Method for preventing plugging of circulating bed material in a circulating fluidized bed reactor apparatus

Abstract

A method of preventing plugging of a circulating bed material in a circulating fluidized bed reactor apparatus (10), the method comprising the steps of collecting a continuous flow bed (52, 54) of solid particles in a gas lock in a return leg of the reactor, measuring a gas lock bed pressure value within the continuous flow bed of solid particles, forming a gas lock bed height indication signal based on the measured gas lock bed pressure value, and the method defining phase comprising defining and storing to a digital control system a range of normal gas lock bed height indication signals formed as a function of reactor load under normal solid particle circulating flow conditions, and defining and storing to the digital control system an alarm criterion related to reactor load, satisfying the alarm criterion comprising the current gas lock bed height indication signal being outside the range of normal gas lock bed height indication signals for the current reactor load, and the method using phase comprising comparing the current gas lock bed height indication signal with the alarm criterion related to reactor load, and reducing the reactor load in case the current gas lock bed height indication signal satisfies the alarm criterion related to reactor load, for preventing plugging of the gas lock.

Description

Technical Field

[0001] This invention relates to a method for preventing blockage of circulating bed material in a circulating fluidized bed reactor apparatus, according to the preamble of the appended independent claims. Therefore, the invention particularly relates to preventing blockage in the return branch of a circulating fluidized bed reactor, especially in the airlock of the return branch. Background Technology

[0002] A circulating fluidized bed reactor, such as a circulating fluidized bed boiler, typically includes a furnace, a particle separator for separating particles from exhaust gas emitted from the upper part of the furnace, and a return branch for returning the separated particles from the particle separator to the lower part of the furnace. The return branch includes a gas damper, such as a wall seal or annular seal, to prevent upstream gas from flowing in the return branch.

[0003] One problem that can sometimes occur in circulating fluidized bed reactors is the return branch, most commonly the airlock within it, which becomes clogged. This clogging can be caused by various reasons, including sediment falling from the upper portion of the return branch, bed material particles being crushed to a size too small to be fluidized as required for proper airlock operation, or bed material particles agglomerating into agglomerates that prevent material flow. Complete or near-complete clogging of the return branch typically leads to reactor shutdown, which can result in laborious and time-consuming maintenance operations. In many cases, the clogging can be removed simply by cooling the reactor, then cleaning the return branch, and finally restarting the reactor, which may result in a production interruption that typically lasts a day or even longer. It has been shown that in some cases, return branch clogging and reactor shutdown can be avoided if near-clogging is anticipated and appropriate preventative measures are initiated sufficiently in advance.

[0004] Patent document KR 101879637 B1 discloses a method for controlling the operation of a ring seal by adjusting the supply of fluidizing air to a particle bed within the ring seal based on a measured pressure difference within the bed. Specifically, the method discloses the steps of measuring the airlock pressure value Δp within the continuous fluidized bed of solid particles and comparing the measured Δp value with a reference pressure difference Δp value measured and calculated under initial operating conditions. US Patent No. 8292977 discloses an apparatus for controlling the amount of circulating particles in a combined circulating fluidized bed system based on controlling the removal of exhaust gas and product gas from the system, in order to control the pressure in the vaporization chamber and outlet chamber in the return branch of the system. None of these documents address the observation of blockage or the prediction and prevention of near-blockage in the ring seal or return branch.

[0005] Patent document JP 4254004 B2 discloses an apparatus for estimating the sand circulation volume in a circulating fluidized bed boiler using a model based on measurements of vertical pressure and temperature distribution in the furnace, pressure and temperature at the inlet and outlet of the heat exchange chamber in the boiler's return branch, and the amount of water supplied to the heat exchanger and the temperature of the steam obtained from the heat exchanger. Patent document JP 4443481B2 discloses a system for diagnosing blockage of bed material in the bed material circulation path, relating to a bed height adjustment device for a pressurized fluidized bed boiler. The bed material circulation path includes multiple differential pressure gauges, thermometers, and flow meters of pumped air at selected locations along the path. Using these measurements and a database of blockage locations, the occurrence of blockage is determined. Neither of these documents teaches how to predict or prevent approaching blockages.

