WO2006048003A1

WO2006048003A1 - Method and device for accelerated burning of porous ceramic moulded parts

Info

Publication number: WO2006048003A1
Application number: PCT/DE2005/001971
Authority: WO
Inventors: Bernd Geismar
Original assignee: Ctb Ceramic Technology Gmbh
Priority date: 2004-11-03
Filing date: 2005-11-02
Publication date: 2006-05-11
Also published as: DE102004053624B4; DE102004053624A1

Abstract

The invention relates to a method and to a device for the accelerated burning of porous ceramic moulded parts having an open-pore passage structure with a reduced diameter. The aim of the invention is to substantially improve the burning process of ceramic moulded parts by increasing the heating speed thus preventing the formation of cracks and to significantly reduce the burning time for the inner heat transfer surfaces of moulded parts. Said aim is achieved by virtue of the fact that in moulded parts, heat is initially transferred from the inside in the outside of the moulded part at a temperature (T1), which is characteristic to the convective heat transfer, by separating the entire hot gas flow (Vg) into a plurality of partial flows (A111An). Said partial flows (A1^An) are introduced into the inner flow path (19) of the moulded part and a uniform flowing through of said flow path produces an approximately constant flow and prevents a turbulent flow in the flow path, heat is then transferred from the inside to the outside and is maintained until the temperature (T2) is reached by the thermal radiation of the hot gases which exceeds the temperature (TI) reached by the convective transfer of heat, and additional heat is introduced in the form of thermal radiation from the outside to the inside, and from the inside to the outside of the moulded parts by maintaining the flow and a simultaneous impingement of the moulded part with the partial flows (A1111An-I) along the inner flow path (19) and an additional partial flow (B) which is separated from the hot gas flow is produced along an outer flow path (S) at a temperature (T2) which is characteristic for thermal radiation.

Description

Method and device for accelerated burning of porous ceramic moldings

The invention relates to a method for accelerated burning of porous ceramic moldings having a small diameter open-pore passageway structure, in a gas, oil or electrically heated kiln, wherein the moldings are exposed to a hot gas flow of predetermined temperature and atmosphere within the combustion chamber, wherein the heating and Firing temperature is adjusted by controlling the heating power.

The invention further relates to a device for accelerated burning of porous ceramic moldings having a small diameter open-pore passageway structure, with a perpendicular to a belonging to a ceramic furnace arranged combustion chamber, at least one firmly anchored in the combustion chamber ring support for vertical Auflagerung at least one ceramic molding, one with the

Combustion chamber in fluid communication channel to

Supplying the hot gases in the loaded with ceramic moldings

Burning shaft, a gas or oil burner or electric

Heating register for generating the hot gases and a channel connected to the combustion chamber for discharging the hot gases.

From EP 0 362 400 B1 a method for firing ceramic honeycomb structure bodies at a predetermined temperature in a predetermined atmosphere is known in which the temperatures inside and outside of the ceramic honeycomb bodies are determined by temperature sensing means, the heating power of the burner means being dependent on controlled by the temperatures thus determined to achieve a match between indoor and outdoor temperature.

The ceramic moldings are on shelves that are carried by a mobile base in the oven. Two thermocouples are introduced into the molded body, by means of which the temperature is determined. The moldings are completely surrounded by plates, on which the flames of the burners are directed for heating the moldings. In order for the hot gases reach the moldings, holes in the plates and vent passages are introduced into the shelves. With a vent fan at the outer end of the vent passage is achieved that the firing atmosphere flows through the interior of the moldings.

To expel the organic binder and to heat the moldings, the latter are slowly heated to 600 ⁰ C. Due to the insulating properties of porous Molded parts can cause thermal stress in the event of too rapid heating, which leads to crack formation in the molded parts. For very large moldings, therefore, the heating rate, for example 1 to 25 ⁰ C, must be kept very small in order to avoid cracking.

To form the desired ceramic moldings are then heated to a firing temperature of 1300 to 1600 ⁰ C. The firing temperature is then maintained for several hours to equalize the temperature in the molding and to form the ceramic properties. This is followed by the cooling of the molding to below 150 ⁰ C by introducing cold air at a cooling rate of up to 300 ° C / h. The entire process is thus extremely time and energy intensive and of relatively low productivity.

This known method of combustion is characterized in that the heat transfer to the molded part takes place substantially from outside to inside, so that the heat transfer to the outer heat transfer surface of the molded part remains limited and only low heating rates are possible.

In this prior art, the present invention seeks to significantly improve the firing of porous ceramic moldings by increasing the heating rates while avoiding cracking and significantly shorten the burning time by harnessing the internal heat transfer surface of the moldings.

