WO2011073948A2

WO2011073948A2 - Cyclone burner

Info

Publication number: WO2011073948A2
Application number: PCT/IB2010/055896
Authority: WO
Inventors: Mads Nielsen
Original assignee: FLSmidth AS
Current assignee: FLSmidth AS
Priority date: 2009-12-18
Filing date: 2010-12-16
Publication date: 2011-06-23
Anticipated expiration: 2012-06-18
Also published as: WO2011073948A3

Abstract

A description is given of a cyclone burner for converting solid fuel comprising a substantially rotationally- symmetric whirling chamber (1) having an inlet (7) for introducing gas and fuel and means (7) for bringing the gas and fuel into rotation in the whirling chamber (1) and an outlet (4) for the gas and the converted fuel where the outlet (4) is centrally positioned at the outlet end (3) of the whirling chamber (1). The cyclone burner is characterized in that the inlet (7) for in¬ troducing the gas and fuel is connected to the whirling chamber (1) at the outlet end (3), and in that the whirling chamber (1) is arranged so that its axis of symmetry (8) is angled relative to the horizontal plane.

Description

Title of Invention: Cyclone Burner

[1] The present invention relates to a cyclone burner for converting solid fuel comprising a substantially rotationally- symmetric whirling chamber having an inlet for introducing gas and fuel and means for bringing the gas and fuel into rotation in the whirling chamber and an outlet for the gas and the converted fuel where the outlet is centrally positioned at the outlet end of the whirling chamber.

[2] Cyclone burners of the above-mentioned type are well known in the industry, being used inter alia in power plants. From US7261047B2, for example, is known a horizontally positioned cyclone burner where the fuel is introduced at the back end of a cyclone chamber whereafter it flows along with the gas stream towards a conical outlet end where particle separation takes place. In this type of cyclone burner, the fuel must be substantially converted before it reaches the outlet end, otherwise the result would be build-up of fuel at this location, eventually leading to complete interruption of the fuel flow and/or its discharge by entrainment out of the chamber. The associated disadvantage is that the amount of particles must be so small or the particles must be so finely divided as to ensure almost complete conversion of the particles before they reach the outlet end of the burner. As a result, the total amount of retained fuel in the compartment will be at a comparatively modest level, therefore necessitating an unnecessary degree of comminution of the fuel in order to ensure an acceptable degree of conversion for a given chamber volume. Another consequence of the horizontal design is that the fuel will not be substantially distributed along the length of the compartment, but instead it will accumulate at one of the ends of the chamber, entailing poor control of the temperature distribution in the chamber and leading to undesirable formation of slags.

[3] It is an objective of the present invention to provide a cyclone burner whereby the aforementioned disadvantages are eliminated or significantly reduced.

[4] This is achieved by a cyclone burner of the kind mentioned in the introduction and being characterized in that the inlet for introducing the gas and the fuel is connected to the whirling chamber at the outlet end and in that the whirling chamber is arranged so that its axis of symmetry is angled relative to the horizontal plane.

[5] By angling the whirling chamber in such a way that the outlet for the gas and the converted fuel is facing downwards and by simultaneously introducing the gas and fuel close to the outlet end of the whirling chamber, the result will be that the gas and fuel, moving in counter-current out of the outlet, are forcibly led along the wall of the whirling chamber back towards the back end of the chamber at which location they will subsequently be led towards the eddy flow centrally in the whirling chamber and then discharged through the outlet. Hence a significant amount of fuel can be retained, thereby reducing the need for comminuting the fuel to a very small particle size. The angle of the whirling chamber relative to the horizontal plane will influence the effect of the force of gravity on the rotating fuel in the chamber. At a given gas stream and gas velocity, a small angle will allow a greater amount of fuel to be retained than achievable if a larger angle is applied for the same gas stream and gas velocity.

However, if the angle is too small the whirling chamber may lose its self-discharging capability if excessively filled, potentially giving rise to an undesirable accumulation of the fuel. Therefore, the angle is also important in terms of preventing accumulation of fuel. It is preferred that the angle between the horizontal plane and the axis of symmetry of the whirling chamber is kept within the range of 10 to 80 degrees, preferentially within the range of 20 and 60 degrees and most preferentially between 30 and 40 degrees. The angle for optimization of operating characteristics varies in dependence of quality, size and type of fuel.

[6] Converted fuel is taken to mean fuel which has been introduced to the whirling

chamber, where, subject to sub-stoichiometric or over- stoichiometric conditions, the fuel has undergone combustion, pyrolysis, gasification or mechanical comminution due to forces of collision and friction.

