A method for determining the grindability coefficient of lignite based on grinding dynamics

Abstract

The invention discloses a method for determining the grindability coefficient of lignite based on grinding dynamics, comprising the following steps: 1) preparing and weighing several coal samples, each 50g±0.01g; 2) controlling the working speed of the Hastelloy grinder within the range of 20-120R, and grinding several coal samples within a specified time until the Hastelloy grinder automatically stops; 3) using a test sieve to screen the grinding product after grinding and recording the test data; 4) using the grinding dynamics formula to process the grinding test data for lignite, and obtaining the grindability coefficient K to characterize the grindability of lignite. The beneficial effects of the invention are as follows: using the Hastelloy grinder to carry out the grinding test, and obtaining the grindability coefficient k based on the grinding dynamics model as an indicator of the grinding difficulty of lignite, providing a reference for the efficient operation of the pulverizing system, and also broadening the applicable coal types of the Hastelloy measuring instrument.

Description

Technical Field

[0001] The invention relates to the technical field of coal grinding parameter determination, and in particular to a method for determining a grindability coefficient of lignite based on grinding dynamics. Background Art

[0002] In coal-fired power plants, in order to ensure full utilization of coal, coal must be ground into qualified coal powder. Before grinding, it is necessary to quantitatively evaluate the difficulty of coal grinding. At present, the commonly used index at home and abroad is the HGI measured by the Hadgrove method. The larger the HGI, the easier it is to crush the coal into powder, and the less energy consumption per unit, while the smaller the index is, the opposite is true. The HGI measured by the Hadgrove instrument in the experiment of bituminous coal, anthracite and other hard coals according to the Hadgrove method is highly referenceable, and the operation method is simple, highly repeatable and widely used. However, this method is not suitable for lignite. If the Hardgrove method is still used to characterize the difficulty of lignite grinding, it is likely to mislead the selection of coal mills. The VTI test instrument with better applicability to lignite is too bulky and inconvenient to operate. At present, there are still a large number of cases in China where the Hardgrove method is used to characterize the grindability of lignite, which is not conducive to the safe operation of coal mills. Existing research lacks a grindability index test method based on the Hadgrove measuring instrument that has good adaptability to lignite and is relatively simple and accurate to operate. Summary of the invention

[0003] The purpose of the present invention is to solve the shortcoming that the Hardgrove grindability index tester is only applicable to the grindability index test of bituminous coal and anthracite, broaden the range of coal types suitable for the grindability test of the Hardgrove grinding instrument, and propose a method for measuring the grindability coefficient of lignite based on grinding dynamics.

[0004] The technical solution of the present invention is as follows:

[0005] A method for determining the grindability coefficient of lignite based on grinding dynamics comprises the following steps:

[0006] 1) Prepare and weigh several coal samples, each 50g±0.01g;

[0007] 2) Control the working speed of the Hastelloy grinder within the range of 20-120R, and grind several coal samples within the specified time until the Hastelloy grinder automatically stops;

[0008] 3) After grinding, the ground product is sieved using a test sieve and the test data is recorded;

[0009] 4) The grinding dynamics formula is used to process the grinding test data of lignite, and the grindability coefficient K is obtained to characterize the grindability of lignite.

[0010] Furthermore, the specific process of step 1) is as follows:

[0011] 1.1) The lignite is crushed into 0.63-1.25 mm as required. The total weight of coal particles in this size range is not less than 400 g. The prepared 0.63-1.25 mm coal samples are air-dried according to the prescribed air method. After reaching the air-dried state, they are screened again to ensure that the coal sample particle size range is 0.63-1.25 mm.

[0012] 1.2) The prepared sample is evenly divided into 6 parts, and the particle size of each coal sample is kept uniform.

[0013] Furthermore, in the step 2), the working speed of the Hastelloy grinder is 20R, 40R, 60R, 80R, 100R, and 120R, 6 groups are used for grinding, and the grinding test time is 1 to 6 minutes with a step length of 1 minute.

[0014] Further, the step 3) is specifically as follows:

[0015] 3.1) The ground coal sample is placed on a test sieve stacked in the order of large sieve holes on the top and small sieve holes on the bottom, and then put into a vibrating sieve machine for vibrating; while ensuring that the vibrating sieve machine can operate safely and stably, two groups of ground products can be vibrated and sieved at the same time to improve work efficiency;

[0016] 3.2) The vibrating screening process is divided into three stages, with the duration of 10 minutes, 5 minutes and 5 minutes respectively. The screen bottom is brushed once after each vibrating screening stage to prevent the screen holes from being blocked and to prevent the coal sample on the screen from leaking out of the gap of the screen cover;

[0017] 3.3) Weigh the total mass of the coal sample after vibration screening. The error should not exceed ±0.5g, otherwise it will be discarded and redone. Record the mass of the coal sample in each particle size range.

