DE102007006980A1 - Solid fuel gasification method, involves spraying gasification agent in freeboard, and spraying gasification agent over gasification agent nozzle in height of one meter to five meter through upper limit of fluidized bed in free board - Google Patents

Abstract

The method involves extracting dust loaded raw gas in an upper side of a gasification chamber (4) and a bottom product in a lower side of the chamber of a fluid-bed gasifier (1). A gasification agent (8) e.g. oxygen, is sprayed with different compounds in the chamber. A gasification agent (14) is sprayed in a fluidized bed (5), and a gasification agent (17) is sprayed in a freeboard (6). The agent (17) is sprayed over a gasification agent nozzle (22) in a height of one meter to five meter through an upper limit of the fluidized bed in the free board.

Description

The The invention relates to a process for the gasification of solid fuels in the fluidized bed under elevated pressure using of Vergasungsmittelgemischen, consisting of oxygen and water vapor and / or carbon dioxide, wherein dust-laden raw gas on the upper side and Bottom product below the gasification chamber of the fluidized bed gasifier be deducted and in the case of an external aftertreatment of Fine dust can be almost dispensed with.

The gasification space of the fluidized-bed gasifier usually consists of a fluidized bed and a freeboard arranged above the fluidized bed. In the fluidized bed and often in the freeboard, the gasification means are injected by means of Vergasungsmitteldüsen, which are arranged in so-called nozzle levels at different heights of the gasification chamber. The gasification agents are usually oxygen O ₂ and water vapor H ₂ O (g) or air. It is also possible to provide carbon dioxide CO ₂ as a gasification agent.

The in the gasification of solid fuels in the gasification chamber of the fluidized bed gasifier resulting gasification residues consist of ashes and residual cokes. If in the gasification room liquid fuels or liquids to be disposed of mitvergast be come their gasification residues, which are mineral or metallic residues and residual cokes (consisting of from coke and ashes). The gasification residues are in terms of their grain size in coarse grained and fine-grained gasification residues to divide. The former are below the gasification room withdrawn as a bottoms product, the latter leave the gasification room Upper side with the raw gas as fine dust. The fine dusts be in a the fluidized bed gasifier downstream dust collector separated from the dust-laden raw gas. Due to the high Proportion of coking carbon must be the fine dust be further processed. One possibility is to feed them to an external furnace. To do this the particulate matter cooled under pressure, from the Pressure system discharged and finally a combustion boiler be supplied. After combustion, the combustion ash separated from the flue gases. The process of thermal treatment is multi-level, very complex and reduces the efficiency of the overall process.

A Another possibility to treat the fine dust, is to return them to the fluidized bed gasifier and in this way to increase their residence time in the gasification space. at the gasification, however, form very fine-grained ashes, which are also discharged with the raw gas. The loading of the dust-laden raw gas with these fine-grained ashes would rise so much that a full Return of the fine dusts no longer it is possible. A large part of the fine dust would have to accept the disadvantages described above be further treated in an external afterburning.

To solve the problem is in DE 44 13 923 proposed to enter at least a subset of the fine dusts via a gasification agent nozzle operated with an oxygen-containing gasifying agent and at the same time as a dust burner at a height of up to 3 m above the fluidized bed in the fluidized bed gasifier, wherein the oxygen-containing gasification agent accounts for more than 20% by volume of oxygen should contain. The aim is the thermal decomposition of the organic trace substances entrained with the fine dusts and the incorporation of inorganic trace substances into the matrix of the ash. A process procedure is described as being particularly advantageous in which the ash constituents in the oxygen flame are heated above the softening point and agglomerated. The gasification agent should also contain more than 30 vol .-% oxygen. Unfortunately, the proposal is also not suitable to completely treat the fine dust thermally, since in the oxygen flame, not all the ash of the recycled particulate matter can be granulated. A large part of the ash continues to accumulate as very fine-grained ash and accumulates in the raw gas to the extent that can not be dispensed with an external aftertreatment.

In EP 1 201 731 A1 describes a method which is intended to effect the granulation of the ash components in the fluidized bed by means of injection of additional gasifying agents which are characterized by a higher oxygen content and / or a higher temperature. The oxygen content is ≥ 21 vol .-% and / or the preheating ≥ 400 ° C. This proposal also does not teach, according to which the exiting from the fluidized bed gasifier fine dust can be completely thermally treated. This is due to the fact that due to the strong solid mixture in the fluidized bed so high temperatures are reached only in locally narrow areas before the gasification agent that the ash components can agglomerate. On the other hand, since the carbon content in the fluidized bed is very high (> approx. 60% by mass based on the solids), even in these areas only a small proportion of fine-grained ashes released by combustion can be assumed Agglomeration is available. Most of the fine-grained ashes are outside the Flames, is not agglomerated and discharged with the raw gas. An external aftertreatment of fine dust is still essential here.

