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(11) | EP 0 111 793 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Method and apparatus for atomizing slurry-type fuel |
| (57) @ A method and apparatus for atomizing slurry-type fuels includes introducing a slurry-type
fuel under pressure into a mixing chamber and introducing an atomizing fluid under
pressure into the mixing chamber in a tangential direction along the periphery of
the mixing chamber and the atomizer fuel exiting from the mixing chamber through an
orifice. The degree of atomization of the slurry-type fuel may be adjusted by varying
the pressure differential between the slurry-type fuel and the atomizing fluid entering
the mixing chamber. |
[0001] The present invention relates to a method of and apparatus for atomizing slurry-type fuel such as a dispersion of particulate coal in water and/or oil, for combustion.
[0002] Owing to increased oil prices, and possible limited availability, the use of residua) fuels for combustion in boilers and the like may no longer be economically feasible. Solid fuels, such as coal, are generally more available and are cheaper than such residual fuels. However, solid fuels cannot be substituted for residual fuel in boilers which are designed to burn residual fuel unless such boilers are refitted at great capital expense.
[0003] To eliminate or at least minimize such refitting, liquid fuels have been developed which comprise a particulate solid hydrocarbon, such as coal or lignite, dispersed in a continuous liquid phase such as oil, water or mixtures thereof. Such "slurry-type" fuels can be pumped in a manner similar to residual fuels. However, slurry-type fuels generally have higher viscosity due to large amounts of particulate coal in the slurry. In addition, slurry-type fuels are more difficult to atomize and combust since the solid particles have a tendency to clog atomizing nozzles used to introduce the fuel into combustion chambers.
[0004] An aim of the. present invention is to provide a method and apparatus for atomizing slurry-type fuels, for combustion both in industrial boilers, where it is desirable to achieve combustion of the fuel in a short distance to prevent flame impingement on furnace walls, and in kilns where a long flame is desired to transfer heat of combustion more effectively from the flame to a material being processed in the kiln.
[0005] In one aspect, the invention provides an atomizer for a slurry-type fuel comprising a mixture of solids and liquids, characterized by a nozzle body having first conduit means therein for passage of a slurry-type fuel and second conduit means therein for passage of an atomizing fluid; a nozzle tip, attached to the nozzle body, having internal surface means partly defining a mixing chamber, atomizing fluid conduit means communicating with said second conduit means, and means defining an orifice communicating with said mixing chamber, for enabling atomized slurry-type fuel to exit the mixing chamber; and spinner means disposed within said nozzle tip for defining, with said internal surface means, the mixing chamber, said spinner means including axial port means communicating with said first conduit means for passage of the slurry-type fuel into the mixing chamber, and groove means, communicating with the atomizing fluid conduit means, for introducing the atomizing fluid into the mixing chamber.
[0006] The groove means are operative to impart a swirling motion into the atomizing fluid as a result of the passage of atomizing fluid therethrough.
[0008] Desirably, the groove means are configured and operative for introducing the atomizing fluid in a tangential direction along the periphery of the mixing chdmber.
[0009] Conveniently, the internal surface of the nozzle tip is conical in shape, and said spinner means presents a frusto-conical surface for engaging the internal conical surface to define the mixing chamber therebetween.
[0010] In a further aspect, the invention provides a method of atomizing a slurry-type fuel comprising a mixture of solids and liquids, characterized by the steps of introducing the slurry-type fuel into a mixing chamber along an axis of the mixing chamber; introducing an atomizing fluid into the mixing chamber in a generally tangential direction along the periphery of the mixing chamber, said atomizing fluid being introduced into the mixing chamber at a rate sufficient to swirl and atomize the slurry-type fuel within the mixing chamber; and providing an orif ice' in the mixing chamber aligned with the axis of the mixing chamber to enable the atomized slurry-type fuel to exit the mixing chamber under the combined pressure forces of the slurry-type fuel and the atomizing fluid.
[0011] In yet another aspect the invention provides a method of atomizing a slurry-type fuel, characterised by the steps of introducing a slurry-type fuel under pressure into a mixing chamber having a conical internal surface, said slurry-type fuel being introduced in a single rod-like stream along an axis of the mixing chamber; introducing an atomizing fluid under pressure into the mixing chamber in a tangential direction along the periphery of the mixing chamber and toward the apex of the conical internal surface, said atomizing fluid being introduced into the mixing chamber at a rate sufficient to swirl and atomize the slurry-type fuel within the mixing chamber; providing a single orifice in the apex of the conical internal surface to enable the atomized slurry-type fuel to exit the mixing chamber under the combined pressure forces of the slurry-type fuel and the atomizing fluid; and adjusting the degree of atomization of the slurry-type fuel by varying the pressure differential between the slurry-type fuel and the atomizing fluid entering the mixing chamber.