[0018] Furthermore, the grinding kinetics formula in step 4) is as follows:

[0019]

[0020] Where R——mass of coarse particles after t time / g

[0021] R0——The original content of coarse particles in the material to be ground R0 / g

[0022] t——grinding time / min

[0023] k——Proportional coefficient (easy wear coefficient)

[0024] m——depends on the uniformity of the material and the particle size of the steel balls

[0025] exist The intercept and slope in the formula are obtained by linear fitting in the coordinate system, and the k value can be calculated and recorded as the grindability coefficient.

[0026] Furthermore, the grindability coefficient K in step 4) is linearly fitted with the HGI obtained from the Hastelloy grindability standard material to obtain a conversion formula, and the HGI of the lignite is inferred from the k value of the lignite obtained by measurement.

[0027] The beneficial effects of the present invention are as follows: a grinding test is carried out using a Hastelloy grinder, and the grindability coefficient k is obtained based on a grinding kinetics model as an indicator of the difficulty of grinding lignite, providing a reference for the efficient operation of a pulverizing system, while also broadening the types of coal applicable to the Hastelloy measuring instrument. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a flow chart of the grindability index k determination test of the present invention;

[0029] Figure 2 This is a fitting data diagram of the wear coefficient k determination test of the present invention. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with the accompanying drawings.

[0031] A method for determining the grindability index of lignite based on grinding dynamics. The instruments required mainly include a constant temperature drying oven, a Haugh index tester with adjustable rotation speed, a vibrating screen, and a test sieve with a 180-mesh diameter of 200 mm and a sieve cover and a sieve bottom plate that meets the requirements of GB / T6003.1. In the process of determining the grindability index of lignite using this method, the ground product is sieved using a vibrating screen to obtain the mass of coal samples above the 180-mesh sieve. According to the grinding dynamics formula, The intercept and slope in the grinding dynamics formula obtained by linear fitting in the coordinate system can be calculated to obtain the k value, which is recorded as the grindability coefficient. k can be directly used as the grindability index of coal. It is also possible to use multiple groups of bituminous coal, anthracite or coal Hardgrove grindability standard substances to obtain the conversion relationship between HGI and k, and infer the HGI of lignite from the measured k value of lignite.

[0032] The specific steps are as follows:

[0033] 1) The lignite is crushed to a certain size of 0.63mm~1.25mm according to GB / T2565-2014. The total weight of coal particles in this size range is not less than 400g. The prepared 0.63mm~1.25mm coal samples are air-dried according to the air method specified in GB474. After reaching the air-dried state, they are screened again to ensure that the coal sample particle size range is 0.63mm~1.25mm.

[0034] Table 1 Grindability index k determination test example Coal industry and element analysis

[0035]

[0036] 2) The prepared sample is evenly divided into 6 portions, each portion is 50g±0.01g, and the particle size of each coal sample is uniform.

[0037] 3) Adjust the working speed (error ±0.25r) of the Hastelloy index tester to 20R (1min), 40R (2min), 60R (3min), 80R (4min), 100R (5min), and 120R (6min), respectively, weigh 50g±0.01g of the coal sample to be tested for grinding test, and make sure that the working speed has been set before starting the Hastelloy grinding tester. The setting of different speeds will have a very low effect on the goodness of fit of the grinding kinetics equation of the grinding process. Experiments have found that 20-120R can not only more completely reflect the changes in the grinding products at different grinding input energies, but also this range has a high goodness of fit for the grinding kinetics model. The grinding test duration is 1 to 6 minutes, with a step length of 1 minute. Considering that the grinding kinetics equation has good adaptability in the range of 5% to 100% of the coarse extreme residue, it is not advisable to set too long a grinding time.

[0038] Table 2 Example (No. 1 coal) Grinding coefficient k test data record table

[0039]

[0040] 4) The ground coal sample is placed on a test sieve with the sieve holes stacked in order of larger mesh size on the top and smaller mesh size on the bottom, and is put into a vibrating screen for vibrating; while ensuring that the vibrating screen can operate safely and stably, two groups of ground products can be vibrated at the same time to improve work efficiency.

[0041] 5) The vibration screening process is divided into three stages, with the vibration screening time being 10 minutes, 5 minutes, and 5 minutes respectively (when the grinding test time is 5 or 6 minutes, the vibration screening time can be appropriately extended by 2-3 minutes). After each vibration screening stage, brush the bottom of the sieve once to prevent the sieve holes from being blocked and to prevent the coal sample on the sieve from leaking out of the gap in the sieve cover.

[0042] 6) Weigh the total mass of the coal sample after vibration screening. The error should not exceed ±0.5g, otherwise it will be discarded and redone. Record the mass of the coal sample in each particle size range.

