COMBINED CYCLE

Going for the record

8 April 2004



With its first standardised single shaft CC package Siemens has brought concept-to-concept buld time down to 22 months. Now, in preparation for the boom the company expects in European CC plants, it plans to decrease it even further.


Siemens has moved some way towards creating off-the-shelf power plants with the introduction of a standardised single shaft combined cycle gas turbine block, the first example of which is currently being installed at the 2x380 MW Gas Natural Arrubal plant in Spain. Its two units are the company’s eleventh and twelfth in all on the Iberian peninsula. By early 2005 the second example, at Tahaddert in Morocco, will have been brought on line. But a multi-shaft version will have to wait – the company’s believes that the market is not large enough to support the necessary R & D.

The development is part of what Siemens sees as a natural route for the power plant business, proceeding from the customised solution approach as practised in the eighties, through the reference plant philosophy based on a modular approach, through to the standardised power block, and is a response to the widely perceived need to drive down prices in a liberalised and highly competitive market.

There are fundamental, sometimes diametric, differences between the two approaches. The designer of a customised plant starts with externals such as site conditions,existing HV switchgear, water supply and treatment and so on, then selects a plant to fit in with them. He then successively refines the process by considering aspects such as fuel supply, cooling arrangements and the addition of suitable HRSG, I&C. etc. The combination of these predetermines the GT, ST and generator.

By contrast the standardisation approach starts with a turbine generator set and selects standard components that match it for capability and site conditions. From a design point of view this is more difficult and requires the existence of versatile components with a degree of variability that can be utilised without operating efficiency, and other, losses. But the advantages of such a system are self evident – reduced hardware costs owing to economies of scale, reduced system design and processing time, lower risk of failure and an easier specification and permitting process.

Arrubal is also an example of what Siemens is calling its ‘long term partnership’ arrangement, a concept it is promoting heavily as delivering increased reliability and perfomance and reduced insurance premiums. This O & M deal, which lasts typically 12 to 20 years, hands over plant maintenance to the component or plant supplier. Siemens has made no secret of its ambitions in this direction, preferring the certainties of long term contracts to the extreme competitiveness and low profitability of the steam and gas turbine supply market. It is no wild speculation that its corporate policies to promote standardisation and EPC contracting have been devised as an indirect promotion of its O & M ambitions.

Critical realisation

Power plants have usually been planned and built according to the specification of individual customers, an inherently expensive process. The liberalisation of the power markets has called for closer scrutiny of build and life-cycle costs, and Siemens looked for new ways of matching these costs to changing market conditions. The main focus was to standardise planning and construction while offering solutions flexible enough to meet customer requirements. The aim was to develop a competitive power plant concept based on the critical realisation that slight climatic differences among locations cause only minor variations in efficiency and output, making it possible to design power plants so that layout, components and systems were suitable for a whole range of projects. The idea was backed up by experience – retrospective analysis of different projects and bids for the Mediterranean region showed only negligible differences in efficiency for optimised designs when compared to the standardised design. It became apparent that key components such as the gas turbine, steam turbine and generator could be standardised, and can be supplied with a range of optional add-ons according to the building-block principle.

Econopac to turnkey

Siemens' first venture along these lines was to standardise core power plant components, resulting in the so-called Econopac, which incorporates the gas turbine, housing, auxiliary systems, air intake system, exhaust gas

system, electrical equipment, and instrumentation and control system. With it comes a guarantee of a specified gas turbine efficiency and gross power output.

Next came the 'power train' solution. This extension of the Econopac constitutes the central plant section in a single-shaft combined-cycle plant. It comprised the Econopac, generator and steam turbine all arranged on a common shaft and with a clutch between generator and steam turbine. The product also includes auxiliary and automation systems as well as the electrical equipment for the main components. As a development of this came the ‘power island’ concept. This incorporates all of the components and systems that are important for a plant's efficiency and output. For single-shaft gas turbine plants it consists of the power train plus the heat-recovery steam generator.

The logical next step was the ‘power block’ concept, incorporating the turbine building with all necessary components and systems as well as the HRSG together with the trunking and cabling that connect it to the turbine building. The power block is identically designed and equipped for a specified range of climatic conditions. Gross output, efficiency and delivery time are guaranteed by the supplier.

The power block

The ‘power block’ concept is the product of a long-term design effort to develop and standardise the reference power plant, although the RPP's flexibility with regard to customer- and site-specific requirements is retained where the power block concept is inappropriate. All core components are specified in the planning scope which is used unaltered for various different projects. Project risk, where it is the product of non-conformance, delays and non-availability of components, can be significantly reduced. Projects can progress more smoothly because potential areas of uncertainty and unforeseen events can be largely ruled out by learning from feedback from earlier, almost identical plants, and if forced outages do occur, the necessary spares are more readily available. Construction time is reduced and the use of known components speeds up permitting procedures. Using co-ordinated components from the same supplier may improve plant performance. The concept makes potential improvements faster and easier to implement. Siemens is convinced that it will make great inroads in the CC market.

