FR2888920A1 - Hydrocarbon catalytic reforming kiln maintenance procedure uses catalytic tube temperature sensor(s) connected to data acquisition system to determine tube life - Google Patents

Abstract

The maintenance procedure for a hydrocarbon catalytic reforming kiln consists of fitting at least one catalytic tube (7) in the kiln with a temperature sensor connected to a data acquisition system that allows for continuous recording of temperature variations during the kiln's operation. The recorded temperatures are converted into a duration of the remaining life for each tube, on which a replacement plan can be based. The temperature sensor is attached to a downstream portion of the tube in relation to the reaction mixture's circulation, with measurements taken by at least one thermocouple and recorded by a SCADA (Supervisory Control And Data Acquisition) system capable of operation over a period of about ten years.

Description

The present invention relates to a method of maintaining a furnace of

  catalytic reforming of a hydrocarbon reaction mixture, comprising at least one catalyst tube, according to which the temperature of said tube is monitored, as well as to an installation implementing said maintenance method.

  Hydrocarbons are one of the main sources of synthesis gas. Synthesis gas is produced by converting CnH 2 hydrocarbons into carbon monoxide (CO), carbon dioxide (CO2) and dihydrogen (H2). The gases produced are then used to carry out numerous chemical reactions. Thus, the dihydrogen may be used in particular to carry out hydrogenation reactions or, after addition of nitrogen N 2, to produce ammonia; a mixture of CO, CO2 and H2 can lead to the synthesis of methanol, and the mixture CO and H2 is the basis of oxo syntheses, etc. One of the most used processes to achieve this transformation is the catalytic reforming of natural gas. In such a process, natural gas, comprising mainly methane, is reacted with steam in the presence of a catalyst to produce dihydrogen and carbon oxides. Although the conversion of CO to CO2 and H2 is exothermic, the reforming reaction is generally endothermic and is generally carried out at a temperature close to 1000 C. It should be noted that the natural gas must be previously freed from the sulfur compounds that it contains, these being generally poisons for the catalysts used.

  In practice, the catalytic reaction of hydrocarbon reforming by steam is carried out under pressure on the catalyst contained in tubes heated externally by radiation up to a temperature of about 1000 ° C., that is to say say in tubular ovens. These catalyst tubes are arranged vertically and the circulation of the reaction mixture is from top to bottom.

  A reforming furnace comprises a zone of radiation, a combustion chamber in which the catalyst tubes are arranged, and a convection zone through which the fumes and combustion gases produced in the combustion chamber are discharged. The combustion gases discharged through the convection zone are used to preheat the reaction mixture of hydrocarbons and water vapor, and possibly other reaction fluids, such as nitrogen in the case of a production of ammonia. The convection zone is usually installed either above the firebox, vertically next to the oven, or horizontally.

  More specifically, the catalyst tubes used are generally centrifuged tubes of alloy steel. The tube must withstand the high pressures and temperatures used in such a process, while ensuring good heat transfer to the reaction mixture circulating therein. In addition to having a resistance adapted to very high temperatures, these tubes must be made of a material also having a very good creep resistance at such temperatures.

  In view of the heating cycles and high temperatures to which the catalyst tubes are subjected, their aging and integrity must be monitored in the most accurate and reliable manner possible. Indeed, although designed to withstand very high temperatures, the materials used to make these tubes have a maximum temperature limit relatively close to the temperature conditions to which they are subjected, and a reconciliation of this maximum limit value results in a significant decrease in the life of the tubes. For example, a constant operation at 20 C above the temperature for which the tubes were designed, typically 1000 C, halves the life of the tubes, from a decade to about five years . This problem is of particular importance during start-up phases or changes in the composition of the reaction mixture. Monitoring and history of the temperatures to which the tubes are subjected is therefore a crucial aspect of the catalytic hydrocarbon reforming process.

