Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/0004—Gaseous mixtures, e.g. polluted air
  • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
  • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
  • G01N33/0036—Specially adapted to detect a particular component
  • G01N33/0047—Specially adapted to detect a particular component for organic compounds
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N5/00—Analysing materials by weighing, e.g. weighing small particles separated from a gas or liquid
  • G01N5/02—Analysing materials by weighing, e.g. weighing small particles separated from a gas or liquid by absorbing or adsorbing components of a material and determining change of weight of the adsorbent, e.g. determining moisture content

Definitions

• the present invention relates to the field of techniques for analyzing and measuring pollutants in a gas flow. More particularly, it relates to a device and method for continuously measuring tars of a gas, these tars can be in the form of traces and at high temperature (T> 800 ° C).
• One of the major problems encountered in vapo-gasification processes is to be able to continuously evaluate the quality of the gas generated to ensure that it meets the requirements required for its application (generation of electricity, energy mechanical, heat, fuel synthesis or formation of hydrogen).
• the evaluation of the specifications of the synthesis gas requires knowing the composition of the gas and therefore, among other things, the concentration of the different polluting species; they are sulfur, nitrogen, chlorine compounds, alkali metals, dust and tars.
• the presence of tars in the gases resulting from gasification poses numerous problems in the various applications concerned, such as the deterioration of the blades of the turbines or the loss of activity of the catalysts by deactivation, in particular in the metal and zeolitic catalysts.
• Tars can pose other problems, especially in pyrolysis or gasification reactors where, under the action of heat, they give rise to a deposit of heavy hydrocarbon compounds, called coke, on the walls of the reactor, this phenomenon carrying the coking name. Following this deposition, the heat transfers to the reactor are reduced.
• the formation of coke also tends to increase the pressure losses in the ducts and in the absence of corrective action eventually clogs the pipes. Coke comes from a complex mechanism that breaks down into a catalytic sequence and a thermal
• a first difficulty is related to the meaning of the generic term "tar”, which differs according to the field of application considered.
• tars In the context of air pollution, metallurgy, waste incineration, co-generation and the production of synthetic fuels, the term “tars” is generally used to refer to all organic compounds having a molecular weight greater than that of benzene - 78 g / mol - but there is no official definition for this term, and the literature reports about thirty definitions for the word "tar”
• the tars cover a broad spectrum of species (more than 2000) whose physicochemical characteristics (polarity, volatility, molar mass, chemical affinity) vary over a wide range of values, which makes it particularly difficult to obtain measurement showing the total amount of tars.
• Physicochemical characteristics polarity, volatility, molar mass, chemical affinity
• Several classifications of these different compounds have been proposed so far, such as the classification of Milne & Evans (1998) which lists the different tars in three classes:
• Class 1 primary species
• Class 2 secondary species
• Class 3 tertiary species
• the main components are polycyclic aromatic hydrocarbons (PAHs), volatile organic compounds (VOCs) and phenols.
• PAHs polycyclic aromatic hydrocarbons
• VOCs volatile organic compounds
• phenols phenols
• the device must be able to provide a measurement every minute, or at least the measurement occurrence must be compatible with a monitoring that can be considered as continuous (of the order of a minute) including trace concentrations;
• the temperature of the gas to be measured can be in the high temperature range (T> 800 ° C) which constitutes a strong measurement constraint;
• the methods proposed to date for the determination of the tar concentration of a gas can be divided into four main families: - a first family that groups the analysis methods based on liquid chromatography or gas phase coupled with a detector.
• the most common detectors for tar measurement are the flame ionization detector (Flame Ionization Detector) and the mass spectrometer. The latter is commonly used for the analysis of the combustion gases of steelworks.
• the acquisition of such a device which remains above all a laboratory device, remains expensive and is not always able to perform quantitative measurements because of the difficulty of interpretation of the spectra and the low repeatability of the measurements. .
• the chromatography does not make it possible to measure continuously for low detection thresholds (of the order of 1 mg / Nm 3 ).
• the Commonly used methods for the pre-concentration of traces are solid phase extraction (SPE) and, in recent years, solid phase microextraction (SPME). These techniques consist in the absorption or adsorption of chemical species on a support covered with an absorbing or adsorbent species. This is for example a fused silica fiber coated with a polymer, which may be for example a liquid polymer such as polydimethylsiloxane (PDMS).
• PDMS polydimethylsiloxane
• UV absorption which is very close to that of infrared absorption, is that water vapor does not interfere with UV.
• the latter is used for example for the detection of polycyclic aromatic hydrocarbons in soils contaminated as mentioned in patent EP0446975 entitled "Installation of the rapid analysis of tar components and method for such an analysis”.
