Patent Description:
The method and device are advantageously used in an essential step in the production of chemical pulp. More specifically, said essential step relates to the recovery of pulp cooking chemicals from what is called black liquor, which is a rest product from such production in order to achieve chemical pulp with different specified properties. The chemical composition of these chemicals may, as a consequence, vary. The recovery takes place in a boiler wherein the temperature during the recovery process normally is in the order of about <NUM> (<NUM> °F). At said temperature, the remaining wooden fiber is burnt and the pulp cooking chemicals may be recovered. Before its introduction into the boiler, the black liquor is concentrated to a water solution which contains about <NUM>-<NUM> percent of solid material. This solution is then sprayed into the recovery boiler, which is a kind of a chemical reduction furnace. A chemical reduction furnace is a reactor wherein processes of evaporation, gasification, pyrolysis, oxidation and reduction, occur mutually dependently during recovery of the chemicals. Organic materials such as lignin and other wood extracts maintain the combustion in the furnace, and the heat that is produced dries the spent cooking chemicals as they fall to the floor or bottom of the boiler. Here the dried chemicals pile up into a char bed. The char bed is further heated to form a liquid smelt that is discharged through one or more discharge openings and smelt spouts in a lower part or bottom of the boiler.

The combustion process requires the introduction of large volumes of air into the boiler. This air amounts to about <NUM> percent of the material introduced in the boiler. The air is forced into the boiler from wind boxes or ducts disposed at several levels in surrounding relationship to the boiler, through a plurality of air inlet ports in the walls of the boiler, viz. : primary, secondary and tertiary air inlet ports. The primary air inlet ports, through which about <NUM> to <NUM> percent of the air is introduced, are disposed in the side walls in a lower portion of the boiler, close to the char bed. The secondary air inlet ports, through which about <NUM> percent of the air is introduced, are disposed around the boiler at higher level than the primary air inlet ports, and below the entry through which the black liquor is sprayed into the boiler. While the primary air inlet ports provide a relatively large volume of air with considerable turbulence for maintaining a fireball in the char bed, the secondary air inlet ports provide a finer control and distribution of air above the char bed and distribute the air evenly in the black liquor spray to support the combustion thereof. The black liquor sprayed into the boiler, having a consistency similar to heated oil, swirls, burns and falls towards the bottom of the boiler in the form of combustion products comprising char material and smelt.

Some of the smelt and char material that comes into contact with the wall of the boiler will be cooled by the inflowing air, thus building up deposits around the periphery of the air inlet ports. In accordance with customary practice, the char buildup is periodically dislodged, either manually by a worker inserting a rod into the air inlet ports, or by a mechanical cleaning apparatus. The dislodged char material falls into the smelt pool in the bottom of the boiler. A mechanical cleaning apparatus for cleaning air inlet ports in a recovery boiler is previously known from <CIT>.

Smelt spouts are on the other hand designed to drain the smelt from the boiler, and to keep the smelt pool at a safe level. If the smelt spout is not cleaned periodically, the smelt will oxidize and form a crust which will clog the smelt spout. Clogged smelt spouts can cause the level of smelt inside the boiler to rise, resulting in inefficient and unpredictable operation, resulting in a reduction in the amounts of chemicals that can be recovered, a decrease in the amount of steam produced per unit of fuel, and increased emission of noxious gases such as carbon monoxide and sulfur dioxide.

Smelt spouts of soda recovery boilers are often cleaned manually by a worker inserting a long metal rod into the spout. Vigorous lateral and reciprocating movements of the rod by the worker dislodges any char or oxidized encrusted smelt that will be clogging the spout. Such manual rodding of the smelt spout is inefficient and also extremely unsafe. The temperature of the smelt amounts to an order of <NUM>, and although the rods utilized to clean the spouts are usually up to six meters long or more, there is great danger that a worker who manually rods such smelt spouts can be burned. Smelt spout openings are, due to the high temperature, cooled by water circulating in jackets surrounding both the discharge opening of the boiler and the spout, and during rodding the water jackets can be ruptured by the manual rodding operation. A broken water jacket may result in an explosion of the boiler because of the volatility of the smelt in the presence of water. One cubic meter of water released results in <NUM> cubic meters of steam released in just a moment of time.

