Field of the invention

The invention relates to a method and an apparatus for conveying hot Geldart group C materials. In particular, the invention relates to a slide plate for a slide for Geldart group C materials, a slide with the slide plate and a method of con- veying hot Geldart group C materials.

Description of the related art

Conveying particulate matter is a common problem in many technical fields and many different apparatuses and means have been suggested. In cases where the particulate matter is extremely hot or cold, abrasive, corrosive or for other rea- sons difficult to handle by mechanical conveying means like screw or belt con- veyors a common approach is to fluidize the particulate matter and then let it slide (air-gravity conveying) or to blow the fluidized matter (air-jet conveying). If fluidization is an option or not, depends on the so called “Geldart group" to which the material is associated. As found by D. Geldart, particulate materials can be characterized by their ability to be fluidized: “The behavior of solids fluidized by gases falls into four clearly recognizable groups, characterized by density difference (p _s — p ) and mean particle size. The most easily recognizable features of the groups are: powders in group A exhibit dense phase expansion after minimumfluidization and prior to the commen[ce]ment of bubbling; those in group B bubble at the minimum fluidization velocity: those in group C are difficult to fluidize at all and those in group D can form stable spouted beds." (D. Geldart: Types of gas fluidization, Powder Technology, Vol. 7, No. 5, 1973, p. 285-292).

One example of a Geldart group C material is cement clinker raw meal ('raw meal' for short), which is an intermediate product in modern cement clinker lines. Raw meal may be uncalcined, partially calcined or at least almost fully calcined. In present state of the art cement clinker lines, the hot calcined raw meal exits a direct heat exchanger, the so called calciner, and is transported by the fumes produced in the calciner (fume jet transport) to a cyclone. In the cy- clone, the hot raw meal is separated from the fumes and falls down into the raw- meal inlet of the kiln. A problem of this process is the CO2 emission of the direct heat exchange calciner and the kiln: It has been estimated that about 8% of the overall man-made CO2 emission is associated to the cement clinker manufactur- ing process (Olivier, Janssens-Maenhout, Muntean and Peters, Trends in global CO2 emissions: 2016 Report, The Hague: PBL Netherlands Environmental Assess- ment Agency, http://edgar.jrc.ec.europa.eu/news docs/jrc-2016-trends-in- global-co2-emissions-2016-report-103425.pdf, accessed 22 Jan. 2020, page 65). As already apparent, the CO2 emission of the cement clinker process is in part in- herent to the process, as limestone (CaCOs) is calcined into lime (CaO) in the cal- ciner, thereby releasing CO2. The corresponding chemical reaction is described by the formula CaCOs + heat-> CaO + CO2 and is thus an endothermal chemical reaction. This reaction is herein referred to as calcination. Another portion of the CO2 is produced by burning fuel to provide the thermal energy driving the above endothermic calcination in the calciner, to sinter the lime with the other constit- uents of the raw meal to clinker in the kiln and to produce the electrical power for operating the plant. Depending on the design and operating parameters of a cement clinker line, approximately 50-60% of the released CO2 are released in the calcination step. The other approximately 50-40% are released by said burn- ing fuel (see e.g., Johanna Lehne and Felix Preston, Making Concrete Change Innovation in Low-carbon Cement and Concrete, Chatham House Report, London 2018).

It has been suggested to capture and store the CO2 produced in the clinker man- ufacturing process. A promising approach for capturing the CO2 is the so-called Regenerative Calcium Cycle (RCC). The RCC consists essentially of capturing CO2 in flue gases by an exothermal reaction of the CO2 with CaO to CaCOs. The reaction reads CaO + CO2 CaCOs +heat, is thus exothermal and referred to as carbonation. Subsequently, the CaCOs is decarbonized (i.e., calcined) in a cal- ciner, thereby releasing CO2 and CaO, enabling to thereby obtain at least essen- tially pure CO2. The CO2 can be stored, e.g., in geological formations (commonly referred to as CO2-sequestration) or used in other processes. In any case it is not released to the environment. The CaO can be subjected to carbonation, again.

As suggested in FR 2 921 059 Al, the RCC can be integrated into the cement clinker process, i.e., the calciner for (pre-)calcination of the raw meal is the source of the CaO being required in the carbonation step of the RCC. The CaCOs obtained in the carbonation step is subsequently provided to the calciner to ob- tain fresh CaO, i.e., a portion of the CaO / CaCOs circles in the process. In this ap- proach, preheated raw meal is provided to a calciner, wherein in this process the calciner is necessarily an indirect heat exchanger for heating the CaCOs. This ena- bles to remove almost pure CO2 from the calciner. This almost pure CO2 can be stored or used for other industrial or agricultural purposes. A first portion of the calcined raw meal is provided to the kiln to complete the transformation of the raw meal into clinker. The remaining portion of the calcined raw meal is provided to a carbonator. In the carbonator, the CaO in the calcined raw meal reacts with the CO2 contained in the flue gases from the kiln to CaCOs. The flue gases from the kiln are thus subjected to CO2-removal. The CO2 bound in CaCOs produced in the carbonator is added to the raw meal entering the calciner, where the CO2 is released. Thus, essentially all CO2 being produced in the cement clinker process can be separated and stored or used as source for the chemical industry.

