Adsorption and absorption play a big role in reducing air pollution in many applications around the world. Studies show that the largest single use of absorbers this year will be to capture SO2 from power-plant flue gas. Adsorbers will be used by many chemical process industries (CPI) to capture volatile organic compounds (VOCs) and odors. A small, but fast growing industrial segment uses ozone and oxidants in combination with absorbers.
In 2012, industrial plants are expected to spend around $2.9 billion for absorbers to capture acid gases and $1.2 billion for adsorbers to capture VOCs. Power plants will spend $7.8 billion for absorbers to remove SO2 and HCl. They will also spend $500 million for adsorption systems to capture mercury (Table 1).
A new technology is developing to convert oxides of nitrogen (NOx) to NO2 and then absorb it. This will add another $150 million in sales bringing total absorption/adsorption spending to over $12 billion this year.
| Table 1. Absorber/adsorber revenues 2012 $ millions | |||
| Technology | Industrial | Power | Total |
| Absorption | 2,886 | 7,847 | 10,733 |
| Adsorption | 1,208 | 500 | 1,708 |
| Ozone/ oxidation | 100 | 50 | 150 |
| Total | 4,194 | 8,397 | 12,591 |
Industrial absorption
Absorbers are used in many segments of the CPI and other industries. The chemical industry uses absorbers to capture acid gases, such as hydrogen chloride and sulfur dioxide, which are released in various processing steps. The plating industry uses absorbers to capture the fumes from the plating tanks. The food industry eliminates odorous emissions with absorbers. Other major purchasers are pulp mills, mines, steel mills and waste-to-energy plants. Since more plants in these industries are being built in East Asia than elsewhere, it is not surprising that this one region will account for 36% of the purchases this year (Table 2).
| Table 2. Industrial absorption revenues, $ Millions | |
| World Region | 2012 |
| World total | 2,886 |
| Africa | 110 |
| CIS | 73 |
| East Asia | 1,046 |
| Eastern Europe | 111 |
| Middle East | 106 |
| NAFTA | 550 |
| South & Central America | 210 |
| West Asia | 190 |
| Western Europe | 487 |
One of the biggest surprises in the absorption market is the sudden appearance of the shipping industry as a major user. There are over 100,000 large ships roaming the world’s oceans and inland lakes. Many use what is called bunker fuel, which can contain up to 4% sulfur. This industry emits 12 million ton/yr of SO2. New regulations endorsed by many countries will prevent ships from entering ports if they are not either absorbing the SO2, or using low-sulfur fuels. The economics dictate the purchase of absorbers using seawater as the scrubbing liquor.
Adsorption
Activated carbon is the workhorse of the adsorption industry. It is used in the granular form as well as a powder. It is also impregnated onto filter media. Activated carbon is used to remove VOCs generated in the coating of products, printing, chemical processing and many other industrial applications. It is also used to purify recirculating indoor air in residential and commercial buildings. However, the revenues in this sector are not included in this analysis, which only focuses on industrial stack-gas adsorbers (Table 3).
| Table 3. Industrial Adsorption Revenues, $ Millions | |
| World Region | 2012 |
| Total | 1,208 |
| Africa | 38 |
| CIS | 44 |
| East Asia | 430 |
| Eastern Europe | 36 |
| Middle East | 45 |
| NAFTA | 235 |
| South & Central America | 82 |
| West Asia | 73 |
| Western Europe | 221 |
The growth of the manufacturing base in East Asia has created a market for activated carbon that is larger than that in any other region.
Mercury removal. Power plants are also turning to adsorption. Activated carbon and other adsorbents are being used to capture mercury. New regulations in the U.S. are forcing power plants to reduce mercury by 90%. The injection of activated carbon is the route many operators will take. The carbon requirements for this application are huge. In the U.S., it is likely that the purchases by power plants for mercury removal will exceed all other environmental purchases (for both air and water). This will effectively double the market for activated carbon in the U.S.
New developments. There are a number of new developments in adsorption technology. It has been found that impregnating activated carbon with bromine enhances mercury capture. The added cost of impregnation is more than offset with the reduction in consumption.
One of the problems with activated carbon is that it ends up with the flyash, much of which is sold to be used in cement. The carbon, however, decreases cement strength. A solution for this has been the development of “cement friendly” activated carbons. Albemarle (Baton Rouge, La.; www.albemarle.com) is a major supplier of the cement friendly version. Several companies have developed alternatives to activated carbon that are also cement friendly. The economics and efficiency of these alternatives are still under examination.
