US3724445A

US3724445A - Heater for asphalt concrete roadways and the like

Info

Publication number: US3724445A
Application number: US00129404A
Authority: US
Inventors: E Cutler
Original assignee: Cutler Repaving Inc
Current assignee: Cutler Repaving Inc
Priority date: 1971-03-30
Filing date: 1971-03-30
Publication date: 1973-04-03
Anticipated expiration: 1990-04-03

Abstract

Fuel such as pentane is heated to 300* F to 400* F and then mixed with the air needed to oxidize the carbon and produce a smokeless exhaust. The mixture is delivered into a shallow chamber of which the pavement to be heated is the bottom. The roof of the chamber is of infra-red brick and has depending side walls and end walls extending down close to the pavement to be heated, providing heat-radiating surfaces. The spent gases are aspirated through holes in the roof near its edges to keep the pressure in the chamber automatically identical with the atmospheric pressure outside. The intensity and rapidity of the heat transfer into the roadbed is such that exposure to the naked flame in the chamber can only be continued for a fraction of a minute without getting the surface hot enough to injure the pavement. The completion of the process is as disclosed in my earlier U.S. Pat. No. 3,361,042 and includes roweling all the softened roadbed to dislodge heated material and additional cooler material lower down, and a second heating of the roweled surface.

Description

United States Patent 091 Cutler 1 1 Apr. 3, 1973 [54] HEATER FOR ASPHALT CONCRETE [57] ABSTRACT ROADWAYS AND THE LIKE Fuel such as pentane is heated to300 F to 400 F and [75] Inventor: Earl F. Cutler, Lawrence, Kans. then mixed with the air needed to oxidize the carbon and roduce a smokeless exhaust. The mixture is [73] Asslgnee' Eggs Repaying Lawrence deliv red into a shallow chamber of which the pavement to be heated is the bottom. The roof of the [22] Filed: Mar. 30, 1971 chamber is of infra-red brick and has depending side walls and end walls extending down close to the pave- [21] Appl' 129404 ment to be heated, providing heat-radiating surfaces. The spent gases are aspirated through holes in the roof [52] U.S. Cl. ..l26/27l.2 A near' its edges to keep the pressure in the chamber au- [51] Int. Cl ..E0lc 23/14 tomatically identical with the atmospheric pressure [58] Field of Search...l26/27l.2 R, 271.2 A, 271.2 C outside. The intensity and rapidity of the heat transfer into the roadbed is such that exposure to the naked [56] References Cited flame in the chamber can only be continued for a fraction of a minute without getting the surface hot UNITED STATES PATENTS enough to injure the pavement. The completion of the 1,458,070 6/1923 Long m1 .Q ..126/27l.2AX P as disclosed in y earlier 3,279,458 10/1966 Moench ..126/271.2 A 3,361,042 and includes roweling all the softened 2,566,473 9/1951 Wilson ..126/271.2C roadbed to dislodge heated material and additional 3,311,104 3/1967 Wollner et a1. ..l26/27l.2 A X cooler material lower down, and a second heating of 1,500,340 7/1924 Smith "126/2712 A th led urfa 1,736,227 11/1929 .....126/271.2 A 1,961,877 6/1934 Gars ..l26/27l.2 A 11 Claims, 9 Drawing Figures Primary Examiner-Charles J. Myhre Attorney-Olson, Trexler, Wolters & Bushnell PATENTEUAFM I975 3 724 445 SHEET 1 [IF 3 M m, was UM;

HEATER FOR ASPHALT CONCRETE ROADWAYS AND THE LIKE SUMMARY OF THE INVENTION A readily combustible hydrocarbon such as pentane is intimately mixed in gaseous condition with all the air needed to oxidize all the carbon to carbon dioxide, and produce a smokeless exhaust free of pollutants. The pentane is usually received in liquid form and is changed to gas in a combined pilot light and vaporizer at one corner of the chamber. A small ordinary blowtorch constituting a' pilot burner delivers a small jet of flame to one or two adjacent main heating burners, and .a coil of metal tubing wound around the pilot burner receives liquid pentane, and delivers it at about 350 F in gaseous form. Combustion is accelerated by preheating the fuel to temperatures believed to result in a small amount of cracked nascent material. 300 F to 400 F is found to get good results in getting rapid blue flame burning later.

