Decommissioning a Carbon Nanotube CVD Reactor
1. Purpose and Scope
1.1.The purpose of this procedure is to provide EHS and mechanical guidelines for the safe decommissioning of the CVD Reactor.
1.2.The scope of this procedure is limited to the CVD Unit Reactor, which includes catalyst preheat, reaction vessel and product cooler.
2. Definitions
2.1.EHS-Environment, Health and Safety
2.2.PPE-Personal Protective Equipment
2.3.PAPR-Powered Air Purifying Respirator
2.4.HEPA-High Efficiency Particulate Air
2.5.Authorized Personnel- Affected company and contractor employees that have reviewed this procedure.
3. Referenced Documents
3.1.MSDS for Carbon Nanotubes
3.2.Drawing-CVD Unit Reaction PID # (redacted)
3.3.Drawing CVD Unit Product Cooling PID # (redacted)
3.4.CNT Safe Handling Procedure
3.5.PAPR SOP
3.6.Safety Training Presentation
4. Safety
4.1.Work areas and laydown area shall be cordoned off to prevent entry by unauthorized personnel. Signs shall be clearly posted to designate area.
4.2.NIOSH research shows that full face air purifying or powered air purifying respirators with N100 filters are expected to provide sufficient respiratory personal protection with an assigned protection factor of 50. NIOSH research also indicates that Tyvek type coveralls and impervious gloves (nitrile) are expected to provide sufficient dermal personal protection.
4.3.In the event, PPE is damaged during work activities, individual is required to change out PPE.
4.4.Required PPE when Opening Reactor Vessel and/or associated piping to atmosphere
4.4.1. P100 PAPR Full Face Respirator with hood with P100 HEPA filter.
4.4.2. Tyvek Jumpsuit, ActiveGARD 200 or equivalent
4.4.3. Nitrile Gloves
4.4.4. Engineering Controls, such as vacuum with HEPA filtration should be used to capture nanomaterials when opening process equipment to atmospheric conditions.
4.5.Required PPE when blowing down and other activities external to the referenced equipment
4.5.1. P100 Half Face Respirator for respirable and non-respirable particulates, 0.3 microns or higher
4.5.2. Long-sleeved Lab Coat or uniform shirt and pants.
4.5.3. Nitrile Gloves
4.5.4. Safety Glasses, ANSI Z87.1
4.5.5. Engineering Controls such as vacuum with HEPA filtration should be used to capture blow down materials.
4.6.Sampling and Industrial Hygiene
4.6.1. Surface sampling
4.6.1.1. Single Walled Carbon Nanotubes (SWNT) will predominantly be present in bulk or settled dust form on manufacturing and laboratory surfaces and in aerosol form as airborne agglomerates and aggregates; their length scale may range from single nanometers to micrometers. Most agglomerates will be in the 20 nm to 300 nm or larger size range. This has been confirmed by electron microscopic examination of surface wipe samples collected in the area of the CVD manufacturing unit, as well as in other laboratory and common areas sampled throughout the company occupied areas.
4.6.1.2. Previous surface sampling done in the area confirms the classification of “dirty” and “clean” surfaces based on visual appearance. It is proposed to use polyethylene or saran wipe sample media to collect a surface samples for analysis for optical microscopy followed by field emission scanning electron microscopy (SEM) or, if necessary, transmission electron microscopy with energy dispersive x-ray analysis (TEM/EDX); to differentiate amorphous carbon filaments from graphitic fibers and agglomerates.
4.6.1.3. Surface wipe sampling will be performed on visually “dirty” (based on previous sampling results) locations at the discretion of the monitoring Industrial Hygienist.
4.6.1.4. Upon discussion with client, surface samples may also be analyzed chemically by inductively coupled plasma (ICP) for components of catalyst including iron, manganese and molybdenum.
4.6.2. Aerosol sampling
4.6.2.1. Respirable dust gravimetric analysis by NIOSH method 0600 and chemical analysis for synthetic graphite by OSHA method ID 142 for comparison to the respirable dust OSHA Permissible Exposure Limit (PEL) and the synthetic graphite ACGIH Threshold Limit Value (TLV) referenced in the company’s MSDS for Carbon Nanotubes.
4.6.2.2. A limited number of air samples will also be collected on polycarbonate filters supported upon mixed cellulose ester filters for optical and electron microscope analysis to characterize and confirm particulate and agglomerate nature and morphology.
4.6.2.3. Selected air samples for respirable dust may also be chemically analyzed for components of the metallic catalyst.
