EP0014812B1 - Burners for solid fuels combined with liquid and/or gaseous fuels - Google Patents

Description

The present invention relates to a burner for the combustion of solid, pulverized or finely divided fuels, alone or in combination with liquid and / or gaseous fuels, for ovens and apparatuses relating to thermal technology, more particularly for rotary ovens, exchangers of heat by suspension in the gases, grates and combustion chambers, for which it is necessary to be able to carry out, even during operation, a very wide adjustment of the shape of the flame.

Such burners must allow fuels and combinations of fuels to burn under optimal process conditions using the available air, either as combustion air or that of primary air which can be conveyed through the burner.

It is therefore necessary to adjust the shape of the flow of fuel and air and also, in the case of slightly abrasive solid fuels, that of the transport gas-pulverized coal mixture, in the widest ranges so as to achieve the necessary combustion results.

Furthermore, it is necessary, and in particular in the case of abrasive solid fuels, to achieve high availability times for the burner and the heated installation.

The construction of the burner must therefore be chosen so that the mixture of transport gas and solid fuel is deflected as little as possible and circulates at the lowest possible speed.

To avoid any damage to the installation subject to fire, it must also be possible to adjust the most suitable flame form at any time.

The economy of the operation is also favorably influenced by an optimal adaptation of the course of the combustion because, by doing this, one is constrained to use the least possible fuel.

In addition, it must be possible to use fuels with an average calorific value, for example with a low proportion of volatile products or a very high ash content.

It is known that in order to partially fulfill these conditions, burners are used which consist of a single circuit through which the quantity of fuel chosen or available flows beforehand mixed with air and / or gas through a nozzle-injector. carrier.

In this case, it is only possible to have a very limited influence on the flame shape, because the transport air flow is modified and consequently the ejection speed changes.

One can also exert a certain influence, always limited, by acting on the fuel by modifying its fineness or its nature.

A notable improvement was obtained when a two-circuit burner was used where the transport air-fuel mixture flows in an axial direction through the external channel and where the divergence and rotation are influenced by an air component clean, which can be adjusted and introduced inside the fuel-air stream.

In a central tube, it is also possible to introduce a liquid or gaseous component for start-up and ignition.

The axial component of the supplied air being already loaded with fuel, it can only vary within a very limited range, which greatly reduces the influence it can have on the shape of the flame. In addition, the solid fuel must be brought by the tube at the speed which gives the necessary flow speed on the basis of the volume flow used. This consequently increases the wear and also places greater stress on the wearing parts which are in the intake part as a result of higher volume flow rates.

The possibility of influencing the flow from this circuit is very limited, because, for reasons of risk of wear, it is necessary to eliminate too large deviations through the parts provided to ensure divergence or even rotation . Also, it is no longer possible to use two-part ejectors which, by axial sliding allow, for a given volume flow, to regulate the flow speed.

In the event of particularly heavy wear, the outer jacket tube pierces and a parasitic flame is formed, which can cause very serious damage.

It is also known that, for the combustion of pulverulent solid fuels, burners have also been used consisting of three concentric tubes, into which the different components of clean air, transport gas, carbon dust have been tangentially introduced to produce a certain rotation. Due to the absence of flow pieces to create divergence and rotation, one can obtain, particularly in the intermediate ranges, only a very limited effect.

In particular, it was not possible to produce specific forms of flow, such as a strong axial flow with low divergence, due to the imposed rotation.

Likewise, the flow velocity from the clean air circuits could not be changed for a given volume flow.

The burner must therefore offer the possibility of adjusting the shape of the flame and therefore the course of combustion in the largest possible range and this on.

The fuel must be ignited immediately after it leaves the burner.

In the burner and in the installation which follows, the abrasiveness of the fuels must cause as little wear as possible.

To allow the power to be adjusted at any time, the highest possible regulation range for the fuel flow must be offered.

It must be able to operate with all possible combinations of fuels, such as several solid fuels of different qualities or solid fuels with liquid and / or gaseous fuels.

The flame shape must be preserved, especially when the proportion between the different types of fuel is to be adjusted while running.

With regard to fuels which have unfavorable characteristics from the point of view of combustion, a good ignition must nevertheless be obtained and combustion must take place within the desired time.

