JPH0571901B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for measuring the amount of water contained in a hydrated substance in a short time and with high accuracy by a drying method, and an apparatus therefor. Infrared moisture meters are popular as instruments that quickly and non-contact measure the moisture contained in solid samples, but this method uses a reflection method that uses near-infrared rays, so For some types of powder and granular materials, especially those that are black like coal and have various luster depending on the brand, the output value of the moisture meter and
There was a problem in that the relationship with the moisture value determined by the standard drying method specified by JIS differed greatly depending on the brand, making it virtually impossible to use this moisture meter. Therefore, in order to accurately measure the moisture content of a water-containing substance such as powdered coal, the best way is to heat-dry the sample, measure its weight before and after drying, and calculate the moisture value from the difference. It is certain. However, as detailed below, this method has the inherent drawback that the measured values will be inaccurate if the drying time is not long enough. The problem is that it cannot be adopted at all. Now, the first step is to measure moisture using this drying method.
To explain with a diagram, the samples are at points A, B, and C in the diagram.
As shown at point, point D, and point E, the sample is dried through a sample preheating period, a constant rate drying rate period, and a decreasing rate drying rate period. (The transition point C from the constant rate drying rate period to the decreasing rate drying rate period is the critical moisture content Hc.)
The end point of drying is theoretically E in the diagram, where the moisture content no longer changes even if drying continues.
point, that is, the point at which the equilibrium water content reaches He,
It takes a very long time to reach that point,
In reality, when setting the drying time to a certain value under constant external drying conditions, if the moisture content reaches H at a certain time θ when the drying progresses and enters the lapse rate drying rate period, then The difference e between the estimated Max moisture value H ₁ after drying for θ ₁ hour, Min moisture value H ₂ after drying for θ ₂ hours, and the above moisture value H,
Generally, the time θ is selected so that e' falls within an allowable range. However, in order to reduce the error, it is necessary to make the drying time θ sufficiently long, but this immediately means that the measurement time becomes longer, which is a problem especially when the sample moisture fluctuation range is wide. . Furthermore, setting the drying time θ requires a rigorous preliminary test, which is extremely complicated. In addition, since the moisture value is calculated based on the weight before and after drying, in the case of finely powdered samples, as the degree of dryness of the sample increases, the loss entrained in the exhaust gas cannot be ignored. In this case, a problem arises in that the error becomes large. The present invention was made for the purpose of providing a method for accurately measuring moisture in a short time while employing a drying method, and an apparatus for the same.
The gist of the present invention is as follows: 1. A method for measuring the moisture content of a sample by heating it in a dryer, in which the amount of moisture evaporated by the time when the sample reaches the critical moisture content due to heating is measured, and the measurement result is A method for measuring the moisture content of a hydrous substance, characterized in that the moisture content of the sample is determined based on the weight of the sample fed to a dryer and a predetermined limit moisture content. 2. Determine the point at which the critical moisture content of the sample is reached due to heating by determining whether the temperature of the sample increases, the rate of moisture evaporation from the sample decreases, the humidity of the exhaust gas decreases, or the temperature of the exhaust gas increases. , the moisture content of the sample is determined based on the measurement result, the weight of the sample supplied to the dryer, and a predetermined limit moisture content. Moisture measurement method. 3 A method of measuring the moisture content of a sample by heating it in a ventilated dryer, which measures the amount of moisture in the gas supplied to the dryer and the gas released by the time the sample reaches the critical moisture content due to heating. The moisture content according to 1 above, characterized in that the moisture content of the sample is determined by calculation based on the measurement results, the weight of the sample supplied to the dryer, and a predetermined limit moisture content. Measurement method. 4. The moisture measuring method as described in 3 above, characterized in that the amount of moisture in the supplied or discharged gas is determined by measuring the temperature, humidity, and flow rate of the gas. 5 A dryer 1 that heats a sample, a sample supply system 2 that is equipped with a sample measuring mechanism and supplies the weighed sample to the dryer 1, and a temperature, humidity and flow rate measuring mechanism that supplies gas for drying the sample to the dryer 1. a gas supply system 3 for supplying to the dryer 1; a gas exhaust system 4 for discharging gas containing water vapor evaporated from the sample from the dryer 1;
and a calculation device 5 that calculates the moisture content of the sample based on the moisture content in the supplied gas, the moisture content in the exhaust gas, the weight of the sample, and a predetermined limit moisture content.
A moisture measuring device for water-containing substances consisting of: It is in. That is, the present invention focuses on the fact that if the properties of the sample and the external drying conditions are the same, the value of the critical moisture content Hc and the shape of the drying curve in the lapse rate drying rate period are the same, and the critical moisture content Hc is By knowing the point reached by an increase in the temperature of the sample, a decrease in the rate of water evaporation from the sample, a decrease in the humidity of the exhaust gas, or an increase in the temperature of the exhaust gas, drying after that point is omitted, The moisture content of the test sample is estimated based on the amount of moisture evaporated from the sample up to that point, the weight of the sample fed to the dryer, and the predetermined critical moisture content Hc. In other words, as shown in Fig. 2, a curve showing the relationship between drying time and moisture content, and Figs. 3 and 4 showing the corresponding drying time-sample temperature curve, and moisture content-moisture evaporation rate curve, The transition point C from the constant rate drying rate period to the decreasing rate drying rate period in Figure 2, that is, the time when the critical moisture content Hc is reached, coincides with the time point when the sample temperature begins to rise in Figure 3.
