DE3217030A1 - Process for carbonising and gasifying carbonaceous solids - Google Patents

Abstract

The invention relates to a process for carbonising and gasifying carbonaceous solids in a rotary kiln with addition of oxygen-containing compounds of the alkali metals and alkaline earth metals and maintenance of defined temperatures in the carbonisation zone and gasification zone and of a defined positive pressure in the gasification zone. In this way, a gas of high calorific value and a low content of pollutants and dust is obtained at reduced equipment cost and with reliable operation.

Description

KMa 5163

1 '% \ "- . ' Process for the charring and gasification of '\ carbon-containing solids

• The invention relates to a method according to \ ,. Preamble of claim 1. . -

· * .. ^χ · 7 X

-K-For charring of carbonaceous solids,

especially of lignite and subbituminous coal, ^ -. Various methods are already known. The rinsing. gas smoldering process delivers a gas that is produced by the; - "■

The flue gases of the direct smoldering heating are diluted .:

ι. Another known method uses a we-;

ventilation layer for degassing fine-grained coal. The coal must be pre-dried and in fine-grain form the hot coke bed swirled up by air or combustion gases. To smolder j of lignite, an entrained flow process is also known in which fine coke is used as the heat transfer medium, which is in the Circulation is performed and heated by combustion of gas or tar or by partial combustion. Even here the coal has to be largely pre-dried.

It is also known to be carbonaceous To carbonize solids in an indirectly heated rotary kiln (DE-PS 263 025 and 424 724). The rotary kiln serves only for smoldering; the degassed carbonaceous solids must therefore together with the other non-volatile residues of the carbonization from the rotary kiln discharged and sent to a separate further treatment.

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To the. Gasification of carbonaceous solids are above all a printing process that works with a bulk material reactor is known, one with a fluidized bed working method as well as an entrained flow method. The trouble-free operation of these processes is strong ' on the properties of the coal used, in particular on its ash content. The hygroscopic Properties of the ash lead to the formation of pulpy masses, which easily clog the gas channels and therefore require frequent cleaning of these channels, which interrupts generator operation has the consequence.

In the case of coal gasification in the bulk reactor, it also poses a particular problem over the whole. Cross-section of the reactor to achieve the same flow rates for the gases; at unequal Otherwise, flow resistances can easily result in the charge burning through (with the known phenomenon of the top fire). The process using the fluidized bed leads to a considerable discharge Amount of carbon introduced with the fly ash.

A major disadvantage of this known method for coal gasification is that they are used for Gasification of carbonaceous solids with high ash content are not suitable. An autothermal Countercurrent gasification, as is customary for lumpy fuels, can be used in the case of waste incinerators with high ash content.

mean

substances (so-called mountains) are not used. The gasification residues (up to 75% of the brought in

• 4 *

% \ - fuel) would be the countercurrent! . ,, ", Preheat gasification agent to such a high temperature, ·; ',. -Öass- the fire zone of the generator would cinder after a short time and operation would come to a standstill.

The state of the art also includes a ''? '.;: Proposal to gasify the smoldered coal in an indirectly heated rotary kiln (DE -PS 263,025) üer serving to _smoldering. '. \ rotary kiln should herein at a temperature below ·.' ß 5 00 ⁰ C and the serving for gasification second rotary kiln (of substantially larger diameter) operated at a temperature of about 85O ⁰ C Choose this old method, however, has not become established in practice, the use of two separate.. rotary kiln for smoldering and gasification (including: a third rotary drum for pre-drying the i 'yet' coal comes) represents a significant technical up ^one wall In view of the high temperature difference (of over 350 ⁰ C) between the charring zone and _:

the gasification zone it is in the known method

i also not possible to accommodate the two reaction zones in a single, indirectly heated rotary kiln.

Finally, the state of the art also includes the proposal to remove the coal before it is degassed and gasified; Add hydrated lime or other metal oxides in order to bind the released sulfur (thus

to obtain sulfur-free gas) and the gasification | process to accelerate (DE-PS 11 300 and 430 904). !;

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The invention is based on the object of developing a novel method, avoiding the shortcomings of the known methods, which allows carbonization and gasification of carbon-containing solids (including low-quality waste materials such as household waste and waste materials) with significantly reduced plant engineering effort and high operational reliability Sewage sludge), so dprchzuführe that a gas with a high calorific value is produced, which contains ^only a small proportion of pollutants and dust.

