CN105358716A - Foundry equipment and method of controlling said equipment - Google Patents

Abstract

A method or plant for dry slag granulation of hot liquid slag using a casting plant comprising an endless conveyor with a plurality of casting moulds arranged to move the casting moulds in a first section from a slag pouring zone through a cooling zone to a discharge zone and back to the slag pouring zone in a second section, the method comprising the following successive steps: pouring a quantity of hot liquid slag into the casting mould in position N in a slag pouring zone; moving the casting mould containing the hot liquid slag to a position N + N within the cooling zone; adding solid metal particles to a casting mould containing hot liquid slag in a position N + N by throwing a determined quantity of said metal particles from a distribution device arranged above said mould and comprising at least one hopper for storing said solid metal particles; discharging the cooled solidified slag from the mould in a discharge zone, wherein the actual amount of hot liquid slag poured into the casting mould is measured in a position between N and N + N, wherein the movement speed is adjusted based on the measured amount of hot liquid slag, wherein the amount of metal particles is determined based on a fixed slag/metal particles ratio, wherein the amount of metal particles added by the dispensing device is controlled by opening at least one driven sliding gate provided at the hopper outlet during a time determined based on said speed, and wherein the opening degree of the at least one driven sliding gate is determined based on the determined amount of metal particles, the determined opening time and the characteristics of the at least one sliding gate.

Description

Foundry equipment and method of controlling said equipment

technical field

The present invention generally relates to the granulation of slag (slag) from the metal industry and more particularly from the iron industry.

Background technique

Traditionally, metallurgical slags are granulated in water.

Water quenching ensures rapid solidification of metallurgical slags, which is a necessary condition for obtaining valuable products in the case of blast furnace slags. The hot liquid slag stream is first fragmentized with a water jet into very small particles and these particles are transferred to a water tank. The energy from the hot slag is extracted by direct contact between the hot liquid slag and the water. Since this has to take place at ambient pressure, the temperature of the slag drops immediately to a temperature level below 100°C.

However, the main disadvantage of the water granulation process is that the sulfur contained in the hot liquid slag reacts with the water and generates sulfur dioxide (SO ₂ ) and hydrogen sulfide (H ₂ S).

Furthermore, it must be noted that care must be taken to reduce the temperature of the slag sufficiently fast enough to obtain a vitrified or amorphous slag rather than to obtain a (partially) crystalline slag, which is disadvantageous in the market Lose a lot of price (about 15 times).

It may also be desirable to recover at least some of the heat from the slag in a usable form. In order to exploit this possibility in an efficient manner, it is necessary to rapidly cool the slag to a temperature level that is low enough to make handling of the material easier, but high enough to conserve energy at usable levels .

One possibility to overcome the disadvantage of generating toxic gases and recover at least part of the heat consists in mixing liquid slag with cold slag particles of the same chemical composition. The slag can then undergo heat recovery in a heat exchanger. However, it has been found that due to the high viscosity of the liquid slag it is not easy to mix the cold slag particles with the liquid slag and it is therefore not possible to cool the liquid slag fast enough to obtain vitrified slag.

Another approach to adding (cold) solid metal particles to hot liquid slag has been proposed (WO2012/034897, WO2012/080364). As a result, the slag solidifies rapidly in a glassy state without producing toxic gases. Furthermore, solid metal particles are chemically inert and can be easily separated, recycled and reused (see WO2012/034897). Finally, the heat from both the solidified slag and the metal particles can be recovered into suitable means such as heat exchangers (see WO2012/080364).

In practice, however, the efficiency of the above solutions is highly dependent on proper pouring of the slag and correct dosing of the metal particles. Said efficiency is even worsened by the fact that unless technically complex or energy-demanding additional equipment (such as actual slag filling level determination devices in newly filled molds, conveying of heated or refractory linings) is foreseen ladles and/or equivalent), otherwise the inflow of liquid slag cannot normally be controlled. Any suitable metering of metal particles becomes complicated and even unstable without such additional measures.

technical problem

It is an object of the present invention to provide a method for dry slag granulation and a corresponding device which allow benefiting from reduced environmental impact and increased energy recovery potential while being easy to implement and safe and efficient to use .

Contents of the invention

In order to achieve this object, the invention proposes a method for dry slag granulation of hot liquid slag using a casting plant comprising a circulating conveyor with a plurality of casting moulds, the circulating conveyor being arranged to move said casting molds in a first section from a slag pouring zone through a cooling zone to a discharge zone and return said casting molds in a second section to said slag pouring zone, said method comprising the following successive steps :

a) pouring a certain amount of hot liquid slag into the casting mold in position N in said slag pouring zone,

b) moving the casting mold containing said hot liquid slag into position N+n in said cooling zone,

c) adding said solid metal particles to said casting mold containing said hot liquid slag in position N+n by dropping a defined amount of said solid metal particles into said mold from a dispensing device, said a dispensing device is arranged above said mold and comprises at least one hopper for storing said solid metal particles,

d) discharging cooled solidified slag from said mold at said discharge zone,

wherein the actual amount of hot liquid slag poured into said casting mold in step (a) is measured at a position between N and N+n, where n is a number between 1 and 10, preferably between 1 to 4, most preferably n is 2,

wherein the moving speed V of the _{casting machine} in step (b) is adjusted on the basis of the measured amount of hot liquid slag,

wherein the amount of metal particles required for step (c) is determined based on a fixed slag/metal particle ratio λ,

wherein the amount of metal particles added by said distributing means in step (c) is controlled by opening at least one actuated sliding door provided at the outlet of said hopper during a time t determined on the basis of said speed V _caster , And wherein, the opening x of the at least one actuated sliding door is determined based on the determined amount of metal particles, the determined opening time t and properties of the at least one actuated sliding door.

As already mentioned, the main reason for the difficulties faced in practice is that not only the uncontrollability of the slag, but also the variable flow of the slag has to be dealt with, while it is important to have a certain ratio between the slag and the metal particles.