In addition, since this coincides with the point at which the water evaporation rate begins to decrease in Figure 4, we know that the critical water content Hc has been reached due to an increase in the temperature of the sample or a decrease in the rate of water evaporation from the sample. be. Although not shown, it is also possible to know that the critical moisture content Hc has been reached by a decrease in the humidity of the exhaust gas or an increase in the temperature of the exhaust gas. Since the present invention has the above configuration,
According to the present invention, measurement errors are small even if the variation in sample moisture is large. There is no need to set the drying time, and the trouble of testing for setting is eliminated. For example, in the case of granular coal, the measurement time is 4~
The time can be shortened to about 9 minutes, making rapid measurement possible. Not only does it not be necessary to take into account errors due to loss entrained in the exhaust gas due to overdrying, but also the measurement of the weight of the sample after drying itself can be omitted, so measurement errors after drying can be eliminated. Even with substances such as granular coal, which have many differences between brands, there is no variation. This is an excellent effect. Therefore, the present invention can be said to be highly practical in industry. The sample in the present invention can be dried by various methods, but the most convenient method is the ventilation drying method, so the case where the ventilation drying method is adopted will be described below as an example. FIG. 5 is an explanatory diagram showing an example of the method and apparatus of the present invention. In FIG. 5, 1 is a dryer, 2 is a sample supply system, 3 is a gas supply system, 4 is a gas discharge system, 5 is a sample temperature measuring mechanism, 6 is a calculation device, and 7 is an output device. First, look at the flow of the sample. The sample sampled by the sampling device (sampling step 2)
a), its weight is measured with a scale (weighing step 2b), and then it is put into the dryer 1 (loading step 2).
c). The sample is then placed in the dryer 1 for the time required for moisture measurement, that is, until the sample reaches the critical moisture content Hc (until the temperature of the sample begins to rise, the rate of moisture evaporation from the sample decreases). contact with the drying gas for a period of time (until the humidity of the exhaust gas begins to decrease or the temperature of the exhaust gas begins to increase) and is then discarded. On the other hand, the flow of drying gas is as follows. A gas 3a whose temperature and humidity are kept constant is blown in a constant flow by a blowing mechanism 3b such as a fan. Normally, in order to speed up the drying speed, a method is used to raise the temperature of the gas using a heating mechanism 3c such as a heater. Control may be performed. In addition, in order to improve measurement accuracy, the gas flow rate, temperature, and humidity may be measured accurately by passing through the flow rate, temperature, and humidity measurement step 3e before entering the dryer 1. good. The following description is given for the case where this step 3e is provided. However, if the gas flow rate, temperature, and humidity are constant and there is no problem with accuracy, this measurement step 3e is unnecessary. The gas that enters the dryer 1 comes into contact with the sample and is discharged along with the moisture in the sample, so measure the flow rate, temperature, and humidity of this discharged gas (the flow rate, temperature, and humidity of the discharged gas). Measurement step 4a). Further, the temperature of the sample in the dryer 1 is continuously measured (sample temperature measuring mechanism 5), and the time when the sample temperature starts to rise is determined to be the time when the water content reaches the limit Hc. At this time, if it is difficult to directly measure the sample temperature, the temperature may be represented by, for example, the exhaust temperature. In addition, instead of measuring the sample temperature or exhaust temperature, a calculation device (not shown in FIG. 5) that measures the amount of water evaporation per unit time is used. ) may be calculated at appropriate intervals, and the point at which the water evaporation rate from the sample begins to decrease may be determined to be the point at which the critical water content Hc is reached.
In addition, if the conditions of the supply gas for drying are constant, the critical moisture content is the point at which the humidity of the exhaust gas begins to decrease.