• Patent WO9833058 relates to a method for on-line analysis of polycyclic aromatic hydrocarbons by collecting the aerosols by means of a filter and subjecting it to excitation via UV radiation. It is then a question of comparing the spectral image obtained with the different spectra listed in a database.
• Another technique commonly used in the continuous control of combustion gases is FTIR (Fourier Transform InfraRed) infrared spectrometry.
• FTIR Fastier Transform InfraRed
• Various documents evoke this technique such as for example the documents WO2006015660, WO03060480 and US5984998.
• the literature does not mention a possibility of measuring tars, the products commonly followed being CO, CO2, O 2 , H 2 and H 2 O.
• Patent WO030227650 relates to the use of the Laser-Induced Breakdown Spectroscopy (LIBS) technique for the detection of polycyclic aromatic hydrocarbons (PAHs) and monoaromatics. This fast method is suitable for monitoring PAHs.
• LIBS Laser-Induced Breakdown Spectroscopy
• PAHs polycyclic aromatic hydrocarbons
• PAHs polycyclic aromatic hydrocarbons
• the LIBS technique consists in vaporizing and ionizing in the form of plasma the species sampled by means of a laser. However, it requires the use of a support on which the species to be analyzed are present. It therefore requires a sampling step and does not allow for an online measurement of the gas;
• the two detectors are placed at different points of the same sampling line of the gas to be measured and are separated by a filter which aims to trap the tars by impaction and condensation.
• One of the limitations of the flame ionization technique is the disturbance of the measurement by combustible gases such as CH 4 , H 2 and CO, which is a real limitation since the synthesis gas is a mixture of CO and H 2 and that it also contains methane.
• the response depends on the oxygen content of the gas to be measured.
• knowledge of the composition of the tars as well as the response factors of the various compounds is essential in order to obtain a quantitative measurement of the total tars.
• There are other electronic methods that allow continuous tracking of tars these are cell detectors electrochemical and semiconductor sensors.
• An electrochemical cell consists of a membrane permeating the compounds to be analyzed; on the other side of the membrane is a liquid electrolyte which in the presence of the species to be detected generates a redox reaction at the origin of a measurable electric current.
• This device is not suitable for measuring temperature, further the selectivity of the membrane is not suitable for sampling a large number of components whose physico ⁇ chemical properties vary over a wide range of values.
• Semiconductor sensors have similar limitations in terms of temperature resistance, but they can measure a larger number of pollutants. An important limitation of this device also lies in the rapid contamination of the sensitive layer of the semiconductor placed above the substrate.
• the measurement is made by isokinetic sampling for a range of temperatures ranging from 0 to 900 ° C. and a pressure ranging from 0.6 to 60 bar and for a tars concentration ranging from 1 to 300 mg / Nm 3 .
• This protocol is thus unsuitable for measuring tar tracks ( ⁇ 1 mg / Nm).
• the gravimetric methods are adapted to the measurement of so-called "heavy" tars (more than 3 aromatic cycles with regard to the polycyclic aromatic hydrocarbons PAHs) but little to that of the volatile organic compounds.
• None of the devices presented is able to perform a continuous measurement with a measuring occurrence of the order of one minute. Moreover, the devices presented do not measure all the tars, whether they are in the solid phase or in the gaseous state.
• the objective is to carry out a quantitative and continuous measurement of all the tars in a gas stream at high temperature.
• the measurement must be representative of the total concentration of tars prevailing in a main wherein a synthesis gas flows under given temperature and pressure conditions.
• the invention relates to a continuous measurement device for concentration of tars of a gas, characterized in that it comprises a pipe for sampling a partial flow of the gas, and a scale to which leads the sampling line and to which is suspended a body serving as a catalyst and support for coking tars, the body being movable in a gas pipeline enclosure.
• a harmful phenomenon is thus used which is the deactivation of the catalysts by coke deposition in order to carry out a measurement in the particular field of continuous monitoring of traces of tars in a gas flow.
• a device for adjusting the temperature of the gas sampled is added at the place of the thermobalance or just upstream, in particular in order to set a determined and often higher temperature at the place catalytic body, where coking needs to be promoted.
• the rest of the device, and in the first place the sampling line will, on the other hand, often be provided with means dedicated to maintaining the temperature of the gas at the value of that which prevails in the main flow, in order to avoid condensation and reactions of tars.
• the elements of the devices other than the catalytic body will preferably be chosen from a material having little affinity for the formation of coke so as not to foul and especially not to reduce the concentration of the tars before the gas arrives. to the right of the catalytic body.
