JPS6360078B2 - - Google Patents

Description

BACKGROUND OF THE INVENTION CROSS-REFERENCE TO RELATED APPLICATIONS This application is a result of the same development effort and is co-registered with the present application entitled “Aromatics from Heavy Hydrocarbons (BTX)”.
(by Swami Narayama, Axel R. Johnsson and Herman H. Webke). FIELD OF THE INVENTION This invention relates generally to the pyrolysis of hydrocarbons to produce olefins. More specifically, the present invention relates to the cracking of heavy hydrocarbons, such as naphtha, kerosene, atmospheric gas oil, vacuum gas oil, and residual oil, to produce olefins. Most particularly, the present invention relates to the use of cracked light hydrocarbons as a diluent and heat source for heavy hydrocarbon cracking. Description of the Prior Art There are currently a variety of methods available for cracking heavy hydrocarbons to produce olefins. Typically, the hydrocarbons to be cracked are fed to a furnace consisting of both convective and radiant zones or sections. The hydrocarbons are first brought to temperature in the convection zone and then sent to the radiant zone where they are exposed to intense heating from a radiant burner. An example of a conventional furnace and method is shown in US Pat. No. 3,487,221 (Harry). After decomposition, the effluent is rapidly cooled to terminate the decomposition reaction. The use of steam as a diluent in the cracking of hydrocarbons is also well known. This diluent steam reduces the hydrocarbon partial pressure in the cracking coil which reduces the mixture molecular weight. The reduced partial pressure prevents the formation of undesirable coke products inside the radiant tube. Additionally, increasing diluent steam increases the yield of desired components during digestion.
On the other hand, the use of steam in a hydrocarbon stream requires greater furnace capacity and equipment than is required for hydrocarbons without steam. Additionally, when using steam, energy and equipment must be provided to generate and heat the steam. Ultimately, the economic optimum lies in the steam to hydrocarbon ratio. In the past, light hydrocarbons were commonly used to produce olefins in pyrolysis processes. Generally, light hydrocarbons can be cracked with diluent steam ranging from 0.3 to 0.6 pounds per pound of hydrocarbon. More recently,
Demand for olefins has exceeded the availability of light hydrocarbons. Therefore, the industry has turned to heavier hydrocarbons as feedstocks for olefin production. It has been found that larger amounts of diluent steam are required for heavier hydrocarbons than for lighter hydrocarbons. Heavy hydrocarbons are hydrocarbons 1
It has been found that approximately 0.7 to 1.0 pounds of steam per pound is required. The general suggestion is that heavier hydrocarbons require a higher amount of diluent to obtain the desired hydrocarbon partial pressure needed to reduce the coking rate in the radiant coil during pyrolysis. Requires steam. In comparison, diluent steam requirements increase furnace size and utility usage. The industry has advocated diluents other than steam in pyrolysis in the past. For example, in US Pat. No. 4,021,501 (Daiel) the use of butane as a diluent during the cracking process is proposed. In US Pat. No. 4,002,556 (Satsuchiel), a proposal is made to use hydrogen donor diluents. Therein, the hydrogen donor is a partially hydrogenated material and readily releases hydrogen under pyrolysis conditions. This material is injected at multiple points into the cracker to maintain the hydrogen transfer ratio to cracking ratio at a substantially uniform level throughout the reactor. The industry has also used hydrocarbons as quenching materials for direct quenching of thermal cracking effluents. In U.S. Pat. No. 2,928,886 (Nisbet), the cracked gas effluent is quenched by direct contact with an oil-in-water emulsion (5%-15% oil). Additionally, it is known to use aromatic hydrocarbons and gas oils as quench oils to increase the olefin yield of cracked feedstock oils. The basic concept is disclosed in French Patent No. 1349293 (Metal Gesell Shaft) and Japanese Patent No. 41/19886 (Sumitomo Chemical). Very recently, light hydrocarbons have been cracked under high severity conditions and the cracked effluent is then simultaneously quenched with heavy hydrocarbons, and the heavy hydrocarbon quench is used to remove the sensible heat from the cracked effluent. A method of decomposition at low severity by using US Pat. No. 4,268,375 (Jeyongson). In all known methods, the heavy hydrocarbons are first partially cracked with a minimal amount of diluting steam, and then the cracked light hydrocarbon effluent is used as a diluent under high severity conditions. There is no single way to cause complete decomposition. SUMMARY OF THE INVENTION It is an object of the present invention to provide a process by which heavy hydrocarbons can be cracked using a minimal amount of steam, i.e. considerably less diluent steam than the conventional 0.7 to 1.0 pounds of diluent steam per pound of hydrocarbon. There is a particular thing. Another object of the invention is to crack heavy and light hydrocarbons in one combined process. It is a further object of the present invention to crack the light hydrocarbons at high coil exit temperatures essentially to their maximum conversion and simultaneously crack the heavy hydrocarbons to an intermediate stage, after which the cracked light hydrocarbons effluent. It is an object of the present invention to provide a method for combining materials with partially cracked heavy hydrocarbon effluent to