Firetube steam boiler having improved efficiency

An improved boiler for generating steam includes a housing that has a proximal end and a distal end, with a water-entry port at the proximal end. A plurality of firetubes are disposed lengthwise in the housing, and the firetubes extend substantially the length of the housing between the proximal end and the distal end. The firetubes are used to pass the heated flue gas through the housing. A pair of side baffles are affixed to the inner surface of the housing that extend at least partially down the length of the housing to separate a portion of the last pass of firetubes near the housing from the remaining firetubes in the housing. At least two cross-sectional baffles are positioned adjacent the side baffles to direct the flow of water opposite to the flue gas flow in the separated part of firetubes.

BACKGROUND OF THE INVENTION

A firetube steam boiler as illustrated inFIG. 1is commonly known in the art as used for steam generation. A conventional firetube steam boiler6may have a Scotch Marine design. The boiler has a closed housing or tank in which water or another fluid is vaporized. The vaporized fluid exits the boiler at saturation temperature for use in various processes or heating applications. Water partially fills a boiler tank or housing with a small volume left above to accommodate steam.

Various heat sources for steam generation may be used, such as a product of combustion of any type of fossil fuel (in a gas, liquid or solid condition) or waste gases of any process. With the first case, different type of burners may be used to perform fossil fuel combustion in the furnace. In the last case, the device for steam production names as a Heat Recovery Steam Generator. Usually (for example, Scotch Marine design) the furnace is immersed in the same water-filled vessel where also the steam generation occurs. Hot flue gas passes are generated in the furnace and pass through tubes (also named as firetubes, because hot flue gas travels inside of the tubes) that extend through the same water-filled closed vessel as furnace.

Water in the vessel of a conventional boiler is always saturated and has an almost uniform temperature through the vessel volume. Usually fresh water enters into the vessel at temperature much less than saturation temperature. However, due to a small ratio of fresh water mass to the mass of water inside of vessel, the temperature uniformity has only local character and does not impact to the heat transfer intensity. The flue gas passes through the furnace and firetubes to an exhaust port, such that the heat transferred by convection and radiation from the flue gas to the saturated water generates steam. The steam then extracts from the top segment of the housing of the boiler for use as desired.

Firetube boilers may include several bundles of firetubes through which the flue gas travels back and forth in the housing. For example, if the boiler includes two bundles of firetubes, the flue gas passes in one direction through a first bundle of firetubes, and then in an opposite direction through the second bundle of firetubes. This is typically referred to as a “three-pass” boiler, since the furnace is used to organize fossil fuel combustion and is considered as a first pass before traveling through the firetubes.

BRIEF SUMMARY OF THE INVENTION

A improved firetube steam boiler is disclosed herein for generating steam using a heat source affixed to the boiler distributing heated flue gas into the boiler. The improved boiler includes a housing that has a proximal end and a distal end, with the housing further having an inner or interior surface and an outer or exterior surface. A water-entry port is positioned at the proximal end and a water outlet port at the distal end. A plurality of firetubes are disposed lengthwise in the housing, and the firetubes extend substantially the length of the housing between the proximal end and the distal end. The firetubes are used to pass the heated flue gas through the housing.

The improved boiler includes a pair of vertical, side baffles that affixed to the inner surface of the housing. The side baffles extend at least partially down the length of the housing, and perhaps the whole length, and separate a portion of said last pass firetubes near the housing from the remaining firetubes in the housing. In addition to the side baffles, the improved boiler will include at least two cross-sectional or substantially horizontal baffles adjacent the side baffles. The horizontal baffles are positioned in the housing between the distal end and the proximal end of the housing, with the horizontal baffles directing the flow of water in said housing from said inlet port proximate the tubes with the coolest gasses to draw or extract the most heat from the coolest tubes.

DESCRIPTION OF THE INVENTION

Looking to the attachedFIGS. 2-5, a four-pass boiler10is illustrated having a design to efficiently improve the heating and evaporating of a heat transfer liquid11, such as water, held in the boiler10using heated flue gasses from a furnace13. The boiler10includes a shell or housing12having a lateral length between a proximal endplate14and distal endplates16aand16b. The housing12may have cylindrical shape as illustrated inFIGS. 2aand2cand is used to hold the heat transfer liquid11. The housing12is further supported by a frame25to securely position the housing12on a ground surface.

The boiler10includes a means for heating and boiling the liquid11which includes a conventional heat source15for generating high temperature flue gas (combustion products) into a furnace13. High temperature flue gas passes through the series of tube-bundles17,18and19positioned in the housing (shell)12and extending the length of the housing12from the proximal endplate14to the distal endplates16aand16b(as best shown inFIG. 1). The heat source may be any type known in the art, such as a combustible fuel-fired burner8(seeFIGS. 2 and 4). In the case of a Heat Recovery Steam Generator, alternative high temperature waste gas from any process may be employed as a heat source.