This object is achieved in a method of the type mentioned in the preamble of claim 1 by the characterizing Features of claim 1 solved.

According to the invention, the charring and the gasification for the first time in two zones of a single rotary kiln interspersed with solids one after the other carried out. This procedural measure compared to that to the state of the art (see. In particular DE-PS 263 025) to a significant reduction in the Leads to investment costs, but is only possible because additional features according to the invention are essential Reducing the temperature difference between the gasification zone and the smoldering zone is achieved.

Namely, the carbon-containing solids become oxygen-containing compounds of the alkali and alkaline earth metals admittedly, a number of beneficial effects arise, one of which is above all one of the catalytic effects of these additives in both reaction zones. By adding this

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£. % .Surcharges will in particular be found in the , Gasification zone adjusting water gas reaction cat- \ 4ytically influenced so that there is a substantial lowering of the necessary gasification temperature > result. According to the invention, j is sufficient in the gasification zone

.. ^, An outer wall temperature between 600 and 800 ⁰ C '■; ■ "-._ (d / ie material temperatures in the rotary kiln are 70 to | 10: 0 ⁰ C under these outside wall temperatures of the indi- \ - rectly heated rotary kiln) Da. in the carbonizing \ IQ invention Au £ enwandtemperatur is set between × 500 and 700 ⁰ C, can in this way the temperature difference between the gasification zone · and the carbonizing less than about 200 ⁰ C are held. this allows without major structural problems and Avoidance of malfunctions due to very different thermal expansions, the gasification zone and the smoldering zone are housed in one and the same rotary kiln.; ·

In addition to the catalytic effect (which mainly leads to a lowering of the gasification temperature) result from the addition of oxygen-containing compounds of the alkali and alkaline earth metals Other advantages.

In this way, there is a substantial increase in the yield of carbonization gas and tar during the carbonization and at the same time a decrease in the volume of condensation water. This desired effect can be on it are based on the fact that - the smoldering is partially superimposed by a gasification of the smoldering coke that has already formed with the inherent moisture content of the carbonaceous solids and with that produced during pyrolysis Crack water occurs.

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?. "-. By adding the oxygen-containing compounds the "alkali and alkaline earth metals are pollutants (especially sulfur compounds, but also hydrohalic acids) integrated and remain in the '.; solid residue. Phenols that are involved in 'thermal coal processing as acidic organic .compounds arise from the basic Substances converted into the non-volatile salts of the alkali and alkaline earth metals, which are present as solids in the

IQ rotary kiln remain behind and are cracked due to the long residence time of the pests in the rotary kiln. These toxic phenols cannot get into the gas scrubbing condensate. Correspondingly, the addition of basic substances greatly restricts the gaseous discharge of highly toxic cyanide compounds.

It is also essential for the method according to the invention that that the supply of water and / or steam is regulated so that in the gasification zone an overpressure of up to 1 bar is set. In the detailed investigations on which the invention is based namely it turned out that in this area of a slight excess pressure the optimum of the gasification reaction lies. Within this pressure range, on the one hand, the water vapor can rise to a sufficient extent and diffuse into the coal, while on the other hand the reaction products diffuse out of the coal can.

The optimum pressure to be selected for the individual case does not only depend on the pressure range mentioned on the nature of the carbon-containing solids, but also essentially on the formation of the rotary horse © py

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oven off. When using a provided with lifting vanes rotary kiln, in which thus the solids are largely lifted and pass freely fall through the gas space of the rotary kiln, di supply of water and / or water vapor is regulated ^1, j that in the gasification zone a pressure between 10 'and 1000 mm WS, preferably between 40 and 400 mm WS. When using a rotary kiln \ furnace ν with a smooth inner wall, wherein thus the upper ■ surface contact between -LEN solids and the gas pnase lower, according to the invention in the past, -gasungszone a pressure between 100 and 5000, mm WS preferably between 250 and 3500 mm WS, set.

