Method for predicting and evaluating fluidization failure at the time of exclusively firing biomass using fluidized-bed combustion furnace

Abstract

To perform a safe operation of a fluidized-bed combustion furnace by predicting and evaluating a risk of fluidization failure in advance at the time of exclusively firing a biomass in the fluidized-bed combustion furnace.SOLUTION: An input amount, at which a biomass having such achievement that fluidization failure has not occurred in an actual machine stops fluidization in a simulation test of a small fluidized-bed combustion test machine 1, is found, and an approximate value not reaching the input amount is used as a reference value. Different kinds of other biomass are applied through the small fluidized-bed combustion test machine 1, so as to find an input amount for stopping fluidization. A first condition is made impossible for the biomass with the input amount lower than the reference value. A specimen obtained by mixing combustion ash of each biomass and silica sand 4 (fluidization medium) of a fluidized-bed combustion furnace is sintered under a high-temperature condition in a combustion temperature area of the actual machine so as to produce sintered ash and find an agglutination degree. A second condition is made impossible for the biomass having the agglutination degree out of a predetermined fluidization safe area, so as to evaluate the biomass, for which both of the first and second conditions are not impossible, as proper fuel.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for predicting and evaluating poor fluidity during biomass combustion using a fluidized bed combustion furnace. [Background technology]

[0002] In recent years, expanding the use of renewable energy has become an important issue in promoting measures against global warming, and the effective use of biomass (organic matter derived from plants and animals) as renewable energy is being considered.

[0003] For example, the CO2 generated when plant biomass is burned is absorbed from the atmosphere during the growth process of the plants that make up the biomass, so the total increase or decrease in CO2 is thought to be ±0 (carbon neutral).In addition, it is expected that this will enable a more stable supply of fuel than energy acquisition methods such as solar power generation, which are easily affected by the weather.

[0004] There are various types of plant-based biomass, such as coconut shells (the shells left over after palm oil is extracted from palm kernels), bamboo, and rice straw. Fluidized bed combustion furnaces, which are highly adaptable to various types of biomass fuels, are widely used as a means of burning this type of plant-based biomass without any problems.

[0005] Incidentally, prior art literature information relating to such a fluidized bed combustion furnace for exclusively burning biomass includes, for example, Patent Document 1 below. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-209438 Summary of the Invention [Problem to be solved by the invention]

[0007] However, when various types of biomass are burned exclusively in a fluidized bed combustion furnace, alkaline components such as potassium contained in the biomass cause agglomeration, in which the bed material (bedding material) such as silica sand and the combustion ash form lumpy solids within the fluidized bed. There is concern that this agglomeration can lead to poor fluidity. However, until now, there has been no effective means of predicting and assessing the risk of poor fluidity in advance, and while there has been an increasing demand to make effective use of various types of biomass as fuel, it has been difficult to accurately determine what type of biomass should be selected as fuel in order to operate a fluidized bed combustion furnace safely without concerns about poor fluidity.

[0008] The present invention has been made in consideration of the above-mentioned circumstances, and aims to ensure the safe operation of a fluidized bed combustion furnace by predicting and evaluating in advance the risk of poor fluidity when burning biomass exclusively in the fluidized bed combustion furnace. [Means for solving the problem]

[0009] The present invention provides a method for predicting and evaluating the risk of poor fluidity when biomass is combusted using a fluidized bed combustion furnace, comprising: The amount of biomass that has a proven track record of not causing poor fluidity in an actual machine is determined to be the amount at which fluidity stops in a simulated test using a small fluidized bed combustion tester, and the approximate value that does not reach this amount is set as the reference value.Other types of biomass are tested in the small fluidized bed combustion tester to determine the amount at which fluidity stops, and the first condition is not met for biomass whose amount of input is below the reference value. A sample of the combustion ash of each biomass mixed with the fluidized bed combustion furnace bed material is sintered under high temperature conditions within the combustion temperature range of the actual equipment to produce sintered ash, and the sintered ash is subjected to a rattling test to determine the degree of adhesion from the ratio of the weight of the sintered ash after the test to the weight of the sintered ash before the test. If the degree of adhesion is outside the predetermined safe fluidity range, the second condition is deemed unacceptable. Biomass that is not acceptable under at least one of the first and second conditions is evaluated as biomass that may cause poor flow, while biomass that is not acceptable under both the first and second conditions is evaluated as suitable fuel.

