WO2012095560A2

WO2012095560A2 - Method and arrangement for gasifying carbon-bearing materials

Info

Publication number: WO2012095560A2
Application number: PCT/FI2012/050015
Authority: WO
Inventors: Paterson Mckeough
Original assignee: Andritz Oy
Priority date: 2011-01-10
Filing date: 2012-01-09
Publication date: 2012-07-19
Also published as: FI20115023L; FI20115023A0; AR084810A1; WO2012095560A3; UY33861A

Abstract

The subject of the invention is a new method and arrangement for converting a carbon- bearing feed material into a gas having sufficiently small contents of tars and lighter hydrocarbons for the application in question. The method employs one or more fluidized-bed processing stages and gas exiting one or more of these stages is subjected to a reforming treatment either in the presence or absence of catalyst. Gas exiting the reforming stage is mixed with a stream of solids, the main component of which is bed material and another component of which is char, the said stream of solids having been led from one or more of the fluidized-bed processing stages, preferably from that to which the carbon-bearing feed material is fed. Downstream of the mixing stage, solids are separated from the gas and then recycled or led to one or more of the fluidized-bed processing stages. The method and arrangement enable heat to be transferred from the hot reformed gas to the gasification stage(s) in an efficient and cost-effective way

Description

METHOD AND ARRANGEMENT FOR GASIFYING CARBON-BEARING MATERIALS Technical field

The method and arrangement deal with the conversion of solid or liquid carbon-bearing feed materials into gaseous products. The carbon-bearing feed materials include coal of any rank, residual petroleum fractions, peat, woody biomasses, agricultural biomasses, biomass residues, urban bio-wastes and bio-sludge. The product gas may be utilized, for example, as a fuel gas in a boiler, in a furnace, in an engine or in a gas turbine. Alternatively, it may serve as a feedstock for the synthesis of a chemical or a fuel, e.g. methanol, from the hydrogen and/or the carbon monoxide it contains. The gas employed in these latter applications is termed synthesis gas. For the synthesis-gas applications, as well as for many of the fuel-gas applications, the contents of condensable components (e.g. tars, heavy hydrocarbons) need to be reduced to low levels, either in the gasifier itself or in a subsequent operation. Furthermore, for many synthesis-gas applications, it is advantageous to also convert light hydrocarbon components, such as methane and ethylene, into hydrogen and carbon monoxide by reacting them with steam or carbon dioxide. These conversion reactions of tars and hydrocarbons are usually referred to as reforming reactions. A high extent of reforming of tars, and, in many cases, also of light hydrocarbons, is an objective of the present method. Another key feature is the employment of fluidized-bed processing techniques in the gasification step(s).

Prior art

As a general method, gasification is a well known way converting solid or liquid carbon-bearing material into gaseous products. Gasification can be carried out over a wide range of temperatures and employing different types of equipment (e.g. McKeough, P. and Kurkela, E.: Production and conversion of biomass-derived synthesis gas. Proc. 2008 Nordic Wood Biorefinery Conference, Stockholm, March 11- 13, 2008, pp. 10-15). Whether or not it is advantageous to carry out the gasification at elevated pressure depends on the application. When relatively high gasification temperatures, e.g. in the range 1100 - 1300 °C, are employed, the concentrations of tars and hydrocarbons in the product gas are sufficiently low for many applications. Note that, for the synthesis-gas applications, subsequent gas clean-up is, in any case, required to reduce the amounts of certain detrimental trace components, e.g. hydrogen sulphide, to very low levels before the catalytic synthesis step. The high-temperature gasification reactors are typically suspension-fired entrained-flow reactors. These may be operated above the temperature where melting of the ash of the feed material occurs. One of the other main types of gasification reactor is one employing a fluidized bed. Both bubbling-fluidized-bed (BFB) and fast-fluidized-bed (FFB) technologies have been applied. (Note that the gasifier based on FFB is commonly referred to as a circulating- fluidized-bed (CFB) gasifier.) One limitation of the fluidized-bed gasifier is the need to operate below the temperature at which the bed solids would begin to agglomerate or sinter. For example, when gasifying biomass feed materials in fluidized beds, the gasification temperature is typically limited to about 850 °C. Furthermore, thermal decomposition of biomass yields relatively large amounts of light hydrocarbons and tars. The outcome is a relatively high level of these components in the raw product gas produced from biomass by fluidized-bed processing. In the case of coal gasification, the trend is the same: the concentrations in the product gas of fluidized-bed gasifiers, operating at around 1000 °C, are higher than those in the product gas of entrained-flow gasifiers, operating at around 1300 °C.

For feed materials with relatively low ash contents, e.g. many biomass materials, the bed material employed in fluidized-bed gasifiers is usually mainly comprised of separately introduced material, such as sand or dolomite. In the case of higher-ash materials, e.g. many types of coal, accumulated ash-derived material may form a significant part, or even the main part, of the bed material.

In the case of fluidized-bed gasification of biomass, separate reforming of the raw product gas is usually considered to be the most competitive way to reduce the contents of tars and, if necessary, light hydrocarbons to low levels (e.g. C. Hamelinck, A. Faaij, H. den Uil, H. Boerrigter, Production of FT transportation fuels from biomass; technical options, process analysis and optimisation and development potential. Energy, the International Journal, Vol. 29, No. 11, September 2004, pp. 1743-1771). So-called autothermal reforming is usually considered as the appropriate type of reforming process for application in conjunction with a gasification process. In autothermal reforming, partial oxidation of the gas is used to provide the heat for the reforming process. Autothermal reforming may be performed either in the presence or absence of catalyst. Catalytic autothermal reforming may be, and typically is, carried out at lower temperatures than non-catalytic autothermal reforming. The typical range for catalytic autothermal reforming is 850 - 1000 °C, while for non-catalytic autothermal reforming of moderate or high severity, the typical temperature range is 1100 - 1300 °C. Note that terms such as thermal reforming, thermal cracking, thermal treatment and high- temperature treatment are also used when referring to non-catalytic autothermal reforming.

