WO2017113162A1

WO2017113162A1 - Method for injecting fluid-propelled particulate solid fuel and oxidant and injector for same

Info

Publication number: WO2017113162A1
Application number: PCT/CN2015/099810
Authority: WO
Inventors: Ben Liu; Remi Tsiava; Xiaobing PAN; Zhijun Zhou
Original assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2015-12-30
Filing date: 2015-12-30
Publication date: 2017-07-06
Anticipated expiration: 2018-06-30
Also published as: CN108700287B; CN108700287A

Abstract

Method and injector for injecting fluid-propelled particulate solid fuel and oxidant, whereby at least three fast oxidant jets and at least three slow oxidant jets are injected around the solid fuel jet, the oxidant jets being injected along a contour (40) which surrounds the fuel injection opening (12) and along which contour (40) at most three slow oxidant jets are injected between two fast oxidant jets.

Description

Method for injecting fluid-propelled particulate solid fuel and oxidant and injector for same

The present invention relates to the combustion of fluid-propelled particulate solid fuel in a combustion chamber, for example in order to heat said combustion chamber or in order to heat a charge present in said combustion chamber.

Different types of fuel are burnt in industrial combustion processes, such as for example used in glass-melting furnaces.

From a technical point of view, quality gaseous fuels, such as natural gas and shale gas, are often the preferred type of fuel, in particular as they are easy to transport, inject, dose and combust.

In particular in areas where the price of gaseous fuels is high and particulate or pulverized solid fuels, such as pulverized coal or petcoke (a.k.a. petroleum coke) , are available at lower cost, it may be economically preferable to combust pulverized solid fuels, including in installations originally designed for the combustion of gaseous fuels.

However, in such a case it is generally not sufficient to merely replace the gaseous fuel with fluid-propelled pulverized solid fuel.

It was indeed found that, when replacing gaseous fuels with pulverized solid fuels, for example in glass-melting furnaces, the energy efficiency of the process dropped due to incomplete combustion of the solid fuel. This was also the case when the oxidant gas injected in contact with the solid fuel for the combustion of same had a very high oxygen content

Even when the injection velocities of the fuel and the oxidant gas were adjusted in order to prolong the residence time of the solid fuel in the fuel/oxidant gas stream/flame in the furnace and to delay precipitation of the unburnt or partially burnt solid fuel, the degree of combustion of the solid fuel remained low with respect to when gaseous fuel was used. Moreover, increased erosion of the furnace structure was observed due to friction between the structure (furnace walls) and the unburnt or partially burnt solid fuel in said stream/flame.

There is therefore a need for a method of injecting and combusting solid pulverized fuel and for an injector for pulverized fuel and oxidant which enable a higher degree of combustion of solid pulverized fuel within the confinement of an industrial combustion installation such as a glass-melting furnace.

Whereas this need is apparent for installations originally designed for burning gaseous fuels, it will be appreciated that an injector enabling a high degree of pulverized solid fuel combustion in a relatively compact flame may also be desirable for other industrial combustion installations and processes not originally designed for gaseous fuels, including for new industrial solid-fuel combustion installations to be constructed.

Processes and equipments for injecting and burning fluid-propelled particulate solid fuel in a combustion chamber are known in the art.

For example, CN-A-101709876 describes a premix or semi-premix burner for burning gas-propelled petcoke powder. The burner comprises a hollow inner tube for transporting and injecting gas-propelled petcoke powder and a surrounding narrow annular channel for air (used as gaseous combustion oxidant) between the inner tube and an outer tube. The inner tube terminates in a nozzle and the outer tube terminates in a tapered cap. The terminal end of the tapered cap defines the terminal injection opening of the burner.

CN-A-101709876 more specifically discloses such a burner whereby the outer surface of the inner nozzle is provided with a large number of ribs which define a ring of evenly distributed air injection passages with a rectangular cross section between the inner nozzle and the tapered cap. The air injected through said rectangular air passages contacts the gas-propelled petcoke powder and mixes therewith upstream of the terminal injection opening of the burner.

CN-A-101709876 also mentions the use of said burner for burning petcoke powder in a glass-melting furnace.

It is a property of premix and semi-premix burners that the fuel ignites within or in close proximity to the burner.

Whereas this may be useful for certain applications, in other applications, in particular high-temperature applications, this may lead to overheating of the burner tip causing rapid failure of the burner.

When overheating of the burner tip may occur, it is preferable to use a fuel-and-oxidant injector whereby the oxidant contacts the fluid-propelled particulate solid fuel downstream of the injector, i.e. inside the combustion chamber of the installation. Such injectors are generally referred to as “post-mix” injectors, but may also be referred to as “non-premix” injectors.

In postmix injectors, the fluid-propelled particulate solid fuel is typically supplied via an inner tube of the injector and the oxidant via an outer channel of the injector.

It has, however, been found that with such a post-mix injection configuration only a relatively small amount of the oxidant supplied by the outer channel mixes with the fluid-propelled fuel at the distance from the injector where the oxidant jet first impacts the fuel jet and in the immediate vicinity thereof.

It has indeed been observed that, downstream of said first impact, the remainder of the oxidant tends to form an oxidant sheath flowing essentially parallel with the fluid-propelled particulate fuel jet and with the flame generated by combustion of said fuel, the oxidant being progressively consumed by the flame essentially in the peripheral zone in which the oxidant is in contact with the fluid-propelled particulate fuel jet/flame.