[0006] It is well known that harmful defluidization of fluidized beds can be caused by the agglomeration or sintering of bed particles, and therefore several recommendations for bed materials have been proposed to avoid or minimize this problem. U.S. Patent No. 4,075,953 suggests that in the combustion of organic waste in fluidized beds, the tendency for bed material melting and agglomeration, as well as particle breakage, can be reduced by using bed materials containing olivine sand. In their article "Biomass FBC Combustion-Bed Agglomeration Problems" (Proc. of the 13th International Conference on Fluidized Bed Combustion, 1995, 'Biomass FBC Combustion-Bed Agglomeration Problems', pages 515-522), Grubor et al. suggested that the agglomeration and sintering problems during the combustion of harvested biomass in fluidized beds can be minimized by using iron oxide as the bed material. European Patent EP 1075626 B1 suggests that the risk of sintering can be reduced when burning difficult-to-burn fuels in a fluidized bed by using bed materials with mineral particles containing less than 5% quartz.

[0007] US Patent No. 4,544,375 proposes to monitor the average density of bed particles by measuring the ash content relative to the carbon content in the bed, for example by measuring the pressure drop in the fluidized bed, and to remove ash from the fluidized bed when the ash content relative to the carbon content exceeds a predetermined value, thereby preventing ash sintering and fluidized bed defluidization.

[0008] It is generally known that rapid pressure fluctuations occur in fluidized beds, which are related to the size and number of bubbles in the bed. CEDavies and K. Fenton, in Powder Technology, July 1996, Vol. 88, No. 1, pp. 89-93, showed that pressure fluctuations in fluidized beds decrease with increasing particle size, while Chirone et al., in Chem. Eng. J, Vol. 123, 2006, pp. 71-80 (Chem. Eng. J. 123(2006) 71-80), showed that from the onset of agglomeration, pressure fluctuations in fluidized beds decrease to 60-70% of their initial values ​​over approximately two hours, and then abruptly transition to a fixed bed upon defluidization, causing a significant peak in pressure changes. Therefore, monitoring and analyzing changes in pressure fluctuations in the bed allows for early identification of the bed approaching defluidization. Accordingly, J. Shabanian et al., in Procedia Engineering 102 (2015), pp. 1006-1015, proposed that the differential pressure drop within the bed decreases as the bed approaches defluidization due to bubble growth, an effect that can be used to detect defluidization conditions early in bubbling fluidized beds. Methods for observing or preventing agglomeration in static fluidized beds are generally ineffective, if applicable, for observing and preventing blockage in the airlock of the return branch in continuously flowing fluidized beds.

[0009] The object of the present invention is to provide a method for preventing clogging of the circulating material in the return branch of a circulating fluidized bed reactor, a method that is simple to use in practice, and wherein the limitations of the methods disclosed in the prior art documents are minimized or eliminated. Summary of the Invention

[0010] The solutions defined in the appended independent claims solve or at least minimize the aforementioned problems of the prior art. The dependent claims define advantageous embodiments of the invention.

[0011] According to one aspect, the present invention provides a method for preventing clogging of circulating bed material in a circulating fluidized bed reactor apparatus, the method comprising the steps of: defining a reactor load at a digital control system of the reactor; supplying fuel and combustion gas to a furnace of the circulating fluidized bed reactor apparatus at a predetermined rate based on the reactor load; burning fuel with combustion gas in the furnace and dispersing flue gas and solid particles from the furnace into a flue gas passage; separating solid particles from the flue gas in a particle separator arranged in the flue gas passage and circulating the solid particle stream from the particle separator back to the furnace via a return branch; and collecting a continuous fluidized bed of solid particles in an airlock in the return branch, wherein the method comprises the steps of: measuring an airlock bed pressure value within the continuous fluidized bed of particles; generating an airlock bed height indication signal based on the measured airlock bed pressure value; wherein the defining phase of the method comprises the steps of: sequentially changing the reactor load defined at the digital control system to a plurality of load values; defining and storing to the digital control system a range of normal airlock bed height indication signals as a function of reactor load formed under normal solid particle circulation conditions; and defining and storing to the digital control system a range of reactor load-related (reactor load dependent) parameters. The method includes a dependent alarm criterion, which includes the current airlock height indication signal being outside the range of the normal airlock height indication signal for the current reactor load, indicating a deviation in the solid particle circulation flow. The method also includes the following steps: comparing the current airlock height indication signal with the reactor load-related alarm criterion at predetermined intervals, and reducing the reactor load if the current airlock height indication signal meets the reactor load-related alarm criterion, to prevent airlock blockage.