The required severity of the reforming step is dependent on the application. For many of the synthesis-gas applications, high-severity reforming is required for a high conversion, not only of tars, but also of light hydrocarbon components. An exception is methane synthesis when obviously it is advantageous to keep the extent of reforming of methane as low as possible prior to the synthesis step, in which case a reforming step of moderate severity may be acceptable. For fuel-gas applications requiring gas of low tar content, a low-severity reforming step may be sufficient.

When the amount of heat removed or lost from the combined gasification-reforming process section is constant, the temperature of the gas leaving the section gives a good indication of the so called cold-gas efficiency of the gasification-reforming process. In general, the higher the gas temperature, the lower is the cold-gas efficiency. (The cold- gas efficiency gives a measure of how much of the heating value of the feedstock is recovered as heating value in the product gas. Note that, under these circumstances, the H2/CO ratio in the product gas also affects the cold-gas efficiency to some extent.) Thus - at least when the gas leaving the reformer is led directly to the downstream processing steps without any recycle of heat to the gasifier - the cold-gas efficiency of the alternative based on catalytic autothermal reforming is higher than that of the corresponding alternative based on non-catalytic autothermal reforming, assuming that a higher reforming temperature is employed in the latter case. Compared to non-catalytic autothermal reforming, disadvantages of the catalytic autothermal reforming alternative include catalyst costs, higher sensitivity to gas impurities, such as sulphur compounds and dust, and higher sensitivity to disturbances in process conditions. Note that the relative insensitivity of non-catalytic autothermal reforming to gas impurities means that it may be applied to gases produced from a wider range of feedstock.

The operability of a catalytic autothermal reforming step, when applied in conjunction with a gasification process, can obviously be improved by filtering the gas prior to reforming. However, typically, the maximum temperature at which the gas can be filtered in a reliable and cost-competitive way is significantly lower than the temperature of the gas exiting a single-stage gasification reactor. Thus, it is usually necessary to cool the gas prior to filtration, which, in turn, lowers the cold-gas efficiency of the process.

Using part of the sensible heat in the gas exiting the reformer as a source for part of the heat required for the endothermic gasification process is one way of increasing the cold- gas efficiency of the gasification-reforming process. Naturally, the temperature of the gas leaving the combined gasification-reforming process section is lower than it would be in the absence of such recycling of heat. Methods that have been previously proposed to achieve this end are discussed next.

The main approach previously applied to achieve this end is based on splitting the gasification process into two stages and applying non-catalytic autothermal gas- reforming between the two stages. For example, a method based on this principle is the subject of German patent DE2927240 (priority date 05.07.1979). In this method, the first step is a carbonization step. The gas produced in this step is subjected to high- temperature treatment (non-catalytic autothermal reforming) and is then contacted with the solid product (char) of the first step, after which the char is further gasified. Thus, part of the sensible heat of the gas exiting the high-temperature gas-treatment stage is exploited in the char-gasification stage and the temperature of that gas is lowered. It should be noted that carbonization, which is alternatively referred to as pyrolysis or thermal decomposition, is the essential first phase of the gasification process irrespective of whether the process is carried out in one stage, as normally, or in two stages, as in the method of patent DE2927240. Essentially the same approach is also the basis of the methods of patent documents DE19618213 and DE4404673. A novel feature of the former method is a way of withdrawing the gas from the pyrolysis step with minimal dust loading, while, in the latter case, the novel feature is the direct injection of the pyrolysis char, as small particles, into the gas stream exiting the high- temperature thermal-treatment stage (non-catalytic autothermal reforming). A specific process based on the method of DE4404673 has been developed and tested. The process is described in the publication: Rudloff, M., Biomass-to-liquids (BTL) from the Carbo- V® process: technology and the latest developments, 2nd World Conf. on Biomass for Energy, Industry and Climate Protection, Rome, Italy, 2004, p. 1875. Note that a feature of this process is that the char stream from the primary pyrolysis-gasification stage is de-pressurized and cooled, after which the char is ground to a fine powder before introduction into the char-gasification stage.

The principle according to which part of the sensible heat of the hot gas exiting the reformer is utilized as a source of heat for the endothermic gasification reactions is termed herein as the general principle of heat transfer from the reforming step. Drawbacks of the previously known methods based on this general principle include (1) the relatively complicated reactor technology employed in the first stage (pyrolysis, carbonization), (2) the difficulty in transferring char on a continuous basis from the first stage to the second stage (char gasification) without pressure let-down and possibly intermediate cooling of the char and (3) limited possibilities to independently adjust the extent to which heat from the reforming step is utilized in the char-gasification stage. Drawback (1) has a negative impact on equipment costs and availability. Drawbacks (2) and (3) have negative impacts on the energy efficiency of the process, meaning that, in their absence, the net efficiency advantage resulting from the transfer of heat from the reforming step to the char-gasification stage would be even greater.

In the prior art, fluidized-bed gasification has not been applied in conjunction with the general principle of heat transfer from the reforming step. The known methods based on the principle employ reactor technology that does not require the presence of a separate bed material. In these known methods, e.g. the method according to DE4404673 outlined above, the hot gas exiting the reformer is directly contacted with a stream of solids comprised essentially of char material, only, the said char having been produced in the first pyrolysis-gasification stage. As a consequence, the char is heated to a temperature that is high enough for char gasification to proceed at an acceptable rate. The known methods do not employ a separate medium to carry sensible heat from the exit gas of the reformer to the char-gasification stage. It should also be noted that, in the known methods, the amount of sensible heat carried by the char material entering the char-gasification stage is very minor, usually negligible, compared to the amount of heat needed to drive the endothermic gasification reactions.

The previously known methods that employ the general principle of heat transfer from the reforming step incorporate a non-catalytic autothermal reforming step. Catalytic auto thermal reforming is outside the realms of these known methods.

Description of the invention

The present invention provides an improved method for gasifying carbon-bearing feed materials so that (1) the conversion efficiency is exceptionally high and (2) the amounts of tars and certain hydrocarbons in the product gas are at levels sufficiently low for the application in question. The novel features upon which the improvements are based are laid out in the attached claims.

A problem that the invention sets out to solve is that of obtaining a product gas in which the contents of tars and lighter hydrocarbons are sufficiently small for the application in question, but without the loss of conversion efficiency usually associated with the incorporation of the required gas-reforming step. The invention is based, in part, on the general principle of heat transfer from the reforming step, as defined earlier. However, the principle is realized in a new way that deviates appreciably from that of the prior art and eliminates certain drawbacks of the prior art.

