US2113536A - Production of unsaturated hydrocarbon gases - Google Patents

Description

April 5, 1938. J. J. GREBE ET Al. 2,113,536

PRODUCTION OF UNSATURATED HYDROCARBON GASES Filed March 5, 1936 3 Sheets-Sheet l /1 1 l f 1/ /f/ ,/f,

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PRODUCTION OF UNSA'URATED HYDHOCARBON GASES J. J. GREE ET AL 2,113,536

Filed March 5, 193s s snets-sheet s Patented Apr. 5, 1938` UNITED STATES PATENT OFFICE PRODUCTION F UNSATURATED HYDRO CARBON GASES Application March 5, 1936, Serial No. 67,336

1 Claim. (Cl. 2130-170) 'This invention relates to a method and apparatus for producing unsaturated hydrocarbon gases by pyrolysis or cracking of hydrocarbons. More particularly, it is concerned with improve- 6 ments in the cracking of hydrocarbon oils yby means of superheated steam, whereby heavy oils or tars may be cracked to produce a gas mixture high in oleiines or acetylene.

A method of cracking hydrocarbon oils to pro- !0 duce gaseous olei'lnes is described in United States Patent No. 1,962,502, which consists in vaporizing oil, preheating the vapors and then mixing such vapors with superheated steam in amount and at a temperature such that the l oil is heated to a suitable cracking temperature, substantially all of the heat required for the cracking being supplied by the superheated steam. The oil vapors are preheated to a temperature of about 550 to 700 C., while the superheated steam is supplied at a temperature between about 950 and 1200 C., so as to produce in the resultant mixture a temperature between '700 and 1000 C., this lbeing the range within which gaseous olenes are chiefly formed. The

cracking is carried out in the presence of surfaces of magnetic iron oxide, FesOr, which acts as an anti-catalyst to prevent carbon formation. The hot reaction gases, having a. high content of gaseous olenes, are passed in heat exchange with the incoming oil to vaporize and preheat the same, then further cooled to condense water and separate the latter from the permanent gases.

The commercial practice of the aforesaid o method has disclosed certain limitations and disadvantages. It was -found that the preliminary vaporization of the oil an., preheating of the vapors, while proceeding satisfactorily with a petroleum distillate such as kerosene, could not be carried out practically with heavier oils, be-

cause such heavy oils in some cases could not be vaporized and in other cases would be partially cracked in the process, accompanied by tar and carbon formation which soon caused stoppage of the preheating coils. The method, therefore, was successful for use only with light oils which could be vaporized and preheated without incipient cracking and resultant formation of tar and carbon.

Another limitation was caused by the inability of commercial superheaters to deliver superheated steam for long continued operation at a. temperature appreciably higher than about 1000 to 1050 C., due to the fact that no practical construction metals were known which could withstand high temperatures or the action ofcombustlon gases and steam at such temperatures for an extended period of time. The available metals are subject to distortion and embrittlement by the action of the heat, as well 5 as to severe chemical attack by the hot gases.

It is an object of the present invention to provide an improvement in the method of the aforesaid Patent No. 1,962,502, whereby heavy oils can be cracked successfully to produce un- 10 saturated gaseous hydrocarbons with the same facility as in the case of light oils. A further object is to increase the production of ethylene relative to the higher olenes. Still another object is to increase the production of unsatul5 rated gases of the acetylene series. Another object is to make practically possible in an economical manner the supplying of superheated steam at temperatures much higher than are now feasible with usual metallic equipment. 20 Other objects will' appear as the description proceeds.

The heavy oil.;, for the cracking of which our method or process is primarily intended, include crude petroleum, heavy distillate oils, gas oil, 25 residuum oils, fuel `oil, tar oils, as well as tars derived from wood and coal distillation.

