US3042507A - Method for cracking and subsequent gasifying of hydrocarbons - Google Patents

Description

July 3, 1962 G. HILGERS 3,042,507

METHOD FOR CRACKING AND SUBSEQUENT GASIFYING OF HYDROCARBONS Filed March 24. 1960 arent 3,042,507. Patented July 3, 1952 hcc 3,042,507 ll/IETHOD FOR CRACKING AND SUBSEQUENT GASIFYING GF HYDRQCARBONS Giovanni Hilgers, Hau, Post Bechen uber Bergisch Gladbach, Germany Filed Mar. 24, 1960, Ser. No. 17,353 Claims priority application Germany Mm. 28, 1959 7 Claims. (Cl. i3-211.5)

This invention is directed to a process of making a fuel gas which is of high caloric value and produces a llame of high luminosity. lt relates to a low temperature process for cracking hydrocarbon oils, and particularly to an improved method of carrying out the cracking in such way that the soot ordinarily forming therein is gasiiied without causing an undesirable rise in temperature in the reaction space of the cracking operation.

When hydrocarbon liquids or oils are cracked, free carbon forms as soot. The free carbon must be eliminated from the gas. When operating continuously with a shaft-type gas generator, on the continuous ilow principle, the free carbon can be eliminated by oxidizing it with a gasifying agent to form CO, or by converting it with steam to COr-l-Hg. The conversion of the solid carbon into gaseous CO passes through the CO2 stage, with a subsequent reduction of CO2 by means of the carbon.

However, the gasication of the soot with the aid of H2O or CO2 is possible only with gas generators in which a very high temperature obtains. At lower temperatures, i.e. at temperatures of about 900 C., the gasilication with the aid of H2O or CO2 is possible only if the dwelling time of vthe soot in the gas generator is relatively long. In gas generators in which the substances to be gasied move together with the gasifying agents in a continuous unidirectional flow through the equipment, the dwelling time of the gases, and hence of the soot being formed, is very short. With these short dwelling times, below approximately l second, the available reaction time is not suicient for reaction of the line carbon with CO2 or H2O steam. Consequently, in such cases resort had to be made to the expedient of gasifying the carbon with the aid of O2. This process is a combustion process in which very much heat is liberated, particularly if it is carried out up to formation of CO2, whereas when gasifying the carbon with the aid of CO2 or H2O the heat liberated by the exothermic oxidation of the carbon is again counterbalanced by the endothermic process of the CO2- or H2O-cracking. Consequently, when the free carbon is gasied with the aid of O2 there is diiliculty in maintaining the temperature of the gas generator in the desired low range beneath approximately 900 C. 'The purpose of this invention is to avoid the excessive amount of heat that results from the gasification of the free carbon with the aid of oxygen.

The inventor recognized that the excessive amount of heat can be greatly minimized by having the conversion of the free carbon with oxygen carried out not to the formation of CO2, or only to a slight extent to said formation, and have the gasification to a dominant extent carried out only up to the formation of CO. In order to achieve this, an addition of CO2 gas is supplied to the gas generator, aside from oxygen or oxygen-containing gases, and also steam. The additionally supplied CO2 gas is added in a quantity which is equal to or smaller than the CO2 quantity that would be present in lthe production gas at the operating temperature of the gas generator if no additional CO2 were supplied. It has been found that in this manner the formation of CO2 during gasification of the `free carbon is prevented.

As a result, the development of heat which accompanies the CO2 formation is likewise eliminated, and it is readily possible to keep the operating temperature of the gas generator at the desired value.