The present invention employs one or more fluidized-bed processing stages for the physical handling and chemical conversion of the carbon-bearing feed material and incorporates a processingstep for the partial or complete reforming of tars and hydrocarbons in the gas. The product gas can be utilized and/or further upgraded and then utilized in various synthesis-gas and fuel-gas applications. The present invention contains two novel and significant departures from the prior art:

1) In contrast to the prior art, the method is based on fluidized-bed processing stage(s) and uses bed material as a heat-carrying medium for transferring heat from the reformed gas to the gasification stage(s). The bed material carries most of the heat that is transferred.

2) In contrast to the prior art, the method includes a mixing step, in which part or all of the hot gas from the reforming step is mixed with, predominately, bed material, which is led from one or more of the fluidized-bed processing steps, preferably from that to which the feedstock of the process is fed. Another component of this stream of solids is char. However, the stream contains far more bed material than char material.

Thus, in the method of the present invention, the general principle of heat transfer from the reforming step, as defined earlier, is realized in a distinctly new way. Utilization of bed material to transfer heat from the high-temperature gas exiting the reforming step to a gasification stage is not obvious for a number of reasons including (1) the apparent risk of sintering and agglomeration of bed material in the mixing stage and (2) the apparent challenge associated with re-circulating solids to a gasification stage operating at higher pressure.

The present invention also relates to an arrangement for producing, from one or more carbon-bearing feed materials, a gas which can be utilized and/or further upgraded and then utilized in various synthesis-gas and fuel-gas applications, the arrangement comprising one or more fluidized-bed processing stages for physical handling and chemical conversion of the carbon-bearing material. The arrangement further comprises:

- a reformer connected, either directly or via intermediate processing devices, to one or more of the fluidized-bed stages for the purpose of subjecting gas exiting one or more of the fluidized-bed stages to a reforming process, - a mixing device connected, either directly or via intermediate processing devices, to the reformer and to one or more of the fluidized-bed stages for the purpose of mixing gas exiting the reformer with a stream of solids, which have been discharged from one or more of the fluidized-bed stages, and

- a separator located at a point downstream of the mixing device and connected, either directly or via intermediate processing devices, to the mixing device and to one or more of the fluidized-bed stages, or alternatively located in conjunction with the mixing device and connected, either directly or via intermediate processing devices, to one or more of the fluidized-bed stages, for the purpose of separating solids from the gas, after which solids so separated are led to one or more of the fluidized-bed stages.

Examples of the possible intermediate processing devices referred to above are a cooling device, a filtering device, and a fluidized-bed processing device. According to certain embodiments, the device employed in at least one of the fluidized- bed stages is a fast-fluidized-bed (FFB) reactor.

According to other embodiments, the device employed in at least one of the fluidized- bed stages is a bubbling-fluidized-bed (BFB) reactor.

The mixing device and a subsequent fluidized-bed processing stage may be incorporated into a single fluidized-bed processing device.

According to one embodiment employing a fast-fluidized-bed reactor, the reactor has two parts, an upper part and a lower part, which are of different geometrical design and/or are joined with a connector of special geometrical design in order minimize back-mixing of solids from the upper part to the lower part.

Remarkable benefits ensue from the employment of circulating bed material both in the gasification stage(s) and as a heat-carrying medium for transferring heat from the reformed gas to the gasification stage(s). Introducing bed material as a heat carrier creates an additional degree of freedom. Heat is readily transferred in both the downstream and upstream directions and the extent of heat transfer from the reformed gas may be adjusted by varying the rate of circulation of the bed material. Thus, in multi-stage embodiments of the present method, the circulating bed material also serves as a heat carrier between the gasification stages. One benefit of this is that the complicated reactor designs required for the first stage (pyrolysis, carbonization) of the previously known methods may be avoided. Another benefit is that the circulating bed material conveniently conveys char from one step to another. Compared to the previously known methods employing the general principle of heat transfer from the reforming step, these features render processes based on the new method more amenable to operation on a continuous basis, particularly at elevated pressures.

Further benefits derive from the incorporation of the mixing stage, referred to above. The gas exiting the mixing stage need not be further chemically processed within the borders of the gasification-reforming process but may, instead, be withdrawn as the product gas of the combined gasification-reforming process. Incorporation of this feature gives rise to process configurations far removed from any of those of the known methods employing the general principle of heat transfer from the reforming step.

Another remarkable feature of the new method is that a moderate rate of circulation of the bed material is, in general, sufficient to ensure that the temperature reached after the mixing of the reformed gas with the stream of solids is lower than the temperature at which the solids would agglomerate or sinter. It is noteworthy that, in most cases of practical interest, increasing the rate of circulation of the bed material benefits the process in two ways. Firstly, the temperature of the mixing stage is lowered thus helping to avoid agglomeration and sintering problems. Secondly, the extent of heat transfer from the reformed gas to the gasification stage(s) is increased.

As mentioned above, pyrolysis is the essential first phase of a gasification process. Carbon contained in the solid pyrolysis product (char) is subsequently gasified with steam and/or carbon dioxide in the other main phase of the overall gasification process. In a normal one-step gasification process, the pyrolysis and char-gasification phases are carried out in a single reactor. As presented in more detail later, one embodiment of the present new method employs a single gasification reactor. However, the majority of the embodiments of the present invention employ at least two gasification stages. In these embodiments, the stage to which the feedstock is fed is termed the primary stage. In respect of the reactions involved in the gasification process, the primary stage usually encompasses the greater part of the pyrolysis phase. The greater part of the char- gasification phase is then usually carried out in one or more of the subsequent stages. However, char-gasification reactions may also occur to some extent in the primary stage of the multi-stage embodiments of the present method. It should be emphasized that, in the multistage embodiments of the present invention, it is not required that the reactions in any stage be restricted to those of one type only, e.g. to pyrolysis reactions only, or to char-gasification reactions only.

The typical fluidized-bed processing stage has adjunct equipment such as cyclone separator(s), connecting duct(s) and screw feeder(s). When not specifically referred to separately herein, adjunct devices are considered herein to be constituent parts of the fluidized-bed processing stage in question.

