US1983992A - Process for the thermal decomposition of hydrocarbons - Google Patents

Description

Dec. 11, 1934. F. M. PYZEL 1,983,992

PROCESS FUR THE THERMAL DECOMPOSITION 0F HYDROCARBONS Filed Aug. 18, 1951 Patented Dec. 11, 1934 UNITED sTA Es PROCESS FOR THE THERMAL DECOMPOSI- TION OF HYDROCARBONS Frederic Marinas Pysel, Piedmont, to Shell Development Company,

Calif., assignor San Francisco,

Calif., a corporation of Delaware Application August 18, 1931, Serial No. 557,880 7 Claims. (01. 22-212) This invention refers more particularly to the control of the thermal decomposition of hydrocarbon. into various products.

It has been found that in the'art of cracking hydrocarbon materials different types of compounds are produced at various temperatures. In actual cracking'practice, most of these groups of products have been made simultaneously due mainly .to the fact that neither heating nor reaction times can be controlled in an eflicient manner. Another disadvantage of existing processes, particularly in cases when products are to be made which require high temperatures, is that the heat contained in the cracked product is often going to waste. V

I have found that such waste can be avoided and the production of specific groups of'cracked products can be accurately regulatedby firstly bringing a certain quantity of material to be cracked to a temperature at which those desired products are manufactured which require the highest temperatures.

Into the hot cracked gases so produced I then inject in one or more steps the same or different hydrocarbon materials to be cracked in such a way and in such quantities that the temperatures to which a new material is subjected and the time during which these new materials are subjected to these conditions can be closely regulated.

A purpose of this invention is therefore to ac curately regulate the cracking of hydrocarbon material into various products.

Another purpose of this invention is to utilize the heat contained in a stream of cracked material to crack additional quantities of hydrocarbon material.

Further advantagesand features of my invention will be better and more fully understood from the following detailed description of a specific manner of executing my invention, throughout which reference is made to the attached drawing:

With reference to this drawing, 1) represents a vertical converter filled with refractory material which is heated by means of burners (2). Hydrocarbon fuel is delivered to these burners through suitable piping- (3). A control valve (4) is placed in this line to control the flow of fuel to the burners. Individual burners may be regu-' lated by smaller valves (5). Air controlled by a valve (25) is supplied to the converter through a manifold (6) connected to a blower (7). The air is forced into the converter adjacent the burners (2). A stack (8) is connected to the lower part of the converter. The top of .the stack has a valve (9) opening into the atmosphere. A'steam line (10) controlled by valve (11) is connected with the stack near the top. Another line (12) for admitting hydrocarbons, is controlled by a valve (13) and is connected to the stack close to its top. At the top .of the converter, a valve (14) which can be opened to the atmosphere may be used A hydrocarbon line 15) controlled by a valve (16) discharges into the oiftake pipe from the top of the converter. This pipe (1'1) leads from the top of the converter and is connected to a downcomer pipe (18) which has a closed end (19). Other hydrocarbon injectors such as (23) and (24) may be placed in the ofltake pipe and downcomer. Apipe Joining the downcomer leadsinto a wash box (20) having an upper outlet (21) and a lower outlet valve (22) An overflow pipe is-connected to the side of the wash box.

The operationof the system is as follows: Valves (4) and (9) being open and with valve (14) shut, hydrocarbon is admitted to burners (2). The necessary air for combustion is supplied through manifold (6) from blower ('1).

The flames are directed downward and heat the refractory material in the body of the converter. When the temperature of the refractory material has been raised to the desired point, heating is stopped by closing valve (4) and shutting off the air blast. The stack valve (9) is closed and hydrocarbon material to be decomposed is admitted to the apparatus through pipe (12). This hydrocarbon is somewhat heated by the hot stack and is decomposed by coming into contact with the hot refractory material in the converter. ,The cracked products are carried up through the converter and are discharged into pipe (1'1). Hydrocarbon material may be added through pipes (15), (23) and (24). Through which of these injectors hydrocarbon'is added will depend upon operating conditions. As the stream is carried along pipe (17) and through the downcomer pipe (18) the newly added material becomes mixed with the gases that issued from the converter and is therebythermally decomposed. From the bottom of the downcomer the stream is led into the wash box (20) where the carbon is separated from the gaseous and more volatile constituents. The carbon is removed from the wash box through pipe (25) to suitable filters or centrifuges. The other products are removed by pipe (21) for subsequent treatment.

After hydrocarbon material to be cracked has been passed into the converter for some time, the refractory material becomes too cool for efficient conversion. It is therefore necessary to stop the flow of hydrocarbon material and reheat. However, if the burners (2) were at once started, hydrocarbon mixtures present in the converter might cause an explosion, It is therefore advisable to first remove any combustible material remaining in the converter. For this purpose steam line (10) is provided. Hydro carbon entering through lines (12) and (15) is first. shut off. The valve (14) in the top of the converter may then be opened. steam from line (10) is forced through the refractory material to thoroughly purge it of any combustible material before commencing to reheat. Having completely purged the converter, the steam is shut off, valve (14) is closed, stack valve (9) is opened and the burners lighted. The control of the reaction time and the temperature at which reaction takes place can be closely regulated by my process. With a given rate of flow of gases from the converter, the time of cracking can be controlled by the distance of the injection point from the wash box. The temperature at which the hydrocarbon material is cracked can be controlled by the relative proportions of hydrocarbon added in successive steps. This temperature can also be controlled by the temperature at which the hydrocarbon is introduced into the stream and also by the physical state in which it is introduced. I

As an example of the use to which my invention can be put, I may crack natural gas to produce a gas rich in hydrogen to be used for the synthetic production of ammonia.

