GASIFICATION REACTOR COMPRISING A PRESSURE ABSORBING COMPLIANT STRUCTURE

TECHNICAL FIELD

The present invention relates to a reactor for gasification of feedstocks for gasification, adapted to handle feedstocks for gasification comprising organic and inorganic compounds, wherein said compounds during gasification in the presence of oxygen and/or air at a gasification temperature, wherein the melting temperatures of the constituent inorganic compounds is at least 100° C. lower than the gasification temperature, are converted to a hot reducing gas above 950° C. but below 1300° C. and comprising CO, CO₂, H₂and H₂O (g), and a salt melt, wherein said reactor comprises an outer reactor shell and an inner refractory lining, wherein a compliant structure is placed in a ring-shaped coaxial expansion space between said outer reactor shell and said inner refractory lining.

The invention also relates to a method for manufacturing and disposing a compliant structure between a reactor shell and an inner refractory lining in a gasification reactor.

STATE OF THE ART

Black liquor is a valuable product produced in very large quantities in pulp mills during the production of paper pulp from wood raw material. In a thermo-chemical reactor developed by Chemrec AB, black liquor from pulp mills can be gasified with oxygen or with air-oxygen mixture, with the purpose of recovering both energy and chemicals from the black liquor. In the gasification reaction, a corrosive salt melt and an energy-rich gas are produced. The salt melt is cooled by a water spray in the lower portion of the reactor, where it is subsequently dissolved and forms green liquor. The green liquor is then used for production of new cooking chemicals in the pulp mill. The gasification reaction can be carried out at atmospheric pressure, or at an elevated, relatively high gas pressure in the reactor system. The gasification reaction produces an energy-rich and hot gas, and a hot salt melt. The reaction suitably takes place at a temperature of about 1000° C. in a steel reactor lined with ceramic materials.

The chemicals produced during the gasification of black liquor mainly consist of a mixture of Na₂CO₃, Na₂S and NaOH, melting at about 740° C. and forming a low-viscosity salt melt, which has a good wettability to ceramic bricks. The melt thus produced in the reactor maintains the temperature of the reactor, which is about 1000° C. It can therefore penetrate deep into the hot furnace brickwork, before it solidifies in the cooler outer portions of the brickwork. The penetrating melt reacts slowly with the hot portion of the furnace brickwork and forms new solid ceramic phases therein, which causes the furnace brickwork to slowly but inevitably increase in volume and size during operation. For this reason, there has to be a sufficient expansion space between the inside of the reactor wall and the outside of the furnace brickwork during the operation of the reactor to avoid the occurrence of dangerously high mechanical loads in the reactor wall. As a rule, ceramic materials have a very high compressive strength, for which reason an expanding ceramic lining can overload a reactor shell, even if mechanically very strong, if the expansion is allowed to continue for a long time.

Gasification plants, intended to be used for energy and chemical recovery in pulp mills, are expected to be capable of continuous operation for a very long period of time. Scheduled maintenance shutdowns are performed only once every 12-18 months in modern pulp and paper mills and are then carried out in 1-2 weeks. Therefore, unscheduled shutdowns in the gasification plant can result in costly disturbances in the energy and chemical recovery system of the mill. Longer production shutdowns for repairs of the gasification plant or the recovery system results in a considerable loss of pulp and paper production. For this reason, very high demands are made on the operational availability of such a plant. Since a gasification plant produces large quantities of a hot and corrosive salt melt which is subsequently dissolved in water and forms an alkaline green liquor that is used in the chemical recovery process, and large volumes of an energy-rich and combustible gas containing poisonous substances, high demands are made on a good system safety in the gasification plant.

The gasification reaction of black liquor from a pulp mill can be schematically described by a chemical reaction equation, see the equation below, where entering black liquor, BL(aq), and oxygen, O₂(g), are mixed and react, or rather are burned, in a partial combustion in the gasifier, wherein a salt melt, Me₂A(l), and an energy-rich gas, G_x(g), are produced, at the same time as heat is generated by the partial combustion. The equation below also indicates approximate molar quantities converted in such a reaction at a temperature of about 1000° C. From the equation, it is evident that when one mole of Bl(aq) is gasified with 13 moles of oxygen, 2,7 moles of salt melt with the typical composition Me₂A(l), and 77 moles of various gaseous substances, herein briefly designated as G_x(g), are produced, at the same time as heat is generated.

1BL(aq)+13O₂(g)→2,7Me₂A(l)+77G_x(g)+heat

The contents of the constituent elements in black liquor can be determined by chemical analysis. The composition of black liquor BL(aq), also called thick liquor, from Swedish Kraft mills can be well described by a simple chemical equation, including a water content typical of black liquor, see the equation below. Thick liquor from sulphite mills has a substantially different composition with, among other things, a considerably higher sulphur content in the black liquor. Pulp mills collecting their wood raw material from areas close to the sea will get elevated chloride contents in the black liquor.

BL(aq)=Na_8,5K_0,5C_31,5H_35,5O_22,3S_1.5N_0,1Cl_0,1.19,5H₂O

The produced gas phase, G_x(g), comprises a large number of different gaseous substances. The predominant substances in the gas phase are primarily the molecules H₂, H₂O, CO, CO₂, H₂S, CH₄and N₂, but also small amounts of gaseous sodium and potassium compounds, such as NaOH(g), NaCl(g), KOH and KCl(g), are formed.

The produced salt melt, Me₂A(l), comprises a mixture of positively and negatively charged ions. The melt can be described as a homogeneous ion melt, primarily comprising the ions Na⁺, K⁺, CO₃²⁻, S²⁻, Cl⁻and OH⁻. Also small amounts of various other ions are present in the melt, such as, for example, Ca²⁺, Mg²⁺, SiO₄⁴⁻, PO₄³⁻, SO₄²⁻, and S₂²⁻, originating from the wood raw material but also from chemicals added in the pulp mill.

