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26350 No.20 June 1999

Gas Turbine Based Power Plants: Technology and Market Status Robert Taud, Juergen Karg and Donal O’Leary This Note provides an overview of the issues related to the development and utilization of gas-turbines (GT) when used either in open-cycle or combined-cycle (CC), and is divided into three major parts: • natural gas-fired plants. • non-natural-gas fired plants utilizing fuels such as low Btu gases, ash-forming fuels oils (e.g. crude oils and heavy oils), naphtha, condensates or gases from the iron and steel industry. • integrated gasification combined cycle (IGCC). Technology and environmental performance, design, costs and trends in market demand are discussed. The paper indicates how ongoing research and development trends can deliver further efficiency and performance benefits.

Major points discussed in the Note include • Industrial gas turbines are a well-established technology, manufactured by major industrial groups in Europe, Japan and North America whose performance has benefited greatly from the large expenditures over the last fifty years on the development of aero-jet engines. Ongoing development and near term introduction of the most advanced products will improve GTefficiency to about 40% in the case of the largest GT units (250 MW to 350 MW). GTs, in combination with waste heat recovery steam gen-

erators that supply steam to steam turbines thus forming a combined cycle (CC) plant, are already achieving efficiencies well over 50%, with these projected to approach 60% within the next few years with corresponding plant capacities being in the range of 375 MW to 500 MW. • Using low cost salts such as Epsom salts as inhibitors the GT components of combined cycle plants can be successfully fired with contaminated fuel oils of high sodium and vanadium content. Use of such fuels demand less sophisticated gas turbine

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Robert Taud is Head of Product Marketing in the Product Center of the Gas Turbine/Combined Cycle Power Plant Division of Siemens Power Marketing Group (KWU) in Erlangen,Germany. Juergen Karg is the Manager of IGCC Power Plants and Gasification Technology for KWU. Donal O’Leary, Sr., Power Engineer of the World Bank, is on assignment with KWU under the Siemens/World Bank Staff Exchange Program. This paper has been prepared under the Siemens/World Bank Partnership Program (c.f. note on page 8). The paper was reviewed and edited by Masaki Takahashi and Stratos Tavoulareas.

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Gas Turbine Based Power Plants: Technology and Market Status

technology with lower inlet temperatures and rigorous monitoring so that formation of corrosive salts and acids is entirely inhibited. • In some countries, deregulation followed by competition has caused downward pressure on generator’s prices thus benefiting GT technology since power from these units can be produced at very competitive rates especially in the current environment of low oil and gas prices. Tightening environmental standards have also helped to increase market share of GTs since their low specific emissions of SOx, NOx, particulates and ash provide them with a comparative advantage over other power generation technologies. Their relatively low level of greenhouse gas (GHG) emissions may also be noted. • GT turbines prices which had been falling steadily for some years have recently stabilized and firmed as suppliers cope with full order books. • GTs have the ability to handle a wide variety of fuels of varying quality, including low calorific value as well as contaminated fuels (the latter requiring great care for their successful use). IGCC that utilize refinery fuels and gasified coal is expected to become a widespread commercially proven technology. This is likely to occur first in developed countries (e.g. Italy) for refinery applications. In the case of developing countries and especially for coal-based applications, commercial competitiveness is still to be demonstrated. This results partly from the fact that in developing countries technical operating risks are perceived to be greater with some consequences for commercialization of the technology. • The cost and construction time of GT based plants have been reduced in part because of design standardization and automation as well as their modularity i.e. plant construction and commissioning can be staged in accord with the demands of the power system (c.f. Energy Issues No. 18). The paper provides an example of a project that burns a non-natural gas fuel, the 220 MW CC Valladolid power plant (Mexico) which burns heavily contaminated fuel oil.

Natural Gas Fired Plants Market Demand Contract awards for the last five years for fossil fuel-fired power plants (above 50 MW) averaged 63 GW per year and, sales are forecasted to average about 67 GW per year over the period 1999–2004 The market in Asia Pacific is declining, while that of Europe is showing moderate growth (from a low level). Strong growth in North America is reflected in the growth of the 60Hz market. In the past, the proportion of power plants with gas turbines, i.e., opencycle and combined cycle (combining gas and steam turbines) was around 54% of total fossil fuel-fired power plants. For the next five years (until 2005), this proportion is expected to rise to 63%. For open and combined cycle power plants, this means that sales are expected to grow from 34 GW per annum to 42 GW per annum. This growth is predominantly due to market developments in North America. In addition, open-and combined-cycle gas turbine plants are expected to take an ever increasing share of the power market in developing countries where low cost natural gas is available.

