WO2010049836A1

WO2010049836A1 - Method and apparatus for analyzing particle-laden gases

Info

Publication number: WO2010049836A1
Application number: PCT/IB2009/054499
Authority: WO
Inventors: Rene Bruno Nielsen; Karsten Brink Floor; Lars Kristensen; Morten Drivsholm; Mads Peter Rasmussen
Original assignee: Flsmidth A/S
Priority date: 2008-10-30
Filing date: 2009-10-13
Publication date: 2010-05-06
Also published as: DK200801491A; TW201018900A; DK176920B1

Abstract

A description is given of a method for analyzing particle-laden gases extracted from a processing plant, such as process gases from a minerals processing plant where the extracted particle-laden gases are introduced to a compartment where they are brought into rotation so that the particles under the action of centrifugal force are separated from the gases and thrust against the wall of the compartment and where the gases and particles are subsequently diverted from the compartment. The method is characterized in that the gases are analyzed in a central part of the compartment while the gases and particles are separated. As a result, the reaction time for analyzing the gases will be very short due to the fact that the gas/particle separation and the analysis of the gases will take place in the very compartment whereto the particle-laden gases are introduced.

Description

Title of Invention: METHOD AND APPARATUS FOR ANALYZING PARTICLE-LADEN GASES

[1] The present invention relates to a method for analyzing particle-laden gases extracted from a processing plant, such as process gases from a minerals processing plant where the extracted particle-laden gases are introduced to a compartment where they are brought into rotation so that the particles, under the action of centrifugal force, are separated from the gases and thrust against the wall of the compartment and where the gases and particles are subsequently diverted from the compartment. The invention also relates to an apparatus for carrying out the invention.

[2] For production processes involving high fuel consumption rates, such as cement manufacturing processes, it is essential to know the exact composition of the gases present during the process. Knowledge about the composition of gases is essential for several reasons, i.a. for optimizing the combustion process, for avoiding hazardous process situations, for reducing emission levels, for improving the quality of the product and for protecting the equipment of the processing plant.

[3] The present method for analyzing the process gases involves extraction of a sample from the processing plant, with subsequent filtration of the sample due to the fact that the sensors deployed for gas analysis must perform the measurements on the basis of pure gases. It will always be necessary to clean the filters, normally approximately every ten minutes, which entails that the analysis cannot be performed continuously due to the fact that the cleaning operation will require approximately a 30-second suspension of the analysis. If the gases contain a substantial amount of particles, it will furthermore be very difficult or impossible to keep the filters clean, and this will have an adverse impact on the effectiveness of the gas analysis. The method for analyzing the process gases is further complicated by the fact that the composition of the gases will change over time and in dependence of temperatures. Therefore, it is very important that the sample is quickly taken from the processing plant to the sensors deployed for analyzing the composition of the gases, which entails that the particles must rapidly be separated from the gases to be analyzed. The method described will typically have a reaction time (the total time elapsing from the sampling stage to completion of measurement) of 30-90 seconds which is a major problem, i.a. when the analysis is to be used for protecting an electrostatic precipitator. As it is, the consequence of the long reaction time could be that it will not be possible to react swiftly to the composition of the gases, potentially causing damage to the electrostatic precipitator. For active protection of the electrostatic precipitator, the reaction time must be less than 5 seconds.

[4] A plant of the kind mentioned in the introduction is known from US patent 3 070

990. Here the particle-laden gases are extracted from a processing plant and subsequently introduced to a cyclone in which they are brought into rotation so that the particles under the action of centrifugal force are separated from the gases and thrust against the wall of the cyclone. The gases are discharged through an outlet at the top of the cyclone and the particles are diverted through an outlet at the bottom of the cyclone to a sampling container which can be dismantled so that the sample can be extracted and analyzed. After the gases have been discharged at the top of the cyclone, they can be directed to a unit for analysis. Hence, the analysis of the gases will not be performed until they have been discharged from the cyclone and directed to a separate analyzing unit. The consequence of this will be that the time elapsing from the sampling stage to the completion of analysis will be relatively long, and this is a problem i.a. because the composition of the gases will change over time and in dependence of temperatures. On completion of analysis, the gases are vented to the atmosphere, entailing energy losses since the thermal energy in the gases is not utilized. Furthermore the gases will often cause pollution, and, therefore, venting the gases directly to the atmosphere poses problems. Furthermore, the process will not be continuous because of the need to dismantle and empty the sampling container when the latter is full.

[5] It is the objective of the present invention to provide a method as well as an apparatus whereby the aforementioned disadvantages are eliminated or significantly reduced.

[6] This is obtained by a method of the kind mentioned in the introduction and being characterized in that the gases are analyzed in a central part of the compartment while the gases and particles are separated.

[7] The apparatus according to the invention for analyzing particle-laden gases extracted from a processing plant comprises a compartment and means for introducing the particle-laden gases to the compartment and means for bringing the particle-laden gases into rotation so that the particles under the action of centrifugal force will be separated from the gases and thrust against the wall of the compartment as well as means for diverting the gases and particles through at least one outlet. The apparatus is characterized in that it comprises means for analyzing the gases in a central part of the compartment while the particles and gases are separated.

