LU84251A1 - FLUIDIZED GASOGENIC WITH MULTIPLE COMPARTMENTS - Google Patents

Description

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MULTI-COMPARTMENT FLUIDIZED GAS

The present invention relates to a fluidized gasifier; f with multiple compartments. - 'ί

The ever increasing prices of liquid fuels; - - ¾ · - liquid or gaseous derived from petroleum on the one hand and the problem i,; 5 waste disposal on the other hand caused an interest in the gasification of different solids in order to produce a gas with sufficient calorific value.

These solids can be laundry shales, very ashy or sulfurous coals, urban waste, forestry or agricultural waste. The gases obtained can, for example, feed gas engines, diesel engines, gas turbines or be used as a substitute for natural gas or as synthesis gas.

Several gasification processes are known, distinguished mainly by the method of contact of the gas and the solid. Already old processes use the principle of the moving bed where the solid flows by gravity. This device lacks flexibility vis-à-vis the feed and often requires a calibration of the solid to a dimension greater than 5 cm so that it can flow advantageously and ensure a uniform distribution of gases.

The entrained bed process in which the finely divided solid is placed in pneumatic transport is also known.

These installations are generally very large and require complex dedusting systems. .

A third and more advantageous method consists in using fluidized beds ensuring good mixing of the. solid charge. With relatively small dimensions, they make it possible to achieve significant gas-solid contact times.

They allow easy loading and emptying; in fact, the solid flows practically like a liquid through a hole made in the wall or in the bottom of the apparatus.

The simplest devices use air to produce a gas containing a significant part of nitrogen.

To remove this nitrogen ballast, 35, oxygen-enriched air, or even pure oxygen, is also used, but J / then it rises to high temperatures requiring expensive materials. Obtained gases composed essentially of CO, C02, H2 and CH ^. To air or to oxygen, it is possible to add or substitute water vapor which promotes gasification and makes it possible to increase the hydrogen content of the gas. Finally, hydrogen can be used as a gasifying agent, alone or in combination with steam to produce a gas rich in methane.

There are also different modes of supplying heat to endothermic gasification reactions.

In the oldest devices, gasification is carried out simultaneously with a partial combustion of the charge, with air or with oxygen, to supply the necessary calories, with the drawbacks linked to the use of this type of gasifying agents.

15 An alternative is to use electrical resistances immersed in the bed. Heat can also be transferred by heat exchangers immersed in the bed; often, however, the areas available in the gasifier are insufficient to balance the heat balance of the operation.

Another interesting alternative comprises a double system comprising a combustion device and a gasification device. In the first, solid, liquid or even gaseous products are burnt in the air resulting from the pyrolysis and gasification of the starting material. The device operates at around 900 ° C. The calories released by combustion are stored as sensible heat by the solid. This is then returned to the gasification device, operating at around 300 ° C. where part of the sensible heat of the solid is transferred. The gasification fluid is steam or recycled gases. In the solid, it is possible to introduce inert particles acting as a thermal flywheel or catalytically active particles which selectively promote conversion to one or the other product. They can also react exothermically in the atmosphere of the gasifier.

I When calculating the profitability of a jjg * gasification operation, the problem of thermal losses, during 3. r transport from one device to another etc., becomes critical for small units. However, the costs of collecting and transporting waste increasing sharply with the collection radius, preference should be given in this case to small decentralized units. In addition, under these conditions, hydrogen or l oxygen should be prohibited as a gasifier because of their high price and the use of expensive materials.

The present invention aims to provide a new simple gasifier, using the principle of the fluidized bed as well as the double system described above and eliminating by its great compactness a major part of the heat losses while ensuring an intense heat transfer between combustion. and gasification.

It is known, in fact, that the expansion of a fluidized layer increases with the speed of fluidization and that (on the other hand, the pressure drop in a fluidized layer balances the weight of solid per unit of section. Consequently, if a fluidized communicating vessel is produced, with different gas speeds in the two branches, the equilibrium heights will be different. Therefore, by providing for an overflow at the upper part of the system, the two levels are balanced causing a circulation of the solid.

25 However, the object of the invention is achieved by means of a gasifier using the principle of the fluidized bed and the double system comprising a combustion device and a gasification device, providing for the separation of the combustion fumes and the products of gasification, characterized in that it comprises at least one part of gasification and one part of combustion, each consisting of at least one compartment, these adjacent parts communicating through the bottom, so as to ensure a circulation effect by overflow 35, due to a difference in expansion of the fluidized layer.

According to an embodiment of the invention, '[the device can comprise two parts where one of them. ^ Gn · *> "** ·“ eBçwve •' *: - 4 - .; T ^ 3 '-1,> ^ Λ! - *, - V; *.: I • i-!' 1 ♦ - '<-' g it consists of two compartments and the other in a "Λ \ &} compartment, the three compartments being adjacent, each compartment of the part comprising the two 0Γ v compartments communicating by the bottom with the other ·· - · 5 part, an effect of circulation by overflow due to a difference of overflow of the fluidized layer being ensured between the two compartments of the same part.

