JP6107382B2 - Evaluation method of solid fuel - Google Patents

Description

  The present invention relates to a method for evaluating solid fuel, and more particularly, a method that makes it possible to more accurately and easily determine the combustion speed, combustion efficiency, and calorific value related to the combustibility of solid fuel from the measurement of gas generated during combustion. About. The present invention also relates to a method for evaluating solid fuel, in particular, the combustion rate related to the flammability of the solid fuel, the frequency factor and activation energy related to the chemical reaction specific to the solid fuel that determines the combustion rate, and the combustion efficiency. The present invention relates to a method that enables quantitative determination with higher accuracy by combining measurement of gas generated during combustion and a method of numerical fluid dynamics.

  Thermal energy from the combustion of solid fuels such as coal and biomass and their dry-distilled char and coke are widely used as important energy sources such as ironmaking processes, power generation, and high-temperature burners. Since the combustibility of these solid fuels greatly affects productivity and efficiency under various process conditions, a method for evaluating solid fuels is important.

  Conventionally, there is a calorific value measurement method defined in JIS M8814 as one of the fuel evaluation methods, but it is disclosed that correction is necessary for actual operation (Patent Documents 1 and 2). The reason why the correction is necessary is not completely clear, but the calorific value evaluation method defined in JISM8814 requires the calorific value due to complete combustion, but in fact often results in incomplete combustion. The calorific value is reduced.

There is a method of analyzing the degree of such incomplete combustion as combustion efficiency, and ηCO = [CO ₂ ] / ([CO obtained from the fraction [CO], [CO ₂ ] of CO and CO ₂ in the generated gas. ] + [CO ₂ ]).

  As other fuel evaluation methods, a plurality of methods for obtaining an ignition temperature and a combustion rate using a thermobalance have been proposed. Evaluation of ignition temperature and burning rate with a thermobalance are very important factors in process design and modeling, and an improvement method of an experimental method using a thermobalance has been proposed (Non-Patent Document 1). Due to equipment limitations, it is difficult to achieve the same heating rate as in an actual process by heating with electric heating, and combustion under a high-speed gas flow rate as in the actual process affects the weight loss measurement itself. Therefore, it was unsuitable for the experiment.

  In addition, when the combustion speed is high, it is considered that the amount of fuel that can be burned in a reaction furnace, a combustor, or a combustion environment per unit time increases, thereby increasing energy and production efficiency. On the other hand, when the combustion rate is high, the gasification rate of the fuel is high, but the possibility of incomplete combustion increases, and as a result, the heat generation amount decreases. In the combustion burner when burning under such conditions, auxiliary combustion is essential, but there are many combustion environments in which auxiliary combustion cannot be performed by burning carbonaceous materials in the sintering process. Also, in actual use of solid fuel, it is often burned at a very high temperature by being put into a high-temperature reactor, combustor, or combustion environment regardless of the ignition temperature.

  Therefore, in evaluating a solid fuel, it is necessary to determine the combustion rate, combustion efficiency, and heat generation amount of the fuel itself independently of the process.

  For such purposes, methods for analyzing combustion of solid fuel from gas generated by combustion have been proposed (Non-Patent Documents 2 and 3). In these methods, the carbon material is dropped into an electric furnace that has been soaked at a high temperature to simulate rapid heating, or the carbon material is prefilled in the furnace and heated in an inert gas atmosphere, and then oxygen is added. The technique of igniting by sending in is taken. Although these methods can determine the relationship between the combustion temperature and the combustion rate depending on the furnace temperature set regardless of the ignition temperature, there are problems in measuring the temperature of the carbonaceous material, and thus the calorific value cannot be determined. Furthermore, it is not easy to measure the amount of true gas blown by the charcoal in the electric furnace. Further, when the generated gas passes through a high-temperature electric furnace, it is not easy to burn the carbonaceous material itself and evaluate its ηCO by causing an excessive secondary reaction.

There was also a problem in measuring the temperature of the solid fuel. It is not easy to measure the combustion temperature of falling solid fuel. Even when the combustion temperature of the filled solid fuel is measured, it is difficult to accurately measure the temperature because the temperature changes as the solid fuel decreases with combustion. The combustion speed of the solid fuel is governed by the chemical reaction of C + O ₂ → CO ₂ , which is the overall reaction of combustion, and the reaction speed k is the reaction frequency factor A, the activation energy of the solid fuel Ea, the combustion temperature T, When the gas constant is R, it is represented by an Arrhenius type of k = Aexp (−Ea / RT). Such a reaction is generally greatly influenced by the magnitude of the reaction temperature. Even if the combustion temperature T can be obtained, the reaction frequency factor A includes the frequency factor inherent to the chemical reaction of the solid fuel, as well as the oxygen partial pressure of the combustion atmosphere and the gas blowing rate. to be influenced. Therefore, even if the combustion rate k at a constant combustion temperature can be measured including a new experimental method, the essential frequency factor and activation energy of the solid fuel cannot be obtained. It could only be understood as the burning rate. Furthermore, it has been difficult to analyze with high accuracy, such as whether the frequency factor or the activation energy has changed as the eigenvalue of the carbonaceous material related to the combustion rate, which has influenced the combustion rate.

Japanese Patent Laid-Open No. 10-288301 JP 2010-96482 A

Iron and Steel, 72 (1986) 1537 Fuel, 81 (2002) 727 Supervised by Chemical Society of Japan "Fundamentals and Applications of Combustion and Gasification Technology" (2009)

  The present invention provides a method for performing evaluation of solid fuel by performing a combustion experiment simulating necessary conditions, obtaining a combustion speed, combustion efficiency, and calorific value by gas measurement.

  In addition, we conducted a combustion experiment that simulates the necessary conditions for solid fuel evaluation, and obtained the combustion rate, combustion efficiency, and calorific value by gas measurement. And a method for enhancing the accuracy by using a method of computational fluid dynamics.

  The present inventors have studied various combustion experimental methods and numerical fluid dynamics methods for evaluating solid fuel under the necessary combustion conditions, and can control the combustion temperature, oxygen partial pressure, and gas blowing rate Thus, a combustion experiment method having the following features [1] to [13] that can measure the combustion rate, activation energy, frequency factor, combustion efficiency, and calorific value has been developed.

