FR2637677A1 - INDUSTRIAL OVEN - Google Patents

Abstract

This oven is of the type comprising several burners 12 to which secondary air can be brought into the zone of the flame of the burners, by suitable ducts, intended for the firing of molded materials and products, by adjusting the atmospheric conditions. well defined oven, according to given set values. There is provided at least one measuring device 26 in the furnace 10 for the quantitative and analytical recording of at least one gas component of the atmosphere of the furnace and a control unit for recording the value measured by the furnace. measuring device 26 and comparison with a given set value, the control unit being designed so as to adjust the quantity of secondary air sent to the burners 12, as a function of the determined difference between the measured value and the value of setpoint.

Description

INDUSTRIAL OVEN

  The invention relates to an industrial furnace comprising

  as many burners to which secondary air can be brought into the burner flame zone, by suitable ducts, for cooking materials and molded products made therefrom, by adjusting the conditions of oven atmosphere well defined, according to given setpoints. An oven of this type can be designed to operate continuously, as for example fourstunnels or roller ovens, or discontinuously such as for example ovens.

  mobile hearth. With regard to the material to be cooked, the

  The invention is unrestricted, although the claimed industrial furnace is primarily used for the firing of ceramic products, including special ceramic materials and molded products made from these materials. Examples are furnaces for cooking porcelain, refractory materials,

  sanitary ceramics, ferrites, etc. -.

  The problems mentioned below for known ovens

  are in reference to a mobile hearth furnace for cooking

  sound of sanitary ceramics, but this is also true for

other applications.

  Inside a mobile hearth furnace of this type,

  definite atmosphere conditions are required; in part-

  In most cases, the oxygen content must be constant

  the atmosphere of the furnace, because the enamels ob-

  by oxidation may react and change color as a result of changes in the oxygen content

  of the atmosphere of the oven. If, for example, the oxy-

  gene passes below a minimum value that can be calculated, the enameling generally becomes darker, and its color changes are irreversible, so

  that the load must eventually be rejected.

  The problems that arise in maintaining the oven atmosphere at a constant level result in particular from two points of view: on the one hand we can not

  avoid frequent changes in the pressure in

  exhaust gases. On the other hand, the calorific

  The primary sources of energy used often vary to a significant extent. This applies in particular

  gas-fired ovens, especially when using

  reads coke oven gas, but also natural gas. Thus the calorific value of the coke oven gas can vary between 200 and 400 kcal depending on the source. This results in corresponding variations of the furnace atmosphere. In the state of the art, attempts are made to overcome the problems caused by changes in enameling, in particular

  operating the burners constantly with an excess

  oxygen tooth. This requires a larger inflow of air

  aunt and therefore necessarily also a heating

  constituents of air other than oxygen, and finally

  increased energy consumption which, following the

  field of application- can be up to 30%.

  The object of the invention is to indicate a possibility of designing an industrial furnace so that the atmosphere of the furnace can be maintained at a constant given level, the energy consumption being at the same time reduced to

minimum possible.

  The following considerations are at the basis of the solution according to the invention: To minimize energy consumption, the burners (the power of the burners) must, if possible, not be influenced and be adjusted to the smallest possible capacity. Yes

  the burners are adjusted taking into account the fluctuation range.

  of the calorific value of the energy source used

  (eg gas) on the lowest calorific value, for example the oxygen content of the atmosphere

  is only influenced by secondary air.

  Because the burners are set in a fixed way taking into account the lowest heating value of the

  source of energy used, there is no further adjustment

  burner and, as a result, the oxygen content of the furnace atmosphere can only be located - without additional measurements below

  desired. If we measure the oxygen content of the

  the oven atmosphere, an average of one

  oxygen deficiency for a short time or

  at a certain time interval, and compensate

  a corresponding increase in the secondary air supply

  without increasing the power of the burners.

  The aim is achieved with an industrial furnace of the aforementioned type having the following characteristics: - At least one measuring device is provided in the furnace for the quantitative and analytical recording of at least one gas component of the atmosphere of the furnace. oven, - a control unit for recording the

  measured by the measuring device and compared

  sound with a given set value, the unit of con-

  control being designed so as to regulate the amount of secondary air supplied to the burners, according to the difference determined between the

  measured value and the set value.

