EP0118041A2

EP0118041A2 - The method of supplying soot-free products from the partial oxidation of hydrocarbon to the fuel stream of the ACR process

Info

Publication number: EP0118041A2
Application number: EP84101128A
Authority: EP
Inventors: Cyril B. Tellis; William B. Henstock
Original assignee: Union Carbide Corp
Current assignee: Union Carbide Corp
Priority date: 1983-02-04
Filing date: 1984-02-03
Publication date: 1984-09-12
Also published as: CA1209944A; JPS59146909A; EP0118041A3

Abstract

An energy efficient method for providing a soot-free gaseous fuel for an Advanced Cracking Reactor which is produced by partial oxidation of a hydrocarbon fuel to form gaseous products and non-gaseous products. The gaseous products are separated from the solid materials with minimum heat loss and can then be utilized as fuel for the ACR.

Description

TECHNICAL FIELD

This invention is concerned with a process for advantageously practicing the Advanced Cracking Reactor (ACR) process. Utilizinq this invention, a fuel oil such as a heavy residual fuel oil, and preferably the atmospheric vacuum residue fractions from the distillation of crude oil, is partially oxidized to produce a gaseous mixture of hydrooen and carbon monoxide (hereinafter termed "synthesis gas") and solid materials such as soot and metal oxides. The gaseous products are separated from the solid materials and are fed to the combustion zone of an ACR where they are mixed with oxygen and steam. The gaseous products act as the fuel for effecting the combustion reaction in the ACR. The products of the combustion reaction are thereafter contacted with a liquid stream of hydrocarbon feedstock and the combination of the two are fed through a throat portion of the ACR into the diverging diffuser/reactor section of the ACR. The hydrocarbon feedstream is therein convertea into the desired composition of cracked products which contains a larqe fraction of ethylene.