The key features of the invention are:

(1) Gas exiting one or more of the fluidized-bed stages is, either directly or after intermediate processing, subjected to a reforming process, preferably an autothermal reforming process, either in the presence of one or more catalysts or in the absence of catalyst.

(2) In a subsequent mixing stage, which may also employ fluidized-bed technology, part or all of the gas exiting the gas-reforming stage is mixed with a stream of hot solids, the main component of which is bed material and another component of which is char, the said solids stream having been led from one or more of the fluidized-bed stages, or from their adjunct equipment, with the further condition that the temperature of the stream of hot solids, prior to mixing, is lower than the temperature of the gas exiting the gas-reforming stage, and including the possibility that some or all of the char may be gasified in the mixing stage.

(3) At some point downstream of the mixing stage, or in conjunction with the mixing stage, solids are, to a large extent, separated from the gas and returned or led to one or more of the fluidized-bed processing stages. In respect of the separation of solids mentioned in feature (3) above, the objective is to achieve a very large extent of separation: in the range 80 - 100 %, preferably in the range 95 - 100 %, and most preferably in the range 99 - 100 %. In the preferred arrangement for embodiments of the new method, the fluidized-bed stage, from which the stream of hot solids is led for the purpose of mixing with the reformed gas, is the fluidized-bed stage to which the carbon-bearing feed material is fed. In the typical multistage embodiments of the new method, the average temperature of the fluidized-bed stage to which the carbon-bearing material is fed, i.e. the primary pyrolysis-gasification stage, is lower than that of the other subsequent fluidized-bed gasification stage(s). The carbon-bearing feedstock is heated up, dried (if fed in a moist state) and, to a large or to a complete extent, pyrolyzed in this primary stage. In line with the preferred arrangement described above, solids are led from this stage and mixed with the exit gas of the reforming stage. The temperature of this gas is higher than the temperature of the solids. Thus, the gas is cooled to some extent and the solids are heated to some extent in the mixing stage. Solids are, to a large extent, separated from the gas, often directly after the mixing stage, and are then recycled or led to a gasification stage. With this arrangement, part of the sensible heat of the reformed gas is effectively transferred from the gas to the last mentioned gasification stage.

The typical single-reactor embodiment of the new method requires a temperature differential over the reactor. In a fast-fluidized-bed (FFB) reactor, for example, this can be achieved by carrying out a large part of the char gasification in the lower part of the reactor and introducing the feedstock higher up. Provided there is no addition of oxidant higher up, both the subsequent heating-up (and final drying) of the feed material and the subsequent pyrolysis/gasification reactions of the feed material tend to cool the up- flowing bed and gases. The extent of cooling depends mainly on the ratio of the mass flow of the bed material to the mass flow of the feedstock and on the degree of back- mixing of solids from the upper part of the reactor to the lower part. The lower the ratio of bed material flow to feedstock flow and the less the back-mixing of solids, the greater is the temperature differential over the reactor. With a temperature differential in place, a single-reactor embodiment of the new method is accomplished by withdrawing solids from the upper part of the reactor; e.g. from the adjoined cyclone, mixing these solids with the hot reformed gas, and then, after separation of solids, returning such solids to the lower part of the reactor.

In typical embodiments of the new method, the temperatures of the gas and the solids exiting the fluidized-bed stage, to which the carbon-bearing feed material is fed, are in the range 500 - 900 °C, the temperature of the gas-reforming stage is in the range 800 - 1300 °C, and the temperature of the mixing stage is in the range 700 - 1000 °C.

The new method results in a considerable increase in cold-gas efficiency compared to that of the corresponding conventional process that employs essentially the same gasification and reforming steps, but without heat transfer from the hot reformed gas to a gasification step. Compared to the known methods employing the general principle of heat transfer from the reforming step, the present new method offers a number of significant advantageous features which are not possible to realize within the realms of the previous methods. These features include the following:

In the mixing stage, the extent of cooling of the reformed gas - and so the extent of transfer of heat to the gasification stage(s) - can be altered by varying the circulation rate of the bed material.

The gas exiting the mixing stage may be withdrawn as the product gas of the combined gasification-reforming process. Several exceptionally compact and cost-effective embodiments of the present invention are based on configurations employing this feature.

When two or more gasification stages are employed, the bed material not only serves as a heat carrier for the transfer of heat from the reformed gas to a gasification stage, but also serves as a heat carrier between the gasification stages. The circulating bed material also conveniently conveys char from one step to another. Compared to the previously known methods employing the general principle of heat transfer from the reforming step, these features render processes based on the new method more amenable to operation on a continuous basis, particularly at elevated pressures. For example, in processes based on the present method, char is readily transferred from the primary pyrolysis- gasification stage to the other gasification stage(s) on a continuous basis and without intermediate let-down in pressure. Another benefit of employing bed material as a heat carrier is that the reactor for the heat-demanding primary pyrolysis-gasification stage can be realized in a more straightforward manner than is the case in the previously known methods based on the general principle of heat transfer from the reforming step. As a result of these and other benefits of the utilization of circulating bed material, processes based on the new method are more cost-competitive than those based on the known methods that employ the general principle of heat transfer from the reforming step.

The previously mentioned advantage may be taken one step further by arranging for all the gasification reaction phases to be conducted in a single reactor operated with a temperature differential.

Overall, in comparison to the previously known methods employing the general principle of heat transfer from the reforming step, application of the present new method significantly improves the techno-economical performance of the combined gasification-reforming process.

Brief description of the drawings:

The present new method is described in more detail with reference to the drawing in which:

Figures 1-5 are block flow diagrams illustrating alternative ways of connecting the stages that comprise the method of the invention.

Figures 6-12 depict more detailed exemplary embodiments of the invention.