The The object of the invention is a method of treatment of fine dusts in fluidized bed gasification of solid fuels under increased pressure, which allows to an external aftertreatment of the fine dust possible completely renounce.

• – dass die dem Vergasungsraum insgesamt zugeführten Vergasungsmittel in erste und zweite Vergasungsmittel aufgetrennt werden,
• – dass die ersten Vergasungsmittel in die Wirbelschicht und die zweiten Vergasungsmittel in das Freeboard eingedüst werden,
• – dass die zweiten Vergasungsmittel weit überwiegend oder vollständig aus Sauerstoff (> 60 Vol.-%) bestehen und mindestens 20% und höchstens 50% des insgesamt zugeführten Sauerstoffes und 0% bis höchstens 25% des insgesamt zugeführten Wasserdampfes umfassen
• – und dass die zweiten Vergasungsmittel über mindestens eine Vergasungsmitteldüse in einer Höhe von 1 m bis höchstens 5 m über der oberen Begrenzung der Wirbelschicht mit Gasströmungsgeschwindigkeiten von > 20 m/s in das Freeboard eingedüst werden.

According to the invention the object is achieved by a process for the gasification of solid fuels in the fluidized bed under elevated pressure using Vergasungsmittelgemischen consisting of oxygen and water vapor and / or carbon dioxide, wherein dust-laden raw gas on the top side and bottom product are subtracted on the underside of the gasification space of the fluidized bed gasifier and wherein gasification agent with different Injected compositions into the gasification room, thereby solved

• - That the total gasification agent supplied to the gasification space are separated into first and second gasification agent,
• That the first gasification agents are injected into the fluidized bed and the second gasification agents are injected into the freeboard,
• - That the second gasification means largely or entirely of oxygen (> 60 vol .-%) and comprise at least 20% and at most 50% of the total oxygen supplied and 0% to at most 25% of the total supplied water vapor
• - And that the second gasification agents are injected via at least one gasification agent nozzle at a height of 1 m to no more than 5 m above the upper boundary of the fluidized bed with gas flow velocities of> 20 m / s in the freeboard.

The Invention makes use of the knowledge that with suitable Separation and supply of the gasification agent the ash the returned fine dust in their Graining predominantly due to melt agglomeration to be fully enlarged can that the melting enamel agglomerates drop down and discharged as a bottom product from the fluidized bed gasifier. By this form of thermal treatment is the raw gas deprived of enough fine dust to those remaining in the raw gas and In the dust collector separated fine dust as far as possible completely back into the fluidized bed gasifier to be able to.

When performing melt agglomeration, the flow circulation above the fluidized bed plays a central role. In the freeboard of the fluidized bed gasifier above the so-called splash zone, a zone of the central upflow with decreasing loads of particulate matter and forming a zone of the central upflow, annular zone of the downward flow with increasing downwards loadings of fine dust forms. The flow cross section of the zone of the central upward flow widens upward and at the latest at the gasifier head comprises the available flow cross section of the gasification space. In the manner according to the invention, the second gasification agents, which predominantly or completely consist of oxygen (> 60% by volume), are injected at high velocity (> 20 m / s) into this central upward flow. As a result, the temperature rises in the upward flow primarily by the homogeneous, exothermic reactions of gas combustion, in which arise from the fuel gases (hydrogen H ₂ , carbon monoxide CO and methane CH ₄ ) carbon dioxide CO ₂ and water vapor H ₂ O, very strong. For the second gasification agents to pass through the zone of annular downflow into the zone of central upflow, gas exit velocities of at least 20 m / s are sufficient.

By the high reaction rates of the homogeneous oxidation reactions ("Mixed is the same reaction") it comes above the Place of supply of the second gasifying agent to a in the longitudinal extension limited hot spot - zone in the zone of the central upward flow. The Spontaneous volume expansion provides for an intensive Cross-mixing, with a diffusion of high temperatures over the cross section of the upward flow is accompanied. Almost all the particulate matter needs this hot spot zone with the highest temperatures.