A mechanical device for cleaning a smelt spout and discharge opening in the wall of a soda recovery boiler is previously disclosed in <CIT>. A rod-shaped cleaning tool is rotationally arranged about its longitudinal axis in a carrier that is movably supported on wheels. The carrier and tool can be driven in reciprocating motion for moving the cleaning tool back and forth through the discharge opening and along the path of the smelt spout, which extends at a downwards slanting angle from the discharge opening in the boiler wall.

The present invention refers to an apparatus comprising a cleaning rod driven in reciprocating, axial extension and retraction movements upon cleaning a smelt discharge opening of a chemicals recovery boiler, wherein a linear actuator is controllable for driving the cleaning rod in the axial movements.

A cleaning apparatus of similar kind is previously known from <CIT> (see Figs. <NUM>-<NUM>). In a cleaning sequence of dislodging encrusted material from the smelt spout, the cleaning rod is freely pivoting on a trunnion mount to allow the rod to move upwardly or downwardly along the spout while the rod is extended or retracted by the linear actuator. In an attempt to avoid contact of the cleaning rod with the bottom of the smelt spout, <CIT> suggests that the cleaning rod be guided from a roller assembly that runs on edges of side walls to the smelt spout. It can however easily be foreseen that this solution may suffer badly from the harsh environment including high temperatures and splashes that would in practice hamper the operation of the roller assembly.

<CIT> discloses a cleaning rod which is sliding along the bottom of a smelt spout both in approach of a smelt discharge opening and in withdrawal therefrom. Axial movements of the cleaning rod are in both directions initiated by a drive means including linear actuators. The axial movements of the cleaning rod are accomplished by moving the entire cleaning apparatus back and forth. The cleaning apparatus is supported on a carrier which is moving on wheels that are guided on rails in the floor. The cleaning rod is pivotally journaled, however, pivoting of the cleaning rod is the passive result of the cleaning rod being advanced or retracted while sliding along the inclined bottom of the smelt spout. In compensation for consumption of the cleaning rod, a sensor is arranged to monitor a change in inclination of the cleaning rod between operative and rest positions. Readings from this sensor are used for incrementally extending the cleaning rod to desired length in separate operation, i.e. in an operation not being performed during the cleaning of the smelt spout.

It is an object of the present invention to provide an alternative and improved apparatus for cleaning smelt spouts and discharge openings in the wall of a chemicals recovery boiler.

Another object of the present invention is to provide a not only improved but fully safe method for cleaning smelt spouts and discharge openings in the wall of a chemicals recovery boiler by use of a cleaning apparatus that is installable for operation in alignment with a smelt spout and smelt discharge opening.

Another object of the present invention is to provide an improved cleaning apparatus and method aimed for increasing the operational stability of a chemicals recovery boiler.

Still another object of the present invention is to provide an improved cleaning apparatus and method aimed for reducing the exposure of workers to hazardous areas of a chemicals recovery boiler.

Yet another object of the present invention is to provide an improved cleaning apparatus that is safe to operate, and virtually eliminates the risk of rupturing the smelt spout during cleaning.

Still another object of the present invention is to provide an improved cleaning apparatus that is relatively light in weight and which can be manually installed or removed from a chemicals recovery boiler, quickly and easily as compared to prior art solutions.

It is finally an object of the present invention to provide a cleaning apparatus for installation in fixed or temporarily fixed relation to the smelt spout and discharge opening in the wall of a chemicals recovery boiler. Misalignment or dislocation caused by thermal expansion of the boiler body is thereby avoided or reduced to a minimum.

At least some of these objects are met in an apparatus comprising a cleaning rod driven in reciprocating, axial extension and retraction movements upon cleaning a smelt discharge opening of a chemicals recovery boiler, wherein a linear actuator is controllable for driving the cleaning rod in the axial movements. A pivot actuation means is controllable for pivoting the cleaning rod about an axis upon cleaning a smelt spout associated with the smelt discharge opening. One or more sensors are arranged to provide control basis for correlation of the axial movements with the change in pivot angle during pivoting of the cleaning rod.

The combination of movements and actuator control built into the cleaning apparatus so defined provide the technical and operative conditions required for automation, thus offering the possibility for avoiding hazardous, manual cleaning work. In that sense, the cleaning apparatus may be seen as an automatic or at least semiautomatic robot which only requires, at its utmost, a start signal from an operator to initiate a cleaning sequence.

If a fully automatic procedure is aimed for, this can be achieved by arranging the start of the cleaning sequence dependent on certain conditions relating to the chemicals recovery process. One such condition that can be monitored and forming a basis for commencement of cleaning is, e.g. the temperature in the smelt spout which can be monitored by a temperature sensor.

