Patent Grant
7954438
The present invention relates to biomass fueled stoves and boilers and, in particular, to a high efficiency wood or other biomass fueled stove/boiler wherein multiple combustion chambers and exhaust gas conduits are collectively surrounded by a liquid thermal transfer chamber to capture released heat energy and wherein exhaust gases to repetitively subjected to turbulent, pre-heated, pressurized combustion air to burn off hydrocarbons and other pollutants.
A wide variety of low-pressure wood and alternative biomass fuel (e.g. wood, coal, corn and other seeds, chips, pellets, crop waste etc.) stoves and boilers have been developed for residential and commercial use. Many of the boiler assemblies are constructed as stand-alone, weatherproof assemblies that are remotely located adjacent a heated building. Low pressure liquid supply lines are conducted from the boiler to an insulated, liquid distribution system at the heated facility. The heated facility is thereby isolated from any fire danger and exhaust gases are dispersed to the environment.
Many existing wood fueled stoves and boilers are relatively inefficient and exhaust smoke and flue gases that contain high concentrations of hydrocarbons that are hazardous to the environment. Efforts increasingly have been extended to improve stove/boiler efficiencies to increase thermal capture and reduce carbon emissions.
The present invention and novel biomass fueled stove/boiler was developed to provide a stove/boiler that is compatible with wood, coat, pellets and other biomass materials and is capable of burning the organic biomass fuel materials at efficiencies in excess of 90% with substantially reduced hydrocarbon emissions. The stove/boiler includes refractory lined burn chambers and a surrounding liquid thermal transfer chamber. The thermal transfer chamber and other heated surfaces are covered with sprayed urethane foam insulation to assure optimal heat transfer.
Preheated, pressurized combustion air is supplied to a primary burn chamber via surrounding horizontal and vertical orifice containing conduits. Exhaust gases are substantially directed via positive or negative fan directed pressurization into a lower, secondary burn/ash collection chamber via a secondary burner supplied with preheated, pressurized secondary combustion air. The secondary burner directs preheated pressurized combustion air into a shaped combustion space to produce turbulence and enhance combustion of hydrocarbons and pollutants.
The secondary exhaust gases are directed from the secondary burn/ash chamber via several fluted, fire or exhaust tubes that extend at acute angles through the liquid thermal transfer chamber to a further heated mixing chamber before being exhausted from an insulated stove flue. The wall geometry and cross-sectional shape of the fire tubes promote internal turbulence and heat transfer. The tubes can be straight or can include appropriate bends. The shaping and angular extension of the exhaust tubes promotes optimal heat energy collection, hydrocarbon combustion and carbon ash collection.
One or more tertiary fuel burners (e.g. oil or gas (natural or propane)) can be fitted to the primary burn chamber, between the primary and secondary burn chambers or at the secondary burn chamber. The tertiary burners can sustain exhaust gas combustion, facilitate cold starts or operate to adjust for changing fuel supply costs and availability.
An associated stove controller operates and/or responds to a combustion air source, airflow baffles, liquid supply and return pumps, sensors, switches and servos in conjunction with sundry operating sensors to accommodate several operating modes. The sensors monitor relevant operating parameters to optimize safety and burner efficiency and minimize back drafts.
It is a primary object of the invention to provide a high efficiency biomass fueled heating appliance (e.g. wood fueled boiler or stove).
It is further object of the invention to provide a boiler or stove wherein turbulent, pressurized, pre-heated combustion air is injected from orifices displaced horizontally and vertically about a primary burn chamber.
It is further object of the invention to provide a boiler or stove wherein exhaust gases are exposed to turbulent, pressurized, pre-heated secondary combustion air at a secondary burner and secondary burn chamber and directed to a heated mixing and exhaust chamber.
It is further object of the invention to provide a boiler or stove wherein exhaust gases are directed past a secondary burner having shaped surfaces and orifices from which pre-heated, pressurized secondary combustion air is directed to induce reflections and produce turbulent combustion in a secondary burn chamber.
