Liquid heaters and vaporizers – Cleaning
Reexamination Certificate
2001-08-31
2003-06-24
Lu, Jiping (Department: 3749)
Liquid heaters and vaporizers
Cleaning
C122S390000, C122S392000, C134S16700R, C015S316100
Reexamination Certificate
active
06581549
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to sootblowers for removing combustion residues from interior surfaces of a boiler furnace and more specifically to ports through which a sootblower lance penetrates the wall of a boiler.
BACKGROUND
The accumulation of fireside deposits on the internal heating surfaces of boiler furnaces drastically reduces their thermal efficiency and, if not removed, requires periodic shutdowns of the boiler for manual cleaning. The principal means of removing fireside deposit accumulations in boiler furnaces is through the use of a cleaning device known as a sootblower. In general, a sootblower includes an elongated hollow lance that is inserted through a wall of a boiler furnace to position the end of the lance adjacent internal surfaces to be cleaned. The end of the lance is provided with a head having specialized nozzles. Compressed air or steam may be forced under pressure through the lance so that it is ejected at high velocity through the nozzles and against internal surfaces to dislodge and clean away combustion deposits. One major advantage of cleaning a boiler furnace with a sootblower is that the boiler does not need to be shut down in order to accomplish the cleaning because cleaning is carried out while the boiler is in operation.
In some cases, steam or compressed air may prove to be insufficient to remove tenacious combustion residues from interior surfaces of a boiler furnace and in these cases, water jet sootblowers have proven successful. A water jet sootblower has a head provided with nozzles that are specially designed to create a tightly collimated stream or jet of high velocity water when fed with water under pressure through the lance. The water jet or jets issuing from these nozzles impacts and penetrates the layers of residue on interior surfaces of the boiler. Expansion of this water as it is converted to steam within the residue produces pressure, which causes the residue to fracture and debond from the surfaces so that it can be cleaned away more easily.
One method of cleaning the internal or fire side surfaces of a boiler wall with a water jet sootblower is to fit two nozzles on a lance tube in such a manner that the water jets emerging from these nozzles are directed back to the boiler wall through which the lance tube extends. As the lance tube is rotated and advanced further into the boiler, the water jets impact and scribe a spiral pattern on the wall, dislodging and cleaning away tenacious combustion deposits such as slag. In another configuration designed to clean the boiler wall opposite to the wall through which a lance extends, a so called water cannon may be used. A water cannon refers to a sootblower wherein the lance tube is fitted with a head that directs a high velocity collimated jet or jets of water substantially axially from the end of the lance. The lance is inserted through a wall of the boiler opposite to the wall that is to be cleaned. Water is then supplied through the lance at high pressure and the resulting water jets are directed toward, impinge upon, and remove deposits from the opposite wall.
When using a water cannon to clean the opposite wall of a boiler, it is desirable to be able to manipulate the lance in order to move the head around to clean a large area of the opposite wall. To provide for such manipulation, cardon joints have been used at the location where the lance tube tip penetrates the boiler wall.
FIGS. 1 and 2
, annexed hereto, illustrate a traditional cardon joint and show a water cannon lance mounted within a cardon joint installed in a boiler wall. In general, a traditional cardon joint is made up of two concentrically disposed rings mounted in a wall box that, in turn, is mounted in a wall of the boiler. The rings are pivotally mounted within the wall box on orthogonal axes, referred to as the X-axis and the Y-axis, the inner ring being pivotally mounted within the outer ring and the outer ring being pivotally mounted within the wall box. This configuration provides freedom to point the nozzle of a water canon secured within the inner ring in any direction as the concentric rings rotate about the X and Y axes, as illustrated by the arrows in FIG.
1
.
Referring to
FIGS. 2 and 3
, which illustrate a prior art cardon joint, the joint assembly is mounted in a wall of a boiler furnace with one side facing the fireside of the boiler and the other side facing the outside of the boiler. In use, a lance tube is mounted and secured in the opening of the central ring of the cardon joint. When the lance is in its normal rest orientation perpendicular to the wall of the boiler, the rings of the cardon joint align and are substantially coplanar with respect to each other as shown in FIG.
2
. In such a configuration, the gaps between the inner ring and the outer ring and between the outer ring and the frame of the wall box are at a minimum. If the boiler furnace has a negative pressure with respect to the outside atmosphere, which is normal, then a small amount of air is drawn through these gaps and this acts as a seal and an insulator against the extreme heat within the boiler. However, in the event that the boiler furnace should develop a positive internal pressure, hot boiler gases with temperatures in excess of 2000 degrees Fahrenheit can pass outwardly through the gaps, which heats the cardon joint and ultimately can result in its destruction and failure.
This situation is exacerbated when a water canon is being used with a cardon joint in the normal way by manipulating the cannon lance up and down and around. Under these circumstances the concentric rings of a traditional cardon joint are not aligned and coplanar but instead become cocked or skewed with respect to one another and with respect to the wall box frame as shown in FIG.
3
. Obviously, under these conditions, the gaps between the rings and between the outer ring and the frame are much larger and, at the extreme X-Y position of the lance, are maximized. Here, escape of hot boiler gasses under conditions of positive furnace pressures is significantly more prevalent and can result in a host of undesirable consequences. In addition, even under negative furnace pressures, it is more difficult to maintain the insulating seal that results from a draft of outside air through the gaps of the cardon joint when the gaps are large.
Some boilers intentionally are built to operate with a positive draft, i.e. positive furnace pressures. In these instances, the interior of the boiler is always at a higher pressure than the surrounding atmosphere and hot boiler gasses can escape through the gaps of the cardon joint. In order to mitigate the consequences of this, air at a pressure higher than that within the boiler is applied to the outside of the cardon joint to maintain a positive pressure differential and prevent the escape of hot boiler gases. A common way of achieving this is to fit a flexible fabric-like plenum around the cardon joint and pressurize the plenum to maintain a positive pressure on the joint. Such an arrangement is illustrated in FIG.
4
. The sootblower or water cannon lance extends through an opening in the fabric plenum and through the cardon joint and can be manipulated in the usual way, the plenum flexing as needed to permit manipulation of the lance.
Field experience has shown that the heat and constant flexing of the fabric plenum during use leads to failure of the plenum material. The failure point usually is close to the opening in the plenum through which the lance extends as illustrated in FIG.
4
. This is the area of the plenum where the fabric experiences the tightest bend radii and undergoes the most stress. Failure of the plenum material allows some of the pressurized gas within the plenum to escape, resulting in the requirement of larger and larger amounts of seal air to maintain plenum pressure during operation. As the failure worsens, it can become impossible to maintain a positive pressure differential between the inside of the plenum and the inside of the boiler. This is particularly
Atchley Jeffrey A.
Stewart Michael W.
Clyde Bergemann, Inc.
Lu Jiping
Womble Carlyle Sandridge & Rice PLLC
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