| Explosion accidents occur occasionally in recent years because of abnormal gasemission, and this has become a serious problem in coal production industries inChina. The abnormal gas emission has great hazard and is difficult to control. Basedon the fluid mechanics principle, fan frequency control theory, PLC automatic controltechnology, monitoring and control technology, and computer software developmenttechnology, the automatic control theory and methods of the complex ventilationnetwork were studied by theoretic analysis, experiments and field confirmation. Thesemethods can effectively dilute the abnormal gas emission by frequency control way.Firstly, the influence of fan’s frequency variance and wind modulation on thebranches’ wind quantity was analyzed by the theory of ventilation network windquantity modulation theory and wind network resolution theory. Then, the sensitivedegree of the branches’ wind quantity to the fan’s frequency variation was describedand the sensitive branches were decided. By theoretic analysis and example proof, therelationship between the branch’s wind quantity (Qi) and the sensitive degree(Pi)wasgotten, i.e. the branches having the greatest wind quantity have higher sensitivitycharacteristic and it’s easier to modulate the wind quantity by frequency control, andvice versa. For the sensitive branches, the wind quantity changes obviously when thefan frequency is modulated.Secondly, by analyzing the influence factors of the abnormal gas emission andthe investigation data, the abnormal gas emission was classified into three kinds basedon the concentration change of the abnormal gas emission in the return airway windflow in the mining working face, which are rapid-increase and rapid-decrease mode,rapid-increase and slow-decrease mode, and fluctuation mode. By theoretic derivationand example analysis, the working face in coal mine which diffuses gas abnormallyusually is the sensitive ones. In order to control the abnormal gas emission at theworking face, two automatic wind modulation and diluting methods were put forward.The first wind modulation method is f-w follow-up control, which modulates the windaccording to f-w theory, i.e. according to the predicted quantity (w) of the abnormalgas emission of a certain branch during a predicting period, the needed windquantity (Q) of the branch was gotten during each predicting period by iterativecomputation, then the corresponding frequency f, was gotten according to theequation Q-f and the fan can be modulated dynamically and finally the transfinite gaswas diluted. The second one is curve lookup automatic method, which references the basic theory of the f-w follow-up control method. However, this method adopts thefan’s curve lookup method to replace the Q-f function equation direct calculationmethod to calculate the fan’s frequency, i.e. the fan’s characteristics curve satisfyingthe required wind quantity was found firstly by network resolution, then the fan’soptimal working frequency was determined according to the relationship between thefan’s characteristics curve and its frequency and lastly the wind was modulated todilute the transfinite gas with this frequency. The two wind modulation methods werecompared and we found that both methods have their own good points andshortcomings. However, these don’t affect their application.Thirdly, a ventilation network pipeline experimental model, a wind fan’sperformance testing platform and an automatic control platform of “abnormal gasemission-frequency control in wind-adjusting and gas-diluting” were set up in thelaboratory. The corresponding fan’s performance curve library was established withthe fan’s performance testing platform, which laid a good experimental basis for thecurve lookup automatic wind modulation method. For a safety consideration, the CO2was used to take place of CH4to simulate the three absolute gas emission modes inthe experiment. With the automatic control platform of “abnormal gas emission-frequency control in wind-adjusting and gas-diluting” and the pipeline experimentalmodel, the three absolute gas emission modes were simulated with CO2releasing flowby controlling valves and flow meters. The CO2is diluted with the f-w follow-upcontrol method and the curve lookup automatic wind modulation method. Theexperimental results showed that the fan’s frequency changes according to the f-wfollow-up control method and the curve lookup method strictly, all the CO2in threemolded is diluted efficiently and rapidly in a short time and the CO2concentration canbe controlled under a predetermined level.Lastly, the field experiments were done in the Tangshangou Coal Mine, whichlocated in Datong City, Shanxi Province. The corresponding wind quantity wasmeasured at three points when the fan runs at27Hz,29Hz,31Hz,33Hz and35Hz.The results verified the feasibility of wind modulation methods by frequency control.By comparative analysis, the validity of the sensitivity of the branch’s wind quantityto the fan’s frequency variation and the sensitive branch determination theory wereproved and the feasibility of the f-w follow-up control wind modulation method andthe curve lookup automatic wind modulation method were certified. The theory in thispaper provides a new pathway for preventing and controlling the abnormal gas emission in coal mine. |
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