Study On Factors Affecting Of Contact Gas Alarm's Hysteresis

With the accelerated development and utilization of natural gas resources,clean and efficient natural gas has brought convenience to industrial production,but due to natural gas pipeline aging or man-made destruction,valve sealing material falling off and other reasons often cause natural gas leakage,a slight accident will cause an explosion,resulting in The occurrence of dangerous phenomena.Industrial gas alarm is a common safety device for detecting gas leakage.It can effectively send out early warning after gas leakage,thereby reducing the incidence of fire,explosion,poisoning and other vicious accidents caused by gas leakage.In order to detect gas in time In order to avoid greater damage due to leakage,industrial gas alarms have been installed in places prone to flammable gas leakage,such as underground pipeline corridor gas tanks,gas stations and chemical plants.The leaked gas diffuses into the interior of the alarm through the breathing hole of the contact gas alarm,and contacts the combustible gas sensing element inside the alarm to trigger the alarm.However,the external protective casing of the alarm will hinder the diffusion of gas,so the gas alarm itself has an alarm lag phenomenon.In addition,the hysteresis of the alarm is different when there are ventilation conditions,different degrees of clogging of the breathing holes,and different environmental temperatures and relative humidity.This article assumes that the outside of the alarm is covered with a certain concentration of natural gas,simulates the diffusion process of natural gas into the interior of the alarm,studies the alarm of the alarm,and studies the natural gas under the conditions of ventilation and different clogging of breathing holes,different temperatures and humidity The hysteresis of the alarm is proposed,and two methods of reducing the hysteresis of the alarm are proposed according to the simulation results.The results can provide a reference for the safe use of industrial gas alarms.In this paper,a mathematical model of natural gas diffusion into industrial gas alarms is established based on the mass conservation equation,momentum conservation equation,energy conservation equation,and composition equation.The finite volume method is used to combine the boundary conditions and initial conditions to discretely solve the control equations..Numerical simulation of the contact industrial gas alarm under normal conditions,the initial concentration of natural gas outside the alarm is 2%,3%,4%,5%,the natural gas concentration at the alarm sensor is 4.3s,2.1s,After 1.3s,the alarm concentration reaches 1%after 0.9s.When there is a wind of 1m / s in the horizontal direction,the hysteresis is very serious.When the natural gas concentration outside the alarm is 2%,it takes 43 s to alarm,and even when the natural gas concentration outside the alarm reaches the lower explosion limit,it still takes 11 s.Call the police.Clogged breathing holes,different temperatures,and different relative humidity also have a certain effect on the alarm hysteresis.Among them,the alarm time is linear with the overall change of temperature and relative humidity.The higher the temperature,the shorter the alarm time,and the lower the relative humidity,the shorter the alarm time.The effect of clogged breathing holes on the alarm time is that as the degree of blockage increases,the greater the increase in alarm time.Aiming at the problem of hysteresis in industrial alarms,this paper proposes two methods to reduce the hysteresis.First,a new type of alarm housing is designed,which is optimized from the natural gas diffusion process,and the alarms after using the new housing are simulated and tested.,The results show that: after using the new type of enclosure,the hysteresis of the alarm during ventilation can be significantly reduced.Compared with the use of a normal alarm enclosure,there is 1m / s wind in the horizontal direction,and 2% and 3%respectively outside the alarm.For 4% and 5% concentration natural gas,the alarm time is reduced by 34 s,19.5s,12.5s,and 9.1s respectively.Under normal circumstances,different degrees of clogging of the breathing holes,different ambient temperatures,and different relative humidity,the use of the new alarm housing can also effectively reduce the alarm time,but the effect is not as obvious as when there is ventilation.The second method to reduce the lag of the alarm is to use a sensor with a low induction level,which is optimized from the sensing end,and a sensor with an induction concentration of 0.8% is used for simulation.The results show that although the induction concentration is only reduced by 0.2%,it is in various situations The alarm time has been reduced by about 50%.For example,when there is 1m / s wind in the horizontal direction and the natural gas concentration outside the alarm is 2%,3%,4%,5%,the alarm time is 21 s,12s,7.6s,7.6s,5.5s,respectively 21 s,12s,7.4s,5.5s.Under normal circumstances,when the natural gas concentration outside the alarm is 2%,3%,4%,5%,the alarm time is 2.1s,1.1s,0.6s,0.4s,which is reduced by 2.2s,1s,0.7s,0.5s.Finally,this article provides reasonable suggestions for the design,use and daily maintenance of industrial gas alarms,which can make the design and use of alarms more scientific.