Figure 2. Cost Breakdown for CC Power Plants Integrated Services Project Management/Subcontracting

4%

Plant and Project Engineering/Software

2%

Plant Construction/Commissioning/Training

8%

Transport, Insurance

1% 15%

Lots Civil Works

15%

Gas and Steam Turbine Set

32%

Balance of Plants

16%

Electrical Systems

7%

Instrumental and Control

4%

Boiler Island

11% 85%

Basis for example: 350/700 MW CC Plant with a V94.3A Gas Turbine

Energy Issues

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In comparison with coal-fired power plants, open and closed cycle power plants are characterized by lower capital investment costs. On the other hand, fuel costs play a relatively more important role. Worldwide gas prices range from US$ 2.0/GJ to US$ 4.5/GJ, with prices in Latin America (Southern Cone), some Asian countries and North America being at the lower end of the range. Thus, for example in the USA, Bangladesh and Argentina open and closed cycle power plants can be particularly attractive investments.

Technology/Performance/ Environment/Design Trends Over the last 50 years, the efficiencies of gas turbines have increased from 33% to 38% (LHV) and those of combined cycle plant from 48% to 58%. At present, there are a rather small number of global manufacturers and suppliers offering GT-products covering a wide range of power output. The products of the different suppliers can be grouped in clusters by comparable output. For all major manufacturers, small (50 MW) and medium classes (50 to 200 MW) includes proven existing GT-models with lower efficiencies and operating temperatures, but with robust and reliable performance; the large classes (above 200MW) are those that deliver higher-performance. The latest gas turbine technology also reflects the expertise of aero-jet engine manufacturers. As a result, using pressure ratios of around 17, performance features have been achieved for heat rates in the range of 9,400-9,800 kJ/kWh and for efficiencies up to 38%. These performance improvements have been achieved through • improved compressor design • higher turbine inlet temperature (approximately 1250°C ISO) • advanced blading (design, materials, coating) • optimal design of the turbine blade cooling system, with or without need for external coolers • improved cooling of the combustion system sections (chamber, canes, transitions) • less pressure drop in the turbine exhaust.

Less than 25-ppm NOx emissions can be expected from these plants. This compares with the maximum allowable levels of 60 ppm for GTs fired with natural gas as set out in the World Bank’s “Thermal PowerGuidelines for New Plants”. Because of better materials (alloys and coatings), with a higher resistance to high temperature oxidation and corrosion, combined with better cooling techniques, gas turbines are expected to reach a unit capacity of around 250 MW to 350 MW) and efficiencies of 40% over the next years . In conjunction with optimized main steam parameters and with improved plant component efficiencies, this in turn will increase CC plant capacity to the 375 MW–500 MW range, with CC efficiencies around 60%. (See also Figure 1). From a plant aspect, plant construction time has been shortened by the concept of predesigning, introduction of modules and by advanced project management and scheduling?. Inter alia, this was effected by simplification of the electrical and instrumentation and control systems as well as the foundation and overall civil works construction requirements. In addition, plant operation has been simplified by, for example, allowing full 100% steam bypass operation in the event of steam turbine malfunctions.

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Gas Turbine Based Power Plants: Technology and Market Status

Cost Trends Typical combined-cycle block are in the range of 50 MW to 500 MW and costs range from US$ 500–US$ 750 /kW. It is noteworthy that GT turbine manufacturers have currently little spare manufacturing capacity (due in large measure to strong sales in North America) and this has possibly been a factor in causing prices recently to level off. Prices had been on a downward trend for some time. Impacts on Design and Manufacturing in Developing Countries Figure 2 shows the cost breakdown based on Siemens’ experience for combined cycle plants (350 MW–700 MW capacity). Up to approximately 25%35% of the costs of CC plants can be provided locally in countries such as Argentina, Brazil, China, India, Malaysia, the Philippines, South Africa and Thailand. These include some of the engineering services (project engineering/project management as well as plant erection/commissioning) as well as some or all of the civil works; balance of plant, electrical systems and the boiler island.