The new method may be embodied in any one of numerous ways. First of all, depending on how the different process steps are connected to each other, there are a number of basic configurations. Five such configurations - Configurations 1, IB, 2, 3, 3B - are depicted in the attached FIGS. 1- 5, respectively. In these figures, the process steps and streams that embody the essential features of the present invention are marked with unbroken lines. The numbers and letters in FIGS. 1 - 5 refer to the following streams and processing stages:

1. Feedstock stream (FIGS. 1 - 5), i.e. the carbon-bearing feed material

2. Gas streams containing oxygen and possibly steam (FIGS. 1 - 5)

3. Intermediate gas streams (FIGS. 1 - 5)

4. Product-gas stream (FIGS. 1 - 5)

5. Flue-gas stream, if char combustion stage included (FIGS. 1 , 3, 4)

6. Solids streams, with bed material as main component (FIGS. 1 - 5)

A. Primary fluidized-bed stage; pyrolysis-gasification (FIGS. 1 , 3, 4, 5)

B. Gas-reforming stage; non-catalytic or catalytic (FIGS. 1 - 5)

C. Gas-solids mixing stage with post-mixing separation stage incorporated (FIGS. 1 , 2, 3)

D. Further fluidized-bed stage(s); e.g. gasification, combustion, riser stage(s)

(FIGS. 1 , 3, 4)

AD. Two gasification stages (pyrolysis-gasification and char gasification) in a single fluidized-bed reactor (FIG. 2)

E. Gas-solids mixing stage (FIG. 4)

ED. Gas-solids mixing stage and fluidized-bed stage in a single fluidized-bed reactor (FIG. 5)

In Configuration 1 (FIG. 1), the gas from the primary pyrolysis-gasification stage (A) is subjected to the reforming treatment (B), while the product gas (4) of the overall gasification-reforming process is the gas exiting the mixing stage (after separation of solids) (C). Configuration IB (FIG. 2) is a simplified version of Configuration 1 : the two gasification stages are conducted in a single reactor (AD) operated with a temperature differential. In Configuration 2 (FIG. 3), the gas from another gasification stage (D) is subjected to the reforming treatment (B), while the product gas (4) is still the gas exiting the mixing stage (C). Configuration 3 (FIG. 4) differs from Configuration 1 in that the gas from the mixing stage (E) is further processed in a subsequent fluidized-bed stage (D) and the gas (4) exiting this later stage is the product gas of the overall gasification-reforming process. In this configuration, the post-mixing separation of solids may be performed either directly after the mixing stage or after a subsequent stage. Configuration 3B (FIG. 5) is a simplified version of Configuration 3: the mixing stage and the subsequent fluidized-bed processing stage (char gasification, riser stage) are conducted in a single reactor (ED); e.g. the mixing stage in the lower part of a fast-fluidized-bed

(FFB) reactor and the subsequent processing stage in the upper part of the same reactor.

As indicated in FIGS. 1, 3 and 4, one of the fluidized-bed processing steps may be a char-combustion step, in which case the resultant flue gas exits the gasification- reforming process as a separate stream.

In the following, further light is shed on the invention by describing a number of embodiments of the invention in more detail. These embodiments are depicted in FIGS. 6 - 12. The numbers and letters in these figures refer to the following streams and processing stages:

1. Feedstock stream (FIGS. 6 - 12), i.e. the carbon-bearing feed material

2. Solids stream, with bed material as the main component (FIGS. 6, 8, 10)

3. Intermediate gas stream (FIGS. 6, 8, 10)

4. Intermediate gas stream (FIGS. 6 - 12)

5. Gas stream containing oxygen and possibly steam (FIGS. 6 - 12)

6. Solids stream, with bed material as the main component (FIGS. 6 - 12)

7. Gas stream exiting gas-reforming stage (FIGS. 6 - 12)

8. Solids stream, with bed material as the main component (FIGS. 6 - 12)

9. Intermediate gas stream (FIGS. 10, 11)

10. Gas stream containing oxygen and/or steam and possibly recycled gas (FIGS. 6 - 12)

11. Gas stream containing oxygen and possibly steam (FIGS. 11, 12)

12. Product-gas stream (FIGS. 6 - 12)

13. Water-quench stream for emergency temperature control (FIGS. 6 - 12)

14. Fly-ash stream (FIGS. 8, 9, 12)

15. Bottom-ash streams (FIGS. 6 - 12) A. Primary fluidized-bed stage; pyrolysis-gasification; fast fluidized bed (FIGS. 6, 7, 8, 9), bubbling fluidized bed (FIGS. 10, 11 , 12)

B. Gas-reforming stage; non-catalytic (FIGS: 6, 7, 10, 1 1), catalytic (FIGS. 8, 9, 12) C. Gas-solids mixing stage (FIGS. 6 - 12)

D. Solids-separation stage (FIGS. 6 - 11)

E. Fluidized-bed stage; char gasification; fast fluidized bed (FIGS. 6, 7, 8, 9, 1 1 , 12), bubbling fluidized bed (FIG. 10)