[0012] This invention is based on the inventors' observation that pressure values ​​measured within a fluidized bed of continuous flow of particles in an airlock can indicate abnormal behavior hours before a shutdown leading to blockage in the return branch. Because airlock bed pressure values ​​typically fluctuate rapidly, according to the invention, a smoother bed height indication signal is advantageously generated based on the measured airlock bed pressure values. However, depending on the method and apparatus used to measure the airlock bed pressure, in some cases, the airlock bed pressure value itself may be used as the airlock bed height indication signal.

[0013] Due to the continuous flow of solid particles through the fluidized bed in the airlock, the airlock pressure and airlock height indication signals can enter an irregular oscillating state, where they cyclically increase and decrease with considerable amplitude just before actual blockage occurs. Therefore, when abnormal behavior of the airlock height indication signal is observed, measurements can be initiated to avoid the serious consequences of blockage of the return branch before any harmful effects occur. A key aspect of the method according to the invention is the monitoring and analysis of the airlock height indication signal obtained from the airlock pressure value.

[0014] Because the continuously flowing fluidized bed in the airlock is formed by particles separated from the flue gas emitted from the furnace by a particle separator, the airlock bed height depends primarily on the reactor load, and especially on the rates at which combustion gases and fuel are supplied to the furnace. To enable the observation of abnormal airlock bed height indication signals, it is necessary to calibrate the airlock bed height indication signal by sequentially changing the reactor load to multiple load values ​​and, under normal solid particle circulation conditions, forming or measuring the bed height indication signal as a function of the reactor load. By using this series of bed height indication signals, the range of the normal airlock bed height indication signal related to the reactor load can be defined and stored in the reactor's digital control system. Alarm criteria related to the reactor load can then be defined and stored in the digital control system to identify anomalies or deviations in the solid particle circulation flow. The satisfaction of alarm criteria advantageously includes at least the airlock bed height indication signal falling outside the range of the normal airlock bed height indication signal for the current reactor load.

[0015] The airlock height indication signal, used to define the range of the normal airlock height indication signal, and the corresponding alarm criteria related to reactor load, are advantageously based on the airlock pressure differential measured within the airlock, i.e., the difference between the pressure value measured in the lower portion of the fluidized bed within the airlock and, for example, the pressure value measured at a higher position in the return branch. The alarm criteria related to reactor load can also be defined as a more complex function of the airlock pressure value, including, for example, the time derivative, oscillatory changes, or trends of the airlock pressure value, as will be explained below.

[0016] As mentioned above, the range of the normal airlock bed height indication signal depends on the rate at which fuel and combustion gases are supplied to the furnace. However, when inert bed material is supplied to the furnace, the range of the normal airlock bed height indication signal also depends on the inert bed material supply rate. With variations in the type or particle size of the fuel and inert bed material supplied to the furnace, the range of the normal airlock bed height indication signal typically also depends on the type and particle size of the fuel and inert bed material. It may then be necessary to store the normal range of the airlock pressure signal in the digital control system as a database defined by the appropriate range of supply rates and the types of fuel and inert bed material supplied to the furnace as needed. In some cases, it may be useful to also define the range of the normal airlock bed height indication signal as a function of other operating parameters of the reactor unit, such as the flue gas recirculation rate. In this specification, the term "load-dependent" generally refers to the dependence on any operating parameter of the reactor, as described above.

[0017] The fluidized bed in the airlock of a circulating fluidized bed reactor is typically a bubbling bed, which exhibits rapidly fluctuating bed pressure due to the rising of bubbles through the bed. Such fluctuations in bed pressure may depend on, for example, the particle size of the bed, but are generally unrelated to problems in the particle flow through the fluidized bed in the airlock. As mentioned in the description of related art, CEDavies and K. Fenton disclosed in Powder Technology, Volume 88, Issue 1, July 1996, pages 89-93, and Chirone et al. disclosed in Chem. Eng. J, Volume 123, pp. 71-80, 2006, based on the analysis of rapid fluctuations in bed pressure caused by bubbles. When fluidization problems of solid particles are caused by different reasons, such as sediment falling from above the bed, bed material particles being crushed to too small a size to be properly fluidized, or bed material particles agglomerating into large agglomerates that prevent fluidization, the rapid pressure fluctuations in bed pressure caused by bubbles can manifest differently. The method of this invention differs from these methods in that it does not observe and analyze these rapid fluctuations, but rather focuses on smoother changes in bed pressure caused by changes in the actual bed height due to variations in particle flow conditions. The advantage of using a bed height indication signal to identify flow problems in circulating bed materials is that it provides a similar indication of near-blockage in the return branch caused by various reasons.