US 3,813,210 A suggests a kiln for converting raw meal into cement clinker. The kiln has two portions, namely an elongated, stationary, inclined through having a perforated floor for supporting the raw meal and a rotary kiln for sintering cal- cined raw meal into clinker. In the through, the raw meal is first preheated and subsequently calcined by providing a flow of a hot gas from a combustion chamber below the perforated floor into the raw meal. From the calciner section of the through the calcined raw meal is directly provided to the inlet of the ro- tary kiln.

WO 2017/125579 suggests a cement clinker plant with a U-shaped reactor for drying municipal waste by the addition of preheated raw meal in a first leg of the U-shaped reactor. In the second leg, the dried waste is pyrolyzed. The such ob- tained product gas is provided to a calciner. The two legs are connected by an in- clined perforated floor via which gas is injected in pulses to enhance a flow of material from the first to the second leg.

Summary of the invention

The invention is based on the observation that the teaching of FR 2 921 059 Al is conceptual and that its practical implementation reveals new technical problems one of which is to convey the calcined raw meal - a Geldart group C material- to the kiln's raw meal inlet (kiln inlet, for short) without cooling it down, as the cal- cined raw meal is no longer transported by the fumes of the calciner. The techni- cally simplest solution would be to store the calcined raw meal until it cooled down to a temperature allowing for an easy handling of the calcined raw meal. This approach, however, is inefficient as the raw meal has to be heated up again requiring heating installations and causing a significant increase in energy con- sumption. The object of the invention is thus to provide a slide plate, a slide and a method for conveying a Geldart group C material, like e.g., calcined raw meal as provided, e.g., by an RCC process, to a kiln inlet while keeping installation cost as well as operating costs for the apparatus low. The solution of the problem is provided by the slide plate, the slide segment and the method of the respective claims. Advantageous embodiments are subjects of the dependent claims.

The solution is based on the observation, that pre-calcined raw meal is a Geldart group C powder and hence very difficult, if not impossible to fluidize without ad- ditional mechanical agitation due to the cohesion between the powder particles. A fluidization-based air-gravity conveying mechanism is thus not promising. As well due to the cohesion, chutes or slides for calcined raw meal require a slope of at least 60°. These chutes have been used, but their slope imposes constraints on the relative vertical positions of the kiln inlet and the calciner outlet, as the horizontal distance is in practice dictated by the location of the already existing preheater tower. The required height of the calciner outlet has a huge impact on the installation costs for the calciner and the chute. Further, with an increase of the height of the calciner, the length of the chute increases and thus the energy losses as well. One may consider an air-jet conveyor mechanism enabling a hori- zontal or even upward raw meal transportation, but operating costs increase sig- nificantly as either the air jet has to be preheated to the raw meal temperature of typically 850°C to 1000°C or the raw meal is cooled down by the air jet. In ad- dition, the energy consumption for driving correspondingly dimensioned fans is non negligible as well as the installation costs. Conveying screws will not with- stand the corrosion and have to be cooled, which again requires reheating of the calcined raw meal.

A solution to the above summarized problem is a slide plate for a slide for Gel- dart group C materials (or other types of particulate matter), wherein the slide plate has a longitudinal axis. At this point it is noted that the application of the invention is not limited to the RCC, but can instead be used in many other appli- cations and enables to reduce construction heights being defined by conven- tional chute heights. The longitudinal axis is preferably essentially parallel to the conveying direction of the Geldart group C material being transported using the slide plate. The slide plate ('plate', for short) has an up-facing surface for sup- porting a Geldart group C material, like, e.g., hot calcined raw meal. The plate further has a lower surface, being at the opposite side of the plate than the up- facing surface. The plate further has a front-side surface facing preferably at least essentially towards the conveying direction and a rear-side surface facing prefer- ably at least essentially against the conveying direction. The front-side surface and the rear-side surface may connect the up-facing surface and the lower sur- face. The slide plate is preferably made of and/or at least comprise a ceramic re- fractory. The ceramic refractory has a number of through holes providing a fluid communication between fluid inlets in the lower surface and fluid outlets in the up-facing surface. This slide plate allows to provide a preferably very gentle gas flow, which flows essentially in between of the up-facing surface and a Geldart group C material being deposited on top of the up-facing surface. The gas flow almost forms a gas cushion in between of the Geldart group C material and the up-facing surface, thereby reducing the critical angle of the slide for the Geldart group C material on the plate. In practice the gas cushion is not perfect, as gas finds its way through the bed of the Geldart group C material. The process is, however, believed to be understood as a bed of Geldart group C material being formed by coherence of the material floating on the gas cushion. This picture is obviously simplified but already provides an idea why the slope of the slide can be reduced significantly below 60° relative to the horizontal.

The invention can be used not only for conveying hot Geldart group C materials, but as well to convey cold Geldart group C Materials, e.g., uncalcined raw meal. The invention can for example as be used in a preheater tower of a cement clinker line to connect/convey raw meal from one preheater stage to the next one. In this example the height of the preheater tower can be reduced, which again leads to a significant reduction of the construction costs. Only to avoid misunderstandings, the critical angle of the slide is the angle at which the Geldart group C material starts sliding over the grate plate, i.e., at lower inclinations of the up-facing surface of the slide plate, the Geldart group C material accumulates on the slide plate, while at steeper angles, the Geldart group C material slides down the slide plate.