The main advantage of this method is that by simply measuring the amount of hot liquid slag inside the casting mold after step (a) and before step (c), the entire process can be controlled.

First, this measurement is used to control the amount of liquid slag in the mould. In fact, it seems clear that the mold of the circulating conveyor should be filled with a suitable (maximum) amount of slag which leaves enough space in the casting mold for the fixed slag/metal particle Add a certain amount of metal particles than λ. Thus, the measurement of the amount of hot liquid slag allows controlling said amount by adjusting the speed of the conveyor, for example by slowing the speed of the conveyor when the amount is lower than the expected (appropriate) amount, and when the amount of liquid slag exceeds The amount is controlled by accelerating the conveyor when the (appropriate) amount is expected. If the amount of liquid slag is approximately the expected amount, no speed adjustment is required.

Second, the above-mentioned measurement of the amount of liquid slag is used to determine the actual required amount of metal particles for that particular foundry mould.

In another aspect, the invention also proposes an apparatus for dry slag granulation of hot liquid slag, said apparatus comprising a circulating conveyor with a plurality of casting moulds, said circulating conveyor being arranged to take the first Moving said casting molds in one section from a slag pouring zone through a cooling zone to a discharge zone and returning said casting molds in a second section to said slag pouring zone, and wherein said apparatus further comprises:

a distribution device arranged in the cooling zone above the mold at position N+n and comprising at least one hopper for storing solid metal particles, the distribution device comprising a at least one sliding door at the outlet, the actuation of which allows controlling the amount of metal particles dispensed by the dispensing device,

At least one sensor capable of measuring the actual amount of poured hot liquid slag in the casting mold in a position between the slag pouring position N and the metal particle addition position N+n, where n is between 1 and 10 between numbers, preferably between 1 and 4,

A control unit to: adjust the moving speed of the conveyor V _caster based on the measured amount of hot liquid slag; determine the amount of metal particles to be added by the distribution device based on a fixed slag/metal particle ratio λ necessary amount; controlling the amount of metal particles to be added by said distribution means by opening said at least one actuated sliding door provided at the outlet of said hopper during a time t determined on the basis of said speed V _caster ; and The opening x of the at least one actuated sliding door is determined based on the determined amount of metal particles, the determined opening time t and properties of the at least one sliding door.

In the context of the present invention, it should be noted that the conveyance of the mold in the pouring zone and in the cooling zone is preferably substantially linear, ie the one or more inclination angles are substantially constant in the pouring zone and in the cooling zone. Furthermore, in this context the position indicated relative to the position N of the mold being filled in the slag pouring zone is merely exemplary. In fact, the actual position of the distribution device in the position indicated here by N+n may be located at a distance d which is not a multiple of the length l of the mold, i.e. when the mold in position N is located in a slagrunner (out of slag trough), the filling of metal particles into the mold in position N+n does not necessarily occur. Thus, the distance d between the mold being filled in the slag pouring zone and the distribution device may be any distance between 0.1 l and 9 l, preferably between 0.5 l and 3 l, in particular about 1 l (i.e. n is about 2 ). In practice, only the lower value of the distance d is limited to allow measurement of the actual amount of hot liquid slag poured in the casting mould. The upper limit generally depends on the fact that the slag should still be in a sufficiently liquid state to allow proper infiltration of metal particles into the slag.

In another aspect of the invention, the method or the apparatus further comprises: measuring the actual combined amount of slag and metal particles in the casting mold, i.e. the slag/particle mixture, in a position downstream of position N+n after step (c) the amount (of means); based on the measured combined amount of slag and metal particles and the previously determined amount of hot liquid slag to calculate the actual amount of metal particles added in step (c); and if the calculated actual amount of metal particles If the added amount does not correspond to the previously determined amount of metal particles, the properties of the at least one sliding door are adjusted.

The main advantage of this further preferred embodiment is that it allows adjustment (or Correction) the amount of metal particles.

Advantageously, the characteristic of said at least one sliding door comprises the mass flow rate of _particles ( _particles /x curve) as a function of said opening x, wherein said opening is the sliding door in the open and closed state (or substantially closed state, see below) must be moved. In fact, this parameter basically defines the amount of particles that flow through the sliding door per unit of time, depending on the opening of the sliding door. This parameter can be represented as a discrete curve and can be determined experimentally depending on the particular type of sliding door and the particular type of particles (see detailed description below).

In yet another embodiment, the actual amount of hot liquid slag poured into the casting mold after step (a) and/or the actual combined amount of slag and metal particles in the casting mold after step (c) is measured by of: determining the height h of slag in said mold, height h of _slag , of slag/metal particle _mixture , respectively; and calculating the corresponding volume V _slag and/or V _mixture based on the known shape of the foundry mould, and determining the mass M of slag _slag and/or determine the mass Mparticle' of the metal _particles based on the difference between _Vmixture and _Vslag .

Preferably, the amount is measured by measuring the height of the slag or slag/metal particle mixture within the casting mold contactlessly, eg by means of one or more laser distance meters. Other devices, such as radar, acoustic or optical detection devices, etc. may also be used.

In yet another aspect of the invention, the conveyor is preferably a so-called double-slope caster, wherein the amount of liquid slag in the mold can also be controlled by placing the first zone of the circulating conveyor The slag pouring zone in a section is arranged to convey the casting mold at a first inclination angle α which limits the effective maximum filling volume of the mold in the slag pouring zone to a value V _α , Any excess slag will be poured back to the upstream casting mold in position N-1, N-2 etc., and wherein the cooling zone is arranged with a second inclination angle β less than α such that all The effective maximum filling volume of the mold in the cooling zone has a value V _β greater than V _α .

