GB2251927A

GB2251927A - Controlling gas pressure in an oven

Info

Publication number: GB2251927A
Application number: GB9200232A
Authority: GB
Inventors: Rainer Kurzeja
Original assignee: Riedhammer GmbH and Co KG
Current assignee: Riedhammer GmbH and Co KG
Priority date: 1991-01-07
Filing date: 1992-01-07
Publication date: 1992-07-22
Anticipated expiration: 2012-01-07
Also published as: ITMI913502A0; FR2671393B1; DE4100232A1; GB9200232D0; ITMI913502A1; FR2671393A1; IT1252676B; GB2251927B; DE4100232C2

Abstract

The gas pressure prevailing in the interior of an oven is controlled by introducing cold air into the flue gas channel of the oven and varying its quantity, position of delivery or temperature, so as to vary the rate at which flue gases escape from the oven interior, in response to measurements of the gas pressure. <IMAGE>

Description

2 2 'S 19 2 7 1 ARRANGEMENT FOR MEASURING AND CONTROLLING THE GAS PRESSURE

PREVAILING IN THE INTERIOR OF AN OVEN The invention concerns an arrangement for measuring and controlling the gas pressure prevailing in the interior of an oven.

The flue gases or the outgoing air of ovens, particularly industrial ovens such as for example shuttle kilns or chamber kilns for the firing of green ceramic bricks, are usually conducted away by a chimney leading to the outside. Differences of pressure in the interior of the oven and thermic lift sustain the flow of flue gas. This can cause undesirable changes of the gas pressure in the interior of the oven. It is known, in order to set the constant of the gas pressure in the interior of the oven which is necessary for the process technology, to measure by means of a.. measuring device the instantaneous gas pressure pevailing in the interior of the oven and in the event of deviations from a predetermined set.value because of over-pressure or under- 2 pressure in the interior of the oven, to actuate a control flap provided in the chimney or flue system which control flap opens further in the case of an over-pressure being registered or in the case of the pressure being too low, closes, if appropriate, to the point of complete closure of the crosssection of the chimney.

The essential disadvantage of the known control flap lies in the fact that it is subject to considerable wear particularly because of the partially extreme thermic load, for example when firing formed ceramic parts. This has the consequence that the control flap has only a short life and after a certain amount of wear functions only in a limited manner or not at all. It must then be replaced.

The object of the invention is accordingly to offer a means of measuring and controlling of the gas pressure prevailing in the interior of an oven whereby sure and reliable control of the flow of flue gas/outgoing air can be achieved as far as possible without wear.

The invention is based on the recognition that this objective can be attained with surprising simplicity and reliability in an entirely different manner avoiding the use of mechanical closure means, namely by forcible introduction of cold air into the stream of flue gas. The central thought of the invention is accordingly to control the quantity of flue gases/outgoing air by a relatively cooler blocking stream of air. If for instance cold air is blown into the chimney at right angles to the direction of flow of the flue gas, there arises a kind of "air barrier" which holds back the hotter outgoing air. If the quantity of cold air is reduced, to zero if appropriate, more flue gas can again flow out through the chimney across the "air barrier". The effect described above

3 can however be achieved not only by controlling the quantity of the cold air introduced, but also by its temperature or direction of flow.

The invention has at the same time recognised that the greater the temperature difference between the cold air and the flue gas stream, the greater is the "blocking effect" of the cold air introduced and viceversa: the smaller the temperature difference between the cold air and the flue gas, the more outgoing air can escape outward through the chimney past the "blocking point".