Air is compressed in a conventional blower to a suitable pressure such as nineteen inches of water column. The freshly heated fuel is mixed thoroughly with the air and the mixture is delivered to burners that are in a shallow chamber of which the pavement to be heated is the bottom. The burners are disposed in such pattern that the chamber has a multiplicity of closely spaced flames that substantially fill the chamber with lambent flame. The rest of the chamber is an insulating roof with narrow depending side walls along its periphery extending down close to the pavement to be heated. The 'spent effluent is exhausted through the roof at its periphery to keep the pressure in the chamber automatically substantially the same as the atmospheric pressure outside.

The solid roof and sidewalls are adapted to radiate most of their heat in red and infra-red wavelengths. The entire chamber fills with gentle bluish flame transparent to the long wave length heat from the radiant roof and side walls. Radiant screens associated with some of the burners radiate energy in the ultra red visible spectrum for effectively delivering heat energy to pebbles and other non-black material in the roadbed.

The intensity and rapidity of the heat transfer into the roadbed is such that exposure to the naked flame in the chamber can only be continued for a fraction of a minute without getting the surface hot enough to injure the pavement. The operator controls the time duration of heating by varying the speed of the roof over th pavement.

The completion of the process is as disclosed in my earlier U.S. Pat. No. 3,361,042 and includes roweling all the softened roadbed to dislodge heated material and additional cooler material lower down, and a second delivery of heat to the roweled surface followed by conventional smoothing and cooling.

BRIEF DESCRIPTION OF THE FIGURES In the accompanying drawings:

FIG. 1 is a view partially structural and partially a functional diagram of one heating unit and taken approximately along line I- l of FIG. 2,

FIG. 2 is a plan view looking downward approximately along line 2-2 of FIG. 1 showing one corner of the chamber;

FIG. 3 is a vertical fragmentary section taken approximately along line 3--3 of FIG. 2;

FIG. 4 is a similar fragmentary section taken approximately along line 4--4 of FIG. 2;

FIG. 5 is a fragmentary sectional view taken on a vertical plane through one of the lower burners;

FIG. 6 is a fragmentary sectional view of the fuel-air mixing chamber taken along line 6-6 of FIG. 1;

FIG. 7 is a fragmentary sectional view taken along line 77 of FIG. 2;

FIG. 8 is a fragmentary sectional view taken on a vertical plane through one of the upper burners as seen from line 8-8 of FIG. 1; and

FIG. 9 is an enlarged fragmentary sectional view taken along line 9--9 of FIG. 8. 1

DETAILED DESCRIPTION In the embodiment of equipment selected for illustration, the machine is of the general type disclosed in my aforesaid U.S. Pat. No. 3,361,042 and the present invention is an improved heating unit for such machines. The heating unit comprises a main roof 10 that is 10 or 12 feet long in the transverse dimension indicated in FIG. 1, and about 6 feet wide in the direction of movement along over the pavement 12. A continuous peripheral side wall 15 completely encloses the edges of the chamber 14 between the roof l0 and the pavement 12. The wall 15 extends so that there is a small crack 17 between the wall 15 and the pavement 12. The side wall 15 includes end portions 16 at the lateral ends of the roof 12 which have small longitudinal grooves 18 adapted to receive the reversely hooked edges 20 of laterally extending baffles 22 to obstruct drafts striking the equipment from the side from getting under the edges of the side walls in sufficient volume to disturb the heating taking place inside.

These baffles 22 may be in short sections and each section may overlap an adjacent section. The baffles may be needed in windy weather.