Therefore, another advantage of an embodiment comprising such a double-slope conveyor is that the mold of the circulating conveyor is filled with a limited amount of slag. For a given mould, the limited amount of slag depends on the angle of inclination of the mold as it is being filled: the steeper the slope, the greater the amount of slag until the slag overflows or pours into the immediately adjacent mold or molds (i.e., at the mold being filled). the mold or molds immediately upstream) the less slag can be filled into the mold. Therefore, at an inclination angle α, the effective maximum filling volume (ie useful volume) can be defined as V _α . If the inclination angle is reduced (less steep or even horizontal), the actual fill level in the mold is reduced and the effective maximum fill volume (i.e. useful volume) of the mold is increased to V _β , thereby increasing the volume to be filled in the cooling zone. The added solid metal particles provide space. Therefore, if the inclination angle β in the cooling zone is lower than the angle α in the pouring zone, a theoretical maximum amount of metal particles corresponding to V _β - V _α can be added to the mold without risk of spillage or splashing .

In a preferred embodiment of the present invention, the inclination angle α in the slag pouring zone and the inclination angle β in the cooling zone are selected such that: the mold in the slag pouring zone The effective maximum filling volume _Vα is between 0.25 and 0.75 times the effective maximum filling volume _Vβ of the mold in the cooling zone, preferably between 0.30 and 0.60 times, even more preferably between 0.45 times to 0.55 times. In particular, the inclination angles α and β are chosen such that V _α is approximately 1/2V _β .

Although largely dependent on the geometry of the mold, in practice a suitable angle β is usually between 0° (horizontal) and 50°, more preferably between 10° and 40°, while the angle α Typically 5° to 20° greater than angle β.

Where a dual-slope conveyor is used, the casting mold movement can also be controlled by monitoring at least two (or more) immediately upstream of the casting mold being filled (positions N-1 and N-2) the temperature of the casting mold, and changing the moving speed in step (b).

Particularly preferably, the device is controlled by reducing step (b) if the temperature of the casting mold in position N-1 does not increase significantly due to lack of counterflow of hot liquid slag from position N (pouring position) and if the temperature of the casting mold in position N-2 increases due to the reverse flow of hot liquid slag from the casting mold in position N-1, increase the moving speed in step (b). Thus, in other words, if the temperature of the mold immediately upstream (N-1) of the mold being filled does not increase to a value close to the temperature of the hot liquid slag, i.e. has a temperature well below this value, no slag pours back, The filling of the mold is therefore sufficient at best, but may not be complete: the conveyor is then slowed down. On the other hand, if only the molds in N-1 are hot (containing liquid slag) and the molds in N-2 are not, then the speed of the conveyor is considered appropriate and no speed change is required. Finally, if not only the molds in N-1 but also the molds in N-2 become hot, the speed of the conveyor is too low and must be increased.

Monitoring of the temperature may be carried out by any suitable means, for example with a thermocouple or similar; however, it is preferably accomplished in a non-contact manner, for example by a pyrometer.

Another general problem associated with an uncontrollable and variable slag flow is that the addition of (determined amounts of) metal particles must be done within the deadlines imposed by the slag flow. Thus, the difficulty that arises is that the time available to introduce the required addition of metal particles into a partially filled casting mold is limited in the event that the conveyor needs to constantly move the mold further. Thus, an important advantage of the present method is that the use of a sliding door for metering the amount of solid metal particles allows rapid opening and closing, thereby greatly reducing the time required to introduce the correct amount of particles.

A suitable sliding gate (valve) typically comprises a sliding plate arranged to close the opening (in this case the outlet of the hopper) by pushing and/or turning the sliding plate, usually along a sliding frame located in front of the opening. The sliding of the plates can be achieved parallel to or preferably perpendicular to the conveying direction of the mould. Thus, in the context of the present invention, the sliding movement may be translational (such as a linear sliding door), rotational (such as a revolving sliding door; the axis of rotation is preferably parallel to or perpendicular to the plane formed by the opening) or even a combination thereof (eg curved sliding doors). Therefore, the related term "opening degree" used herein should be understood as the magnitude of sliding movement (push and/or rotation) required to open the sliding door.

In a preferred embodiment of the sliding door, a fixed plate with a plurality of spaced apart holes is placed in front of the opening (the outlet of the hopper) and thus (only) partially blocks this outlet. The respective movable sliding plates present corresponding holes which can be slid in front of the holes of the fixed plate for opening the door and which can be slid to different positions for closing the holes of the fixed plate. Preferably, the holes have a generally rectangular or square shape for a linear sliding door, or a generally fan-shaped shape for a rotary sliding door with an axis of rotation perpendicular to the opening, and between adjacent holes in the sliding plate The space between is sized to substantially close the corresponding aperture of the fixing plate. The main advantage of multiple holes is that the travel of the sliding door (ie the sliding distance between the open and closed states) is significantly reduced, which is advantageous since the time available to achieve this action is limited.

In another preferred aspect, the sliding door includes two or more rows of apertures. In such cases, it is even more preferred to have adjacent rows of holes arranged in a staggered (zigzag) fashion to further improve the even distribution of the particles in the slag.

In yet another aspect, the dispensing device comprises two or more individually controllable actuated sliding doors, each connected to an outlet of the same hopper or a different hopper. Advantageously, the dispensing device comprises a hopper (or two) with two individually controllable actuated sliding doors, each covering substantially half of the surface of the casting mould. The provision of two (or more) independently actuated sliding doors allows for flexibility in opening times when the mold is moving under the dispensing device, and in redundancy if one of the doors fails or becomes blocked.

The one or more sliding doors are driven by any suitable means (eg pneumatic means, hydraulic means), and/or by one or more electric motors. Preferably, the actuation of the sliding door is achieved by one or more hydraulic cylinders.

In yet another aspect, the travel of the sliding door is limited such that the aperture of the fixing plate is not fully closed. The advantages of this approach are twofold: the actuation is even faster, and there is significantly less wear and tear on the sliding doors and fixed plates. In fact, it has been noted that for a metal particle of a given diameter, it is sufficient to close the sliding door to leave a residual opening for each hole, where each remaining opening typically represents the diameter of the particle (or at the same time using a different The diameter of the particle is 0.3 to 1.5 times the diameter of the smallest particle), preferably about 0.8 to 1.3 times, most preferably about 1.1 to 1.25 times.

