Patent Application
20250109340
This application claims the benefit of priority under 35 U.S.C. § 119 of German Application 10 2023 004 053.3, filed Oct. 1, 2023, the entire contents of which are incorporated herein by reference.
The present invention pertains to a quenching system and to a process for a quenching system for cooling cracked gas from a cracked gas furnace.
There are different raw materials, which are further processed in a cracking furnace, for operating an ethylene furnace, which is also called a cracked gas furnace or a cracking furnace. Such raw materials are heated to a high temperature in a cracking furnace and subsequently cooled down with a quenching system, which is also designated by QS, for short.
Depending on the raw material, a specially configured quenching system or QS is needed because the physical properties of the raw materials are different. Gas as a raw material may be cooled down to a greater extent, e.g., from 900° C. to 150° C., than a liquid raw material, which is cooled down from about 900° C. to 350° C. because the condensation of gas only starts at markedly lower temperatures.
A quenching system for a liquid feed mode consists of a primary heat exchanger or PQE, for short, and of a secondary heat exchanger or SQE, for short, which are connected in series. In this case, the PQE and the SQE are connected as vaporizer and evaporator, respectively, and are also operated as such.
EP 3 032 209 B1 may be mentioned as state of the art. A quenching cooling system consisting of a primary quench cooler as a double tube heat exchanger and a secondary quench cooler as a tube bundle heat exchanger comprising at least one tube bundle is known from EP 3 032 209 B1. The tube bundle is enclosed by a jacket, forming a jacket space, which is configured between two tube sheets, which are arranged at spaced locations from one another, between which tube sheets respective bundle tubes of the tube bundle are held in the tube sheet on both sides.
A process and a device for cracking liquid hydrocarbon residues with steam is well known from U.S. Pat. No. 8,158,840 B2, wherein a separating device for steam/liquid is used to treat a heated-up steam/liquid mixture and to ensure a steam flow with reduced residue content. The process comprises an indirect heat exchange of liquid distillation residues with feed water or boiler feed water to provide liquid distillation residues and preheated feed water; diverting at least some of the preheated feed water to a steam drum; and recovery of steam having a steam pressure of at least about 4100 kPa from the steam drum. The device comprises, among other things, a liquid feed cracking furnace, a separating device for steam/liquid as well as a primary heat exchanger and a secondary heat exchanger.
A heat exchanger for cooling cracked gas in an ethylene plant, in which heat exchanger heat exchanger tubes, through which the cracked gas flows, are inserted at their respective ends into a tube plate each and are enclosed by a jacket, on both end faces of which an end chamber each, partly defined by one of the tube plates, is intended for feeding and discharging cracked gas, is known from EP 1 939 412 B1. As a cooling medium, water flows through the interior of the heat exchanger, which interior is enclosed by the jacket and is split into two subspaces, which lie one behind the other in the direction of flow of the cracked gas and which are provided with their own respective feed pipe and exhaust pipe for the cooling medium, by means of a partition, which runs at right angles to the heat exchanger tubes and through which the heat exchanger tubes pass.
Drawbacks of the arrangement of a quenching system that is applied for cooling cracked gases from a cracked gas furnace can be seen in that the heat balance during the cooling down of cracked gas has up to now not yet been accomplished to a satisfactory extent from economical and environmental points of view. A cracked gas leaves a cracked gas furnace in a temperature range of 800° C. to 900° C. at a pressure of 0.5 barg to 2 barg or 0.05 Mpag to 0.2 Mpag. A heat exchanger arranged directly behind the cracked gas furnace would have to be manufactured from high-alloy steels if such a construction shall be embodied. Such a configuration would lead to a high effort technically and would be very expensive economically compared to conventional technology. Fivefold to tenfold higher costs may be assumed. Hence, it is absolutely expedient to precool cracked gases from a cracked gas furnace in a conventional primary quench exchanger or PQE cooled with water/steam.
