Patent Application
20090173292
The present invention relates generally to the field of steam boilers, and more particularly to a corrosive resistant steam boiler.
Steam boilers are well-known in the prior art and have been used in residential heating applications for years. Most steam boiler systems known in the prior art include a boiler connected to radiators by a pipe system. The pipe system allows steam to rise into the radiators, pushing the ambient air out of the radiators, until a steam vent valve on the radiator closes due to the temperature rise. The steam then condenses against the inside surface of the radiator and trickles back to the boiler by gravity through the same pipe system. Thus, most steam heating systems are open systems that are filled with air during the off cycle. The air is forced out the system when the boiler is steaming. At the end of a call for heat, the steam field collapses and draws air back into the system.
Generally, residential steam boilers are constructed of cast iron with vertical flue passages or flue ways. These vertical flue ways pass through a steam collection volume, sometimes referred to as a steam chest or steam space. The boiler is filled with water to a defined water level inside the casting. The casting acts as a heat exchange unit and a heat source is used to heat the water inside the boiler. Steam then collects above the waterline in the steam space before exiting up through the pipe system to the radiators. Occasionally, water must be added to the boiler because of intended and unintended loses. Intended loses may include lose of water to flush or blow down the mechanical float water level control, lose of water to flush or blow down sediment from the bottom of the boiler, and lose of water due to the escape of steam through the vent valves. Unintended loses may include leaking radiator vents and leaking in the pipe system.
However, prior art boilers tend to corrode or degrade over time and with use. Thus, it would be beneficial to provide a boiler which is more resistant to the corrosive effect of heat and impurities in the system.
With parenthetical reference to the corresponding parts portions or surfaces of the disclosed embodiment, merely for purposes of illustration and not by way of limitation, the present invention broadly provides a steam boiler (15) comprising a fuel burning device (16) disposed in a combustion chamber (52) and adapted to burn a fuel to form combustion gases (19), a passage (30) extending between a water inlet (20) and a steam outlet (22), the passage having a water space (31) and a steam space (32), a flue passage (33) extending between the combustion chamber and a flue outlet (24) and having a gas heat transfer space (34), a heat exchange element (43) between the gas heat transfer space and the water and steam spaces, the heat exchange element having a gas-side surface (35) that absorbs heat from the combustion gases and an opposed water-side surface (38) that radiates heat, the water-side surface having a first portion (39) adjacent to the water space and a second portion (40) adjacent to the steam space, the gas-side surface having a first portion (36) opposite the water-side first portion and a second portion (37) opposite the water-side second portion, the water-side first portion having a surface area and the water side second portion having a surface area, the gas-side first portion having a surface area and the gas-side second portion having a surface area, and a heat shield (41, 42, 45, 48) covering at least some of the surface area of the gas-side second portion.
The heat shield (41) may cover all of the surface area of the gas-side second portion and the heat shield (42, 45, 48) may cover some of the surface area of the gas-side first portion. The surface area of the gas-side second portion may be less than or approximately equal to the surface area of the water-side second portion. The surface area of the gas-side first portion may be greater than the surface area of the water-side first portion. The surface area of the gas-side second portion may be greater than the surface area of the water-side second portion and the surface area of the gas-side first portion may be greater than the surface area of the water-side first portion. The gas-side first portion may comprise a pin deck (44). The heat exchange element may comprise a cast iron section (26-29) having an interior volume and the interior volume may comprise the water space and the steam space. The heat exchange element may comprise a first cast iron section (26) connected to a second cast iron section (27), the first cast iron section and the second cast iron section may form a volume (34a) there between, and the volume may comprise the gas heat transfer space. The first cast iron section may have an interior volume and the interior volume may comprise the water space (31a) and the steam space (32a). The second cast iron section may have an interior volume and the interior volume of the second cast iron section may comprise a second water space (31b) and a second steam space (32b). The heat shield (45) may comprise a metal plate (46) covering at least some of the surface area of the gas-side second portion (37), and an air space (47) between the metal plate and at least some of the surface area of the gas-side second portion. The heat shield (48) may comprise an insulation layer (49) bonded to at least some of the surface area of the gas-side second portion. The heat exchange element may have a ratio between the surface area of the gas-side first portion and the surface area of the water-side first portion of greater than one, and the heat exchange element may have a ratio between the surface area of the gas-side second portion and the surface area of the water-side second portion that is less than the ratio between the surface area of the gas-side first portion and the surface area of the water-side first portion.
