Field of the invention

The invention relates to cement clinker manufacturing and in particular to a cal ciner of a cement clinker plant. The calciner has a conduit enclosing a reactor space by a side wall. The side wall defines an inlet in and an outlet out of the reactor space, thereby enabling a macroscopic flow of a fluid via the enclosed reactor space along a trajectory from the inlet to the outlet.

Description of the related art

Cement clinker, clinker for short, is the key intermediate product in the manufac- ture of concrete. Manufacture of clinker typically comprises prewarming of ground raw material (as well referred to as 'raw meal') in a pre-heater tower by direct contact of the raw meal with exhaust gas from a rotary kiln. The pre heated raw material is subsequently provided to a pre-calcining unit, the so called calciner and from there into the rotary kiln. In the kiln, calcination is final- ized and the clinker is sintered. The sintered clinker is discharged from the hot end of the rotary kiln onto a cooling grate of a clinker cooler. The clinker resting on top of the cooling grate is cooled by direct contact with a coolant. Typically, the coolant is a gas or a mixture of gases, usually air. A portion of the coolant is strongly heated while cooling the clinker down, at least in the area close to the kiln. This strongly heated coolant has a temperature of approximately 750-

1300°C and carries a high amount of dust. The heated coolant is extracted from the clinker cooler at the kiln hood and/or the cooler roof and fed via a so-called tertiary air duct to the calciner. The heated coolant-dust stream is usually re ferred to as tertiary air. This tertiary air can be used for preprocessing of the raw material in the calciner or an upstream combustion or gasification unit, such as a combustion chamber. Often kiln exhaust gas is as well fed to the downstream end of the calciner. The calciner is typically essentially a conduit with a circular cross section in which a mixture of fuel, raw- material and hot gases (e.g. said tertiary air, kiln exhaust gas, ...) including oxygen (O2) react to heat the raw mate rial and to at least pre-calcine the raw meal. The process in the calciner thus in cludes a so-called secondary firing, requiring oxygen. , a calciner is a flow reactor providing a corresponding reactor space.

The calciner is mostly an elongated mostly vertically extending conduit in which the mixture flows essentially vertically upwards while the reactions (combustion and pre-calcination) take place. The upstream end is thus at the bottom and the downstream end at the top, as the mixture of gas, fuel, raw material and resi- dues flows from the bottom end to the top end. The top end of the calciner is connected by so called connection tubes to a cyclone (or any other gas-solid sep aration means) in the vicinity of the kiln's raw meal inlet for separating at least a majority of the pre-calcined raw meal (and solid fuel residues) from the hot gas es. The pre-calcined raw material is provided to the kiln and the hot gases can be used as a heat source, typically in the pre-heater tower.

In other words, the raw materials which are necessary for the production of ce ment clinker are at least partly de-carbonized in the calciner, using the thermal energy provided by the tertiary air and optionally the kiln exhaust gases, directly, whereas the oxygen contained in the tertiary air is used for the combustion of fuel in the secondary firing, to further increase the temperature of the raw mate rial in the mixture.

A typical flow of the mixture in the calciner is essentially laminar, as there is es sentially no mixing of the gas flow orthogonal to the flow direction. Inhomogene ities in the distribution of raw material, fuel and oxygen at the inlet end of the calciner are thus essentially maintained while the mixture of fuel, gas and raw materials reacts. Thus, the temperature, fuel, CO2, O2 and CO-concentration as well as raw material concentration is in-homogeneous over the cross section of the calciner. For example, a piece (including droplets) of fuel in the calciner may be surrounded by gas having a certain oxygen content. Thus, initially the fuel and the oxygen react as intended, but when the oxygen content decreases, the com bustion may be incomplete causing a raised CO-concentration. Another piece of fuel may be surrounded by a gas with a higher oxygen content, enabling the an other piece of fuel to entirely react as intended with the oxygen in its vicinity and potentially there may be even some oxygen left. Accordingly, in this portion of the stream the CO-concentration is lower than in other portions of the stream.

