EP3290493A1 - Process and apparatus for pressurized gasification in a fixed bed - Google Patents

Abstract

Process and plant for converting a solid, carbonaceous fuel, such as coal or coke, to a raw synthesis gas comprising mainly hydrogen and carbon monoxide and to ash, using a shaft reactor, wherein the discharged ash is returned, at least in part, to the reactor and with the fuel goes through the fixed bed.

Description

Field of the invention

The invention relates to a process for the conversion of a solid, carbonaceous fuel, such as coal or coke, to a raw synthesis gas comprising mainly hydrogen and carbon monoxide and to ashes, using a shaft reactor, in which the fuel is arranged as a fixed bed and passes through it continuously, the Fixed bed is flowed through at elevated pressure and at elevated temperature of a gasification agent comprising oxygen and steam and wherein the shaft reactor is filled via a respective pressure lock with the fuel and the ash is discharged from it.

The invention further relates to a system for carrying out the method.

State of the art

By means of fixed bed pressure gasification reactors, solid fuel such as coal, coke or other carbonaceous fuel is gasified with steam and oxygen as a gasifying agent at elevated temperature and, in most cases, under positive pressure to a syngas containing carbon monoxide and hydrogen to give a solid ash which overflows an ash discharge grate, which in many cases is designed as a rotary grate is discharged from the reactor. This type of reactor is often referred to as FBDB (= Fixed Bed Dry Bottom) pressure carburetor.

• Trocknungszone: In der Trocknungszone wird im oder am Brennstoff gebundene Feuchte desorbiert und mit dem Rohsynthesegasstrom aus dem Festbettdruckvergasungsreaktor ausgetragen.
• Pyrolysezone: Hier werden leichtflüchtige Verbindungen aus dem Brennstoff freigesetzt und ausgetrieben. Es erfolgt hier eine Verschwelung oder Verkokung des Brennstoffs.
• Vergasungszone: In der Vergasungszone erfolgt die eigentliche umsetzung des Brennstoffs mit dem Vergasungsmittel, das zumeist Luft oder Sauerstoff, sowie Wasserdampf und ggf. Kohlendioxid als Moderator enthält, zu den Zielprodukten der Vergasung, nämlich Wasserstoff und Kohlenmonoxid.
• Verbrennungszone: Hier wird die für die Vergasung, Pyrolyse und Trocknung notwendige Wärmeenergie durch Verbrennen des restlichen Teils des Brennstoffes zu Asche erzeugt.
• Aschebett, das Aschebett deckt das Austragsrost ab und schützt es vor den hohen Temperaturen der Verbrennungszone.

In the fixed bed, the fuel passes from top to bottom following temperature zones with increasing temperature in this direction:

• Drying zone: In the drying zone, moisture bound in or on the fuel is desorbed and discharged from the fixed bed pressure gasification reactor with the crude synthesis gas stream.
• Pyrolysis zone: Here, volatile compounds are released from the fuel and expelled. There is here a charring or coking of the fuel.
• Gasification zone: In the gasification zone, the actual reaction of the fuel with the gasification agent, which mostly contains air or oxygen, as well as water vapor and possibly carbon dioxide as moderator, takes place to the target products of the gasification, namely hydrogen and carbon monoxide.
• Combustion zone: Here the heat energy required for gasification, pyrolysis and drying is produced by burning the remaining part of the fuel into ashes.
• Ash bed, the ash bed covers the discharge grate and protects it from the high temperatures of the combustion zone.

For further procedural details reference is made to the relevant literature, cf. Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition, Vol. 15, page 367 ff , The gasification typically starts at temperatures of about 700 ° C and proceeds at high speed at temperatures of 800 ° C, see. Ullmanns Encyklopadie der Technischen Chemie, 4th Edition (1977), Volume 14, p. 384 , The local Fig. 10 shows a typical temperature profile of the gas temperature in a fixed bed pressure gasification reactor, in particular in the temperature zones discussed above.

In order to utilize the production capacity of the reactor as much as possible, it is necessary to have as uniform a flow as possible of the fuel solids bed to reach the gasification agent. To achieve this, it is necessary to set a suitable particle size distribution in the fixed bed. Too high a proportion of small particles can lead to blockages of the flow, too high a proportion of large particles can lead to channeling, ie to places with very low flow resistance.