The temperature increase in this zone is greater when the loading of the gas with coking coal is lower and vice versa. With increasing loading of coking carbon, the endothermic, heterogeneous gasification reactions increase and there is a damping of the temperature rise. The injection of the second gasification agent is effective with respect to the temperature increase above the fluidized bed (from about 1 m above the fluidized bed) and especially in the low-solids flow areas above the splash zone (up to about 5 m above the fluidized bed). Now, when at least 20% and at most 50% of the total supplied oxygen and 0 to at most 25% of the total water vapor supplied are fed as second gasification agents, the temperatures in the central upflow zone rise to levels equal to or above the softening temperatures of the fine ashes lie. In this case, more oxygen must be added as a percentage or the volume fraction of the oxygen increased the greater the temperature difference between the ash softening temperature and the temperature of the fluidized bed and the greater the concentration of coking carbon. It should be noted that the separation of the gasification agent, the temperature that occurs in the fluidized bed, the kinetic reaction temperature comes closer, the higher proportion of endothermic gasification agent leads to a higher carbon conversion in the fluidized bed. The kinetic reaction end temperature is determined by the reactivity of the coking carbon and thus by the properties of the fuels used. The temperature difference between the ash softening temperature and the fluidized bed temperature is referred to below as the temperature window for the endothermic reactions.

in the In case of a small temperature window of approx. <200 K, it is possible to use the second gasification agent just above the fluidized bed in the splash zone or even at the upper end of the fluidized bed.

In the zone of the central upward flow almost the entire entrained with the gas flow fine ash at least softened, melted and agglomerated. The high temperatures promote melt agglomeration the eluate-resistant incorporation of volatile alkalis and heavy metals into the forming slag. By the associated with the agglomeration Grain enlargement can the melt agglomerates no longer be carried by the gas stream. You get into the annular downward flow and thus down into the fluidized bed and from there into the bottom draw.

The endothermic, heterogeneous reactions of the gasification of the entrained coking carbon with carbon dioxide CO ₂ and water vapor H ₂ O proceed much more slowly than the homogeneous combustion reactions. They come into play with increasing altitude in the zone of the central upflow as well as in the zone of the annular downflow. As a result, the temperatures in these areas fall to values below the ash softening temperatures, so that there is no risk of adhesion of softened or melted ash particles neither at the gas outlet of the fluidized bed gasifier nor near the wall.

The values to be set in the concrete case of application supplied oxygen and the concentration of oxygen the second gasification agent are according to the respective Fuel and the conditions of the fluidized bed gasifier adapted. To the task of agglomeration of ashes in the desired To fulfill the scope, as little oxygen as possible in percentage and used in as low a concentration as possible. Another advantage of the invention is to be mentioned that by the high temperatures in the zone of the central upward flow organic trace substances over the prior art stronger thermally decomposed and therefore the concentrations in particular the lowered aromatic hydrocarbons such as benzene and naphthalene become.

Based on the in 1 illustrated, greatly simplified schemes, the invention will be explained in more detail. In the fluidized bed gasifier ( 1 ) by means of the coal entry ( 2 ) Dry brown coal ( 3 ) having a water content of 12% by mass and an ash softening temperature of 1100 ° C. The gasification room ( 4 ) of the fluidized bed gasifier ( 1 ) consists of the fluidized bed ( 5 ) and the freeboard ( 6 ) above the upper end ( 7 ) the fluidized bed ( 5 ). The fluidized bed ( 5 ) is located in the lower part of the gasification room ( 4 ) of the fluidized bed gasifier ( 1 ). As gasification agent ( 8th ) become oxygen ( 9 ) and water vapor ( 10 ). Volume flow and composition of total supplied gasification agent ( 8th ) are adjusted so that a gas temperature at the gas outlet ( 11 ) of the fluidized bed gasifier ( 1 ) of 1000 ° C. For the separation and the supply of the gasification agent ( 8th ), the knowledge of the temperature window is important, which in the present case is about 250 K, since a temperature of about 850 ° C is established in the fluidized bed.

