Device and method for measuring porosity of coal pile

Abstract

The invention discloses a device and a method for measuring the porosity of a coal pile. The existing measuring method has the defects of complicated operation, unsuitability for field measurement or capability of only measuring the porosity in pores in coal. The invention includes; the air outlet end of the air pump is connected with the upper part of the barrel body through an air pipe, and the micro differential pressure transmitter is connected in the barrel body through a pipeline. The method is used for measuring the porosity of the coal pile.

Description

Technical Field

[0001] The invention belongs to the technical field of fuel energy saving and loss reduction in thermal power plants, and particularly relates to a device and a method for measuring the porosity of a coal pile. Background Art

[0002] At present, people realize that the occurrence and development of low-temperature oxidation of coal is an extremely complex, dynamically changing, and automatically accelerating physical and chemical process. Its essence is a slow automatic oxidation, heat release, and temperature rise process. So far, there is no complete theory to explain this complex and comprehensive phenomenon and its laws. Domestic and foreign scholars have never stopped the relevant research on the mechanism of low-temperature oxidation of coal, trying to have a comprehensive understanding of the entire development process of low-temperature oxidation of coal, and have made great efforts to apply the research on low-temperature oxidation of coal to actual production.

[0003] Abroad, Alazmi, B and Hooman, K believed that the influence of wind flow on coal piles changes from natural convection to mixed convection and then develops into forced convection. Therefore, the spontaneous combustion of coal piles must fully consider the changes in wind speed; Akguna F et al. established a two-dimensional non-steady-state calculation model for spontaneous heating and spontaneous combustion of coal piles, and fully studied the effects of coal pile height, stacking time, angle, particle size porosity, etc. on spontaneous heating and spontaneous combustion of coal piles. It is believed that when the porosity is 0.15-0.2, the self-heating temperature of the coal pile is slower due to reduced permeability; Ejlali conducted a study on the spontaneous combustion of coal piles under multiple wind speed conditions and believed that the air intake volume is a factor that affects the maximum temperature change of the coal pile more significantly; Ejlali et al. believed that porosity is a key parameter affecting the internal self-heating and spontaneous combustion of the coal pile and the maximum temperature change.

[0004] FIERRO V et al. proposed that if the porosity of the coal pile is close to 0.15 below the surface 1.5m deep, it will have a good protective effect on the coal pile. Generally, when the average porosity of the entire coal pile is lower than 0.2, the natural ignition period of the coal pile will be prolonged. If the porosity is controlled below 0.1, even if the highly active coal is piled, spontaneous combustion will not occur. However, since it is very difficult to compact the coal pile, it is difficult to effectively compact the periphery of the coal pile during the compaction process, and it is even more difficult to compact small-particle coal piles. At the same time, when the coal pile is compacted alone for protection, there is a possibility of accelerated spontaneous combustion at the junction of the compacted area and the non-compacted area. Therefore, FIERRO V recommends compacting the coal pile to 0.15-0.2 and then using other measures to protect the coal pile.

[0005] Coal is a porous medium with an extremely complex structure. The pore size in coal is uneven, ranging from less than 10nm to 100,000nm. There are many types of pores and complex morphology. Domestic and foreign scholars have mainly studied the pore structure characteristics of coal and the influence of pore structure on macroscopic properties such as strength characteristics, adsorption, and permeability. There are few research results on the changes in pore structure during coal spontaneous combustion. Therefore, in general, when conducting numerical simulations of coal spontaneous combustion, the parameters of the pore structure are mostly set to fixed values ​​or some empirical formulas are used. At present, there are two methods for determining porosity: traditional method, mercury injection method, and nitrogen adsorption method. Low-temperature oxidation of coal occurs more between coal particles, so the porosity between particles is the key to low-temperature oxidation of coal. Although the traditional method can measure the porosity between coal particles, the porosity is calculated by measuring the dry bulk density and true density of coal. The method is cumbersome and requires a large amount of chemical reagents, and cannot be measured on site; while the mercury injection method and nitrogen adsorption method measure the porosity in the capillary pores inside coal. The mercury injection method is a commonly used method for measuring coal porosity. Its principle is to use external pressure to inject mercury into the pores of coal. The amount of mercury injected into the coal sample is related to the size and distribution of the coal pores, and the pressure of mercury injection is related to the pore size in the coal body. The smaller the pore size in the coal body, the greater the required mercury injection pressure, and vice versa. The pore size range measured by the mercury injection method is very large, up to 3nm~120μm, but it is not suitable for the porosity measurement of large pores. The nitrogen adsorption method mainly measures pores with a pore size of less than 100nm.

