JPS6329582B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method and apparatus for preventing solid material deposition on tubular reactor walls. Tubular reactors are well known and widely used in the chemical processing industry. It is also known that tubular reactors become fouled by deposits of solid substances and often have to be shut down for cleaning. Examples of processes that produce contamination include polymerization reactions, hydrocarbon cracking, and high temperature hydrocarbon reactions that generally involve the formation of elemental carbon. When the reactor walls are covered with deposits, many difficulties arise: (i) the heat transfer rate between the tube walls and the material in the tube center is reduced; (ii) the temperature regulation becomes poor and the reaction control is adversely affected. (iii) resulting in decreased formation of desired products and/or increased formation of undesired by-products;
Tubes often heat up, reducing reactor life;
(iv) Shutdown and cleaning cycles are often required, and the longer the reactor tube, the more expensive and difficult the cleaning operation; (v) damage to the reactor or auxiliary equipment occurs if the reactor tube becomes clogged and the safety valve blows out; . All of these difficulties compromise the safety of the entire reactor operation. Moreover, these problems become even more acute when long residence times and/or high processing temperatures are required, such as in cracking operations. If deposits form inside the reactor tubes, these can be treated by mechanical means (e.g. high-pressure water or steam jets), solvents (e.g. silane or hot hydrocarbons) or chemical reactions (e.g. oxidation and/or reduction).
can be removed by However, these methods
All require removal of part or all of the reactor for the cleaning cycle. It is clear that it is preferable to prevent solid deposition in the tubular reactor rather than removing it after formation. Several methods are known in the art for this purpose. Namely, (1) a method of controlling reaction conditions such as temperature and pressure;
(2) how to adjust the catalyst feed rate to prevent rapid reaction and consequent overheating; (3) how to add inhibitory chemicals such as amines, polyisobutylene or steam-hydrogen mixtures; (4) how to control solid materials and reactor walls; (5) recirculating a portion of the product from the reactor to the inlet to increase the linear flow rate in the reactor and maintain turbulence. U.S. Patent No. 3919074 describes black oil as 316
A method is described in which recirculation is performed in an industrial size reactor to reduce contamination when heated to -427°C. Such recycling methods have the disadvantage that the recycling introduces a certain concentration of undesirable reaction products, such as coke precursors, into the reactor inlet, thus increasing the source of contamination. According to this method, even under the temperature conditions of the patent, contamination is reduced but not completely prevented. At higher temperatures, as in the test series described below, recirculation increases the apparent rate of fouling, ie, reduces the operating time before the reactor tube becomes completely clogged. Additionally, using recirculation in small-scale devices may make it impossible to achieve the desired turbulence because of the excessive pressure drops required for it in small diameter pipes. A novel feature of the present invention is the addition of an oscillatory flow component to the reactant mass flowing within the tubular reactor. The additional oscillating velocity component is designed to create turbulence in the reactor. The agitation provided by the turbulent flow prevents solid deposition on the reactor walls, thus preventing the risk of reactor blockage and reactor shutdown. The present invention thus provides a method for treating a liquid that flows through a tubular container at a velocity that produces predominantly laminar flow conditions, and in which solids may form and deposit on the walls of the container. maintaining a continuous supply of liquid to the container inlet at a rate that results in a laminar flow of liquid as it moves to the outlet; (b) applying a normally varying pressure pulse to the liquid stream at a flow section near one end of the container; (c) a surge chamber adapted to receive and discharge liquid and connected to the flow near the other end of the container opposite the point of application of the varying pressure pulse; (d) the pressure is maintained such that during the cycle the liquid flow conditions in the vessel between the point of pulse application and the surge chamber reach a peak instantaneous Reynolds number within the turbulence zone; A method for effectively controlling the frequency and amplitude of the pulses, characterized in that: (e) ejecting liquid substantially continuously from a downstream outlet of the surge chamber. The invention further provides an apparatus for treating liquids having a tendency to deposit solids on the walls of the tubular reactor, comprising: (a) a tubular reactor in which the treatment is carried out; (b) a chamber communicating with the reactor and in the treated liquid. (c) a pulsating mechanism near one end of the reactor comprising means for inducing vibrations in the reactor; means proximate the other end; (d) means for ensuring a substantially continuous feed to the reactor system comprising the reactor, a pulsation mechanism and means for including a surge; and (e) a reactor system. Means at the outlet of the reactor system for maintaining the pressure inside the reactor system. Optionally, the pressure retention means may have means for preventing backflow of reaction products from the downstream processing means to the reactor system outlet. One specific example of the invention is shown in FIG. A tubular reactor for the heat treatment of coke-forming heavy oil petroleum fractions, such as decant oil, comprises a reactor tube 1, a pulsation mechanism 2, means 3 for containing a surge, an inlet tube 4, a supply means 5, an outlet tube 6 and a pressure - Consists of backflow control means 7. The reactor tube has an internal diameter appropriate to the reactor design capacity and allowable pressure drop. Usually, 1/