The gist of the present invention is as follows [1] to [13].
[1] A method for evaluating a solid fuel mainly composed of carbon used in an iron making process,
The solid fuel, of the combustion conditions for the combustion as a sintering machine of the heat source, the combustion temperature of the solid fuel _{T (K), P O2 (} kPa) oxygen partial pressure, required for combustion to be fed into the solid fuel surface Combustion that simulates the combustion of solid fuel using V (m ³ / s) as the blast volume per unit time of a simple atmospheric gas, and at least one of the combustion temperature T, oxygen partial pressure P _O2 , and blast volume V as a variable variable Conducting the experiment,
Measuring the fraction of the gas generated by the solid fuel combustion experiment and mixed in the atmospheric gas;
Of the gas generated by the solid fuel combustion experiment and mixed in the atmospheric gas, the CO ₂ fraction is [CO ₂ ] and the CO fraction is [CO], which is defined by the formula (1). Combustion efficiency of fuel combustion ηCO,
ηCO = [CO ₂ ] / ([CO] + [CO ₂ ]) (1)
From the total amount of CO and CO ₂ generated per unit time ([CO] + [CO ₂ ]) × V (m ³ / s), the gas constant R (Pam ³ K ⁻¹ mol ⁻¹ ) and combustion Using the temperature T (K) and the combustion gas pressure P (Pa), the combustion rate r (mol / s) obtained from the equation (2),
r = ([CO] + [CO ₂ ]) × V × P / RT (2)
The process of simultaneously seeking
Evaluating the combustibility of the solid fuel from the combustion efficiency ηCO and the combustion speed r;
A method for evaluating solid fuel, comprising:

[2] A method for evaluating a solid fuel mainly composed of carbon used in an iron making process,
The solid fuel, of the combustion conditions for the combustion as a sintering machine of the heat source, the combustion temperature of the solid fuel _{T (K), P O2 (} kPa) oxygen partial pressure, required for combustion to be fed into the solid fuel surface Combustion that simulates the combustion of solid fuel using V (m ³ / s) as the blast volume per unit time of a simple atmospheric gas and at least one of the combustion temperature T, oxygen partial pressure P _O2 , and blast volume V as a variable variable Conducting the experiment,
Measuring the fraction of the gas generated by the solid fuel combustion experiment and mixed in the atmospheric gas;
Of the gas generated by the solid fuel combustion experiment and mixed in the atmospheric gas, the CO ₂ fraction is [CO ₂ ] and the CO fraction is [CO].
Combustion efficiency ηCO of combustion of the solid fuel defined by the formula (1),
ηCO = [CO ₂ ] / ([CO] + [CO ₂ ]) (1)
Total amount of CO and CO ₂ generated per unit time ([CO] + [CO ₂ ]) × V (m ³ / s), gas constant R (Pam ³ K ⁻¹ mol ⁻¹ ), combustion temperature T ( K), using the combustion gas pressure P (Pa), the combustion rate r (mol / s) obtained from the equation (2),
r = ([CO] + [CO ₂ ]) × V × P / RT (2)
The process of simultaneously seeking
Dividing the combustion rate r by the surface area S of the solid fuel to obtain a combustion rate K (mol / m ² / s) per unit area;
The solid fuel frequency factor A (mol / m ² / s) and the activation energy Ea (kJ / mol), the combustion rate K (mol / m ² / s) per unit area of the combustion temperature T (K) By the equation (6) defined as a function,
K = Aexp (Ea / RT) (6)
Using the obtained frequency factor A and the activation energy Ea, the numerical value fluid with the combustion temperature T, the oxygen partial pressure P _O2 , the water pressure P _H2O , and the air flow rate V (m ³ / s) of the combustion experiment as initial values Calculating the dynamics of CO and CO ₂ as gas amounts [CO] _Cal and [CO ₂ ] _Cal , respectively,
Combustion efficiency ηCO _Cal of combustion of the solid fuel defined by equation (7),
ηCO _Cal = [CO ₂ ] _Cal / ([CO] _Cal + [CO ₂ ] _Cal ) (7)
Combustion rate r _Cal (mol / s) obtained from equation (2),
r _Cal = ([CO] _Cal + [CO ₂ ] _Cal ) × V × P / RT (8)
Simultaneously calculating
_{Dividing the} combustion rate r _Cal by the surface area S of the solid fuel to calculate a combustion rate K _Cal (mol / m ² / s) per unit area estimated by a gas calculated by computational fluid dynamics calculation When,
[CO] calculated by the calculation of numerical fluid dynamics about the quantitative values [CO] and [CO ₂ ] of the CO and CO ₂ gas generated in the combustion experiment, the combustion efficiency ηCO of the individual fuel, and the combustion speed K per unit area Comparing each of _Cal , [CO ₂ ] _Cal , ηCO _Cal , and K _Cal ;
A method for evaluating solid fuel, comprising:

[3] determined that the case was the difference between the quantitative value and the calculated value is within 5% compared, the measurement accuracy of the frequency factor ^{A (mol / m 2 / s} ) and the activation energy Ea (kJ / mol) is sufficient The method for evaluating a solid fuel according to [2], wherein:

[4] The case difference quantitative value and the calculated value is within 1% of the comparison, determines the measurement accuracy of the frequency factor ^{A (mol / m 2 / s} ) and the activation energy Ea (kJ / mol) is to be sufficient The method for evaluating a solid fuel according to [2], wherein:

[5] The solid fuel is a carbon material, and the gas generated by the combustion experiment is not affected by the furnace wall temperature of the external heating furnace other than the reaction due to the heat generated from the carbon material. The solid fuel evaluation method according to any one of [1] to [4].

[6] The method for evaluating a solid fuel according to any one of [1] to [5], wherein the combustion is incomplete combustion.

[7] Using the combustion efficiency ηCO and the combustion speed r, the calorific value by combustion is expressed by the thermochemical reaction formula C + (1/2) O ₂ → CO +110 kJ / mol of the formula (3) and the formula (4) (3)
CO + (1/2) O ₂ → CO ₂ +282 kJ / mol (4)
Any one of [1] to [6], wherein a calorific value Q (kJ / s) per unit time is obtained from a thermochemical reaction per 1 mol equivalent of carbon represented by the following formula (5): 2. The method for evaluating a solid fuel according to item 1.
Q (kJ / s) = r × ηCO × 282 (kJ / mol) + r × (1−ηCO) × 110 (kJ / mol) (5)

[8] A device for performing a combustion experiment simulating the combustion of solid fuel is composed of a quartz tube for dividing the outside air and the combustion atmosphere, and a lamp heating device. 7] The solid fuel evaluation method according to any one of [7].

