Continuous Voc(Volatile Organic Compounds) Concentrators...
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1 CONTINUOUS VOC (VOLATILE ORGANIC COMPOUNDS) CONCENTRATORS BY THERMAL SWING HONEYCOMB ROTOR ADSORBENT Tsutomu Hirose, Hiroshi Okano, Kenichiro Yamada, Keimei Furuki and Yuuji Fujioka, Seibu Giken Co., Ltd., Fukuoka, Japan Introduction Photochemical smog as air pollution is caused by photochemical oxidant and suspended particle matters which are formed from a gas mixture of volatile organic compounds (VOC) and nitrogen oxides (NO x ) under the radiation of ultraviolet ray. For example in Japan, as reported by the Department of Environment in last Feburuary, 1) the warning of photochemical smog was first announced in Nagasaki and Kumamoto prefectures last year and followed by 25 prefectures to count the worst frequency in the past. Kyushu University and National Institute of Environment collaboratively have reported 2) a computer simulation taking into account the hydrodynamic flow of a air mass from the Asian Continent for the photochemical smog which happened in a wide area of west Japan on May 8 this year. The governmental regulations for the VOC emission are getting more and more severe in many countries in a worldwide movement to the environmental protection. In Japan, the air pollution control law revised in 2004 has been enforced in April 2006 and the aim is to reduce the annual emission in 2010 by 30% relative to the total emission of 1.5million tons in 2000 by a combination of the governmental regulations and voluntarily efforts of emission sites. Measures for environmental preservation are required to be accelerated in a worldwide scale since the environmental pollution is spreading across the countries’ border along with a remarkable development in economy in the South East Asia in recent years. The VOC concentrator discussed in this paper is based on a selective adsorption of VOC on porous solid and provides a technology of efficient treatment. It will play our best card for reduction of VOC effluent which has been discharged in the atmosphere because of a large amount of dilute gas. This type of the VOC concentrator has encountered some difficulties in the actual applications since VOC species and discharge conditions were changed in a wide variety depending on a type of industry. For example, VOC with low boiling point was difficult to be adsorbed and concentrated, VOC with high boiling point was easily adsorbed but hardly desorbed, and polymerizing VOC was accumulated to deteriorate the performance. However, the solution has been asked for such a hard matter very frequently along with the recent regulations and consciousness for the environmental preservation. To response the above requirements the VOC concentrator has been improved for higher efficiency by the present authors and Seibu Giken Co., Ltd. Japan. The purpose of this investigation is to describe the details of honeycomb rotor adsorbers and discuss the performance of VOC abatement to derive some general principles for design and operation of honeycomb rotor VOC concentrators. VOC Destruction System and Concentrator The combustion (oxidative decomposition) is applied the most widely among other destruction methods of VOC because of a simple system configuration, applicability to a wide range of VOC, high reliability and low investment cost. In the case of high concentration of VOC as shown in Fig. 1, the
Transcript of Continuous Voc(Volatile Organic Compounds) Concentrators...
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CONTINUOUS VOC (VOLATILE ORGANIC COMPOUNDS) CONCENTRATORS BY THERMAL SWING
HONEYCOMB ROTOR ADSORBENT
Tsutomu Hirose, Hiroshi Okano, Kenichiro Yamada, Keimei Furuki and Yuuji Fujioka, Seibu Giken Co., Ltd., Fukuoka, Japan
Introduction
Photochemical smog as air pollution is caused by photochemical oxidant and suspended particle matters which are formed from a gas mixture of volatile organic compounds (VOC) and nitrogen oxides (NOx) under the radiation of ultraviolet ray. For example in Japan, as reported by the Department of Environment in last Feburuary, 1) the warning of photochemical smog was first announced in Nagasaki and Kumamoto prefectures last year and followed by 25 prefectures to count the worst frequency in the past. Kyushu University and National Institute of Environment collaboratively have reported 2) a computer simulation taking into account the hydrodynamic flow of a air mass from the Asian Continent for the photochemical smog which happened in a wide area of west Japan on May 8 this year.
