Mitsubishi Heavy Industries Technical Review Vol. 53 No. 4 (December 2016)
3High-Availability (99.6%) Geothermal Power Plantfor Mexico

Engineering Headquarters,
M i ts u b i s h i H i ta c h i P o w e r S y s t e m s , L t d .

In geothermal power generation, the steam is mostly saturated at the inlet to the steam
turbine and the amount of moisture in the turbine is high, and as such erosion tends to occur. In
addition, impurities contained in the steam or hot water cause the deposition of scale in various
devices or the corrosion of metal materials. Therefore, it is essential for stable operation to ensureand enhance the performance and reliability of power generating facilities including steam turbines.
This article describes our efforts to enhance performance and to ensure the reliability of the power
generating facilities we have delivered in recent years.

|1. Introduction
Mitsubishi Hitachi Power Systems, Ltd. (MHPS) has supplied geothermal power generating
facilities including more than 100 steam turbines exceeding 3 GW since 1951, when we delivered atest steam turbine for power generation in Japan. With the experiences and technologies forgeothermal power generation facilities we have obtained through our history, we have developed avariety of techniques to prevent corrosion and have made efforts to enhance the performance offacilities including the specifications of entire plants so that they can be adapted to the properties ofgeothermal steam, which vary from one region to another.
This article describes our latest performance and reliability enhancement technologies basedon the experience obtained through the work on the Los Azufres Geothermal Power Plant inMexico, which we delivered with our cutting-edge technology in February 2015, and for which theoperational rate guaranteed for one year was satisfied in February 2016. In March 2016, ourcompany delivered geothermal power generating facilities to the Domo de San Pedro Geothermal
Power Plant in Mexico, and our efforts on this plant are also introduced here.

|2. Los Azufres Geothermal Power Plant
2.1

Project Outline

This power plant is located in Los Azufres, Michoacan State, which is 250 km west ofMexico City, the capital of Mexico (Figure 1). This project was ordered by Comision Federal deElectricidad (CFE, Head office in Mexico City) to Mitsubishi Heavy Industries, Ltd., (MHI) whichis the direct ancestor of MHPS, as the geothermal power plant for the Los Azufres III Phase I
Power Plant. Our company oversaw the design, manufacture, procurement, installation, civil workand commissioning of the main equipment including the steam turbine and auxiliary machines,
while Mitsubishi Electric Corporation supplied the generators.
Our company has delivered 5 geothermal power plants for the Los Azufres geothermal field,
as well as 6 plants for the Cerro Prieto geothermal field in Mexico, which is ranked No. 5 in theworld in terms of geothermal resources. With these existing plants, the new plant has met brisk
demand for electric power in Mexico, where steady economic growth is expected.

Mitsubishi Heavy Industries Technical Review Vol. 53 No. 4 (December 2016)
4

Figure 1 Overview ofLos Azufres III Phase I

2.2

Figure 2 Cutaway View ofLos Azufres III Phase I Turbine

Project Features

At this geothermal power plant with a sending-end output of 50,000 kW, the performancewas enhanced by adopting a single casing axial flow turbine (Figure 2), and the construction
period was shortened by lowering the height of the turbine housing. Unlike thermal powergeneration using fossil fuel, etc., in geothermal power generation, the pressure and temperature of
the main steam are very low and the amount of thermal energy that can be converted in a turbine(adiabatic heat drop) is very small. Therefore, the performance improvement rate resulting from thereduction of exhaust loss becomes much larger than that in thermal power generation.
In an axial flow turbine, a diffuser with which pressure recovery can be expected withoutchanging the flow direction of the turbine exhaust can be installed between the turbine exhaust andthe condenser. Therefore, the exhaust loss can be reduced compared with that in upward anddownward exhaust turbines.
In the case of a downward exhaust turbine, the condenser is installed first, and then theturbine casing is set up. By adopting an axial flow turbine, however, the installation work for theturbine and that for the condenser can be conducted in parallel, which can shorten the time for
installation compared with a downward exhaust turbine. Furthermore, with an axial flow turbine,
the height of the turbine housing can be substantially reduced, resulting in a reduction inconstruction costs.

2.3

Combination of axial flow turbine and direct-contact condenser

One end of the axial flow turbine is coupled with a generator at the governor side, and theother end of the turbine is in the exhaust chamber. Therefore, a second turbine cannot be coupled toit. Accordingly, an axial flow turbine is applied only to a single flow turbine. In this project, anintegral shroud blade, which is the longest in the world for a 60Hz-area geothermal turbine, wasapplied to the final-stage blade of the steam turbine. The application of the long and large blade
realized a single flow turbine, contributing to the enhancement of performance, as well as making
the facility more compact than a double flow downward exhaust turbine facility. The turbine
housing was downsized as much as possible, which minimized the effect on the landscape. Inaddition, our company adopted a combination of an axial flow turbine and direct contact typecondenser for the first time. Photos of the axial flow turbine and the direct contact condenser
delivered to the Los Azufres Power Plant are shown in Figures 3 & 4, and a comparison of thedifferences in turbine performance and the height of the turbine housing by exhaust direction ispresented in Figure 5 and Table 1.

