EP0714496B1

EP0714496B1 - Device for manoeuvring an air-control mechanism in a furnace

Info

Publication number: EP0714496B1
Application number: EP94925059A
Authority: EP
Inventors: Bengt Gustafsson
Original assignee: Kvaerner Pulping AB; Kvaerner Pulping Technologies AB
Current assignee: Metso Fiber Karlstad AB
Priority date: 1993-08-23
Filing date: 1994-08-10
Publication date: 2000-03-29
Anticipated expiration: 2014-08-10
Also published as: WO1995006226A1; CA2168220A1; PT714496E; DE69423765D1; AU7510494A; EP0714496A1; SE9302731D0; ATE191271T1; BR9407451A; SE9302731L; SE502092C2; ES2146659T3

Abstract

The invention relates to a device for manoeuvring an air-control mechanism (1) in a furnace provided with a number of air-supply ports (3) in its walls (2), in which the said ports (3) communicate with an air box (4) and in which each port (3) is provided with a control member (5) which can be axially displaced forwards and backwards for positional adjustment relative to the said port for the purpose of determining the volume of air passing through the port, and in which the said control member (5) is additionally arranged to be moved past the set air-regulating position, so that its end (10) penetrates the port (3) in order to remove coatings which have been deposited in the said port, in which the control member (5) is connected to a mechanical jack screw (13) for the realization of its axial motions both for air-regulating positional adjustment and for removal of the coatings, in which the said jack screw (13) is driven by an electric motor (14). The axial position of the control member (5) is here clearly determined by the gear ratio of the jack screw (13) and the rotation speed and running time of the motor (14).

Description

The present invention relates to a furnace containing a device for manoeuvring an air-control mechanism, in a so-called "soda furnace", or soda pan for combustion of waste liquor from pulp production, in which combustion air is supplied through a number of air-supply ports in the furnace walls. The ports communicate with so-called "air boxes", which are fed with air from outside. Each port is further provided with a control member in order to determine the air volume passing through the port.

PRIOR ART AND PROBLEM

The aim of the equipment is to regulate the quantity of combustion air which is supplied to the furnace and, by virtue of so-called "poking", to keep the ports free from the coatings which are formed in the mouth of the ports.

The air quantity is regulated by a control member, often in the form of a control sleeve, throttling the annular gap area which is formed between the inner sides of the air port and the tip of the control sleeve. The gap area is changed by the axial end position of the control sleeve being varied relative to the air port.

In soda furnaces, coatings are formed, during the combustion process, on the inner sides of the furnace walls. The coatings threaten to block the air ports, with the consequence of deteriorating combustion results. In order to remove such coatings, so-called "poking" of the air ports is carried out, which is done by the control member being moved past the set air-regulating position so that its end penetrates the air port, whereupon the coatings which have formed are wiped off. The control sleeve is often configured such that combustion air is allowed to flow internally through the sleeve and into the furnace whenever the control sleeve is in the advanced poking position, thereby enabling the sleeve to be cooled.

In previously known constructions, compressed-air driven pistons are used in order to realize the principal axial displacement of the control member (control sleeve) relative to the air-supply port. A difficult problem with such compressed-air systems is that the pressure of the compressed-air network often varies due to condensation, for example, or other causes. In the event of such undesirable falls in pressure, for example if the pressure suddenly drops from 6 bar to 4 bar, it can happen that the control sleeve, in the poking operation, is unable to get through the port, with the consequence that it gets stuck and, despite air cooling, is burnt through.

It has simultaneously been shown that the poking motion of the compressed-air driven control sleeve is not sufficiently powerful to remove particularly serious coatings in a safe and reliable manner.

The control sleeve further needs to be able to be positionally adjusted within an air-regulation zone so that the sleeve can be moved past the set air-regulating position, whereupon its end penetrates the air port and is subsequently returned with great accuracy to the set air-regulation position. This is particularly important in connection with soda pans whenever it is wished to use the so-called ROTAFIRE\-method (see SE-9102546-0), in which, by virtue of a specially regulated air supply, a rotation of the combustion gases in the horizontal plane is created, so that the waste liquor injected into the furnace chamber is slung by the gas rotation out towards the walls of the furnace, whilst simultaneously undergoing drying and pyrolysis.