The temperature may have a local maximum, as well. These inhomogeneities are problematic, as they may lead to an inhomogeneous pre-calcination of the raw material and in addition to uncontrolled oxidation of CO or other combustibles in the cyclone or any other downstream (referencing here to the flow of the gas) gas treatment. An uncontrolled oxidation may even be discontinuous, like an explosion and even if it is continuous, heat is produced in a section of the clinker plant where it is not required, and which section is typically not designed for the corresponding elevated temperatures. The situation is even worse, if the calciner exhaust gases are split at its top and provided to two connection tubes connect ing the calciner with two parallelly operating pre-heater towers (via separate gas-solid separation means): In this case the gas inlet temperatures of the two pre-heaters can be different. Further, the CO-, O2-, CO2-, fume-, etc. concentra tions in two streams provided to the two pre-heater towers are different. This is not acceptable when designing a cement clinker plant.

To address these problems it has been suggested to place a cyclone (see DE 4026814 C2) for separating particles from the gas at the top end of calciners and to recirculate the particles into the calciner. The degree of pre-calcination is enhanced by the suggestion of DE 4026814 C2.

EP 0003 123 A1 suggests a calciner with a conical upright chamber. Kiln exhaust gas enters at the bottom portion of the chamber and flows upwards, passes fuel injectors and an air inlet for receiving preheated air from a clinker cooler ex haust. At the bottom portion of the chamber are guide vanes providing an angu lar momentum to the kiln exhaust gas flowing upwards. The guide vanes enable to adjust the cooler exhaust air to secondary air proportion in the reaction space above the cooler exhaust air inlet.

FR 2538521 A1 and EP 2690074 A1 each suggest a calciner with longitudinal symmetry axis. The calciners have a varying free diameter to adjust the flow ve locity of the raw meal suspension in the respective sections of the calciner.

Summary of the invention The invention is based on the observation that the additional cyclone as suggest ed by DE 4026814 C2 has the disadvantage of being huge, heavy and expensive.

In particular, retrofitting of existing installations with a calciner is difficult if not impossible as there is often simply no space for a bulky cyclone. In addition, the solid-gas separation at this stage of the process is problematic as the hot ground raw material may adhere. Further, already existing pre-heater towers are usually not designed to support the additional load of a cyclone.

The problem to be solved by the invention is to enable retrofitting existing ce ment clinker installations with a calciner even when there is limited space for an additional cyclone or when existing pre-heater towers cannot take the additional load of a cyclone.

Solutions to the problem are described in the independent claims. The depend ent claims relate to further improvements of the invention.

A usual, a calciner of a cement clinker plant according to the invention has a conduit providing a continuous flow reactor space. The conduit thus has a reac tor space being enclosed by a side wall of the conduit, defining an inlet in and an outlet out of the enclosed reactor space, thereby enabling a macroscopic flow of a fluid via the enclosed reactor space along a trajectory from the inlet to the out let. The fluid can be a mixture of at least two of tertiary air, fuel, raw material, fumes and/or clinker dust. The trajectory is preferably a straight line. The trajec tory may be curved as well, e.g. have the shape of an inverted U, but for simplici ty herein we will consider it to be a straight line. The trajectory may be consid ered as a line being positioned in the center of the reactor space. The trajectory can be considered as the longitudinal axis of the conduit (, in case it is not curved) or of straight sections of the conduit. The conduit has at least a first sec tion with a first sidewall portion having a first surface enclosing a first portion of the reactor space. As normally understood, the term section of the conduit refer ences to a portion of the conduit being delimited by section planes being or thogonal to the trajectory. A section of the conduit, hence, has a wall forming a ring surface. In other words, the first surface is a ring surface, hereinafter 'ring' for short. The terms "first surface" (more general n ^th surface) and "first ring" (more generally n ^th ring, n being a positive integer) may thus be used inter changeably. The portion of the trajectory extending through the respective (n ^th ) section of the conduit is the respective (n ^th ) ring's or section's longitudinal axis.

In operation, the raw-meal, fuel, tertiary-air, exhaust gas mixture flows through the lumen defined by the rings from section to section along the trajectory.

In a preferred embodiment, this at least one first section is below the upper end of the calciner, i.e. below the typical U-shaped section of a calciner and prefera bly forms a part of the rising pipe being upstream of the U-shaped top section. It can as well be a portion of the downpipe, i.e. downstream of the U-shaped top section.

