US3610594A

US3610594A - Oxygen deficient material reducing system and apparatus therefor

Info

Publication number: US3610594A
Application number: US32146A
Authority: US
Inventors: Robert M Williams
Original assignee: Williams Patent Crusher and Pulverizer Co Inc
Current assignee: Williams Patent Crusher and Pulverizer Co Inc
Priority date: 1970-04-27
Filing date: 1970-04-27
Publication date: 1971-10-05
Anticipated expiration: 1988-10-05

Abstract

A system for reducing raw materials in an oxygen deficient atmosphere to prevent fire and explosions and to maintain a humidity condition in the system to improve the transportation of the material from its zone of reduction to a discharge where the gaseous medium of low or deficient oxygen content is retained for recirculation. The system includes a primary circulation system for transporting the reduced medium and a secondary circulation system for obtaining a low or oxygen deficient gaseous atmosphere for starting up the primary system and for maintaining the oxygen deficiency and improved efficiency of operation of the primary system.

Description

United States Patent Inventor Robert M. Williams Ladue, Mo.

Appl. No. 32,146

Filed Apr. 27, I970 Patented Oct. 5, I971 Assignee Williams Patent Crusher It Pulverizer Co.,

Inc. Saint Louis, Mo.

OXYGEN DEFICIENT MATERIAL REDUCING SYSTEM AND APPARATUS THEREFOR 10 Claims, 2 Drawing Figs.

US. Cl 263/15, 34/72 Int. Cl B08 l5/00, F26b 21/06 Field of Search 263/l 5 R; 34/72 [56] llelerenecs Cited UNITED STATES PATENTS 3,477,650 1 M96) Williams 34/72 3,5 l4,279 5II970 Jensen et al. 263/l5 X Primary Examiner-John J. Camby Attorney-Gravely, Lieder 8L Woodrulf ABSTRACT: A system for reducing raw materials in an exygen deficient atmosphere to prevent fire and explosions and to maintain a humidity condition in the system to improve the transportation of the material from its zone of reduction to a discharge where the gaseous medium of low or deficient oxygen content is retained for recirculation. The system includes a primary circulation system for transporting the reduced medium and a secondary circulation system for obtaining a low or oxygen deficient gaseous atmosphere for starting up the primary system and for maintaining the oxygen deficiency and improved elficiency of operation of the primary system.

BRIEF DESCRIPTION OF THE INVENTION This invention relates to a system for reducing raw materials to a particulate condition in an oxygen deficient or inert atmosphere, and to apparatus for practicing the same.

The need for means to condition raw material for commercial or industrial uses is admitted, but a system for setting up operation of such means under conditions of safety to person nel and equipment has not been readily available to the industry until the advent of the improvements herein to be disclosed. The problems requiring attention are explosion within the operating system, spontaneous combustion within the material being reduced while such material is being reduced and after its discharge, and the processing of materials that would chemically deteriorate due to the presence of oxygen. It is also important to the efficient handling of reduced material to maintain the proper humidity or moisture conditions so the transportation system will not clog or prevent the free flow of the material.

The factors involved in obtaining a safe, efficient and effective system include control over the level of inertness of the internal gaseous medium to explosion and spontaneous combustion, the freedom from excessive moisture, leakage of external air into the system, and control over the application of heatito condition the gaseous medium for maximum ability to carry off moisture without reaching explosive or spontaneous combustion levels. The presently preferred form of the invention has as its important objectives the organization of operating apparatus in a novel, unique and improved system.

Briefly, the invention may be practiced by apparatus which embodies a material reducing unit connected into a primary inert gaseous medium transportation system energized by a blower and including primary means to separate the reduced medium from the flow of gaseous medium, and a secondary circulating system in which a portion of the gaseous medium of the primary system is constantly being conditioned as to humidity, temperature and oxygen deficient levels and then returned to the primary system at a pressure level to inhibit the leakage of ambient air into the primary or secondary systems.

In practice, the system contemplates in its preferred mode of operation at least two stages. A first stage involves utilizing portions of the primary and secondary systems for purging the apparatus of oxygen so that a desired oxygen deficient gaseous medium is established for transporting the material being reduced to its zone of discharge from the primary system as a final product. In the first stage the gaseous medium is burned to consume oxygen, dried and cooled to the desired operating level. In the second stage the primary system is coupled to the secondary system so that the two systems operate to maintain the desired conditions and meet the standard of safety.

