Sustained ignition secondary combustion unit

Claim 2

A sustained ignition secondary combustion unit for the secondary combustion of smoke products from primary fuel burning, either as a built in or retrofitted component of a furnace or stove or as a self contained separate unit comprising: first level means for conducting secondary air comprising a secondary air inlet and channel; second level means for conducting smoke products from primary fuel burning comprising a smoke products inlet and channel, secondary combustion zone, and exhaust outlet, said outlet defining the direction of flow of secondary combustion products; partition means separating the levels comprising a high temperature material, said partition formed with openings communicating between the levels in the area of the secondary combustion zone; said openings between the levels being substantially surrounded or bounded by a high temperature porous or fiber-like material having surface area portions contacting the secondary air from the first level and smoke products from the second level whereby said porous or fiber-like material may be maintained at a sufficient temperature by contact and combustion of secondary air and smoke products which diffuse into the porous or fiber-like material for sustaining ignition and secondary combustion of smoke products in the second level in the vicinity of the porous or fiber-like material, and for producing high temperature products of secondary combustion in the second level at the secondary combustion zone and downstream in the exhaust outlet direction.

Claim 3

The secondary combustion unit of claim 1 further comprising a housing enclosure comprised of insulating high temperature material.

Claim 4

The secondary combustion unit of claim 1 wherein said partition means is comprised of heat conducting material for exchange of heat generated by secondary combustion in the second level to the secondary air within said first level thereby preheating said secondary air.

Claim 5

The secondary combustion unit of claim 3 wherein said first level and second level are constructed and arranged for counterflow of the secondary air on one side and high temperature products of secondary combustion on the other side of said partition.

Claim 6

The secondary combustion unit of claim 4 wherein said secondary air channel comprises multiple or tortuous pathways having said partition means in common with the portions of said second level where high temperature products of secondary combustion occurr, for additional heat exchange and preheating of the secondary air.

Claim 7

The secondary combustion unit of claim 5 wherein the portions of said second level where high temperature products of secondary combustion occurr comprise multiple or tortuous pathways corresponding and complementary to the pathways of said secondary air channel for extended heat exchange.

Claim 8

The secondary combustion unit of claim 1 further comprising thermal siphon means for enhancing the draft at the outlet of the second level.

Claim 9

The secondary combustion unit of claim 1 wherein said openings comprise tube elements defining passageways extending between the levels, said tube elements comprised of a high temperature porous or fiber-like material extending into the secondary combustion zone of the second level whereby said tube element may be maintained at a sufficient temperature, by contact and combustion of secondary air and smoke products diffused into the fiber-like material of the tube elements, for sustaining ignition and secondary combustion of smoke products in the vicinity of said tube elements, said tube elements also having the effect of preheating secondary air as it passes through said defined passageways.

Claim 10

The secondary combustion unit of claim 8 wherein said tube elements comprise a ceramic fiber material.

Claim 11

The secondary combustion unit of claim 9 wherein said ceramic fiber material comprises Kaowool Paper.

Claim 12

The secondary combustion unit of claim 8 wherein said tube elements are formed with at least two different dimensions, tube elements upstream in the direction of travel of the smoke products comprising relatively smaller diameter and longer length for initial contact with the smoke products, and tube elements downstream in the direction of travel of the smoke products comprising relatively larger diameter and shorter length.

Claim 13

The secondary combustion unit of claim 11 wherein said upstream tube elements of relatively smaller diameter and longer length are also positioned along the outsides of the secondary combustion zone.

Claim 14

The secondary combustion unit of claim 8 or claim 11 wherein said first and second levels are constructed and arranged for counterflow of secondary air and high temperature products of secondary combustion relative to each other on either side of said partition means and wherein said secondary air channel comprises an extended tortuous passageway for delivering some of the secondary air to the tube elements upstream in the direction of travel of smoke products after extended preheating.

Claim 15

The secondary combustion unit of claim 1 further comprising after chamber means comprising mixing baffles in a housing of high temperature low thermal conductivity material, coupled to the outlet of said second level.

Claim 16

The apparatus of claim 1 further comprising a stove or furnace having a primary combustion chamber and a flue gas exhaust pathway for coupling to a chimney said stove or furnace comprising a sustained ignition secondary combustion unit as defined in claim 1 wherein the second level smoke products inlet is coupled into the flue gas exhaust pathway of said stove or furnace.

Claim 17

The apparatus of claim 15 wherein said said stove or furnace comprises a downdraft stove or furnace and wherein the secondary combustion unit is installed below the primary combustion chamber.

Claim 18

A stove or furnace as set forth in claim 16 wherein the secondary air inlet channel is bounded by the partition means below and by the primary combustion chamber above.

Claim 19

A stove or furnace as set forth in claim 15 further comprising after chamber means coupled at the second level outlet of the secondary combustion unit, said after chamber means comprising mixing baffle means within a high temperature withstanding material housing and having an outlet for coupling to a chimney.

Claim 20

The stove or furnace of claim 18 further comprising heat exchanger means coupled to the outlet of said after chamber means.

Claim 21

The secondary combustion unit of claim 1 wherein said second level means for conducting smoke products from primary fuel burning doubles back on itself by means of partition means of a heat conducting material, such that heat from ongoing or completed secondary combustion is transferred to the smoke products for preheating said smoke products.

Claim 22

The secondary combustion unit of claim 1 further comprising within said second level and upstream of secondary combustion zone a membrane of high-temperature porous or fiber-like material having one surface contacting the secondary air of said first level and the other surface contacting said smoke products of said second level; said porous or fiber-like material of said membrane being maintained at a sufficient temperature to support continuous combustion within said porous or fiber-like material by contact and combustion of said secondary air and said smoke products diffusing into said porous or fiber-like material; said membrane thereby preheating the smoke products passing through the second level before said smoke products reach the secondary combustion zone; said smoke products being preheated by the heat of combustion taking place within said membrane as they pass nearby or contact said membrane.

