Tapping the Earth’s Energy
BY AWAKE! WRITER IN THE PHILIPPINES
Beneath the surface of the earth lies a huge treasure. It is not gold, silver, or precious stones. Rather, it is a tremendous store of heat called geothermal energy.
MUCH of this heat is stored in underground layers of molten rock, or magma. The earth’s heat is indeed a treasure because it is a clean source of energy that offers distinct advantages over oil, coal, natural gas, and nuclear power.
The temperatures deep inside the earth are in the order of hundreds and even thousands of degrees Fahrenheit. The amount of heat conducted to the earth’s surface from this interior in one year is thought to equal some 100 billion megawatt hours of energy—many times the electrical power used worldwide. An astounding amount of energy indeed! Harnessing this treasure, though, is a challenge.
Accessing the Treasure
A certain amount of earth’s heat is present in the ground, even near the surface. This can be tapped using heat pumps connected to loops of piping buried in the ground. The energy thus gathered can be used to heat homes in the wintertime or perform other useful work. Moreover, people living near hot springs or other geologically active areas have been able to use the available heat from the earth in additional ways. The ancient Romans, for example, used hot springs for baths.
The greater concentration of heat lies under the earth’s crust, in a layer called the mantle. The average thickness of the crust is about 20 miles [35 km]—much deeper than the drilling capacity of present technology. This crust, however, is made up of a number of plates and is thinner at certain places, especially where the plates meet. At these locations the magma is able to rise closer to the earth’s surface and heat the water trapped in rock layers. This water is usually only one or two miles [2 to 3 km] below the surface of the ground, well within the reach of modern drilling techniques. It can be mined and put to good use. Let us see how.
Putting the Heat to Work
At sea level, water boils at 212 degrees Fahrenheit [100°C]. But underground, pressures are much higher, and water remains liquid at higher temperatures.* Where the drilling taps into water that is above 350 degrees [175°C], the water can be used to drive electrical generators.
Water at high temperatures is usually found in areas of recent volcanic activity, such as the Pacific Ring of Fire, a region of both active and dormant volcanoes in the Pacific area. The country of the Philippines is located in this ring. And in recent years significant progress has been made here in tapping geothermal resources for the production of electricity. In fact, the Philippines has become one of the world’s largest producers of power from geothermal energy. Over 20 percent of all electricity used in the country comes from this source.
To learn more about how electricity is produced from the earth’s heat, Awake! visited a large geothermal facility called Mak-Ban, in the Philippine province of Laguna. This installation has the capacity to generate 426 megawatts of power. Let’s take a brief look at how this is done.
A Visit to a Geothermal Plant
After we leave the main highway, a two-lane road leads us to a geothermal field. Approaching the plant located on this field, we come into an area laced with big steam pipes going from the geothermal wells into the generating plants. More pipes can be seen bringing steam from the wells on nearby hills. At regular intervals the pipes have loops in them. We learn that these loops allow for expansion and contraction of the huge pipes as they heat and cool.
Near the village are the offices of Philippine Geothermal, Inc., where the operations process manager, Roman St. Maria, welcomes us. Soon we begin our guided tour of the site with Roman.
Close by the offices are some production wells. “We utilize the same technology that is used for drilling oil wells,” says Roman, “except that the holes are larger in diameter.” He continues: “The wells, in fact, become the conduits through which pressurized hot water and steam are brought to the surface. And that is the product we deliver to the power plant.” Two nearby wells are very close to each other. When we ask why, our guide explains: “Only on the surface are they close. Underground, one is straight down. The other allows us to control its direction. This is necessary because of the cost of land. Drilling wells close together helps us to save on expenses.”
Wanting to know more about the process, we ask: “We have read that you use flash-steam technology at this site. What does that mean?” Roman explains: “The deepest well we have here is almost 3,700 meters [12,000 feet] in depth. Hot water is under high pressure at great depths. But when you bring it to the surface, the pressure drops and most of the water flashes, or turns into steam—thus the name flash-steam technology.”
Down the pipeline from the wells is the separator. Here the steam is separated from the hot water or geothermal brine. But the steam is still not ready for power generation. Roman elaborates: “Droplets of water remain in the flowing steam. These droplets contain minerals that might deposit on the turbine and damage it. So from the separator, the steam goes to the scrubber. The job of the scrubber is to remove those droplets.”
Our guide points to large insulated pipes that take the scrubbed steam to the electrical generating plant, about a half mile [1 km] away. Since condensation forms along the way, the steam is given another scrubbing before it enters the turbine that drives the generator.
We now come to the top of a hill overlooking the geothermal site. “This field’s total area is about seven square kilometers [three square miles],” points out Roman, adding: “We have 102 wells here, 63 of which are production wells. Many of the others are reinjection wells.” Our next question is: “What are reinjection wells?” Roman answers: “We generate so much hot water and steam every hour that it is necessary to inject separated water back into the ground reservoir to avoid damaging the environment. One hundred percent of liquid effluent is reinjected.” We learn that this reinjection also helps to recharge the geothermal field.
How does a geothermal power plant affect the overall appearance of the area? The most noticeable evidence of its existence is the steam vented from the power plant. Otherwise, what we see are coconut palms and other foliage. Many homes are also nestled in the valley below. It seems that with careful management, geothermal power can coexist with people and the environment.
Installations such as the one we visited use only high-temperature steam for power generation. However, efforts have recently been made to extract energy from fluids that are less than 400 degrees Fahrenheit [200°C]. As a result, binary-cycle technology has been developed. This method uses tapped hot fluid to vaporize a secondary fluid, which in turn drives a turbine/generator set.
Pluses and Minuses
There is a lot to be said for geothermal energy. Countries that develop power from it reduce their dependence on oil. Every ten megawatts of electricity generated for a year represents a savings of 140,000 barrels of crude oil per year. Furthermore, geothermal resources are immense, and the danger of depletion is much less than it is with many other energy sources. Pollution problems are also greatly reduced. In addition, geothermal energy production costs are quite low compared with those of many other energy forms.
On the negative side, there are some environmental concerns. Geothermal steam usually contains hydrogen sulfide, which is toxic in high quantities and a nuisance in low quantities because of its sulfurous smell. However, treatment processes for removing it are effective and more efficient than emission-control systems at fossil-fuel power plants. Moreover, particulates in the effluent may contain small amounts of arsenic or other toxic substances. When these are reinjected into the ground, the danger is kept to a minimum. Contamination of groundwater supplies can also be a problem if the geothermal wells have not been sealed to great depths with steel casings and cement.
Our Creator has given us a planet with varied treasures. Geothermal energy is just one of these. And men are only beginning to learn how to utilize it. Future developments will no doubt help us see how to use our treasures more beneficially and how at the same time to care properly for the grand globe that has been entrusted to us.—Psalm 115:16.
The boiling point of water increases to about 450, 600, and 1,110 degrees Fahrenheit [230, 315, 600°C] at the depths of 1,000, 5,000, and 10,000 feet [300, 1,525, and 3,000 m] respectively.
[Diagram/Pictures on page 15]
(For fully formatted text, see publication)
Mak-Ban geothermal plant, Philippines (Simplified view)
Production well → Separator → Steam → Scrubber → Scrubber → Turbine
↑ Brine → Reinjection well ← Water ← Cooling tower
ELECTRICAL GENERATING PLANT
Men opening steam valve on page 13: Courtesy Philippine National Oil Corporation; pipeline on page 13 and aerial view and inset of electrical generating plant on page 15: Courtesy of National Power Corporation (Philippines); production well and steam pipeline on page 15: Courtesy of Philippine Geothermal, Inc.