application of factorial experimental design to determine...
TRANSCRIPT
Background and Motivation Equipment description36L Dust Explosion Vessel Control system
Application of Factorial Experimental Design to Determine the Optimum Test Parameters for a 36 L Dust Explosion Equipment
D. Castellanos, V.H. Carreto, C.V. Mashuga, M.S. Mannan
Between 1980 to 2005, several dust explosions in US have resulted in more 100 deaths and
Equipment capabilities
Control systemRemote control using LabView as interfaceManual control(1) vacuum system
(2) Air reservoir(3) Fast acting valve (FAV)(4) Dust container(5) Rebound nozzle(6) Electrodes and igniters(7) Pressure transducers.
*Imperial Sugar company dust explosion:Savannah, Georgia. February 7, 2008 13 d h 40 k i j d
LabView allows:
Precise timing control for FAV time and ignition delay Data analysis, saving and exporting options
FAV and ignition delay pulses areconnected to LabView “counters”which are simultaneously activatedb t l AC i l
KSt is calculated by recording pressure profileand calculating the slope every 10 datapoints. Maximum slope value represents(dP/dt)max which is subsequently corrected byth l l (36 Lit )
• In attempting to identify dust explosionhazards and reduce these type of accidents,different explosion apparatus have beendesigned.• Accurate calibration of the test equipmentis essential to obtain reliable information thatis independent of the equipment used.• Lack of systematic calibration guidelines,and the great amount of influencing factorson explosive characteristics increase thenumber of tests and time required to
700 injuries (CSB)*.
Equipment capabilities
Basic fundamentals Property Definition Standard Industrial application
Pmax
Maximum explosion overpressure generated in the test chamber
ASTM E 1226 (Thermodynamic parameter) Used to design enclosures and predict the severity of consequence.
(dp/dt)maxMaximum rate of pressure rise
ASTM E 1226 (Kinetic parameter) Predicts the violence of an explosion. Used to calculate KSt
KSt Dust deflagration index ASTM E 1226 Measure the relative explosion severity compared to other dusts.
Minimum explosiveMeasure the minimum amount of dust
KSt values Clarification0 St0 0-200] St1[200-300] St2> 300 St3
Common dusts can explode, including: Organics (sugar, flour, grains, milk), plastics, metals(magnesium , aluminum), coal .
Combustible solid small particle size(<63um)/within flammable limitsOxygen concentration sufficient tosustain the flame propagationI iti b Mi i I iti
A dust explosion requires 5 elements within specific ranges:
13 deaths, 40 workers were injured* Source: U.S. Chemical Safety Board
by an external AC signal. the vessel volume (36 Liters).complete the calibration process.
OBJECTIVE: Guide the calibration process using 2k factorial to define properoperation conditions of a 36L vessel.
Determination of proper equipment operation conditions
MEC Minimum explosive concentration
ASTM E 1515 dispersed in air required to initiate an explosion.
Increasing ExplosibilityIgnition source above Minimum IgnitionEnergy) (MIE).
Th f (A B C) d l l f h f l d d h i ff i ifiMATERIAL: Corn
Stage 1. Semi-quantitative analysis
Stage 2. Turbulence analysis at different operation conditions
MATERIAL: Niacin6020 6020
OBJECTIVE: Refine calibration process and define the optimum fast acting valveignition delay times.
I A B C AB AC BC ABC yi (bar-m/s)
1 -1 -1 -1 1 1 1 -1 13.8
1 -1 1 -1 -1 1 -1 1 7.44
1 1 -1 -1 -1 -1 1 1 6.78
1 1 1 -1 1 -1 -1 -1 6.62
1 1 1 1 1 1 1 1 12 27
2k factorial approach: recommendations and conclusions = 23 2 + 2 + 2 + 2 + 2 + 2 + 2
Three factors (A, B, C) and two levels for each factor were selected to study their effect in a specificvariable “y” (in this case y = KSt value).
