CA1124521A

CA1124521A - Process for the catalytic gasification of solid fluids with steam

Info

Publication number: CA1124521A
Application number: CA326,105A
Authority: CA
Inventors: Siegfried Peter
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-04-24
Filing date: 1979-04-23
Publication date: 1982-06-01
Also published as: DE2817835C2; US4508543A; AU4639479A; AU529906B2; DE2817835A1

Abstract

ABSTRACT OF THE DISCLOSURE

A process for the catalytic gasification of solid fuels with steam is provided wherein the catalysts are first dissolved in steam at high pressure and the pressure of the steam containing catalysts in dissolved form is subsequently reduced to reaction pressure.

Description

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Canadian Patent 1,074,117 discloses a process for catalyzing the reaction be~ween coal and steam by dissolving catalytically active compounds ln high-pressure steam. As su~-stances which, according to the process of the invention, are easily soluble in high-pressure staam and show good catalytic activity with respect to the reactlon between coal and steam, there are mentioned alkali metal compounds such as hydroxides or salts, carbonates, chlorides, borates, acetates, and the like; as well as salts of alkaline earth metals such as chlorides, aoetates etc. Alkaline earth ~etal hydroxides also result in acceleration of the reaction.
Solubili~y of the compounds in high-pressure steam will, however, drop rapidly with decreasing pressures so that the catalytic effect of the above process is especially evident only at pressures above lO0 bar. As there is considerable in-terest in processes providing exce~lent acceleration even at lower pressures, working at pressures of from 40 to 70 bar seems to be desirable for VariQUs reasons, one of these reasons being, for instance, that the steam pressures available from light water reactors do not exceed 65 to 70 bar. Thus, if nuclear heat is to be employed in the gasifiers in order to improve upon the economy of the gasification operation, the available steam pressure will be restricted to the above value.

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Solubility of the above mentioned catalytically active com-pounds in steam at 750 to 900C. and 65 bar is relatively low Some catalytic effect is still noticeable under these conditions but it is so low that an improvement or increase of the effect is urgently requirecl. Surprisinyly, the above difficulties may now be overcome by clissolving catalyst in steam at high pressures and subsequently feeding the steam into the reactor under release of pressure. Even though catalyst solubility will drop suddenly and drastically when the pressure of the steam is released and the concentration of saturation after pressure release is well below the catalyst concentration, the catalyst thus introduced into the coal bed remains highly active.

It is an object of -the present invention to provide a process for the catalytic gasification of solid fuels with steam wherein the catalysts are first dissolved in high-pressure steam under conditions at which the catalyst/steam system is supercritical, whereupon the pressure of the steam co~taining dissolved catalysts is reduced to reaction pressure.
In the process of the invention, there is formed an oversaturated solution of catalyst in steam.

Experiments have shown that catalysts thus introduced into the coal bed in the form of an oversaturated solution will still be active after having passed through a filling layer of a height of 40 cm. or more. This proves that in layers of the above height, formation o~ methane from carbon monoxide and hydrogen and, respectively, coal and hydrogen

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is catalyzed and a corresponding incxease in temperature is measured stil~. The ~entioned ~atalytically ~ctive compounds accelerate not only the reaction ~etween coal and steam under formation of carbon monoxide and hydrogen but any subsequent reactions as well. If catalyst-containing steam is fed in the above described manner to a coal bed externally heated to a constant temperature of e.~. 750C., a temperature drop of about 50C. may be observed in the steam feedin~ zone while the temperature increase in a zone about 30 to 40 cm. above the steam feeding zone amounts to about 70 C. On repeatin~ the reaction without catalyst addition under otherwise identical conditions, one will observe a lower temperature drop in the steam feeding zone and the temperature increase above the steam feeding zone will be negligible.

The proce~s of the present invention may also be realized in the following manner: Catalyst in an amount exceeding the actually required concentration is dissolved in steam at 400C. and 220 bar, the steam thus being above the range of its critical temperature of 374.2C. and its critical pressure of 217.5 bar and showing a correspondingly high density.
Dissolution is readily accomplished because of the high density of the steam. Steam loaded with large amounts of catalyst is then led to the reactor and mixed at the reactor inlet with the main stream of steam which has been heated to reaction temperature. The temperature of the main stream may be sufficiently high to bring the temperature of the combined streams to the desired level of from 750 to 900C. Here too, mixing of the two streams will result in formation of an oversaturated solution of catalyst. The catalyst thus _ 4 ~-~2~2~

introduced into the reactor is highly active as it is capa~le of following the reaction ~ront without ~ny dif~i-culty.

In another embodiment of the present invention, steam which contains dissolved catalyst and i5 prefera~ly maintained 2 to 100C. above its critical temperature is subjected to pressure release on being mixed with the main stream of steam. For instance, steam at a pressure o~ 220 bar, thus being within the range of its critical pressure, may be subjected to pressure.release while being combined and mixed with the main stream having a pressure of 60 bar.

In a further embodiment, an aqueous solution of catalyst preferably maintained 0 to 100C. below its critical temperature of 374.2C., i5 added to the main stream of steam within the reactor. Sudden vaporization or optionally vaporization on pressure release under simultaneous mixing with the main stream will result-in the desired oversaturated solution.

