Jon Hafsmo and Tuan Do, BP
Vlad Rosen and Orland Northam, Siemens Power Generation
Vietnam’s Phu My 3 power plant is one of the biggest and most exciting power projects under construction in South-East Asia. The 700 MW plant will set a benchmark for future gas fired projects in the region.
Figure 1. Project location
In March 1995, the Vietnamese government granted the Integrated Power/Urea (IPU) consortium sole authorization to conduct the full feasibility study for the IPU Project. By 1998 it became clear that the urea part of the project would not be commercially viable and that the power plant, to become known as Phu My 3, would be viable as an integral component of the Nam Con Son gas project.
•The Phu My Industrial Zone was a natural site for the power plant due to the presence of infrastructure for existing power plants, its linkage with the natural gas pipeline for the gas from the offshore gas fields, the proximity of major power consumers and short transmission distances to rapidly growing consumer centres.
•The Phu My 3 project, consisting of the construction of a combined cycle power plant as an integral part of Vietnam’s power development plan at the Phu My Industrial Zone, was to be developed under a BOT (Build, Operate, Transfer) scheme. Under the terms of the BOT arrangement, the BOT company would operate the power facility for 20 years before transferring it to Vietnam’s state utility company, Electricity of Vietnam (EVN). The BOT regulations included tax exemptions for the power plant equipment that resulted in substantial cost savings.
The project was tendered internationally and four major suppliers submitted their proposals based either on a single or a multi-shaft configuration. Siemens initially offered its single-shaft concept plant. By being one of the main consumers of the gas coming from the newly developed gas fields, the delivery schedule for the plant was one of the key issues for the project. Another key schedule issue was the availability of the 500 kV grid for which the plant was specified and built in full understanding with EVN.
In response to the various technical requirements without exceeding the project financial frame, the following options were considered during the clarification/evaluation phase:
•One power train with bypass stack, plant with two bypass stacks for an early simple cycle operation
•Grid connection switchyard (GCS), double winding 500/220 kV main transformer, simplified high voltage switchyard
•Multi-shaft configuration with or without bypass stacks to increase the operational flexibility and ease of maintenance
•Civil construction options including the main cooling water channel, various buildings.
The IPU Consortium finally selected a multi-shaft configuration following closely Siemens reference power plant concept, with 500 kV high voltage equipment but without bypass stacks. Subsequently, a recommendation to award Siemens the status as preferred Engineering, Procurement and Construction (EPC) contractor for the power project was approved by the Ministry of Industry in August 1999. The main reasons for Siemens being selected as the EPC contractor for the Phu My 3 power project were a commercially competitive offer, the power plant design allowing for high efficiency and low emissions generation of electricity, as well as Siemens’ previous construction experience with the Phu My 2.1 extension power plant also in the Phu My Industrial Zone. The project is the first privately financed project under a BOT arrangement.
The owner had initially targeted to start the construction of the power plant in mid 1998 and put the plant into commercial operation in July 2000. Nearly two years elapsed before construction could begin in earnest. During the course of development, the IPU consortium and the EPC contractor had to overcome several challenges, including: having to change the site layout as a result of negotiations with the site developer, IPIDCO/UDEC; and the land lease procedure was delayed and was not effective until all the permits and approvals were obtained and the contracts were signed.
Figure 2. The Phu My 3 project agreement structure
The project is scheduled to commence commercial operation 25 months after commencement of the EPC activities.
Overall site arrangement
The combined cycle power plant will be located some 70 km south east of Ho Chi Minh City near the village of Phu My in the Ba Ria-Vung Tau province, adjacent to the Thi Vai and Sao rivers. The plant will be located immediately to the south of the plots designated for the Phu My 1, 2 and 4 power plants. The parcel of land allocated to the power project occupies approximately 24 hectares and is adjacent to the site for a future fertilizer project. The layout of the equipment was decided in consideration of space factors for operability, maintainability and avoidance of problems during construction.