BACKGROUND ART

U. S. Patent No. 4,134,824, describes the integration of some of the features of the partial oxidation process into the ACR process. In said the the asphaltic residue of a crude oil feedstock which supplies a crude oil distillate fraction stream for the reaction, is fed as a fuel to the combustion step of the ACR process. In the combustion step, the asphaltic stream is combined with a "fluid fuel" and oxygen to be partially combusted in the presence of super-heated steam to form a reducing stream of hot combustion products. The partial combustion products are thereafter passed through the combustion zone and during the course of such passage, a crude oil distillate fraction stream is injected into the partial combustion products stream. The combination of hot partial combustion products and the crude oil distillate fraction flow at high velocities through a converging zone, the typical throat section of the ACR reactor, into a diverging zone in which the streams increase in velocity and cracking of the crude oil distillate fraction occurs. The cracking steo is followed by Quenching and product recovery.
The Advanced Cracking Reactor (ACR) process is explained in detail in U. S. Patent No. 4,136.015. It is described therein as involvina the production of a hot gaseous combustion product stream in a first-stage combustion zone in the presence of super-heated steam. The hydrocarbon feedstock to be cracked is then injected and mixed with the hot gaseous combustion product stream. That mixture is then fed into a cracking zone. The effluent from the reaction zone contains a stream which is rich in ethylene and contains varying concentrations of acetylene, propylene and butadiene. The typical ACR process will produce hydrogen, methane, acetylene, ethylene, ethane, propylene, propane, butenes, 1,3-butadiene, butanes, carbon monoxide, carbon dioxide methyl acetylene, propadiene, and similar gaseous products. Typical liquid products are pyrolysis gasoline, benzene, toluene, xylenes, C₈ non-aromatics, tars and pitches.
U. S. Patent No. 4,134,824 describes the utilization of the partial oxidation process to produce a product stream containing hydrogen, carbon monoxide, carbon dioxide, steam, sulfur compounds, and other minor components, sometimes referred to as synthesis gas. The partial oxidation reaction mechanism is therein described as involving an exothermic partial combustion of a portion of a hydrocarbon feedstream which supplies heat to the endothermic steam cracking of the balance of the feed. Besides carbon monoxide, hydrogen, carbon dioxide, hydrogen sulfide and other trace impurities, partial oxidation produces soot in non-equilibrium amounts. The composition of the products, particularly hydroqen/carbon monoxide ratio, sulfur and soot are generally determined by the type of feedstock, the oxygen/fuel ratio and the amount of steam used. The process of U. S. Patent No. 4,134,824 utilizes the asphaltic fraction of a fuel oil as part of the feed to the combustion reaction that is utilized for generating the temperature necessary for cracking of the distillate portion of the feedstock into the desired products of the cracking reaction, as described above. Consequently, U. S. Patent No. 4,134,824 effects in situ in the combustion zone, a partial oxidation reaction to thereby generate synthesis gas which is carried through the ACR reactor. Indeed, the synthesis gas in U. S. Patent No. 4,134,824 is utilized as a heat carrier gas for transporting the ACR feedstock into the reaction zone and for supplying the endothermic heat of reaction.
U. S. Patent No. 4,264,435 is essentially the same process as U. S. Patent No. 4,134,824. The alleged difference in U. S. Patent No. 4,264,435 resides in the suggestion that a substantial amount of super-heated steam which is injected into the combustion gases allegedly effects a shift in the reaction resulting in a product with a more desirable composition having a temperature of 1200° to 1800°C. This stream is thereafter contacted with the hydrocarbon feed in the typical ACR manner. The process of U. S. Patent No. 4,264,435, as is the case with U. S. Patent No. 4,134,824 effects the partial oxidation reaction in situ in the combustion zone and the synthesis gas formed thereby serves to carry the heat of the combustion reaction to the cracking reaction downstream.
_'U. S. Patent No. 4,321,131 describes a reforming step in which steam is combined with a fuel and fed to a reforming catalyst such as a metal catalyst of Group VIII, see column, lines 30 to 37 and the synthesis gas product formed is fed to the combustion zone of the ACR reactor with oxygen in the presence of steam to produce the combustion products stream, as defined previously.
In the processes of _U. S. Patent No. 4,264,435 and No. 4,321,131 , one problem reoccurs. In each of these processes, the technology that is utilized and with which synthesis gas formation is involved, generates a carbonaceous material which in one form or another must be treated during the overall operation of the ACR process. For example, in U.S. Patent No. 4,134,824 and U. S. Patent No. 4,264,435 processes, the partial oxidation process within the ACR process causes the formation of soot which will be carried through the reactor and deposited along the cracking reactor zone walls. Even though the typical ACR process will generate some carbonaceous deposit, the partial oxidation process will generate an increased concentration of such carbonaceous deposits and will thereby necessitate a greater frequency of carbon removal treatment in order to effectively operate the ACR process. The Lowe process on the other hand, causes steam and fuel to be reformed within a catalytic reaction step in which there will be generated a certain amount of carbonaceous material and such carbonaceous material, instead of going to the ACR reaction, will form within the reforming catalyst. This will necessitate a frequent treatment of the catalyst beds in order to restore their activity resulting from carbon deposits which caused the catalyst to be deactivated.
Another problem that is associated with the nrocess of U. S. Patent No. 4,264,435 and U.S. Patent No. 4,134,824 is that by virtue of starting with an untreated crude oil product, the combustion products will contain ash which will eventually contaminate the ceramic linino of the ACR reactor. Such ash can create an acid flux on the wall and could therefore result in breakage of the ceramic as well as corrosion.

SUMMARY OF THE INVENTION

The process of this invention avoids the aforementioned problems which are associated with partial oxidation in the combustion portion of the ACR or which are effected by a reforming process over a reforming catalyst.
The process of this invention provides a two-step process in which any gaseous, liquid, or solid hydrocarbon fuel can undergo a partial oxidation step whereby the synthesis gas product is physically separated from the soot and ash which are qenerated in such a way as to retain much of its sensible heat and such synthesis gas product is thereafter fed to the combustion zone of the ACR process and is utilized as a fuel to generate the desired beat for the cracking reaction. Neither U.S. Patent No. 4,134,824 nor U. S. Patent No. 4,264,435 utilizes synthesis gas as a fuel for producing the desired temperature of the cracking reaction, whereas the Lowe patent does describe a process which utilizes synthesis gas for that purpose.