BRIEF DESCRIPTION OF THE DRAWINGS A presently preferred embodiment of the invention is shown in the accompanying drawings, wherein:

FIG. IA is a generally schematic flow diagram showing the cooperation of components of apparatus and conduits making up the primary flow system in which the raw material is introduced, processed to a reduced condition and transported to inhibit explosion and spontaneous combustion; and

FIG. IB is a generally schematic flow diagram showing the cooperation of components of apparatus, conduits and controls making up the secondary flow system which is operatively related to the primary system of FIG. I in the manner indicated.

the drawings. The apparatus comprises a material reducing unit I having a suitable connected prime mover II to drive LII the material reducing rotor therein. The material to be reduced is deposited in hopper l2 and moves through chute 13 into the unit 10 through a suitable air lock inlet I4. The unit is connected into a material moving blower responsive system which includes a primary blower I5 having its outlet conduit 16 connected to the unit l0, and its suction side connected by conduit 17 to the outlet of a cyclone separator 18.

The separator 18 receives the reduced material through a conduit 19 leading from the reducing unit 10, thus completing a circulating path in which reduced material is transported to the separator 18 for discharge through the outlet valve 20 and the transporting gaseous medium is returned by way of conduit l7, blower l5 and conduit I6.

As the important object of this improvement is to operate the apparatus under conditions that will prevent fire and explosions, or deterioration of the product, the gaseous medium moved by the primary blower 15 is conditioned to be low or deficient to oxygen and at a temperature below the flash point of the material being reduced and discharged as a final product at valve 20. The objective is accomplished in a novel manner by establishing a source of desired low or oxygen dcf|- cient gaseous medium, such as prepared air in which the oxygen has been substantially consumed so the level of retained oxygen is of the order of about 5 percent. and the temperature is below the temperature which would produce spontaneous combustion of the reduced material as discharged into a suitable bin. It is further important to regulate the moisture level in the system so that the normal moisture brought into the system by the raw material at valved inlet [4 is controlled to prevent impairing the elficient flow thereof to and through the separator 18. The objectives are attained with the components of apparatus as follows.

The outlet conduit I6 from blower I5 is provided with a normally open control valve 2| downstream from the connection of a branch conduit 22. The conduit 22 connects to a secondary separator 23 where the fines remaining in the gaseous medium are separated and discharged at outlet valve 24. Conduit 25 leads from the separator 23 to a secondary blower 26 which establishes flow in conduit 22. The blower 26 has an outlet conduit 27 which may exhaust to atmosphere at normally closed pressure responsive valve 28. However, the conduit 27 connects to two

bypass conduits

29 and 29A. Bypass conduit 29 equipped with a manual control valve 30 connects into a furnace 3| where the gaseous medium is burned in the combustion chamber and mixes with the hot exhaust from the furnace stack 32 and into conduit 32A. Conduit 32A, provided with a normally open manual control vulvc 33 leads back to the reducing unit 10 to provide the necessary oxygen deficient hot gaseous medium needed to transport and dry the reduced material through conduit I) to the primary separator 18.

The second bypass conduit 29A connects between the exhaust conduit 27 and a dehumidifier unit 34 where moisture is extracted and drained oft" at pipe 35. The dehumidified gaseous medium is cooled by unit 34 and exhaust through conduit 36 which connects into the furnace 3] through conduit 36A adjacent the first bypass conduit 29 between the furnace 3] and valve 30. A manual control valve 37 is inserted in conduit 36A just beyond the connection of a branch conduit 38, and a normally closed manual control valve 39 is inserted in this branch conduit 38 adjacent the junction with conduit 36A. Branch conduit 38 connects to the inlet ofa circulating blowcr 40, and the outlet conduit 41 from the blower 40 is connected into the furnace outlet conduit 32A downstream of the manual control valve 33.

An auxiliary or starting up conduit 42 is provided between the conduit 25 for secondary blower 26 and the furnace outlet stack 32. This conduit 42 is provided with a water spray discharge unit 43 which is necessary to rapidly cool the hot furnace gas discharge, which gases would he too hot for practical purposes. A normally closed manual control valve 44 is inserted in conduit 42 ahead ol'thc flow to the water spray unit 43. A suitable water supply 43A is connected to unit 43.

As is shown in the drawing, the furnace 31 is provided with a burner unit 45 supplied with primary combustion air by blower 46 and conduit 46A. The fuel for the burner unit 45 is supplied by a suitable pipe 47 from a source (not shown) remote from the furnace 31.

