JPS6153655B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for measuring moisture in solid samples. More specifically, the present invention relates to a moisture measuring method that can automatically measure the moisture content of powder mixtures in a short period of time, which is directly linked to process control. Methods for measuring the moisture content of solid samples include the heating loss method and the heating moisture collection method as absolute methods, and the neutron absorption method as relative methods. The heating loss method and the neutron absorption method are often used to measure the moisture content of powder mixtures such as iron ore and coke on a factory scale. The heating loss method is adopted by JIS and other standards, and is a method that is generally used as an absolute method. In this method, the sample is crushed and reduced to 20 mm or less than 10 mm,
The moisture content is determined by drying with heat at 1 to 2 kg and measuring the loss on drying. However, in this method, it is necessary to dry in a state where fine powder etc. do not dissipate, usually in a stationary state, and it also has to be dried to a constant weight, so the measurement takes a long time, usually 4 to 6 hours. , and the data feedback is too slow when applied online. In addition, in order to minimize the sample amount (1 kg or more) in order to shorten the drying time, there are many pretreatment steps such as pulverization and reduction, which requires a lot of pretreatment equipment and increases the equipment cost for online automation. In addition, there is a drawback that the moisture value is lowered due to volatilization of moisture during pretreatment. In the neutron absorption method, a neutron beam is transmitted through a tank filled with a sample, and the moisture content is determined by measuring the attenuation rate, which corresponds to the absorption rate due to moisture. Calibration is performed using the heating loss method described above. In addition to this, there is a drawback that accuracy is significantly impaired due to differences in the fineness composition of the samples. The purpose of the present invention is to use a powder mixture as a sample without any pretreatment such as pulverization reduction, to measure moisture content in a short time with high accuracy, to automate the measurement, and to incorporate it into process control. The object of the present invention is to provide a moisture measurement method that allows rapid feedback. The moisture measurement method according to the present invention includes: (a) drying a sample of known weight (W) in a rotary dryer while supplying air whose moisture content and amount (V) have been measured; (b) drying the sample in the dryer; (c) Calculate the amount of condensed water, assuming that the measurement ends before the sample is completely dry. (d) Correction based on the set values of △A/△t and H The residual moisture content after measurement interruption is calculated using the coefficient (f).
In addition, the amount of condensed water from the incoming air is corrected by the capture coefficient (h), which is determined from the difference in humidity between the incoming air and the exhaust air from the cooler, and the moisture (M) is calculated using the formula: M = { (A + Wf - Vh/W}×100%.Hereinafter, the method of the present invention will be described in the following section.
This will be explained in detail based on the diagram. In FIG. 1, 3 is a rotary dryer. The rotary dryer 3 has a double structure, consisting of a fixed outer drum 32 and an inner drum 33 rotated by a drive source (not shown). After the sample of the powder mixture is collected, it is weighed by a weighing machine 1 without being crushed or reduced, and then fed into an inner drum 33 of a dryer 3 through a chute 2. The appropriate amount of sample to be measured at one time is 20 to 50 kg. Therefore, a sample collected for process control or for determining the moisture content of a lot can be directly subjected to measurement without being reduced. A hanging air blocking plate 37 is provided at the tip of the chute 2, and blocks air circulation except for allowing sample input. On the other hand, the moisture content of the drying air is measured by a hygrometer 8, and the air is sucked into the blower 4 (described later), enters between the outer drum 32 and the inner drum 33, is heated by the heater 31, and is heated by the air vent 35 into the inner drum. Enter within 33.
The sample is dried by heated air and the heated inner drum 33 while being agitated by rotation within the inner drum 33 . 34 is a sample spill prevention plate. The drying temperature naturally depends on the type of sample, but for coke, iron ore, etc., it is set at 105±5°C. The hot air containing evaporated moisture from the dryer 3 is accompanied by dust due to stirring of the sample, so it is passed through a filter 5 to remove this dust and then sucked by a blower 4. The connection between the tip of the suction pipe of the blower 4 and the inner drum 33 of the dryer 3 is slid into close contact with each other to prevent atmospheric air from being sucked in. Further, a moisture detection end is provided in the hot air path sucked into the proar 4 as shown in the figure, and the moisture in the hot air is measured by a moisture meter 8. The temperature of the hot air discharged from the blower 4 generally drops to about 80° C. due to heat radiation from the blower 4 and the like. This temperature drop is preferable because it reduces the load on the cooler 6 as long as the temperature does not drop below the dew point. The hot air from the blower 4 is then led to a cooler 6 where most of the moisture in the air is condensed. Cooler 6
The capacity of the cooler 6 is required to cool the hot air and condense most of the moisture contained in it, and in order to improve the accuracy of the moisture measurement value, the moisture value of the exhaust air from the cooler 6 must be equal to the humidity of the incoming air. It is desirable to cool to a cooling temperature that is approximately equal to or slightly less than the minute value. A fin-type cooler or the like is suitable for the cooler 6, and it is preferable that the inner wall etc. be hydrophobically treated with Teflon, beeswax, etc. in order to efficiently collect water condensed by cooling. The water condensed in the cooler 6 is led to the water meter 7,
Its weight is measured. A general example of the moisture content of the hot air drawn into the blower 4 and the cumulative amount of condensed water measured by the water meter 7 is shown in FIG. 2 as a graph. Moisture H (H ₂ OKg/Nm ³ of dry air) in the hot air immediately after the start of measurement is equal to the moisture in the atmosphere, and gradually increases as the sample dries, and the temperature of the hot air sucked into the blower 4 increases. When the temperature is 100°C or lower, the humidity passes through a constant moisture range close to saturation, and as the drying approaches the end, the humidity gradually decreases and returns to a value equal to the atmospheric humidity. On the other hand, since the cooler 6 generally cools the hot air to a temperature that is approximately equal to or lower than the dew point temperature of the atmosphere, the water is measured using the water meter 7 immediately after the start of measurement, while the water has not yet evaporated from the sample. The amount of water A is based on the amount of moisture in the atmosphere. As the sample dries, the cumulative amount of water A gradually increases, and when the drying period reaches the end, the cumulative rate decreases, and once the drying is finished, the rate of cumulative water content returns to the rate due only to the condensation of moisture in the atmosphere. The final change in the differential coefficient △A/△t (H ₂ OKg/min) of the amount of condensed water A with respect to time is expressed as the third