It is further object of the invention to provide a boiler or stove wherein fan directed positive or negative pressurized primary and secondary air flow is created to direct and expose exhaust gases to pre-heated, turbulent, pressurized primary and secondary combustion air.
It is further object of the invention to provide a boiler or stove wherein a secondary burner directs pre-heated, pressurized secondary combustion air in a reflective space to turbulently mix with and promote exhaust gas combustion.
It is further object of the invention to provide a boiler or stove wherein exhaust gases are directed via angularly aligned exhaust tubes having wall surfaces shaped and directed to produce internal turbulence and that extend at acute angles between internal burn and exhaust chambers to an external flue.
It is further object of the invention to provide a boiler or stove including one or more alternative fuel fired burners to facilitate the reduction of hydrocarbon emissions and/or cold startups and/or adjust operation to fuel costs and availability.
It is further object of the invention to provide a boiler or stove including baffles and air control assemblies to restrict back drafts.
The foregoing objects, advantages and distinctions of the invention are obtained in a presently preferred biomass fueled boiler or stove assembly described below. The boiler/stove provides turbulent, pre-heated, pressurized primary and secondary combustion air to combust a wide variety of biomass mass fuels with high efficiency from optimally located primary and secondary chambers. An insulated, liquid thermal transfer chamber surrounds the primary and secondary burn chambers and captures released heat energy.
The boiler supplies primary combustion air via a injection assembly. Positively pressurized air is admitted to the fire box via horizontal and vertical orifice containing conduits. Exhaust gases are directed via a secondary pressurized burner into a lower, secondary burn/ash collection chamber.
Preheated, pressurized primary combustion air is directed from horizontally and vertically directed outlets at the primary burn chamber. The horizontal conduits are arranged below the vertical center of the primary burn chamber. A substantial portion of the exhaust gases are directed from the primary burn chamber into a lower, secondary burn/ash chamber. Pre-heated, pressurized air is directed from secondary burner orifices to create a turbulent flame front and exhaust gas temperatures on the order of 1220 to 1500° F. to burn the emissions. Combustion of the exhaust gases and unburned hydrocarbons continues in the secondary burn chamber which also collects ash and solid matter. The secondary combustion air is directed from orifices at a secondary burner assembly constructed to produce reflections and turbulent air flow.
The secondary exhaust gases are directed via several fluted fire or exhaust tubes that extend from the secondary chamber through the surrounding insulated thermal transfer chamber. Shaped heat transfer surfaces defined by fluting and convolutions at the fire tubes produce internal turbulence, enhance the heat transfer surface to the liquid thermal transfer media, and maintain exhaust gas temperatures to facilitate optimal hydrocarbon combustion.
The wall geometry and cross-sectional shape of the fire or exhaust tubes are selected to promote internal turbulence and heat transfer without requiring a discrete turbulator assembly. The walls can be configured in a variety of shapes and forms that promote turbulence (e.g. with parallelogram, square, star or other grooves, projections or fluting, V-shaped edges or corners when viewed in cross section) versus round or smooth cross-sectional shapes. The fire tubes can also be straight or include appropriate convolutions, bends, twists and/or turns.
The fire tubes preferably project at an acute angle in the range of 45 to 80 degrees versus conventional fire tubes that typically lay horizontal and/or may wind in a horizontal serpentine path. The angular displacement of the present fire/exhaust tubes facilitates carbon removal from the tubes. That is, gravity directs ash and carbon falling from the tubes back into the secondary burn/ ash chamber where the carbonized ash and solids from the primary burn chamber are continually subjected to secondary combustion.
A tertiary burner can be fitted to the primary burn chamber to facilitate cold starts and/or provide for boiler operation with a secondary fuel (e.g. gas—natural or propane, oil or other petrochemical fuels). A second gas fired burner and pressurized combustion air supply can also be provided at the secondary burn/ash chamber. The tertiary gas fired burner(s) sustains combustion of the exhaust gases during startup and low temperature stove conditions.