We have found that heavy oils can be cracked successfully on a commercial scale by injecting n the oil substantially as liquid directly into a 30 current of steam superheated to a temperature materially above about 1000 C., e. g. between 1000 and 1350 C., thus avoiding the necessity for separately vaporizing the oil and preheating the vapors, and also preventing carbonization 35 and the attendant difficulties caused thereby. We have alsol found that by using such highly superheated steam the yield of ethylene relative to higher olenes is increased, this result being more marked whenthe steam is superheated to 40 temperatures above about 1200 C. 'I'his is of great practical advantage, inasmuch. as ethylene is more desirable commercially than the higher olenes, and the expense of separating the ethylene from the higher olenes is reduced in the 45 proportion that the content of higher olenes in the gaseous product is lowered. It has 'also been found that our improved method is adapted to producing directly a gaseous product having a higher content of acetylene than is obtained by other processes based upon a thermal treatment of hydrocarbons. In 'a range of temperatures between 700. and 1000 C. the gaseous products of the cracking are chiefly olenes, but, as the cracking temperature is raised to around 1000 C. 65

and higher, commercial yields of acetylene are obtained.

In order to produce superheated steam economically on a commercial scale at temperatures in excess-of about 1000 C., suitable for use in our improved method or process, we have adapted a stove type of superheater in which a pervious mass of high temperature refractory material is first heated to a high temperature and then used for transmitting heat tothe steam. This type of apparatus requires the use of alternate periods of heating the refractory material and for superheating steam by contact with the hot refractory to a suiilciently high temperature for mixing with the oil to crack the same under the desired conditions. Such intermittent mode of operation, comprising alternate periods of firing and of cracking, tends to cause temperature variations in the gases during the respective periods. These variations, however, particularly in the cracking period, may be reduced greatly by disposing a body of heat absorbent material in the path of the current of superheated steam, to serve as a heat storage or ballast, absorbing heat during the early part of the cracking period and giving it up during the later part of the period, thereby smoothing out the temperature curve in the cracking zone and enabling a control of the cracking temperature within a few degrees.

By our improved method we are able to crack heavy oils injected directly into a current of the superheated steam of sufficiently high temperature and produce an equal or higher yield of unsaturated gases at a steam consumption no greater than was formerly required to crack vaporized and preheated light oils according to the method of the aforesaid Patent No. 1,962,502. Although in our method the reactions in the cracking zone take place in a temperature range whereat steam and hydrocarbons are known to react to form water gas, i. e. CO-i-Hz, the instan- -taneous cracking of the oil, followed by immediate cooling, produces a gas mixture containing negligible amountsof CO and only such amounts of hydrogen as are derived principally from the decomposition of the heavy hydrocarbons. We have also found that under the conditions of our improved method the use of magnetic iron oxide is not required to prevent carbon formation, and continuous operation may be maintained without the presence of any known anti-catalyst for carbon formation.

Our improved method and apparatus therefor is fully described in the annexed drawings and following specification.

In said annexed drawings:-

Fig. 1 is an elevation, largely in section, of a preferred `form of apparatus comprising a selfcontained unit for superheating steam and cracking oil.

Fig. 2 is a horizontal cross section on the line 2-2 of Fig. 1.

Fig. 3 is a horizontal cross section on the line 3-3 of Fig. 1.

Fig. 4 is a diagrammatic plan view of an apparatus including two superheating and cracking units interconnected to give continuous gas production.

Fig. 5 is a curve sheet showing the variation in yield of unsaturated gases according to the cracking temperature.

Referring to Figs. 1-3, the apparatus comprises a vertical superheater section I, of relatively large size, with which is combined a crack' ing section 4. superheater section I is formed by a cylindrical steel shell,` having a conical top, the whole provided with a lining of refractory and heat insulating material. Within superheater I, at the left, is a vertical heatstorage chamber 5, enclosed by arcuate walls 6, which rise to a point some distance below the top'of shell I, the one wall following the curvature of the outside shell, and the opposite wall having a reverse curvature, as shown particularly in Figs. 2 and 3. The space 1 to the right of wall 6 forms a second chamber which is the superheater chamber proper, and is fllled with refractory brick checker-work nearly to the top of wall 6, leaving an open combustion space 8 at the top of superheater section I. At the bottom of superheater chamber 1 is a ue 9 leading to a stack I0, in which flue is a steam inlet pipe II and stack valve I2. At the top of combustion space 8 is an opening I3 communicating with an air chamber I4, within which opening I3 is located an oil or gas burner I5. Communicating with vertical chamber 5 near the bottom is a horizontal cracking chamber 4, lined with refractory material, such as fire brick. An expansion joint I6 is provided in the outer steel casing I1 of cracking chamber 4, which joins at its further end with a condenser and cooler I9.