The Arrubal plant

The two block Arrubal plant is the first project to be implemented under this new concept. Its time schedule, a new reference, confirms (so far) that the standardised power block, the core element of the plant, can cut construction times for single-shaft cornbined-cycle plants by at least two months, making it possible to build such a plant in 22 months from start to grid connection. This is put down to faster sourcing of components and a more rigorous organisation of activities on the construction site. Further time savings are possible because certain data, eg for the boiler foundations, mechanical components and connecting piping, are known from the start. The significance of this is that connecting a 400 MW combined-cycle power plant to the grid two months earlier can bring the customer a financial advantage of up to r5 million from interest savings and power sales over this period. Shorter construction times are conditional not only upon the technology and processes used in plant construction but also upon a tighter time schedule, appropriately qualified employees and using the correct tools for faster sequencing. A good example of the latter time schedules with links to internal and external reporting. These reports are entered in a database which can be accessed to obtain comprehensive linked documentation such as drawings or specifications of individual components.

Siemens says that its current construction time of 22 months for single-shaft combined-cycle power plants is the market leader. But it plans to get faster. One of its goals is to cut processing times further based on detailed analysis of the 3000 or so activities involved in a project time schedule.

CC Prospects in the Western European power plant market.

Between 1980 and 2000 total installed generating capacity in Western Europe increased from 450 GW to 670 GW, while generation increased from 1830 TWh to 2920 TWh. Most of the increase was supplied by CC and renewables, a trend that is expected to continue for the next 20 years, while nuclear build slowed to a stop in the early nineties. By 2020, total installed generating capacity will have to expand to 880 GW to meet the increasing demand for power, of which about a third is expected to be CC plants. In fact most new plant is expected to be either CC or renewables, at the expense mainly of coal plant.

The European electricity market is still characterised by the effects of deregulation and liberalisation. But as far as opening up the market to greater competition is concerned the picture is far from uniform. Only six countries have completely liberalised their power markets to date: Austria, Denmark, Finland, Germany, Sweden and Great Britain. Italy has liberalised 70% of its market followed by the Netherlands (63%), Luxembourg (57%), Ireland (56%), Belgium (52%), and France and Greece (with 34% each). But liberalisation has also had adverse effects: plants remain in operation for longer than economically and environmentally expedient. Essential investment in new or modernisation projects is being deferred. As a consequence the power plant fleet is becoming increasingly superannuated.

But an increase in annual electricity demand to 3900 TWh is anticipated for 2020. New power plants must therefore be brought on line to avoid bottlenecks and breakdowns. Loyola de Palacio, the EU Energy Commissioner, has expressed it this way: 'In Europe we need to build one new power plant a week or every two weeks to replace our existing stock of superannuated plants'. According to de Palacion if nothing is done Europe will find itself without any more room to manoeuvre in four to six years' time.

The promotion of CCGT is a strategy aimed not only at new build but specifically at coal replacement. In 2000, 11 % of the world's coal fired fleet, capacity nearly 1100 GW, was more than 40 years old, and 60 % was more than 20 years old, in a sector where average plant service life is 22 years. These plants between them emit 5.5 billion tonnes of CO2 per year. Replacement with more efficient coal plant achieving 42 % or so compared to the current average of 33% has the potential to reduce this by 1.5 billion tonnes; replacement with CCGT at 57 % efficiency would achieve 3.6 billion, around 30 % of the Kyoto target.

Investment in new power plant requires clear frames of reference, but the key issue of emissions rights trading is still an unknown factor. The principles to be adopted in allocating emissions rights and the specific economic implications of this policy must be known before power supply companies can take major decisions relating to power plant investment.

It is plain that the CO2 allocation plan and emissions trading will significantly affect the use of fossil fuels throughout Europe, possibly producing more long-lasting changes in the sector than deregulation. High generating efficiency and plant operating flexibility are certain to be major factors. If the EU is to fulfill the requirements laid down in the Kyoto Protocol two options that suggest themselves are increased build of gas-fired combined-cycle plants and replacement of old coal-fired plants with new, state-of-the-art designs.

notes, although an identical single block plant to come in line in 200? is currently under construction at Tahaddart in Morocco.

However, one should not get carried away by these kinds of figures.

Since the Energy Industry Act came into force in 1998, Spain has been banking on competition and free enterprise. The full deregulation of the common Iberian power market planned with Portugal (current state of deregulation: 45%) has been put back six months to July 2004. Spanish electricity prices have fallen sharply against those of its competitors. (Spanish power industry association, UNESA, states that the average price for electricity fell by a nominal 17% or 28% in real terms between 1997 and 2002.)

However it is worth remembering that, to take western Europe as an example, the expected increase in installed capacity would create by 2020 new emissions that even an increase of efficiency to 57 % generally would not be able fully to offset.


Tables

Table 1. Salient features of the standardised power block
Table 2. Arrubal main data

The Arrubal site in March 2004 The Arrubal site in March 2004
First installed turbine at the plant First installed turbine at the plant
Standardised power block main components Standardised power block main components


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