In a preferred example, a distance d between the boundaries limiting at least one of the through holes in the conveying direction is at or in between of 0.75mm and 0.01mm, hence 0.75mm > d > 0.01mm; preferably 0.5mm > d > 0.05mm, even more preferred 0.25mm > d > 0.08mm. The relatively small dimension d of the through holes ensures that the flow rate through the plate is low and that the pressure difference, i.e., the pressure drop, between the pressures below the lower surface and the up-facing surface of the plate is greater than the pressure drop between the bottom of the Geldart group C ma- terial on the up-facing surface and the space above the Geldart group C material. Hence, the gas flow is essentially defined by the slide plate and the flow inhomo- geneities are reduced. Preferred example values of the distance d are d = 0.1mm or d = 0.2mm, hence particularly preferred 0.2mm > d > 0.1mm.

In a particularly preferred example, at least one of the through holes (particularly preferred the majority of the through holes or even all through holes) is a slot with a slot width w and a slot clearance d, wherein the slot width w extends per- pendicular within an angle of ±a and a£{45°,40°,30°,15°,10°,5°,2.5°,l°,0°} to the longitudinal axis and wherein the slot width w is greater than the slot clearance d, (w > d) . For example, the width w may be a number n of times greater than the clearance d (d • n = w) and n > m, m G {25, 50, 75, 100, 150}. These slots provide for a homogenous air cushion below the particulate matter, which may be even a Geldart group C material. The slot clearance d is thus at least essentially the distance d between the boundaries limiting at least one of the through holes, namely the respective slot in the conveying direction.

In operation, the slide plate may preferably have a gas flow rate j _g through the slide plates at or below 0.1/Vm ³ per second [s] and area [m ² ] of the support sur- face of the plate, wherein Nm ⁵ stands for a cubic meter of the gas under normal conditions, being standard pressure and standard temperature T = 0°C and m ² references to the size of the support sur- face of the slide plate. In a particularly preferred example is the gas flow rate at

, . or below one of 0. Lower values are preferred. These low gas flow rates are sufficient to significantly reduce the critical angle of the slide for the Geldart group C material on the slide plate, thereby reducing fan installation and operating costs. Further, potentially unintended interaction between the gas and the particulate matter, an example of which are Geldart group C materials, are reduced. In the example of conveying hot raw meal, e.g., from a calciner outlet to a kiln inlet, cooling of the hot raw meal is reduced, even if gas at ambient or only slightly elevated temperatures is used to form the gas cushion. In a pre- ferred example, the gas may be heated prior to injection it into the through holes of the slide plate. In practice the support surface of the slide plate is the portion of the up-facing surface onto which the particulate matter slides in operation of the slide. For example, the slide plate may be located to separate an upper chan- nel and a lower channel of a slide segment or a slide, wherein the bottom sur- face of the upper channel may be provided by at least a portion of the slide plate's up facing surface. The portion of the slide plate contributing to the bot- tom surface is the support surface of the slide plate. In a functional language, the portion of the slide plate being configured to support the particulate matter to be conveyed by the slide is the support surface. In some examples, the entire up- facing surface may be considered as the support surface. In other examples, the slide plate may extend into a slot of a side wall of the slide, e.g., into a slot de- fined by refractory cladding of the slide. In these other examples, the portion of the up-facing surface which engages into the slot is not configured to support the particulate matter and hence this engaging portion does not contribute to the support surface of the slide plate. In operation, the Geldart group-C material slides down the upper channel and gas reducing the friction between the slide surface and the Geldart group-C material is provided via the lower channel to the through holes in the at least one slide plate.

Preferably, the support surface may be a strip surface extending at least essen- tially in the center of the up-facing surface and connecting the front-side surface and the rear-side surface. The width of the strip may be defined by the spacing of sidewalls of the slide. In case these side walls are not (yet) present, the width of the strip may be defined by the width of the area having the through holes.

Preferably, the pressure gradient Ap _T between the bottom-facing surface of the slide plate and the up-facing surface of the slide plate is smaller than or equal 2kPa. In case the slide plate separates a lower ventilation channel extending be- low the slide plate from an upper channel above the slide plate, the pressure gra- dient is wherein p _t and p _u denote the gas pressures in the lower and the upper channels, respectively. Particularly preferred, the pres- sure gradientAp^ is smaller than these A lower boundary for the pressure gradient can be found experi- mentally: If the Geldart group C material flow stops or fluctuates the lower boundary is found. The lower boundary depends on the Geldart group C material to be conveyed, the surface roughness of the slide plate and the thickness of the layer to name most relevant factors. Further, the lower boundary decreases with an increasing slope angle of the slide. Obviously, if there is no pressure gradient the gas flow through the through holes stops , preferably k Sk k

In a preferred example, the slide plate has a fluid outlet of at least one of the through holes being closer to the front-end side surface than the fluid inlet of said at least one of the through holes. The gas flow exiting the through hole thus has a momentum in the conveying direction. Accordingly, the gas flow or at least a portion of the gas flow follows the up-facing surface of the slide plate in the conveying direction (Coanda effect). In a particular preferred example, at least the forward boundary of the through hole, i.e., at least the wall segment defining the forward-facing end of the through hole, merges at least essentially tangen- tially into the up-facing surface. Thereby, the gas flow adheres particularly well to the up-facing surface, enabling to further reduce the gas flow rate and hence maintain an even higher temperature of the Geldart group C material on the up- facing surface of the plate.

