GB2293645A

GB2293645A - Furnace zone pressure regulation

Info

Publication number: GB2293645A
Application number: GB9519036A
Authority: GB
Inventors: Andreas Boettcher; Bernd Stender; Friedherz Becker
Original assignee: Riedhammer GmbH and Co KG
Current assignee: Riedhammer GmbH and Co KG
Priority date: 1994-09-29
Filing date: 1995-09-18
Publication date: 1996-04-03
Anticipated expiration: 2015-09-18
Also published as: PT101776B; CZ251695A3; DE4434780C1; FR2725266B1; FR2725266A1; PT101776A; ES2129295B1; ITMI951961A1; ITMI951961A0; ES2129295A1; CZ284683B6; GB2293645B; GB9519036D0; IT1277639B1

Description

1 2293645 Device for regulating the gas pressure in adjacent zones of a

continuous furnace

Description

The invention relates to a device for regulating the gas pressure in adjacent zones of a continuous furnace.

According to the invention, the term "continuous furnace" includes all types of continuously operating furnaces in which the material to be fired is fed into the furnace at one point, then passes through the furnace and is removed at another point. Both the prior art and the invention are described in greater detail below with reference to a tunnel furnace for firing ceramic shaped parts without limiting the subject matter of the invention in this respect.

A tunnel furnace is usually subdivided into three main zones, namely - in the conveying direction of the material to befired - a pre-heating zone, a firing zone and a cooling zone.

As EP 0 348 603 B1 indicates, a problem which has hitherto remained unsolved is how to set the mass flow balance of the furnace air (hereinafter uniformly referred to as gas) to the desired optimum as a function of the respective furnace and material to be fired. Here, the gas quantities and their temperature have a reciprocal effect. The quality of the fired material is quite crucially dependent upon the march of temperature, the furnace atmosphere and the gas quantity in the individual furnace zones as well as the flow rate of the gas during the furnace campaign.

DE 41 00 232 C2 describes a device for regulating the gas pressure prevailing in a furnace chamber. Here, it is above all a matter of determining the actual gas pressure and then regulating it by means of the quantity of the exhaust gas flow. What is suggested in concrete terms is to adjust the 2 gas pressure by means of a controllable cold air supply in the exhaust gas channel.

To separate gas flows of differing atmosphere in various zones of a furnace, EP 0 199 032 B1 describes a device having means of extracting at least some of the gas flow of a first furnace portion immediately upstream of the other second furnace portion and at least partial feedback via feedback channels into the side walls of the first furnace portion at an angle of 900 +/- 200 relative to the original flow direction. In other words, in said device a "gas barrier" is set up between adjacent furnace portions. In said manner, above all a mixing of the gases in adjacent zones of a continuous furnace is prevented.

The invention is based on the idea that a similar effect, namely the demarcation, in terms of gas, of adjacent zones of a continuous furnace, may also be achieved in a quite different manner, namely by regulating the gas pressure in the transition region between adjacent zones.

The object of the invention is equally to adjust an optimum mass flow balance of the gas between adjacent furnace zones, which is adapted to the respective furnace and material to be fired.

In its most general form of construction, the invention relates to a device for regulating the gas pressure in adjacent zones of a continuous furnace, having the following features:

a first measuring point for measuring the gas pressure at one end of a first furnace zone, a second measuring point for measuring the gas pressure at the beginning of a second furnace zone immediately adjacent to the first furnace zone, 3 a supply means for introducing gas into the second furnace zone at a distance from the second measuring point, an extraction means for extracting gas from the second furnace zone in the immediate vicinity of the second measuring point at the side remote from the first measuring point, the extraction means being controllable as a function of the pressure ratios between the adjacent furnace zones, which are determined in a time- dependent manner at the measuring points.

In other words, the object of the invention is to adjust identical pressure conditions in the transition region of adjacent zones of a continuous furnace. A direct consequence of identical pressure conditions in adjacent zones is that no exchange of gas may occur between the zones.

There follows a description of the invention with reference to a device which is disposed in the transition region between a firing zone and a cooling zone of a tunnel furnace.

It is known to feed cold air into the cooling zone of a furnace. Depending on the temperature and quantity of the cooling air, the pressure conditions in the cooling zone vary. The device according to the invention then ensures that the varying pressure conditions in the cooling zone are not translated to the adjacent firing zone. In said manner, the individual zones of the continuous furnace, in this case the firing and cooling zones, may be individually adjusted, thereby allowing an optimized passage through the furnace and an improved quality of the fired material.

The cooperation of the two pressure measuring points with the adjacent extraction means for the gas (the furnace air) is crucial to reliable operation of the device. If, for example, 4 the measured value (P2) of the second measuring point at the beginning of the cooling zone increases, while the measured value (P1) of the first measuring point at the end of the firing zone remains unchanged, then the ratio P1: P2 drops to a value < 1. The control device then causes the extraction means adjacent to the second measuring point to extract an increased quantity of gas from the furnace, whereupon the pressure P2 falls again until the ratio P1: P2 is restored to the value 1.