[0018] According to the invention, the airlock pressure signal used to indicate abnormal behavior of the particle flow through the fluidized bed is advantageously averaged over a predetermined time, preferably at least 10 seconds, and even more preferably at least 30 seconds. Accordingly, alarm criteria associated with the reactor load, i.e., criteria used to interpret the possible approach of airlock blockage, include averaging the airlock pressure signal over the predetermined measurement time. Therefore, if such airlock height indication signal is outside the range of normal airlock height indication signals, it can be inferred that blockage may be approaching, and appropriate countermeasures should be initiated.

[0019] According to embodiments of the invention, the definition phase of the method includes defining and storing, in the digital control system, an upper limit related to the reactor load for the airlock bed height indication signal, and meeting the alarm criteria related to the reactor load includes the current airlock bed height indication signal being higher than the upper limit for the current reactor load. Proximity blockage of the return branch may cause the bed height to momentarily increase above its normal range, which is then observed as an increased airlock bed pressure value. It should be noted that this effect is the opposite of the effect of agglomeration near a fixed fluidized bed, which manifests as a decrease in bed pressure, as reported by J. Shabanian et al. in Procedia Engineering, Vol. 102, pp. 1006-1015, 2015.

[0020] According to an embodiment of the invention, the method includes an algorithm for observing oscillations in the airlock bed height indication signal, and an alarm criterion related to reactor load includes the presence of oscillations. As an example, the presence of oscillations can be based on the observation that the appropriately averaged airlock bed height indication signal exceeds a predetermined upper limit at least three times within a predetermined time period (e.g., 5 minutes).

[0021] According to an embodiment of the invention, the method includes another step of measuring the furnace bed pressure signal within the rapidly fluidized bed of particles in the furnace, or in other words, the furnace bed pressure signal at the lower portion of the furnace. Then, the satisfaction of alarm criteria related to reactor load advantageously includes requiring that the furnace bed pressure signal exhibit a decreasing trend while the airlock bed pressure signal exhibits an increasing trend. This simultaneous occurrence of a decreasing trend in the furnace bed pressure signal and an increasing trend in the airlock bed pressure signal indicates that the amount of solid particles in the furnace is decreasing because an increased amount of particles accumulates in the return branch pipe.

[0022] According to an embodiment of the invention, the criterion for the decreasing trend of the hearth pressure value includes observing a monotonically decreasing amount of at least 5% in at least three consecutive average hearth pressure values. Correspondingly, the criterion for the increasing trend of the airlock height indication signal includes observing a monotonically increasing value of at least 5% in at least three consecutive airlock height indication signals.

[0023] According to the present invention, various countermeasures can be initiated when alarm criteria related to reactor load are met, i.e., when an indication of impending blockage is received. As mentioned above, since blockage involves the flow of particles through the bed collected in the airlock, the primary countermeasure is to reduce the particle flow by decreasing the reactor load, i.e., the supply rate of combustion gas and fuel to the furnace of the reactor. Reducing the particle flow can be achieved by shaking the bed in a manner that eliminates the risk of blockage and induces stable flow of particles. Reducing the load also lowers the reactor temperature level, which in turn reduces the viscosity of the flowing particles in the case of alkali-concentrated materials, thereby leading to improved flowability of the material in the airlock system.

[0024] When an indication of impending blockage is received, another preferred response to prevent blockage is to begin feeding inert bed material into the furnace, or to increase the rate at which inert bed material is fed into the furnace. Increasing the supply of inert bed material can reduce the harmful effects caused by fuel particles, such as the formation of sticky compounds. In addition to altering the average composition of the bed material, the supply of inert bed material generally enhances the alteration of the bed material. It is advantageous to increase the supply of inert bed material simultaneously with other responses such as beginning to remove bottom ash from the furnace or increasing the rate at which bottom ash is removed from the furnace.