Where compressed-air cylinders are used for the displacement of the control sleeve, an often complicated and expensive auxiliary system is required for the air-regulating positional adjustment having the above-stated function. The problem with the prior art is here, therefore, to get the control sleeve, without deviations, to resume its set air-regulating position directly following completion of a poking motion.

Such auxiliary systems are usually controlled via a limit switch, which can operate electrically, pneumatically or mechanically and is described, for example, in Swedish patent specifications SE-379 846 and SE-462 440.

OBJECT OF THE INVENTION

The object of the present invention is to eliminate the above problems by producing a device for manoeuvring an air-control mechanism in a furnace, which device is able, at the desired force and in a safe and reliable manner, to perform a poking motion in order to remove coatings which have been deposited in the said air ports, and at the same time to completely obviate the need for complicated and expensive auxiliary systems for positionally adjusting the control member (i.e. the control sleeve) for air regulation and get it to resume the set position following completion of a poking motion. The object is also, by virtue of a considerably simplified positional adjustment, to facilitate the complicated controlling of the control sleeves 5 in connection with use of the above-specified ROTAFIRE\-method.

TECHNICAL SOLUTION

The above object is achieved by the fact that the invention provides furnace with a device for manoeuvring an air-control mechanism according to subsequent Patent claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below with the aid of an illustrative embodiment and with reference to the following drawings, in which:

Fig. 1 shows a side view of an air-control mechanism according to the invention,

Fig. 2 shows a sectional view of a jack screw driven by an electric motor, according to an embodiment of the invention,

Fig. 3 shows a diagrammatic horizontal section through a so-called "soda pan".

DESCRIPTION OF A PREFERRED EMBODIMENT

In Figure 1, the reference numeral 1 denotes in general terms an air-control mechanism in a furnace such as, for example, a soda furnace. The walls 2 of the furnace are constituted by parallel-running and welded-together water-cooled tubes, which, amongst themselves, are either sealed tight or combined with the aid of intermediate fins (not shown) in order to achieve a gastight wall. By bending apart two neighbouring tubes, sufficient space is created for an air-supply port through which the furnace is provided with combustion air in the desired quantity. A number of such air-supply ports (hereinafter referred to as air ports) communicate with an air box 4 situated on the outer side of the wall 2. The air box 4 is connected, in turn, to a feed pipe (not shown), through which the air box 4 is provided with warmed air.

The wall 2 is further covered, on the outer side, with insulating material (not shown in the figure).

The air boxes 4 are situated at different levels and along different walls of the furnace. The air boxes 4 are further divided into sections, whereby each section supplies a certain number of air ports 3 with combustion air. The same air box 4 is able, for example, to supply two, four or more air ports 3.

Connected to each air port 3 there is a control member 5 in the form of a sleeve, hereinafter referred to as the control sleeve 5. It should be noted, however, that the control member 5 can also be differently configured. The control sleeve 5 can be axially displaced forwards and backwards, in a known manner, for positional adjustment relative to a frame piece 6 defining the air port 3. The cross-sectional area within the frame piece 6 of the air port 3 increases in the direction from the wall 2, i.e. to the right in Fig. 1. The quantity of air which is allowed to flow into the furnace is regulated by the fact that the control sleeve 5, as a result of the above-described axial displacement, varies the annular gap area 7 which is formed between the inner sides of the frame piece 7 and the end 10 of the control sleeve 5. The axial displacement here takes place in the directions of the double arrow 8. The control sleeve 5 is additionally arranged to be moved past the set air-regulating position, so that its end 10 penetrates the air port 3 in order to remove coatings which have been deposited in the said air port. This process is given the name "poking" and is performed at regular intervals in order to keep the air ports 3 free from coatings which threaten to block the air ports 3 such that the desired quantity of combustion air is eventually no longer able to be supplied to the furnace. The poking is therefore realized by the control sleeve 5 executing a forward stroke to the dashed position 11 in the figure, after which it is retracted back to the set air-regulating position which obtained prior to the poking.

