CA1059065A - Arc reforming of hydrocarbons - Google Patents
Arc reforming of hydrocarbonsInfo
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- CA1059065A CA1059065A CA242,081A CA242081A CA1059065A CA 1059065 A CA1059065 A CA 1059065A CA 242081 A CA242081 A CA 242081A CA 1059065 A CA1059065 A CA 1059065A
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
- C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
- C01B3/32—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air
- C01B3/34—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents
- C01B3/342—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents with the aid of electrical means, electromagnetic or mechanical vibrations, or particle radiations
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J12/00—Chemical processes in general for reacting gaseous media with gaseous media; Apparatus specially adapted therefor
- B01J12/002—Chemical processes in general for reacting gaseous media with gaseous media; Apparatus specially adapted therefor carried out in the plasma state
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Abstract
ABSTRACT OF THE DISCLOSURE:
A process for the production of reducing-gas mixtures of carbon monoxide and hydrogen by the partial oxidation of at least one hydrocarbon with an oxygen-containing gas or a mixture of oxygen-containing gases, in stoichiometric ratios. The process comprises selecting a predetermined equilibrium temperature, forming an arc plasma by striking an arc in a portion of the reactants in gaseous phase, reacting the remaining portion of reactants with the arc plasma to obtain a gaseous reaction mixture having an average temperature at least equal to the pre-determined equilibrium temperature but lower than the temperature of the plasma and following the reaction mixture to reach homo-geneity at the said average temperature. The process of the invention does not necessitate thorough pre-cleaning or pre-purification of the starting materials and, accordingly, off-gas from an integrated ore reduction process may be used as main oxidizing gas. The reducing gas produced is suitable for the direct reduction of ores.
A process for the production of reducing-gas mixtures of carbon monoxide and hydrogen by the partial oxidation of at least one hydrocarbon with an oxygen-containing gas or a mixture of oxygen-containing gases, in stoichiometric ratios. The process comprises selecting a predetermined equilibrium temperature, forming an arc plasma by striking an arc in a portion of the reactants in gaseous phase, reacting the remaining portion of reactants with the arc plasma to obtain a gaseous reaction mixture having an average temperature at least equal to the pre-determined equilibrium temperature but lower than the temperature of the plasma and following the reaction mixture to reach homo-geneity at the said average temperature. The process of the invention does not necessitate thorough pre-cleaning or pre-purification of the starting materials and, accordingly, off-gas from an integrated ore reduction process may be used as main oxidizing gas. The reducing gas produced is suitable for the direct reduction of ores.
Description
` 1059065 The pre3en-t invention rclates to a process-for the pro-duction o~ reducing-gas mi~tures of carbon monoxide and hydrogen by the partial oxidation of a hydrocarbon. More par-ticularly, the in~ention is concerned with -the reforming of a hydrocarbon into carbon monoxi.de a-nd hydrogen, wi-thout the aid of a catalyst, by e~posing the hydrocarbon and an oxygen-containing gas to an electric arc, The reducing gas produced in accordance with the in~ention is suitable for the direct red.uction of ore~, including iron ore~
~he reforming of methane (CH4) or other hydrocarbons i~ oP considerable importance, particularly in the metallurgical world. It is the partial oxidation of the hydroc~rbon to pro-I duce a reducing gas consisting of carbon monoxide (C0~ and hydrogen (H2) using oxygen (2) or an oxygen-containing gas suc~
a~ carbon dioxide (C02) or water vapor (H20). Using methane as an example of a hydrocarbon, the reaction may be schematized by the following equation, the symbol "0" representing the oxidi.zing ~ ga~:
¦ CH4 -~ "0" C0 ~ 2H2 (I) i~ "0" ie 2~ the general equation then becomes:
CH4 ~ 1/202 ~ C0 * 2H2 (2) and: CII~ ~ H20 > C0 ~ 3H2 (3) if "0" i~ I~20, and:
CM4 ~ C02 > 2C0 ~ 2H2 (4) if "0" is ~2 Reactions (3) and (~) are of ~ery great intere~t metal-lurgically because they enable the off-gases from an integrated ore reduction ~rocc.~3 to be u~ed as the oxidi~ing ga3 for the reformirg process; in the Midrex proce3c~S for cxamplc, gaseous mixture3 of C0~ and II20 arc produccd when iron oxidc i9 reduced lOS9065 to metallic iron by a reducing-gas consis-ting essentially of C0 and H2. Bo-th reaction~ (3) and (4) are endothermic and both are favoured by high temperature.
The usual reforming process is to pass the gaseous reactants over a heated metallic catalyst, such a~ iron or nickel.
The presence of a catalyst i~ preferred ~ince it improves the reaction kinetic~ hen using H20 and/or C02 a~ oxidi~ing gas, high temperatures are also required to move the equilibrium gas compo~ition to the right in equations (3) and/or (4) and to provide heat for the endothermic reactions, In the particular case of methane, at temperatures below about 610C for reaction (3) and 640C for reaction (4), the back reactions are more important than the forward reactions and the amount of C0 and H2 produced will be very small. These temperatures are lower for higher hydrocarbons, for instance 460 and 410C respectively in the case of n-octane, C8H18~ At higher temperatures, however, the forward reactions become increasingly important and, at about 1000 ~ for methane, proceed substantially to completion (lower temperature~ for higher hydrocarbons) ~he reaction kinetics at this temperature, however, are unfavorable, and to achieve complete reaction very long residence times of the order of several minutes must be used or the reaction must be carried out in the presence of a catalyst. ~he use of a catalyst reduces the reaction times to a few seconds, approximately two ~econds.
The alternative of utilizing higher temperatures to speed up the reaction is economically unattractive.
When use is made, on the other hand, of molecular oxygen as main oxidizing gas, the external supply of heat is not re~uired for the reaction since it is known that equation (2) must be vierled as rather breaking down into the following three equations:
` l~S~t;5 " , .
!.
4CH4 ~ 20 ~ C2 + 2H20 ~ 3CH4 (5) 4 ~ ~2 ~ -- > 2CO -~ 2H2 (6) 2CH4 ~ 2H20 > 2~0 ~ 6H2 (7) i.e., a first reaction stage which is exothermic and i9 represented by equation (5), and a second reaction stage which i9 endothermic and corresponds to equations (6) and (7), both reaction stage~ occurring without interruption and extending directly from the first into the seco-nd It therefore suffice~
to trigger the combustion o~ the hydrocarbon in the presence of oxygen to produce, owing to the exothermic reaction (5), a very hot gaseous mlxture of C02~ H20 and unreacted ~I4 and to allow the reaction of these hot gases to proceed to completion accord-ing to equations (6) and (7) by adequate exposure to the necessary heat for the endothermic reaction stage, ~hich heat may be thus supplied directly from the exotherrnic reaction stage (U.S patent No. 3,536,455 of October 27, 1970 to ~ogdandy et al).
~his technique involves long residence times since the hot gases must be passed through a latticework of a refractory heat-storage material maintained at temperatures in excess o~ 1100~ so that both reactions (6) and (7) proceed to completion. In any ca~e, molecular oxygen is necessary in order to provide a fir~t reaction which in exothermic, liberating heat for the secondary endothermic reactions.
It has also been proposed, in U.S, patent No 3,620,699 of November 16, 1971 to Reynolds et al, to control the temperature of combustio-n of a hydrocarbonaceous liquid in the presence of substantially pure oxygen to a lower limit of approximately 1100~, by feeding a tempera-ture-moderating gas to the combu~tion zone, thereby enabling both reactions (6) and (7) to proceed to completion. This moderator consists of a gas mixture which-may be either a portion of cooled reducing gas from the combustion 1~59(~65 zone~ a portion of cooled and cleaned of~`-gas from an integrated ore reduction process, or a ~ixture of both of said cooled gases.
~he Co2 and II20 contained in such off-gas serves in this case to chemically cool the reaction temperature, in addition to contributing to a small extent to the produc-tion of the desired end products, in accordance with the endothermic reactions (6) and (7) No catalyst is needed as the temperatures and pressures utilized are high enough to speed up the reaction; no residence or reaction times, however, are mentioned in the patent.
It must be pointed out, in connection with catalytic reformers, that these suffer from an important disadvantage, namely that slight contamination by certain elements such as sulfur resul-ts in the poisoning of the catalyst. ~his means that both the hydrocarbon and oxidizing gas must be free from such elements. This ~everely limits the availability of both; in other words, it is more difficult to use cheaper materials such as waste oil a~ h~drocarbon or offDga~ from ore reduction processes as oxidizing gas, since these would require purification before use.
It is therefore an object of the present invention to provide a process for the production of reducing gas mixtures of carbon monoxide and hydrogen, which does not neces~itatethorough pre-cleaning or pre-purification of the starting materials. In accordance ~ith the invention, off-gas from an integrated ore reduction process may be used as main oxidi~ing gas, without detriment to the reaction.
It is a further object of the invention to provide a proce~s for the reforming of hydrocarbons u-tilizing an oxygen~
containing Oas and to reduce reaction times beyond those obtained with a catalyst.
It is yet another objec-t of the invention to provide 1~9~65 a simple and e~ficient way of producing a reducing gas which may be utilized directly for the reduction of metal ores.
