FR2580660A1 - Multitubular reactor for the gasification of solid carbonaceous fuels - Google Patents

Abstract

A reactor making it possible to produce continuously gases rich in H2 and CO from particulate carbonaceous or hydrocarbon matter. It consists of three fluidisation chambers: a fluidisation chamber 3 for feeding the tubes 6 of the multitubular bundle, a sedimentation chamber 12 and a combustion chamber 10. Gasification with steam takes place inside the tubes 6 which are heated by virtue of the combustion in air of the residues in the combustion chamber 10. The reactor according to the invention is particularly intended for the production of a gas containing no nitrogen, without the use of pure oxygen.

Description

 The present invention relates to a continuous process for producing a gas stream rich in hydrogen and carbon monoxide by partial oxidation of a solid fuel. More specifically, the present invention relates to the production of a synthesis gas by non-catalytic partial oxidation from either ground coal, or coke obtained by cracking petroleum, or from asphalts, or from ground plant residues. The vaporization reduction, that is to say gasification with water vapor, being endothermic, part of the solid fuel is burnt, in the presence of air, to obtain the heat necessary for the reaction. The present invention relates more specifically the reactor, ie the gasifier, making it possible to carry out this process.

 Nothing in the prior art has already been done or suggested according to the principle of the present invention in which a mixture of water vapor and solid carbonaceous fuel flows vertically inside the tubes of one. multitubular bundle, while the part of this unreacted fuel is burned in a fluidized regime and in the presence of air, in the intertubular space, to supply through the walls of the tubes, the heat necessary for vapor gasification.

 The present invention relates to a continuous process for producing a gas stream comprising mainly, H2, CO, C02, H20, CH4, H2S, COS and small amounts of Ne and Ar, by introducing solid particles into a fluidization chamber or these particles are fluidized by steam at a temperature between 2000 and 500 C and. under a pressure varying between 0 and 100 bars; the gas-solid suspension then circulates in the vertical tubes in which the temperature is gradually brought to a value of up to 11,500 C by heating the tubes.

At the outlet of these tubes, a sedimentation chamber makes it possible to recover the gas stream, while the solid particles which have partially reacted are directed towards a combustion chamber in a fluidized bed in which the multitubular bundle is immersed. The gas stream constituted by the combustion gases of these solid residues, rich in N2 and C02, is not mixed with the gaseous stream of steam gasification, which considerably improves the quality of the latter.

 Here are the advantages that one gains from using the multitubular reactor in place of autogenous reactors operating with substantially pure oxygen as in the oxy-gas-gasification processes described in the prior art: (1) obtaining a synthesis practically free of nitrogen, without consumption of pure oxygen; (2) high conversion rate ic carbonaceous material since the low reactive residues are burned in the reactor and therefore without the need to melt or agglomerate the ash to improve this conversion rate; (3) high conversion rate of carbonaceous material since there is not, as in conventional fluidized reactors, short-circuiting of the solid between the inlet and the outlet, due to the intense mixing due to the phenomenon fluidization; (4) elimination of a significant part of the CO 2 by the combustion gases and therefore without the need for a costly absorption operation; (5) possibility of recovering a significant part of the sensible heat from the synthesis gas stream and from the combustion gas stream in the reactor itself, which improves the synthesis gas yield; (6) development studies facilitated by the modular nature of the reactor, each tube, the diameter of which is always less than or equal to 15 cm, which can be considered as a module for the study of the vapor gasification reaction.

 The solid carbonaceous fuels are preferably ground so that 100% of the materials pass through a 3-mm sieve. An average particle diameter close to 0.4 mm is satisfactory since it allows, under the optimal conditions of the process, to obtain good fluidization in the fluidization chamber without using excessively high flow rates of water vapor. The ground fuel is introduced into a storage hopper which feeds, through an airlock, the fluidization chamber.

 The term solid carbonaceous fuel is intended to include different materials and mixtures thereof chosen from the group comprising coals, petroleum cokes, petroleum cokes deposited on solid mineral particles, wood, vegetables, rubber. The moisture content of particulate solid carbonaceous fuels is between about 0 and 20% by weight. In some cases it is necessary to pre-dry to reach the desired level.