The above phenomenon may result in (a) an excessively long flame, (b) incomplete combustion of the particulate fuel, and (c) if part of the particulate fuel precipitates from the entrainment fluid under the effect of gravity before it is mixed and burnt with the oxidant, deposits of unburnt or partially burnt fuel and ash inside the combustion chamber or onto/into the charge present in the combustion chamber.

It is an aim of the present invention to at least partially overcome the above disadvantages of post-mix injectors.

In accordance with the present invention, this aim is achieved by increasing the portion of the oxidant issued from the outer passage of a post-mix injector which effectively mixes with the fluid-propelled particulate fuel at and immediately downstream of the distance from the injector where said oxidant from the outer passage first impacts the fluid-propelled fuel jet.

The present invention relates more specifically to a method and an mix injector enabling the above, as well as industrial processes in which said method is used and industrial installations equipped with the injector.

The present invention relates more specifically to a method of injecting a fluid-propelled particulate solid fuel and an oxidant into a combustion chamber. The method comprises the following steps:

·injection of a jet of fluid-propelled particulate solid fuel into the combustion chamber with a fuel injection velocity v_f, said fuel jet being injected into the combustion chamber via a fuel injection opening having a circumference corresponding to a first two-dimensional geometric contour, hereafter referred to as “first contour” , said first contour presenting a geometric center or centroid；

·injection of n₁ first jets of oxidant, hereafter referred to as “fast oxidant jets” , said fast oxidant jets being injected into the combustion chamber via n₁ first injection openings, said fast oxidant jets being injected with a first oxidant injection velocity v_O1, called “high oxidant velocity” , the number n₁ of first injection openings being equal to or greater than 3；

·injection of n₂ second jets of oxidant, hereafter referred to as slow oxidant jets, said slow oxidant jets being injected into the combustion chamber via n₂ second injection openings, said slow oxidant jets being injected with a second oxidant injection velocity v_O2, called “low oxidant velocity” , the number n₂ of second injection openings being likewise equal to or greater than 3.

The first contour is typically circular when a flame with a circular cross-section is desired and elongated when a “flat flame” is desired, i.e. a flame with an elongated cross section perpendicular to the propagation direction of the flame.

According to the method of the present invention, each one of said n₁ first oxidant injection openings and each one of said n₂ second oxidant injection openings intersects a second contour. Said second contour, which corresponds to a closed curve connecting the n₁ + n₂ oxidant injection openings either in clockwise or in counterclockwise direction, surrounds the first contour and is spaced from the first contour. In other words, the second contour surrounds the outer circumference of the fuel injection opening, while being spaced apart from the fuel injection opening and its outer circumference.

In addition, along said second contour, at most three slow oxidant jets of the n₂ slow oxidant jets are injected between two successive fast oxidant jets of the n₁ fast oxidant jets. In other words, the succession of the first and second oxidant injection openings along the second contour is such that at most three (3) second oxidant injection openings are positioned between two successive first oxidant injection openings. The high oxidant injection velocities v_O1 and the low oxidant injection velocities v_O2 are furthermore such that the lowest of the high oxidant velocities v_O1 is greater than or equal to 1.25 times the highest of the low oxidant velocities v_O2.

Preferably, at most two slow oxidant jets of the n₂ slow oxidant jets are injected along the second contour between two successive fast oxidant jets of the n₁ fast oxidant jets, more preferably at most one (i.e. one or zero) of the n₂ slow oxidant jets is located between every two successive fast oxidant jets of the n₁ fast oxidant jets along the second contour.

In the present context, the terms “jet” , “stream” and “flow” are used as synonyms.

Likewise, the terms “pulverized” and “particulate” are used as synonyms. Consequently, unless otherwise indicated, the expression “pulverized fuel” is used to mean “particulate fuel” without restriction as to how said particulate fuel was obtained or manufactured.

In the present context, two oxidant jets or two oxidant injection openings are said to be “adjacent” when they immediately succeed one another along the second contour.

By means of the above configuration of slow and fast oxidant jets around the fuel jet, adjacent fast and slow oxidant jets can be injected so as to impact the fuel jet at substantially the same distance from the fuel injection opening (measured in the direction perpendicular to the plane of the fuel injection opening) . Alternatively, adjacent fast and slow oxidant jets may also be injected so that one or more and possibly all of the fast oxidant jets impact the fuel jet immediately upstream of an adjacent slow oxidant jet. When not all of the fast oxidant jets impact the fuel stream upstream of where an adjacent slow oxidant jets impacts the fuel jet, the remaining fast oxidant jets impact the fuel stream at substantially the same distance from the fuel injection opening as an adjacent slow oxidant jet.

When the injection directions of the fuel and oxidant jets are parallel, the position of an oxidant injection opening with respect to the fuel injection opening determines the distance from the fuel injection opening at which the corresponding oxidant jet (i.e. the oxidant jet injected through said oxidant injection opening) impacts the fuel jet. When the oxidant jet is injected in a direction which is different from the direction of the fuel jet, then the distance from the fuel injection opening at which an oxidant jet impacts the fuel jet is determined by the position of the corresponding oxidant injection opening with respect to the fuel injection opening and also the injection direction of the oxidant jet with respect to the injection direction of the fuel jet (for example towards the fuel jet or away from the fuel jet) .

It will be appreciated that, due to the naturally occurring widening of the injected jets downstream of the respective injection openings, an oxidant jet can impact the fuel jet even if the oxidant jet is injected in a direction parallel to the fuel jet or in a direction inclined somewhat away from the injection direction of the fuel jet.