These objects are accomplished, according to -the invention, by the decomposition in the presence o~ an electric arc of a portion of the reactants into reactive species, followed - by the reaction of these species with each other and v~th the remaining portion of the reactantsO ~he reaction time is almost instantaneous since at least part of the reactant3 are in the active form.
In accordance with the present invention, there i9 thus provided a process for the production of reduci-ng ga~
mixtures o~ carbon monoxide and hydrogen by the partial oxidation of at least one hydrocarbon with an oxygen-containing gas or a mixture of oxygen-containing gases, in stoichiometric ratios The process of the invention comprise3 selecting a preaetermined equilibrium temperature, forming an arc pla~ma by striking an arc in a portion of the reactants in gaseous phase, reacting the remaining portion of reactants with the arc plasma to obtain a gaseous reaction mixture having an average temperature at least equal to the predetermined equilibrium temperature but lower than the temperature of the pla3ma and alloY~ing the reaction ~ixture to reach homogeneity at the said average temperature.
~pplicants have found quite unexpectedly that when a gas is decomposed into reactive species at very high temperatures (5000-8000C), as in an arc-plasma generator, and additional gases are introduced into the arc plasma ~ormed9 some of the molecules introduced will also reach a very high temperature and undergo decomposition and, as the very hot gas mixes with the cooler gases, thQ reactive fragment~ in the plasma and those subsequently formed react with each other and with undecomposed molecules to yield, provided the ga3eou3 mixture i~ allowed to reach ho~ogeneity at the average temperature attained, a gas `` 1059~65 , having th.e e~uilibrium composition at -that -temperature. It i9 not necessary -to raise the temperature of all the gases additionally introduced to the very high of the plasma. It suffices to attain an average temperature that is at least equal to -the temperature of the desired chemical eqv.ilibrium. In a prèferred embodiment, however, for practical purposes only, the energy supplied ~ill be such to raise the reacting gases to an average temperature that i~ substantially equal to the pre-determined equilibrium temperature and to carry out the reaction at that temperature.
Plasms techniques are known ana have been employed to create phy~ical or chemical changes in material~, at very high temperatures ~or instance, the direct reduction of metal oxide to metal i~ reported in U.S patent ~o 3,765,870 of October 16, 1973 to ~ey M,G et al ~he metal oxide entrained by a carrier gas is subjected to the intense heat of an arc plasma formed from a hydrocarbon gas which is raised to an extremely high temperature sufficient to free hydrocarbon radical ion3 It i~
understood, however, that the chemical reduction occuring in the metal oxide ore i9 promoted by the very high temperature of the arc plasma and that the reducing hydrocarbon radi.cal ion~ only assist in ~eparating the metal from the metal oxide ore It i~
al~o kno~n to directly contact a fluidized bed of par-ticles with sn arc plasma for exposing materials to very high temperatures In U S patent No 3,404,078 of October 19t, 1968 to William M
Goldberger, for example, a bed of electrically conductive fluidized particles is employed a~ an integral electrical par~ of the plasma generator so that no energy losge9 occur between the heating zone of the apparatus and the fluidized bed~ ~he bed ~0 particle 9 in the immediate region of the pla~ma can th~ls undergo the desired physical or chemical changes5 alternatively, reactants can be introdvced irl t~e hea-ting z~ne .Yuch that the resulti.ng ~059065 heated products are passed into the fluidezed bed for efficient cooling thereof at lower temperatures. In any case, arc plasmas have been u~ed hitherto mainly as heat sources to promote chemical reactions, and have not been utilized to entirely participate in a reactive manner, at temperatures much lower than the very high temperature of the plasma, to the production of the de~ired end substances.
When gases are reacted in plasma generators, otherwise known a~ arc heaters, these ~hould po~sess arc stability and good mixing characteristics in order to obtain optimum results.
Spurious arc extinctions can be eliminated by providing a short interelectrode gap which generally create~ a stable arc Also, on the commercial scale, the arc should not be argon-stabilized, since separation of argon from the product gases would be an undeeirable ~tep in the proce~s. Good mixing can be obtained by injecting the reacting gases at high velocity and/or by intro-ducing the remaining portion of reactants tangentially into the plasma ~or causing a turbulent mixing thereof v~ith the plasma.
In addition, the plasma may be magnetically rotated at high ~peed by mean9 of a 9ufficiently ~trong magnetic ~ield, thereby enhancing turbulent mixing of the reactants. ~he gaseou~ reaction mixture which i9 thu~ obtained by mixing the plasma ~ormed from a portion of the reactants with the remaining portion o~ reactants is then allowed to reach homogeneity in a reaction zone which directly communicates with the plasma zone and i~ preferably an e~ten~ion thereof.
Accordingly, in a further preferred embodiment of the invention, the reforming process i9 carried out in a stabilized arc heater having a plasma zone and a reaction zone in direct communication with the plasma zone, and comprises the steps of selecting a predetermi~ed equilibrium -temperature, striking ~OS9~65 an electric arc in a gap between electrodes while injecting a portion of the reactallts in ga3eous pha~e through the gap -to form in the plasma zone an arc plasma flowing into the reaction zone, and mixing the remaining portion of reactant~ with the arc plasma to obtain, in the reaction zone~ a gaseous reaction mixture having an average temperature substantially e~ual to the pre-determined equilibrium temperature, the reactants being supplied -in stoichiometric ratios a-nd the gaseous reaction mixture reach-ing homogeneity in the reaction zone at the said average tempera-ture.
In accordance with another preferred embodiment, the portion of reactants which serves to form the arc plasma consists essentially of the hydrocarbon component and the remaining portion of reactants lrhich i9 mi~ed with the arc plasma consists of the other reacting component, that is the oxygen-containing ga3 or mixture of oxygen-containing gases The reverse, of course, is also contemplated and con3titutes a further preferred embodiment of the invention.
According to yet another preferred embodiment of the invention, both portions are respectively fractions of the sum total of reactants premixed together.
~he remaining portion of reactants can be introduced into the arc plasma in a variety of way3~ The remaining portion can be fed, for instance,upstream of the plasma zone so as to directly impinge on the arc plasma as the latter i3 formed or it can be fed douinstream of the plasma zone but before the reaction zone~ The combination of both po3sibilities i9, of course, also contemplated and, in such an instance, the remaining portion of reactants will be suitably divided between upstream and down-stream inlets. Xowever, where the remaining portion of reactants consists of off-gases which are not thoroughly cleanea, as the oxidizing gas component, it is preferable to feed all or mo~t 105~65 .
do~qnstream o~ the plasma zone 30 as -to avoid unnecessary errosion o~ the electrodesl A~ mentioned previously, reactions (3) and-(4) are of great interest me-tallurgically because they enable the of~-gas from certain reduction processes to be used as the oxidizing gas component for the reforming process. Depending on the metallur-~gical process, the of~~gas mi~l~ be any of the following: sub-stantially pure C02; ~2 with unreacted C0; substantially pure H20 vapour; H20 with unreacted H2; mixtures of C02 and lI20;
mixtures of C02, C0, H20 and H2 It is understood, of course, that C02 and H20 are the reacting oxygen-containing gases and that at least one of these must always be present.
It was also mentioned that, in a preferred embodiment of the invention, the amount of electrical energy supplied is such to raise the tempera-ture of all the gases to substantially the predetermined equilibrium temperature and to carry out the reaction in this quantity of gas at that temperature. ~or the partial oxidation of ~H4 with H20 and/or C02, an e~uilibrium temperature of approximatively 1000C is adequate. At this temperature~ as already discus~ed, equilibrium is well over to the right in equations (3) and (4) with very little CII4, ~2 or H20 remainingr This temperature is not only suitable for methane but also for higher hydrocarbons since, for higher hyd~ocarbons, the free energies of formation substantially favor the reaction at temperatures lo~ler than 1000C. It must be understood, how-ever, that the approximate temperature o~ 1000~ does not con-stitute a limitation and tha-t any e~uilibrium temperature can be selected provided that equil~briRm i5 shifted9 a-t the pre-determi-ned temperatureS to the right in equations (3) and/or (4) An average temperature that is substantially cqual to the predetermined temperatllre is obtained by n~a-tching the e~ct~oe energy input to the gas input, i.e., supplying electrical energy lOS9C1 65 in an amount that is equal to the amount of energy required to raise the temperature of all the gases to -the de~ired equilibrium temperature and that required for the overall chemical reactions at that te-mperature. '~here the o~ygen-containing gas in H20, the energy requirement in the case of methane (reaction (3)) can ~e calculated by means of the followqng formula:
~3 = ~Hco _ ~ XcH ~ ~H o + T(hC0 ~ 3hH ) (8) wherein: ~Hco - heat of formation of CG at room temperature ~HCH = heat of formation of CH4 at room temperature ~HH20 = heat of formation of H20 at room temperature hCo = molar heat capacity of C0 h~I = molar heat capacity of ~2 = predetermined equilibrium temperature minus roo~ temperature It is understood that the unit~ chosen for calculation are self-consistent. If the oxygen-^ontaining gas i9 C02 (reaction (4)), the energy requirement can be similarly calculated by the formula:
4 C0 ~ CH4 ~HC02 ~ 2~(hC0 ~~ hH2) (9) wherein ~Hco = heat of formation of C02 at room temperature.
~he reforming process according to the invention can be applied, of course, to any hydrocarbon which may be designed by the general formula CmHn and includes saturated and unsaturated (olefinic as well as acetylenic) aliphatic and cyclic hydro-carbons as well as aromatic hydrocarbons A mixture of H20 and C2 can also be utilized as oxidizing gas~ In such sn instance 9 the above two equations (8) and (9) can be made general and combined together. In addition, i~ the reacting gases contain other gases, such as C0 and H2, which do no-t participate in the reaction, a term or terms must be inclu~ed to account for the energy required to heat such gas or gases to the predetermined 10~9~65 e,quilibrium temperature. ~husg a general reac-tion equation can be written:
(a ~ b)C,mEIn ~ amC02 ~ bmH2 (2am ~ bm)C0 + (bm ~ an ~ bn)H2 ~ xX + yY ~ ,,, (10) , 2 2 ~herein: xX + yY + ,., represents the presence, if any, of non-participating gase~ X and Y in their re-spective molar quantities x and y;
a is the molar quantity o~ C02 ;
b is the molar quantity of H20 ;
m is the number of carbon atom~ in the hydrocarbon processed; and n i~ the number of hydrogen atoms in -the hydrocarbon.