The governmental regulations for the VOC emission are getting more and more severe in many countries in a worldwide movement to the environmental protection. In Japan, the air pollution control law revised in 2004 has been enforced in April 2006 and the aim is to reduce the annual emission in 2010 by 30% relative to the total emission of 1.5million tons in 2000 by a combination of the governmental regulations and voluntarily efforts of emission sites. Measures for environmental preservation are required to be accelerated in a worldwide scale since the environmental pollution is spreading across the countries’ border along with a remarkable development in economy in the South East Asia in recent years.
The VOC concentrator discussed in this paper is based on a selective adsorption of VOC on porous solid and provides a technology of efficient treatment. It will play our best card for reduction of VOC effluent which has been discharged in the atmosphere because of a large amount of dilute gas. This type of the VOC concentrator has encountered some difficulties in the actual applications since VOC species and discharge conditions were changed in a wide variety depending on a type of industry. For example, VOC with low boiling point was difficult to be adsorbed and concentrated, VOC with high boiling point was easily adsorbed but hardly desorbed, and polymerizing VOC was accumulated to deteriorate the performance. However, the solution has been asked for such a hard matter very frequently along with the recent regulations and consciousness for the environmental preservation. To response the above requirements the VOC concentrator has been improved for higher efficiency by the present authors and Seibu Giken Co., Ltd. Japan. The purpose of this investigation is to describe the details of honeycomb rotor adsorbers and discuss the performance of VOC abatement to derive some general principles for design and operation of honeycomb rotor VOC concentrators.
VOC Destruction System and Concentrator
The combustion (oxidative decomposition) is applied the most widely among other destruction methods of VOC because of a simple system configuration, applicability to a wide range of VOC, high reliability and low investment cost. In the case of high concentration of VOC as shown in Fig. 1, the
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exhaust gas can be treated by the direct combustion very efficiently at low running cost for spontaneous combustion while in the case of low concentration some additional fuel is needed to maintain the combustion. Low concentration VOC has been discharged frequently into the atmosphere due to the above difficulties in economic treatment as well as lack of regulations. Even when the combustible destruction is recommended for reduction of low concentration VOC along with the enforcement of new regulations, it will cause another issue of additional emission of CO2 as a greenhouse gas. A combination of the conventional direct combustion for the final destruction and a new preconcentrator of VOC to reduce the load in the oxidizer will be able to destruct a large volume of low concentration VOC effluent economically with less stress on the environment. The preconcentrator is usually based on adsorption onto various porous solids and a remarkable progress in the adsorptive VOC concentrator was made by the introduction of thermal swing honeycomb rotor adsorbers in Japan in late seventies. It purifies VOCladen air by adsorption of VOC while VOCconcentrated air is recovered by desorbing VOC with a small amount of hot air. The concentrator was developed to treat a VOCladen air at a high flow rate first in application to a painting booth of the car manufacturing by fabricating fibrous active carbon paper into a honeycomb or monolith rotor. However, a range of operation was limited due to high possibility of burning down by ignition of heavy ketones like cyclohexane and isophorne. Seibu Giken Co., Ltd. Japan completed first in 1988 a fireproof honeycomb rotor concentrator with hydrophobic zeolite as adsorbent. Thus the difficulties with active carbon have been solved and the VOC concentrator has been applied widely to exhaust gas including heavy ketones and alcohols. 3)
VOC Concentrator and System Structure
An integrated flow sheet of the VOC destruction by a combination of a concentrator and an oxidizer is shown in Fig. 2. The VOC concentrator consists of a honeycomb rotor as shown in Fig. 3, a driving unit of the rotor, a sealed rotor casing, up and downstream chambers with sealed zone separators, a regenerating heater or heat exchanger and blowers.