[0006] Coal is a typical non-uniform porous medium. Its pore structure characteristics determine the adsorption and fluidity of gas in coal, so the pore structure of coal has a crucial influence on its spontaneous combustion characteristics. Changes in pore structure will lead to significant changes in porosity, permeability, permeability coefficient, and specific surface area. Determining the inter-particle porosity of coal is of great significance for preventing coal spontaneous combustion and environmental pollution. Existing measurement methods either have the disadvantages of being cumbersome to operate and not suitable for on-site measurement, or can only measure the porosity in the capillary pores inside coal. Summary of the invention

[0007] In order to overcome the defects of the prior art, a device and a method for measuring the porosity of a coal pile are provided, which are used to measure the porosity of coal in large coal piles in thermal power plants. The method is simple and easy, and can measure the porosity of coal of different types, different pile heights and different stacking states.

[0008] The above objectives are achieved through the following solutions:

[0009] A device for measuring the porosity of a coal pile comprises a cylinder, an air pump and a micro differential pressure transmitter. The air outlet of the air pump is connected to the upper part of the cylinder through an air pipe, and the cylinder is connected to the micro differential pressure transmitter through a pipeline.

[0010] The device for measuring the porosity of a coal pile, wherein the cylinder is a cylinder with a porous plate at the bottom.

[0011] A method for measuring the porosity of a coal pile, the method comprising the following steps:

[0012] Step 1: During the process of loading coal into the coal piles of different types, select multiple locations on the coal pile platform at a height of 2m to 4m, scrape off 0.1cm to 0.2cm of the top coal, dig a coal pit of a specified size of 0.5m×0.5m×0.5m, and collect all the coal in the pit;

[0013] Step 2: Fill the collected coal sample into a sample tube with a porous plate at the bottom;

[0014] Step 3: Measure the gas flow rate q through the flow meter V , and then make the gas pass through the sample tube filled with coal sample and flow out from the porous plate below the sample tube;

[0015] Step 4: Use a differential pressure transmitter to measure the pressure difference ΔP across the two sides of the sample;

[0016] Step 5: Calculate the porosity using the following formula

[0017] Step 6: Repeat steps 1 to 4 again on the coal pile platform at a height of 4m to 6m;

[0018] Step 7: Repeat steps 1 to 4 again on the coal pile platform at a height of 6m to 8m;

[0019] Step 8: Use the porosity data measured on coal pile platforms at three different heights as the horizontal axis and the coal pile height as the vertical axis to establish a curve chart of coal pile porosity and coal pile height. When used, the porosity between coal particles in the coal pile of corresponding height can be found from the curve chart.

[0020] Beneficial effects:

[0021] 1. The present invention is simple to measure, does not require the aid of complex instruments and equipment and a large amount of chemical reagents, and the measurement results are accurate, with no significant difference compared with the traditional method.

[0022] 2. The present invention can be applied on-site at the production site, which is suitable for on-site work needs. Traditional determination methods cannot be used for on-site determination, and samples can only be sent to the laboratory for further analysis after collection, which cannot meet the urgent needs on site.

[0023] 3. The patent of the present invention has a fast measuring speed and is suitable for coal piles of different coal varieties and different stacking forms. It is of great significance for preventing coal spontaneous combustion and environmental pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1It is a structural schematic diagram of the present invention;

[0025] Figure 2 is a flow chart of the present invention;

[0026] In the figure: 1. air pump; 2. flow meter; 3. air pipe; 4. cylinder; 5. micro differential pressure transmitter. DETAILED DESCRIPTION

[0027] A device for measuring the porosity of a coal pile comprises a cylinder 4, an air pump 1 and a micro differential pressure transmitter 5. The air outlet of the air pump is connected to the upper part of the cylinder through an air pipe 3, and the cylinder is connected to the micro differential pressure transmitter through a pipeline.

[0028] The device for measuring the porosity of a coal pile, wherein the cylinder is a cylinder with a porous plate at the bottom.

[0029] The method for measuring the porosity of a coal pile comprises the following steps: filling the collected coal sample into a sample tube with a porous plate at the bottom, using an air pump as an air source, and measuring the flow rate q of the gas from the air pump through a flow meter. V After entering the upper part of the sample tube, the sample flows out from the porous plate below. The differential pressure transmitter is used to measure the pressure difference ΔP on both sides of the sample. Then, according to the definition formula Calculate the porosity, where S and L are the cross-sectional areas of the sample (m 2 ) and height (m), μ is the dynamic viscosity of air (Pa.s).

