In spite of its name, products from Solar Turbines are not powered by the sun. A unit of Caterpillar, the world’s largest construction equipment company, Solar Turbines designs, makes, and services industrial gas turbines. It has installed more than 15,000 units in more than 100 countries. Its products are used in oil and gas production, natural gas transmission, and crude oil pumping systems, as well as for electrical and thermal power generation. In addition to gas turbine engines, gas compressors, and gas turbine-powered compressor sets, Solar Turbines offers mechanical-drive packages and generator sets. Besides manufacturing, Solar Turbines offers ancillary services such as financing, installation, and aftermarket parts support.
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Solar turbines range from the Solar Saturn 1.2MW with an efficiency of 24.3% and a heat rate of 14,023 BTU/kW h (16,000 kJ/kW h) to the Titan, which is rated at 21.745 MW, at an efficiency of 40% and a heat rate of 9695 BTU/kW h (10,230 kJ/kW h).
FIELD AND SIMULATED FIELD EXPERIENCE
Sudhangshu Bose, in High Temperature Coatings, 2007
Oxidation and Hot Corrosion in Industrial Gas Turbines
In the United States, documentation of field experience on coatings and alloys is more readily available for industrial gas turbine (IGT) engines than for aircraft engine applications, primarily because of the involvement of Electric Power Research Institute (EPRI), which caters to a consortium of power utilities and manufacturers in many areas of technology. EPRI-sponsored testing provides independent assessment of coatings for gas turbine power plants. An example of coatings performance assessment (McMinn et al., 1988) is EPRI’s testing of coatings in Pratt & Whitney built FT4 turbine at Long Island Lighting Co (LILCO). The details of the materials tested are summarized in Table 10.4.
Irwin M. Hutten, in Handbook of Nonwoven Filter Media, 2007
Turbines are a form of engine and therefore are included in this chapter on engine filtration. Turbines are rotating devices designed to generate energy, either mechanical or electrical. The gas turbine in a jet aircraft engine is an example of mechanical energy generation. The turbine rotates a compressor that compresses the inlet gas. One or more ignition chamber injects and ignites fuel to heat and expand the gas and provide the exhaust thrust necessary to drive the aircraft. In large-scale power plants, the turbine operates a rotating electrical generator to produce electricity for the realm that is serviced by the power plant.
There are several types of turbines; including steam turbines, hydroelectric, solar turbines, wind turbines, and gas turbines. The complexities of the gas turbine machine are of interest to the filter and filter medium manufacturer, because of stringent requirements for inlet gas cleanliness. According to the US Department of Energy(197) gas turbines basically involve three main sections:
The compressor, which draws air into the engine, pressurizes it, and feeds it to the combustion chamber literally at speeds hundreds of miles per hour.
The combustion system, typically made up of a ring of fuel injectors that inject a steady stream of fuel (e.g. natural gas) into the combustion chamber where it mixes with the air. The mixture is burned at temperatures of more than 2,000°F. The combustion produces a high temperature, high pressure gas stream that enters and expands through the turbine section.
- The turbine is an intricate array of alternate stationary and rotating aerofoil-section blades. As hot combustion gas expands through the turbine, it spins the rotating blades. The rotating blades perform a dual function: they drive the compressor to draw more pressurized air into the combustion section, and they spin a generator to produce electricity.