This object is achieved by a method of the type mentioned in the introduction with the features of claim 1 and by a Device solved with the features of claim 13. Advantageous embodiments of the method and the device are the dependent claims.

The solution according to the invention is characterized in that the hot gases are forced to pass through the inner Strörαungswege of the molding, whereby a heat transfer from the interior to the outside of the molding takes place and it succeeds, the inner heat transfer surface, which is many times greater compared to the outer heat transfer surface is to use. The incoming hot gas stream is divided by the passage structure present in the molded body, in particular honeycomb channels, into a multiplicity of partial streams and directed into the channels. The partial flows are distributed evenly over the passage cross section. There is a convective heat transfer from the hot gas to the material of the molding uniformly distributed over the cross section. As soon as the convective heat transfer into the heat transfer by radiation passes by increasing the temperature of the hot gas flow, the positive guidance of the hot gas flow is released. The molding is flowed through by the hot gas both inside and outside flows around. There is a heat transfer from outside to inside and from inside to outside. The outer and inner heat transfer surface is used.

The targeted controlled combination of convective heat transfer with the thermal radiation achieves a significant acceleration of the firing process with simultaneous elimination of the tendency of the molded bodies to crack.

Further advantages and details will become apparent from the following description with reference to the accompanying drawings. The invention will be explained in more detail below using an exemplary embodiment.

Show it:

1 is a combustion arrangement according to the prior

Technology,

2 is a schematic diagram of the device according to the invention with mainly convective heat transfer,

3 is a schematic diagram of the device according to the invention in heat transfer in the radiation area,

4 shows a section of a porous molding with inner and outer flow paths,

5 shows a flow chart for the sequence of the method according to the invention.

Fig. 1 shows a combustion arrangement according to the prior art, in which the kiln 1, for example catalyst support, are placed on shelves 2. The shelves 2 are supported by a mobile base 3. The average temperature rise rate is 50 ° C / h, so that the firing temperature of, for example, 1400 ⁰ C is reached in 28 hours. The temperature is passed through burner 4 on the desired temperature increased. The burners are laid in the opposite side walls 5 of the kiln 6. The side walls of the shelves 2 are planked with flame breaker plates 7 made of refractory material and the top and bottom of the shelf with shelves 8 occupied. So that the combustion atmosphere can reach the interior of the shelf, there are holes 9 in the shelves 8 at the catalyst supports 1 facing sections. Through the holes 9, the hot gases enter the interior of the catalyst support 1 and at the same time flush around the outer surface of the catalyst support 1. By means of a vent passage 10 which is formed in the base 3 and in the bottom of the furnace 6, and arranged at the end of the vent passage bleed fan 11, the furnace atmosphere is conveyed through the moldings. After reaching the firing temperature of 1400 ⁰ C, this is maintained for 2 hours and then cooled at a rate of 150 ° C / h. For the entire firing process thus a total time of approximately 40 hours.

Fig. 2 and Fig.3 show the basic structure of the device according to the invention with a chimney draft-like combustion chamber 12 of a combustion chamber shown only hinted 6. The vertically ascending arranged combustion chamber 12 is downstream with a horizontally extending channel 13 for supplying the hot hot gases into the combustion chamber 12 and upstream connected to a horizontally extending channel 14 for discharging the hot gases. In the wall 15 of the combustion chamber 12, an annular support 16 of metal or other suitable temperature-resistant material is fixedly mounted, the Support plane is arranged perpendicular to the flow direction of the hot gases in the combustion chamber 12 and allows a free passage of the hot gases. The cross-section of the combustion chamber 12 is dimensioned so that the hot gases can flow through the combustion chamber 12 at a flow rate of about 5 to 20 m / s.

In the case of charging the combustion chamber 12 with the kiln 1 to be burned is first placed on the annular support 16, a refractory honeycomb disc 17 of about 25 mm thickness, the outer diameter of the inner diameter of the support 16 is sized slightly larger. On the honeycomb disk 17 is a green honeycomb disk 18th

(unburned) set. The honeycomb discs 17 and 18 correspond to the material and the shape of the burning material 1 to be fired, for example alumina. The kiln 1 to be fired is then vertically stacked onto the green honeycomb disk 18 with its end faces, so that a molding column of up to 5 kiln parts is produced whose internal flow paths 19 (honeycomb channels) lie in the flow direction of the incoming volumetric flow of the hot gases (see FIG. 4) ). In the combustion chamber 12, a plurality of molded part columns may be arranged one above the other like a pile.

This arrangement ensures on the one hand the dimensional stability of the stacked burning material and on the other hand, the uniform passage of the hot gases through the inner flow paths 19 of the combustible material 1, without generating turbulence.