The production of a fuel gas of high caloritic value which burns with a luminous dame, for production of high radiant energy, is predicated upon using in the reaction space a temperature generally between 760 and the maximum of 900 C. Such temperatures, however, are just at the limit where one may expect the commencement of a suicient CO-formation from COZ-Q-C in the reaction space provided the dwelling time is suiliciently long. However, the dwelling time of the particles in the reacting gas is extremely short when gasifying the carbon dust or soot forming in the cracking of hydrocarbons. These particles, being extremely small, move together with the gas in continuous unidirectional tlow in the case of all continuous-flow gas generators (for example, according to German Patent 945,534). The dwell time is the interval vof time required for the hydrocarbons or the produced gases to pass through the reaction space from the entrance point of the hydrocarbons to the outlet point for the produced gases. This dwell time is up to about 1 second, or less, which is also the case with oil-gas generators operating on the unidirectional ow principle of gas and hydrocarbons. With Such dwell periods of l second or less, practically no formation, or only a very slight formation of ICO from CO2 and carbon takes place at low temperatures, i.e. at less than about 900 C. The same applies to the cracking with steam. Consequently, when oil is being cracked, with a subsequent gasification, the starting or initiating conditions for the reduction of CO2 or H2O, by means of the carbon previously separated from the gas, are extremely unfavorable. It is therefore necessary, for the gasifying of the free carbon, to supply the gas generator with additional oxygen or combustion air, from the outside.

yIf the cracking andl gasifying method is to be made economical, one must operate by utilizing the sensible heat of the production gases for heating the combustion air `and `for producing the steam used for cracking. However, if the free carbon is to be completely gasied with the aid of oxygen, the residual heating of the gasifyingagent occurring in the gas generator, the radiation losses and the cracking heat require less heat than is liberated by the gasifying process itself. In addition to the heat evolving from the CO-formation and CO2-formation, a further considerable quantity of heat is added due to the fact that, at the relatively low temperatures 0btaining in the cracking zone, a portion of the segregated H2 burns to H2O. Consequently, a heat surplus is produced which would result in undue increase in temperature unless it is dissipated by cooling of the gas generator. Such cooling is uneconomical if the heat cannot be usefully employed for steam generation or the like purposes. To be sure, it is possible to prevent the formation of the heat surplus, by relinquishing a complete gasification of the segregated carbon particles. In this case, however, soot and tar vapors are contained in the production gas.

As explained above, it is an object of my invention, therefore, to avoid the occurrence of excess heat and to bring about the production of a high caloric gas without free carbon, in a simple and economical manner when cracking Iand gasifying hydrocarbons at relatively low temperatures, .that is, lower than or not yhigher than about 900 C., and with short dwell periods in the reaction space of the gas generator, these periods being less than about l second, while supplying steam to the hydrocarbons to be converted to production gas.

To this end, and in accordance with my invention, additional CO2 gas, either in pure form or in form of combustion gases, is supplied to the gas generator. As stated above, I have discovered that `such an addition of CO2 gas in the gasication of hydrocarbons has the result that the CO2 formation, and hence the generation of heat accompanying such CO2 formation, is prevented or at least greatly minimized. In this manner the heat balance of the cracking and gasifying process can be equalized. According to the method of my invention, therefore, the gas generator can readily be supplied with such a quantity of gasifying air as is required for the complete gasification ofthe involving free carbon into CO, without incurring a detrimental excessive heat. Consequently, the gas thus being produced is free of soot particles. Furthermore, the temperature of the gas generator can readily be controlled and regulated by a corresponding control of the CO2 supply. As explained above, I have found it preferable to use the additional supply of CO2 in a quantity which is smaller, or not larger, than the CO2 quantity that would be contained in the useful gas produced in the gas generator at the chosen operating temperature without the supply of additional CO2 gas.

According to another feature of the invention, the additional CO2 gas is supplied to the gas generator together with the other gasifying agents, that is, the gasifying air or oxygen, and steam. When using gas generators which operate with recycling of a portion of the production gas, particularly in the interior ofthe reaction space, the additional or supplemental CO2 gas may also be `supplied together with the recycled gases returning into the reaction space. With such gas generators, furthermore, the additional CO2 gas may also be supplied completely or partially, together with the hydrocarbon to be cracked, and, if desired, the remainder of the CO2 gases as well as the other gasifying agents may be admixed with the production gases that are being returned into the reaction space. In such cases, it is preferable to adjust the ratio of the CO2 gas being additionally supplied to the combustion air as follows. Taking under consideration the proportion of CO2 to CO contained in the gas being returned, i.e. recycled, the said ratio is adjusted so that, in the reaction of the free carbon being returned together with the air oxygen to form CO, the equilibrium condition according to Boudouard is satisfied and the temperature is not appreciably increased.