There is no need to use a diameter smaller than 8 inches (3.2 mm). This is because, according to the method of the present invention, turbulent flow can easily occur in such a small tube even when starting from a zero-indestructible flow. At the upper end of the scale, the method is limited only by the energy level that must be subjected to pulsation. In practice, only economic considerations limit the maximum diameter, due to the cost of imparting dynamic energy to the reactive material in adding pulsating flow to a stationary flow. The reactor tubes can be designed in the form of multiple parallel tubes, a single length of coiled tube, or one or more series of coiled tubes. If necessary, replace this with a gas or oil burner,
It can be heated by an electric heater or indirectly by a heating medium, or it can be cooled by suitable means. The frequency of the pressure pulses and the amount of liquid displaced can be designed to meet the needs of a particular reaction situation. Construction and operating economics usually influence reactor sizing and are judged against chemical requirements such as reaction rate and possible chemical equilibrium. The resulting persistent flow velocity is in the laminar band and would require increasing the velocity by a factor of 10 or more to achieve turbulent flow. Under the influence of the pulsating mechanism,
Frequently, the velocity changes and the Reynolds number varies within the laminar flow zone, resulting in a turbulent flow zone if properly adjusted for displacement and frequency. If the peak instantaneous Reynolds number is in the turbulence band, the average Reynolds number may be somewhat lower. The critical value required for turbulence is not clearly defined, depending on the shape of the flow channel. For circular tubes the critical value is in the range 2000-3000. In the present invention, a peak Reynolds number of 2700 appears to be sufficient to generate turbulence and prevent solids deposition on the reactor walls. However, a Reynolds number of 3000 is a value that includes a safety margin, so the fluctuating flow characteristics are preferably a combination of sub-audio frequencies and displacement capacities that result in peak Reynolds numbers of 3000 or more. The pulsating mechanism may, for example, consist of a rigid chamber containing a reciprocating piston or a diaphragm, optionally driven by positive mechanical drive means. The design volume of the chamber may take into account the vibrating piston or diaphragm and the displaced liquid volume to ensure that the peak oscillating velocity added to the liquid flow in the reactor tube is in the turbulent flow zone. In another arrangement, a pressurized substantially inert gas may be used to pulse the liquid surface within the solid chamber. Pressure pulses in the inert gas space of the chamber are controlled by electrical, pneumatic, and electrical equipment installed on the line connecting the chamber to a high-pressure gas source, using suitable means to relieve the gas pressure during the reverse part of the pulse cycle. It can be controlled by pressure or mechanically driven valves. In some cases, liquids that are immiscible with the processing material may be used in place of the gases described above. The means for containing the surge must be capable of accommodating a volume at least equal to the volume of liquid displaced by each vibration of the pulsating mechanism. The means for containing the surge may include a gas, optionally isolated from the reaction mass by a diaphragm. In another arrangement, the means for containing the surge may consist of a piston or diaphragm in the second chamber similar to the pulsating mechanism, the piston or diaphragm being a means for maintaining pressure above the reaction liquid, e.g. and a spring or pressurized gas on the opposite side. Optionally, the two chambers may be mechanically connected, and if each reciprocating mechanism is driven by a positive mechanical drive means, the vibration mechanism and the means for containing the surge are driven by the same positive mechanical drive means. It can be driven by mechanical drive means. However, in this case the phases are 180° out of phase, ie, as one piston or diaphragm moves forward, the other moves backward. The feed line to the reactor may have means for maintaining the desired feed rate, such as a pump or, if the upstream pressure is sufficient, a tube or pipe equipped with a non-return valve. The product outlet line may have conventional tubing or piping and means for maintaining pressure and/or preventing fluid backflow from downstream processing stages to the reactor system. The use of such means depends on the pressure within the reactor system compared to the downstream pressure. For example, such means may be a check valve or a pump if the reaction pressure is lower than the downstream pressure during part or all of the pulsation cycle. This means, for example, that if the reactor pressure exceeds the downstream pressure,
It can be a pressure regulating valve. It may be located near the inlet or outlet of the reactor, provided that the applied vibration velocity is transmitted through the reactor tube to the surge vessel at the other end. The invention is illustrated by the following test series, which are not intended to limit the scope of the invention. Test Series - Conventional Methods and Systems A heavy oil fraction consisting of full range decanted oil was fed into a tubular reactor 10 feet (3.05 m) long and 3/8 inch (9.5 mm) inside diameter. A reactor tube in the form of a single coil was immersed in an electrically heated bed of fluidized sand. The reactor temperature was 493°-504°C. about 9
The feed rate was adjusted to obtain a residence time at the reaction temperature of -11 minutes. The times for the three tests before the reactor became clogged with coke were as shown in the table. Calculations of Reynolds numbers in all test series are necessarily approximate, since the density and viscosity of the reacting material at the conditions indicated are estimated rather than measured values, and each test Started with a new reactor tube. The longest test lasted 48 hours, and the reactor had to be shut down and cleaned after each test, and tubes clogged with coke had to be replaced.