[0010] In other words, if the input amount at which biomass that has a proven track record of not causing poor flow in an actual machine stops flowing is determined in a small-scale fluidized bed combustion tester, and an approximate value that does not reach this input amount is used as a reference value, then when other types of biomass are similarly tested in the small-scale fluidized bed combustion tester to determine the input amount at which they stop flowing, biomass whose input amount is larger than the reference value can be qualitatively evaluated as a fuel that is extremely unlikely to cause poor flow.

[0011] However, because the amount of ash generated differs for each type of biomass, it is conceivable that in small-scale mock tests using a small-scale fluidized bed combustion tester, there may be cases where the amount of ash generated is so small that a judgment of failure is not made. In larger-scale actual equipment, it is expected that the biomass combustion ash will not be distributed evenly within the fluidized bed and will segregate, or that localized areas of high temperature will form within the fluidized bed. Therefore, even under such circumstances, it is necessary to evaluate the ease with which the ash itself and the silica sand will solidify to determine whether there is any concern that agglomeration will occur.

[0012] Therefore, a sample made by mixing combustion ash of each biomass with the fluidized bed combustion furnace bed material is sintered under high temperature conditions in the combustion temperature range of the actual equipment to produce sintered ash, and the sintered ash is then put into a rattler tester to determine its degree of stickiness.The closer the degree of stickiness is to 1.0, the more likely it is to solidify.By defining a region where sintering is so low that it is not confirmed as the safe fluidity region, biomass with a degree of stickiness falling within this safe fluidity region can be evaluated as a highly safe fuel even at the level of an actual equipment.

[0013] Therefore, if each biomass is put into a small fluidized bed combustion tester to determine the input amount at which flow stops, and biomass whose input amount is below a standard value is deemed unacceptable as a first condition, and biomass whose degree of adhesion is outside the specified flow safety range is deemed unacceptable as a second condition, biomass that is unacceptable under at least one of the first and second conditions will be evaluated as biomass that may cause poor flow, and only biomass that is not unacceptable under both the first and second conditions will be evaluated as suitable fuel.

[0014] Furthermore, in carrying out the present invention more specifically, the occurrence of agglomeration in an actual fluidized bed combustion furnace can be compared with the degree of sticking, and the range of the degree of sticking that does not cause poor flow in the actual fluidized bed combustion furnace can be identified as the safe fluidity region.

[0015] In particular, when the fluidized medium is silica sand, it is preferable to sinter a sample made by mixing silica sand and biomass combustion ash in a 1:1 ratio under high-temperature conditions within the combustion temperature range of the actual equipment to produce sintered ash, and to identify the region where the degree of adhesion obtained for the sintered ash is less than 0.2 as the safe fluidized region. [Effects of the Invention]