Upgrading Fossil-Fueled Power Plants The operators of established power plants often seek to improve plant performance beyond what can be achieved through routine maintenance; in particular, operators look for higher output, additional heat extraction, improved pollution control and improved plant control.. A common approach is to incorporate a gas turbine into an existing fossil-fired steam generation system. The most common configuration is called parallel powering (See Figure 3), where gas turbine exhausts are used in the existing steam cycle. This is achieved by feeding the exhausts into a heat-recovery steam generator (HRSG) which provides additional steam to the existing steam turbine. Typically, parallel powering requires the addition of a gas turbine, associated electrical and instrumentation and control equipment, civil engineering, HRSG, additional piping and pumps as well upgrading the steam turbine. Generally, parallel powering can be undertaken fairly separately from the existing part of the plant, with a final integration phase and a plant down time of 1.5 to 2 months. The typical cost is in the range $US$ 300–500/kW.

Figure 4. Operational Experience with Naptha and Heavy Oil-Fired CC Plants Naptha Class Projects Plant Name Paguthan

Location India

Fuel Naptha, Distillate, Natural Gas

Gas Turbine Model 3 x V94.2 1 GUD 3.94.2

Rating 630 MW

Operating Hours 19,000 hours

Santa Rita

Philippines

Naptha, Condensate, Distillate, Natural Gas

4 x V84.3A 4 GUD 1S.84.3A

950 MW

Construction phase

Faridabad

India

Natural Gas, Naptha, HSD

2 x V94.2 1 GUD 2.94.2

440 MW

Engineering phase

Latest Plants with Ash-Forming Fuels Plant Name Valladolid

Location Mexico

Fuel Residual Oil

Gas Turbine Model 2 x V84.2 1 GUD 2.84.2

Rating 220 MW

Operating Hours 24,000 hours

Kot Addu

Pakistan

Furnace Oil (heavy oil)

4 x V94.2 2 GUD 2.94.2

820 MW

60,000 hours

Rousch

Pakistan

Heavy OIl

2 x V94.2 1 GUD 2.94.2

390 MW

Commissioning phase

Gas turbines delivered for ash-forming fuels have in total accumulated approximatey 140,000 operating hours

Energy Issues

Gas Turbine-Based Plants Utilizing Fuels Other Than Natural Gas While natural gas and light oil distillates are the preferred standard fuels for gas turbines, many other fuels have been used successfully. Such fuels include: low Btu gases; ash-forming fuel oils (such as crude oils and heavy oils), naphtha, condensates and gases from iron and steel industries. These fuels are often available in developing countries when higher quality fuels are not. Market Demand Due to the variety of application, reliable statistics on the extent of non-natural gas-fired

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turbines in operation are not available. Figure 4 provides a sample of naphtha- and heavy oil-fired power plants in operation and in the planning stage. As this table shows, some plants (e.g., Kot Addu and Valladolid) have logged 30-60,000 hrs of successful operation over five years or more. Up to 25% of the gas turbine output (in MWs) to be built in the next 10 years could use non natural gas fuels. Naphtha and condensates are expected to be the dominant fuels in this category with a few thousand MW of new capacity being added every year.

Figure 5. Gas Turbines for None Standard Fuels; Critical Fuel Properties Critical Fuel Properties

Fuels

Effect on Standard Fuel System

Low Viscosity (reduced lubricity)

Naptha, Kerosene, Condensates

Effect on fuel supply system (e.g. pump design)

Low density (high volume flow)

Naptha, Condensates burner nozzles

Limits for fuel supply system and

Low flash point, Low boiling point (high vapour pressure)

Naptha, Kerosene, Liquefied Petroleum Gases (LPG) High Speed Diesel (HSD) Condensates

Increased explosion protection effor t Increased ventilation effort

Low ignition point

Naptha, Condensates

Effect on premix capability Increased explosion protection effor t Increased ventilation effort

Contaminants (high temperature corrosion, ash deposits)

Contaminated fuel oils, Crude oils, Heavy Oils Heavy residues

Effect on blading and hot gas path counter-measures: • temperature reduction (reduced performance) • Fuel treatment (washing/inhibitor dosing)

Low heating value (high volume flow)

Process and synthesis gases (low calorific gases), Low BTU natural gas

Effect on layout of compressor, burner nozzles, fuel supply system

High heating value (low volume flow)