The salt melt has low viscosity down to a temperature of about 740° C., at which it solidifies into a substantially solid salt, consisting of Na₂CO₃(s) and Na₂S(s). After this, there is still a small residual volume of an alkaline salt melt with a considerable content of Na⁺ and OH⁻and Cl⁻ions, which does not solidify until at a temperature of about 400° C. The salt melt is highly corrosive to metals already at a temperature of about 550° C. At a temperature above about 750° C., most metals corrode very quickly if they get in contact with the salt melt. The steel in the reactor shell must of course not be subjected to any significant corrosion or to an inadmissibly high temperature, or be subjected to a high mechanical load from the ceramic lining, neither of local nor general nature, beyond precisely stipulated mechanical strength criteria for the design of the reactor.

In order to maintain a high operational safety and achieve a good recovery of energy, and to avoid disturbances in the chemical recovery and to prevent damages to the ceramic lining or the reactor shell, it is preferred that the gasification reaction takes place at an optimum temperature, and with a suitably large supply of oxygen. Too high a reactor temperature will render the salt melt very corrosive to the ceramic lining, which shortens the service life of the lining. Too low a reactor temperature causes the gasification reaction to proceed very slowly, the reactor gets a negative thermal balance, wherein the gasification reaction stops completely and the salt melt solidifies.

Furthermore, the salt melt becomes heavily contaminated with soot and poorly combusted black liquor by operation at too low a reactor temperature.

Accordingly, the melt solidifies at about 740° C., a temperature which is located deep inside the ceramic lining. This leads to another mechanism causing volume expansion. When the reactor cools down, a volume reduction of the melt and the ceramic lining occurs. The thus resulting additional “volume of cracks” from the cooling is filled with melt from the hotter inside of the ceramic lining through the capillary force. In this way, gradually more and more melt is drawn into cracks and joints of the lining, until the melt finally solidifies. This phenomenon will in time cause the ceramic lining to expand in size and adds further to the volume increase produced by chemical reactions between melt and ceramic, and which has been described above. This internal physical expansion is specific to gasifiers gasifying a feedstock at a temperature considerably exceeding the solidification temperature of the melt. The difference becomes clear by a comparison with so called slagging coal gasification (gasification above the melting point of the coal slag). In such a gasifier, the gasification temperature is maintained slightly above (approx. 50° C.) the melting temperature of the coal slag. The slag will then solidify in the surface layers of the ceramic lining, which will therefore gradually expand and leave the surface through so called spalling. The ceramic material deeper inside from the surface will in principle remain unaffected by the coal slag. For this reason, the described volume expansion does not take place in same way as when gasifying black liquor, where the solidification front of the melt is located deep inside the material.

To avoid that the outer steel shell of the reactor is subjected to too high a temperature and then could be damaged by corrosive substances in the gas phase or by the salt melt requires, on the one hand, an inner ceramic barrier that is resistant to the salt melt at a temperature of about 1000° C. for a long period of time, and, on the other hand, a suitable thermal insulation inside the reactor to prevent the reactor shell from being overheated and limit unnecessary heat losses through the reactor wall to the environment. As a rule, several different types of ceramic materials are used as thermal insulation and as chemical barrier inside the reactor, but also other barrier materials, in one or several layers, and which in some cases also have specific properties of value for the structure as a whole.

When a reactor having an inner ceramic barrier is heated from room temperature to about 1000° C., there is a thermal expansion of the ceramic of about 0,8%, whereas the outside reactor steel shell expands considerably less, about 0,25%, since the temperature increase of the reactor shell is relatively small, only about 200° C. The actual thermal expansion is of course dependent on the selection of material and the temperature profile in the reactor, but the indicated values are typical of most furnace designs. For a cylindrically shaped, large reactor having a diameter of about 2 m, and an expected operating temperature on the ceramic lining of about 1000° C., at an initial start-up of the reactor, it is required that there is a radial expansion space of at least 8 mm between the inside of the reactor shell and the outside of the ceramic barrier in the form of a ring formed coaxial expansion space and also a corresponding axial expansion space, depending on the height of the reactor, to avoid contacting between the reactor steel shell and the ceramic lining.

A plurality of mainly high-melting ceramic phases, primarily oxide-containing phases based on the elements Al, Cr, Ca, Mg, Si, and Zr, such as, for example, α-Al₂O₃, Cr₂O₃, 3Al₂O₃.2SiO₂, Na₂O.11Al₂O₃, Na₂O.7Al₂O₃, MgO, MgO.Al₂O₃, CaO and ZrO₂, have proved to be relatively resistant to or slow-reacting with the corrosive salt melt that is produced during the gasification of black liquor. Also mixtures of two or several such ceramic phases, containing α-Al₂O₃, Na₂O.11Al₂O₃, Na₂O.7Al₂O₃, Na₂O.MgO.5Al₂O, MgAl₂O₄and MgO, can be used. Also a mixture consisting of α-Al₂O₃and various types of so called β-alumina phases, where some Na⁺ ions in the β-alumina structure have been replaced with Li⁺, K⁺, Mg²⁺ and Ca²⁺, has been tested. A prerequisite for a good function as both a chemical and a thermal barrier, however, is that the ceramic phases are not subjected to a temperature above about 1300° C. in the presence of the salt melt for a long period of time.

A problem with the constituent ceramics is primarily the above-mentioned chemically and mechanically induced volume increase. Furthermore, at high temperatures, the ceramic lining can react directly with alkaline substances present in the gas phase, which, of course, can easily penetrate by diffusion into all open pores in the lining. These undesired chemical reactions, in combination with accumulated mechanical stresses caused by volume changes, means that the properties of the ceramic can deteriorate in several different ways, so that the materials physically disintegrate into smaller pieces.

Accordingly, as already mentioned, it is a very noticeable problem that results from reactions between the ceramic lining, the salt melt and the gas phase, since many of these reactions result in an increase of the proportion of solid phases in the lining, which, in its turn, causes the ceramic to slowly increase in volume and the required expansion space between the inside of the reactor vessel and the outside of the ceramic lining to be slowly consumed, after which the reactor vessel can be subjected to a dangerously high mechanical load from an expanding lining.