Preferably, the bottom side of the slide plate has at least one recess and/or pro- trusion providing a first stop surface facing towards the front-end surface and/or a second stop surface facing towards the rear-end surface. This recess and/or protrusion enable/s to define the location of the slide plate on an inclined sup- port structure having corresponding protrusions and/or recesses, respectively. The support structure may be referred to as a slide plate support.

The slide plate may be used as a support plate for hot Geldart group C materials of a conveyor slide ('slide', for short). For example, the slide may comprise a housing with a housing wall and the housing wall may enclose a circumferentially closed channel. The housing may comprise a slide plate support, supporting the slide plate in the channel. The slide plate may separate at least a segment of the channel into an upper channel and a lower channel. The lower surface may pro- vide a ceiling of the lower channel. The up-facing surface may provide a bottom of the upper channel. The at least one through hole of the at least one slide plate provides for a fluid communication between the upper channel and the lower channel. The channels can as well be referred to as conduits, i.e., they have at least essentially parallel channel axes.

For example, the slide plate support may be a refractory cladding inside the housing, thereby defining the width of the channel. This width may as well be width w of the strip surface of the slide plate being mentioned above.

A first side portion of the lower surface may reside on a first portion of the slide plate support. A second side portion of the bottom side surface may reside on a second portion of the slide plate support. Thus, a middle portion of the lower surface may be in between of the first side portion and the second side portion. This middle portion provides the lower end of the (at least one) through hole in the slide plate.

As indicated above, the slide plate may comprise at least one recess and/or pro- trusion, e.g., at its bottom side. The slide plate support, e.g., the refractory clad- ding may have at least one protrusion and/or recess, respectively, wherein the protrusion engages into the recess and provides for a positive locking of the slide plate on the slide plate support. Thereby the slide plate can be maintained at its intended position.

The up-facing surface of the at least one slide plate may support a refractory cladding of the upper channel. For example, the slide plate may as well or alter- natively have at least one protrusion and/or recess on its up-facing side. This pro- trusion and/or recess may engage into and/or be engaged by a recess or a pro- trusion, respectively of a refractory cladding, thereby preventing the refractory cladding and the slide plate from sliding relative to each other.

The extension of the at least one protrusion parallel to the longitudinal axis is preferably at least 1mm smaller, preferably at least 2mm smaller than the extension of the recess into which the protrusion engages as well measured par- allel to the longitudinal axis. The slide plate support and the slide plate can thus move relative to each other within the boundaries of the gap being defined by the difference of the extension parallel to the longitudinal axis. This increases the longevity of the slide as tensile stress is reduced. Similarly, in case of a protru- sion-recess engagement between the slide plate and a refractory cladding above the slide plate, the extension of the at least one protrusion parallel to the longi- tudinal axis is preferably at least 1mm smaller, preferably at least 2mm smaller than the extension of the recess into which the protrusion engages as well meas- ured parallel to the longitudinal axis.

In a preferred example, the up-facing surface of at least one, at least two or of all the sliding plate(s) has/have a slope smaller than 25° relative to the horizontal. Preferably, the slope is smaller than 20° or 15° or 12° relative to the horizontal. 10° has shown in experiments as a slope still enabling a safe transport of the hot Geldart group C material and a very low gas flow, i.e., very low cooling losses. The lower limit for the minimum slope angle still providing for reliable transport depends on the gas flow rate and the material to be conveyed. According to presently available experimental data it is believed that 5° (or even slightly lower, e.g., 4°, 3°) can be considered as a lower boundary for Geldart group-C materials like raw meal, but operation at these low slope angles requires as an increase of the gas flow rate per surface area through the through holes. Such in- crease can be obtained by increasing the pressure drop p^, if necessary, above the maximum values indicated herein. Such an increase of the gas flow rate has the disadvantage of an increase in operation cost and in case hot Geldart group- C material is conveyed that cooling of the conveyed material is enhanced, unless the gas is heated prior to be injected into the through holes. The slope may be lowered further, e.g., by anti-stiction coatings of the up-facing surface, a further reduction of the axial distance of the through holes or other measures reducing the friction between the slide and the material to be conveyed. Further, the most upstream slide plate or number of upstream slide plates may have a slope being greater than the slope of at least one of the at least one downstream slide plates. This increased angle ensures that the hot Geldart group C material starts slipping over the most upstream grate plate(s). Stiction is overcome and subsequently the reduced slope is sufficient to maintain the Gel- dart group C material in motion while keeping the gas flow through the through holes low.

In addition or alternatively, the most upstream slide plate or number of up- stream slide plates may have more through holes and/or through holes with an increased cross section than at least one of the at least one downstream slide plates. Both measures increase the gas flow rate per surface area of the at least one respective upstream slide plate at a given pressure differential between the upper and the lower side of the slide plate and thereby contribute to avoid con- gestions of the slide, while keeping the gas flow through the downstream slide plates small. Experiments have shown that the risk for slide congestions is higher in the vicinity of the inlet portion of the slide than in the middle section of the outlet portion. Thus, the risk for slide congestions can be significantly reduced by increasing the slope of (only) the upstream and/or a (preferably small) number of upstream slide plates, as suggested in the previous paragraph and/or by increas- ing the gas flow per surface area through this upstream or a (preferably small) number of upstream slide plates. The still small total gas flow through the slide plates contributes to low operating costs and further in case of conveying a hot Geldart group-C material unintended cooling by the gas flow is maintained at a very low level.