Activated carbon is also competing with absorption. Bromine can be added to the coal. This converts insoluble elemental mercury into a soluble oxidized compound. The oxidized mercury is then absorbed along with the SO2. About half the plants in the U.S. will take this approach rather than use activated carbon.
Power plant absorption
The biggest use for absorption technology is in power plants (Table 4). Coal-fired generators around the world generate 60 million tons of SO2. About 30 million tons are captured by absorption. The remaining 30 million tons are discharged to the atmosphere, where the most serious effect is to react with ammonia and calcium in the air to form submicron sulfate particles. These fine particles are very damaging to human health.
| Table 4. Power Plant absorber revenues, $ millions | |||
| World Region | 2012 | World Region | 2012 |
| Total | 7,847 | Middle East | 108 |
| Africa | 77 | NAFTA | 1,854 |
| CIS | 0.00 | South & Central America | 37 |
| East Asia | 4,742 | West Asia | 88 |
| Eastern Europe | 319 | Western Europe | 618 |
There has been continuous progress to make these absorbers more efficient and cost effective. Most use either the spray-tower or tray-tower design. The improvements have been in the two following areas:
• Higher efficiency due to better flow patterns
• Less scaling due to better chemistry control
Ozone and oxidation
A small but rapidly growing market segment involves the use of ozone or oxidation chemicals to convert NOx to NO2. The conversion results in a soluble compound that can be captured by an absorber. This same approach can be utilized to deal with odors and organic compounds.
Ozone can be effective in several ways. Here are some of the ways it reacts:
NO + O3= NO2 + O2 (1)
This is a favorable reaction because NO2 can be absorbed.
VOCs + O3= CO2 + H2O (2)
This is a favorable reaction because it eliminates the VOCs.
H2S + O3 = SO2 + H2O (3)
This is good for odor reduction.
Hg + O3 = HgO + O2 (4)
This is very good because it renders the mercury soluble so that it can be captured in the scrubber.
BOC, which is now part of The Linde Group (Munich, Germany; www.linde.com) patented a system to combine the ozone generator with a scrubber that would absorb the soluble NO2 created by the NOx reaction with ozone. This system was licensed to DuPont (Wilmington, Del.; www.dupont.com), which has sold a number of systems for petroleum refineries.
Another approach is to use hydrogen peroxide instead of ozone. Some breakthroughs by the URS Corp. (San Francisco, Calif.; www.urscorp.com) and FMC Corp. (Philadelphia, Pa.; www.fmc.com) partnership have resulted in efficient removal of the NO2 in downstream scrubbers where there is a high sulfite content in the scrubbing liquor. Inhibited oxidation lime systems have high sulfite levels. This technology is cost effective for smaller, older utilities.
One of the biggest applications for ozone technology is lift stations, which are used to elevate sewage for further gravity flow to a sewage treatment plant. There are other odor emission points in the treatment process that can be ducted to small units or to a combined large unit
Ozone can be used to reduce both H2S and NH3. The wet scrubber approach using ozone has been compared to biofilters with a pilot plant installed by Xylem Wedeco GmbH at a municipal plant in Osnabrueck, Germany. Results were reported by A Reid, J. Mielcke and M. Kampmann of Wedeco at the IOA World Congress in Strasbourg in 2005.
During the testing of the pilot scrubber with ozone versus the existing biofilter, the biofilter achieved an 82% ammonia reduction, while the scrubber with ozone achieved an efficiency of 98%. The reduction in H2S was also superior in the wet pilot unit. This leads to the conclusion that the wet scrubber with ozone should be selected when anticipated odor levels are high or emission limits are low. Since there is a very low odor threshold (0.002–0.15 ppm) for H2S and a 5 ppm threshold for ammonia, high reduction levels are often required.
The estimated cost of the scrubbers is higher at €0.70 compared to €0.55 per 1,000 m3. But the cost is not prohibitive and the efficiency is necessary in many cases.
Edited by Dorothy Lozowski
Author
Robert McIlvaine has been producing market information reports for the environmental, energy, contamination control and process industries for over 30 years. Visit his website at: www.mcilvainecompany.com for more information.