Preferably, the first section has at least one first surface portion being inclined towards the trajectory and a second surface portion being inclined away from the trajectory. Inclining a surface portion towards the trajectory means, as usual that the distance between the trajectory (which is defined as the line in the mid- die of the first section) and the first surface portion decreases in the flow direc tion. Accordingly, a surface being inclined away from the trajectory has an in creasing distance from the trajectory in the flow direction. These inclinations of the surface portions enable to create vortices in the flow which provide for more homogeneous distribution of the constituents of the flowing fluid in the calciner. Another advantage is that the fuel efficiency is increased and the length of the calciner can be reduced.

For example, by inclining the first and second surfaces as described above, the cross-sectional area of the reaction space may be varied along the trajectory, i.e. in the direction of the intended fluid flow. Thereby, turbulences can be produced in the fluid. These turbulences reduce inhomogeneities in the fluid across the cross-sectional area of conduit. In other words, the first section preferably has a first portion and a downstream second portion, wherein the cross-sectional area in the first portion may de- or increase whereas the cross-sectional area in the second portion in-or decreases along the trajectory, respectively. For clarification it is noted, that as usual, a sequence of section planes being orthogonal to the trajectory defines a corresponding sequence of cross-sectional areas of the reac tor space along the trajectory, respectively.

For example, the first section may be downstream of a receiving section of the conduit. For example, the conduit may be installed at least essentially upright (i.e. vertical°±15°, ±10°, even more preferred ±5°, or better) to provide a corre sponding upward fluid flow. In this case the first section may be positioned above a receiving section.

The side wall portion of the receiving section may enclose a portion of the reac tor space, which is the reactor space portion of the receiving section. Preferably, the side wall of the receiving section encloses an at least essentially circular cy lindrical reactor space portion. At least essentially means here, that the deviation of the radius r(cp) from the mean radius r _m are smaller or equal 15%, i.e.

Max(V (r(<p) - r _m ) ² ) < 0.15 <1.15-r _m , preferably 0.9· r _m ^r(cp) <l.l-r _m , even more preferred 0.95· r _m £r(cp) <1.05-r _m or even 0.975· r _m £r(cp) <1.025-r _m , or better; as usual f indicates an an gle in a section plane orthogonal to the cylinder axis, i.e. f is the azimuth). In practice, the wall enclosing the reactor space has a metal skin with some lining or (inner) cladding of some fire-proof material, like refractory, bricks or other kind of fire-proof materials. Thus, the surface defining the reactor space of the receiv ing section is in practice not perfectly cylindrical but limited by the fire-proof material.

In between of the receiving section and the first section may be an intermediate section connecting the receiving section with the first section by an intermediate portion of the side wall, enclosing an intermediate portion of the reactor space. The cross-sectional area at the up-stream end of the intermediate section is preferably smaller than the cross-sectional area at the downstream end of the intermediate section. The intermediate section contributes to maintaining an essentially constant mean flow speed of the fluid in the receiving section and in the first section. Unintended deposition of raw material is reduced as well as the energy required for providing the fluid flow through the calciner. For example, the mean cross-sectional area along the trajectory of the first section may be equal within ±30% (preferably ±10%, more preferred ±5%, even more preferred ±2.5% or better) to the cross-sectional area of the receiving section.

In a preferred example, the first surface may have at least a one segment herein after referred to as first first surface segment (, indicating that there may be at least a second first surface segment as well). The first first surface segment is thus a ring segment of the first surface. The first first surface segment may have a downstream (first) edge, wherein the edge extends along a first line, preferably along a first straight line. The downstream edge provides for turbulences in the fluid flow and thereby contributes to a homogenization of the fluid.

As already indicated above, the first surface may have at least one second first ring surface segment. This second first surface segment may have an up-stream edge. The upstream edge of the second first surface segment and the down stream edge of the first first surface segment may meet, thus the corresponding wall segments may form a first edge having the contour of the first line. In other words, the first first surface segment and the second first surface segment each have an edge, which extend along the first line. Preferably, the first first surface segment and the second first surface segment are inclined relative to each other. These optional constructional improvements contribute both to a simple and thus cost efficient calciner and to an improved homogenization of the fluid.

