Performance and Economic Improvement in Vapor Adsorbers Using Structured Activated Carbon Media

Transcription

1 Performance and Economic Improvement in Vapor Adsorbers Using 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 Agenda 1. Introduction to Atmospheric Corrosion 2. Strategies for Corrosion Prevention 3. Technology 4. Honeycomb vs. Pellet: Performance 5. Honeycomb vs. Pellet: Economics 2

3 Introduction to Atmospheric Corrosion

4 Atmospheric Corrosion 1 Corrosion the disintegration of an engineered material due to chemical reactions with its surroundings Critical Humidity Not a constant Depends on corroding material, tendency to adsorb moisture, and presence of atmospheric pollutants. 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 4

5 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. H 2 S, SO 2, Cl 2 ) Oxygen from the atmosphere dissolves into the electrolyte M + M + M + Cathodic Reaction O 2 + 2H 2 O + 4e - 4 OH - Anodic Reaction M M + + e - Electron Transfer Corroding Metal 5

6 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

7 Strategies for Corrosion Prevention

8 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

9 Corrosion Prevention 2 A vapor adsorber may be used to purify the air that is used to pressurize a protected space. Purified Air Contaminated Air Vapor Adsorber HVAC Contained in Protected Room Pressurized by Purified Air 9

10 Structured Activated Carbon Technology

11 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 ( Å) macropore (> 500 Å)

12 What is Activated Carbon? Adsorption for Corrosion and Odor Control Adsorption. 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)

13 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

14 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

15 Structured Carbon 3 The structured activated carbon media is composed of a homogeneous structure. The composition is consistent throughout the entire structure. Carbon Binder The entire wall of each cell is composed of a combination of activated carbon and ceramic binder. 2000X Magnification The open structure in the media is critical to good mass transfer (and performance). 15

16 Honeycomb vs. Pellet: Performance

17 Activated Carbon Product Types Traditional Revolutionary Powder Granular Pellets Honeycomb Faster Higher Adsorption Kinetics Pressure Drop Slower Lower Fast Kinetics Low Pressure Drop Ease of Use

18 Concentration in Bed, % of inlet Honeycomb vs. Pellet: Performance 1 Kinetic Performance and Mass Transfer Advantage 120% 100% 100% 100% 84% Pellets ft/min HM Media ft/min 80% 60% 50% 40% 20% 23% 12% 0% 0% 0% Depth in Bed, inches 18

19 Pressure Drop, in_h 2 O/ft_bed Honeycomb vs. Pellet: Performance 2 Improved Energy Efficiency Reduced Pressure Drop ft/min 3 in_h 2 O/ft_bed Standard Operating Conditions 500 ft/min 2 in_h 2 O/ft_bed HM Media Pellet Superficial Air Velocity, ft/min Pressure drop in honeycomb media is much lower than in traditional pellet media. 19

20 Honeycomb vs. Pellet: Performance 3 100% 80% 60% 40% 20% 0% 100% % 60% 40% 20% % 100% % 60% 40% Mass Transfer and Cube Rotation STAGE 1 CONSUMED - ROTATE HONEYCOMBS Modules in Stages 4, 3, and 2 each move down one stage AIR OUT New module(s) added to Stage 4 20% 0% AIR IN Old module(s) discarded from Stage 1 20

21 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

22 Honeycomb vs. Pellet: Economics

23 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

24 Honeycomb vs. Pellet: Economics 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 yr 4 $1.5X $X 24

25 Questions? 25