It was found that by injecting the oxidant in a multitude of oxidant jets around the fuel jet instead of as a single annular jet around the fuel jet, all other factors being equal, the degree of combustion of the pulverized solid fuel was somewhat increased, but that an even higher degree of fuel combustion remained desirable.

In accordance with the present invention, this was achieved by the combination of fast and slow oxidant jets and their position with respect to one another (along the second contour) and with respect to the fuel jet as described above.

It is speculated that with the prior-art post-mix solid fuel and oxidant injection method, at the point of impact between the oxidant jet (s) and the fuel jet downstream of their respective injection openings only a minor portion of the oxidant initially intermingles with the fuel jet, whereas most of the oxidant thereafter follows a flow pattern around and parallel to the fuel jet/the flame thereby restricting fuel combustion to the frontier area between the oxidant jet and the fuel jet/flame.

With the configuration of fast and slow oxidant jets in accordance with the present invention the amount of oxidant which effectively penetrates the fuel jet at the point of impact was found to have increased, thereby increasing the degree of fuel combustion at the early stages of the flame.

Without wishing to be bound by this potential explanation, it is believed that with the use of a combination of fast and slow oxidant jets as described above, the impact of the fast oxidant jets and the fuel jet destabilizes the surface of the fuel jet and thus allows a greater portion of the oxidant from the nearby slow oxidant jets to mix with the fuel of the fuel jet/flame at the point of impact between the two jets or immediately thereafter.

It is appreciated that it is known to increase turbulent mixing of fuel and oxidant by means of a purposeful selection injection velocities with which all of the fuel and all of the oxidant are injected, in particular with respect to one another. However, such process parameter restrictions may not be compatible with the requirements of the industrial process/furnace in which the solid fuel combustion is to take place, such as power flexibility and temperature profile. Changes to the fuel injection velocity and to the oxidant injection velocity furthermore generally cause the shape of the flame to change, for example from a long tight flame to a shorter bushy flame, whereby the changed flame shape may result in a temperature profile which is not appropriate for the requirements of the process and/or increased erosion and/or thermal damage, etc.

This is not or, at the very least, to a much lesser extent the case for the method according to the present invention which includes the injection of both fast and slow oxidant jets.

It is likewise appreciated that it is known to equip burners and injectors with devices, such as swirlers and bluff bodies to increase turbulent mixing of fuel and oxidant. These devices likewise generally cause the shape of the flame to change, with the consequences as described above. They furthermore complicate the structure of the injector, and therefore increase its production costs. Moreover, in particular in high temperature environments such as glass-melting furnaces, such additional devices can reduce the robustness of the injector. Finally, when these devices come into contact with the stream of solid fuel, they are subjected to rapid erosion by the fuel particles.

The method according to the present invention can improve mixing between the fuel and the oxidant without use of such devices, as will become apparent hereafter in the description of the fuel-and-oxidant injector according to the present invention.

In order to further increase the portion of the fast and slow oxidant jets which effectively mixes with the fluid-propelled particulate fuel at and immediately downstream of the distance from the injector where said oxidant jets first impact the fluid-propelled fuel jet, the lowest of the high oxidant velocities v_O1 is advantageously greater than or equal to 1.30 times the highest of the low oxidant velocities v_O2, preferably greater than or equal to 1.50 times the highest of the low oxidant velocities v_O2..

For easy execution of the method, it is preferred that the high oxidant velocity v_O1 of each of the n₁ fast oxidant jets is the same (in which case said velocity is also equal to the lowest of the high oxidant velocities v_O1 mentioned above) .

Likewise, execution of the method of the invention is simplified when the low oxidant velocity v_O2 of each of the n₂ slow oxidant jets is the same (in which case said velocity is also equal to the highest of the low oxidant velocities v_O2 mentioned above) .

Thus, according to a straightforward embodiment of the method according to the present invention, all of the n₁ fast oxidant jets are injected with the same high oxidant velocity v_O1 and all of the n₂ slow oxidant jets are injected with the same low oxidant velocity v_O2, whereby said high oxidant velocity v_O1 is at least 1.25 times said low oxidant velocity v_O2, preferably at least 1.30 times and more preferably at least 1.50 times.

The degree of fuel combustion can further be increased when the fuel injection velocity v_f, with which the fluid-propelled particulate solid fuel is injected into the combustion chamber, is smaller than the high oxidant velocity v_O1 of each one of the n₁ fast oxidant jets and even more so when the fuel injection velocity v_f is smaller than or equal to the low oxidant velocity v_O2 of each one of the n₂ slow oxidant jets.

According to one embodiment, the number n₁ of fast oxidant jets is identical to the number n₂ of slow oxidant jets. In that case, fast and slow oxidant jets may alternate along the second contour (i.e. with one fast oxidant jet being injected between every two successive slow oxidant jets along the second contour and one slow oxidant jet being injected between every two successive fast oxidant jets along said second contour) .

According to a useful embodiment, the second contour is isomorphic or substantially isomorphic which the first contour defined by the fuel injection opening. For example, the first and second contour may both be circular or substantially circular.

The first and second contour are preferably also concentric or substantially concentric.

When the first and second contour are concentric, they present the same geometric center.

Preferably, the lateral distance between the first and second contour is constant or substantially constant.

The fluid-propelled particulate solid fuel is preferably gas-propelled particulate solid fuel. The particulate solid fuel is more preferably propelled by air, oxygen-enriched air, recycled flue gas or a combination of recycled flue gas with air or with oxygen-enriched air.