It may seem easy to increase the expansion space between the expanding ceramic lining and the inside of the reactor vessel by using wide open gaps, or a thick compliant ceramic fibre mat, such that the ceramic lining could be allowed to expand considerably without being able to come in dangerous contact with the walls of the reactor vessel.

Unfortunately, a wide gas gap or a thick porous fibre mat has a very low thermal conductivity as compared to a dense and corrosion resistant ceramic lining. Typically, a porous ceramic fibre mat has 1/50- 1/100 of the thermal conductivity of said ceramic. Also a relatively thin fibre mat, that allows for a certain but small expansion space, will therefore result in a flat temperature profile through the ceramic lining as well as a very steeply dropping temperature profile through the fibre mat. Such an unfavourable temperature distribution will, on the one hand, result in an average temperature of the ceramic lining that is too high, and, on the other hand, in a higher temperature on the inside of the ceramic lining toward the melt, which faces an internal strongly radiating hot flame where black liquor droplets react with oxygen. This results in faster chemical reactions between the salt melt and the ceramic lining and in a more rapid expansion of the ceramic. In the worst case, the salt melt may penetrate through the entire ceramic lining and solidify therein, and thereby rapidly destroy the required expansion space for the lining.

The patent publication U.S. Pat. No. 3,528,647 discloses an insulating structure between the steel shell and the lining in metallurgical furnaces. The structure consists of two components: on the one hand, an insulating member of a hard material closest to the lining, and, on the other hand, a stress-absorbing member of a soft material closest to the steel shell. The insulating member consists of silica with bound water and asbestos fibres. The purpose of this component is to avoid heat transfer from the lining to the steel shell. The stress-absorbing member consists of a material which is elastic and capable of deformation, such as fibre felts of mineral wool fibres or glass fibres. According to the teaching of the publication, it is desirable that the insulating material should have a low thermal conductivity to minimize heat transfer. In metallurgical furnaces, however, the expansion occurs only by thermal expansion, whereas the expansion in gasification plants occurs also by chemical reaction. Expansion by chemical reaction is much greater than the expansion resulting from a normal temperature increase of the bricks, i.e. thermal expansion. Furthermore, fibre felts are a very soft material, which means that they do not offer a necessary and controlled resistance to chemical expansion. Furthermore, fibre felts insulate too much, for which reason the temperature gradient criterion is not fulfilled for the gasification plant.

U.S. Pat. No. 6,725,787 discloses a refractory vessel for gasification of black liquor. A crushable liner, having a predetermined yield limit, is to be found in the expansion gap between the metal shell of the vessel and the ceramic lining. Said liner, consisting of a crushable metal foam, provides a controlled resistance to expansion of the ceramic lining. However, after a number of starts and shutdowns of the gasification plant, the resistance ability of the metal foam has been exhausted after having crushed the metal foam completely.

BRIEF DESCRIPTION OF THE INVENTION

It is an object of the present invention to eliminate or at least minimize the above-mentioned problems.

Thanks to the invention as defined in claim 1, a relatively constant resistance force, to a ceramic lining expanding in a gasifier during operation, is obtained over a large deformation range, without causing mechanical overloading of the reactor shell of the gasifier or of the lining inside the reactor.

Furthermore, thanks to the resilience of the compliant structure, a resistance force is obtained which, in a repeated thermal cycle of start and stop type, substantially maintains its ability to generate a certain counter-pressure when restarting the gasifier, resulting in the great advantage that a relatively constant resistance force on the ceramic lining is obtained again when the ceramic lining once more expands by thermal and chemical expansion.

According to one aspect of the invention, it is provided that said compliant structure is adapted to be compressed and deformed with respect to its size in the radial direction of the reactor shell by at least 60%, at a normal pressure of preferably no more than 2 MPa, more preferably in the range of 0.5-1.5 MPa at the same time as a suitably large thermal conductivity can be maintained in the compliant structure. Further that said compliant structure has a resilience of preferably 2-4%, more preferably of 3-4%, during depressurization from operating pressure to atmospheric pressure, and that said compliant structure has a global porosity of at least 60% of the ring formed coaxial expansion volume, henceforth termed expansion space, between the reactor shell and the ceramic lining, preferably of at least 80%, more preferably of at least 90%.

According to another aspect of the invention, it is provided that said structure comprises one or several hollow metal profiles, preferably having a closed section, the cross-section of which exhibiting at least one symmetry axis intersecting the central axis of the metal profile/profiles. Thanks to this symmetry, the metal profiles can be substantially deformed without tilting over toward their profile neighbours, which may cause undesired overlaps between the profiles. A stable deformation in the radial direction of the reactor shell, on the other hand, provides an optimal deformation range.

According to still another aspect of the invention, it is provided that the cross-section of said metal profiles forms a polygon, that said metal profiles have at least 1 longitudinal symmetry axis, and that said metal profiles extend with the central axis in the longitudinal direction of the reactor and substantially in parallel with the central axis of the reactor shell. Thanks to this, straight metal profiles can easily be mounted circumferentially inside a cylindrical reactor vessel, and substantially the entire inside of the cylindrical inner surface can be covered with profiles, with a suitable spacing between the profiles.

According to one aspect of the invention, it is provided the cross-sectional dimensions of said compliant structure is more than 1,5% of the inner radius r of the reactor wall, and that said metal profiles are positioned with such a selected spacing x′ between the outsides of the respective metal profiles that the distance x between the respective metal profiles is at least one millimetre when the metal profiles are deformed/compressed to a maximum. Thanks to the fact that the metal profiles are deformed in a stable manner in the radial direction of the reactor shell, the maximum width of the profiles, when the profiles have been deformed to a maximum, can be calculated, wherein the minimum allowable spacing distance between the profiles, without risking overlapping or plate buckling where they contact each other, can easily be calculated.

