Patent Grant
7387090
This invention relates to apparatus and systems for generating steam. The new system and method may allow for control of the steam generating process to output a desired steam quality from a multipath or multipass steam generator using crossover preheating of influent water flow in multiple fluid flow conduits or pipes.
Currently steam generators may be used to convert water to steam that may not be saturated. The water conversion may convert 70 percent to 80 percent of influent water to steam. The percent conversion achieved may be known as the steam quality. The unconverted or residual water may be effluent water from the steam generation process.
A single fluid flow conduit or multiple fluid flow conduits may be disposed in a heating container or vessel that may be heated by a combustible fuel, such as, a petroleum product, coal or the like. The fluid of water and steam may be heated in two steps in a steam generator convection section and in a radiant section. The steam generator may be structured for the influent water to be heated first in the convection section that may be downstream in the heated gas flow from the radiant section of the heating container. A heating gas may be at a lower temperature in the convection section relative to the radiant section. The convection section heated water may then be routed to the radiant section for heating to produce a steam effluent.
As water may be converted to steam the velocity of the fluid that may be a water and steam mixture may increase as a result of an increase in the volume of the fluid flowing in the conduit. This increase in velocity may result in an increased pressure drop in the conduit and increased conduit deterioration or wear. To reduce this effect multiple fluid flow conduit, such as, dual path or dual pass, steam generators may be used to generate steam. A dual conduit steam generator may have two approximately parallel or similar fluid flow conduits through which approximately the same total amount of water flows as may flow in a single fluid flow conduit steam generator. In a dual conduit steam generator the total water flow may be divided between the two conduits such that the fluid velocity in each conduit may be reduced which may reduce the wear on the conduits.
In a dual conduit steam generator the steam quality of the two conduit flows may be unequal as a result of differences in heat transfer rates or other factors. It may be necessary to control the water flow rate in each conduit to reduce conduit damage that may result from more water conversion to steam in one conduit relative to the other conduit. Controlling the water flow through each conduit as a function of steam quality may maintain the steam quality between each conduit as approximately equal. This method or process may result in each conduit flow producing approximately equal steam quality, but having unequal water flow.
In order to improve steam generator performance a portion of the heat energy in the water exiting the convection section may be used to heat the cooler influent water prior to its entering the convection section. Water exiting the convection section may be diverted prior to entering the radiant section and may be used to preheat the influent water. Existing steam generator systems may preheat the influent water to a temperature that may be a controlled fixed value.
The present invention is directed to systems and methods for control of a steam generating process having a steam generator with multiple water flow conduits disposed in a convection section and a radiant section. A first conduit may have a first diverted convection section water that may flow through a second preheater of a second conduit intermediate a first element of the convection section and a first radiant section. The second conduit may have a second diverted convection section water that may flow through a first section preheater intermediate a second element of the convection section and a second radiant section. A first temperature controlled valve may control the first diverted convection section water flow rate and a second temperature controlled valve may control the second diverted convection water flow rate.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.
The following detailed description represents the best currently contemplated modes for carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention.
Referring to
A first water portion 32 may flow through a first preheater 34 and then through a first element 36 of a convection section 40. A portion of the first water portion 32 may be diverted as may be controlled by a first temperature controlled valve 39 to flow through a second preheater 44 to preheat a second water portion 42 in the second conduit 22. The preheater 34, 44 may be a double walled pipe having the water portions 32, 42 flowing in an inner pipe and the diverted convection section water portions 38, 48 flowing in an outer pipe. The first diverted convection section water 38 may exit the second preheater 44 and merge with the first water portion 32 to inflow into the first radiant section 50. A first steam flow channel 54 may exit the first radiant section 50 to merge with a second steam flow channel 56 to be discharged from the steam generator 10.
In a like process the second water portion 42 may flow through the second preheater 44 and a second element 46 of the convection section 40. A portion may be diverted as second diverted convection section water 48 to flow through the first preheater 34 and exit therefrom to merge with the second water portion 42 to inflow into a second radiant section 52. A second steam flow channel 56 may exit the second radiant section 52 to merge with the first steam flow channel 54 to be discharged from the steam generator 10.
There may be temperature sensors 60, 62 to monitor water portions 32, 42 temperature intermediate the preheaters 34, 44 and the convection section 40. There may also be steam pressure measurement elements 64, 66 prior to the merging of the steam flows 54, 56 for measuring steam quality.
The water portions 32, 42 flow rate may be controlled to be approximately equal and the steam quality between the first steam flow 54 and the second steam flow 56 may be controlled to be approximately equal by controlling the outlet temperature of each preheater 34, 44.
The steam quality control may be implemented by a control system (not shown) by controlling the amount of diverted convection section water 38, 48 flows through each preheater 34, 44 using temperature controlled valves 39, 49. This process may compensate for differences in the heat transfer characteristics of the two conduits 20, 22 by transfer of a portion of heat energy from the water portion 32, 42 having the higher heat transfer to that having the lower heat transfer. The result may be that each steam flow 54, 56 may have approximately the same steam quality and fluid flow rate.
While the invention has been particularly shown and described with respect to the illustrated embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.
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| Number | Date | Country | |
|---|---|---|---|
| 20070144457 A1 | Jun 2007 | US |
