20/06/2011 Seminar on Geothermal Exploitation Santiago de Chile

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1 Contents Power Plants Steam Power plants Binary Power plants Geothermal Power Plants Single flash systems Binary systems 1 Equipment Well head Gathering piping system Steam separators and moisture separators Turbine generators Condensers NCG gas removal systems Cooling Towers 2 Simplified single-flash backpressure schematic Single flash power cycle 4 2 Separator Simplified single-flash condensing schematic TS - Diagram for steam 2 4 Separator CW

2 Single flash process- Working cycle One of the Design Objective To produce as much energy as possible from each kg geothermal fluid we extract from the geothermal reservoir Example: Let us assume that we know the reservoir enthalpy We know the condensing temperature, We need to estimate the separation temperature and pressure that gives us maximum energy 7 8 Backpressure, an alternative Example 9 10 Silica Solubility Silica Solubility

3 Basics for binary Power Plants Uses similar principle as conventional fossil or nuclear plants. Binary Power Plants Instead of water/steam the working fluid is Propane, i or n-butane, i or n Pentane, Ammonia or refrigerants with boiling point much lower than water at same pressure. Paratunka 1967, 670 kw First indirect plant in Larerello 1912, 250 kw with water/water cycle 13 Simple schematic and pressure-enthalpy diagram Various Cycles Hybrid, flash and Binary 16 Single flash + Binary 18 3

4 Single flow, top exhaust, impulse turbine Geothermal Steam Turbines 19 Types of steam turbines 20 Double flow, top exhaust reaction turbine Imulse turbine The turbine change the direction of flow of a high velocity steam jet. The resulting impulse spins the turbine and leaves the steam with diminished kinetic energy. There is no pressure change of the steam in the turbine moving blades. All the pressure drop takes place in the stationary blades. Reaction turbine These turbines develop torque by reacting to the steam pressure or mass. The pressure of the steam changes as it passes through the turbine rotor blades. The turbine must be fully immersed in the fluid flow (such as with wind turbines). The casing contains and directs the steam, maintains the suction imparted by the draft tube Single flow, multy pressure, top exhaust turbine The Condenser

5 Direct condenser Shell and Tube Condenser Non+condensable gases The Gas extraction systems In geothermal steam there will always be some traces of non condensable gases. The amount is usually in the range of 0-3% of the separated steam flow. In some cases up to 20% Since the gas in non-condensable this gas must be sucked out of the condensers, otherwise it will simply build up there, blocking the heat exchange between the cooling water and the steam There are several methods to remove the gases Methods of removing NCG Steam Ejector Steam ejectors, SE Two stages with intercondenser and sometimes and aftercondenser Liquid ring vacuum pumps, LRVP Hybrid systems One stages Steam ejector + LRVP Two stages Steam ejector + LRVP Compressors The pressure energy in the operating steam is converted into kinetic energy in the nozzle and this high velocity of the steam entrains the gas being pumped. The resulting mixture at the resulting velocity enters the diffuser where this velocity energy is converted to pressure energy so that the pressure of the mixture at the ejector discharge is substantially higher than the pressure in the suction chamber but lower than the pressure of the motive steam

6 Steam Ejector Velocity and Pressure Liquid Ring Vacuum Pump The compression is performed by a rotating ring of liquid, usually water, as the impeller rotates in eccentric position relative to the pump casing, the sealing liquid flows against the casing by the centrifugal force and the sealing liquid circulating flow is made, as the impeller is in an eccentric position a decreasing cavity is produced inside the pump. This cavity becomes smaller since the inside face of sealing liquid circulating flow gradually approaches the discharge port and compresses the gas in the inside Compressor Two stage Steam Ejector Hybrid, Steam ejector + LRVP Two stage ejector system

7 Air leakage and dissolved air in cooling water Estimated air leakage into the low pressure part Flanges Seals Due to sub-atmospheric pressure in condensers Dissolved air in cooling water Cooling Must be taken into account if the condenser is cooled directly Cooling Cooling tower Rivers, lakes or seawater Cooling with air Cooling tower Traditionally used for a flash cycle Air Cooler Often used for binary cycle Cooling tower Schematic Unit 6 - Cooling Tower and CW-Pumps Schematic drawing of a wet cooling tower

8 Reykjanes Power Plant Example Reykjanes Power Plant Reykjanes 50 MW Single flash - 3 units Reykjanes - Steam separator station Reykjanes - Brine exhaust silencers Reykjanes - 50 MW steam turbine Double flow Double exhaust Cross over Duct CW In/out Condenser Generator Control valve Steam strainer Main stop valve Steam traps and drain pipes

9 Reykjanes - Sea water cooling Example Svartsengi Power Plant Why construct a power plant so close to the pool? Svartsengi - Overview Blue Lagoon Medical Clinic Cosmetics Production Power Plant High Pressure dry steam area, Steam Cap Re-injection pipeline Water dominated area Svartsengi - Formation of the steam cap Svartsengi - Steam cap area and collecting pipes Geothermal well Steam cap

10 Svartsengi Resource Park - Schematic Svartsengi Power Plant (2009) Svartsengi, Unit 5 - Turbine / Generator Svartsengi, Unit 5 - Condenser Svartsengi, Unit 5 - Water heaters Svartsengi, Unit 5 - Gas Removal system

11 Svartsengi, Unit 5 - Cooling Tower Svartsengi, Unit 6. T/G - Moisture removal vessels Svartsengi, Unit 6- Piping Svartsengi, Unit 6 - Condenser Cross Over Duct MP Outlet LP Inlet MP Inlet HP control valve HP main stop valve HP steam strainer Oil Unit HP=High pressure, 16 bara MP=Medium press. 6,5-6,7 bara LP=Low pressure, 1,2 bara Svartsengi, Unit 6 - Condenser Unit 6 - Cooling Tower and CW-Pumps Cross Over Duct NCG Extraction Condenser dome VAC tank connection Drain from ejector syst. CW Outlet CW from aux systems CW Inlet

12 Unit 6, Cooling Tower - Winter conditions Example - Binary Power Plant Binary Power Plant - Azores Sao Miguel Azores - Pico Vermelho Plant Pico Vermehlo - 10 MW PFD 10 MW binary Power Plant - Plan View

13 Typical well pad Well head and safety equipment Safety valve with a rupture disk assembly on upstream side Well head, steam separator, brine tank, rock muffler and gathering pipelines Well head, master valve and branch valve Separator and brine tank Typical well pad Brine tank and brine pups Vertical steam separator Well head, steam separator, brine tank, rock muffler and gathering pipelines Brine pumps Condensers, vaporizer and preheaters

14 Turbine (s) and generator Reinjection pumps