Electric heating – Metal heating – By arc
Reexamination Certificate
2002-06-01
2004-03-23
Elve, M. Alexandra (Department: 1725)
Electric heating
Metal heating
By arc
C219S121690, C219S121850
Reexamination Certificate
active
06710285
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to the field of laser cleaning. More particularly, the present invention relates to particulate removal from the heat exchange and other inner surfaces in a boiler. Specifically, a preferred embodiment of the present invention relates to a laser deslagging device for boilers.
2. Discussion of the Related Art
Electrical power generating plants commonly employ systems in which boilers are fueled by coal or oil. These in turn produce steam for driving turbines to produce electricity. Typical boilers include, among other components, a furnace evaporator section and various heat exchange units such as superheaters, reheaters, precipitators, fire boxes, slope area, economizers and, air heater sections. A furnace evaporator section is provided with water walls, while the various heat exchange units include tubing for carrying the medium, in the form of water or steam. These are heated, while combustion gases flow past the water walls and over the tubing.
Despite all efforts to optimize the fuel burning process, all combustion gases contain a certain amount of solid and/or molten particulates, including ash and soot, that form deposits on the water walls and tubing surfaces. These deposits (often referred to as slag) interfere with the transfer of heat energy from the combustion gases to the medium being heated. Moreover, if these deposits are permitted to form a layer of a certain thickness, the outer surface of such layer may reach a temperature at which constituents thereof become sintered or molten. This results in deposits which grow rapidly, resist removal, create partial or total blockages in the gas flow paths of the boiler, result in heavy accumulations which may fall and hence cause mechanical damage within the boiler, create boiler inefficiency, and cause corrosion damage due to diffusion of molten or vapor materials into the tubing surfaces.
A variety of devices and methods are used to clean slag and similar deposits from boilers, furnaces, and similar heat exchange devices. Some of these rely on chemicals or fluids that interact with and erode deposits. Water cannons, steam cleaners, pressurized air, and similar approaches are also used. Some approaches also make use of temperature variations. And, of course, various types of explosives are commonly used to create strong shock waves to blast slag deposits off of the boiler.
The use of explosive devices for deslagging is a particularly effective method, as the large shock wave from an explosion, appropriately positioned and timed, can easily and quickly separate large quantities of slag from the boiler surfaces. However, this process is costly, since the boiler must be shut down (i.e. brought off line) in order to perform this type of cleaning. Thus, valuable production time is thereby lost. This lost production time includes not only the hours during which the cleaning process is being performed, but also the several hours prior to cleaning when the boiler must be taken off line to cool down, and the several hours subsequent to cleaning for the boiler to be restarted and brought into full operational capacity.
This process also presents a degree of danger common to the use of any explosive. Were the boiler to remain on-line during cleaning, the immense heat of the boiler would prematurely detonate any explosive placed into the boiler, before the explosive has been properly positioned for detonation, rendering the process ineffective and possibly damaging the boiler. Worse, loss of control over the precise timing of detonation would create a serious danger for personnel located near the boiler at the time of detonation. Therefore, it has been necessary to shut down any heat exchange device for extended periods of time when explosives-based deslagging is desired.
Sootblowers are devices used to project a stream of blowing medium, such as water, air, or steam, against the heat transfer surfaces of the tube bank located within the boiler. The blowing medium is used to dislodge various combustion byproducts, including soot, slag, and ash, which become deposited on the heat transfer surfaces. By using the blowing medium to dislodge the encrustations, the thermal and mechanical shock provided by the medium fractures the encrustations, breaking them free, and dislodges them from the heat transfer surfaces. Although these devices do not often require the boiler to be shut down, they are often not extremely efficient in their removal of slag. Those devices that employ water or steam further require a drainage device to remove the newly created soot-slurry.
What is needed therefore is a slag removal device that has the ability to remove a high percentage of the slag from a boiler, without requiring the boiler to be shut down. Further, what is also needed is a safe and efficient means to clean a boiler. Heretofore these requirements have not been fully met without incurring various disadvantages.
SUMMARY AND OBJECTS OF THE INVENTION
By way of summary, the present invention is directed to a laser deslagging device for the cleaning of boilers. A primary object of the invention is to provide an apparatus that eliminates slag from on-line boilers and/or furnace component surfaces while in use.
Another important object of the invention is to provide a device, as aforesaid, which utilizes light as the cleaning medium.
A further object of the invention is to incorporate existing laser technology to create a device for cleaning molten slag that builds up in boilers, without causing any damage to the boiler or posing considerable risk to the operators.
Another object of the invention is to provide an apparatus that is ruggedized and reliable, thereby decreasing down time and operating costs. Yet another object of the invention is to provide an apparatus that has one or more of the characteristics discussed above but which is relatively simple to manufacture, transport, operate and assemble.
A preferred embodiment of the invention incorporates laser technology to be used for cleaning slag from a boiler, furnace or similar fuel-burning or incineration device, by directing a laser beam at the part of the boiler to be cleaned for a time sufficient to remove the slag from the substrate. The removal process comprises directing the beam at the area to be cleaned whilst the boiler is in use. The method may comprise operating the boiler in its normal, high temperature condition while the slag removal process occurs.
The deslagging system preferably is comprised of a laser and an operating unit and a machine to transport the system's components. The system also preferably includes a computer with basic laser operational software, a processor, sufficient memory and a database. In one preferred embodiment, the computer is connected to a targeting and imaging system that allows the operator of the laser operating unit to view the inside of the boiler from the computer screen. The computer is also preferably connected to the laser and has a Q-switch which turns the laser operating unit on and off at the command of the operator.
The laser beam may be deployed by a gun, rotating ball or other means of deployment inside the boiler. The laser is preferably connected to the deployment device via fiber optic cabling. The length of the fiber optic cabling allows the laser beam to be transported from the laser to the deployment device.
These, and other, aspects and objects of the present invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating preferred embodiments of the present invention, is given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.
REFERENCES:
patent: 4996951 (1991-03-01), Archer et al.
patent: 5113802 (199
Brown Robert K.
Cammarata, Jr. Frank A
Boyle Fredrickson Newholm Stein & Gratz S.C.
Elve M. Alexandra
First Call Explosive Solutions, Inc.
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