serve as a diluent for heavy hydrocarbons. Yet another object of the present invention is that the equipment size and utility requirements for the process are reduced to the extent that currently heavy hydrocarbon The objective is to provide a method that can be made smaller than what is required for decomposition. Yet another object of the present invention is to provide substantial utility reductions and construction cost savings based on reduced area requirements and minimization of dilution steam generation equipment. To this end, methods and apparatus are provided for cracking light hydrocarbon feedstocks and heavy hydrocarbon feedstocks in one combined system. The light hydrocarbon feed oil is conventionally cracked in a first stage using a conventional amount of diluent steam. The light hydrocarbon feed is cracked by first supplying dilution steam to raise the temperature of the feed in the convection section of the furnace, and then converting the light hydrocarbon feed to maximum conversion in the radiant zone of the furnace. Proceed by decomposing up to the ratio. At the same time, the heavy hydrocarbon feed oil is supplied with a small amount of diluent steam and heated to a temperature in the range of 1000° in the convection zone of the furnace. This heavy hydrocarbon feed oil is then partially cracked in a radiant zone at temperatures above 1100° and up to 1450°. The light hydrocarbon feed oil cracked at a high conversion rate and this partially cracked heavy hydrocarbon feed oil are combined.
Further decomposition of heavy hydrocarbons can occur in one of several ways: (i) in the radiation zone - under direct flame control; (ii) In the radiation belt - but out of the direct line of radiation exposure. (iii) Adiabatically - completely isolated from radiation and convective contributions. It can also be outside the furnace. and (iv) by a combination of these modalities. In the common line, the cracked pyrolysis gas from the light feed oil is actually quenched to stop or reduce the reaction of the light effluent. At the same time, the heat from the light hydrocarbon feed oil cracked at high conversion provides additional heat to crack the heavy hydrocarbon feed oil. The furnace design developed for this process includes a section of the furnace suitable for partially cracking the heavy hydrocarbon feed oil, a section for maximizing the conversion of the light hydrocarbon feed oil, and its light carbonization. Sections are employed which provide individual regulation of the heat supplied to a common line in which the hydrogen pyrolysis gas is quenched and the partially cracked heavy hydrocarbon effluent is further cracked to a desired level of conversion. Conventional quenching methods and conventional separation systems are also provided to complete the process. DESCRIPTION OF THE DRAWINGS The invention is better understood when considered in conjunction with the drawings. In these drawings, FIG. 1 is a schematic diagram of the process of the invention, shown as being suitable for application using a conventional pyrolysis furnace, and FIG. 1 is a schematic diagram of a furnace specifically designed to crack heavy hydrocarbons; FIG. DESCRIPTION OF PREFERRED EMBODIMENTS As noted above, the process of the present invention is directed to providing a means for cracking heavy hydrocarbon feed oils without the need for large amounts of diluent steam.
Previously, this large steam requirement was necessary to provide the partial pressure necessary to suppress coke formation in the radiant section of the cracking furnace. Contemplated heavy hydrocarbon feed oils are naphtha, kerosene, atmospheric gas oil, vacuum gas oil, and residual oil. moreover,
The process of the invention can be carried out in conventional furnace equipment, but as will be seen, furnaces uniquely adapted and specifically designed for the process of the invention are also provided. The method of the present invention is conveniently characterized as "duocracking." As best seen in FIG. 1, a conventional furnace 2 comprising a convection zone 6 and a radiant zone 8 is equipped with convection and radiant piping in which the method of the present invention can be carried out. The convection zone 6 of the present invention is arranged to receive a feed oil inlet line 10 for a light hydrocarbon feed oil and an inlet line 18 for a heavy hydrocarbon feed oil. Coils 12 and 20, through which the light and heavy hydrocarbon feed oils pass, respectively, are located in the convection zone 6 of the furnace. Piping 14 and 2
2 are provided to send dilution steam to convection coils 12 and 20, respectively. The radiant zone 8 includes a coil 16 for cracking light hydrocarbon feed oil to a high conversion rate and a coil 24 for partially cracking heavy hydrocarbon feed oil. A common coil 26 is also provided in which the heavy hydrocarbon feed oil is broken down to high severity in one of the four manners previously described and the effluent from the light hydrocarbons is actually quenched. The reaction ends. An effluent discharge pipe 28 is provided and conventional quenching equipment, such as a USX (double tube exchanger) and/or a TLK (tubular transfer line exchanger), is provided to quench the cracked effluent. There is. This system also includes a separation system 4, which is conventional. As seen in FIG. 1, separation system 4 separates the quenched effluent into residual gas (line 32), ethylene product (line 34), propylene product (line 36),
butadiene/ _C4 product (line 38), pyrolysis gasoline/BTX crude product (line 40), light fuel oil product (line 42) and fuel oil product (line 4).
