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| A physicist says he can clean the air the same way you get dirt
off your car--by washing it. Windmills have their Don Quixotes; convection towers have their Mel Prueitts. The Los Alamos National Laboratory guest physicist has designed a special structure that he's convinced can reduce air pollution by actually bathing the air. Prueitt says that about 100 units of his patented design, each the size of a 60-story skyscraper and costing about $10 million, could clean half the air in a place like Los Angeles, where it rarely rains between spring and fall. In Southern California, for instance, these 200-meter-high towers--made of steel masts with Teflon-coated fiberglass stretched around the frames like 150-meter-wide lamp shades--would be deployed around Los Angeles, Orange, Riverside, and San Bernardino counties like rooks on a chessboard, taking in smoggy air at the top, washing it with pumped-in seawater, then blowing a breeze of clean, cool air out their fluted skirts so softly it would be difficult to fly a kite near the bottom. The towers work on the principle of convection, harnessing the phase-change energy associated with re-humidifying dry air. Basically, during the cosmic rinse cycle, dry, dirty air is drawn into the towers and moistened by a mist spraying from a grid at the top. As the dampened and cooled air falls to the bottom, the particles of pollution are attracted to the water droplets, and cleansing occurs. At the bottom, the water is treated to restore it to normal salinity, then returned to its source. All this air circulation creates enough wind to form a draft, which pulls ever more dirty air in its wake. There's another benefit: free electricity. The wind in the tower turns turbines at ground level, which generate the energy to draw the water, with several megawatts of surplus electricity left over. "We'd be doing the same thing that nature does," Prueitt says. "All pollution sooner or later gets rained out of the air and ends up in the ocean. We short-circuit the process. We pick up pollution [in the towers] and put it in the ocean quicker, so people don't have to breathe it." Dumping polluted water into the sea, however, is sure to raise a few eyebrows. Some critics see this as just another scheme to sweep pollution under a different rug. David Hamilton, an architect with Verge Studios in Atlanta, incants the environmentalists' mantra: "This sounds like another techno-fix for a serious environmental problem. We cannot avoid the consequences of our actions by simply inventing a technology to make them go away. The answers are not 200-meter 'lamp shades,' but conservation and new nonpolluting technologies." Others agree that the emphasis should be on addressing prevention of air pollution rather than on treating air soiled by bad habits; electric automobiles are a favorite suggestion. Indeed, one could finance a fleet of 50,000 $20,000 electric cars for the $1 billion sticker price on 100 towers. To be fair, Prueitt does not promote his megastructures as a panacea for pollution. He has merely taken the convection tower concept--which originated as a power-generation facility only--and moved it into the realm of smog clouds in order to clean some of the air while the power gets generated. Most of the air around us could use the bath. A study last year by the Natural Resources Defense Council estimated that nationwide, the effects of smog cause 64,000 premature deaths annually, 8,800 in Southern California alone--170 people a week. The idea of using convection towers to clean the air while generating power originated with scientist Phillip Carlson in the mid-Seventies. At Lockheed Corporation at the time, Carlson proposed building towers in the desert, driving the convection process with seawater to cool the air. Carlson's concept has recently gained attention at Technion, the Israel Institute of Technology, where professor Dan Zaslavsky has demonstrated the economic feasibility of convection towers. He wants to erect a single huge 'energy tower' over a half-mile high in the Israeli desert, drawing water from the nearby Red Sea. Zaslavsky's tower, an airtight cylinder using sheet metal to cover a lattice shell 1,000 meters tall by 500 meters wide, would cost more than $1 billion and generate 500 megawatts of power a year. Construction of a pilot plant is to begin soon. Prueitt's towers are significantly smaller, but a Bunyanesque lamp shade would surely dominate the mood of any neighborhood. "There will no doubt be protests from the areas where the towers are to be built," says Charles Lave, professor of economics at the University of California, Irvine. "I tend to like engineering solutions because it's a lot easier to reduce the consequences of people's behavior than to change the behavior itself." Lave points out that when it comes to energy conservation and improving air quality, consciousness-raising campaigns aimed at getting people to drive less have failed, whereas engineering solutions such as emission controls on cars and increased fuel efficiency have succeeded. While sympathetic to the idea, Lave asks, "what community would want these giant structures blocking views and creating shadows?" At least one expert thinks the visual assault may be good for us. "We're in an era where we seem to distrust technology," maintains Steven Moore, professor of architecture at Texas A&M. "We've been scarred. We discovered technology isn't all it's cracked up to be. There have been too many serious unintended consequences of technology, an example being atomic power. Simultaneously, technology has become increasingly invisible, [and] what seems to be happening is that society has lost its sense of cause and effect. We no longer want to see the things that make our lives easy. We're in a kind of a bind. We want electricity, we want computerization, we want all that, but we want it masked and out of the way. It's that attitude that does us the most damage, because it masks the conditions of our lives." So, while Prueitt's proposal may be radical, Moore is "receptive" because, he says, it would "make the conditions of our lives powerfully