As seen in FIG. 1, a conventional rotary fan 26 with an axial inlet at 28 compresses air to a working pressure equivalent to a water column of nineteen inches, plus or minus 3 or 4 inches. The downwardly moving air passes through conduit 27 into fuel-air mixer 29 having a mixing chamber 32. The air in the chamber 32 is deflected into a vortex by curbed. guiding baffles 30 (See FIGS. 1 and 6). Fuel from pipe 33 enters the chamber 32 at two inlets 34, 34. The inlets 34 are located at different radial distances from the center of Provided at one corner of the chamber 14 is a pilot burner 43 which is shown enlarged in FIG. 7 and which may take the form of a blow torch of conventional construction. A fuel line 45 is connected to a source of hydrocarbon fuel (such as liquid pentane) carried by the machine, the line 45 including a fuel supply valve 47 which is open when the machine is in operation. The part of the fuel line 45 within the chamber 14 is formed in a coil 49 around the burner tube of the pilot burner 43 so that incoming fuel may be preheated. to about 350 F prior to being sent through supply pipe 33 in gaseous form to the mixing chamber 32. By preheating the fuel, as aforesaid, it has been found that a more efficient heating is provided by the

burners

39, 41, resulting in more BTU s being delivered to the pavement 12.

Referring again to FIG. 7 the pilot burner 43 and coil 49 may be mounted in any convenient manner as by U- shaped sheet metal member 51 which is suspended from the roof l and with the intake end of the pilot burner 43 projecting through the side wall 15. A suitable small pilot-lighting access (not shown) may be provided, and in addition there is a pilot supply line 53 with a valve V.

Referring now to the top burner shown in FIGS. 8

and 9, the nylon tube 36 delivers the fuel-air mixture to a rigid metal standard tube 38, which is embedded in the roof and extends down along the axis of a conical cavity in the lower face of the roof. The roof cavity is divided into a small, upper mixing chamber 40 by a spreader plate 42, upon which rests a finely perforated diaphragm 44 with a supporting nut 46 below both. The gas from the tube 38 issues radially through lateral out lets 48 and the slight turbulence in the small chamber 40 completes the intimate mixing of the ingredients. Directly below these parts is the much larger annular cavity 50 in which combustion occurs, and the resultant flame spreads down gently from the diaphragm 44 within a contour indicated in dotted lines at 52. The lower end of the tube 38 receives a bottom closure nut 54 with a threaded shank 56. A radiant screen 60 with large openings 61, rests in the upper portion of the flame, which spreads downwardly with gentle movement. The expansion of the flaming gas takes place in the lower annular cavity 50 and the mouth of that cavity has a diameter about 12' times that of the inner diameter of the tube 38. The supporting nuts for the radiant screen define a relatively stagnant space along the axis of the burner and there will be a small relatively stagnant cone at the bottom of the nut 54. Contact with this obstacle will remove fractions of the cone under the nut 54. The flame passing on down will move in to replace whatever is removed. Along the axis of the tube 38 and below the nut 54, the central portion of the expanding flame will move downwardly a little faster than the outer lateral portions and the resulting relatively large quiescent bulb will extend down and gently spread out on the pavement below. The screen 60 is preferably of an alloy metal that radiates in the visible spectrum of red and above. Such alloy may for example be one containing about 3035 percent nickel, 19-23 percent chromium and the remainder iron.

Referring now to FIG. 5, the upstanding delivery tube 62 of burner 41 receives combustible mixture from the nylon tube 37. The burner 41 is shaped to define an upper torus-like chamber 66 and the flame begins at the end of the tube 62 and generates a vortex 68 in which rapid combustion takes place. The flame issues through a central opening 70 in the bottom of the upper chamber into a second substantially duplicate chamber 72 in which the central flow again engenders a complete closed torus 74. By the time the gas reaches the bottom of the torus 74, it is almost completely through burningand incandescent with a light blue transparent flame. This central stream then starts down down and brush the surface of the pavement gently and spread out into an outer torus 76, almost three times the diameter of the torus 74. With each enlargement of its cross section the stream decreases its linear velocity in an inverse ratio and the merged mass of flame from all the burners. Thus, the combined action of the flames from the burners'39, 41 results in a mass oflam bent flame that substantially fills the chamber 14.