  As mentioned above, the oxygen content of the furnace atmosphere is an essential parameter

  for cooking sanitary ceramics. For this purpose

  application is currently very

  often, mobile hearth furnaces

  enclosed oven. A modern mobile hearth furnace, as used for some time by the applicant under the name "SweepFire", has on each of the opposite sides a row of gas burners, the burners on one side of the furnace passing exactly between the burners

  on the opposite side. When the oven is switched on, the zone

  turning the flame of the burners is naturally very hot, while the other parts of the enclosure of the

  oven are hardly heated yet. To improve

  improve heat transfer, burners work

  at the beginning with a very large amount of secondary air

  aunt, so that temperatures rise from

  1000 C at about 150 ° C. At the same time, secondary air

  daire is injected under high pressure, and the oven is

  ordered so that it is first of all the burners

  their on one side of the oven that work; as a result, the heated air is forced back into the area of the opposite wall; the first row of burners is then lowered and the row of burners of the opposite wall is operated at full speed, so that a current of heat is produced in the opposite direction to that which has just been described; after which the speed of the row of burners which last worked is reduced and the first row of burners ensures the continuation of the operation, the power of the burners between the different intervals being able to vary between 10 and 100%, or between 100 and 10% . As the temperature increases in the oven, the amount of secondary air is reduced until it tends to 0 when the temperature reaches 600 to

650 OC.

  From this temperature range, it becomes

  necessary, because of the described problems due to oxidation

  possible enameling, to maintain constant

  oxygen content of the furnace atmosphere.

  The mentioned measuring device is put into service, and is used for the quantitative analysis of the oxygen content of

  the atmosphere of the oven. If a set value determines

  If the value is not reached, the difference between the actual value and the setpoint value is recorded by the control device which delivers a signal to the secondary air supply ducts. These secondary air ducts have adjustment members that open more or less, depending on the intensity of the signals delivered by the control unit and until the measuring device registers the setting again. the setpoint value, which is recorded by the control unit, which then ensures that the adjusting elements, mounted in the secondary air supply ducts, close again,

  or at least operate with less secondary air.

  If, for any reason whatsoever,

  to have an even greater oxygen deficit in the

  oven, during partial opening of the supply ducts

  With secondary air, this would of course also be recorded by the measuring device and the control elements mounted in the inlet ducts would open even more, following a corresponding signal delivered.

  by the control system, in order to increase

  the amount of secondary air.

  The measuring device or the control unit can be programmed according to the time, if one

  wish the oven atmosphere to have a different content

  oxygen during the cooking process (eg during temperature rise or during cooling). Preferably, the gas measuring device must

  be placed in a place in the oven where figures signify

  ficatives can be determined. In this respect, it is preferable to have the measuring device in the area of the gas discharge duct (from the extraction> of the furnace, but the measuring device could also be placed in the duct of the furnace. evacuation

gas itself.

  To determine the oxygen content of the atmosphere

  of the furnace, it is particularly interesting to use an oxygen-based oxygen

of zirconium.

  Programmelectronic engineering ag, ch-4143 offers an oxygen meter of this type under the name "SB / I". The oxygen content of the

  gas is determined by a permanent measurement of an

  gas sample sucked continuously. The apparatus is

  killed by an oxygen measuring cell to which the gas to be measured is sent by a pump also mounted in the device, as well as any analytical electronics

  that can be placed in the device itself.

  same or separately. Analytical electronics serve to ameliorate

  the signal from the oxygen sensor, as well as

  delogarithmisation, in order to obtain a proportional signal

  the oxygen content, as well as the voltage / current conversion, in order to obtain an output signal of 0 to 20 mA. Finally, the temperature of the heated measuring cell is also adjusted to avoid distorting the measured values. When the gas to be measured contains

  solid particles or vapors that can be

  In the measurement cell, it is preferable to mount filters and / or cooling traps upstream of the measuring cell. It must also be ensured that the flow of gas through

  the measuring cell is constant. This can happen

  kill, for example, using a bypass valve.

  We can, of course, also

  positive measurement of the aforementioned type in the oven. It is

  possible then to calculate the average of the different

  and to order a corresponding setting of the

  secondary air stream, through the unit

control.