• the catalytic body is advantageously a plate compound or, more generally, a solid with a specific surface area to density ratio in order to offer the largest surface area for catalysis for a given volume and while minimizing the weight of the catalytic body, for reasons of sensitivity of the measurement.
• the addition of a flux homogenizer upstream of the pipeline enclosure favorably introduces a uniform flow of gas around the catalytic body and improves the regularity of the measurement.
• a flux concentrator in the pipeline enclosure around the catalytic body directs substantially all the bypass flow over the catalytic body and improves the efficiency of the catalyst.
• a driving gas injector in the pipe enclosure protects the part electronic sub-assembly of measurement by microscope.
• At least one buffer capacity is favorably located on the pipe upstream of the enclosure to regulate the derived flow, and here again to improve the accuracy of the measurement.
• a diaphragm can be located on the pipe downstream of the buffer capacity to help set the value of the flow through the pipe section and the catalytic body.
• the balance comprises a symmetrical flailing oscillating at one end of which the catalytic body is suspended and at an opposite end of which a non-catalytic body of the tar coking is suspended, the catalytic body and the non-catalytic body having identical weights.
• This form of balance making a differential measurement, only one of the bodies weighing down during the measurement, is particularly precise thanks to its symmetry. It is further advantageous that the non-catalytic body is mounted movably in a second chamber identical to that of the catalytic body, to contribute to a regularity of measurement by symmetry of the flow. A pressure equalizer between the two speakers adds to this regularization.
• the enclosure encompassing the catalytic body is vertical and comprises an opening for recovering the catalytic body to a bottom, the replacement of the catalyst body from one measurement to another is a lot ease.
• a change element of the catalytic body movable between the bottom opening of the pipe section and a change station of the catalytic body.
• an auxiliary sensor for measuring the concentration of a gas produced during coking downstream of the catalytic body and located on a gas evacuation pipe, or preferably, an auxiliary colorimetric sensor of the catalytic body.
• This use of colorimetry is possible since the catalytic body gradually changes color as the coke deposit develops.
• the coupling of the gravimetric measurement with a measurement by colorimetry makes it possible, after having calibrated the measurement by colorimetry by means of the gravimetric measurement, to use if necessary the measurement by colorimetry alone, since its detection threshold is very low, lower than that of the scale allows relaying it for very low concentrations of tars or for a preliminary stage of a measurement.
• the colorimetric sensor is designed to make differential measurements on the catalytic body and the non-catalytic body when the latter exists.
• the measurement can be improved by a flowmeter located on the bypass line.
• An important aspect to consider is the simultaneous, frequent presence of tars in phase gaseous and solid phase.
• the above method favors the detection of tars in the gas phase, these being predominant or even exclusive in many applications, especially at relatively high temperature of the gases.
• an auxiliary of the device makes it possible to measure the concentration of tars in the solid phase.
• the auxiliary device for measuring tars in the solid phase may comprise a solid particle trap that can be weighed.
• a solid particle sorting cyclone can be added to send to the solid particle trap only particles that can be considered as tars.
• the invention also relates to a continuous measurement method for concentration of tars of a gas, characterized in that it consists in taking a partial flow of the gas and in directing this flow towards a body serving as catalyst and support for coking. tars. We have the ability to adjust the temperature of this flow to promote coking.
• the weighing is either continuous in the strict sense, or at least carried out at close intervals, of the order of a minute or less, which do not allow previous devices and processes for the most part.
• coking is the catalytic aspect of coking which is preferably used in the invention, whereas the coking is mainly likened to thermal cracking.
• the catalytic phenomenon occurs especially during the formation of the first deposition layer, which is generally carried out by adsorption of the heavy hydrocarbon components of the coke, while the thermal coking phenomenon generally becomes predominant.
• the invention will therefore be particularly useful for measuring low concentrations of tars.
• the coking catalyst material will be chosen by its nature, its shape and its manufacture so that the catalytic effect will be greater than the thermal effect in the target temperature range, generally from 200 to 1200 ° C.
• the basic process can be enriched with an additional measure of concentration of tars in the solid phase of trapping these solid tars on a support.
• the main measure of micro-weighing can be supplemented by auxiliary measurements based on variations in the catalytic body color or on concentrations of gas from coking, and in particular dihydrogen gas, since the formation of coke is generally accompanied by dehydrogenation of the tarry compounds.
• a final aspect that characterizes the invention is the choice of the catalytic body (nature, composition, shaping, geometry ). It depends on four fundamental parameters that are: - the catalytic properties of the material;
• Volume mass large enough to have a measurement that is as accurate and representative as possible; - a material for which methane does not coke or very little; a color and shape that is compatible with colorimetric measurement.
