One or more aspects of the present invention relate to method, apparatus and system for thermodynamic cycle optimization for a steam turbine cycle. In particular, one or more aspects relate to improving thermodynamic cycle performance in steam turbines utilizing excess heat that is normally wasted in conventional steam turbines.
Currently, excess heat flow from a steam seal header is dumped to a condenser as illustrated in
Hence, before admitting the dump steam into the low pressure stage, the temperature of the dump steam needs to be brought down within acceptable limits. Conventionally, this is achieved through attemperation, mixing with low grade steam, and so on. But such conventional methods can be wasteful in that the heat of the dump steam lost through attemperation is not used for useful work. This reduces the steam turbine cycle efficiency. Also the heat transfer is limited by the sink temperature of the heat exchanger (in the case of feed water heater line). The dump steam cannot be cooled below the feed water heat temperature conventionally without using attemperation.
It would be desirable to utilize the excess heat, and thereby enhance the efficiency of the steam turbine cycle.
An aspect of the present invention relates to a steam turbine that comprises a high pressure turbine stage, a low pressure turbine stage, a steam seal header, a boiler, and a heat pump. The high pressure turbine is fluidly connected to a high pressure steam source to receive a high pressure entry steam from the high pressure steam source. The high pressure turbine stage is structured to convert energy of the high pressure entry steam into mechanical energy and output a high pressure exhaust steam. The low pressure turbine stage is fluidly connected to a low pressure steam source to receive a low pressure entry steam from the low pressure steam source. The low pressure turbine stage is structured to convert energy of the low pressure entry steam into mechanical energy and output a low pressure exhaust steam. The steam seal header is fluidly connected to an output of the high pressure turbine stage and fluidly connected to an input of the low pressure turbine stage. The steam seal header is structured to receive at least a portion of the high pressure exhaust steam from the high pressure turbine stage and output a dump steam to the low pressure turbine stage such that the dump steam comprises the portion of the high pressure exhaust stream. The boiler is fluidly connected to a work fluid source to receive work fluid from the work fluid source. The boiler is structured to generate primary steam by applying heat to the work fluid. The heat pump is fluidly located in between the steam seal header and the low pressure turbine stage, and is also fluidly located in between the work fluid source and the boiler. The heat pump is structured to transfer heat from the dump steam to at least a portion of the work fluid.
The invention will now be described in greater detail in connection with the drawings identified below.
These and other features of the present invention will be better understood through the following detailed description of example embodiments in conjunction with the accompanying drawings, in which:
Novel method, system, and apparatus for thermodynamic cycle optimization for a steam turbine cycle are described. In one aspect, the described method, system, and apparatus utilize heat pumps to transfer the excess heat from a dump steam in a useful manner. For example, the heat from the dump steam can be transferred to an exiting feed water heater flow and/or to leak-off flows from pressure packing and valve stems. In this way, the mismatch between the dump steam and the reentry steam temperature at a header of a steam turbine stage can be brought within acceptable limits.
Typically, the pressure difference between a seal steam header (SSH) and a low pressure (LP) turbine stage is the main factor in driving the flow. Thus, in many instances, the dump steam will be provided to the header of the low pressure turbine stage. The dump steam may be provided to the header of any turbine stage where there is an availability of suitably high pressure steam and provisions on the shell at the required sections in the steam turbine.
If there is another source of dump steam such as an intermediate pressure (IP) turbine stage, the steam seal header 240 can be fluidly connected to an output of the intermediate pressure turbine stage to receive intermediate pressure exhaust steam, or at least a portion thereof, from the intermediate pressure turbine stage seal packing. In this instance, the dump steam can comprise a portion of the high pressure exhaust steam and/or a portion of the intermediate pressure exhaust steam.
Note that the terms low pressure and high pressure should be interpreted in a relative sense and not in an absolute sense. For example, low pressure turbine stage is not limited to the lowest pressure turbine stage. The phrase “low pressure turbine stage” simply indicates that relative to a high pressure turbine stage or an intermediate pressure turbine stage, the low pressure turbine stage works with lower pressure steam. In one aspect, the pressure of the steam entering the low pressure turbine stage (low pressure entry steam) is lower than the pressure of the steam entering the high pressure turbine stage (high pressure entry steam) or the pressure of the steam entering the intermediate pressure turbine stage (intermediate pressure entry steam). Similarly, high pressure turbine stage does not necessarily refer to a highest pressure turbine.