DETAILED DESCRIPTION OF THE INVENTION

There is a substantial body of art directed to the manufacture of synthesis gas by the partial oxidation of hydrocarbon fuels. Illustrative of prior art is the following: British Patent 1,390,590; British Patent 1,445,549: British Patent 1,458,448; U. S. Patent No. 2,698,830; U. S. Patent No. 3,705,108; U. S. Patent No. 3,743,606; U. S. Patent No. 3,816,332; U. S. Patent No. 3,945,942; U. S. Patent No. 3,989,444; U. S. Patent No. 4,081,253; U. S. Patent No. 4,007,018; U. S. Patent No. 4,007,019; U. S. Patent No. 3,990,865; U. S. Patent No. 4,318,712 and U. S. Patent No. 4,282,010.
These patents variously describe the partial oxidation of a gaseous liquid or solid hydrocarbon fuel by reaction with oxygen in the presence of steam at a temperature ranging from about 800°C up to 2000°C, preferably at a temperature of about 1000° to about 1800°C, more particularly at a temperature ranqing from about 1200°C to about 1600°C to produce a stream which contains carbon monoxide, hydrogen, water and carbon dioxide as the gaseous products and soot and ash as the solid products. These well-known methods for producing synthesis gas may be used in the present invention.
There is also a substantial body of art directed at Quenching processes. Illustrative of this prior art are the following: U. S. Patent No. 3,719,029, U. S. Patent No. 3,576,519, U. S. Patent No. 3,671,198, U. S. Patent No. 3,285,847, U. S. Patent No. 3,907,661 and U. S. Patent No. 4,150,716.
Since the hydrocarbon stream has not been treated in advance to remove sulfur products, the gas stream that comes from the reaction also contains hydrogen sulfide and carbonyl sulfide. The hot gaseous effluent plus the soot in the ash are fed to a separation system whereby the soot and ash are removed from the gaseous stream. This can be accomplished by a number of procedures.
In the present invention, the gaseous effluent from the partial oxidation process passes directly from the reaction zone to a quencher. It is here that the bulk of the soot is removed by direct contact with this hydrocarbon Quench liquid. In this Quenching step, just enouqh heat is removed to stop the partial oxidation reaction and lower the temperature of the gaseous fuel to a point where it can be transported and handled by normal eauipment.
This is in contrast to the common quenching processes for partial oxidation reactions, whereby the temperatures of the gases are lowered considerably further so that the gases are suitable for other processing steps, such as acid gas removal or compression. Since the gases of the instant invention are to be used directly for fuel, the temperatures are lowered just to the point that the gases are usable in practical equipment. Thus, the process does not entail the energy losses and inefficiencies that are part of conventional quenching steps, and which waste part of the heat produced by the exothermic partial oxidation reaction.
The Quenching is done most conveniently by direct contact with a recirculating heavy hydrocarbon quench liquid. Several types of quenching apparatus which are direct liquid contact are known and are in use. Quenchers in which the quench liquid is sprayed into the gas stream would be especially suitable; those in which the gas stream flows through a body of quench liquid (immersion quenchers) are also suitable. However, other types of Quencher which would also be suitable can be conceived of, and could be used to practice this invention.
Some procedures utilize water to extract the solid soot and ash from the gaseous stream and other techniques utilize a hydrocarbon oil to effect the same results. The advantage of utilizing a hydrocarbon oil is that the oil plus the soot and ash products therein may be recycled directly back to the feed of the partial oxidation step and when water is used to effect quenching, another separation step must be introduced.
When the solid products are separated from the gaseous products, some heat is removed by the Quench fluid, thus lowering the temperature of the product gases. As little of this sensible heat as possible should be removed so that such heat can add to the heat production by the combustion reaction of the ACR. Therefore, the quenching and soot extraction is carried out in a manner such that the qases exit at a fairly high temperature, while still removing the bulk of the soot.
The gaseous effluent which is taken off from the separation step is typically a hot stream at a temperature ranging from.300_°C up to 1200°C. preferably at a temperature from 600°C to 1000°C. That stream will contain hydrogen, carbon monoxide, carbon dioxide, water, hydrogen sulfide, and carbonyl sulfide. Usually, users of synthesis gas do not want hydrogen sulfide and carbonyl sulfide in the products of that stream and will take steps to remove them. However, in the practice of the instant invention, hydrogen sulfide and carbonyl sulfide do not adversely affect the operation of the ACR.process. Consequently, those products may be left in the effluent coming from the soot/ash removal step. This provides the advantaqe of using a hot synthesis gas stream as a feedstream to the ACR combustion step. Consequently, a savings in fuel costs and oxygen are provided.
The synthesis-gas-containing stream which is obtained from the partial oxidation reaction is fed while hot to the burner of the combustion zone of the ACR wherein it is mixed with oxygen in an amount sufficient to effect essentially complete combustion of the hydrogen and carbon monoxide values within the synthesis gas. Utilizing the ratio of one-half mole of oxygen for each mole of hydrogen and one-half mole of oxygen for each mole of carbon monoxide, one should select an amount of oxygen which will leave the gas stream with a residual amount of synthesis gas still present.
The oxygen can be preheated to temperatures of up to approximately 800°C before it is fed into the ACR combustion zone. In the typical operation of the process of the invention, approximately 90 per cent or more of the synthesis gas is converted to combustion products. Since the usual synthesis gas which will be obtained will contain about a 1 _: 1 molar ratio of hydrogen to carbon monoxide, then one will utilize approximately 1/2 mole of oxygen for each mole of synthesis gas.
The remainder of the ACR process is practiced exactly as is described in the prior art. The feedstock which is fed to the ACR reaction may be shrouded in steam as described in U. S Patent No. 4,136,015 and U. S. Patent No. 4,142,963. The steam can be preheated to a temperature of 300°C-1200°C before it is fed into the Advanced Cracking Reactor combustion zones. The combustion product stream and the hydrocarbon feedstock can be thereafter fed to the cracking zone (termed in the prior art as the diffuser/reactor zone) wherein crackinq takes place to produce the desired products of the ACR process.
The conventional ACR is cbaraoterized in U.S. Patent No. 4,136,015. In particular the concept of a throated region through which the gas streams are passed at sonic velocity to obtain super-sonic velocities in a diverging diffuser/reactor zone is a preferred system for carrying out the ACR process. Quenching below the reactor zone as described in _U. S. Patent No. 4,136,015 and U. S. Patent No. 4,142,963 is a preferred method of operation as well as the further Quenching of the product streams as described in U. S. Patent No. 4,150,716.
The feed of hydrocarbon feedstream into the combustion chamber to be admixed with the combustion product stream can be carried out in an angular direction as described in U. S. Patent No. 3,855,339, utilizing the steam shroud principal described in U. S. Patent No. 4,142,963.
In the preferrea embodiment a steam shroud can also be injected along the diffuser/reactor walls by virtue of an inlet located at about the end of the throated section.