In another aspect, the method and apparatus of the present invention also comprise means for precisely determining the position of the mold(s), and in particular the molds located below the dispensing means. Any conventional means can be used for this purpose, in particular contact means and/or non-contact means, such as switches, lasers, sensors and the like.

Preferably, the solid metal particles are dosed from a height of about 0.1 m to 3 m and preferably about 0.2 m to 2 m to obtain a rapid and efficient mixing of the slag and solid metal particles. The precise height (ie, the precise amount of energy) required for the particles to penetrate the liquid slag to the desired depth depends on the composition of the slag, the temperature of the slag, the density and diameter of the solid metal particles, etc. Since throwing metal particles into the hot liquid slag may cause some splashing or splashing, the dispensing device preferably includes splash guards arranged at least on the sides below the hopper and sliding doors, extending approximately to the upper side of the mould. top.

Advantageously, the solid metal particles have a density of at least 2.5 g/cm ³ . Due to the density difference between the slag and the metal particles, the metal particles and the slag are thoroughly mixed.

Preferably, the solid metal particles are spherical in order to have good mixing properties and to ensure fast and efficient cooling of the slag.

Preferably, the solid metal particles have a diameter of at least 2mm, which is preferably greater than 5mm and most preferably greater than 10mm. Advantageously, the solid metal particles have a diameter of less than 80mm, preferably less than 50mm and most preferably less than 25mm.

Preferably, the solid metal particles are made of a metal selected from the group of iron, steel, aluminium, copper, chromium, nickel, their alloys and their alloys with other metals.

In practice, steel balls are preferably used due to the ease of obtaining steel balls of different diameters.

During and/or after discharge of the slag cake from the conveyor, preferably the slag cake is crushed into particles of a size of about 40-120 mm and a bulk density of about 2-5 g/cm ³ , preferably crushed into a size of about Particles with a diameter of 40-90 mm and a bulk density of approximately 2-5 g/cm ³ .

Thereafter, the still hot slag particles and heated solid metal particles are preferably charged into a heat exchanger, cooled with countercurrent flow of cooling gas and discharged from the heat exchanger.

According to a preferred embodiment, the heat exchanger is subdivided into a plurality of subunits, each of which has a particle inlet, a particle outlet, a cooling gas inlet and a cooling gas outlet, wherein at least one subunit passes through the particle The inlet port contains hot slag particles and heated solid metal particles, the cooled slag particles and cooled solid metal particles are discharged from the at least one subunit through the particle discharge port, the cooling gas inlet port and the The cooling gas outlet is closed during the charging and discharging of particles, and wherein, while charging and discharging the particles, at least one other subunit is injected with a flow of cooling gas through the cooling gas inlet and drawn from said cooling gas discharge. The outlet is cooled by withdrawing a stream of heated cooling gas, the particle inlet and the particle outlet are closed during the cooling of the particles, and wherein the heated cooling gas is used for energy recovery.

Therefore, the method according to a preferred embodiment of the invention proposes the use of a heat exchanger comprising a plurality of subunits which operate discontinuously. Since it is advantageous to obtain a constant hot gas flow at the outlet of the heat exchangers in order to ensure the most efficient use of the power generation cycle, multiple heat exchanger subunits are alternately operated in such a way as to ensure a substantially constant hot gas flow. By doing so, substantially continuous gas processing separate from batch material processing can be obtained.

At each moment when one of the heat exchanger subunits is in the emptying/filling phase, no cooling gas flows through this heat exchanger subunit during emptying/filling.

The same amount of particles is filled into and extracted from the exchanger. At the same time, no material enters or leaves other heat exchanger subunits; thus, the above-mentioned particles can be completely isolated from the environment during cooling.

Preferably, one of the subunits is loaded with hot slag particles and heated solid metal particles through the particle inlet, while simultaneously discharging cooled slag particles and cooled solid metal particles through the particle discharge of the subunit.

Once the heat exchanger subunit is filled, the particle inlet and particle outlet are sealed and the subunit is reconnected to the cooling gas flow, while the other heat exchanger subunit may be disconnected. Hence, the cooling gas flow through these heat exchanger subunits does not encounter any leakage, preventing dust and energy from remaining in the system. Therefore, the heat exchanger subunit only needs to be depressurized during the charging and discharging of slag.

According to a preferred embodiment, the hot slag particles and the heated solid metal particles are first charged into an insulated pre-chamber before being charged into one of the heat exchanger subunits. )middle. Preferably, the prechamber is insulated by a refractory lining or material stone box. The low thermal conductivity of slag provides excellent insulation properties.

The slag particles and solid metal particles may also be charged into a post-chamber after cooling and after being discharged from the heat exchanger sub-unit. In other words, the cycle time and the amount of charged particles can be chosen such that the heat transfer within the heat exchanger subunit can be controlled and kept quasi-steady. Thus, by choosing the cycle time accordingly, the outlet gas temperature fluctuations caused by the charging/discharging of the heat exchanger subunits will be minimized.

According to another preferred embodiment, the hot liquid slag is solidified into a slag cake and cooled to about 650°C to 750°C by mixing with solid metal particles. Advantageously, mixing the hot liquid slag with approximately the same volume of solid metal particles preferably results in a mixture containing from about 40% to about 60% by volume solid metal particles. The required volume of metal particles depends on the desired target temperature, the density and heat capacity of the metal particles, and the like. For steel balls, 40% to 60% (volume percent of total volume) is preferred.

Preferably, the heat exchanger subunit operates at a pressure (ie absolute pressure measured at the bottom of the slag layer in the subunit) of 1.2 bar to 4 bar.