The reason why the additional CO2 quantity is equal to or smaller than the CO2 quantity which would be contained in the production without the additional supply of CO2 is as follows. This quantity relation is required in order to `control the gasifying process in the desired manner by corresponding adjustment of the additionally supplied quantity of CO2, the control being such that excessive heat is prevented. The additional C02 quantity can vary only between the limits of zero and that quantity which would be contained in the production gas without the addition of CO2. An addition of a further quantity beyond the maximum limit could not possibly have any favorable effect upon the process.

The `CO2 is introduced into the process at various locations, but it is in most cases preferable to introduce it together with the other gasifying agents, i.e. the oxygen and steam. Where the CO2 is first contacted with the oil, the CO2 is employed under pressure, so that it then serves to atomize the oil prior to entering into the gas generator.

It is preferable, for a better performance of the operation and also for the economical utilization of the generated heat, to bring the gas approximately to the reaction temperature before introducing the gas into the reaction space.

The Boudouard equilibrium mentioned above indicates d the ratio between CO and C-i-COZ at a `given temperature, in accordance with the following equation:

ZCOSC-l-CO2 -1-3 8 Kal.

This equilibrium becomes displaced at increasing temperature toward the CO side, so that at l000 C. virtually only CO is contained in the system.

When the gas generator is `one in which none of the produced gas is returned or recycled into the reaction space, it is preferable to first contact the -hydrocarbons which are to be cracked with the CO2 gases, and only thereafter with the `other gasifying agents. The latter agents are preferably supplied gradually, stepwise.

It is also preferable to preheat the gasifying agents, as well as the supplementing CO2 gas, prior to introducing them into .the reaction space. The preheating temperature is preferably approximately that obtaining in the reaction space.

The fact that the development of excessive heat during gasification can be prevented by the new method is apparent from the following Tables 1 and 2. The values of these tables were ascertained by operation of a gas producer to which CO2 gas was supplied in the form of combustion, i.e. ue, gas. The flue gas thus supplied was gained by burning the useful gas produced in the generator. The operating temperature of the gas generator was approximately 850 C.

Table l presents the data of a gas analysis and of the quantities of heat liberated by the CO, COZ- and H2O- formation, and the quantities `of heat bound or absorbed by the cracking operation. The quantity of H2O was calculated from the hydrogen balance of the process. Table 2 presents the heat balance of the total process, taking under consideration the heat that can be recaptured, in practice, from the sensible heat of the production gases, and the heat consumption resulting from radiation losses and steam generation, and also from heating air and steam up to the operating temperature of the gas generator of approximately 850 C., as example.

TABLE 1 Analysis 0f the Production Gas and of the Heat General10n During Cracking and Gasifying of Hydrocarbons With CO2 Addition TABLE 2 Heat Balance of the Cracking Operation With Inclusion of the Addition of CO2 Heat SourcekcaL/Nm Gas Heat generation according to Table 1 Utilizable heat in exit gases Used for preheatiug air aud recycled gas-. -250 Steam generation n Radiation losse -76 Heat excess. -l-O TABLE 3 Analysis of Production Gas and Heat Generation by Cracking and Gasijcation of Hydrocarbons Tables 1 and 2. represent an example in which the CO2 gases are supplied in such a quantity that no excess of heat results. Lines 1 and 2 of Table l signify that lwithout supply of `CO2 gas there would be contained 0.06 Nm.3 CO2 per Nrn.3 gas in the production gas. However, previously a quantity of 0.037 Nm.3 CO2 per Nm was added. The subtractive difference, or remaining quantity, of 0.023 Nm CO2 per Nm, which is additionally generated during the gasifying process, produces a heat of 100 kcal. per Nm. As shown in Table 2, this does not result in excessive heat. The example according to Table 1 operates with recycling of the gas, and the 0.037 Nm.3 of CO2 were contained in the recycled gas. Consequently, this CO2 quantity may also be designated as addition to the gasifying agents.