F. Gas-filtration stage (FIGS. 8, 9, 12)

G. Riser stage (FIG. 10)

The embodiment depicted in FIG. 6 is based on Configuration 1. Two gasification reactors - both based on fast-fluidized-bed (FFB) technology -are employed. The carbon-bearing feed material (1) is led to the primary pyrolysis-gasification stage which is carried out in the upper FFB reactor (A). The heat required for this stage is provided by the sensible heat contained mainly in the bed material (2) and in the gas (3) coming from the lower FFB char-gasification reactor (E). The gas (4) from the primary stage (upper reactor) is led to the reformer (B). In this embodiment, non- catalytic autothermal reforming is employed. An oxygen-containing gas (e.g. oxygen of any purity, oxygen-enriched air, air) (5) is added to the reformer and the heat required for this stage is generated through partial oxidation of the gas. Solids (6) are led from the primary stage (A) to the mixing stage (C) where they are mixed with the hot gas (7) exiting the reforming stage. Note that gasification of char may also occur to some extent in the mixing stage and in its adjunct equipment and that this would further improve the cold-gas efficiency of the process. To prevent gas from the primary pyrolysis-gasification stage (A) bypassing the reformer via the solids outlet of the cyclone separator adjoined to the stage, a device is needed to increase the pressure drop between the base of the cyclone and the mixing stage. Well-known devices for this purpose include fluid-seal pots, cone valves and screw feeders. A screw feeder is shown in FIG. 6. As a result of the mixing, the gas (7) from the reformer is cooled to some extent in the mixing stage while the solids (6) are heated to some extent. Solids are, to a large extent, separated from the gas in the cyclone separator (D) and are recycled to the lower FFB char-gasification reactor (E) as stream 8. A device, such as a fluid-seal pot, is needed to facilitate the return of the solids against pressure. The gas leaving the cyclone (D) is the raw product gas (12) of the combined gasification-reforming process. A gas stream (10) composed of an oxygen-containing gas (e.g. oxygen of any purity, oxygen-enriched air, air), and possibly also containing steam and/or recycled gas, is employed as the fluidizing medium for the lower FFB reactor (E). The oxygen in this stream also serves as the necessary reactant for the partial oxidation reactions occurring in this stage of the overall gasification process. The embodiment depicted in FIG. 7 is based on Configuration IB. It differs from that shown in FIG. 6 by employing a single gasification reactor based on fast- fluidized-bed (FFB) technology. The reactor is operated with a temperature differential, the average temperature in the upper part of the reactor (A) being lower than that in the lower part (E). The carbon-bearing feed material (1) is introduced into the reactor at some intermediate elevation. As a result of both subsequent heating-up (and drying) of the feedstock and subsequent reactions, the introduction of the feedstock cools the up-flowing bed and gases, thus establishing the required temperature differential over the reactor. The char-gasification stage of the overall gasification process is primarily conducted in the lower part of the reactor (E). Compared to the embodiment in FIG. 6, the two separate FFB reactors of the embodiment in FIG. 6 have been replaced by the single FFB reactor of the embodiment in FIG. 7. Other features of the embodiment of FIG. 7 are similar to those of the embodiment of FIG. 6. It should be noted that, in order to minimize the extent of back-mixing of the solids from the upper part of the reactor to the lower part, or for possible other reasons, the geometrical design of the upper part of the single reactor of the embodiment in FIG. 7 may be different from that of the lower part of the reactor. Furthermore, the two parts of the reactor may be joined to each other in alternative ways based on different geometrical design. The embodiment depicted in FIG. 8 is, like the embodiment of FIG. 6, based on

Configuration 1. It differs from the embodiment of FIG. 6 by employing a catalytic method rather than a non-catalytic method for the autothermal reforming stage (B). It also incorporates a gas-filtration step (F) upstream of the catalytic reformer. The temperature of the gas-filtration stage is close to that of the gas (4) exiting the primary pyrolysis-gasification stage (A).

The embodiment depicted in FIG.9 is, like the embodiment of FIG. 7, based on Configuration IB. It differs from the embodiment of FIG. 7 by employing a catalytic method rather than a non-catalytic method for the autothermal reforming stage (B). It also incorporates a gas-filtration step (F) upstream of the catalytic reformer. The temperature of the gas-filtration stage is close to that of the gas (4) exiting the single gasification reactor.

The embodiment depicted in FIG. 10 is based on Configuration 3 and employs non- catalytic autothermal reforming. The gas stream (9) from the post-mixing separation stage (D), rather than serving as the product gas of the combined gasification- reforming process, as in the previous embodiments, is led to a riser stage (G) based on fast-fluidized-bed (FFB) technology. The gas (12) exiting this stage is the raw product gas of the combined gasification-reforming process. This embodiment employs bubbling-fluidized-bed (BFB) technology rather than fast-fluidized-bed (FFB) technology for the two gasification stages (A and E). The riser stage is incorporated in order to recycle solids from the mixing stage to the BFB gasification stages.

The embodiment depicted in FIG. 1 1 is based on Configuration 3 and employs non- catalytic autothermal reforming. The gas stream (9) from the post-mixing separation stage (D), rather than serving as the product gas of the combined gasification- reforming process, is led to a char-gasification stage (E) based on fast-fluidized-bed

(FFB) technology. Partial oxidation is needed in this stage and, to this end, oxygen- containing gas (e.g. oxygen of any purity, oxygen-enriched air, air) (11) is also added. The gas (12) exiting this stage is the raw product gas of the combined gasification-reforming process. The primary pyrolysis-gasification stage (A) is based on bubbling-fluidized-bed (BFB) technology and uses a gas stream (10) with a high content of steam, and possibly also containing oxygen, as the fluidizing medium. The embodiment depicted in FIG. 12 is based on Configuration 3B. The mixing stage (C) and the following fluidized-bed char-gasification stage (E) are incorporated into a single reactor. This embodiment differs from the embodiment of FIG. 11 in two additional respects: a catalytic method rather than a non-catalytic method is employed for the autothermal reforming stage (B) and a gas-filtration step

(F) is added upstream of the catalytic reformer. The temperature of the gas-filtration stage is close to that of the gas (4) exiting the primary pyrolysis-gasification stage (A) which is based on bubbling-fluidized-bed (BFB) technology. One area of application of the present gasification method is in the production of synthesis gas. The raw synthesis gas is further treated and then converted into one or more of a number of different chemicals and fuels. A tail gas is often produced as a byproduct of the synthesis step and, in certain cases, it may be advantageous to recycle the tail gas to the gas-reforming stage. The recycled tail gas may be introduced at any one of a number of locations upstream of the reforming step or directly into the reformer. For example, it may be added to the fluidizing gas of the primary pyrolysis-gasification stage, or it may be added between the primary stage and the gas filter (if applied). The temperature of the tail gas is usually relatively low so that, in this latter case, the filtration temperature is lowered with respect to the temperature of the gas exiting the primary stage - a feature which may be beneficially exploited. When the primary pyrolysis-gasification stage of a process utilizing the present new method is based on fast-fluidized-bed (FFB) technology; as e.g. in the embodiments of FIGS. 6, 7, 8 and 9, an advantageous location for introduction of recycled tail gas is in the primary pyrolysis-gasification stage at a point upstream of the cyclone separator adjoined to the stage. The introduction of tail gas at such a location lowers the temperature of the solids that are separated by the cyclone and subsequently led to the mixing stage, and thereby increases the extent of heat transfer to the gasification stage(s). The present method is not restricted to the use of inert bed material. For example, the bed material may be one that catalyzes certain desired gasification reactions or one that reacts with certain gaseous components. Neither is the present method restricted to a narrow range of operating pressures. For example, it may be applied to processes operating near atmospheric pressure or to processes operating at elevated pressures.