Description of drawings

Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 is a schematic cross-sectional view of a preferred embodiment of a dry slag granulation plant;

Figure 2 is a schematic illustration of some components of a sliding gate valve useful for a dispensing device;

Figure 3 is a perspective top view of an embodiment of a double sliding door (hopper not shown) with staggered holes;

Figure 4 is a cross-sectional view of a portion of the dry slag granulation plant of Figure 1;

Figure 5 is a schematic diagram of another preferred embodiment of the method according to the invention;

Figure 6 is a schematic diagram of yet another preferred embodiment of the method according to the invention; and

Figures 7(a) and 7(b) are diagrams illustrating a preferred embodiment of a self-calibrating method of operating the devices described herein.

Other details and advantages of the invention will become apparent from the following detailed description of several non-limiting embodiments, with reference to the accompanying drawings.

detailed description

Figure 1 schematically shows a cross-sectional view of a preferred embodiment of a dry slag granulation plant comprising a slag caster 1 with a linear circulating conveyor 10 comprising a plurality of casting molds 11 . It is to be noted that so-called double slope linear slag casters can also be used (see eg Figure 4).

The mold 11 is transported in a first section from the slag pouring zone A through the cooling zone B to the discharge zone C, where the mold is emptied of the solidified slag cake contained therein. In the second section, the now empty mold is conveyed back to the slag pouring area.

Hot liquid slag 21 from the slag ditch 20 is poured into the casting mold 11 passing below the slag ditch 20 .

In the specific case of a double-slope conveyor (as in Figure 4), the inclination angle α is relatively steep so that the maximum effective volume V _α (i.e., the volume of slag in the upstream mold N-1 when it overflows into this mold volume) is smaller than the useful volume V _β of the mold when it reaches the position in cooling zone B (position >N+2 in FIG. 1 ), where the inclination angle β is smaller. Preferably, the angles α and β are chosen such that V _α is about ½ V _β .

When the mold containing the hot liquid slag reaches a position between the pouring position N and the position N+2 of the distribution device 30 (ie, N+1 in FIGS. 1 and 4 ), the sensor (preferably a laser range finder ( Sh _slag )) to measure the height of the hot liquid slag in the mold (h _slag ).

The results of this measurement are used on the one hand to adjust the speed of the conveyor (V _{-casting machine} ) and on the other hand to determine the amount of particles in the hot slag to be subsequently added to the casting mould.

When the mold containing the hot liquid slag reaches a position below the distributing device 30 (for example, N+2 in FIGS. An amount of solid metal particles 33 (eg steel balls) in a storage hopper 31 (the amount is determined based on the measured amount of slag and a predefined slag/particle ratio) is introduced into the mould. The particles 33 fall into the mold by the action of gravity and mix with the hot liquid slag 21 .

A splash guard 36 may be provided to prevent liquid slag and steel balls from splashing from the mold during charging.

During the introduction of the metal particles 33 into the hot liquid slag 21, the slag cools rapidly and solidifies in an amorphous state. The mold, now containing a solidified cake of slag and added metal particles such as steel balls, then cools down further during advancement to discharge zone C where it is emptied by inverting the mold. The solidified slag cake is then crushed into pieces and may proceed to a heat recovery unit (not shown).

In yet another preferred variant of the method, the height of the solidified slag/particle mixture in the mold (h _mixture ) is measured using another sensor, preferably also by means of a laser distance meter (Sh _mixture ). Using this value as feedback information about the actual addition of particles, the process can be adjusted (self-correcting process). Further details are given below.

FIG. 2 shows a schematic diagram of part of the linear sliding gate valve 35 . A preferred sliding gate valve for use in the present invention includes a retainer plate 353 having a plurality of spaced apart holes 354 . There are also spaced holes 352 in the corresponding sliding plate 351, but these holes are positioned such that the holes 352 can be brought from a closed position to an open position by sliding linearly (by sliding in the direction indicated by the arrow in FIG. 2 ), wherein In the closed position, all holes 354 of the fixed plate are closed by those parts of the sliding plate (substantially, see above) that do not have holes, and in the open position, the holes 352 are substantially aligned with the holes 354 .

Figure 3 shows a perspective top view of a preferred embodiment of a double (linear) sliding gate valve 35 without an overhead hopper for temporary storage of metal particles. For illustrative purposes, only one of the valves also includes a splash guard 36 disposed below the valve. The sliding plate 351 of each valve is driven relative to the fixed plate 353 by individual hydraulic cylinders 355 .

Figure 4 corresponds substantially to the lower part of the embodiment of Figure 1 during operation. Furthermore, it is worth mentioning that, for the purposes of the present invention, the dual-slope conveyor shown in Figure 4 could also be a single-slope conveyor.

As can be seen in FIG. 4 , the casting mold in position N is filled with hot liquid slag 21 from the slag trench 20 .

In the case of a single-slope conveyor, the adjustment of the casting machine is based on the amount of liquid slag in the mold in position N+1 by the height of the slag (h- _slag ) measured using the sensor (Sh- _slag ) as described above. Speed (V _{-casting machine} ).

In the case of a double slope conveyor (as shown in Figure 4), the amount of liquid slag can additionally be controlled by the specific shape of the conveyor itself and optionally by means of one or more temperature sensors. If the amount of slag from the slag trench exceeds the (local) capacity (V _α ) of the mold, the excess slag overflows by gravity into the immediately adjacent mold in position N-1. If the volume (flow rate) from the slag trench is even higher, the slag is poured from the mold in N-1 to the mold in N-2 (this is actually the case shown in Figure 4). It is known that the mold arriving from the second section of the conveyor 10 has a temperature that is very different from that of the liquid slag (for simplicity this temperature will also be referred to as "ambient temperature", although this temperature will typically be between 50°C to 300°C or even higher), it has been found that by controlling the mold temperature (T _N-1 and T _N-2 ) at the two positions N-1 and N-2, it is possible to provide simple and effective control of the casting process. control (also see below). It will be appreciated that more than two temperatures may of course be monitored if deemed necessary or desirable.