According to a particularly preferred embodiment of the invention, the gasifier comprises four compartments, two of which are assigned to the combustion part and the other two to the gasification part, the parts being adjacent and communicating through the bottom and the effect of circulation by overflow due to a difference in expansion of the fluidized layer being used in each of the two parts of the device.

The bottom of the combustion part can be fluidized with air, the latter serving at the same time to supply the oxygen necessary for combustion.

20 According to a variant, it can advantageously ~~ fluidize the bottom of the gasification part with steam. The use of steam has the advantage of promoting gasification and makes it possible to> increase the hydrogen content of the gas by the reaction: 25 CO + h2o ^ = ± co2 + h2.

The gasification part can also be fluidized by recycled gases. This device has the advantage of being very economical.

In order to completely avoid the mixture of the gases to be produced and the combustion fumes, it is possible, according to a particularly preferred embodiment of the invention, to fluidize the bottom of the combustion part with steam and inject the air necessary for combustion at a level above the communication ports. In this 3 ^ case, the section of the device must increase with the height of the device.

5 * I '

It is also possible to inject steam and / or recycled gases into the gasification part by a second duct situated at the same level as the air supply duct in the combustion part, i.e. above the communication ports "

This way of proceeding makes it possible to economically obtain good quality gases.

The device of the invention advantageously comprises a waste feed into the gasification compartment through a hopper and a worm. The injection is made directly into the layer, to limit the distillation of tars. It is understood that the supply can be made by any other means known to those skilled in the art, for example, by a butterfly valve, by an annexed fluidized bed or by a pneumatic line, without departing from the scope of the present invention . The supply can however also be done in the other part of the device.

A racking of ash and sand is provided in the bottom of the combustion compartment.

The device of the present invention may also include a cyclone system for purifying the gas and recycling the fines which may still contain carbon.

According to a variant of the invention, two of the compartments are provided with packing elements which are too heavy to be fluidized, thereby regulating the expansion of the fluidized layer. In this case, circulation between the four compartments becomes possible, without having to finely adjust the flow rates.

According to another variant, two of the compartments can be lined with a dense network of exchanger tubes, thereby regulating the expansion of the fluidized layer. The effect on the expansion of the fluidized layer 35 is similar to that obtained by the lining: the expansion increases in the interstices.

It is also possible to charge solid particles 1 catalytically active in the gasification, such as for example MgCO 4.

The invention will be better understood with the aid of the drawings without, however, presenting a limiting character of the invention. Identical marks are used to represent identical elements.

- Figure 1 shows the principle of communicating vessels to which different fluidization rates have been applied, - Figure 2 shows the vessel of Figure 1 for which an overflow has been allowed, - Figure 3 shows an embodiment three comparisons, 15 - Figure 4 shows a preferred embodiment of the invention in vertical section and - Figure 5 shows the same gasifier as that of Figure 4 in a plan view.

The basic principle of the invention is illustrated in FIGS. 1 and 2. If the fluidization speed of branch 2 of the vessel 1 is higher than that applied to branch 3, the equilibrium level of the bed will be higher than that of branch 2. When the wall 4 separating the two branches is lowered so as to allow an overflow (FIG. 2), the two levels are balanced and cause a circulation of the solid according to the arrows.

Figure 3 shows an arrangement where the three compartments 51, 52 and 53 are adjacent to each other.

Good circulation and good mixing in the compartment 51 can be ensured by the appropriate position of the gas injection or of the supply. One can also provide compartments of different shape, for example hexagonal, all having the same dimensions 35 / and fulfilling the conditions already mentioned above.

i 7

A particularly preferred embodiment of the invention is shown in Figures 4 and 5. The gasifier has four compartments, two of which are used for combustion and the other two for gasification. Within each part, the two compartments are transported at different fluidization rates which causes the following circulation ï the solid particles pass from compartment 1 (combustion) to compartment 2 (combustion) by overflow because the speed of fluidization of 1 is greater than 10 that of 2? the solid particles pass from compartment 2 to 3 through the bottom 5, from 3 to 4 by overflow since the fluidization speed of 3 is greater than that of 4, and from 4 to 1 through the bottom 6.

The combustion gases are evacuated via line 7 and the fluidizing gases via line 8, which makes it possible to separate them.

To completely avoid the mixture of the gases to be produced and the combustion fumes, it is possible, according to this particularly preferred mode of the invention, to fluidize the bottom 9 of the combustion part 1, 2 with steam and inject the air necessary for combustion at a level 11 located above the communication orifices 5,6. In this case, the section of the device must increase with the height of the device. In FIGS. 4 and 5 it can also be seen that steam and / or recycled gases can be injected into the gasification part from the bottom and through a second duct 12 situated at the same level as the supply duct of air 11 in the combustion part, that is to say above the communication orifices 5,6. This procedure makes it possible to obtain, in an economical manner, good quality gases.