According to the invention, the control member 5 is connected to a mechanical jack screw 13 for the realization of its axial motions both for air-regulating positional adjustment and for the removal of coatings by poking. The jack screw 13 is here driven by an electric motor 14, whose rotation speed, running time and direction of running are controlled by a control unit 15 which is coupled to the electric motor 14 via a cabling element 16, which is well protected against the dirty environment and the high temperatures which obtain in the vicinity of the furnace.

The jack screw 13 will now be more closely described with reference partly to Fig. 1 and partly to Fig. 2, which shows a partially cut view of the gear housing 18 of the jack screw 13, with connected electric motor 14.

The electric motor 14 here drives an axle 19 mounted in the gear housing 18 at two

mounting points

20, 21. A worm screw 23 is additionally configured integrated with the axle 19. This worm screw 23 is engaged with a corresponding worm wheel 24, which is engaged internally with a trapezoidally threaded spindle screw 25 directed perpendicular to the axle 19. The spindle screw 25 can therefore be displaced axially (in a direction perpendicular to the plane of the paper in Fig. 2), in known fashion, whenever the worm screw 23 is rotated with the aid of the electric motor 14.

The jack screw 13 is connected via a fixture 27 to an axle 28, which, together with a parallel guide rod 29, is connected to the control sleeve 5. The axle 28 runs within a cylindrical holder 31, which is fixed to the air box 4 and supports the gear housing 18 of the jack screw 13.

An electric motor-driven jack screw 13, adjusted to realize the axial motion of the control sleeve 5 according to the present invention, makes it significantly easier to perform the air-regulating positional adjustment in the axial direction of the control sleeve 5, compared with previously known solutions using compressed-air driven cylinders and requiring expensive auxiliary systems for positionally adjusting the control sleeve 5 for air-regulation and for getting it to resume the set position following completion of the poking motion. In the case of the solution using a jack screw according to the invention, no such auxiliary systems are required since the position of the control sleeve 5 is clearly determined by the gear ratio of the jack screw 13 and the rotation speed and running time of the motor and can therefore easily be adjusted with the aid of the control unit 15.

In the poking operation, the control sleeve 5 according to the invention moves at an axial speed of around 20 mm/s, which calls for a relatively high gear ratio of the jack screw 13. A gear ratio of at least 1:5 and preferably 1:7 has here been found to be suitable for the powerful removal of even seriously solidified coatings in the air port 3.

The invention offers a host of major advantages over known solutions using compressed-air driven systems. The solution according to the invention yields, for example, 2-3 times greater compressive force than corresponding compressed-air driven systems, which means significantly more reliable removal of the coatings in the air ports. The solution further offers a compact equipment unit with few vulnerable mechanical parts and quiet and powerful running.