In a particularly preferred example, the first line is inclined relative to the trajec tory. This means that a parallel projection of at least one of the first lines onto the trajectory intersects the trajectory in a non-orthogonal angle. In a side view, the first line is thus inclined relative to the flow direction in the first section. This inclined edge provides for a rotation of the fluid around the trajectory. Thus, the direction of the (macroscopic, i.e. assumed laminar) fluid flow has two compo nents, a first component being parallel to the trajectory and a second component being tangentially to a circular cylinder which is centered on the trajectory. The additional tangent component (being described by an angular speed) results in a helical flow and thus the inclination of the first line does not necessarily but may enhance homogenization of the fluid over the cross sectional area. At least, it contributes to evenly distribute the products leaving the reactor via a Y-junction (i.e. a bifurcation as well referred to as y-piece) into two conduction tubes. The inclined (oblique) line provides in addition for a rotor in the flow, wherein the rotor axis is parallel to the line. This turbulence together with the super posi- tioned helical flow provides for a particularly effective homogenization of the constituents and temperature in the flowing suspension.

For example, the parallel projection of the first line may intersect the trajectory in an angle y. The absolute value of the angle y may take any value between 0° and 90°, i.e. 0< y<90°, for example 10° < y <80°, preferably 20° < y <70°. For ex ample the absolute value of the angle y may be at least essentially 45° (or 30°), wherein at least essentially means 45°±15° (or 30°±15°), preferably 45°±10° (or 30°±10°), even more preferred 45°±5° (or 30°±5°) or better. These angular ranges provide a preferred balance of additional energy consumption for propelling the fluid through the first section and angular velocity of the fluid flow.

As already apparent from the above, the inclined surface segments, e.g. the first first and the second first surface segments, may be ring segments of a section of the conduit. The different surface segments of the ring can in some embodi ments be distinguished by their different angular positions, i.e. they may span or extend over different, i.e. non identical, azimuth ranges. At least two different, preferably differently inclined, surface segments of a section of the conduit (e.g. the first fist and the second first surface segment) span over overlapping ranges along the trajectory and/or over overlapping azimuthal ranges.

Preferably, at least one cross section of the section of the conduit extends through the at least two preferably inclined surface portion. At the connection of the two surface segments the cross section of the ring preferably shows a change in curvature, e.g. a kink. As explained above, the two different surface segments may preferably have congruent edges extending along the first line as explained above.

In a particular preferred example, the first surface is discontinuously symmetric under a rotation around an axis being defined by the trajectory portion of the first section. This may sound complicated, but it indicates, that there are multiple first and second surface segments defining multiple first lines (and thus a corre sponding number of first edges) and that these elements are repetitively posi tioned around the trajectory and configured that a rotation of the first section in increments of 360° (2p) maps the first surface on itself. The rotation may be at an angle a of 360°/n (i.e., a=360°/h=2p/h), wherein n is an integer with n>l. In practice smaller numbers of n, e.g. l<n<17 (or l</i<37) are preferred. The dis continuous symmetry simplifies construction as the constructional elements can have straight edges and plane surfaces, while at the same time the number of flow homogeneity increasing edges, surface segments, first lines, etc. is aug- mented.

The conduit may have at least one second section positioned downstream the first section, wherein the side wall portion of the second section has a second surface enclosing the reaction space of the second section. This second surface is preferably congruent to the first surface. For example, the first section and the second section may be identical and/or may be positioned one on top of the other. The second section may be rotated around the trajectory relative to the first section. In other words, mapping the second surface onto the first surface requires at least a rotation of the second surface around an axis being defined by the trajectory portion of the second section. Assuming the trajectory to be a straight line, in addition a translation parallel to the trajectory is required. If the trajectory is curved, additional rotations may be required. In a preferred exam ple, the first and second surfaces are congruent and are discontinuously sym metric under a rotation around an axis being defined by the trajectory portion of the first or second section, respectively. In this example, the second portion is preferably rotated by half of the angle defining the optional discontinuous sym metry of the first surface, (which is given by the smallest angle of rotation which maps the first surface onto itself). To stay in the above example the smallest an gle may be a=360°/n. The rotation of the second section relative to the first sec- tion may then be b=3607(iti·h), wherein m may be an integer, preferably a small integer, e.g. l<m<5, alternatively: l<m<17 or l<m<37). These measures as well improve evenly distributing products leaving the reactor via a Y-junction (i.e. a bifurcation as well referred to as y-piece) into two conduction tubes, while keep- ing construction costs low.