In case of a quench cooler cooled with water/steam, the material temperatures are markedly lower than in the case of a quench cooler cooled with gas because of the higher heat transfer, among other things. The precooling of cracked gases should have a temperature value of 700° C. to 550° C., so that low-alloy to medium-alloy steels can be used in a quench cooler for the further cooling down of cracked gases in order to lower costs significantly and to protect the environment.
The object of the present invention is to provide a quenching system and a process for a quenching system for cooling cracked gases from a cracked gas furnace using different raw materials, which improves the high requirements imposed in terms of the technical and environmental arrangement and mode of operation in regard to reliability and costs and guarantees a simple possibility in regard to necessary repairs and maintenance.
The present object of the present invention is generically accomplished by means of a quenching system according to the invention and a process according to the invention, wherein a transfer line exchanger for a cooling medium consisting of a gas mixture+steam or TLE-G/G, for short, is arranged and configured as a secondary quench exchanger, that the TLE-G/G is connected in series to a primary quench exchanger or PQE via a gas transfer line, which is mounted at the inlet end of a cracked gas in the TLE-G/G, and that the TLE-G/G is connected to the cracked gas furnace via a return line of preheated cooling medium.
Furthermore, the TLE-G/G is equipped with a feed line for a cooling medium consisting of HC+steam. An exhaust line for cooled-down cracked gas is arranged at the outlet end of the TLE-G/G.
Furthermore, the TLE-G/G is connected to the cracked gas furnace via a return line of preheated cooling medium. Furthermore, a feed line conveying the cooling medium consisting of gas mixture and steam is arranged at the TLE-G/G at the lower part in front of the outlet header of the vertically oriented TLE-G/G.
The TLE-G/G is advantageously connected via a return line to the cracked gas furnace for returning cooling medium consisting of hydrocarbon gas+steam or hydrocarbon+steam or HC+steam, for short, which has been preheated in the TLE-G/G.
In addition, the TLE-G/G is equipped with a pipeline for forwarding cracked gas having been cooled down to temperatures ranging from 450° C. to 300° C. for further processing.
A compensator is preferably provided at the upper end of the TLE-G/G behind the cracked gas inlet header. A gas inlet pipe for the feed line of a cooling medium is advantageously arranged at the jacket of the TLE-G/G. A number of baffles are preferably mounted in the jacket space of the TLE-G/G, the number of such baffles depends on the respective predefined load case and will be determined accordingly. The cooling medium is guided alternatingly by 180° around the outside of tube bundle during the counterflow process around the baffles of the TLE-G/G.
Furthermore, a gas outlet pipe for the return line of the preheated cooling medium is preferably arranged at the jacket of the TLE-G/G at the upper end in front of the inlet header of the vertically oriented TLE-G/G. Segments free from tube bundles are advantageously provided in areas of the baffles in the jacket space of the TLE-G/G.
The size of the segment, through which free flow is possible, is preferably dimensioned to be between 10% and 20% of the cross-sectional area of the internal diameter of the jacket of the TLE-G/G.
The tube bundle of the TLE-G/G are advantageously arranged in a triangular configuration for a flow of a cooling medium, wherein the side length of the triangle is 1.2 times to 1.3 times that of a tube diameter of a tube bundle.
A compensator, compensating different thermal expansions between a tube bundle and the jacket, is advantageously installed around the jacket of the TLE-G/G at the upper end behind the inlet header of the cracked gas from the TLE-G/G.
Cleaning pipes are preferably arranged close to the tube sheet of the cracked gas outlet header of a vertically oriented TLE-G/G in the area of the jacket space of the TLE-G/G. In this case, in the area of the jacket space of the TLE-G/G, two to four closable cleaning pipes are preferably provided with a diameter of 200 mm to 500 mm each, wherein the cleaning pipes are mounted at a distance of 100 mm to 200 mm from the lower tube sheet.
According to a predefined level of contamination due to coke deposits in the case of a horizontally oriented TLE-G/G, two to four cleaning pipes are each provided, with a diameter of 200 mm to 500 mm, lengthwise in the lower area of the jacket space.