 The term solid carbonaceous fuel can also include particulate solids obtained by spraying or impregnating porous or non-porous mineral particles with asphalts or other petroleum residues. Spraying can be carried out in the fluidization chamber of the multitubular reactor, the residual solid obtained after combustion being recirculated to this chamber.

 The weight ratio of water vapor to solid carbonaceous fuel is preferably expressed as the ratio of the weight of water vapor to the weight of carbon (C) transformed in the reactor and present in the feed stream. This ratio is between 0.2 and 3, Q. It is important not only to control the kinetics of the gas-solid reactions but also to control the flow of the gas-solid suspension in the tubes of the beam, i.e. the gas residence time and the residence time of the gas. solid in the reaction zone.

The multitubular reactor makes it possible to efficiently produce and control the circulation of particulate solids between the different reaction zones while avoiding mixing of the solids and that of the reaction gases, which makes it possible to avoid both the short-circuiting of the carbonaceous fuel towards the outlet intended for solid residues and that of the fumes towards the outlet intended for synthesis gas. These objectives are achieved thanks to the simultaneous implementation of the following techniques
a) the fluidization chamber located at the base of the reactor makes it possible to supply a large number of vertical tubes very regularly with the gas-solid suspension, the regularity of this supply can be further improved by injecting equal streams of steam in each tube.

The tube bundle can thus consist of at least 300 tubes, for a fluidization chamber with a diameter equal to 4 meters, while maintaining the same mass flow rate of solid in each tube, this flow rate being equal to that of the total supply. carbonaceous fuel to the fluidization chamber divided by the number of tubes.

car chaque tube, immergé dans un bain fluidisé ne présentant pas de gradient horizontal de température, aura un profil de température vertical identique à celui de tous les autres tubes. Les taux de transformation du combustible carboné sont donc sensiblement égaux pour tous les tubes puisque les. temps de séjour du solide et les -profils de température sont similaires. Un tube représente donc un module de la réaction de vapogazéification, ce qui facilite beaucoup l'étude en réacteur pilote.b) each tube is thus supplied with the same flow rate of solid and the same flow rate of gas; equal amounts of gas will be formed in each tube by the reaction

because each tube, immersed in a fluidized bath having no horizontal temperature gradient, will have a vertical temperature profile identical to that of all the other tubes. The conversion rates of carbonaceous fuel are therefore substantially equal for all the tubes since the. solid residence times and temperature profiles are similar. A tube therefore represents a module of the vapor gasification reaction, which greatly facilitates the study in a pilot reactor.

 c) The upper chamber, designated as the sedimentation chamber, has a double role: the upper zone is used for the partial sedimentation of fines, while the lower zone where the partially reacted solid particles are present at the fluidized state, is used to feed, via vertical tubes, the combustion chamber located below.

 d) It is observed that the solid particles present in these vertical tubes are maintained in the fluidity state by a phenomenon known as self-fluidization. In fact, the vapor gasification reaction continues during the stay of the particles in these tubes and this reaction leads to an increase in the gas volume. By assimilating the fluidized matter to a liquid, these tubes are generally designated, in which the fluidized phase descends downwards while preventing the passage of the gas present in the lower chamber, under the name of hydraulic seals (downcomer in terminology in English language ).

 e) The combustion chamber is between the sedimentation chamber and the fluidization chamber. In this chamber the movement of the particles is generally descending and the particles depleted in carbon by the reactions of vapor gasification and combustion in air, are drawn off at the base of this chamber or else they are partly made up in the fluidization. The solid present in the combustion chamber is fluidized by an appropriate quantity of air; this quantity - must be sufficient to fluidize the solid and sufficient to cause the total combustion of the carbonaceous material. It is known that the phenomenon of fluidization, as a result of rapid mixing of the particles, tends to suppress the vertical or horizontal temperature gradients . It is also known, in interior art, that horizontal baffles make it possible to avoid vertical mixing and it is therefore possible to establish a vertical temperature profile in the combustion chamber. The desired result is therefore obtained: the fluidization chamber and the bottom of the bundle tubes are brought to a relatively low temperature (below 5000 ° C., for example) while the top of the tubes and the sedimentation chamber are brought to a relatively low temperature. high (greater than 900 "C, for example).

