Gas Turbine.docx

Gas Turbine 不是要比 GT25000 和 LM2500 的功率-温度曲线

LM2500 系列：

GT25000：

注意哦，上一幅图很狡猾的使得曲线更平滑些，具体你真要算一下才知道哦。

Gas turbine selection: Heavy frame or aeroderivative By Amin Almasi · On April 25, 2012

Optimum gas turbine selection can be done after good comparison of the different types of turbines There are variations between aeroderivative and heavy frame industrial gas turbines including weight, size, efficiency, design, bearing type, and lubrication oil system. Heavy industrial frame or aero-derivative Heavy frame industrial gas turbines compared to aeroderivative gas turbines are usually slower in speed, narrower in operating speed range, heavier, larger, have higher air flow, slower in start-up and need more time and spare parts for maintenance. Heavy frame industrial gas turbines use hydrodynamic bearing.

A heavy duty gas turbine (GE 10, left) and an aeroderivative LM6000. Aeroderivative gas turbines use anti-friction bearing. Advanced aircraft engine and space technologies have been used to provide maintainable, flexible, light weight and compact

aeroderivative gas turbines. The key to maintainability is the modular concept which provides for removal of components and replacement without removing the gas turbine from its support mounts. The heavy frame industrial units, by contrast, require more amount of effort to remove and replace components (especially combustor parts) and more effort to inspect or repair the sections. The user should weigh needs and requirements against the variety of gas turbines offered. Traditionally, preference has been to place the aeroderivative units in remotely located applications (including offshore) and to place heavy frame industrial units in easily accessible base-load applications. The heavy frame industrial gas turbines consume more fuel and more air than the aeroderivative units. They are exposed to a greater quantity of the contaminants in air that cause corrosion. Today aeroderivative gas turbines offer 10-15% more efficiency compared to heavy frame industrial type gas turbines. Some engineers predict aeroderivative gas turbines may replace traditional heavy frame industrial type gas turbines in the future! Hot end or cold end drive In a hot end drive configuration the output shaft is at the turbine end where exhaust gas can reach high temperatures and it may affect bearing operation and life. Also, it may be difficult to service the unit as the assembly must be fitted through the exhaust duct. Constraints of the hot end drive: output shaft length, high temperature, exhaust duct turbulence, exhaust duct pressure drop and maintenance accessibility. Insufficient attention to any of these details often results in power loss, vibration, shaft (or coupling) failure and increased down-time for maintenance. In the cold end drive configuration the output shaft extends out the front of the aircompressor. Here the driven equipment is accessible, relatively easy to service, and is exposed to ambient temperature only. Drawback: air-compressor inlet must be configured to accommodate the output shaft and the driven equipment. This inlet duct must be turbulent free and provide vortex free (uniform) flow throughout the operating speed range. The problem resulting from a poor design could be catastrophic, for example, inlet turbulence can induce surge in air-compressor resulting in complete destruction of the unit. However, inlet duct turbulence could often be eliminated at the expense of pressure drop. In modern gas turbine applications “hot end drive” is usually used. Single-spool or multi-spool Single-spool integral-output-shaft gas turbines (both hot end drive and cold end drive) are used primarily to drive electric generator. The integral shaft gas turbine is uncommon for mechanical drive applications. The high torque required to start pumps and compressors under full pressure results in high turbine temperature during the start-up cycle when cooling air flow is low or non-existent. Integral shaft gas turbine may only be used in very

large LNG compressor trains (such as Frame 7 or Frame 9, using helper/start electric motor). A split output shaft gas turbine could be considered as a single spool gas turbine driving a free power turbine. The air-compressor-turbine shaft (air-compressor and its turbine shaft assembly) is not physically connected to the power turbine shaft, but they are coupled aerodynamically. This makes starting easier in mechanical drive. It is usually referred to as “split shaft mechanical drive gas turbine”. It could attain self sustaining operation before it picks up the load of the driven equipment. The power turbine can be designed to operate at the same speed as the driven equipment and eliminate the need for a gearbox (typical gearbox losses are 2-5%). This design is limited to the hot end drive configuration. In dual spool split output shaft gas turbine, independent low and high pressure air-compressors and turbines generate the hot gases that drive the free power turbine.