In the burners in which one can, to influence the shape of the flame by the flow system, introduce only an often very small proportion of the combustion air in the form of primary air, the rest of the air of combustion flowing uncontrolled into the hearth from the downstream coolers, it is important to be able to adjust to the value that best suits, for a given volumetric flow in operation, the flow speed of the various components clean air that combine to create the shape of the flame.

Document US-A-2/335/188 describes a burner for solid fuels, pulverized or finely divided, combined with liquid and / or gaseous fuels allowing wide adjustments of the shape of the flame and of the flow rate of the fuel and air, the burner comprising a first central duct which conveys a fluid fuel, a second annular duct which surrounds the central duct and which conveys clean air, a third annular duct which surrounds the second duct and which constitutes a water chamber, a fourth annular conduit which conveys a mixture of solid fuel particles suspended in a transport gas, a fifth annular conduit which constitutes a water chamber and a cylindrical casing which surrounds the fourth conduit and which conveys clean air and the front ends of the second and fourth duct include an adjustment device provided with a remote control member which makes it possible to modify in mar che, the direction of the air at the outlet of said conduits.

The objectives of the invention are achieved by means of burners, as defined in claim 1. According to a preferred embodiment, the adjustment devices are rosettes composed of two separate parts which can be offset axially or angularly, at a distance , by means of control rods.

In many use cases, for example when used in rotary ovens, it is necessary to keep the proportion of primary air supplied via the burner as low as possible to influence the shape of the flame. , so as to recover a greater proportion of the heat lost from the coolers installed downstream of the process.

For this purpose, shutters are installed upstream and as close as possible to the burner, which make it possible to adjust the volume flow rates in the various circuits and to distribute, during operation, the primary air as a function of the different forms of flow.

To protect the burner from wear, easily replaceable wear parts are available at all changes of direction of the circuit carrying the pulverized coal.

The charcoal dust which is deposited is again mixed with the transport gas before the outlet section, using an accessory arranged in the corresponding circuit.

Until now, generally and customarily, the intake portion has been mounted on the burner support and in the event of repair, it was necessary to remove the burner from the oven.

Thanks to the fixing of the casing tube on the burner support, it is possible to carry out repairs on the internal parts during operation and also to significantly reduce the intervention times.

Furthermore, by transposing to other cases of operation which require the replacement of certain parts of the burner, it can be carried out particularly quickly.

As the shape of the flame depends almost entirely on the streams of clean air placed on both sides of the circuit for supplying the pulverized coal and transport gas mixture, the possibilities of adjustment are not limited by the risks of wear due to the pulverized coal.

It is therefore possible to carry out all the forms of flow by adapting them to the specific conditions of the installation receiving the calories and to the optimal conduct of the heating.

It is also possible, if desired, to work against the current. In addition, asymmetrical flame forms can be obtained by using special devices placed in the clean air circuits.

Despite all these possibilities, and even by using very abrasive fuels, the wear in this burner is considerably reduced compared to previous embodiments which were already characterized by limited possibilities of adjusting the flame shape. In fact, in each case, the carrier gas-pulverized coal mixture can be brought in at the lowest possible speed without flashback in the circuit. By this fact, the conditions necessary for an immediate ignition of the fuel are also improved.

Even in the admission part, long lifetimes are reached thanks to the adoption of low speeds and optimal deflections and the use of particularly reduced flow rates of transport air leading to the installation of wear parts of small dimensions.

The fact that the transport gas-pulverized coal circuit is located between two clean air circuits, eliminates, in the event of very significant wear, the risk of the outer casing being pierced and of damaging the central circuit conveying the liquid fuel and / or gaseous fuel. Thus, very serious accidents are avoided.

The fact that the pulverized coal which has been deposited is put back into the circuit has the advantage of retaining a homogeneous jet which does not lead to a unidirectional supply of calories.

Optionally, the transport gas-pulverized coal circuit can receive several different types of pulverized coal, which are supplied by separate pneumatic systems.

The transition to very different solid fuels is facilitated because the adjustment of the flame shape is effected almost without intervention on the transport gas-pulverized coal circuit.

