Design, manufacture, and supervision the installation of MGS custom gearboxes for the cooling towers of the Miravalles Geothermal Power Plant in Costa Rica

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ABS Costa Rica designed and manufactured four custom-made gearboxes, through its brand MGS Gears, with the highest manufacturing quality criteria, which is essential for reliable operation at 1750 rpm

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The customer

In 1949, ICE, Instituto Costarricense de Electricidad (Costa Rican Electricity Institute), became the public entity in charge of Costa Rica’s electrical development. Today, it has become a group comprised of four state-owned electricity and telecommunications companies: Radiográfica Costarricense S.A. (RACSA), Compañía Nacional de Fuerza y Luz S.A. (CNFL) and Cablevisión. In 1949, ICE, Instituto Costarricense de Electricidad (Costa Rican Electricity Institute), became the public entity in charge of Costa Rica’s electrical development. Today, it has become a group comprised of four state-owned electricity and telecommunications companies: Radiográfica Costarricense S.A. (RACSA), Compañía Nacional de Fuerza y Luz S.A. (CNFL) and Cablevisión. Since the middle of the last century, through ICE, Costa Rica has been committed to a sustainable energy development model that contributes to its economic and social development.

Miravalles Geothermal Plant

Geothermal energy is clean, almost inexhaustible, with low production costs, minimal environmental impact, and available regardless of weather conditions. ICE is a pioneer in the exploration of geothermal fields. In its continuous effort to develop renewable energy sources, ICE initiated in the 1960s the first studies on Costa Rica’s geothermal potential for electricity generation. These concluded with the discovery of nine vast deposits in the northern province of Guanacaste. In 1988, construction began on the Miravalles Geothermal Project on the southern slopes of the Miravalles volcano. After seven years, on March 25, 1994, the first unit with 55 megawatts (MW) capacity started operations. In the following ten years, four more teams came into operation, constituting the Miravalles Geothermal Field, with an installed capacity of 165.5 MW and a monthly production of 84.8 gigawatt-hours (GWh) operating at its maximum capacity, enough energy to supply 283,000 residential consumers with an average consumption of 300 KWh. Miravalles I was inaugurated in 1994 and Miravalles II in 1998. Each plant has a 55 MW unit. The technology is “condensing”: the steam obtained turns the turbines and is then condensed and re-injected into the reservoir. It supplies approximately 224,000 Costa Rican homes per month. (Source-ICE)

The Case

In 2020, ABS Costa Rica received from the Costa Rican Electricity Institute (ICE) the need for a custom mechanical drive solution to be installed in the Cooling Towers of the Miravalles I and II Geothermal Project Cells. The previously installed gearboxes were beginning to show some signs of failure. An in-depth review was needed to explain their behavior and propose a long-term solution that would extend the life of the equipment and improve production performance. 

ABS Costa Rica and MGS Gears Technical Solution

After a first analysis, ABS Costa Rica detected failures originated in the high-speed bevel gear-pair, probably due to wear, which is common in 90° or bevel right angle catalog gearboxes as the ones initially installed, and proposed their replacement by new gearboxes custom designed and manufactured by its brand MGS based on the technical specifications of the Instituto Costarricense de Electricidad (ICE) with the following criteria and objectives:

Standardize the gearboxes so that they can be installed in two types of cooling tower cells (Miravalles I and Miravalles II cells) and can be interchangeable between the different towers of the plant. This has a positive impact on maintenance cost savings, as it eliminates the duplication of spare parts, reduces inventory, and allows a more efficient assessment of overall performance.

Increase the Service Factor of the new gearboxes. ABS Costa Rica designed and manufactured four custom-made gearboxes, through its brand MGS Gears, with the highest manufacturing quality criteria. A case-hardened and tempered steel alloy was used for the bevel gears to achieve high wear resistance and very high gearing precision, which is essential for reliable operation at 1750 rpm. In addition, its geometry was considerably improved by using a globally recognized manufacturing profile that contributes to standardization and ensures component quality. Stronger, closer to the theoretical and ideal rolling tooth shape, and much smoother and more efficient.

To improve the reliability and maintenance of the equipment, it was also decided to incorporate monitoring sensors to remotely control its condition about the temperatures of all its bearings to analyze vibrations, oil level, and a series of other conditioning factors that allow establishing complete and real-time control of the condition of the gearbox and all its components. In addition, to achieve greater efficiency in the reception and sharing of data, the monitoring was integrated with the SCADA (Supervisory Control and Data Acquisition) system, which is currently used by ICE to receive and manage all the information generated in the process for supervision, quality control, data storage, etc.

Currently, the custom-made MGS gearboxes are installed and fully operational at the Miravalles geothermal power plant.

How does a geothermal plant work?

The principle of operation of a Geothermal Power Plant is to channel the Earth’s heat to convert it into Electrical Energy. In especially favorable areas, mainly where the Earth’s crust is thinner and more irregular, the “breath” of the Earth is harnessed by an extraction shaft that can reach 3000 meters deep, which allows the natural vapors to rise to the surface and be directed to a turbine.

The turbine transforms the kinetic energy of the high-pressure steam into mechanical motion, which, once transferred to a generator, is converted into electricity. The current is transferred to a transformer, increasing its voltage and distributing it to the grid.

After being used to drive the turbine, the steam is channeled to a condenser (or heat exchanger), which lowers its temperature and transforms it into water. Thanks to a cooling tower, the water temperature is further reduced.

There are two options for the water: either it is used in the condenser, where it contributes to lowering the temperature of the steam, or it is reinjected underground, where it will be converted back into steam and give new life to another production cycle to create new renewable energy.

ABS and MGS GEARS, Technical Excellence for the Heavy Industry

For over 20 years, we have been offering products, and engineering solutions for all types of industrial applications drives using gearboxes and components capable of adapting to any assembly requirement, space availability, required torque and ratio, etc. We count on a wide range of special bearings and power transmission solutions for the RENEWABLES industry to help optimize your production processes and extend the life of your industrial equipment.

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