~he energy requirement for reaction (10) i~ then given by the formula: ' E - (2am ~- bm) ~Hco ~ (bm + a2 + b2n) ~HH2 (a ~ CmHn am QHco2 ~ bm ~HH20 + ~ [(2am ~ ~m) hco + (bm + an + bn)hH +
xhX ~ yh,y ~ ~,] (11) ~herein : ~HC ~ the heat of formation of the hydrocarbon ' CmHn ~t room temperature; ~nd h~ and ~ are the respective molar heat capacities of the non-participating gases X and Y.
~his is the amount of energy required to process a certain volume of ga~ made up of the molecular ratios a3 shown in equation (10).
Any self-consistent units can be chosen for the calculationr ~or example, i~ K,cals./g.mole and C are selected, the energy is in K,cal~, and the volume of input gas, in liters, i 9:
V~ = 22.4-(a ~ b ~ am ~ bm ~ x ~ y ~,,,) (12) at stalldard temperature and pressure. Changing this into units that are more relevant i-n the present context requires multiplying the energy in g~ca]s. by 1.163 ~ 10 3 to obtain kilowatt hours (K~) and the ~olume in liter~ by 3.531 x 10 2 to ob-tain standard cubic fee-t (SC~) ~hese values are -then used in the final calculation of the electrical energy input per unit time, e.g.
kilowatts (KW), for the desired g~s input per unit time, e.g.
SC~/hour, In the final calculation, heat losse~ must also be considered9 but they will be specific to the equipment used.
The reforming process according to the i~vention is normally carried out at atmospheric pressureO The input ~ gas ratios must also be ajusted so that the stoichiometry of the reaction (or reactions, where more than one hydrocar-bon and/or more than one oxidizing gas is processed) is main-tainedO ~or example, in reaction (3), one mole of water must be supplied for each mole of methaneO
Since generally at least part of the reacting gases are introduced at high velocity, the portion of reactants which serves to form~h~ arc plasma being normally injected at approximately sonic speed, and part of the reactants are in the active form (plasma state), the process of the invention permits to achieve reaction times of the order of 10 1 seconds, or even less, the precise time depending on the equipment usedO This is in contrast to the very much l~nger residence times necessary in catalytic or other reXormers~
An arc reformer also has the added advantage of having very much smaller dimensions than other reformersO Since the arc reformer is not influenced by sulphur or many other impurities with respect to the partial oxidation of hydrocarbons to produce C0 + H2 ~ it is not necessery to have materials in a refined or completely dust-free form. Accordingly, gas from destructive distillation of waste organic matter, lignite, coal, etc. , after condensation of exce~s water, can be prones-sed according to the invention to produce a reducing gasO
~059~365 With suitable solid feeding arrangements, carbon or solid carbonceous material can also be processed. Another advantage is that the invention permits the use o~ ore reduction off-gas which need not be rigorously cleaned o~ sulphur or other con-taminants that would otherwise be detrimental to catalytic reformers.
Preferred embodiments of the cubject invention v~ll now be described in greater detail, with reference to the appended drawings, wherein:
~igure 1 schematically represent~ in cross-section an arc heater adapted for carrying a reforming process according to the invention, and ~ igure 2 is a block-diagram of a reforming process according to the invention integrated wi~h an ore reduction process, showing heat and materials balances.
Re~erring first to ~igo 1, the arc reformer 10 is seen to include a pair of generally cylindrica:l electrodes 12 and 14 which are coaxially disposed on a common axis 16 and spaced by a narrow annular gap 18. Electric field breakdown in the inter-electrode gap initiates an arc discharge 20 at each current zeroof an alternating current backup source o~` power~ whereupon the arc is immediately blo~n into the interior of the apparatus by the force of a gas 22 injected at approximately sonic speed through the narrow gap 18. The gas 22 comprises a portion of the reactants for producing H2 + C0 and serves to generate in the plasma zone 24 an arc plasma upon decomposition of the gas into reactive species by the intense heat deveLoped by the arc 22.
~he a~c plasma formed is represented by a plurality of broken lines 26 and has a direction of flow towards the reac-tion zone 28 which commlunicates with the pla sma æone 2~ and i~ an extension thereof. The arc discharge 20 and the arc plasma 26 are magnetic-ally rotated at extremely high velocities (in the order of 1000 1059~65 rev./sec )~ by interac-tion with a D C magnetic fieïd arisi-ng from solenoid field coils 30 located within each electrode assembly.
The remaining portion of reactants is divided in t~o fractions 32 and 36~ one fraction 32 being fed through inlet 34 upstream of the plasma zone 24 and the other fraction 36 through inlets 38 and 40 dovrnstream of the plasma zone. Inlet 34 opens axially into the apparatus so that the feed introduced -there-through directly impinges on the arc plasma 26 as the latter is formed, while inlets 38 and 40 open radially for injection into the plasma flow. ~angential inle-ts as well as a single annular inlet are, of cour~e, also contemplated for mixing fraction 36 with the arc plasma formed, downstream of the plasma region.
Where the off-gas of an integrated ore reduction process i9 utilized as the oxidizing-gas component, as will be discussed later in connection with ~igure 2, it is most suitable to feed the totality thereof through inlets 34, 38 and 40 and feed all the hydrocarbon component through the arc, that is to say through the interelectrode ga~ 18. In addition, as already pointed out, should the off-gas be not thoroughly cleaned,it i9 most advantageous to feed all downstream of the plasma zone, in order to avoid unnecessary errosion of the electrodes 12 and 14.
In such an instance, inlets 38 and 40 will be the only prevailing inlets for introducing the off-gas.
In any case, the cooler gases introduced at 34~ 3~ and 40 encounter the very hot fragmented gas 26 under turbulent motion and mix and react with it in the reaction zone 28. ~he amount of energy transferred to the gas 22 and then carried by the plasma 26 i9 sufIicient to raise the -temperature of the other gases 32 and 36 and to supply energy for the endothermic oxidation reactions, resulting in an average temperature, in the reaction zone, that i~ substantially equal to the temperature ~14-lOS9al65 of the desired chemical equilibrium. As homogeneity i9 attained in the reaction zone, es~entially complete conversion is achieved with residence times in the order of lO 1 second~, and the effluent gas 42 comprise~ a mixture of C0 + H2 at equilibrium composition.
A suitable plasma generator for the reforming process of the inventlon is the Marc 31 generator made by Westinghouse Electric Corp , of Pittsburg, Penn~ylvania. ~his generator i9 a self-stabilized A.C arc heater provided with an interelectrode gap of approximately 0.04 inche 9 . ~he electrodes are tubular shaped copper electrode~ having each 5 inches inside diameter by 10 inches long, giving the heater an in-ternal volume of about 0.25 sq.ft. ~uch apparatus, however, must be provided at its outlet with a tube defining the reaction zone 28 in order to per-mit good mixing and attainement of homogeneity ~his reactor tube will advantageou~ly con~titute an extension of the outlet, and thus extend several feet from the outlet and be of the same internal diameter as the latter. Suitable inlet means for mixing and reacting the remaining portion of reactants with the arc plasma must, of course, al~o be provided.
An example of the w8y in which the reforming proce~ of the invention can be integrated with an ore reduction proce~s i9 shown-in ~igure 2. It i9 shown used in conjunctian with a Midrex type reduction shaft. In such a process, a reducing gas consisting essentially of C0 and H2 is introduced into a vertical shaft at 750-850C countercurrent to iron oxide in lump or pellet form. ~he reactions in the shaft produce metallic iron and a ga~ richer in C02 and H20O Part of this gas, after removing some of the water9 is used for the partial oxidation of additional CH4 to C0 and H2. ~igure 2 shows one way in which the overall proce~s can be run, utilizing an arc reformer in accordànce 1059~65 with the invention I-t includes the op~ion of pre-heating the gas mixture prior to reforming, u~ing part of the exce~s off-gas as fuel.