In one embodiment, the cleaning apparatus comprises one or more sensors monitoring at least one of the rod axial and pivoting movements, wherein the operation of at least one of the linear actuator and the pivot actuation means is based on output from the one or more sensors.

In one embodiment, the pivot actuation means is arranged for adjusting the speed of the pivoting movement based on readings from a rod axial motion sensor monitoring the axial movements during pivoting of the cleaning rod.

A rod axial motion sensor can be realized as one of: a proximity sensor; one or more limit switches or an end position sensor; or an encoder in a servomotor of the linear actuator, e.g..

The linear actuator is in one embodiment arranged for adjusting the speed of axial movement based on readings from an angle position sensor which is monitoring the change in pivot angle during pivoting of the cleaning rod.

An angle position sensor can be realized as one of: a set of light sensors or photo cells monitoring the pivot area of the cleaning rod; a fixed position video camera with associated image processing software; or an encoder in a servomotor of the pivot actuation means, e.g..

The axial and pivoting movements can thus both be actively controlled and balanced such that speed or amount/length of axial travel is proportionate to applied speed or amount of change in angular position during pivoting. In this disclosure, the coordination of axial and pivoting movements is defined as "correlation", in order to underline that each movement depends on the other.

This correlation between axial and pivoting movements provides the technical effect and advantage that damage to the smelt spout can be avoided by ensuring that the cleaning rod travels along the smelt spout under maintenance of a clearance to the metallic bottom of the smelt spout.

The cleaning apparatus may be arranged for supporting the cleaning rod in permanent or temporary alignment with the smelt spout and the smelt discharge opening. These features provide the optional implementation of one cleaning apparatus per each smelt spout/discharge opening in the boiler, or the choice of successively cleaning the smelt spouts/discharge openings by use of a movable cleaning apparatus that can be shifted from one smelt spout to the other.

In one embodiment, the cleaning apparatus is supported in a fixture that is connectable to the boiler. In alternative embodiments the cleaning apparatus may be supported in a fixture which is freestanding from the boiler, although it may be located in fixed relation to the boiler.

These features can be alternatingly applied in set-ups where boiler movement caused by thermal expansion needs to be accounted for. Thus, in the first mentioned alternative the cleaning apparatus is arranged to follow any movement of the boiler that is due to thermal expansion, whereas in the second alternative thermal expansion is not allowed to affect the suspension and alignment of the cleaning apparatus.

In one embodiment a fixture frame comprises, in a side facing the boiler, positioning means mating with corresponding positioning means arranged on an adapter that is connectable to the boiler.

This embodiment ensures a correct alignment with the smelt spout and discharge opening through a forced mating between the cleaning apparatus and a docking member attached to the boiler.

The following features and details define advantageous embodiments of the cleaning apparatus:
The cleaning rod is supported in a swing that is pivotally arranged between a couple of arms, one end of which, respectively, is anchored in the fixture or the boiler wall.

In one embodiment, the swing comprises a rack and pinion drive, or a ball-screw, or a trapezoidal threaded bar mechanism operable for moving a driver, in which the cleaning rod is anchored for axial movements in extension and retraction.

In one embodiment, the change in angular position of the cleaning rod is monitored by an angle position sensor which is operatively coupled to a pivot axis of the cleaning rod or the swing.

The pivot actuation means may be an angular actuator or a linear actuator.

The cleaning apparatus may be pivotally connected to the boiler.

In one embodiment, the cleaning rod is pivotally supported in the outer ends of a couple of arms, the inner ends of which are pivotally journaled at the boiler.

The latter embodiment provides overload protection for the cleaning apparatus, in particular for the components of a cleaning rod drive mechanism included in the cleaning apparatus.

A pivotal connection of the cleaning apparatus to the boiler further adds to the protection of the smelt spout by permitting the cleaning apparatus to "lift" from the spout in case the cleaning rod, accidentally, would hit heavily against the bottom of the smelt spout.

The objects of the invention are likewise met in a method of cleaning a smelt spout and a smelt discharge opening of a chemicals recovery boiler by using a cleaning apparatus comprising a cleaning rod driven in reciprocating, axial extension and retraction movements, wherein the method comprises: sequentially extending and retracting the cleaning rod in a step of cleaning the smelt discharge opening; and pivoting the cleaning rod in a step of cleaning the smelt spout, wherein axial movements are correlated with the change in pivot angle during pivoting of the cleaning rod based on readings from one or more sensors.

