Merchant Power Plants: Midlothian: a model merchant

At the beginning of the 20th century, electricity was still something of a miracleà‚– a novelty confined to relatively few of the world’s homes and factories. By the end of the century, electrical power had become arguably the most essential ingredient in the world’s economy; without it, life as we know it for most of the world’s population would be completely unrecognizable, and virtually all of Man’s technological and cultural achievements over the past 120 years would simply not have happened.

Electricity underpins and integrates the world’s economy, and it enables not only industry, but also the hyper-connected,

24 hour global real-time network we rely on for communications, finance, and trade. Without it, our world would come to a halt.

Restructuring … again

Right across the globe the electric power industry is going through a major transformation. Dozens of countries have already radically changed their electricity sector over the past decade, and many others are either in the process of restructuring or are planning to restructure. While the details of this restructuring process vary from one country to another, the trend is the same: government involvement is being reduced in favour of private ownership and the dictates of market forces.

Regardless of which energy sources are used to generate the world’s power, electricity’s central role in the economy will certainly continue in the new century. Modern technology, production and equipment all rely on electricity in order to function, while any equipment that contains embedded microprocessors, such as televisions, computers, and communications hardware, depend on a constant supply of high-quality electrical power. The fact is that e-commerce would be impossible without electricity.

Because electricity is inextricably linked to the world economy, any economic expansion will inevitably result in an increased demand for electricity, and with it the need for an increasingly reliable electric infrastructure.

The expected rapid move to highly competitive power markets has in most cases simply not happenedà‚– or at least, not as fast as anticipated. Whether it is gauged by the number of customers in the market or by the amount of unregulated electric consumption, the US electrical power industry has yet to pass the halfway point in what is likely to be more than a ten-year restructuring process.

This slow pace of change has complicated the development of competitive markets for energy sales and services. It is likely that this trend will continue, and the power industry is almost certain to face another round of restructuring in an attempt to correct the shortcomings in the market, whether they are real or perceived.

This somewhat confused and unsatisfactory state of affairs means that, just as the role of electric power in the economy is changing, the US power industry itself is in the throes of what must be seen as a prolonged and untidy transition from tight regulation to fluid and unpredictable market forces.

Power aplenty

Figure 1. Midlothian will feature six KA24-1 ICS power trains
Click here to enlarge image

Across the country a lot of new power plants, both merchant and rate-based, are being developed or constructed with a combined capacity that is currently in excess of 175 000 MWà‚– by any yardstick, an astonishing figure, and one that has tripled in the last two years. In fact, according to the Electric Power Supply Association, there are strong indications that plant developers are accelerating construction and bringing forward proposed completion dates. In two of the more capacity-constrained areas of the east central and upper Midwest, for example, the proposed capacity for 2001 has jumped fourfold in the past year, from 4300 MW to almost 17 000 MW.

More significant than the absolute numbers of megawatts is the percentage of current installed capacity that these new projects representà‚– in Texas, for example, new projects account for more than ten per cent of current capacity. Of course, because of financing difficulties, political pressures, equipment supply problems and energy source deficiencies, some of these proposed plants will never be built. But many will, and merchant power will no longer be just an industry buzzword but an economic reality.

From coast to coast, a whole new generation of merchant plants currently being developed are beginning to come on-line, and they will provide an unprecedented opportunity to examine how power generation will look in the 21st century. Being able to design, build, staff, operate and maintain these new facilities from the ground up, without being restricted by existing designs, contracts and budgets, will allow plant developers and operators to show the world how successful an open merchant market can be.

A model merchant plant

One excellent example of a potentially successful merchant plant is International Power’s Texas energy facility, Midlothian. This plant, currently being completed in the TXI Railport industrial park some 48 km south of Dallas, features a technology and a development plan that make it a truly representative blueprint for the future.

Figure 2. Midlothian is expected to be complete by the end of 2001
Click here to enlarge image

When the last of the plant’s six units comes on-line in December 2001, Midlothian will be one of the largest combined cycle gas turbine facilities in the countryà‚– though its future will be tied to the Texas market which, according to National Power PLC, International Power’s parent, is one of the best electricity markets in the USA. With around

59 000 MW of capacity, Texas alone consumes almost as much power as the whole of Britain. Importantly, Texas is also an island market, with very little interconnection to adjoining power grids, and it includes more than 25 000 MW of older gas plants that for a long time set marginal prices.

The Texas grid area supports a competitive wholesale electric market for most (approximately 85 per cent) of Texas. Established in August 1996, the Texas grid was created to address three major issues: providing a secure operating environment for the bulk electric system; ensuring the efficient use of the electric transmission system by all the market participants; and coordinating future transmission planning. The grid’s market operations began in September 1997, and it currently has an installed capacity of over 59 000 MW.