The flow direction of the cold air introduced also permits the control of the flow of the flue gas. If the cold air is introduced at right angles to the direction of flow of the flue gas or in the extreme case even in a direction opposite to that of the flow of flue gas, the flue gas has practically no longer the possibility to flow out through the chimney. By this blockage of the flow of flue gas the pressure in the interior of the oven is simultaneously increased again. If the direction of flow of the cold air is at an angle of < 90 but in the direction of flow of the flue gas, there still remains a blocking effect but smaller than in the preceding cases. The control of the quantity of cold air introduced, its temperat ure or direction of flow ensues with the help of the measuring device mentioned. If this detects a deviation from the predetermined set value, it gives an appropriate signal to the source of compressed air, the means of heating of the cold air or the positioning elements of the air delivery members, whereby this control can ensue continuously or intermittently. In this respect the term "control" includes also "steering".

In its most common form of construction the arrangement for measuring and controlling of the gas pressure prevailing in 4 the interior of an oven is characterised in that it has a measuring device to detect the pressure p-evailing in the interior of the oven which measuring device in the event of deviations from a predetermined set value gives a signal to a cold air delivery member provided in the flue channel outside the interior of the oven and by means of which the quantity of cold air, its temperature and/or the direction of flow of the delivery member can be altered in such a manner that the pressure prevailing in the interior of the oven is brought back to the set val ue by means of the blocking air stream introduced into the flue gas channel.

The invention propose various alternative forms of design in respect of the construction of the air delivery members:

One possibility is to provide in the wall region of the flue gas channel one or more nozzles or slits which can be connected to a source of compressed air. The nozzles/sl its may not only be provided directly in the wall, for example in annular form, but it is also possible to construct them for example as part of an annular air delivery pipe, whereby the cost of installation is reduced.

In this case one or more air delivery pipes are provided at the wall or in the flue gas channel/chimney and the air flows out through the holes/slits of the delivery pipes.

The nozzles/slits are preferably arranged side by side in a preferably horizontal plane and, if two air delivery pipes are provided, aimed in directions substantially opposite to each other. In this manner the air can be injected at right angles to the f 1 ow of the f 1 ue gas f rom two opposi te wal 1 surf aces of the chimney.

The air delivery pipes themselves are preferably so arranged that they can be rotated about their longitudinal centre line. In this manner the direction of outflow of the air can be altered in such a way that it is directed against the direction of flow of the flue gas at right angles to the stream of flue gas, but also in its direction of flow. The blocking air stream is hereby strengthened or weakened depending on the direction of flow of the cold air. Numerous possible designs for changing the position of the air delivery pipes are available to a person skilled in the art. In this respect an actuating drive (a mechanism) which can be activated by the measuring device is proposed merely by way of an example. In this the air delivery pipes can at their ends be passed out through the chimney wall and connected outside to the mechanism so that the latter is not exposed to the stream of hot gas.

In the same manner the source of compressed air can be coupled to the air delivery pipes - for example at the opposite end. This consists in the simplest case of a blower. The control of the blower and hence the quantity of cold air may be regulated not only directly by the measuring device or its control unit in dependence on the pressure value detected in the interior of the oven, but it is also possible to operate the blower with constant output and to provide a control flap externally to the flue gas system between the blower and the air exit openings which control flap alters the cross-section and hence the quantity of air supplied. This control flap is then also preferably directly adjustable by me ans of appropriate signals of the measuring device.

In the simplest case the blower draws in surrounding air and delivers it when required - by means of the air delivery members into the path of the flue gas. However as explained 6 above, control of the blocking effect of:bhe blocking air stream can also be achieved by means of the temperature of the cold air supplied. An advantageous embodiment of the invention therefore provides for the blower or the delivery members to be so constructed as to be capable of being heated. The heating again is also adjustable by means of the said measuring device and it is so in dependence on the gas pressure prevailing and measured in the interior of the oven at the time. The delivery of cooler outgoing air of the oven is also possible.