[0016] According to the method for predicting and evaluating poor fluidity when exclusively burning biomass using a fluidized bed combustion furnace of the present invention, when exclusively burning biomass in a fluidized bed combustion furnace, the risk of poor fluidity occurring can be predicted and evaluated in advance, thereby ensuring safe operation of the fluidized bed combustion furnace and achieving the excellent effect of accurately determining what type of biomass should be selected as fuel in order to operate the fluidized bed combustion furnace safely without concerns about poor fluidity. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram showing an example of a small-scale fluidized bed combustion tester used in the present invention. [Figure 2] 2 is a table showing the results of a simulation test using the small fluidized bed combustion tester of FIG. 1. [Figure 3]FIG. 1 is a schematic diagram of an electric furnace for sintering samples used in the present invention. [Figure 4] FIG. 1 is a front view showing an example of a rattle tester for measuring the degree of adhesion. [Figure 5] 1 is a graph showing the relationship between the degree of sticking and temperature in a rattler test. [Figure 6] 10 is a table showing an overall evaluation based on the results of the first and second conditions. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0019] 1 to 6 show an example of an embodiment of the present invention. FIG. 1 shows an example of a small-scale fluidized bed combustion tester 1 used in the present invention, which is a small-scale device that simulates a fluidized bed combustion furnace at the laboratory level. It is equipped with a diffuser plate 3 in the middle of a vertically extending reaction tube 2. Silica sand 4 is contained in the tube above the diffuser plate 3 as a fluidizing medium. The tube below the diffuser plate 3 serves as a wind box, into which air 6 is sent from a compressor 5. The air 6 is blown upward through the many small holes in the diffuser plate 3, fluidizing the silica sand 4 in the tube and forming a fluidized bed. Meanwhile, biomass fuel 7 is introduced from the top of the reaction tube 2. While being heated by an electric heater 8 around the reaction tube 2, the biomass fuel 7 is combusted in the fluidized bed at the operating conditions (850°C) of an actual machine.

[0020] Here, the flow rate of the air 6 from the compressor 5 is controlled by a flow meter 9 so that the silica sand 4 flows at a constant fluidization speed, while the pressure fluctuations in the pipe through which the air 6 flows are monitored by a pressure meter 10 so that it is possible to confirm that the flow has stopped (when the flow stops, a flow path through which the air 6 can flow stably is created, and pressure fluctuations disappear).

[0021] In addition, the temperature inside the fluidized bed is measured via a K-type thermocouple 11 and recorded in a data logger 12, and the oxygen concentration inside the pipe above the air diffuser plate 3 is measured by an oxygen sensor 13, making it possible to confirm that the added biomass fuel 7 has burned out (combustion is judged to have been completed when the oxygen concentration drops and then returns to normal).

[0022] Then, biomass fuel 7 is gradually added to the reaction tube 2, and once it has completely burned, the next amount is added. This process is repeated until the fluidized bed stops flowing, and the amount added when the fluidized bed stops flowing is recorded. The cessation of flowing is determined based on the loss of pressure fluctuation measured by the pressure gauge 10, but it is also possible to visually confirm through the observation window that the fluidized bed is stationary and not flowing.

[0023] Figure 2 is a table showing the results of simulation tests in the small-scale fluidized bed combustion test equipment 1 for four types of biomass A, B, C, and D, which are candidates for fuel 7. Of these, biomass B is a proven fuel that has already been used in actual equipment and has not caused poor fluidity. Since the test results showed that biomass B stopped flowing at an input of 123.6g, the reference value was set at 120g, an approximation of this input amount, and biomass A and C, which had input amounts below this reference value of 120g, were deemed unacceptable as a first condition. As for biomass D, since it did not stop flowing even when 120g was input, it was concluded that it met the first condition at this stage and the test was terminated.

[0024] In this case, for biomass A and C, a correlation was confirmed between the potassium concentration, which is a component that promotes agglomeration, and the calcium concentration, which is a component that inhibits agglomeration, and the amount of input, compared to biomass B.However, for biomass D, the test result was that ``flow did not stop'' even though the potassium concentration in the ash was relatively high.

[0025] This is thought to be because biomass D did not produce enough ash to stop the fluidization compared to other fuel 7. In a larger-scale actual device (an actual fluidized bed combustion furnace), it is possible that the ash may not be distributed evenly and may segregate, or that localized areas with high temperatures may be created. Therefore, it is necessary to also evaluate whether there is a concern that agglomeration may occur under such circumstances.