In FIG. 4 , mold N+2 is located below distribution device 30 and is ready to be filled with metal particles 33 . The amount of metal particles to be added is determined as described in detail below.

The casting mold at position N+3 in Figure 4 shows such a mold in which a calculated amount of metal particles has been added to the liquid slag. At this point, the slag solidifies substantially in an amorphous state due to the instantaneous addition of a large number of cold particles. It seems clear that the position for inserting particles indicated by N+2 in Figure 4 does not necessarily have to be the second position after the filling position, as long as the slag is still hot and in a liquid state.

Optionally, the amount of slag/particle mixture is measured thereafter to verify that the results match the expected amount. If the verification result does not match the expected amount, this value is used as feedback information to adjust the process, as described further below.

By any known contact or non-contact means (such as switches, sensors, lasers, etc.), the precise position of the mold within the conveyor, in particular its position below the slag trench and/or the distribution device, can be determined.

Description of the process - the purpose of the adjustment

During dry slag granulation, liquid slag 21 is cooled by adding cold metal particles 33 such as steel balls. The purpose of this cooling is to achieve:

· Rapid cooling of slag

· High mixing temperature for further heat recovery

Therefore, the dosing of steel balls must be precise and the steel/slag ratio must be respected.

To achieve the conveying of the material, the slag caster 10 technology has been chosen. The slag 21 is poured upstream in the pouring zone A at the beginning of the conveyor 10 and then the steel balls 33 are added in the cooling zone B, as shown for example in FIGS. 1 and 4 .

The dosing of the steel balls 33 in the cooling zone B and the slag filling of the mold 11 in the position N should be adjusted. In the mode of regulation so far described, regulation is performed by measuring the amount of slag in the mold in position N+1 and by adding a calculated amount of steel balls 33 to the mold as it passes under the distribution device 30 . The amount of hot liquid slag in the mold is controlled by varying the speed of the casting machine 10 .

Since the loading time is limited, the metering of the steel balls 33 is carried out using, for example, a sliding gate valve 35 as shown in FIGS. 2 and 3 .

Description of the preferred mode of adjustment

As already mentioned above, the metal particles are preferably steel balls. The dosing of such steel balls and the slag filling of the mold must be adjusted. Preferably, this adjustment is made by changing the following two parameters:

·Speed of casting machine

• The amount of metal pellets (steel balls) charged into each mold.

Because the loading time of the metal particles is limited, one or more gate valves such as those shown in FIGS. 2 and 3 are used for dosing.

Each mold is loaded only when it is under the door, so it is not undefined which mold the pellet is loaded into.

The material loaded through the door depends on two parameters:

The opening of the door (x);

• Door opening time (t).

As can be seen in Figure 5, the basic adjustment steps may be those described as follows:

1. Inject liquid slag (unknown amount) into the mold in position N;

2. Once the mold has reached position N+1, use the laser to measure the slag level (h _slag ),

a) From this height (h _slag ), convert the volume of slag in the mold (V _slag ), and then convert the mass of slag in the mold (M _slag ),

b) Based on the slag/steel ratio (λ), determine the steel balls (M _{steel balls} ) necessary for the mold,

c) adjust the speed of the caster (V _caster ) based on the recorded _slag height (hslag);

3. Once the mold has reached position N+2, load steel balls,

a) Determine the opening time (t) of the sliding door based on the casting machine speed ( _{Vcasting machine} ),

b) Determine the opening (x) of the door based on the following parameters, which are

ⅰ. The required steel ball quality M _{steel ball} determined above

ⅱ. Open time (t)

ⅲ. Characteristics of sliding doors ( curve).

This first adjustment method can be summarized as shown in FIG. 5 .

In another preferred embodiment, the method also includes the following steps:

4. Once the mold has reached position N+3, use the laser to measure the height of the steel ball/slag mixture (h _mixture ),

a) From this height (hmixture), the volume of _mixture in the mold ( _Vmixture ) is converted. Determine the steel balls actually added in the mold (M _{steel balls'} ).

5. Feedback information - adjustment of door characteristics

a) If M _{steel ball} = M _{steel ball'} , the correct amount of steel ball has been put in → no adjustment curve,

b) If M _{steel ball} ≠M _{steel ball'} , then adjust curve to fit the measured mixture height. This adjustment is described below.

This further preferred adjustment method can be summarized as shown in FIG. 6 .

Adjustment of door characteristics

If the amount of the measured steel ball does not match the theoretical amount (M _{steel ball} <>M _{steel ball'} ); then the curve should be adjusted curve. Determine the difference ΔM _{steel ball} , since the loading time t is known, calculate the difference between the calculated flow and the actual flow

if Then no correction is applied and an alarm is issued. if A correction is then performed on the mass flow characteristic curve of the metering valve.

curve The curve is a discrete curve. This curve can be corrected by adjusting the respective opening length xn (cf. _Fig . 7(a)) for each flow value in the table (cf. Fig. 7(b)). The farther the location is from x, the smaller the correction will be.

The correction to be applied to x (positions included between _xi and _xi+1 ) to achieve the desired flow rate is Δx. The corrected open length is x'=x+Δx.