[8] The method and the apparatus according to the invention will thus make it possible to minimize the reaction time for analyzing the gases, since the gas/particle separation as well as the analysis of the gases will take place in the very compartment whereto the particle-laden gases are introduced. Trials conducted have shown that the reaction time can be reduced to less than 5 seconds which is a significant improvement in comparison with the reaction time for the present-day analysis systems.

[9] In principle the gases may be analyzed for the contents of all types of gases since the method is independent of the type of gases. However, it will typically be relevant to perform a content analysis of e.g. CO, CH₄, C₃H₈, NO_x or O₂ in the gases.

[10] In a preferred embodiment the gases will, on completion of analysis, be mixed with the particles and diverted from the compartment through a joint outlet. Since the analysis of gases is performed directly in the compartment while the particles and gases are separated, there is no need for separate outlets since subsequent separation will not be necessary. Furthermore, a joint outlet would be advantageous for the discharge operation since this will simplify the process instead of discharging through several outlets. Subsequent to the discharge through the joint outlet, the gas/particle mixture may be recirculated to the processing plant. As a result, the entire process will be continuous and the thermal energy in the gases and the material in the extracted sample will be returned to the processing plant. Here it is preferred that the gas/particle mixture is recirculated to the processing plant at a point located after the inlet (viewed in relation to the gas flow in the processing plant) to the compartment to prevent the same gases from being re-extracted for analysis. By returning the extracted sample to the processing plant it is further obtained that the gases are led through the cleaning equipment of the processing plant, thereby eliminating the need for separate equipment for cleaning the extracted gases before they are vented to the atmosphere.

[11] The means for diverting the gases and particles may in principle be constituted by any suitable means as long as they are capable of diverting the gases and particles from the compartment. It is preferred that the same means will furthermore have the capability to suck the particle-laden gases into the compartment in order to eliminate the need for additional means for this purpose. The means may comprise a fan which is either located before or after the compartment. However, it is preferred that the means comprise an ejector mounted in the outlet so that the ejector, in addition to diverting the gas/particle mixture from the compartment, will also suck the particle-laden gases into the compartment. A further advantage associated with the use of an ejector is that such use will not involve any noteworthy wear. It is preferred that the ejector is operated by air having a temperature which is so high that the surface temperature on the ejector will exceed 100 ⁰C, thereby avoiding sulphur condensation on the ejector.

[12] The means for bringing the particle-laden gases into rotation may comprise any suitable means as long as they are capable of bringing the particle-laden gases into rotation. For example, the means may comprise a number of fixed devices in the upper part of the compartment where the devices are configured and positioned so that the introduced particle-laden gases which can be introduced at the top or at the side of the upper part of the compartment will be forced into rotation. However, it is preferred that the means comprise a tangential inlet which is connected to the upper part of the compartment. Such an inlet which is generally known from cyclone separators will cause the particle-laden gases to be brought into rotation in the compartment when gases are introduced at sufficiently high velocity.

[13] It is preferred that the part of the compartment in which the gases and particles undergo separation is rotary-symmetrical and that it is shaped in circular-cylindrical form. It is further preferred that the compartment comprises a conical part which comprises an outlet. It is further preferred that the relationship and dimensions of inlet and outlet and of the circle-cylindrical part and the conical part of the compartment are consistent with principles known from the construction of cyclone separators.

[14] The means for analyzing the gases in the central part of the compartment while the particles and gases are separated may in principle be constituted by any suitable means. However, it is preferred that the means comprise laser units, comprising a transmitter and a receiver, for analyzing the gases. When measurements are carried out by laser units, the measuring principle 'infrared single-line absorption spectroscopy' is used in order to take advantage of the fact that each type of gases has different absorption lines at specific wavelengths. When laser units are used, it is preferred that they are capable of producing a narrowly focused beam in order to avoid deflection or losses in the means encasing the laser beams into the central part of the compartment. The means for analyzing the gases in the central part of the compartment may in principle perform measurements at any conceivable angle in the compartment. However, the means should preferably be positioned so that they perform measurements horizontally into the compartment.

[15] The compartment may be located in relation to the processing plant so that its centreline is parallel to the vertical plane. Furthermore, the compartment may be angled relative to the vertical plane. If the compartment is placed at an angle, it is preferred that the angle between the centreline of the compartment and the vertical plane is between 0 ° and 90 ° . It is hereby obtained that the measuring distance (the distance in the compartment between the means for analyzing the gases) across the compartment will correspond to that attainable by a vertically positioned compartment, even if the diameter of the compartment is reduced. A smaller diameter of the compartment will result in accelerated reaction time since the volume of the compartment, and hence the flow rate of gases, will be reduced. The reaction time depends to a substantial degree on the flow rate of gases which means that a lower gas flow rate will result in accelerated reaction time. A further advantage of angling the compartment in relation to the vertical plane is that it will be possible to reduce the angle of the outlet in relation to the location in the processing plant whereto the gas/particle mixture will be recirculated. This will lead to a reduction of the pressure loss through the outlet. [16] The invention will now be explained in greater details with reference to the drawing, being diagrammatical, and where

