Salta combined cycle plant: built for export

The expected demand growth for electric energy in Chile's Northern Interconnected Grid (Systeme Interconnectado Norte Grande – SING) over the next few years, in particular due to increased copper mining activity, is seen by Chilean power producer Gener (formerly Chilgener) as an excellent opportunity to expand its business activities in the region.

A study of the various alternatives for supplying this area resulted in the development of the InterAndes/TermoAndes project. This project entails the generation of electricity at the combined cycle natural gas plant located in the Province of Salta, in Argentina, and its transmission to Chile's Northern Interconnected Grid via overhead 345kV lines over a distance of approximately 408 km. The power will be fed into the system at the Atacama substation, at the extreme southern area of the SING, precisely where the major mining companies (the principal consumers of electricity) are concentrated.

This approach was found to deliver lower overall costs and greater operating flexibility than alternative ways of supplying power to the SING. Specifically, the cost of the InterAndes/TermoAndes project is lower than that of building and operating new coal-fuelled units in the north of Chile. The project is also more cost-effective than building and operating a natural gas pipeline from northern Argentina to the Pacific coast to fuel new natural gas units, and then transmitting the electricity back to the major power consumption load centres of the Andes area.

In fact, the owner estimates that the total investment of $330 million dollars associated with the project - $240 million dollars to build the Salta power plant plus the $90 million dollars involved in the construction of the transmission line – add up to only half of the investment required by competing gas projects which involve the construction of a gas line between Campo Durán (in Argentina) and Tocopilla or Mejillones, along with the construction of a power plant and a return transmission line back into the Andes where the principal customers are located.

Another advantage of the InterAndes/ TermoAndes approach is that it offers great potential for the future development of power trading between Chile and Argentina. The project is the first to involve exporting electricity from Argentina.

Organisation and contracts

On the utility side, there are three companies with clearly differentiated functions involved in the InterAndes/TermoAndes project: TermoAndes SA; InterAndes SA; and Gener SA.

TermoAndes SA – the Buenos Aires based subsidiary of Chilean power company Gener – is responsible for both the construction of the power station and its subsequent administration and operation. A turn-key contract for construction of the power station was awarded on 13 August, 1997 to a consortium made up of Siemens AG (Germany), Abengoa SA (Spain), Siemens SA (Argentina) and Teyma Abengoa (Argentina). Siemens AG is consortium leader.

InterAndes SA (also an Argentinian subsidiary of Gener) is responsible for the construction, administration, and subsequent operation of the 408 km high tension line that will connect the power station with the Chilean system in the northern area of the country. The transmission line, currently around 80 per cent complete, with construction progressing well in both Chile and Argentina, will cover the 265 km between the Salta substation to the Chilean-Argentinean border at the Sico Pass, and then 143 km from the Sico Pass to the Atacama substation.

The construction contracts were awarded on 22 April, 1997 to a consortium formed by Abengoa SA (Spain) and Teyma Abengoa (Argentina).

Gener SA, Chile's privatised electric utility, will purchase the energy produced by TermoAndes SA and will transport it and distribute it among its customers in the SING.

As well a securing the supply of natural gas to fuel the plant the owner also signed in 1996 two power supply contracts – totalling 110 MWe and each with a minimum term of 12 years – with the mining companies Zaldivar and Lomas Bayas. This enabled Gener to secure the equipment and system supply contracts required for implementation of the project.

The power plant is located on a one hundred hectare parcel of property owned by Gener, in the vicinity of General Güemes in Salta province. The power company plans continued development of the project, entailing the installation of a second power transmission line between the Salta plant and the Atacama substation by the end of the year 2000, along with a corresponding increase in the plant's total power generating capacity to 1000 MWe.

The first electricity from Salta, which the plant will initially generate in simple-cycle gas turbine duty (giving a capacity of 406 MWe), is expected to flow between Argentina and Chile as early as January 1999. Operation of the plant in combined-cycle duty (at its full net capacity of 632.7 MWe) is scheduled to start in August 1999.

This schedule, announced in August 1997, represents an acceleration of the original timetable because of the growth in demand for the plant's electricity and the economic attractiveness of the project.

As of August 1998, work on the 15 km gas pipeline was ongoing, both gas turbines and the first generator were on site and already erected, the exhaust gas system was under construction, virtually all equipment needed for the open cycle were at site, civil works for combined cycle were already underway and HRSG erection was scheduled to start in September.

The project is being financed from the owner's own capital and by project financing through a bank consortium led by Deutsche Morgan Bank.

Plant design

Salta is a GUD 2 x V94.3A, with a multi-shaft configuration designed for baseload operation. It consists of two gas turbines, each with a capacity of 203 MWe, two heat recovery steam generators to produce steam and a 226.7 MWe steam turbine.

