Research And Application On Mine Main Fan Ventilation Instability Control

As an important index of mine ventilation system safety and reliability, main fan is required to operate stably, with little fault, no surge and a reasonable working point. Therefore, effective control to prevent mine main fan from ventilation instability has great significance on the safety of ventilation system as well as mine.The concept of"main fan side ventilation system"as a whole including two main fans and air doors is introduced in the dissertation and its actual model is established through reconstruction of original ground air duct ventilation system. With ventilation equal theory, the model can be equivalent to a special displacement fan at the outlet of air shaft. Based on analysis of all key parameters which may influence its working point, a novel ideal to keep mine ventilation stability through preventing main fan from abnormal operation and controlling fan side of ventilation system stability at the same time is put forward. Compared with the shortage of conventional controlling single-fan for ventilation stability, the strategy of controlling main fan side ventilation system has higher reliability in achieving the stability of ventilation system.In the prevention of ventilation instability due to main fan running abnormally, based on the requirement analysis of main fan fault diagnosis for ventilation stability, main fan common faults are reclassified as"fatal fault and non-fatal fault"and their definitions are given. Then a novel method with the integration of Fault Tree Analysis (FTA.), Artificial Immune System (AIS.) and Artificial Neural Network (ANN.) for main fan fault early-warning and diagnosis is proposed, in which fault tree inference can identify fatal fault from non-fatal fault quickly. For the non-fatal fault, further fault classification and abnormal degree detection will be achieved by AIS and ANN. Based on Negative-Selection Algorithm, AIS fault diagnosis doesn't need field fault samples, therefore, difficulty on main fan fault diagnosis due to lack of fault samples is solved successfully. Then many immune detectors on behalf of all kinds of fault with different abnormal degree are generated randomly and selected with rules for the training of a BP ANN, which will be used to realize main fan multi-fault classification.On another side of ventilation instability due to main fan switchover, considering the uncertainty of whether main fan standby can start successfully, main fan warm-standby before switchover is proposed, in which the risk of main fan starting failure during main fan switchover originally can be avoided. Considering the root cause of gas concentration exceeding limit during main fan switchover in traditional way is lack of ventilation power, a novel strategy for main fan switchover is proposed to realize ventilation power supplying continually and reliably during the whole process of switchover. As axial flow fan has an unstable working area, and in order to prevent main fan working point from falling to surge area during switchover, the equivalent resistance at the inlet of main fan is calculated, and the limit for main fan safety operating during main fan switchover has been deduced.Considering the characteristics of main fan switchover aiming at ventilation unceasing, a kind of sequential control scheme is put forward for main fan automatic switchover. Based on numerical simulation of equivalent resistance and flow rate during main fan switchover with four air doors in uniform motion, the cooperating way and the optimal delay time in sequential control have been gotten. For certain extent ventilation instability still exists during main fan switchover with sequential control, a kind of control based on fuzzy control theory is put forward in the dissertation, in which, the limit of main fan safety operating during main fan switchover is treated as a restriction in fuzzy controller designing. In order to accomplish the main fan switchover operation, three of four air doors actuate in each scheduled way, and their resistance changes and corresponding flow rate fluctuation of two main fans in parallel are considered as disturbance, and the objective of ventilation stability is achieved through adjusting the rest one of four air doors. In order to check the validity of fuzzy controller, field data during main fan switchover are collected to train a BP ANN, which is used to replace real ventilation system in control system simulation. And the simulation indicates that fuzzy controller is well designed to realize the objective of ventilation stability during main fan switchover.Considering that main fan surge is not only an important reason for ventilation instability but also a serious threat to main fan security, with the requirement analysis of main fan surge ventilation instability control, a way for main fan surge forecast with the combination of either axial displacement exceeding limits or working point across surge limit line is given. Fatherly, a level-based surge eliminating strategy is put forward too, which can control the working point nearly under the surge alarm line while main fan surge occurs.Finally, with a scientific research project of Ping Coal Mine Group, the achievement in the dissertation has been applied into a main fan monitoring system in a high gas mine. Field operation shows that ventilation stability during main fan switchover has been realized, and gas concentration exceeding limits due to main fan ventilation instability has been eliminated. The data of flow rate and gas concentration proves the feasibility of main fan ventilation instability control.