Patent Application
20170175998
1. Field
The present invention relates to heat recovery steam generators. Specific embodiments relate to methods for pre-assembling, transportation and installation of modules of a heat recovery steam generator.
2. Description of the Related Art
A heat recovery steam generator or HRSG is an energy recovery heat exchanger that recovers heat from a hot gas stream. An HRSG produces steam that can be used in a process (cogeneration) or used to drive a steam turbine (combined cycle).
For example, in a combined cycle power generation, the exhaust gas from a combustion turbine becomes the heat source for the Rankine cycle portion of the combined cycle. An HRSG disposed downstream of the combustion turbine exhaust recovers the waste heat available in the combustion turbine exhaust gas. The recovered heat is used to generate steam at high pressure and high temperature, and the steam is then used to generate power in the steam turbine/generator.
The HRSG is basically a heat exchanger composed of a series of functional units, namely, economizers (preheaters), evaporators, reheaters, and superheaters. The functional units comprise heat exchanger tubes disposed in a flow path of the exhaust gas from the combustion turbine. The heat exchanger tubes carry a medium comprising water and/or steam to which heat from the exhaust gas is transferred, to produce steam at high temperature and pressure.
In a modular HRSG construction, the various functional units may be constructed as separate modules. The modules may be pre-fabricated and transported to an installation site where they are installed. In a modular HRSG construction, the on-field installation cost may be reduced by providing a higher degree of pre-fabrication. However, shipping costs associated with transportation of pre-fabricated modules increases with higher degree of pre-fabrication.
A modular HRSG construction typically results in a compromise between the on-field installation cost and shipping cost, as a result of which both of these costs cannot be simultaneously contained. For example, current approaches make it possible either to achieve a lower on-field installation cost by providing a high degree of prefabrication, but with the result of correspondingly high shipping costs, or to alternately achieve a lower shipping cost by providing a lower degree of fabrication, but with the result of high on-field installation cost.
An object of the invention is to provide an improved heat recovery steam generator construction.
A further object of the invention is to provide improved techniques for pre-assembling, transportation and installing a module of a heat recovery steam generator.
The above objects are achieved by the features of the independent claims.
According to one aspect, a method is provided for installing a heat recovery steam generator that includes a plurality of pre-assembled modules. The method includes arranging a pre-assembled module at an installation site. The pre-assembled module includes a functional unit of the heat recovery steam generator housed in a casing structure. The casing structure includes a top casing, a bottom casing and a side casing. An open side is defined opposite to the side casing. As per the method, the module is arranged horizontally at the installation site with the open side facing downward and the side casing facing upward. The method further includes attaching an exterior structural steel component to the side casing in a horizontal position without lifting the module. The module with the attached structural steel component is then lifted to a vertical position and secured to a foundation.
The proposed method provides reduced installation cost and improved safety during installation.
During installation, the exterior structural steel is to be attached to the side casing of the module. In the state of the art installation method, the module was arranged at the installation site with its open side facing upward and the side casing facing downward. In this case, the exterior structural steel component was first lifted in a vertical position and guy-wired, which obstructed accessibility and posed a potential safety hazard. The module was lifted to a vertical position and then connected to the vertically arranged exterior structural steel component, typically by bolting or welding to the side casing at different elevations, which again posed potential safety hazards.
In contrast, as per the proposed method, arranging the pre-assembled module at the installation site with the open side facing downward and the side casing facing upward makes it possible to attach the exterior structural steel component to the side casing while the module is still horizontal, without having to lift the module. This approach reduces the installation efforts and costs as the exterior structural steel is much lighter than the pre-assembled module and is much easier to maneuver. Furthermore, this approach improves the safety of the installation procedure by eliminating the need to work at elevation to connect the module to the exterior structural steel component.
According to another aspect, a method is provided for pre-assembling a module of a heat recovery steam generator for subsequent transportation to an installation site. The method includes building a functional unit of the heat recovery steam generator. The functional unit comprises a plurality of heat exchange tubes configured for carrying a fluid medium comprising water or steam or a mixture thereof. The method further involves building a casing structure for housing the functional unit. The casing structure defines a portion of a flow conduit for a hot gas and comprises a top casing, a bottom casing and a side casing, whereby an open side is defined opposite to the side casing. As per the proposed method, the casing structure is built with the open side facing downward and the side casing facing upward.