The control means for the apparatus described above is best seen in H6. 2 and includes components as follows. The combustion air supply conduit 46A from the furnace blower 46 is provided with a motor operated valve 48 which is intended to regulate the combustion air supply in a predetermined manner to be described. The fuel supply pipe 47 is provided with a diaphragm type control valve 49 having the control chamber side connected by a pipe 50 to the burner air supply chamber 51. The control air pressure in pipe 50 for the fuel control valve 49 is regulated by the valve 48 in air conduit 46A and is subject to modulation through a branch pipe 52 which leads to a motor-operated valve 53 which regulates the fuel supply valve setting in response to an oxygen analyzer device 54 located in conduit 25. The device 54 is a commercial unit which may be (for example) either a Model 715 of Beckman Instrument Co. or Model 802 of Mine Safety Applicances Co. In order to set a minimum fuel supply the flow out of pipe 50 through branch pipe 52 is limited by a fixed orifice 55 so that a desired supply of fuel in supply pipe 47 is maintained. The motor operated valve 48 is connected to a temperature responsive unit 56 having its bulb in the reducing means It) to respond to temperature at that zone. The valve 53, on the other hand, is connected to respond to the oxygen analyzer 54. Suitable connections 57 and 58 are provided for the respective control means.

OPERATION OF THE APPARATUS The apparatus described in connection with FIGS. 1 and 2 is operated in two stages to insure safe functioning when the raw material is first admitted to the reducing unit 10. The first stage purges the unit and conduits l6, 17, 19 and primary separator 18 of oxygen before the primary blower is activated with reducing unit 10. Once the conduit system has been purged the second stage is initiated by starting the unit 10 and blower l5 and raw material is admitted at the inlet valve [4.

in the first stage of

operation circulating blowers

40 and 26 and energized, primary blower I5 is off, the pressure respon' sive valve 28 is closed against a pressure setting below that of the pressure of primary blower 46,

bypass valves

30 and 37 are partially closed, valved 39 is opened to allow part of the circulation of gas to enter the main system, valve It is closed, valve 33 is closed, valve 44 is opened, and the spray unit 43 is supplied with water. This setting sets up a circulating path from the blower 40 through the conduit 32A to unit 10, conduits l9, l7 and 22, through the conduit 25, blower 26 which is operating and conducts 27, 29A, the dehumidifier 34 and through the bypass conduit 38 back to the circulating blower 40. The furnace 3! is fired up at this stage by admitting fuel (gas in this case) at pipe 47 upon operating the furnace prima ry air blower 46. The blower 46 creates pressure in the chamber 51 which pressurizes the pipe 50 to open the supply valve 49.

The primary blower 15 is not operated and valve 21 is closed at the first stage. Since the blower 15 is at ambient temperature the lower temperature of the gaseous medium would exceed the blower motor horse power limits and drag oversized material out of the reducing unit 10 to create a fire hazard and contaminate the final product. Thus, not running blower l5 and closing valve 21 will allow the desired circulation in the system at a lesser velocity to avoid the undesired cffccts mentioned. Since damper 37 is only partially closed, gasses also are circulated through the heater 3| by conduit means 36A, and as will be explained later, this gas will become products of combustion, thereby reducing the oxygen content and heating the gas, which is later cooled with water at spray unit 43. The system is thereby made oxygen deficient in a short time.

At the start up first stage the ratio of fuel to air at the burner 45 is two to one and the hot gases of combustion will pass through the stack 32, conduit 42 and spray unit 43 to the conduit 25 to join the flow in conduit 25 caused by the circulating blower 40 and blower 26. The oxygen analyzer 54 will monitor the oxygen in the gaseous medium flowing in conduit 25 and as the system oxygen is decreased it will begin to modulate the motor valve 53 to open and reduce the air pressure in the control pipe 50 to shut down on the fuel supply. This is necessary to prevent unburned raw fuel to be discharged through the furnace stack 32. The temperature-responsive unit 56 will modulate the motor valve 48 in the furnace lower conduit 46A so that the air pressure to the burner is controlled in relation to temperature, and the gas to air ratio is gradually reduced to a one to one rate of fuel supply. The orifice 55 in pipe 52 will limit the reduction in fuel supply at valve 49 to maintain the one to one ratio. It is best to locate the oxygen analyzer 54 at the exhaust conduit 25 from the system of conduits l9 and 17 so that an accurate reading of the oxygen level may be obtained, although other locations may be selected as desired.

During the first stage operation. a flow through the furnace 31 is created and the hot products of combustion are cooled in the water spray unit 43. The spray is converted to steam and is carried over to dehumidifier 34 where it is extracted and may be reused in unit 43. The cooled dry gaseous medium is pumped by blower 40 into the system downstream of the closed valve 33. This gaseous medium is gradually depleted of its oxygen as a portion of the gas recycles through the furnace and is utilized to burn the gas supplied at a two to one ratio, and the decrease is monitored by the unit 54 at conduit 25. The oxygen in the entire system will rapidly decrease as the furnace at the start operates on a fuel to air ratio of two to one. Once the system oxygen content is lowered, the reduction of oxygen in the system then requires less fuel and, to avoid release of unburned fuel, the monitoring of the control valve 53 will gradually reduce the quantity of fuel to the lower limit to establish a one to one ratio of fuel to air.

