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Rotary air valves used for material feed and explosion protection are required to meet the criteria of NFPA 69 (2014) 12.2.4.2.

12.2.4.2 rotary valve design criteria (close clearance)

12.2.4.3 THE DESIGN CRITERIA IN 12.2.4.3.1 THROUGH 12.2.4.3.9 SHALL BE APPLICABLE TO EITHER CONCEPT DEFINED IN 12.2.4.2.

- 12.2.4.3.1 DESIGNED VALVE BODY & ROTOR FOR Pred BY 3RD PARTY. - 12.2.4.3.2 THE DESIGN BASIS INCLUDES THE SPECIFIC EXPLOSION CHARACTERISTICS

(KST,AND PMAX) OF THE POWDER BEING HANDLED. - 12.2.4.3.3 PRES. RESISTANCE CERTIFIED BY A KNOWLEDGEABLE TEST

AUTHORITY. - 12.2.4.3.4 AT LEAST 6 VANES ON ROTOR. - 12.2.4.3.5 AT LEAST 2 VANES EA. SIDE IN MINIMUM CLEARANCE AT ALL TIMES. - 12.2.4.3.6 METAL BODYAND ROTOR. VANES. - 12.2.4.3.7 ROTARY VALVE BEARINGS EXTENALLY MOUNTED. - 12.2.4.3.8 EXPLOSION DETECTION DEVICE OR INTERLOCK TO AUTO-STOP VALVE. - 12.2.4.3.9 THE NEED FOR PERFORMANCE TESTING OF VALVE DETERMINED BY

A.H.J.

12.2.4.5 CLOSE CLEARANCE ROTARY VALVES. - 12.2.4.5.1 CLOSE-CLEARANCE VALVES 1MTH A CLEARANCE OF 0.2 MM (0.0079") - 12.2.4.5.2 THE CLEARANCE BETWEEN VALVE AND BODY SHALL BE SMALL

ENOUGH TO PREVENT THE PASSAGE OF FLAME BETWEEN ROTOR AND VALVE HOUSING.

- 12.2.4.5.3 THE ACTUAL CLEARANCES ARE MEASURED AFTER ASSY, A MAINTENANCE PROGRAM TO ADDRESS WEAR IS THE RESPONSIBILITY OF THE END USER.

- NFPA 70 GROUND STRAP REQUIRED. - 12.2.5.3(3) 1 M/S (200 FPS) RIM SPEED MAX

OPERATING PRESSURE 4.5 PSIG

EXPLOSION VENTING ABOVE AIRLOCK BY OTHERS

NOMINAL BURST PRESSURE OF PRESSURE RELIEF VENTING 1.5 PSIAAT 100F

Kst value 299 (bar m/sec)

Pred = 14.5 PSIA

MAX. ROTOR TO HOUSING TEMPERATURE DIFFERENTIAL 25F

DESIGN TEMPERATURE 70F

OPERATING TEMPERATURE RANGE-40F TO 90F

DO NOTAPPLY STRESS, WELD OR CUT ON THIS UNIT

STATIC LOAD 2500 LBS

SERIAL NUMBER 6197

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1- Stress analysis

Table 1 shows parameters used in the stress analysis

Table 1. Stress analysis detail

Material (including bolts) Yield stress Surface pressure exerted Mesh type Mesher used Jacobian points Max element size Min element size Mesh quality Total nodes Total elements Maximum aspect ratio Percentage of elements with aspect ratio < 3 Percentage of elements with aspect ratio > 10

The static stress analysis was performed using SOLIDWORKS Simulation. Housing, end bells, and knife door were analyzed in a single setup. Housing was fixed from the bottom flange. End bells and knife door were bolted to the housing.

As per NFPA 69.12.2.3.3.1, the valve body should have sufficient strength to withstand reduced explosion pressure in the vented enclosure above airlock housing, Pred (bar g), which is determined by customer. As Pred of wood dust is not >14.9 psi therefore 15 psi was exerted to the inner surfaces of the housing, the end bells, and the knife door. Results show no significant deformation in the model under above mentioned pressure, hence the valve body has sufficient strength to withstand 15 psig of pressure. Figure 1 shows contour of von Mises stress on the model. The maximum stress was found at the endbell with the value of 8378 psi about 23% of the material's yield point.

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Figure 1. Von Mises stress for the housing, the end plate, and the knife door.

2- Airlock explosion test

2-1 Introduction

This section is a summary of our research into the maximum safe clearance as per NFPA69 12.2.4.5.2 we can use to prevent the passage of flame between the rotor and housing for a rotary airlock knife feeder (isolator) that will perform as well as the (0.0079") 0.2mm x 3mm wide tip clearance specified in NFPA 69 2014 section 12.2.4.5.1

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2-2 Dust explosion computational model development

Dust cloud explosion is a complex problem from a computational point of view and is a function of different parameters such as dust thermophysical properties, water content of the mixture, particle size, etc. Hence any computational model needs to be evaluated using standard explosibility tests in order to yield accurate results. The numerical model in this work utilizes a single step global chemistry model to account for the conversion of combustible part of dust particles into and . Equation 1 shows the single step global reaction:

. . 1.058 → 1.191 1

This reaction is extracted from Ansys material database and is recommended for wood volatiles reactions.