[0025] According to another embodiment of the invention, the method includes changing the type of fuel supplied to the furnace to another type of fuel upon meeting an alarm criterion related to reactor load. Alternatively or additionally, the method may include the additional step of initiating or increasing the supply of limestone to the furnace upon meeting an alarm criterion related to reactor load. Upon meeting an alarm criterion related to reactor load, the method may also include the step of initiating or increasing the supply of an agent suitable for reducing the formation of alkaline compounds with low melting temperatures to the furnace. Suitable agents include alkali getters, such as clay or kaolin. Advantageously, upon meeting an alarm criterion related to reactor load, any of the above embodiments includes the additional step of issuing a potential blockage alarm in the digital control system.

[0026] In cases where alarm criteria related to reactor load cease to be met, the method advantageously includes the step of removing all or some of the aforementioned countermeasures, and in particular, the method then includes the step of increasing the reactor load.

[0027] The above brief description of the invention, as well as other objects, features, and advantages, will be more fully understood by referring to the following detailed description of presently preferred, but merely illustrative, embodiments according to the invention, taken in conjunction with the accompanying drawings. Attached Figure Description

[0028] Figure 1A circulating fluidized bed reactor suitable for use with the method according to the invention is illustrated schematically.

[0029] Figure 2a and Figure 2b Examples of airlock pressure values ​​measured when nearing blockage and under normal solid particle circulation conditions are shown, respectively. Detailed Implementation

[0030] Figure 1 The figure schematically illustrates an exemplary circulating fluidized bed reactor apparatus, a circulating fluidized bed boiler system 10, in which the method according to the invention can be used. The boiler system includes a furnace 12, the upper portion of which is in gas flow connection with a particle separator 14. The upper portion of the particle separator is connected to a flue gas passage 16 for conveying flue gas to conventional further treatment related to, for example, flue gas purification or superheating of steam. The lower portion of the particle separator is connected to a return branch 18 through which particles separated in the particle separator can be conveyed back to the lower portion of the furnace 12. The return branch 18 includes conventional gas seals 20 for preventing gas from flowing from the furnace through the return branch to the particle separator 14. The boiler system also includes many other conventional elements known to those skilled in the art; however, these elements are not described in this patent application because they are not relevant to the invention.

[0031] When boiler system 10 is in operation, fuel is drawn from... Figure 1 Fuel, not shown, is supplied to the furnace via a fuel feeder 22, such as a feed trough or screw conveyor. Fuel is supplied at a rate controlled by a conventional control device 24, such as a closed hopper or screw speed drive. Correspondingly, inert bed material is supplied to the furnace via an inert bed material feeder 26, such as a feed trough or conveying screw. Fuel, ash formed during fuel combustion, and inert bed material form a bed of particulate solid material in the furnace 12. The inert bed material, along with any possible additives such as limestone that may be relevant to purifying flue gas or improving bed quality, are advantageously supplied from… Figure 1 The corresponding supply device, not shown, supplies material to the furnace at a rate controlled by an auxiliary material supply control device 28, such as a closed hopper or screw speed drive. The boiler system may also include multiple separate systems for supplying different types of fuel, inert bed material, and additives.

[0032] Fuel is combusted in furnace 12 by combustion gases introduced into the furnace via a main combustion gas passage 30, through a bellows 32 and a bottom grille 34 located below the furnace, and via an auxiliary combustion gas passage 36 terminating above the bottom grille. The main combustion gas passage 30 and the auxiliary combustion gas passage 36 include airflow control devices 38, such as fans and / or control valves, which are connected to… Figure 1The combustion gas supply device (not shown) is in a flow connection and is used to control the rate at which the main combustion gas and auxiliary combustion gas are supplied to the furnace 12, respectively.

[0033] The bed of particulate solid material formed in the furnace is fluidized by the combustion gas at such a high velocity that it forms a so-called fast fluidized bed, which does not have a defined upper surface but fills the entire furnace 12 with a density decreasing upwards. Figure 1 In the furnace 12, the rapid fluidized bed is symbolically depicted by a sawtooth-shaped upper layer. The fuel supply control device 24, the auxiliary material supply control device 28, and the combustion gas flow control device 38 are arranged to receive control signals from the digital control system 40 of the boiler system 10, which is therefore used to limit the load of the boiler system during operation.