In the case of a process for a quenching system for cooling cracked gas from a cracked gas furnace using different raw materials, which comprises a cracked gas furnace, a primary quench exchanger and a secondary quench exchanger, which are connected in series, it is considered to be especially advantageous when a transfer line exchanger for a cooling medium consisting of a gas mixture and steam or a TLE-G/G is arranged and configured as a secondary quench exchanger. In this case, the TLE-G/G is connected in series to the primary quench exchanger or PQE via a gas transfer line.
At the TLE-G/G a feed line conveying the cooling medium consisting of a gas mixture and steam is advantageously arranged at the lower part in front of the inlet header of the vertically oriented TLE-G/G. The TLE-G/G is preferably connected via a return line to the cracked gas furnace for returning cooling medium preheated in the TLE-G/G. Furthermore, the TLE-G/G is equipped with a pipeline to forward cracked gas that has been cooled down to temperatures ranging from 450° C. to 300° C. for further processing.
It is especially advantageous that a compensator is provided at the upper end behind the cracked gas inlet header in the TLE-G/G.
Furthermore, it is advantageous that at the jacket of the TLE-G/G, a gas inlet pipe for the feed line of a cooling medium is arranged at the lower part in front of the outlet header of a vertically oriented TLE-G/G.
It is further advantageous when a number of baffles are mounted in the jacket space of the TLE-G/G, the number of such baffles depends on and will be determined by the respective predefined load case. In this case, the cooling medium is advantageously guided alternately by 180° around the outside of the tube bundle during the counterflow process around the baffles of the TLE-G/G. A gas outlet pipe for the return line of the preheated cooling medium is especially advantageously arranged at the jacket of the TLE-G/G at the upper end in front of the inlet header of a vertically oriented TLE-G/G.
Furthermore, segments free from tube bundles are advantageously provided in the jacket space of the TLE-G/G in areas of the baffles.
The size of the segment, through which free flow is possible, is preferably dimensioned to be between 10% and 20% of the cross-sectional area of the internal diameter of the jacket of the TLE-G/G. The tube bundle of the TLE-G/G are preferably arranged in a triangular configuration for a flow of a cooling medium, wherein the side length of the triangle shall be 1.2 times to 1.3 times that of a tube diameter of a tube bundle.
A compensator compensating different thermal stresses between the tube bundle and the jacket is advantageously installed around the jacket of the TLE-G/G at the upper end behind the inlet header of the cracked gas from the TLE-G/G.
Furthermore, cleaning pipes are preferably arranged close to the tube sheet of the cracked gas outlet header of a vertically oriented TLE-G/G in the area of the jacket space of the TLE-G/G.
Two to four closable cleaning pipes with a diameter of 200 mm to 500 mm each are preferably provided in the area of the jacket space of the TLE-G/G, wherein the cleaning pipes are mounted at a distance of 100 mm to 200 mm from the lower tube sheet of the outlet header of the TLE-G/G.
Another advantage is that according to a predefined level of contamination due to coke deposits in the case of a horizontally oriented TLE-G/G, two to four cleaning pipes each with a diameter of 200 mm to 500 mm lengthwise are provided in the lower area of the jacket space.
Further details and advantages of the present invention are explained in more detail on the basis of an exemplary embodiment shown in the drawings. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.
In the drawings:
Referring to the drawings,
Coils 11 are arranged in front of the cracked gas furnace 10, which lead to the suggested primary quench exchanger or PQE 12 as precooler. In the conventional PQE 12 as precooler, cracked gases are precooled to about 700° C. to 550° C. or lower. The PQE 12 is provided with a feed pipe 17 and with an exhaust pipe 18. Cooling water is fed in via the feed pipe 17, and the water/steam mixture that has formed during the precooling is forwarded via the exhaust pipe 18.
A known function of the PQE 12 will not be further discussed below. The PQE 12 as a precooler shall only precool the high temperatures of the cracked gases of 800° C. to 900° C. from the cracked gas furnace 10 to a temperature of about 700° C. to 550° C. A selection of materials and the costs connected therewith for the TLE-G/G 14 connected in series to the PQE 12 are then considerably simplified and greatly reduced.