Table 10.5. Coating Ranking Based on Performance in FT4 Industrial Gas Turbine Engine (1 High, 5 Low)
Coating Location of Worst Coating Attack Maximum Coating Thickness, µm (mil) Coating Ranking Based on Test Comments CoCrAlY Outer shroud 56 (2.2) 1 No substrate attack, isolated shallow penetration of coating Pt–Rh–aluminide Lower platform 102 (4.0) 1 No substrate attack, isolated penetration of coating, general thinning, voids in coating Rh–aluminide Lower platform 64 (2.5) 2 Shallow attack on substrate, coating penetrated at several locations, protective elsewhere Rh–aluminide(HIPed) Outer shroud 74 (2.9) 2 Shallow attack on substrate, coating penetrated at several locations, protective elsewhere Aluminide All locations 48 (1.9) 4 Complete local coatingpenetration, uniform coating attack, some substrate attack Aluminide(HIPed) Outer shroud, Mid-span 48 (1.9) 5 Complete coating defeat at many locations, some substrate attack Pd–aluminide Lower platform 173 (6.8) 5 Extensive coating penetration, some debonding
Several overlay and aluminide coatings have been field tested in Solar Turbines Mars T-14000 industrial gas turbines (Kubarych and Aurrecoechea, 1993). These coatings included Chromalloy produced simple aluminide RT-21 of average thickness 75 μm (3 mil), platinum aluminide RT-22 of thickness 65–115 µm (2.5–4.5 mil), and two overlay coatings designated VPS and 1386 of average thickness 100 pm (4 mil). The coatings were deposited on two different nickel base superalloys, the polycrystalline Mar-M 247 and single-crystal CMSX-4. The engine ran on natural gas for 4333 hours with 44 starts before inspection. Natural gas is generally a clean fuel, does not contain any significant amount of sulfur, and therefore, does not induce hot corrosion. After removal of some of the blades, the engine continued with replacements for more than 8000 hours with the goal to eventually accumulate a total of 20,000 hours of exposure. The estimated temperature over most of the airfoil was moderate, less than 980°C (1800°F). Without cooling holes, the temperature at the blade tip rose close to 1090–1120°C (2000–2050°F). Posttest visual observation as well as microstructural analysis showed:
All four coatings successfully protected the substrate alloy.
Both RT-21 and RT-22 degraded at the leading edge because of aluminum depletion leading to the transformation of β (NiAl) to γ′ (Ni3Al).
For the MCrAlYs, the transformation of β(NiAl) to γ′ (Ni3Al) at the leading edge was practically complete.
RT-22 was slightly better than RT-21 with less γ′ formation on degradation.
The use of natural gas in the test preempted any hot corrosion. Thus, the degradation mode was predominantly oxidation. RT-22 faring better than RT-21 in degradation to γ′ validates the benefit of Pt.
Large industrial gas turbine engines, used in power generation, require significantly higher component lives than do smaller power plants and aircraft engines. For example, turbine blades in IGTs are expected to last 70,000 to 100,000 hours, whereas lives of typical aircraft engine turbine blades are 15,000 to 20,000 hours. Oxidation, coating and substrate cracking, and hot corrosion, therefore, have additional significance for IGT. A number of alloys and coatings have been developed particularly for IGT applications. A few aircraft engine alloys and coatings have also been modified to accommodate IGT requirements. Schilke et al. (1992) have reviewed material issues in General Electric’s large frame power plants. The review provides a glimpse of coatings used in IGTs in GE machines and their performance, summarized in Table 10.6.
Several points are evident from Table 10.6. As expected, platinum aluminide, both as single-phase and in two-phase coatings, provides protection against hot corrosion. This result, when combined with a 1.5 × improvement of corrosion life by overlays over Pt aluminide, indicates that the hot corrosion is present in both type I and type II form. Also, the success of aluminizing over MCrAlYs indicates that the Al reservoir in the overlay coating is inadequate to meet the oxidation life requirements of the IGT parts.
Table 10.6. General Electric’s Coatings for IGT Turbine Application
Coating Performance characteristic Comments Platinum aluminide(single phase solid solution or solid solution + PtAl2) 2X corrosion life relative to uncoated IN-738 Used between late 1970 and mid 1983 LPPS Overlays 1.5X corrosion life improvement relative to platinum aluminide Introduced early 1980 GT-29 Baseline MCrAlY GT-29+ Aluminized over MCrAlYUsed for firing temperature 1065°C (1950°F) in air cooled first blade and for firing temperature 955°C (1750°F) in uncooled first blade Standard coating since 1990 Overaluminizing improves oxidation resistance GT-29 In+ Used on internal surfaces in vanes GT-20 Used on vanes Developed for aircraft engine
High-temperature oxidation, as well as hot corrosion of LPPS-deposited CoCrAlY and CoNiCrAlY, have been reported by Kameda et al. (1997, 1999) on René 80 superalloy turbine blades of land-based gas turbines with various exposure times ranging between 8946 and 22,000 hours. Coating thickness varied between 120 and 200 μm (4.8–8 mil) for CoCrAlY coating tested in an engine burning liquefied natural gas (LNG). The CoNiCrAlY coating, tested with combined LNG and kerosene fuel, had thickness between 140 and 250 μm (5.6–10 mil). The CoCrAlY coating, exposed to a turbine environment burning LNG, underwent severe oxidation and loss of ductility after 21,000 hours of exposure. No hot corrosion was observed, obviously because of the inherent cleanliness of LNG. The use of combined fuel, however, induced not only oxidation, but also grain boundary sulfidation for CoNiCrAlY. The reduction in ductility was much more severe.