[7] It is preferred that the whirling chamber comprises a conical section connected to a cylindrical section, where the centrelines of the two sections coincide and where the outlet is located in the cylindrical section. It is further preferred that the end faces at each end of the whirling chamber are plane and that the area of the end surface of the conical part is roughly equivalent to the area of the outlet opening. It is preferred that the cylindrical section has a length which is 0.1-0.5 times the diameter of the cylinder and that the angle of the conical section is 15-60 degrees, preferentially 20-45 degrees, relative to the cylindrical section. One or several gas nozzles may advantageously be fitted to the end surface of the conical section to increase the rate of separation of the small particles which may accumulate on this end surface. The nozzle or nozzles may further be used for co-firing with other fuels, such as coal, oil or gas.

[8] The means for bringing the gas and the fuel into rotation may in principle comprise any suitable means as long as they are capable of bringing the gases and fuel into rotation. For example, the means may comprise a number of fixed devices in the whirling devices which are formed and positioned so that they will impart rotation to the gas and the fuel. However, it is preferred that the means comprises a tangential inlet which is connected close to the outlet end of the whirling chamber. A tangential inlet which is a common feature of cyclone separators will cause the gas as well as the fuel to be brought into rotation in the chamber when being fed hereto at sufficient velocity. [9] Several tangential inlets for gas and fuel may be provided at the outlet end of the whirling chamber, and the inlets may introduce gas and fuel separately or in combination. However, it is critical to the function of the whirling chamber that all inlets are located very close to the outlet end, and, therefore, it is preferred that the inlets are displaceably fixed on the circumference of the whirling chamber close to the outlet end at which the outlet is centrally located.

[10] In one embodiment the whirling chamber is connected to means which during

operation of the cyclone burner is capable of varying the angle of the whirling chamber relative to the horizontal plane. It is hereby achieved that the optimum angle can be identified during operation, also making it easy to optimize the amount of fuel retained in the chamber and its location (and hence the temperature profile of the chamber) on the basis of changes in the fuel composition.

[11] In another embodiment the outlet is connected to an outlet pipe which is formed so that the converted fuel is horizontally discharged, thereby achieving a substantially horizontal flame propagation. It is preferred that the outlet pipe protrudes into the whirling chamber in order to stabilize the eddy flow in the whirling chamber.

[12] The cyclone burner may in principle be used for all types of industrial processes which require a source of heat. For example it may be used for manufacturing cement clinker where cement raw materials are introduced to a cement processing plant where the cement raw materials are supplied with thermal energy and converted into cement clinker. Here a cyclone burner may at least provide some of the thermal energy. If the cyclone burner is used in the cement processing plant, its outlet may be fitted to a burner lance extending into the rotary kiln, thereby allowing the converted fuel to be fed and ignited at a distance further inside the rotary kiln. With this type of arrangement, it will be possible to use heated process gases, e.g. from a clinker cooler, in the inlet of the whirling chamber.

[13] The invention will now be explained in further details with reference to the drawing, being diagrammatical, and where

[14] Fig. la shows a cross-sectional view of a cyclone burner according to the invention and Fig. lb shows the same cyclone burner viewed inclined from the top, and

[15] In Fig. la and Fig. lb a cyclone burner is shown with a whirling chamber 1 which comprises a foremost cylindrical section 2 with an outlet end 3 in which a cylindrical outlet 4 is positioned concentrically and having a diameter which is smaller than that of the cylindrical section 2. The rearmost part of the whirling chamber 1 is composed of a conical section 5 where the large diameter of the cone is connected to the cylindrical section 2 and where the diameter of the conical section 5 is reduced until terminated with a plane circular endplate 6 having a diameter which is roughly equivalent to that of the outlet 4. However, the endplate 6 may also have a diameter which differs sig- nificantly from the diameter of the outlet 4. Four tangential inlets 7 are connected to the cylindrical section 2 of the whirling chamber 1, being displaceably fixed on the circumference of the whirling chamber 1 close to the outlet end 3 which here comprises a circular endplate in which the outlet 4 is centrally positioned. For optimum performance, the inlets 7 must be positioned in immediate proximity of the outlet end 3. The whirling chamber 1 is angled so that its axis of symmetry 8 forms an angle to the horizontal plane. By angling the whirling chamber 1 so that it is inclined downwards, while gas and fuel are simultaneously introduced tangentially close to the outlet end 3, it is achieved that the introduced gas and fuel, in counter-current to the flow out of the outlet 4, will be forced along the cylindrical section 2 of the whirling chamber 1 and back up the conical section 5 for subsequent routing at this location towards the eddy flow centrally in the whirling chamber 1 and subsequently out through the outlet 4. An outlet pipe 10, the centreline of which coincides with the axis of symmetry 8 of the whirling chamber 1, is fitted to the outlet 4 and connected to a horizontal discharge duct 11 with a bend in order to attain a substantially horizontal flame. In Fig. la the axis of symmetry 8 of the whirling chamber 1 forms an angle of about 35 degrees to the horizontal plane. It is preferred that the angle is kept within the range of 30-40 degrees.