Feed air (exhaust gas from the factory) is supplied to a process zone of the honeycomb rotor and VOC is removed by adsorption with efficiency
Fig. 1 Various methods of VOC destruction and range of application
VOC Con
centratio
n [ppm
]
Flow rate [m 3 /min] 400 800 1,200
500
1,600 2,000
Direct/Catalytic Oxidizer
Regenerative Thermal Oxidizer
Concentrator+Oxidizer
1,000
1,500
2,000
0 0
VOC Con
centratio
n [ppm
]
Flow rate [m 3 /min] 400 800 1,200
500
1,600 2,000
Direct/Catalytic Oxidizer
Regenerative Thermal Oxidizer Regenerative Thermal Oxidizer
Concentrator+Oxidizer
1,000
1,500
2,000
0 0
Fig. 2 Schematic diagram of the VOC concentrator oxidizer system
ＶＯＣs
Heat Exchanger
Honeycomb Rotor
Rotor Drive Process Zone
Process Fan
PreFilter
Desorption Fan
Heat Ex.
Concentrated VOC
Cooling Zone
Purified Air
Oxidizer
Desorption Zone
ＶＯＣs ＶＯＣs
Heat Exchanger
Honeycomb Rotor
Rotor Drive Process Zone
Process Fan
PreFilter
Desorption Fan
Heat Ex.
Concentrated VOC
Cooling Zone
Purified Air
Oxidizer
Desorption Zone
Cp0
Cp1
Feed Air
Cr0
ＶＯＣs
Heat Exchanger
Honeycomb Rotor
Rotor Drive Process Zone
Process Fan
PreFilter
Desorption Fan
Heat Ex.
Concentrated VOC
Cooling Zone
Purified Air
Oxidizer
Desorption Zone
ＶＯＣs ＶＯＣs
Heat Exchanger
Honeycomb Rotor
Rotor Drive Process Zone
Process Fan
PreFilter
Desorption Fan
Heat Ex.
Concentrated VOC
Cooling Zone
Purified Air
Oxidizer
Desorption Zone
Cp0
Cp1
Feed Air
Cr0
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higher than 95% while clean air is discharged into the atmosphere. The honeycomb rotor, which rotates by the driving motor during adsorption, moves to a regeneration zone before adsorption breakthrough takes place. Adsorbed VOC is then desorbed by hot air stream at high concentration in the regeneration zone. The honeycomb rotor rotates and moves to a cooling zone after desorption to cool the honeycomb rotor by cooling air down to a temperature under which it can adsorb VOC again. Then the honeycomb rotor moves back to the process zone to adsorb VOC again and thus exhaust gas can be treated continuously on this principle. The cooling zone works simultaneously as recovery of regeneration heat and air temperature leaving the cooling zone reaches about 100 C by heat recovery. The hot air is returned to the regeneration zone as regeneration air after heating to improve the energy utilization.
Concentrated VOC desorbed is destructed in an incinerator or oxidizer by oxidative decomposition and discharged as harmless clean air, as shown in Fig. 2. Heat of combustion in the oxidizer is utilized to preheat air supplied to the oxidizer by heat exchange and air leaving the heat exchanger is supplied again to another heat exchanger for heat recovery to the regeneration air for further energy utilization. With this system the volume of effluent to be treated in the oxidizer can be reduced down to as low as 1/10 – 1/20 and thus the oxidizer can be scaled down proportionally, resulting in a low investment cost. In addition, the VOC concentration entering the oxidizer is enriched to 1020 times to enable the spontaneous combustion, resulting in a low running cost as well. Thus, we succeeded in realizing the VOC destruction system of an energy saving type in which no additional energy is necessary except for the blower driving.