The configurations and the embodiments of the present invention are not limited to those presented herein.

In the following three examples, performances of certain embodiments of the present new method are compared to those of corresponding reference processes based on known methods. Where possible, the process specifications of the reference processes have been set to match those of the corresponding process based on the present method.

Example 1. In this example, the embodiment of the new method is that of FIG. 8, based on catalytic autothermal reforming, and the feedstock is a particular woody biomass. Three reference processes are considered. Reference process I is based on a known method that employs non-catalytic autothermal reforming and incorporates transfer of heat from the reformed gas to a gasification step. In addition to employing a non-catalytic reforming step, reference process I differs significantly from the process based on the present new method by (1) not being based on fluidized-bed processing, (2) not employing bed material as the main means for carrying out the heat transfer, and (3) not incorporating a stage where such a heat carrier is mixed with the reformed gas. Both the other reference processes employ both (1) a single fluidized-bed gasification stage and (2) catalytic autothermal reforming without heat transfer from the reformed gas to the gasification stage. Reference process II does not include a filtration step prior to reforming, while reference process III incorporates gas filtration at 600 °C prior to reforming. Key process temperatures, the oxygen consumptions and the cold-gas efficiencies of the four processes are compared in the following table. Example 1 Process Reference Reference Reference based on process process process new method I II III

(FIG. 8)

Woody Woody Woody Woody

Feedstock

biomass biomass biomass biomass

Oxygen-containing Oxygen + Oxygen + Oxygen + Oxygen + feed gas streams steam steam steam steam

Type of autothermal Non-

Catalytic Catalytic Catalytic reformer catalytic

Heat transfer from

reformed gas to a Yes Yes No No gasification stage

Exit temperature of

primary pyrolysis- 600 °C 500 °C

gasification stage

Exit temperature of

850 °C 850 °C 850 °C 850 °C char-gasification stage

Gas -filtration

600 °C - - 600 °C temperature

Exit temperature of

900 °C 1400 °C 900 °C 900 °C gas -reforming stage

Temperature of raw

755 °C 850 °C 900 °C 900 °C product gas

0₂ consumption,

0.37 0.40 0.41 0.46 kg/kg dry feedstock

Cold-gas efficiency

84 % 81 % 81 % 76 % (LHV basis)*

*(LHV-energy content of the product gas after shifting to H₂/CO=2) x 100 / (LHV-energy of the gasifier feedstock); LHV = lower heating value

The data in the above table show that, in terms of cold-gas efficiency, the process based on the new method is superior to the reference processes, particularly when the reference process does not incorporate heat transfer from the reformed gas to the gasifier and, like the process based on the new method, does employ gas-filtration prior to catalytic reforming. Note that (1) the same or nearly the same cold-gas efficiency can be achieved with the embodiment of FIG. 9 as is achieved with the embodiment of FIG. 8, when the extent of back-mixing of solids from the upper part of the reactor to the lower part is insignificant and (2) there are no previously known methods employing the general principle of heat transfer from the reforming step in conjunction with catalytic autothermal reforming. The cold-gas efficiency of the process based on the new method would be further improved by any gasification of char occurring in the mixing stage.

Example 2. In this example, the embodiment of the new method is that of either FIG. 6 or FIG. 10, based on non-catalytic autothermal reforming, and the feedstock is a particular high-volatile bituminous coal. The meaningful reference process in this case is a high-temperature entrained-flow gasification process. Key process temperatures, the oxygen consumptions and the cold-gas efficiencies of the two processes are compared in the following table.

*(LHV-energy content of the product gas after shifting to H₂/CO=2) x 100 / (LHV-energy of the gasifier feedstock prior to feeding system); LHV = lower heating value

The cold-gas efficiency of the process based on the new method and employing bituminous coal as feedstock is clearly higher than that of the conventional reference process. Note that the same or nearly the same cold-gas efficiency can be achieved with the embodiment of FIG. 7 as is achieved with the embodiments of

FIG. 6 and FIG. 10, when the extent of back- mixing of solids from the upper part of the reactor to the lower part is insignificant. The cold-gas efficiency of the process based on the new method would be further improved by any gasification of char occurring in the mixing stage.

Example 3. In this example, the embodiment of the new method is that of either FIG. 6 or FIG. 10, based on non-catalytic autothermal reforming, and the feedstock is a particular woody biomass. This embodiment employs air as the oxygen- containing feed gas and the reforming step is conducted at mild severity, which means, in this particular case, at the same temperature as that employed in the char- gasification stage. The process would be suitable for the production of a fuel gas, which, after further processing, could be combusted in a gas turbine. The reference process is a single-stage air-blown gasification process. Key process temperatures and the cold-gas efficiencies of the two processes are compared in the following table.

*(LHV-energy content of the product gas) x 100 / (LHV-energy of the gasifier feedstock); LHV = lower heating value The cold-gas efficiency of the process based on the new method is higher than that of the conventional reference process. Note that the same or nearly the same cold- gas efficiency can be achieved with the embodiment of FIG. 7 as is achieved with the embodiments of FIG. 6 and FIG. 10, when the extent of back- mixing of solids from the upper part of the reactor to the lower part is insignificant. In comparison to the reference process, the process based on the new method has the additional advantage of allowing the char-gasification temperature and the reforming (tar- cracking) temperature to be adjusted independently of each other. The cold-gas efficiency of the process based on the new method would be further improved by any gasification of char occurring in the mixing stage.

Claims

1. A method for producing, from one or more carbon-bearing feed materials, a gas which can be utilized and/or further upgraded and then utilized in various synthesis-gas and fuel-gas applications, the method employing one or more fluidized-bed processing stages for physical handling and chemical conversion of the carbon-bearing material; wherein:

a) gas exiting one or more of the fluidized-bed stages is, either directly or after intermediate processing, subjected to a reforming process, b) in a subsequent mixing stage, part or all of the gas exiting the gas- reforming stage is mixed with a stream of solids, the main component of which is bed material and another component of which is char, the stream of solids having been led from one or more of the fluidized-bed stages, or from their adjunct equipment; and, prior to mixing, the temperature of the stream of solids is lower than the temperature of the gas exiting the gas-reforming stage; and c) at a point downstream of the mixing stage, or in conjunction with the mixing stage, solids are, to a large extent, separated from the gas and returned or led to one or more of the fluidized-bed processing stages.

