Liquid heaters and vaporizers – Cleaning
Reexamination Certificate
2001-08-01
2002-07-30
Lu, Jiping (Department: 3749)
Liquid heaters and vaporizers
Cleaning
C122S390000, C122S392000, C015S316100
Reexamination Certificate
active
06425352
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates generally to a method and apparatus for removing combustion deposits from the surfaces of fossil fuel boilers, and in particular to a method and system to optimize sootblower operating parameters by measuring the effects of sootblowing operations, and adjusting the sootblower operating parameters used in subsequent sootblowing operations based upon the effects measured.
(2) Description of the Prior Art
The combustion of coal and other fossil fuels during the production of steam or power produces combustion deposits, i.e., slag, ash and/or soot, that accumulates on the surfaces in the boiler, decreasing boiler efficiency by reducing heat transfer. These deposits are periodically removed by directing a cleaning medium, e.g., air, steam, water or mixtures thereof, against the surfaces upon which the deposits accumulate with cleaning devices known generally in the art as sootblowers.
To completely eliminate the negative effects of combustion deposits on boiler efficiency, the boiler surfaces, and in particular the heat transfer tubes, would need to be essentially free of deposits at all times. However, the continuous cleaning that would be required to maintain this cleanliness would be prohibitively expensive. In addition, injection of the cleaning medium into the boiler reduces boiler efficiency and prematurely damages heat transfer surfaces if over cleaned. Boiler surfaces, and in particular heat transfer tubes, can also be damaged as a result of erosion by high velocity air or steam jets and/or thermal impact occurring by impinging a jet of relatively cool cleaning medium, especially air or liquid, onto a hot, clean surface. Therefore, it is equally important that these surfaces are not unnecessarily cleaned.
Sootblowers are normally operated on a time schedule based on past experience, or on measured boiler conditions, in particular the reduction of heat transfer by the heat transfer tubes. Boiler conditions may be determined by visual observation, by measuring boiler parameters, or by the use of sensors on the boiler surfaces to measure conditions indicative of the level of ash accumulation, e.g., heat transfer rate degradation. Numerous methods and apparatus have been described in the prior art for measuring boiler conditions, or for determining the optimum timing of sootblowing operations. Representative patents are:
U.S. Pat. No.
Inventor(s)
4,408,568
Wynnyckyj et al.
4,454,840
Dziubakowski
4,466,383
Klatt et al.
4,475,482
Moss et al.
4,488,516
Bueters et al.
4,552,098
Wynnyckyj et al.
4,718,376
Leroueil et al.
4,722,610
Levert et al.
4,996,951
Archer et al.
5,181,482
Labbe et al.
The cost of operation of fossil fueled boilers is highly dependent upon optimizing the boiler's heat transfer efficiency, while minimizing the cost required to operate sootblowers. Control of the timing of sootblower operations is highly important in operating boilers in a efficient manner. However, there is a continuing need for further refinements in the control of boiler operations, and in particular sootblowing, that would further improve efficiencies, and resultant operating costs.
SUMMARY OF THE INVENTION
The present invention is directed to a method and apparatus for improving the operational efficiencies of fossil fueled boilers. The invention relates especially to a method and system for adjusting one or more sootblowing operating parameters based upon the effectiveness of the immediately preceding sootblowing operation. The method and system may additionally include steps and apparatus to control the timing of sootblowing operations.
The method and system described in detail herein provides for the control of the operating frequency or timing of sootblowing operations. However, unlike prior art methods and apparatus, the present invention additionally provides for the control of the operating parameters of sootblowers or other devices used to clean deposits from boiler surfaces.
The term sootblower or sootblowing “operating parameters” as used herein means the adjustable factors controlling the manner in which a sootblower directs a fluid against a surface, including jet progression rate, rotational speed, spray pattern, fluid velocity, media cleaning pattern, and fluid pressure. Each of these “operating parameters” may be adjusted to increase or reduce its contribution to the effectiveness of the cleaning fluid on the surface, this contribution to the medium effectiveness is referred to herein as the “aggressiveness” of the parameter. That is, increasing the “aggressiveness” of a parameter will contribute to the increased effectiveness of the cleaning medium in a subsequent operation, while decreasing the aggressiveness will have the opposite effect.
The present system, like some systems described in the prior art, includes a plurality of sensors to monitor the extent of combustion deposits on boiler surfaces, and one or more sootblowers to direct a cleaning medium against the surface or surfaces being monitored. However, the present invention differs in at least two major respects.
First, prior art sensors have been used to measure the extent of deposits as the deposits accumulate on a boiler surface, and activate a sootblowing operation when the deposits accumulate to a predetermined extent. In the present invention, sensors may be used for this purpose, but are additionally and primarily used to measure the amount of deposits remaining immediately after a sootblowing operation as a means to evaluate the efficiency of the sootblowing operations.
Second. data acquired by prior art sensors has been used only to determine the time of sootblowing operations. While sensor data may be used for this purpose in the present invention, the sensor data is used primarily used to adjust the sootblowing operating parameters used during the next sootblowing operation.
More specifically, the present system is comprised of at least one sensor on a boiler surface and at least one sootblower positioned to direct a cleaning fluid against the boiler surface near the sensor location. In addition, the present system includes a processor in communication with the sensor and a sootblower controller for receiving data from the sensor and adjusting the operating parameters of the sootblower based upon the data received from the sensor.
In most boilers, a plurality of sensors and sootblowers will be used, with one or more sensors being present on a surface to be cleaned by a given sootblower. For the sake of simplicity and ease of description, the present invention will often be described in terms of a single sensor and a single sootblower. It should be understood, however, that the invention also contemplates a plurality of sensors and sootblowers.
In the practice of the method of the invention, the operating parameters, e.g., the jet progression, jet pattern, lance rotational speed, fluid velocity and fluid pressure parameters, of a given sootblower are initially set at levels based on past operations or experience. The sootblower is then operated to clean a given surface when timing, operator observation, or monitored conditions indicate that deposits have accumulated in an amount requiring cleaning of the surface.
Immediately after the sootblowing operation, the sensor is used to measure the heat transfer improvement resulting from the cleaning operation, and thereby the effectiveness of the immediately preceding operation in cleaning the surface. The acquired data is fed back to a central processor, where the data is compared against a desired cleanliness standard that is stored in the processor.
If the comparison indicates that the surface has been cleaned to less than the desired standard, the processor transmits a signal to the sootblower controller to adjust at least one of the operating parameters to provide more aggressive cleaning. On the other hand, if the cleaning standard has been achieved or exceeded, the processor transmits a signal to the controller to reduce the aggressiveness of at least one of th
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