• FIG. 1 schematically represents a device and a method according to the invention, the objective of which is the continuous measurement of tars in the gaseous and solid state contained in a gaseous flow in temperature;
• FIG. 2 is an exemplary embodiment of the thermogravimetry subassembly for continuous tracking of tars by microscope
• FIG. 3 is another embodiment of the thermogravimetry subassembly. This is a magnetic suspension thermobalance that has been adapted to the case of our application;
• FIG. 4 shows different forms for the catalytic body, support coking
• FIG. 5 represents a microperforated nacelle that can be suspended from the rod of the thermobalance and that can contain the coking material 30;
• FIG. 6 represents a cogging monitoring curve by micro-weighing for a gas having a constant concentration of tars, toluene having been used as a tracer.
• FIG. 1 there is shown schematically a device dedicated to the measurement of tars by micro-weighing and / or colorimetry.
• the gaseous mixture to be analyzed flows inside a main pipe 80 made of stainless steel, for example AISI 310 or AISI 316.
• a main pipe 80 made of stainless steel, for example AISI 310 or AISI 316.
• alloys based on nickel and chromium for example Inconel are commonly used as material constituting conduits that can withstand temperatures of 1200 ° C. and above and have the advantage of having a very weak catalyst effect for the coking phenomenon, which makes it possible to limit the deposit of coke or soot on the internal surfaces of the pipes.
• Said pipe 80 comprises means 81 and 82 for continuously measuring the pressure Pp and the temperature T P prevailing therein.
• the nature and the composition of the gas mixture vary according to the intended application.
• the predominantly present species are CO and H 2 , these two compounds constitute the gaseous matrix.
• gases such as CO 2 , CH 4 , H 2 O and tars are found.
• the gas flow upstream of the Fischer-Tropsch process is at a temperature of about 300 ° C. and at a pressure of up to 30 bar.
• part of the main flow ⁇ p is diverted to two sampling devices and gives rise to secondary flows ⁇ d i and ⁇ d2 .
• the overall measuring device comprises two devices, the first is assigned to the discontinuous measurement of tars in the solid phase and the second to the continuous measurement of tars in the gaseous state. It is this second device for continuous measurement of tars in the gaseous state which is the subject of the invention and which will be mainly described; the first device is optional and is a simple auxiliary to complete the measurement.
• the flow taken satisfies the following relationship: ** - ⁇ !%
• the first device serves only to verify the absence of solid tars.
• the first device assigned to the measurement of tars in the solid phase, comprises an isokinetic sampling device 83 conforming to ISO 9096 and / or ISO 2066 standards.
• the isokinetic sampling 83 is connected by stainless steel metal conduits 84 to a control organ. sorting of particles such as for example a cyclone 1 or a set of cyclones that separates particles larger than a few ⁇ m, in particular coal particles or "char", by-products of the pyrolysis of biomass, and particles of a more modest size, such as soot resulting from the polycondensation of tars. Said soot are then collected by impaction on a filter medium 2 so as to be in a second time weighed.
• the second device intended for the continuous measurement of gaseous tars, consists of three major subassemblies which are:
• a system for sampling, processing and conveying gases (3, 4, 5, 6, 7, 8 and 9);
• thermobalance (10) adapted to the case of our application which is the continuous measurement of the concentration of tars in a gaseous flow temperature by monitoring the phenomenon of coking tars (conversion of tars into carbon load) by micro-weighing;
• An analysis system coupled to the micro-weighing system, according to the desired application, using an optical colorimetric measurement system, an H 2 analyzer or a CO 2 analyzer.
• the first two subsets are essential to the good performance of the invention, the third improves the results by allowing to corroborate or supplement the second subset in the case of extremely low concentrations of tars.
• the second device is located downstream of the first on the main pipe 80 so as not to disturb it.
• the gas sampling, treatment and routing system is heat-insulated and maintained at the temperature T p in order to avoid creating "cold zones" which would favor the condensation of the tars. It is also about conveying the gas to be analyzed up to the thermobalance 10 under conditions of temperature and pressure as close as possible to those prevailing in the main pipe 80 in order to avoid condensations and tar reactions. It is therefore necessary to have a measurement of the concentration of gaseous tars that is as representative as possible of the concentration of gaseous tars in the main pipe 80.
• the temperature maintenance of the pipes and various other elements can be done by means of an electric heating device or by circulation of hot nitrogen around said conduits and other processing and transporting organs of the gas to be analyzed.
• the gas sampling, treatment and routing system comprises means 85 and 86 making it possible to measure the temperature and the pressure at various points.
