Patent Application
20090126653
This invention is in the field of firebox boilers and in particular such boilers where the firebox is enclosed in hollow water walls that are filled with water or like boiler liquid.
Firebox boilers typically comprise a firebox containing one or more burners fueled by coal, natural gas, fuel oil, or the like. A boiler shell, also referred to as a boiler drum, is mounted above the firebox and contains water or a like boiler liquid such as a mixture of glycol and water. Fire-tubes are mounted inside the boiler shell and extend substantially horizontally from one end of the boiler shell to the other, and hot combustion gases from the firebox pass through the fire-tubes to an exhaust.
In a three pass fire-tube boiler, for example, the combustion gases rise from the burner to the top of the firebox and along under the boiler shell to a rear end of the boiler shell where they enter a lower set of fire-tubes, and pass through the boiler shell to a turn around chamber on the front end of the boiler shell where the combustion gases then enter an upper set of fire-tubes and pass through the boiler shell again to an exhaust chamber on the rear end of the boiler shell, and then out through an exhaust stack. Thus the combustion gases pass the boiler shell three times before being exhausted—once under the boiler shell, then through the boiler shell from rear end to front end, then back from front end to rear end. On each pass, heat is transferred from the hot combustion gases to the water in the boiler shell.
Other configurations of such boilers are also well known where the combustion gases pass through the boiler various numbers of times along various paths.
In order to draw more heat from the combustion gases, it is further well known to enclose the firebox with hollow walls filled with water, commonly referred to as water walls, comprising an inner wall and an outer wall with a space between them. Holes are provided between the top of the water walls and the boiler shell such that water circulates between the water walls and the boiler shell. Typically, such boilers are connected to pipes for heat distribution, with hot water or steam exiting the boiler shell through a pipe connected at a top end thereof, and returning as water or condensate through a pipe connected at a bottom of one of the water walls.
Typically, the firebox is a rectangular shape with side water walls extending from the front end to the rear end along each side, and front and rear end water walls extending from one side to the other to enclose the firebox and form a combustion chamber. The inner and outer walls are typically relatively flat plates, and so stay bolts pass through the water walls to secure the inner and outer walls together when the water is pressurized during operation of the boiler. The spacing of the stay bolts will depend on the contemplated operating pressure of the boiler, but in a typical water wall a significant number of stay bolts is required.
Firebox boilers with water walls are disclosed for example in U.S. Pat. Nos. 134,284 to Huntington, 262,976 to O'Brien, and 539,844 to Wilson. The boilers of Huntington and Wilson illustrate boilers where the water walls enclose the bottom of the firebox as well as the sides and ends. The early steam boiler disclosed by O'Brien shows water walls along each side curving toward each other at the rear end, however the water walls do not enclose the firebox on the front end, or meet at the rear end. The water walls in O'Brien act only as a heater for feed water entering the boiler shell, and a check valve prevents water from moving out of the boiler shell back into the water walls.
A problem with such conventional boilers is that the rectangular shape of the firebox results in corners that are farther from the burner than the side and end walls. Water in the corners thus is heated more slowly than in the closer portions of the water walls resulting in uneven temperatures that create stresses that lead to structural failure. Uneven heat transfer to the water also reduces efficiency in steam boilers, as all water must reach the same temperature in order to satisfactorily produce steam. When operating as a water boiler, circulation in the water walls is impeded because of the corners, leading to stresses due to uneven temperatures that can cause cracking in the corners, or stay bolt failures.
U.S. Pat. No. 626,118 to White recognizes the problem in the corners of the water walls, and rounds the corners of the outer wall to add strength. Japanese Patent 06221508 to Suehiro Tomio provides an expanded corner to absorb thermal stress.
Conventionally, the stay bolts connecting the inner and outer walls of water walls are subject to corrosion and failure. U.S. Pat. No. 1,808,488 to Baker provides convex side and end water walls that curve outward at the bottom and then back inward at the top to provide structural strength and avoid the necessity of providing stay bolts between the inner and outer walls. The side and end water walls meet at conventional square corners where they are connected by a port through the respective walls to allow circulation.
Vertical cylindrical fireboxes with horizontal fire-tubes are also known, however are limited in capacity since the length of the fire-tubes, and thus the length of each pass through the boiler shell is limited. The boiler shell could be extended beyond the walls of the cylindrical firebox to increase the length of the fire-tubes however such a configuration results in uneven heating of the portion of the boiler shell that is not directly over the firebox, and thus leads to further problems associated with stress and circulation.
It is an object of the present invention to provide a boiler firebox that overcomes problems in the prior art.
The present invention provides in one embodiment, a boiler firebox comprising right and left side water walls. An arcuate front end water wall is connected to a front end of the right side water wall and is connected to a front end of the left side water wall, and curves outward from the front end of the right side water wall and then inward to the front end of the left side water wall. An arcuate rear end water wall is connected to a rear end of the right side water wall and connected to a rear end of the left side water wall, and curves rearward from the rear end of the right side water wall and then forward to the rear end of the left side water wall. The end and side water walls enclose a combustion chamber, and are connected at ends thereof such that water can circulate through the end and side water walls.
In a second embodiment the invention provides a boiler comprising a firebox with right and left side water walls and front and rear end water walls enclosing a combustion chamber, and connected at ends thereof such that water can circulate through the end and side water walls. A boiler shell is mounted above the firebox such that the boiler shell is in fluid communication with the side and end water walls and such that water in the boiler shell is heated by a burner in the firebox. An output port is operatively connected to the boiler shell, a first water input port is provided adjacent to a bottom of a central portion of a first water wall, and a second water input port is provided adjacent to a bottom of a central portion of an opposite second water wall. Circulating water flows out of the boiler through the output port, through a distribution network and back into the boiler through the first and second water input ports.
