Optimization of the active component grinding process and hydrophobization of the obtained powder fire extinguisher

Abstract

This work presents a grinding process of monoammonium phosphate (MAP) as an active component in a powder fire extinguisher (PFE). The aim was to determine the grinding time for reaching the optimal particle size of MAP necessary for permanent fire extinguishing. MAP grinding was performed by using a laboratory ceramic ball mill and a vibrating cup mill. The grinding process was controlled by sieving using a 100 µm sieve at precisely defined time intervals. The efficiency of a PFE depends on the share of the -100 µm fraction of the active component, which has to exceed 60 %. The optimal grain size with 64 % of fraction of particle size -100 µm was obtained after 33 min of grinding of ≈3000 µm mm grain size MAP by using a ball mill (single-stage grinding). In two-stage process, by grinding the same initial MAP sample (≈3000 µm) in the vibro mill for 10 min, powder with the upper limit grain size of 300 µm and the mean grain diameter of 120 µm was obtained. This sample with a reduced size was further ground in the ceramic ball mill yielding 67.5 % of the fraction of particle size -100 µm after 19 min. The total time of the two-stage grinding process was 29 min. By analyzing the grinding time of MAP required to get the lowest required share of the fraction of particle size -100 µm that provides the effectiveness of formed PFE it can be concluded that 64 % of this fraction was obtained after 33 min of single-stage grinding, while only after 26 min in the two-stage process. Thus, the grinding time was reduced by 7 min indicating certain energy savings. Stability and hydrophobicity of the obtained PFE were achieved by coating with magnesium stearate (MgSt) at the content of 2 % in a ball mill for 15 min. The coating was confirmed by the standardized procedure for verification of PFE hydrophobic properties in contact with water drops. To obtained PFE had component mass ratios of MAP:AS:CC:QS:MgSt=55:20:18:5:2 (AS-ammonium sulfate; CC-calcium carbonate, QS-quartz sand) and was further characterized by chemical and granulometric analyses. The fire extinguishing efficiency of the PFE was tested in controlled conditions, whereby fires were initiated by burning solid materials and flammable liquids. In both cases, immediate elimination of flames was achieved, thus proving the efficiency of the PFE obtained in this work for practical applications.

U radu je prikazan postupak mlevenja monoamonijum fosfata (MAP) kao aktivne komponente u praškastom sredstvu za gašenje požara (SGP). Cilj je bio da se utvrdi vreme mlevenja MAP koje je potrebno za dobijanje optimalne granulacije za potpuno gašenje požara i eliminisanje plamena. MAP je mleven u laboratorijskom keramičkom mlinu sa kuglama i vibro mlinu sa prstenastim radnim elementima. Proces je kontrolisan prosejavanjem na situ 100 μm. Utvrđeno je da se mlevenjem granula MAP veličine ≈3000 μm u laboratorijskom mlinu sa kuglama optimalna krupnoća od 64 % frakcije čestica veličine -100 μm dobija nakon 33 min mlevenja. Za postizanje iste finoće proizvoda u dvostepenom mlevenju vreme je skraćeno na 26 min (10 min u vibro mlinu i 16 min u mlinu sa kuglama). Stabilnost i hidrofobnost SGP je postignuta oblaganjem magnezijum stearatom (MgSt) pri udelu od 2 % u mlinu sa kuglama u trajanju od 15 min. Efikasnost gašenja je testirana na poligonu u realnim uslovima. Na tačno određenom mestu za testiranje, u kontro-lisanim uslovima, izazvan je požar paljenjem čvrstih materijala i zapaljivih tečnosti. U oba slučaja je došlo do trenutne eliminacije plamena. Na taj način je potvrđena efikasnost formiranog SGP i mogućnost njegove upotrebe u praksi.