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; m</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; m</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}$

Now that the correction Δx for x has been calculated, the position value x _n of the material flow table will be replaced by the corrected value x′ _n . Update by using the following formula:

For values of x _n above x:

${\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; x</span>}}{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ></span>\mathrm{<span\; class="notranslate">\; i</span>}$

For values of x _n below x:

${\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; x</span>}}{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; i</span>}$

Compute limit values:

x _min ≤ x′ _n ≤ x _max

x _min = the minimum allowable opening length of the dosing valve

xmax = the _maximum allowable opening length of the metering valve

in:

x′ _n : new value in [mm]

x _n : old value in [mm]

N: total number of values in the material flow table

n: position considered in the material flow table (n=1...N)

K ₁ : constant factor to prevent over-correction (K ₁ ≥ 2)

Legend:

1 casting equipment

10 cycle conveyor

11 casting mold

20 slag ditch

21 hot liquid slag

30 distribution device

31 Hopper

32 hopper outlet

33 solid metal particles, such as steel balls

35 sliding door valve

351 slide plate

352 Hole in slide plate

353 fixed plate

354 hole in fixed plate

355 hydraulic cylinder

36 splash guard

A slag pouring area

B cooling zone

C discharge area

Sh _slag sensor for measuring the height of hot liquid slag

Sh _Mixture Sensor for height measurement of slag/granulate mixture

α The inclination angle of the conveyor in the slag pouring zone A

The inclination angle of the conveyor in the beta cooling zone B

V _α the effective maximum filling volume of the mold in the slag pouring area A

V is the effective maximum _filling volume of the mold in cooling zone B

T _N-1 Temperature sensor for mold position N-1

T _N-2 Temperature sensor for mold position N-2

Claims (26)

1. the method for using casting equipment (1) hot liquid slag to be carried out to dry slag granulation; described casting equipment comprises the cyclic conveyor (10) with multiple casting mould (11); described cyclic conveyor is configured to described casting mould is moved to discharge area (C) from slag pouring area (A) by cooling zone (B) at the first section and makes described casting mould the second section, return to described slag pouring area, and described method comprises following consecutive steps:

A) in described slag pouring area, a certain amount of hot liquid slag (21) is poured into a mould to the casting mould in the N of position,

B) casting mould accommodating described hot liquid slag is made to move to N+n place, position in described cooling zone,

C) accommodate in the described casting mould of described hot liquid slag by the solid metal particle (33) of determined amounts is put into from distribution device (30) the N+n of position, described solid metal particle is added in described casting mould, described distribution device is arranged on the top of described casting mould and at least one hopper (31) comprised for storing described solid metal particle

D) from described casting mould, the solidification slag cooled is discharged at described discharge area, wherein, the actual amount of the hot liquid slag in described casting mould is poured in measuring process (a) in position between N and N+n, wherein n is the numeral between 1 to 10, preferably between 1 to 4

Wherein, based on the speed V of movement in amount set-up procedure (b) of measured hot liquid slag _{casting machine},

Wherein, based on the amount of fixing slag/metallic particles than the metallic particles needed for λ determining step (c),

Wherein, by based on described speed V _{casting machine}at least one driving sliding gate (35) at outlet (32) place being arranged on described hopper is opened during the time t determined, carry out the amount of the metallic particles added by described distribution device in rate-determining steps (c), and wherein, based on the characteristic of the amount of determined metallic particles, determined opening time t and at least one sliding gate described determine described at least one drive the aperture x of sliding gate.

2. method according to claim 1, also comprises the steps: the actual binding capacity measuring slag and metallic particles in described casting mould after step (c) in the downstream position of position N+n; The actual addition of metallic particles in calculation procedure (c) is carried out based on the binding capacity of measured slag and metallic particles and the amount of hot liquid slag previously determined; And if the actual addition of the metallic particles calculated is not inconsistent with the amount of the metallic particles previously determined, then the characteristic of adjustment at least one sliding gate described.

3. the method according to any one of claim 1 or 2, also comprises at least one step following:

E () crushes the slag of solidification, and/or

F () reclaims heat in a heat exchanger.

4. according to the method in any one of claims 1 to 3, wherein, the characteristic of at least one sliding gate described comprises the mass rate of the metallic particles with described aperture x change _particle( _particle/ x curve).

5. method according to any one of claim 1 to 4, also comprises at least one sensor (Sh _slag, Sh _mixture), at least one sensor described can by determining the height h of slag in described casting mould respectively _slag, slag/metallic particles height h _mixturemeasure the amount of the amount of hot liquid slag in described casting mould and/or the mixture of slag and metallic particles, and wherein, control unit can calculate corresponding volume V based on the known form of described casting mould _slagand/or V _mixture, and determine the mass M of slag _slagand/or based on V _mixtureand V _slagbetween the mass M of difference determination metallic particles _particle'.

6. method according to any one of claim 1 to 5, wherein, at least one sensor described comprises laser ranger.

7. method according to any one of claim 1 to 6, wherein, can also by the described slag pouring area (A) in the first section of described cyclic conveyor to be arranged to carry described casting mould to control the amount of the liquid slag in described casting mould with the first inclined angle alpha, the effective maximum packing volume of described mould in described slag pouring area is defined as numerical value V by described first pitch angle _αany excessive slag is come down in torrents the upstream casting mould be back in position N-1, N-2 etc., and wherein, described cooling zone (B) is set to have the second angle of inclination beta, this second pitch angle is less than α, makes the numerical value V that the effective maximum packing volume of described mould in described cooling zone has _βbe greater than V _α.

8. method according to claim 7, wherein, the described inclined angle alpha in described slag pouring area and the described angle of inclination beta in described cooling zone are selected as, and make the effective maximum packing volume V of described mould in described slag pouring area _αbetween the effective maximum packing volume V of described mould in described cooling zone _β0.25 times to 0.75 times between, preferably between 0.30 times to 0.60 times, be even more preferably 0.45 times to 0.55 times.

9. method according to any one of claim 1 to 8, wherein, at least one driving sliding gate (35) described comprises a line or multirow hole (352), preferably includes two row or more line interlacing hole.

10. method according to any one of claim 1 to 9, wherein, described distribution device (30) comprises two driving sliding gates that can control separately, and each sliding gate preferably covers the about half on the surface of described casting mould.

11. methods according to any one of claim 1 to 10, wherein, at least one driving sliding gate (35) described comprises one or more hydro-cylinder (355).

12. methods according to any one of claim 1 to 11, wherein, the movement of described casting mould can also be controlled by following manner: monitoring is positioned at the temperature of at least two casting moulds of the casting mould upstream (position N-1 and N-2) be just filled, and change the speed of movement in step (b).

