Harnessing the heat of Hades

Press, 12 November 1977, Page 16

Harnessing the heat of Hades

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PHYLLIS KERR

Back in 1953 the Geographic Board recommended the name “Kawerau” for the projected mill town in the Bay of Plenty, and a large strip of land stretching from the Rotorua-Whakatane highway, near Te Teko, to Mount Tarawera. Mount Edgecombe, rising to 2946 feet, dominates the area. Vid the Tarawera River through its centre. Scrub-clothed pumice supported, m the 19305, a population of rabbits, deer, and wild horses; now the area has become the site of a vast enterprise, the Tasman Pulp and Paper Mill, which spills out pulp and paper, timber and chips, to the markets of New Zealand, Australia, Japan, and China.

A literal translation of the word “Kawerau” is “countless carriers,” and so it is particularly suitable for the newsprint industry. The Maoris now living there are happy with the name, for some of them are descended from members of the Tini-o-Kawe-rau tribe. which sailed from the legendary Hawaiiki in the fourteenth

centry. In the Bay of Plenty they found the Onepu Springs, and probably stayed there for the convenience of its hot waters and bubbling pools offered. Traces of that settlement can still be seen on the hills opposite the springs. I drove along the road out of the town of Kawerau and passed the huge Tasman mill. Geysers of steam, capped and free, clouded the hills and valleys to my left. They rose from those same Onepu Springs, now called the Kawerau Geothermal Field. Its amazing potential w’as hidden from the understanding of its first inhabitants.

Behind a rake of trucks on the railway line, near the road, a capped bore sits. “That’s Bore 21,” they told me. “And what power there is below it.” Drilled in 1975, it proved to be one of the highest-producing bores in the world; it is said to be capable of producing sufficient steam to generate enough electricity for the needs of a city of 25,000 people. I was filled with awe by

nature’s power, seemingly unlimited, in this geothermal field, which lies within the volcanic belt of the North Island, stretching 150 miles north-east in direction from the volcanoes of Ruapehu and Ngauruhoe to the volcanic White Island in the Bay of Plenty.

In these days of expen-

sive electricity production, and when it is realised there can be an end to fossil fuels, it is vitally necessary for governments to search for other sources of power. “Hades’ heat,” where it can be found and harnessed, could supply a large area with its needed power. Geologists say that, because of the "mechanisms associated with the movements of continents,” the near-surface layers of the earth’s crust are much hotter in some regions than in others. If this were not so there might be hot springs, volcanoes and earthquakes everywhere

(or indeed, nowhere). One such region, of which New Zealand is a part, is the margin of the Pacific, including Indonesia, the Philippine Islands, Japan, Kamchatka, Alaska, California, and Mexico. The origin of geothermal steam and its movement to the earth’s surface has been studied over many

years by geophysicists in these and various other parts of the world. The generally accepted theory presupposes a hot interior of the earth where temperatures may reach 4000 degrees, and which is overlain by impervious strata heated by the hot central mass. Rainwater percolates slowly down through the earth to the impervious layer, where it spreads out, and at the same time becomes heated to high temperatures. Reduced in density there, it rises again towards the earth’s surface, finding its way through cracks and faults in the

rock structure. Where the steam breaks through the surface the boiling pools, geysers, and bubbling mud of the thermal areas are formed. These indications that a geothermal steam supply lies below are the best starting points for productive drilling. All successful bores in the world were

drilled within half-a-mile of such springs; but this theory no longer obtains, and they told me that the Geyser field in California is the best present example of the gradual extension of productive drilling to many miles away from hot springs.

