and Hydrocarbons Stefan Schälike Axel Schönbucher

Transcription

1 Multiple Fires o Organic Peroxides and Hydrocarbons Stean Schälike Klaus-Dieter Wehrstedt Axel Schönbucher BAM Federal Institute or Materials Research and Testing Department 2 Chemical Saety Engineering Division 2.2 Reactive Substances and Systems Berlin The views expressed in this paper are those o the authors and should not necessarily be taken to be those o BAM. Stean Schälike Multiple Fires 1 Mass burning rates o peroxide pool ires Mass burning rates o multiple peroxide and HC pool ires Flame heights o multiple peroxide and HC pool ires Thermal radiation o peroxide pool ires Conclusions Stean Schälike Multiple Fires 2

2 Mass burning rates according to Hottel (1959): Q ba,tot m A P ( hv cp,v T,bp cp, T,a ) [kg/(m² s)] mass burning rate m Q Aba,tot A P h v c p,v [kw] total [m²] pool surace area [kj/kg] enthalpy o vaporization [kj/(kg K)] heat capacity o uel vapor c p, [kj/(kg K)] heat capcity o the liquid uel T [K] boiling temperature n-pentane, d = 25 m,bp 006k /( ² ) [K] ambient temperature T,a m 0.06 kg/(m² s) Stean Schälike Multiple Fires 3 Model or the mass burning rate o HC pool ires according to Burgess und Hertzberg (1962): h m h v c 3 10 kg/(m²s) h h v c rad h c [kj/kg] enthalpy o combustion S c kg/(m²s) F, 4 rad F, u F 0.5 F F, 0.4 F, F 0.5 : Fraction o heat : View actor between radiated lame and pool S 0.06m/s : Emissivity ratio : Limit burning velocity or natural u convection c UEL 31kg/m³ 3.1kg/m 0.031= =0 096kg/m³ : Maximum uel concentration or v lame propagation Stean Schälike Multiple Fires 4

3 Di-tert-butyl peroxide, (DTBP), d = 3.4 m m 0.30kg/(m²s) Tert-butyl peroxybenzoate (TBPB), d = 3.4 m m 0.37kg/(m²s) Tert-butyl peroxy-2-ethyl hexanoate (TBPEH), d = 34m 3.4 m 0.53kg/(m²s) Stean Schälike Multiple Fires 5 Microcalorimetric measurements or DTBP, TBPB show a 1st order kinetic: Tonset 365K, TSADT 358K, TSADT 338K DTBP (aliphatic) TBPB (aromatic) Reason: Aromatic compounds show a lower heat capacity and consequently Liquid phase decomposition during the burning (reaction time t r 5 10 s) has to be taken into account. Thermocouple measurements at dierent heights o the liquid (let side o the arrows) und gas phase (right side o the arrows) o a DTBP pool ire (d = 0.06 m) Stean Schälike Multiple Fires 6

4 An additional heat rate due to liquid phase decomposition Q taken into the energy balacnce: Q Q m d ba,tot A ( P h v c T p,v,b c T ) p,,a d has to be Q d Um h A P( h d) d [kj/kg] heat o decomposition Q U [ ] conversion Q d can be modeled as an ideal, isotherme, continuously stired tank reactor (CSTR): Da k(t) t r k(t) Da [ ] irst order Damköhler number [s] space time k [s -1 ] reaction rate constant k s -1 Stean Schälike Multiple Fires 7 Da U Da Heat rates in peroxide pool ires d = 3. 4 m DTBP TBPB Q [kw] d Q [kw] ba,rad Q [ ] d / Q ba,rad Q d /AP [kw/m²] Q ba,rad,p / Q ba,rad,hc [ ] The observed higher mass burning rates o peroxide pool ires can be explained by the additional heat rate due to liquid phase decomposition Q. Q d Stean Schälike Multiple Fires 8

5 Model or the mass burning rates o peroxide pool ires based on energy balance according to Burgess und Hertzberg: m,th ( h ) 1 Q /A Suc h c T c T c d P v p,v b,b p,,a m 030kg/(m²s) 0.30kg,exp m 0.31kg / (m²s),th DTBP m,exp 0.37kg /(m²s) m,th 0.39kg /(m²s) TBPB Stean Schälike Multiple Fires 9 Simpliied model: m,th 1.1 ( h c) Using linear regression or against the tabulated T onset Malow (2005): Q / A 1.27 T K d P onset according to Wehrstedt und Calculating using the particular decomposition products and heats o vaporization shows an average value o: kg / (m²s) hv cp,vt,b cp,t,a 220 kj/kg aromatic compound h c T c T 250 kj/kg aliphatic compound v p,v,b p,,a Stean Schälike Multiple Fires 10