A large substation at the north end of the Phu My complex will gather all incoming transmission lines. The 500 kV switchyard for the Phu My 3 project will be approximately 1 km south of this GCS. Despite some limitations, it can accommodate both ship and barge type of cargo delivery. Heavy equipment, such as generators, transformers, and turbines delivered on overseas charter vessels to Singapore has to be unloaded on barges with self-unloading cranes for the further transportation to the Serece port.
Figure 3. The contract structure of the Phu My 3 power project
Natural gas, as the primary fuel, will be provided via a 70 km pipeline from the Dinh Co gas processing terminal which is receiving gas via a 370 km new pipeline from the Lan Tay gas field in Offshore Block 6.1 in the South China Sea.
Plant design concept
For achieving best performance at the specified ambient conditions in south east Asia, a triple-pressure, single-reheat cycle has been selected. The plant rated capacity at ISO conditions is 760 MW with a design efficiency of 58 per cent at generator terminals and reflects Siemens’ modular design having at its core two V94.3A gas turbines
The two advanced V94.3A gas turbines discharge their exhaust energy into two heat recovery steam generators (HRSG). These HRSGs supply main steam, reheat steam and low pressure steam to a KN-type reheat steam turbine, which consists of one HP/IP cylinder with opposed steam flow and a single two-flow low pressure cylinder.
The plant configuration selected is made up of standardized modules, the main modules being the gas turbines generator sets, two outdoor HRSG, steam turbine generator set, water-steam cycle system, instrumentation and control equipment, electrical power system as well as pre-designed, pre-engineered buildings or civil construction structures.
The prime mover selected for the plant is the model V94.3A, an advanced heavy duty gas turbine, structured as a completely pre-engineered model. The V94.3A is a single-shaft machine with horizontally split casings, disk-type rotor with center tie bolt and cold end drive. The combustion system consists of an annular combustion chamber with 24 hybrid burners.
The burners are designed to operate on both gas and liquid fuel in dry-low NOx mode without water injection. The system also has provisions for water/fuel oil emulsion injection for NOx control in diffusion mode.
Thus, the standard combustion system can accommodate a smooth conversion to fuel oil premixing. The annular combustion chamber consists of three casing sections forming an inner cone and two outer half shells. The metallic walls of the combustor are protected against high temperature exhaust gas in the same way as the proven silo combustion chambers of the V94.2 gas turbine: by ceramic tiles, each one clamped by four tile holders.
Pollutant emissions generally include NOx CO, UHC (unburned hydrocarbons), SOx, smoke and particulate matter (PM). SOx, UHC, smoke and PM are negligible when burning natural gas, and CO emissions in the load range above 60 per cent are below 10 ppm, which is typical for all gas turbines featuring combustion chambers with ceramic tiles.
The steam turbine, which drives an air cooled generator, is a three-stage, reheat, two-casing machine. It is built as a two casing turbine with a combined opposed-flow HP/IP turbine and a double-flow LP turbine. The turbine features: monoblock rotors jointed to a single shaft together with the generator; a single bearing between turbine sections and a single cross-over pipe. The cross-over pipe design allows easy opening of the LP turbine for maintenance purposes.
For the volumetric design flow at the LP turbine exhaust operating at back pressure of 0.070 bar, a 977 mm last stage blade allowing a standardized 10 m nominal exhaust cross section has been selected. It is throttle controlled, with full-arc steam admission directly into the reaction-drum blading. Sliding pressure operation with full arc injection allows the control valves to fully open over the entire pressure range. This maintains efficiency close to the full-load level.
The Phu My 3 CCPP with its two V94.3A gas turbines is an advanced power station generating a total of 717 MW net output with a net heat rate of 6334 kJ/kWh at site conditions, when burning natural gas. The plant is also designed to provide a high level of operating flexibility with extremely low pollutant emission. The environment will also benefit from burning natural gas in these gas turbines, which will provide a benchmark for future power plants in the entire Asia-Pacific region.