4) is adapted to separate. Optionally, piping 24A is provided to convey partially cracked heavy hydrocarbons from convection coil 20 directly to common piping 26. Under certain conditions, this heavy hydrocarbon can be partially decomposed in the convective zone 6, thereby making further decomposition in the radiant zone unnecessary. Essentially, the process of the invention is carried out by passing ethane, propane, normal butane and isobutane, propylene, mixtures thereof, raffinate or naphtha through piping 10 to a convection coil 12 in the convection section 6 of the furnace 2. . naphtha, kerosene,
A heavy hydrocarbon feed oil, such as atmospheric gas oil or vacuum gas oil, is routed through line 18 to convection coil 20 . The dilution steam is sent by line 14 to the convection coil 12 through which the light hydrocarbon feed oil is being passed. Preferably, the dilution steam is superheated steam at a temperature in the range of 800° to 1000°.
The dilution steam is mixed with the light hydrocarbon feed oil at a ratio of approximately 0.3 to 0.6 pounds of steam per pound of feed oil. The light feed oil and diluent steam complex is heated in the convection section 6 to a temperature of approximately 1000 to 1200 °C. This heated hydrocarbon is then passed through a coil 16 in the radiant zone of the furnace 2. In this radiant section, the light hydrocarbon feed oil is preferably cracked under high severity conditions to a temperature between 1500 and 1700 degrees with a residence time of about 0.1 seconds to 0.3 seconds. At the same time, heavy hydrocarbon feed oil is fed via line 18 to convection coil 20 in convection zone 6 of furnace 2. The diluted steam is conveyed by line 22 to convection coil 20 and contains about 0.15% diluted steam per pound of hydrocarbon.
Mix with heavy hydrocarbons at a ratio of 0.20 pounds of steam. This mixture is mixed in the convection zone 6 of the furnace 2 at 850
Temperature between 〓 and 1200〓, preferably 900〓 and 1000〓
The temperature is raised to between 〓 and 〓. The heavy hydrocarbon feed oil from the convection section 6 is then routed to the radiant coil 24 where it is heated from 1250
Partially decomposed at a temperature of 1450° with a residence time of approximately 0.05 to 0.20 seconds. This partially cracked heavy hydrocarbon feed oil is routed to common line 26, and the completely cracked light hydrocarbon pyrolysis gas from line 16 is also routed to this common line 26. In the common line 26, the fully cracked light feedstock effluent provides heat to effect a more complete cracking of the partially cracked heavy hydrocarbons. As a result, the light hydrocarbon feed oil effluent is quenched in this common line 26 by the cooler partially cracked heavy hydrocarbons. This complex mixture is further decomposed and then quenched in conventional quenching equipment before being separated into various specific products. The furnace 102 of FIG. 2 has been specifically developed for the method of the present invention. As in a conventional furnace, a convection zone 106 and a radiation zone 8 are provided. However, a separate coil 120 in the convection zone is provided for the passage of heavy hydrocarbons, and another coil 112 is provided for the passage of light hydrocarbons. The radiant zone 108 includes a radiant coil 116 and a plurality of burners 1 for high severity cracking of light hydrocarbon feed oil.
40 are arranged. In practice, coil 11
6 can be a shell-and-tube coil, and the burner is about 60 to 65% ethane, 85% to 95% propane, 90 to 95% C ₄ , 95 to 98% rough inate or light naphtha, It has a composite heating capacity that achieves the lightening rate level. The short coil 116 provides low residence time but high coil exit temperature. Such short coils improve selectivity. Longer coils of 116 can also be used which can provide the above conversions of light components but provide lower coil exit temperatures. Any of these can be used to advantage as is well known to those skilled in the art. An array of radiant burners 140 provides the necessary heat to cause high severity cracking of light hydrocarbons in coil 116. The radiant section 108 also includes a coil 124 for partial cracking of heavy hydrocarbons, which may be monotube. An array of burners 142 provides the heat necessary to partially decompose heavy hydrocarbons. Burners 14 arranged facing a common pipe 126
6 provides individual heating of the common tube 126 in which the heavy hydrocarbons are completely cracked and the light hydrocarbon effluent is quenched. The available heat in the light hydrocarbon effluent now provides enthalpy for continued cracking of the heavy hydrocarbons. By selecting appropriate flow rates of the light and heavy hydrocarbon streams, the required amount of heat to complete heavy hydrocarbon cracking can be provided. However, the tubes 126 can now be individually fired by burners 146 to provide the additional heat needed beyond that provided by the light hydrocarbon effluent. Maintaining the coil 126 inside the hot box environment provides an atmosphere in which the heavy hydrocarbons absorb heat from the light effluent isothermally under controlled conditions. Heavy hydrocarbons, which reach higher temperatures instantaneously by mixing, have a
It is held for a short residence time of 0.02 to 0.05 seconds to provide the desired conversion level. Keeping coil 124A shaded from direct radiation provides an atmosphere in which the heavy hydrocarbons absorb heat adiabatically from the light effluent. The subsequent introduction of light hydrocarbon cracking effluent into the heavy hydrocarbon stream in coil 124A also provides a controlled temperature increase profile for the heavy hydrocarbons. Higher conversion levels of heavy hydrocarbons are achieved by increasing the mixture temperature to 1500-1600° by adding additional heat by burner 146 if necessary. Under these increased thermal conditions, complete conversion of heavy hydrocarbons occurs with shorter residence times of 0.01 to 0.02 seconds. Examples of the process of the invention compared to conventional methods demonstrate the yield advantages of the invention. In that example,
The following process conditions are maintained:

【table】

TABLE The dual cracking yield data reported in this example is only the contribution of gas oil in the combined cracking step. Ethane contribution was obtained by decomposing ethane under the same process conditions as the mixture. This ethane contribution was subtracted from the mixture yield to obtain only the gas oil contribution under "duocracking" process conditions.