LPG, gaseous and liquid

Effect on layout of burners, fuel supply system Limited start-up and part-load capabillity

High H2 content

Process and synthesis gases (low calorific gases)

High flame velocity, Effect on premix capability

High dew point

Gases with high boiling components

Droplets causes erosion and non constant heat flow

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Gas Turbine Based Power Plants: Technology and Market Status

behavior (e.g. ignitability, flame velocity and stability) and plant emissions. Technological adaptation and additional equipment and operational requirements are necessary to cope with these difficult fuel properties. These include GT-layout ( compressor and turbine) for the changed mass flows, different burner technology (burner design and burner nozzles), additional startup/shutdown fuel system and safety measures. Performance, availability and operation & maintenance (O&M) expenses will be affected. To illustrate this, Figure 5 shows important non-standard fuel properties and their effect on a standard fuel design.

Technology/Performance/Design Trends Design and operation of these plants requires more attention than natural gas fired plants particularly in relation to fuel properties such as calorific content, density, chemical composition including concentration of contaminants, as well as different combustion

An example of gas turbine combined cycle plant burning a non-conventional fuel is the 220 MW Valladolid plant in Mexico. This plant has been operating since 1994 burning heavily contaminated fuel oil, containing up to 95 ppm sodium and potassium and up to 300 ppm vanadium. Sodium, potassium and vanadium impurities tend to form ash particles in the combustion process, forming deposits that can corrode the gas turbine blades. Such fuels have to be treated. Sodium and potassium have to be reduced to very low limits.

Figure 7. Comparison of Suppl Flows, Emissions and Byproducts of Different 600MW-Class Power Plants

Plant Pulverized-Coal-Fired Steam Power Plant

Coal/Natural Gas (g/kWh)

Limestone (g/kWh)

CO2 (g/kWh)

SO2 (mg/kWh)

NO2 (mg/kWh)

Ash (g/kWh)

Gypsum (g/kWh)

Rejected Heat (MJ/kWh)

320

12

770

560*

560*

32

19

4,0

22**

730

525*

525*

56***

56***

3,2

140

275

29 (Slag) 4 (Sulfur)

Combined Cycle Power 300 Plant with Pressurized Fluidized Bed Combustion Integrated CoalGasification GUD Power Plant

285

700

Natural-Gas-Fired GUD Power Plant

125

345

* 200 mg/m 3 Flue gas (STP, Dry basis, 6 vol. % O 2)

** Molar Ca/S-ratio=2

315

*** Ash/Gupsum/Limestone mixture

3,0

2,3

Energy Issues

Figure 8. Main Criteria for Selection of the IGCC Integration Concept Integration Options 1. Non-integrated (independent) ASU 2. Partially integrated ASU 3. Fully integrated ASU Criteria for Selection of the Integration Concept • Gasification process and waste heat recovery (syngas cooler, quench, cooler/saturation cycle) • ASU process • Fuel gas analysis (with or without nitrogen return) • Limits for NOx emissions • Overall plant efficiency • Investment costs • Operational aspects • Site-specific aspects • Necessary modifications of standard gas turbines • Available fuel flow

Vanadium requires magnesium additive dosing and reduction of inlet temperature (the latter resulting in reduced plant performance). In the case of the Valladolid plant, “Epsom salts”, consisting mainly of magnesium sulfate (MgSO4 7 H20), were dissolved in water injected into the gas turbine combustor. Magnesium reacts with vanadium forming a stable water-soluble product (magnesium vanadates). This is deposited downstream of the combustor on the gas turbine blades where it causes only minor blade corrosion and can be removed through blade washing. At Valladolid, it was determined that washing every 150 hours was necessary to keep aerodynamic performance of the blades, plant efficiency and reliability near to design levels. Good manhole access was a critical factor to ensure that servicing and maintenance during turbine washing shutdowns was simplified. It is planned to convert the Valladolid plant to natural gas operation in the near future.