The process going on in the arc reformer can be ~ummarized by the following equation:
1.692CH4 + 0.769C02 +0.923H20 ~1.54CO + 2.69H2 > 4CO + 7H2 (13) This is a particular example of equation (10), with CO and H2 on the left hand side of the equation going into the arc reformer as non-participating gases Equation (11) can therefore be used to calculate the energy requirement. Selecting 1000C as the pre-determined equilibrium temperature for the reaction, and taking into account that the re~action described by equation (13) results in sufficient CO and H2 to produce 2.44 atomic weights of ~e, the following materials and energy requirements are obtained for the reduction process in ~igure 2.
CH4 required = 0.693 mols CH4/atom ~e = 8898 SC~ CH4/short ton ~e ~nergy required - 73 K.cals/atom ~e = 1268 K~/short ton ~e Putting this into more practical terms:-To produce iron at the xate of l short ton per hour CH4 required - 8898 SCF/hour Off-gas mixture: CO 8080 SCF/hour C2 4040 SC~/hour H2 14130 SC~/hour H20 4-850 SC~/hour TOTA~ 31100 SC~/hour 31100 SC~/hour Total gases entering reformer: 39998 SC~/hour (~.e. gas input) Re~ulting gases: CO 21000 SC~/hour H2 36700 SC~/hour 57700 SC~/hour 57700 SCI'/hour 1059~65 Erlergy requircd:
Theore tical (100~o efficiency) 1.268 megawatts Assuming 807~ efficiency 1.585 megawatts In other words, 1.~68 megawatts i~ the theoretical energy required for the partial oxidation of methane at a flow rate of 8,898 SC~/hour with off-gas at a flow rate of 31,100 SC~/hour, at an average temperature of approximately 1000C, for producing a reducing-gas mixture of CO and H2 at a flow rate of 57,700 ~C~/hour ~he assumed 80% efficiency is for the conversion of electrical energy to heat energy in the arc reformer. It is a reasonable value for such conversion, but could be either higher or lower depending on the design of the unit. Assuming such an efficiency (80%) means that a one megawatt arc reformer unit can proce~s:-CH4 5610 SC~/hour Off-gas mixture (CO, CO29 H2, H20) 19650 SC~/hour ~otal gases en-tering reformer 25260 S~/hour (gas input) ~his will produce enough CO/H2 mixture to produce metsllic iron at the rate of 0~632 short ton~/hour.
The above calculations have not taken into account the burning of off-gas or the u~e of waste heat for preheating the gases entering the re:Eormer. ~or example, there i~ more than enough exce~s off-gas to allow preheating to 400C ~his would result in reducing the theoretical energy required for -the pro-duction of enough reducing gas for the production of one short ton of iron from 1.268 to 1.033 megawatts In addition, the example should not be taken as the only way in ~lrhich either the reforming reaction itself or the overall reduction plus reforming operation can be run. It should be take~
~0 only a~ a representation of the materials balance that would pre-vail in thi~ particular overall process Dnd as an indication of the energy requirements of the reformingr process itself. It i3 --17~
16~59~65 not inteMded as an optir,lization for the overall reduction plus reforming operation; other factors such as the temperature of operation of the reduction tower need to be considered in such an optimi~ation.
~he reforming of methane (CH4) or other hydrocarbons i~ oP considerable importance, particularly in the metallurgical world. It is the partial oxidation of the hydroc~rbon to pro-I duce a reducing gas consisting of carbon monoxide (C0~ and hydrogen (H2) using oxygen (2) or an oxygen-containing gas suc~
a~ carbon dioxide (C02) or water vapor (H20). Using methane as an example of a hydrocarbon, the reaction may be schematized by the following equation, the symbol "0" representing the oxidi.zing ~ ga~:
¦ CH4 -~ "0" C0 ~ 2H2 (I) i~ "0" ie 2~ the general equation then becomes:
CH4 ~ 1/202 ~ C0 * 2H2 (2) and: CII~ ~ H20 > C0 ~ 3H2 (3) if "0" i~ I~20, and:
CM4 ~ C02 > 2C0 ~ 2H2 (4) if "0" is ~2 Reactions (3) and (~) are of ~ery great intere~t metal-lurgically because they enable the off-gases from an integrated ore reduction ~rocc.~3 to be u~ed as the oxidi~ing ga3 for the reformirg process; in the Midrex proce3c~S for cxamplc, gaseous mixture3 of C0~ and II20 arc produccd when iron oxidc i9 reduced lOS9065 to metallic iron by a reducing-gas consis-ting essentially of C0 and H2. Bo-th reaction~ (3) and (4) are endothermic and both are favoured by high temperature.
The usual reforming process is to pass the gaseous reactants over a heated metallic catalyst, such a~ iron or nickel.
The presence of a catalyst i~ preferred ~ince it improves the reaction kinetic~ hen using H20 and/or C02 a~ oxidi~ing gas, high temperatures are also required to move the equilibrium gas compo~ition to the right in equations (3) and/or (4) and to provide heat for the endothermic reactions, In the particular case of methane, at temperatures below about 610C for reaction (3) and 640C for reaction (4), the back reactions are more important than the forward reactions and the amount of C0 and H2 produced will be very small. These temperatures are lower for higher hydrocarbons, for instance 460 and 410C respectively in the case of n-octane, C8H18~ At higher temperatures, however, the forward reactions become increasingly important and, at about 1000 ~ for methane, proceed substantially to completion (lower temperature~ for higher hydrocarbons) ~he reaction kinetics at this temperature, however, are unfavorable, and to achieve complete reaction very long residence times of the order of several minutes must be used or the reaction must be carried out in the presence of a catalyst. ~he use of a catalyst reduces the reaction times to a few seconds, approximately two ~econds.
The alternative of utilizing higher temperatures to speed up the reaction is economically unattractive.
When use is made, on the other hand, of molecular oxygen as main oxidizing gas, the external supply of heat is not re~uired for the reaction since it is known that equation (2) must be vierled as rather breaking down into the following three equations:
` l~S~t;5 " , .
!.
4CH4 ~ 20 ~ C2 + 2H20 ~ 3CH4 (5) 4 ~ ~2 ~ -- > 2CO -~ 2H2 (6) 2CH4 ~ 2H20 > 2~0 ~ 6H2 (7) i.e., a first reaction stage which is exothermic and i9 represented by equation (5), and a second reaction stage which i9 endothermic and corresponds to equations (6) and (7), both reaction stage~ occurring without interruption and extending directly from the first into the seco-nd It therefore suffice~
to trigger the combustion o~ the hydrocarbon in the presence of oxygen to produce, owing to the exothermic reaction (5), a very hot gaseous mlxture of C02~ H20 and unreacted ~I4 and to allow the reaction of these hot gases to proceed to completion accord-ing to equations (6) and (7) by adequate exposure to the necessary heat for the endothermic reaction stage, ~hich heat may be thus supplied directly from the exotherrnic reaction stage (U.S patent No. 3,536,455 of October 27, 1970 to ~ogdandy et al).
~his technique involves long residence times since the hot gases must be passed through a latticework of a refractory heat-storage material maintained at temperatures in excess o~ 1100~ so that both reactions (6) and (7) proceed to completion. In any ca~e, molecular oxygen is necessary in order to provide a fir~t reaction which in exothermic, liberating heat for the secondary endothermic reactions.
It has also been proposed, in U.S, patent No 3,620,699 of November 16, 1971 to Reynolds et al, to control the temperature of combustio-n of a hydrocarbonaceous liquid in the presence of substantially pure oxygen to a lower limit of approximately 1100~, by feeding a tempera-ture-moderating gas to the combu~tion zone, thereby enabling both reactions (6) and (7) to proceed to completion. This moderator consists of a gas mixture which-may be either a portion of cooled reducing gas from the combustion 1~59(~65 zone~ a portion of cooled and cleaned of~`-gas from an integrated ore reduction process, or a ~ixture of both of said cooled gases.
~he Co2 and II20 contained in such off-gas serves in this case to chemically cool the reaction temperature, in addition to contributing to a small extent to the produc-tion of the desired end products, in accordance with the endothermic reactions (6) and (7) No catalyst is needed as the temperatures and pressures utilized are high enough to speed up the reaction; no residence or reaction times, however, are mentioned in the patent.
It must be pointed out, in connection with catalytic reformers, that these suffer from an important disadvantage, namely that slight contamination by certain elements such as sulfur resul-ts in the poisoning of the catalyst. ~his means that both the hydrocarbon and oxidizing gas must be free from such elements. This ~everely limits the availability of both; in other words, it is more difficult to use cheaper materials such as waste oil a~ h~drocarbon or offDga~ from ore reduction processes as oxidizing gas, since these would require purification before use.
It is therefore an object of the present invention to provide a process for the production of reducing gas mixtures of carbon monoxide and hydrogen, which does not neces~itatethorough pre-cleaning or pre-purification of the starting materials. In accordance ~ith the invention, off-gas from an integrated ore reduction process may be used as main oxidi~ing gas, without detriment to the reaction.