Conversely, if the second measured value (P2) drops, i.e. the pressure in the cooling zone falls in the transition region to the firing zone, the ratio P1: P2 increases to a value > 1. To increase pressure, the control device then throttles the extraction means until the pressure value at said point once more corresponds to the pressure value P1 and the ratio P1: P2 is again 1.

The gas quantity extracted via the extraction means may be controlled by means of a suitable valve in the extraction line.

Consequently, the extraction means may be controlled in such a way that the pressure ratio P1: P2 determined at any one time may be held constant at a value of 1 by means of variations in the extraction quantity of the gas in the second furnace zone. viewed over time, the value is of course not constantly 1 but in the case of deviations the described correction process occurs.

The supply means for the cooling air is disposed at a distance from the measuring points and the extraction means, e.g. at the end of the cooling zone. The following description of an embodiment provides concrete information about the point at which said supply means may, for example, be disposed. In principle, however, the supply means may be disposed at any desired point; suitable supply lines may also be provided at a plurality of points, as the embodiment likewise reveals.

It therefore also follows that a further extraction means may be disposed between the supply means and the extraction means for equalizing the mass flow balance of the gas in the second furnace zone.

If, for example, the temperature and quantity of the supplied air remain constant but the gas quantity removed from the first extraction means falls, the direct consequence is that an increased gas quantity is carried away through the second extraction means in order to keep the pressure conditions constant again in the described sense. Accordingly, in the present embodiment, the second extraction means also is connected for measurement purposes to the two measuring point and/or the f irst extraction means.

The second extraction means may then, like the first extraction means, be controlled as a function of the pressure ratio determined with the aid of the measuring points. Both extraction means are therefore in a reciprocal relation.

In order to effect, for example, intensive cooling, a further embodiment provides for the immediately adjacent arrangement, preferably downstream of said supply means in the direction of passage through the furnace, of a gas extraction line and a gas supply line, through which greater gas quantities may be supplied and immediately extracted again. In said manner, ',shock cooling" may be effected at a locally restricted point of the cooling zone. The pressure measuring device of the type described earlier remains independent of such cooling.

The cooling effect of said shock cooling may be controlled in a temperature-dependent manner, a temperature detector being suitably disposed in the furnace between the gas supply line and the gas extraction line.

6 A suitable temperature detector may also be provided in the region of the first supplymeans.

A further optimization of the device is achieved in an embodiment in which a line, into which mixed air is supplied, opens out into the extractionmeans which is adjacent to the measuring points. With the aid of the mixed air, a "throttling" of the gas quantity withdrawn from the furnace may likewise be achieved.

An important advantage of the described device is that it may be retrofitted in existing furnace installations.

As a rule, a cold air supply is already provided. In said case, all that is required for basic implementation of the device is the arrangement of two pressure measuring points in the transition region of the firing and cooling zones as well as the installation of an adjacent extraction line for the furnace air. The further features described earlier are accordingly optional.

The device may be disposed not only between the firing and cooling zone of continuous furnaces but also - if required at any other point, the principle however remaining unchanged.

The device is equally suitable for roller hearth furnaces, tunnel kilns with kiln cars sliding plate furnaces or the like.

Naturally, the invention is not subject to any restrictions with regard to the nature of the material to be fired. The individual parts of the device merely have to be adapted, in terms of their dimensions, to the respective application.

Further features of the invention arise from the features of the subclaims and from the other application documents.

7 The invention is described in greater detail below with reference to an embodiment. Said embodiment shows - in a diagrammatic view - a cooling zone of a tunnel furnace in the region adjoining a firing zone, having a device according to the invention for regulating the gas pressure in both zones.

The reference numeral 10 denotes the rear portion of a tunnel furnace. The conveying direction of the material to be fired is indicated by the arrow T. Situated at the point identified by the line L is the transition region from the firing zone B to the cooling zone K. Immediately upstream of the end of the firing zone is a first pressure measuring point 12 with a suitable pressure sensor. Disposed adjacent thereto immediately downstream of the separating line L and at the beginning of the cooling zone K is a second measuring point 14, which likewise comprises a pressure sensor. The gas pressure at the corresponding points of the firing and cooling zones is determined by means of the pressure sensors. Lines lead from the pressure sensors into an evaluation unit 16 and from there to a computer 18.

Disposed immediately downstream of the second measuring point 14 in conveying direction T is a gas extraction line 20, through which gas may be extracted from the cooling zone T. A line 22 runs from the computer 18 to a servomotor 24, by means of which a throttle valve 26 inside the extraction line 20 may be controlled in the manner to be described below.

At a distance from the extraction line 20, a cold air supply line 28 opens into the cooling zone K. The supplied quantity of cold air may likewise be regulated by means of a valve 30 controllable by a motor (at 32), namely in the present case as a function of the furnace temperature prevailing in said region of the cooling zone K. Said temperature is determined by means of a temperature detector 34 which is disposed - in conveying direction T - upstream of the supply line 28, the temperature value being acquired in a temperature controller 8 36 which, in accordance with the measured temperature, supplies a signal to the servomotor 32 and hence adjusts the cold air supply quantity.