Arrhenius Reaction rate (Equation 2) with parameters reported in Table 2 was used.

The forward rate constant is written as follows:

/ 2

Table 2. Arrhenius reaction rate parameters.

A E (J/Kgmol) Fuel rate exponent, m Oxidizer rate exponent, n Temperature exponent R (J/mol-k)

2-3 Particle size distribution

Size of combustible particles play a significant role in the modeling process. Rosin-Ramler method was used to mimic the particle size distribution reported by Fike. Table 3 shows wood particle parameters used in the simulations.

Table 3. Wood particle parameters.

Particle Min Diameter (m) Particle Max Diameter (m) Particle Mean Diameter (m) Density (Kg/m3) Cp (J/Kg-K) Vaporization temp (K) Volatile component fraction (%) Binary diffusivity (m2/s)

2-4 Validation

To calibrate and validate the reaction presented in Equation 1 the results from experimental explosibility test with dried, all fine SPF wood dust as per ASTM E1226 grinding specifications and a Kst of 202.3 by

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Fike Canada Incorporated (FIKE REPORT NO. CTL11667338-Rev0) was used. Table 4 shows the experimental parameters and the results of the explosibility test, and Figure 2 shows the 20_L Siwek apparatus used for explosion testing.

Table 4. Fike explosibility test parameters and results

Supplied Material Classification Moisture Content Was the sample dried? Moisture Content (As Tested) Was the sample ground? Pmax (barg) Pmax Corrected (barg) (dP/dt)max KSt (bar m/sec) Ignition Source

Figure 2. Siwek 20-L Apparatus

Figure 3 shows the numerical domain generated to replicate the dust explosion test results under ASTM E1226 standard.

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Figure 3. Axisymmetric model of Siwek 20-L apparatus

Figure 4 shows particles in the container and the reaction zone at beginning of explosion.

Figure 4. 20L container with wood particle and reaction area

Table 5 shows the details numerical Siwek 20_L apparatus.

Table 5. Detail of Axisymmetric model of Siwek 20-L apparatus.

Grid size (m) Radius (m) Mesh type Mesher used

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Figure 5. Pressure versus time curve for dust explosion

Figure 5 shows computational results for pressure versus time curve in dust explosion. Pmax value matches the experimental values presented in Table (note the 1 bar initial pressure in the chamber). The other important explosibility parameter is the Kst. To compare the experimental values with the computational results Equation 3 was used:

KdPdtV /

3

Hence:

KdPdtV / ≅

delPdelt

V / 8.4211.5e 3

0.02 / 202.3 barm/sec

Calculated Kst value is in good agreement with the experimental data. Table summarized the comparison between computational model results and experiment.

Table 6. Simulation results vs experimental data from FIKE REPORT NO. CTL11667338-Rev0

Simulation FIKE REPORT NO. CTL11667338-Rev0 Pex (bar) 8.42 8.46 Kst (bar m/sec) 202.3 203

2-5 Cylindrical container

In order to reduce computational cost a 2D Axisymmetric model was used for the simulations consisting of a cylindrical shape with a blade separating two volumes. Figure 6 shows the geometry at the beginning of the simulation. Wood particle are added at the start of simulation to match the concentration reported in Fike report. A spark increases the temperature of the particles in the right hand side of the cylinder. A blade separates the heated charge from the left hand side which is connected to a pressure outlet boundary

0

1

2

3

4

5

6

7

8

9

10

0 5 10 15 20

Ab

solu

te P

ress

ure

(b

ar)

Time (ms)

Sim results

Experiment (FIKE REPORT NO. CTL11667338-Rev0)

del t

del P

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condition with 1 atm pressure. To reduce computational cost the middle part of the left hand side of the blade is removed. Blade dimensions are variable for each simulation. For this set of calculations 0.0078”X0.25”, 0.012”X0.5”, and 0.014”X0.5” was used. The computational time for each case was 200, 164, and 172 CPU hour respectively. Walls are assumed to be made of Steel and with a constant temperature of 300 K throughout the sims. The code calculates the heat transfer rate based on the gas temperature at any given location.

Figure 6. Distribution of wood particles using Rosin-Ramler

Figure 6 shows distribution of wood particles at the begining of the simulation. Figure 7, Figure 8, and Figure 9 show the results for tested clearances.

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Figure 7. Temperature contour for 0.0078”X0.25” clearance

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Figure 8. Temperature contour for 0.012”X0.5” clearance

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Figure 9. Temperature contour for 0.014”X0.5” clearance

2-6 Conclusion

These simulations use a Kst of 202.3 from dried, all fine SPF wood dust as per ASTM E1226 grinding specifications, which we know is not the case in "as found" shavings within the sawmill industry, providing us with a much greater safety margin, when using 0.012" as a maximum clearance for a shavings only feeder. Shavings were tested by Fike "as found" at a Kst of 21.