The method according to the present invention is suitable for any type of particulate solid fuel, including, for example, particulate solid biomass. Preferred solid fuels are coal and petcoke.

The first and/or second oxidant jets, and preferably both, are advantageously jets of an oxidant with an oxygen content of between 50％vol and 100％vol, preferably of at least 80％vol, more preferably of at least 90％vol.

According to a preferred embodiment of the method according to the invention, more than 50％ of the oxygen injected into the combustion zone by means of the fast and slow oxidant jets is injected below the geometric center of the first contour. In other words, most of the oxygen injected via the fast and slow oxidant jets is injected into the combustion zone below the geometric center of the fuel injection opening.

Such an embodiment can be particularly useful for a number of applications. For example, when the combustion zone contains a charge to be heated which is located below the particulate-solid-fuel flame, it makes it possible to draw the flame towards the charge for more efficient heating. When the injector is located below an air port, this embodiment provides a more efficient use of the oxidant injected via the fast and slow oxidant jets, in particular when the said jets are jets of oxygen-rich oxidant, i.e. jets of an oxidant having a higher oxygen content than that of air.

According to a specific embodiment of the present invention, at least half of the n₂ slow oxidant jets are injected below the center of the fuel injection opening, preferably a majority of the n₂ slow oxidant jets. This embodiment is again of particular interest when the injector is located below an air port.

The method according to the present invention can be used in a wide range of industrial combustion installations. The method is, for example, particularly adapted for use in a combustion chamber of a reverberatory furnace.

The combustion chamber may be a melting chamber, and in particular a glass-melting chamber.

The combustion chamber may be a side-fired chamber or an end-fired chamber, the method being particularly suited for use in end-fired combustion chambers, as for example known in the field of glass-melting.

As mentioned above, one particular configuration in which the present invention can beneficially be employed is a combustion chamber equipped with a combustion air port injecting air into said combustion chamber. Examples of such combustion chambers are, for example, glass-melting furnaces equipped with regenerators or recuperators for preheating combustion air injected via one or more air ports. In the case of a combustion chamber with an air port, the fluid-propelled particulate solid fuel and the fast and slow oxidant jets are advantageously injected through injection openings located within or adjacent said combustion air port, preferably underneath said combustion air port.

When the fluid-propelled particulate solid fuel and the fast and slow oxidant jets are injected through injection openings located adjacent an air port, it may be advantageous to inject at least one of the fast or slow oxidant jets between the combustion air port and the geometric center of the first contour, i.e. between, the combustion air port and the geometric center of the fuel injection opening. In that case, a majority of the oxidant jets injected between the combustion air port and the geometric center of the first contour are preferably fast oxidant jets in order to promote rapid mixing of the air injected via the air port with the particulate solid fuel jet and/or flame.

The present invention also relates to a device for injecting pulverized solid fuel and oxidant into a combustion zone which is suitable for use in the method according to the invention and to the use of such a device for combusting particulate solid fuel in the combustion zone of an industrial installation.

The present invention more specifically proposes a fuel-and-oxidant injector comprising a first conduit defining a fuel passage therewithin for supplying fluid-propelled pulverized or particulate solid fuel and a second conduit surrounding the first conduit and laterally spaced therefrom, an oxidant passage being thus defined between said first and second conduits. The fuel passage terminates in a fuel injection opening. The outer circumference of said fuel injection opening defines a first two-dimensional geometric contour.

As indicated above with respect to the method of the invention, said first contour is typically circular when a flame with a circular cross-section is desired and elongated when a “flat flame” is desired.

The oxidant passage terminates in a flange which surrounds the fuel injection opening and which extends from the first to the second conduit. The flange presents a multitude of perforations positioned along a second two-dimensional contour.

This second contour, which corresponds to a closed curve, connects the multitude of perforations either in clockwise direction or in counterclockwise direction. The second contour surrounds the first contour while being spaced apart therefrom.

Each one of said multitude of perforations defines an oxidant injection opening in the flange in fluid communication with the oxidant supply passage. The corresponding multitude of oxidant injection openings are thus positioned around the fuel injection opening along the second contour.

The multitude of perforations in the flange comprises n1 smaller perforations, called “first perforations” and n2 larger perforations, called “second perforations” , with n1 and n2 each being greater than or equal to 3. Each first perforation defines a first oxidant injection opening having a first injection cross-section area S1, and each second perforation defines a second oxidant injection opening having a second injection cross-section area S2. The cross-section area of the larger, i.e. second perforations is greater than the cross-section area of the smaller, i.e. first perforations.

In particular, according to the present invention, the cross-section area of the smallest of the n2 second oxidant injection openings is at least 1, 12 times the cross-section area of the largest of the n1 first injection openings, preferably at least 1, 5 times and advantageously not more than 58 times.

According to the invention, the succession of the oxidant injection openings along the second contour is furthermore such that at most three of the (larger) second oxidant injection openings are positioned between two successive (smaller) first oxidant injection openings, preferably at most two and more preferably at most one (i.e. one or zero) of the second oxidant injection openings being positioned between two successive first oxidant injection openings along the second contour.

The injector is thus a post-mix injector as discussed above.