  At present, measurements of the temperature of the tubes are carried out by pyrometric measurements in a discontinuous manner. Measurements can also be made using thermocouples. Such measurements are localized and punctual, and do not allow to know the temperature differences to which the catalyst tubes are subjected. In addition, the pyrometric measurements are carried out by means of a manhole opened by an operator, which modifies the temperature inside the oven at the level of the manhole.

  One of the main risks arising from this lack of accurate data is the inadvertent breakage of one or more catalyst tubes during operation, which implies stopping the installation outside predefined maintenance intervals. In addition, during transient phases such as a restart following a maintenance stop or a change in the composition of the reaction mixture, there is always the risk that an overheating will not be detected and corrected immediately, the service life of catalyst tubes can then be reduced significantly.

  The object of the present invention is to overcome the disadvantages mentioned above and consists in that of a method for maintaining a catalytic reforming furnace of a hydrocarbon reaction mixture, comprising at least one catalyst tube, according to which the temperature of said tube, characterized in that it comprises the following steps, namely: equipping at least one catalyst tube with at least one temperature sensor, - connecting each temperature sensor to a data acquisition system, - recording continuously change the temperature measured by each temperature sensor during the entire use of the oven, - convert the recorded temperature measurements to a remaining life for each followed catalyst tube, with a view to planning the replacement .

  Thus, continuous recording of temperature data of the tubes provides a precise history of temperatures over a long period of time for each catalyst tube equipped with a temperature sensor. In this way, any temperature overruns and hot spots can be monitored and recorded to estimate their impact on the integrity of the catalyst tubes. Such a temperature history makes it possible to calculate an estimate of the remaining lifetimes of each equipped catalyst tube and thus to anticipate the replacement of the tubes during a maintenance shutdown according to the temperature overruns that have been observed throughout. the use of the oven. This significantly reduces the risk of rupture of the tubes during operation and increase their life.

  Continuous temperature data acquisition also makes it possible to monitor the temperature accurately during transient phases such as a restart or a change in the composition of the reaction mixture. Thus, the reactivity of operators in case of overheating is greatly increased and immediate action can be taken to correct this overheating.

  Furthermore, it should be noted that the temperature sensors are permanently integrated in the catalyst tubes and that temperature measurements therefore do not require intervention of an operator unlike pyrometric measurements. The temperature disturbances caused by the opening of a manhole by an operator are avoided as well as the risks incurred by the operator during such a measurement.

  Advantageously, the control method comprises an additional step for obtaining a value of the maximum temperature of the catalyst tube and / or a value of a skin temperature of the catalyst tube from a temperature measurement. Values of the skin temperature of the tube and the maximum temperature of the tube can be obtained from the temperature measured using correlations established according to the position of the temperature sensor.

  Advantageously, at least one temperature sensor is fixed downstream of the catalyst tube relative to the direction of circulation of the reaction mixture. Indeed, it is downstream of the catalyst tube that the temperature is the highest. In this way, the measured temperature is substantially equal to the maximum temperature of the catalyst tube.

  Preferably, the temperature measurements are performed by at least one thermocouple.

  Preferably, the acquisition and recording of the temperature measurements are carried out by means of a SCADA type system (Supervisory Control And Data Acquisition). Such a system allows the management of a large number of data sources and the real-time recording of these data.

  The present invention also relates to an installation comprising at least one furnace intended for the catalytic reforming of a reaction mixture of hydrocarbons flowing in at least one catalyst tube, characterized in that it comprises a suitable data acquisition system. continuously recording temperature measurements obtained by at least one temperature sensor equipping at least one catalyst tube, and a calculation system capable of converting the recorded temperature measurements into a remaining lifetime for each followed catalyst tube, to plan for replacement.

  Advantageously, at least one temperature sensor is a thermocouple disposed downstream of the catalyst tube relative to the flow of the reaction mixture.

  Advantageously, the data acquisition system is a SCADA type system.