• the sampling system comprises a sinter 3 which can be metallic.
• the material constituting the frit 3 must be carefully selected in order to limit the catalytic effect leading to the formation of coke and thus the destruction of tars; it may be for example a formed material based on silicon carbide SiC.
• the frit 3 can just as well and this in a nonlimiting manner be quartz, ceramic or glass fiber. Said frit 3 is maintained in temperature by means of a heating device in order to avoid the condensation of tarry compounds favored in particular by the loss of charge that it induces.
• the frit 3 serves as a particle filter but allows a portion of the gas flow to flow into a sampling line 87 leading from the main pipe 80 to the thermobalance 10 and carrier of various equipment that will now be described to measure.
• the sampling line 87 is insulated and maintained at the temperature T p of the flow prevailing in the main pipe 80.
• a shutoff valve 89, a purge duct 112 and a pressure reducer 90 are placed between the frit 3 and a first buffer volume 4.
• the first buffer volume 4 is a capacity equipped with means for measuring the pressure and the temperature in it. It comprises a nitrogen filling and emptying system 88 which, combined with a pressure regulating device, makes it possible to smooth the flow rate and the pressure of the gas to be analyzed.
• a safety valve 5 is placed at the top of the buffer volume 4 in order to avoid any overpressures and to guarantee the safety of the device.
• a second dynamic buffer volume 6 slower than that of the first buffer volume 4 operates a finer smoothing of the flow and pressure; it follows the first buffer volume 4 and also comprises a nitrogen filling and emptying system 111 and a safety valve 7.
• a heat exchanger 8 is placed downstream of the second buffer volume 6 in order to adapt the temperature of the gas to be analyzed before introducing it into two thermostated chambers of the thermobalance 10.
• the exchanger 8 will constitute a preheating zone of the gas to be analyzed in order to obtain a better efficiency of the thermogravimetry device; the temperature in the thermostatted enclosures of the thermobalance 10 is determined for an optimum of the coking rate of tars by catalytic effect.
• a diaphragm 9 is positioned before the junction of the sampling line 87 to the thermobalance 10 to limit the flow.
• FIG. 2 schematically represents a first embodiment of the thermobalance 10.
• the various embodiments presented below have been all the specificity of presenting two furnaces with thermostatic enclosures, it is called balances called "symmetrical configuration".
• a thermobalance having a single thermostatic chamber, without being excluded from the invention, would require to perform after each measurement a blank in order to overcome various sources of measurement error such as hydrostatic thrust and fluctuations debit for example.
• Thermobalance 10 comprises:
• An enclosure composed of several parts, including an upper chamber 90 housing a beam 20 and a pair of lower and vertically elongated thermostatically regulated enclosures 91 and 92 extending at the top up to the upper enclosure 90 and down to an accessibility cap 33;
• a protective gas supply system 26 for example He or N 2 , to protect an electronic weighing device by insufflation of an inert gas in the upper chamber 90;
• a purge gas supply system 22, comprising a heating system 23 for limiting the temperature drop in the thermostatted enclosures 91 and 92 during purging of the system.
• the purge gas may be an inert gas for example, or air; - A tubular heating system of Joule effect 36 at least partially enclosing each of the thermostatted enclosures 91 and 92; A device for homogenizing the temperature and the flow of the gas to be analyzed disposed at the inlet of each of the thermostatically controlled chambers 91 and 92;
• a flux concentrator device 29 which acts by restricting the flow section offered to the gas;
• a cooling device 31 involving a cooling liquid, for example water, for cooling the two thermally regulated enclosures 91 and 92 at the periphery and seals at the lower and upper portions of the thermostatted enclosures 91 and 92;
• a pressure equalization system 27 between the two thermostatted enclosures 91 and 92;
• An accessibility plug 33 at the bottom of each thermostated chamber 91 and 92 in order to limit the temperature drop in the thermostatted enclosures 91 and 92 while allowing access thereto for operations of replacing a catalytic body 30 and a non-catalytic body 35 to be described;
• a micro-weighing device having a resolution of less than one microgram, comprising an electronic and mechanical device.
• the mechanical device comprises a symmetrical flail 20 housed in the upper enclosure 90 and two rods 28 suspended from the beam 20 and housed respectively in the thermostatically controlled enclosures 91 and 92.
• the electronic device is not shown, being known per se, and measures the rotation of the axis of the beam 20;
• a catalytic body 30 both a support and a catalyst for the coking reaction with its attachment system to one of the rods 28, which can be, as the case may be, a perforated nacelle (105 in FIG. 5), a support ring or any other form for securing the rod 28 to the catalytic body 30.