13. methods according to claim 12, wherein, if the temperature of the casting mould in the N-1 of position does not increase due to the adverse current lacked from the hot liquid slag of position N, then reduce the speed of movement in step (b), and wherein, if the temperature of the casting mould in the N-2 of position increases due to the adverse current of the hot liquid slag from the casting mould in the N-1 of position, then increase the speed of movement in step (b).

14. methods according to any one of claim 1 to 13, wherein, the closedown of at least one sliding gate described is embodied as makes the hole of retaining plate (353) (354) not be fully closed, each hole is preferably made to leave residue opening, described residue opening is usually expressed as 0.3 times of the diameter of described metallic particles to 1.5 times, more preferably about 0.8 times to 1.3 times, most preferably between 1.1 times to 1.25 times.

15. 1 kinds for carrying out the equipment (1) of dry slag granulation to hot liquid slag; comprise the cyclic conveyor (10) with multiple casting mould (11); described cyclic conveyor is configured to described casting mould is moved to discharge area (C) from slag pouring area (A) by cooling zone (B) at the first section and makes described casting mould the second section, return to described slag pouring area; and wherein, described equipment also comprises:

Distribution device (30), described distribution device to be arranged in described cooling zone and to be positioned at above the described mould at N+n place, position and to comprise at least one hopper (31), described hopper is for storing solid metal particle (33), described distribution device also comprises at least one sliding gate (35) at outlet (32) place being positioned at described hopper, the amount controlling the metallic particles distributed by described distribution device is allowed to the driving of at least one sliding gate described

At least one sensor (Sh _slag), described sensor can measure the actual amount of the hot liquid slag in the casting mould in the position be poured between slag pouring position N and metallic particles point of addition N+n, and wherein n is the numeral between 1 to 10, preferably between 1 to 4,

Control unit, described control unit in order to: the amount based on measured hot liquid slag adjusts the speed V of described transfer roller movement _{casting machine}; Determine the necessary amounts of the metallic particles that will be added by described distribution device than λ based on fixing slag/metallic particles; By based on described speed V _{casting machine}open at least one driving sliding gate described in the exit being arranged on described hopper during the time t determined, control the amount of the metallic particles that will be added by described distribution device; And based on the characteristic of the amount of determined metallic particles, determined opening time t and at least one sliding gate described determine described at least one drive the aperture x of sliding gate.

16. equipment according to claim 15, wherein, the characteristic of at least one sliding gate described comprises the mass rate of the metallic particles with described aperture x change _particle( _particle/ x curve).

17. equipment according to any one of claim 15 or 16, also comprise at least one sensor (Sh _slag, Sh _mixture), at least one sensor described can by determining the height h of hot liquid slag in casting mould respectively _slagwith the height h of slag/metallic particles _mixturemeasure the amount of the amount of hot liquid slag in described casting mould and/or the mixture of slag and metallic particles, and wherein, described control unit can calculate corresponding volume V based on the known form of described casting mould _slagand/or V _mixture, and determine the mass M of slag _slagand/or based on V _{mixed compound}and V _slagbetween the mass M of difference determination metallic particles _particle'.

18. according to claim 15 to the equipment according to any one of 17, and wherein, at least one sensor described comprises laser ranger.

19. according to claim 15 to the equipment according to any one of 18, wherein, can also by the described slag pouring area in the first section of described cyclic conveyor be set to carry described casting mould to control the amount of liquid slag in described casting mould with the first inclined angle alpha, the effective maximum packing volume of described mould in described slag pouring area is defined as numerical value V by described first inclined angle alpha _αany excessive slag is all come down in torrents the upstream casting mould be back in position N-1, N-2 etc., and wherein, described cooling zone is set to have the second angle of inclination beta, this second pitch angle is less than α, makes the numerical value V that the effective maximum packing volume of described mould in described cooling zone has _βbe greater than V _α.

20. equipment according to claim 19, wherein, the described inclined angle alpha in described slag pouring area and the described angle of inclination beta in described cooling zone are selected as, and make the effective maximum packing volume V of described mould in described slag pouring area _αbetween the effective maximum packing volume V of described mould in described cooling zone _β0.25 times to 0.75 times between, preferably between 0.30 times to 0.60 times, be even more preferably 0.45 times to 0.55 times.

21. according to claim 15 to the equipment according to any one of 20, and wherein, at least one driving sliding gate described comprises a line or multirow hole, preferably includes two row or more line interlacing hole.

22. according to claim 15 to the equipment according to any one of 21, and wherein, described distribution device comprises two driving sliding gates that can control separately, and each sliding gate preferably covers the about half on the surface of described casting mould.

23. according to claim 15 to the equipment according to any one of 22, and wherein, at least one driving sliding gate described comprises one or more hydro-cylinder (355).

24. according to claim 15 to the equipment according to any one of 23, wherein, the movement of described casting mould can also be controlled by following manner: monitoring is positioned at the temperature of at least two casting moulds of the casting mould upstream (position N-1 and N-2) be just filled, and change the speed of movement.

25. equipment according to claim 24, wherein, if the temperature of the casting mould in the N-1 of position does not increase due to the adverse current lacked from the hot liquid slag of position N, then can reduce the speed of described casting mould movement, and wherein, if the temperature of the casting mould at N-2 place, position increases due to the adverse current of the hot liquid slag from the casting mould in the N-1 of position, then can increase the speed of described movement.

26. according to claim 15 to the equipment according to any one of 25, wherein, the closedown of at least one sliding gate described can be made to be embodied as makes the hole of retaining plate (355) (354) not be fully closed, each hole is preferably made to leave residue opening, described residue opening is usually expressed as 0.3 times of the diameter of described metallic particles to 1.5 times, more preferably about 0.8 times to 1.3 times, most preferably between 1.1 times to 1.25 times.