According to still another aspect of the invention, it is provided that said metal profiles have mirror-symmetrical cross-sections, with the mirror plane passing through the centre of profile and the central axis and being aligned substantially perpendicularly to the tangential direction of the reactor shell. Thanks to the mirror symmetry and direction perpendicularly to the reactor shell of the profile, a stable deformation is obtained throughout the entire deformation process without any risk of the metal profile tilting over.

According to still another aspect of the invention, it is provided that a barrier material, with such a good thermal insulation that the metal profiles in the compliant structure do not become hotter than about 400° C. during normal operation of the reactor, is placed between said ceramic lining and said compliant structure. Thanks to an additional thermal insulation, it is prevented that any residual melt can reach the metal profiles and cause corrosion on them. Since the residual melt solidifies at 400° C., it cannot reach the metal profile.

According to still another aspect of the invention, it is provided that a porous ceramic blanket is placed between and inside the metal profiles, said blanket filling the free volume inside and between the metal profiles and thereby reducing the heat transport through the compliant structure due to both reduced gas convection and reduced heat radiation. Thanks to the ceramic blanket, the total thermal conduction to the wall of the reactor vessel can be limited.

According to still another aspect of the invention, it is provided that some of the metal profiles are disposed with the central axes perpendicular to the central axis of the reactor shell, between the inside of the reactor shell and the ceramic lining, in the form of coils or concentrically split rings, and the remaining portion of the inside is covered by metal profiles where the central axes are disposed substantially in parallel with the central axis of the reactor shell, so that they together surround the entire inside of the reactor shell. Thanks to the fact that the metal profiles can relatively easily be shaped into coils or rings, solid or split ones, the reactor top which, for durability reasons, usually has a dome shape, can relatively easily be covered with metal coils or concentric profile rings. In the same way, also the reactor outlet, which is usually cone-shaped, can be covered with concentric rings or coils.

According to still another aspect of the invention, it is provided that said feedstock for gasification comprises spent liquors resulting from the production of paper pulp, such as black liquor or sulphite thick liquor. These spent liquors are energy-rich, and provide good operating economy and a comparatively high energy yield.

BRIEF DESCRIPTION OF THE FIGURES

In the following, the invention will be described in greater detail with reference to the attached figures of the drawings, in which:

FIG. 1 shows a circular sector, having an area of about one sixth of a radial cross-section, through the middle of a gasification reactor;

FIG. 2 shows cross-sections of a some different types of pipe profiles;

FIG. 3 shows the design of FIG. 1 on a slightly larger scale;

FIG. 4 shows the counter pressure, P (MPa), against a reactor shell as a function of deformation/compression of a compliant structure, when said structure is deformed between a ceramic lining and the inside of a reactor wall and cross sections of pipe profiles 12-a before and after being compressed;

FIG. 5 shows result graphs from tests on a pipe profile made of the ferritic high strength steel Doga1800DP, wherein the profile has been subjected to a number of pressurization/depressurization cycles.

DETAILED DESCRIPTION OF THE FIGURES

For a detailed description of a conceivable, possible design of a gasification reactor according to the invention, it is referred to gasification reactors developed by Chemrec AB. However, other designs and constructions of the gasifier vessel may also be conceivable, without departing from the scope of the invention. However, to be able to achieve the advantages according to the invention, it is preferred that the gasification reactions take place at such a high temperature that the salt content of the liquor forms a melt, which is handled at a temperature considerably (>100° C.) above the melting point of the salts.

FIG. 1 shows a circular sector, having an area of about one sixth of a radial cross-section 15, through the middle of a cylindrically shaped gasification reactor 100. Said reactor 100 is intended for gasification of feedstocks for gasification, preferably spent liquors resulting from the production of paper pulp, said feedstocks for gasification comprising organic and inorganic compounds, wherein said compounds during gasification in the presence of oxygen and/or air as oxidizing medium at a gasification temperature, wherein the melting temperatures of the constituent inorganic compounds is at least 100° C. lower than the gasification temperature, are converted to a hot reducing gas above 950° C. but below 1300° C. and comprising CO, CO₂, H₂and H₂O, and a salt melt, said reactor comprising an outer reactor shell 7 having a central axis C, said central axis C coinciding with the central axis of the reactor 100, and an inner refractory, ceramic lining 2, 3, 4, which is preferably constituted by one or several ceramic layers, wherein a compliant structure 5 having a resilience is to be found between said reactor shell 7 and said lining 2, 3, 4, and wherein a compliant structure 5 is placed in a ring-shaped coaxial expansion space 6 between said outer reactor shell 7 and said inner refractory lining 2, 3, 4. Said compliant structure has a resilience and comprises a plurality of substantially parallel arranged metal profiles 12, adapted to distribute the compressive load between said reactor shell 7 and the inner refractory lining 2, 3, 4 in that the metal profiles 12 are positioned such that they form substantially parallel, pressure-absorbing bridges having gap areas (22) in between said pressure-absorbing bridges. Said profiles 12 are elastically deformed in a first compression interval ΔY1 and plastically deformed in a second compression interval ΔY2 (as shown in FIGS. 4 and 5).

Gasification temperature refers to the global temperature out of the reactor 100, i.e. which can be considered to correspond to the average temperature that the gas 9 and melt 1 have when they leave the reactor 100. The reaction temperature inside the reactor 100 is considerably higher in certain areas.

In a preferred embodiment, said compliant structure 5 is disposed in an expansion space 6, which space 6, in its turn, is disposed between said reactor shell 7 and said lining 2, 3, 4. The compliant structure 5 can be deformed/compressed when it is subjected to pressure and then partially recover elastically during depressurization. On its inner surfaces, the expansion space 6 can preferably be provided with a barrier material 13, 14, between which the compliant structure 5 is disposed. The barrier material 13, 14 can preferably comprise one or several layers. FIG. 1 also indicates the radial direction 15 of the reactor shell, and that the compliant structure 5 has thickness y extending in the radial direction 15 of the reactor shell.

It can be preferred that a barrier material 13, with such a good thermal insulation that said metal profiles 12 in the compliant structure 5 do not become hotter than about 400° C. during normal operation of the reactor, is placed between said lining 2, 3, 4 and said compliant structure 5.