EXAMPLES

EXAMPLE I

A partial oxidation process produces a product gas consisting of 50 mole percent hydroqen and 50 mole percent carbon monoxide. This gaseous fuel is burned in essentially pure oxygen, with added steam, to produce a heat carrier for the ACR process. The temperature of the heat carrier is 2000°C. and the heat carrier is produced at the rate of 3.38 kg-moles/45 kg of feed. Oxygen is used at 95 percent of the stoichiometric amount.
After its production by partial oxidation, the fuel gas is Quenched and cooled to 100°C and fed to the ACR burner. Oxygen is fed to the ACR burner at 25°C and steam at 350°C. With these temperatures, the flow rates necessary to produce the desired heat carrier at the requisite temperature, and the resulting composition of the heat carrier is illustrated in Table A.
Example I indicates how fuel can be produced for the ACR, using a partial oxidation process under the present state of the art.

EXAMPLE II

A fuel gas for the ACR process is produced and used in an identical way to Example I, except that the qas is only partially quenched to 800°C. With the fuel gas at this temperature, the flow rates necessary to produce the desired heat carrier at the requisite temperature and the resulting composition of the heat carrier are illustrated in Table A.
Example II illustrates the results that can be achieved when practicing the process of this invention. By reducing the quench temperature to a range of approximately 600°C-1000°C, less fuel and oxygen are needed to generate a heat of reaction temperature of 2000°C. In Example II the quench temperature was 800°C, and there were fuel savings of 1-37 kg/45 kg feed, and a 1.40 kg/45 kg feed reduction in the amount of oxygen utilized. Not only has a significant fuel and oxygen savings been realized, but additionally the amounts of carbon dioxide and carbon monoxide in the ACR effluent have been reduced. This allows for savings in subsequent acid-gas removal processes.

Claims

1. A method for providing gaseous fuel for an Advanced Cracking Reactor, which involves partially oxidizing a hydrocarbon fuel and quenching the gaseous products of such partial oxidation process to remove the bulk of the solid products while removing a minimal amount of the sensible heat of the partial combustion products, and feeding the remaining high-temperature gaseous products of said partial oxidation, usually at 300°C-1200°C to the combustion zone of the Advanced Cracking Reactor wherein such is combusted with oxygen and mixed with a hydrocarbon feedstream and then fed through the throat portion of the Advanced Cracking Reactor into the diffuser/reactor portion of said reactor wherein cracking of the hydrocarbon feedstream is effected.

2. The method of Claim 1 wherein the gaseous products of the partial oxidation process are Quenched with a heavy oil or water.

3. The method of Claim 1 wherein the oxygen is preheated to a temperature of u^p to approximately 800°C before it is fed into the Advanced Cracking Reactor combustion zone.

4. The method of Claim 1 wherein the steam can be preheated to a temperature of 300°C-1200°C before it is fed into the Advanced Cracking Reactor combustion zone.

5. The method of Claim 1 wherein the feeastock of the partial oxidation process is any qaseous liquid or solid hydrocarbon fuel.