Associated stove controls, servos, air baffles and the like supply turbulent, preheated, pressurized combustion air to the primary and secondary burn chambers. Air flow is also controlled to minimize back drafts with the opening of either the primary or secondary burn chamber doors.
An exhaust manifold is coupled to the primary burner and the fire tubes from the secondary burn chamber to control exhaust gas flow to a solenoid controlled damper at the primary flue stack fitted to the back of the stove enclosure. The liquid thermal transfer chamber and any surfaces exposed to the flow of the liquid thermal transfer media are insulated with heat resistant foam.
Rear compartments at the stove enclosure contain liquid supply and return fittings, pump(s), fan(s) and sundry stove sensors, servos, baffles and other controls. Appropriate sensors are provided and coupled to the control circuitry and a microprocessor controller to provide for several operating modes. The sensors and switches monitor several different operating parameters including stack temperature, water temperature, flame conditions, oxygen levels, and door conditions.
Still other objects, advantages, distinctions, constructions and combinations of individual features of the invention will become more apparent from the following description with respect to the appended drawings. The description to each combination should therefore not be literally construed in limitation of the invention. Rather, the invention should be interpreted within the broad scope of the further appended claims.
The following figures disclose presently preferred constructions of the invention. Similar components and assemblies are referred to in the various drawings with similar alphanumeric reference characters and callouts.
Referring to
The door 6 is constructed to provide an airtight fit with an enclosed primary burn chamber 12. The primary burn chamber 12, ash chamber and associated exhaust gas flow paths are surrounded by an insulated liquid thermal transfer chamber 14. An upright, insulated exhaust gas flue 16 is supported to the rear surface of the boiler 2.
The primary burn chamber 12 provides a floor 18 and side walls 20 constructed or covered with bricks 22 formed from suitable refractory materials capable of withstanding normal operating temperatures and conditions. Approximately centered in the floor 18 is a port or opening 24 containing several laterally displaced refractory baffles 26 that open to an underlying secondary burner 28 and lower lying secondary burn chamber and ash collection chamber 30. The assembly 28 is loosely referred to as a “burner” for convenience only since it conducts secondary combustion air and does not operate as a fueled burner.
Internal air pressures induce combustion exhaust gases to substantially flow into the secondary burner 28. A fan assisted, positively pressurized boiler 2 is presently provided, although a negatively pressurized boiler 2 could also be constructed. A portion of the combustion exhaust gases and smoke are drawn off the top of the primary burn chamber 12 where the gases are directed to the flue 6 via a primary exhaust conduit 32, reference
Baffles can be included at the conduit 32 to further facilitate back draft control. Similarly and although not depicted, additional provisions can be made at the secondary burn chamber 30 and/or door 8 and/or boiler controls to prevent back drafts from the secondary burn chamber 30 upon opening the ash door 8.
During normal operation, the bulk of the exhaust gases are directed downward past the secondary burner 28 and into the secondary burn and ash chamber 30. Ash or solid waste combustion byproducts are removed from the ash chamber 30 via the door 8. The exhaust gases are directed from the secondary burn chamber 30 via several fluted and/or convoluted fire or exhaust tubes 36. The bores or inner diameters of the tubes 36 are shown in cutaway at
The exhaust gases from the primary and secondary burn chambers 12 and 30 are collected at the manifold 34 and directed past a controlled baffle or damper 38 to the flue 6. A laterally directed linkage arm assembly 40 is mounted to pivot and control the damper 38. The exhaust gas volume is controlled in relation to monitored operating temperatures to provide optimum burning of hydrocarbons and other pollutant materials. Delivered operating efficiencies at industry “high heating value” (HHV) and “low heating value (LHV) ratings have been obtained in the ranges of 60% to 80% HHV and 65% to 90% LHV. Collectively, general delivered efficiencies have been measured in the range of 60% to 91% for the stovelboiler 2.
