuel injection nozzles.

7. The combination of claim 5 wherein at least one of said magnesium injection nozzles is in a vertical plane at right angles to the vertical planes of said fuel injection nozzles.

References Cited Reese et al.: Prevention of Residual Oil Combustion Problems by Use of Low Excess Air and Magnesium Additive, Journal of Engineering for Power, April 1965, pp. 229-236.

CHARLES J. MYHRE, Primary Examiner.

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