• the catalytic body 30 is suspended at the level of the flux concentrator 29 of the thermostated enclosure 91;
• a non-catalytic body 35 of the same weight as the catalytic body 30 is suspended from the other rod 28 to balance the beam 20, also at the height of the flux concentrator 29;
• a heating assembly comprising tubular furnaces 36 surrounding the thermostatted enclosures 91 and 92 at the bodies 30 and 35, a heat-insulating coating 93 surrounding the thermostatted enclosures 91 and 92 and the tubular furnaces 36 and heat exchangers 94 placed in the coating lagging connected to a thermostated bath of the cooling system 31 to maintain the assembly at a constant temperature;
• the catalytic body 30 may be, for example, activated alumina, zeolite or activated carbon. Light-colored materials are preferred in order to be able to couple the measurement by micro-weighing to a measurement by colorimetry.
• the shape of the catalytic body 30, illustrated by examples in FIG. 4, is fundamental because it conditions the representativeness and accuracy of the measurement. For this purpose it may be envisaged to use different shapes and masses depending on the tar content in the gas to be analyzed and / or the need or not for coupling to a colorimetric measurement.
• the target measurement range between 0.1 mg / Nm 3 and 100 mg / Nm 3 of tar content in the gas, can be divided into ranges as mentioned below: - Measuring range 1: from 0.1 to 1 mg / Nm 3 ;
• - Measuring range 2 from 1 to 10 mg / Nm 3 ;
• m nacelle + alu mm e or iHnaceiie + aiumine represents the sum of the mass of the nacelle and that of the coking material (in this case alumina for example).
• the mass of coke formed is given by the following expression:
• ⁇ ⁇ represents the duration of the measurement expressed in minutes
• V cokage [At] represents the average coking rate on ⁇ t expressed in mg / min. It should be noted that ⁇ t is of the order of magnitude of the minute.
• the form of the catalytic body may be, and not limited to, a plate, a hollow cone, a ball, etc. or a combination of such shapes, including combinations of any shape plates.
• the coking rate ⁇ CO kage, dimensionless quantity, is given by the following expression: m ⁇ c ⁇ oke coking m tars Oeke where m represents the mass of coke formed during .DELTA.t, goudmm m represents the mass of tars in the flow for a duration ⁇ t.
• the coking rate ⁇ CO kage at a given moment depends mainly on:
• m goudmm represents the mass of tars contained in the stream for a duration ⁇ t expressed in mg
• Q 1n represents the volume flow rate of gas expressed in Nm 3 / min
• [tars] m represents the mass concentration in tars expressed in mg / Nm 3 ;
• the coking rate ⁇ CO kage is a quantity that connects
• coking rate is an indicator of the performance and representativeness of the measure.
• SECOND SUBASSEMBLY SECOND MODE Figure 3 schematically shows a second embodiment of thermobalance. It is a magnetic suspension thermobalance 95 which has the advantage of making a physical decoupling between the electronic part and the mechanical and magnetic part of the apparatus. This makes it possible to work under pressure and to have no dilution phenomenon via the mixing which takes place between the gas to be analyzed and the shielding gas of the electronic part; a dilution that can be limiting in the case of the detection of low concentrations of tars.
• An upper chamber 96 containing the electronic part (not shown) and a beam 41 with at both ends a magnet 43 and its support 42 is traversed continuously by a stream of nitrogen injected in the middle by a pressure supply system 46.
• Stoppers 40 limit the movements of the beam 41, especially when the suspension rods (here 67) are uncoupled as will be described later.
• the inerting gas is continuously extracted from the enclosure upper 96, then recycled into it, by means of a pump 44.
• Said upper chamber 96 is physically separated from the thermostatically controlled enclosures 97 and 98, locations of the flow of the gas to be analyzed and the measurement, by ceramic walls 45 which also separate these from the outside.
• On both sides of these walls 45 are the magnets 43 already mentioned and other magnets 60 and their supports 61 which allow to suspend by magnetism rods 67 of the thermobalance 95, which are suspended at their other end respectively a catalytic body 58 for coking and a non-catalytic body 69.
• a radial magnetic suspension system makes it possible to raise and lower the rods 67 that have been shown in low configuration in the lower chamber 97 which is thermostatically controlled on the left and in the up position.
• the radial suspension comprises magnets 62 fixed to the rods 67, magnetic cores 63 fixed in the enclosures 97 and 98 and coils 64 outside the enclosures 97 and 98, able to excite the magnetic cores 63 to form linear motors with the magnets 62 and lower the rods 67 to the bottom of the device or raise them up to to restore the attraction at a distance between the pairs of magnets 43 and 60.