The temperature in the gasification zone is optimally kept between 700 and 750 ^° C.

As additives within the group!

the oxygen-containing compounds of the alkali and. Alkaline earth metals especially calcium hydroxide, calcium carbonate and calcium oxide proven. The addition is expediently in fine-grain form.

In-depth investigations into the amount of additives showed that it is expedient to use 1 to 7.5% by weight, preferably 1.5 to 2.5% by weight (based on the weight of the carbonaceous solids) may be added.

There are various options for extracting the gases from the rotary kiln. When smoldering and Gasification of solids with a high concentration of nitrogen is particularly useful if this takes place in the smoldering zone carbonization gas generated and that in the gasification zone

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'■ ".-. -._ \ generated. Gasifier product at opposite ends \, the rotary kiln are deducted. In this loading • tfiebsweise ^ it proves to be particularly advantageous that in the carbon-containing solids' \ nitrogen present in the carbonizing through the

^ • Strongly basic effect of the oxygen-containing compounds "-: v.,: ,,. bonds of alkali and alkaline earth metals practically

is completely expelled in the form of ammonia ·. ·. The ammonia contained in the carbonization gas can then be converted into a downstream combustion chamber due to substoichiometric combustion for the most part Formation of molecular nitrogen and water are decomposed, so that the sake of environmental protection very undesirable formation of NO compounds is avoided.

In the case of carbonaceous solids that contain only a small amount of nitrogen, carbonization gas can be used and gasification product can also be withdrawn together from the rotary kiln. One possibility . consists in adding carbonization gas and gasification product in the rotary kiln in cocurrent to the solids lead and pull it off at the end of the rotary kiln facing away from the entry side of the solids (direct current operation). The other mode of operation provides for carbonization gas and gasification product in the rotary kiln To lead countercurrent to the solids and on the entry side of the solids from the rotary kiln deduct.

The method according to the invention is suitable for charring and gasification of carbonaceous solids

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is; '' -%> , substances of all kinds. For the reasons explained above · λ it is just for the use of undried; Lignite and / or peat with a water content of f *

- ι

">. Up to 65% by weight suitable. Tests also showed ·, An. * **

JJ ₅ ,, that _; | ä8s procedure also for carbon-containing waste

^ fi ^ materials ", such as household waste and sewage sludge, also for gas; f-riy; .- rich young coal and / or subbituminous coal, before-1

is partially usable. ■ | ' ,

In the drying, charring and gasification of carbonaceous solids with high inherent moisture, i _ ' where the smoldering zone is a separate drying zone ^! '■.', Preceded, results in an · essential energy; ' Energy savings due to the fact that the steam-containing vapors produced during the drying of the carbon-containing solids are introduced into the gasification zone

will. ■ |

The j obtained by the method according to the invention Gasification product can not only be used as heating gas for a wide variety of technical purposes, but can also be used as a raw material for various chemical processes. !

Further features of the invention emerge from the following description of some examples. In the Show drawing

1 shows a diagram of a system for carrying out the method according to the invention; Fig. 2, 3 and 4 schematic representations of modified

Systems for carrying out the invention;

Procedure.

The shown in Fig. 1: System contains an in- ■

directly heated rotary kiln 1, its interior

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is divided into a smoldering zone 2 and a gasification zone 3. An entry screw 4 is used for entry of the carbonaceous solids fed in at 5. A discharge screw 6 is used to discharge the at 7 drawn off solid residue.

The carbonization gas produced in the carbonization zone 2 is drawn off through the nozzle 8, and that in the gasification zone 3 resulting gasification product is withdrawn through the nozzle 9. In the gasification zone 3 is water and / or steam are injected through a nozzle device 10.

Fixed combustion chambers are used for indirect heating of the rotary kiln 1 on the circumference of the furnace 11, which in the illustrated embodiment, carbonization gas via line 12 and possibly additionally (or to start up) heating gas is supplied via line 13. The deduction of the indirect The gases used in the rotary kiln 1 are heated via the line 14.