[0012] It is important that the atomization of the slurry-type fuel occurs inside a mixing chamber in order to reduce the required operating supply pressure both of the slurry-type fuel and of the atomizing fluid within the atomizer. This is to be compared with known devices which atomize fuel at or outside a nozzle, which requires higher operating pressures and results in less efficient atomization.
[0013] More particularly, the method of the present invention includes introducing a slurry-type fuel under pressure into the mixing chamber in a single rod-like stream along an axis of the mixing chamber, which has a conical interior surface, and providing a single orifice in the apex of the conical internal surface to enable the atomized slurry-type fuel to exit the mixing chamber, and adjusting the degree of atomization of the slurry-type fuel by varying the pressure differential between the slurry-type fuel and the atomizing fluid entering the mixing chamber.
[0014] It has been found that the method and apparatus of the present invention can be used to atomize slurry-type fuels without clogging of the apparatus which would necessitate shutting down of the boiler or kiln in order to repair or replace the apparatus.
[0015] In order that the invention may be more readily understood, and so that further features thereof may be appreciated, an embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIGURE I is a cross-sectional view of an atomizer embodying the invention, showing a nozzle body, a nozzle tip removably attached to the nozzle body along with spinner means disposed within the nozzle tip;
FIGURE 2 is an enlarged, partly broken away, perspective view of a part of the atomizer of Figure I, showing the nozzle tip and the spinner in greater detail and illustrating a mixing chamber and a diagrammatical representation of atomization of a slurry-type fuel within the mixing chamber and exit of the atomized spray through an orifice in the nozzle tip.
[0016] Referring to Figure 1, an atomizer 10 in accordance with the present invention includes a nozzle body 12, a nozzle tip 14, which is removably attached to the nozzle body 12 by means of a threaded portion 16 that engages a mating threaded portion 18 on the nozzle body 12, and a spinner 20 disposed within the nozzle tip 14. The spinner 20 is shaped to define a mixing chamber 28 between the spinner 20 and an internal surface 30 of the nozzle tip 14. The internal surface 30 may be conical in shape. All of the components of the atomizer 10, namely the nozzle body 12, the nozzle tip 14 and the spinner 20 may be formed from metal or any other suitable material.
[0017] The nozzle body 12 includes a first conduit system, or means, 36 which includes an inlet 38 which is preferably radially disposed in the nozzle body 12 and is in fluid combination with an axial passageway 40, for passing slurry-type fuel to the nozzle tip 14 and spinner 20.
[0018] An atomizing fluid inlet 46 and a second conduit system, or means, 48 which includes a manifold adjacent to spinner 20 are provided to supply an atomizing fluid, such as air or steam, to the spinner 20 and thereafter to the mixing chamber 28 as will be hereinafter described in conjunction with Figure 2.
[0019] As more clearly shown in Figure 2, the nozzle tip 14 includes a cavity 52 providing the conical internal surface 30 that partly defines the mixing chamber 28 between itself and the spinner 20.
[0020] At the apex of the conical internal surface 30 a single orifice 62, that is aligned with the longitudinal axis 64 of the nozzle tip 14, communicates with the mixing chamber 28 to enable atomized slurry-type fuel to exit the mixing chamber 28 as indicated in Figure 2 by the spray pattern 66.
[0021] The spinner 20 comprises a shaft portion 72 and a head portion 74 that has a frusto-conical surface 76 thereon for engaging the internal conical surface 30. An axial port 82 extends through the spinner -head portion to communicate with the first conduit means 36 for the passage of slurry-type fuel therethrough and into the mixing chamber 28. A single port 82 is utilized in order to introduce the slurry-type fuel into the mixing chamber 28 in a single rod-like stream 86 substantially along the axis 64 of the nozzle tip 14.
I
[0022] A set of grooves 90 are disposed in the head portion 74 of the spinner 20 and disposed at an angle to the axis 64 for communicating with the atomizing fluid manifold. When steam or air is passed through the second conduit system 48 and manifold through the grooves 90 it is passed into the mixing chamber 28 in a tangential direction along the periphery of the mixing chamber 28 with a swirling motion.
[0023] It is to be appreciated that a slurry-type fuel may include solid particles which may be as large as those passing through a size 50 mesh (approx. 0.3mm), hence the design of a nozzle in accordance with the present invention provides for a first conduit system that has few obstructions therein, to avoid plugging by slurry particles. The diameter of the first conduit system 36 as well as the diameter of the axial port 82 in the spinner 20 may be approximately 0.09 inches (2.3mm) to accommodate such particles. Smaller, or larger conduits may be used depending upon the size distribution of the solid particles within the slurry-type fuel.