The TLE-G/G 14 is connected in series via a gas transfer line 13 to the PQE 12. The precooled cracked gas from the PQE 12 is sent on the tube side into the TLE-G/G via the gas transfer line 13. The cracked gas is further cooled down to temperatures of 450° C. to 300° C. in the TLE-G/G 14. A cracked gas is forwarded via a pipeline 19 for further processing.
A feed line 15 is arranged at the lower end in front of the outlet header of the vertically oriented TLE-G/G 14 for the cooling medium consisting of a gas mixture and steam or hydrocarbon gas and steam or hydrocarbon and steam or HC+steam, for short. A gas mixture having a temperature of 200° C. to 290° C. and consisting of HC+steam is fed on the jacket side to the TLE-G/G 14 via the feed line 15 and flows through the TLE-G/G in the counterflow process.
A return line 16 is arranged at the upper end in front of the inlet header of the TLE-G/G 14, which return line 16 is guided to the cracked gas furnace 10. The gas mixture consisting of HC+steam, which has been preheated in the TLE-G/G 14 to 400° C. to 550° C., is returned into the cracked gas furnace 10. The already preheated gas mixture consisting of HC+steam is further heated to 800° C. to 900° C. in the cracked gas furnace 10, wherein the gas mixture consisting of HC+steam is cracked. The cracked gas mixture or cracked gas is then fed to the PQE 12 as the precooler again. The process is repeated.
An accurate function of a cracked gas furnace will not be discussed in more detail here because its function is well known in the state of the art.
In a jacket space 30 of the TLE-G/G 14, the gas mixture consisting of HC+steam is introduced via a gas inlet pipe 31 mounted at the lower end in front of the outlet header of the vertically oriented TLE-G/G and is repeatedly guided alternately by 180° around the outside of each bundle tube 36 during the flow by means of baffles 33 that are arranged in the jacket space of the TLE-G/G. The HC+steam mixture leaves the TLE-G/G 14 via a gas outlet pipe 32, which is mounted at the upper end in front of the inlet header of the vertically oriented TLE-G/G.
The number of the baffles 33 depends on the respective predefined load case and will be determined accordingly. The pressure loss in the jacket space 30 is especially high due to repeated deflections of the HC+steam mixture and should be reduced to a minimum to achieve a good efficiency of the quenching system. Hence, a tube bundle/tube sheet 37 shall have an especially good configuration such that no bundle tubes 36 are located in the area of a segment 34, through which the flow passes. The segments 34 remaining free from bundle tubes 36 contributes significantly to the reduction of the pressure loss and are essential for the process. The size of the segment 34, through which free flow is possible, is between 10% and 20% of the cross-sectional area of the jacket internal diameter and depends on the respective predefined load case.
The advantages in case of the preferred TLE-G/G quench cooler for a quenching system can be seen in that cracked gases are heated in a cracked gas furnace and in the process cracked, precooled by a primary quench exchanger or PQE and then guided on the tube side by the TLE-G/G and cooled down further.
Unlike in conventional quench coolers, no water/steam mixture is used in the TLE-G/G as cooling medium on the jacket side, but rather a gas mixture and steam consisting of hydrocarbon gas and steam or, for short, HC+steam or hydrocarbon+steam is used. Such a mixture consisting of HC+steam is preheated in the TLE-G/G and at the same time it cools down cracked gases or cracking effluent from a cracked gas furnace, which are used for the production of ethylene and then for the production of plastic. The preheated mixture consisting of HC+steam is returned to the cracked gas furnace for further heating and is cracked in the cracked gas furnace and is fed again to the TLE-G/G via the PQE.
The energy needed for heating a cracked gas furnace is reduced due to the advantageous procedure or heat recovery, which has a highly positive impact economically and environmentally in the overall process in terms of costs and consumption.
A conventional PQE as a precooler shall be used in front of the TLE-G/G in order to operate the cracked gas furnace efficiently not only during the initial operation, but generally also in case of scheduling, implementation and later repairs or maintenance.
While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2023 004 053.3 | Oct 2023 | DE | national |