It is self-evident that one or more arrangements of the said type can be provided in the flue gas channel or chimney of an oven. A person skilled in the art can select their provision and specific construction according to the instance of application concerned. Care must however be taken in every case to ensure that the control of the stream of flue gas and hence the influence on the pressure prevailing in the interior of the oven can only be effected when resistance is appliedagainst the stream of flue gas by means of colder air It is evident from the above that the described arrangement completely dispenses with mechanical blocking units. It works exclusively with air. Problems of wear as in the state of the art therefore no longer pertain. The air control is much more precise than the mechanical control. The arrangement described can_ readi 1 y be i nstal 1 ed subsequentl y i n exi sti ng oven uni ts.

The arrangement is applied with particular advantage where high oven temperatures and consequently high flue gas temperatures prevail. In this connection industrial ovens should be mentioned first and foremost. The range of applications extends to ovens working intermittently such as shuttle and chamber kilns as well as to continuous ovens such 7 as tunnel kilns or similar. In the case of the last named group it is for instance known to subdivide the individual zones of the kiln by so called "bulkheads" in order to be able to set different kiln ambiences and pressures in individual regions of the kiln. In this case arrangements of the said type will be provided in the corresponding flue gas channels appertaining to the individual zones of the kiln. Finally, the arrangement also has the important advantage in that when working with a cooler stream of blocking air the hot flue gases are cooled (in a defined manner).

The invention will be described below in greater detail by means of an example of a design, the single drawing showing a very schematised representation of a shuttle kiln for the firing of ceramic formed parts the chimney of which kiln is equipped with an arrangement in accordance with the invention.

Reference number 10 identifies a shuttle kiln which has the usual form of construction and is therefore not further described here. A kiln bogie 12 is shown on which is located the cerami c ware 14 to be f i red. In the roof 16 of the ki 1 n 10 are shown two flue gas openings 18a, b each of which issues in corresponding flue gas channel 20a, 20b emanating jointly in vertical chimney 22 extending upwards.

The flue gas from the interior 24 of the kiln will therefore in the normal event take the path through the flue gas openings 18a, b, the flue gas channels 20a, b and the chimney 22 to the surrounding atmosphere.

As can be seen from the drawing, passing through the chimney #1 22 immediately in front of its two opposing walls 22a, b are tubular ducts 28a, b which in the region of the chimney walls 22c, d extending at right angles thereto are retained in such 8 a manner that they can be rotated and which issue in a common tubular duct 30 in the region behind the wall 22c.

In the region within the chimney 22 the tubular ducts 28a, 28b have arranged one behind the other in an axial direction openings (nozzles) 32 the function of which will be described below in greater detail.

A blower 34 is provided at the free end of the tubular duct 30 by means of which fresh air is delivered to the tubular duct 30 and the tubular ducts 28a, b. This fresh air can subsequently exit through the nozzles 32 into the interior of the chimney 22. This will also be described below in greater detail.

It will further be seen from the drawing that couplings 36a, b are provided between the rear wall 22c of the chimney 22 and the region where the tubular ducts 28a, 28b are connected to the tubular duct 30. These serve the purpose of operating the sections of the tubular ducts 28a, b between the couplings 36a, b and the free ends of the tubular ducts 28a, b in such a manner that they can be rotated. For this purpose the free ends of the tubular ducts 28a, b protruding beyond the front wall 22d are connected to an arrangement of rods 40 which is in turn coupled to a reversible actuating drive 42. By means of the actuating drive 42 and the arrangement of rods 40 the tubular ducts 28a, 28b can be rotated and hence the position of the nozzles 32 altered.

outside the kiln a measuring device 44 is further provided which measures the pressure prevailing in the interior 24 of the kiln by way of a transmission line 46. The measuring device 44 further has a control unit which, when the detected gas pressure deviates from a predetermined set value, gives a 9 signal to the actuating drive 42 which correspondingly sets the arrangement of rods 40 in motion, whereby the direction of the nozzles 32 is altered. In this manner the direction of flow of the cold air supplied by the blower 34 is altered at the same time. If for example a further out-flow of flue gas is to be prevented altogether, the signal given by the measuring device 44 to the actuating drive.42 will result in the nozzles 32 being aimed directly against each other. In this manner a blocking air stream is formed across practically the entire cross-section of the chimney 22 and the passage of flue gas beyond this point is prevented.