Mixing of the two vapor streams is suitably accomp:Lished with the aid of an injector-type reactor. -Here, the catalyst-containing steam and the main stream are guided concentrically so that the main stream envelops the catalyst-contain.ing stream. A cylindrical baffle or guide element wi:Ll promote mixing efficiency. Suitably, the two streams are mixed when entering the reactor at a point helow the reaction zone.

~ - 5 -Ihe process of the invention is applicable to e.g. steam gasification of pit coal, lignite, oil coke, heavy oils, oil residues, oil shale and the like.
The following examples illustrate the process of the invention without being limitative. Unless stated otherwise, all percentages given are by volume.

Pit coal coke prepared by heating pit coal to 700C.
was ground and reacted with pure steam in an autoclave. At a pressure of 140 bar and a temperature of 850C., there were obtained 2.4 liters NTP of gas per liter of coke charge per minute, the gas containing 55% of hydrogen, 11% of methane, 4%
of carbon monoxide, and 30% of carbon dioxide after condensa-tion of the steam.
In a second series of tests, ground coke was impregnated for one hour with a 0.2 molar solution of potassium carbonate in water. The solution was drained o~f and the ground coke dried and reacted with pure steam in an autoclave`at 850C.
and 140 bar. Per liter of coke charge and per minute, there were obtained 2.5 liters NTP o a gas which, after condensation of the steam, contained 56% of hydrogen, 11% of methane, 4~ of carbon monoxide, and 29% of carbon dioxide. Thus, considering measuring errors, reaction rate as well as composition of the gas had remained the same.
In a third series of experiments, a sample o~ the above coke was reacted at a pressure of 1~ bar and a temperature ~ Z~52~L
of 850C. with steam which had been prepared by vaporizing an aqueous 0.~2 molar solution of potassium carbonate at 300 bar and 500 C. and was subjected to pres~ure release when entering the reactor. The flow rate in the pressure release valve and the line following the pressure release valve was so high that those portions of potassium carbonate insoluble in steam after pressure release and heating to reaction temperature were entrained with~he steam in extremely finely divided form. Per liter of coke charge and per minuke, there were obtained 5.8 liters NTP of a gas which, after condensation of steam, contained 56~ of hydrogen, 11.5% of methane, 2~ of carbon monoxide, and 30.5~ of carbon dioxide. Thus~ the reaction rate was more than twice as high as that obtained under otherwise idential conditions with coke impregnated with a solution having ten times the above potassium carbonate content.

Pit coal coke prepared by heating pit coal to 700C. was ground and reacted for one hour with a 0.2 molar solution of potassium chloride in water. The solution was drained off and the coke dried and reacted with pure steam in an autoclave at 800C. and a pressure of 70 bar. Per liter of coke charge and per minute, there were formed 2.4 liters NTP of a gas which, after condensation of steam, contained 58~ of hydrogen, 8.5% of methane, 7~ of carbon monoxide, and 26.5~ of carbon dioxide.
In another series ~f experiments, a sample of the above coke was reacted in an autoclave at a pressure of 70 bar and a temperature of 800C. with steam which had been prepared by ~ ;2452~

vaporizing a Q.~2 molar solution of potassium chloride at 300 bar and 500C. and was subjected to pressure relaase when entering the reactor. The flow rate of the ~team in pressure release valve and line was suf~iciently high to effect entrain-ment of very ~inely divided particles o~ ~hose potassium chloride portions which, after pressure reduction to 70 bar and heating to reaction temperature, were insoluble in steam.
Again, it must be left undecided whether an oversaturated solution of potassium chloride in steam or a very fine mist of potassium chloride was formed in this manner. Over-saturation was so stable that the steam still contained considerahle amounts of catalyst even a~ter having passed through a coke charge having a height of 110 cm. When the process gas was cooled to condense excess water therefrom, a catalyst-containing solution was formed. Per liter of coke charge and per minute, there were obtained 5.2 liters NTP of a gas which, after condensation of steam, contained 58% of hydrogen, 10 % of methane, 5 % of carbon monoxide, and 27 % of carbon dioxide. Thus t the reaction rate was more than doubled over that obtained under otherwise identical conditions with coke impregnated with solution, the potassium carbonate content of which was ten times higher.

Pit coal pr~pared by heating caking pit coal to 700 C. was ground and reacted with catalyst-containing steam in an autoclave at a preSsure of 60 bar and a temperatuxe of 800C. The mixture of potassium chloride and sodium hydroxide serving as catalyst was di.stributed in steam in the following manner: An aqueous solution containing 0.1 mole of potassium ;

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chloride and 0.1 mote of sodium h~droxide per 10~0 grams of water was vaporized under a pressure of 30~ ~r at 400C~
Under these conditions, the steam/catalyst system is super-critical at concentrations below the curve of its solution pressure diagram; this means that in the mentioned concentra-tion range, the mixture of steam and salts will be present as one-phase mixture. The steam containing high concentrations of cataly~t was concentrically introduced and mixed with steam at 850C. and 60 bar flowing through a line and was subsequently fed into the reactor. The ratio of the two vapor streams was selected to give a mixed stream having a pressure of 60 bar and containlng 0.02 moles of catalyst per 1000 grams of steam. On pressure xelease, the catalyst-containing steam originally maintained at a pressure of 300 bar will reach a state below its critical range, undergo an equilibrium decomposition and form a vapor phase which contains only minor amounts of dissolved catalyst besides solid catalyst particles. Surprisingly, the rate of nucleus formation and crystal growth is so low under these circumstances that no salt precipitation takes place in the pressure re~ease valve and the catalyst is carried into the coke charge in such a finely divided form that it remains highly active.