More precisely, in one embodiment, the speed of the axial movement is increased progressively with increasing pivot angle.

In an alternative embodiment, the method comprises the steps of:.

During the pivoting motion, the tip of the cleaning rod is advantageously maintained at a distance within about <NUM> to <NUM> from the bottom of the smelt spout, or at a minimum distance of about <NUM> to <NUM> from the bottom of the smelt spout.

In a further step of automation of the cleaning process, initiation of a cleaning session is based on readings from a temperature sensor that monitors the temperature in the smelt spout.

The invention will be further explained below with reference made to the accompanying, schematic drawings, wherein.

With reference to <FIG>, a chemicals recovery boiler <NUM> is shown schematically. The boiler <NUM> is suspended from an upper structure <NUM> of a building that houses the boiler. A cooling jacket, indicated by reference number <NUM>, is typically arranged on the exterior of the boiler. The cooling jacket <NUM> typically comprises an array of conduits in which water is circulated. Smelt products can be discharged from the boiler via a smelt spout <NUM> that extends at a downwards slanting angle from a smelt discharge opening <NUM> in the wall <NUM> of the boiler <NUM>. The smelt spout <NUM> is typically oriented in a plane that is perpendicular to the boiler wall <NUM>. In fact, a number of smelt spouts <NUM> and discharge openings <NUM> may be distributed around the body of the boiler.

In <FIG>, the smelt spout <NUM>, discharge opening <NUM> and a cut out portion of the boiler wall <NUM> are shown in a side view, substantially in parallel with the boiler wall. <FIG> shows the smelt spout of <FIG> in a front view, perpendicularly to the boiler wall. The solid black string and plug in <FIG> is a schematic representation of smelt material which has cooled down in the smelt spout and is clogging the discharge opening. In <FIG>, reference number <NUM>' points to the bottom of the smelt spout <NUM>.

Since encrustation of smelt in the smelt spout is usually related to the temperature in the smelt, the necessity of cleaning the smelt spout from encrustations can be determined by monitoring the temperature in the smelt spout. To this purpose a temperature sensor <NUM>" may be arranged on the smelt spout. A heat camera may alternatively be arranged to measure the temperature in the smelt that is pouring down the spout. The readings from the temperature sensor <NUM>" or heat camera can form the basis for an automatic initiation of a cleaning session, if appropriate.

An apparatus <NUM> arranged for cleaning and removing encrusted material from the discharge opening <NUM> and from the smelt spout <NUM> will now be described with reference made to the left and right-hand perspective views of <FIG> respectively. The subject embodiment of the cleaning apparatus <NUM> comprises a frame including two parallel arms <NUM> and <NUM>, reaching from an inner end that is pivotally journaled at the boiler wall <NUM> to an outer end which provides pivotal suspension of a drive mechanism <NUM> for a cleaning rod (which later will be described). More precisely, in the illustrated embodiment the arms <NUM> and <NUM> are pivotally journaled in a fixture frame <NUM> which is arranged to be connected to the boiler wall <NUM>.

The fixture frame <NUM> is a box-like design comprising left and right support sections <NUM> and <NUM>, defining between them a central slot <NUM> which is dimensioned to receive an upper end of the smelt spout <NUM> as the fixture frame <NUM> and cleaning apparatus <NUM> are aligned with the smelt spout and the discharge opening <NUM>.

Each support section <NUM> or <NUM> comprises a set of reinforcement elements <NUM> designed to take up the load from the cleaning apparatus via a sub-frame <NUM>, by which sub-frame the inner end of each arm is journaled pivotally in the fixture frame <NUM>, on a pivot <NUM> respectively. To be more specific, the sub-frames <NUM> extend below the arms <NUM> and <NUM> so as to support the cleaning apparatus <NUM> in a mainly horizontal position from which the cleaning apparatus is permitted to move pivotally upwards, for reason which will be discussed below.

As disclosed herein, basically, the arms <NUM>, <NUM> can be designed as self-supported or cantilever members. However, in alternative embodiments, the free outer ends of the arms <NUM> and <NUM> may be supported from the boiler building, such as suspended in ropes hanging down from a structural element in the building. If appropriate, suspension of the outer ends of the arms <NUM> and <NUM> may include a degree of elasticity, such as through tension springs inserted in supporting ropes, e.g..