Oil to be cracked is supplied to chamber 4 through injector I8. Within chamber 5 is a pier 20 of refractory material with an arched opening at the lower end opposite the inlet to cracking chamber 4, as shown in Figs. 1 to 3.

superheater section I is equipped with one or more explosion disks 2| and a sight glass 22.

Materials are supplied to the apparatus as followsz-Fuel for combustion is carried to burner I5 by pipe 23 having a control valve 24, and steam for cleansing and blanketing the burner, as hereinafter explained, is supplied during certain periods through steam pipe 26 in which is valve 25. Air for combustion is supplied to air chamber I4 by air-duct 28 controlled by valve 21. Steam introduced into flue 9 through pipe II is controlled by valve 29. Oil injector I8 in cracking section 4 is supplied with oil and with' steam for atomizing the oil through pipes 32 and 33, respectively, which are controlled by valves 30 and 3I. Cooler I9 is supplied with water through water pipe 35, in which is a valve 34, and gaseous products are removed either through vent pipe 31, controlled by valve 36, or by gas' line 39, controlled by valve 38, While cooling water and condensates are removed through drain 40. Reactor 4 is equipped with temperature indicating means, such as thermocouple 4I.

The apparatus operates upon a cycle made up of three periods, namely, a firing period, a purge period, and a cracking period. During the first, or firing, period fuel injected through burner I5 is burned in combustion space 8. 'Ihe hot combustion gases sweep through the checkerwork inv chamber 1, to heat the same to a high temperature, and thence out through flue 9 to stack I0. At the start of the firing period valves 24 and 21 for fuel and air supply to burner I5, also stack valve I2 are opened, all other valves being closed. Combustion proceeds until the upper checker-work in section 1 reaches a suitable high temperature, i. e. a temperature of about 1300 C. or higher, as observed by the color of the checker-work when viewed through sight glass 22 or as indicated by an optical pyrometer, not shown. In starting a new unit, it is of course necessary to determine experimentally the proper rates of firing to give the desired temperature in a given firing period.

'I'he i'lring period is followed by a brief purge period, the purpose of which is to sweep the apparatus free of air and combustion gases. Stack valve I2, fuel valve 24, and air valve 21 are closed, cooler vent valve 36 and water supply valve 34 are opened, and steam is admitted to flue 9 and burner I5 by opening valves 29` the steam and injected into the current of superheated steam in chamber 4. The proportions of oil supplied to injector I8 and of steam admitted to' the superheater through pipe II are adjusted to give the desired temperature of the mixed gases and vapors in the cracking zone, which may be indicated, for example, by pyrometer 4i. The oil is cracked down to gas almlostv instantaneously, by transfer of heat from the superheated steam. The hot gases admixed with steam pass immediately into cooler I8, wherein they are brought in contact with a water vspray which cools the gases and condenses the excessV steam, the cooled gases being conducted away to a gas holder through pipe 39, while the condenser water ows out through outlet 48.

When the temperature in the cracking chamber 4 falls to a point below which it is not desired to continue cracking, oil control valve 30, steam valves 25, 28 and 3l, water valve 34 and gas line valve 38 are closed, stack valve I2, air valve 2'I and fuel feed valve 24 are opened and burner I5 is ignited, thus starting a new cycle of operation, which is constantly repeated as the process is continued. g

To operate the apparatus," automatic valve-operating mechanism of any suitable known, type may be employed for coordinating the vopening and closing of the various valves.

Since a single-unit installation, such as described, produces gas intermittently, two similar units may be arranged to operate in parallel on cycles so related that a continuous supply of gas is produced, as shown diagrammatically in Figure 4, the operation of which will be readily apparent from the foregoing description.

In practice the following results have been obtained in operating a superheater-reactor unit as shown in Figs. 1 to 3. The apparatus had an internal diameter of 4 feet 9 inches and an overall height of about 30.feet, the brick checkerwork occupying a space of 20 feet in height and 13 square feet in cross-sectional area, in which the brick were laid to form straight, vertical gas passages two inches square. The heat ballast chamber had an open cross-sectional area of two square fee't. The cracking' chamber consisted of a steel shell lined with fire brick forming a combustion space approximately six inches in diameter and 48 inches long, which communicated with a water spray cooler.