In another aspect, a heat exchanger is provided comprising a first passage extending between a water inlet and a steam outlet, the first passage having a water space and a steam space, a second passage extending between a fluid or gas inlet and a fluid or gas outlet, the second passage having a heat transfer space, a heat exchange element between the heat transfer space and the water and steam spaces, the heat exchange element having a gas-side surface adapted to absorb heat from the heat transfer space and an opposed water-side surface adapted to radiate heat, the water-side surface having a first portion adjacent to the water space and a second portion adjacent to the steam space, the gas-side surface having a first portion opposite the water-side first portion and a second portion opposite the water-side second portion, the water-side first portion having a surface area and the water side second portion having a surface area, the gas-side first portion having a surface area and the gas-side second portion having a surface area, and a heat shield covering at least some of the surface area of the gas-side second portion.
Accordingly, the general object of the present invention is to provide an improved steam boiler that is resistant to corrosion. These and other objections and advantages will become apparent from the foregoing and ongoing written specifications, the drawings, and the appended claims.
At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms “horizontal”, “vertical”, “left”, “right”, “up” and “down”, as well as adjectival and adverbial derivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”, etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms “inwardly” and “outwardly” generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate.
Referring now to the drawings, and more particularly to
As shown in
Castings 26-29 are joined with tie rods extending between front casting 26 and rear casting 29, such that openings 51a-51c and recess 53 form combustion chamber 52. The castings are also configured such that a vertically extending flue passage 33a is provided between adjacent castings 26 and 27, a vertically extending flue passage 33b is provided between castings 27 and 28, and a vertically extending flue passage 33c is provided between castings 28 and 29, respectively. These flue passages communicate between combustion chamber 52 and flue gas exhaust outlet 24. Vertically extending flue ways 33a-33c are defined by outer opposed vertical surfaces 35a and 35b, outer opposed vertical surfaces 35c and 35d, and outer opposed vertical surfaces 35e and 35f, respectively, of castings 26-29. These passages provide a heat transfer space 34.
Castings 26-29 have an upper hollow region that defines vertical passages 30a-30d, respectively. Passages 30a-30d allow for water and steam to communicate between water inlets 20a-20d and steam outlets 22a-22d, respectively. Vertically extending passages 30a-30d are defined by vertical inner surfaces 38a and 38b, vertical inner surfaces 38c and 38d, vertical inner surfaces 38e and 38f, and vertical inner surfaces 38g and 38h, respectively, of castings 26-29.
As shown in
The portion of the casting between passage 30 and flue passage 33 acts as a heat exchange wall 43. Walls 43a-43f of castings 26-29, respectively, allow for the transfer of heat from combustion gases 19, which pass through flue passage 33, to water 25 in passage 30, thereby heating water 25 to form steam that will pass from outlets 22 to a pipe system 23 and peripheral radiators, thereby heating the radiators and providing radiated heat to a residence or other facility. Wall 43 has two opposed outer surfaces, namely water side surface 38(b-g) and gas side surface 35(a-f).
Gas side surface 35 has a lower portion 36 opposite lower portion 39 of water side surface 38 and an upper portion 37 opposite upper portion 40 of water side surface 38. Each of these portions has in turn a certain surface area.
In the preferred embodiment, lower portion 36 of gas side surface 35 is provided with a conventional pin deck 44, while upper portion 37 of gas side surface 35 does not include a pin deck. Instead, upper portion 37 is a flat vertical planar surface. As a result, the enhanced outer surface area of lower portion 36 is greater than the flat outer surface area of upper portion 37. Because inner water side surface 38 is a flat vertical planar surface on both its lower portion 39 and its upper portion of 40, the surface area of lower portion 36 of gas side surface 35 is substantially greater than the surface area of lower portion 39 of water side surface 38. However, the surface area of upper portion 37 of gas side surface 35 is substantially the same as the surface area of upper portion 40 of water side 38. As a result, greater heat transfer across wall 43 will occur from lower portion 36 of gas side surface 35 to lower portion 39 of water side surface 38 relative to heat transfer between upper portion 37 of gas side surface 35 and upper portion 40 of water side surface 38. As a result, water space 31 of passages 30 will receive greater emitted heat from wall 43, while steam space 32 of passages 30 will not be heated to as great an extent as water space 31. Thus the heat transfer is focused from combustion gases 19 to water 25 in water space 31.