In a third embodiment the invention provides a boiler firebox comprising a right side water wall comprising an right inner wall and a right outer wall and a left side water wall comprising an left inner wall and a left outer wall. A front end water wall comprises an arcuate front inner wall connected to a front end of the right inner wall and connected to a front end of the left inner wall, and curving outward from the front end of the right inner wall and then inward and connected to the front end of the left inner wall, and a front outer wall connected to the front end of the right outer wall and to the front end of the left outer wall. A rear end water wall comprises an arcuate rear inner wall connected to a rear end of the right inner wall and connected to a rear end of the left inner wall, and curving outward from the rear end of the right inner wall and then inward and connected to the rear end of the left inner wall, and a rear outer wall connected to the rear end of the right outer wall and to the rear end of the left outer wall. The right, left, front, and rear inner walls enclose a combustion chamber, and water can circulate through a water chamber formed between the inner and outer walls of the end and side water walls.
Curving the end walls eliminates corners that are present in conventional firebox boilers, and thereby reduces the circulation and stress problems associated with such corners. The curved end walls further provide structural strength so that the number of stay bolts can be reduced, thereby reducing the problems associated therewith. A semi-circular arcuate shape provides a smooth transition between end and side walls for improved water circulation, and also provides significant structural strength.
Providing two input ports for circulating water reduces the amount of cooler water entering at each input port, and thus reduces the temperature variation in water in the water chamber near the input ports, and so reduces stress caused by temperature variations.
While the invention is claimed in the concluding portions hereof, preferred embodiments are provided in the accompanying detailed description which may be best understood in conjunction with the accompanying diagrams where like parts in each of the several diagrams are labeled with like numbers, and where:
The boiler of the present invention illustrated in
In the firebox 2 of
In the conventional firebox 2P of
For the same length and width of firebox, because the side and end water walls the firebox 2 of
The curved shape also provides increased structural strength to the end water walls 6 compared to the flat end water walls 6P, such that it is contemplated that the number of stay bolts connecting the inner and outer walls 10, 12 can be reduced, and the problems associated with failure of stay bolts can thereby be reduced as well.
While it is contemplated that other arcuate shapes will provide beneficial results, in the illustrated arcuate end water walls 6, the walls 6 are curved or arced to form one half of a circle, or a semi-circle, such that the inner and outer walls 10, 12 of the end water walls 6 meet the corresponding inner and outer walls 10, 12 of the side water walls 4 tangentially and curve in a constant radius from one side to the other. The semi-circular shape of the end water walls 6 provides a smooth and unrestricted circulation path around the water chamber 14, improving water circulation such that temperature variances in the water are further reduced. The semi-circular shape provides significant structural strength to the end water walls 6 as well.
A boiler shell 18 is mounted above a front portion of the firebox 2 and in fluid communication with the side and end water walls 4, 6 through circulation ports 20 and water channel 22 between the top of the rear end water wall 6R and the rear face of the boiler shell 18. The boiler shell 18 forms a top wall of the front portion of the firebox 2, and a lower rear face 24 of boiler shell 18 is exposed to a rear portion of the firebox 2.
A plurality of fire-tubes 26 extends horizontally from the lower rear face 24 through the boiler shell 18 to a front face 28 of the boiler shell 18. The illustrated boiler 1 is a three pass boiler including a turn around chamber 30 at the front end of the boiler shell 18 and a second upper set of fire-tubes 26 extending from the front face 28 of the boiler shell to an upper rear face 32. Combustion gases from the burner 16 thus pass under the boiler shell 18 to the rear face 24 thereof, through the lower fire-tubes 26 into the turn around chamber 30, and from there through the upper fire-tubes 26 to an exhaust chamber 36 at the upper rear face 32 of the boiler shell 18, and then out through a stack 36.
The water channel 22 between the top of the rear end water wall 6R and the rear face of the boiler shell 18 is formed by a upper and lower transition plates 40, 42. The lower transition plate 42 joins a top end of the inner wall 10 of the rear water wall 6R to a top of the lower rear face 24 of the boiler shell 28, and the upper transition plate 40 joins a top end of the outer wall 12 of the rear water wall 6R to the boiler shell 18 above the lower transition plate 42. The water channel 22 allows water to flow between the water chamber 14 in the rear water wall 6R and the boiler shell 18.
In the firebox boiler of the prior art as seen in
In hot water boilers of the prior art, as seen in
In order to reduce temperature variations, the present invention provides a first water input port 50A adjacent to a bottom of a central portion of one water wall and a second water input port 50B adjacent to a bottom of a central portion of an opposite water wall. Thus the ports 50A, 50B are located either on opposite end walls 6 or opposite side walls 4 and are connected by conduits to first and second ports of a T-connector 52. In operation, circulating water flows out of the boiler 1 through an output port 54, through a distribution network and back into the T-connector 52 where the flow divides with about half the flow entering one end of the boiler 1 through the first water input port 50A and half entering the opposite end of the boiler 1 through the second water input port 50B. Thus the temperature variation in the water in the water chamber 14 near the first and second water input ports 50A, 50B is reduced since only one half the volume of cooler water is entering each port.
Thus the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous changes and modifications will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all such suitable changes or modifications in structure or operation which may be resorted to are intended to fall within the scope of the claimed invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2491535 | Jan 2005 | CA | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/CA2006/000002 | 1/4/2006 | WO | 00 | 1/5/2009 |