• the rods 67 and the elements which are connected to them exert a force corresponding to their weight on the beam 41 despite the absence of contact.
• the inlet 24 of the gas to be analyzed in each enclosure lower 97 or 98 is placed under all these magnets and components 60 and 64.
• the flow of the gas is directed on the catalytic body 58 and the non-catalytic body 69 by flow concentrator devices 53 before escaping from the thermostatically controlled enclosures 97 and 98 through outlets 70.
• FIGS. 1, 2 and 3 The analysis device coupled to the micro-weighing will now be described with reference to FIGS. 1, 2 and 3, which involves, according to the desired application, an optical colorimetric measurement system 56, an H 2 18 analyzer, a CO analyzer. 2 52.
• Said optical colorimetric measurement system comprises an optical device 99 and an image acquisition and processing module 34. This device makes it possible to perform a continuous measurement in the sense that the occurrence (of the order of one minute) of measurement is sufficient for online monitoring of the concentration of tars. Said optical colorimetric measurement system 56 makes it possible to take measurements for tar concentrations for which it is not possible to carry out a microscale measurement. It is a question of observing the color change of the catalytic support and catalyst body of the coking reaction which takes place at the time of adsorption of the first layer of coke. Beyond this first layer, the layer growth of the deposited coke continues, but this latter is then under the effect of a thermal reaction and no longer both catalytic and thermal. In the embodiment of FIG.
• the colorimetric device compares the colors of the bodies 30 and 35, the optical devices 99 being placed at the bottom of the accessibility plugs 33 and directed vertically, in the axis of the pipe sections; in the embodiment of Figure 3, where carousels 59 occupy the bottom of the pipe sections, an optical device 99 is directed horizontally, through the heat-insulated wall 93, at the height of the catalytic body 58 when it is in the measuring position just below the flux concentrator 53.
• FIG. 3 a variant has been illustrated according to which the measurement is not differential and no optical device 99 is directed towards the body. non-catalytic 69. However, this is not specific to respective embodiments and reverse arrangements could be chosen for each of them.
• the colorimetric device is first calibrated during a series of preliminary measurements where the results it gives on the progressive darkening of the catalytic body 30 or 58 are correlated with the increase in that of here, measured by thermobalance 10 or 95; then the colorimetric device is able to make autonomous measurements, particularly appreciated when the gravimetric measurement does not provide sufficient precision when the weight of the coke deposited on the catalytic body 30 or 58 is still too small, or that the tar content is very weak ; it can also give measurements used to corroborate those obtained by gravimetry.
• An analyzer H 2 18 is placed downstream of the thermogravimetry device 10 monitoring coking. It may be for example a paramagnetic type analyzer. This is to obtain additional information on the decomposition of tars because at the time of the formation of coke, the tar compounds are dehydrogenated. Such an analyzer can be used in the case of an application where the gas matrix contains no or little hydrogen. Between the gas outlet of the thermobalance 10 and the analyzer H 2 18 are arranged in the order indicated, the following items on the exhaust pipe 113:
• thermobalance 10 An exchanger 11 for lowering the temperature of the gases at the outlet of the thermobalance 10;
• Measuring means such as a flow meter 12 and a volumetric counter 13;
• a micrometric valve 14 allowing fine adjustment of the flow passing through the thermostatically controlled enclosures; and, after the confluence of the two branches of the exhaust pipe 113: A condenser 15 for condensing the different condensable species such as tars that have not been coke or water vapor;
• a CO 2 analyzer 52 analyzes the gases present in a temperature-controlled oven 54 in which the coke formed on the surface of the catalytic body 30 is burned by adding oxygen arriving from a duct equipped with a heat exchanger 52 once the used catalytic body has been removed by the device of the carousel 59. It is to evaluate the amount of coke formed. For this, it must be ensured that the temperature-controlled oven 54 is free of any trace of CO 2 before the coke deposited is burned by combustion. The amount of CO2 emitted during coke combustion is measured and correlated with the amount of coke.
• a automated mechanical device such as for example an automated articulated arm 55 performs the loading and unloading of the samples between the carousel 59 and the thermostat oven. After combustion of the coke by addition of oxygen, it is possible to reuse a limited number of times the catalytic body 30.
• the added oxygen is supplied by a supply system comprising a heating means 51.
• the temperature of the main line T p greater than 300 0 C, limits condensation of gaseous tar in the filter medium 2.
• Downstream of the isokinetic sampling device 83 a portion of the main flux ⁇ p is taken from a drawn flow ⁇ d 2 secondary. The particles are trapped by the frit 3 maintained at the temperature T p .