Referring to FIGS. 1 and 2, it is seen that adjacent to the corners of the roof 10 are groups of

openings

80, 82, one group of openings being at the long side of the roof l0 and the other group of openings 82 being at the shortsideof the roof. One group of each of these

openings

80, 82 is shown in FIG. 2, it being understood that a like arrangement is present at the other three corners of the roof. Extending into the

openings

80, 82 are

short pipes

83, 84 the upper ends of which are joined by

support plates

85, 86. The openings with the pipes therein provide an exit flow path' adjacent to the periphery of the chamber 14 for the discharge of burnt gases.

Above the open upper ends of the pipes 83,

84am headers

88, 90, there being a pair of such headers 88, at each of the four corners of the roof 10. The

headers receive the burnt gases and convey them to exhaust uptakes 92 at each corner of the roof.'The gases then flow upwardly and to atmosphere via corner stacks 94.

Connected to the conduit 27 above the mixer 29 are aspirator tubes 96, there being one tube 96 extending to the bottom of each corner stack 94 and opening therein. These aspirator tubes 96 result in a portion of the air stream from the fan 26 being utilized for providing a draft in the stacks 94, the remaining portion of the stream being sent to the mixer 29, a previously described. By reason of the use of the aspirator tubes 96 to produce the induced draft, the exhaust gases are withdrawn from the chamber 14 in an amount that is equal in volume but not in weight to that of the fuel-air supply flow into the burners. Also, the aspirating tubes 96 provide such effective draft that the stacks need only be high enough to permit the stream from the aspirating tube to blend with the rest of the gases present, and the stacks can be short enough not to get in the way with branches of trees or the like along the side of the road.

In staring an operation with liquid pentane, the pilot burner 43 is first lit and allowed to burn a minute or two to. warm up the tube 49. The pentane supply will issue immediately when the valve 47 is opened. There is also available gaseous pentane, which can pass through the same equipment and get the same result. A

slightly lower working temperature in the intake end of the pilot burner itself is wiped outduring the subsequent heating of the gas. The operator will let the equipment remain stationary for from one to three minutes depending on the temperature of the pavement, and then traverse the heater along the road as fully explained in my aforesaid earlier patent. It will be obvious that when the weather is such that the ambient temperature is say 40 F, the heating of the pavement to the desired final temperature may take two or three times as long as would be required on a day with the thermometer at 90 F in the shade. it will also be obvious that the second heating (after the material warmed by the first heating has been disturbed and mixed with cooler portions dislodged from the underlying roadbed) causes the effective surface exposed to the action of the heater to be much greater. The temperature gradient after the second heating will thus extend much farther down and still be as hot at the top surface as is safe for the material of the pavement. The brick roof will deliver a maximum fraction of its radiant heat at red and infra-red wavelengths, which are the wavelengths most readily absorbed by the typical black asphalt concrete. However the screens 60 for the top burners 39 are of a metal alloy that emits a great deal of light of shorter wavelengths in the visible spectrum. These short wavelengths are separated from the pavement only by flame that is substantially transparent to the short wavelengths so that pebbles and other bits of material that are not black, and thus tend to reflect a great deal of any infra-red radiation, will receive the shorter wavelengths that are more effective in delivering radiant energy to such materials.

In the steady state operation, the mass of flame in the chamber 14 tends to drift quiescently toward the discharge openings to the headers. Furthermore, by providing the discharge from the gases at the corners of the chamber 14, there is relatively little gas flow across the crack 17.