  Thanks to the configuration according to the invention of an industrial furnace, the oxygen content of the furnace atmosphere can be maintained without problem in a variation range of less than + 0.5%, without influencing in any way the burners that operate at their power

the weakest.

  While for cooking sanitary ceramics, the oxygen content of the furnace atmosphere represents a

  decisive influence on the cooking of the por-

  This size is the CO content. The cooking must, in particular, be done at high temperatures, in a reducing atmosphere. The corresponding control of the furnace atmosphere takes place in the furnace by means of a suitable CO measuring cell. If the value of CO found if it is below the set value, it requires a corresponding supply of secondary air rich in

  CO, which can be done by means of appropriate recycling.

  fumes, through the secondary air ducts. In this case, the amount of flue gas is adjusted again by appropriate control elements, placed in the inlet ducts, according to the differences determined with respect to

  to the set point. If one works with a recy-

  If the fumes are clogged, it is recommended that the burners be operated, at least stoichiometrically, so that the amount of oxygen required for combustion is available.

  If the burners operate in a very

  As a rule, CO levels will generally be

  the oven atmosphere too high. These are again

  indicated by the measuring device, and the deviation from the setpoint triggers - as described above - a signal sent to the secondary air duct adjusters which, in this case, operate with secondary air containing oxygen, so

to ensure good combustion.

  Depending on the area of application and depending on

  the need to maintain constant

  oven is equipped with one or more gas analysis devices or control units, or the secondary air ducts are

  supplied with adequate secondary air.

  As another example of a domain

  of application, ovens for cooking charcoal

  (graphite), ferrites or other ceramic materials

special characteristics.

  The furnace may be a furnace operating discontinuously, for example a mobile hearth furnace; but he

  can also be a continuous oven, for example an oven-tun-

  nel or a roller oven. For these types of furnaces too, it is necessary to respect defined and determined atmospheric conditions, within certain zones, along

the route of the product to be cooked.

  A subdivision of the furnace into different zones which are practically "isolated" is obtained for example by means of appropriate slide valves which slide from above and / or from below in the passage channel of the oven, and do not give off an area for the passage of the product to

  cook. Such an oven is described in DE-OS 30 16 852.

  In such an oven, each zone of the oven is designed in the manner described above. In this case it is necessary to operate the burners or the secondary air ducts separately for each zone, in order to

allow individual adjustment.

  Although the expense of installing a measuring device or control unit, or appropriate regulators mounted in the secondary air supply ducts, is low, the furnace described provides for

  the first time the possibility of settling

  and maintain constant conditions of atmospheric

  data, including time. The burners

  in this case they are set to the lowest calorific value of the fuel (gas, coal,

  fuel oil), resulting in considerable energy savings.

  It is obvious that the existing furnace

  aunts can be transformed without

  very short time and without great complexity.

  Various other features of the invention

  come out of the detailed description which follows. A way

  embodiment of the invention is shown, in

  of non-limiting example, in the accompanying drawings, in the-

  which: Figure 1 is a longitudinal sectional view of a hearth furnace, Figure 2 is a sectional view of a burner block

  with secondary air inlet, oven of Figure 1.

  In FIG. 1, the mobile hearth furnace is designated as a whole by reference numeral 10. In principle,

  the oven is of usual construction, which makes it super

other explanations.

  FIG. 12 shows a burner 12 placed in the left lateral wall 14 at the height of auxiliaries of

baking 16 of an oven car 18.

  Several of these burners 12 are placed, spaced from each other, at the same height, in the wall 14, and an equivalent number of burners are in the opposite wall 20. These burners are not visible because they are offset with respect to the row with the

burner 12. -

  An oxygen measuring cell 26 which will be described hereinafter in more detail, is placed in the zone of a

  extraction of fumes 22, on the vault 24.

  A control unit (not shown) is inte-

  to the oxygen measuring cell 26.

  The oxygen measuring cell 26 determines the

  instantaneous oxygen in the furnace atmosphere,

  the operation of the latter. The determining value

  is compared in the control unit to a given setpoint. If the determined value deviates from the set value, the difference is converted into an electrical signal which is connected, by lines not shown, to adjustment members 28, in the zone

  inlet ducts 30 in the region of the burners 12.