In many cases, a particle size distribution has proved to be favorable, in which at least 90% by weight of the particles are in a size range of 10 to 50 mm and the remaining portion is distributed in equal parts to the above and below the size range. The particle size is determined according to ASTM D4749.

• Die Siebung des Brennstoffs vor seiner Einfüllung in den Reaktor,
• die Steuerung der Temperatur in der Verbrennungszone des Festbetts durch die Einstellung des Mengenverhältnisses von Sauerstoff zu Dampf im Vergasungsmittel, wobei eine Erhöhung des Sauerstoffanteils zur Temperaturerhöhung, eine Erhöhung des Dampfanteils zur Temperatursenkung in der Verbrennungszone führt. Die Höhe der Temperatur in der Verbrennungszone beeinflusst die Möglichkeit der Aschepartikel zu agglomerieren und damit die Größe der gebildeten Aschepartikel,
• die Einstellung der Ascheschmelztemperatur durch eine geeignete Zusammensetzung des Brennstoffs, wie z.B. eine geeignete Mischung verschiedener Kohlesorten.

In order to influence the particle size in a fixed bed, the following ways are available so far:

• The sieving of the fuel before its introduction into the reactor,
• Controlling the temperature in the combustion zone of the fixed bed by adjusting the ratio of oxygen to steam in the gasification agent, wherein an increase in the oxygen content to increase the temperature, an increase of the vapor content for lowering the temperature in the combustion zone. The level of temperature in the combustion zone affects the ability of the ash particles to agglomerate and thus the size of the formed ash particles,
• the setting of the ash melting temperature by a suitable composition of the fuel, such as a suitable mixture of different types of coal.

But these described ways of influencing the particle size in a fixed bed are often insufficient to achieve the desired result. So there are z. B. Coals, which tend to their particles disintegrate when heated in a fixed bed, so that in these cases, despite a prior screening of the fuel, the proportion of fine particles undesirably high and a uniform flow of the fixed bed is impaired.

The object of the invention is therefore to provide a method which is able to perform the gasification of carbonaceous fuel in a fixed bed more effectively and to improve the gasification of the fuel bed.

Description of the invention

The object is achieved by a method according to the features of claim 1 and by a system according to the features of claim 9. Further advantageous embodiments of the method according to the invention can be found in claims 2 to 8.

Inventive method:

A process for converting a solid, carbonaceous fuel, such as coal or coke, to a raw synthesis gas comprising mainly hydrogen and carbon monoxide and to ashes, using a shaft reactor in which the fuel is arranged as a fixed bed and continuously passing through it, the fixed bed, at elevated pressure Pressure and at elevated temperature, flowing through an oxygen and steam comprising gaseous gasification agent and wherein the shaft reactor is filled via a respective pressure lock with the fuel and the ash is discharged from it, characterized in that a portion of the discharged ash is returned to the reactor and with the fuel passes through the fixed bed.

Inventive plant:

• Einen Festbettdruckvergasungsreaktor, umfassend ein schachtförmiges Reaktorgefäß, einen Vergasungsmitteleinlass, einen Produktgasauslass, ein Ascheaustragsrost, eine Druckschleuse zur Zuführung des Brennstoffs, eine weitere Druckschleuse zur Abführung der Asche,
• optional einen Schleusenkanal für den Transport der Asche mit Wasser zur Siebvorrichtung,
• optional eine Vorrichtung zur Abtrennung von Aschefeinpartikeln aus dem für den Transport im Schleusenkanal verwendeten Wasser,
• eine Siebvorrichtung zur Absiebung der Asche, so ausgebildet, dass als Feinpartikel Partikel mit einer Größe von kleiner 10 mm, kleiner 20 mm, kleiner 30 mm oder kleiner 40 mm und/oder als Grobpartikel Partikel mit einer Größe von über 20 mm, über 30 mm, über 40 mm oder über 50 mm abgesiebt werden können,
• optional jeweils eine Wiege- und Dosiereinrichtung zur Bestimmung der zur Brennstoffzuführvorrichtung bzw. zur Asche-Brennstoff-Mischeinrichtung zurückgeführten Asche- und Brennstoffmenge,
• optional eine Trocknungseinrichtung zur Trocknung der zurückgeführten Aschemenge,
• eine Mischeinrichtung zur Vermischung von Asche und Brennstoff,
• Transportmittel für Asche und für Brennstoff.