The cleaning apparatus <NUM> can be arranged for permanent or temporary alignment with the smelt spout <NUM> and the discharge opening <NUM>. In this connection, alignment refers on one hand to the orientation of the cleaning apparatus in parallel with the smelt spout as seen in a horizontal plane, and to the positioning of the cleaning apparatus with respect to the vertical height of the smelt discharge opening on the other hand.

In permanent alignment, the fixture frame <NUM> can be mounted to the boiler wall or to any structural element which is attached to the boiler wall. Permanent alignment may alternatively foresee that the cleaning apparatus is stationary supported in a structure that is freestanding from the boiler. An example of the latter is given in <FIG>, for the purpose of illustration. In this embodiment, the arms <NUM>' and <NUM>' are designed as angled consoles, depending from a fixture beam <NUM>'. The beam <NUM>' may be anchored in a structural element of the boiler building or may itself constitute a structural element of the building. In the embodiment of <FIG> the vertical height can be adjusted by arranging the arms <NUM>', <NUM>' extendable as suggested through the bolt and long-hole connection <NUM>'. Suspension of the cleaning apparatus on bolts which are inserted through oblong holes formed in the arms <NUM>' and <NUM>' further provides a form of overload protection to prevent excessive loads from being transmitted to the components of the cleaning apparatus by permitting the cleaning apparatus to move upwards while sliding on the bolts.

In temporary alignment, the cleaning apparatus may be movably supported in a structure that is freestanding from the boiler, or movably supported in a structure that is connectable to the exterior of the boiler. In a case where the cleaning apparatus is to be moved from one smelt spout to another in sequential cleaning operations, e.g., the cleaning apparatus may be arranged movable on a rail that runs horizontally at a fixed distance from the boiler. Such a rail can be supported in structural parts of the boiler building, or supported on the exterior of the boiler.

Albeit there are several options available for a skilled person to adapt the suspension of the cleaning apparatus to a specific boiler application through a corresponding design of supporting structures, an essential aspect and requirement in any application is the correct alignment between the cleaning apparatus on one hand, and the smelt spout and discharge opening in the boiler wall on the other hand. Affordable tolerances in this respect should preferably be defined in millimeters in order to avoid harmful contact with the boiler wall and the smelt spout during the cleaning operation.

In the embodiment of <FIG>, the required precision is achieved in that the cleaning apparatus <NUM> is arranged for docking with an adapter element <NUM> that is mountable on the boiler. A correct alignment and positioning, horizontally as well as vertically, is accomplished by mating the fixture frame <NUM> with positioning means <NUM> formed on the adapter element <NUM>. The positioning means <NUM> can be realized in the form of studs <NUM>, which project from the adapter element <NUM> for insertion in corresponding holes <NUM>' that are formed in the opposite side <NUM> of the fixture frame, facing the boiler and the adapter element. The studs <NUM> can be threaded bolts for permanent connection of the cleaning apparatus <NUM> to the boiler wall/adapter element. Of course, any suitable interacting means and guides, besides the mentioned studs or bolts and stud or bolt holes, may be used to urge the cleaning apparatus into mating position with the smelt spout and the discharge opening.

In the outer end of the arms <NUM> and <NUM>, the drive mechanism <NUM> for a cleaning rod is arranged to pivot about an axis S which is defined by a couple of pivot pins (invisible in <FIG>, but one is shown in <FIG> and here denoted by its reference number <NUM>). The pivot pins <NUM> are journaled in a couple of console elements <NUM> and <NUM>, each of which is attached in an outer end of an arm <NUM> or <NUM> respectively. Between these console elements, a swing <NUM> is suspended pivotally by its mounting to the pivot pins <NUM>, which are coupled to the opposite, longitudinal sides of the swing.