[9] The method for evaluating a solid fuel according to [8], wherein the quartz tube has a structure in which both end portions are sealed and an atmosphere gas can be circulated.

[10] The temperature of the solid fuel is measured by embedding a thermocouple in the solid fuel, and the difference between the temperature of the thermocouple embedding position of the solid fuel and the surface temperature is corrected, and the combustion temperature of the solid fuel is measured. The method for evaluating a solid fuel according to any one of [1] to [9], which is characterized in that it is characterized.

[11] Any one of [8] to [10], wherein the solid fuel is placed on a support base in the quartz tube so that the upper surface of the solid fuel is positioned on the central axis of the reaction tube that is turned sideways. The solid fuel evaluation method according to claim 1.

[12] After the oxygen partial pressure of the atmospheric gas in the quartz tube is once reduced to zero, the solid fuel is heated to a predetermined temperature by a heating device, and then an atmospheric gas having a predetermined oxygen partial pressure is circulated in the quartz tube. The method for evaluating a solid fuel according to any one of [7] to [11], wherein combustion is started and a combustion experiment is performed.

[13] Control the combustion temperature of the solid fuel, the oxygen partial pressure of the circulating gas, and the blast volume per unit time, and use these as variable variables to conduct a combustion experiment, and determine the combustion temperature and the CO and CO ₂ generated by the combustion. Measures changes in concentration (fraction) and oxygen partial pressure, and determines solid fuel by calculating combustion efficiency ηCO, combustion speed r (CO equivalent of CO + CO ₂ generation per unit time) and calorific value The method for evaluating a solid fuel according to [12].

[14] Compare the shape of the solid fuel worn by the actual combustion experiment with the wear state and shape of the solid sample estimated by the computational fluid dynamics method. Evaluation method.

  The present invention provides a method capable of measuring a more effective combustion rate, combustion efficiency, and calorific value by performing evaluation of solid fuel under combustion conditions including incomplete combustion assuming actual use. Therefore, it is expected that solid fuel will be used effectively in power generation and industrial processes using coal and its dry distillation products.

It is a schematic diagram which shows the structure of the experimental apparatus used by this invention. It is a figure which shows an example of the measurement result obtained in a combustion experiment. It is a result of Example 1 which conducted the combustion experiment, and is a figure which shows the case of (a) preheating temperature 800 ° C, (b) preheating temperature 1200 ° C, and (C) preheating temperature 1400 ° C, respectively. It is a figure which shows the combustion speed in Example 2 which performed the combustion experiment. It is a figure which shows (eta) CO in Example 2 which performed the combustion experiment. It is a figure which shows the emitted-heat amount in Example 2 which conducted the combustion experiment. It is a figure for calculating | requiring activation energy from the non-dimensional combustion speed. It is a figure which shows the prediction of the combustion rate by a CFD combustion model. It is a figure which shows wear and tear of the carbonaceous material confirmed by the combustion experiment.

  The configuration of the experimental apparatus used in the present invention is shown in FIG. The experimental apparatus includes a combustion reaction unit 1 and a gas measurement unit 2 for measuring gas generated by combustion.

  The solid fuel evaluated in the present invention is a substance mainly composed of carbon, which provides thermal energy by combustion, for example, coal, biomass, and char or coke, which are dry distillation products thereof.

For the purpose of evaluating solid fuel, in order to conduct a combustion experiment that simulates combustion of solid fuel when burning using a combustion burner or as a heat source in a sintering machine, the solid fuel is one of the combustion conditions. It is necessary to control the combustion temperature, the oxygen partial pressure, and the blast volume per unit time of the atmospheric gas necessary for the combustion sent to the surface of the solid fuel. Therefore, the combustion reaction part of the experimental apparatus used in the present invention includes the combustion temperature T (K) as the combustion condition, the oxygen partial pressure P _O2 (kPa), and the air flow rate V (m ³ / s) necessary for combustion. Can be controlled.

  The combustion reaction section 1 requires a heating device 3 for controlling the combustion temperature and a reaction tube 4 for dividing the outside air and the combustion atmosphere. Although the method of heating the combustion atmosphere by the heating device is not limited, the inventors configured the lamp heating device and a quartz tube that confines the combustion atmosphere.

  As the heating device 3, it is possible to use not only a lamp heating device but also a small electric furnace, but since the lamp heating device can focus only on a solid fuel by condensing at a fixed point, it can also be rapidly heated. It is desirable to improve the accuracy of measurement of combustion efficiency. As described in the experimental procedure described later, the solid fuel is preheated to control the combustion temperature. In the case of using a general small electric furnace, it takes about 10 to 20 minutes to preheat to 1000 ° C., but lamp heating can preheat in about 1 minute at most. Since it is not desirable in the combustion evaluation of solid fuel that the wear of the solid fuel occurs due to a change in atmosphere during preheating, it is effective to use a lamp heating device that can preheat in a shorter time.

The combustion efficiency of solid fuel is closely related to the secondary combustion of CO gas generated by combustion (CO + (1/2) O ₂ → CO ₂ ). When a small electric furnace is used, the electric furnace heats the atmosphere through the furnace wall and the furnace wall, so that the furnace wall and the atmosphere temperature are constant regardless of the calorific value of the carbonaceous material. As a result, the secondary combustion of the CO gas generated by the combustion of the solid fuel has a larger effect of the secondary combustion due to the furnace wall and the atmospheric temperature other than the heat generation of the solid fuel itself. As a result, in the solid fuel combustion field It becomes difficult to separately evaluate the secondary combustion and the secondary combustion due to heating of the electric furnace.

  Lamp heating can heat solid fuel in a pinpoint manner. In lamp heating, the efficiency of heating varies depending on the type of substance to be heated, according to the light absorption rate specific to the substance. Gases with very low light absorption and atmospheric gases are not heated, and the temperature rise is negligible. Further, by using a quartz tube having a low absorption rate as a reaction tube for dividing the combustion atmosphere, the reaction tube can be kept at a low temperature with respect to the solid fuel heated to a high temperature. Although the results may differ depending on the solid fuel to be used, the quartz tube to be formed, and the atmospheric gas species to be introduced, the inventors used a general lamp heating device with an output of about 2000 W, and used graphite as the solid fuel. As a result, it was confirmed that the quartz tube directly under the lamp was kept at 200 ° C. or lower and the atmospheric gas was kept at 100 ° C. or lower even when irradiated with light at an intensity capable of heating to about 1400 ° C. As described above, by the lamp heating, the combustion experiment can be performed in a state where the gas generated by the combustion experiment is not affected by the furnace wall temperature of the external heating furnace other than the reaction caused by the heat generated from the solid fuel.