  Preferably, the data acquisition system is capable of recording temperature measurements continuously over a period of about ten years. The theoretical lifetime for which the catalyst tubes are designed being about ten years, such a memory capacity allows for a complete history of the catalyst tubes.

  The implementation of the invention will be better understood with the aid of the detailed description which is explained below with reference to the appended drawing in which: FIG. 1 is a partial schematic representation of a furnace of a plant of catalytic reforming of hydrocarbons according to the invention.

  FIG. 2 is a partial schematic representation of the furnace combustion chamber shown in FIG.

  FIG. 3 is a partial schematic representation of a catalyst tube disposed inside the combustion chamber of the oven of FIG.

  Figure 4 is a partial front view of a catalyst tube equipped with a temperature sensor.

  A catalytic reforming furnace 1 according to the invention, as shown in FIG. 1, comprises a combustion chamber 3 equipped with burners 4 connected to a fuel supply 5 and to an oxidizer feed 5b, and a convection chamber 6. intended for the evacuation of the gases and fumes generated by the burners 4.

  More specifically, the burners 4 are intended to heat the catalyst tubes 7 passing vertically through the combustion chamber 3, as shown in FIGS. 1 to 3. Each catalyst tube 7 has, on the one hand, a first end 8 located in top through which is introduced a reaction mixture comprising hydrocarbons and steam, and secondly, a second end 9 located at the bottom connected to a collector 10 of the products of the catalytic reforming reaction.

  The reaction mixture is introduced into the catalyst tube 7 by a feed 11 designed so as to circulate the reaction mixture beforehand in the convection chamber 6 in order to preheat it with the gases and fumes evacuated.

  More specifically, the feed 11 of the reaction mixture comes from an outlet 12 of a hydrocarbon desulphurization unit in which water vapor is injected from a pipe 13. Accessally, the outlet 12 of hydrocarbons desulphurized may be supplemented by an injection 14 in 002 from another unit producing 002, in order to recycle the latter.

  As shown in Figures 2 to 4, at least some catalyst tubes 7 are each equipped with a thermocouple 15, the latter being fixed at the second end 9 of the catalyst tube 7, that is to say at the foot of this one. As shown in FIG. 4, each thermocouple 15 is housed in a thermal protection casing 16 in order to protect it from the direct heat of the burners 4, and is connected by a cable 17 to an external (not shown) acquisition and acquisition system. data recording. The data acquisition and recording system is a SCADA-type system for real-time data processing. More specifically, the thermocouples 15 are fixed in catalyst tubes 7 selected to be representative of a temperature profile in the oven 1. Of course, each catalyst tube 7 may be equipped with a thermocouple 15 of its own.

  In operation, the burners 4 heat the catalyst tubes 7 in which circulates the reaction mixture. Typically, the tubes are heated to an interior temperature of about 600 C at the first high end 8 and an interior temperature of about 950 C at the second low end.

  The temperatures measured by each thermocouple 15 are transmitted to the data acquisition and recording system by which they are first converted to skin temperature values of the catalyst tubes 7 and / or maximum temperature values for each catalyst tube 7 equipped with a thermocouple 15. These values of skin temperatures and / or maximum temperatures are obtained from mathematical correlations applied to the measured temperatures. Since the thermocouples 15 are preferably fixed at the second end 9 of the catalyst tubes 7, the temperatures measured are very close to the maximum temperatures of the catalyst tubes 7.

  The temperature data thus obtained are recorded in real time by the acquisition and recording system.

  An estimate of the remaining life of the catalyst tubes 7 can be calculated from the temperature data thus recorded. The calculation of this remaining life uses the relationship of Larson Miller, one of the most used laws to describe time to failure. For a detailed study of the temperature break and an example of life-time calculation as a function of temperature, reference can be made to the article Journal of Corrosion Science and Engineering, Volume 6 Paper H012 available at the following address http : //www2.umist.ac.uk/corrosion/JCSE/Volume6/Default.html.

