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Performance and Economic Improvement in Vapor Adsorbers Using Structured Activated Carbon Media
Paula S. Walmet, Ph. D., John D. Perry, Ph.D., and David A. Schaaf MeadWestvaco Corporation
2012 OWEA Annual Conference
June 20, 2012
2 Structured Activated Carbon
Agenda
1. Introduction to Atmospheric Corrosion
2. Strategies for Corrosion Prevention
3. Structured Activated Carbon Technology
4. Honeycomb vs. Pellet: Performance
5. Honeycomb vs. Pellet: Economics
Introduction to Atmospheric Corrosion
Atmospheric Corrosion 1
• Corrosion – the disintegration of an engineered material due to chemical reactions with its surroundings
• Electrolyte – Fundamental requirement for electrochemical corrosion
◦ Substance with free ions that allow electrical
conductivity
◦ Most commonly a thin film of water that forms at
critical humidity
• Critical Humidity ◦ Not a constant
◦ Depends on corroding material, tendency to
adsorb moisture, and presence of
atmospheric pollutants.
4 Structured Activated Carbon
Atmospheric Corrosion 2
• Atmospheric corrosion proceeds by balancing anodic and cathodic reactions.
• During the reaction, metal is dissolved into the electrolyte, and oxygen from the atmosphere is reduced in the solution.
• This reaction is often accelerated by the presence of contaminants in the air (e.g. H2S, SO2, Cl2)
Corroding Metal
Anodic Reaction
Cathodic Reaction
M+ M+ M+
M M+ + e-
O2 + 2H2O + 4e- 4 OH-
Electron Transfer
Oxygen from the atmosphere dissolves into the electrolyte
5 Structured Activated Carbon
Atmospheric Corrosion 3
• The miniaturization of electronic components and the increase in availability continues to make the corrosion of electronics a matter of increasing concern.
• Another challenge faced with the increasing component density and decreasing size is the measurable impact of smaller and smaller defects.
Corrosion creates bridges between the electronic connections,
destroying the computer card.
6 Structured Activated Carbon
Strategies for Corrosion Prevention
Corrosion Prevention 1
• Eliminate the root cause of the corrosive gas ◦ May require large capital expense or be invasive to the process
◦ Sometimes the result of excursions or other uncontrolled releases
◦ Potentially from widespread source or external source
• Isolate the sensitive equipment ◦ Coat all vulnerable components with barrier material
◦ Enclose all equipment in impermeable housing
◦ Relocate process to cleaner environment
• Create a protected environment ◦ Purify air in a space to reduce contaminants
◦ Pressurize a space with clean air from alternative source
◦ Pressurize a space with purified air
8 Structured Activated Carbon
Corrosion Prevention 2
A vapor adsorber may be used to purify the air that is used to pressurize a protected space.
Contaminated
Air
Purified Air
Vapor
Adsorber
HVAC Contained in Protected Room
Pressurized by Purified Air
9 Structured Activated Carbon
Structured Activated Carbon Technology
What is Activated Carbon?
Range of Products
Raw Materials
• Wood, Coal, Coconut, etc.
Activation Process
• Chemical, Thermal
Pore size depends on both raw
material + process
micropore (pore width < 20 Å)
mesopore (20 – 500 Å)
macropore (> 500 Å)
What is Activated Carbon?
Adsorption for Corrosion and Odor Control
• is the binding of molecules to a surface
• Physisorption occurs due to weak attractive interactions known as van der Waals forces
• Chemisorption is driven by a chemical reaction at the exposed surface and typically involves addition of an active chemical (e.g. carbonate, KI, oxides)
Adsorption….
Structured Carbon 1
Activated carbon can be produced in a variety of forms depending on the desired final application.
Granular carbon is the initial form derived from the activation process.
Powdered carbon is typically produced by grinding granular carbon into smaller particles.
13 Structured Activated Carbon
Structured Carbon 2
Powdered carbon can be extruded into alternative configurations to provide enhanced performance.
Pellets can provide excellent performance with lower pressure
drop than granular carbon.
Honeycombs provide a fully structured media bed.
14 Structured Activated Carbon
Structured Carbon 3
The structured activated carbon media is composed of a homogeneous structure. The composition is consistent throughout the entire structure.
The entire wall of each cell is composed of a combination of
activated carbon and ceramic binder.
The open structure in the media is critical to good mass transfer (and
performance).
2000X Magnification
Carbon
Binder
15 Structured Activated Carbon
Honeycomb vs. Pellet: Performance
Activated Carbon Product Types
Granular Powder Pellets Honeycomb
Adsorption Kinetics
Pressure Drop
Slower
Lower
Faster
Higher
Traditional Revolutionary
Fast Kinetics
Low Pressure Drop
Ease of Use
Honeycomb vs. Pellet: Performance 1
Kinetic Performance and Mass Transfer Advantage
100%
84%
50%
12%
0%
100%
23%
0%0%
20%
40%
60%
80%
100%
120%
0 3 6 9 12
Depth in Bed, inches
Co
ncen
trati
on
in
Bed
, %
of
inle
t
Pellets - 100 ft/min
HM® Media - 500 ft/min
18 Structured Activated Carbon
Honeycomb vs. Pellet: Performance 2
0.1
1
10
10 100 1000
Superficial Air Velocity, ft/min
Pre
ssu
re D
rop
, in
_H
2O
/ft_
bed
__
HM® Media
Pellet
Standard
Operating
Conditions
100 ft/min
3 in_H2O/ft_bed
500 ft/min
2 in_H2O/ft_bed
Improved Energy Efficiency – Reduced Pressure Drop
Pressure drop in honeycomb media is much lower than in traditional pellet media.
19 Structured Activated Carbon
4
1
2
3
AIR IN
AIR OUT
New module(s)
added to Stage 4
Old module(s)
discarded from Stage 1
Modules in Stages 4,
3, and 2 each move
down one stage
Honeycomb vs. Pellet: Performance 3
0%
20%
40%
60%
80%
100%
0 1 2 3 4
1 3 42
0%
20%
40%
60%
80%
100%
0 1 2 3 4
1 3 42
0%
20%
40%
60%
80%
100%
0 1 2 3 4
STAGE 1 CONSUMED -
ROTATE HONEYCOMBS
1 3 42
Mass Transfer and Cube Rotation
20 Structured Activated Carbon
Honeycomb vs. Pellet: Performance 4
Mass Transfer Advantage
The mass transfer of contaminants into the carbon
is faster and more efficient in the honeycomb media.
• Easier access to carbon
0.2 mm (honeycomb) vs. 2 mm (pellets)
• Shorter mass transfer zone at higher velocity
• Equivalent performance with 5X air flow
• Full removal of contaminants from air stream
21 Structured Activated Carbon
Honeycomb vs. Pellet: Economics
Honeycomb vs. Pellet: Economics 1
Better Energy Efficiency
The pressure drop in honeycomb media is much lower
than in traditional, loose fill media.
• Lower energy consumption at higher velocities
• Smaller beds needed for same air volume
• Lower capital cost to provide equivalent performance
• Lower energy cost to move the air.
23 Structured Activated Carbon
1000 CFM Vapor Adsorber
Pellet Versacomb™
Vapor Adsorber Cost Higher Lower
4 Year Cost Analysis
HEPA Final Filter Required Not Required
Carbon Replacement Every 3-4 years One fourth per year
Vacuum Truck Rental Required Not Required
Energy ($/kW-hr) Higher Lower
Total Cost @ yr 4 $1.5X $X
Honeycomb vs. Pellet: Economics 2
24 Structured Activated Carbon
Questions?
25 Structured Activated Carbon