GEOTHERMAL PROGRESS

But like solar energy, it will be, eventually. There are basically two sources: the "hot rock" that is everywhere, but so deep that harnessing of its energy lies in the more distant future; and the underground hot water and steam that are more easily accessible, but occur only in a few places.

Even the second, easier kind is beset with problems. At present, only the steam is being used (in California, Mexico, Italy, New Zealand and some other places) after it has been separated from the water. The hot water remains unused, and its energy, about half of the total available, goes, well, down the drain.

There are two main reasons why this is so. There are efficient steam turbines, and efficient hydraulic turbines; but to design an efficient "total flow" turbine that runs on both liquid and vapor simultaneously is as easy as governing Northern Ireland by a coalition government.

The other reason is that the hot water isn't hot water, but brine, fouled by all kinds of salts and minerals, which cause scaling tough, mineral deposits on the pipes and turbine blades; the first to get clogged, of course, is the small opening of the nozzle forming the jet for driving the turbine. Scaling is what has so far prevented the harnessing of high-salinity geothermal brine in the Salton Sea area of Southern California.

Progress on both points is reported from the Lawrence Livermore Lab., Calif., which, like its sister lab in Los Alamos, N.M., is working on the harnessing of geothermal energy. A laboratory turbine with a single "total flow" nozzle has been designed, and preliminary results indicate that a full-scale design would achieve an efficiency of at least 45%, but that more advanced designs could reach efficiencies in the 60 to 70% range, a figure in excess of that for any geothermal plant now in existence.

This assumes that the system would be capable of working with high-salinity brine. But would it?

Here, too, progress is reported. A chemical method of controlling scale has been demonstrated: Hydrochloric acid was injected into the brine. This prevented scaling in a nozzle through which brine flowed for 24 hours, whereas a control nozzle squirting non-acidified brine had its quarter-inch opening closed to nearly one-third during the same time. Similarly, a stationary simulated turbine blade experienced no scaling under the flow of acidified brine, and there was no evidence of corrosion or erosion.

The amount of hydrochloric acid required, says LLL, is modest, and would add less than 0. l cents/kWh to the operating cost of a geothermal plant.

Dr Austin, LLL geothermal program leader, is very encouraged by these tests, though, of courses there are years of work ahead before the total-flow turbine becomes commercially feasible.