The system shown in FIG. 1 also includes a cyclone 15 for dedusting the carbonization gas Cyclone 16 for dedusting the gasification product, a combustion chamber 17 and a waste heat boiler 18. In the combustion chamber 17 takes place with a metered air supply (arrow 19) a gradual combustion of the Carbonization gas and the gasification product. In the upper part of the combustion chamber 17 there is a substoichiometric rate Combustion of the carbonization gas, thereby the

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The ammonia contained in the carbonization gas decomposes with the formation of nitrogen and NO formation avoid. The flue gases exiting from the combustion chamber 17 (arrow 20) come together with the to indirect heating of the rotary kiln 1 used gas (discharged via line 14) in the waste heat boiler 18, where the sensible heat of these gases is used to generate steam.

In the system shown in Fig. 1, the carbonization gas generated in the carbonization zone 2 and the Gasification product arising in the gasification zone 3 at opposite ends of the rotary kiln 1 withdrawn (arrows 21, 22). This mode of operation is particularly useful when highly nitrogenous Solids are carbonized, so that the carbonization gas contains a high proportion of ammonia is. It goes without saying that - in contrast to the illustrated embodiment - carbonization gas and gasification product can also be recycled separately.

The addition of oxygen-containing compounds of the alkali and alkaline earth metals is not shown in FIG. 1 to the carbonaceous solids. The addition of these additives can be done before the feed screw 4 take place; however, it can also be mixed in in the smoldering zone.

In the further exemplary embodiment shown schematically in FIG. 2, the same components are used for the same Reference numerals as used in FIG. 1.

- 112 - <-

The carbonization gas generated in the carbonization zone and the gasification product formed in the gasification zone 3 are here together - in countercurrent to the solids - through the nozzle 8 on the entry side of the rotary kiln pulled off (arrow 23). A part of this mixed gas is fed to the combustion chambers 11 for indirect heating of the rotary kiln 1 supplied (line 12). The rest of the mixed gas will Via the line 24 to another recovery (for example in a combustion chamber 17 as in Fig. 1) forwarded.

In contrast, Fig. 3 shows a variant in which the carbonization gas generated in the carbonization zone 2 and the in the gasification zone 3 produced gasification product in cocurrent with the solids through the rotary kiln. Oven 1 are guided (arrow 25) and the mixed gas is drawn off through the nozzle 9. Part of this mixed gas (Line 12) is used again for indirect heating of the rotary kiln 1, while the remaining gas (line 26) is fed to a separate recovery.

Fig. 4 shows an embodiment in which the Rotary kiln 1 is preceded by a hearth furnace 27 for drying the carbonaceous solids. The coal is fed into the hearth furnace 27 at 28 and, after drying, passes through the feed screw 4 in the smoldering zone 2 of the rotary kiln 1. The solids pass from the smoldering zone into the gasification zone 3, which is provided with a nozzle device 10 for supplying water and / or steam.

solid residue
It is produced by the discharge screw 6

carried out. The carbonization gas is drawn off at 29 and the gasification product at 30.

The water vapor-containing substances that arise in the drying zone Vapors are fed via line 31 to the nozzle device 10 and directly into the Gasification zone 3 introduced. To a condensation of the drying zone (hearth furnace 27) of the gasification zone 3 supplied water vapor, the line 31 is expediently thermally insulated.

The invention will be further explained with the aid of a few examples of the method.

Example 1 (carbonization and gasification of lignite):

Carbon-containing solids: Rhenish lignite

Composition: 21.5% C

54% H ₂ O

5% ash, 18.5% volatiles

1% S.

a) Carbonization and gasification with the addition of lime:

Procedure: Use a plant ge

according to Fig. 1 (separate gas discharge from the smoldering zone and gasification zone)

Addition of 12 kg Ca (OH) -

per t of feed coal

Good temperature: 500 ⁰ C

Throughput: 0.4 t / h

Pressure: 1.01 bar in the rotary kiln

Carbonization gas:

Composition:

(dry, without steam

content) H ₂ 40

CO 4 CO ₂ 21 CH ₄ 24 ^C 2 ^H 4 ¹ ' ³

Higher hydrocarbons 8

N ₂ 1.3 H ₂ S 0.4

Calorific value: 18040 kJ / Nm ³ dry Density: 0.90 kg / Nm ³ dry carbonization gas volume (dry): 69 Nm ³ / h dust content: 420 mg / Nm ³ dry carbonization gas volume (moist): 331 Nm ³ / h,

H ₂ S content: 0.06%
Dust content: 110 mg / Nm ³ moist

Gasification product:

Composition: H "67%

CO ₂ 30% CO 3%

Calorific value: 7224 kJ / Nm ³ dry

Density: 0.7 kg / Nm ³ dry

Gas quantity: 509 Nm ³ / h dry

Dust content: 400 mg / Nm ³ 5

Discharge: 45 kg / h with a loss on ignition of 31%

b) Carbonization and gasification without the addition of lime (for comparison)

10

Procedure: as under a), but good temperature

temperature of 850 ⁰ C

Carbonization gas:
15th

20th

dry): H_ N ₂ 38 , 3 % CO H ₀ S 4th % co ₂ 22nd % CH ₄ 22nd , 3 % 1 , 4 % Higher coals hydrogen 8th % 1 % 3 %

25th

Calorific value: 17910 kJ / Nm ³ dry

Density: 0.90 kg / Nm ³ dry carbonization gas volume dry: 59 Nm ³ / h dust content: 3000 mg / Nm ³ dry carbonization gas volume moist: 327 Nm ³ / h

oO

H ₂ S content: 0.6%, dust content: 54 0 mg / Nm ³

- ■ 2ο-

Discharge: 31 kg / h with a loss on ignition of 43%

A comparison of the data for the carbonization gas under a) and b) shows that achieved by adding lime substantial improvement.

c) Smoldering and gasification with common gas extraction:

Procedure: according to FIG. 2

Product temperature: kg 500 ⁰ C the addition of 12 Ca (OH) ₂ per ton of feed coal.
The natural moisture of the lignite is used as the gasification agent

used (feeding of the vapors expelled in the drying zone into the gasification zone / according to Fig. 4).

Mixed gas (consisting of carbonization gas and gasification product):

Composition H ₂ 63%

CO 3%

CO ₂ 29%

CH ₄ 2%

Higher hydrocarbons 1%

N ₀ 1.7%

2

H ₂ S 0.3%

Calorific value: 8753 kJ / Nm ³ dry

Density: 0.74 kg / Nm ³ dry Amount: 554 Nm ³ / h dry Dust content: 280 mg / Nm ³ moist

Discharge: 33 kg / h with a loss on ignition of 40%

Example 2: (carbonization and gasification of sewage sludge)
10

Carbon-containing solids: centrifuged Sewage sludge

Composition: 75% water 18% organic content

7% inorganic content

a) Smoldering and gasification with separate gas vent
20th

Procedure: 1 product temperature corresponding to FIG. 500 ⁰ C Flow rate: 0.5 t / h Pressure: 1.02 bar in the rotary kiln lime addition: 15 kg / t feedstock

Carbonization gas:

Composition (dry): H ~ 55%

CO 3%

CO ₂ 14%

CH ₄ 17%

C ₂ H ₆ 4%

, Higher hydrocarbons 5%

^N 2 1 ^/5%

H ₂ S 0.5%

Calorific value: 19500 kJ / Nm ³
Density: 0.635 kg / Nm ³
Carbonization gas volume dry: 95 Nm ³ / h

moist: 560 Nm ³ / h

Gasification product:

Composition: H ₂ 64%

• 32% CO 4%

Calorific value: 7000 kJ / Nm ³
Density 0.7 kg / Nm ³
Amount: 170 Nm ³ / h

Discharge: 55 kg / h with loss on ignition 14%

b) Smoldering and gasification with common gas extraction

Procedure: according to Fig. 2

Material temperature: 500 ⁹ C Addition of lime: 15 kg / t charge material The moisture content of the centrifuged sewage sludge serves as the gasification agent.