[0034] Due to the rapid fluidized bed, the flue gas generated during combustion flows out of the furnace carrying a relatively large amount of solid particles. In the particle separator 14, most of the entrained solid particles are separated from the flue gas and returned to the furnace via the return branch pipe 18. Therefore, when the boiler is in operation, there is a continuous flow of solid particles via the return branch pipe. The airlock 20 advantageously includes a lower branch pipe 42 and a riser branch pipe 44 in direct particle flow connection with the particle separator 14, the lower portion of which is in particle flow connection with the lower portion of the lower branch pipe 42. Therefore, solid particles flowing downward in the lower branch pipe 42 continue to reach the riser branch pipe 44 below the lower edge of the first partition wall 46 that separates the riser branch pipe from the lower branch pipe. Thereafter, the solid particles flow upward in the riser branch pipe 44 and, as an overflow, flow from the upper portion of the riser branch pipe over the upper edge of the second partition wall 50 that separates the downflow pipe 48 from the riser branch pipe 44 to the downflow pipe 48 leading to the furnace 12.

[0035] The continuous flow of solid particles via the airlock 20 forms a first particle bed 52 leading to the lower portion of the downward branch pipe 42 and a second particle bed 54 leading to the riser branch pipe 44. The airlock advantageously includes means 56, 58 for supplying fluidizing gas to the first and second particle beds, respectively. The fluidizing gas is supplied to the first and second particle beds 52, 54 at a relatively low rate, thus making the first and second particle beds so-called bubbling beds, which behave more or less like a liquid with a defined upper surface.

[0036] The upper surface of the second particle bed 54 is always at the height of the upper edge of the second partition wall 50 during operation. If there is no friction or other non-ideal fluidization causing obstruction of the particle flow through the first and second fluidized beds 52, 54, the upper surface of the first particle bed 52 will be at the same height as the second particle bed 54. However, in practice, the upper surface of the first particle bed 52 is always at a higher height than the upper surface of the second particle bed 54 during boiler system operation. The height difference between the first and second particle beds 52, 54 depends on the load, i.e., the rate at which the particle flow passes through the airlock, and also on the different non-ideal fluidizations causing obstruction of the particle flow. Non-ideal fluidization can be, for example, due to sediment falling from the upper portion of the return branch, particle crushing of the bed material to a size too small for proper fluidization, or particle agglomeration that hinders the flow of solid material. In other embodiments of the invention, the geometry of the airlock can be... Figure 1 The geometries shown are different, but the important point is that in the operation of the boiler system, a particle bed is formed in the airlock, and the height of the particle bed depends on the rate at which the particle flow passes through the airlock and the possible obstruction to the particle flow.

[0037] Because deterioration of fluidization in the first and second particle beds 52, 54 can gradually lead to blockage of the circulating bed material flow, the present invention is based on monitoring and analyzing the fluidization state and the height of the first particle bed. When impending blockage is observed in an early stage, appropriate countermeasures can be initiated in a timely manner to prevent blockage of the circulating bed material flow. Observing impending blockage is advantageously based on measuring the airlock bed pressure value by pressure gauge 60 in the continuous flow bed of solid particles in the airlock, particularly in the lower portion of the first fluidized bed 52 in the lower branch 42, because the measured airlock bed pressure value usually fluctuates rapidly. Observing impending blockage is also advantageously based on an airlock bed height indication signal, which is formed based on the measured airlock bed pressure value, for example by averaging the airlock bed pressure value over a predetermined time such as 10 seconds.

[0038] Due to the continuous and relatively intense flow of solid particles via the airlock 20 and, particularly, via the first fluidized bed 52, the airlock pressure value measured by the pressure gauge 60, as well as the airlock height indication signal, tends to enter a state of irregular oscillation due to even small particle flow obstruction or non-ideal fluidization. Therefore, just before actual blockage occurs, the airlock height indication signal cyclically increases and decreases by a considerable amplitude. Thus, when abnormal behavior of the airlock height indication signal is observed, appropriate countermeasures can be initiated to avoid blockage of the return branch 18.