  Figure 2 shows, in detail, the arrangement of the burners. Reference numeral 12 denotes a burner block in

  which forms a burner flame.

  In the section of the burner block, turned towards the enclosure of the oven 34, passes an annular channel 36 which is connected to the inlet duct 30 in which is placed

the adjusting member 28 described.

  From the annular channel 36 extend, in

  rection of the chamber 34 of the furnace, oblique nozzles 38, arranged in a star, which are open towards the inside

of the burner block 32.

  Secondary air is sent concentrically

  than the burner flame (not shown) by the

  inlet ducts 30, the annular channel 36 or the nozzles 38, the burner flame speed being increased by

  the injected supply of secondary air.

  If, for example, the measuring device 26

  oxygen deficiency in the furnace atmosphere, the

  This deficit is determined by the control unit, and a calculator determines the amount of secondary air needed to increase the oxygen content again.

  furnace atmosphere, up to the set

  born. At the same time, an electrical signal from the

  control tee, is given to some or all of the adjustment members 28 which open more or less, depending on the given signal, and therefore allow a secondary air inlet in the enclosure of the oven, by

  the conduits 30 or the annular channel 36 and the nozzles 38.

  Depending on the further evolution of the oxygen content of the furnace atmosphere, the adjusting members 28 are then generally strangled or closed; it is understood that they can also, if necessary, be opened again, in order to increase the oxygen content

  of the furnace, by a more important secondary air supply.

  The furnace shown is used for cooking sanitary ceramics, the cooking products being represented by

  schematically only in Figure 1. The

  positive measuring 26 and the sets thereof are preferably operated from only a range of temperatures above 600 C, range

  in which defined atmospheric conditions are

are of particular importance.

  During cooking, between 600 C and the time

  sintering temperature, the power of the burners 12 remains unchanged. This power has been adjusted beforehand taking into account the low heating value of the cooking gas used. The energy consumption is thus severely reduced and the oxygen content of the oven

  is exclusively regulated continuously, by secondary air.

  Instead of the adjustment members 28 shown schematically, it is of course also possible to use other throttling devices, such as valves, etc. It is also possible to connect the various inlet ducts 30 leading to each other. to the burner 12, by a common annular conduit, and to adjust the arrival

  secondary air by a central regulator.

Claims (10)

- CLAIMS -   An industrial furnace having a plurality of burners (12) to which secondary air can be supplied to the burner flame zone by suitable conduits (30) for firing materials and molded products made from those by setting well-defined oven atmosphere conditions according to   data set, having the following characteristics:   1.1 At least one measuring device (26) is provided in the furnace (10) for quantitative recording   and analytic of at least one gas component of the   furnace mosphere, and 1.2 a control unit for recording the measured value by the measuring device (26) and comparison with a given set value, the control unit being arranged in a manner 1.3 to adjust the quantity of secondary air supplied to the burners (12), depending on the determined difference between   the measured value and the set value.   Oven according to claim 1, characterized in that   that the control unit is designed so that the   their measured values are determined over intervals of given time.   Oven according to Claim 1 or 2, characterized in that the measuring device (26) is placed in the area of the oven vault (24).   4. Oven according to one of claims 1 to 3, characterized   characterized in that the measuring device (26) is placed   in the area of a gas evacuation device (22).   Oven according to one of claims 1 to 4,   characterized in that the measuring device (26) is a measuring probe.   Oven according to one of claims 1 to 4,   characterized in that the measuring probe is a probe of   oxygen measurement, based on zirconium dioxide.   7. Oven according to one of claims 1 to 6, characterized   in that the secondary air intake is placed in   ring around the flame of the burners.   Oven according to one of claims 1 to 7, characterized   in that the arrival duct (s) (30) of   the secondary air supply comprises (ent) a provision throttling device (28).   9. Oven according to one of claims 1 to 8 for   sanitary ceramic cooking, the oven being an oven mobile hearth.   Oven according to one of claims 1 to 8 for   baking ceramic materials and molded products, the furnace being a continuous furnace and different sections of the furnace being delimited relative to each other by slide valves which penetrate into the enclosure of the   oven, from the vault and / or the oven floor.