Patent Application
20110210555
This invention relates to industrial gas turbines in single cycle and combined cycle power plant systems.
The first gas turbine designs were used for airplane applications, which require maximum output at take-off and reduced power during cruise. These engines were designed to obtain maximum thrust by matching the maximum output from the compressor to the turbine section. This philosophy was carried over to the first applications of gas turbines as power drives for other applications. During the 1950's, the first applications for electrical power generation were made with engines that were small in output by today's standards and were not considered major suppliers for power generation. As gas turbine technology evolved with the development of combined cycle applications and larger capacity engines, the design philosophy of matching the maximum compressor capability (mass flow rate) to a turbine section at a base load design point was continued. This has resulted in gas turbine electrical power plants that have large variations in power output with changes in ambient conditions, since the density of the ambient air may be less than the assumed design point conditions on any given day, and the compressor may thus be incapable of supplying its full design mass flow rate, and the downstream components such as the combustor and turbine must then be throttled back to match the actual mass flow output of the compressor. This reduction in power output usually occurs coincident with times of peak power demand, such as on unusually hot days. Power output may change on the order of 30% with a change in ambient temperature from 90° F. to 10° F. for example. To compensate for the loss in power with changes in ambient conditions, some designs utilize steam augmentation (injecting steam into the gas turbine at the combustor), wet compression (injecting water into the compressor inlet), or afterburners. These methods add expense and are not practical in all areas, such as where water is a scarce resource.
The invention is explained in the following description in view of the drawings that show:
The present inventors have discovered a new gas turbine engine configuration which provides both cost reduction and operational improvement. The inventors have recognized that the prior art approach to gas turbine engine design, i.e. matching the compressor to the turbine at a base load design point, results in the compressor being the limiting component for operations during non-optimal ambient conditions. The compressor of a prior art gas turbine driven electrical power system is always operating at maximum output when the plant is called to produce its maximum electrical output. However, the downstream components of the system, such as the combustor, gas turbine, electrical generators, heat recovery steam generators (HRSG), steam turbine and balance of plant, will only be operating at maximum output when the ambient conditions are adequate for the compressor to produce its design maximum mass flow rate. During sub-optimal ambient conditions, such as at high temperatures, the compressor will produce less mass flow than its design mass flow, and therefore, all downstream components of the system must be operated at below their respective maximum design capacity because the compressor is the limiting component in the system. All down stream components are sized for the maximum expected output of the compressor, but they normally operate at less than maximum capacity due to less than optimum ambient conditions and loss in engine capability over time with aging. The cost for all the supporting equipment is therefore not optimum.
A gas-turbine-driven electric power generating system according to an embodiment of the invention has a compressor sized to produce an airflow that is adequate to support maximum design points of the other system components during a least-dense ambient condition within the system design range of ambient conditions. The compressor is designed to operate effectively (i.e. without surging or other undesirable operating conditions) to produce adequate compressed airflow to support full power operation of the system over a full range of least-favorable to most-favorable ambient conditions. A variable inlet on the compressor may be used to automatically modulate the inlet airflow for full power output despite varying ambient conditions, and to restrict mass airflow to the needed amount. A margin of capacity may be included in the compressor to compensate for system efficiency degradation with time, so the system maintains a rated output over its entire design lifetime.
The system 20A of
“Maximum design point” or “maximum design power output” herein is an operating level of a system or component that maximizes its power output or throughput under continuous operation without accelerated wear or loss of safety or efficiency. It also may be called the rated output. For example, an electrical power generating system or plant may have a rated output of 200 MW. Industry-accepted tolerances may apply. “Design range of ambient conditions” herein means a range of atmospheric conditions under which a system or component is designed to operate.
The compressor 28A supports the maximum design point of the engine 26A even at the least dense expected ambient condition. Therefore, any more favorable ambient condition can produce excessive airflow from the compressor. In one embodiment, this may be compensated by a variable inlet 72 of the compressor using control logic 74 and a control mechanism that adjusts the inlet 72 in response to changing ambient conditions to produce the rated power output of the gas turbine engine throughout a full design range of ambient atmospheric conditions. A sensor 76 at the inlet or in the compressor may provide input on ambient conditions and/or mass flow conditions to the control logic 74. Variable inlet guide vanes may provide a mechanism to vary the inlet 72 as later described.
Each component of the gas turbine engine 26A downstream of the compressor 28A, and each component of the electrical power generating system 20A, may operate continuously at its respective maximum design point, providing full utilization of all components at full efficiency under all conditions. No capacity is idle anywhere except at times in the compressor, minimizing cost of the system 20A for a given rated output.
This changes the economics and operation of power systems. No longer will system output decrease as the air density decreases, requiring a utility with a given load requirement to compensate for the expected loss in power. In addition, all components that comprise a system (other than the compressor) can be operated at their design point at all times, maximizing capital utilization. No longer will customers buy a system for a given load only to watch the power decrease with ambient temperature and with time as the system degrades, instead the variable guide vanes will modulate open to compensate for less than optimal ambient conditions and for normal wear within design limits. All of this is accomplished without reducing the life of components or over-firing the engine.
For a gas turbine system of 200 MW simple cycle output or 300 MW combined cycle output, the larger compressor is expected to add $0.5 to $1.0 million dollars to the engine cost. But in the environment of the northeast United States, a system designed per the present invention, when compared to the prior art systems, will produce on average about 45 MW more output per day during the year, and generate about $25 million additional revenue per year for a base-loaded power plant from the same capital expenditure plus the additional cost for the compressor. This greatly increases the value of such a plant.
In
The rated power output of the electrical power generating system 20A, 20B may be defined at a reference ambient condition, such as International Standards Organization ISO 2314 or ISO 3977-2, or it may be defined at an average ambient condition at the installation site. However, despite departures from the reference condition the compressor provides sufficient airflow to produce constant system output at the maximum design point of the other components of the system throughout a full design range of ambient atmospheric conditions. Thus, the system 20A, 20B may have a rated power output over the entire design range of ambient conditions.
While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.