Under its contract, Siemens AG has produced two latest-generation V94.3A gas turbines in its Berlin manufacturing plant; while the steam turbine and three generators have come from the company's manufacturing plant in Mülheim/Ruhr. The Siemens scope of supply also includes all the instrumentation & control equipment, which is Teleperm XP.

The Salta plant is based on the Siemens reference plant template, the basis for the plant design being the Siemens ZDX standard power plant. Use of such a template reduces planning and construction times and aims to achieve high plant reliability through the use of field proven components.

The only major redesign work needed in the Salta case was to allow for the fact the region has a relatively high risk of earthquakes. The whole plant is being constructed with this in mind, eg reinforced foundations, steel structures etc. The plant, including all major components, has to be designed and executed in accordance with UBC, seismic zone 3.

Cooling systems

The Hamon cooling towers used at Salta are of the counter flow type. Air is drawn vertically from the air inlet in the lower part of the tower, travels across the fill against the stream of water and is discharged to the atmosphere at high velocity through a specially designed FRP fan stack. The Hamon Coolfilm fill is of the film flow type, consisting of packs made of glued PVC formed sheets. The hot water distribution configuration is also the result of extensive research. A concrete riser and a header for each cell introduce hot water. PVC distribution pipes are fitted into the headers and uniformly cover the plan area of each cell. These pipes are fitted with Hamon non-clog nozzles. The complete system is highly corrosion resistant and provides an even water distribution, essential for good thermal performance. Sinusoidal Hamon wave type drift eliminators are installed above the water distribution tubes to remove the water droplets from the exhaust air.

Each cell is fitted with an axial flow fan driven via a right angle double reduction gear box with a long drive shaft manufactured in composite material, mounted with flexible couplings. The motors are installed outside the fan stack, on the fan deck.

The final design of the tower and its components is a combination of modern computer based methods coupled with an extensive service history for the components used and a substantial programme of research and development carried out at the Hamon research centre in Belgium. Moreover, in this particular case, the cooling tower has also benefitted from a standardization (or modularization) process conducted by Siemens with Hamon for all wet evaporative cooling towers used in their power plants. This is why this Hamon cooling tower is very similar to others built in Pakistan, Thailand and more recently, two towers in Brazil. The Salta tower design has of course been adapted to the specific requirement of the project, mainly the seismic load.

HRSGs

The Salta plant's two Heat Recovery Steam Generators (HRSGs) were designed and engineered by NEM bv of the Netherlands. The unfired HRSGs have a horizontal gas-path, three pressure levels with reheat and are of the natural circulation type. The boilers are mounted outdoors with a steel structure designed to the highest earthquake level (after an earthquake, the boilers have to be operational within one week!). The solid fin tubes are configured in a staggered way in vertically orientated 'harps'. The boiler is built up with three such harps beside each other along the entire gas path. The HRSGs have a cold casing

Flue gases leave the gas turbine at a rate of 567.3 kg/s and temperature of 580^oC and enter the HRSG via the inlet duct. Passing through the arrays of HRSG fin tube harps, the gases transfer heat to the fins on the tubes, travel to the outlet duct and finally exit the exhaust stack at the end of the boiler, at a temperature of 88.1^oC. A cold silencer is mounted in the outlet duct to minimize the acoustic emission of the plant.

At the end of the steam turbine, condensed steam is extracted from the condenser to be pumped into the condensate preheat section at the end of the boiler's gas path. From there it flows to the LP drum and/or is pumped further as feedwater via IP- and HP-economizers to, respectively, IP- and HP-steam drums. In the LP-evaporator, 30.2 t/h of LP-steam is generated and superheated to 4.7 bar/227^oC in the LP-superheater. This steam goes to the LP-section of the steam turbine. The evaporator and superheater sections of the IP-system generate 42.1 t/h of IP-steam at 316^oC and 26.3 bar, which is mixed with cold reheat steam at 360^oC and 26.5 bar returning from the HP-section of the steam turbine at 225.7 t/h. The mixture is superheated to 550^oC and 25.4 bar in the reheat section, and flows into the IP-section at 267.8 t/h. In addition, 231.5 t/h of HP-steam is generated in the HP-evaporator section and superheated to 550^oC and 99.5 bar in a two-stage HP-superheater, from where it exits the HRSG and flows to the HP-section of the steam turbine.

The HRSG erection sequence is as follows:

1. Main columns with casing panels

2. Bottom beams and panels

3. Lower and upper parts of the side panels

4. Top panels

5. Secondary steel structure components

6. Trolley beams and suspension rod harps

7. Harps, bumpers, baffles and flue gas guide plates

8. LP, IP and HP steam drums mounted

9. Inlet duct and outlet duct stack

10. Interconnecting pipework

11. Remaining steel structure

12. Attic and basement panels

13. Inlet and outlet expansion joints.

Both HRSGs have to be completely ready for commercial operation at the beginning May 1999, although the order was only awarded in January 1998.

Tables

Summary of supply responsibility
Project profile