Each support 16 are two shut-off 20, for example, valve gate, associated with the closed state Flow cross section of the schonsteinzugartigen combustion chamber 12 exclusively on the free passage cross section DF of the inner flow paths 19 in the end face of the combustible limit. The slides sit upstream upstream of the respective support 16 and are in a cassette 21, which penetrate the wall 15 of the combustion chamber 12. In the closed state, the front plate ends of the slide surround the cylindrical outer jacket of the directly on the green honeycomb disc 18 standing Brenngut 1, so that only the frontally free passage cross-section DF is available for the passage of the hot gas stream. The plates of the slide are made of a suitable refractory material and are actuated via a push linkage 22 each by separate drives 23, which in turn are connected to a control unit 24 and are controlled jointly by the latter. Between link 22 and drive 23 is in each case a displacement sensor 25 which detects the displacement of the plates.

The gas burner 4 is supplied via control valves 26, a corresponding amount of natural gas, liquid gas o. The like. For generating a corresponding amount of hot gas. In the present example, an oxygen-poor hot gas stream with <8% oxygen is produced, which enters the combustion chamber 12 via the channel 13 at an inflow velocity of approximately 5 to 20 m / s, where the combustible material 1 flows uniformly through and around the combustion chamber 12 through the channel 14 leaves.

By temperature sensors 27, which dive directly into the hot gas stream generated, the temperature of the combustion gas is detected. Furthermore, the Mass flow of the hot gas and the oxygen concentration in the

Hot gas determined by respective sensors 28 and 29. The sensor 27, the encoder 25 and the sensors 28 and 29, respectively, pass the signals to the control unit 24, which processes the signals after their digitization and the control valves

26 on the burner 4 for adjusting the mass flow and the

Oxygen concentration in the hot gas and all actuators 23 for opening and closing the slide 19 simultaneously actuates.

Fig. 5 illustrates the principle of the method according to the invention, with the porous moldings with axially extending to the cylinder axis passage structure in honeycomb form, hereinafter called honeycomb body or kiln, are to be accelerated.

The amount of heat generated with the burner 4 and to be transferred to the kiln 1 can be described with the following equation:

ΔQ = α _abs × A _ü × Δt × (T _gas -T _mat ), where

Q heat quantity, α _abs convective heat transfer coefficient as a function f (α _k , α _s , a) with α _{k more} convective

Heat transfer coefficient (free and forced convection), α _s Heat transfer coefficient by radiation, a Temperature coefficient

(Heat diffusion coefficient of the material used), 1 O

At) heat transfer surface from A ₀ and Ai with

A ₀ outer transfer surface (shell surface of the firing material), Ai inner transfer surface (honeycomb surface of the honeycomb channels), t heating time T _gas mean temperature of the gas T _mat mean temperature of the material of the firing material.

From the above equation, the main parameters for accelerated burning arise. Accordingly, the amount of heat transferred mainly depends on the geometry of the honeycomb body and above all on the utilization of the available heat transfer surfaces.

The honeycomb body in this example has an outer diameter of 100 mm, a height of 200 mm and has 950 honeycomb channels.

The outer heat transfer surface of such a body is about 785 cm ² and its inner heat transfer surface about 50 times the outer surface. Does this increase?

Outer diameter of the honeycomb body, for example, 3 times, so is the ratio of the inner to the outer

Heat transfer surface already at 100.

The heated hot gas stream V _g flows through the channel 13 into the combustion chamber 12. All valves 19 arranged one above the other are closed, ie only the passage cross-section DF of the porous combustion material 1 is available for flowing through with hot gas. The hot gas stream is when hitting the front side of the combustible material 1 through the honeycomb channels of the honeycomb discs in a variety of Single streams A ₁₁₁₁ A _n separated, which enter the formed by the honeycomb channels inner flow paths 19 of the combustible material 1. The hot gas flow is equalized and the individual streams flow depending on the honeycomb size at about 0.5 to 10 m / s through the flow channels 18, where they release the heat in the surrounding material. There is a convective heat transfer from the inside to the outside of the kiln. This heat transfer is maintained until the temperature of the hot gas V _{9 reaches} a value at which the convective heat transfer passes into the heat transfer by radiation. In the present example, this temperature is 700 ^° C.

