Development And Characteristic Research On CMC/AlCit Gel Used In Mine Fire Preventing And Extinguishing

As a complex self-heating process,the spontaneous combustion of coal is one of major disasters existed in coal mines.At present,the techniques used to prevent coal spontaneous combustion around the world playing its own superiority.However,there are some deficiencies and it can't maximally satisfy the need to control coal spontaneous combustion.In recent years,the development and application of new materials,especially high-molecular polymer,are much faster than traditional materials.The gel prepared by the polymer combines holding water,plugging and cooling,which has be widely applied in many fields.Accordingly,this paper focuses on the development and characteristic of CMC/AlCit gel to prevente and extingusich coal mine fire,and the main results and conclusions are obtained and summarized as follows.(1)CMC/AlCit gel consists of polymer sodium carboxymethylcellulose(CMC),corss-linker Aluminum Citrate(AlCit)and glucono delata lactone(GDL)with pH modifier,and its three-dimensional net structure is formed by delay cross-linked reaction to meet the requirements of easy preparation,a controllable gelation time,long gel-life,relatively high thermostability etc..According to the gelation time,gelation effect,economic cost and the required of fire extinguishing in coal mine,the gel ratio used to plug and extinguish is 3%CMC+8%Al Cit+2%GDL which takes 2-3 minutes,while used to inhibit is 2.5%CMC+8%AlCit+1.5%GDL which takes about 10 minutes.Research indicated that saline water,initial pH and temperature have a significant impact on gelling time and effect.(2)Based on rheological test analysis,the whole gel process of CMC/AlCit crosslinking system can be divided into three periods: induction period(100-200s),acceleration period(200-1200s)and termination period.At the end the system will form a three-dimensional network through the coordination key formed by the reaction of-COO-of the CMC molecular chain and Al3+.The critical concentration of CMC and Al Cit is 2% and 5% respectively,and the addition of fly ash should be less than 30%.The rheological constitutive equation is 76.002.340.4 ?(10)(28)??(5)after 180 seconds,which belongs to the yield of pseudoplastic fluid.Its shear-thinning propertie is beneficial to transport in the pipeline and pile up in fire extinguishing area,which ensure the gel formation in designated time and place.The starting pressure is approximate 820 Pa which much higher than the air leakage pressure in the working face.Besides,the gel has good viscoelasticity and thixotropy,which can effectively block the goaf cracks and air leakage,and reduce the emission of toxic and harmful gases.As the result,the gel can be used to deal with the fire in the wall of roadway and top-caving area.(3)The self-made sealing performance device was used to determine the bearing capacity of gel under different coal loading height and CMC/Al Cit gelling ratio,the maximum pressure can be up to 8673 Pa,and has a strong compressive strength.The life time is prolonged 1.88-2.54 times than mornal water at 180?,so it has good water immobilization and thermostability.(4)The index gas of the coal treated with CMC/AlCit gel was reduced by 34.5% while the the crossing-point temperature and the apparent activation energy were increased 13.9? and 38% respectively compared with the original coal during the programmed heating process.The TG,DSC and FTIR tests have shown that the change of mass mitigated,the release of heat decreased,activation energy increased,and the aliphatic C-H functional group increased 20% while the C=O reduced 30% with the treated coal samples by CMC/AlCit gel.The laboratory studies indicate that CMC/AlCit gel has favorable inhibition performance by slowing the reaction speed,inhibiting the reaction process between coal and oxygen,and finally decreasing propensity of spontaneous combustion of coal,and is better than CaCl2.(5)The small and middle fire suppression tests have been conducted on simulated coal dump,seam roof and pillar.The experiments demonstrated that CMC/AlCit gel implements comprehensive fire-prevention by means of the following several aspects: blocking air-leakage,lowering oxygen levels,inerting surface activity,capturing more than 90% of water,mitigating of heatings and so on,and it has advantages of good security,economy,stability and lower cost and resurgence.(6)The preparation and operation schemes of CMC/Al Cit gel for fire prevention and extinghuing on the spot were established,which can be used in different spontaneous combustion hazard areas such as coal roof,pillar,goaf and hydraulic roof supports.Finally,CMC/AlCit gel was applicated in the Nanfeng colliery,and effectively control the fire.In a word,CMC/AlCit gel has a remarkable ability to prevent and extinguish coal mine fire,which provides a new technical means,and has a broad popularization and application prospects.