As indicated earlier, the first and second oxidant injection openings are preferably positioned with respect to one another and with respect to the fuel injection opening, so that streams of oxidant injected through adjacent first and second oxidant injection openings impact a fuel stream injected through the fuel injection opening so that the oxidant stream injected through the first oxidant injection opening, i.e. the fast-oxidant stream, impacts the fuel stream at a distance from the fuel injection opening which is the same or immediately before the distance from the fuel injection opening at which the adjacent oxidant stream from the second oxidant injection opening, i.e. the slow oxidant stream, impacts said fuel stream.

With the configuration of oxidant injection openings in accordance with the present invention the amount of oxidant which effectively penetrates the fuel stream at the point of impact between the fuel and oxidant streams is increased, thereby increasing the degree of fuel combustion at the early stages of the flame. Without again wishing to be bound by this potential explanation, it is believed that the use of a combination of smaller and larger oxidant injection openings as described above generates oxidant streams of different velocity whereby the impact of the higher- velocity oxidant jets (or fast oxidant jets) issued from the smaller first oxidant injection openings destabilize the surface of the fuel stream and thus allow a greater portion of the oxidant from the lower-velocity oxidant jets (or slow oxidant jets) issued from the larger second oxidant injection openings to mix with the fuel at the point of impact between the fuel jet and the lower velocity oxidant jet.

The present invention thus provides a fuel-and-oxidant injector for improved particulate solid fuel combustion which is particularly simple, reliable, robust, suitable for high-temperature environments and easy to operate.

According to one embodiment of the injector, the second contour is isomorphic or substantially isomorphic with the first contour. Preferably, the second contour corresponds to an enlarged projection onto the flange of the outer circumference of the fuel injection opening.

The first and second contours are preferably concentric or substantially concentric. In that case, the lateral distance between the first and second contours is constant or substantially constant.

The first and second contours are typically circular or substantially circular. However, as mentioned above, the first and second contours may have other shapes depending, in particular, on the cross-section of the flame to be obtained.

Likewise, the oxidant injection openings typically are also circular or substantially circular, although these too may have another shape.

According to a preferred embodiment useful for most applications, all the first perforations are identical (in which case all of the first oxidant injection openings are also identical) and/or all of the second perforations are identical (in which case all of the second oxidant injection openings are likewise identical) .

Generally, all perforations in the flange are either (smaller) first oxidant injection openings or (larger) second oxidant injection openings located on the second contour.

However, exceptionally, some embodiments of the injector may present additional oxidant injection openings in the flange which are neither first nor second oxidant injection openings, for example an oxidant injection opening not located on the second contour and/or an oxidant injection opening with an injection cross section area A which does not satisfy the criteria for the injection cross section area S1 of the first oxidant injection openings nor for the cross section area S2 of the second oxidant injection openings.

Typically, the first and second perforations will be evenly distributed around the fuel injection opening.

Other figurations may nevertheless be envisaged. For example, in the case of a horizontal flat flame, most of the first and second perforations may be located below and above the fuel injection opening, as opposed to on the left and on the right of the fuel injection opening.

Similarly, more (first and/or second) oxidant injection openings may be positioned below the fuel injection opening or the (first and/or second) oxidant injection openings below the fuel injection opening may be positioned closer to one another than the other oxidant injection openings on the second contour, in order to prevent early precipitation of the unburnt or partially burnt fuel particles from the fuel stream/flame, i.e. so as to delay precipitation of said particles.

The total number (n1 +n2) of first and second perforations depends in practice on the process in which the injector is to be used and on the furnace configuration.

According to one embodiment, the number n1 of (smaller) first oxidant injection openings is equal to the number n2 of (larger) second oxidant injection openings. In that case, it may be advantageous to have an alternation between first and second injection openings along the second contour, i.e. a first opening, followed by a second opening, followed by a first opening, etc., so as to maximize the oxidant penetration in the fuel stream at or immediately following the point of impact.

Alternative successions of first and second perforations may however be useful. For example, more of the (larger) second oxidant injection openings may be positioned below the fuel injection opening than above so as to inject more oxidant below the fuel stream and thereby to delay precipitation of the unburnt or partially burnt fuel particles.

As will be explained below, it may be useful for the second perforations to comprise an upstream section adjacent the oxidant passage and a downstream section adjacent the oxidant injection opening, whereby the cross-section area of the upstream section (perpendicular to the oxidant flow direction) is smaller than the cross-section area of the downstream section of the given second perforation. Alternatively, both the first and the second perforations may comprise an upstream and a downstream section as described above.

In order to maximize the degree of combustion of the pulverized solid fuel, the fuel-and-oxidant injector is preferably operated with an oxygen-rich oxidant, i.e. an oxidant having an oxygen content higher than that of air. Thereto, the oxidant passage of the injector is fluidly connected to a source of such an oxygen-rich oxidant, the oxidant having for example an oxygen content of between 50％vol and 100％vol, preferably of at least 80％vol and more preferably of at least 90％vol. The oxidant source can notably be an Air Separation Unit (ASU) , a pipeline for transporting oxygen-rich oxidant or a reservoir of liquefied oxygen-rich oxidant.

In operation, the fuel passage of the fuel-and-oxidant injector is fluidly connected to a source of fluid-propelled pulverized fuel, preferably fluid-propelled pulverized coal or fluid-propelled pulverized petcoke. Devices for generating a stream of fluid-propelled pulverized solid fuel are well known in the art. The fluid entraining the pulverized solid fuel may be a liquid or a gas. Preferably, the fluid-propelled pulverized solid fuel is pulverized solid fuel propelled by a gas, the gas being preferably air, oxygen-enriched air, recycled flue gas or a combination of recycled flue gas with air or with oxygen-rich oxidant.