As is "common practice, the device of the invention advantageously comprises a supply 13 of the waste into the gasification compartment by a hopper and a worm. The injection is made directly into the layer to limit the distillation of the It is well understood that 1. ' feeding can be done by any other means ”- '^ ίΗΙ

8 I

known per se, for example by a butterfly valve or an annex 1 fluidized bed. 1

We must also plan a racking of the ashes! and sand from the bottom of the combustion compartment. The 5 ashes can be sieved and the sand can be reinjected into the combustion compartment in order to play the role of thermal flywheel as already noted above.

The device of the present invention may also include a cyclone system (not shown in the figures) for purifying the gas and recycling the fines which may still contain carbon.

Gas distributors are those commonly used in simple fluidized beds such as, for example, perforated plates, bell plates, perforated tubes, etc.

The perforated tubes, however, allow easier disposal of the ash, especially when bottom ash is formed.

These can still pass between the distribution tubes.

In order to further improve the thermal transfer from combustion to gasification, solid particles catalytically active in the gasification can be charged, such as for example MgCO 2. Around 900 ° C, in the combustion part, the dolomite decomposes into MgO and (X ^ ·

Around 700 ° C, during gasification, these two compounds react to form carbonate, releasing energy.

25 The use of MgCO 3 therefore makes it possible on the one hand to increase the amount of heat transferred to the gasification part and on the other hand to eliminate part of the COj from the gases produced by the gasification, thereby increasing the calorific value of this gas.

It is therefore noted that this new device benefits from the advantages obtained by the processes working in a fluidized bed while maintaining greater compactness and better heat transfer; heat transfer takes place through the circulation of solid particles, through the partition wall between the combustion and gasification parts. In addition, other means known per se to increase heat transfer, such as the use of MgCO ^

Yy or exchanger tubes can also be used.

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It is understood that all circuits and ancillary devices, commonly used in this field of application, can be connected to this new device. For example, an auxiliary circuit allowing the injection of a gaseous, liquid or solid fuel to start the installation or devices making it possible to recover the sensible heat of the combustion fumes to make steam, to preheat the air of combustion and / or to pre-treat the feed.

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Claims (14)

1. Gasifier device using the principle S "'of the fluidized bed and the double system comprising a combustion device and a gasification device, providing for the separation of combustion fumes and gasification products, characterized in that it comprises at at least one gasification part and one combustion part, each consisting of at least one compartment, these parts being adjacent and communicating through the bottom so as to provide a circulation effect by overflow due to a difference in expansion of the fluidized layer. 2. Device according to claim 1 15 characterized in that it comprises two parts where one of them consists of two compartments and the other in a compartment, the three compartments being adjacent to each other, each compartment of the part comprising the two compartments communicating through the bottom 20 with the other part, an overflow circulation effect due to a difference in expansion of the fluidized layer being ensured between the two compartments of the same part. 3. Device according to claim 1 25 characterized in that it comprises four compartments, two of which are assigned to the combustion part and the other two to the gasification part, the parts being adjacent and communicating through the bottom and the circulation effect by overflow due to a difference in expansion of the fluidized layer being used in each of the two parts of the device. 4. Device according to one of the preceding claims, characterized in that the bottom (9) of the combustion part (1, 2) is fluidized with air serving at the same time to supply the oxygen necessary for combustion . 11 5. Device according to one of the preceding claims, characterized in that the bottom c (10) of the gasification part (3f 4) is fluidized with steam. 6. Device according to one of claims 1 to 4 characterized in that the gasification part is fluidized by recycled gases. 7. Device according to one of Claims 1 to 4, characterized in that the bottom (9) of the combustion part (1,2) is fluidized with steam and in that the air required for combustion at a level (11) located above the communication orifices (5,6). 8. Device according to one of the preceding claims 15, characterized in that steam and / or recycled gases are injected into the gasification part. a second conduit (12) located above the communication orifices (5, 6). 9. Device according to one of the preceding claims 20, characterized in that it comprises a feed (13) of the waste into the gasification part by a hopper and a worm. 10. Device according to one of the preceding claims, characterized in that a withdrawal of the ashes' 25 and of the sand is provided in the bottom of the combustion part. 10. Claims 1 11. Device according to one of the preceding claims, characterized in that it comprises a cyclone system for purifying the gas and recycling the fines 30 which may still contain carbon. 12 J 12. Device according to one of the preceding claims, characterized in that the compartments are provided with packing elements which are too heavy to be fluidized, thereby regulating the expansion of the layer 35. fluidized. r • * 13. Device according to one of claims 1 to 11 characterized in that the compartments are lined with a dense network of exchanger tubes, thereby regulating the expansion of the fluidized layer. 14. Device according to one of the preceding claimsq, characterized in that solid and catalytically active particles are charged in the gasification. --- 't.