Others may readily adapt the invention for use under various conditions of service by employing one or more of the novel features disclosed or equivalents thereof. For instance, it may sometimes happen that suitable pentane is not available and some other hydrocarbon in the general class of naptha or petroleum ether has to be used. If such a makeshift substitute tends to smoke a littie, the air entering the inlet 28 can be seeded with the products of combustion rising in the stacks 94. For this purpose there are indicated in FIG. 1, seeding tubes 98 with their intake ends in the stacks 94 and their delivery ends at 100 in the intake opening 28. This can be designed and positioned to deliver from 5 to 15 percent of the total volume drawn in by the main fan, and when the completed mixture gets into the flame it will already contain a little ionized material that will expedite the initiation and propagation of the flame and enhance the completeness of the combustion.

In addition to the advantages provided by the radiant heating and the preheating of the fuel, the efficiency of the equipment is further enhanced by the arrangement and operation of the

burners

39, 41. Thus, the burners cooperate to heat the walls of the chamber 14 only up to an effective emission temperature sufficient to emit a maximum fraction of radiation in the long red and infra-red wavelengths. The radiant screen 60 in the upper burner 39 is in the flame at the level of maximum flame temperature and the spherical bulb of flame at 52 is approximately in tangential contact with the pavement and the conical cavity of the burner. Burner efficiency is also enhanced by the fact that in the lower burners 41 the gas is guided and retarded to issue into the chamber 14 with a flow cross-section that is of many times greater than where ignition takes place, thus lowering the flame velocity in the chamber 14. Furthermore, in the lower burner 41, the small upper and

lower chambers

66, 72 thereof form the gas into the small vortexes 68, 74 with their vertical axes in continuation of the direction of gas entry. Each vortexis such that movement of the gas in circles in radial planes containing the axis of the vortex reduces the linear distance flame propagation must travel to reach every point in the circling mass. Also, the small vortex 74 changes into direct flow at the bottom of the burner 41 to contact the pavement with a gentle flame.

The invention is claimed as follows:

1 Equipment for heating the upper strata of asphalt concrete pavement, or the like, comprising chamberforming walls including a roof wall adapted to overlie an area to be heated by combined radiation and direct contact heating, and said walls including downwardly extending peripheral side wall portions that leave only a small crack between their lower edges and said pavement; power air blower supply and heating means for producing a multiplicity of flames in said chamber below said roof; said heating means comprising a multiplicity of burners that produce flames with cross-sections many times greater than where ignition takes place, said burners being disposed in a pattern such that the flames merge and form a substantially continuous mass of flame extending across said chamber to provide a substantially uniform temperature to which the pavement exposed to said chamber is subjected; and exhaust means having an exit flow path through said chamber-forming walls for removal of the products of combustion from within said chamber.

2. Equipment according to Claim 1 in which said exhaust means is adapted to withdraw from said chamber gases equal in weight but many times greater in volume than the mixture supplied to said chamber, whereby the static pressure inside said chamber at said crack is kept substantially equal to the atmospheric pressure outside.

3. Equipment according to claim 1, each burner having walls within which the expansion of the gases is guided and retarded.

4. Equipment according to claim 1 in which the burners are arranged in a checkerboard pattern in said chamber, the radially expanding lower portion of each flame being arrested by encountering lower portions of surrounding flames.

5. Equipment for heating the upper strata of asphalt concrete pavement, or the like, comprising chamberforming walls including a roof wall adapted to overlie an area to be heated by combined radiation and direct contact heating, and said walls including downwardly extending peripheral side wall portions that leave only a small crack between their lower edges and said pavement; power air blower supply and heating means for producing a multiplicity of flames in said chamber below said roof; said flames being spaced closely enough to merge and substantially entirely fill said chamber with quiescent lambent flame; exhaust means having an exit flow path through said chamber-forming walls for removal of the products of combustion from within said chamber, each flame being associated with a burner, each burner having walls within which the expansion of gases is guided and retarded to issue into the chamber with a flow cross-section many times greater than where ignition takes place, with corresponding reduction in linear velocity, certain of said burners, identified for convenience as lower burners, defining small chambers shaped to direct and entering stream of gas into small vortexes with their vertical axes in continuation of the direction of entry, whereby the movement of gas in circles in radial planes containing the axis of a small vortex substantially reduces the linear distance flame propagation must travel to reach every point in the circling mass; the entire vortex changing into direct downward flow to contact the pavement.

