Patent Application
20130220238
None.
Heat recovery steam generators are well known in the power generation industry as an efficient means of electricity production. Hot exhaust gas from gas turbines is inputted into the heat recovery steam generator, along with a flow medium such as water, to create steam to drive a steam turbine or for process use. Heat recovery steam generators can be single pressure units, where water is converted to steam at a single pressure range, or multiple pressure units, where water is converted to steam at least at a low pressure range and a high pressure range.
Heat recovery steam generators generally comprise an economizer, an evaporator with a steam drum, and a superheater. The economizer heats a flow medium, such as water, using heat from the gas turbine. The flow medium is then transferred to the evaporator and steam drum where it forms steam. Once the steam reaches the superheater, it is heated to convert the saturated steam into superheated steam. In steam generators with multiple sections, often times the low pressure steam drum is used as a storage tank for the suction of a high pressure boiler feed pump. The water is taken from the low pressure drum and pumped to the economizer of the higher pressure sections of the heat recovery steam generator.
One consideration in the design of steam generators is flow-accelerated (or flow-assisted) corrosion. Flow-accelerated corrosion occurs when a fluid (such as water or a steam water dual-phase mixture) passing through a portion of the steam generator causes a protective layer of oxide on a metal surface to dissolve. The metal corrodes, which creates a new oxide layer. As more water passes through the portion of the steam generator, the corrosive cycle continues, resulting in additional metal loss. Flow-accelerated corrosion is dependent upon pH levels, oxygen levels, phase of the fluid (water or steam water mixtures are susceptible), and the velocity and turbulence of the fluid flow (therefore making it dependent on geometry of tubes and pipes). To reduce flow-accelerated corrosion, chemicals are used to increase the pH level of the fluid entering the low pressure steam drum of the low pressure unit. Volatile chemicals are carried away with the low pressure steam and do not remain in the water of the low pressure drum. This is critical when the low pressure drum is used for suction to the higher pressure units and the associated attemperator water supply as water cannot be treated with solids when the water is used as feedwater for the higher pressure units.
In some heat recovery steam generators, feedwater flows to the boiler feed pump in one of two ways. The feedwater can flow from the economizer to the boiler feed pump directly or from the low pressure steam drum to the boiler feed pump. Where the feedwater flows from the economizer to the boiler feed pump, there is no reserve water supply for the boiler feed pump in the event it has a fault of any kind. Where the feedwater flows from the steam drum to the boiler feed pump, the water used for steam generation must be treated with volatile chemicals. However, water treated with these volatile chemicals increases flow accelerated corrosion in the evaporator because it flashes off with the low pressure steam leaving the water phase of the mixture in the steam drum with low pH. Further aggravating the issue of flow accelerated corrosion in the low pressure steam section is temperature. The low pressure evaporator, which also takes its supply water from the low pressure steam drum is in the temperature range of greatest susceptibility for flow accelerated corrosion. Therefore the need is to protect the low pressure evaporator pressure components from flow accelerated wear while keeping non-volatile chemistry out of the feedwater to the higher pressure feed water pump suction.
All US patents and applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety.
Without limiting the scope of the invention, a brief summary of some of the claimed embodiments of the invention is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below.
A brief abstract of the technical disclosure in the specification is also provided for the purposes of complying with 37 C.F.R. §1.72. The abstract is not intended to be used for interpreting the scope of the claims.
The present invention provides a partitioned drum, which serves as a reservoir in the event of a failure of the water supply. In the event of such a failure, the higher pressure boiler feed pump is supplied with water for a given retention time, which is commonly calculated to be between about two and five minutes.
A partitioned drum for a heat recovery steam generator comprises a first chamber in fluid communication with a chemical source for treating a flow medium and a second chamber in fluid communication with both a flow medium source and the first chamber. The first chamber has at least one outlet for the flow medium. The flow medium is conveyed from the flow medium source through the second chamber of the partitioned drum to the first chamber of the partitioned drum. In at least one embodiment, a non-volatile chemical from the chemical source is added only to the flow medium in the first chamber. Thus, the non-volatile chemical is not added to the flow medium present in the second chamber. Prior to the flow medium entering the second chamber, the flow medium is treated with a volatile chemical, which are carried away with the low pressure steam and do not remain in the water of the low pressure drum. Throughout the rest of the application, the flow medium present in the second chamber will be referred to as “untreated” because the non-volatile chemical is not added to the flow medium present in the second chamber, and in at least one embodiment, the non-volatile chemical is only added to the flow medium present in the first chamber. In other words, the non-volatile chemical source is only in communication with the first chamber, not the second chamber.
The chemical used to treat the flow medium in the first chamber may be selected from the group consisting of phosphates and other solid, non-volatile chemicals. In one embodiment, the first outlet of the second chamber is connected to a boiler feed pump of the heat recovery steam generator. A second outlet of the second chamber can be in communication with the first chamber for transferring an untreated flow medium from the second chamber to the first chamber. In one embodiment, the partitioned drum is used in a low pressure section of the heat recovery steam generator.
In one embodiment, the partitioned drum comprises a first body having an inner surface defining the first chamber and a second body disposed within the first chamber. The second body has an inner surface that defines the second chamber.
While this invention may be embodied in many different forms, there are described in detail herein specific preferred embodiments of the invention. This description is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated.
For the purposes of this disclosure, like reference numerals in the figures shall refer to like features unless otherwise indicated.