[0039] Figure 2aAn example of the average airlock bed pressure difference measured over approximately 4.5 hours under normal solid particle circulation flow conditions in a circulating fluidized bed boiler is shown, where the load increases from the start to the new value between approximately 1.5 hours and 2.2 hours. Figure 2b The image shows similar airlock bed pressure values ​​measured at ten-second intervals over a period of approximately ten minutes, several hours prior to a shutdown that caused blockage in the return branch of the circulating fluidized bed boiler. As can be seen, when... Figure 2a Compared to the corresponding pressure value in the middle, Figure 2b The bed pressure differential showed considerable variation. Figure 2b In such cases, the particle circulation spontaneously recovers from the abnormal bed pressure changes for approximately twelve hours, but eventually the bed fluidization deteriorates to an irreversible state, causing a shutdown. If the abnormal airlock bed pressure has been observed in time, the shutdown can be avoided.

[0040] Because the continuously flowing fluidized bed in the airlock 20 is formed by particles separated from the flue gas emitted from the furnace 12 by the particle separator 14, the height of the airlock bed depends on the boiler load, and especially on the rate at which the combustion gas and fuel are supplied to the furnace. This is achieved by comparing the average airlock bed pressure difference before and after a load change, such as... Figure 2a This effect can also be seen in the diagram. Therefore, by periodically comparing the current airlock bed height indication signal with the range of the normal airlock bed height indication signal related to boiler load, the approaching blockage can be observed. The range of the normal airlock bed height indication signal related to boiler load is obtained by measuring the airlock bed pressure or bed height indication signal under multiple boiler load conditions under normal solid particle circulation flow conditions. As an example, for... Figure 2a In the example shown, at the load used to obtain the data on the right side of the figure, the normal airlock height indication signal can range from about 0.13 to about 0.16.

[0041] The normal airlock height indication signal range related to boiler load and alarm criteria related to boiler load are advantageously stored in the digital control system 40. The fulfillment of alarm criteria, for example, if the airlock height indication signal falls outside the range of the normal airlock height indication signal for the current boiler load, then indicates an anomaly or deviation in the solid particle circulation flow. Figure 2b In the example, the average airlock pressure differential value causes the offset to significantly exceed the approximate range of the normal airlock height indication signal for the load, i.e., from 0.13 to 0.16 as described above. Alarm criteria related to boiler load can also be defined by more complex functions of the airlock pressure value, including, for example, the time derivative or trend of the airlock pressure value.

[0042] The device can advantageously include a pressure gauge 62 at a higher height in the return branch 18, typically above the upper height of the first fluidized bed 52 in the lower branch 42. Then, based on the pressure difference measured by the two pressure gauges 60, 62, some disturbances from the pressure signal can be reduced by defining the range of the normal airlock bed height indication signal and corresponding alarm criteria related to boiler load. Observation of abnormal flow conditions can also be performed using pressure values ​​measured by a pressure gauge 64 in the lower portion of the furnace 12 and / or a pressure gauge 66 in the upper portion of the furnace. When circulating particles temporarily accumulate in the return branch 18, a decrease in bed pressure within the furnace may be observed, thus confirming an abnormal condition in the return branch.

[0043] The airlock bed height indication signal depends on the reactor load, i.e., the rate at which fuel and combustion gases are supplied to the furnace. Therefore, in the defined state of this method, the airlock bed height indication signal is measured under several load conditions defined by the digital control system 40 to define the load-dependent range of the normal airlock bed height indication signal. The airlock bed height signal can also depend on other operating parameters of the boiler system, for example, the rate at which inert bed material is supplied to the furnace. Therefore, advantageously, the range of the normal airlock bed height indication signal is defined and stored in the digital control system 40 as a database of all relevant operating variables of the boiler system, such as the supply rate and type of fuel and auxiliary materials.

[0044] If near-clogging of the circulating bed material is observed in a timely manner, boiler shutdown can usually be avoided by initiating appropriate countermeasures using the digital control system 40. Possible countermeasures include, for example, reducing the boiler load, increasing the supply of inert bed material or additives via control device 28, and increasing the rate of bottom ash removal from the furnace via bottom ash removal device 68. When the bed material circulation returns to its normal state, the countermeasures, or at least some of them, can be terminated.

[0045] While the invention has been described herein by way of example in conjunction with what is now considered to be the most preferred embodiments, it should be understood that the invention is not limited to the disclosed embodiments, but is intended to cover various combinations or modifications of its features and several other applications included within the scope of the invention as defined in the appended claims.