This is shown graphically in the figure. The time at which the moisture content H of the hot air shifts to the same value as the atmospheric humidity He in Figure 2, which indicates the completion of drying the sample, and the time at which △A/Δt shifts to the value αe based on the atmospheric humidity in Figure 3. theoretically match, and the amount of water in the sample can be calculated based on the amount A of condensed water up to this time. However, firstly, when the sample is almost dry, the amount of dust mixed in the hot air increases, and the filter 5 becomes clogged, causing the resistance of the filter 5 to become excessive, resulting in measurement problems, such as the need to correct the ventilation amount by increasing the resistance of the filter 5. etc. are required. Furthermore, although the moisture H in the hot air is very sensitive as an indicator of the dry state in the sample, it is not accurate enough to determine a low value, that is, the transition point He to atmospheric moisture. In addition, the differential coefficient △A/△t of the amount of condensed water with respect to time can be estimated from the general graph shown in Fig. 3, and the inflection point αe of the value of △A/△t can be grasped with high accuracy. It is difficult. Therefore, in the method of the present invention, moisture measurement is carried out at Hs just before the moisture value H of the hot air reaches the above-mentioned He.
and the differential coefficient of the amount of condensed water with respect to time (△
A/Δt) is aborted at a point αs just before reaching αe, and the amount of remaining moisture due to the abort of measurement, that is, the amount of moisture not collected as condensed water in the sample, is corrected by a correction coefficient (f). The time required to reach Hs and αs described above is theoretically the same time. That is, the correction coefficient (f) changes depending on how Hs and αs are set. Hs and αs
By keeping He and αe close to each other, the correction coefficient becomes a small value. Correction factor (f) is 0.01
Hs and αs are set to be less than (H ₂ OKg/Kg of sample), and the f value is calculated by conducting a moisture measurement test using the method of the present invention on a sample whose moisture value is known according to the JIS method or the like. As mentioned above, Hs and αs should theoretically be reached at the same time, but in reality they do not necessarily arrive at the same time due to errors and the like. In the method of the present invention,
The measurement ends when both Hs and αs become lower. That is, the set value of the humidity H of hot air
If only Hs is used, the end point determination accuracy is poor and the residual moisture varies widely. By using αs in combination, the determination accuracy can be improved. In addition, when performing only with αs, the error becomes large if the water content of the sample and the atmospheric humidity are low and ΔA/Δt is low overall. On the other hand, since the hot air is cooled to below the dew point temperature of the atmosphere in the cooler 6, the amount of condensed water A contains moisture from the atmosphere, so this is corrected. That is, the atmospheric moisture He (H ₂ OKg/dry air Nm ³ ) and the air moisture Hc (H ₂ OKg/Nm 3 ) discharged from the cooler 6.
The amount of air sucked and discharged by the difference h between the dry air Nm ³ )
(dry air Nm ³ ). Since the cooling temperature of the cooler 6 is fixed or measured, the moisture content Hc of the air discharged from the cooler 6 is calculated as the saturated moisture at this temperature. Since the amount of dry air passing through the measurement device is constant, the amount of dry air V can be calculated by correcting temperature, moisture, etc. from the wind speed at the blower, and by installing a flow meter in an appropriate part of the system. established,
It can be easily calculated to correct for temperature, humidity, and pressure. As described above, the method of the present invention measures the water content of a sample by heating and drying the sample to cool and condense the evaporated water and then measuring its weight. Furthermore, measuring the amount of condensed water until complete drying causes various problems and even reduces measurement accuracy, so the measurement is stopped slightly before complete drying and the residual moisture is corrected by appropriate means. Also, the amount of moisture entrained in the drying air and condensed together with the sample moisture is corrected. That is, the sample moisture value M according to the method of the present invention is calculated by the following formula. M={(A+Wf-Vh)/W}×100% Where, A: Amount of water measured with a water meter (Kg), W: Amount of sample (Kg), V: Amount of air used for drying (dry Nm ³ ), f: Correction coefficient for calculating residual moisture content (H ₂ O
Kg/Kg of sample), h: Coefficient based on the difference between atmospheric moisture and cooler exhaust air humidity (H ₂ OKg/Nm ³ of dry air). In the formula, Wf is a correction term for residual moisture content, and Vh is a correction term for atmospheric moisture. Of course, when the cooler exhaust air humidity is higher than the atmospheric humidity, the symbol - changes to +. Although the method of the present invention is carried out for each sample, it can be continuously and automatically measured for each sample lot using an automatic measurement control means as shown in FIG. In FIG. 1, 9 is a controller that determines the end point of drying and controls the operation of each device, and 10 is a computer. In many cases, the dryer 3 still remains preheated from the previous measurement. First, the dryer 3, heater 31, blower 4, and cooler 6 are operated. When the air flow in this device is in a steady state, the water meter 7 starts measuring the condensed water in the cooler 6, and the controller 9 and computer 10 start operating. A sample of 20 to 50 kg weighed by the weighing machine 1 is put into the dryer. Calculator 1 calculates h using cumulative water volume A and △A/△t of water meter 7, atmospheric temperature He and cooling air humidity Hc.
0 and sent to the controller 9. When the H and ΔA/Δt values reach the preset Hs and αs, the controller 9 stops the water meter 7 from measuring the water volume and turns off each device. Stop the system with a time lag and in an order that does not interfere with maintenance. The water volume measurement value A of the water meter 7 is sent to the computer 10, and based on the separately measured W and V values, the calculated h value, and the set f value,
The moisture value M (%) of the sample is calculated using the above formula.
The measured sample is discharged by a discharge means (not shown) and prepared for the next measurement. The specifications of an embodiment of the apparatus for carrying out the method of the present invention are as follows. (1) Sample input amount: 20-50Kg, maximum 50Kg (iron ore). (2) Air flow rate: 20 to 30Nm ³ /min, air speed inside the dryer approximately 1m/min. (3) Hot air temperature: 105±5℃ (4) End point judgment humidity: 0.03 to 0.04 (H ₂ OKg/dry air Nm ³ ) (5) End point judgment △A/△t (=αs): 0.2 [H ₂ O
Kg/min] or less. (6) Drying time: 20 minutes max. (7) Condensed water amount: Maximum 5Kg (8) Residual water amount correction coefficient (f): 0.01 [H ₂ OKg/
Sample Kg〕 or less (9) Correction coefficient based on moisture difference (h) 0.~0.003
[H ₂ OKg/Nm ³ of dry air] The following table shows the measured moisture values of the samples measured by the method of the present invention using the above-mentioned apparatus and compared with the measured moisture values by the JIS method.