[0024] A nozzle in accordance with the present invention may have an overall length of 2 inches (50mm) and an overall diameter of 0.80 inches (20mm) for a 3 MMBtu/hr (3165 MJ/hr) firing rate. The spinner head portion may be have a diameter of approximately 0.24 inches (6mm) to define a mixing chamber having a depth between a front surface 100 of the head portion 74 of the spinner and the orifice 62, of approximately 0.80 inches (20mm). The widest portion of the mixing chamber 28, opposed from the orifice 62, may have a diameter of approximately 0.16 inches (4mm) while the orifice may have a diameter of approximately 0.085 inches (2.2mm). These dimensions, correspond to a specific configuration of the present invention. Nozzles for higher or lower firing rates will, of course, have corresponding changes in dimensions.
[0025] It is particularly important that atomization of the slurry-type fuel is achieved by the swirling motion of an atomizing fluid, such as steam or air, inside the mixing chamber 28 of the atomizer 10. This method of atomization is to be compared with known atomizers which effect atomization of fuel external to the atomizer by discharging the fuel in swirl motion into a combustion chamber.
[0026] As the slurry-fuel is atomized within a mixing chamber the required operating pressure of the atomizer is reduced. In addition, because the pressure within the mixing chamber may be controlled the extent of atomization occurring therein may be controlled by adjusting the input pressure of both the slurry-type fuel and the atomizing fluid. More particularly, the differential in pressure between the atomizing fluid input and the slurry-type fuel input may be adjusted to control the degree of atomization.
[0027] As an example, utilizing a slurry-type fuel comprising solid coal particles sized to pass a 50 mesh screen (0.3mm) and a 19.5 API gravity fuel oil, the slurry-type fuel pressure may be 145 psi (1000 kNm-2) and the atomizing fluid pressure may be 130 psi (900 kNm-2) thus giving a differential pressure of 15 psi (100 kNm-2).
[0028] Because both the fuel and atomizing fluid are discharged from a single orifice, atomizer erosion is significantly reduced since the surface area of the orifice per discharge of atomized fluid is considerably less than with the use of multiple ports or orifices for discharge of atomized fluid.
[0029] A further advantage of the present atomizer apparatus and a method for atomizing slurry-type fuel of the present invention is the flexibility to alter operating conditions of the atomizer through minor modification of the atomizer. The degree of atomization (drop size distribution) and the angle of the atomizer interior conical surface 30 are easily varied to enable a desired degree of atomization to be obtained. For example, fine fuel atomization can be obtained through changing the following design variables:
(I) reducing the diameter of the orifice 62;
(2) increasing the number of grooves 90; and
(3) reducing the area, or cross section of the grooves 90 to enable the use of a high pressure drop across the grooves thereby to increase the ejection velocity of the atomizing fluid.
[0030] Similarly, an increase in spray cone angle can be achieved by increasing the tangential momentum of the atomizing fluid with regard to the axial momentum of the atomizing fluid. Hence, a larger cone angle can be obtained through a variation of the following design variables:
(I) increasing tangential angle of the grooves 90;
(2) reducing the height (L) of the mixing chamber 28;
(3) reducing the diameter (D) of the mixing chamber;
(4) increasing the diameter of the orifice 62; or
(5) reducing the length (l) of the orifice 62.
[0031] For a fuel having the aforesaid coal particle distribution passing a 50 size mesh (0.3mm) and a 19.5 API gravity oil, the L, D, and dimensions of an atomizer in accordance with the present invention as shown in Figure 2 may be approximately L = 0.08 inches (2mm); D = O.16 inches (4mm); I = 0.05 inches (1.25mm).
[0032] Modifications to the present apparatus to affect the operating conditions and the degree of atomization of slurry-fuel in accordance with the present invention can be easily -accommodated by replacing either the spinner 20 and/or the nozzle tip 14. The replacement of these parts can be readily made in the field with no modification to the atomizer body. This is an important feature because the compatibility of the atomizer with a multitude of combustion applications can be made. For example, if the atomizer is intended for use with an industrial boiler it may be desirable to achieve the combustion of the fuel in a short and stubby flame to prevent flame impingement on an opposing or adjacent furnace wall and to achieve complete combustion of the fuel in a relatively short residence time available in a boiler-type furnace. To achieve this objective, the spinner 20 and the nozzle tip 14 can be selected to provide a fine atomization and largest practical spray cone angle to enhance the intimate mixing between the fuel and combustion air within the furnace.
[0033] In another application, such as an atomizer provided for use in a kiln operation, a long protracted flame may be desired in order to extend the combustion of the flame and the resultant heat of the transfer therefrom to a bed of material therebeneath for processing. In order to satisfy these heat transfer requirements the spinner 20 and the nozzle tip 14 can be selected to provide a spray pattern with a relatively narrow cone angle and coarse atomization qualities to project the combustion materials along the axis of the atomizer 10 a relatively greater distance in order to promote combustion of the combustible materials at a greater distance from the nozzle.