TABLE TEST SERIES - CONVENTIONAL METHODS AND SYSTEM Another test was conducted using a tubular reactor 20 feet (6.1 m) long and 3/8 inch (9.5 mm) inside diameter. A series of decant oils were fed to the reactor at a very low rate and 80% of the product was recycled to the reactor resulting in an average residence time of about 4-8 minutes. A reactor tube in the form of a single coil was immersed in series into an electrically heated fluidized sand bed. The reactor temperature was controlled at 487°C-494°C. The test results shown in the table showed the negative effects of recycling a portion of the heat-treated product to the reactor. The longest time before complete reactor blockage was 12 hours compared to 48 hours with no recirculation in the series.

Table Series - Examples of the Invention The test series illustrates the use of the invention. Decanted oil as used in the series and above was fed to the pulsating reactor with a gear pump at a rate of about 1700 g/hour. A reactor tube in the form of a single coil was immersed in an electrically heated fluidized sand bed as in series. The tests are summarized in a table. For Test-A, the length is 67 feet (20.4
m), a 1/4 inch (6.4 mm) inner diameter reactor tube was used. Reactor residence time is approximately 9.9 minutes, average temperature is 502℃
It was hot. A pulsating mechanism located at the reactor tube inlet has a chamber displacing 4 ml per stroke and
It consists of a diaphragm that vibrates at 115 strokes/minute. A surge vessel was partially filled with nitrogen and placed at the reactor tube outlet. The test lasted for 57 hours with no blockages or pressure overruns in the reactor tubes. When the reactor was removed, the inner surface of the tube was free of deposits. Test-B, like Test-A, continued smoothly for 82 hours continuously and then was shut down normally. Test-B used a 34 foot (10.4 m) long, 3/8 inch (9.5 mm) inner diameter reactor tube. The average reactor temperature was 529°. The pulsation mechanism consisted of a chamber displacing 7 ml per stroke and a piston vibrating at 58 strokes/min. The surge container had the same characteristics as Test-A. At the end of the experiment, the inner surface of the reaction tube was virtually free of deposits.

[Table] *Normal shutdown without reactor blockage The series of tests uses a vibrating flow reactor to ensure that no blockage occurs in the reactor during heat treatment of decant oil under specified processing conditions. showed that. The present invention is designed to reproduce the generally turbulent flow in an industrial tubular reactor, without recirculating any part of the product, in a pilot plant (regardless of the size limitations of the pilot plant). ), and can be advantageously used in industrial thermal reactors (operating below their design capacity). In the case of heat-treated decant oils, recycling a portion of the heat-treated product has an adverse effect: it increases the tendency for coke formation and deposits to occur in the reactor and thus shortens the reactor run. Another important application of the present invention is in industrial reactor applications that are prone to reactor blockage due to polymerization and solids formation in the layered boundary layer. The invention can also be used very advantageously in industrial crackers and cokers where the pyrolysis products have a tendency to polymerize or solidify in the reactor tubes when the flow exhibits a Reynolds number below the turbulence zone. . Another advantageous application of the present invention is in small- to medium-sized industrial heater applications, since they generally create turbulent flow without the need to size smaller than 2 inches inside diameter, which is difficult to clean. Because you will get it. It will be understood by those skilled in the art that oscillating flow reactors are applicable to reactor systems in which reactants undergo several types of processing. The above tests describe systems in which heat is transferred to the reactor. The principle is also valid in cooling systems, ie where heat is removed from the reactants in the tubes. The use of turbulent flow is even more important in cooling systems because the viscosity of the reactants increases with decreasing temperature, reducing the Reynolds number and thus creating an undesirable tendency toward laminar flow. Under this situation, higher volumes and/or oscillation frequencies may be required to maintain the Reynolds number within the turbulence zone. The methods and apparatus described above are also applicable to substantially adiabatic chemical reactions, such as reactions that yield polymers with high viscosities and a tendency to deposit on tube walls. Although the foregoing experiments demonstrate preferred embodiments of the invention,
Various modifications and applications may be made without departing from the spirit and scope of the invention, as will be understood by those skilled in the art.

