Full Scale Experimental Testing of Aerosol Filling Facilities Experiments and Validation

Transcription

1 Full Scale Experimental Testing of Aerosol Filling Facilities Experiments and Validation FLUG User Group Meeting 29 th November 2017 Tim Jones Principal Consultant

2 Introduction Background Project Overview Initial Analysis Experimental Program Validation

3 Background Almost all domestic aerosols are propelled by a liquefied compressed gas. Since CFCs were banned in the 70 s these are mainly flammable LPG propellants (propane/ butane/ Pentane blends) Aerosols are filled with propellants in dedicated unmanned buildings external to normal product. Up to 500cans per minute (each with up to 200ml of LPG) are filled. Many layers of protection for the flammable gas operation: Zoning /Ventilation /Unmanned operation/ gas detection /automatic shutdown /etc.

4 Background Pressure relief is last line of defense

5 Background Typical building design Factory Lifting Top Hat Roof Gas House Conveyor for cans

6 Background Inside the gas house Gasser

7 Project Overview Historically building have been design based on NFPA standards Calculations using these standards indicated that the withstand of the walls were close to the expected overpressures FLACS analysis conducted by Gexcon To validate FLACS analysis experimental program was conducted over 2 phases FLACS analysis was repeated as a validation exercise

8 Design Specification Circular building with top down ventilation out through subfloor vent Wall strength to NFPA 30B (100lb/ft 2-48mbar) Relief design to NFPA 68 Relief pressure (Pstat) <20mbar Light weight roof (should be <12.2kg/m 2 ) with restraint chains (1.4 to 2m length) Challenge existing circular roof design comes in closer to 30kg/m 2

9 NFPA 68 Correlations Reduced pressure a function of: Gas type Vent area Relief pressure Internal surface areas These correlations suggested overpressures are borderline compared to the capacity of the walls. Some uncertainty with respect to what areas should be considered.

10 Initial FLACS Analysis FLACS analysis was carried out by Gexcon. Calculated overpressures of 1 barg. These pressure would lead to catastrophic failure of the gas houses. Gas houses would have to rebuilt around the world cost of > 10m

11 Initial FLACS Analysis

12 Initial FLACS Analysis Some simplifications had to be made in the FLACS analysis. FLACS is unable to resolve curved surfaces directly therefore they are represented by the porous sub model. The roof itself is a top hat arrangement with slanted side. Again these cannot be resolved by the grid. Although pressure relief panels can be modelled there is no account for a moving mesh. Based on engineering judgement it was felt that the overpressure were overpredicted. Due to the costs associated with rebuilding the gas houses it was decided to embark on an experimental program.

13 Experimental Program Started with a blank piece of paper and was when MMI got involved. Experiments were defined, test rig was designed, fabricated and assembled onsite at Spadeadam. Rig was a full scale representation. FEA analysis conducted to ensure test rig would remain elastic

14 Experimental Program

15 Experimental Program All experiments considered 100% fill of the gas house Phase 1: 1A: Polythene sheet roof, ignition at bottom of gas house 2A: Same as 1A, ignition at bottom of gas house 3A: Repeat of 1A due to insufficient fuel, ignition at bottom of gas house 4A: Same as 1A with actual roof, ignition at bottom of gas house 5A: Same as 4A, ignition at bottom of gas house

16 Test 1A

17 Test 1A

18 Test 4A

19 Test 4A

20 Test 4A

21 Phase 1 Summary Tests 1A and 3A define a lower limit for the design pressure for the walls for an idealised roof. Average pressure on the walls was 0.08 barg with a peak of 0.09 barg. With the roof overpressures increased to 0.1 barg average and 0.18 barg max. Client was happy! Might not have to knock down all the gas houses and rebuild them. Repeatability was also good between tests (1A and 3A and 4A and 5A). Therefore decision was made to not conduct multiple test for Phase 2.

22 Experimental Program Second phase looked at sensitivities Phase 2: 6A: Polythene sheet roof, ignition inside the gasser

23 Test 6A Second phase looked at sensitivities Gasser

24 Experimental Program Second phase looked at sensitivities Phase 2: 6A: Polythene sheet roof, ignition inside the gasser 7A: Polythene sheet roof, ignition at bottom of gas house, preignition turbulence

25 Experimental Program Second phase looked at sensitivities Phase 2: 6A: Polythene sheet roof, ignition inside the gasser 7A: Polythene sheet roof, ignition at bottom of gas house, preignition turbulence 8A: Frangible roof, ignition at bottom of gas house

26 Test 8A Foam Panels

27 Test 8A

28 Experimental Program Second phase looked at sensitivities Phase 2: 6A: Polythene sheet roof, ignition inside the gasser 7A: Polythene sheet roof, ignition at bottom of gas house, preignition turbulence 8A: Frangible roof, ignition at bottom of gas house 9A: Polythene sheet, ignition at bottom of gas house, grated floor removed

29 Test 9A

30 Test 8A

31 Test 8A

32 Phase 2 Summary Ignition in the gasser led to overpressures increasing from 0.08 to 0.25 barg. 220% increase. Addition of pre-ignition turbulence increased overpressures from 0.08 to 0.15 barg. 88% increase. The removal of the grating led to a reduced overpressures from 0.08 to 0.07 barg. 15% reduction. The frangible roof increases overpressures from 0.08 to 0.28 barg compared to the polythene roof test. Compared to the steel roof overpressures were increased from 0.14 to 0.28 barg. Increases were due to three factors: Residual blockage of the fixed roof structure Sections of the panels remaining in-place following the explosion. Limited by design wind speeds

33 Phase 2 Summary Could reduce overpressures by using tapered panels.

34 FLACS Validation Experimental results are lower than initial FLACS analysis. Approximately a factor of 3. Further work was carried out for Test 1A by Gexcon.

35 FLACS Validation Maximum pressure distribution With gasser walls

36 FLACS Validation Maximum pressure distribution With gasser walls No gasser walls

37 FLACS Validation Pressure evolution within gas house

38 FLACS Validation Pressure evolution within gas house with no gasser walls

39 FLACS Validation Sensitivity conducted on the ignition location with no gasser walls. Differences of up to 40% observed for changes in ignition location by only 0.5 m.

40 FLACS Validation Summary For Test 1A the overpressures were 0.08barg and FLACS calculated overpressures of ~0.25barg. Reduced overpressures seen when the gasser was removed and for sensitivities with respect to ignition location but still higher than experimental results. Sensitivities with the commercial version of FLACS have been exhausted and currently investigating if modifications to the solver could be made to better match experimental data.

41 Current Status of the Project There was a fear from the project that the overpressures based on the frangible roof were too high and there was a reluctance to re-engineer the roofs. The steel roof tests showed positive results with respect to pressure therefore shock absorbing springs have been retrofitted to chains to reduce shock load and keep the roof attached to the structure. Client would like to have an analytical solution to design of gas houses in the future therefore still interested in the work being done by FLACS. MMI have also started a project with Cambridge University, in conjunction with the client, to trial their CFD codes to simulate the experiments.

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45 Engineering a Safer World Engineering a Safer World mmiengineering.com mmiengineering.com