6. Equipment for heating the upper strata of asphalt concrete pavement, or the like, comprising chamberforming walls including a roof wall adapted to overlie an area to be heated by combined radiation and direct contact heating, and said walls including downwardly extending peripheral side wall portions that leave only a small crack between their lower edges and said pavement; power air blower supply and heating means for producing a multiplicity of flames in said chamber below said roof; said flames being spaced closely enough to merge and substantially entirely fill said chamber with quiescent lambent flames; and exhaust means having an exit flow path through said chamberforming walls for removal of the product of combustion from within said chamber, certain of said flames originating in conical, downwardly opening cavities in the lower surface of said roof, with ignition over a small circle intermediate the ends of said cones propagating radially both inward and outward to build an approximately spherical bulb having tangential contact with its cone and with the pavement.

7. Equipment according to claim 6 in which an openmesh screen lies in each flame, said screen being of material adapted to emit radiation of relatively short wavelengths efficient in heating light colored material.

8. Equipment for heating the upper strata of asphalt concrete pavement, or the like, comprising chamberforming walls including a roof wall adapted to overlie an area to be heated by combined radiation and direct contact heating, and said walls including downwardly extending peripheral side wall portions that leave only a small crack between their lower edges and said pavement; power air blower supply and heating means for producing a multiplicity of flames in said chamber below said roof; exhaust means having an exit flow path through said chamber-forming walls for removal of the products of combustion from within said chamber, a

mixing chamber to receive compressed air from said power blower; fuel supply conduit means for delivering fuel to said mixing chamber; and a multiplicity of mixture conduits, one for each flame, receiving combustible mixture from said mixing chamber and delivering to each flame its aliquot portion of mixture.

9. Equipment according to claim 8 in which said fuel supply conduit means has a portion having heat transfer contact with said blowtorch for preheating the fuel en route to said mixing chamber.

10. Equipment for heating the upper strata of asphalt concrete pavement, or the like, comprising chamberforming walls including a roof wall adapted to overlie an area to be heated by combined radiation and direct contact heating, and said walls including downwardly extending peripheral side wall portions that leave only a small crack between their lower edges and said pavement; power air blower supply and heating means for producing a v multiplicity of flames in said chamber below said ro'of; exhaust means having an exit flow path through said chamber-forming walls for removal of the products of combustion from within said chamber, and

conduit seeding means provided for returning to the inlet of said power blower a minor fraction of the fresh exhaust gases from said chamber.

1 1. Equipment for heating the upper strata of asphalt concrete pavement or the like comprising chamberforming means including a roof for overlying an area to receive the heat and downwardly extending wall portions that leave only a small crack between said wall portions and said area, means for producing a multiplicity of closely spaced flames substantially in said chamber such that the flames substantially entirely fill the chamber with lambent flame, and means defining an exit flow'path through said chamber-forming means for the removal of the products of combustion within the chamber; the wall surface of said chamber being of a material that radiates a major-portion of its radiant heat at red and infra-red wavelengths, and said chamber also containing a multiplicity of members associated with respective flame producing means for radiating a substantial amount of energy in the visible spectrum above red.