It may be determined that this is the point when the condition becomes Hc. Then, when it is determined that the sample has reached the critical moisture content Hc as described above, the measurement of the flow rate, temperature, and humidity of the gas supplied to the dryer 1 and the measurement of the flow rate, temperature, and humidity of the exhaust gas are discontinued. Based on the difference in the cumulative amount of water vapor in the gas entering and exiting the dryer, which has been calculated by the arithmetic unit 6, the amount of moisture evaporated in the sample until the critical moisture content Hc is reached is calculated. Based on the amount of water evaporation until this critical moisture content Hc is reached and the critical moisture content Hc determined in advance under the drying conditions during actual measurement, the moisture content or water content of the sample is calculated by the calculation device using the following calculation formula. 6 and outputs the result to an output device 7 such as a printer or display device. The formula for calculating the water content in the sample is as follows. Calculation formula Let the sample weight before drying be W ₀ (Kg). This is the water content w (Kg) and the dry stock amount S (Kg)
Let the critical water content be Hc (KgH ₂ 0/Kg dry stock), and let the water content at this time be w' (Kg). When the amount of water evaporated until reaching the critical water content Hc is Q (Kg), the following equation holds true. w+S=W ₀ (i) w−Q=W′ (ii) w′／S=Hc (iii) From equations (i) and (ii), w′=w ₀ −S−Q (iv) Equation (iii) , (iv), W ₀ −w′/Hc−Q=w′ w′=(W ₀ −Q)/(1+1/Hc) (v) From equations (ii) and (v), w=Q+(W ₀ -Q)/(1+1/Hc) Therefore, the moisture value M (%) is M=100×{Q+(W ₀ -Q)/(1+1/Hc)}/
It can be obtained as W ₀ . Here, W ₀ is the amount measured by the measuring instrument,
Q is a quantity that can be ascertained by measuring the flow rate, temperature, and humidity before entering the dryer, and the flow rate, temperature, and humidity of exhaust gas, and Hc is a quantity that can be ascertained in advance by testing. Therefore, since W ₀ , Q, and Hc are known,
The moisture value M (%) is determined. The moisture measuring method and measuring device of the present invention can be applied to ceramic raw materials,
It can be applied to any water-containing substances, including steel and metal raw materials, chemical raw materials and products, rubber and fibers, food raw materials and products, and especially to powder and granular materials that cannot be measured with conventional infrared moisture meters. It is also useful in that it can also be applied. Next, the moisture content of various brands of granular coal as a raw material for coke for metallurgy is measured according to the present invention. *When measured according to the standard drying method specified in JISM8811-6. Show a comparison.

【table】

[Table] As shown in the above table, it can be seen that according to the present invention, moisture can be measured with almost the same accuracy as the measurement results using the JIS standard drying method, even though the measurement time is extremely short.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing a method for measuring moisture using a general drying method, Figure 2 is a curve showing the relationship between drying time and moisture content, and Figures 3 and 4 are diagrams showing the relationship between drying time and moisture content.
Drying time-sample temperature curve, moisture content-corresponding to the figure
FIG. 5 is an explanatory diagram showing a moisture evaporation rate curve, and FIG. 5 is an explanatory diagram showing an example of the method and apparatus of the present invention. A, B, C, D, E...Points on the curve,...Sample preheating period,...Constant rate drying rate period,...Loss rate drying rate period, H, _H1 , _H2 ...Moisture content, Hc…
...Limit water content, He...Equilibrium water content, θ, θ ₁ , θ ₂
... Time, 1 ... Dryer, 2 ... Sample supply system, 2
a...Sampling process, 2b...Measuring process, 2
c...Input step, 3...Gas supply system, 3a...Gas with constant temperature and humidity, 3b...Blower mechanism,
3c... Heating mechanism, 3d... Arrow, 3e... Measuring process of flow rate, temperature, and humidity, 4... Gas exhaust system,
4a... Measuring process of flow rate, temperature, and humidity of exhaust gas, 5... Sample temperature measurement mechanism, 6... Arithmetic device,
7...Output device.

Claims (1)

[Claims] 1. A method of measuring the moisture content of a sample by heating it in a dryer, in which the amount of moisture evaporated by the time the sample reaches the critical moisture content due to heating is measured, and the measurement result is measured. A method for measuring the moisture content of a hydrous substance, characterized in that the moisture content of the sample is determined based on the weight of the sample fed to a dryer and a predetermined limit moisture content. 2. Determine the point at which the critical moisture content of the sample is reached due to heating by determining whether the temperature of the sample increases, the rate of moisture evaporation from the sample decreases, the humidity of the exhaust gas decreases, or the temperature of the exhaust gas increases. , the amount of moisture evaporated up to that point is measured, and the moisture content of the sample is determined based on the measurement result, the weight of the sample fed to the dryer, and a predetermined limit moisture content. Moisture measurement method according to scope 1. 3 A method of measuring the moisture content of a sample by heating it in a ventilated dryer, which measures the amount of moisture in the gas supplied to the dryer and the gas released by the time the sample reaches the critical moisture content due to heating. The moisture content of the sample is determined by calculation based on the measurement results, the weight of the sample supplied to the dryer, and a predetermined limit moisture content. Moisture measurement method described in Section 1. 4. The moisture measuring method according to claim 3, wherein the moisture content in the supplied or discharged gas is determined by measuring the temperature, humidity, and flow rate of the gas. 5 A dryer 1 that heats a sample, a sample supply system 2 that is equipped with a sample measuring mechanism and supplies the weighed sample to the dryer 1, and a temperature, humidity and flow rate measuring mechanism that supplies gas for drying the sample to the dryer 1. 1, a gas exhaust system 4 equipped with a temperature, humidity and flow rate measuring mechanism, and exhausting gas containing water vapor evaporated from the sample from the dryer 1; A moisture measuring device for a water-containing substance, comprising a calculation device 5 that calculates the moisture content of a sample based on the amount of moisture in the gas, the weight of the sample, and a predetermined limit moisture content.