  For the purpose of heating the solid fuel pinpoint, it is desirable to install a water-cooled mirror in the lamp heating device for reflecting and condensing the irradiated light. It is effective to adjust the height and position of the condensing point so that the water-cooled mirror can be adjusted to collect light at the center position of the reaction tube. Moreover, the controller 5 which can control an output is connected for temperature control in any heating device.

  Depending on the type of the heating device, the portion of the reaction tube 4 where the combustion atmosphere can be controlled and the material of the reaction tube vary. When lamp heating is used as the heating device, a quartz tube that does not hinder the control of the combustion atmosphere is effective. When an electric heating device is used as the heating device, a quartz tube or a mullite tube having high heat resistance is effective. Further, at both ends of the reaction tube 4 as shown in FIG. 1, it is desirable to take measures for hermetically maintaining for atmospheric control and preventing damage due to heating. The inventors used a stainless steel support at both ends of the reaction tube, and constituted the reaction tube by a quartz tube that was cooled with water and hermetically held with an O-ring. The size of the part constituted by the quartz tube is not specified, but for the purpose of airflow control, it is effective that the inner diameter is 100 mm or less and the length is 1000 mm or less, and more desirably, the inner diameter is 40 mm or less. The length is desirably 500 mm or less. On the other hand, the minimum size needs to be larger than the size that allows solid fuel to be taken in and out and locally heated, and needs to have an inner diameter of 1 mm or more and a length of 10 mm or more.

  An atmosphere gas 7 with a controlled oxygen partial pressure is blown into the reaction tube 4 where the combustion reaction takes place. The inventors have confirmed that the oxygen partial pressure in the reaction tube 4 can be controlled by controlling the air, air-fuel mixture, or nitrogen gas with a plurality of mass flow controllers and blowing air. It is also effective to arrange a honeycomb for the purpose of rectification at the inflow portion of the atmospheric gas 7 in the reaction tube 4 for the purpose of controlling the air flow for burning the solid fuel 8.

An actual combustion experiment is performed by heating the solid fuel 8 arranged in the reaction tube 4 configured in the above example with the heating device 3. The amount of the solid fuel 8 to be evaluated is not specified as long as it is an amount that can be accommodated in the reaction tube, but it is desirable that the amount of the solid gas 8 blown into the reaction tube is not hindered. Moreover, it is desirable for the purpose of controlling the combustion temperature that the size is within a range that can be heated by the heating device. The inventors used a reaction tube having an inner diameter of 40 mm and a length of 500 mm, and when heated by a lamp heating apparatus, using a solid fuel having a thickness of 5 mm, a diameter of 10 mm, and a weight of about 1 g, It was confirmed that the combustion temperature was easily controlled without inhibiting the above. If it is within the range of 1 mg to 1 kg, there is no problem. On the other hand, if the amount of solid fuel is less than 1 mg, the current technology has problems in temperature measurement and detection of gas generated during combustion, and is not suitable for evaluation by the method of the present invention. In addition to direct temperature measurement with a thermocouple, radiant heat measurement, two-color thermometer measurement, and thermography measurement are effective for measuring the temperature of combustion at this time. The inventors performed direct measurement using a thermocouple, and confirmed that the combustion temperature could be measured by the temperature measuring device 10 connected to the R thermocouple 9 embedded in the center of the solid fuel 8. It is also possible to measure the combustion temperature at the time of combustion from the insertion position into the solid fuel 8. If the solid fuel has a high thermal conductivity, the temperature measured at the buried position can be used as the surface combustion temperature. It is also effective to correct the temperature at the buried position by measuring the temperature difference between the case where the thermocouple is attached and the buried position. The inventors of the present invention have examined the temperature of the thermocouple affixed to the surface, the center of the disk, and the position of the depth of 2.5 mm by examining the experiment conducted using a solid fuel of a disk-type graphite material having a thickness of 5 mm and a diameter of 10 mm. It was confirmed that the temperature difference was about 50 ° C. when it was buried at the center position of, and was corrected and used for evaluation of solid fuel. It is also effective to place the quartz tube (reaction tube 4) on the trapezoidal support base 11 as shown in FIG. 1 so as not to damage the quartz tube (reaction tube 4) due to the temperature during combustion. The inventors prepared an alumina trapezoidal support with a width of 10 mm on the upper surface, a length of 30 mm, a width of 15 mm on the lower surface, a length of 40 mm, and a height of about 10 mm. Was placed so as to be approximately in the center of the reaction tube.

  The atmospheric gas 8 flowing through the reaction tube 4 in FIG. 1 conveys the gas generated by the combustion, passes through the gas measuring unit 2 at the subsequent stage, and is exhausted.

Here, the gas measurement method is not particularly defined, but in order to obtain a target measurement value, the gas flow meter 12 and the gas analyzer 13 capable of separately measuring CO / CO ₂ are essential. In particular, for the gas analyzer 13, it is effective to use an infrared spectroscopic device, a mass spectrometer, and an oxygen sensor capable of high-speed repeated measurement and capable of time-resolved measurement. Furthermore, it is desirable to connect a barometer 14 for the accuracy of gas measurement. In addition, the order of connection of each measuring apparatus is not ask | required.

A first experimental procedure using the apparatus configured in the above example will be described below.
After embedding the R thermocouple 9 in the solid fuel 8 and placing it in the center of the reaction tube 4, the front and back of the reaction tube 4 are connected by a pipe joint and a quick coupling or the like and sealed. After confirming that there is no gas leakage by circulating an atmospheric gas having an arbitrary oxygen partial pressure, measurement of each measuring device is started. Subsequently, lamp heating is performed with an arbitrary output, and combustion of the solid fuel 8 is started. After an arbitrary period of time has elapsed after the start of combustion, the heating lamp of the heating device 3 is turned off, the burned solid fuel 8 is naturally cooled, and the generation of combustion gas ends while checking the measured value by the gas analyzer 13. Wait for.