[16] The whirling chamber 1 is heated by use of oil, gas or other medium to a level of approximately 800 °C so as to ensure self-ignition and conversion of the solid fuel which is introduced through the tangential inlets 7. When switching from oil/gas to solid fuel, the air/fuel ratio is kept at an over-stoichiometric or near- stoichiometric level to ensure effective ignition and additional heating. Once the target operating temperature has been reached, the fuel rate is increased so that the whirling chamber 1 will have the exact capability to convert all the input fuel to gas. This is achieved at a temperature of 900-1100 °C and at an air/fuel ratio of 25-40 % (air deficit) of the stoichiometric level necessary for complete combustion. The aim is to operate at the lowest possible temperature and at a minimum air/fuel ratio, which is achieved by increasing the volume of fuel particles so that it will be slightly higher than the volume which can be converted in the whirling chamber 1. Hence the rotating amount of particles is gradually increased and more and more particles will be forcibly led upwards towards the conical section 5 of the whirling chamber 1, while, at the same time, the particles at this location will be moving closer to the centre of the whirling chamber 1. The particles rotate at increased angular velocity when moving upwards with the gas towards the gradually diminished radius of the cone. Because of the increased centrifugal force thereby generated, the upward-flowing gas stream and the force of gravity will separate the particles in such a way that the large particles will remain near the inlets 7 in the whirling chamber 1 and hence near the gas entry point (which is ad- vantageous for the conversion of the large particles) while the small particles are simultaneously entrained in the gas stream moving upwards towards the small conical end of the whirling chamber 1. At some point in time, the accumulation of the small particles will reach an extent where their rotation is arrested, with some of the particles 'dropping ' down into the central gas stream which is discharged through the outlet 4. The particles which are most easily entrained in the outgoing gas stream will be those having a relatively large surface relative to mass, i.e. the smallest and lightest fuel particles, whereas any large/heavy particles will to a certain extent have a tendency to drop out of the gas stream and back into the rotating particle mass. The now continuously separated stream of fine particles will restore the balance in the whirling chamber 1, whereby the volume of retained particles will find an equilibrium position. The separated particles are burnt out together with the gas in the subsequent flame. The overall aim is to ensure that the air/fuel ratio is adjusted exactly so that the particles will have time to burn out sufficiently in the subsequent flame. In order to maintain full circulation of the entire particle mass, the air is introduced through the inlets 7 with a high tangential velocity in the whirling chamber 1. Regulation of air volume and velocity is achieved by adapting the area in the inlets 7 and the air pressure ahead of the inlets 7.

[17] The cyclone burner may be connected to means (not shown in the drawing) which during operation may vary the angle of the whirling chamber 1 relative to the horizontal plane, allowing the effect of the force of gravity on the separation process to be increased or decreased. The more vertical the position in which the whirling chamber 1 is placed, the more difficult it will be to lift the fuel upwards towards the pointed end of the conical section 5, and conversely the closer the whirling chamber 1 is positioned relative to the horizontal position. The optimum angle is achieved when the whirling chamber 1 contains the maximum fuel volume without arresting the rotation at the pointed end of the conical section 5 since, otherwise, the fuel will form a static pile (this will typically occur when operating close to the horizontal position). The angling may also contribute towards changing the temperature profile in the whirling chamber 1 where it is important to attain an even and relatively low temperature distribution in order to avoid melting of ash components and consequential cakings.

Claims

A cyclone burner for converting solid fuel comprising a substantially rotationally-symmetric whirling chamber (1) having an inlet (7) for introducing gas and fuel and means (7) for bringing the gas and fuel into rotation in the whirling chamber (1) and an outlet (4) for the gas and the converted fuel where the outlet (4) is centrally positioned at the outlet end (3) of the whirling chamber (1) characterized in that the inlet (7) for introducing the gas and fuel is connected to the whirling chamber (1) at the outlet end (3), and in that the whirling chamber (1) is arranged so that its axis of symmetry (8) is angled relative to the horizontal plane .

A cyclone burner for converting solid fuel according to claim 1 characterized in that the whirling chamber (1) comprises a conical section (5) connected to a cylindrical section (2), where the outlet (4) is located in the cylindrical section (2).

A cyclone burner for converting solid fuel according to claim 1 or 2 characterized in that the angle between the horizontal plane and the axis of symmetry (8) of the whirling chamber (1) is within the range of 10 to 80 degrees.

A cyclone burner for converting solid fuel according to claim 3 characterized in that the whirling chamber (1) is connected to means which during operation of the cyclone burner is capable of varying the angle of the whirling chamber (1) relative to the horizontal plane.

A cyclone burner for converting solid fuel according to any of the preceding claims characterized in that the outlet (4) comprises an outlet pipe (10) which protrudes into the whirling chamber (1).

A method for manufacturing cement clinker where cement raw materials are introduced to a cement processing plant where the cement raw materials are supplied with thermal energy and converted into cement clinker characterized in that a cyclone burner supplies at least some of the thermal energy.