The stove/boiler 2 is designed to operate with biomass fuels, however, a tertiary, gas or oil fired burner 52, such as disclosed at U.S. Pat. No. 6,718,889, is fitted to a conduit 54 at a rear wall of the primary burn chamber 12. The tertiary burner 52 is principally operated during cold starts until the stove 2 reaches operating temperatures. Alternatively, the burner 52 can be used as a primary heat source when wood or other biomass materials are unavailable or too costly or during periods when operating personnel aren't available to tend the stove/boiler 2.
The 80% plus operating efficiencies of the stove/boiler 2 are obtained in part by injecting pressurized air into the primary and secondary burn chambers 12 and 30 and at the exhaust fire tubes 36. Preheated, pressurized combustion air is injected into the primary burn chamber 12 via a hollow conduit assembly 60 that substantially circumscribes the primary burn chamber 12 and through which the conduit 54 passes. The assembly 60 includes horizontal segments 62 that circumscribe the rear and side walls of the primary burn chamber 12. The horizontal segments 62 are located at or below the vertical height of the primary burn chamber 12 to maintain the combustion air near the primary combustion zone for the particular combustion material. Primary combustion typically occurs in the lower third of a pile of combustible material or near the ash pile.
Vertical segments 64 extend from the ends of the segments 62 and project parallel to the sides of the door 6. The assembly 60 is thus located slightly above the refractory floor 18 and below the midway point of the primary burn chamber 12 to promote combustion.
Orifices 66 displaced along the segments 62 and 64 dispense pressurized combustion air conducted through the conduit assembly 60 into the primary burn chamber 12. The pressurized combustion air mixes with the combustion gases and smoke to produce turbulence and enhance the burning of hydrocarbons. The size and location of the orifices 66 are selected to optimize fuel combustion within the chamber 12. The primary combustion air admitted to the stove/boiler 2 exhibits a nominal positive pressure in the range of 0.1 to 1 inch of water column (WC) within the primary burn chamber 12. The positive pressure is obtained with primary and secondary combustion air fan assist assemblies discussed below. It is to be appreciated negatively pressurized stove/boiler 2 could be constructed to draw primary and secondary combustion air and exhaust gases through the assembly 2 with fan or other airflow assist assemblies.
The pressurized air is supplied from an air manifold or plenum 66 mounted to the rear wall of the thermal transfer chamber 14. The chamber 14 is fed by a fan 68, reference
Turning attention to
Pressurized and preheated secondary combustion air is conducted via conduit 74 to the side wall of the secondary burner 28 and into a cavity 81 behind front wall 82. A portion of the pressurized air is diverted into right and left wing chambers 83 and 85 that depend from the sides of the burner 28 into the secondary burn chamber 30. Internal baffles 86 at the wing chambers 83 and 85 divert a portion of the secondary combustion air into the depending portions of the wing chambers 83 and 85.
The disruption and partial bleeding of air flow into the wing chambers 83 and 85 induces turbulence in the cavity 81 and wing chambers 83 and 85. The turbulence and re-direction of air produces a delay in the air flow before the air is ejected from orifices 88 arranged over the arcuate burner wall 82. The delay facilitates the preheating of the secondary combustion air from the conduit 74 in the cavity 81 before being ejected into the channel 80 and secondary burn chamber 30, reference
The secondary combustion air directed from the orifices 88 strikes and reflects the exhaust gases in the channel 80 between the walls 82 and 84. The resulting mixing and turbulent flow optimizes the ignition and combustion of hydrocarbons and other combustibles in the exhaust gases that flow through the channel 80 and into the secondary burn/ash chamber 30.
The mixing of the secondary combustion air with the exhaust gases in the channel 80 again produces reflections and consequent turbulent flow between the faces of the panels 94 and the rear wall 82 of the burn/ash chamber 30. Like the burner 28, the burner 90 thus produces turbulent flow that optimizes the combustion of hydrocarbons and other combustibles in the gases.
Combustion continues in the secondary burn/ash chamber 30 upon subjecting the exhaust gases to additional pressurized and heated air supplied from the conduit 76. A fuel fired burner (e.g. propane or natural gas or oil) like the burner 52 can be fitted to the conduit 76 to sustain and enhance combustion in the secondary burn chamber 30. The secondary burn/ash chamber 30 is also lined with refractory materials to maintain secondary burn temperatures.