Claims

1. A method for preventing clogging of circulating bed material in a circulating fluidized bed reactor (10), the method comprising the following steps: The reactor load is defined in the digital control system (40) of the circulating fluidized bed reactor device. Based on the reactor load, fuel and combustion gases are supplied to the furnace (12) of the circulating fluidized bed reactor at a predetermined rate. The fuel is burned in the furnace using the combustion gases, and flue gas and solid particles are dispersed from the furnace into the flue gas passage. Solid particles are separated from the flue gas in a particle separator (14), which is arranged in the flue gas passage, and the solid particles from the particle separator are circulated back into the furnace via a return branch pipe (18). The solid particles are collected in a continuous fluidized bed (52, 54) within an airlock in the return branch pipe. The method is characterized by comprising the following steps: The airlock pressure within the continuous flow bed of the solid particles was measured. An airlock height indication signal is generated based on the measured airlock pressure value. The definition phase of the method includes the following steps: The reactor load defined at the digital control system is sequentially changed into multiple load values. The range of the normal airlock height indication signal, which is a function of the reactor load and is formed under normal solid particle circulation conditions, is defined and stored in the digital control system. Alarm criteria related to reactor load are defined and stored in the digital control system. Satisfaction of these alarm criteria includes the current airlock height indication signal being outside the range of the normal airlock height indication signal for the current reactor load, indicating a deviation in the circulated solid particle flow. The stage of using the method includes the following steps: The current airlock height indication signal and the alarm criteria related to reactor load are compared at predetermined intervals. If the current airlock height indication signal meets the alarm criteria related to the reactor load, the reactor load is reduced to prevent blockage of the airlock.

2. The method according to claim 1, characterized in that, The airlock bed height indication signal is generated by averaging the airlock pressure values ​​measured within a predetermined measurement time.

3. The method according to claim 2, characterized in that, The predetermined measurement time is at least 10 seconds.

4. The method according to claim 3, characterized in that, The predetermined measurement time is at least 30 seconds.

5. The method according to any one of claims 1-4, characterized in that, The definition phase of the method includes defining and storing an upper limit for the airlock height indication signal in relation to the reactor load in the digital control system, and the satisfaction of the alarm criterion related to the reactor load includes the current airlock height indication signal being higher than the upper limit for the current reactor load.

6. The method according to any one of claims 1-4, characterized in that, The alarm criteria related to the reactor load are met by the current airlock height indication signal being higher than a predetermined upper limit at least three times within a predetermined time period.

7. The method according to any one of claims 1-4, comprising the step of measuring the furnace bed pressure value within the particle bed in the furnace, characterized in that, The alarm criteria related to the reactor load are satisfied when the airlock height indication signal shows an increasing trend while the furnace pressure value shows a decreasing trend.

8. The method according to claim 7, characterized in that, The criteria for the decreasing trend of the furnace bed pressure value include observing a monotonically decreasing value of at least 5% in at least three consecutive average furnace pressure values, and the criteria for the increasing trend of the airlock bed height indication signal include observing a monotonically increasing value of at least 5% in at least three consecutive airlock bed height indication signals.

9. The method according to any one of claims 1-4, characterized in that, The method includes the step of initiating or increasing the rate of inert bed material supply to the furnace upon meeting the alarm criteria related to reactor load.

10. The method according to any one of claims 1-4, characterized in that, The method includes the step of initiating or increasing the rate of bottom ash discharge from the furnace to enhance bed material variation when the alarm criteria related to reactor load are met.

11. The method according to any one of claims 1-4, characterized in that, The method includes the step of changing the type of fuel supplied to the furnace when the alarm criteria related to the reactor load are met.

12. The method according to any one of claims 1-4, characterized in that, The method includes the step of initiating or increasing the supply of limestone to the furnace upon meeting the alarm criteria related to reactor load.

13. The method according to any one of claims 1-4, characterized in that, The method includes, upon meeting the alarm criteria related to reactor load, initiating or increasing the supply of a reagent suitable for reducing the formation of alkaline compounds that melt or become viscous in the furnace at the current temperature.

14. The method according to any one of claims 1-4, characterized in that, The method includes the step of issuing an alarm in the digital control system for potential blockage when the alarm criteria related to reactor load are met.

15. The method according to any one of claims 1-4, characterized in that, The method includes the additional step of increasing the reactor load if the alarm criteria related to reactor load are no longer met.

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