Geothermal Power Plant Geothermal Energy Resource in the Philippines https://www.geoenergymarketing.com/ener gy-blog/geothermal-country-overviewphilippines/ Geothermal Energy A form of energy conversion in which heat energy from within Earth is captured and harnessed for cooking, bathing, space heating, electrical power generation, and other uses. Three Types of Geothermal Energy: • Liquid-Dominated and Vapor-Dominated Reservoir • Thermal Energy • Enhanced Geothermal Liquid-Dominated and Vapor-Dominated Reservoir • Liquid-Dominated (LDRs) and Vapor-Dominated Reservoirs (VDRS) were common with temperatures greater than 200 °C (392 °F) and are found near young volcanoes surrounding the Pacific Ocean • Flash Plants are commonly used to generate electricity from LDR and VDR. Most wells generate 2-10 MWe. Steam is separated from liquid via cyclone separators, while the liquid is returned to the reservoir for reheating. Pacific Ring of Fire https://www.mirror.co.uk/science/what-pacific-ring-fire-facts-12342864 Thermal Energy • Heat for these purposes can be extracted from cogeneration at a geothermal electrical plant. • Heating is cost-effective at many more sites than electricity generation. At natural hot springs or geysers, water can be piped directly into radiators. In hot, dry ground, earth tubes or downhole heat exchangers can collect the heat. https://www.slideshare.net/shahbazshaikh21/geothermalenergy-74763210 Enhanced Geothermal • Enhanced Geothermal Systems (EGS) actively inject water into wells to be heated and pumped back out. The water is injected under high pressure to expand existing rock fissures to enable the water to freely flow in and out. • The Technique was adapted from oil and gas extraction, but the geologic formations are deeper, and no toxic chemicals are used, reducing the possibility of environmental damage. https://doi.org/10.1016/j.rser.2017.09.065 Geothermal Power Plant Geothermal Power Plant uses Hydrothermal Resources that have both water (hydro) and heat (thermal). Three types of Geothermal Power Plant 1. Dry steam plants 2. Binary cycle power plants 3. Flash steam plants Efficiency of Geothermal Plant compared to other Power Plants Moon H., Gawell K., Zarrouk S. J., "EFFICIENCY OF GEOTHERMAL POWER PLANTS: A WORLDWIDE REVIEW," in New Zealand Geothermal Workshop Proceedings, Auckland, New Zealand, 2012. Dry Steam Plants • A Vapor - Dominated geothermal resource produce dry steam at Temperature above 200 0C. • The dry steam from the geothermal reservoir is extracted to turn the generator turbines. • These plants emit only excess steam and very minor amounts of gases https://openei.org/wiki/Geothermal_Steam_Power_Plant Binary Cycle Power Plants • This plant transfers the heat from the low to moderately heated (below 200°C) geothermal fluid to a secondary fluid with a much lower boiling point that water pass through a heat exchanger. The heat causes the second liquid to turn to steam, which is used to drive a generator turbine. https://geothermalenergyosu.weebly.com/different-types-ofgeothermal-energy.html Flash Steam Plants This plant extracts the high-pressure hot water from deep inside the earth that is converted to steam by decreasing the pressure. This is done by spraying fluid into a tank held at a much lower pressure than the hot water, causing some of the hot water to rapidly vaporize, or "flash." The produced steam then drives a turbine, which drives a generator. When the steam cools, it condenses to water and is injected back into the ground to be used again. https://ww2.energy.ca.gov/almanac/renewables_data/geother mal/types.html Schematic Diagram of Geothermal Power Plant T-S Diagram of a Geothermal Power Plant Performance of Geothermal Power Plant 1. Mass Flow Rate of Steam, ms : ππ = π₯ ∗ πππ€ Where: πππ€ = πππ π ππ ππππ’ππ π€ππ‘ππ π₯ = ππ’ππππ‘π¦ πππ‘ππ π‘βπππ‘ππππ ππππππ π Solving for steam quality (π₯) and considering a throttling like process during the extraction of ground water: β1 = β2 = βπ2 + π₯(βππ2 ) 2. Turbine Output ππ‘ = ππ (β3 − β4 ) ∗ ππ‘ Where: ππ‘ = π‘π’πππππ ππππππππππ¦ 3. Generator Output ππ = ππ’πππππ ππ’π‘ππ’π‘ ∗ πΊππππππ‘ππ πΈπππππππππ¦ ππ = ππ β3 − β4 (ππ‘ )(ππ ) 4. Heat Rejected in the Condenser ππ = ππ β4 − β5 5. Over-all Plant Efficiency πππ£ππ−πππ ππ’πππππ ππ’π‘ππ’π‘ × ππ = (πππ€ )(β1 ) πππ£ππ−πππ ππ (β3 − β4 )(ππ‘ ) ππ = (πππ€ )(β1 ) Sample Problems A flash steam geothermal power plant is located where underground hot water is available as saturated liquid at 700 kPa. The ground hot water flow rate is maintained at 29.6 kg/s at the well head with a pressure of 600 kPa. The flashed steam enters a turbine at 500 kPa and expands to 15 kPa upon entry to the condensed. Considering an 88% turbine efficiency and 95% generator efficiency, determine: a) The power produced by the turbine, kW b) The power output of the Power Plant, kW c) The Over-all Plant Efficiency, % Given: ππ πππ€ = 29.6 π π1 = 700 πππ π3 = 500 πππ π4 = 15 πππ Required: a) ππ‘ b) ππππ c) πππ£ππ−πππ Solution: from steam table: β1 = βπ@ 0.70 πππ = ππ½ 697.22 ππ at 500 kPa; βπ = βππ = ππ½ 640.23 ππ ππ½ 2108.5 ππ β3 = βπ@ 0.50 πππ β3 = ππ½ 2748.7 ππ Enthalpy of steam upon entry to the condenser is taken from Mollier Chart: Solving for π₯2 : β1 = β2 = βπ + π₯2 βππ ππ½ 697.22 ππ = ππ½ 640.23 ππ + ππ½ π₯2 2108.5 ππ π₯2 = 0.027 Solving for ππ : ππ = 0.027 × πππ€ ππ 29.6 π = 0.027 ππ = 0.80 ππ/π ππ½ β4 = 2211 ππ a) Turbine Output ππ‘ = ππ (β3 − β4 ) ∗ ππ‘ = ππ 0.80 π ππ½ 2748.7 ππ − ππ½ 2211 ππ = 378.54 ππ b) Power Plant Output πππππ‘ππ’ππ’π‘ = ππ β3 − β4 ∗ ππ‘ ∗ ππ = 378.54 ππ ∗ 0.95 = 359.61 ππ ∗ 0.88 c) Over-all Plant Efficiency πππ£ππ−πππ πππππ‘ ππ’π‘ππ’π‘ = × 100% (πππ€ )(β1 ) 359.61 ππ = 29.6 ππ/π = 1.74% ππ½ 697.22 ππ × 100%