The swing <NUM> comprises a chassis frame <NUM> having longitudinal and transverse frame members. Inside the chassis frame <NUM>, a driver <NUM> is arranged to slide on a couple of guide bars <NUM> and <NUM> that are extended in the length of the chassis frame, between the transverse frame members. The driver houses a couple of slide bearings <NUM> and <NUM> which are journaled on the associated guide bars <NUM> and <NUM>. Between the slide bearings, a threaded nut <NUM> is non-rotationally affixed to the driver <NUM>. A threaded bar <NUM> passes the nut in threaded engagement. One end of the bar <NUM> is rotationally journaled in the inner end of the chassis frame, whereas the opposite end of the bar <NUM> projects from the chassis frame for operative engagement with an actuator <NUM> which is controllable for rotation of the bar <NUM> in either direction of rotation. The nut <NUM> and the bar <NUM> can be realized as a ball-screw. The nut <NUM>, the bar <NUM> and the actuator <NUM> function similar to a rack and pinion drive operable for moving the driver <NUM> in rectilinear, reciprocating motion, i.e. in extension and retraction motion, along the guide bars, by controlling the direction of rotation in the actuator <NUM>. In that sense the actuator <NUM> is a linear actuator <NUM>.

The linear actuator <NUM> advantageously includes a servomotor with encoder that provides feedback on the revolutions of the motor axis to a control system that correlates the operation of the linear actuator with the operation of a pivot actuation means, as will be further described hereinafter.

The driver <NUM> further includes structural members in the form of a couple of plates <NUM> and <NUM>, which are interconnected through the housings <NUM> and <NUM> that accommodate the slide bearings <NUM> and <NUM>. As is best seen in <FIG>, these plates <NUM> and <NUM> project below the chassis frame <NUM> to provide an anchorage for a cleaning rod <NUM> under the swing. Obviously, the driver may alternatively be shifted <NUM>° for holding the cleaning rod above the swing, if appropriate. A support bracket (not illustrated) may optionally be arranged in the inner end of the chassis frame to help guiding the cleaning rod in its back and forth movement. The cleaning rod <NUM> is an elongate, solid or tubular element.

In this connection, it can be pointed out although not explicitly illustrated in the drawings, that the cleaning rod <NUM> may be anchored in the driver <NUM> by means of elastic elements, such as rubber or polymer bushings, in order to prevent shocks from impact with encrusted material to be transferred to the components of the drive mechanism. It serves also to be mentioned, although not being an essential part of the present invention, that the cleaning rod may be arranged for carrying exchangeable cleaning tools in its forward end or tip <NUM>'.

Pivoting of the cleaning rod drive mechanism <NUM> is accomplished and controlled through a pivot actuation means. In the embodiment of <FIG> the pivot actuation means comprises an angular actuator <NUM> which is drivingly coupled to one of the pivot pins <NUM>. An angle position sensor <NUM> may be realized as an incremental encoder which monitors the change in pivot angle about the pivot axis S, and thus provides an indication of the angular position of the cleaning rod. The angular actuator <NUM> and the angle position sensor <NUM> are thus both operatively coupled to the pivot axis S of the swing <NUM>. The readings made by the sensor <NUM> form the basis for controlling the operation and supply of power to the angular actuator <NUM>.

However, the readings made by the angle position sensor <NUM> are also used for controlling the speed or amount by which the cleaning rod <NUM> is retracted or extended upon pivoting of the cleaning rod <NUM>.

In this connection, reference is made to <FIG> for alternatives to the angle position sensor <NUM> depicted in <FIG>.

When the cleaning rod drive mechanism is pivoted for cleaning the smelt spout by running the tip <NUM>' of the cleaning rod along the spout, the axial movement of the cleaning rod is correlated with the change in its angular orientation in order to compensate for change in the distance between the bottom of the spout and the cleaning rod as the latter is swung about the pivot axis S. If for example the swinging motion is made at constant speed, then the speed of axial movement may need to be increased, in some cases increased progressively, towards the end of the spout.

An example of the correlation between the axial and pivotal movements of the cleaning rod is illustrated in the diagram of <FIG>. The curve in the diagram represents the acceleration of the retraction movement (x) as a function of increasing pivot angle (ϕ).

The diagram of <FIG> intends to illustrate the functionality built into the cleaning apparatus for ensuring that there is always a clearance maintained between the metallic spout bottom and the tip of the cleaning rod. However, depending on the prevailing geometrical conditions, the correlation between the axial and pivotal movements of the cleaning rod may show other characteristics than those shown in <FIG>. In other alternatives, e.g., it may be more appropriate to apply a constant retraction or extension of the cleaning rod while adjusting the velocity of the pivoting motion by regulation of the power that is supplied to the pivot actuation means.

In all cases, the correlation is computed in a control unit running a software coded routine which uses the dynamic inputs from one or more sensors or detectors together with, e.g., static data, such as the spatial coordinates and inclination of the smelt spout and the maximum extension of the cleaning rod, which can be used to initiate the pivoting motion. Instead of static data or in combination therewith, proximity sensors may be used to define continuously the position of the cleaning rod in extension and retraction modes.