[Brief explanation of the drawing]

FIG. 1 shows one embodiment of the invention. DESCRIPTION OF SYMBOLS 1... Reactor tube, 2... Pulsation mechanism, 3... Means for containing surge, 4... Inlet pipe, 5... Supply means, 6... Outlet pipe, 7... Pressure-backflow control means.

Claims (1)

Claims: 1. A method for treating a liquid that flows through a tubular container at a velocity that produces predominantly laminar flow conditions and in which solids may form and deposit on the walls of the container, comprising: maintaining a continuous supply of liquid to the container inlet at a rate that results in a laminar flow of liquid as it moves to the outlet; (b) applying a normally varying pressure pulse to the liquid stream at a flow section near one end of the container; (c) a surge chamber adapted to receive and discharge liquid and connected to the flow near the other end of the container opposite the point of application of the varying pressure pulse; (d) the pressure is maintained such that during the cycle the liquid flow conditions in the vessel between the point of pulse application and the surge chamber reach a peak instantaneous Reynolds number within the turbulence zone; Effectively controlling the frequency and amplitude of the pulses, the method comprising: (e) substantially continuously discharging liquid from a downstream outlet of the surge chamber. 2. The method of claim 1, wherein the flow reaches a peak instantaneous Reynolds number greater than 3000. 3. In an apparatus for treating liquids having a tendency to deposit solids on the walls of the tubular reactor, comprising: (a) a tubular reactor in which the treatment is carried out; (b) a chamber communicating with the reactor and a turbulent flow during each vibration. (c) a pulsation mechanism near one end of the reactor comprising means for inducing continuous sub-audible vibrations in the process liquid of sufficient frequency and amplitude to achieve a band peak instantaneous Reynolds number; means near the other end of the reactor opposite the pulsating mechanism for containing a surge of liquid produced by an oscillating flow; (d) comprising a reactor, a pulsating mechanism and a means for containing the surge; and (e) means at the outlet of the reactor for maintaining pressure inside the reactor system. 4. The apparatus of claim 3, wherein the reactor tube has an internal diameter ranging from 1/1 inch (3.2 mm) upwards. 5. Device according to claim 3, wherein the pulsation mechanism has a chamber and a piston or a chamber and a diaphragm, provided with means for inducing a reciprocating movement. 6. Apparatus according to claim 5, wherein the surge containment means comprises a chamber and a piston or a chamber and a diaphragm with means for maintaining pressure on the processing liquid. 7. The device of claim 6, wherein the surge containment means is mechanically attached to the pulsation mechanism. 8. The device of claim 7, wherein the surge containment means are mechanically attached to the pulsation mechanism and both pistons or diaphragms are connected to the same reciprocation inducing means. 9. The device of claim 3, wherein the surge containment means is a container partially filled with inert gas. 10. The device of claim 3, wherein the means for controlling the liquid flow at the outlet of the system are of the group consisting of non-return valves, pumps and pressure regulating valves. 11 A method of treating a liquid that flows through a tubular container at a velocity that produces predominantly laminar flow conditions and in which solids may form and be deposited on the walls of the container, (a) as the liquid moves to the outlet of the container; maintaining a continuous supply of liquid to the container inlet at a rate that results in a laminar flow of liquid; and (b) substantially continuously discharging the liquid from an outlet at the end of the container remote from the inlet. (a) applying a regular varying pressure pulse to the liquid stream at a flow section near one end of the container; (c) maintaining by the pulse a positive liquid displacement to and from a surge chamber connected to the flow near the other end of the vessel; (c) between the point of pulse application and the surge chamber during the cycle; effectively controlling the frequency and amplitude of the pressure pulses such that the liquid flow conditions in the vessel during the period reach a peak instantaneous Reynolds number within the turbulence zone. 12 Apparatus for treating liquids which have a tendency to deposit solids on the walls of a tubular reactor, comprising: (a) a tubular reactor in which the treatment is carried out; (b) a substance to the reactor inlet at one end of the reactor; and (c) means at the reactor outlet remote from the inlet for maintaining pressure inside the reactor. a chamber through which the fluid flows, and means for inducing continuous sub-audible oscillations in the liquid flow in the reactor of sufficient frequency and amplitude to achieve a peak instantaneous Reynolds number of the turbulence band during each oscillation. , a pulsating mechanism near one end of the reactor, and (b) means near the other end of the reactor opposite the pulsating mechanism for containing a surge of liquid caused by the oscillating flow; A device characterized by having: