Jerzy Jurewicz & Boulos_Analysis of safety aspects associated with the plasma synthesis and handling of nanopowders – from design stage to industrial implementation
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Jerzy Jurewicz & Boulos_Analysis of safety aspects associated with the plasma synthesis and handling of nanopowders – from design stage to industrial implementation
1. Analysis of safety aspects associated
with the plasma synthesis and handling of
nanopowders – from design stage to
industrial implementation
J.W. Jurewicz, M.I. Boulos,
Tekna Plasma Systems Inc.
2935 boul. Industriel, Sherbrooke, Qc, Canada J1L 2T9
1
2. Outline
• Presentation of Tekna Advanced Materials
• Risk Management Process
• Design Considerations
• Plasma Processing Units
• Building Infrastructure
• Safety Barriers System
• Conclusion
2
3. Tekna Advanced Materials Inc.
• The mission of Tekna Advanced Materials Inc. (TAM) is to
develop and commercially manufacture high added value
advanced materials using thermal plasma technology.
• There is an increasing demand for powders at the micron,
sub-micron and nano-sized (< 100 nm) level for a wide range
of applications varying from microelectronic, to the
biomedical and the cosmetic industry.
• Intensive research effort is dedicated to the assessment of
the potential hazard that nano-sized materials can have on
human health. These materials have to be handled with
utmost care and well defined procedures in order to minimize
the chances of human exposure.
3
4. Tekna Advanced Materials Inc.
This paper explains the approach undertaken by Tekna
engineers to design, built and run a viable operation for the
commercial production of advanced materials including
nanostructered materials and powders.
4
5. Outline
• Presentation of Tekna Advanced Materials
Risk Management Process
• Design Considerations
• Plasma Processing Units
• Building Infrastructure
• Safety Barriers System
• Conclusion
5
6. Risk Management Process [1]
[1] “Risk management – Principles and guidelines on implementation”, IEC/ISO 31000:2009 –
CAN/CSA-IEC/ISO 31000-10 (2010) 6
7. Accident Sequence[2]
← THE ACCIDENT SEQUENCE →
Normal condition Initial phase Concluding phase Injury phase
▲ ▲ ▲
Lack of control Loss of control Energy/Toxicity exposure
[2] Sklet S., “Safety barriers: Definition, classification and performance”, J. Loss Prevention
in the Process Industries, 19, pp. 494-506 (2006)
7
8. Accident Sequence & Principle of Barriers [2]
← THE ACCIDENT SEQUENCE →
Normal condition Initial phase Concluding phase Injury phase
▲ ▲ ▲
Lack of control Loss of control Energy/Toxicity exposure
PREVENT PROTECT
PREVENT CONTROL MITIGATE
AVOID PREVENT CONTROL PROTECT
Barriers ⇒ generic functions of process safety management
[2] Sklet S., “Safety barriers: Definition, classification and performance”, J. Loss Prevention
in the Process Industries, 19, pp. 494-506 (2006)
8
9. Principle of Barriers[2]
• Safety barriers are physical and/or non-physical means
planned to prevent, control, or mitigate undesired events or
accidents
[2] Sklet S., “Safety barriers: Definition, classification and performance”, J. Loss Prevention
in the Process Industries, 19, pp. 494-506 (2006)
9
10. Process Safety Management [2]
Risk
1
Acceptation
of residual risk
Risk identification
Identification
and its characteristics /
and
parameters
imposition
2 of barrier to Is barrier
reduce the 4 efficiency
Identification of frequency acceptable
3 YES
possible system’s and/or the ?
failure and its consequence of
characteristics a failure NO
10
11. Nano-Materials (NM) Risk Assessment
Uncertainty*
.....On the whole, a consensus is beginning to emerge,
risk assessment for chemical should be appropriate for NM,
but
they most likely need some methodological modifications.
Exactly what modifications are needed is not consistently
made clear, and how long it will take to make these
modifications is not often stated......
* K.H. Grieger et all., “Redefining risk research priorities for nanomaterials”, J. Nanopart. Res., Vol.
12, 2, pp. 383-392 (2010) 11
13. Nano-Materials (NM) Risk Assessment
Uncertainty*
Concerning Risk Assessment:
.....However, how long will this [Risk Assessment] process take
especially given the diversity of NM and applications ?
A recent analysis estimates that testing existing nanoparticles
in the USA alone will
cost between $249 million and 1,18 billion and
take 34-53 years for completion.
* K.H. Grieger et all., “Redefining risk research priorities for nanomaterials”, J. Nanopart. Res., Vol.
12, 2, pp. 383-392 (2010) 13
14. Nano-Materials (NM) Risk Assessment
Uncertainty
..... In some cases, the precautionary principle has been
invoked to support decisions in the absence of full scientific
certainty......[*]
Conclusions[**]
……Presently, quantitative health hazard and exposure data
are not available for most nanomaterials. Therefore, health
risk evaluation for the workplace currently relies to a great
degree on professional judgments for hazard identification,
potential exposures and the application of appropriate safety
measures
* K.H. Grieger et all., “Redefining risk research priorities for nanomaterials”, J. Nanopart. Res., Vol. 12, 2, pp.
383-392 (2010)
**ISO/TR 12885, “Nanotechnologies – Health and safety practices in occupational settings relevant to
nanotechnologies”, pp. 1-79 (2008) 14
15. Outline
• Presentation of Tekna Advanced Materials
• Risk Management Process
Design Considerations
– Hazards’ parameters
– Hazard evaluation by control banding
– Efficiency of risk management strategies
• Plasma Processing Units
• Building Infrastructure
• Safety Barriers System
• Conclusion
15
16. Design Considerations
The nano-particles are characterized (among others) by their
very high specific surface area which is the origin of their
high reactivity leading to both pyrophoric properties for
combustible materials and/or to toxicity to humans.
The pyrophoric properties may be attenuated by:
– Passivation process - formation of a controlled thickness
oxide layer over the particle surface;
– Encapsulation process – formation of thin layer of
secondary material (like carbon or polymer) over an entire
surface of particle;
– On-line wet collection of nano-powder in an inert liquid;
16
17. Design Considerations
The toxicity parameters include the dose (effective, toxic and
lethal) and the time of exposition.
The risk management program should aim at both minimizing
the dose and shortening time and/or frequency of
exposition.
The possible ways to minimize the dose are (among others):
– handling the nano-particles in tightly closed
environment (as long as possible) and
– use the local ventilation for the case where the products
have to be handled in open atmosphere.
17
18. Design Considerations – Hazard Evaluation
S.Y.Paik et all.[3] considers two categories of hazard evaluation:
severity and probability of exposure to nanomaterials.
As the severity is mainly material dependant, this parameter
was treated as generic without particular identification during
the initial stage of project.
The probability of exposure is strongly process design
dependant and as such was the principal guiding parameter
during the conception stage of the entire operation.
[3] Paik S.Y., D.M. Zalk, P. Swuste, “Application of a Pilot Control Banding Tool for Risk Level
Assessment and Control of Nanoparticle Exposure”, Ann. Occup. Hyg., Vol. 52, No 6, pp.
419-428 (2008)
18
19. Design Considerations – Hazard Evaluation
Probability of Exposure [3]
Parameter Points
Estimated amount of > 100 11-100 0-10 Unknown
nanomaterial [mg] 25 12,5 6,25 18,75
High Medium Low None Unknown
Dustiness / Mistiness
30 15 7,5 0 22,5
Number of employee with > 15 11-15 6-10 1-5
similar exposure 15 10 5 0
Daily Weekly Monthly Less than Unknown
monthly
Frequency of operation
15 10 5 0 11,25
>4h 1-4 h 30-60 min < 30 min Unknown
Duration of operation
15 10 5 0 11,25
19
20. Design Considerations – Hazard Evaluation
Probability of Exposure [3]
Parameter Points
Estimated amount of > 100 11-100 0-10 Unknown
nanomaterial [mg] 25 12,5 6,25 18,75
High Medium Low None Unknown
Dustiness / Mistiness
30 15 7,5 0 22,5
Number of employee with > 15 11-15 6-10 1-5
similar exposure 15 10 5 0
Daily Weekly Monthly Less than Unknown
monthly
Frequency of operation
15 10 5 0 11,25
>4h 1-4 h 30-60 min < 30 min Unknown
Duration of operation
15 10 5 0 11,25
Material Pending Values aimed at during design
20
21. Efficiency of Risk Management Strategies [4]
[4] C. Ostiguy, B. Roberge, L. Ménard, C. Endo, “ Best Practices Guide to Synthetic Nanoparticle
Risk Management”, Studies and Research Projects, Report R-599, IRSST (2009) 21
22. Design Considerations
All above mentioned risk management strategies were
analysed in the light of existing hazard management
approach as offered by Tekna Plasma Systems Inc. in
commercial plasma processing units.
It was decided to apply bottom-up design method to build up
the commercial production facility by adding additional layers
of protection / prevention to already existing ones.
At the same time, the economic aspects and processing costs
reduction have been addressed as well.
22
24. Outline
• Presentation of Tekna Advanced Materials
• Risk Management Process
• Design Considerations
Plasma Processing Units
– Spheroidization Unit
– Nanopowders Synthesis Unit
• Building Infrastructure
• Safety Barriers System
• Conclusion
24
25. Plasma Processing Unit – Spheroidization
Some of the typical characteristics of Tekna’s commercial
induction plasma processing unit
• Continuous operation 24/5-7 including
raw material feeding, product cooling &
withdrawal - the latter ones are done
pneumatically under controlled
processing atmosphere;
• All plasma processing operations are
automated (including plasma ignition)
through in-house conceived computer
programme with up to 5 levels of
alarms (if required by process safety);
• Deflagration containment design.
25
26. Nano-Powders Synthesis
1 Plasma Torch
4 Pneumatic
5 Glove Box Transfer Unit
2 Plasma Reactor
3 Filter
Continuous liner packing
to replace the glove box
26
27. Outline
• Presentation of Tekna Advanced Materials
• Design Considerations
• Plasma Processing Units
Building Infrastructure
o Cooling Water System
o Washing / Rinsing Water System
o Ventilation System
• Safety Barriers System
• Conclusion
27
28. Cooling Water System
• Total power to be dissipated – 2,5 MW
• Dissipation method :
space (building) heating
during cold season prior to
water evaporation in cooling
tower;
• Cooling water exit temperature
is kept constant by controlling
fan speed through a frequency
drive;
28
29. Cooling Water System – Impurities Control
Suspended and/or dissolved solids control:
• Cooling water origin:
– Primary water intake – rain water / melted snow collected
in 28 m3 water tank from the roof of an entire building - (no
dissolved solids – weak charge of suspended solids)
– Secondary water intake – city water originating from
Memphremagog lake (weak charge of dissolved solids, no
suspended solids)
• Solid particles collected from dust laden outside air by
cooling water - the water tank design allows them to
sediment at bottom collection well
29
30. Cooling Water System – Impurities Control
Suspended and/or dissolved solids control:
• Biological charge growth is controlled by
intensive (> 40000 µWs/cm2) UV irradiation of
cooling water in closed loop circuit
30
31. Cooling Water System – Impurities Control
Suspended and/or dissolved solids control:
Leak of materials from plasma processing system – no
possibility due to mechanical isolation of primary DI water
loop from cooling water loop through stainless heat
exchanger – water quality (resistivity) is monitored
31
32. Cooling Water System – Impurities Control
Cooling water is free of corrosion prevention chemicals (the
entire cooling system is either of polymer or stainless steel
origin) allowing to dispose the excess of rain water into
environment without manmade contaminants.
The solids collected from outside air as sediments at the
bottom collection well are evacuated periodically
32
33. Washing / Rinsing Water System
Among procedures to minimize the exposition to nano-sized
particulates, the wet collection/cleaning of reactor’s
interiors as well as possible spills is strongly recommended.
The production halls are equipped (among others) with gray
and deionized (DI) water distribution systems.