Plant for carrying out a method according to one of the preceding claims, comprising:

• A fixed bed pressure gasification reactor comprising a shaft-shaped reactor vessel, a gasification inlet, a product gas outlet, an ash discharge grate, a pressure lock for supplying the fuel, another pressure lock for removing the ash,
• optionally a lock channel for transporting the ash with water to the screening device,
• optionally a device for the separation of ash particles from the water used for transport in the lock channel,
• a sieve for screening the ash, designed so that as fine particles with a size of less than 10 mm, less than 20 mm, smaller than 30 mm or smaller than 40 mm and / or as a coarse particle particles with a size of about 20 mm, about 30 mm , above 40 mm or above 50 mm,
• optionally a weighing and metering device for determining the quantity of ash and fuel returned to the fuel supply device or to the ash-fuel mixing device,
• optionally a drying device for drying the recirculated ash,
• a mixing device for mixing ash and fuel,
• Means of transport for ashes and for fuel.

By "elevated pressure" and "elevated temperature" are meant pressure and temperature values above ambient pressure or room temperature. Suitable pressure and temperature values can be found by the person skilled in the art mentioned above.

The presence of ash particles leads to a loosening, d. H. to evenly between the particles of the fuel fixed bed existing gaps and thus allows its more uniform flow with gasification agent. The pressure loss of the gasification agent is reduced, whereby a larger amount of gasification agent can flow through the fixed bed. The more uniform distribution and the greater amount of gasification agent used in the fixed bed, the production capacity of the fixed bed gasification reactor can be increased.

The loosening achieved by the ash particles also improves the fluidity of the bed of the packed bed. The tendency of the bed to bridge at bottlenecks is thus reduced. In particular, the outflow of ash through the annular gap between rotary grate and reactor inner wall is less disturbed by bridge formation of the ash.

Due to the positive effect of ash in a fixed bed can be dispensed with setting the ash melting temperature by mixing different types of coal in the fuel bed in many cases.

A particular advantage in the use of the ash particles produced in the gasification process itself is that these particles were already exposed to the process conditions, in particular the high temperatures, so that they only tend to disintegrate in a further passage through the fixed bed to a small extent.

Preferred embodiments of the invention

A preferred embodiment of the invention is characterized in that the ash is screened before its return to the reactor for the separation of fine and coarse particles, the screening comprises at least two screening stages and can be done with decreasing or increasing mesh size and wherein the sieve fraction with medium Particle size is at least partially recycled to the reactor and the separated particles are fed to a further treatment or use outside the process. The sieving sets the particle size distribution of the recirculated ash to the range which is most suitable for uniform flow through the bed of solids. This is especially the range of average particle sizes of the ash particles. Too high a proportion of small particles can lead to blockages of the flow, too high a proportion of large particles can lead to channeling, d. H. to places with particularly low flow resistance. Which size range is most suitable in the specific application must be determined by tests. It depends on the apparatus conditions of the reactor, the process parameters that can be set and, in particular, on the quality of the fuel.

A further preferred embodiment of the invention is characterized in that the ash discharged from the reactor via the pressure lock is rinsed with water for screening and is separated again from the water during the screening of the fine and coarse particles. In this method of transport, the ash is cooled simultaneously. The method does not require complicated apparatus, is therefore reliable and inexpensive. Particularly advantageously, this method can also be used when water is scarce, by circulating the water used, it being passed through a device for separating ash fine particles, which are discharged for further treatment outside the process.

A further preferred embodiment of the invention is characterized in that the water used is circulated, wherein it is passed through a device for the separation of ash particles, which are discharged for further treatment outside the process. Since the recycled water was already saturated or partially saturated with water-soluble ash constituents in this way, such solution effects are reduced in a new use of the already used water. This increases the stability of the ash particles.