  Next, in order to facilitate temperature control, a second experimental procedure different from the first experimental procedure will be described. After embedding the R thermocouple 9 in the solid fuel 8 and placing it in the center of the reaction tube 4, the front and back of the reaction tube 4 are connected by a pipe joint and a quick coupling or the like and sealed. An inert gas such as nitrogen gas is circulated through the reaction tube 4 to confirm that there is no gas leakage, and then the reaction tube 4 is purged to reduce the oxygen partial pressure to a level that is not detected by the gas analyzer 13. Thereafter, the solid fuel 8 is heated to an arbitrary temperature by the heating device 3, and then an atmospheric gas having an arbitrary oxygen partial pressure is circulated to start combustion. After an arbitrary period of time has elapsed after the start of combustion, the heating lamp of the heating device 3 is turned off, the burned solid fuel 8 is naturally cooled, and the measured value by the gas analyzer 13 is confirmed while waiting for the combustion gas to end.

Although the predetermined gas analysis is possible in both the first and second experimental procedures, the inventors can control the combustion temperature and oxygen partial pressure more easily than in the second experimental procedure. I confirmed that there was. An example of the gas analysis result obtained by the second experimental procedure is shown in FIG. The upper chart shows the transition of oxygen partial pressure. After the start of the experiment, the oxygen partial pressure is temporarily reduced by purging with nitrogen gas. From the reading of the gas analyzer, the oxygen partial pressure decreases from the point indicated by 21 in the solid line indicating the change in oxygen partial pressure in the upper diagram of FIG. When oxygen is no longer detected by the reading of the gas analyzer 13, the solid fuel 8 is heated by the heating device 3. At this time, the output of the heating device 3 is controlled so that the temperature reading indicated by the thin solid line in the lower diagram of FIG. Subsequently, as shown in the upper diagram of FIG. 2, the combustion of the solid fuel 8 is started by circulating an atmospheric gas having an arbitrary oxygen partial pressure, which is indicated by the gray and black thick lines in the lower diagram of FIG. 2. Thus, the generation of CO and CO ₂ is detected by the gas analyzer 13. At the same time, the temperature measurement value in the solid fuel 8 is read as indicated by the thin solid line in the lower diagram of FIG. 2, and the gas concentration (fraction) generated during combustion at each combustion temperature can be detected.

Next, a procedure for obtaining the combustion efficiency, combustion speed and calorific value of the solid fuel from the experimental results will be shown.
First, the combustion efficiency ηCO is obtained from the ratio of generated CO and CO ₂ . For simplicity, it is possible to directly check the ratio of the output value of the gas analysis value, but more precisely, the generated concentration (fraction) is quantified and used. The inventors made a calibration curve in advance using CO and CO ₂ gas having known concentrations (fractions), and estimated the concentration (fraction) of the generated gas. The fraction of generated CO [CO], when the fraction of CO ₂ and [CO _2], ηCO formula (1)
ηCO = [CO ₂ ] / ([CO] + [CO ₂ ]) (1)
Ask from. ηCO is 1 when [CO] is 0, indicating complete combustion. When ηCO is less than 1, it indicates that incomplete combustion occurs, and as ηCO approaches 0, the degree of incomplete combustion increases and the amount of heat generation decreases.

Secondly, the combustion rate r (mol / s) is determined by assuming that the total generation amount of CO and CO ₂ per unit time is ([CO] + [CO ₂ ]) × V (m ³ / s). (Pa m ³ K ⁻¹ mol ⁻¹ ), combustion temperature T (K), and combustion gas pressure P (Pa), the equation (2),
r = ([CO] + [CO ₂ ]) × V × P / RT (2)
Ask from. It is also effective to measure the actual mass of the solid fuel before and after combustion and compare it with the mass loss determined from the combustion rate by gas analysis.

Third, the calorific value is obtained. The above-mentioned combustion efficiency ηCO and the combustion speed r are determined in combination. At this time, the calorific value associated with combustion is expressed by Equations (3) and (4).
C + (1/2) O ₂ → CO +110 kJ / mol (3)
CO + (1/2) O ₂ → CO ₂ +282 kJ / mol (4)
The calorific value Q (kJ / s) per unit time is apparent from the thermochemical reaction per 1 mol equivalent of carbon represented by the following formula (5)
Q (kJ / s) = r × ηCO × 282 (kJ / mol) + r × (1−ηCO) × 110 (kJ / mol) (5)
Is required.

  It can be evaluated that the closer the combustion efficiency ηCO is to 1, the better the complete combustion and the better the combustibility of the solid fuel. Moreover, it can be evaluated that the higher the combustion speed r, the better the combustibility of the solid fuel. The higher the combustion efficiency ηCO and the faster the combustion speed r, the greater the amount of heat generated as a result of combustion.

  Finally, an activation energy Ea and a frequency factor A of the chemical reaction in the combustion unique to the solid fuel are obtained from the experimentally obtained combustion speed r, and a procedure for improving accuracy using a numerical fluid dynamics technique is shown.

First, in order to make the combustion rate r (mol / s) dimensionless, the combustion rate K (mol / m ² / s) per unit area is obtained by dividing by the surface area S (m ² ) of the solid fuel. Here, as the surface area S, it is desirable to use an average value of surface area measured values before and after the combustion experiment.

Secondly, the burning rate K is Arrhenius type using activation energy Ea and frequency factor A K = Aexp (−Ea / RT) (6)
Analysis by the chemical reaction rate. Although the Arrhenius type chemical reaction analysis method does not matter, the inventors plot the graph of FIG. 7 with the reciprocal of the combustion temperature T on the horizontal axis and the logarithm of the combustion speed on the vertical axis, and connect each combustion speed with a straight line. It has been confirmed that dividing into three is effective. Here, the activation energy Ea and the frequency factor A specific to the solid fuel are obtained for the chemical reaction rate-determining step having a combustion temperature of 1000 K or less in the three divided regions. Note that the region exceeding 1000K usually indicates that the combustion speed is delayed due to the oxygen diffusion rate control around the solid fuel, and is greatly affected by the combustion conditions other than the solid fuel. Not in.

  Third, the accuracy of the obtained frequency factor A and activation energy Ea is confirmed using a computational fluid dynamics technique. Among the activation energy Ea and the frequency factor A obtained by the combustion gas reaction analysis, a plurality of factors affect the frequency factor A in particular. Therefore, the combustion of solid fuel is expressed by Computational Fluid Dynamics (CFD). It is confirmed that the basic parameters (A, Ea) specific to the solid fuel, which are modeled by the method and obtained by experiments, are obtained independently of the combustion conditions.