The data of Kameda et al. do not afford one-on-one comparison between CoCrAlY and CoNiCrAlY for fighting hot corrosion because they were tested using different fuels. However, the presence of sulfides in posttest analysis indicates that the corrosion is most likely to be type I. Life of the alloys and coatings in the IGT environment is influenced not only by the type of contaminants, but by their quantitative levels in the fuel, as shown by Schilke et al. (1992) (Fig. 10.4). For every 1 ppm increase in equivalent sodium, the life debit is approximately 50%. The source of sodium is likely to be in the form of a combination of chloride and sulfate. The latter is directly involved in hot corrosion. The chloride works in two ways. It produces sulfate salts in the combustor by reacting with SO2 formed from oxidation of sulfur in the fuel. Additionally, sodium chloride accelerates the spallation of the alumina scale, which protects the alloys and the coatings from further oxidation.
Solar Thermal Electricity and Solar Insolation
Salahuddin Qazi, in Standalone Photovoltaic (PV) Systems for Disaster Relief and Remote Areas, 2017
A steam turbine is a form of steam engine that extracts thermal energy from pressurized steam and converts it to rotary motion which is used to drive an electrical generator. A solar turbine works on the same principle as any steam-driven generator powered by the fossil fuels except the way the steam is produced to power the turbine. In a solar turbine, steam is generated by using a transmission fluid that is heated by capturing sunlight with a number of parabolic mirrors which in turn boils the water. The most important difference between powering steam turbines by fossil fuels and solar energy is the operation cycle. Due to the intermittent nature of solar radiation, solar turbines need to work efficiently during repeated starts and stops throughout the day. As a result, steam turbines for CSP plants should match the applications specific demands including a number of starts, rapid-startup capabilities and re-heat options for maximum performance.
One weakness of the current solar turbine is that transmission fluids cannot be heated above 400°C, although turbines are capable of operating with steam heated up to 540°C which would generate more power. This shortcoming could be overcome by placing the turbine on a high tower with the mirrors aimed to focus the sunlight directly on the steam boiler instead of using transmission fluid in the pipes. The majority of CSP plants except the parabolic dish operate according to Rankine thermodynamic cycle, wherein a steam turbine coupled to an alternator converts thermal energy into electricity. Steam turbines are only practical for very large CSP installations.
A STUDY OF A SOLAR-MAGNETOHYDRODYNAMIC POWER CYCLE
L. Juan, S. Hernández, in Energy Developments: New Forms, Renewables, Conservation, 1984
In this paper, a scheme of a solar-magnetohydrodynamic installation for the production of electrical power is proposed and analyzed. The proposal is based upon recent technological achievements in both involved areas: solar concentrators and receivers, and magnetohydrodynamic (MHD) converters.
The usual methods for producing electrical power from solar energy have low efficiencies. In photovoltaic conversion, one of the so-called methods for direct-conversion to electricity, the efficiency as well as the electric power levels attained are relatively low. Another method for producing electrical power, from solar energy, based upon the classical scheme evaporator (solar boiler) – steam turbine – turbogenerator has efficiencies of about 30 to 35 percent, generally.
