Technology: Diesels in the Desert

Although the oceans lap at their shores, more than 18,000 miles of the world’s coastlines are virtually uninhabited because of the lack of available fresh water. Visionaries have long dreamed of using sea water to make these deserts bloom, but University of Arizona Scientist Carl Hodges is actually doing something about it. And not by means of futuristic and costly nuclear-powered desalination plants, but by efficient use of simple diesel-electric engines like those that now provide power to remote communities all over the world. A pilot project on Mexico’s Gulf of California is already accomplishing in miniature what Hodges hopes to achieve on a global scale.

With the aid of Rockefeller Foundation funds, Hodges and other scientists from the University of Arizona and from Mexico’s University of Sonora have designed and built an integrated, diesel-electric-based system that supplies electrical power, makes sea water drinkable, and contributes to lush vegetable growth near the small (pop. 5,000), arid fishing town of Puerto Penasco. Heart of the system is a 60-kw. Caterpillar diesel generator. But unlike other diesel-powered systems, in which about two-thirds of the fuel energy is wasted as heat, the Mexican installation feeds its hot exhaust gases and heated coolant water into a heat exchanger. Sea water pumped through the exchanger is heated to 160° F., and then passed into a tower evaporator. About 10% of the heated water is vaporized, condensed into pure water on the sea-water-cooled coils of an adjacent condenser tower and stored in a fresh water tank.

Fringe Benefits. Still at a temperature of 90° F., the unvaporized sea water from the evaporator tower is used to control temperature and humidity levels in nearby greenhouses. Even the exhaust gases, consisting largely of carbon dioxide, are put to work. From the heat exchanger, they are pumped through a scrubber, which rids them of harmful sulfur dioxide, and into the greenhouses, where they provide the proper level of carbon dioxide for ideal plant growth. “Like the old joke about the efficiency of meat-packing plants,” says Hodges, “we are even using the squeal of the pig by tapping every beneficial aspect of this engine.”

Puerto Penasco’s people are already receiving fringe benefits of a technology that may someday support thousands of new desert towns. In addition to moistening the greenhouse soil, the 6,000-gal. daily output of pure water is given to the local hospital and school and is bottled and sold as “Agua Solar” to help defray the plant’s operating expenses. And the cucumbers, squash, tomatoes and other vegetables produced in the greenhouses are given away free to local residents.