The proposed method makes it possible to attach the exterior structural steel component to the module in a horizontal position at installation, without lifting the module. As mentioned above, this feature improves the safety of the installation by eliminating the need to work at elevation to connect the module to the exterior structural steel component.
According to yet another aspect, a method is provided for transporting a pre-assembled module of a heat recovery steam from a pre-assembly site to an installation site. The method includes loading the pre-assembled module into a transportation container at the pre-assembly site. The pre-assembled module comprises a functional unit of the heat recovery steam generator housed in a casing structure. The casing structure comprises a top casing, a bottom casing and a side casing, whereby an open side is defined opposite to the side casing. As per the method, the pre-assembled module is loaded in a horizontal position in the container with the open side facing downward and the side casing facing upward. The method involves transporting the container with the loaded pre-assembled module to the installation site. As per the method, the pre-assembled module is unloaded at the installation site, such that the unloaded the pre-assembled module is disposed at the installation site in a horizontal position with the open side facing downward and the side casing facing upward.
The above-described method provides reduced transportation costs and improved safety during transportation.
By transporting the pre-assembled module with the open side facing downward and the side casing facing upward, it is ensured that the center of gravity of the module being transported is lowered in comparison to the state of the art where the modules are transported with the open side facing upward and the side casing facing downward. The explanation for this technical effect lies in the fact that the side casing with internal insulation has lower mass density than the heat exchanger tubes. In the proposed method, the side casing with internal insulation occupies a top portion of the module being transported while the heat exchanger tubes occupy a bottom portion, thereby lowering the center of gravity of the module being.
Furthermore, in the proposed method for transportation, shipping dimensions are smaller than with a pre-assembled module with the exterior structural steel attached.
According to yet another aspect, a heat recovery steam generator is provided. The heat recovery steam generator includes a plurality of modules connected in series. Each module comprises a functional unit of the heat recovery steam generator. In the proposed heat recovery steam generator, at least one of the modules is pre-assembled and/or installed by the above described methods.
The heat recovery steam generator described in the illustrated embodiments has a simpler construction with respect to the state of the art.
The invention is shown in more detail by help of figures. The figures show preferred configurations and do not limit the scope of the invention.
In the drawings, the axes X and Y are arbitrarily chosen such that the X-Y plane is parallel to the plane of the horizontal. The axis Z is always assigned to the vertical direction, i.e. perpendicular to the X-Y plane.
In the illustrated embodiments, a “horizontal” direction or orientation may be understood to be any direction or orientation that is parallel to the plane of the horizontal, i.e., parallel to the X-Y plane. The terms “upward” and “downward” are defined with respect to the vertical direction which is parallel to the Z-axis.
The illustrated embodiment shows a horizontal HRSG 1 in which the exhaust gas flows in through the modules 10 along a horizontal direction, in particular, parallel to the axis Y in
In a modular HRSG construction, the modules 10 including the various functional units of the HRSG, such as economizer, evaporator, reheater, and superheater, etc are prefabricated. The prefabrication takes place, for example, in a workshop or a manufacturing facility, where individual components of a functional unit are assembled to form a pre-assembled module. The pre-assembled module is then shipped, for example, in a transportation container, to an HRSG installation site, where the individual modules are installed such that the functional units are arranged in series, to construct a heat recovery steam generator as illustrated in
A modular HRSG construction affords a number of benefits. For example, a modular construction provides increased standardization of the HRSG, thereby resulting in shorter delivery time. Also, a higher degree of prefabrication at the workshop results in reduced cost and effort at the installation site. Furthermore, a high level of quality may be achieved by prefabricating the modules at the workshop to the maximum extent possible. However, a high degree of prefabrication also increases the cost and complexity associated with shipping of the prefabricated parts.