[17] Fig. 1 shows a sectional view of a processing plant comprising an apparatus according to the invention for analyzing particle-laden gases extracted from the processing plant, and

[18] Fig. 2 shows a second embodiment of the apparatus according to the invention

[19] In Fig. 1 is seen a sectional view of a processing plant 1 in which a kiln 2 is connected to a discharge duct 3 from which particle-laden gases are extracted via an inlet 4 from the processing plant 1. The extracted particle-laden gases are directed via the inlet 4 to a compartment 5 to which they are introduced at sufficiently high velocity to ensure that they are brought into rotation so that the particles under the action of centrifugal force are separated from the gases and thrust against the wall 6 of the compartment. Rotation of the particle-laden gases is accomplished since the inlet 4 is positioned tangentially in the upper part of the compartment 5. The configuration of the compartment 5 is similar to that of the compartment in a cyclone separator with an upper circle-cylindrical part and a lower conical part terminating in an outlet 7. While the gases and the particles are separated, the gases are analyzed in a central part of the compartment 5. The analysis is performed by laser units comprising a laser transmitter 8 and a laser receiver 9, both of which penetrate the wall 6 of the compartment and the layer of particles on the inside of the compartment wall 6. The transmitter 8 as well as the receiver 9 are led through ducts 10 which pass through the compartment wall 6 and through the layer of particles. On completion of analysis, the gases and particles are brought together again and diverted from the compartment 5 through the joint outlet 7. Subsequently the gas/particle mixture is returned to the discharge duct 3 in a position which is located after the inlet 4 to the compartment 5 to prevent the same gases from being re-extracted for analysis. An ejector 11 located in the outlet 7 will ensure that the particle-laden air is sucked into the compartment 5 and that the gas/particle mixture is recirculated to the discharge duct 3. Hence the entire process involving extraction and analysis of the gases will be continuous. Furthermore, the thermal energy as well as the material in the extracted particle-laden gases will be returned to the processing plant.

[20] In Fig. 2 is seen a second embodiment of the apparatus where the centreline 12 of the compartment 5 is angled in relation to the vertical plane. This will ensure that the measuring distance across the compartment 5 will correspond to that attainable with a vertically positioned compartment, even if the diameter of the compartment 5 is reduced. A smaller diameter of the compartment 5 will lead to accelerated reaction time, since the volume of the compartment 5, and hence the gas flow rate, will be reduced. It is further obtained that the angle of the outlet 7 relative to the discharge duct 3 , whereto the gas/particle mixture is recirculated, will be reduced, thereby reducing the pressure loss through the outlet 7. The laser transmitter 8 and laser receiver 9 are horizontally positioned in the angled compartment. However, they may also be angled in relation to the horizontal plane.

Claims

[Claim 1] A method for analyzing particle-laden gases extracted from a processing plant (1), such as process gases from a minerals processing plant where the extracted particle-laden gases are introduced to a compartment (5) where they are brought into rotation so that the particles under the action of centrifugal force are separated from the gases and thrust against the wall (6) of the compartment (5) and where the gases and particles are subsequently diverted from the compartment (5) characterized in that the gases are analyzed in a central part of the compartment (5), while the gases and particles are separated.

[Claim 2] A method according to claim 1 characterized in that upon completion of analysis the gases and particles are brought together and diverted from the compartment (5) through a joint outlet (7).

[Claim 3] A method according to claim 2 characterized in that the combined gas/particle mixture is recirculated to the processing plant (1).

[Claim 4] A method according to any preceding claim characterized in that the particle-laden gases are introduced tangentially to the upper part of the compartment (5).

[Claim 5] An apparatus for analyzing particle-laden gases extracted from a processing plant (1), such as process gases from a minerals processing plant, with said apparatus comprising a compartment (5) and means (4) for introducing the particle-laden gases to the compartment and means (4) for bringing the particle-laden gases into rotation so that the particles, under the action of centrifugal force, are separated from the gases and thrust against the wall (6) of the compartment (5) and means (11) for diverting the gases and the particles through an outlet (7) characterized in that the apparatus comprises means (8 ,9) for analyzing the gases in a central part of the compartment (5), while the particles and gases are separated.

[Claim 6] An apparatus according to claim 5 characterized in that the means (8, 9), analyzing the gases in the central part of the compartment (5) comprise laser units.

[Claim 7] An apparatus according to claim 5 or 6 characterized in that the means (8, 9), analyzing the gases in the central part of the compartment penetrate the wall (6) of the compartment (5) and the layer of particles on the wall (6) of the compartment.

[Claim 8] An apparatus according to any of claims 5-7 characterized in that the compartment (5) is formed in similar manner to the compartment in a cyclone separator.

[Claim 9] An apparatus according to any of claims 5-8 characterized in that the means for diverting the gases and particles comprise an ejector (11).

[Claim 10] An apparatus according to any of claims 5-9 characterized in that the angle between the centreline (12) of the compartment (5) and the vertical plane is between 0 ° and 90 °.