GEOTHERMAL DRILLING

Geothermal drilling technology is adapted from the oil industry. Most of the geothermal wells are drilled with a rotary-type drilling rig. Because of the hard, abrasive, and high-temperature volcanic rocks of geothermal systems, the drilling bits require hard abrasive resistant teeth such as diamond or tungsten carbide. Hence, geothermal drilling is an expensive activity in geothermal development. Most geother­mal wells are drilled 1 to 2 km deep to intersect faults and fractures so as to increase the success rate of production from permeable zones. This is enhanced by directional or deviated wells as opposed to vertical wells of earlier development. Directional drilling also allows drilling of more than one well on a single well pad, especially in difficult terrains...

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Mitigating Factors and Reinforcing Factors

Various factors can mitigate Malthusian population dynamics (as Malthus recognized), including techno­logical progress and the possibility of a ‘‘demo­graphic transition’’ under which fertility declines at sufficiently high incomes. (The combination of technological progress and a demographic transition has, of course, allowed most of the modern world to avoid the Malthusian trap over the two centuries that have passed since the time of Malthus.) On the other hand, as Malthus also realized, there are factors that tend to exacerbate Malthusian dynamics, including reliance on open-access resources and lack of property rights more generally.

2.7 Easter Island and Malthusian Overshooting

At a superficial level, Easter Island might look like a simple example of Malthusian population o...

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Hot Water (Liquid-Dominated) Systems

Hot water systems are the most common geothermal systems suitable for power generation. In a hot water system, both the liquid and steam phases appear at the wellhead because the water flashes as it ascends the wells. The dryness fraction at the wellheads is normally less than 0.3. Depending on the wellhead pressures, the power cycle selected can be a single­pressure steam system (Fig. 3) or a dual-pressure one (Fig. 4). It is common to flash the water phase to produce more steam in a low-pressure flasher or separator. In practice, there is no real distinction between a flasher and a separator. Both are pressure

Hot Water (Liquid-Dominated) Systems

FIGURE 5 Power cycle for hot water or two-phase geothermal systems with binary ORC...

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Two-Phase (Liquid-Dominated) Systems

Two-phase systems are liquid-dominated systems. In two-phase geothermal systems, the geothermal fluids contain both water and steam at roughly an equal weight ratio (i. e., dryness, x~0.5) at the wellhead. The water phase needs to be removed by a separator, and the steam is piped to the steam turbines (Fig. 3). The separated water can be reinjected directly or, depending on the fluid pressure, can be flashed to produce a lower pressure steam for power generation before being reinjected (Fig. 4).

Two-Phase (Liquid-Dominated) Systems

FIGURE 3 Power cycle for single-pressure hot water or two – phase geothermal systems. B, barometric leg; C, condenser; G, generator; H, hot well; PW, production well; RW, reinjection well; S, separator; ST, steam turbine.

Two-Phase (Liquid-Dominated) Systems

FIGURE 4 Power cycle for dual-pressure hot water or two – phase g...

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MALTHUSIAN POPULATION DYNAMICS

2.5 A Cautionary Tale?

The basic facts regarding Easter Island are no longer in serious dispute. It is, however, important to understand why Easter Island suffered an internally generated collapse based on resource overuse. The real question is whether Easter Island is an unusual and isolated case or whether it is a cautionary tale for the modern world. It is therefore important to uncover any general principles that might be inferred from the Easter Island experience.

2.6 Malthusian Population Dynamics and Overshooting

One important idea that might shed light on Easter Island derives from Malthusian population dynamics...

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2. GEOTHERMAL POWER CYCLES

When a geothermal resource has been deemed suitable for power generation, a decision is required to select a suitable power cycle. A power cycle consists of a series of thermodynamic processes that converts heat energy to electricity. The most common geothermal power cycle is the Rankine cycle, consisting of two isothermal and two adiabatic processes. More than one power cycle can be used for a geothermal resource. Indeed, other direct uses can be combined with power generation.

Geothermal power cycles can be classified into five major types: steam Rankine cycle, organic Rankine cycle (ORC), total flow cycle, Kalina cycle system (KCS), and trilateral flash cycle (TFC)...

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Geothermal Power Generation

KENG CHOON LEE

Geopower NZ Limited

Mount Roskill, Auckland, New Zealand

tracer A chemical injected into a well to detect the water flow path.

turbine nozzle A wheel of fixed blades to direct steam flow to a wheel of rotating turbine blades. wellhead The area around the casing head flange. wellhead pressure (WHP) Fluid pressure in a well just below the master valve.

Energy can be converted from one form to another. Geothermal power generation is the production of electrical energy from the heat (thermal) energy of the earth (geo). Electricity is a much more con­venient, clean, and useful form of energy than is heat. Geothermal energy has been used directly for its heat and therapeutic effect for thousands of years by the Romans, Chinese, and Turks...

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ECONOMIC CONSIDERATIONS

Geothermal projects require a relatively large initial capital investment, with small annual operating costs thereafter. Thus, a district heating project, including production wells, pipelines, heat exchan­gers, and injection wells, may cost several million dollars. In contrast, the initial investment in a fossil fuel system includes only the cost of a central boiler and distribution lines. The annual operation and

Подпись: in Cooling out water Подпись: * CondenserПодпись: Liquid ammoniaПодпись: Weak ammonia- water solutionECONOMIC CONSIDERATIONSECONOMIC CONSIDERATIONSGeothermal.

In water Out
Generator

ECONOMIC CONSIDERATIONS

Expansion valve

.Evaporator coil

Pump

maintenance costs for the two systems are similar, except that the fossil fuel system may continue to pay for fuel at an ever-increasing rate, whereas the cost of the geothermal fuel is stable...

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