It is a further object of the invention to provide a proce~s for the reforming of hydrocarbons u-tilizing an oxygen~
containing Oas and to reduce reaction times beyond those obtained with a catalyst.
It is yet another objec-t of the invention to provide 1~9~65 a simple and e~ficient way of producing a reducing gas which may be utilized directly for the reduction of metal ores.
These objects are accomplished, according to -the invention, by the decomposition in the presence o~ an electric arc of a portion of the reactants into reactive species, followed - by the reaction of these species with each other and v~th the remaining portion of the reactantsO ~he reaction time is almost instantaneous since at least part of the reactant3 are in the active form.
In accordance with the present invention, there i9 thus provided a process for the production of reduci-ng ga~
mixtures o~ carbon monoxide and hydrogen by the partial oxidation of at least one hydrocarbon with an oxygen-containing gas or a mixture of oxygen-containing gases, in stoichiometric ratios The process of the invention comprise3 selecting a preaetermined equilibrium temperature, forming an arc pla~ma by striking an arc in a portion of the reactants in gaseous phase, reacting the remaining portion of reactants with the arc plasma to obtain a gaseous reaction mixture having an average temperature at least equal to the predetermined equilibrium temperature but lower than the temperature of the pla3ma and alloY~ing the reaction ~ixture to reach homogeneity at the said average temperature.
~pplicants have found quite unexpectedly that when a gas is decomposed into reactive species at very high temperatures (5000-8000C), as in an arc-plasma generator, and additional gases are introduced into the arc plasma ~ormed9 some of the molecules introduced will also reach a very high temperature and undergo decomposition and, as the very hot gas mixes with the cooler gases, thQ reactive fragment~ in the plasma and those subsequently formed react with each other and with undecomposed molecules to yield, provided the ga3eou3 mixture i~ allowed to reach ho~ogeneity at the average temperature attained, a gas `` 1059~65 , having th.e e~uilibrium composition at -that -temperature. It i9 not necessary -to raise the temperature of all the gases additionally introduced to the very high of the plasma. It suffices to attain an average temperature that is at least equal to -the temperature of the desired chemical eqv.ilibrium. In a prèferred embodiment, however, for practical purposes only, the energy supplied ~ill be such to raise the reacting gases to an average temperature that i~ substantially equal to the pre-determined equilibrium temperature and to carry out the reaction at that temperature.
Plasms techniques are known ana have been employed to create phy~ical or chemical changes in material~, at very high temperatures ~or instance, the direct reduction of metal oxide to metal i~ reported in U.S patent ~o 3,765,870 of October 16, 1973 to ~ey M,G et al ~he metal oxide entrained by a carrier gas is subjected to the intense heat of an arc plasma formed from a hydrocarbon gas which is raised to an extremely high temperature sufficient to free hydrocarbon radical ion3 It i~
understood, however, that the chemical reduction occuring in the metal oxide ore i9 promoted by the very high temperature of the arc plasma and that the reducing hydrocarbon radi.cal ion~ only assist in ~eparating the metal from the metal oxide ore It i~
al~o kno~n to directly contact a fluidized bed of par-ticles with sn arc plasma for exposing materials to very high temperatures In U S patent No 3,404,078 of October 19t, 1968 to William M
Goldberger, for example, a bed of electrically conductive fluidized particles is employed a~ an integral electrical par~ of the plasma generator so that no energy losge9 occur between the heating zone of the apparatus and the fluidized bed~ ~he bed ~0 particle 9 in the immediate region of the pla~ma can th~ls undergo the desired physical or chemical changes5 alternatively, reactants can be introdvced irl t~e hea-ting z~ne .Yuch that the resulti.ng ~059065 heated products are passed into the fluidezed bed for efficient cooling thereof at lower temperatures. In any case, arc plasmas have been u~ed hitherto mainly as heat sources to promote chemical reactions, and have not been utilized to entirely participate in a reactive manner, at temperatures much lower than the very high temperature of the plasma, to the production of the de~ired end substances.
When gases are reacted in plasma generators, otherwise known a~ arc heaters, these ~hould po~sess arc stability and good mixing characteristics in order to obtain optimum results.
Spurious arc extinctions can be eliminated by providing a short interelectrode gap which generally create~ a stable arc Also, on the commercial scale, the arc should not be argon-stabilized, since separation of argon from the product gases would be an undeeirable ~tep in the proce~s. Good mixing can be obtained by injecting the reacting gases at high velocity and/or by intro-ducing the remaining portion of reactants tangentially into the plasma ~or causing a turbulent mixing thereof v~ith the plasma.
In addition, the plasma may be magnetically rotated at high ~peed by mean9 of a 9ufficiently ~trong magnetic ~ield, thereby enhancing turbulent mixing of the reactants. ~he gaseou~ reaction mixture which i9 thu~ obtained by mixing the plasma ~ormed from a portion of the reactants with the remaining portion o~ reactants is then allowed to reach homogeneity in a reaction zone which directly communicates with the plasma zone and i~ preferably an e~ten~ion thereof.
Accordingly, in a further preferred embodiment of the invention, the reforming process i9 carried out in a stabilized arc heater having a plasma zone and a reaction zone in direct communication with the plasma zone, and comprises the steps of selecting a predetermi~ed equilibrium -temperature, striking ~OS9~65 an electric arc in a gap between electrodes while injecting a portion of the reactallts in ga3eous pha~e through the gap -to form in the plasma zone an arc plasma flowing into the reaction zone, and mixing the remaining portion of reactant~ with the arc plasma to obtain, in the reaction zone~ a gaseous reaction mixture having an average temperature substantially e~ual to the pre-determined equilibrium temperature, the reactants being supplied -in stoichiometric ratios a-nd the gaseous reaction mixture reach-ing homogeneity in the reaction zone at the said average tempera-ture.
In accordance with another preferred embodiment, the portion of reactants which serves to form the arc plasma consists essentially of the hydrocarbon component and the remaining portion of reactants lrhich i9 mi~ed with the arc plasma consists of the other reacting component, that is the oxygen-containing ga3 or mixture of oxygen-containing gases The reverse, of course, is also contemplated and con3titutes a further preferred embodiment of the invention.
According to yet another preferred embodiment of the invention, both portions are respectively fractions of the sum total of reactants premixed together.
~he remaining portion of reactants can be introduced into the arc plasma in a variety of way3~ The remaining portion can be fed, for instance,upstream of the plasma zone so as to directly impinge on the arc plasma as the latter i3 formed or it can be fed douinstream of the plasma zone but before the reaction zone~ The combination of both po3sibilities i9, of course, also contemplated and, in such an instance, the remaining portion of reactants will be suitably divided between upstream and down-stream inlets. Xowever, where the remaining portion of reactants consists of off-gases which are not thoroughly cleanea, as the oxidizing gas component, it is preferable to feed all or mo~t 105~65 .
do~qnstream o~ the plasma zone 30 as -to avoid unnecessary errosion o~ the electrodesl A~ mentioned previously, reactions (3) and-(4) are of great interest me-tallurgically because they enable the of~-gas from certain reduction processes to be used as the oxidizing gas component for the reforming process. Depending on the metallur-~gical process, the of~~gas mi~l~ be any of the following: sub-stantially pure C02; ~2 with unreacted C0; substantially pure H20 vapour; H20 with unreacted H2; mixtures of C02 and lI20;
mixtures of C02, C0, H20 and H2 It is understood, of course, that C02 and H20 are the reacting oxygen-containing gases and that at least one of these must always be present.
It was also mentioned that, in a preferred embodiment of the invention, the amount of electrical energy supplied is such to raise the tempera-ture of all the gases to substantially the predetermined equilibrium temperature and to carry out the reaction in this quantity of gas at that temperature. ~or the partial oxidation of ~H4 with H20 and/or C02, an e~uilibrium temperature of approximatively 1000C is adequate. At this temperature~ as already discus~ed, equilibrium is well over to the right in equations (3) and (4) with very little CII4, ~2 or H20 remainingr This temperature is not only suitable for methane but also for higher hydrocarbons since, for higher hyd~ocarbons, the free energies of formation substantially favor the reaction at temperatures lo~ler than 1000C. It must be understood, how-ever, that the approximate temperature o~ 1000~ does not con-stitute a limitation and tha-t any e~uilibrium temperature can be selected provided that equil~briRm i5 shifted9 a-t the pre-determi-ned temperatureS to the right in equations (3) and/or (4) An average temperature that is substantially cqual to the predetermined temperatllre is obtained by n~a-tching the e~ct~oe energy input to the gas input, i.e., supplying electrical energy lOS9C1 65 in an amount that is equal to the amount of energy required to raise the temperature of all the gases to -the de~ired equilibrium temperature and that required for the overall chemical reactions at that te-mperature. '~here the o~ygen-containing gas in H20, the energy requirement in the case of methane (reaction (3)) can ~e calculated by means of the followqng formula:
~3 = ~Hco _ ~ XcH ~ ~H o + T(hC0 ~ 3hH ) (8) wherein: ~Hco - heat of formation of CG at room temperature ~HCH = heat of formation of CH4 at room temperature ~HH20 = heat of formation of H20 at room temperature hCo = molar heat capacity of C0 h~I = molar heat capacity of ~2 = predetermined equilibrium temperature minus roo~ temperature It is understood that the unit~ chosen for calculation are self-consistent. If the oxygen-^ontaining gas i9 C02 (reaction (4)), the energy requirement can be similarly calculated by the formula:
4 C0 ~ CH4 ~HC02 ~ 2~(hC0 ~~ hH2) (9) wherein ~Hco = heat of formation of C02 at room temperature.
~he reforming process according to the invention can be applied, of course, to any hydrocarbon which may be designed by the general formula CmHn and includes saturated and unsaturated (olefinic as well as acetylenic) aliphatic and cyclic hydro-carbons as well as aromatic hydrocarbons A mixture of H20 and C2 can also be utilized as oxidizing gas~ In such sn instance 9 the above two equations (8) and (9) can be made general and combined together. In addition, i~ the reacting gases contain other gases, such as C0 and H2, which do no-t participate in the reaction, a term or terms must be inclu~ed to account for the energy required to heat such gas or gases to the predetermined 10~9~65 e,quilibrium temperature. ~husg a general reac-tion equation can be written:
(a ~ b)C,mEIn ~ amC02 ~ bmH2 (2am ~ bm)C0 + (bm ~ an ~ bn)H2 ~ xX + yY ~ ,,, (10) , 2 2 ~herein: xX + yY + ,., represents the presence, if any, of non-participating gase~ X and Y in their re-spective molar quantities x and y;
a is the molar quantity o~ C02 ;
b is the molar quantity of H20 ;
m is the number of carbon atom~ in the hydrocarbon processed; and n i~ the number of hydrogen atoms in -the hydrocarbon.
~he energy requirement for reaction (10) i~ then given by the formula: ' E - (2am ~- bm) ~Hco ~ (bm + a2 + b2n) ~HH2 (a ~ CmHn am QHco2 ~ bm ~HH20 + ~ [(2am ~ ~m) hco + (bm + an + bn)hH +
xhX ~ yh,y ~ ~,] (11) ~herein : ~HC ~ the heat of formation of the hydrocarbon ' CmHn ~t room temperature; ~nd h~ and ~ are the respective molar heat capacities of the non-participating gases X and Y.
~his is the amount of energy required to process a certain volume of ga~ made up of the molecular ratios a3 shown in equation (10).
Any self-consistent units can be chosen for the calculationr ~or example, i~ K,cals./g.mole and C are selected, the energy is in K,cal~, and the volume of input gas, in liters, i 9:
V~ = 22.4-(a ~ b ~ am ~ bm ~ x ~ y ~,,,) (12) at stalldard temperature and pressure. Changing this into units that are more relevant i-n the present context requires multiplying the energy in g~ca]s. by 1.163 ~ 10 3 to obtain kilowatt hours (K~) and the ~olume in liter~ by 3.531 x 10 2 to ob-tain standard cubic fee-t (SC~) ~hese values are -then used in the final calculation of the electrical energy input per unit time, e.g.
kilowatts (KW), for the desired g~s input per unit time, e.g.
SC~/hour, In the final calculation, heat losse~ must also be considered9 but they will be specific to the equipment used.
The reforming process according to the i~vention is normally carried out at atmospheric pressureO The input ~ gas ratios must also be ajusted so that the stoichiometry of the reaction (or reactions, where more than one hydrocar-bon and/or more than one oxidizing gas is processed) is main-tainedO ~or example, in reaction (3), one mole of water must be supplied for each mole of methaneO
Since generally at least part of the reacting gases are introduced at high velocity, the portion of reactants which serves to form~h~ arc plasma being normally injected at approximately sonic speed, and part of the reactants are in the active form (plasma state), the process of the invention permits to achieve reaction times of the order of 10 1 seconds, or even less, the precise time depending on the equipment usedO This is in contrast to the very much l~nger residence times necessary in catalytic or other reXormers~
An arc reformer also has the added advantage of having very much smaller dimensions than other reformersO Since the arc reformer is not influenced by sulphur or many other impurities with respect to the partial oxidation of hydrocarbons to produce C0 + H2 ~ it is not necessery to have materials in a refined or completely dust-free form. Accordingly, gas from destructive distillation of waste organic matter, lignite, coal, etc. , after condensation of exce~s water, can be prones-sed according to the invention to produce a reducing gasO
~059~365 With suitable solid feeding arrangements, carbon or solid carbonceous material can also be processed. Another advantage is that the invention permits the use o~ ore reduction off-gas which need not be rigorously cleaned o~ sulphur or other con-taminants that would otherwise be detrimental to catalytic reformers.
Preferred embodiments of the cubject invention v~ll now be described in greater detail, with reference to the appended drawings, wherein:
~igure 1 schematically represent~ in cross-section an arc heater adapted for carrying a reforming process according to the invention, and ~ igure 2 is a block-diagram of a reforming process according to the invention integrated wi~h an ore reduction process, showing heat and materials balances.
Re~erring first to ~igo 1, the arc reformer 10 is seen to include a pair of generally cylindrica:l electrodes 12 and 14 which are coaxially disposed on a common axis 16 and spaced by a narrow annular gap 18. Electric field breakdown in the inter-electrode gap initiates an arc discharge 20 at each current zeroof an alternating current backup source o~` power~ whereupon the arc is immediately blo~n into the interior of the apparatus by the force of a gas 22 injected at approximately sonic speed through the narrow gap 18. The gas 22 comprises a portion of the reactants for producing H2 + C0 and serves to generate in the plasma zone 24 an arc plasma upon decomposition of the gas into reactive species by the intense heat deveLoped by the arc 22.
~he a~c plasma formed is represented by a plurality of broken lines 26 and has a direction of flow towards the reac-tion zone 28 which commlunicates with the pla sma æone 2~ and i~ an extension thereof. The arc discharge 20 and the arc plasma 26 are magnetic-ally rotated at extremely high velocities (in the order of 1000 1059~65 rev./sec )~ by interac-tion with a D C magnetic fieïd arisi-ng from solenoid field coils 30 located within each electrode assembly.
The remaining portion of reactants is divided in t~o fractions 32 and 36~ one fraction 32 being fed through inlet 34 upstream of the plasma zone 24 and the other fraction 36 through inlets 38 and 40 dovrnstream of the plasma zone. Inlet 34 opens axially into the apparatus so that the feed introduced -there-through directly impinges on the arc plasma 26 as the latter is formed, while inlets 38 and 40 open radially for injection into the plasma flow. ~angential inle-ts as well as a single annular inlet are, of cour~e, also contemplated for mixing fraction 36 with the arc plasma formed, downstream of the plasma region.
Where the off-gas of an integrated ore reduction process i9 utilized as the oxidizing-gas component, as will be discussed later in connection with ~igure 2, it is most suitable to feed the totality thereof through inlets 34, 38 and 40 and feed all the hydrocarbon component through the arc, that is to say through the interelectrode ga~ 18. In addition, as already pointed out, should the off-gas be not thoroughly cleaned,it i9 most advantageous to feed all downstream of the plasma zone, in order to avoid unnecessary errosion of the electrodes 12 and 14.
In such an instance, inlets 38 and 40 will be the only prevailing inlets for introducing the off-gas.
In any case, the cooler gases introduced at 34~ 3~ and 40 encounter the very hot fragmented gas 26 under turbulent motion and mix and react with it in the reaction zone 28. ~he amount of energy transferred to the gas 22 and then carried by the plasma 26 i9 sufIicient to raise the -temperature of the other gases 32 and 36 and to supply energy for the endothermic oxidation reactions, resulting in an average temperature, in the reaction zone, that i~ substantially equal to the temperature ~14-lOS9al65 of the desired chemical equilibrium. As homogeneity i9 attained in the reaction zone, es~entially complete conversion is achieved with residence times in the order of lO 1 second~, and the effluent gas 42 comprise~ a mixture of C0 + H2 at equilibrium composition.
A suitable plasma generator for the reforming process of the inventlon is the Marc 31 generator made by Westinghouse Electric Corp , of Pittsburg, Penn~ylvania. ~his generator i9 a self-stabilized A.C arc heater provided with an interelectrode gap of approximately 0.04 inche 9 . ~he electrodes are tubular shaped copper electrode~ having each 5 inches inside diameter by 10 inches long, giving the heater an in-ternal volume of about 0.25 sq.ft. ~uch apparatus, however, must be provided at its outlet with a tube defining the reaction zone 28 in order to per-mit good mixing and attainement of homogeneity ~his reactor tube will advantageou~ly con~titute an extension of the outlet, and thus extend several feet from the outlet and be of the same internal diameter as the latter. Suitable inlet means for mixing and reacting the remaining portion of reactants with the arc plasma must, of course, al~o be provided.
An example of the w8y in which the reforming proce~ of the invention can be integrated with an ore reduction proce~s i9 shown-in ~igure 2. It i9 shown used in conjunctian with a Midrex type reduction shaft. In such a process, a reducing gas consisting essentially of C0 and H2 is introduced into a vertical shaft at 750-850C countercurrent to iron oxide in lump or pellet form. ~he reactions in the shaft produce metallic iron and a ga~ richer in C02 and H20O Part of this gas, after removing some of the water9 is used for the partial oxidation of additional CH4 to C0 and H2. ~igure 2 shows one way in which the overall proce~s can be run, utilizing an arc reformer in accordànce 1059~65 with the invention I-t includes the op~ion of pre-heating the gas mixture prior to reforming, u~ing part of the exce~s off-gas as fuel.