The readings from the sensors or detectors are thus used for controlling the operation of the linear actuator <NUM> and/or the pivot actuation means <NUM>, <NUM> in order to correlate and synchronize the axial and pivotal movements of the cleaning rod. This correlation may include not only a controlled retraction of the cleaning rod, but also a controlled extension of the cleaning rod if required, depending on the subject geometries. In typical cases, the correlation includes controlling the power supply, running time and rotational direction in the linear and/or pivot actuator means so as to maintain the tip of the cleaning rod at a minimum distance of about <NUM> to about <NUM> from the bottom of the smelt spout. In some cases, the distance may vary within about <NUM> to about <NUM> from the bottom of the smelt spout (depending, e.g., on the amount and status of the encrustations which are blocking the smelt spout).

For example, readings by sensors for detecting the angular and axial position of the cleaning rod can be recorded in the control unit during a first setup run wherein the cleaning rod is pivoted along the smelt spout at defined force. The recorded data is thereafter used for controlling the linear actuator <NUM> and the angular actuator <NUM> in successive strokes wherein the cleaning rod is pivoted along the smelt spout with controlled motion and force.

The operation of the cleaning apparatus during a cleaning session is schematically illustrated in the sequential views of <FIG>. Accordingly, in <FIG>, the double arrow x-y illustrates the axial movements (extension (y) and retraction (x)) of the cleaning rod during cleaning of the smelt discharge opening <NUM>.

This motion is mainly horizontal, meaning that the orientation of the cleaning rod preferably lies within a few degrees' interval over or under the horizontal plane. In fact, the expression "mainly horizontal" shall be understood to include a deviation from the true horizontal of less than +/- <NUM>°, such as within an interval of +/- <NUM>°, or even more preferred in the interval of +/- <NUM>° of elevation.

During the cleaning sequence depicted in <FIG>, the angular actuator <NUM> is inactive whereas the linear actuator <NUM> may be alternately driven in both directions of rotation for either extension or retraction of the cleaning rod. In alternative embodiments, the cleaning rod may optionally be arranged for turning around its own axis as is known in the art, in order to facilitate cleaning all parts of the periphery of the discharge opening.

In the sequence (<FIG>) of removing solid or encrusted material from the smelt discharge opening, the cleaning rod may need to be repeatedly retracted and extended until it penetrates the opening. In order to protect the components of the cleaning rod drive mechanism from excessive load the whole assembly may be lifted by pivoting at the pivot points <NUM> which journal the arms <NUM>, <NUM> to the boiler wall <NUM> or to the fixture frame <NUM>. This protective action is indicated by the dashed arrow L in <FIG>.

An overload protection for the cleaning rod drive mechanism may alternatively include a resilient and elastic anchoring of the inner arm ends in the fixture frame <NUM>, or as a third alternative, a resilient and elastic attachment of the console elements <NUM> and <NUM> to the outer ends of the arms <NUM> and <NUM>.

<FIG> illustrates the sequence of cleaning the smelt spout <NUM> by running the tip of the cleaning rod down the smelt spout. Since the cleaning rod tip passes along the smelt spout with a few millimeters' clearance to the smelt spout bottom, a small rest of encrusted material may remain in the bottom of the smelt spout also after the cleaning rod tip has passed. This way, the thin layer of encrusted material which remains in the bottom of the smelt spout protects the spout bottom from the hot smelt that will pour down the spout following upon a cleaning session.

During this sequence, the angular actuator <NUM> is operated for pivoting the cleaning rod as shown by the arrow ϕ, whereas the linear actuator <NUM> is controlled for retraction x of the cleaning rod, in synchronization with the pivoting motion as previously explained.

In this connection it should be observed that the speed of the pivoting motion may be adapted to the flow velocity of the smelt in the smelt spout in order to avoid splatter.

After completed cleaning, the cleaning apparatus is returned to its initial position by reversed operation of the angular actuator <NUM> as illustrated by the arrow R in <FIG>.

The same modus operandi is performed by the slightly modified embodiment shown in <FIG>. The only difference from the previous embodiment is that in the embodiment of <FIG>, the pivot actuation means is a linear actuator <NUM>, such as a piston-cylinder unit, instead of the angular actuator <NUM>.