  Specifically, for each catalyst tube 7, for each temperature recorded by the associated thermocouple, a maximum lifetime of the catalyst tube 7 is calculated at this temperature using the Larson Miller temperature parameter, calculated as a function of the thermal properties of the catalyst tubes 7. Depending on the length of time during which the catalyst tube 7 has remained at this temperature, an equivalent duration of use is calculated by relating the previously calculated maximum lifetime to the service life for which the catalyst tube was designed. The sum of these equivalent periods of use obtained over time is deduced from the theoretical lifetime for which the catalyst tube is designed. When the estimated remaining service life becomes less than the period of time separating two maintenance stops, it is agreed to schedule the replacement of the catalyst tube 7 at the next maintenance stop.

  For example, for a catalyst tube 7 designed to have a lifetime of 100000 hours at 1000 C and having a Larson-Miller temperature parameter of 35.2058; the calculation of the remaining service life is carried out as follows: If, for example, the catalyst tube 7 has been subjected to a temperature of 956 C for 1000 hours, the maximum service life at this temperature is 481277 hours, more than four times the design life, or nominal. Therefore, 1000 hours at 956 C equals 208 hours of operation at 1000 C in terms of aging of the catalyst tube 7. After these 1000 hours, the remaining life of the catalyst tube is therefore 99792 hours. These calculations are repeated for each temperature measurement, and each equivalent calculated life is deducted from the remaining service life. When this calculated remaining life becomes less than the period of time separating two maintenance stops, the replacement of the catalyst tube 7 is programmed for the next maintenance stop.

  Thus, it is easy to identify the catalyst tubes 7 having a remaining remaining life and to program their change during a maintenance stop of the furnace 1.

  Although the invention has been described in connection with particular embodiments, it is obvious that it is not limited thereto and that it comprises all the technical equivalents of the means described and their combinations if they are within the scope of the invention.

Claims (9)

  A method of maintaining a catalytic reforming furnace (1) for a hydrocarbon reaction mixture, comprising at least one catalyst tube (7), according to which the temperature of said tube is monitored, characterized in that comprises the following steps, namely: - equipping at least one catalyst tube with at least one temperature sensor (15), - connecting each temperature sensor to a data acquisition system, - continuously recording the evolution of the temperature measured by each temperature sensor during the entire use of the oven, -convert the recorded temperature measurements to a remaining service life for each followed catalyst tube, in order to plan for replacement.   2. Method according to claim 1, characterized in that it comprises a further step to obtain a value of the maximum temperature of the catalyst tube (7) and / or a value of a skin temperature of the catalyst tube to from a temperature measurement.   3. Method according to any one of claims 1 or 2, characterized in that at least one temperature sensor (15) is fixed in the downstream portion of the catalyst tube (7) relative to the direction of flow of the reaction mixture.   4. Method according to any one of claims 1 to 3, characterized in that the temperature measurements are performed by at least one thermocouple (15).   5. Method according to any one of claims 1 to 4, characterized in that the acquisition and recording of temperature measurements are performed through a SCADA type system.   6. Installation comprising at least one furnace (1) for the catalytic reforming of a hydrocarbon reaction mixture circulating in at least one catalyst tube (7), characterized in that it comprises a suitable data acquisition system continuously recording temperature measurements obtained by at least one temperature sensor (15) equipping at least one catalyst tube, and a calculation system capable of converting the recorded temperature measurements into a remaining lifetime for each tube of catalyst, with a view to planning for replacement.   7. Installation according to claim 6, characterized in that the temperature sensor is a thermocouple (15) disposed downstream of the catalyst tube (7) relative to the flow of the reaction mixture.   8. Installation according to any one of claims 6 or 7, characterized in that the data acquisition system is a SCADA type system.   9. Installation according to any one of claims 6 to 8, characterized in that the data acquisition system is capable of recording temperature measurements continuously over a period of about ten years.