present in the landscape. The message that we need to take such action to clean the air and generate power is something that you could no longer avoid." Even if people could be persuaded to trade an aesthetic jolt for an endless breeze of clean, cool air, where could the towers be sited? These structures have expansive footprints requiring real estate not readily available in densely populated urban areas like Southern California. Prueitt suggests dual use for the land, when necessary, erecting the towers above existing development. He envisions the towers hovering silently, almost cloud-like, above golf courses, parks, playgrounds, shopping malls, schools, and apartment complexes, with parking spread out under the outer skirts. In addition, light, cascading easily through the pellucid tower skin, could provide illumination while shielding those below from ever more harmful ultraviolet rays. Despite concerns, many architects and planners are intrigued by the possibilities of Prueitt's concept. "My initial reaction is one of great enthusiasm," says Willie Miller, an architect at UrbanDesign+Planning in Glasgow. "They would seem to represent a tremendous opportunity to give visual strength and form to a city's skyline. I see them at major entrances to cities, almost like defensive towers, defining routes, giving clarity to urban form--great silver-gray structures, translucent if possible, lit from within." Alison Promin, an architect at Paradigm Affiliates in Denver, can see these utilitarian forms becoming more subtly integrated into the cityscapes--and our psyches. "If there is something that is environmentally helpful that we can treat in an architectural fashion, I don't see why we can't make this thing work," she says. "In urban places where space is tight, suppose all of a sudden I take one of these towers and provide a vertical park with it, a vertical staircase where we actually install platforms and viewing decks, so that instead of just moving around the tower and looking at it, there's a way to make the infrastructure useful and engaging." The point is not to disguise--or exalt--these necessary mechanical systems, but simply to embrace them as organic additions to our architectural landscape. Prueitt's towers seem to generate more discussion than seed money. "Investors generally want to see demonstration projects erected before they commit to financing a full-size version," Prueitt says. "Trouble is, output does not scale linearly with size. A 100-meter tower is not cost effective for producing power, although it could be useful to reduce pollution. The efficiency of a 10-meter tower is actually negative, since it cannot produce enough power to pump the water to the top." If the convection tower idea ever finds financial backing and political blessing, it would be the fulfillment of the scientific dream of harnessing the energy found in natural weather patterns in a controlled environment. Convection in nature occurs when sunlight near the equator warms ocean water, causing evaporation. This warm, moist air rises, condensing into clouds, which then disperse their moisture as rain. The remaining dry air continues to rise into the stratosphere, circulating 30 degrees north and south of the equator in patterns called Hadley cells. When this flow of dry air eventually descends, compression warms it--creating the arid desert bands of the world between 15 and 35 degrees north and south latitude. For generations, scientists have looked for a way to harness the energy associated with re-humidifying dry air. Prueitt may have found it. "Raindrops are not very efficient in scrubbing the air," he explains. "Since [the drops] are so large, most of the particulate matter in the air simply flows around the falling drops. By spraying a fine mist of water, the effective surface area of a given mass of water is greatly increased, and the collection efficiency of the water is considerably enhanced. To make the system even more effective in scavenging particulates, water droplets can be given an electrical charge, which can increase the collection efficiency by a factor of 100." One million gallons of water per day, or more, would be required by the grid of sprayers across the top of each tower. In Los Angeles, the water would come from the ocean; in other cities, the water supply might be a river or lake. Wind turbines at the base of each tower would be driven by the turbulence of circulating air. When attached to electric generators, they could produce nine mega-watts of electricity, enough to power not only the tower's own pumps, but, under the right conditions, feed six megawatts of excess power into the region's electric grid. "Power production depends on weather conditions," Prueitt says. "For example, at 15 percent relative humidity, the towers would produce about six megawatts net of electric power each." The excess power from 100 towers (600 megawatts) could supply approximately 430,000 homes with electricity, further reducing air pollution by decreasing reliance on fossil-burning power plants. Prueitt cautions, however, that "as the ambient humidity goes up, the power output decreases." (Still, the variability in power output would affect only the amount of surplus energy; the towers would always power their own pumps.) In Los Angeles, humidity is higher in the morning and lower in the afternoon; the average annual afternoon relative humidity in Los Angeles is 53 percent. By admission of the city's own Air Quality Management District, Los Angeles also has the worst air in the country. Clearly, we need to do something, but is Mel Prueitt tilting at convection towers? They're as expensive as they are expansive, but perhaps it's time to reexamine paradigms. Here's a technology that can mitigate some of the mess we've made, with an advantageous by-product to boot. Who knows? Someday we may even wax poetic about these monumental pragmatic forms, just as we do now about old wooden water towers, grain elevators, and other relics of our industrial past. DOUGLAS PAGE writes about emerging technologies from Redondo Beach, California. |
Keywords:
Los Alamos National Laboratory, air pollution, convection towers