4.6.2.4. Real time particle detection technology will include the Lighthouse Model 3016 IAQ optical particle counter or equivalent to measure mass concentration or gross number of particles in the in the 300 nm to 10 micron size range; with segregation into 6 bins (300 nm, 500 nm, and 1, 2.5, 5 and 10 microns.) This instrument will provide real time indications of hot spots and general size ranges, although this is not expected to be diagnostic for SWNT presence. Confounding factors include presence of ultrafine carbonaceous particles from natural gas combustion burners, and diesel engines for lift trucks, mobile cranes, etc. Careful consideration of background conditions will be selected for differential sampling.
4.6.2.5. Twelve (12) to sixteen (16) samples per shift will be taken per shift.
4.6.3. Occupational Exposure Limit (OEL) Considerations
4.6.3.1. No existing occupational exposure limits were defined specifically for SWNT in 2008.
4.6.3.2. Mass-based OELs to consider (Note: units are in milligrams per cubic meter (mg/m3))
4.6.3.2.1. Respirable synthetic graphite standards: The then current OSHA PEL was 5 mg/m3 as an 8 hr time weighted average (TWA) for the respirable fraction; the then current, i.e., 2008, ACGIH TLV was 2 mg/m3 as an 8 hr TWA for the respirable fraction; this TLV was listed as for all forms ==except==graphite fibers. Electron microscopic analysis of settled dust and deposits in the company's manufacturing and laboratory areas has shown that the SWNTs are present as particulate-like aggregates and agglomerates rather than in fiber form. This OEL is referenced in the company's Material Safety Data Sheet (MSDS). The basis for the ACGIH TLV is to protect against pneumoconiosis.
4.6.3.2.2. Brunauer-Emmet-Teller (BET) analysis of surface area and porosity of bulk SWNT material may be helpful for placing potential surface area related effects in context.
5. General Equipment Preparation
5.1.Follow all Safety Guidelines as defined in section 4 of this document.
5.2.Blow Nitrogen (Redacted) through CVD Unit to baghouse while running vacuum pump
5.3.Disconnect / block all utilities – air, nitrogen, cooling water
5.4.Disconnect / tag-out all electrical power to unit
5.5.Remove insulation blankets from furnaces
5.6.Disconnect all lines at the top that can be broken and capped (flare/vent, bleeds, pressure taps, etc.)
5.7.Cut 3” crossover, 1-1/2” flare, 1-1/4” product line
5.8.A vacuum with HEPA will be used during cutting to capture residual nano materials.
5.9.Disconnect all wires (power, instrument) by cutting.
6. Catalyst Pre Heat Bottom Disassembly
6.1.Follow all Safety Guidelines as defined in section 4 of this document.
6.2.Verify 1-1/4” valve (Redacted) is closed
6.3.Break Swagelok, 1” catalyst feed line and cap-off
6.4.Break and cap all 1/4” tube lines
7. Reaction Vessel Bottom Disassembly
7.1.Follow all Safety Guidelines as defined in section 4 of this document.
7.2.Reaction Vessel will be lifted on the support hangers
7.2.1. Disconnect and cap all ¼” lines
7.3.Reaction Vessel will be raised on the support hangers
7.3.1. The 8” slide valve between Reaction Vessel & Product Cooler will be closed and the actuator removed.
7.3.2. Separate Reaction Vessel and Product Cooler below the slide valve and install a blind flange on the inlet of Product Cooler.
7.3.3. The 6” slide valve on the outlet of Product Cooler will be closed and the actuator removed.
7.3.4. Note: If no product is found during the 8” blind installation, PPE requirements as outlined in Section 4.5 of this document may be followed.
7.3.5. If product is found, PPE requirements as outlined in Section 4.4 of this document, must be followed.
8. Product Cooler Disassembly
8.1. Product Cooler will be separated from feed hopper from Reaction Vessel and a 6” blind flange will be installed on the Inlet of feed hopper.
8.2.The air inlet valve to feed hopper will be closed and the handle removed.
8.3.The 3” product line will be broken at the mechanical joints where it can be best handled. Plastic caps with clamps will be installed over each end.
9. Waste Disposal
9.1.All protective suits, gloves, wipes, etc. will be bagged and given to company to be placed in their established waste stream for appropriate disposal.
9.2.All SWNT contaminated equipment shall be wrapped in polyethylene plastic (shrink wrap) prior to movement to laydown area. The laydown are will be used as a holding area for disposition of the scrap materials prior to disposal. Owner of manufacturing equipment assumes responsibility for the proper disposal of the materials.
9.3.Equipment will be later dispositioned as scrap and therefore decontamination of individual components are not required.