A further preferred embodiment of the invention is characterized in that particles with a size of less than 10 mm, smaller than 20 mm, smaller than 30 mm or smaller than 40 mm and / or as coarse particles as particles with a size of more than 20 mm, over 30 mm , over 40 mm or over 50 mm. These sizes provide good starting points for experimentally determining which particle size distribution is most appropriate.

A further preferred embodiment of the invention is characterized in that the ash is fed to the solids bed up to a proportion of 30% of the mass of the solid bed. On the one hand, the ash in the solid bed improves and evenens out the flowability of the solid bed, but on the other hand it also represents a dead mass for the gasification process, which does not contribute directly to the production of synthesis gas. Therefore, it makes sense to limit the ash content in the solid bed.

A further preferred embodiment of the invention is characterized in that the ash destined for recycling to the reactor is dried. In many cases, the ash from the ash sluice of the fixed bed reactor is discharged into a channel from which it is flushed with water for further treatment. The recorded Moisture is largely separated from the ash during the screening of the coarse and fine particles. In order to relieve the fixed bed reactor, it may be useful to dry the ash before returning it to the reactor.

A further preferred embodiment of the invention is characterized in that the ash and the fuel provided for recycling are each conveyed by means of conveying means which generate a flow of material and in that the two streams of material are combined and the mixed material stream formed thereby is introduced into the pressure lock or an upstream feed tank become. In order to achieve the intended effect of the invention, a uniform flowability of the packed bed, it is necessary to achieve a uniform distribution of ash in a fixed bed. In principle, it is possible for the fixed bed reactor to be preceded by a mixing apparatus in which the ash is mixed in with the fuel. Due to the often existing mechanical stress of the particles but would increase the proportion of fine particles in the fuel and thus counterproductive effect on the gasification process. A suitable alternative to a mixing apparatus is, in each case by suitable funding, such. B. Conveyor belts, Rüttelrinnen or pneumatic conveyors to produce a continuous flow of material, and combine the fuel and the ash stream and to unite into a single, mixed stream; and to introduce this current into the fuel lock or into a reservoir for the fuel lock.

embodiments

Further developments, advantages and applications of the invention will become apparent from the following description of non-limiting embodiment and numerical examples and the drawings. All described and / or illustrated features alone or in any combination form the invention, regardless of their combination in the claims or their dependency.

Fig. 1

eine schematische Darstellung einer beispielhaften Ausführungsform des erfindungsgemäßen Verfahrens und der erfindungsgemäßen Anlage.

It shows the only figure

Fig. 1

a schematic representation of an exemplary embodiment of the method and the inventive system.

In Fig. 1 comprises the plant 1 comprises a fixed bed pressure gasification reactor 2 with the pressure lock 3 for charging the reactor with fuel 4, z. As coal, and the pressure lock 5 for discharging the generated ash 6. The locks can be closed with the closures 7. In the reactor 2 is the fuel fixed bed 8, which rests on the grate 9. The gasification agents 10 are introduced through the grate 9 into the fixed bed 8 and convert the fuel 4 into raw synthesis gas 11 and ash 6. The raw synthesis gas 11 is discharged above the fixed bed 8 from the reactor 2 for further treatment outside the process.

From the lock 5, the ash 6 is discharged into the lock channel 12 and fed with water 13 as a water / ash mixture 14 of the two-stage screening device 15. This is equipped with a first sieve 16 for screening the ash particles and separating the water from the ash. By adjusting or rebuilding the sieve 16, the size of the sieved ash particles can be changed. In many cases, a size of 10 mm is the most suitable, but the sieve 16 should be adjustable so that even sizes up to 40 mm can be screened off as fine particles. The mixture 17 of ash fine particles and water is discharged from the plant 1 for further treatment. It is also possible for mixture 17 to be led out of the water via a device, not shown, for separating the fine particles, so that the water can be circulated and used again to rinse the lock channel.

The ash 18 is then fed to a second sieve 20 for screening the ash scrap particles 19. By adjusting or rebuilding the sieve 20, the size of the sieved ash particles can be changed. In many cases, a size of 50 mm is the most suitable, but the sieve 20 should be adjustable so that even sizes down to 20 mm are screened off as coarse particles. On the screen 20, the ash 18 can optionally be washed free of ash dust with water 25. The water 25 can be performed in a cycle, not shown, in which it from the Ash dust is released. The coarse particles 19 are discharged from the plant 1 for further treatment.