[0030] Step 1: During the process of loading coal into the coal piles of different types, select multiple locations on the coal pile platform at a height of 2m to 4m, scrape off 0.1cm to 0.2cm of the top coal, dig a coal pit of a specified size of 0.5m×0.5m×0.5m, and collect all the coal in the pit;

[0031] Step 2: Fill the collected coal sample into a sample tube with a porous plate at the bottom;

[0032] Step 3: Measure the gas flow rate q through the flow meter V , and then make the gas pass through the sample tube filled with coal sample and flow out from the porous plate below the sample tube;

[0033] Step 4: Use a differential pressure transmitter to measure the pressure difference ΔP across the two sides of the sample;

[0034] Step 5: Calculate the porosity using the following formula

[0035] Step 6: Repeat steps 1 to 4 again on the coal pile platform at a height of 4m to 6m;

[0036] Step 7: Repeat steps 1 to 4 again on the coal pile platform at a height of 6m to 8m;

[0037] Step 8: Use the porosity data measured on coal pile platforms at three different heights as the horizontal axis and the coal pile height as the vertical axis to establish a curve chart of coal pile porosity and coal pile height. When used, the porosity between coal particles in the coal pile of corresponding height can be found from the curve chart.

[0038] The present invention has carried out a verification test, using the coal pile inter-particle porosity device of the present invention to measure the porosity of Indonesian coal, Shen mixed coal, and Huaneng high-quality mixed coal, and at the same time using the traditional method to measure the porosity. The comparison test results are shown in Table 1:

[0039] Table 1 Verification test results

[0040]

[0041] Coal-fired power plants store a large amount of coal. Different types of coal will be oxidized to a certain extent during the storage process, causing loss. When the temperature of the coal pile rises to a certain degree, it will also cause spontaneous combustion. The lower the coalification degree, the more easily it is oxidized. After being stored for half a year, the chemical loss of high-volatile gas coal and long flame coal is about 5%, and lignite even reaches more than 5%. By controlling the internal porosity of the coal pile and reducing the infiltration of air into the coal pile, the low-temperature oxidation and spontaneous combustion of coal can be effectively reduced. The present invention is a coal pile porosity measurement method, which is applied to the control of coal spontaneous combustion in coal-fired power plants. By accurately measuring the internal porosity of the coal pile, data is provided for adopting technical means to reduce the internal porosity of the coal pile, thereby greatly reducing the tendency of coal spontaneous combustion, reducing the calorific value loss, ash content increase, coal weathering, etc. caused by low-temperature oxidation of the coal pile, and reducing the sulfur dioxide content generated by low-temperature oxidation of coal, thereby reducing environmental pollution.

[0042] Compared with the traditional method, the porosity of the three types of coal measured by the patent of the present invention has high accuracy and can be directly measured on site with high measurement efficiency and fast measurement speed.

Claims

1. A device for measuring the porosity of a coal pile, characterized by: The invention comprises a cylinder, an air pump and a micro differential pressure transmitter. The air outlet of the air pump is connected to the upper part of the cylinder through an air pipe, and the cylinder is connected with the micro differential pressure transmitter through a pipeline.

2. The device for measuring the porosity of a coal pile according to claim 1, characterized in that: The cylinder is a cylinder with a porous plate at the bottom.

3. A method for measuring the porosity of a coal pile according to any one of claims 1 to 2, characterized in that: The method comprises the following steps: Step 1: During the process of loading coal into the coal piles of different types, select multiple locations on the coal pile platform at a height of 2m to 4m, scrape off 0.1cm to 0.2cm of the top coal, dig a coal pit of a specified size of 0.5m×0.5m×0.5m, and collect all the coal in the pit; Step 2: Fill the collected coal sample into a sample tube with a porous plate at the bottom; Step 3: Measure the gas flow rate q through the flow meter V , and then make the gas pass through the sample tube filled with coal sample and flow out from the porous plate below the sample tube; Step 4: Use a differential pressure transmitter to measure the pressure difference ΔP across the two sides of the sample; Step 5: Calculate the porosity using the following formula Step 6: Repeat steps 1 to 4 again on the coal pile platform at a height of 4m to 6m; Step 7: Repeat steps 1 to 4 again on the coal pile platform at a height of 6m to 8m; Step 8: Use the porosity data measured on coal pile platforms at three different heights as the horizontal axis and the coal pile height as the vertical axis to establish a curve chart of coal pile porosity and coal pile height. When used, the porosity between coal particles in the coal pile of corresponding height can be found from the curve chart.

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