Patent Grant
8851024
This disclosure relates to a water reservoir for a steam generation system and to methods of use thereof.
Drum-type steam generation systems generally comprise three major components: an evaporator, a superheater and an economizer. The different components are put together to meet the operating needs of the unit. Some drum-type steam generation systems may not have a superheater or may include additional components such as reheaters.
The
The steam drum 104 is therefore sized based on the steam needs for the drum-type steam generator. However, when additional requirements such as the water hold time exceeds the normal steam drum 104 water storage level for a single drum, it is desirable to increase the size of the steam drum 104. The water hold time (also sometimes termed the “holdup time”) is based on the measured liquid volume between normal water level (NWL) and the lowest (also sometimes referred to as the “lo-lo”) water level trip. The lowest water trip level is the minimum level at which there will be no danger of overheating any part of the steam generator during operation. This lowest water level is generally about 30 centimeters (about 1 foot) above the bottom of the drum, but varies according to drum diameter.
The normal water level is set below the high water level, as needed for water level measurement accuracy, margin to control feedwater flow and steam purity. In general, the location of normal water level results in about 15 seconds to 30 seconds of water volume (depending upon the flow rate) between the normal water level and the water level trip. The volume of water contained in the drum at these different heights can be calculated using simple formulas for the area of a circular segment.
One manner of increasing the water hold time of a single steam drum is to increase the length and/or the diameter of the drum. However, this may not be a viable option where space availability is limited. The use of larger diameter drums increases shell wall thicknesses to accommodate internal pressures. Thicker walled vessels however generally use longer heat up times when compared with thinner walled vessels resulting slower transient during start-up and/or load changes.
It is therefore desirable to increase the water hold time of the steam drum without incurring additional costs associated with increasing space or with increasing the wall thickness.
Disclosed herein is a system comprising an evaporator; a water reservoir in fluid communication with the evaporator; the water reservoir being located upstream of the evaporator; and a first steam drum in fluid communication with the evaporator; the first steam drum being located downstream of the evaporator; where the water reservoir is operative to supply feedwater to the evaporator while maintaining a predetermined water level in the first steam drum.
Disclosed herein too is a method comprising discharging feed water from a water reservoir to an evaporator; where the water reservoir lies upstream of the evaporator and is in fluid communication with the evaporator; and discharging water and steam from the evaporator to a first steam drum; where the evaporator lies upstream of the first steam drum and in fluid communication with the first steam drum; where an amount of water discharged from the water reservoir to the evaporator is effective to increase the water level in the first steam drum to a desired level.
Disclosed herein is an evaporator system that comprises an evaporator, a steam drum and a reservoir. The reservoir is used for holding additional water that is supplied to the evaporator and allows for an increase in the water hold time in the system. Disclosed herein too is a method of increasing the water hold time by providing a water reservoir, which holds water that is supplied to the evaporator when the water level in the steam drum decreases from the normal level. The normal level will hereinafter be referred to as a predetermined level. The evaporator system disclosed herein may be part of a drum-type steam generation system with natural or forced circulation such as heat recovery generation system, steam generation solar receivers, fossil fuel fired steam generation systems and other systems where an increase in the volume of the steam drum is desired to increase water hold up time, but where there are space limitations.
Both the steam drum 204 and the water reservoir 206 are equipped with level sensors to detect when desired liquid levels (e.g., water levels) deviate from desired values. The steam drum 204 comprises a first water level indicator, which is activated when the water level increases above a certain level (e.g., a high water level indicator), drops below a certain desired level (e.g., a low water level indicator) and control the feed water to the reservoir to maintain the predetermined water level. The predetermined water level lies between the high water level and the low water level. The water reservoir 206 also comprises a second water level indicator, which is activated when the water level decreases below a certain desired level (e.g., a low water level trip). The water level indicators may be floats, a manometer (e.g., a distilled water column or a mercury column), conductivity probes or the like, or a combination thereof.
In one embodiment, in one method of operating the evaporation system 200 of the
The presence of the water reservoir 206 in the evaporation system 200 can thus be used to minimize space requirements in at least one direction. In one embodiment, the system comprising the water reservoir is shorter than an equivalent system that does not contain the water reservoir when both systems utilize an equivalent drum diameter, hold up time and produce an equivalent amount of steam.
If the evaporation system 200 were devoid of the water reservoir 206, the steam drum 204 would have to be longer, which depending on the arrangement may be difficult to fit into a confined space or the diameter would have to be increased. In addition, as drum diameter increases the thickness of the walls of the steam drum 204 would have to be increased to the point where the stresses in these walls would increase significantly. The use of a water reservoir 206 prevents these problems.
In another embodiment depicted in the
While the
When the water level decreases below the desired level as indicated by the water level indicator, water from the water reservoir 206 is introduced into the evaporator 202 to comply with the requirement for additional steam, while at the same time compensating for the loss of water in the steam drum 204 or the steam drum 214. If the level of water in the steam drums 204 or 214 decreases below the desired level then additional feedwater is supplied to the water reservoir 206 via the valve 208.
It will be understood that, although the terms “first,” “second,” “third” etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, “a first element,” “component,” “region,” “layer” or “section” discussed below could be termed a second element, component, region, layer or section without departing from the teachings herein.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof.
Furthermore, relative terms, such as “lower” or “bottom” and “upper” or “top,” may be used herein to describe one element's relationship to another element as illustrated in the Figures. It will be understood that relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. For example, if the device in one of the figures is turned over, elements described as being on the “lower” side of other elements would then be oriented on “upper” sides of the other elements. The exemplary term “lower,” can therefore, encompasses both an orientation of “lower” and “upper,” depending on the particular orientation of the figure. Similarly, if the device in one of the figures is turned over, elements described as “below” or “beneath” other elements would then be oriented “above” the other elements. The exemplary terms “below” or “beneath” can, therefore, encompass both an orientation of above and below.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
While the invention has been described with reference to a preferred embodiment and various alternative embodiments, it will be understood by those skilled in the art that changes may be made and equivalents may be substituted for elements thereof without departing from the scope of invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
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| Number | Date | Country | |
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