The present invention also relates to the use of the fuel-and-oxidant injector for injecting pulverized solid fuel and oxidant into a combustion chamber.

The invention thus also covers a method of injecting a pulverized solid fuel into a combustion chamber using any one of the above described embodiments of the fuel-and-oxidant injector whereby, on the one hand, fluid-propelled pulverized solid fuel is injected into the combustion chamber through the fuel injection opening and, on the other hand, oxidant is injected into the combustion chamber through the oxidant injection openings. Inside the combustion chamber and downstream of the fuel injection opening and the first and second oxidant injection openings, the thus injected fuel and oxidant streams impact, causing the fuel to ignite and burn with the oxidant.

As mentioned above, the oxidant is preferably an oxygen-rich oxidant and the fuel is preferably a gas-propelled pulverized solid fuel； the pulverized solid fuel itself being preferably pulverized coal or petcoke.

As will be explained below, it is not necessary in accordance with the present invention that all of the oxygen necessary for combusting the pulverized solid fuel is injected into the combustion chamber via the oxidant passage of the fuel-and-oxidant injector. Indeed, additional oxygen may be supplied to the combustion chamber by other means, for example, via air or oxygen ports of the combustion chamber which inject additional oxygen into the combustion chamber in the form of respectively air and oxygen flows.

The latter method is particularly useful for use in the combustion chamber of a glass-melting furnace.

The invention also relates to furnaces comprising a combustion chamber equipped with at least one fuel-and-oxidant injector according to any one of the embodiments described above.

A furnace according to the present convention thus comprises a combustion chamber having at least one fuel-and-oxidant injector as described above which is installed so that the fuel injection opening and the first and second oxidant injection openings face the inside of the combustion chamber.

According to one embodiment, the combustion chamber is equipped with additional oxygen supply devices for supplying additional oxygen for combusting the pulverized solid fuel within the combustion chamber. For example, the combustion chamber may have an air port in one of its walls for supplying oxygen-containing combustion air to the combustion chamber. In that case, the fuel-and-oxidant injector is preferably positioned within the air port or adjacent the air port in the wall of the combustion chamber comprising said air port. The fuel-and-oxidant injector may thus be a through-port injector or an under-port injector. The injector may also be positioned between two adjacent air ports, etc.

It will be appreciated that due to the simple and compact structure of the injector, said injector can easily be integrated at different locations within an air port or within the combustion chamber. The injector may in particular be integrated in a refractory block which is itself integrated into the combustion chamber.

The simple structure of the fuel-and-oxidant injector of the invention and the simple method of operating same also provide the additional benefit of not requiring complex injector control equipment and protocols.

Moreover, where necessary, the simple structure of the injector also makes it straightforward to equip the injector with a cooling mantle surrounding the oxidant supply passage. In operation, a cooling fluid is then circulated within the cooling mantle so as to protect the first and second conduit, and in particular the flange, against overheating.

The furnace according to the present invention may also comprise at least one recuperator or regenerator for preheating the combustion air supplied by the air port with heat from flue gas evacuated from the combustion chamber.

The furnace may in particular be an alternating furnace. Such furnaces are well known in the art. During operation, one side of the furnace is the firing side, i.e. the side of the furnace where fuel and oxidant is injected into the furnace, the other side being the exhaust side where the combustion gases exhaust the furnace, the two sides being cyclically reversed during furnace operation. Such furnaces are typically equipped with regenerators for preheating combustion air with heat from the exhausted flue gas.

As already indicated above, the present invention is suitable for a wide range of industrial combustion installations. The invention is, for example, particularly adapted for use in a combustion chamber of a reverberatory furnace. The combustion chamber may be a melting chamber, and in particular a glass-melting chamber. The combustion chamber may be a side-fired chamber or an end-fired chamber, the invention being particularly suited for end-fired combustion chambers.

The present invention will be better understood in the light of the following examples, reference being made to figures 1A, 1B, 1C, 2A, 2B, 2C, 3B and 3C, whereby:

·Figure 1A is a schematic front view of a first embodiment of a fuel-and-oxidant injector according to the present invention, figures 1B and 1C being schematic partial cross-section views of said injector according to plans B-B and C-C；

·Figure 2A is a schematic front view of another embodiment of a fuel-and-oxidant injector according to the present invention, figures 2B and 2C being schematic partial cross-section views of said injector according to plans B-B and C-C； and

·Figures 3B and 3C are schematic partial cross section views according to respectively plans B-B and C-C of an alternative embodiment of the fuel-and-oxidant injector of the present invention. The front view of said alternative embodiment may, for example, correspond to either of figures 1A or 2A.

The fuel-and-oxidant injectors illustrated in the figures comprise an inner conduit 10, an outer conduit 20 and a flange 30 connecting the inner conduit 10 to the outer conduit 20 at the injection end of the injector.

The inner conduit 10 defines a central fuel passage 11 which terminates in a fuel injection opening 12 which has a circular circumference defining a first contour 13.

The central fuel passage 11 is surrounded by an oxidant passage 21 located between the inner conduit 10 and the outer conduit 20, the flange 30 being located at the injection end of the oxidant passage 21.

