SOLUTIONS FOR GEOTHERMAL POWER PLANTS

 

Ansaldo Energia and Geothermal Energy


Geothermal energy is a valuable, renewable natural energy comparable to hydroelectric energy and it is environment-friendly because it generates electric power without burning fossil fuel.
Ansaldo Energia’s experience with geothermal power plants dates back to 1913, when the first turbine-generator unit ever driven by geothermal steam rated 250 kW, entered service at Larderello (Italy).
Since then units totalling over 2,000 MW have been installed both in Italy and abroad.

 

GEOTHERMAL STEAM CYCLES

 

Geothermal fluid may be in the form of steam or hot water, or a combination of the two: geothermal fields are named accordingly as “vapour dominated” or “liquid dominated, with single, or double flash system” and their exploitation for power generation involves different plant arrangements to feed steam into the turbines.

 

Equipment for Geothermal Power Plants

 

Ansaldo Energia can provide optimized solutions for geothermal power plants in the range 20 to 150 MW for 50 and 60 Hz markets.


Plant design, supply and installation
 

Ansaldo Energia can provide not only steam turbine - generator sets, but also complete integrated package including architecture, civil, mechanical, electrical and automation design, supply of equipment, installation and commissioning of the power plant.


Steam Turbine
 

Ansaldo Energia is one of the world leading suppliers of geothermal turbines/generators.
The Company’s extensive experience (more than 130 geothermal units installed) has enabled Ansaldo Energia to achieve a
high level of reliability and efficiency as well as remarkable flexibility in terms of adapting to different steam conditions and plant arrangements.
State-of-the art technology, and cutting edge construction methods are used to provide different turbine models for different geothermal steam conditions and power output levels and to upgrade old units to match changed steam conditions.
Careful material selection, due to the presence in the fluid of corrosive chemicals such as H2S, chlorides and salts, is extremely important to ensure reliability and minimize outages for maintenance. Ansaldo Energia has carried out detailed studies to test the corrosion resistance of various turbine materials to geothermal steam.
All turbine components in contact with the fluid are made of stainless steel, including the rotor when required by the fluid characteristics.


Generator

Air cooled generator in closed circuit (TEWAC), featuring a modular, compact design and high efficiency:

  •  Rated output: depends on the size
  • Class F insulation system
  • Power factor 0.8
  • Rated voltage 11.5 or 13.8 kV
  • Static excitation

 

Specific features are introduces for geothermal application to protect the copper from H2S corrosion (special painting, gold plating, tinning, etc.).


Condenser

Since the condensate does not have to be recovered, a spray type direct contact condenser is often used.
The condenser is arranged beneath the turbine or laterally connected by means of a crossover steam duct.
The water is injected into the condensing chamber by means of a network system consisting of manifolds, pipes and spray nozzles.
The condensing chamber is connected to two gas cooler sections where the final condensation takes place, in addition to non condensable gases temperature abatement by means of the spray nozzles on the top and trays arranged beneath the nozzles.
The nozzles of the whirl-jet type are with ample orifice section to prevent clogging and are easily removable for inspection and cleaning.
The Condenser shell and internals are in stainless steel.

 

Non condensable gas removal system

Since the geothermal steam flowing into the condenser contains a large amount of non condensable gas, essentially carbon dioxide (CO2), a high efficiency extraction system shall be provided.
Two options are available:

  • Steam ejectors
  • Centrifugal compressor driven by an electric motor or coupled to the turbo-generator.


The choice between the two is based on the gas percentage in the geothermal steam: steam ejectors are preferred for low gas content.

 

Control System

The control system, based on proven architecture developed by Ansaldo Energia, with reliable hardware, software and system interfaces delivers information to operators and decision makers in an easy usable format and handles operation, maintenance, control efficiency and safety in such a way as to minimize outages.
Control system development is based on functional segregation between:

  • Balance of Plant
  • Steam Turbine Auxiliary control loop and slow control loop
  • Steam Turbine Governor
  • Protection System

 

The control system includes the supervisory system which provides the information needed to assess the mechanical condition of rotating machinery.
These systems continuously measure and monitor a variety of supervisory parameters, providing crucial information for early identification of machinery problems.


Services 

Ansaldo Energia, with its long standing experience in the geothermal power plant sector can provide a wide range of services for both OEM and NON-OEM geothermal plants:

  •  New turbines and generators tailor made for old geothermal plants
  • Steam path upgrading for existing units to match changed steam conditions
  • Repairing damaged equipment
  • Supplying replacement parts
  • Generator rewinding
  • Control system

 

To download Ansaldo Energia Solutions for Geothermal Power Plants brochure, click here