Another possibility to increase the gas flow through only the most upstream slide plate or number of upstream slide plates is to separate the lower gas channel ex- tending at the lower side of the slide plates in at least two compartments, e.g., by a separating wall. Hence the lower gas channel may have an upstream compartment below the upstream slide plate(s) and a downstream compartment below the upstream slide plate(s), being separated by the separation wall. By providing a higher gas flow per slide surface to the compartment below the up- stream slide plates than to the compartment below the downstream slide plates the gas flow through the upstream slide plate(s) can be increased, in addition or alternatively to other measures.

The upper channel of the slide preferably comprises at least one gas opening, wherein the gas opening is connected via at least one control valve to a com- pressed gas source, as well referred to as "reservoir of compressed gas" or "com- pressed gas reservoir". The compressed gas source is configured to provide a gas at a pressure above the gas pressure in the upper channel when the control valve is closed. Preferred values for the gas pressure provided by the gas source when the valve is closed are at or above SOkPa, and/or lOOkPa and/or 200kPa and/or 300kPa and/or 400kPa and/or SOOkPa and/or 750kPa, and/or IMPa above the pressure p _u in the upper channel. A fluid line may connect the com- pressed gas source and the gas opening. The control valve is configured to con- trol the gas flow from the compressed gas source to the gas opening in the upper channel. In other words, the control valve is located in the fluid path from the compressed gas reservoir to the gas opening in the upper channel. Opening the control valve enables to provide a burst of gas to flow from the compressed gas source through the at least one gas opening. This burst of gas may serve to un- clog the upper channel in case of being congested. The duration of the burst of gas is preferably short, e.g., smaller or equal to 200ms and/or 300ms and/or 500ms and/or Is and/or 2s and/or 3s and/or 4s and/or 5s and or 10s.

As already apparent, the at least one gas opening is preferably located at the up- stream end of the upper channel and/or in at least one of the side walls in the upper third, quarter, fifth or tenth part of the slide. In a preferred example the gas opening is located in a part of the side wall delimiting the upper channel. In a particularly preferred example the opening is located in a part of the side wall being adjacent to the most upstream or the second most upstream slide plate.

The cross section of the at least one gas opening is preferably a multiple of a cross section of a through hole in the slide plates, e.g., greater or equal than 10 times and/or 20 times and/or 50 times and/or 100 times, 200 times and/or 500 times than the cross section of a through hole of the slide plates. Hence, the gas flow through the gas opening can be much higher than the gas flow through a through hole in a slide plate.

Multiple slide plates may be aligned to form a slide surface. In a preferred exam- ple, a gasket or any other kind of seal is located in between of aligned slide plates. Thereby, an unintended gas flow from below the slide plate into the par- ticulate matter can be avoided and the power requirement of the fans for oper- ating the slide is further reduced. Further a potentially unintended interaction of the gas with the particulate matter (e.g., cooling) is reduced as well.

The slide plates can be manufactured by casting a slip (including engobes) of a ceramic refractory in a mold having at least a bottom and side walls. After curing, the such obtained greenware may be subjected to a heat treatment, often re- ferred to as "firing". The heat treatment converts the greenware into a ceramic refractory material. This method hence enables to provide a heat resistant slide plate of a ceramic refractory.

In a preferred example, a positive form may be inserted into the mold prior to curing the slip into greenware. The shape of the positive form preferably corre- sponds to the shape of at least one of the through holes of the slide plate to be manufactured. In this sense, the positive form is a positive form of at least one through hole. The positive form is preferably made of a heat degradable material, e.g., of a cel- lulose-based material and/or of polymer- based material like plastic. In this con- text any material which disintegrates during the heat treatment for converting the greenware into a ceramic is considered heat degradable. The degradation may be due to evaporation and/or a chemical reaction like burning, pyrolysis or the like. Alternatively, the positive form may be made of a soluble material, ena- bling to dissolve the positive before or after firing the greenware. In all these cases, the at least one positive form disintegrates during the heat treatment and/or while being subjected to a corresponding solvent and due to the disinte- gration frees the corresponding at least one through hole during the heat treat- ment. Hence, after the heat treatment and/or the treatment of the semi-finished slide plate with the solvent, the slide plate has a through hole at the location and orientation being where the at least one positive form was located prior to the heat treatment. For example, many polymeric plastics can be considered as heat degradable material.

The at least one positive form can be held in place and hence be supported by a rack extending above the mold. In addition or alternatively, the mold may have at least one support opening configured to receive an end section of the at least one positive form. Thus, when mounted, a portion of the positive form may en- gage into the support opening, thereby being supported by the mold in a prede- fined location and in a predefined orientation. An advantage of this method is that the at least one positive form extends over the inner contour of the mold and hence after deforming of the greenware over the contour of the slide plate. Thereby, it can be avoided that the through hole is unintendedly plugged by greenware and subsequently by refractory.