The positional adjustment of the control sleeve 5, which positional adjustment is easy to handle and reliable compared with known compressed-air systems, facilitates in large measure the complicated and, relative to adjacent control members 5, related positional adjustment which is required in applications in soda pans where it is wished to use the so-called ROTAFIRE\-method, in which case, by virtue of a specially regulated air supply, a rotation or vortex motion of the combustion gases is created in the horizontal plane of the soda pan, so that the waste liquor injected into the furnace chamber is slung by the said vortex motion out towards the walls 2 of the furnace, whilst simultaneously undergoing drying and pyrolysis. This application is illustrated in Fig. 3, which shows a horizontal section through a rectangular soda pan. It should however be noted that the soda pan can also be polygonal, such as an octagon, for example, whilst maintaining the function according to the invention. A plurality of ports 3 having associated control members 5 (not shown) are situated along the furnace walls 2, where the mutual axial position of the control members 5 is such that a vortex motion in the horizontal plane of the soda pan is realized by means of the combustion air supplied through the ports 3. More closely described, at least two of the furnace walls 2 are provided with their own individual aggregate 9 having ports 3, disposed alongside one another, with associated control members 5 (not shown), in which those control members 5 which are located on a first side of the centreline 12 of the aggregate have been positioned at a greater axial distance from their respective ports 3 than those control members 5 which are located on the other side of the said centreline 12, in such a way that the supplied combustion air makes a positive contribution to the said vortex motion. In the figure, the vortex motion is illustrated by the arrow 17 and the air currents which make a positive contribution to the vortex motion are indicated by the arrows 22, which flow out in the axial direction of the air ports 3. The air flow through the air ports 3 can be regulated within wide limits by individual positional adjustment of the control sleeve 5, whereupon the air flow from one aggregate 9, for example, in the figure the lowermost aggregate along the one longitudinal side of the furnace, is preferably introduced through, in the figure, the right part of the aggregate. By interaction with at least one further aggregate of air ports 3, situated on one of the other walls 2 of the pan, the vortex motion 17 is thus created in the manner described above. The rotational direction of the vortex motion can be turned at regular intervals in order to reduce unilateral wearing of the components of the hearth. This turning is realized by inverting the positional adjustments of the control sleeves 5, such that those ports 3 which were previously adjusted for low air flow are now instead adjusted for high air flow and vice versa. It can here easily be seen that the particularly simple and reliable positional adjustment of the control sleeves 5 according to the invention considerably facilitates the complicated regulation of the mutual axial position of the control sleeves 5. The same regulation using existing compressed-air driven systems requires expensive and difficult to manoeuvre positioning systems for the compressed-air driven cylinders.

One drawback with the previously known compressed-air driven systems is, as mentioned above, that the pressure of the compressed-air network often varies. If the pressure drops, the control sleeves then get stuck and can be burnt through. The electricity network, on the other hand, has no such variations and the poking force can therefore always be kept at the calculated level.

To sum up, the furnace with the device according to the invention offers considerably improved poking capacity and an extremely reliable way of positionally adjusting the control sleeve 5, and this, moreover, at lower cost compared with previously known devices. The inventor has succeeded in overcoming a technical prejudice by showing that electrically driven apparatus having suitable protection measures can be effectively used even in a very dirty environment exhibiting a high ambient temperature.

The invention is not limited to the embodiment described above and illustrated in the drawings, but can freely be varied within the scope of the following patent claims.

Claims

Furnace containing a device for manoevring an air control mechanism said furnace being of the soda furnace type used for the combustion of waste liquor, provided with a plurality of air-supply ports (3) in its walls (2), in which the said ports (3) communicate with an air box (4) and in which each port (3) is provided with a control member (5) which can be axially displaced forwards and backwards for positional adjustment relative to the said port for the purpose of determining the volume of air passing through the port, and in which the said control member (5) is additionally arranged to be moved past the set air-regulating position, so that its end (10) during a so called poking motion penetrates the port (3) in order to remove coatings which have been deposited in the said port,
characterized in that the control member (5) is connected to a, by an electric motor (14) driven, mechanical jack screw (13), with a gear ratio of at least 1:5, preferably 1:7, for the realization of the control member's (5) axial motions both for air-regulating positional adjustment and for the removal of in particular seriously solidified coatings.
Furnace containing a device for manoevring an air control mechanism according to Patent Claim 1, characterized in that the axial position of the control member (5) is clearly determined by the gear ratio of the jack screw (13) and the rotation speed and running time of the motor (14).
Furnace containing a device for manoevring an air control mechanism according to Patent Claim 1, characterized in that the mutual axial position of the control members (5) is such that a vortex motion in the horizontal plane is realized by means of the combustion air supplied through the ports (3).
Furnace containing a device for manoevring an air control mechanism according to Patent Claim 3, in which at least two of the furnace walls (2) are provided with their own individual aggregate (9) having ports (3), disposed alongside one another, with associated control members (5), characterized in that those control members (5) which are located on a first side of the centreline (12) of the aggregate have been positioned at a greater axial distance from their respective ports (3) than those control members (5) which are located on the other side of the said centreline (12), in such a way that the supplied combustion air realizes the said vortex motion.