  The method used in the CFD model is not limited, but can be used for general-purpose CFD calculation and chemical reaction analysis. By using FLUENT of the company, it is confirmed that a combustion model can be constructed and analyzed. CFD modelers such as FLUENT apply the finite volume method and reproduce the model to be calculated with the basic structure and boundary conditions called mesh. The initial values used in the combustion experiment are input with the gas input, gas output, gas-graphite interface, gas-alumina base interface, and reaction tube outer wall as boundary conditions.

The initial values in the actual calculation of the present invention are input as the combustion conditions the blowing amount of gas input, P _O2 and P _H2O , and the combustion temperature depending on the lamp intensity of the heating device. Further, as information on solid fuel, A and Ea obtained by experiments were input. In addition, the reaction rate constant based on the literature value was input about the secondary combustion of the generated CO gas.

  Using FLUENT, based on these combustion conditions and the initial values of solid fuel, the basic physical formulas of heat transfer, hydrodynamics, and chemical kinetics were calculated for each mesh and discretized by the mesh. By calculating and adding the information in each cell, a numerical solution of the entire model can be obtained. By repeating such calculation, the calculation result is shown by a convergent solution that minimizes the difference between the numerical value of the entire model and the boundary condition.

For the combustion gas reaction analysis model using FLUENT, we examined the validity of the calculation results against the initial values to be input. As a standard model, the CFD calculation model includes graphite pellets for the generation amount and ratio of CO and CO ₂ in the combustion gas obtained by inputting Ea and A of graphite and the combustion conditions of the combustion gas reaction analysis experiment. By comparing with the results of the combustion gas reaction analysis experiment, the accuracy of Ea and A input to the CFD model is analyzed.

  It has been confirmed that the comparison results are within 5% when both experiments and model calculations are performed accurately. More preferably, it is within 1%, but in order to do so, it is effective to increase the number of combustion experiments in the previous step, and to increase the number of meshes in order to improve the accuracy of model calculation.

Example 1
Fuel used for combustion as a heat source in a sintering machine using graphite pellets (manufactured by Kojundo Chemical Laboratory Co., Ltd .: C> 99.99%, φ10 mm, thickness 5 mm) as a solid fuel by the experimental apparatus used in the present invention. A combustion experiment was conducted for the purpose of evaluation. Regarding the combustion conditions in the sintering machine, the combustion temperature of the graphite pellets, the oxygen partial pressure, and the air flow per unit time of the atmosphere gas required for combustion sent to the surface of the solid fuel are controlled. went.

Considering the difference in the combustion temperature in the sintering machine, the change in the pellet temperature during the combustion experiment at preheating temperatures of (a) 800 ° C., (b) 1200 ° C., and (c) 1400 ° C. was examined. For the other combustion conditions, for the purpose of simulating the inside of the sintering machine, the blowing amount was 10 ⁻² m ³ / min, and the combustion switching gas was the atmosphere (oxygen partial pressure = 21 kPa). In the gas analysis, CO, CO ₂ generated by combustion, and changes in oxygen partial pressure were measured.

The results are shown as FIG. 3 (a) preheating 800 ° C., FIG. 3 (b) preheating 1200 ° C., and FIG. 3 (c) preheating 1400 ° C. for each preheating temperature. Each of FIGS. 3A to 3C shows the time variation of the measured values of the combustion temperature and the concentration (fraction) of the gas analyzed as the combustion experiment progresses. In both experiments, generation of CO and CO ₂ accompanying combustion of graphite pellets was confirmed. Figure 3 (a) ~ (b) the upper view of each figure, shows the time variation of the ηCO determined from the measured values and the C equivalents CR burn rate of oxygen partial pressure P _O2. ηCO and CR were obtained from the measurement results of CO and CO ₂ , respectively. ηCO was calculated as a concentration (fraction) ratio (ηCO = [CO ₂ ] / ([CO] + [CO ₂ ])) at each timing of the generated gas, and C equivalent CR of the combustion rate was generated per unit time. The C equivalent of CO + CO ₂ was calculated from r = ([CO] + [CO ₂ ]) × V × P / RT and defined as CR (mg / s).

  From the results of each combustion experiment shown in FIG. 3, for the purpose of evaluating the combustion of graphite pellets, average values were obtained for 30 to 90 s after gas switching of pellet temperature, ηCO, and CR. The pellet temperature in 30 to 90 s after gas switching means the combustion temperature. Each average value is shown in Table 1 for each preheating temperature before combustion, and numerical values are shown in FIGS. 3 (a) to 3 (c). As the preheating temperature increased, the combustion temperature increased. It was also found that both ηCO and CR increased as the combustion temperature increased.

  From the above, in the combustion of graphite pellets, when burned at a higher temperature, the burning rate increases as shown by the CR value in Table 1. It was also found that the combustion efficiency increased as indicated by ηCO in Table 1. Therefore, it has been found that when graphite pellets are used as fuel, use at higher temperatures is effective in terms of both combustion speed and combustion efficiency.

(Example 2)
As a solid fuel, the carbon content is almost the same, and the calorific value at the time of complete combustion is estimated to be about 8000 kJ / mol. Carbonaceous materials A and B are evaluated as fuel when burning as a heat source in the sintering machine. A combustion experiment was conducted for the purpose. As for the combustion conditions in the sintering machine, the combustion temperature is assumed to be 800 to 1800 K assuming the temperature variation in the sintering machine, and the blast volume per unit time of the atmospheric gas necessary for the combustion sent to the solid fuel surface is 10 ^−2. m ³ / min, the combustion switching gas was the atmosphere (oxygen partial pressure = 21 kPa). The gas analysis of CO and CO ₂ generated by combustion and the change in oxygen partial pressure were measured, and the combustion rates r, ηCO, and calorific value of the carbonaceous materials A and B at each combustion temperature were obtained. The obtained combustion rate r, combustion efficiency ηCO, and calorific value are shown in FIGS. 4, 5, and 6, respectively.

  As shown in FIG. 4, in the comparison of the combustion speed r, the carbonaceous material B slightly exceeded in the whole temperature range. The difference at a combustion temperature of 1300 K or higher was small.