Once this temperature is detected with the temperature sensors 26, the control unit 24 triggers a command to the drives 23, which move the plates of the slide 19 in its open position. An outer flow path S for the oncoming hot gas flow V ₉ along the circumference of the lateral surface of the combustion material 1 is released, so that the combustible material can be flowed around by an additionally divided gas flow B. The flow along the inner honeycomb channels in the kiln 1 is continued. At the same time the temperature of the hot gas stream is increased at a rate of 250 to 750 ° C / h until the firing temperature necessary for the formation of the ceramic is reached. During this step, heat transfer by radiation from the hot gas to the honeycomb body 1 occurs both from outside to inside and from inside to outside.

After the firing temperature of for example 1.600 ⁰ C is reached, this, depending on honeycomb thickness and material properties, for a period of 15 to 60 min held. Thereafter, cooling takes place at a rate of 500 to 100 ° C / h. The firing process according to the invention requires only 4 to 6 hours.

In the control unit 24, a programmable logic controller PLC is present, in which the entire program of the combustion regime is stored and ultimately controls the process. For this purpose, depending on the type of ceramic, the geometry and dimensions of the molded body, constantly the oxygen concentration in the hot gas, the mass flow, the temperature regime with heating time and hold time, the temperature gradient, the burning time and gas temperature determined and filed with a stored in the programmable controller PLC As soon as deviations from the preset values are detected, the burner 4 is readjusted via the control valve 26. The prescriptions (setpoint function curves) are characterized by characteristic temperatures T 1 and T 2 at which the transition from convection to radiation takes place.

In the area of convective heat transfer from inside to outside, a heating rate of 250 to 500 ° C / h is used. As soon as Tl is reached, the transition to thermal radiation takes place by the gas temperature at the heating rate of up to 750 ° C / h up to firing temperature, depending on the ceramic composition, increased to 1,400 to 1,600 ⁰ C and at the same time an internal flow and outer flow of the Brenngut 1 is performed. List of used reference numbers

1 kiln / honeycomb body

2 shelf

3 base frame

4 burners

5 side wall of 2

6 kiln

7 flame-breaking plates

8 shelves

9 holes in 8

10 bleed passage

11 exhaust fan

12 combustion chamber

13 channel for supplying the hot gas

14 channel for removing the hot gas

15 wall of the combustion chamber 12

16 edition

17 fired honeycomb disk

18 green honeycomb disc

19 internal flow paths (honeycomb channels)

20 shut-off devices, slides

21 cassette

22 push rods

23 drive

24 control unit

25 encoders

26 control valve

27 temperature sensor

28 Sensor for mass flow

29 Sensor for oxygen concentration

DF free passage cross section

Ai-A _n partial flows B partial flow

S outer flow path Tl limit temperature convective heat transfer

T2 temperature heat radiation

V ₉ hot gas flow

Claims

claims

A process for accelerated firing of porosity porcelain porous bodies having a small diameter open cell passageway structure, in a gas, oil or electrically heated furnace, wherein the moldings are exposed to a hot gas flow of predetermined temperature and atmosphere within a combustion chamber, the temperature being controlled by a control of Heating power is set, characterized in that in the molded part, first, a heat transfer from the interior to the exterior of the molding at characteristic for the convective heat transfer temperature (TCl) by dividing the entire hot gas stream (V _g ) in a plurality of partial streams (A ₁ -A _n ), Introducing these partial flows (Ai-A _n ) into the inner flow paths (19) of the molded part and a uniform flow through these flow paths at approximately constant flow conditions while avoiding turbulent flow generated in the flow path, the heat transfer from the inside nac h is maintained until the temperature (T2) reached by the heat radiation of the hot gases exceeds the limit temperature (Tl) reached by the convective heat transfer, and then an additional heat input in the form of thermal radiation from outside to inside and from inside to inside Outer of the molded part while maintaining the flow conditions by simultaneously loading the part with the part streams (Ai ... A _n _ _B ) along the inner flow paths (19) and with another branched off from the hot gas flow partial flow (B) along an outer flow path (S ) is generated at a characteristic of the heat radiation temperature range (12).

2. The method of claim 1, wherein a transition from the internal convective heat transfer to the heat radiation is controlled via the temperature of the hot gases.

3. The method of claim 1 and 2, d a d u r c h e c e n e c e in that the branching of the further partial flow is performed by opening the outer flow path (S) on each molding column depending on the hot gas temperature.

4. The method according to claim 1, wherein a flow rate of the hot gases in the inner flow path is set to a value between 0.5 and 10 m / s, preferably in the laminar range of the flow, depending on the honeycomb size.

5. The method according to claim 1 to 3, characterized in that the temperature (Tl) for generating the heat transfer from the inside to the outside in the molded part to values between 20 to a maximum of 700 ⁰ C is set.

6. The method according to claim 1 to 3, characterized in that the temperature (T2) for generating the heat transfer from outside to inside and from the inside out to values between> 600 to 1,600 ⁰ C is set.