Preferably, the cross-sectional area of the conduit is at least essentially constant in the first (and/or the second and/or any other) section. In other words, at least two cross sections of the first section preferably have the same free cross- sectional area enabling the gas-dust suspension to flow through the calciner's first section, thereby providing an at least essentially constant flow speed along the trajectory. Preferably, at least a set (e.g. all) of cross sections of the first sec tion have at least essentially the same free cross-sectional area, wherein at least essentially indicates that "the same" is preferred, but variations of ±10%, ±5%, ±2.5% or less of the mean cross sectional aera of the first section can be accepted. For example, these variations be caused by a fire-proof cladding or lining of the reactor wall.

In a preferred example, the inner contour of a first cross section of a section of the conduit (e.g. of the first, second or generally n ^th section, n being a positive integer) may have a broken rotational symmetry, wherein the trajectory in the respective section is considered as rotational axis. For clarification: The first sur- face(the ring) is preferably not rotationally invariant, but instead may for exam ple have a discontinuous rotational symmetry, wherein the respective section of the trajectory is considered as symmetry axis. A second (e.g. downstream) cross section of same first section is preferably congruent to the first cross section (and thus has the same cross sectional aera), but rotated around the trajectory (i.e. the trajectory is the rotational axis, if it is straight). In other words, a simple translation of the first cross section along the trajectory does not map the first cross section on the second cross section, but adding the rotation to the transla- tion does. Thus, the first and the second surface segments both contribute to define the contour of the respective cross-sectional surface. The first first and second first segments may both define different parts of the cross-sectional con tour. Where these two segments meet, the contour shows a change in curvature. Preferably, there is an adapter section between the first section and the second section thereby simplifying assembly of the calciner. The adapter section may have an at least essentially circular cylindrical adapter surface. Alternatively, the cylindrical surface may be defined by a closed directing curve (c.f. Handbook of Mathematics, Bronshtein, Semendyayev, et al., Springer Berlin, 5 ^th ed., Chapt. 3.3.3) having a discontinuous rotational symmetry, e.g. with an angle of =360°/(m-n), as defined above. Both alternatives simplify construction of the conduit. As already apparent, the adapter surface encloses the adapter section's portion of the reactor space.

In the same way (i.e. with or without adapter) any further number of preferably congruent sections may be connected to each other to enhance a homogenous fluid in the calciner. Thus, there may be a third and/or a fourth and/or fifth sec tion.

The conduit may form the calciner or be a part of the calciner. The calciner may be integrated in a cement clinker plant. 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 first example calciner with a bifurcation and conduction tubes. Figure 2 shows a top view of a first section of the calciner of Fig. 1.

Figure 3 shows an example calciner with a bifurcation and conduction tubes.

Figure 4a -d show a first section of the calciner of Fig. 3.

Figure 5a-d shows a number of stacked first sections of a calciner Figure 6 shows a cement clinker plant with a calciner.

In figure 1 a first embodiment of calciner 10 of a cement clinker plant is shown. The calciner 10 has conduit with an inlet 12. As indicated by an arrow 3, a fluid may flow along a trajectory 2 through the reaction space 20 inside the cal ciner 10. At the top of the calciner 10 is an optional bifurcation 60 enabling to connect the reaction space 20 and thus the conduit of the calciner 10 with two connection tubes 90, which may be considered as forming part of the calciner as well. The connection tubes 90 may each be connected via a separate gas-solid separation means with a kiln and a preheater tower.