In some embodiments according to the invention, it may also be preferred that that a barrier material 14 is placed between the inside of the reactor shell 7 and the compliant structure 5, so that the reactor shell 7 is not subjected to high temperatures.

In a repeated thermal cycle of start and stop type, it may be a very desirable advantage for the physical stability of the ceramic lining 2, 3, 4 if the ceramic blocks from which the lining is constructed can always receive a certain supporting pressure, directed inward toward the centre of the reactor, from the reactor shell via the compliant and partially resilient structure 5. Said resilient, compliant structure 5 can compensate for play formed between the ceramic lining 2, 3, 4 and the reactor shell 7, but also minimize the formation of open shrink cracks 10 or voids, which are formed in joints 11 between the different ceramic blocks of the lining when the reactor cools down.

To prevent excessive temperatures on the reactor shell 7, it may be preferred that said reactor shell 7 is cooled to conduct away the heat from the reactor shell 7 to a surrounding cooling medium, usually air 8. For pressure vessel steel, temperatures of about 300° C. are allowable, to be able to meet current strength standards without having to make the wall thickness of the reactor excessively large.

Preferably, said compliant structure 5 comprises one or several thin-walled profiles 12, preferably made of metal. Said profiles may in some embodiments be fixed on a metal plate 19. FIG. 1 shows metal profiles 12 which have a cross-section corresponding to a regular hexagon. The metal profiles 12, in their turn, are preferably constituted by long pipes positioned substantially in parallel with the central axis C of the reactor shell 7, i.e. in the longitudinal direction of the reactor 100. The central axis 21 of the pipe profiles 12 extends substantially perpendicularly to the radial direction 15 of the reactor shell, and the metal profiles, also called pipe profiles 12, are positioned with such a selected spacing between their respective central axes 21 that an initial distance x′(see FIG. 4) is obtained between the closest parts of the outsides of two adjacent metal profiles 12. When the metal profiles 12 are deformed/compressed to a maximum, the distance x′ has decreased to a distance x (see FIG. 4) between the closest parts of the outsides of the respective adjacent metal profiles (12), and wherein x preferably is 0-50 mm and more preferred 0-20 mm. For embodiments where it is preferred that the profiles touches each other in their fully compressed condition the distance x′ may be chosen such that x is 0-0,5 mm. If, on the other hand, it is preferred that the profiles 12 have a distance larger than zero in between them also in a fully compressed condition, the distance x′ may be chosen such that x is 0,5-20 mm. If it is desirable that the profiles 12 overlap each other in a fully compressed condition, the distance x′ may be chosen such that x is −10 to 0 mm, preferably −0,5 to −0,1 mm. Anyhow, it is beneficial that the distance x′ is chosen such that not only elastic deformation but also plastic deformation occurs during compression.

FIG. 2 shows cross-sections of a number of different types of metal profiles 12-a to 12-k. It is preferred that said structure 5 comprises one or several hollow metal profiles, preferably having a closed section, the cross-section of which exhibiting at least one symmetry axis S intersecting the central axis 21 of the metal profile/profiles 12, and wherein the extension of the symmetry axis S intersects the central axis C of the rector shell 7.

For each cross-section, the symmetry axis S is shown in the form of a dashed line. The pipe profile or metal profile is preferably positioned such that the symmetry axis S of the cross-section is parallel with the radial direction 15 of the reactor shell, whereas the central axis 21 of the pipe profile extends substantially perpendicularly to the radial direction 15 of said reactor shell, which means the pipe profiles, in their longitudinal direction, extend substantially in parallel with the central axis C of the reactor shell 7.

In accordance with what is shown in FIG. 2, the cross-sections of the metal profiles 12 can have different shapes, for instance, the cross-sections can consist of different types of polygons, whereas in some embodiments, it can be preferred that the compliant structure 5 comprises a number of circularly shaped metal profiles 12-e, 12-h. In one embodiment, said compliant structure 5 can preferably comprise a number of hexagonally shaped metal profiles 12-a, which extend with the central axis 21 of the hexagon aligned substantially in parallel with the central axis C of the reactor shell 7.

In still another embodiment, said compliant structure 5 comprises a number of elliptically shaped metal profiles 12-c, which extend with the major axis of the ellipse in the cross-section aligned substantially in parallel with the radial direction 15 of the reactor shell 7.

In yet other embodiments, a number of pentagonally shaped metal profiles 12-g, extending in the same manner with the symmetry axis of the pentagon in the cross-section aligned substantially in parallel with the radial direction 15 of the reactor shell 7, can be more preferred. An octagonal shape 12-d can be an alternative to a pentagonal shape.

It is common to said metal profiles 12 that they have at least one mirror-symmetrical cross-section, where the mirror plane coincides with the central axis 21 and where the symmetry axis S is aligned substantially in parallel with the radial direction 15 of the reactor shell 7, i.e. such that S is aligned to intersect the central axis C of the reactor.

In FIG. 2 the original, initial profile height y of said metal profiles in an uncompressed state is shown. The profile height y is to be interpreted as the height of the profile including the profile walls and coinciding the symmetry axis S. The profile height y is also shown on FIG. 3. The thickness t of the wall of the profile is shown in FIG. 3. The height y of said profiles substantially corresponds to the thickness of the compliant structure in its radial direction, hence the profile height y is equal or substantially equal to the thickness y of the compliant structure.

Profiles according to the above-described different embodiments allow a substantial plastic deformation when a certain, moderate load level is achieved, and then provide a relatively constant resistance to deformation over a large deformation range. Furthermore, this type of compliant structures 5 has a suitable thermal conductivity for the furnace structure and the ceramic lining.

The pipe profiles according to the invention are preferably made of steel grades commonly available in the market, which are suited to the environment that is characteristic of the invention. The pipes having the selected cross-section are positioned in the axial direction of the reactor, and are manufactured in lengths adapted to the extension length of the reactor in the axial direction. The pipe length can preferably be adapted to extend along the entire axial length of the reactor, but the pipe lengths can also be shorter, depending on the installation technique and depending on the presence of passages through the reactor wall 7, which makes it necessary to divide the pipes into sections.