[Table] The method of the present invention replaces the conventional method of measuring loss on drying with a heating moisture trapping method, making it possible to dry the sample while stirring, reducing the drying time to about 20 minutes and the overall measurement time. time is reduced to approximately 30 minutes. Since a large amount of sample is used as it is without pre-treatment such as reduction after collection, there is no moisture volatilization during pre-treatment, improving accuracy and reducing equipment costs in the case of automation. . In addition, the method of the present invention is suitable for measuring moisture in process pipes at steel plants, etc., and provides rapid feedback in measuring moisture in iron ore sizing processes, coal blending processes, blast furnace charge control processes, etc. Not only is this possible, but it can also be combined with a sampler to achieve unmanned operation.

[Brief explanation of the drawing]

Fig. 1 is a layout and signal system diagram of an embodiment of equipment for carrying out the method of the present invention, Fig. 2 is a graph of the moisture content of hot air sucked by a blower and accumulated moisture condensed, and Fig. 3 is a graph of condensed cumulative moisture. It is a graph which shows the chronological change of the signature coefficient with respect to the time of water quantity. In the drawings, 1...Weighing machine, 2...Chute, 3...Rotary dryer, 4...Blower, 5...
Filter, 6... Cooler, 7... Water meter, 8...
Moisture meter, 9...controller, 10...calculator.

Claims (1)

[Claims] 1. (a) drying a sample of known weight (W) in a rotary dryer while supplying air whose moisture content (He) and amount (V) have been measured; (b) drying the sample with a known weight (W); The hot air discharged from the machine is cooled by a cooler, the moisture contained in the hot air is condensed, and the weight (A) of the condensed water is measured. The time point is before drying, and the time point is when the differential coefficient of the amount of condensed water with respect to time (condensation rate ΔA/Δt) is less than or equal to αs, which is set as a value slightly larger than the condensation rate αe due to moisture in the atmosphere alone, and when the hot air is (d) The residual moisture content in the sample due to the discontinuation of the above measurement is corrected by the correction coefficient (f), (e) The condensed content from the blown air moisture included in the weight of condensed water (A) above is calculated as the difference between the blown air moisture (He) and the exhaust air moisture after cooling (Ho) (He - Ho).
(f) As a result, the moisture content (M) of the mineral powder mixture is determined by M = {(A + Wf - Vh) / W} x 100%. Moisture measurement method.