Technology Overview

INTRODUCTION This section addresses two of the following frequently asked questions: What is TIC? Why Cool Turbine Inlet Air? What is TIC? A typical schematic flow diagram of a combustion turbine (CT) system is shown in Figure 1. TIC is cooling of the ambient air before it enters the compressor that supplies high-pressure air to the combustion chamber from which hot air at high pressure enters the combustion turbine. TIC is also called by many other names, including combustion turbine inlet air cooling (CTIAC), turbine inlet air cooling (TIAC), combustion turbine air cooling (CTAC), and gas turbine inlet air cooling (GTIAC).

Figure 1. Schematic Diagram of a Typical CT System

Why Cool Turbine Inlet Air? The primary reason turbine inlet air is cooled is to reduce or prevent the often significant loss of power output, compared to the rated capacity, of combustion turbines when ambient air temperature is high. TIC can even help to enhance CT output above its rated capacity. TIC is applicable to all combustion turbines (CTs), whether operating in simple-cycle, cogeneration, and combined-cycle systems. The rated capacities of all CTs are based on the standard ambient air conditions of 59oF and 14.7 psia at sea level, as selected by the International Standards Organization (ISO). One unattractive characteristic of all CTs is that their power output decreases as the inlet air temperature increases as shown in Figure 2.

Figure 2. Effect of Ambient Temperature on the Output of CTs

It shows the effects of inlet air temperature on power output for two types of CTs: Aeroderivative and Industrial/Frame. The data in Figure 2 are typical for the two types of turbines. The actual characteristics of each CT could be different depending on its actual design. The data in Figure 2 show that for a typical aeroderivative CT, an increase in inlet air temperature from 59oF to 100oF on a hot summer day, decreases power output to about 73% of its rated capacity. This could lead to a loss of opportunity for power producers to sell more power just when the rise in ambient temperature increases power demand for operating air conditioners. By cooling the inlet air from 100oF to 59oF, we could prevent the loss of 27% of the rated generation capacity. In fact, if we cool the inlet air to about 42oF, we could enhance the power generation capacity of the CT to 110% of the rated capacity. Therefore, if we cool the inlet air from 100 oF to 42oF, we could increase power output of an aeroderivative CT from 73% to 110% of the rated capacity or boost the output capacity by about 50% of that at 100oF.

How Does TIC Help Increase CT Output? Power output of a CT is directly proportional to and limited by the mass flow rate of compressed air available to it from the air compressor that provides high-pressure air to the combustion chamber of the CT system. An air compressor has a fixed capacity for handling a volumetric flow rate of air for a given rotational speed of the compressor. Even though the volumetric capacity of a compressor is fixed, the mass flow rate of air it delivers to the CT changes with fluctuations in ambient air temperature. This mass flow rate of air decreases with an increase in ambient temperature because the air density decreases when air temperature increases. Therefore, the power output of a combustion turbine decreases below its rated capacity at the ISO conditions (59oF and 14.7 psia at sea level) with increases in ambient temperature above 59oF. TIC allows an increase in air density by lowering the temperature, and thus, helps increase the mass flow rate of air to the CT and results in increased output of the CT.

TECHNOLOGIES Many technologies are commercially available for TIC. These technologies can be divided into the following major categories/groups:

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Evaporative: wetted media, fogging, and wet compression

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Chillers: mechanical and absorption chillers without or with thermal energy storage (TES)

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LNG Vaporization

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Hybrid Systems: combinations of several technologies

