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1. How to install the orifice flowmeter during coal mine gas extraction?
Installation pipeline conditions: (1) The straight pipe section before and after the throttling element must be straight and there must be no visible bending. (2) The straight pipe section used for installing throttling components should be smooth. If it is not smooth, the flow coefficient should be multiplied by roughness to correct sparsity. (3) To ensure that the fluid flow forms a fully developed turbulent velocity distribution in front of the throttling element 1D, and to make this distribution uniformly axisymmetric, the straight pipe section must be circular, and the roundness requirements for the 2D range in front of the throttling element are very strict, with a certain roundness index. Specific measurement method: (A) On the OD, D/2, D, and 2D four vertical pipe sections in front of the throttling element, at least four single inner diameter measurements of the pipeline should be taken at equal distances from the Orange Mountain angle, and the average value D should be taken. The difference between any single inner diameter measurement value and the average value should not exceed ± 0.3%. (B) After the throttling element, eight single inner diameter measurements should be measured at the OD and 2D positions using the above method, and the maximum deviation between any single measurement value and D should not exceed ± 2%. (2) A sufficiently long straight pipe section is required before and after the throttling element, which is related to the form of the local resistance element in front of the throttling element and the diameter ratio β.
(4) The length of the straight pipe section between the first and second resistance
(5) When the upstream side of the throttling element is an open space or a large container with a diameter ≥ 2D, the length of the straight pipe between the open space or large container and the throttling element shall not be less than 30D (15D).
. If there are other local resistance components between the throttling element and the open space or large container, in addition to the minimum straight pipe length 1 specified for attachment between the throttling element and the local resistance component, the total length of the straight pipe section from the open space to the throttling element shall not be less than 30D (15D).2. Calculation formula for drilling and drainage gas volume
The calculation of drilling and drainage gas volume in coal mines mainly uses the formula of multiplying gas flow rate and gas concentration. The specific calculation method and key parameters are as follows
1. Core calculation formula: The basic calculation formula for drilling and drainage gas volume (Q ₘ) is: Q ₘ=Q × C × k, where: • Q: the mixed gas flow rate in the drilling pipeline (unit: m ³/min), which needs to be measured by the flow meter • C: the volume concentration of gas in the pipeline (unit:%), which needs to be measured by the gas sensor • k: the unit conversion factor (usually) Take 0.01 to convert percentage concentration to decimal form Key parameter acquisition method
(1) Gas flow rate (Q) measurement - using specialized equipment such as orifice flow meters, vortex street flow meters, or pitot tubes -