How it happened

In 1998, TXI sold a 24 hectare industrial park to International Power, to develop a gas-fired power plant. A year later an additional 12 hectares were purchased to accommodate a two-unit plant expansion, and according to the industrial park development plan, International Power will become the anchor tenant, and help attract other industries to the park.

The notice to proceed at Midlothian was received in September 1998, and site clearance began in January 1999. Commercial operation is scheduled in to begin in late 2000. Designed as a 1100 MW-capacity plant (though this was recently expanded to 1650 MW), Midlothian will provide a highly competitive choice in the fast-deregulating Texas electricity market. Under a two-year power purchase agreement, the entire output from the plant will initially be sold to TXU Utilities. After this the Midlothian plant’s full capacity will be made available to the merchant market, with the nearby Venus substation acting as the gateway to the Texas grid.

Power train

Alstom Power secured the $400 million turnkey contract from International Power for the 1100 MW gas-fired, air-cooled, combined cycle power plant designed around four KA24-1 ICS single-shaft power trains. International Power, previously known as the independent power producer (IPP) American National Power Inc., is a subsidiary of Britain’s National Power PLC.

As an extension to this contract, Alstom Power has also secured an additional order for the turnkey supply of two more air-cooled KA24-1 ICS standardized combined cycle power plants. These new gas-fired plants will deliver a total capacity of over 500 MW, and the plant is expected to be complete by the end of 2001.

In addition to the six GT24 gas turbines, the contract requires Alstom to supply the associated steam turbines, electrical generators and heat recovery steam generators, and the company will also be responsible for the engineering, procurement and construction work. Alstom Power will also provide the power plant control and distribution systems, and handle the complete installation and commissioning processes.

Figure 3. Alstom has also won contracts for other merchant plants in the USA
Click here to enlarge image

The six units at Midlothian are all based on Alstom’s GT24 “B” version gas turbine. Each turbine train at Midlothian is designed for outdoor use. Units one and two just completed a three month semi-commercial operation period with an availability of above 92 per cent, and have been dispatching successfully over the summer peak period. These two units are shortly due for commercial operation. Units three and four are scheduled for commercial operation by the end of the year and have both been ignited and synchronized. Units five and six will be fully operational by the end of 2001. To enhance power output in the important summer peak period, the plant is equipped with evaporative cooling system for the inlet air.

Alstom Power, which is the engineering procurement construction (EPC) contractor for the Midlothian plant, has already won contracts for several other merchant facilities operated by International Power. These include the 1100 MW Hays facility under construction in San Marcos, Texas, and two plants in Massachusetts: the 570 MW Blackstone plant and the 570 MW Bellingham facility.

The Midlothian plant is expected to be one of the largest merchant power plants in the rapidly deregulating US power market. Merchant plants are optimized to deliver power on demand to meet the actual short-term needs of the open market, rather than the traditional long-term contract and guaranteed prices that are typical of regulated markets. Alstom’s integrated combined cycle technology, with its emphasis on efficiency and reliability with low emissions, will enable International Power to meet the fluctuating demands of the merchant power market.

Highly efficient technology

Alstom’s Single-Shaft Power Train (SSPT) is a sophisticated and innovative cost-saving approach to power generation that improves overall performance. Only one electrical generator for each unit is used, which has a gas turbine coupled to one end and a steam turbine at the other end, creating a “single shaft” alignment of the equipment. The gas turbine is coupled directly to the generator, while the steam turbine high pressure (HP) and low pressure (LP) sections are coupled to the generator through a self-shifting and synchronizing clutch.

Figure 4. Over 175 000 MW of new power capacity is under development in the USA
Click here to enlarge image

Compared to a conventional unit of similar power output, with its multiple generators and their associated equipment, an overall reduction in the complexity and size of the plant is gained. More importantly, this arrangement results in a highly efficient operation. The GT24 is a state-of-the-art sequential combustion gas turbine. The turbine features two separate combustion chambers which, together with three variable inlet guide vanes, allow continuous optimization of firing conditions for both full and part load operations.

Component compatibility

The entire power train (gas turbine, steam turbine, condenser, and heat recovery steam generator) is engineered as a standardized package designed for optimum operating efficiency and component compatibility. The basic components of facilities being built at the Midlothian site are virtually identical to those of International Power’s other units across the country. This component compatibility means that any day-to-day installation problems encountered and solved in one field can either be eliminated before they occur, or quickly solved, when encountered in other unitsà‚– an important consideration that leads to improved construction efficiencies for future installations.

No posts to display