  On the other hand, the combustion efficiency ηCO shown in FIG. 5 has a large difference between the carbonaceous materials A and B, and it was found that the carbonaceous material B tends to cause incomplete combustion particularly in a region exceeding 1300K.

  Further, with respect to the calorific value shown in FIG. 6, it was found that the calorific value of the carbonaceous material B was large up to about 1200K, but the calorific value of the carbonaceous material A increased at a point exceeding 1300K.

  From the above results, regarding the difference between the carbonaceous materials A and B, which was unknown in the comparison based on the assumption of complete combustion, when used in a relatively low-temperature combustion furnace, the carbonaceous material B has a higher combustion rate, and On the other hand, when it is used in a high-temperature combustion furnace, it has become possible to quantitatively evaluate that the carbon material A is advantageous in terms of the calorific value.

(Example 3)
With the experimental apparatus used in the present invention, the burning rate of graphite pellets (manufactured by Kojundo Chemical Laboratory Co., Ltd .: C> 99.99%, φ10 mm, thickness 5 mm) was evaluated as a solid fuel.

Assuming combustion conditions as combustion temperature: 800 to 1800 K, PO ₂ : 21 kPa, H ₂ O: 1 percent, blast volume: 10 ⁻² m 3 / min, the combustion speed r (mol / s) at each combustion temperature is obtained. It was.

Subsequently, in order to make the combustion rate dimensionless, it was divided by the surface area (m ² ) of the solid fuel to obtain the combustion rate K (mol / m ² / s) per unit area at each combustion rate.

Subsequently, the burning rate K per unit area is set to Arrhenius type K = Aexp (−Ea / RT) (6)
The chemical reaction rate was analyzed in the region where the combustion temperature was 1000K or less. As a result, the activation energy Ea was 178 kJ / mol, and the frequency factor A was 4.4 × 10 ⁻⁴ .

Combustion temperature: 1500 K, PO ₂ : 21 kPa, H ₂ O: 1 percent, air flow: 10 ⁻² m ³ / min as combustion conditions in the results of the combustion gas reaction analysis experiment and CFD model constructed using FLUENT Table 2 shows the CFD calculation results obtained by inputting the activation energy Ea and the frequency factor A of the solid fuel as 178 kJ / mol and 4.4 × 10 ⁻⁴ , respectively.

  From the comparison results, it was found that the difference between the experimental value and the calculated value was within 5%, and Ea and A input to the model were almost correct.

Example 4
FIG. 8 shows the calculation result of the microscopic burning rate on the carbonaceous material surface obtained by the CFD model. In FIG. 8, the calculation result with the gas flow from the right side to the left side is expressed by the contrast from black to white because the combustion speed is high.

According to the analysis results of the CFD calculation, the burning speed of the carbonaceous material surface is anisotropic depending on the gas flow. It shows that there is. More specifically, the front part of the gas flow, particularly the upper right and lower right, is 4 × 10 ⁻⁴ mol / m ² / s or more and combustion is faster than other regions, and the rear is 2 × 10 ⁻⁴ mol / m ^2. The result was that the burning speed was slow in most of the region below / s.

  On the other hand, the photograph which caught the mode of the carbonaceous material in each step of the experiment made into 6 steps (1)-(6) every 2 minutes of combustion time is shown in FIG. The black portion in FIG. 9 is the carbon material used for the combustion gas reaction analysis, and combustion is performed under a gas flow in one direction from right to left. Due to the influence of the gas flow in one direction, the front, in particular, the upper right and the lower right of the solid fuel was preferentially worn due to the progress of combustion. This result shows that there is anisotropy in combustion, and was the same result as the calculation result. From these results, the accuracy of both the combustion experiment and the CFD model could be confirmed.

DESCRIPTION OF SYMBOLS 1 Combustion reaction part 2 Gas measurement part 3 Heating device 4 Reaction tube (quartz tube)
DESCRIPTION OF SYMBOLS 5 Control part 6 Sealing cooling part 7 Atmospheric gas 8 Solid fuel 9 R thermocouple 10 Temperature measuring device 11 Trapezoidal support stand 12 Gas flow meter 13 Gas analyzer 14 Barometer 21 Oxygen partial pressure reduction point before preheating 22 Preheating temperature before combustion Control point

Claims (15)