Claims

2. Equipment according to Claim 1 in which said exhaust means is adapted to withdraw from said chamber gases equal in weight but many times greater in volume than the mixture supplied to said chamber, whereby the static pressure inside said chamber at said crack is kept substantially equal to the atmospheric pressure outside.
3. Equipment according to claim 1, each burner having walls within which the expansion of the gases is guided and retarded.
4. Equipment according to claim 1 in which the burners are arranged in a checkerboard pattern in said chamber, the radially expanding lower portion of each flame being arrested by encountering lower portions of surrounding flames.
5. Equipment for heating the upper strata of asphalt concrete pavement, or the like, comprising chamber-forming walls including a roof wall adapted to overlie an area to be heated by combined radiation and direct contact heating, and said walls including downwardly extending peripheral side wall portions that leave only a small crack between their lower edges and said pavement; power air blower supply and heating means for producing a multiplicity of flames in said chamber below said roof; said flames being spaced closely enough to merge and substantially entirely fill said chamber with quiescent lambent flame; exhaust means having an exit flow path through said chamber-forming walls for removal of the products of combustion from within said chamber, each flame being associated with a burner, each burner having walls within which the expansion of gases is guided and retarded to issue into the chamber with a flow cross-section many times greater than where ignition takes place, with corresponding reduction in linear velocity, certain of said burners, identified for convenience as lower burners, defining small chambers shaped to direct and entering stream of gas into small vortexes with their vertical axes in continuation of the direction of entry, whereby the movement of gas in circles in radial planes containing the axis of a small vortex substantially reduces the linear distance flame propagation must travel to reach every point in the circling mass; the entire vortex changing into direct downward flow to contact the pavement.
6. Equipment for heating the upper strata of asphalt concrete pavement, or the like, comprising chamber-forming walls including a roof wall adapted to overlie an area to be heated by combined radiation and direct contact heating, and said walls including downwardly extending peripheral side wall portions that leave only a small crack between their lower edges and said pavement; power air blower supply and heating means for producing a multiplicity of flames in said chamber below said roof; said flames being spaced closely enough to merge and substantially entirely fill said chamber with quiescent lambent flames; and exhaust means having an exit flow path through said chamber-forming walls for removal of the product of combustion from within said chamber, certain of said flames originating in conical, downwardly opening cavities in the lower surface of said roof, with ignition over a small circle intermediate the ends of said cones propagating radially both inward and outward to build an approximately spherical bulb having tangential contact with its cone and with the pavement.
7. Equipment according to claim 6 in which an open-mesh screen lies in each flame, said screen being of material adapted to emit radiation of relatively short wavelengths efficient in heating light colored material.
8. Equipment for heating the upper strata of asphalt concrete pavement, or the like, comprising chamber-forming walls including a roof wall adapted to overlie an area to be heated by combined radiation and direct contact heating, and said walls including downwardly extending peripheral side walL portions that leave only a small crack between their lower edges and said pavement; power air blower supply and heating means for producing a multiplicity of flames in said chamber below said roof; exhaust means having an exit flow path through said chamber-forming walls for removal of the products of combustion from within said chamber, a mixing chamber to receive compressed air from said power blower; fuel supply conduit means for delivering fuel to said mixing chamber; and a multiplicity of mixture conduits, one for each flame, receiving combustible mixture from said mixing chamber and delivering to each flame its aliquot portion of mixture.
9. Equipment according to claim 8 in which said fuel supply conduit means has a portion having heat transfer contact with said blowtorch for preheating the fuel en route to said mixing chamber.
10. Equipment for heating the upper strata of asphalt concrete pavement, or the like, comprising chamber-forming walls including a roof wall adapted to overlie an area to be heated by combined radiation and direct contact heating, and said walls including downwardly extending peripheral side wall portions that leave only a small crack between their lower edges and said pavement; power air blower supply and heating means for producing a multiplicity of flames in said chamber below said roof; exhaust means having an exit flow path through said chamber-forming walls for removal of the products of combustion from within said chamber, and conduit seeding means provided for returning to the inlet of said power blower a minor fraction of the fresh exhaust gases from said chamber.
11. Equipment for heating the upper strata of asphalt concrete pavement or the like comprising chamber-forming means including a roof for overlying an area to receive the heat and downwardly extending wall portions that leave only a small crack between said wall portions and said area, means for producing a multiplicity of closely spaced flames substantially in said chamber such that the flames substantially entirely fill the chamber with lambent flame, and means defining an exit flow path through said chamber-forming means for the removal of the products of combustion within the chamber; the wall surface of said chamber being of a material that radiates a major portion of its radiant heat at red and infra-red wavelengths, and said chamber also containing a multiplicity of members associated with respective flame producing means for radiating a substantial amount of energy in the visible spectrum above red.