Claims (1)

[Claims] 1. A method for producing olefins by thermally decomposing heavy hydrocarbon feedstocks, comprising: (a) steaming heavy hydrocarbon feedstocks to produce olefins of 0.2 pounds per pound of heavy hydrocarbons; (b) Raise the temperature of the heavy hydrocarbons with a steam diluent to a temperature that causes partial thermal cracking; (c) Light carbonization lighter than this heavy hydrocarbon feed oil; (d) completely pyrolyzing the light hydrocarbon feed; (e) feeding the fully cracked light hydrocarbon effluent to the partially cracked heavy hydrocarbon stream; (f) further cracking the combined stream; and (g) quenching the effluent from a cracked composite stream of heavy and light hydrocarbons to terminate the reaction; 2. The method of claim 1, wherein diluent steam is fed to the light hydrocarbon stream at a ratio of 0.3 to 0.6 pounds of steam per pound of light hydrocarbon. 3. The method of claim 1, wherein the heavy hydrocarbon is a material selected from the group consisting of naphtha, kerosene, atmospheric gas oil, vacuum gas oil, and residual oil. 4. The light hydrocarbon is selected from the group consisting of ethane, propane, propylene, normal and isobutane, raffinate and naphtha, or mixtures thereof.
The method described in section. 5. The method of claim 1, wherein light hydrocarbons are decomposed under high severity, short residence time decomposition conditions. 6. The method according to claim 1, wherein heavy hydrocarbons are partially decomposed under moderately severe decomposition conditions. 7 Heavy hydrocarbons are heated in the convection zone of a thermal cracking furnace.
Heating the light hydrocarbons to a temperature of about 1000㎓ in the same pyrolysis furnace convection zone; cracking the light hydrocarbons to the highest possible conversion in the pyrolysis furnace radiation zone. and supplying completely cracked light hydrocarbons and heavy hydrocarbons from the convection zone to a common pipe in which the heavy hydrocarbons are then cracked to a desired degree of completion; as set forth in claim 1. the method of. 8. The method of claim 2, wherein the diluent steam is superheated steam having a temperature in the range of 365° to 1000°. 9 A heating furnace for simultaneously decomposing heavy hydrocarbons and light hydrocarbons; a convection section; b radiant section; c convection coil for heavy hydrocarbons; d convection coil for light hydrocarbons; e a radiant coil in the radiation zone that communicates directly with the convection coil for light hydrocarbons; f a radiant coil in the radiation zone that communicates directly with the convection coil for heavy hydrocarbons; and g a heavy hydrocarbon convection coil and a light hydrocarbon convection coil. a common coil in the radiant band terminating the radiant coil in communication with the coil; 10. The furnace of claim 9, wherein a portion of the radiation band is insulated to provide an adiabatic environment. 11. The method of claim 10, wherein the radiation band coil in communication with the light hydrocarbon convection coil comprises a shell-and-tube arrangement arranged to provide the required amount of heat to cause acceptable conversion of the light hydrocarbons. Furnace. 12. Claim 10 or 12, wherein the radiant coil in communication with the heavy hydrocarbon convection coil is a single-current coil arrangement and is adapted to supply the necessary amount of heat to cause partial conversion of the heavy hydrocarbons. Furnace according to paragraph 11. 13 consisting of a single-current common coil in which the radiant band coil terminates, which coil can add or sustain a discrete amount of heat to bring about the required degree of complete conversion of the heavy hydrocarbons; Claim 1 is arranged so that
The furnace according to item 0 or item 11.