[0026] Therefore, in this example, a stickiness measurement method that has already been proven to predict ash contamination (adhesion) in low-grade coal (sub-bituminous coal) was used, and for biomass B and D that were not deemed unacceptable under the first condition described above, samples of each combustion ash mixed with silica sand 4 were sintered under high-temperature conditions (950°C) in the combustion temperature range of the actual machine (850°C to 950°C: even if the operating condition is 850°C, it is expected that high-temperature areas of 950°C will occur locally) to produce sintered ash.Each of the sintered ashes was then subjected to a rattlesnake test to determine the stickiness, and biomass D, whose stickiness was outside the specified safe fluidity range, was deemed unacceptable under the second condition.

[0027] In other words, the degree of stickiness is a newly defined index for quantifying the hardness of a sintered body by applying the rattle test, which quantitatively predicts the wear resistance and tip stability of a metal powder compact. The degree of stickiness is the ratio of the weight after the rattle test divided by the weight before the rattle test.

[0028] In the rattler test in this example, biomass B and D were heated in a muffle furnace to remove combustible components and produce combustion ash in accordance with the EN standard (EN14775) for ash analysis of solid biofuels. As shown in Figure 3, this combustion ash was mixed with silica sand 4 in a 1:1 ratio to produce a sample, which was then loaded into an alumina boat 14, placed in an alumina tube 16 attached to an electric furnace 15, and sintered by heat treatment under high-temperature conditions within the combustion temperature range of the actual equipment. The hardness (degree of adhesion) of the sintered ash thus produced was measured using a rattler tester 17 as shown in Figure 4.

[0029] Here, the rattler tester 17 is a device used to measure the wear resistance and tip stability of metal powder compacts. It rotates a cylindrical wire mesh 18 (mesh size 1mm) with a diameter of 100 mm and a length of 120 mm at a speed of 80 rpm. When sintered ash is placed in the cylindrical wire mesh 18 of the rattler tester 17 and rotated, the sintered ash is first lifted upward and then falls against the inner wall of the wire mesh, where it is gradually crumbled from the surface. After rotation under certain conditions, the sinterability of the ash is predicted from the weight remaining in the cylindrical wire mesh, and the value obtained by the following formula (1) is defined as the degree of stickiness, and the degree of sinterability is quantified (the closer the degree of stickiness is to 1.0, the harder the sintering is). Stickiness = weight after rattle test / weight before rattle test... (1)

[0030] Here, when evaluating the risk of poor flow based on the degree of agglomeration of sintered ash, by comparing the occurrence of agglomeration in an actual fluidized bed combustion furnace with the degree of agglomeration and identifying a safe fluidity range for the degree of agglomeration that will not lead to poor flow in an actual fluidized bed combustion furnace, it becomes possible to use as an indicator for evaluation whether the degree of agglomeration falls within this safe fluidity range.

[0031] For example, when the fluidized medium is silica sand 4 as in this embodiment, the change in the degree of adhesion of biomass B and D versus temperature is as shown in the graph in Figure 5. Biomass B does not show a significant increase in the degree of adhesion, whereas it was confirmed that the degree of adhesion of biomass D increases rapidly between 850°C and 950°C, the temperature range expected in an actual fluidized bed combustion furnace. In the results of a simulation test using the small-scale fluidized bed combustion tester 1, biomass D was judged to have no fluidization stoppage, but the risk of agglomeration occurring increases rapidly above 850°C, and it was confirmed that at 950°C, the combustion ash and silica sand 4 completely react to form a hard sintered body.

[0032] Here, if the degree of agglomeration is below 0.2, the ash will be in a powder state and no agglomeration will occur; if the degree of agglomeration is in the range of 0.2 or more and 0.4 or less, brittle agglomerations will occur that can be easily broken down by hand; if the degree of agglomeration is in the range of more than 0.4 and 0.8 or less, hard agglomerations will occur that cannot be easily broken down by hand; and if the degree of agglomeration is greater than 0.8, the material will melt and form a glass-like solid mass that cannot be broken down. This fact has been obtained as knowledge based on past investigations into actual equipment, and therefore, if the value of 0.2, at which sinter formation begins to be confirmed, is used as the benchmark, and the region where the degree of agglomeration is less than 0.2 is specified as the safe flow region, it can be concluded that biomass D, which falls outside this safe flow region, does not meet the second condition and cannot be evaluated as a suitable fuel.

