SCC5-4000F Single Shaft (SST5-5000): A single shaft concept for cold cooling water conditions
Holger-Max Emberger, Dr. Martin Alf (Siemens Power Generation (PG), Germany)

Source: Siemens Energy

1. Introduction

Deregulation and liberalization, high loads of renewable energies and high fuel prices change the requirements for new power plants. The customer focus is the optimization of life cycle costs driven by features like high efficiency, high power output and operating flexibility.  Siemens Reference Power Plants are developed with the main emphasis on the above mentioned requirements of modern power markets. Through methods like Quality Function Deployment (QFD) the requirements of power producers are identified and considered in the plant design. A feedback process from projects in construction and commissioning as well as from operating plants ensures a closed lessons learned loop into the Reference Power Plant development.

One result of the QFD workshops is the customer focus on single shaft plants. These plants meet
the power producer’s need for lowest life cycle cost better than 1×1 multi shafts due to higher availability, higher efficiency and less required space. In the 400 MW class, Siemens provides two 50 Hz single shaft Reference Power Plants called SCC5-4000F Single Shaft. Both are based on the SGT5-4000F gas turbine (formerly known asV94.3A), the SGen5-2000H hydrogen cooled generator (formerly known as THRI) and a steam turbine coupled through a self shifting and synchronizing (SSS) clutch to the generator. The steam turbine of choice depends on the condenser back pressure, mainly influenced by the cooling condition:

The SST5-5000 ,combined HP/IP, double flow LP turbine, (formerly known as KN) shows
outstanding performance at low back pressure, the SST5-3000, HP turbine, combined IP/LP turbine, (formerly known as HE) ensures best economic value for higher back pressure.

A second topic addressed by power producers is the need for high operating flexibility. For that reason, all Siemens Reference Plants are designed for both, daily cycling and for base load operation. This flexibility capability was proven through operating units that must cope with different load regimes depending on seasonal electricity demand.The paper addresses the Reference Power Plant development process, the single shaft design referring to a SCC5-4000F Single Shaft (SST5-5000) and features for high operating flexibility.

2 Market environment

Looking at the European power market as a supplier opens up a quite challenging picture. Liberalization and deregulation, massive support of renewable energy in countries like Germany or Spain and the planned shut down of nuclear power stations in various European countries change the power market fundamentally. Further on, it is still unclear how the political and economical boundary conditions will develop in future: The level of liberalization and deregulation of power markets in Europe varies from 10% to 100%, gas and oil prices are fluctuating on a high level, the further development of wind energy is a big question mark and the effects of CO2 certification trading are unsure.

At the same time, there is pressure for replacement of ageing power plants. Huge investments in this uncertain environment are necessary. Therefore, the requirements for new plants are very challenging to cope with the above mentioned uncertainties. Customers ask for high efficient plants due to high gas prices and CO2 regulations. Other environmental issues, like chemical and water consumption, are getting more important and have to be taken into account during plant design. Very flexible fossil fired plants must act as backup for wind power.

 These plants need compensate the high fluctuation of power output of wind turbines. Due to liberalization and deregulation, the load regime of a power plant over its lifetime is unknown. Therefore, power producers demand for plants that provide a maximum operating flexibility.
The ideal design is capable for every load regime from peaking to base load. This market
environment also opens up new business opportunities: The use of hourly and seasonal market arbitrage,participation in ancillary energy markets and the capability for peak shaving can increase theeconomic value of a power plant project.

The task for power plant suppliers is to provide solutions that help customers to overcome these challenges. As an answer Siemens develops high efficient, flexible and environmental friendly Reference Power Plants at lowest life cycle cost and short pay-back times.

3 Reference power plant development
3.1 Investment decision drivers
At the end of the day, an investor’s decision on whether or not to realize a specific project will be mainly based on economic facts such as life cycle costs, the project’s net present value and the internal rate of return, the cost of electricity and the payback period which in turn depend on project specific boundary requirements. By understanding the most important drivers for optimized customer value, product development is focusing on life-cycle-cost optimization.

Efficiency, operating flexibility, reliability and availability, initial invest, operating costs and environmental impact are the main drivers for successful projects (figure 1). The focus on life-cycle-costs has changed the market requirements over the past decade dramatically. Whereas in the past utilities with high technological and financial capacities were the major customer segment, a transition has now been made with emphasis on utilities that are characterized by reduced technology and tight capital resources. This development is driven by liberalization and deregulation of the power markets. The increased competition has resulted in a new and differently structured market where power generation, transmission and distribution have now been separated from another.

In this market environment, power producers ask for efficiency, high operating flexibility and high availability. At the same time short construction times and low initial investments are expected.

Life-cycle cost optimization

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