This position is maintained until the pressure in the interior 24 of the ki 1 n has agai n attai ned the predetermi ned set val ue. If an overpressure is subsequently formed in the interior 24 of the kiln, this is indicated in the measuring device 44 which then gives a corresponding signal to the actuating drive 42 in order to turn the nozzles 32 by means of the arrangement of rods 40 in the direction towards the open end of the chimney 22 at a certain angle whereby the blocking effect of the blocking air stream is reduced and thereby some flue gas can at the same time again be emitted though the chimney 22 to the outside.

Reversely, a complete blockage of the flow of flue gas can again be attained at the appropriate time by reverting the position of the nozzles 32.

It may be seen from the drawing that a regulating element 48 i n the shape of a control flap is provided along the air delivery pipe 30. This is also connected directly to the measuring device 44 or to its control unit. As an alternative or in addition to the control facility by means of the actuating drive 42, the regulating element 48 can therefore, in the event of deviations of the detected gas pressure from the set value, also be altered and hence the quantity of air supplied by the blower 34 varied. It is self-evident that when the pressure of the cold air supplied is reduced the blocking effect of the arrangement in accordance with the invention is diminished whereby more flue gas can again escape or that when the pressure of the cold air increases, the blocking effect is increased and correspondingly less flue gas can flow out.

By means of the arrangement described the quantity of flow of flue gas can be controlled practically in any desired manner, namely so that even the smallest deviations from the set value are corrected by the rate of flow of the flue gas being varied by means of alterations of the direction of flow or the quantity of flow of the cold air.

Simultaneously the flue gas/outgoing air is being cooled.

The control unit integrated in the measuring device 42 consist preferably of a process control computer and works fully automatically.

Claims

CLAIMS:

1. Arrangement for measuring and controlling the gas pressure prevailing in the interior of an oven by means of a measuring device for detecting the gas pressure prevailing in the interior of the oven which measuring device in the event of deviations from a predetermined set value gives a signal to a delivery member for cold air which delivery member is provided externally to the interior of the oven in the flue gas channel and by means of which the quantity of cold air, its temperature and/or the position of the delivery member can be altered in such a manner that the gas pressure prevailing in the interior of the oven is brought back to the set value by means of the blocking air stream which is thus introduced into the flue gas channel.

2. Arrangement in accordance with claim 1, in which the delivery member has provided in the wall region of the flue gas channel at least one nozzle/slit which can be connected to a source of compressed air.

3. Arrangement in accordance with claim 1 or 2, in which the delivery member consist of at least one air delivery pipe equipped with air exit nozzles/slits.

4. Arrangement in accordance with claim 3, in which several air delivery pipes are provided in the flue gas channel at a distance from each other.

5. Arrangement in accordance with any of claims 1 to 4, in which the delivery members are arranged in a direction which is at right angles to the flow of the flue gas.

12 - 6. Arrangement in accordance with any of claims 1 to 5, in which delivery members are arranged so that their direction can be altered individually or together.

S 7. Arrangement in accordance with one of the claims 4 to 6, in which the air delivery pipes can be rotated about their longitudinal centre line.

8. Arrangement in accordance with claim 7, in which the air delivery pipes can be rotated by means of a mechanism which can be actuated by the measuring device.

9. Arrangement in accordance with any of claims 1 to 8, in which the source of compressed air consists of a blower.

10. Arrangement in accordance with any of claims 1 to 9, in which the source of compressed air is so constructed that it draws fresh air from the surrounding atmosphere and supplies it to the delivery members.

11. Arrangement in accordance with any of claims 1 to 10, in which the source of compressed air and/or the delivery members can be heated.

12. Arrangement in accordance with any of claims 1 to 11, in which an air control flap is provided between the source of compressed air and the air exit openings of the delivery members.