Patent Application
20130048265
The present application relates generally to gas turbines and more particularly, to a chiller coil arrangement in a gas turbine inlet filter house.
Gas turbine engines typically include a compressor for compressing incoming air, a combustor for mixing fuel with the compressed air and to ignite the fuel and the air to form a high temperature gas stream, and a turbine section that is driven by the high temperature gas stream. It is generally accepted that lowering the temperature of the inlet air entering the compressor results in an increased power output, and there are known methods for reducing the air inlet temperature to the engine in so-called power augmentation systems. A power augmentation system may include a chiller coil arrangement located in the turbine inlet filter house that reduces the temperature of the inlet air stream. Examples are described in, for example, U.S. Pat. No. 7,007,484 B2 and U.S. Patent Publication No. 2005/0056023 A1.
It has been determined that for gas turbine filter houses with asymmetric geometry, however, the inlet air temperature profile in the duct downstream of the chiller coil is not uniform because of the variable velocity of the inlet air flowing over the coils at different heights within the filter house. Resulting non-uniform air temperature distribution cause undesirable stress on the compressor components.
There is a need, therefore, for a chiller coil system that provides substantially uniform inlet air temperature even when installed in asymmetrical gas turbine inlet filter houses.
Accordingly, in one exemplary but nonlimiting embodiment, the present invention relates to a chiller coil system for an asymmetric gas turbine filter house comprising a plurality of chiller coil modules arranged in a substantially vertical array, each chiller coil module provided with a cooled fluid inlet pipe and a fluid outlet, each outlet pipe connected to a common return pipe, wherein at least some of the inlet pipes is connected to the common return pipe; and mixing control valves for controlling an amount of cooling fluid in the common return pipe to be added to the at least some of the inlet pipes.
In another exemplary but nonlimiting aspect, the invention relates to a chiller coil system for an asymmetric gas turbine filter house comprising a plurality of chiller coil modules arranged in two substantially vertical arrays, each chiller coil module provided with a cooled fluid inlet pipe and a warmed fluid outlet pipe, each warmed fluid outlet pipe connected to a common return pipe; wherein at least some of the cooled fluid inlet pipes are connected to the common return pipe, and wherein a mixing control valve controls an amount of warmed fluid in the common return pipe to be added to the at least some of said inlet pipes.
In still another exemplary but nonlimiting aspect, the invention provides a method of controlling temperature of inlet air flowing across a chiller coil assembly of a gas turbine, wherein the chiller coil assembly comprises a plurality of substantially vertically aligned chiller modules and wherein inlet air flow velocity varies across the chiller modules as a function of vertical height of the chiller modules, the method comprising determining temperature differential of the inlet air downstream of each module, and differentially adjusting temperature of cooling fluid in the plurality of chiller modules to produce a substantially uniform temperature for the inlet air downstream of the chiller coil assembly.
The invention will now be described in greater detail in connection with the drawings identified below.
With reference to
The module arrangement and control valve arrangement for the Group B stack is substantially identical to that of Group A, and therefore, only Group A will be described in detail, except as otherwise noted.
Chilled water (or other suitable cooling fluid) is supplied to the Group A stack of modules via common supply pipe 38. Each module is supplied individually by respective branch pipes 42, 44, 46, 48, 50 and 52. The cooling water exiting the modules via respective return branch pipes 54, 56, 58, 60, 62 and 64 joins to a common return pipe 39 which returns the newly-“warmed” water (due to heat exchange with the inlet air flowing across the module coils) to cooling towers (not shown) which ultimately return chilled water to the supply pipe 38. A separate manual vent valve 60 relieves pressure in the system as necessary. Vent valves 40 and 68 are for automatic vents and are in a normally open position.
Due to the asymmetric nature of the filter house construction, inlet air velocity over the chiller coils varies by location. As already noted above, it has been determined that for some asymmetric filter house configurations, the air velocity through the two lowermost modules 26, 28 of the Group A stack (and laterally-aligned modules 126, 128 of the Group B stack) is higher, thereby resulting in air flow that is warmer due to a shorter residence time in the coil section. Conversely, with decreased velocity across the two uppermost, modules 34, 36, (and laterally-aligned modules 134, 136 of the Group B stack) the inlet air downstream of the chiller coils is cooler due to longer residence time in the coil section. The inlet air temperature through the mid portion of the chiller coils, including modules 30, 32 and 130, 132, lies in between the temperature of the inlet air passing through the upper and lower sets of modules 36, 34 and 28, 26, respectively.