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Integrated Gasification Combined Cycle (IGCC) Plants IGCC plants consist of three main sections: the “gas island” for conversion of coal and/or refinery residues (such as heavy fuel oil, vacuum residues or petroleum coke) including gasification and downstream gas purification (for removal of sulfur, alkali, and heavy metal compounds to meet required emissions levels and gas turbine fuel specifications), the air separation unit (ASU) and the combined cycle (CC) plant. The modular design (gas generation, gas turbine system, HRSG and the steam turbine system) offers the possibility of phased construction as well as retrofitting of CC plants with a gasification plant, thus replacing the “standard” gas turbine fuels (natural gas or fuel oil) by syngas produced from coal or refinery residues. IGCC is in principle a combination of two mature technologies. However based on the lessons learned in several demonstration projects in Europe and the USA proper integration of the main sections is the key to the success of the IGCC projects Although, there are more that 350 gasifiers operating commercially worldwide and at least seven technology suppliers commissioning more than 100 CC units per year there is only limited experience of commercial operation as integrated IGCC plants. Commercial application of IGCC using residual refinery fuels and gasified coal is expected to be proven

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This paper is one of a series on fossil fuel generation tech nologies. The others are on modular plant design and on super critical coal fired power plants. Issues that ar e pertinent in developing countries are addressed. The series has been prepared by staff at Siemens KWU in collaboration with the World Bank. More detailed informa tion is available on-line at http://www.worldbank.org/ html/fpd/em/emhome.htm Energy Issues is published by the Energy, Mining and Telecommunications Sector Family in the World Bank. Energy Issues are intended to encourage debate and dissemination of lessons and ideas in the energy sector. The views published ar e those of the authors and should not be attributed to the World Bank or any of its affiliated organizations. To order additional copies please call 202- 473-32427. If you are interested in writing an Energy Issues note, contact Kyran O’Sullivan, editor, internet address, [email protected]. The series is also available on-line at http://www. worldbank.org/html/fpd/ energy/ The World Bank also publishes the Viewpoint series. Viewpoints are targeted at a multidisciplinary audience and aim to promote debate on privatization, regulation and finance in emerging markets, especially in the energy, transport, water, and telecommunications sectors. The series aims to share practical insights and innovations that cross sectoral boundaries. The series is available on-line at www.worldbank.org/html/ fpd/notes/notelist.html

Gas Turbine Based Power Plants: Technology and Market Status

first in developed countries, such as Italy. In the case of developing countries technical operating risks are perceived to be greater with some consequences for commercialization of the technology. An overview description of IGCC technology is available on the World Bank’s web page at http://www.worldbank.org/html/fpd/em/emhome. htm. This includes a review of generic gasification processes, IGCC performance; IGCC commercial availability; IGCC suitability for developing countries and IGCC deployment issues. Operating experience of five IGCC plants is also reported. Market Demand Through 2015, the potential for refinery-based combined cycle (IGCC) plants is estimated to be 135 GW. Currently over 6 GW of coal and refinery residue based IGCC projects are either under construction or are planned (Figure 6).

Technology/Performance/ Environment/Demand Trends Figure 7 compares the supply flows, emissions and by products of different 600 MW-class plants It may be noted that the environmental performance of IGCC plants in terms of reduced emissions is better than that of pulverized coal-fired steam power plants. Depending on the degree of integration between the gas turbine and the air separation unit (ASU), either standard gas turbine/compressor configurations can be applied or in some cases only limited modifications are required to compensate for the mismatch between turbine and compressor mass

flows which results from the use of gases with low heating values. Three principal options are available. Selection of the appropriate air and nitrogen integration concept depends on a number of factors to be considered on a case by case basis. A summary of the important criteria for selection of the different IGCC integration concepts are provided in Figure 8 Figure 9 sets out the three main integration options. The “fully integrated approach” which was selected for the European coal-based demonstration plants results in the highest efficiency potential, but should be considered as highly sophisticated from the operational point of view. Nevertheless, after some initial operational problems, the Buggenum IGCC facility in the Netherlands has now demonstrated that this type of plant can be operated successfully according to specified availability rating. The non-integrated concept with a completely independent ASU is expected to have advantages with respect to simplified plant operation and possibly in achieving higher availability ratings. On the other hand, the loss in overall IGCC net plant efficiency compared with the fully integrated concept amounts to 1.5 to 2.5 percent. The non-integrated concept is therefore primarily of interest in cases where efficiency is not the key factor (e.g. for the gasification of refinery residues). The concept of partial air-side integration (Option 2) is an interesting compromise solution, with only moderate loss in efficiency but improved plant flexibility compared with the fully integrated concept.