The tube-bundles17,18and19, as illustrated inFIGS. 3a,4and5, are assembled into three bundles for a four-pass boiler10. As a result, the flue gas after furnace13passes through a first bundle of firetubes17in a first direction A from the distal endplate16ato the proximal endplate14, a second bundle of firetubes18in a second direction B from the proximal endplate14to the distal endplate16b, in the third bundle of firetubes19flue gas travels in the same direction A as in first bundle of firetubes17. After passing through the third bundle of firetubes19, the flue gas will be released in an exhaust port20located near the proximal endplate14. Further, the temperature of the flue gas will decrease as the flue gas passes through each set of tubes17,18,19, such that the temperature of the flue gas in the third bundle19will be at its lowest temperature before exiting through exhaust port20.

All of the tube-bundles in a conventional firetube boiler6are immersed in water and are not divided by any baffles from each other. So in conventional firetube boiler6, heat transfers from flue gas to the water at a certain saturation temperature which depends only from pressure in the vessel. The small portion of fresh water mixes with the heated water in the boiler housing, which is a large amount of already saturated water. Further, usually in a conventional boiler there is only an inlet port22ain the middle of the housing. As a result, at the fresh water inlet22aand distribution ports H, the influence of the fresh water on water temperature level in the boiler is negligible. Consequently, the fresh water (in spite of being at much less than saturation temperature) simply loses its ability to extract additional heat from flue gases.

The design of boiler10illustrated inFIGS. 2-5overcomes the lack of conventional boilers by means of organization of fresh water flow in the shell or housing12of the boiler10. With the boiler10illustrated inFIGS. 2-5, a pair of side baffles21affixed the inside of side-surface of the shell12separate the segments of last pass of the third tube bundles19from first and second bundles17and18, as well as the other parts of boiler10that are immersed or substantially immersed in water in the housing12. A pair of fresh water input ports22aare positioned near the proximal endplate14of the separated segments of housing12for supplying of fresh water on opposite sides of the bundles17,18, and19(flue gas exit from last pass tube-bundles19). Looking toFIGS. 3a-5, a curved distribution baffle (or header)22bis positioned proximate each input port22a, with the distribution baffle22bgenerally parallel to the housing12. A series of distribution ports or holes H traverse the length of the distribution baffle22b, and distribute the fresh water from the input port22ainto the area between the distribution baffle22band the substantially vertical side baffles21. As a result, fresh water runs along the segments between the distribution baffle22band the side baffles21before entering into the main part of housing12. The baffles21allow the coolest fresh water to enter at port22aand flow in direction B, counter to the flue gas flow direction A in the tube bundles19, before being mixed with saturated water11in the housing12. During the initial flow of water, the temperature of the water is lower (such as 228 degrees Fahrenheit, although it could be less) than within the center of the housing12.

The design of the boiler10provides the greater temperature differential between coolest gasses in the last pass tube-bundles19and the fresh water surrounding the tubes19due to of organization of counter flow of heat-carrier substances. In other words, the last pass of tube-bundles19performs the function of an economizer that is used to capture the lost or waste heat from the hot stack gas of the boiler6as used with conventional steam generation systems. However, the economizer is a device that has a separate housing and ductworks in addition to the boiler housing, providing a bulky assembly. In contrast, the design described herein gives the user an opportunity to save on economizer housing, ductwork and boiler room.

The improved boiler10will continue to be built as conventional boiler6is built, but the last pass tube-bundles19(whole or part of tube's length depending the water temperature at the outlet of separated segment) will be separated from other parts of boiler at the outer extremes of the boiler, and the bundles19are sandwiched by the cross-sectional or longitudinal, substantially horizontal baffles23between the side baffles21and the housing12. So the substantially horizontal baffles23do not extend across the whole boiler, but instead extend just from the baffles21to the shell12of the boiler10, and further isolate the cooler water from the inlet22awith a smaller portion of the third tube bundles19in segments30a,30b,30cor30d.

Looking toFIGS. 3aand3b, additional cross-sectional or longitudinal (parallel to the tube bundles17,18,19) internal baffles23may be positioned along the length of last pass tube-bundles19. As a result, as fresh water is introduced at the fresh water inlet22aand distribution ports H (the ports H act as a header for water distribution), the flow of water11will be encouraged to flow past the tubes19in segments (30a,30b,30c,30d) parallel to the tubes19before entering into the main body of the boiler housing12near the distal endplate16bof the boiler10. As with conventional boilers, the steam generated in the boiler10leaves the housing through the port24located on the top of housing12. This will further organize the third bundles19to improve the differential between coolest gasses in the last pass tube-bundles19and the fresh water surrounding the tubes19

The dimensions of the boiler10may vary according to the desired use. In the embodiment illustrated, the boiler10has a shell12diameter of approximately 92 inches, and a length of approximately 167 inches. The diameters of the firetubes17,18, and19extending through the housing12are approximately two and one-half inches each.