As combustion of the exhaust gases continues in the secondary burn chamber 30, the gases are directed to the several fluted fire or exhaust tubes 36. The tubes 36 extend at an acute angle between the secondary burn chamber 30 and the exhaust manifold 34 mounted to rear wall of the thermal transfer chamber 14. The tubes 36 are spaced apart from and extend parallel to each other. The tubes 36 extend through the thermal transfer chamber 14 and the liquid flows around each tube 36. The number and spacing between the tubes 36 is selected to facilitate heat transfer from the heated exhaust gases to the liquid media contained in the thermal transfer chamber 14. The tubes 36 project from the secondary burn chamber 30 at an acute angle in the range of 40 to 70 degrees.
The walls of the tubes 36 are shaped and formed to delay and promote turbulent flow through the fire tubes 36. The prolonged, turbulent flow enhances the burning of hydrocarbons contained in the exhaust gases, heat transfer and ultimately enhances efficiency of the stove/boiler 2.
The walls of the exhaust/fire tubes 36 presently define bores that exhibit a parallelogram shaped, transverse cross-sectional profile, see the cutaway of the exhaust/fire tubes 36 at
The acute, angular alignment of the exhaust or fire tubes 36 is arranged to direct carbon deposits that flake from the walls of the exhaust tubes 36 back into the secondary burn/ash chamber 30. Carbon deposits in the tubes 36 can also be manually cleaned upon opening the access panel 42 at the exhaust manifold 34. As the tubes 36 and carbon deposits are scraped or brushed from the interior walls of the tubes 36, the deposits fall into the ash chamber 30 and are removed via the door 8. The continual exposure of the combustible solid materials in the secondary burn chamber 30 and placement of the secondary burn chamber 30 in the thermal transfer chamber 14, assures that essentially all combustible materials are burned and the released heat energy is captured.
As mentioned, the space behind the rear covers 44 and 46 and in front of the insulation that covers the rear wall of the thermal transfer chamber 14 contains liquid supply and return fittings, liquid conduits 106, a liquid pump, fan blower 68, baffles 72, gas/oil burners 52, flame sensors, thermostat sensors, and sundry other stove servos, sensors and controls. The control devices communicate with programmed microprocessor circuitry at the controller 10 and variously supply and receive control signals. The sensors and switches monitor among different operating parameters, stack temperature, water temperature, flame conditions, oxygen levels, and door conditions.
The microprocessor is programmed to control several general modes of operation. A “cold start” mode operates to supply gas to the tertiary gas/oil burner(s) 52 to provide heat to ignite the biomass pile. The tertiary burner(s) 52 are subsequently operated to optimize combustion efficiencies or during a “backup” mode if the stove temperature falls due to fuel depletion.
Once ignited and during a “run mode”, the biomass burns and the stove/boiler 2 is controlled to maintain a thermostatically set temperature and appropriately direct combustion air flow via the blower 68 and baffles 72. During the run mode the duty cycle or on/off times of the baffles 72 are appropriately controlled to maintain optimal burn conditions.
While the invention is shown and described with respect to a presently preferred stove/boiler assembly and several considered improvements, modifications and/or alternatives thereto, still other assemblies and arrangements may be suggested to those skilled in the art. It is also to be appreciated that the foregoing singular and/or combinational features of the stove/boiler can be arranged in different combinations. The foregoing description should therefore be construed to include all those embodiments within the spirit and scope of the following claims.
This is a non-provisional application of provisional application Ser. No. 60/906,897, filed Mar. 13, 2007.
| Number | Name | Date | Kind |
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| 3543700 | Devita et al. | Dec 1970 | A |
| 3907210 | Dow et al. | Sep 1975 | A |
| 4319556 | Schwartz et al. | Mar 1982 | A |
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| Number | Date | Country | |
|---|---|---|---|
| 20080223266 A1 | Sep 2008 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60906897 | Mar 2007 | US |