Claim 23

The secondary combustion unit of claim 21 wherein said membrane comprises a plurality of smoke preheating tubes open only to said first level, and extending into or through said second level, said smoke preheating tubes affording a large membrane surface area for contact by said smoke products, while minimizing restriction of flow through said second level.

Claim 24

The secondary combustion unit of claim 22 wherein said smoke preheating tubes are arranged in rows, the downstream row or rows arranged for receiving secondary air and further comprising first channel means operatively arranged for conducting said air to the next upstream row or rows of tubes, thus further preheating said air by further contact or proximity with the combustion within said porous or fiber-like material forming the walls of the smoke preheating tubes second channel means operatively arranged for conducting this further preheated air to the next upstream row or rows of smoke preheating tubes thereby supplying super heated air to the most upstream row or rows of smoke preheating tubes first contacted by said smoke products.

Claim 25

The secondary combustion unit of claim 21 wherein said tube elements comprise a ceramic fiber material.

Claim 26

The secondary combustion unit of claim 22 wherein said tube elements comprise ceramic fiber paper material rolled to form said tube elements.

Claim 27

A downdraft stove or furnace for sustained ignition and secondary combustion of the smoke products from primary fuel burning comprising: a primary combustion chamber having a primary air inlet for burning solid fuels and grate means for supporting the solid fuels and maintaining a bed of hot coals at the base of the primary combustion chamber, said grate means formed with a concave downward configuration defining an elongate tunnel below the primary combustion chamber, said grate formed with downdraft grate openings; partition means extending along said tunnel dividing the tunnel into upper and lower channels, said upper channel comprising a secondary air channel in heat exchange relationship with the base of the primary combustion chamber but sealed from the grate downdraft openings, said secondary air channel having an inlet for receiving and preheating secondary air, said lower channel comprising a smoke products channel communicating with the primary combustion chamber through the downdraft openings of the grate, said smoke products channel having a flue outlet for establishing a draft through the smoke products channel; said partition means formed with a plurality of openings between the secondary air channel and the smoke products channel defining in the smoke products channel a secondary combustion zone, said openings between the channels being substantially surrounded or bounded by a high temperature porous or fiber-like material having surface area portions contacting the secondary air from the upper channel and smoke products from the lower channel whereby said porous or fiber-like material may be maintained at a sufficient temperature, by contact and combustion of secondary air and smoke products in the porous or fiber-like material, for sustaining ignition and secondary combustion of smoke products in the secondary combustion zone of the lower channel in the vicinity of the porous or fiber-like material and for producing high temperature products of secondary combustion.

Claim 28

A downdraft stove or furnace for sustained ignition and secondary combustion of the smoke products from primary fuel burning comprising: a primary combustion chamber having a primary air inlet for burning solid fuels and grate means for supporting the solid fuels and maintaining a bed of hot coals at the base of the primary combustion chamber, said grate means formed with a concave downward configuration defining an elongate tunnel below the primary combustion chamber, said grate formed with downdraft grate openings; partition means extending along said tunnel dividing the tunnel into upper and lower channels, said upper channel comprising a secondary air channel in heat exchange relationship with the base of the primary combustion chamber but sealed from the grate downdraft openings, said secondary air channel having an inlet for receiving and preheating secondary air, said lower channel comprising a smoke products channel communicating with the primary combustion chamber through the downdraft openings of the grate, said smoke products channel having a flue outlet for establishing a draft through the smoke products channel; said partition means formed with a plurality of openings between the secondary air channel and the smoke products channel defining in the smoke products channel a secondary combustion zone, said openings between the channels being substantially surrounded or bounded by a high temperature porous or fiber-like material having surface area portions contacting the secondary air from the upper channel and smoke products from the lower channel whereby said porous or fiber-like material may be maintained at a sufficient temperature, by contact and combustion of secondary air and smoke products in the porous or fiber-like material, for sustaining ignition and secondary combustion of smoke products in the secondary combustion zone of the lower channel in the vicinity of the porous or fiber-like material and for producing high temperature products of secondary combustion.

Claim 29

The downdraft stove or furnace of claim 26 wherein said openings comprise tube elements defining passageways extending between the levels, said tube elements comprised of a high temperature fiber-like material extending into the secondary combustion zone of the smoke products channel whereby said tubes may be maintained at a sufficient temperature by contact and combustion of secondary air and smoke products in the fiber-like material of the tube elements for sustaining ignition and secondary combustion of smoke products in the vicinity of said tube elements and for preheating secondary air passing through said tube elements.

Claim 30

The downdraft stove or furnace of claim 27 wherein said tube elements comprise ceramic fiber paper material rolled to form said tube elements.

Claim 31

The downdraft stove or furnace of claim 26 wherein said partition means is comprised of a heat conducting material for heat exchange between the high temperature products of secondary combustion and the secondary air.

Claim 32

The downdraft stove or furnace of claim 26 further comprising after chamber means comprising baffle means in a housing of high temperature low thermal conductivity material, coupled to the outlet of said lower channel.

Claim 33

The downdraft furnace of claim 30 further comprising heat exchanger means coupled to said after chamber means.

Claim 34

The downdraft stove or furnace of claim 27 wherein said tube elements vary in dimension from relatively narrower diameter and longer length to relatively larger diameter and shorter length from upstream to downstream in the direction of travel of the smoke products for initial contact of the relatively narrower diameter tube elements with the smoke products.