The upstream portion of the calciner 10 may be considered as a receiving sec- tion 50. In this example, the receiving section 50 is at least essentially circular cylindrical, i.e. it has an essentially circular cylindrical sidewall 51 with a circular cylindrical inner surface 52 enclosing the respective portion of the reaction space 20. Herein, we use the same reference numeral for sidewall portions as for the respective inner surfaces enclosing the reaction space 20, because the side wall portions define the respective surfaces and thus the reaction space 20. As explained above, the invention provides for a particular shape of at least a por tion of the reaction space 20, being defined by the surface enclosing the reaction space 20. Thus, describing the surface (being defined by the side wall(s)) is a de scription of the reaction space 20. The downstream end of the receiving section 50 may be connected to the up stream end of an intermediate section 40. The intermediate section 40 serves as an adapter for connecting the receiving section 50 with a first section 30 and has accordingly an intermediate portion 41 of the side wall with intermediate sur face 42.

The first section 30 has an upstream end and may be connected to the down stream end of the intermediate section 40. As apparent, if the contour of the receiving section 50 and the first section 30 match, the intermediate section 40 may be omitted.

The first section 30 may have a first surface enclosing a first portion 21 of the reaction space 20 (see Fig. 2.). In this example, the first surface is defined by a number (in this example four, other positive integers may be possible as well) of first first surface segments 31 and second first surface segments 32. The first first surface segments 31 are inclined towards the trajectory 2 and each have a downstream (first) edge 33, which first edges 33 in this example each have the shape of a straight line (other shapes are possible as well). Due to the inclination, the distance of the downstream edges 33 to the trajectory 2 is shorter than the distance of the corresponding upstream edge of the first first surface seg ments 31.

An upstream edge of a second first surface segment 32 may be attached to these downstream edges 33, thus a corresponding second first wall section 32 may be attached to the first first wall section 31 thereby forming the first edge 33 as joint edge. These second first surface segments 32 may be inclined away from the trajectory 2, as depicted, i.e. the distance of the first edges 33 to the trajec tory may be smaller than the distance of the downstream end of the second sur faces to the trajectory 2. The inclinations of the first and second first surfac es 31, 32 may induce a macroscopic vortex of the fluid flowing through the reac- tor space 20 and in addition turbulences providing for homogenization of the fluid flowing through the conduit. The macroscopic vortices provide for a com paratively low pressure drop, at least in relation to turbulences.

As can be seen in Fig. 1, the parallel projections of the edges 33 onto the corre sponding section of the trajectory 2 may intersect the trajectory in a non- orthogonal angle. In this specific example, the angle between the trajectory and the projections is about 30°, preferably 30°±15°, preferably 30°±10°, even more preferred 30°±5° or better; but other angles can be chosen as well.

In the depicted example of Fig. 1, the first surface consists of the first first sur faces 31 and the second first surfaces 32. It may include additional surface seg ments. In the depicted example, the first surface 31, 32 has an optional discon tinuous rotational symmetry: A rotation of the first surface by any integer multi ple of a, wherein a=90°=360°/n with n=4 maps the surface onto itself (see Fig. 2). Other discontinuous rotational symmetries may be realized as well (i.e. other values for n as explained above).

Attached to the downstream end of the first section 30 may be an upstream end of a second section 30'. The second section 30' may be, as depicted, a copy of the first section 30, i.e. the second surface may consist of first and second sec ond surface segments 31', 32'and may be congruent to the first and second first surface segments 31, 32. Except for the position in the conduit, the description of the first section 30 may be read as well on the description of the second sec tion 30' and the third sections 30'', by simply adding a prime ' or two primes " to the reference numerals, respectively. Thus, in the depicted example, the optional second section 30' has a second surface 32' which accordingly has first second and second second surfaces 31', 32'. The depicted example of the optional third section 30'' has a third surface which accordingly has a first third surface 31'' and a second third surface 32”. An optional fourth section BO'” (not shown) would thus have first and second fourth surface segments 31"', 32'" and so forth.

In the depicted example, the second section 30' is rotated relative to the first section by an angle b, wherein in this particular example b=a/2, as an example for b=360 ^o /(iti·h), as explained above, i.e. m and n can take other values than 2 and 4, as well. Thus, to map the second section 30' onto the first section 30, it is sufficient to rotate the second section 30' by the angle b and to translate it up stream along the trajectory 2.