The liberated from fine and coarse particles ash 21, which contains only ash particles of medium size is dried in the device 22 and, as well as the fuel 4, the mixing and metering device 23 abandoned. This device doses and mixes the streams of the fuel 4 and the ash 21 in the desired ratio and fültt them as a mixture 24 in the pressure lock. 3

Industrial Applicability

With the invention, a method is provided with which the Durchgasungsverhalten a fixed bed pressure gasification reactor is improved and it can thus be operated at a higher throughput and thus with increased efficiency. The invention is therefore advantageously industrially applicable.

LIST OF REFERENCE NUMBERS

1

Plant according to the invention

2

Fixed bed pressure gasification reactor

3

pressure lock

4

fuel

5

pressure lock

6

ash

7

shutter

8th

fixed bed

9

rust

10

gasification agent

11

raw synthesis gas

12

Schleusenkanal

13

water

14

Water / ash mixture

15

screening device

16

first sieve

17

Mixture of ash particles and water

18

ash

19

coarse particles

20

second sieve

21

ash

22

Apparatus for drying ash

23

ash

24

Mixture of fuel and ash

25

water

Claims (9)

A process for converting a solid, carbonaceous fuel, such as coal or coke, to a raw synthesis gas comprising mainly hydrogen and carbon monoxide and to ashes, using a shaft reactor in which the fuel is arranged as a fixed bed and continuously passing through it, the fixed bed, at elevated pressure Pressure and at elevated temperature, flowing through an oxygen and steam comprising gaseous gasification agent and wherein the shaft reactor is filled via a respective pressure lock with the fuel and the ash is discharged from it, characterized in that a portion of the discharged ash is returned to the reactor and with the fuel passes through the fixed bed. A method according to claim 1, characterized in that the ash is screened before its return to the reactor for the separation of fine and coarse particles, wherein the screening comprises at least two screening stages and can be done with decreasing or increasing mesh size and wherein the sieve fraction with average particle size at least partially recycled to the reactor and the separated particles are sent for further treatment or use outside the process. A method according to claim 2, characterized in that the discharged from the reactor via the pressure lock ash is rinsed with water for screening and separated again during or after the screening of the fine and coarse particles from the water. A method according to claim 3, characterized in that the water used is circulated, wherein it is passed through a device for the separation of ash particles, which are discharged for further treatment outside the process. Method according to one of the preceding claims, characterized in that as a fine particle particles with a size of less than 10 mm, less than 20 mm, less than 30 mm or less than 40 mm and / or as coarse particles particles with a size of about 20 mm, about 30 mm , over 40 mm or over 50 mm. Process according to any one of the preceding claims, characterized in that the ash fraction recycled to the reactor is fed to the solid bed up to a proportion of 30% of the mass of the bed of solids. A process according to claim 4, characterized in that the ash intended for recycling to the reactor is dried before being fed to the solid bed. Method according to one of the preceding claims, characterized in that the ash and the fuel provided for the return are each conveyed by means of conveying means which generate a flow of material and in that the two streams of material are combined and the mixed material stream thus formed is introduced into the pressure lock or an upstream feed tank become. Plant for carrying out a method according to one of the preceding claims, comprising: A fixed-bed pressure gasification reactor comprising a shaft-shaped reactor vessel, a gasification inlet, a product gas outlet, an ash discharge grid, a pressure lock for supplying the fuel, another pressure lock for removing the ash, optionally a lock channel for transporting the ash with water to the screening device, optionally an apparatus for separating off ash particles from the water used for transport in the lock channel, - A screening device for screening the ash, designed so that as a fine particle particles with a size of less than 10 mm, less than 20 mm, smaller than 30 mm or smaller 40 mm and / or as coarse particles particles with a size of over 20 mm, over 30 mm, over 40 mm or over 50 mm can be sieved, optionally a weighing and metering device for determining the quantity of ash and fuel returned to the fuel supply device or to the ash-fuel mixing device, optionally a drying device for drying the recirculated ash, a mixing device for mixing ash and fuel, - means of transport for ash and fuel.

Images