This unit was operated upon a thirty-minute cycle, composed of a 14 minute firing period, during which heat was stored in the superheater checker-work, a purge period of about 1 minute,

including time for changing valves. during which period steam was passed through the whole assembly from the stack opening in the superheater to the condenser blow-off vent, and a 15 minute firing period during which oil was cracked, as previously described in detail.

, When operating( on this 30 minute cycle, the average consumption of materials per hour was 1820 pounds of steam at ve pounds gauge pressure superheated to a temperature of 1155 C.

10 C., measured at' bottom of chamber 5, and 530 pounds of fuel oil having a specic gravity of 0.895, supplied at a temperature of 165 C., which was atomized by" 66 pounds of steam at pounds pressure. In the stated proportions the average temperature in the cracking zone was approximately 850 C. Oil used for combustion was in the ratio of about 0.44 pound per pound of Voil cracked.

On a continuous run of 800 hours, approximately 1,800,000 cubic feet of cracked gas were produced at a production rate varying from 4600 to 5400 cubic feet per hour. An approximate average analysis of the gas, in percentage by weight,

Was:

CH4l 9.3 C2H2 4.2 C21-I4 44.7 CsHs and higher 33.7 CO 1.3

CO2 4.3 N2, O2, etc .0.5

In the foregoing example a cracking temperature was chosen which was adapted to produce approximately a maximum yield of gaseous olenes. However, a considerable range is permissible in the temperature of the cracking Zone, when practicing the present method, depending upon the desired composition of the gaseous product. By operating at higher temperature the percentage of total oleiines in the gas produced is decreased, but the diminution of yield of ethylene proceeds at a much slower rate than that of the higher olenes, while, on the other hand, the percentage of acetylene increases. The variation in gas composition with' changes in cracking temperature is shown approximately by the chart Fig. 5 for temperatures up to 1200 C. For instance, at 1000 C. the gas produced would contain about 41 per cent of ethylene, 14 per cent of higher olefines, and l2 per cent of acetylene, by weight. By raising the cracking temperature above 1000 C. up to l200 or 1400 C., the percentage of acetylene is increased still further, while that of the olenes fall substantially to zero.

As stated, the percentages of the unsaturated gases in the product of our process, according to the curves in Fig. 5, are only. approximate, since various factors influence the composition of the gas within certain limits. In particular, we have found that the ratio of ethylene to higher olenes in the gas can be varied by varying the temperature of the superheat'ed steam employed for cracking the oil, although the aver. age gas temperature Iin the cracking zone may remain substantially the same. With higher steam temperatures' the ratio cf ethylene to higher olei'lnes is higher than with lower steam temperatures. For example, when using steam superheated to about 1070 C. and mixing with 75 oil in proportions to maintain an average tem.- perature of approximately 850 C. in the cracking zone, the ratio by weight of ethylene to higher oleiines in the product was l/1. When, however, superheated steam at about 1230 C. was used, the average temperature of the cracking zone remaining at 850 C. as before, the ratio of ethylene to higher olenes in the product was 1.25/1. In case ethylene is the principal gasecus product desired. it is most advantageous to employ steam superheated to a temperature ma.- terially above 1200 C.- for cracking the oil, the average temperature of the gases in the cracking zone being maintained preferably between 850 and 1000 C.

By reference to the curves in Fig. 5 it will be seen that our improved process is well adapted to the production of acetylene, as well as gaseous oleflnes. At cracking temperatures above about 1000 C. the percentage of acetylene in the product rises rapidly," whereas that of the oleflnes diminishes.

Apparently the formation of acetylene is at the expense of the oleilnes. By raising the temperature in the cracking zone above 1000 C., which is done by employing superheated steam at temperatures materially above 1200 C. and mixing it with the oil in suitable proportion, a good yield of acetylene is obtained. For example, at 1200 C. the gaseous product will contain around 25 per cent, by weight, of acetylene, while the percentage of olefines becomes vanishingly small. A further increase in the cracking temperature, e. g. to as much as 1400 C., will produce still higher yields of acetylene.