The process will now be more specically described with relation to the drawings, in which:

FIG. l is a ilow diagram of the entire process, including the source of the additional carbon dioxide;

FIGURE 2 is `a schematic sectional view of a gas generator into -which said additional CO2 is introduced;

lFIG. 3 is a schematic View ofV another gas generator, in which the CO2, under pressure, is used to atomize the hydrocarbon oil.

With reference to FIG. 1, the CO2 istaken, in form of ue gases, `from `the exit ue 6 of a boiler 1, and is purified in a sulfur remover 2. The sulfur-removing plant may be omitted if desired. A blower 7 passes the CO2-containing gas, preferably 'free of sulfur, into a heat exchanger 3. The same blower sucks from the environment a quantity of ambient air through a conduit 5 which is provided with a regulating device V51, thereby passing oxygen into the heat exchanger 3. Before the CO2 and oxygen are supplied to the heat exchanger 3, a quantity of steam is added at 71 to serve as a further gasifying agent. In the heat exchanger 3, the gasifying agents are brought approximately up to the reaction temperature and are thereafter supplied to the gas generator 4. The gas generator is `further supplied with the hydrocarbon, preferably hydrocarbon oil, to be cracked, by pump 8. The resulting production gas is exhausted at 9, and then passes downwardly through the heat exchanger 3.

In the form shown in FIG. 2, the gas is made to circulate in 4the gas generator. The internal circulation may be produced by tangential gas introduction and/ or with the aid of a blower 40, or other impellers, so that the gas performs a rotational motion about the longitudinal center axis, vand possesses a component of motion parallel to the axis. The CO2 is introduced entirely or partially at 10, into the recycled portion of the produc- -tion gas. The production gas is withdrawn at 9. Some CO2 may be introduced with the oil, as shown. The air, oxygen, steam, or CO2 can `be under pressure, to atomize the oil.

In FIG. 3, the atomizing of the oil takes place in nozzle 80, prior to, or at its introduction into the gas generator 41. It may be eiected with the aid of compressed CO2, or by means of compressed air, oxygen and steam enriched with CO2. The supply of the other gasifying agents, namely air or oxygen, and steam, with or without `further CO2, can be separately carried out, at 81.

As a further speciiic example, We state yas follows:

The duration of the process is advantageously less than one second, the temperature being at 900 C. or, more generally stated, in the range between 760 C. and 900 C. The hydrocarbon oils used may be of the class of paraflins and cyclo-parans, or naphthenes and aromatics, and of other types commonly used to make i1- luminating gas of high caloric value. Examples of particular useful hydrocarbon oils are gasoline, kerosene, gas oil, lubricating oil, mineral oil and petroleum oil. The hydrocarbon oils may consist of from 6 to l2 carbon atoms. The ratio of hydrocarbons to hydrogen is preferably such that the carbon to hydrogen weight ratio is 5 to 9. Air `is used as the gasifying agent, with steam, and CO2 is used in pure form or in the form of ue gas. The process is advantageously carried out at atmospheric pressure.

yI claim:

1. A method of cracking and gasifying a hydrocarbon oil to produce an illuminating gas of high calorific value, comprising cracking the oil with steam at a temperature not higher than about 900 C., and with a dwelling time of the hydrocarbon in the reaction Ispace of not more than about a second, gasifying free carbon, formed in the cracking, by introducing oxygen (O2) and suciently suppressing the formation of carbon dioxide (CO2) in said gasifying of free carbon, by introducing carbon dioxide (CO2) into said reaction space during the gasifying of free carbon, to prevent the temperature from rising above about 900 C. during said free carbon gasication.

2. A method of cracking and gasifying a hydrocarbon oil to produce an illuminating gas of high caloric value, comprising cracking the oil with steam at atemperature not higher than about 900 C., and with a dwelling time of the hydrocarbon in the reaction space of not more than about a second, introducing oxygen (O2)` into the reaction space to gasify the carbon formed in the cracking, and introducing carbon dioxide (CO2) during said free carbon gasification in an amount not greater than the amount produced at the operating temperature without said carbon dioxide (CO2) addition, whereby formation of carbon monoxide (CO) is enhanced, and formation of carbon dioxide (CO2) is sufficiently suppressed to prevent the temperature from rising above about 900 C. during said free carbon gasification.