6 Example TBPEH: Tonset 334 K, Q /A K kw/m² d P kg / (m² s) h c kj/kg hvcp,vt,b cp,t,a 250 kj/kg kw/m² kg/(m²s) 34455kJ/kg m,th 0.55kg/(m²s) 250 kj/kg m exp,exp 0.53kg/(m² g( s) Stean Schälike Multiple Fires 11 Example or a multiple DTBP pool ire with N = 16 Stean Schälike Multiple Fires 12

7 Mass burning rates o a multiple DTBP pool ire with N = 5 The mass burning rates m are up to 1.4 times higher in comparison to single ires. m (D/d 0),int äq,mi Only a small deviation o the mass burning rates between the inner and outer pools: m /m 1.05,mi,ra A maximum at D/d äq 0.4 is observed. The mass burning rates are inluenced until a distance o D/d äq Stean Schälike Multiple Fires 13 Mass burning rate o a multiple n-heptane pool ire with N = 5 The mass burning rates m are up to 1.8 times higher in comparison to single ires. m (D/d 0),int äq,mi Only a small deviation o the mass burning rates between the inner and outer pools: m /m 1.8,mi,ra A maximum at D/d äq 0.12 is observed. The mass burning rates are inluenced until a distance o D/d äq Stean Schälike Multiple Fires 14

8 Flame heights o a multiple DTBP pool ire with N = 5 Single pool ires d = d äq have higher maximum and averaged lame heights in comparison to multiple ires. For large D/d äq a constant lame height o a single pool ire with a diameter o d s is observed. Stean Schälike Multiple Fires 15 Flame heights o a multiple n-heptane pool ire with N = 5 D/d äq A single pool ires d = d äq have higher maximum and averaged lame heights in comparison to multiple ires. The decrease o the maximum and averaged lame heights are more constant in comparison to DTBP pool ires. Stean Schälike Multiple Fires 16

9 Flame heights o a multiple DTBP pool ire with N = 9 D/d äq An increase o the array size leads to an stronger descrease o the maximum and averaged lame height. An array improves the air entrainment leading to a more eicient combustion. lower lame heights higher thermal radiation Stean Schälike Multiple Fires 17 Surace emissive powert o multiple pool ires with N = 5 D/d äq D/d äq In the range o small D/d äq the SEP o mulitple DTBP pool ires shows an enhancement: SEPmulti 1.96 SEPsingle A similar behaviour can be observed or n-heptane at which the enhancement is smaller: SEPmulti SEP SEPsingle 1.32 Stean Schälike Multiple Fires 18

10 The enhancement o the SEP increases with the number o N or small D/d äq : SEPmulti SEP SEPsingle 3.37 D/d äq For larger D/d äq the SEP curve descreases strongly. Stean Schälike Multiple Fires 19 Conclusions A new model or the mass burning rate o peroxide pool ires including a liquid phase decomposition reaction has been developed. The mass burning rates o multiple ires are by a actor o 14(DTBP) 1.4 und 1.8 (nheptane) higher in comparison to single ires with the same surace area. A maximum at D/d äq 0.4 (DTBP) and D/d äq 0.12 (n-heptane) can be observed. The maximum and averaged relative lame heights H/d äq o multiple ires are always smaller in comparison to the respective single ire o the same surace area and which urther decrease with increasing D/d äq. The thermal radiation o mulitple ires is or small D/d äq explicitly higher (actor or DTBP, actor 1.32 or n-heptane) in comparison to single ires. With increasing D/d äq the thermal radition decreases strongly. Stean Schälike Multiple Fires 20

11 Dir. and Pro. Dr. Klaus-Dieter Wehrstedt Special thanks go to: Pro. Dr. Axel Schönbucher Dr. Heike Michael-Schulz The working group Explosive Substances o Chemical Industries Dipl.-Ing. Marek Gebauer Dr.-Ing. Michael Rudolph Dipl.-Ing. Jochen Kebben Bianca Fourier Tobias Nauendor Michael Bulin Ola Mücke United Initiators GmbH & Co. KG For supplying Di-tert-butyl peroxide Stean Schälike Multiple Fires 21