Adsorptive Honeycomb Rotor Matching with Various VOC
Seibu Giken Co., Ltd. provides 6 different types of adsorbent honeycomb rotors for the concentrator, i.e. 5 zeolite types (UZCR IV) and one active carbon type (KCPR). The zeolite honeycomb rotors are manufactured by impregnation of calcined ceramic honeycomb substrate with hydrophobic zeolite together with inorganic binder and recalcination under high temperature to tightly combine the zeolite with the substrate while the active carbon honeycomb rotor is manufactured directly from active carbon fiber paper. The detailed procedure can be found in a paper by Yamauchi et al. 4) and in patents by Kuma and Okano 5) and Kuma. 6, 7) Hydrophobic zeolite adsorbs VOC preferentially
Fig. 3 An example of an adsorbent honeycomb rotor
Table 1 Various honeycomb rotors and compatibility to VOC
Diameter:3550mm Width: 450mm
REGENERA TION ZONE
COOLING ZONE
PROCESS ZONE
1.7x3.2mm
Diameter:3550mm Width: 450mm
REGENERA TION ZONE
COOLING ZONE
PROCESS ZONE
1.7x3.2mm
Acetone
Cyclohexane
× Cyclohexanone
Ethanol
× × × × × Styrene
Xylene
Toluene
Ⅴ Ⅳ Ⅲ Ⅱ Ⅰ
KCPR (Carbon)
UZCR (Zeolite) VOC
Acetone
Cyclohexane
× Cyclohexanone
Ethanol
× × × × × Styrene
Xylene
Toluene
Ⅴ Ⅳ Ⅲ Ⅱ Ⅰ
KCPR (Carbon)
UZCR (Zeolite) VOC
：Excellent, ：Good, ：Acceptable ×：Not recommended
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with less adsorption of water vapor. Adsorbability to a particular VOC species varies depending on pore size, hydrophobicity etc. of adsorbent and by blending several different kinds of zeolite. Each rotor has its own characteristics and is selected according to circumstances in the actual use.
Some examples are shown in Figs. 4 and 5 in terms of the removal efficiency defined simply as a ratio of VOC concentration in product air Cp1 to that in the feed air Cp0. The removal efficiency decreases with increasing VOC concentration since the adsorption isotherm usually is highly nonlinear and the adsorbed amount per concentration decreases with increasing concentration. Figure 4 shows the case of isopropyl alcohol as a typical polar VOC. Type V zeolite rotor gives the best efficiency for the polar VOC. On the other hand, as shown in Fig. 5, type I zeolite rotor seems the best for toluene, a typical nonpolar VOC. Table 1 shows a guide to selection of the honeycomb rotor for several VOCs among about 50 species tested. Application examples are shown in Table 2 depending on the type of industry, but the best choice of the rotor is proposed by the manufacturer according to particular circumstances.
Performance Improvement of Adsorptive Honeycomb Rotor
Fig. 4 Removal efficiency for isopropyl alcohol Fig. 5 Removal efficiency for toluene
Isopropyl alcohol
0
20
40
60
80
100
0 200 400 600 VOC Concentration [ppm]
Rem
ova
l eff
icie
ncy
[%]
Type Ⅲ
Type Ⅴ
TypeⅠ
Isopropyl alcohol
0
20
40
60
80
100
0 200 400 600 VOC Concentration [ppm]
Rem
ova
l eff
icie
ncy
[%]
Type Ⅲ
Type Ⅴ
TypeⅠ
0
20
40
60
80
100
0 200 400 600 800 VOC Concentration [ppm]
Rem
oval
eff
icie
ncy
[%]
Toluene
Type Ⅴ
Type Ⅲ
TypeⅠ
0
20
40
60
80
100
0 200 400 600 800 VOC Concentration [ppm]
Rem
oval
eff
icie
ncy
[%]
Toluene
Type Ⅴ
Type Ⅲ
TypeⅠ
Isopropyl alcohol
0
20
40
60
80
100
0 200 400 600 VOC Concentration [ppm]
