Defining Hazardous Zones – Electrical Defining Hazardous Zones – Electrical Classification Distances Classification Distances

Gary Howard,Gary Howard, Andrei Tchouvelev, Vlad Agranat and Zhong ChengAndrei Tchouvelev, Vlad Agranat and Zhong Cheng

AcknowledgementsAcknowledgements

• Work partially supported by– Natural Resources Canada (NRCan) CTFCA

Clearance Distance Project– Natural Sciences and Engineering Research

Council of Canada (NSERC) Industrial Research Fellowship

Project ObjectivesProject Objectives

• To develop sound scientific and engineering guidelines that can be used to specify quantitative values for:

– Clearance distances for hydrogen equipment and systems

– Hazardous zone classifications

– Declassifying hazardous zones with ventilation

• To interpret the new specifications and to develop scientifically based "rules of thumb" that can be used as input into the Canadian Hydrogen Installation Code and for updates to the Canadian Electrical Code

ApproachApproach

• CFD modeling and thermal effects analysis of typical releases under:Real operating conditionsReal geometriesReal ventilation rates (indoor) and wind velocities

(outdoors)

Release Direction

Release Magnitude

Large/fast Small/slow

Vertical

Horizontal

Simulation ExamplesSimulation Examples

Key Results – Innovative ApproachKey Results – Innovative Approach

• Proposed clearance distances are based on CFD modeling results that were obtained based on hydrogen properties and science

• Proposed clearance distances depend on both storage pressure and storage volume:– Three pressure ranges were selected: up to 25 bars, up to 440

bars and above 440 bars to differentiate between on-site hydrogen generation equipment, and 350 and 700 bars ground storage, compression and dispensing equipment

– Several volume ranges were selected to differentiate between on-site hydrogen generators inventory, small lab type or demo type storage and medium to large scale storage systems

• Proposed clearance distances are based on LFL concentration envelopes plus safety factor of 25%

Example of Scenarios and AssumptionsExample of Scenarios and Assumptions

• H2 leak rates of 5 and 20 scfm (0.0020 and 0.0079 kg/sec) were selected as credible leaks based on experience; the necessary holes sizes to produce this leak rate were calculated for 400 bar storage pressure (0.1 and 0.2 mm respectively)

• Selected leak rates were modeled in downward, upward and horizontal orientations in a 0.5 m/sec wind (IEC 60079-10)

Flowrate(SCFM)

Re #105

4% vol. H2 cloud volume (m3)

Horizontal cloud extension (m) Vertical cloud extension (m)

IEC CFD 8 % vol. 4% vol. 2% vol. 8 % vol. 4% vol. 2% vol.

20 (down) 5.11 2.82 0.41 0.14 0.63* 3.31* 0.6 3* 3*

5 (down) 2.55 0.71 0.10 0.09 0.21 1.62* 0.28 1.18 3*

20 (up) 5.11 2.82 0.52 0.16 0.37 0.87 0.69 2.11 5.55

5 (up) 2.55 0.71 0.23 0.12 0.28 0.69 0.47 1.44 3.95

20 (horiz.) 5.11 2.82 0.11 0.37 1.14 4.81 0.09 0.2 0.42

5 (horiz.) 2.55 0.71 0.02 0.12 0.48 2.02 0.05 0.12 0.25* These clouds touch the ground, which is 3 m below the leak orifice

5 and 20 scfm Simulation Results at 400 5 and 20 scfm Simulation Results at 400 barsbars

5 cfm 0.103 @ 100%2.1 @ 50% LFL

20 cfm 0.42 @ 100%3.7 @ 50% LFL

5 cfm 0.23 @ 100%2.5 @ 50% LFL

20 cfm 0.52 @ 100% 5.6 @ 50% LFL

5 cfm 0.02 @ 100%0.22 @ 50% LFL

20 cfm 0.11 @ 100%1.4 @ 50% LFL

CFD LFL Vol m3

Key Differences with IEC 60079-10Key Differences with IEC 60079-10

• IEC 60079-10 method of hazardous location size calculation is directly proportional to flammable gas concentration, meaning that 4% vol. cloud is twice smaller than 2% vol. cloud:

• In reality the correlation between hydrogen gas clouds of various concentrations is more complicated. CFD modeling indicates that 4% vol. cloud is about an order of magnitude smaller that 2% vol. cloud

Key ResultsKey ResultsProposed Hydrogen Systems Electrical Classification Distances (fragment):

Component Zone 1 from source

Zone 2 from source

Comments

Any volume of gaseous storage or Hydride storage up to 25 bar

zero 0.3 m from valves

Valves are the only source of leak if vent pipes are discharged at a safe location

> 25 bar to <440 bar pressure

Up to 250 l water capacity

zero 0.5 m A leak will be short lived and pressure will reduce quickly

> 250 l to 2000 l zero 1.2 m horizontal and 2.2 m up

Downwind H2 LFL is 4% at 1.14 m

Over 2000 l < 8000 l

zero 1.2 m down and horizontal 2.2 m up

Distance equals CFD model

8000 l and over zero 2 m horizontal and 3 m up

Greater volume has more sites that could leak simultaneously

>440 bar pressure

250 l water .5 m 1 m Double the pressure will increase distance 50%

> 250 l to 2000 l 1 m 2 m horizontal and 3.5 m up

Mass flow rate will be greater with higher pressure. 1 m zone 1 added due to volume and longer leak duration

SummarySummary

• Proposed clearance distances are based on CFD modeling results that were obtained based on hydrogen properties and science

• Proposed clearance distances depend on both storage pressure and storage volume

• Proposed clearance distances are based on LFL concentration envelopes plus safety factor of 25%