It will be appreciated that on smaller size inlet sections, only one vertical stack of modules can be utilized.
In order to achieve a substantially uniform inlet air temperature profile downstream of the chiller coils, the chiller supply/return configuration is modified in accordance with a first exemplary but nonlimiting embodiment described below.
With continuing reference to
Similarly, for the upper-height modules 34 and 36 of the Group A stack, the branch inlet pipes 50, 52 are connected by pipes 78 and 80 to the common return pipe 39 under the control of respective valves 82 and 84 which control the amount of warmed or return water to be added to the branch inlet pipes 50, 52.
The goal is to have coldest water temperature flowing through the lowest module sets 26 and 28 and relatively less colder water through sets 30 and 32 and relatively least cold water through sets 34 and 36. In other words, the water temperature profile through the chiller coil modules 22 is counteracting the velocity profile. In the highest velocity area (lowest height section), residence time is lowest and water temperature is coldest. Progressing towards the top of the stacks of chiller coil modules 22, the velocity is the lowest, resulting residence time is highest and the water temperature is least cold. This evens out the overall air temperature profile across the height of the stacks of modules 22. In other words, in the described system thermal stratification is achieved to counter the effects of variable velocity.
In the exemplary but nonlimiting embodiment, the controlled addition of warmed return water is substantially the same for mid-height modules 30 and 32, and a proportionately greater addition of warmed return water is made with respect to the upper-height modules 34 and 36. It is nevertheless possible to treat each module individually rather than in pairs.
A conventional drain trough 86 catches condensate formed on the outside of the various modules and routes it to a drain box 87. From the drain box, condensed water returns to the cooling towers where it is cooled and recycled to the chiller coils. Alternatively, the condensate can be drained off at the nearest drain point. Both alternatives are practiced in the industry.
Turning to
A chiller coil controller 88 interfaces with a chiller plant controller 90 and a gas turbine controller 92. The chiller coil controller receives signals from sensors/thermocouples 94, 96, 98, 100, 102 and 104, respectively corresponding to: inlet air temperature, inlet air velocity, chilled water return temperature from module pairs, chilled water supply flow, chilled water supply temperature, downstream air temperature. Another embodiment of this system can also be utilized where the chiller coil controller resides in the chiller plant controller.
With these inputs, and with the assistance of control logic that is well within the skill of the art, the chiller coil controller 88 outputs control signals the various mixing valves 74, 76, 82, 84 to achieve the desired coolant temperature profile. In this way, the chiller coil system is regulated to achieve a substantially uniform air temperature downstream of the chiller coils, thus compensating for the different velocity profiles across the coils resulting from the asymmetric filter house geometry.
It is within the scope of this invention to achieve substantial uniformity of inlet air temperature downstream of the coils by other methods as well. For example, the fin density, material of construction, coatings or the geometry of the individual heat exchanger tubes and fins in the various coils, and/or the heat exchange properties or mass flow of the cooling fluid may be altered as needed to obtain the desired uniformity of inlet air temperature.
The chilling coil system as described herein can be employed on essentially all existing gas turbines where transitions are asymmetric or where velocity profile is not uniform, and where the power demands warrant inlet air cooling. It can be also employed on new units where asymmetric transitions are necessary (to save cost of structural steel) when specified along the inlet air cooling.
The chilling coil system as described herein can also be employed on applications requiring inlet air heating for gas turbines where transitions are asymmetric and the gas turbine operation warrants inlet air heating. The principle of design and operation is similar to the system explained above except for the fact that the purpose is to heat the inlet air.
The chiller coil system can also be used in circumstances where the plurality of chiller modules are supplied with coolant at different temperatures from a cooling source. In this arrangement mixing valves and return water mixing are not used; however, all modules are independently supplied with coolant at different temperatures directly from the cooling source.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