The process going on in the arc reformer can be ~ummarized by the following equation:
1.692CH4 + 0.769C02 +0.923H20 ~1.54CO + 2.69H2 > 4CO + 7H2 (13) This is a particular example of equation (10), with CO and H2 on the left hand side of the equation going into the arc reformer as non-participating gases Equation (11) can therefore be used to calculate the energy requirement. Selecting 1000C as the pre-determined equilibrium temperature for the reaction, and taking into account that the re~action described by equation (13) results in sufficient CO and H2 to produce 2.44 atomic weights of ~e, the following materials and energy requirements are obtained for the reduction process in ~igure 2.
CH4 required = 0.693 mols CH4/atom ~e = 8898 SC~ CH4/short ton ~e ~nergy required - 73 K.cals/atom ~e = 1268 K~/short ton ~e Putting this into more practical terms:-To produce iron at the xate of l short ton per hour CH4 required - 8898 SCF/hour Off-gas mixture: CO 8080 SCF/hour C2 4040 SC~/hour H2 14130 SC~/hour H20 4-850 SC~/hour TOTA~ 31100 SC~/hour 31100 SC~/hour Total gases entering reformer: 39998 SC~/hour (~.e. gas input) Re~ulting gases: CO 21000 SC~/hour H2 36700 SC~/hour 57700 SC~/hour 57700 SCI'/hour 1059~65 Erlergy requircd:
Theore tical (100~o efficiency) 1.268 megawatts Assuming 807~ efficiency 1.585 megawatts In other words, 1.~68 megawatts i~ the theoretical energy required for the partial oxidation of methane at a flow rate of 8,898 SC~/hour with off-gas at a flow rate of 31,100 SC~/hour, at an average temperature of approximately 1000C, for producing a reducing-gas mixture of CO and H2 at a flow rate of 57,700 ~C~/hour ~he assumed 80% efficiency is for the conversion of electrical energy to heat energy in the arc reformer. It is a reasonable value for such conversion, but could be either higher or lower depending on the design of the unit. Assuming such an efficiency (80%) means that a one megawatt arc reformer unit can proce~s:-CH4 5610 SC~/hour Off-gas mixture (CO, CO29 H2, H20) 19650 SC~/hour ~otal gases en-tering reformer 25260 S~/hour (gas input) ~his will produce enough CO/H2 mixture to produce metsllic iron at the rate of 0~632 short ton~/hour.
The above calculations have not taken into account the burning of off-gas or the u~e of waste heat for preheating the gases entering the re:Eormer. ~or example, there i~ more than enough exce~s off-gas to allow preheating to 400C ~his would result in reducing the theoretical energy required for -the pro-duction of enough reducing gas for the production of one short ton of iron from 1.268 to 1.033 megawatts In addition, the example should not be taken as the only way in ~lrhich either the reforming reaction itself or the overall reduction plus reforming operation can be run. It should be take~
~0 only a~ a representation of the materials balance that would pre-vail in thi~ particular overall process Dnd as an indication of the energy requirements of the reformingr process itself. It i3 --17~
16~59~65 not inteMded as an optir,lization for the overall reduction plus reforming operation; other factors such as the temperature of operation of the reduction tower need to be considered in such an optimi~ation.
Claims (24)
1. A process for the production of reducing-gas mix-tures of carbon monoxide and hydrogen by the partial oxidation of at least one hydrocarbon with an oxygen-containing gas or a mixture of oxygen-containing gases, in stoichiometric ratios, which comprises selecting a predetermined equilibrium temperature, forming an arc plasma by striking an arc in a portion of the reactants in gaseous phase, reacting the remaining portion of reactants with said are plasma to obtain a gaseous reaction mixture having an average temperature at least equal to the predetermined equilibrium temperature but lower than the tem-perature of the plasma and allowing said reaction mixture to reach homogeneity at said average temperature.
2. Process according to claim 1, wherein said average temperature is substantially equal to said predetermined equi-librium temperature.
3. Process according to claim 1, wherein said portion of reactants in gaseous phase consists essentially of the hydro-carbon and said remaining portion of reactants consists essen-tially of the oxygen-containing gas or mixture of oxygen-containing gases.
4. Process according to claim 3, wherein said remain-ing portion of reactants consists of an ore reduction off-gas.
5. Process according to claim 4, wherein said ore reduction off-gas is selected from the group comprising sub-stantially pure CO2, CO2 with unreacted CO, substantially pure H2O vapour, H2O with unreacted CO, mixtures of CO2 and H2O and mixtures of CO2, CO, H2O and H2.
6. Process according to claim 4, wherein said hydro-carbon is methane and said ore reduction off gas comprises CO2, CO, H2O and H2.
7. A process for the production of reducing-gas mixtures of carbon monoxide and hydrogen by the partial oxida-tion of at least one hydrocarbon with an oxygen-containing gas or a mixture of oxygen-containing gases, in a stabilized arc heater having a plasma zone and a reaction zone in direct communication with said plasma zone, which comprises the steps of selecting a predetermined equilibrium temperature, striking an electric arc in a gap between electrodes while injecting a portion of the reactants in gaseous phase through said gap to form in said plasma zone an arc plasma flowing into said reac-tion zone, and mixing the remaining portion of reactants with said arc plasma to obtain, in said reaction zone, a gaseous reaction mixture having an average temperature substantially equal to said predetermined equilibrium temperature, the reac-tants being supplied in stoichiometric ratios and the gaseous reaction mixture reaching homogeneity in said reaction zone at said average temperature.
8. Process according to claim 7, wherein said portion of reactants in gaseous phase is injected at high speed through said gap to impart turbulent flow to said arc plasma, and said remaining portion of reactants is injected in said arc plasma flow.
9. Process according to claim 7, wherein said re-maining portion of reactants is fed upstream of said plasma zone to directly impinge on said arc plasma as said arc plasma is formed.
10. Process according to claim 7, wherein said remaining portion of reactants is fed downstream of said plasma zone but before said reaction zone to mix with said arc plasma once formed.
11. Process according to claim 7, wherein said remaining portion is divided into two fractions, one fraction being fed upstream of said plasma zone to directly impinge on said arc plasma as said arc plasma is formed and the other fraction being fed downstream of said plasma zone but before said reaction zone to mix with said arc plasma once formed.
12. Process according to claim 7, wherein said portion of reactants injected through said gap consists essen-tially of the hydrocarbon and said remaining portion of reac-tants consists essentially of the oxygen-containing gas or mixture of oxygen-containing gases.
13. Process according to claim 12, wherein said remaining portions of reactants consists of an ore reduction off-gas.
14. Process according to claim 13, wherein said ore reduction off-gas is selected from the group comprising substantially pure CO2, CO2 with unreacted CO, substantially pure H2O vapour, H2O with unreacted CO, mixtures of CO2 and H2O and mixtures of CO2, CO, H2O and H2.
15. Process according to claim 13, wherein said hydrocarbon is methane and said ore reduction off-gas comprises CO2, CO, H2O and H2.
16. Process according to claim 15, wherein said off-gas is fed downstream of said plasma zone but before said reaction zone to mix with the arc plasma once formed.
17. Process according to claims 2 or 7, wherein said predetermined equilibrium temperature is 1000 °C.
18. Process according to claims 1 or 7, wherein said arc plasma is magnetically rotated at high speed by interaction with a magnetic field, and said remaining portion of reactants is injected into the arc plasma in turbulent motion.
19. Process according to claims 1 or 7, wherein both portions are respectively fractions of the sum total of reac-tants premixed together.
20. Process according to claims 1 or 7, wherein the hydrocarbon is selected from the group comprising saturated and unsaturated aliphatic and cyclic hydrocarbons, aromatic hydro-carbons and mixtures thereof.
21. Process according to claims 1 or 7, wherein the oxygen-containing gas is H2O or CO2.
22. Process according to claims 1 or 7, wherein the mixture of oxygen-containing gases comprises H2O and CO2.
23. Process according to claims 1 or 7, wherein the hydrocarbon is supplied from destructive distillation of carbonaceous materials selected from the group comprising waste organic matter, sawdust, garbage, lignite and coal.