A particularly significant thing is that when switching to very different fuels, for example from a solid fuel to a liquid and / or gaseous fuel, it is possible, by adjusting the flame shape by action on the circuits d clean air, compensate for the differences between the thermal characteristics of these fuels.

The absence of adjustment would lead to a displacement of the heating zone.

In installations where the burner carries only a small part of the combustion air called primary air, and where the main part arrives in the hearth from a cooler located downstream without it being able to be influenced, new burner has the advantage of being able to operate with very reduced proportions of primary air and therefore of increasing the recovery of the waste heat coming from the cooler.

The following description refers to the appended drawing which represents, without any limiting character, an axial section of a burner, for example of a rotary oven burner, for burning both solid fuels, in the pulverized state or in fine grains, and liquid and / or gaseous fuels.

The burner is composed of a fuel and air intake part, the fuel and air supply device made up of four coaxial tubes comprising a stabilizer in the solid fuel pipe and an adjustment device. of the flow and ejection of the various combustible components and of the air.

The fuel and air supply device is arranged in an outer casing 13 which has a refractory lining and which is used at the same time for fixing the burner to its support 13a. This fixing is such that all the wearing parts and the linings can be easily replaced even when running thanks to sliding insertion systems. Clean air intakes have shutters or registers that allow you to adjust the chosen volume flow.

To protect against the abrasiveness of solid fuels, the intake duct for the transport air and solid fuel mixture includes easily replaceable wear parts, which can be replaced in a few minutes.

The device which transports the fuels to the nose of the burner where the flame is located comprises four coaxial tubes which define a central conduit and three annular conduits intermediate between two tubes. Going from the axis to the periphery, these four conduits are numbered from 1 to 4. In the first conduit 1, that is to say in the central or axial conduit, there are pipes 1 a and 1 b of supply of liquid and / or gaseous fuel used on the one hand to start the burner and on the other hand to support combustion in the case of burning solid fuels having a particularly low calorific value.

The front end of the central duct 1, that is to say the end situated at the nose of the burner, is equipped with a known device 1 for spraying or ejecting the fuels.

The second duct 2 conveys clean combustion air. This duct comprises at its front end or in the vicinity thereof, a device 5 which is used to adjust the direction of the flow speed of the air leaving the duct 2 by communicating a rotational movement thereto, c 'is to say a tangential component of the speed, and / or a divergent direction compared to the axis.

According to a preferred embodiment, the device 5 is an adjustable rosette made up of two separate mounted halves. One of the two halves is connected to operating rods or rods 7 which allow, even when running and at a distance, to shift the two parts axially and / or in rotation in order to vary the rotation and / or the divergence of the speed. of air flow at the outlet of the device 5.

The third conduit 3 conveys a mixture of transport gas and a solid fuel in the divided state, for example a mixture of pulverized coal suspended in air. The mixture flows axially along the conduit 3 at the lowest possible speed without the need for any device at the front end of the conduit 3. In the case of low-abrasive fuels, it is however possible to equip the 'front end of the conduit 3 of a device which allows to communicate at the output speed of the mixture a diverging direction relative to the axis.

The fourth conduit 4 also carries clean combustion air. It also comprises at the front end or in the vicinity thereof a device 6, similar to device 5, which is used to adjust, even when running, the tangential component and the diverging component of the speed of exit of clean air by remote control 8.

The device 6 is for example a rosette. composed of two parts 6a and 6b which delimit between them air passage channels 6c.

The remote control mechanism 8 comprises rods which allow the two parts 6a and 6b to be offset axially and / or angularly with respect to each other.

While the direction of the clean air speed vector at the outlet of the conduits 2 and 4 is adjusted by means of the rosette devices 5 and 6 controlled remotely by the members 7 and 8, the ducts 2a and 4a which supply air proper respectively the conduits 2 and 4 are equipped respectively with volume flow adjustment members 9 and 10, for example dampers or movable flaps, which make it possible to adjust the value of the speed vector of the air at the outlet of the conduits. The registers 9 and 10 allow the primary air distribution between the ducts 2 and 4 to be adjusted on the fly according to the different forms of flow and flame. Only the clean air ducts 2 and 4 comprise adjustment members having a variable section.