Calculations were performed by computer model of this boiler10under typical conditions, and it was found that the this design could improve the efficiency of the boiler10by as much as three percent or more relative to boilers having traditional designs.

In a second embodiment of the boiler10illustrated inFIGS. 6-8, the boiler10overcomes a problem in conventional boilers by means of organization of fresh water flow in the boiler's shell or housing12. With the boiler10illustrated inFIGS. 6-8, the side baffles21are affixed the inside of side-surface of the shell12and separate the segments of last pass of tube-bundles19from other parts of boiler immersed in water in the housing12. In this embodiment, the baffles21have a substantially vertically oriented straight or curved plate that extends longitudinally along at least a portion of housing12. The fresh water input ports22are positioned near the proximal endplate14(flue gas exit from last pass tube-bundles19) of the separated segments of housing12for supplying of fresh water. As a result, fresh water runs along of separated segments before entering into the main part of housing12. The baffles21allow the coolest fresh water to flow counter to the flue gas flow direction before being mixed with saturated water11in the housing12.

The boiler10will continue to be built as conventional boiler does, but the last pass tube-bundles19(whole or part of tube's length depending the water temperature at the outlet of separated segment) will be separated from other parts of boiler at the outer extremes of the boiler10, and the last pass bundles19are sandwiched by cross-sectional internal baffles27positioned between the baffles21and the housing12. As a result, the cross-sectional baffles27do not extend across the whole shell12of the boiler10, but instead extend just from the baffles21to the boiler's shell12.

The cross-sectional baffles27can be positioned at predetermined locations along the length of the housing12. Looking toFIG. 8, additional cross-sectional internal baffles27are positioned substantially equidistantly along the length of last pass tube-bundles19. The internal baffles27are positioned substantially at right angles with respect to the tubes19, and they are alternately positioned either above or below the upper level of water11held in the boiler10. As a result, as fresh water is introduced at the fresh water ports22, the flow of water11will be encouraged to flow past the tubes19in a serpentine fashion before exiting over upper edge of last baffle27and entering into the main body of the boiler housing12near the distal endplate16bof the boiler10. Such as in the conventional boiler, the generated in the boiler10steam leaves the housing through the port24located on the top of housing12.

It is to be noted that boilers10having firetube passes may incorporate the improved efficiency design. Looking toFIGS. 9-11, a third embodiment of the boiler10is illustrated corresponding to a 2-pass firetube boiler. In this embodiment, there is a single tube-bundle19, that is assembled for the two-pass boiler10so that the flue gas, after traveling through the furnace13, will pass in an opposite direction through the bundle of firetubes19and be released in an exhaust port20located near the proximal endplate14.

Like second embodiment, the design of boiler10illustrated inFIGS. 9-11overcomes the lack of conventional boilers by means of organization of fresh water flow in the boiler's shell or housing12. With the boiler10of this embodiment, the a pair of curved or bent substantially longitudinal baffles21affixed to the inside of side-surface of the shell12separate the segments of last pass of tube-bundles19from other parts of boiler immersed in water in the housing12. Consequently, this embodiment illustrates that the baffles21do not have to be substantially straight as illustrated inFIGS. 6-8, but can be bent to best fit around the tube-bundles19. The fresh water input ports22are positioned near the proximal endplate14(flue gas exit from last pass tube-bundles19) of the separated segments of housing12for supplying of fresh water. As a result, fresh water runs along of separated segments before entering into the main part of housing12. The baffles21allow the coolest fresh water to flow counter to the flue gas flow direction before being mixed with saturated water11in the housing12. The design of the boiler10provides the greater temperature differential between coolest gasses on the last pass tube-bundles19and the fresh water surrounded the tubes due to of organization of counter flow of heat-carrier substances.

In this embodiment, cross-sectional internal baffles27are positioned substantially equidistantly along approximately half of the length of last pass tube-bundles19(seeFIG. 6). As with the prior embodiment, the internal baffles27are positioned substantially at right angles with respect to the tubes19, and they are alternately positioned either above or below the upper level of water11held in the boiler10. As a result, as fresh water is introduced at the fresh water ports22, the flow of water11will be encouraged to flow past the tubes19in a serpentine fashion before exiting over upper edge of last baffle27and entering into the main body of the boiler housing12near the distal endplate16bof the boiler10. Such as in the conventional boiler, the generated in the boiler10steam leaves the housing through the port24located on the top of housing12.

Having thus described exemplary embodiments of a FIRETUBE STEAM BOILER HAVING IMPROVED EFFICIENCY, it should be noted by those skilled in the art that the within disclosures are exemplary only and that various other alternatives, adaptations, and modifications may be made within the scope of this disclosure. Accordingly, the invention is not limited to the specific embodiments as illustrated herein, but is only limited by the following claims.