Tailor-made versus off-the-shelf: modularisation aims to strike a balance

In today`s market-driven business environment, power producers worldwide are taking a bold new look at how they do business. As a result, low power generation cost has increasingly become the most important factor for success among power producers. Reliable planning, expedited licensing as well as fast project implementation are further essentials to ensure project success.

Meeting these new imperatives requires an intelligent synthesis of standardisation and individuality. With a range of so-called reference power plants, the economic benefits of a pre-engineered power plant design can be combined with the flexibility to customise specific requirements through modular options. This allows the need for project-specific adaptations to be met without costly and time-consuming redesigns.

In the combined cycle power area, examples of the successful implementation of the concept are Otahuhu (380 MWe) in New Zealand, Tapada do Outeiro (990 MWe) in Portugal (Figure 1) and Santa Rita (1000 MWe) in the Philippines (Figure 2), all projects provided by Siemens on a turnkey basis.

For coal, the pre-designed reference unit is called Varioplant® and there are a number of projects in the pipeline using this technology.

Tailor-made and off-the-shelf

The analogy of choosing between a tailor-made suit and a ready-made one illustrates the dilemma. Advantages and disadvantages of one over the other are expected by both the customer and supplier. In the case of the power industry, the “tailor” is the designer and supplier of fossil-fired power plants.

In the industrialised countries there has been for many years a market environment in which each power plant was specifically designed for the client and his particular site. Price levels and project time schedules permitted this “tailor-made” concept.

Since the late eighties the market for power plants has changed dramatically. Market growth in plant expansions has migrated from the industrialised countries in Europe, North America and Japan to the emerging countries in Asia and South America (notwithstanding recent tightening of investment flows). In these countries, utilities are typically faced with limited resources of capital that hamper their ability to develop new technologies and meet the power capacity addition requirements needed for economic growth.

It is estimated that more than 70 per cent of clients in the fossil power generation sector focus on reliable performance, high investment security, but above all on optimised solutions in terms of low investment cost or low life-cycle cost.

For the supplier of power plants the key demands to be faced are project cost, construction time and risk guarantees (Figure 3). Project cost and construction time of coal and gas fired units have halved since the 80s. In relation to the construction and operation of these units, the supplier bears increased exposure to warranties and liquidated damages.

This required an innovative approach towards providing plant solutions. Like other suppliers of fossil-fired power plants, Siemens has begun to develop and build standardised power plants based on sound technical solutions, optimised economics and repeated application. Short preparation and construction times as well as a high degree of reliability during operation characterise these plants.

Viability of standardised concepts

With only very few hundred power plants ordered every year from about half a dozen global suppliers, we must work from standard power plant concepts, which nevertheless have to meet a variety of project specific conditions and requirements. The problem is complex since each client – even when refraining from substantial requests for individual design features – has nevertheless to define some basic requirements such as location, fuels, range of power, ambient conditions, local cooling conditions, and emission standards. The client will evaluate each offer according to his own criteria in terms of capital costs, efficiency, service, maintenance, etc. Additional factors, such as provision for cogeneration and district heating and the use of existing sites and their infrastructures must also be taken into account.

To investigate the viability of using a few standard concepts for power plants – called reference power plant concepts – a market survey of all known projects in the time frame 1995-2005 was undertaken. This included combined cycle, open cycle and steam power plants according to power range, frequency and region, as well site characteristics if known.

Based on this analysis of the demand structure, a set of reference power plants has been defined for gas turbine, combined cycle and coal-fired power plants, which is of course subject to modification according to changing market needs. These designs cover a range of powers, efficiencies, fuels and heat extraction arrangements. In designing these reference power plants, the system P&ID, the civil works design, and the design of the main components and major piping larger than 80 mm OD are all generated, which corresponds to about 15 to 20 per cent of the total design and planning hours involved the full project.

Intelligent structuring of options

For the concept to be successful, the approach needs to be able to tailor each power plant as closely as possible to the client’s needs without requiring major redesign of key plant components and structures. The subsequent question was how these conflicting requirements of standardisation and customisation can be moulded into a successful approach.

A first step towards a more flexible design is to offer each major functional unit not only in a single version but also as options, see Figure 4. In Figure 4 we see, for example, that the functional unit “coal handling system” in the basic variant (or base version), is via ship and as an option delivery via rail. This variation will not change to any extent the remainder of the power plant. Turning to the functional unit “boiler plant” the base version is a supercritical Benson boiler and the option is a subcritical drum boiler. This option changes more than just the functional unit “boiler plant”, there will be corresponding modifications in the live steam line, the ash handling etc. As another example, changing options for the condensate and feedwater pump in terms of drive and redundancy will change only certain components of this functional unit, but will leave a major part of the connecting piping system unchanged.