Rem
ova
l eff
icie
ncy
[%]
Type Ⅲ
Type Ⅴ
TypeⅠ
Isopropyl alcohol
0
20
40
60
80
100
0 200 400 600 VOC Concentration [ppm]
Rem
ova
l eff
icie
ncy
[%]
Type Ⅲ
Type Ⅴ
TypeⅠ
0
20
40
60
80
100
0 200 400 600 800 VOC Concentration [ppm]
Rem
oval
eff
icie
ncy
[%]
Toluene
Type Ⅴ
Type Ⅲ
TypeⅠ
0
20
40
60
80
100
0 200 400 600 800 VOC Concentration [ppm]
Rem
oval
eff
icie
ncy
[%]
Toluene
Type Ⅴ
Type Ⅲ
TypeⅠ
Alcohols, Ketones, Amines
Manufacturing process
Liquid crystal manufacturing
Alcohols, Ketones, Amines
Cleaning unit Semiconductor
Styrene, Aldehydes, Esters
Plastics & plywood manufacturing
Plastics, Adhesive
Aromatic hydrocarbones, Alcohols,Organic acids, Aldehydes,
Oil refinery, Petrochemicals
Chmicals
Ketones（MEK, Cyclohexanone, etc.）
Coating & Cleaning unit
Adhesive, Sticky tape, Magnet tape
Toluene, Xylene, Esters, Alcohols
Print process, Dryer
Printing
Toluene, Xylene,Esters, Alcohols
Paint booth, Oven
Painting, Automobiles, Appliances, Buildings, Ship Building
Treated VOCs Facilities Industry
Alcohols, Ketones, Amines
Manufacturing process
Liquid crystal manufacturing
Alcohols, Ketones, Amines
Cleaning unit Semiconductor
Styrene, Aldehydes, Esters
Plastics & plywood manufacturing
Plastics, Adhesive
Aromatic hydrocarbones, Alcohols,Organic acids, Aldehydes,
Oil refinery, Petrochemicals
Chmicals
Ketones（MEK, Cyclohexanone, etc.）
Coating & Cleaning unit
Adhesive, Sticky tape, Magnet tape
Toluene, Xylene, Esters, Alcohols
Print process, Dryer
Printing
Toluene, Xylene,Esters, Alcohols
Paint booth, Oven
Painting, Automobiles, Appliances, Buildings, Ship Building
Treated VOCs Facilities Industry
Ⅲ,Ⅴ
Ⅲ,Ⅴ
Ⅲ
Ⅱ
Ⅱ,Ⅲ
Ⅱ,Ⅰ
Ⅱ,Ⅰ Rotor
Ⅲ,Ⅴ
Ⅲ,Ⅴ
Ⅲ
Ⅱ
Ⅱ,Ⅲ
Ⅱ,Ⅰ
Ⅱ,Ⅰ Rotor
Table 2 Selection example of honeycomb rotors applied to various industries
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Many commercial units are operating at the present with the removal efficiency higher than 95% and the concentration ratio of 520 under the standard specifications of the rotor diameter of 0.33m, the rotor width of 0.40.45m, air velocity of 24m/s, temperature of regeneration air of about 180 C and coexiting humidity less than 80%. Scientific aspects of the effect of the operating conditions such as the rotation speed, air velocity etc. on the removal efficiency were discussed by Yamauchi et al. 4) .
In the course of performance improvement, the best type of zeolite for VOC concentration was developed in collaboration with zeolite manufacturers in addition to a close revision of binder, honeycomb size etc. Two types of high performance rotors have been developed; one is a high removal efficiency type and the other is a low pressure loss type. With the high removal efficiency type, as shown in Fig. 6, we succeeded in improvement in the removal efficiency over a wide range of VOC concentration even for methanol, which has been difficult to be concentrated by adsorption. The concentrator can be substituted with a honeycomb rotor of onerank smaller diameter, leading to an initial cost reduction. As shown in Fig. 7, the low pressure loss type realized to decrease the pressure loss by about 30% with keeping the same removal efficiency as the conventional one, leading to a reduction of running cost for blowers.