The flange 30 comprises a number of “first perforations” 31 and a number of “second perforations” 35. On the injection side of the flange 30, each first perforation 31 terminates in a first oxidant injection opening 32 and each second perforation 35 terminates in a second oxidant injection opening 36, the cross area of the first injection opening 32 being smaller than the cross section area of the second injection openings. In the illustrated embodiments, the cross-section areas of the first oxidant injection openings 32 are identical and the cross-section areas of the second oxidant injection openings 36 are identical, the cross-section area of a second oxidant injection opening 36 being four times the cross-section area of a first injection opening 32.

The first and second

oxidant injection openings

32, 36 are located on a second contour 40 which surrounds the first contour 13, which is spaced from said first contour 13 and which is isomorphic with said first contour 13.

In the embodiment illustrated in figures 1A to 1C, first and second

oxidant injection openings

32, 36 alternate along the second contour 40, a first oxidant injection opening 32 being located between every two successive second oxidant injection openings 36 along said second contour 40 and a second oxidant injection opening 36 being located between every two successive first oxidant injection openings 32.

In the embodiment illustrated in figures 2A to 2C, two second injection openings 36 are located both on the left and on the right of the fuel injection opening 12 and three first injection openings 32 are located both above and below the fuel injection opening 12.

The sequence of first and second

oxidant injection openings

32, 36 along the second contour 40 is such that there are either no second oxidant injection openings 36 between two successive first oxidant injection openings 32 (below and above the fuel injection opening 12) or two second oxidant injection openings 36 between two successive first oxidant injection openings 32 (on the left and on the right of the fuel injection opening 12) .

As shown in figures 1B and 1C, in the first embodiment, the first and

second perforations

31, 32 are cylindrical and thus have a constant cross-section area throughout. Whereas such first and

second perforations

31, 35 are easy to produce, they may result in a preferential oxidant flow path through the larger second perforations 35 compared to through the smaller first perforations 31, due to the greater flow resistance of the latter. Whereas this may not be problematic for some injector configurations or combustion processes, the existence of a preferential flow path through the second oxidant perforations 35 may prove problematic for other fuel-and-oxidant injectors/combustion processes.

The occurrence of preferential oxidant flow paths is at least in part overcome in the embodiment illustrated in figures 2A to 2C. As shown in figure 2C, according to said embodiment, the smaller first perforations 31 are identical to those illustrated in figure 1C, i.e. they are cylindrical and have a constant cross-section area throughout. The second perforations 35, however, have an upstream section 37 adjacent the upstream face (i.e. the face on the side of the oxidant passage) of the flange 30 and a downstream section 38 adjacent the outlet face of the flange 30 (i.e. the face of the flange away from the oxidant passage and towards the combustion zone) . The upstream section 37 of the second oxidant perforations is cylindrical and has the same cross-section area as the first oxidant perforations 31. The downstream section 38 of the second perforations 35 widens towards the oxidant injection opening 36. In this manner, the difference in flow resistance between the first and

second perforations

31, 35 is substantially reduced while the effect of having smaller first and larger second

oxidant injection openings

32, 36 is maintained.

This embodiment is again simple to manufacture in that, to start with, identical perforations can be made at the locations of the small and

large perforations

31, 35 in the flange 30, whereafter at the location of the larger second perforations 35 the outlet section of the perforation is widened as shown in figure 2B.

An alternative embodiment, which is also easy to produce, is shown in figures 3B and 3C. According to this embodiment, both the first perforations 31 and the second perforations 35 present an

inlet section

33, 37 adjacent the inlet face of the flange 30 and an outlet section adjacent the outlet face of the flange 30. The first and

second perforations

31, 35 have identical cylindrical

upstream sections

33, 37, the cross-section area of which is smaller than the area of both the larger second oxidant injection openings 36 and than the smaller first oxidant injection openings 32. The

downstream sections

33, 37 of the first and

second perforations

31, 35 are also cylindrical, the cross section area of the downstream section 33 of the first oxidant perforations corresponding the cross-section of the smaller first oxidant injection openings 31 and the cross-section area of the outlet section 37 of the second oxidant perforations 35 corresponding to the larger cross-section of the second oxidant injection openings 35.

It will be appreciated that the use of second perforations, and optionally also first perforations, having a narrower upstream section and wider downstream section is not only of interest for the injector configurations as shown in figures 1A and 2A, but can also usefully be applied to other embodiments of the fuel-and-oxidant injector of the present invention.

It was found the methods and/or injectors according to the present invention, a significantly higher degree of combustion of solid particulate fuel was achieved compared to when fuel-and-oxidant injectors were used with a cylindrical oxidant injection opening surrounding the fuel injection opening or when fuel-and-oxidant injectors were used having a series of identical oxidant injections openings located around a central fuel injection opening, all other factors being equal. As a consequence, more efficient use of the fuel was achieved, the length of the flame could be reduced and erosion of the internal furnace structure was found to be lower.