The latter mentioned method, though, allows generation of electrical powers in the low megawatts range. For instance, in the recent Solar One plant, put in operation in 1982 in California, the generated electrical power is about 10 MW. This installation consists of a set of 1818 heliostats, automatically following the sun and focused toward a central receiver, as the solar concentrator. (1,2,3)
As a magnetohydrodynamic (MHD) converter can attain an excellent efficiency as compared with a conventional turbine-alternator scheme, and it is capable of directly generating electrical energy on a wide range of power and voltages, it is interesting to study its combination with a solar, concentrator-receiver, scheme. Such a study is covered in this paper, mainly in the sense of demonstrating the technological feasibility of a solar – MHD plant, of analyzing its principal components, and of estimating its size and efficiency. The paper concentrates on the MHD part. (4,5)
It can be mentioned that there exist already, as it is well-known, commercial MHD power plants – with fossil fuels – delivering electrical energy to power networks. (6,7)
Finally, it can be added that, besides the scheme adopted in this paper, there are other alternatives for realizing a solar-MHD system. (5)
The Proposed Solar-MHD Scheme
The solar-MHD scheme proposed in this paper is sketched in Figure 1. The solar subsystem would consist of a concentrator and of the central receiver. The concentrator is, typically, a set of heliostats or reflectors, such as those already used in known solar turbine-alternator plants. (1,2,3) The central receiver is a heat – exchanger which would absorb the solar energy from the concentrator, as heat, and would utilize it for heating an electrical conducting (slightly ionized) gas or liquid. Details of the central receiver will be given in the next Section of the paper.
Founded in 1927, Solar Turbines has been a leader in energy solutions and advanced manufacturing. Today, Solar is a leading provider of industrial gas turbine engines, compressors and mechanical drive packages and a key player in the 1,590 to 31,900 horsepower (hp) segment of the global gas turbine market.
As a major contributor to the production and transmission of the world’s daily output of oil and natural gas, Solar gas turbines produce low exhaust emissions that meet or exceed emission standards around the world.
Solar Turbine’s rugged, reliable industrial gas turbines can operate on a wide variety of fuels, including natural gas, distillates, NGL, LNG, coal-seam methane, hydrogen and renewable fuels, such as landfill and sewage gases. The group manufactures mid-size industrial gas turbines for use in electric power generation, gas compression and pumping systems.
Products from Solar Turbines include:
- Six families of gas turbine engines: Saturn®, Centaur®, Mercury™, Taurus™, Mars®, and Titan™; rated from 1,590 to 31,900 horsepower.
- Ten models of Solar® centrifugal gas compressors and gas turbine-powered compressor sets for both production and pipeline applications, mechanical-drive packages and generator sets ranging from 1 to 24 megawatts.
- Solar also manufactures Turbotronic™ microprocessor-based control systems.
Around the world, more and more people are recognizing the benefits to the environment and the favorable economics of renewable fuels. With low emissions and quiet operation Solar gas turbine engines provide clean, sustainable energy solutions for customers, helping to protect the health of workers and job sites, and respecting residents of communities and neighborhoods around the world.
The Solar brand delivers high value, products and services to customers. More than 70 percent of Solar’s products are exported from the United States. Solar sells, manufactures and services its products in more than 100 countries. Solar participates in two major market segments: Oil and Gas Production and Transmission (O&G), and Power Generation (PG).
Advantages Of Gas Turbines
Compared to other power technologies, Solar gas turbines have a number of advantages:
- Higher reliability and availability
- Lower operating costs
- Utilizes clean and other renewable fuels
- Lowers emissions
- High quality exhaust heat stream can be used in other processes
- High power density
- Broad range of power module blocks
- Reduces construction costs
- Easy to transport and quick startup
- Improve reliability
- Easy to permit
- Worldwide service and support
Gas Turbine Overview
A gas turbine engine is a type of internal combustion engine. Essentially, the engine can be viewed as an energy conversion device that converts energy stored in the fuel to useful mechanical energy in the form of rotational power. The term “gas” refers to the ambient air that is taken into the engine and used as the working medium in the energy conversion process.
This air is first drawn into the engine where it is compressed, mixed with fuel and ignited. The resulting hot gas expands at a high velocity through a series of airfoil-shaped blades transferring energy created from combustion to turn an output shaft. The residual thermal energy in the hot exhaust gas can be harnessed for a variety of industrial processes.
Basic Gas Turbine Components:
Compressor – Takes in outside air and compresses it.
Combustor – Fuel is added to the pressurized air and is ignited.
Turbine – Converts the energy from high velocity gas into rotational power through expansion.
Output Shaft and Gearbox – Delivers rotational power to the driven equipment.
Exhaust – Directs the low emission spent gas out of the turbine section.