Oxygen ( 9 ) and water vapor ( 10 ) of the gasification agent ( 8th ) are separated into first oxygen ( 12 ) and first steam ( 13 ) of the first gasification agent ( 14 ) as well as in second oxygen ( 15 ) and second water vapor ( 16 ) of the second gasification agent ( 17 ). The first oxygen ( 12 ) and the first water vapor ( 13 ) are added to the fluidized bed ( 5 ) injected. The injection takes place by means of the gasification agent nozzles ( 18 ), distributed on three nozzle levels ( 19 ). The second oxygen ( 15 ) and the second water vapor ( 16 ) are used in the mixer ( 20 ) and into the Freeboard ( 6 ) injected. The injection takes place by means of the nozzle level ( 21 ) arranged gasification ( 22 ) distributed evenly over the circumference of the fluidized bed gasifier ( 1 ) are. The nozzle level ( 21 ) is 3 m above the upper end ( 7 ) the fluidized bed ( 5 ). The gasifying agent nozzles ( 22 ) are aligned horizontally and radially.

The quantitative separation of the gasification agents ( 8th ), for reasons of clarity, on the basis of one kilogram of dry lignite ( 3 ) explained. On 1 kg of dry lignite ( 3 ), a total of 0.35 m ³ (iN) of oxygen ( 9 ) and 0.18 kg of water vapor ( 10 ) and quantitatively separated into the first Verga agent ( 14 ), consisting of 0.21 m ³ (iN) of oxygen ( 12 ) and 0.144 kg of first water vapor ( 13 ) and the second gasification agents ( 17 ), consisting of 0.14 m ³ (iN) second oxygen ( 14 ) and 0.036 kg of second water vapor ( 15 ). The oxygen content of the second gasification agent ( 17 ) is 73% by volume. The second gasification agents ( 17 ) comprise 40% of the total oxygen supplied ( 9 ) and 20% of the total supplied water vapor ( 10 ). The second gasification agents ( 17 ) with a gas outlet velocity of 30 m / s into the freeboard ( 6 ) injected.

By supplying the second gasification agent ( 17 ) in the freeboard ( 6 ) forms above the feed in the zone of the central upward flow ( 23 ) a hot spot zone ( 24 ) with a longitudinal extent of several meters. In this hot spot zone ( 24 ) are temperatures of on average 1200 to 1500 ° C a. In the zone of the central upflow ( 23 ) almost all of the entrained with the gas flow fine ashes are at least softened, melted and agglomerated. The melt agglomerates enter the zone of the annular downflow ( 25 ) and thus down into the fluidized bed ( 5 ) and from there into the bottom outlet 26 ).

The dust-laden crude gases ( 27 ), which the fluidized bed gasifier ( 1 ) via the gas outlet ( 11 ), contain only so little particulate matter to the in the raw gas ( 27 ) and in the subsequent dust collectors, such as cyclone and candle filter (not shown here), separated fine dust as far as possible completely into the fluidized bed gasifier ( 1 ).

1

Fluidized bed gasifier

2

coal entry

3

Dry lignite

4

gasification chamber

5

fluidized bed

6

freeboard

7

upper End of the fluidized bed

8th

gasification agent

9

oxygen

10

Steam

11

gas outlet

12

first oxygen

13

first Steam

14

first gasification agent

15

second oxygen

16

second Steam

17

second gasification agent

18

Gasification agent nozzles

19

nozzle levels

20

mixer

21

nozzle plane

22

Gasification agent nozzles

23

Zone the central upflow

24

hot spot zone

25

Zone the annular downflow

26

floor deduction

27

dust-laden raw gases

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 4413923 [0005]
• - EP 1201731 A1 [0006]

Claims (3)

Process for the gasification of solid fuels in the fluidized bed under elevated pressure using Vergasungsmittelgem mixtures consisting of oxygen and water vapor and / or carbon dioxide, wherein dust-laden raw gas on the top and bottom product are withdrawn from the bottom side of the gasification chamber of a fluidized bed gasifier and wherein gasification agents are injected with different compositions in the gasification chamber , characterized in that the total gasification agent supplied to the gasification chamber are separated into first and second gasification agents, that the first gasification agents are injected into the fluidized bed and the second gasification agents in the freeboard, that the second gasification agent predominantly or completely from oxygen (> 60 vol .-%) and comprise at least 20% and at most 50% of the total oxygen fed and 0% to at most 25% of the total supplied water vapor and that the second Ver Gas medium be injected via at least one gasification agent nozzle at a height of 1 m to 5 m above the upper boundary of the fluidized bed with gas flow velocities of> 20 m / s in the freeboard. Method according to claim 1, characterized in that that in the case of small temperature window of about <200 K, the second gasification agent at the upper end of the fluidized bed to about 2 m above the fluidized bed be injected. Method according to claim 1, characterized in that that in the case of temperature windows> 200 K, the second gasification agents in be injected at a height of 2 to 5 m above the fluidized bed.