The gas used as raw material in this example for both the first stage conversion and for the subsequent second stage conversion was a natural gas. containing principally methane and ethane in the proportions of eighty-three parts methane to seventeen parts ethane.

The natural gas is cracked in the converter by being passed through the checker work which has been heated ,to the desired temperatures; for instance, about 2000 F. The gas issuing from the converter will be composed principally of hydrogen and methane.

A typical analysis of this gas being:-

content as well as producing small amounts of ethylene, ethane, benzol and other hydrocarbons in the gas stream.

The following is an analysis of the final gas stream I have obtained:-

Per cent by volume CO: 0.4 Cal-I: I 0.15 .'C:H4' 1.03 Other cnfim 0.32 O: 0.2 CO 10.0 ,H: 67.4 084 18.1 N: 2.8

A particular benefit of my method of operation is that a gas can be produced with a controlled ethylene content. When natural gas is cracked for the production of hydrogen small amounts of acetylene are foFned. In the past the acetylene in the gas stream has caused considerable trouble to operators owing to the explosive nature of this hydrocarbon, when submimd to pressure....'1his danger becomes particularly pronounced when further separation of the gases is made in a low temperature condensation and fractionation apparatus. It has been found that ethylene which liquefies at a temperature comparatively near the temperature at which acetylene solidifies has the power of dissolving any acetylene which ac cumulates in the low temperature condensation apparatus if said ethylene is present in the apparatus in sufficient amounts. By controlling the ethylene content I can influence the proportion of these two hydrocarbons in such a way that the precipitation of solid acetylene in the fraction vantageous to inject special hydrocarbons or hydrocarbon mixtures containing less methane and more heavier hydrocarbons, the cracking conditions being. adjusted so as to obtain the desired products. I I 1 Besides the specific example of 'an application of my invention as shown above, I mayadapt my invention to various cracking requlrenients; I may for this purpose dispense with the refractory filled converter and make use of other types of cracking apparatus. I may also apply pressure to the apparatus. I

In using my invention with different types of cracking apparatus the principle on which the invention is based is followed, namely, to first apply the highest temperature to obtain the products which require the highest conversion temperature and thereafter inject further quantities of hydrocarbon to obtain products which require a lesser temperature to effect formation.

I claim as my invention:

1. In a process of producing hydrogen the steps comprising: passing hydrocarbon gas over highly heated refractory material in a converter, injecting hydrocarbon into the hot gases issuing from the converter, thereby producing ethylene in the gas stream and subsequently removing acetylene from the gas stream by theuse of said ethylene.

2. In a process producing hydrogen, the steps comprising: thermally decomposing a hytirocai' bon gas to produce a reformed gas containing hydrogen and acetylene, producing ethylene in said reformed gas by injecting amounts of hydrocarbon into the reformed gas and subsequently removing the acetylene of the reformed gas by the aid of said ethylene; I

3-. In a process of producing hydrogen, the steps comprising: thermally decomposing hydrocarbon gas to produce a .reformed gas containing hydrogen and acetylene-producing ethylene in said reformed gas by injecting amounts of hydrocarbon into the reformed gas stream and in subsequent fractionation dissolving the acetylene in the ethylene. I I

4. In a process of producing hydrogen, the steps comprising: thermally decomposing-hydrocarbon gas to a reform gas containing hydrogen, ace ylene and'ethylene, increasing the ethylene content of the reform gas by inJecting amounts of hydrocarbon into the reformgas stream and in subseq ent'fractionation dissolving the acetylene in tbet y ena 5. In a process of producing a hydrogen containing gas the steps comprising: passing hydrocarbon material into a refractory filled converter, producing a reformed gas containing acetylene and hydrogen in said converter, allowing said reformed gas to issue from the converter injecting hydrocarbon material into the reformed gas stream rising from the converter, producing ethylene in the gas stream and thereafter in the fractionation of the reform gas, acetylene in the ethylene.

6. In a process of producing a hydrogen containing gas the steps comprising: passing hydrocarbon material into a heated refractory filled converter, producing a gas containing acetylene and hydrogen in said converter, withdrawing said gas from the converter, injecting hydrocarbon material into the stream of gases withdrawn, prodissolving the ducing ethylene in said stream of withdrawn gases by means of thethermal decomposition of said injected hydrocarbon material and in subsequent fractionation of said gas stream dissolving the acetylene in the ethylene.

'7. In a process of producing a hydrogen containing gas the steps comprising: passing natural gas into a heated refractory filled converter, producing a reformed gas containing acetylene and hydrogen in said converter, withdrawing the reformed gas from the converter, injecting natural gas into the reformed gas stream, ethylene in said reformed gas stream by the thermal decomposition of the injected natural gas, thereafter in a liquefaction process of gas fractionation dissolving the acetylene in the ethylene.

FREDERIC MARINUS PYZEL.

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