In the Kawerau field the drilling is to depths of 2000, 3000, and 4000 feet, and penetrates a porous pumice overlay, or sponge — the resevoir for the hot water — through which it moves with relative ease. Above the sponge are siltstone and volcanic rocks, impermeable except for a few cracks, and holding the pressure as does a lid on a boiling pot. When a bore is drilled through that cap rock and into the sponge, the water has an easy escape to the surface. On its way up the bore the pressure is released, and some water turns to steam. The amount of steam and water discharged depends on how quickly the discharged water is replaced by more hot water, and on the permeability of the sponge. Though in many cases the production of steam is associated with other geological features, a bore •drilled near or in a fault is most likely to be a good producer. The job of the geologist is to locate those faults, and that of the driller to get to them. The equipment and techniques used in drilling for steam are similar to those used in oil-well drilling. The story of Tasman is based on the potential of the Kawerau field, for in 1951 the D.S.I.R. was commissioned “to investigate thermal areas in the vicinity of the Kaingaroa State Forest.” The scientists hoped to find a good source of geothermal steam to be used for heating and power generation in the planned pulp and paper mill; large savings were to be made by the use of a supply of cheap energy.

It was from the giant Kaingaroa Forest that the Government, in 1952, offered a permanent annual supply of logs to “an enterprise that could establish a newsprint industry.” The first of nine wells was sunk to prove the Kawerau geothermal area; and the Tasman Pulp and Paper Company was born, to be unique in the world in its use of steam from a geothermal field in those

industries which use forests as their raw material.

The conventional plant used in the mill to generate steam burns black liquor and hog fuel with coal and oil. A second source of power is a group of bores owned by the companj' and producing wet, saturated steam. Tasman first used this latter in the mill’s wood-room; but since 1957 many of its multifarious purposes have been powered by the natural energy. As well, some electricity has been generated.

New Zealand is leading the world in the use of geothermal power for direct industrial purposes. Trials continue, under and above ground, to cover all aspects of steam recovery, and its use and reliability in the industry.

Bores are generally given a trial period of at least three years, to test their long-term performance; one drilled in 1956 is still one of the best producers. Because of the corrosive action of steam in the presence of oxygen, either from the air or from ordinary water, it has been found that equipment has to be made of stainless steel, with fibreglass or asbestos for insulation.

The reports of engineers who are constantly’ working in the field and in the mill are far too complex for a mere layman to understand; suffice it to say that, as an earnest of their ability, their opinions are sought world wide. Last year one was invited to address a seminar of world energy experts in the United States; and visiting earth scientists and energy experts do not omit Tasman, the pioneer, from their itinerary.

Though the D.S.I.R. at Wairakei first showed that it is possible to pipe steam and water together, it was a Tasman engineer who put the discovery to practical use. He separated the steam and the water at the mill rather than at the well-head; a “two-phase flow,” they call it. This was the first time in the world that such a thing had been done on a production bore, and it is estimated that 10 to 15 per cent more steam and 90 per cent more heat can be gained by this mill-site separation.

The experts say that on the completion of the present planning programme, of which Bore 21 is a part, geothermal energy will reduce Tasman’s purchasedfuel costs for steam about 70 per cent, or $3.2M a year. At that stage the company’s total investment in the development of geothermal energy since its beginning, including bores, pipe-lines, silencers, and equipment to use the steam, will be about SSM. Many years ago, legislation was passed to provide

for the payment of royalties. for the use of geothermal steam, as is done for other natural resources, A Government advisory committee recently decided that a more realistic royalty should be charged for Tasman’s use of the powerful Bore 21, and of future bores. It has been suggested that in the “energy crisis,” the charge should be pegged to the price of oil;

but consideration will be given to the cost of switching from oil to geothermal energy, and to the fact that the only reason for the mill’s being sited near those bubbling Onepu Springs was the availability of cheap energy. Similar decisions are made round the world, for Tasman and Wairakei are not alone in the exploitation of geothermal steam. The Italians generate elec-

tricity, and a station is in operation at the Geysers in California. A great deal of domestic heating is done by natural steam in Iceland, and production bores have been drilled in Japan, Russia, Mexico, El Salvador, and in other countries with a similar natural energy potential. “Hades’ Heat” continues to assume more and more importance throughout the world. In New Zealand,

Tasman’s mill in the greatest exporter of manufactured goods in the country; and even without its world-class bore, uses an enormous amount of geothermal steam in holding its place in the “export drive.” But Tasman still awaits its huge additional supply; Bore 21 remains capped, and its silencers are silent behind the railway tracks in Kawerau.