The linear and angular actuators <NUM>, <NUM> and <NUM> may be realized as double-acting or reversible operation drives, powered by air, hydraulic fluid or electricity. The angular actuator <NUM> may alternatively include a single acting, spring return piston/cylinder unit.

In yet an alternative, an external spring may be applied outside the angular actuator, and more specifically for either of two alternative purposes: i) external spring(s) applied and dimensioned for returning the cleaning apparatus to its initial position, or ii) external spring(s) applied and dimensioned to provide a more even load and thus avoiding load peaks in the angular actuator as the cleaning rod tip travels down an unevenly encrusted smelt spout.

In <FIG>, a torsion spring <NUM> is shown in unloaded state (<FIG>) and loaded state (<FIG>) respectively. The spring <NUM> is arranged to apply a counter force that is centered about the pivot axis S as the cleaning rod and cleaning rod drive mechanism are pivoted downwards. For example, one such spring <NUM> can be supported on each pivot pin <NUM> that journals the swing <NUM> to the arms <NUM> and <NUM> respectively. The spring <NUM> comprises a couple of legs <NUM> and <NUM>, which are actuated upon by a couple of pins <NUM> and <NUM>. A first pin <NUM> is stationary arranged on the inner side of the arm <NUM> or <NUM> and serves for arresting the leg <NUM>, whereas a second pin <NUM> is arranged on the outer side of the swing <NUM>, opposite the inside of the arm, the second pin engaging the leg <NUM> for tensioning of the torsion spring <NUM> in the pivoting motion of the swing (<FIG>). The torsion spring <NUM> can be dimensioned to serve either purpose i) or ii) as discussed above.

With reference to <FIG>, the change in angular position of the cleaning rod <NUM> can alternatively be monitored by optical detectors <NUM> overviewing the pathway of the cleaning rod during the pivoting motion. Optical detectors may be realized as light transmitters and receivers arranged transversally to the plane of the pivoting motion. An optical detector of the change in angular position may alternatively be realized as a fixed position video camera <NUM> with associated image processing software.

The change in angular position may alternatively be detected indirectly by means of a proximity sensor <NUM> that detects a change in axial position of the cleaning rod <NUM>. Given the geometrical conditions on the site of operation, the control software can be programmed to adapt the pivoting motion to the change in axial position by corresponding control of the pivot actuation means, such that the tip of the cleaning rod can follow closely the inclination of the smelt spout.

With further reference to <FIG>, reference number <NUM> denotes an encoder included in the linear actuator <NUM> and which registers the number of revolutions made by the motor of the linear actuator, whereas reference number <NUM> denotes one or several end position sensors or limit switches that either detect an end position or detect the moment at which the cleaning rod <NUM> runs free of the smelt spout <NUM>, and/or detect any intermediate axial position of the cleaning rod. Reference number <NUM> refers to an encoder associated with the angular actuator <NUM>.

From the above description it will be realized, that the present cleaning apparatus and method shall not be strictly limited to use and application in connection with recovery of pulp cooking chemicals from black liquor in soda recovery boilers, but that the apparatus' structure and operation is likewise useful in connection with any similar process performed in chemicals recovery furnaces and boilers in general.

Claim 1:
An apparatus (<NUM>) comprising a cleaning rod (<NUM>) arranged for cleaning a smelt spout (<NUM>) and a smelt discharge opening (<NUM>) of a chemicals recovery boiler, supported in a chassis frame (<NUM>), the chassis frame forming a swing (<NUM>) that is pivotally supported about a pivot axis (S) between the outer ends of two arms (<NUM>, <NUM>), the arms extending in parallel, the apparatus further comprising a pivot actuation means (<NUM>; <NUM>) acting on the swing (<NUM>) and controllable for pivoting the swing (<NUM>) and the cleaning rod (<NUM>) about the axis (S), characterized in that a linear actuation means (<NUM>) supported in the swing (<NUM>) is operable for driving the cleaning rod (<NUM>) in reciprocating, retraction and extension movements (x, y) respectively, in the axial direction of the cleaning rod (<NUM>), and wherein one or more sensors (<NUM>; <NUM>-<NUM>) are arranged to provide control basis for correlation of the axial retraction movement (x) of the cleaning rod (<NUM>) with the change in pivot angle (ϕ) of the cleaning rod (<NUM>) during downwards pivoting of the cleaning rod upon cleaning the smelt spout (<NUM>).