The problems mentioned initially are as well solved by a method of conveying hot Geldart group C material on a slide with a slide surface having at least one, preferably a number of through holes. The method may comprise depositing the Geldart group C material on an up-facing surface of the slide, e.g., on an up-fac- i ng side of a slide plate. The method may further comprise the step of providing a gas flow rate j _g of or less than 0.5/Vm ³ of gas per second [s] and surface area [m ² ] of the slide surface through the holes to an up-facing surface of the slide. In preferred examples j _g is at or below one of

Summarizing, the claimed invention enables to reduce the angle of slides for con- veying hot Geldart group C powders, e.g., calcined raw meal, down to about 20° or even below (measured relative to the horizontal). Some of the advantageous embodiments being described in the dependent claims enable to reduce the an- gle even further to about 10°, thereby reducing installation costs and due to the low gas flow through the through holes as well operating costs.

Description of Drawings

In the following, the invention will be described by way of example, without limi- tation of the general inventive concept, on examples of embodiment with refer- ence to the drawings.

Figure 1 shows a perspective view of a slide segment of a slide for a Geldart group C material.

Figure 2 shows a side view of the slide segment.

Figure 3 shows a cross sectional view of the slide segment on the plane A-A as in- dicated in Fig. 2.

Figure 4 shows a longitudinal sectional view of a lower portion of the slide seg- ment. Figure 5 shows a perspective view of a lower portion of the slide segment.

Figure 6 shows a side view of another slide segment, which may be combined with the segment of Fig. 1 and 2.

Figure 7 shows a top view of the slide segment of Fig. 6.

Figure 8 shows a sectional view of the slide segment of Fig. 6 and 7 along the plane A-A in Fig. 7.

The segment of the slide 1 in FIG. 1 may as well be considered as a short slide 1, but in practice mostly a number of the depicted segments may be connected to form a longer slide for a Geldart group C material. Thus, a slide 1 may have a number (at least one) of the depicted segments. The slide 1 extends at least es- sentially parallel to the longitudinal axis 2 and is configured to convey a Geldart group C material in the conveying direction 3.

The slide in Fig. 1 has a housing 30 with a housing wall 31. The housing wall 31 may be, e.g., of sheet metal, being easy to process. The housing wall may prefer- ably have an upper housing portion 311 and a lower housing portion 313, which may be (preferably releasably) attached to each other thereby enclosing a chan- nel with an upper portion 41 and a lower portion 43 (see Fig. 3). As shown, the upper housing portion 311 and the lower housing portion 313 may have an up- per flange 351 and a lower flange 353, respectively, enabling to (preferably re- leasably) attach the upper housing portion 311 and the lower housing por- tion 313 to each other. In addition or alternatively, the slide 1 may have a front- end flange 36 and a rear end flange 37. Preferably, the front face of the front- end flange 36 is a at least a portion of a projection of the rear face of the rear end flange 37 parallel to the longitudinal axis 2. This eases to connect slides 1 to- gether by simply connecting the front-end flange 36 of a first slide 1 to a rear- end flange 37 of a second slide 1, thereby forming a correspondingly longer slide 1 and converting the first and the second slides 1 into slide segments. Of course, the rear face of the rear-end flange 37 may as well be a portion of a pro- jection of the front face of the front-end flange 36 parallel to the longitudinal axis 2.

Inside the housing wall 31 is preferably an insulation layer 38, as shown in partic- ular in Fig. 1 and 3. The insulation layer 38 may be, e.g., of a Calcium Silicate ma- terial or of any other material having a low heat transfer coefficient. In a particu- larly preferred example, the insulation layer 38 may be made of or comprise mi- croporous insulation material, these materials offer rather low thermal conduc- tivities K in the range of approximately 0.02 < K < 0.05 . When using con- ventional isolation material, the thickness of the insulation layer 38 is preferably increased accordingly.

The insulation layer 38 has an upper insulating portion 381 being located in the upper portion of the housing wall 311 and a lower insulating portion 383 being located in the lower portion of the housing wall 313. Each of the two insulation portions forms a U-profile with a middle leg to which two side legs are attached. If mounted, as shown in Fig. 1 and 3, the free ends of the side legs of the upper insulation portion may face the corresponding free ends of the side legs of the lower insulation portion.

The housing 30 may preferably have a refractory cladding 50. The upper housing portion may have an upper cladding and the lower portion housing may have a lower cladding. As can be seen in Fig. 4, the refractory cladding 50 protects the optional insulation layer 38 from abrasion by the Geldart group C material. In case the insulation material 38 has been omitted the optional refractory clad- ding 50 may protect the housing wall 31. Thus, the refractory cladding 50 may be inside the housing wall 31. The optional insulation material 38 may be in be- tween of the refractory cladding 50 and the housing wall 31. The lower portion of the refractory cladding may have a U-shaped cross section with a cladding middle leg 531 and two cladding side legs 532. The cladding mid- dle leg 531 may be supported on the up-facing surface of the middle leg of the optional lower insulating portion 383, as shown. In case the insulating por- tion 383 has been omitted, the cladding middle leg may be supported on or by the bottom of the lower portion of the housing wall 313. The two cladding side legs 532 of the lower portion of the refractory cladding 53, lower cladding side legs 532, for short, may extend towards the upper portion of the housing wall 311. The lower cladding side legs 532 may each provide an up-facing sur- face. The up-facing surface of the cladding side legs 532 may support a slide plate 10.

The slide plate 10 extends along the longitudinal axis 2 and has an up-facing sur- face 11 for supporting a Geldart group C material, like e.g., hot calcined raw meal. The slide plate 10 as well has a lower surface 13, a front-side surface 12 and a rear-side surface 14. The slide plate 10 may be made of a ceramic refrac- tory.