. , · \ Composition: H ₂ 58

* CO 3

CO ₂ 15

CH ₄ 14

C ₂ H ₆ 3

Higher hydrocarbons 4

Calorific value: 11000 kJ / Nm ³
Density: 0.65 kg / Nm ³
Dry amount: 265 Nm ³ / h
moist: 730 Nm ³ / h

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Claims (1)

'Patent claims: 1. Procedure 'for carbonization and gasification of ':. ' Carbon-containing solids under agitation, *' · -. . where the charring zone and the gasification '-'-' . ί zone are indirectly heated and water and / or steam is introduced into the gasification zone,! characterized by the combination "of the following features: a) The carbonization and the gasification are interspersed in two by the solids one after the other Zones of a single rotary kiln carried out; · b) the carbon-containing solids are oxygen-containing compounds of the alkali and Alkaline earth metals added; c) in the carbonizing an outer wall temperature between 500 and 700 ⁰ C and in the gasification zone an outer wall temperature between 600 and 800 ⁰ C is set, wherein the temperature difference between the gasification zone and carbonizing smaller is kept "than 200 ⁰ C; d) the supply of water and / or steam is regulated in such a way that in the gasification zone sets an overpressure of up to 1 bar. ' 2. The method according to claim 1, in particular for strongly ■ ' -, nitrogen-containing solids, characterized marked ^I > ^ advised that the carbonization gas generated in the smoldering zone and the gasification product produced in the gasification zone at opposite ends of the rotary kiln, _; can be removed from the oven. ■ - / ■ ~> 3. Method according to claim 1, characterized in that that the carbonization gas generated in the carbonization zone and IQ ■ the gasification product generated in the gasification zone in the rotary kiln in cocurrent to the solids and withdrawn at the end of the rotary kiln facing away from the entry side of the solids. 4. The method according to claim 1, characterized in that that the carbonization gas generated in the carbonization zone and the gasification product generated in the gasification zone guided in the rotary kiln in countercurrent to the solids and on the entry side of the Solids are withdrawn from the rotary kiln. 5. The method according to claim 1 using a rotary kiln provided with lifting blades, characterized characterized in that the supply of water and / or steam is regulated in such a way that In the gasification zone there is an overpressure between 10 and 1000mm WS, preferably between 40 and mm WS. BATH ORIGINAL . / 6 .. The method according to claim 1 using a ■ \; "Rotary kiln with a smooth inner wall, characterized 'That the supply of water and / or steam is regulated so that in the *. . "gasification zone an overpressure between 100 and ^ -, 5000 mm WS, preferably between 250 and 3500 now WS, . , 7. A method according to claim 1, characterized in that the temperature is maintained in the gasification zone is between 700 and 75O ⁰ C. 8 .. The method according to claim 1, characterized in that the carbonaceous solids 1 to \ .7.5 wt .-%, preferably 1.5 to 2.5 wt .-% of oxygen-containing compounds of the alkali and alkaline earth metals are added - 9. The method according to claim 1, characterized in that the carbon-containing solids calcium hydroxide, Calcium carbonate and / or calcium oxide • be added in fine-grain form. .10. Method according to claim 1, characterized in that that the carbon-containing solids in addition to the oxygen-containing compounds of the alkali and alkaline earth metals, oxygen-containing iron compounds and / or scrap iron are added. 11. The method according to claim 1, characterized by the use of undried lignite and / or peat with a water content of up to 65% by weight. BAD ORIGINAL COPY 1 ? \ 12. Method according to claim 1, characterized ■ * "" church the use of carbon-containing waste " if all materials, such as household waste and sewage sludge. 5 "." ;. 13. The method according to claim 1, characterized by '% ._ the use of gas-rich young coal and / or ' j ~ "siubbituniinous coal. · 14. The method according to claim 1 for drying, Ver-10 'smoldering and gasification of carbonaceous Solids with high intrinsic moisture, characterized by that the smoldering zone is preceded by a separate drying zone and that the at the drying of the carbon-containing solids 15 resulting steam-containing vapors in the Gasification zone are introduced. BAD ORIGINAL COPY