Heat transfer across wall 43 is further limited by a heat shield 41 covering upper portion 37 of gas side surface 35. Heat shield 41 decreases heat transfer from combustion gases 19 in heat transfer space 34 to upper portion 40 of water side surface 38 of heat exchange wall 43. In the preferred embodiment, heat shield 41 is a metal plate that extends over and covers all of upper portion 37 of gas side surface 35. As shown, shield 41a comprises a horizontal plate connected at its right edge to the top edge of a vertical plate. The vertical plate covers upper portion 37a of gas side surface 35a, and the horizontal plate extends over and is supported by the top of front casting 26. This same form is employed with respect to shield 41d on rear casting 29. A vertical plate covers upper portion 37f of gas side surface 35f, and is connected at its top edge to the left edge of a horizontal plate that extends over and is supported by the top of rear casting 29. Shields 41b and 41c comprise two vertically extending plates connected at their top edges by a horizontal support plate. Shield 41b saddles the top of casting 27 such that the first vertical plate covers upper portion 37b of gas side surface 35b and the second vertical plate covers upper portion 37c of gas side surface 35c. Shield 41c saddles the top of casting 28 such that the first vertical plate covers upper portion 37d of gas side surface 35d and the second vertical plate covers upper portion 37e of gas side surface 35e. Thus, the upper portion 37 of gas side surface 35 does not include a pin deck 44 and instead is covered by heat shield 41.
A number of unexpected benefits result from the variation in surface area between upper portion 37 and lower portion 36 of gas side surface 35 and the placement of heat shield 41 over the upper portion 37 of gas side surface 35. Prior art boilers have been known to experience early corrosion to the upper portion 40 of water side surface 38. One of the unexpected benefits of the improved design is that it results in less degradation, in comparison to a conventional steam boiler, to upper portion 40 of water side surface 38. Prior art boilers have also been known to experience excessive amounts of scale build up from calcium and magnesium carbonates on upper portion 40 of water side surface 38. This scale build up is reduced with the improved design. Thus, counter intuitively and unexpectedly, covering upper portion 37 of gas side surface 35 with shield 41, rather than covering the upper portion 40 of water side surface 38 where corrosion was typically found in the prior art, reduced the corrosive effects of temperature and contaminants on water side surface 38. This was found to be particularly beneficial with respect to rear casting 29.
Two additional embodiments of heat exchange wall 43 and heat shield 41 are shown in
While the preferred embodiments show multiple passages 30a-d and multiple flue ways 33a-c there between, with multiple separating heat exchange walls 43a-f, it is contemplated that only a single heat exchange wall with the improved features may be used, or the number of heat exchange walls with the improved features may be otherwise varied as desired. Also, in a boiler with multiple heat exchange walls 43, different embodiments of the heat shield may be used on the different gas side surfaces of the heat exchange walls 43 employed. Thus, the heat shield used may vary among the multiple heat exchange walls 43a-43f within the boiler or even between the two gas side surfaces of a particular casting.
Similarly, it is contemplated that the relative surface area of the upper portions and lower portions of the gas side surfaces 35 may be modified. Thus, the surface area of the gas side upper portion 37 may be less than or approximately equal to the surface area of the water side upper portion 40, the surface area of the gas side lower portion 36 may be greater than the surface area of the water side lower portion 39, or the surface area of the gas side upper portion 37 may be greater than the surface area of the water side upper portion 40 and the surface area of the gas side lower portion 36 may be greater than the surface area of the water side lower portion 39. The differences in surface areas may also vary among the multiple heat exchange walls 43a-43f within the boiler or in a boiler casting (as each of center castings 27 and 28 in the preferred embodiment have two heat exchange walls 43b, 43c and 43d, 43e, respectively).
As shown in
Therefore, while the presently-preferred form of the steam boiler have been shown and described, and several alternative embodiments discussed, persons skilled in this art will readily appreciate that various additional changes and modifications may be made without departing from the spirit of the invention, as defined and differentiated by the following claims.