3. A method of cracking and gasifying a hydrocarbon oil to produce an illuminating gas of high calorilic value,

comprising cracking the oil with steam at a temperature not higher than about 900 C., and with a dwelling time of the hydrocarbon in the gas generating reaction space of not more than about a second, and introducing CO2 gas into the reaction space during the course of the reaction, at least part of the CO2 gas being introduced together with oxygen and steam into the reaction space during the course of reaction.

4. A method of cracking and gasifying a hydrocarbon oil to produce an illuminating gas of high caloriic value, comprising `cracking the oil with steam at a temperature not higher than about 900 C., and with a dwelling time of the hydrocarbon in the reaction space of not more than about a second, gasifying free carbon, formed in the cracking, by introducing oxygen (O2) and suciently suppressing the formation of carbon dioxide (CO2) in said gasifying of free carbon, by introducing carbon dioxide (CO2) into said reaction space during the free `carbon gasification, to prevent the temperature from rising above about 900 C. during said free carbon gasication, and recycling a portion of the product gas whereby at least a portion of said carbon dioxide is provided to enhance the formation of carbon monoxide.

5. A method of cracking and gasifying a hydrocarbon oil with a supply o-f steam and at a temperature not higher than about 900 C., and With a dwelling time of the hydrocarbon in the gas generating reaction space of not more than about a second, characterizedin that CO2 gas is introduced into the gas generating reaction space during the course of reaction, at least part of the CO2 gas being introduced together with oxygen and steam into the reaction space, the CO2 gas and the oxygen and steam being preheated, prior to being introduced into the reaction space, to temperatures near those obtained in the reaction space.

6. The process of claim 1, the hydrocarbon being a hydrocarbon oil having 6 to 12 carbon atoms.

7. The process cf claim 1, the hydrocarbon being taken from the group consisting of gasoline, kerosene, gas oil, lubricating oil, mineral oil, and petroleum oil.

References Cited in the le of this patent UNITED STATES PATENTS 2,133,496 Winkler et al. Oct. 18, 1938 2,660,521 Teichmann Nov. 2.4, 1953 2,673,794 Williams Mar. 30, 1954 2,681,273 Odell June 15, 1954 2,698,830 Jenny Ian. 4, 1955 2,707,147 Shapleigh Apr. 26, 1955 2,720,450 Haug Oct. 11, 1955 2,746,852 Richardson et al May 22, 1956 2,809,104 Strasser et al Oct. 8, 1957 2,904,417 Te Nuyl Sept. 15, 1959 2,941,877 Grahame June 21, 1960 FOREIGN PATENTS 216,790 Australia Aug. 19, 1958

Claims (1)

1. A METHOD OF CRACKING AND GASIFYING A HYDROCARBON OIL TO PRODUCE AN ILLUMINATING GAS OF HIGH CALORIFIC VALUE, COMPRISING CRACKING THE OIL WITH STEAM AT A TEMPERATURE NOT HIGHER THAN ABOUT 900*C., AND WITH A DWELLING TIME OF THE HYDROCARRBON IN THE REACTION SPACE OF NOT MORE THAN ABOUT A SECOND, GASIFYING FREE CARBON, FORMED IN THE CRACKING, BY INTRRODUCING OXYGEN (O2) AND SUFFICIENTLY SUPPRESSING THE FORMATION OF CARBON DIOXIDE (CO2) IN SAID GASIFYING OF FREE CARBON, BY INTRODUCING CARBON DIOXIDE (CO2) INTO SAID REACTION SPACE DURING THE GASIFYING OF FREE CARBON, TO PREVENT THEE TEMPERATURE FROM RISING ABOVE ABOUT 900*C. DURING SAID FREE CARBON GASIFICATION.

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