24. Process according to claim 7, wherein said reac-tion zone is an extension of said plasma zone.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA242,081A CA1059065A (en) | 1975-12-12 | 1975-12-12 | Arc reforming of hydrocarbons |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA242,081A CA1059065A (en) | 1975-12-12 | 1975-12-12 | Arc reforming of hydrocarbons |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1059065A true CA1059065A (en) | 1979-07-24 |
Family
ID=4104778
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA242,081A Expired CA1059065A (en) | 1975-12-12 | 1975-12-12 | Arc reforming of hydrocarbons |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1059065A (en) |
Cited By (19)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0157758A2 (en) * | 1984-04-02 | 1985-10-09 | VOEST-ALPINE INDUSTRIEANLAGENBAU GESELLSCHAFT m.b.H. | Method for producing synthetic gases, in particular reduction gases, and device for carrying out the method |
| FR2565992A1 (en) * | 1984-06-14 | 1985-12-20 | Skf Steel Eng Ab | PROCESS AND PLANT FOR PARTIAL COMBUSTION AND GASIFICATION OF CARBONACEOUS MATERIALS, USING A PLASMA GENERATOR |
| US4588850A (en) * | 1983-08-26 | 1986-05-13 | Huels Aktiengesellschaft | Process for the production of acetylene and synthesis or reduction gas from coal in an electric arc process |
| FR2578263A1 (en) * | 1985-03-01 | 1986-09-05 | Skf Steel Eng Ab | Process and device for the gasification of fossil fuels and the reforming of a gaseous fuel |
| EP0292391A1 (en) * | 1987-05-22 | 1988-11-23 | Electricite De France | Hydrocracking process of a hydrocarbon feed, and apparatus for carrying out this process |
| FR2622893A1 (en) * | 1987-11-06 | 1989-05-12 | Bp France | Process for conversion of heavy or not readily fusible hydrocarbons and residues into branched, light liquid hydrocarbons of low melting point with the aid of CO + xH2 gas mixtures made reactive by energy shock |
| FR2689116A1 (en) * | 1992-03-25 | 1993-10-01 | Schwob Yvan | Prepn. of synthesis gas - by an auto-thermal reaction between methane water vapour and carbon di:oxide in a plasma gas |
| WO1995017021A1 (en) * | 1993-07-09 | 1995-06-22 | Massachusetts Institute Of Technology | Plasmatron-fuel cell system for generating electricity |
| WO1999011572A1 (en) * | 1997-09-01 | 1999-03-11 | Laxarco Holding Limited | Electrically assisted partial oxidation of light hydrocarbons by oxygen |
| FR2768424A1 (en) * | 1997-09-01 | 1999-03-19 | Albin Czernichowski | ELECTRICAL ASSISTANCE FOR PARTIAL OXIDATION OF LIGHT HYDROCARBONS BY OXYGEN |
| US7417385B2 (en) | 2000-11-27 | 2008-08-26 | Ceramatec, Inc. | Systems and method for ignition and reignition of unstable electrical discharges |
| US8350190B2 (en) | 2007-02-23 | 2013-01-08 | Ceramatec, Inc. | Ceramic electrode for gliding electric arc |
| US8618436B2 (en) | 2006-07-14 | 2013-12-31 | Ceramatec, Inc. | Apparatus and method of oxidation utilizing a gliding electric arc |
| US8826834B2 (en) | 2006-07-14 | 2014-09-09 | Ceramatec, Inc. | Apparatus and method of electric arc incineration |
| DE102015218098A1 (en) * | 2015-09-21 | 2017-03-23 | Deutsche Lufthansa Ag | Process for the thermal decomposition of hydrocarbons and corresponding device |
| DE102015218514A1 (en) | 2015-09-25 | 2017-03-30 | Deutsche Lufthansa Ag | Reactor for thermal cracking of hydrocarbons and corresponding process |
| ES2639664A1 (en) * | 2016-04-27 | 2017-10-27 | Blueplasma Power, S.L. | Procedure for the partial oxidation of fuels, device for applying such procedure and gas obtained with such procedure (Machine-translation by Google Translate, not legally binding) |
| WO2020223789A1 (en) * | 2019-05-09 | 2020-11-12 | Pyrogenesis Canada Inc. | Production of syngas using recycled co2 via combined dry and steam reforming of methane |
| CN112689610A (en) * | 2018-08-28 | 2021-04-20 | 欧洲等离子公司 | By treating the gas containing CO2And a gas stream of one or more hydrocarbons to produce synthesis gas |
-
1975
- 1975-12-12 CA CA242,081A patent/CA1059065A/en not_active Expired
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4588850A (en) * | 1983-08-26 | 1986-05-13 | Huels Aktiengesellschaft | Process for the production of acetylene and synthesis or reduction gas from coal in an electric arc process |
| EP0157758A2 (en) * | 1984-04-02 | 1985-10-09 | VOEST-ALPINE INDUSTRIEANLAGENBAU GESELLSCHAFT m.b.H. | Method for producing synthetic gases, in particular reduction gases, and device for carrying out the method |
| EP0157758A3 (en) * | 1984-04-02 | 1986-10-29 | Voest-Alpine Aktiengesellschaft | Method for producing synthetic gases, in particular reduction gases, and device for carrying out the method |
| FR2565992A1 (en) * | 1984-06-14 | 1985-12-20 | Skf Steel Eng Ab | PROCESS AND PLANT FOR PARTIAL COMBUSTION AND GASIFICATION OF CARBONACEOUS MATERIALS, USING A PLASMA GENERATOR |
| FR2578263A1 (en) * | 1985-03-01 | 1986-09-05 | Skf Steel Eng Ab | Process and device for the gasification of fossil fuels and the reforming of a gaseous fuel |
| EP0292391A1 (en) * | 1987-05-22 | 1988-11-23 | Electricite De France | Hydrocracking process of a hydrocarbon feed, and apparatus for carrying out this process |
| FR2615523A1 (en) * | 1987-05-22 | 1988-11-25 | Electricite De France | PROCESS FOR HYDROCRACKING A HYDROCARBON FEEDSTOCK AND HYDROCRACKING INSTALLATION FOR CARRYING OUT SAID METHOD |
| US4941965A (en) * | 1987-05-22 | 1990-07-17 | Electricite De France (Service National) | Process for the hydrocracking of a hydrocarbon feedstock and hydrocracking plant for carrying |
| FR2622893A1 (en) * | 1987-11-06 | 1989-05-12 | Bp France | Process for conversion of heavy or not readily fusible hydrocarbons and residues into branched, light liquid hydrocarbons of low melting point with the aid of CO + xH2 gas mixtures made reactive by energy shock |
| FR2689116A1 (en) * | 1992-03-25 | 1993-10-01 | Schwob Yvan | Prepn. of synthesis gas - by an auto-thermal reaction between methane water vapour and carbon di:oxide in a plasma gas |
| WO1995017021A1 (en) * | 1993-07-09 | 1995-06-22 | Massachusetts Institute Of Technology | Plasmatron-fuel cell system for generating electricity |
| FR2768424A1 (en) * | 1997-09-01 | 1999-03-19 | Albin Czernichowski | ELECTRICAL ASSISTANCE FOR PARTIAL OXIDATION OF LIGHT HYDROCARBONS BY OXYGEN |
| WO1999011572A1 (en) * | 1997-09-01 | 1999-03-11 | Laxarco Holding Limited | Electrically assisted partial oxidation of light hydrocarbons by oxygen |
| US6007742A (en) * | 1997-09-01 | 1999-12-28 | Laxarco Holding Limited | Electrically assisted partial oxidation of light hydrocarbons by oxygen |
| AU740520B2 (en) * | 1997-09-01 | 2001-11-08 | Laxarco Holding Limited | Electrically assisted partial oxidation of light hydrocarbons by oxygen |
| US7417385B2 (en) | 2000-11-27 | 2008-08-26 | Ceramatec, Inc. | Systems and method for ignition and reignition of unstable electrical discharges |
| US8742285B2 (en) | 2006-07-14 | 2014-06-03 | Ceramatec, Inc. | Method of oxidation utilizing a gliding electric arc |
| US8618436B2 (en) | 2006-07-14 | 2013-12-31 | Ceramatec, Inc. | Apparatus and method of oxidation utilizing a gliding electric arc |
| US8826834B2 (en) | 2006-07-14 | 2014-09-09 | Ceramatec, Inc. | Apparatus and method of electric arc incineration |
| US8350190B2 (en) | 2007-02-23 | 2013-01-08 | Ceramatec, Inc. | Ceramic electrode for gliding electric arc |
| DE102015218098A1 (en) * | 2015-09-21 | 2017-03-23 | Deutsche Lufthansa Ag | Process for the thermal decomposition of hydrocarbons and corresponding device |
| DE102015218514A1 (en) | 2015-09-25 | 2017-03-30 | Deutsche Lufthansa Ag | Reactor for thermal cracking of hydrocarbons and corresponding process |
| ES2639664A1 (en) * | 2016-04-27 | 2017-10-27 | Blueplasma Power, S.L. | Procedure for the partial oxidation of fuels, device for applying such procedure and gas obtained with such procedure (Machine-translation by Google Translate, not legally binding) |
| US11013098B2 (en) | 2016-04-27 | 2021-05-18 | Blueplasma Power, S.L. | Process for the partial oxidation of fuels and the device for applying said process |
| CN112689610A (en) * | 2018-08-28 | 2021-04-20 | 欧洲等离子公司 | By treating the gas containing CO2And a gas stream of one or more hydrocarbons to produce synthesis gas |
| CN112689610B (en) * | 2018-08-28 | 2023-11-17 | 欧洲等离子公司 | By treatment of CO-containing 2 And a process for producing synthesis gas from a gas stream of one or more hydrocarbons |
| WO2020223789A1 (en) * | 2019-05-09 | 2020-11-12 | Pyrogenesis Canada Inc. | Production of syngas using recycled co2 via combined dry and steam reforming of methane |
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