The embodiments illustrated herein address at least the above issue and provides a solution which provides a high degree of pre-fabrication and lower shipping costs while also reducing the on-field installation cost and effort. Embodiments of the inventive concept may be directed to a method of pre-assembly of a module, a method for transporting a pre-assembled module to an installation site, and a method for installing a pre-assembled module at the installation site.
The pre-assembly further includes building the casing structure 12 that houses the functional unit including, for example, the heat exchange tubes 11 and the headers 14. The casing structure 12 includes a top casing 12a, a bottom casing 12b and a side casing 12c connecting the top casing 12a and the bottom casing 12b. The side casing 12c is disposed to cover one of the sides of the module 10 but not on the other, whereby an open or uncovered side 15 is defined opposite to the side covered by the side casing 12c.
A layer of insulation 16, such as a ceramic insulation, may be disposed along the inner surface of the casing structure 12, including the top and bottom casings 12a-b and the side casing 12c. A liner 16a may be disposed to line the inner surface of the insulation 16. In one embodiment, for example if the module 10 includes an evaporator, a steam drum may be attached externally to the top casing 12a of the module at the pre-assembly stage.
The module 10 is built horizontally. That is to say, at the time of pre-assembly, the heat exchange tubes 11 are oriented in a horizontal direction, e.g. parallel to the plane of the workshop floor. In particular, the module 10 is built such that the open side 15 faces downward, i.e. facing the workshop floor, while the side casing 12 faces upwards. Reinforcement structure 17, such as a truss may be provided to support the module 10 during transportation. The module 10 is subsequently transported to the installation site in essentially the same position. In the illustrated embodiment, the pre-assembly does not include attachment of the main structural steel 13 to the module 10, which is done at the installation site.
It is to be noted that at the time of on-field installation, the module 10 is rotated by 90 degrees such that the heat exchange tubes 11 run along a vertical direction, whereby the top casing 12a would face upward and the bottom casing 12b would face downward.
The present method provides several technical benefits not perceived in the previously used methods in which the module was prefabricated and transported with the open side facing upward and the side casing facing downward. In the present method, by transporting the pre-assembled module with the open side 15 facing downward and the side casing facing upward 12c, it is ensured that the center of gravity of the module 10 is significantly reduced. This is because the heat exchange tubes 11, which form the bulk of the weight of the module 10, now occupy a bottom portion of the module 10, while the much lighter side casing 12c with the insulation 16 occupy a top portion of the module 10. A lower center of gravity aids ease of shipping while reducing safety hazards during transportation of the module 10. Furthermore, in the illustrated method, shipping dimensions are smaller than with a pre-assembled module with main structural steel attached.
At the installation site, the module 10 is unloaded from the container 30 and disposed essentially in the same position as it was transported, i.e., in a horizontal orientation, with the open side 15 facing downward and the side casing 12c facing upward.
Subsequently, as illustrated in
In a subsequent step, as illustrated in
The installation method illustrated in
In contrast, as per the proposed method, arranging the pre-assembled module at the installation site with the open side facing downward and the side casing facing upward makes it possible to attach the structural steel to the side casing while the module is still horizontal, without having to lift the module. This approach reduces the installation efforts and costs as the structural steel is much lighter than the pre-assembled module and is much easier to maneuver. Furthermore, this feature improves the safety of the installation by eliminating the need to work at elevation to connect the module to the structural steel.
In summary, the present technique exemplified by the illustrated embodiments provide improved safety and ease of construction while significantly reducing total installed cost by providing particularly reduced shipping cost and on-field installation effort. For example, it has been seen that in a combined cycle installation involving two modular HRSG constructions involving 10-12 modules each, a saving of $600,000-$800,000 may be achieved on the total installed cost (including prefabrication cost, shipping cost and on-field installation cost) by employing the present technique over the existing ones.
While specific embodiments have been described in detail, those with ordinary skill in the art will appreciate that various modifications and alternative to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims, and any and all equivalents thereof.
This application claims priority to the U.S. provisional application No. 62/010,102 filed Jun. 10, 2014, which is incorporated by reference herein in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2015/032115 | 5/22/2015 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62010102 | Jun 2014 | US |