All of the technologies listed above have inherent advantages and limitations. Many published articles are available on these technologies. A number of these publications are listed in the Library section. Wetted media is one of the evaporative cooling technologies in which cooling is achieved by evaporation of the water added to the CT inlet air. Historically, it is the first technology to be used for TIC. In this technology, the inlet air is exposed to a film of water in one of the many types of wetted media. A honey-comb-like medium is one of the most commonly employed media. Wetted media can cool the inlet air from the ambient dry-bulb temperature by 85% to 95% of the difference between the ambient dry-bulb and wet-bulb temperature. It is one of the lowest capital and operating cost options. The extent of cooling is limited by the wet-bulb temperature. It works most efficiently during hot and dry weather and is less effective when ambient humidity is high. On an overall basis, this is the most widely used technology. Fogging is another evaporative cooling technology. The basic idea in this technology is to add water to the inlet air by spraying very fine droplets of water. Fogging systems can be designed to produce droplets of variable sizes, depending on the desired evaporation time and ambient conditions. The water droplet size is generally less than 40 microns and on an average it is about 20 microns. The water used for fogging typically requires demineralization. Fogging systems can cool the inlet air by 95% to 99% of the difference between ambient dry-bulb and wet-bulb temperature. Its capital cost is very comparable to that for the wetted media. It is the second most frequently applied technology for TIC.

Wet Compression is yet another evaporative cooling technology in which more fog is added to the inlet air than can be evaporated under the conditions of the ambient air. The air stream carries the excess fog into the compressor section of the CT where it further evaporates, cools the compressed air and creates extra mass for boosting the CT output beyond that possible with the evaporative cooling technologies. The cooling of the compressor section reduces work in the compressor section, allowing increased power available from the system. Wet compression also leads to additional power augmentation due to the increased mass flow of the water and fuel in the system in order to maintain constant firing temperature. Wet compression is a complementary technology and can provide added benefit to any other TIC technology. Mechanical Chiller systems cancool the inlet air to lower than wet bulb temperature and when properly designed can maintain any desired inlet air temperature down to as low as 42oF, independent of ambient wet-bulb temperature. The mechanical chillers used in these systems could be driven by electric motors, steam turbines or engines. Drawing the inlet air across cooling coils, in which either chilled fluid or refrigerant is circulated, cools it to the desired temperature. Mechanical chiller-based TIC systems are more capital intensive than evaporative systems and when using electric motors, these systems also have the highest parasitic loads. The chilled water can be supplied directly from a chiller or from a TES (Thermal Energy Storage) tank that stores ice, or chilled fluid. A TES system is typically used when there are only a limited number of hours per day when inlet air cooling is needed. TES can reduce overall capital costs because it reduces the chiller capacity requirements as compared to the capacity required to match the instantaneous on peak demand for cooling. Since the chillers in TES systems are operated during the off-peak period using low-cost electricity for charging the TES tank, such a system increases the net power capacity during the on-peak period. Absorption Cooling systems are similar to the mechanical refrigeration systems except that instead of using mechanical chillers, these systems use absorption chillers that require thermal energy (steam or hot water) as the primary source of energy and require much less electric energy than the mechanical chillers. Absorption cooling systems can be used to cool the inlet air to about 50oF. These systems can be employed with or without chilled water TES systems. Absorption chillers can be single-effect or double-effect chillers. The single-effect absorption chillers use hot water or 15-psig steam (18 lb./RT-hr) while the double-effect chillers require less steam (10 lb./RT-hr) but need the steam at higher pressure (115 psig). Compared to mechanical chillers, absorption cooling systems have lower parasitic loads but higher capital costs. The primary successful applications of Absorption chillers in power plants are where excess thermal energy is available and the conversion of this energy to high-value electric energy creates a winning situation for the user. LNG Vaporization systems are useful for power plants located near a liquefied natural gas (LNG) import or storage facility. In supplying natural gas for power plant or other applications, LNG must be vaporized by some heat source. For applications in TIC, the inlet air is used as such a heat source. Hybrid Systems incorporate some combination of two or more technologies, such as mechanical and absorption chillers, evaporative and chilling, and fogging or chilling with wet compression. The objective of hybrid systems is to maximize net power output during hot weather. Each hybrid system needs to be optimized for a specific plant based on the weather data, power demand and electric prices and availability of thermal energy.