Claims

Method of injecting a fluid-propelled particulate solid fuel and an oxidant into a combustion chamber, comprising:

·injecting a jet of fluid-propelled particulate solid fuel into the combustion chamber with a fuel injection velocity v_f via a fuel injection opening (12) having a circumference corresponding to a first two-dimensional geometric contour (13) with a geometric center,

·injecting n₁ first jets of oxidant, called fast oxidant jets, via n₁ first injection openings (31) into the combustion chamber with a first oxidant injection velocity v_O1, called high oxidant velocity, with n₁ ≥ 3,

·injecting n₂ second jets of oxidant, called slow oxidant jets, via n₂ second injection openings (35) into the combustion chamber with a second oxidant injection velocity v_O2, called low oxidant velocity, with n₂ ≥ 3,

·whereby each one of said n₁ first and n₂ second oxidant injection openings (31, 35) intersects a second contour (40) which surrounds the first contour (13) , which second contour (40) is spaced from the first contour (13) ,

·whereby, along said second contour (40) , at most three successive slow oxidant jets of the n₂ slow oxidant jets are injected between two successive fast oxidant jets of the n₁ fast oxidant jets, and

·whereby the lowest of the high oxidant velocities v_O1 is greater than or equal to 1.25 times the highest of the low oxidant velocities v_O2, preferably greater than or equal to 1.30 times the highest of the low oxidant velocities v_O2, more preferably greater than or equal to 1.50 times the highest of the low oxidant velocities v_O2.
Method according to claim 1, whereby along the second contour (40) , at most two successive slow oxidant jets of the n₂ slow oxidant jets are injected between two successive fast oxidant jets of the n₁ fast oxidant jets, preferably at most one of the n₂ slow oxidant jets being located between two successive fast oxidant jets of the n₁ fast oxidant jets.
Method according to any one of the preceding claims, whereby the fuel injection velocity v_f is smaller than the high oxidant velocity v_O1 of the n₁ fast oxidant jets.
Method according to any one of the preceding claims, whereby the first and second contour (13, 40) are (a) concentric or substantially concentric and/or isomorphic or substantially isomorphic
Method according to any one of the preceding claims, whereby the fluid-propelled particulate solid fuel is gas-propelled particulate solid fuel, the particulate solid fuel being preferably propelled by air, oxygen-enriched air, recycled flue gas or a combination of recycled flue gas with air or with oxygen-rich oxidant.
Method according to any one of the preceding claims, whereby the oxidant of the first and second oxidant jets has an oxygen content of at between 50％vol and 100％vol, preferably of at least 80％vol, more preferably of at least 90％vol.
Method according to any one of the preceding claims, whereby more than 50％of the oxygen injected into the combustion zone by means of the fast and slow oxidant jets is injected below the geometric center of the first contour (13) .
Method according to any one of the preceding claims, whereby the combustion chamber is equipped with a combustion air port injecting air into the combustion chamber and whereby the fluid-propelled particulate solid fuel and oxidant are injected through injection openings located within, next to or underneath said combustion air port, preferably underneath said combustion air port.
Fuel-and-oxidant injector comprising:

·a first conduit (10) defining a fuel passage (11) therewithin for supplying fluid-propelled pulverized solid fuel,

·a second conduit (20) surrounding the first conduit (10) and laterally spaced therefrom so as to define an oxidant passage (21) between the first and second conduit (10, 20) ,

whereby:

·the fuel passage (11) terminates in a fuel injection opening (12) having an outer circumference defining a first two-dimensional geometric contour (13) ,characterized in that:

·the oxidant passage (21) terminates in a flange (30) surrounding the fuel injection opening (12) and extending from the first to the second conduit (10, 20) ,

·the flange (30) presents a multitude of perforations (31, 35) positioned along a second two-dimensional contour (40) , said second contour (40) surrounding the first contour (13) and being spaced apart from the first contour (13) , each said perforation (31, 35) defining an oxidant injection opening (32, 36) in the flange (30) in fluid communication with the oxidant passage (21) ,

·said multitude of perforations (31, 35) comprising:

i. n1 first perforations (31) each first perforation defining a first oxidant injection opening (32) having a first injection cross-section area S1, with n1 ≥ 3 and

ii. n2 second perforations (35) each second perforation defining a second injection opening (36) having a second injection cross-section area S2, with n2 ≥ 3,

whereby the smallest of the second injection cross-section areas S2 is at least 1,12 times the largest of the first injection cross-section areas S1, preferably between 1,5 and 58 times,

·along the second contour (40) , at most three second oxidant injection openings (36) are positioned between two successive first oxidant injection openings (32) , preferably at most two second oxidant injection openings (36) and more preferably at most one second oxidant injection opening (36) .
Fuel-and-oxidant injector according to claim
whereby the second contour (40) is isomorphic or substantially isomorphic and/or concentric or substantially concentric with the first contour (13) .
Fuel-and-oxidant injector according to any one of the preceding claims, whereby the second perforations (35) comprise an upstream section (37) adjacent the oxidant passage (11) and a downstream section (38) adjacent the second oxidant injection opening (36) of the given second perforation (35) , and whereby the upstream section (37) has a cross-section area which is smaller than the cross-section area of the downstream section (38) of the given second perforation (35) .
Fuel-and-oxidant injector according to any one of the previous claims,

·whereby the oxidant passage (21) is fluidly connected to a source of an oxidant, said oxidant having preferably an oxygen content of between 50％vol and 100％vol, more preferably of at least 80％vol and most preferably of at least 90％vol, and

·whereby the fuel passage (11) is fluidly connected to a source of fluid-propelled pulverized fuel, preferably gas-propelled pulverized fuel.
Method of injecting a pulverized solid fuel into a combustion chamber using a fuel-and-oxidant injector according to any one of the preceding claims, whereby:

·fluid-propelled solid pulverized fuel is injected into the combustion chamber through the fuel injection opening (12) and

·oxidant is injected into the combustion chamber through the oxidant injection openings (32, 36) .
Furnace comprising a combustion chamber having a fuel-and-oxidant injector according to any one of claims 1 to 7, said fuel-and-oxidant injector being installed so that the fuel injection opening (12) and the oxidant injection openings (32, 36) face the inside of the combustion chamber.