Figure 3 Photo ofLos Azufres III Phase I Turbine

Figure 4 Photo ofLos Azufres III Phase I
Direct-Contact Condenser

Mitsubishi Heavy Industries Technical Review Vol. 53 No. 4 (December 2016)
5Figure 5 Comparison of Turbine Exhaust Direction
Table 1Specifications of Los Azufres III Phase I Turbine

Delivery
TypeRated output
Rated speed
Main steam pressure
Main steam temperature
Exhaust pressure

2015
SC1F: Single Casing Single (Axial) Flow
50,000 kW at net output
3,600 rpm
8.0 bara
170.4°C
0.095 bara

2.4 Plant Optimization
Since the delivery location of the spray jet type direct contact condenser was 2,909 m above
sea level, the relationship between the cooling tower basin water level and the condenser waterlevel was optimized in order to ensure sufficient spray pressure, even under low barometricpressure conditions. In addition, the condenser water level control was verified in the design stage
in advance, and turbine water induction could be prevented.

2.5 Project Execution & Availability
In this project, substations, transmission lines, optical communication and remote control
rooms, in addition to the plant facilities, were included in the supply range, and CFE’s original
design standards had to be followed for each facility. We entrusted Power Engineers, Inc. (PEI,USA) with some of the design and successfully accomplished the project as an exclusive EPC
contractor.
During the one-year period for which a certain operation rate was guaranteed a highavailability of 99.6% in terms of electric power (kWh) throughout the year was accomplishedwithout any serious problems arising in the major facilities, and the guaranteed operation wassuccessfully completed, exhibiting high reliability.

|3. Domo de San Pedro Geothermal Power Plant
3.1

Project Outline

This power plant is located in Domo de San Pedro, Nayarit state in the mid-west region ofMexico (Figure 6). In 2014, our company received the order of this project for a geothermal power
generation facility with 25,500 kW net output, under a full turnkey contract, from GEODESA(Geotermica para el Desarrollo S.A.P.I. de C.V.), a Mexican power generation company, anddelivery was completed in 2016. This was the 13th geothermal power generation facility weprovided in Mexico.

Mitsubishi Heavy Industries Technical Review Vol. 53 No. 4 (December 2016)
6Figure 6 Overview of Domo de San Pedro

To this point, we had received orders for a total of 12 geothermal power plants from CFE, 6plants for each of the two geothermal power fields including Los Azufres, and this geothermal
power plant follows these orders. Our company commands an approximately 40% share in terms ofthe capacity of thermal and geothermal power generation facilities in Mexico, which is one of ourmost important markets.

3.2

Project Features

A single casing upward exhaust turbine, the same as we delivered to Cerro Prieto IV inMexico, was adopted for this 25,500-kW geothermal power plant. Thus, both the enhancement ofreliability and the shortening of the design and installation period were achieved.
This was a project for Mexico's first geothermal power plant operated by a private company,and high proposal capabilities of the supplier were required. Based on our abundant experience as
not only a geothermal turbine manufacturer, but also an EPC contractor, we could successfully
deliver this plant.

3.3

Plant Optimization

For the turbine type, the turbine that we delivered for Cerro Prieto IV in Mexico was used as
the model plant. However, the condenser, ejector, inter-condenser and after-condenser wereintegrated so that the narrow site could be effectively used (Table 2).
Table 2

Specifications of Domo De San Pedro Turbine

DeliveryType
Rated output
Rated speed
Main steam pressure
Main steam temperature
Exhaust pressure

2016
SC1F: Single Casing Single (Upward) Flow
25,500 kW at net output
3,600 rpm
8.0 bara
170.4°C
0.136 bara

|4. Conclusion
Our company applied the world’s longest final-stage blades to a 3,600-rpm geothermal
turbine at the Los Azufres geothermal power plant. In spite of the turbine’s compact size, theseblades significantly improved the turbine efficiency, achieving the high availability of 99.6%
during the one-year period for which a certain operation rate was guaranteed.
The subsequent construction of the Domo de San Pedro geothermal power plant was also
successfully completed. As the exclusive EPC contractor, we successfully completed a total of two
geothermal power plants in Mexico in 2015 and 2016.