As shown in
In operation, a flow medium (such as water) provided by tank 50 enters either the drum 24 or the low pressure economizer 22 where exhaust heat from a gas turbine (not shown) is used to heat up the flow medium. The flow medium is then transferred to the low pressure steam drum 24 and the low pressure evaporator 26, where the absorbed heat causes the flow medium to evaporate into a steam. This steam is then superheated in the low pressure superheater 28. The steam exits the low pressure superheater to drive a low pressure turbine 70, to use in other processes, or for release from the system.
Some of the heated flow medium from the steam drum 24 is transferred to the boiler feed pump 60 where it is pumped to the intermediate pressure economizer 32 and to the high pressure economizer 42. The heated flow medium goes through the intermediate pressure economizer 32 and then is transferred to the intermediate pressure steam drum 34 and the intermediate pressure evaporator 36 to form steam. This steam is then superheated in the intermediate pressure superheater 38. Likewise, in the high pressure section 40, the heated flow medium from the boiler feed pump 60 goes through the high pressure economizer 42 and then is transferred to the high pressure steam drum 44 and the high pressure evaporator 46 to form steam. This steam is then superheated in the high pressure superheater 48. Steam exiting the intermediate pressure superheater 38 and the high pressure superheater 48 drive the intermediate pressure turbine 80 and the high pressure turbine 90, respectively. Alternatively, the steam is used in other processes or for release from the system.
Steam drum 100 is a partitioned steam drum having two chambers 102, and 104. In some embodiments, steam drum 100 is preferably a cylindrical body having an inner surface and a wall contacting a portion of the inner surface to separate chamber 102 and 104. In at least one embodiment, the wall has the same circumference as the cylindrical body. The wall may be joined to the cylindrical body by a weld or another permanent or releasable affixation mechanism that effectively seals, blocks or otherwise prevents fluid from being transferred between the second chamber 104 and the first chamber 102 at the joint of the wall and the cylindrical body. In other embodiments, such as the embodiment shown in
By separating steam drum 100 into two separate chambers 102, 104, water in chamber 102 can be treated with non-volatile chemicals from a chemical source, while water in chamber 104 receives no additional treatment from the chemical source. The water in chamber 104 can be used as feedwater for the boiler feed pump, or when necessary can flow to or be transferred to chamber 102 as supply demands.
In at least one embodiment, the first chamber 102 is in fluid communication with a chemical fluid source (not shown), the superheater 28, the second chamber 104, and the evaporator 26. The first chamber 102 only receives the flow medium from the second chamber 104. Steam can exit from the first chamber 102 to the superheater 28, and the flow medium can exit from the first chamber 102 to the evaporator 26. In at least one embodiment, the second chamber 104 is in fluid communication with the economizer 22, the first chamber 102, and the boiler feed pump 60. Flow medium enters the second chamber 104 from the economizer 22. The flow medium can exit the second chamber 104 either to the boiler feed pump 60 or the first chamber 102. Thus, the first chamber 102 only receives flow medium from the economizer through a connection to the second chamber 104, rather than directly, and the first chamber 102 and the boiler feed pump 60 are not connected. This prevents flow medium treated with the non-volatile chemicals from being used in the boiler feed pump 60.
In at least the embodiment shown in
In at least one embodiment, the partitioned drum 100 serves as a reservoir like a conventional drum in the event of a failure of the water supply to the drum 100. In the event of a critical failure of water supply to the partitioned drum 100, when the second chamber 104 lacks the requisite flow medium for the boiler feed pump, a pressure change causes the flow to reverse in the connection shown at 118. The flow medium from the first chamber 102 is transferred, conveyed or otherwise flows into at least the second chamber 104. It should be noted that this fluid from chamber 102 may be treated with the non-volatile chemicals. Thus, in emergencies, the feed pump 60 is supplied with water treated with non-volatiles for the retention time of between about two and five minutes, allowing time for a controlled shut down or recovery of the feedwater source.
Although the above disclosure describes a steam drum where the first chamber 102, which is defined by first body 106 has treated water and the second chamber 104, which is defined by a second body 108 disposed within the first chamber 102, has untreated water, the invention also contemplates embodiments where the first chamber 102 is for untreated water and the second chamber 104 is for treated water. In such an embodiment, the first body 106 has at least one outlet for transferring untreated water from the first chamber 102 to at least one of the boiler feed pump 60 and the second chamber 104. The second body 108 has an outlet for steam from the second chamber 104, an inlet for conveying untreated water from the first chamber 102 to the second chamber 104. In one embodiment, the second body 108 also has a chemical inlet for conveying chemicals to the second chamber 104. Any treated water present in the second chamber 104 is separated from the untreated water in the first chamber 102 so that the water in the second chamber 104 remains untreated.
The above disclosure is intended to be illustrative and not exhaustive. This description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the claims where the term “comprising” means “including, but not limited to”. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims.
Further, the particular features presented in the dependent claims can be combined with each other in other manners within the scope of the invention such that the invention should be recognized as also specifically directed to other embodiments having any other possible combination of the features of the dependent claims. For instance, for purposes of claim publication, any dependent claim which follows should be taken as alternatively written in a multiple dependent form from all prior claims which possess all antecedents referenced in such dependent claim if such multiple dependent format is an accepted format within the jurisdiction. In jurisdictions where multiple dependent claim formats are restricted, the dependent claims should each be also taken as alternatively written in each singly dependent claim format which creates a dependency from a prior antecedent-possessing claim other than the specific claim listed in such dependent claim below.
This completes the description of the preferred and alternate embodiments of the invention. Those skilled in the art may recognize other equivalents to the specific embodiment described herein which equivalents are intended to be encompassed by the claims attached hereto.