[0034] Additionally, an atomizer in accordance with the present invention has the unique capability of burning slurry-type fuels efficiently at very small firing rates. Presently available small conventional atomizers are not suitable for slurries because of the internal restrictions and passageways of the atomizers that generally lead to rapid blocking thereof. The present atomizer utilizes a single orifice and hence provides, even at a reduced scale, fuel passages that are sufficiently large to avoid internal blockages. The use of a single discharge orifice also limits the use of hard material inserts to a single location which further simplifies the fabrication and reduces the cost of the atomizer assembly 10. Such hard material inserts, which may be used as liners (not shown) in the orifice 62, may be used to reduce erosion of the orifice surfaces by the solid particulate materials and hence extend the useful life of the atomizer.
1. An atomizer for a slurry-type fuel comprising a mixture of solids and liquids,
characterized by a nozzle body having first conduit means therein for passage of a
slurry-type fuel and second conduit means therein for passage of an atomizing fluid;
a nozzle tip, attached to the nozzle body, having internal surface means partly defining
a mixing chamber, atomizing fluid conduit means communicating with said second conduit
means, and means defining an orifice communicating with said mixing chamber, for enabling
atomized slurry-type fuel to exit the mixing chamber; and spinner means disposed within
said nozzle tip for defining, with said internal surface means, the mixing chamber,
said spinner means including axial port means communicating with said first conduit
means for passage of the slurry-type fuel into the mixing chamber, and groove means,
communicating with the atomizing fluid conduit means, for introducing the atomizing
fluid into the mixing chamber.
2. An atomizer according to Claim I, wherein the nozzle tip is removably attached
to the nozzle body.
3. An atomizer according to Claim I, or Claim 2, wherein the axial port means is operative
for passing the slurry-type fuel into the mixing chamber in a single stream.
4. An atomizer according to Claim 2, or Claim 3, wherein the groove means are configured
and operative for introducing the atomizing fluid in a tangential direction along
the periphery of the mixing chamber.
5. An atomizer according to Claim 4, wherein the groove means are further configured
and operative for imparting momentum to the atomizing fluid flow along the nozzle
body axis as it is introduced into the mixing chamber.
6. An atomizer according to any one of Claims I to 5, wherein the first conduit means
and the axial port means are sized to enable free passage of a slurry-type fuel having
solid particles which can be passed through a size 50 mesh.
7. An atomizer according to any one of Claims I to 6, wherein the said internal surface
of the nozzle tip is conical in shape, and said spinner means presents a frusto-conical
surface for engaging the internal conical surface to define the mixing chamber therebetween.
8. An atomizer according to any one of Claims I to 7, wherein the orifice is aligned
on a longitudinal axis of the nozzle tip.
9. A method of atomizing a slurry-type fuel comprising a mixture of solids and liquids,
characterized by the steps of introducing the slurry-type fuel into a mixing chamber
along an axis of the mixing chamber; introducing an atomizing fluid into the mixing
chamber in a generally tangential direction along the periphery of the mixing chamber,
said atomizing fluid being introduced into the mixing chamber at a rate sufficient
to swirl and atomize the slurry-type fuel -within the mixing chamber; and providing
an orifice in the mixing chamber aligned with the axis of the mixing chamber to enable
the atomized slurry-type fuel to exit the mixing chamber under the combined pressure
forces of the slurry-type fuel and the atomizing fluid.
10. A method according to Claim 9, wherein the slurry-type fuel is introduced into
the mixing chamber in a single rod-line stream.
I I. A method according to claim 9 or claim 10, further comprising the step of adjusting
the degree of atomization of the slurry-type fuel by varying the pressure differential
between the input pressure of the slurry-type fuel and the input pressure of the atomizing
fluid entering the mixing chamber.
12. A method of atomizing a slurry-type fuel, characterised by the steps of introducing
a slurry-type fuel under pressure into a mixing chamber having a conical internal
surface, said slurry-type fuel being introduced in a single rod-like stream along
an axis of the mixing chamber; introducing an atomizing fluid under pressure into
the mixing chamber in a tangential direction along the periphery of the mixing chamber
and toward the apex of the conical internal surface, said atomizing fluid being introduced
into the mixing chamber at a rate sufficient to swirl and atomize the slurry-type
fuel within the mixing chamber; providing a single orifice in the apex of the conical
internal surface to enable the atomized slurry-type fuel to exit the mixing chamber
under the combined pressure forces of the slurry-type fuel and the atomizing fluid;
and adjusting the degree of atomization of the slurry-type fuel by varying the pressure
differential between the slurry-type fuel and the atomizing fluid entering the mixing
chamber.