The lower surface 13 of the plate 10 has side portions which may reside on the lower cladding side legs 532. Thus, the lower cladding side legs 532 may support the slide plate 10.

The lower cladding portion and the slide plate 10 may enclose a lower chan- nel 43. For example, the lower channel 43 may be delimited by a center stripe of the lower surface 13 of the slide plate 10, the inwards facing surfaces of the lower cladding side legs 532 and the up-facing surface of the lower cladding mid- dle leg 531 (see Fig. 4 and 5). The center stripe of the lower surface 13 of the plate 10 is thus in between of the side portions of the lower surface 13 of the plate 10 residing on the up-facing surfaces of the lower cladding side legs 532 (see Fig. 3). As can be seen in Fig. 4 and Fig. 5 the lower cladding side legs 532 may have pro- trusions 533 engaging in complementary shaped recesses 123 in the lower sur- face 12 of the slide plate, preventing the slide plate 10 to slide parallel to the lon- gitudinal axis 2. The maximum extension of the protrusions is preferably slightly smaller than the space provided by the corresponding recess to thereby allow the slide plate 10 to float with the limits given by the distance between the ex- tensions of the protrusions and the recesses on the lower refractory side legs 532. In between of the up-facing surface 11 of the slide plate 10 and the up- per cladding side legs is preferably a gasket.

The housing may further form an upper channel 41. Like in the depicted exam- ple, the housing may have an upper cladding 51. The upper cladding may have an inverted U-shape with a middle leg 511 from which two side legs 512 extend downwards to the up-facing surface of the slide plate 10. The lower side of the middle leg 511 defines the ceiling of the upper channel 41. A portion of the up- facing surface 11 of the slide plate, the so called the center stripe of the up-fac- ing surface 11 of the plate 10 provides the bottom of the upper channel 41 and the inward facing sides of the upper cladding side legs 512 define the width of the upper channel 41 and in this example as well the width of the center stripe. The width of the upper channel 41 is preferably at least essentially the same as the width of the lower channel 43.

As shown in Fig. 4 and 5, the slide plate 10 may preferably have a number of through holes 20 extending from an inlet opening 23 in the slide plate's lower surface 13 to an outlet opening 21 in the slide plate's up-facing surface 11. Like in the depicted preferred example, the through holes 20 may be slots with a slot width w extending at least essentially perpendicular to the longitudinal axis 2. The slot clearance d is preferably at least essentially constant along the slot width. As can be seen, the slot width w is preferably a multiple m of the slot clearance d, wherein m is greater than 1 and not necessarily an integer, i.e., m > 1 and m G R, wherein R denotes the set of real numbers. Preferably, the through holes are inclined in the conveying direction, i.e., the outlet opening 21 is closer to the front-side surface 12 of the slide plate 10 than the inlet open- ing 23 of the respective through hole. This inclination of the through holes 20 has shown to reduce the gas flow rate required to maintain the Geldart group C ma- terial flowing.

It has been observed that the particles of Geldart group C materials form brittle but very soft clusters. These clusters may be considered as cohesion bound ag- glomerates of particulate matter. The reduction of the critical angle is believed to be caused by a gas cushion being formed by the gas flow between the slide plate and clusters of the bed of particulate matter. Holes, crevasses, or other kind of interstices have been observed to form between these clusters by the gas flow. The gas then flows through these interstices to the upper side of the bed being formed by the particulate material. Thus, the particulate material is not fluidized by the gas flow. The gas cushion so to speak reduces the cohesion of the particu- late matter to the slide plate's top surface and hence reduces the friction. In other words, the gas flow via the through holes 20 provides for a reduction of the cohesion of the particulate matter to the top surface 11 of the slide plate 10 and hence reduces the friction between the top surface 11 and the bed of partic- ulate matter. This reduced friction directly translates in a significant decrease of the required minimum slope angle of the slide. Slope angles of or below 25°, 20°, 15°, 12°and 10° have been found to be steep enough to reliably provide for con- veying even Geldart group C materials. An increase in gas flow rate through the through holes provides for a reduction of the minimum slope angle for a reliable conveying of Geldart group C materials.

In operation, a flow of a Geldart group C material may be unloaded to a first end portion of the upper channel 41. The Geldart group C material may thus be de- posited on the up-facing surface 11 of the slide plate 10. Further, the lower channel 43 may be provided with a gas pressure p _t , greater than the gas pres- sure p _u in the upper channel 41, hence preferably p _t > p _u . Due to the pressure gradient a gas flow through the through holes 20 is provided. The gas flow reduces the cohesion between the Geldart group C material (or any other particulate matter) and the up-facing surface 11 of the slide plate 10. The Geldart group C material may thus slide down an only slightly inclined slide. Slightly inclined means herein that inclinations of or below 25°, 20°, 15°, 12°and 10° relative to the horizontal can be realized, some experiments showed a possi- ble reduction down to 10° and slightly below this slope. These inclinations are much smaller than the inclination of the prior art slides, which usually have a slope of at least 60° and contribute to a significant reduction of the construction costs of the corresponding plant.

Preferably, the housing 10 has an inspection and maintenance opening 60 being shown closed in Fig. 1, 2, 3, 4 and 5. The opening 60 may as well be used as gas inlet opening to provide a gas flow to the lower channel 43.