[0033] Figure 6 is a table showing the overall evaluation based on the first and second conditions. In the simulated test using the small-scale fluidized bed combustion tester 1, those that did not stop flowing even when the standard value of 120 g was added were given an "O", and those that did stop flow were given an "X". Meanwhile, in the rattler test, those that were less than 0.2 at 950°C, which is the high-temperature condition in the combustion temperature range expected in an actual fluidized bed combustion furnace, were given an "O", and those that were 0.2 or greater were given an "X". Only Biomass B, which received an "O" in both the simulated test using the small-scale fluidized bed combustion tester 1 and the rattler test, was given an overall evaluation of "O", and the rest were given "X".

[0034] In other words, the test results in this example concluded that of the candidate fuels, biomass A, B, C, and D, all but biomass B, which is a proven fuel that has not caused poor flow in actual equipment, cannot be evaluated as suitable fuels, and it was reaffirmed that biomass B can continue to be used as a safe suitable fuel.

[0035] As described above, according to this embodiment, when biomass is exclusively burned in a fluidized bed combustion furnace, the risk of poor fluidity occurring can be predicted and evaluated in advance, thereby ensuring safe operation of the fluidized bed combustion furnace, and it can be accurately determined what type of biomass should be selected as fuel 7 in order to operate the fluidized bed combustion furnace safely without concerns about poor fluidity.

[0036] The method for predicting and evaluating poor fluidity during biomass combustion using a fluidized bed combustion furnace according to the present invention is not limited to the above-described examples, and various modifications can be made without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0037] 1. Small fluidized bed combustion test equipment 4 Silica sand (fluid medium) 7 fuel 17 Rattler Test Machine

Claims

1. A method for predicting and evaluating the risk of poor fluidity when biomass is combusted using a fluidized bed combustion furnace, comprising: The amount of biomass that has a proven track record of not causing poor fluidity in an actual machine is determined to be the amount at which fluidity stops in a simulated test using a small fluidized bed combustion tester, and the approximate value that does not reach this amount is set as the reference value.Other types of biomass are tested in the small fluidized bed combustion tester to determine the amount at which fluidity stops, and the first condition is not met for biomass whose amount of input is below the reference value. A sample of the combustion ash of each biomass mixed with the fluidized bed combustion furnace bed material is sintered under high temperature conditions within the combustion temperature range of the actual equipment to produce sintered ash, and the sintered ash is subjected to a rattling test to determine the degree of adhesion from the ratio of the weight of the sintered ash after the test to the weight of the sintered ash before the test. If the degree of adhesion is outside the predetermined safe fluidity range, the second condition is deemed unacceptable. A method for predicting and evaluating poor fluidity when exclusively burning biomass using a fluidized bed combustion furnace, characterized in that biomass that is unsuitable for at least one of the first and second conditions is evaluated as biomass that may cause poor fluidity, while biomass that is not unsuitable for both the first and second conditions is evaluated as suitable fuel.

2. A method for predicting and evaluating poor fluidity when exclusively burning biomass using a fluidized bed combustion furnace, as described in claim 1, characterized in that the occurrence of agglomeration in an actual fluidized bed combustion furnace is compared with the degree of agglomeration, and the range of the degree of agglomeration that will not cause poor fluidity in the actual fluidized bed combustion furnace is identified as the fluidity safety zone.

3. A method for predicting and evaluating poor fluidity during biomass combustion using a fluidized bed combustion furnace as described in claim 2, characterized in that when the fluidized medium is silica sand, a sample made by mixing silica sand and biomass combustion ash in a 1:1 ratio is sintered under high temperature conditions within the combustion temperature range of the actual equipment to produce sintered ash, and the region where the degree of adhesion obtained for the sintered ash is less than 0.2 is identified as the fluidity safety region.

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