Therefore, our present process is adapted to the production of gaseous oleflnes or o f acetylene, or both, the percentage yield of gaseous products being controllable by regulating the temperature of the superheated steam and of the mixed gases in the cracking zone. Depending upon the cracking conditions desired, the temperature to which the steam is superheated will be varied accordingly, in general ranging from about 1000 to as high as 1800D C. Forproducing chiefly gaseous olenes suitable superheated steam temperatures are between 1000 and 1350 C., whereas, when acetylene is the principal product desired, steam temperatures of from 1200 to as high as 1800 may be used. Under the temperature conditions described the cracking of the oil proceeds at substantially atmospheric pressure. In practice, however, it is advantageous to maintain a moderate steam pressure, e. g. about 2 to 10 pounds gauge, in the superheating and cracking zones, so as to maintain a sufficient rate of flow in the process.

It is important to cool the gases from the cracking zone rapidly to a point below the normal cracking temperature, in order to avoid side reactions leading to the formation of saturated hydrocarbons and carbon monoxide. As already stated, the cracking to form unsaturated gases takes place practically instantaneously, hence many purposes can be employed without additional drying. The cooling of the hot reaction gases may be accomplished in other ways known to the art, however, and may be conducted in one or more stages, as desired. The cooling to a temperature below the cracking point, i. e. below about 600700 C., should be rapid, but below that the rate and extent of cooling is limmaterial as far as this invention is concerned.

In the practice of our invention we are enabled to crack hydrocarbon oils under conditions most favorable for production of high yields of unsaturated gases without formation of appreciable amounts of tar and carbon. We have found that in long-continued operation of the process no carbon accumulations are formed in the cracking chamber, hence there is no necessity to employ special materials or anti-catalysts to inhibit carbonl formation. Our apparatus avoids the use of metallic surfaces for transferring heat to the oil vapors being cracked, thereby permitting the required high temperature conditions to be maintained continuously for long periods of time under conditions whereat usual metallic construction materials would be rapidly burnt, corroded and destroyed. The process is, therefore, independent of the limitations of metallic apparatus when exposed to steam and combustion gases at high temperatures. The process is likewise more economical of heat than would be possible in other processes employing externally heated tubes or retorts for cracking the oil.

The particular object of the invention, to enable the cracking of heavy hydrocarbon oils and the like to produce unsaturated gases, is successfully accomplished Without sacrifice of yield or experiencing difllculty due to formation of tar and carbon, or to rapid deterioration of apparatus, such as has heretofore limited the production of rich unsaturated gases from heavy oils. By enabling the cheaper heavy oils to be used successfully as raw naterial an important economic advantage is gained as compared with'all processes heretofore used for producing unsaturated hydrocarbon gases. It is to be remarked that the usual steam consumption in our improved process, using heavy oil, which may vary from about 3 to 8 pounds of superheated steam per pound of oil cracked, depending upon conditions and the type of the oil, is equal to the results obtained in the process of the Aaforesaid Patent No. 1,962,502, wherein it was necessary to employ a light distillate and to vaporize the same and preheat the vapors before mixing them with the superheated steam. The process is not limited to cracking heavy oils or tars, however, but is also adaptable to cracking light oils and distillates, such as the kerosene and gasoline fractions obtained in the distillation of petroleum, as well as hydrocarbons generally, including both liquid and gaseous materials.

Other modes of applying the principle of our invention may be employed instead of the one explained, change being made as regards the means and the steps herein disclosed, provided those stated by the following claim or its equivalent be employed.

We therefore particularly point out and distinctly claim as our invention:-

The methodfor producing unsaturated hydrocarbon gases which comprises passing hot combustion gases into contact with a pervious refractory mass to transfer heat to the same from said gases, thereafter passing steam in contact with the so-heated mass to absorb heat from the same into the steam whereby superheated steam at a. temperature above 1000 C. is obtained, injecting a heavy oil substantially in the liquid phase into said superheated steam only in such proportion that the temperature of the superheated steam remains above about '100 C. un-

til the gaseous reaction product is contacted with a liquid quenching medium.

JOHN J. GREBE.

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