Perpetuity

St. Philip Neri School

Hydrothermal-Circulation System

Located in the southwestern Australian Outback, Perpetuity replaces the abandoned Super Pit Gold Mine, once the most productive mine on the continent. Civil engineers viewed the 600-meter-deep and 6-square-kilometer open pit as an energy “gold mine“. The potential to generate clean, renewable energy was not far below the citizens’ feet.

Named Hydrothermal-Circulation System (HCS), this hybrid uses geothermal technology and silicon-based thermoelectric materials to capture and convert the Earth’s heat, and subsequently the city’s waste heat, into electricity. The innovative power plant generates electricity without using steam or fossil fuels. The long-term infrastructure requires a power generation plant (Figure 1) and support facilities including transmission lines, water supply, water flow monitoring systems, and maintenance shops.

(Figure 1)

Because 99.9% of the Earth’s crust is hotter than 100oC, mechanical engineers took advantage of this heat to design and install a geothermal closed-loop pipe system deep into the earth. The metallic piping system contains saline ground water that has been processed by a series of filters and a reverse osmosis system. Circulating in a continuous cycle, the potable water captures the Earth’s heat and transfers it to the power plant. There, the water passes through silicon membranes which absorb the heat, excite the atoms, and cause electrons to be released. The electrons are collected for processing by electronic circuitry and/or nanowire batteries, producing usable alternating current (AC) electricity. The now cool water goes back through a pump/filter, and the cycle starts again.

Electricity is transmitted and distributed from the power plant to the city in three ways. The main power distribution process (Figure 2) uses heavy gauge copper cables that run to power junction boxes and circuit breaker panels located on each of the floors of the superstructure and likewise to surrounding buildings.

Main Power Distribution (Figure 2)

In addition, Perpetuity’s electrical engineers determined that 55-60% of all energy generated dissipates as waste heat. Material engineers proposed silicon nanowire membranes as a semiconductor to harvest and convert the secondary heat generated by the city’s industry. The heat then passes over the membranes, and in a process similar to the main power generating facility, AC electricity is created via mini-power plants.

Lastly, chemical and materials engineers incorporated silicon into the structure of rechargeable lithium-ion batteries, creating portable power. By replacing the carbon material in batteries with silicon nanowires, ten times more lithium can be stored, creating a longer battery life.

Land usage, water pollution, and supplies for thermo-electric devices have little impact on natural resources. Since Perpetuity is located within an open-pit mine, directional drilling techniques reduced the amount of land used. Most geothermal schemes affect both surface and ground waters; HCS’s closed-loop piping system with continuously circulating water eliminates water pollution possibilities. Plentiful resources are available for silicon membrane production as silica makes up 27.7% of the Earth's crust and is the second most abundant element. Additionally, reverse osmosis removes 90-98% silica from the ground water, replenishing the resources.

The primary environmental impacts of geothermal energy production are disposal of waste rock and filtered minerals. To reach the target temperature, the metallic piping system was established 2,200 meters into the earth. Civil engineers had the removed rock crushed into aggregate; it was used for concrete and road pavement. Minerals filtered from the water serve multiple purposes. Perpetuity’s industries use filtered sulfur for fertilizers, cement, and adhesives. Zinc is used in the nano-composite coating that lines the HCS’s pipes. In addition to thermoelectric devices, silica is used to make glass.

Geothermal energy production has unsurpassed benefits. HCS uses a renewable resource, heat, instead of nonrenewable, polluting fossil fuels and/or nuclear power for energy. When compared to other energy sources, this sustainable system has fewer mechanical failures and requires less land usage for the facilities. HCS is not affected by weather or sunlight

availability; it works day and night. No hazardous wastes exist, and minimal waste products are generated.

Geothermal heat extraction’s main risk involves pipeline failure. Perpetuity’s computer engineers developed a fully automated, centralized system that monitors the closed-loop network’s overall function. If water flow levels are outside the preset allowable range, the system automatically signals the actuator to shut off the water’s flow in the affected loop, simultaneously activating redundant systems. Pipes can then be repaired by maintenance personnel.

An initial issue was Perpetuity’s location on land governed by the Aboriginal Lands Trust. Approval was necessary before any development could begin. To obtain approval, the following actions were completed: site plan and land use proposals were filed, discussions with relevant Indigenous stakeholders were held, and assurances were made that Aboriginal heritage sites would not be impacted.

Another obstacle was the selection of the pipes for the closed-loop system. Civil engineers considered these factors: water carrying capacity, durability, cost, jointing process, maintenance, and the ability to transfer heat into the circulating water. After reviewing all options, material and mechanical engineers determined extruded steel pipes the most suitable. Chemical engineers developed a zinc nano-composite coating to line the pipe’s core thus reducing corrosion.

After analyzing tradeoffs (cost, appearance, efficiency), Perpetuity’s Board of Engineers determined that Hydrothermal-Circulation is the most sustainable and abundant energy resource. It has an initially high capital investment, but operation and maintenance costs are low due to no fossil fuel expenditures. Electricity generated by the HCS costs $.02 a KW hour compared to $.10 a KW hour from typical power plants. Once the piping system is buried in the earth, no one can see or hear the system. The power plant appears as just another beautiful building within the city.

American Dream: Geothermal states, “Every geothermal energy facility that has been built in the last 100 years is still in production.” Hydrothermal-Circulation System is the best energy solution for Perpetuity.

Figure 1- 30 words

Figure 2- 16 words

Body of essay- 951 words

Total- 997 words

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