In some embodiments according to the invention, some of the metal profiles 12 may be circumferentially disposed around the outer side of the ceramic lining 2, 3, 4, in said expansion space 6, i.e. between the inside of the reactor shell 7 and the ceramic lining 2, 3, 4, and having their central axes 21 substantially perpendicular to the central axis C of reactor shell 7. These profiles 12 may preferably be in the form of a coil or concentric rings. In a cross-sectional view said coil is represented as a plurality of profiles. Depending on how close the coil is initially winded around the ceramic lining 2, 3, 4, the distances x′, x between each profile in a cross-sectional view will vary. In some embodiments the distance x may be larger than zero after the profiles 12 have been compressed, while in other embodiments the coil may be so closely winded that, in a cross-sectional view, the distance x in between said profiles 12 is zero after the profiles have been compressed. The remaining portion of the inside is covered by metal profiles 12 where the central axes (21) are disposed substantially in parallel with the central axis C of the reactor shell 7, so that they together surround the entire inside 7 of the reactor shell.

In the embodiments where said profiles 12 are disposed with the central axes 21 perpendicular to the central axis C of the reactor shell 7, each profile, when using piecemeal bended profiles instead of coils, surrounding the ceramic lining may be welded at its ends so as to rigidly fix its ends to each other thereby arranging each profile to be a closed profile with no beginning and no end. However, in some embodiments it may be preferred that the profiles are open at its ends, i.e. that the ends of the profile are not welded together or in some other way fixed to each other. A selected spacing may exist between the ends of the profile whereby said spacing may contribute to the possibility to compress the profiles further in the radial direction 15 of the reactor shell and causing the profiles to expand in the direction of their central axis 21.

All the profiles shown in FIG. 2 have at least one mirror plane through the cross-section plane. It may be an advantage that the profiles are positioned such that the mirror plane is substantially perpendicular to the pressure vessel wall and parallel to the radial direction 15 of the reactor vessel, as well as parallel to the central axis 21 of the profile, to thereby reduce any risk that the profiles 12 fold down asymmetrically when they are flattened between the reactor shell 7 and the ceramic lining 2, 3, 4. The pipe profiles 12-f, -g, -h can be manufactured by folding elongated metal plates into desired profiles 12, after which the plate edges 20 are welded together. The profile 12-i is constituted by profile 12-a and 12-j, which are stacked on top of each other and then welded together at the waist 20. A profile of type 12-i has almost twice as large a deformation capacity as compared to profile 12-a, without requiring any larger C/C distance between the profiles than profile 12-a in the compliant structure 5. The profile 12-k is constituted by a number of elliptical pipes of type 12-c, which are welded 18 to a metal plate 19 and form a panel. Such panels can then be placed in the reactor vessel and be welded together into a continuous compliant structure 5 therein, with the pipe profiles 12 facing the reactor shell 7 and the metal plate 19 facing the ceramic lining.

FIG. 3 shows a compliant structure 5 where the panel comprises a number of hexagonal pipes 12-a. It is appreciated that also pipes with other cross-sections, e.g. cylindrical 12-e, pentagonal 12-g, can be used in the same way to construct the panel. When such a compliant structure 5, consisting of pipe profiles welded to a plate is compressed by an expanding lining, this preferably results in the plate 19 being stretched out, which can provide an additional resistance force to the lining, without necessarily increasing the pressure load on the reactor vessel 7.

FIG. 3 also shows an embodiment according to the invention, where a ceramic blanket 16, 17, filling the free volume between the metal profiles 12 as well as inside the metal profiles 12 and thereby reducing the heat transport through the compliant structure 5 both due to reduced gas convection and reduced heat radiation, is placed between and inside the metal profiles 12.

A global metal filling factor s can be calculated for the compliant structure 5. With support from FIG. 3, the volume ratio for the illustrated embodiment can be calculated as V_Me/V_tot=6R·t·L/3R·y·L=1.155·t/R, where V_totis the total space between two symmetry axis S of two consecutive metal profiles and V_Meis the total volume of all the metal profiles within said space V_tot, R is the circumscribed radius of the profile, y is the profile height=2RA/0.75, L is the profile length, t is the profile wall thickness and the spacing distance of the profiles, the C—C distance equals 3R, which results in an initial distance x′(see FIG. 4 also) between the profiles corresponding to R. The insertion of a measurement value of t/R=0.0571 results in 6=0,066. This means that the structure 5, when constituted by hexagonal profiles 12-a with a t/R=0.0571, contains only 6.6% dense material and 93.4% global porosity. The metal filling factors for this calculated example is thus 0.066.

It is appreciated that the reactor wall shown in FIG. 3 actually has a curved overall shape, as is shown in FIG. 1. The section shown in FIG. 3 constitutes such a small portion of the whole reactor wall that the wall, for reasons of simplicity, is shown as a plane wall in FIG. 3.

FIG. 4 shows the counter-pressure P(MPa) (of the y-axis) against the reactor shell 7 as a function of deformation/compression s (of the x-axis) of thin-walled hexagonally shaped pipe profiles 12, when they are deformed/compressed between the ceramic lining 2, 3, 4 and the inside of the reactor shell 7. Over a range of deformation from 0% to about 6% of the original profile height (y) initially an elastic deformation occurs in a first compression interval (ΔY1), then a plastic deformation occurs in a second compression interval (ΔY2), up to about 70% of the original height y, at a relatively constant counter-pressure P, i.e. wherein ΔY2>ΔY1 and more preferred ΔY2>>ΔY1. Preferably ΔY2 is >3ΔY1 and more preferred ΔY2 is >5ΔY1. Thereupon, at a deformation level of about 70% of the original height of the profiles, the forces needed to compress the profile further increases rapidly and eventually after further increase of the pressure the walls of the profiles 12 are pressed against each other which leads to that no further compression can be made.