Factors Low Level High LevelA FAV Fast acting valve time, ms 300 400B IG Ignition delay time, ms 20 50C RP Reservoir pressure, psia 221 264
The factors are systematically combinedthrough all the levels.
Each combination of factors levelsrepresents the set of operation conditionsused during a dust explosion test.
The variation of Y given by each factor iscalculated by the following expression:
0
20
40
0
5
10
15
RP221 FAV200
IG20
RP221 FAV100
IG20
RP221 FAV75 IG20
RP264 FAV200
IG20
RP264 FAV100
IG20
RP264 FAV75 IG20
RP315 FAV100
IG20
RP315 FAV75 IG20
Kst
[bar
-m/s
]
Pm
[bar
]
0
20
40
0
5
10
15
RP315FAV100
IG10
RP315FAV100
IG20
RP315FAV100
IG30
RP315FAV100
IG50
Kst [
bar-
m/s
]
P m[b
ar]
Pmax
KSt
The 2k factorial approach provided information of each independentfactor effect and possible factors interaction effects on the observed
The methodology finalized1 -1 -1 1 1 -1 -1 1 12.27
1 -1 1 1 -1 -1 1 -1 10.32
1 1 -1 1 -1 1 -1 -1 6.84
1 1 1 1 1 1 1 1 6.80
70.87 -16.79 -8.51 1.59 8.11 -1.11 4.53 -4.29 qi
8.86 -2.10 -1.06 0.20 1.01 -0.14 0.57 -0.54 Qi=qi/8
(Qi)2 4.40 1.13 0.04 1.03 0.02 0.32 0.29
Y 61% 16% 1% 14% 0% 4% 4% 100%
Stage 3. Results Validation and Conclusions
This methodology guided the calibrationprocess toward shorter FAV times.
The results from this experimental analysishelped to identify FAV as the moreinfluencing factor in the observed variableKSt. Effect of FAV corresponds to 61%. - Dispersion time (FAV) of 50 ms
- Ignition delay time betweendispersion and ignition activation(IG) of 25 ms- Reservoir pressure (RP) of314.7 psia
factor effect, and possible factors interaction effects on the observedvariable (Kst) guiding the calibration process toward FAV times shorterthan 300 ms.Since the variable observed (Kst) does not have a linear behavior with thefactors studied, the selection of a proper range between the levels for anyof the three factors used in the analysis was essential to obtain usefulresults. If the range of the influencing analyzed is very short, notappreciable changes can be observed in Kst. On the other hand, if therange is too long, high Kst values can be under covered.
with the following set ofoperations conditions
Future Work : Dust explosion simulations with DESC
METHODOLOGY
Test
#g/m3
Pex Pmbar
(dP/dt)
bar/s
KStbar-m/s
Deviation from
reference valuepsia bar
1 550 131 8.0 8.5 747 247 KSt = 239 bar-m/s2 550 129 7.9 8.4 706 233
OBJECTIVE: Verify that the equipment operating conditions are useful to reproduce valuesfrom Round Robin tests.
The optimal concentration for Pmax is 450 g/m3 , andoptimal concentration for KSt is 550 g/m3 .
Use pressure-time profiles from dust explosions in both apparatus to analyze the effect of the vesselshape and size on the turbulence. Use FLACS and DESC simulations to calculate the decay of root meantsquare velocity and the turbulent length scale and compare them with experimental values.
MATERIAL: Niacin (Calibration round Robin, Kühner 2003)
OBJECTIVE: Compare the 36 L at the MKOPSC with an standard 20 L dust explosionequipment using CFD simulations.
Dev = 8.45 %3 550 130 8.0 8.5 715 236
4 450 131 8.0 8.5 671 222Pmax= 8.6 barDev = 2.09 %5 450 132 8.1 8.6 783 259
6 450 132 8.1 8.6 749 247
The calibration methodology was useful to determinethe proper operating conditions of a 36 L dustexplosion equipment reducing the number of testrequired.The results obtained were in good agreement withthe values reported in the literature.
Same methodology can be used as guide for calibrating other equipment with different configurationswhere the turbulence plays an important role on the explosion results.