[0043] 7) The 6 groups of data recorded in the grinding test were processed according to the grinding dynamics formula, and the total weight of each group of 180 mesh sieve was taken as the mass of the coarse particle after grinding time t, R0 = 50g. The grinding kinetics formula is linearly fitted in the coordinate system (using origin software), and its correlation coefficient should not be less than 0.95. The slope and intercept of the fitting curve are recorded, and the k value in the grinding kinetics formula is obtained through calculation.

[0044] The grinding dynamics formula is:

[0045]

[0046] Where R——mass of coarse particles after t time / g;

[0047] R0——The original content of coarse particles in the material to be ground R0 / g;

[0048] t——grinding time / min;

[0049] k——proportional coefficient (wear coefficient);

[0050] m——depends on the uniformity of the material and the particle size of the steel balls;

[0051] Table 3 Grindability index k determination test data processing

[0052]

[0053] Table 4 Grindability index k fitting data table

[0054]

[0055] 8) The grinding test method mentioned above can be used to obtain the grindability coefficient k of the lignite to be tested using grinding dynamics. The larger the k value, the easier it is to crush the coal into powder and the less energy consumption per unit, while the smaller the index, the opposite is true.

[0056] 9) In order to facilitate the comparison of the coal grindability evaluation index measured in this method with the HGI measured by the Hardgrove method commonly used at home and abroad, a variety of bituminous coals and anthracites can be used to measure the HGI of coal and perform the above-mentioned grinding test on them to obtain the corresponding k value, and linearly fit k and the corresponding HGI to obtain the conversion relationship between the two.

[0057] When using a variety of anthracites or bituminous coals to calibrate the linear relationship between the parameter k and HGI in the grinding dynamics, a variety of particle size sieves can be used for screening. This is conducive to the flexible selection of the R value in the grinding dynamics formula when fine powder adhesion occurs during the grinding process of the coal sample to be tested. The selection of R should be lower than the lower limit of the feed particle size, otherwise the fitting correlation will be relatively low. For example, when the feed coal particle size is 0.63-1.25 mm, the selection of the particle size R of the coarse particles to be ground should not exceed 0.63 mm.

Claims

1. A method for determining the grindability coefficient of lignite based on grinding dynamics, characterized in that: The steps include: 1) Prepare and weigh several coal samples, each 50g±0.01g; 2) Control the working speed of the Hastelloy grinder within the range of 20-120R, and grind several coal samples within the specified time until the Hastelloy grinder automatically stops; In the step 2), the working speed of the Hastelloy grinder is 20R, 40R, 60R, 80R, 100R, and 120R, with a total of 6 groups of rotations for grinding, and the grinding test duration is 1 to 6 minutes, with a step length of 1 minute; 3) After grinding, the ground product is sieved using a test sieve and the test data is recorded; 4) The grinding test data of lignite was processed by using the grinding dynamics formula to obtain the grindability coefficient K to characterize the grindability of lignite; The grinding kinetics formula in step 4) is as follows: Where R——mass of coarse particles after t time / g R0——The original content of coarse particles in the material to be ground R0 / g (take 50g) t——grinding time / min k——Proportional coefficient (easy wear coefficient) m——depends on the uniformity of the material and the particle size of the steel balls exist The intercept and slope in the formula are obtained by linear fitting in the coordinate system, and the k value can be calculated and recorded as the grindability coefficient; The grindability coefficient K in step 4) is linearly fitted with the Hardgrove grindability index HGI obtained from the Hardgrove grindability standard material to obtain a conversion formula, and the Hardgrove grindability index HGI of the lignite is inferred from the measured k value of the lignite.

2. The method for determining the grindability coefficient of lignite based on grinding dynamics according to claim 1, characterized in that: The specific process of step 1) is as follows: 1.1) The lignite is crushed into 0.63-1.25 mm according to the requirements. The total weight of the coal particles in this size range is not less than 400 g. The prepared 0.63-1.25 mm coal samples are air-dried according to the specified air method. After reaching the air-dried state, they are screened again to ensure that the coal sample particle size range is 0.63-1.25 mm; 1.2) The prepared sample is evenly divided into 6 parts, and the particle size of each coal sample is kept uniform.

3. The method for determining the grindability coefficient of lignite based on grinding dynamics according to claim 1, characterized in that: The step 3) is as follows: 3.1) The ground coal sample is placed on a test sieve stacked in the order of large sieve holes on the top and small sieve holes on the bottom, and then put into a vibrating sieve machine for vibrating; while ensuring that the vibrating sieve machine can operate safely and stably, two groups of ground products can be vibrated and sieved at the same time to improve work efficiency; 3.2) The vibrating screening process is divided into three stages, with the duration of 10 minutes, 5 minutes and 5 minutes respectively. The screen bottom is brushed once after each vibrating screening stage to prevent the screen holes from being blocked and to prevent the coal sample on the screen from leaking out of the gap of the screen cover; 3.3) Weigh the total mass of the coal sample after vibration screening. The error should not exceed ±0.5g, otherwise it will be discarded and redone. Record the mass of the coal sample in each particle size range.

Images