In FIG. 4 it can be seen that the force P (y-axis) needed to compress the profile after the material has plasticized is relatively constant, i.e. the force P for the interval ΔY2 is substantially horizontal, and that a pressure interval from where plasticization starts until the counterpressure starts to increase rapidly can be identified as an interval around P, i.e. P_min<P<P_max, and where P_minis the minimum counter-pressure and Pmax is the maximum counter-pressure P_maxin said second compression interval (γY2). Preferably a variation of said counter-pressure P is less than P±15%, and more preferred less than P±10%. On the x-axis the compression in percentage of the metal profile height is shown.

Depending on the properties of the profiles 12, e.g. cross-sectional shape, wall thickness etc., the first and second compression intervals ΔY1, ΔY2, may be of varying lengths. Preferably, the first compression interval ΔY1, i.e. where the elastic compression occurs, is 0-15%, and most preferred 0-8%, whereas the second compression interval ΔY2, i.e. where the counter-pressure is relatively constant, preferably is 15-85%, more preferred 8-90%.

Said compliant structure (5) is adapted to be compressed and deformed, in the radial direction (15) of the reactor shell (7), by at least 60% of the original, initial height (y) of said metal profile 12 at a normal pressure of preferably no more than 2 MPa, more preferably in the range of 0.5-1.5 MPa. Circumstances may however lead to that also higher counter-pressure are of interest.

It is further preferred that said metal profiles 12 have a resilience of preferably at least 2-5% of the original height y of said metal profiles, more preferably of 3-4%, during depressurization from operating pressure to atmospheric pressure and that said compliant structure (5) has a global porosity of at least 60% of the ring-shaped coaxial expansion space (6), preferably of at least 80%, more preferably of at least 90%.

By measuring the deformation force and the deformation of test specimens from the pipe profiles 12, cut into suitable lengths for the measurement, and taking into consideration the fact that the profiles 12 are distributed with a uniform C/C spacing (i.e. the distance between the central axis 21 of one pipe profile and the corresponding central axis 21 of the nearest pipe profile), the average pressure against the reactor shell can be calculated. Since the pipe profiles have a thin wall relative to the reactor shell, and are preferably regularly distributed with a uniform C/C spacing around the entire reactor shell, the load on the reactor shell from the profiles 12 can be regarded as a uniform internal pressure which is relatively small in comparison to the maximum design pressure of the reactor.

In accordance with what has been mentioned previously, the metal profiles 12 are suitably positioned with such a selected spacing between their respective central axes 21 that an initial distance x′ (see FIG. 4) is obtained between the outsides of two adjacent metal profiles 12. In the embodiment shown in FIG. 3, x′ is approximately equal to R, according to the calculation above. When x′ is approximately equal to R, the distance x between the compressed metal profiles 12 will be approximately zero.

In some embodiments it may be preferred to use profiles in said expansion space 6 that are pre-stressed to plasticization already when being arranged in said expansion space 6. This preparation of the profiles leads to that the horizontal part of the compression curve will be prolonged and may increase the life length of the ceramic lining installation.

FIG. 5 shows results from compression tests carried out by means of a thermal gradient apparatus on a cylindrically shaped metal profile made of a ferritic high strength steel called Doga1800DP. On the x-axis, the percentage deformation of the original height of the profile is shown as a function of the normalized load on the y-axis per mm (kN/mm) contact surface of the steel pipe. The temperature was adjusted before each test to obtain the same temperatures of the two contact surfaces that are estimated to be prevailing for the entire refractory solution. The temperature of the specimen can therefore be assumed to exhibit the same temperature gradient as if it had it been placed in a gasifier according to the invention.

In each of the tests, a number of depressurization cycles were performed at regular intervals. From the curves, it can be seen that tests on similar specimens produce similar results. In general, the mechanical testing results confirm the results from the simulations, both when the curve shapes and the load magnitudes are concerned.

The curve in FIG. 5 shows that in the plastic deformation interval, i.e. the second compression interval ΔY2, the profile maintains its compression/decompression ability during de-load and re-load, i.e. when the profile is depressurized from operating pressure to atmospheric pressure and re-pressurized back to operating pressure. Over a range of deformation from 0% to about 7% of the initial, original profile height y of the metal profiles 12, initially an elastic deformation occurs in a first compression interval ΔY1, then a plastic deformation occurs in a second compression interval ΔY2, up to about 85%, at a relatively constant counter-pressure, i.e. wherein ΔY2>ΔY1. Thereupon, at a deformation level above 85%, the hollow spaces within the profiles 12 are rapidly, fully consumed and the walls of the profiles 12 are pressed against each other.

The hot salt melt 1 produced during the gasification flows partly on the surface of the ceramic lining 2, and can penetrate into the hotter portion of the lining 2, 3 and form new solid ceramic substances therein, when it reacts with the ceramic material. This causes the lining to have a larger volume than it had originally when it was installed. Such volume-increasing reactions causes the hot portion of the lining 2, 3 to slowly but inevitably increase in volume and size during normal operation of the reactor. As a rule, ceramic materials have a high pressure resistance, which is the reason why a ceramic lining of normal thickness can easily overload a reactor shell 7, even if mechanically strong, if the reaction is allowed to continue for a long period of time and if there is no appropriate expansion space for the ceramic lining inside the reactor. Therefore, in case of long-term operation of the reactor, there is preferably a sufficiently large compliant structure 5 between the inside of the reactor shell 7 and the outside of the ceramic lining 4 to avoid that dangerously high mechanical loads are produced in the reactor steel shell 7. Also, high pressure loads in the ceramic lining can, per se, cause pieces of the lining 2 to crack away from the inside and be lost through so called spalling, wherein the service life of the lining is impaired due to reduced thickness of material. In the worst possible case, large internal stresses can also cause an inside collapse of the lining to occur, which could rapidly lead to a dangerous local overheating of the reactor wall 7 occurring in areas where the ceramic lining has been lost. The damages could be particularly severe in a dome-shaped reactor top, where the lining needs to receive some support from its neighbours to maintain the stability of the top.