Reactivation System for Deteriorated Honeycomb Rotors
Exhaust gas from factories related to semiconductors and liquid crystals involves sometimes VOC of low saturated vapor pressure such as DMSO (Dimethyl sulfoxide), MEA (Methyl ethyl amine) etc. or VOC easy to polymerize. When these VOCs are processed in the concentrator incorporated with a hydrophobic zeolite rotor, they are difficult to be desorbed at the standard temperature of 180200 C and accumulated in the rotor to cause the deterioration of the removal efficiency during a long term operation for years. We arrange the following two measures for this issue, i.e. 1) Reactivation by spray washing with water and 2) High temperature reactivation. The details of the reactivation system are discussed elsewhere 8) in this 2007 AIChE Annual Meeting.
Methanol 0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0 1 2 3 4
Air velocity [m/s] P
ress
ure
drop
[kP
a]
Low pressure loss rotor
Concentration [ppm]
Rem
oval
eff
icie
ncy
[%]
0
20
40
60
80
100
0 200 400 600
Conventional rotor
High efficiency rotor
Methanol
Low pressure loss rotor
Conventional rotor High efficiency rotor
Methanol 0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0 1 2 3 4
Air velocity [m/s] P
ress
ure
drop
[kP
a]
Low pressure loss rotor
Concentration [ppm]
Rem
oval
eff
icie
ncy
[%]
0
20
40
60
80
100
0 200 400 600
Conventional rotor
High efficiency rotor
Methanol
Low pressure loss rotor
Conventional rotor High efficiency rotor Low pressure loss rotor
Conventional rotor High efficiency rotor
Fig. 6 Comparison in the removal efficiency of ethanol between the conventional and improved rotors
Fig. 7 Comparison in the pressure loss between the conventional and improved rotors
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Concluding Remarks
The EU commandment at the present claims that VOC emission should be less than 50 mg TOC/m 3 and it is getting so stringent that 20 mg TOC/m 3 be a standard level in the future. We must not be unconscious with CO2 emission due to a combustive destruction of VOC since the issue of the global warming by CO2 has been closed up recently. In such a world circumstances, we are forced to destruct efficiently a large amount of dilute VOC although a powerful technology has been unavailable and thus much dilute VOC was discharged into the atmosphere so far. The VOC concentrator discussed here is a useful tool to solve the problem and a combination with the thermal oxidizer can lead to energy saving and CO2 reduction by the VOC concentrator. In developing countries as well as developed ones, much progress is expected in the environmental measures with the VOC concentrator.
Literature Cited 1) Press release by the Department of Environment, February 9, 2007 2) National Institute of Environment, Japan, May 21, 2007 3) Okano, H., Y. Tanaka, Konbatekku (in Japanese), 98100, January 2005 4) Yamauchi, H., A. Kodama, T. Hirose, H. Okano, K. Yamada, “Performance of VOC Abatement by
Thermal Swing Honeycomb Rotor Adsorbers,” Ind. Eng. Chem. Res., 46, 43164322(2007) 5) Kuma, T., H. Okano, “Active Gas Absorbing Element and Method of Manufacturing”, United States Patent 4886769, 1989.
6) Kuma, T., “Method of Manufacturing A Gas Absorbing Element or Catalyst Carrier Having A Honeycomb Structure”, United States Patent 5194414, 1993.
7) Kuma, T., “Gas Adsorbing Element and Method for Forming Same”, United States Patent 5348922, 1994.
8) Yamada, K., K. Furuki, Y. Fujioka, H. Okano and T. Hirose, “Development of High Temperature Desorption System in the Adsorptive Concentrator for Heavy Component of VOC (Volatile Organic Compounds),” Extended Abstracts of 2007 AIChE Annual Meeting, #329L(Fundamentals and Applications of Adsorption and Ion Exchange (02E14)).