The conduit 3 which conveys the mixture of carrier gas and solid fuel in the divided state does not have a dead zone in which solid fuel dust could be deposited, creating a risk of a standing fire.

It can be seen in the figure that the pipe 3a which brings the mixture of pulverized fuel and carrier gas into the pipe 3 is connected to the rear end of the pipe 3 by making a very slight angle with it, hence a change in minimum direction.

In addition, the smallest possible amount of solid fuel transport gas is used so that the speed in line 3 remains low. The arrangement of the conduit 12, slightly inclined relative to the conduit 3, and the low speed of the mixture make it possible to obtain long lifetimes of the wearing parts 12 despite the abrasiveness of the solid fuels, in particular pulverized coal. Thanks to the use of a reduced quantity of gas transporting the pulverized solid fuel, the wearing parts 12 have relatively small dimensions and can be replaced in a very short time thanks to a judicious construction.

Due to the fact that the pipe 3 which carries the solid fuel is located between two pipes 2 and 4 which convey clean air which can serve as combustion air for the solid fuel, it is possible to use for pneumatic transport of the fuel solid, an auxiliary combustible gas which improves the ignition of solid fuel, especially when the latter has a low volatile matter content and is rich in ash. In addition, this arrangement of the conduit 3 between two annular conduits 2 and 4 which isolate it from the outer casing 13 and the central tube 1, eliminates the risks of damaging the outer casing 13 or the central tube bringing the liquid fuel or gaseous as a result of the abrasive action of certain pulverized solid fuels.

All these provisions mean that repair costs are low, even after a long period of use.

The reference 11 represents a gasket which is inserted in the duct 3, preferably at the entry of the latter, for example a turbulator or stabilizer with fins which communicate to the mixture a swirling rotary movement thanks to which the dust of solid fuel which are deposited on the walls of the conduit 3 are taken up and mixed again with the carrier gas.

The suspension of solid fuel particles in the carrier gas is stabilized and homogenized by the device 11, which clearly improves ignition.

The device according to the invention comprising four coaxial conduits allows a gradual start, without intervention on the equipment.

At startup a liquid or gaseous fuel is brought through the central tube 1 under the most favorable conditions, which avoids any risk of damaging the refractory lining if the linings are missing.

The burner according to the invention makes it possible to use several qualities of pulverized coals, either separately or simultaneously in all the proportions compatible with their calorific value. The transition to other solid fuels in the finely divided state is facilitated by the fact that the possibilities for adjusting the flame are very wide.

The combination of a central tube for supplying gaseous fuel to the burner nose and a separate conduit for pneumatically conveying solid fuel mixed with a transport gas makes it possible to temporarily supply the burner with combustible gas alone while varying the shape of the flame within wide limits.

A burner according to the invention can also be used to simultaneously burn solid fuels in the divided state and liquid and gaseous fuels.

During mixed operation, removing one of the fuels does not require changing the shape of the flame.

An advantageous application of the burners according to the invention is the equipment of cement kilns in which the solid fuel is particularly abrasive and requires devices which resist corrosion and abrasion.

Of course, without departing from the scope of the invention tion, various modifications may be made by those skilled in the art to the devices which have just been described by way of nonlimiting example.

Claims (2)

1. Burner of solid, pulverized or finely divided fuels and of liquid and/or gaseous fuels permitting to control whilst switched on, the shape of the flame and the flowing speeds of the fuels and air, characterized in that it comprises, inside a tubular external casing (13) equipped with a refractory coating, three other co-axial tubes which define four conduits: a first central conduit (1) which contains several pipes (1a, 1b) which supply liquid and/or gaseous fuels to a device (1 c) for pulverizing or injecting said fuels, a second annular conduit (2) directly surrounding the central conduit (1) and which transports clean air, a third annular conduit (3) directly surrounding the second conduit and which transports a mixture of solid fuel particles in suspension in a transporting gas and a fourth external conduit (4) which is externally defined by the said casing (13) and which transports clean air and the front ends of the second and fourth conduit comprise a regulating device (5, 6) provided with a remote-control member (7, 8) permitting to change, in service, the direction of the air coming out of the said conduits.

2. Burner according to claim 1, characterized in that the mixture flowing in the third conduit (3) is composed of particles of a solid fuel in suspension in a combustible gas.

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