The 3×100 MWe San Pedro de Macorís plant, located in the Dominican Republic, uses three Siemens GUD1S.64.3A single shaft combined cycle modules. Based on the V64.3A gas turbine, the GUD1S.64.3A is the latest and smallest member of the Siemens combined cycle (GUD) family.

The plant was built for CESPM, a consortium consisting of Cogentrix, USA, and CDC, England. The project was executed on the basis of a turnkey EPC contract.

After financial close in April 2000, the EPC contract was signed with Siemens Power Generation and construction started in May 2000. After a construction period of only 15 months, the first unit entered the commissioning phase and was handed over to the customer on schedule, on 19 November 2001. Unit 2 followed in December 2001 and unit 3 in January 2002, five weeks ahead of schedule.

The project site is located about 65 km east of the capital Santo Domingo and about 5.5 km north west of the city of San Pedro de Macorís, near the river Higuamo.

After the civil work contractor mobilised at site, the first concrete was poured in late June 2000. Steel structure erection started in October 2000. United Steel Structures International (USSI) provided the turbine buildings and miscellaneous support structures as pre-engineered systems, all hot dip galvanised. Each of the three turbine buildings was erected to a substantially complete status in a record time of seven weeks, so that the first turbine building was closed in December 2000 with the main crane ready for operation, allowing electromechanical installation work to start in January 2001.

Due to excellent transport co-ordination, almost all materials and components arrived at site on time, which again allowed work to proceed continuously and to follow the planned construction sequences.

The first heavy load transport for the first unit, consisting of gas turbine, gearbox, generator, steam turbine, condenser, lube oil tank, transformers and three PCCs (factory preassembled containers) arrived at site on 11 January 2001. By 25 April 2001 the lube oil system was ready for the pressure test, which took place on 26 April.

Cogentrix de La República Dominicana was formed to operate and maintain the facility, with a staff of 31 employees (two expatriates and 29 Dominicans).

Plant configuration

The plant design concept aims to achieve highest efficiency, highest reliability and availability, shortest project implementation, lowest capital investment and therefore lowest life cycle costs.

To achieve these objectives, advanced engineering tools based on the SIGMA platform were used. This included CAD plant layout based on Intergraph 3D, as well as P&ID design using pre-configured functional standard modules linked to an electronic database.

Each of the three 1S.V64.3A modules at San Pedro de Macorís, consists of a V64.3A gas turbine plus duct-fired, dual-pressure, non-reheat HRSG, to be operated exclusively on No 2 fuel oil.

The condenser is cooled by a forced draft cell-type cooling tower.

Due to the choice of No 2 fuel oil, water injection is necessary to reduce NOx emissions.

Using a configuration with three identical blocks allows a reduction of redundancies for the main pumps in the feed and condensate system. This consequently reduces capital costs and maintenance requirements.

A tailor-made spare parts concept reduces the potential outage time for the units.

Under the given ambient conditions, with fuel oil and water injection, the San Pedro de Macorís plant achieves an output of 3×99.2 MW and 48.2 per cent net efficiency. Using natural gas as fuel these figures are equivalent to about 3×101 MW and 52 per cent at ISO conditions.

To reduce losses and to increase plant performance as well as efficiency at San Pedro de Marcorís, a HET (high efficiency turbogear) type gearbox was chosen to step down the gas turbine shaft speed from 5400 rpm to 3600 rpm (60 Hz).

The turbine building is a compact steel building of simple rectangular design and contains the gas turbine, generator and steam turbine with their associated components.

The auxiliaries for the generator are directly arranged beside the generator. The auxiliary components (coolers, etc) are located in a lower annexe of the turbine house. The air-intake filter house is located over the annexe at the side of the main bay of the turbine building. An overhead travelling crane runs over the full length of the building and can lift heavy equipment in the building for installation and maintenance.

The electrical and I&C equipment are located in several factory-preassembled containers which are heated and air conditioned as required.

Flexible operation

Having a combined cycle single shaft arrangement with the steam turbine at one end, the generator in the centre and a SSS clutch between the generator and the steam turbine, the gas turbine can be started independently without any restrictions arising from the actual condition (hot, warm or cold) of the steam turbine and the cooling system.

At higher condenser back pressures at high ambient temperatures in particular, a rigid coupled steam turbine could be at risk from ventilation (ie overheating of last stage blades) if it were to be operated without the cooling system in operation during gas turbine start-up.

The clutch also acts as a fully lubricated gear-tooth coupling to enable unrestricted axial expansion of the steam turbine shaft relative to the generator. This allows optimised axial clearances for the steam turbine blading, resulting in improved efficiency.

The clutch engages automatically once the steam turbine approaches the operating rotating speed of the generator (3000 or 3600 rpm). The clutch automatically disconnects the steam turbine whenever the steam turbine slows down relative to the generator.

With the clutch allowing the gas turbine to be started and operated independently of the steam turbine, the gas turbine can be started up relatively fast and the steam turbine can be accelerated at a suitable rate once the gas turbine is on load.

The steam turbine can be shut down at any time, leaving the gas turbine operating in open-cycle mode. In this mode, steam is dumped to the condenser via the bypass station.

The main components

Gas turbine

The V64.3A gas turbine was derived from its predecessor, the V64.3, as well as from the larger advanced machine, the V84.3A, using the principles of aerodynamic and geometric scaling and applying a scaling factor of 0.7.

The V64.3A is a 70 MW class gas turbine specially designed for application in mid size cogeneration and combined cycle plants, able to accommodate cycling duty (daily start-stop) as well as baseload operation.

This 5400 rpm single shaft engine is geared down to 3000/3600 rpm for 50/60 Hz electrical grids (3600 rpm, 60 Hz, in the case of San Pedro de Macorís). It is of single casing design incorporating aero engine features such as advanced aerodynamics and materials, film cooling and thermal barrier coating technology.

The basic design has been adopted from previous gas turbine models and includes the following features:

• disk-type rotor with central tie bolt and radial serration;

• two outboard bearings;

• cold end generator drive; and

• axial exhaust diffuser.

The HET gearboxes used for stepping down from 5400 to 3600 rpm were supplied by Maag, Switzerland. The HET design reduces losses and thus contributes to increased plant efficiency. The double helical spline gear with horizontal offset is arranged on a concrete foundation and adjusted via plates and shims. The gear has a nameplate rating of 85 MW and a service factor of 1.3, according API 613. Potential misalignment is compensated for by the quill shaft design. A motor operated turning gear is installed on top.

Heat recovery steam generator (HRSG)

The horizontal flow two pressure non reheat heat recovery steam generator is of natural-circulation drum-type and generates steam in high-, and low-pressure sections.

The No2-oil-fired duct burner system provides supplementary firing for additional steam generation.

The heat recovery steam generator, which is designed for outdoor installation, was supplied and installed by Doosan (formerly Hanjung) of Korea.

The cooling tower

The forced draft wet cell cooling tower was supplied by BDT/UK. It consists of six identical cells and operates according to the counterflow principle. The wooden structure supports the cooling elements, the drift eliminators and the fans, which are mounted on top.

Operating experience

Since handover, the units have operated according to the grid dispatch requirements over the whole load range, from minimum up to full load, continuously and in cycling mode with daily starts and overnight shut downs.

  At the time of writing, units 1, 2 and 3 had accumulated around 230, 200 and 195 starts with 5300, 4200 and 3500 operating hours respectively.

Recently, the first minor inspection was conducted on the three gas turbines. This planned outage required less than a week of plant shut-down and the machines were found to be in good condition.

Basic data for the San Pedro de Macorís combined cycle plant