• the intermittent operation of a feed under nitrogen pressure at the frit 3 avoids clogging of the latter.
• the shutoff valve 89 passes the flow ⁇ d 2, the pressure of the sample gas is modified by a pressure reducer 90 disposed upstream of the first buffer volume 4.
• the pressure variations recorded in the first buffer volume 4 are regulated by the expansion volumetric of the lower part of the first buffer volume 4, separated from the gas to be analyzed by a membrane.
• the negative or positive expansion of the lower part is controlled respectively by increasing or decreasing the nitrogen pressure.
• the safety valve 5 opens and allows a part of the flow to pass to a control circuit. discharge.
• the stream is routed to the second buffer volume 6, the operation of which is identical to that of the first buffer volume 4; only differs the operating dynamics, which in the case of the second buffer volume 6 is lower than that of the first buffer volume 4.
• the heat exchanger 8 makes it possible to adapt the temperature of the gas flow before it is admitted into the thermobalance thermostatted enclosures 10.
• thermobalance 10 The temperature prevailing in the thermostatted enclosures is an optimum between the coking rate of tars and phenomena such as thermal cracking and steam reforming of the coke due to a high temperature and the presence of water vapor in the gas matrix.
• the diaphragm 9 makes it possible to attenuate the flow and pressure fluctuations present in the sampling, routing and gas treatment system. The operation of the thermobalance 10 will now be described with reference to FIG.
• the gas to be analyzed is admitted through the inlet orifice 24 and passes through the homogenization zone of the gases 25.
• the gas to be analyzed is mixed with the protective gas 26.
• the convergence device 29 of the flow The gas to be analyzed directs the flow on the catalytic body 30, where the catalytic effect of the latter is at the origin of the coking of most of the gaseous tars which will be adsorbed on the surface of the latter.
• the surface of the catalytic body 30 is not completely covered with a deposit layer of hydrocarbon compounds called coke, the contribution of the catalytic effect to the formation of coke is much greater than that of the thermal effect.
• the recovery rate can be evaluated by colorimetric measurement or by micro-weighing.
• thermobalance 10 is open at its bottom and the assembly 20, 24, 25, 28 and 30 down to a carousel type automatic sample changer device that replaces the catalytic body 30 with a new sample.
• the old sample is then conveyed to an enclosure in which it will be placed in contact with an oxygen-rich atmosphere in order to operate the combustion of the coke and to evaluate the quantity of coke deposited via the measurement by a CO2 analyzer.
• the coke deposition causes an increase in the weight which is measured continuously by the thermobalance 10.
• the evaluation of the slope of the curve representing the increase of the mass of the sample as a function of time corresponds to the coking rate measured on the curve 100, plus specifically at a portion 101 of steep slope between a preliminary portion 102 of inactivity and a final portion 103 corresponding to thermal coking.
• the knowledge of the coking rate makes it possible after calibration of the thermobalance 10 to calculate the concentration of gaseous tars in the main stream ⁇ p . Before making the measurement it is necessary to adjust the micrometer valves 14 in order to equalize the gas flows to be analyzed in the two thermostatted chambers of the thermobalance.
• An H 2 18 analyzer makes it possible to measure the dihydrogen concentration at the gases leaving the thermobalance 10, this measurement combined with the measurement by micro-weighing gives elements of response on the composition of the tars. It makes it possible to make the link between the coking rate and the H 2 emission rate resulting in particular from the dehydrogenation of tar that occurs during coking.
• the various components of the tare measuring device are dimensioned as a function of the volume flow rate of gas flowing in the main pipe and the pressure and temperature conditions, respectively P p and T, prevailing in the latter.
• Diameter of connecting ducts 1/8 inch or 3 mm
• Diaphragm size 9 1/16 inch or 1.5 mm
• thermobalance 10 Height of the thermobalance 10: 850 mm - Width of the thermobalance 10: 500 mm
• thermobalance 10 Length of thermobalance 10: 450 mm
• Coolant temperature 60 0 C - Inert gas temperature: 200 to 1200 ° C
• Inert gas pressure 2.5 bar - Inert gas volume flow rate: 6 Nm 3 / h
• thermobalance thermostatic chamber 0 to 4 bar - Diameter of thermostatic chamber: 15 to 20 mm
• Coking material activated alumina
• Condenser temperature 15 -15 to + 20 ° C.
• Sensitivity of the micro-weighing device ⁇ l ⁇ g.

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• 2006
  • 2006-12-28 FR FR0656007A patent/FR2910967B1/fr not_active Expired - Fee Related
• 2007
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