Disposed between the extraction line 20 and the supply line 28 is a further extraction line 38 which is basically identical in construction to the extraction line 20. Here too, the gas quantity to be extracted at any one time may be controlled by a throttle (a valve) 40 with the aid of a motor 42, which receives (via the line 46) the corresponding signals from a mass governor 44 which, for measurement purposes, is connected (by line 48) to the computer 18.

Disposed at the end of the tunnel furnace 10, i.e. at the end of the cooling zone K, are two further lines 50, 52, of which the end line 52 is used to supply cold air and the line 50 upstream thereof is used to extract gas. It is evident from the drawing that the two lines 50, 52 are disposed immediately adjacent to one another and have disposed between them a temperature detector 54, by means of which the actual temperature at said point of the furnace chamber is measured and passed through a line 56 to a temperature controller 58, which in turn controls a motor 60 (via the line 62), the motor 60 controlling an associated valve 64 in the supply line 52 and hence the supplied quantity of cold air.

The extraction line 50 is of a corresponding construction and includes a valve 66, which is conveyed by a motor 68 into the respectively required position, the motor 68 receiving its signal via a line 70 from a mass governor 72 which, for measurement purposes, is connected by the line 74 to the temperature controller 58.

The device operates as follows:

The actual pressure (P1) at the end of the firing zone B continuously measured by the first measuring point 12.

is 9 Similarly, the actual pressure value (P2) at the beginning of the cooling zone K is continuously determined by the second measuring point 14. The values P1 and P2 are evaluated by the evaluation unit 16 in the computer 18. If it emerges that, e.g. as a result of an increased supply of cold air through the line 28, the pressure P2 exceeds the pressure P1, the throttle valve 26 is then opened by the servomotor 24 so that an increased quantity of gas is extracted from the cooling zone K, whereupon the pressure value P2 drops. The servomotor 24, and hence the throttle valve 26, is reset as soon as P1 equals P2. The pressure conditions at the end of the firing zone will therefore correspond to those at the beginning of the cooling zone, thereby preventing any exchange of atmosphere between the two zones.

In the opposite case, the procedure is correspondingly reversed in the manner already described earlier.

Depending on requirements, the computer 18 may be designed in such a way that it opens or closes not only the throttle valve 26 but also the valve 40 in the extraction line 38 in order already at said point to extract an increased quantity of gas from the cooling zone K or to reduce the removed gas quantity.

The lines 50, 52 at the end of the cooling zone K are used to shock-cool the fired material in order that at the furnace exit 76 said material may be immediately removed from kiln furniture. During said cooling process, cold air is temperature-dependently - (temperature detector 54) supplied through the line 52 and removed again immediately upstream by the extraction line 50 so that at said point an increased gas exchange and hence an intensified cooling action is achieved.

Claims

Claims Device for regulating the gas pressure in adjacent zones of a continuous furnace having the following features:

1.1 a first measuring point for measuring the gas pressure P1 at one end of a first furnace zone 1.2 a second measuring point for measuring the gas pressure P2 at the beginning of a second furnace zone immediately adjacent to the first furnace zone 1.3 1.5 a supply means for introducing gas into the second furnace zone at a distance from the second measuring point, 1.4 an extraction means for extracting gas from the second furnace zone in the immediate vicinity of the second measuring point at the side remote from the first measuring point, the extraction means being controllable as a function of the pressure ratios (P1: P2) between the adjacent furnace zones which are determined in a time-dependent manner at the measuring points.

2. Device according to claim 1, wherein the extraction means is controllable in such a way that the pressure ratio (P2: P1) determined at any one time is held constant at a value of 1 by variations in the extraction quantity of the gas in the second furnace zone.

Device according to claim 1 or 2, wherein the extraction means comprises an extraction line, in which a valve is disposed in a controllable manner.

4.

Device according to one of claims 1 to 3, wherein disposed between the supply means and the extraction means is a further extraction means for equalizing the mass flow balance of the gas in the second furnace zone.

5. Device according to claim 4, wherein the second extraction means is controllable as a function of the pressure ratios (P1: P2) acquired with the aid of the measuring points.

6. Device according to one of claims 1 to 5, wherein disposed immediately adjacent to one another - in the direction of passage through the furnace - downstream of the supply means are a gas supply line gas extraction line greater gas quantities.

7.

and a for supplying and extracting Device according to claim 6, wherein the gas supply quantity and the gas extraction quantity are controllable in a temperature-dependent manner in the region of the gas supply line respectively.

and the gas extraction line

8. Device according to one of claims 1 to 7, wherein a line for the controllable supply of mixed air opens into the extraction means which is adjacent to the measuring points.

9. Device according to one of claims 1 to 8, wherein the gas introduced via the supply means is controllable in a temperature-dependent manner.

12

10. Device according to one of claims 1 to 9, wherein the first measuring point is associated with a firing zone and the second measuring point is associated with a cooling zone of the continuous furnace.

A device for regulating the gas pressure in adjacent zones of a continuous furnace, substantially as herein described with reference to the accompanying drawing.