 The present invention will be better understood by referring to the diagram in Figure 1 and which shows in detail the process described above.

This diagram is only illustrative and not limiting of the process of the invention.

 Referring to the diagram, the carbonaceous fuel having a particle size so that 100% of material passes through a sieve of 1 mm, is introduced through an airlock 1 and then along a line 2 into the fluidization chamber 3. The vapor of fluidization water is introduced under the fluidization grid 4 through line 5. The tubes 6, made of refractory steel, are supported by the plate 7 of the tube bundle, delimiting the upper part of the fluidization chamber 3. In this chamber are immersed the manifold 8 for distributing water vapor from the tubes 6 and the manifold 9 for distributing air from the combustion chamber 10. The tubes are engaged or welded, at their upper part, in a tube bundle plate 11 serving to separation between the sedimentation chamber 12 and the combustion chamber 10, an expansion joint 13 being located at the periphery of this plate. The plate 11- supports the refractory steel tubes 14 whose role as a hydraulic seal makes it possible both to ensure, by overflow, the supply of particulate solid to the chamber. combustion and reduce the passage of smoke to the chamber 12. A slight gas leak from the combustion chamber to the sedimentation chamber, or vice versa, can be moles ree; it is controlled and reduced by acting via valves on the pressure difference between the two chambers. These valves are installed on the synthesis gas circuit 15 or that of the fumes16,.

after separation of the fines using cyclones and cooling. The number of overflow tubes is chosen large enough for. the combustion chamber is supplied with solid uniformly over all. its section; in general one overflow tube is sufficient for each group of eight tubes. of the beam and its diameter can be chosen smaller than that of these tubes. The base of these tubes is also partially closed to further reduce the gas flow in these tubes. Their upper part is located at a certain height above the plate so that a fluidized zone 17 allows a regular supply of these overflow tubes. One or more baffles 18 make it possible to obtain a favorable temperature profile in the combustion chamber and therefore in the vapor gasification tubes. Thus, the lower part of the combustion chamber can be kept at a relatively low temperature, which makes it possible to protect the metal parts of the reactor which withstand the most significant mechanical stresses. One or more airlocks 19 finally make it possible to withdraw the residual particulate matter which can in certain cases be reintroduced into the fluidization chamber.

This introduction can also be carried out using holes drilled in the plate 7 supporting the tube bundle.

 It will be noted that both inside and outside the tubes of the tube bundle there are relatively dense gas-solid suspensions, which makes it possible to obtain very good performance for heat transfer.

 In the diagram of Figure 1 the gases of lines 15 and 16 are at high temperatures, of the order of 10000 C in the general case.

After elimination of the fines using cyclones, part of the sensible heat of these gases can be recovered in boilers producing water vapor.

 In a preferred embodiment of the process, this heat is recovered in the reactor itself using vertical tubes of refractory steel which make it possible to establish gas circuits oriented towards the bottom of the reactor. The recovery of a significant part of the sensible heat makes it possible to reduce the quantity of carbonaceous material which has to be burned in the combustion chamber and consequently to increase the quantity of gasified gas, that is to say the yield of synthesis gas. .

 -In another preferred embodiment of the process, the reactor is partitioned vertically using baffles. This constitutes: thus in the combustion chamber real modules independent of each other. A module can include the equivalent of 4 or 8 tubes of zeification vapoga; it is mainly characterized by the property that its height is very large compared to the dimensions defining its section which can be square or hexagonal.

 These two preferred embodiments are illustrated jointly in the diagram of Figure 2. This diagram is merely illustrative but it is not limiting. It describes the internal arrangement of the reactor as it would be at level M 'identified in Figure 1 when using both tubes for the recovery of sensible heat and vertical baffles to define a module. It also illustrates another mode carrying out a process by which a part of the solid having undergone the steam gasification treatment is recirculated downwards, that is to say towards the fluidization chamber using some of the tubes of the bundle; this embodiment has the advantage of increasing the residence time of the solid in the reactor and of diluting the solid carbonaceous fuel, which in certain cases can be agglutinating or sticky, with non-sticky particles.