• The gray water serves as washing fluid for all plasma
processing interiors during their periodic cleaning or when
changing the treated materials; the powder laden water is
then evacuated through sub-floor conduits to one of the
collecting tanks where it is left for solids decantation and
subsequent treatment; similarly, in the case of materials spill
on the floor, the leftovers are washed down by city water and
evacuated to the same collecting tank;
33
34. Washing/Rinsing Water System
• The DI water serves as final rinsing water as well as safety
shower water – for such application the water has to be kept
lukewarm.
This water is constantly treated by UV radiation to prevent
bacterial growth - similarly to the cooling water circuit.
34
35. Local Ventilation System
Designing Considerations :
•Design according to the standard ANSI/AIHA Z9.2 – 2006 –
«Fundamentals Governing the Design and Operation of Local
Exhaust Ventilation Systems»
•Exhausted air leaving premises has to be cleaned to HEPA
standard (99,97 % of arrestance) through progressive retention
of particles through a sequence of filters with increasing
arrestance to avoid rapid clogging of a final filter
35
38. Ventilation System
• Pre-filter and primary filter are housed in one box and are fed
from 2 exhaust arms;
• Each final filter (HEPA) collects spent air from 2-3 primary
filters;
• Both primary and final filters’ pressure losses are monitored
locally (gauge) and remotely (control room) – an operator is
aware of the actual pressure loss value and a visual and
audio alarms are set as well;
• The exhaust fan (located over the roof) is driven by a
frequency controlled drive allowing to maintain constant air
evacuation rate in spite of increasing pressure losses in the
chain of filters – in the case of an emergency, the evacuation
rate increases automatically to its maximal value.
38
39. Outline
• Presentation of Tekna Advanced Materials
• Risk Management Process
• Design Considerations
• Plasma Processing Units
• Building Infrastructure
Safety Barriers System
– Example: Flammability hazard
– Example: Nanoparticles spill hazard
• Conclusion
39
40. Safety Barriers System - Examples
• Hazard – Flammability of processing gases/products:
– Hydrogen in-situ production rate follows its consumption –
no stocking
– PLC activated vacuum/pressure inerting of processing
vessels including air lock charged with powdered raw
material and feeder hoper for each charging operation;
– Monitoring of residual oxygen concentration in processing
vessels;
– Controlled passivation of pyrophoric products;
– Stocking of pyrophoric products under inert atmosphere;
– Equipment designed to withstand deflagration;
– Process off gas (already saturated with inerting water
vapour) is exhausted to outside through the flash arrestor;
40
42. Safety Barriers System
• Air lock exit from production hall ⇒
• Personal Protection Equipment ⇓
Motorized air blower
unit equipped with
splash protected gas,
vapour & particulates
(HEPA class) filtering
unit
42
43. Outline
• Presentation of Tekna Advanced Materials
• Risk Management Process
• Design Considerations
• Plasma Processing Units
• Building Infrastructure
• Safety Barriers System
Conclusion
43
44. Conclusion (1)
The bottom-up design approach from Tekna built standard
thermal plasma processing units to entire production facility
allowed to address and successfully resolve all major safety
and economic issues involved with the production of
advanced nano-sized materials by:
Conceiving multiple – level barriers against Nano-Particle
spill hazard;
Minimizing the frequency of exposure to hazardous materials
through (among others) high level of process automation
including final products packaging and separate production
halls for higher hazard level materials;
44
45. Conclusion (2)
• Establishing and implementing the adequate operational
procedures;
• Cooling water cost reduction by recovery of rain / snow;
• Space heating by spent heat from plasma processing units;
• Minimizing the waste disposal costs through in-house
recycling procedures and elimination of water conditioning
chemicals (replaced by UV radiation);
• On-site, consumption regulated, production of hydrogen;
• Recycling (after conditioning) the major part of consumed
gas;
• Optimizing the production rate of each product according to
its specifics.
45
46. Acknowledgments
Institute de recherche
Tekna Plasma Systems Inc. Robert Sauvé en santé et
en sécurité du travail
• Loïc Brochu • Claude Ostiguy
• Jean-Pierre Crête
• Nicolas Dignard
• David Héraud
• François Hudon
46