The key to this flexible design lies in breaking up the power plant into functional units and further into modules, so that most options will change only a single module or at the worst one or two in the neighbourhood, minimising the engineering hours needed to include this option.

The functional units of a coal fired plant are shown in Figure 5, highlighting the condensate supply module, in this case, an option with a redundancy of 3 x 50 per cent. If we change to the 2 x 50 per cent option then one feedwater pump and its associated piping system are eliminated. However regardless of the variation in the number of pumps, the remaining major piping remains and is independent of the chosen level of redundancy. Even the geometrical CAD information for the condensate supply module is very large so handling the huge quantity of information involved can only be done with very powerful IT-tools. The information associated with the module is not limited just to geometry but also extends to bills of materials, boundary conditions, scheduling, costs etc.

A similar approach is used for combined cycle plant design, with functional units and, within them, modules. Typical modules for a combined cycle plant are shown in Figure 6. For the single-shaft combined cycle plant shown it is arranged around the main components, the gas turbine, the steam turbine and the generator.

Advanced design tools

When developing those modular basic power plant concepts a huge amount of data is generated for which powerful computer tools are necessary. The concept of modularisation can achieve its full potential only if this huge amount of data can be handled easily, including development of the information itself, storage and linkage to other data. This allows the savings in development and construction times as well as in engineering costs to be fully realised.

At Siemens KWU the computer tool for planning and logistics is called SIGMA. In developing and constructing power plants, this is used in the following areas:

Providing system and component information using a 2D CAD tool for PI&D’s;

Providing three dimensional geometrical information on the power plant for civil construction, steel construction, component layout, piping, HVAC and cable trays;

Linking the above information to the logical structure of the plant in order to develop bills of materials and for linking associated documentation;

Construction of the power plant. The software developed for the generic basic power plant concept is linked to a logical hierarchical project structure into which subsupplier information, material data, material cost, and specific schedules are added in order to manage activities such as sourcing, ordering, controlling costs and scheduling.

As shown in Figure 7 we have arranged these software modules around an Oracle database, while for the graphical 2D and 3D information we work with Intergraph systems. The plant structure, plant construction and control is done with SAP and for communications and work flow we have Lotus Notes.

A pioneering effort is our management system for data and documents called PDME. PDME is the information hub, where all data and documents are stored, within which all people engaged in a project can search, copy, mail and store their work input and work output. This means that everyone involved always has the latest data and documents, depending on their access rights.

Since the SIGMA software tool is not only used for designing power plants but also for project management during construction, it has been also necessary to link all our engineering and project sites worldwide.

Flexibility and investment security

An important and growing section of our clients demands “power generation machines” to engage in a highly competitive business, with a minimum capital cost and construction time. Their focus is on realising inexpensive, yet high-performance and reliable power plants. This meets their main concern: high investment security. Beyond that technical details are not of primary interest. However, the solutions offered must also provide the necessary flexibility to accommodate a certain amount of customer-specific requirements.

This objective can be met by using pre-engineered reference power plant designs that have a modular structure and offer pre-engineered options. For the customer this means the following benefits:

Detailed, very instructive information for the client is available in the very early stages of a project or when evaluating the bid.

When starting the project the total bill of materials, including technical specifications, is available.

Shorter manufacturing times are achieved in our own shops and at the sub-suppliers, for example by pre-ordering castings and forgings.

Improved construction quality due to the earliness and completeness of design documents, checked for consistency.

Use of proven, reliable components with high performance and reliability.

Early availability of all necessary documentation in a complete form.

Effective project execution.

Milestone project

The 380 MWe Otahuhu combined cycle power plant in New Zealand, illustrates a milestone project that fits into today’s business environment (see Figure 8).

Using the advanced 3A-series gas turbine it achieved a record plant efficiency level of 58 per cent in 1998.

The project was awarded as a turnkey contract and, employing a pre-engineered modular single-shaft plant configuration, the contractual schedule was 20 months, another record.

Advanced engineering tools were used for the power plant design, which also supported logistics and project execution. On the left of Figure 8, the 3D–CAD model of the plant, as described above – planned in virtual reality – on the right, the plant in reality, successfully in place at the Otahuhu site.