Referring to this diagram representing a section AA ′, the position of the vertical baffles C fixed to the four tubes Tu is noted by clamps made of refractory steel. These baffles have a height less than that of the fluidized zone because a normal fluidized zone is maintained above the plate 7 to promote the mixing of the particles before they are drawn off through the airlocks 19. The tubes Tri and T2 play the same role that you
bes 6 of Figure 1 but the gas-solid suspension circulates upwards in the annular space located between these tubes and T3 tubes. The T3 tubes come from the upper part of the sedimentation chamber and end in the fluidization or a series of manifolds evacuates the synthesis gas to the outside of the reactor. The steam gasification zone therefore receives both heat from the combustion chamber (intertubular space) through the walls of the tubes T1 and T2 and part of the sensible heat of the synthesis gas through the walls of the tubes T3 . Likewise, the T4 tubes are used to transfer part of the sensible heat of the fumes to the fluidized phase of the intertubular space which in turn transmits it to the vapor gasification tubes. These tubes come from the upper part of the chamber combustion and end in the f-luidisation chamber where a series of manifolds evacuates the smoke towards the outside of the reactor; they therefore pass through the plate 7. T5 represents a hydraulic seal intended to supply the combustion chamber of the module with particulate solid coming from the sedimentation chamber. T6 represents a downpipe of this same solid towards the fluidization chamber. Small amounts of water vapor are injected at the bottom of this tube, which allows the vapor gasification reaction to continue while avoiding blockage of the tube by defluidization.

This modular construction significantly simplifies the construction of horizontal baffles which are of small section and supported, for example, by the tube T6. We can therefore increase the number n of these baffles and thus achieve a series of n perfectly mixed combustion reactors which means that in each of these reactors the temperature is homogeneous, but different from one reactor to another. A temperature profile is therefore obtained which has stages but is almost continuous if n is large enough, while the downward flow of the particles has a character fairly close to the piston character (in the sense of the theory of chemical reactors). The applicant has thus been able to show that it is possible to obtain essentially piston flow of the solid particles both in the steam gasification tubes and in the intertubular combustion zone. The applicant has also shown that by recovery of the sensible heat of the gases the yield (expressed by the lower combustible power of methane or methanol which it would be possible to synthesize with the synthesis gas and related to the PCI of the carbon material fed to reactor) can be increased by about 20%. ~
Depending on the type of carbonaceous material to be treated, and after having carried out preliminary tests in a pilot simulation unit, one can choose the size of the tubes (height, diameter) and build a module whose operation faithfully represents the operation of a large capacity industrial unit. The set of tubes shown in Figure 2 can be placed in a cylindrical shell and we thus obtain the pilot industrial demonstration unit, the results of which can be directly extrapolated to reactors treating more than 1000 tonnes-day of material. carbonaceous.

Conversely, we have calculated, from results of
heat transfer, size and operating conditions (time of
stay of solid and gas, flow rates of solid, air and water vapor) of a
pilot simulation unit made up of two concentric tubes, allowing
to gasify lignites from Gardanne (Houillères de Provence-France). This
-simulation unit is shown in Figure 3. The central tube U1 is
a NS 30 steel tube from UGINOX, seamless, with an external diameter of 21.3 mm and a thickness of 2.6 mm; the outer tube U2, also made of steel
NS 30, has an outside diameter of 42.4 mm and a thickness of 3.2 mm. The height of the central tube is 6 m. The external tube is both heated by electric resistors R and insulated with alumina wool A which makes it easier to start and compensate for heat losses when the steady state is reached. The airlocks S1 and S2 are intended to feed the crushed lignite and to extract the ash. The fluidization tank is heated to 250 ° C and supplied with a flow D1- of steam.

D2, D3 and D4 respectively represent the flow rates of air, synthesis gas and fumes, pressure switches for controlling the pressures in the sedimentation chamber and in the combustion chamber. Concentric baffles are mounted in the combustion chamber.