2. A method as in Claim 1, wherein the stream of solids, which is mixed with the reformed gas, is led from the fluidized-bed stage, to which the carbon-bearing feed material is fed, or from the adjunct equipment of the fluidized-bed stage, to which the carbon-bearing feed material is fed.

3. A method as in Claim 1, wherein the reforming process is a non-catalytic auto thermal reforming process.

4. A method as in Claim 1, wherein the reforming process is a catalytic auto thermal reforming process.

5. A method as in Claim 1, wherein some or all of the char entering the mixing stage is gasified in the mixing stage or in its adjunct equipment.

6. A method as in Claim 1, 2, 3, 4 or 5, wherein in step c) (i) solids are separated from the exit stream of the mixing stage, (ii) the resulting gas stream is the product gas of the process, and (iii) the stream of separated solids is led to a fluidized-bed stage other than the stage to which the carbon-bearing feed material is fed.

7. A method as in Claim 1, 2, 3, 4 or 5, wherein in step c) (i) solids are separated from the exit stream of the mixing stage, (ii) the resulting gas stream is the product gas of the process, and (iii) the stream of separated solids is recycled to a fluidized-bed reactor to which the carbon-bearing feed material is also fed.

8. A method as in Claim 1, 2, 3, 4 or 5, wherein in step c) (i) solids are separated from the exit stream of the mixing stage, (ii) both the resulting gas stream and the stream of separated solids are led to a fluidized-bed stage other than the stage to which the carbon-bearing feed material is fed, and (iii) the gas exiting this fluidized-bed stage is the product gas of the process.

9. A method as in Claim 1, 2, 3, 4 or 5, wherein (i) the mixing stage and a subsequent fluidized-bed processing stage are incorporated into a single fluidized-bed processing unit, and (ii) the gas exiting this processing unit is the product gas of the process.

10. A method as in Claim 7, wherein the fluidized-bed reactor is based on the fast- fluidized-bed principle.

11. A method as in Claim 6, wherein the fluidized-bed stage, to which the stream of separated solids is led, is a char-gasification stage based on the fast-fluidized- bed principle, and the fluidized-bed stage, to which the carbon-bearing feed material is fed, is also based on the fast-fluidized-bed principle, and the solids exiting the former stage are led to the latter stage.

12. A method as in Claim 6, wherein the fluidized-bed stage, to which the stream of separated solids is led, is a char-gasification stage located in the lower part of a fast-fluidized-bed reactor, and the fluidized-bed stage, to which the carbon- bearing feed material is fed, is located in the upper part of the same fast- fluidized-bed reactor.

13. A method as in Claim 8 or 9, wherein the fluidized-bed stage, to which the carbon-bearing feed material is fed, is based on the bubbling-fluidized-bed principle, a riser stage based on the fast-fluidized-bed principle is either located after or incorporates the mixing stage, and the fluidized-bed stage, to which the solids are next led, is a char-gasification stage based on the bubbling-fluidized- bed principle, after which the solids are returned to the bubbling-fluidized-bed stage to which the carbon-bearing feed material is fed.

14. A method as in Claim 9, wherein gasification of the char exiting the fluidized- bed stage, to which the carbon-bearing feed material is fed, is, to a significant or to a complete extent, accomplished in the fluidized-bed processing stage in step (i), and the processing unit is based on the fast-fluidized-bed principle.

15. A method as in Claim 10, 11, 12, 13 or 14, wherein the gas from the fluidized- bed stage, to which the carbon-bearing feed material is fed, is filtered and then led to the gas-reforming stage, and the gas-reforming stage employs a catalytic auto thermal reforming process.

16. A method as in Claim 12, wherein the two parts of the reactor are of different geometrical design and/or are joined with a connector of special geometrical design in order minimize back-mixing of solids from the upper part to the lower part.

17. A method as in Claim 1, 2, 3, 4 or 5, wherein one of the fluidized-bed stages is a char-combustion stage yielding a flue gas which exits the process as a separate stream.

18. A method as in any one of Claims 1 to 17, wherein the bed material is a chemically active material, reacting itself and/or promoting one or more of the desired conversion reactions.

19. A method as in any one of Claims 1 to 17, wherein the flow-rate of the solids stream that is mixed with the exit gas of the gas-reforming stage is adjusted so that the temperature of the mixed gas-solids stream formed in the mixing stage is below the temperature at which the solids would agglomerate or sinter.

20. A method as in Claim 10, 11 or 12, wherein gas recycled from a downstream processing step, such as synthesis step, is introduced into the fast-fluidized-bed stage, to which the carbon-bearing feed material is fed, at a location upstream of the cyclone separator adjoined to the stage.

21. An arrangement for producing, from one or more carbon-bearing feed materials, a gas which can be utilized and/or further upgraded and then utilized in various synthesis-gas and fuel-gas applications, the arrangement comprising one or more fluidized-bed processing stages for physical handling and chemical conversion of the carbon-bearing material; and further comprising:

- a reformer connected, either directly or via intermediate processing devices, to one or more of the fluidized-bed stages for the purpose of subjecting gas exiting one or more of the fluidized-bed stages to a reforming process,

- a mixing device connected, either directly or via intermediate processing devices, to the reformer and to one or more of the fluidized-bed stages for the purpose of mixing gas exiting the reformer with a stream of solids, which have been discharged from one or more of the fluidized-bed stages, and

22. An arrangement as in Claim 21, wherein the device employed in at least one of the fluidized-bed stages is a fast- fluidized-bed reactor.

23. An arrangement as in Claim 21, wherein the device employed in at least one of the fluidized-bed stages is a bubbling-fluidized-bed reactor.

24. An arrangement as in Claim 21, 22 or 23, wherein the mixing device and a subsequent fluidized-bed processing stage are incorporated into a single fluidized-bed processing device.

25. An arrangement as in Claim 21, wherein a fast- fluidized-bed reactor is employed and this reactor has two parts, an upper part and a lower part, which are of different geometrical design and/or are joined with a connector of special geometrical design in order minimize back-mixing of solids from the upper part to the lower part.