Per liter of coke charge and per minute, there were obtained 3.8 liters MTP of a gas which, after condensation of steam, contained 64~ of hydrogen, 2~ of methane, 2~ of carbon monoxide and 32~ of carbon dioxide. Experiments conducted ~ith pure steam under identical conditions resulted in 1.6 liters NTP of a gas containing 62~ of hydrogen, 2% of LS~

methane, ~% of car~on monoxide, and 32% of carbon dioxide after steam condensation. Thus, the reaction rate under use of catalyst wa~ a~out twice as high as that achieved without the use of catalyst.

EX~MPLE 4 ~

Ground pit coal was reacted with catalyst~containing steam in an autoclave at 800C. and a pressure of 70 bar.
The steam containing the catalyst had been prepared by vaporizing at 800C. and 500 bar an aqueous solution containing 0.02 moles of KCl and 0.02 moles of LiCl per :L000 grams of water; pressure on the steam was reduced to 70 bar while the steam was fed into~the reactor. Aftex pressure release, the catalyst originally dissolved in h1gh-pressure steam was present in form of an oversatùrated solution.
Oversaturation was so stable that the steam still contained considerable amount of catalyst even after having passed through a coke charge having a height of 110 cm.
When the process gas was cooled to condense excess water therefrom, a catalyst-containing solution was formed.
Per liter of coke charge and per minute, there were obtained 3.2 liters NTP of a gas containing 56~ of hydrogen, 10~ of methane, 4~ of carbon monoxide, and 30~ of carbon dioxide.
Steam conversion under the mentioned conditions amounted to about 22%. If a sample of the above coke was reacted with pure steam at the same temperature and pressure and under identical conditions, there were obtained 2.1 liters NTP of gas per liter of coke charge and per minute, the ga~ containing 58.5% of hydrogen, 9% of methane, S% of carbon mono~ide, and 27.5% of carbon dioxide. Steam conversion in this case amounted to about 14~.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the catalytic gasification of solid fuels with steam wherein the catalysts are first dissolved in steam at high pressure and the pressure of said steam containing catalysts in dissolved form is subsequently reduced to reaction pressure and wherein catalysts in concentrations exceeding those actually required is dissolved in a partial stream of said high-pressure steam under conditions at which the catalyst/steam system is supercritical, so as to form an oversaturated solution of catalyst in steam and whereupon the resulting steam is sub-jected to pressure release while being mixed with a main stream of steam.

2. The process according to claim 1, wherein catalyst in concentrations exceeding those actually required is dissolved in a partial stream of high-pressure steam or in water, the temperature of which is maintained at 0° to 100°C., whereupon the pressure of said catalyst-containing steam or water is re-duced to reaction pressure while said steam or water is mixed with a main stream of steam.

3. A process as claimed in claim 2, wherein the tem-perature is maintained at 0° to 20°C., above its critical tem-perature of 374.2°C.

4. The process according to claim 1, 2 or 3, wherein steam-volatile alkali metal compounds are used as catalysts.

5. The process according to any one of claims 1, 2 or 3, wherein carbonates, halides, borates, tetraborates, and hydroxides of alkali metals or mixtures thereof are used as catalysts.

6. The process according to any one of claims 1, 2 or 3, wherein carbonates, halides, borates, tetraborates, and hydroxides of potassium are used as catalysts.

7. The process according to any one of claims 1, 2 or 3, wherein carbonates, halides, borates, tetraborates, and hydroxides of sodium are used as catalysts.

8. The process according to any one of claims 1, 2 or 3, wherein carbonates, halides, borates, tetraborates, and hydroxides of lithium are used as catalysts.

9. The process according to any one of claims 1, 2 or 3, wherein mixtures of lithium chloride and potassium chloride are used as catalysts.

10. The process according to any one of claims 1, 2 or 3, wherein mixtures of sodium borate or sodium tetraborate and potassium chloride are used as catalysts.

11. The process according to any one of claims 1, 2 or 3, wherein mixtures of sodium carbonate and potassium chloride are used as catalysts.

12. The process according to claims 1, 2 or 3, wherein the concentration of catalyst in the steam to be reacted with coke is between 0.001 and 0.5 mole per 1000 grams of steam.

13. The process according to claim 1, 2 or 3, wherein the concentration of catalyst in the steam to be reacted with coke is between 0.01 mole and 0.2 moles per 1000 grams of steam.