The simulation reactor shown in the diagram of the
FIG. 3 makes it possible to predict the performance of a module constituted by several tubes of larger diameter and greater height for which the residence times of the gases and of the solids would be identical to those of the simulation reactor. As shown in this diagram, it does not take into account the recovery of the sensible heat of the gas and the effect of recycling the particles from the sedimentation chamber to the fluidization chamber.

EXAMPLE
The following example illustrates an embodiment of the method according to the invention. It is merely illustrative but is not limiting. The process is continuous with flow rates specified on an hourly basis for all currents.

1230 g of Gardanne lignite crushed into particle form so that 100% of material passes through a 0.250 mm sieve. At least 80% passes through a 0.200 rtin sieve are introduced into the fluidization chamber heated to 250 ° C. This lignite contains 315 g of ash and 169 g of water. Its PCI is equal to 5050 kcal. The constitution of the organic matter of this coal can be represented by the formula C HO, 8 0O, 12
N0.01 S0.028. The fluidization chamber is fluidized by 710 9 of water vapor. The combustion chamber is fluidized by 159 g.moles of air.

The temperature at the top of the vapor gasification zone is equal to 9700 C while the pressure is maintained at 30 Bars. The temperature at the top of the combustion zone is equal to 1040 "C, the pressure also being maintained at 30 Bars.

The synthesis gas of the current D3 has the following composition (in g.moles)
H2 40.2; CO 13.3; COi 3.70; H2S 1.33; CH4 1.26; N2 0.44; H20 31.7.

The fumes from stream D4 have the following composition: C02 28.9; 02 2.9
N2 127. Synthetic gas would make it possible to synthesize 14.5 moles of methane whose PCI would be equal to 2726 kcal., That is to say that the methane yield can be estimated as being equal to 55%. It can be shown that the recovery, in the reactor itself, of the sensible heat of the synthesis gas and of the fumes would make it possible to obtain a methane yield of 75%, as a result of the reduction in the quantity of carbon which it it is necessary to burn in the combustion chamber.

 The process of the invention has been described generally and with the aid of an illustrative but nonlimiting example. Those skilled in the art may make various modifications to it without departing from the scope of the present invention.

Claims (9)

1 - Process for producing a gas rich in H2 and CO characterized by 1) the use of a multitubular bundle to transfer heat from a zone of combustion of carbonaceous residues towards a zone of steam gasification of the material to be treated. 2) the introduction of the carbonaceous material into a fluidized chamber supplying a large number of tubes and the recovery of the residues in a sedimentation chamber 3) The combustion of these residues in a fluidized combustion chamber, in the presence of air, the tubes of the multitubular bundle being immersed in this chamber. 2 - Process according to claim 1, characterized in that horizontal and vertical baffles placed in the combustion chamber are used to improve the performance of the reactor and to transform it into a modular reactor. 3 - Method according to claims 1 or 2, characterized in that one recovers part of the sensible heat of the gaseous effluents by using certain tubes of the multitubular bundle. 4 - Process according to any one of claims 1 to 3, characterized in that a part of the carbonaceous particles having undergone the vapor gasification reaction is recirculated to the fluidization chamber by using certain tubes of the multitubular bundle. 5 - Process according to any one of claims 1 to 4, characterized in that the particulate hydrocarbon material can be prepared by spraying in the fluidization chamber and that inert particles are recirculated to this chamber. 6 - Method according to any one of claims 1 to 4, characterized in that when the particulate hydrocarbon material is of plant origin and does not contain enough mineral matter to constitute the fluidized combustion bed is added inert mineral particles to form the fluidized bed. 7 - Process according to any one of claims 1 to 6, characterized in that the pressure is advantageously between 0 and 100 bars and that the temperature difference between the top and the bottom of the reactor is at least equal to 3000 C . 8 - Method according to any one of claims 1 to 7, characterized in that the material of the tubes of the multitubular bundle is either a refractory steel, or a ceramic having a high thermal conductivity. 9 - Method according to any one of claims 1 to 8, characterized in that the tubes of the multitubular bundle have internal linings for increasing the residence time of solid particles.