Downstream the second section 30' is an optional third section 30”. The third section 30” may be, as depicted, a copy of the first section 30, as well, i.e. the third surface may have at least first and second (third) surface segments 31”,

32”. Thus, the third surface 31”, 32” may be congruent to the first and second first surface segments 31, 32 as well as to the first and second second surface segments 31', 32'. In principle the conduit of the calciner 10 has a number of first sections that are stacked onto each other. Only to enable a simple distinction, we will reference to these sections 30' and 30” by their positions relative to the first section 30.

The third section 30” may be connected via an optional downstream intermedi ate section 40' and an optional bifurcation 60 with at least one connecting tube 90.

As already apparent, the wording ‘connecting sections of the conduit’ is intended to mean assembling the sections to provide a conduit providing a fluid communi cation between the sections of the conduit. A connection of two sections may be a direct connection as shown in Fig. 1 for the first section 30 and the second sec- tion 30' or as well an indirect connection as shown in Fig. 1 for the receiving sec tion 50 and the first section 30 being connected to each other by the optional intermediate section 40 in between of them. Another example is depicted in Figures 3 and 4a-d. The general construction is very similar to the first example as depicted in Fig. 1 and 2, wherein Fig. 3 corre sponds to Fig. 1. The description of the first example can essentially be read on Fig. 3 and 4a-d as well and we will focus on only the differences of the second example to the first example. Fig. 4 a is perspective view of the first section 30,

Fig. 4b a side view of the first section 30, Fig. 4c a sectional view of the first sec tion 30 along the plane A-A as indicated in Fig. 4b, and Fig. 4d is a top view of the first section 30.

Like the first example, the calciner 10 in Fig. 2 and 4a-d has a conduit with multi- pie sections, a receiving section 50, an intermediate section 40, a first section 30, a second section 30', third section 30”, and a downstream intermediate sec tion 40' (see Fig. 3). As in the first example, any of these sections may be omit ted, provided a single one of these remains part of the calciner 10. The main dif ference of the second example compared to the first example is the contour of the reaction space 21 of the first section 30 (and the second and third sec tions 30', 30”, analogously) as defined by the side wall 31, 32 and 34 and the corresponding first first surface segment 31, the second first surface segment 32 and a third first surface segment 34. The third first surface segment 34 has the contour of a circular cylinder surface, wherein the cylinder axis defines the tra- jectory 2. The upstream end of the inclined first first surface segment 31 forms a second edge 35 with the third first surface 34. This second edge 35 is closed to form a ring and meets both ends of the (first) edge 33 (see Fig. 4a-d). As above, the first edge 33 is defined by the downstream edge of the first first surface segment 31 and the upstream edge of the second first surface segment 32. The downstream end of the second surface 32 merges into the third surface 34 thereby defining the downstream portion of the second edge 35.

As depicted in Fig. 4b, the edges 33 of the first section 30 are inclined by an angle y relative to the trajectory 2. To be more precise, a parallel projection of the first line 33/ first edge 33 onto the trajectory intersects the trajectory as depicted in an angle y (and as well 180°- y). In this example y=30°, but y is not limited to this value. The angle y can take any reasonable value between 0° and 90° (i.e. 0< y <90°). For example, 10° < y <80°, preferably 20° < y <70°.

As in the first example, the first and second first surface segments 31, 32 (and the corresponding wall sections) can be at least essentially plane.

Figures 5a-d show another example of stacked first, second and third sec tions 30, 30', 30” of a calciner 10. Each of these first, second and third sections 30, 30', 30” may replace any of the first, second and third sections 30, 30', 30” in the examples being depicted in Fig. 1 and Fig. 3.

Fig. 5a is perspective view of the stacked sections 30, 30' and 30”, Fig. 5b a side view of the of the stacked sections 30, 30' and 30”, Fig. 5c a sectional view of the stacked sections 30, 30' and 30”along the plane B-B as indicated in Fig. 5b, and Fig. 5d a sectional view of the of the stacked sections 30, 30' and 30” along the plane A-A as indicated in Fig. 4b. Again, the description of the first, second and third sections above can be read on this example as well. We will mainly discuss differences of the example of Fig. 5a-d to the other examples.