Figures 6 to 8 show another slide segment 1 of a Geldart group C material con- veying slide. The slide segment of Fig. 6 to 8 may be mounted and is hence pref- erably configured to be mounted to the rear end of a slide segment of Fig. 1. For example, the rear-end flange 37 of the slide segment of Fig. 1 and 2 may be bolted to the front-end flange 36 of the another slide segment 1 as shown in Fig. 6 to 8.

The slide segment in Fig. 6 to 8 has a housing 30 with an inlet 5 for receiving par- ticulate matter, e.g., a Geldart group C material. As can be seen best in Fig. 8, the inlet 5 is above a slide plate 110 and enables to feed the particulate matter into an upper channel 41. The bottom of the upper channel 41 is delimited by slide plates 110 and 10, having through holes 20 which are shown only in Fig. 6, as the section plane A-A extends through an optionally continuous land. The slide plates 110 and 10 are essentially identical to the slide plates 10 of the slide seg- ment in Fig. 1 to Fig. 3, details of which being depicted in Fig. 4 and 5 and the de- scription of the slide plates 10 as provided in the context of Fig. 1 to 5 may be read as well on the slide plates 110 and 10 as shown in Fig. 6 and 8.

The slide plate 110 in Fig. 6 and 8 is upstream of the slide plate 10 and may have preferably have a steeper slope angle than the downstream slide plate 10. This increased slope angle contributes to an even more reliable operation of the slide and reduced mean slope of the slide. Experiments showed that slide congestions (e.g., due to sticky particulate matter) start always at the upstream end of the slide. Once the particulate matter flows down the slide, lower angles (less steep slopes) are sufficient to maintain even a Geldart group C material in motion. Thus, the steeper slope angle of the upstream slide plate 110 enables to further reduce the slope angle of subsequent slide plates 10, thereby further reducing the height required to install a slide with a given horizontal extension. In any em- bodiment the upstream slide plate 110 may have a higher number of through holes and/or through holes with a greater gross section than the immediate or another downstream slide plate. Both measures contribute to increase of the gas flow rate through the upstream slide plate 110 and thereby to reduce the risk of slide congestions.

Very similar to the slide segment 1 in Fig. 1 to 3, the upper channel 41 is prefera- bly delimited to the top and to the sides by a refractory cladding 50 comprising upper cladding side legs 511 and upper cladding middle legs 512. In between of the outer housing wall 31 and the refractory cladding 50 may preferably be an in- sulation layer 38 (see Fig. 8).

The slide plates 110 and 10 in Fig. 8 separate the upper channel 41 from a lower channel 43. Hence the lower channel 43 extends below the slide plates 110 and 10. As well very similar to the lower channel in Fig. 3, the bottom and the sides of the lower channel 3 are delimited by a lower cladding middle leg 531 in between of two lower cladding side legs 532. Again, an optional insulation layer 38 may preferably be located in between of the housing wall 31 and the portions of the lower cladding.

The lower channel 43 may extend into a gas inlet 45 and may hence be in fluid communication with the gas inlet 45 (see Fig. 8). By attaching a gas source to the gas inlet 45, a gas can be inserted into the lower channel 43 and thereby a pres- sure gradient between the lower channel 43 and the upper channel 41 can be provided. Accordingly, a portion of the gas may flow through the through holes 20 to the up facing surface 11 of the slide plates 110, 10 and may reduce the friction between the slide plates 110, 10 and the particulate matter which may have been inserted into the upper channel 41 via the particulate matter in- let 5.

As already apparent, already a single slide segment 1 be it the slide segment 1 of Fig. 1 to 3 or the slide segment 1 of Fig. 6 to 8 may each be used as a slide, if the distance via which material is to be conveyed is sufficiently short. In case the dis- tance is longer, multiple slide segments may be attached to each other to thereby constitute an accordingly longer slide.

General remarks:

The terms "at least essentially constant", "at least essentially the same as" or the like as used above are to be understood that constant or the same dimensions, respectively, are preferred, but deviations can be accepted. Typically, acceptable deviations are within one of ±20%, ±15%, ±10%, ±5%, ±2.5% and ±1% wherein lower values are preferred.

The terms "at least essentially parallel", "at least essentially perpendicular” or "at least essentially orthogonal", respectively and the like as used above are used to indicate that parallel or perpendicular (orthogonal), respectively, is preferred but that deviations can be accepted. Typically, acceptable deviations from the in- tended direction or orientation, whatever applies, may be within one of ±30°, ±20°, ±15°, ±10°, ±5°, ±2.5° and ±1% wherein lower values are pre- ferred.

List of reference numerals

1 slide (segment) for Geldart group C materials (segment of)

2 longitudinal axis

3 conveying direction

5 material inlet.

10 slide plate

110 slide plate

11 up-facing surface of the slide plate

12 front-side surface of the slide plate

13 lower surface of the slide plate

14 rear-side surface of the slide plate

20 through hole

21 fluid outlet

23 fluid inlet

30 housing

31 housing wall

311 upper portion of housing wall (deliming the upper channel)

313 lower portion of housing wall (deliming the lower channel)

351 upper flange

353 lower flange

36 front-end flange

37 rear-end flange

38 insulation layer

381 upper insulating portion

383 lower insulating portion

41 upper channel lower channel gas inlet of lower channel refractory cladding upper cladding middle leg upper cladding side legs lower cladding middle leg lower cladding side legs protrusions opening