7. The method of claim 1 to 6, d a d u r c h e c e n e z e c h e s in that are used as firing cylindrical moldings with axially extending open pores in honeycomb structure.

8. The method of claim 1 to 6, d a d u r c h e c e n e c e s in that there are used as the kiln moldings having an open-pore sponge structure.

9. Method according to claim 1 to 8, characterized in that cast, foamed or extruded ceramic molded parts are used.

10. The method of claim 1 to 9, e e c e n e c e by the following steps: a) forming a molding column by frontal stacking of the moldings; b) introducing the acted upon by an outer and inner and flow path with hot gas

Molding columns in one or more floors of the combustion chamber; c) adjusting a first temperature (Tl) at which substantially convective heat transfer from the hot gas to the mold takes place by controlling the temperature of the hot gases, d) shutting off the outer flow path and simultaneously introducing the hot gas into the inner flow path formed by the open-pore passage structure and simultaneously flowing axially through the structure of each mold column with hot gas to produce the convective heat transfer from the inside to the outside of each mold part; e) setting a second temperature (T2) at which substantially a heat transfer by radiation takes place on the Forrαteil, by controlling the temperature of the hot gas; g) opening the outer flow path and simultaneously flowing inside and outwardly flowing the mold parts with hot gas to produce the heat transfer by radiation both from outside to inside and from inside to outside; h) Holding the heat transfer by radiation until the temperature (T2) reached by controlling the temperature of the hot gases is reached.

11. The method according to claim 6, characterized in that the temperature (Tl) for the convective heat transfer to between 500 and 700 ⁰ C is set.

12. The method according to claim 1 to 3, characterized in that the temperature (T2) for the heat transfer by radiation to values between> 600 to a maximum of 1,600 ⁰ C is set.

13. An apparatus for accelerated burning of porous ceramic moldings having an open-pore passage structure, with a belonging to a ceramic furnace combustion chamber, communicating with the combustion chamber in flow communication channel for supplying the hot gases in the loaded with ceramic moldings combustion chamber, an electric heater, Gas¬ or oil burner Generating the hot gases, a connected to the combustion channel for discharging the hot gases, characterized in that the combustion chamber (12) is formed chimney-pull, and that in the combustion chamber (12) perpendicular to the flow direction of the hot gas at least one porous support (16) for supporting the ceramic moldings (1) is provided, and that on the support (16) standing arranged ceramic molding (1) with its formed by the passage structure axial inner flow paths (19) in the flow direction of the hot gases for dividing the hot gas flow in a plurality of the inner flow passages passing through streams (Ai ... A _n ) is arranged for the purpose of heat transfer inside the ceramic molding, each pad at least two shut-off (20) associated with are that allow a flow cross-section of the hot gas flow, which corresponds at least to the free passage cross-section (DF) of the ceramic molding and additionally opens an outer flow path (S) along the molding, and that measuring means (27,28,29) for detecting the gas temperature, the gas mass flow and the oxygen concentration in the hot gas as a control Gr and that the measuring means (27,28,29) and shut-off means (20) with a control unit (24) for driving the heating device, the burner (4) and a drive (23) for the shut-off means (20) for opening and closing the outer flow path (S) for a further partial flow (B) for introducing radiant heat into and onto the molded part.

14. The apparatus according to claim 13, characterized in that one or more molded part (s) (1) stacked on the support (16) are arranged and form a molding column.

15. Device according to claim 13 and 14, in that one or more supports (16) are arranged one above the other like a pile in the combustion chamber (12).

16. Device according to claim 13 to 15, characterized in that between support (16) and

Molded part (1) a refractory honeycomb disc (17) and green honeycomb disc (18) of the same material and the same shape and passage structure as the molding is arranged.

17. Device according to claim 13 to 16, characterized in that the support (16) has a diameter slightly smaller than the honeycomb discs (17, 18).

18. The apparatus according to claim 13, characterized in that the blocking means (20) is a slide which is connected to a push rod (22) via a position sensor (25) and the drive (23) with the control unit (24) for triggering the operation of the slide is in communication.

19. The apparatus of claim 13 and 18, characterized in that the blocking means (20) by means of a cassette (21) gas-tight through the wall (15) of the combustion chamber (12) is guided.

20. Device according to claim 13, characterized in that the measuring means (27) is a temperature sensor.

21. Apparatus according to claim 13, characterized in that the measuring means (28) for detecting the gas mass flow of the hot gases or the inflows is a mass flow sensor.

22. Device according to claim 13, characterized in that the measuring means (29) for

Detecting the oxygen concentration in the hot gas is an oxygen sensor.