A method for evaluating carbon-based solid fuels used in steelmaking processes,
The solid fuel, of the combustion conditions for the combustion as a sintering machine of the heat source, the combustion temperature of the solid fuel _{T (K), P O2 (} kPa) oxygen partial pressure, required for combustion to be fed into the solid fuel surface Combustion that simulates the combustion of solid fuel using V (m ³ / s) as the blast volume per unit time of a simple atmospheric gas, and at least one of the combustion temperature T, oxygen partial pressure P _O2 , and blast volume V as a variable variable Conducting the experiment,
Measuring the fraction of the gas generated by the solid fuel combustion experiment and mixed in the atmospheric gas;
Among the gases generated by the solid fuel combustion experiment and mixed in the atmospheric gas,
The fraction of CO ₂ [CO _2], the fraction of CO as [CO], and combustion efficiency ηCO combustion of the solid fuel as defined in formula (1),
ηCO = [CO ₂ ] / ([CO] + [CO ₂ ]) (1)
From the total amount of CO and CO ₂ generated per unit time ([CO] + [CO ₂ ]) × V (m ³ / s), the gas constant R (Pam ³ K ⁻¹ mol ⁻¹ ) and combustion Using the temperature T (K) and the combustion gas pressure P (Pa), the combustion rate r (mol / s) obtained from the equation (2),
r = ([CO] + [CO ₂ ]) × V × P / RT (2)
The process of simultaneously seeking
Evaluating the combustibility of the solid fuel from the combustion efficiency ηCO and the combustion speed r;
A method for evaluating solid fuel, comprising: A method for evaluating carbon-based solid fuels used in steelmaking processes,
The solid fuel, of the combustion conditions for the combustion as a sintering machine of the heat source, the combustion temperature of the solid fuel _{T (K), P O2 (} kPa) oxygen partial pressure, required for combustion to be fed into the solid fuel surface Combustion that simulates the combustion of solid fuel using V (m ³ / s) as the blast volume per unit time of a simple atmospheric gas and at least one of the combustion temperature T, oxygen partial pressure P _O2 , and blast volume V as a variable variable Conducting the experiment,
Measuring the fraction of the gas generated by the solid fuel combustion experiment and mixed in the atmospheric gas;
Of the gas generated by the solid fuel combustion experiment and mixed in the atmospheric gas, the CO ₂ fraction is [CO ₂ ] and the CO fraction is [CO].
Combustion efficiency ηCO of combustion of the solid fuel defined by the formula (1),
ηCO = [CO ₂ ] / ([CO] + [CO ₂ ]) (1)
Total amount of CO and CO ₂ generated per unit time ([CO] + [CO ₂ ]) × V (m ³ / s), gas constant R (Pam ³ K ⁻¹ mol ⁻¹ ), combustion temperature T ( K), using the combustion gas pressure P (Pa), the combustion rate r (mol / s) obtained from the equation (2),
r = ([CO] + [CO ₂ ]) × V × P / RT (2)
The process of simultaneously seeking
Dividing the combustion rate r by the surface area S of the solid fuel to obtain a combustion rate K (mol / m ² / s) per unit area;
The solid fuel frequency factor A (mol / m ² / s) and the activation energy Ea (kJ / mol), the combustion rate K (mol / m ² / s) per unit area of the combustion temperature T (K) By the equation (6) defined as a function,
K = Aexp (Ea / RT) (6)
Using the obtained frequency factor A and the activation energy Ea, the numerical value fluid with the combustion temperature T, the oxygen partial pressure P _O2 , the water pressure P _H2O , and the air flow rate V (m ³ / s) of the combustion experiment as initial values Calculating the dynamics of CO and CO ₂ as gas amounts [CO] _Cal and [CO ₂ ] _Cal , respectively,
Combustion efficiency ηCO _Cal of combustion of the solid fuel defined by equation (7),
ηCO _Cal = [CO ₂ ] _Cal / ([CO] _Cal + [CO ₂ ] _Cal ) (7)
Combustion rate r _Cal (mol / s) obtained from equation (2),
r _Cal = ([CO] _Cal + [CO ₂ ] _Cal ) × V × P / RT (8)
Simultaneously calculating
_{Dividing the} combustion rate r _Cal by the surface area S of the solid fuel to calculate a combustion rate K _Cal (mol / m ² / s) per unit area estimated by a gas calculated by computational fluid dynamics calculation When,
[CO] calculated by the calculation of numerical fluid dynamics about the quantitative values [CO] and [CO ₂ ] of the CO and CO ₂ gas generated in the combustion experiment, the combustion efficiency ηCO of the individual fuel, and the combustion speed K per unit area Comparing each of _Cal , [CO ₂ ] _Cal , ηCO _Cal , and K _Cal ;
A method for evaluating solid fuel, comprising: 3. The combustion temperature T (K) and the combustion gas pressure P (Pa) are average values for 30 to 90 seconds after the atmospheric gas necessary for combustion is sent to the surface of the solid fuel. The evaluation method of the solid fuel of description. If the difference between the quantitative value and the calculated value the comparison is within 5%, the measurement accuracy of the frequency factor ^{A (mol / m 2 / s} ) and the activation energy Ea (kJ / mol) is determined to be sufficient 4. The method for evaluating a solid fuel according to claim 2, wherein the solid fuel is evaluated. The measurement accuracy of the frequency factor A (mol / m ² / s) and the activation energy Ea (kJ / mol) is sufficient when the difference between the compared quantitative value and the calculated value is within 1%. The method for evaluating a solid fuel according to claim 2 or 3 . The solid fuel is a carbon material, and the gas generated by the combustion experiment is not affected by the furnace wall temperature of the external heating furnace other than the reaction caused by the heat generated from the carbon material. 6. The method for evaluating a solid fuel according to any one of 5 above. The combustion method for evaluating solid fuel according to any one of claims 1-6, characterized in that the incomplete combustion. Using the combustion efficiency ηCO and the combustion speed r, the calorific value of combustion is expressed by the thermochemical reaction formula C + (1/2) O ₂ → CO +110 kJ / mol (3) in the formulas (3) and (4).
CO + (1/2) O ₂ → CO ₂ +282 kJ / mol (4)
The calorific value Q (kJ / s) per unit time is obtained from the thermochemical reaction per 1 mol equivalent of carbon represented by the formula (5), according to any one of claims 1 to 7. Evaluation method for solid fuel.
Q (kJ / s) = r × ηCO × 282 (kJ / mol) + r × (1−ηCO) × 110 (kJ / mol) (5) Apparatus for performing combustion experiments simulating the combustion of solid fuel, claim 1-8 for the quartz tube for dividing the outside air and the combustion atmosphere, and characterized by being constituted by using a lamp heating device 2. The method for evaluating a solid fuel according to item 1. 10. The method for evaluating a solid fuel according to claim 9 , wherein the quartz tube has a structure in which both ends are sealed and an atmosphere gas can be circulated. The solid fuel is embedded thermocouples to measure the temperature of the solid fuel, by correcting the difference between the temperature of the surface of the thermocouple embedded position of the solid fuel, and measuring the combustion temperature of the solid fuel evaluation method of a solid fuel according to any one of claims 1-10. The solid fuel placed on the support base of the quartz tube, according to any one of claims 9 to 11 the upper surface of the solid fuel, characterized in that to be located at the center axis of the reaction tube was sideways Evaluation method for solid fuel. After the oxygen partial pressure of the atmospheric gas in the quartz tube is once reduced to zero, the solid fuel is heated to a predetermined temperature by a heating device, and then an atmospheric gas having a predetermined oxygen partial pressure is circulated in the quartz tube to perform combustion. The solid fuel evaluation method according to any one of claims 8 to 12 , wherein a combustion experiment is started. The combustion temperature of the solid fuel, the oxygen partial pressure of the circulating gas, and the air flow per unit time are controlled, and these are used as variable variables to conduct a combustion experiment. The combustion temperature and the concentrations of CO and CO ₂ generated by combustion (min Rate) and oxygen partial pressure are measured, and combustion efficiency ηCO, combustion rate r (C equivalent of CO + CO ₂ generation per unit time) and calorific value are obtained, and solid fuel is evaluated. Item 14. The method for evaluating a solid fuel according to Item 13 . The shape of the solid fuel that has worn the actual combustion experiments, the solid fuel according to claim 2 or 3, characterized in that to compare the wear state and the shape of the solid sample is estimated by a method of the computational fluid dynamics Evaluation method.