Again, the stacked sections 30, 30'and 30”may be congruent to each other, as depicted and they may be rotated by an angle of b=45° relative to their respec tive neighbored section(s) 30, 30' and 30”. Other angles are possible as well. For simplicity, we will refer to the first section 30 only, as a skilled person under stands the corresponding details of the second and third sections 30', 30” can be identified by simply adding a prime or a double prime to the corresponding ref erence numeral.

As can be seen best in Fig. 5a, the first section has an upstream conical side wall portion 36, providing a fourth first surface segment 36. In the upstream conical sidewall portion, the radius of the reactor space 20 increases along the trajecto ry 2. The conical side wall portion 36 emerges into a cylindrical side wall portion 34. As can be seen, in this example the cylindrical side wall portion 35 consists of a number of congruent ring segments with a circular cylindrical symmetry. Thus, in this example the radius of the reactor space 20 remains constant where con fined by these side wall portions 34. Downstream of the cylindrical side wall por tions 34 may be another conical side wall portion 36 (providing a further fourth first surface segment 36), but in this downstream portion the radius of the reac tor space decreases preferably at least essentially (±10° or better) to its initial value.

The first section 30 may further have at least one first first surface segment 31 being inclined towards the trajectory 2 and a second first surface segment 32 being inclined away from the trajectory 2. In the cross sectional view the first and second first surface segments 31 and 32 can be identified particularly easy. As can be seen in Fig. 5a to 5d, the first and second first surface segments 31 and 32 may form an edge 33, which may be inclined as explained with respect to Fig. 4b. These first and second first surface segments 31 and 32 may be delimited by a second edge 35.

Figure 6 shows a cement clinker plant. Raw materials 120 are provided to a pre heater tower 130. In the pre-heater tower 130, the raw materials 120 are pre warmed by flue gases from a kiln 100 and/or a calciner 10 using cyclones 131.

The preheated raw material is fed to the inlet of the calciner 10, e.g. to the in let 12 of the calciner 10 in one of Figures 1 or 4. From the calciner 10 the raw material and the gas are provided via connection tube 90 to a cyclone 131 of the pre-heater tower 130. The calciner 10 may preferably comprise a conduit with at least a first section 30 as depicted in Figures 1, 3 or 5. It may as well have a sec ond or a third section as explained above. Additional sections may be provided as well. The pre-treated raw material is next fired in the rotary kiln 100 and re- leased as clinker to a clinker cooler. In the clinker cooler the hot clinker is cooled down by a coolant. A portion of the heated coolant is provided by a tertiary air duct 150 to the inlet of the calciner 10 as well. Another portion of the heated coolant enters the kiln 100 and is used as secondary air. The remaining part of the heated coolant can be used to provide thermal energy to other (sub)processes.

The hot gas exiting the cyclonelBl may be used as heat source in the preheater tower 130. As apparent, for simplicity only a single connecting tube 9f and only a single preheater tower 130 are depicted. In practice, there may be multiple, e.g. two preheater towers 130. In this case each preheater tower 130 receives a por tion of the gas raw material mixture via a corresponding connection tube 90 from the calciner 10.

List of reference numerals

2 trajectory / longitudinal axis

3 direction of fluid flow

10 calciner

12 inlet

13 outlet

20 reaction space

21 reaction space of first section

30 first section

31 first first surface segment

32 second first surface segment

33 first edge (of the first section)

34 third first surface segment

35 second edge (of the first section)

36 fourth first surface segment 30' second section 31' first second surface segment 32' second second surface segment 33' first edge (of second section) 34' third second surface segment 35' second edge (of second section) 36'' fourth second surface segment 30'' third section 31" first third surface segment 32" second third surface segment 33" first edge (of third section) 34" third third surface segment 35" second edge (of the third section) 36" fourth third surface segment (upstream) intermediate section

(upstream) intermediate portion of side wall / intermediate surface (downstream) intermediate section

(downstream) intermediate portion of side wall / intermediate sur face receiving section receiving portion of side wall / receiving surface Y-junction / bifurcation connecting tube kiln raw material pre-heater tower cyclone cyclone clinker cooler tertiary air duct