In order to prevent that the salt melt penetrates through the ceramic lining and possibly reaches the compliant structure 5 and damages the reactor wall, it is preferred that the temperature of the salt melt is so low that the salt melt solidifies into a substantially solid salt inside the colder portions 3, 4 of the ceramic lining. As already mentioned, the main portion of the melt solidifies at a temperature of about 740° C., whereas a small volume proportion of the melt will be enriched in contaminants, such as NaCl and NaOH, meaning that the entire melt solidifies first at about 400° C. In general terms, however, it can be stated that chemical reactions between the salt melt and a high-melting ceramic lining is rather slow at temperatures below about 600° C. The thickness of the different ceramic linings and the thermal conductivity of the materials are preferably selected such that the inside 2 of the ceramic lining/barrier is so hot that the salt melt is substantially always free-flowing and easily flows out of the reactor at a normal operating temperature, while the colder portion of the ceramic lining 4 causes the salt melt to solidify completely. Thereby, it can be prevented that the melt penetrates cracks and pores deeply into the outer portions of the lining and, in the worst case, reaches the reactor wall.

The selection of materials for the innermost ceramic lining/barrier is primarily dictated by the fact that the materials should have a good chemical resistance to an alkaline melt and should therefore have a high melting temperature. In some areas of the reactor, at times the melt may have a temperature above 1050° C. Suitable ceramic materials are chemically resistant to an alkaline melt, and have no or a very small open porosity. Furthermore, it is preferred if they are relatively resistant to rapid temperature changes. Unfortunately, such materials are relatively good thermal conductors.

Preferably, the combination of the thickness, chemical resistance and thermo-mechanical properties of the different refractory ceramic linings/barriers, and the thermal conductivity of the materials, may need to be adapted such that the melt is substantially free-flowing on the inside of the innermost ceramic lining 2. Furthermore, the inside of the ceramic barrier preferably has a temperature of about 1000° C. to prevent the produced salt melt 1 from being contaminated with soot from incompletely reacted black liquor. The underlying ceramic barrier materials 3, 4, 13 are preferably selected such that the thermal conductivity of these ceramic linings/barriers will be substantially lower than the one of the innermost ceramic lining 2. It is appropriate that these intermediate ceramic materials have a thermal conductivity that is ⅓- 1/10 of the one of the innermost ceramic lining 2, partly to reduce the heat losses through the barriers and partly to prevent the melt from reaching the compliant structure 5. Since the intermediate ceramic linings/barriers 3, 4, 13 will have a lower working temperature and, in addition, not need to be subjected to the influence of a passing salt melt, the corrosion requirements on these materials are reduced, but they still, however, have to be capable of resisting very prolonged chemical attacks by the melt, which penetrates relatively deeply into the ceramic barrier. It may be preferred that the intermediate ceramic barriers 3, 4 do not expand to any significant extent, in case of a long contact time with the salt melt, so that the expansion space in the structure 5 is not exhausted.

The invention also relates to a method for manufacturing and disposing a compliant structure 5 between a reactor shell 7 and an inner refractory lining 2, 3, 4 in a gasification rector, wherein said compliant structure 5 comprises one or several hollow metal profiles 12, which is/are positioned with a C/C spacing corresponding to 0.3-0.7 of the circumference of said hollow profile 12, preferably 0.4-0.6 of said circumference. The initial distance x′ between two adjacent profiles will be chosen according to what has already been described regarding the initial distance x′ and the distance x for deformed/compressed profiles above.

Said profile/profiles 12 is/are fixed to a sweep 19, preferably made of metal and preferably having approximately the same plate thickness as said profile/profiles 12, whereby a section of profiles on a metal sweep 19 is formed, which are joined, preferably welded together, into a continuous, compliant structure 5, wherein the profile side of the sections is pointed outwardly towards the reactor shell 7.

Before joining, said sections 19 are finished to the correct radius of curvature for said reactor.

A plurality of said profiles 12 are fixed in parallel, centred in the middle by a longitudinal weld 18, with the central axis 21 of the profiles extending substantially in parallel with the vertical central axis C of the reactor.

The invention is not limited by what has been described above, but can be varied within the scope of the following claims. For example, it is appreciated that the reactor according to the invention is well suited for gasification of different types of spent liquors from chemical and semi-chemical paper pulp production, such as black liquor and different types of sulphite spent liquors, for example Na- or K-based sulphite spent liquors.

Furthermore, it is appreciated that the invention is applicable to gasification of many other types of organic materials and wastes, for example municipal waste. The invention is especially applicable to feedstocks for gasification which comprise salts, which have to be kept at a temperature far above (>100° C.) the melting point (melting temperature) of the salts in the gasification reactor, something which, in its turn, results in the melt penetrating deep into the ceramic lining 2, 3, 4 before it solidifies.

It is, of course, also possible to mix different types of spent liquors within wide limits as well as to mix spent liquors with different bio-oils, and to gasify the mixture in the reactor according to the invention. In connection with the gasification, it is also possible to mix a smaller amount of fine granular dust into the spent liquor, for example electrical precipitator dust from recovery boilers, said dust containing relatively low-melting compounds such as Na₂CO₃and Na₂SO₄.

Within the scope of the invention, it is also conceivable to the skilled person to position not only one, but two or more rows of metal profiles next to each other, as seen in the radial direction of the reactor, to achieve the advantages according to the invention. Furthermore, in some embodiments, it can be preferred to dispose the metal profile in a coil around the major part of the inner refractory lining. Such a helically shaped compliant structure would, among other things, result in the difference that the length extension of the metal profile contributes to the resilience force.

Further, and also within the scope of the invention, the compliant structure, i.e. the profiles, may be made of other materials than metal as long as the material of the compliant structure has the preferred function of being both elastically and plastically deformable.

GASIFICATION REACTOR COMPRISING A PRESSURE ABSORBING COMPLIANT STRUCTURE

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