Unlike the conventional system illustrated in
One way to extract the heat from the dump steam is to transfer the heat to work fluid flowing to a boiler. In the
Note that while some of the preheated work fluid can bypass the heat pump 250, at least some can also flow through the heat pump 250. That is, in addition to being fluidly located in between the steam seal header 240 and the low pressure turbine stage 230, the heat pump 250 can be fluidly located in between the FWH 270 and the boiler such that at least a portion of the preheated work fluid flows through the heat pump 250. The heat pump 250 can transfer the heat from the dump steam to the portion of the work fluid flowing through it to reduce the temperature of the dump steam entering the low pressure stage 230. Preferably, the temperature of the dump steam is sufficiently reduced to be within acceptable temperature limits.
By using the heat pump 250 to transfer heat from the dump steam to the work fluid, additional work can be extracted from the dump steam. Also, greater thermodynamic efficiency can be gained by further heating the work fluid entering the boiler 480.
In an aspect, the heat pump 250 can include one or several heat transfer devices 255. The arrows on the heat transfer devices 255 indicate the direction of heat transfer. Preferably, the heat transfer devices 255 are solid state heat transfer devices. Examples of solid state heat transfer devices include thermoelectric devices, thermionic devices, and thermoelectric-thermionic combination devices. The heat transfer devices 255 can be used as heat pumps via the peltier effect.
While not illustrated, it is fully contemplated that one or more flow control mechanisms can be put in place, such as controllable valves, fluid pumps, etc. so as to control flow rates of any of the dump steam flow, the work fluid flow within the heat pump 250, and the work fluid flow that bypasses the heat pump 250. It is also contemplated that the electrical power applied to the solid state heat transfer devices 255 can be controlled. In this way, rate of heat transfer from the dump steam to the work fluid can be controlled as well.
In
Also in
But instead of the FWH 270, a leak-off collector 360 is shown. The leak-off collector 360 can collect leak-off steam flows from end packings, from valve stems of one or more turbine stages, or from both. The leak-off collector 360 can output leak-off flow to the FWH 270 (not shown in
As seen in
For explanation, the reader's attention is directed to
In one aspect, the stages are differentiated by the pressure of the entry steams. That is, the pressure of the high pressure entry steam is higher than that of the intermediate pressure entry steam, which is higher than that of the low pressure entry steam. Recall that “high pressure”, “intermediate pressure” and “low pressure” should be interpreted in a relative sense.
Further, the high, intermediate, and low pressure turbine stages 410, 420, 430 need not be consecutive. That is, there can be intervening stages between the high and intermediate pressure stages 410, 420 or between the intermediate and low pressure stages 420, 430. Yet further, the number of stages at a particular pressure is not limited to one. For example,
Referring back to
As seen in
As indicated above, the aspects described in this disclosure can be applied to a steam turbine system two stages. Thus, the intermediate pressure turbine stage 420 is not strictly necessary. However, when the system 400 does include the intermediate pressure turbine stage 420, the steam seal header 440 can also be fluidly connected to an output of the intermediate pressure turbine stage 420 to receive at least a portion of the intermediate pressure exhaust steam such that the dump steam also comprises a portion of the intermediate pressure exhaust stream.
The heat pump 450 can be fluidly located in between the steam seal header 440 and the low pressure turbine stage 430 and in between the work fluid source, e.g. the condenser 460, and the boiler 480. In this instance, the heat pump 450 can transfer heat from the dump steam to at least a portion of the work fluid.
The system 400 can also include a FWH 470, which can be fluidly located in between the work fluid source and the boiler 480, and the heat pump 450 can be fluidly located in between the FWH 470 and the boiler 480. In this instance, the heat pump 450 can transfer heat from the dump steam to at least a portion of the preheated work fluid.
Note that in
In this embodiment, the leak-off collector 560 can be a work fluid source. Thus, the heat pump 450 can be fluidly located in between the work fluid source, e.g., the leak-off collector 560, and the boiler 480, and can transfer heat from the dump steam to the work fluid. The dump steam can comprise a portion of the high pressure exhaust steam from the high pressure turbine stage 410. When the system 500 also includes the intermediate pressure turbine stage, the dump steam can include a portion of the intermediate pressure exhaust steam as well. Like
Of course, the embodiments may be combined as illustrated in
The disclosed aspects are applicable to turbine systems other than the specific examples described thus far. The number of steam seal headers and heat pumps are not limited. Also, excess heat from any exhaust flow that would not be utilized in the conventional system can be converted for useful purposes in light of the disclosed aspects.
There are numerous advantages associated with the disclosed aspects. Among them are:
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.