When the system has been heated and purged and the gaseous medium is desirably oxygen deficient and the second stage is ready to begin in which the circulating blower 40 is shut down, the valves Zl and 33 opened, valve 44 closed, spray unit 43 shut off, valve 39 closed, and

valves

30 and 37 set at desired open settings so that the dehumidifier 34 may continue to operate to extract moisture brought into the system by the raw material. The primary blower I5 is operated at this time, and the oxygen analyzer 54 and temperature unit 56 will continue to monitor the oxygen level and temperature in the system and adjust the fuel to air ratio to maintain the desired oxygen deficient level of the system. At this time exhaust valve 28 in conduit 27 will function to balance the input of furnace primary air and fuel and maintain a positive system pressure so leakage is always out to ambient atmosphere.

What is claimed is:

1. In a system for reducing raw material to a final product and for transporting the reduced material to a final product outlet defined by separator means by a flow of oxygen deficient gaseous medium: the improvement ofa primary flow circuit connecting the raw material reducing means to said separator means for separating the final product from the gaseous medium and returning the gaseous medium for recirculation; a secondary flow circuit connected into said primary flow circuit for extracting portions of the gaseous medium from the primary flow circuit, said secondary flow circuit in cluding burner means to condition the extracted gaseous medium by burning up oxygen therein and returning the oxygen deficient gaseous medium to the primary flow circuit; and auxiliary means to reduce the oxygen in the primary flow circuit for starting said system, said auxiliary means being conncctcd into at least a portion of said secondary flow circuit to reduce the oxygen level of the gaseous medium in said primary and secondary circuits to a predetermined oxygen deficient level and at an accelerated rate.

2. The improvement set forth in claim I wherein said auxiliary means to reduce the oxygen in the primary flow circuit includes a flow connection between said secondary flow circuit and said oxygen burner such that part of the gaseous medium in said secondary flow circuit is substantially oxygen depleted.

3. The improvement set forth in claim 1 wherein said auxiliary means includes a connection in parallel with said oxygen burner to pass oxygen deficient gaseous medium into said primary fiow circuit.

4. The improvement set forth in claim I wherein said aux iliary means includes control means operable to exclude the latter from connection to said primary and secondary flow circuits.

S. In apparatus for reducing raw material in a gaseous medium conditioned to inhibit explosion and fire, the improved combination of raw material reducing means, a separator, blower means, first conduit system connecting said reducing means, separator and blower in series to move said reduced material from said reducing means to said separator to separate said gaseous medium for return to said reducing means; burner means to supply hot oxygen deficient gaseous medium into said first conduit system adjacent said reducing means; second conduit system connected into said first conduit system downstream of said blower and to said burner means to extract a portion of the gaseous medium from said first conduit system, third conduit system connected into said first and second conduit systems in bypass of said burner means, fourth conduit system connected across said second conduit system from downstream of said burner means, valve means in said conduit systems controllable to recirculate portions of the gaseous medium through said burner means and back to said second conduit system and to return other por tions of the gaseous medium to said first conduit system, means in said fourth conduit system to humidify and cool and the hot gaseous medium flow therein, and means in said second conduit system upstream of said burner means to dehumidify the gaseous flow.

6. The improved combination of claim 5 and including fuel supply means connected to said burner mans, a source of combustion air supply connected to said burner means, and control means in the apparatus to regulate the amount of fuel and combustion air supplied to said burner means at a variable ratio that consumes oxygen in said first and second conduit systems.

7. The improved combination of claim 6 wherein said control means includes oxygen analyzer and temperature responsive units, said oxygen analyzer unit being disposed in one of said conduit systems, and said temperature responsive unit being located to sense temperature at said raw material reducing means.

8. ln apparatus to reduce raw material to a final product in an oxygen deficient gaseous atmosphere; raw material reducing means, a separator having a final product discharge from the gaseous atmosphere, a gaseous atmosphere primary blower means, and conduits connected between said reducing means, separator and blower to define a primary gaseous atmosphere circulating system; burner means connected into said primary circulating system to supply dried oxygen deficient hot gases thereto; a secondary blower connected into said primary circulating system conduit downstream from said primary blower means and into said burner means in a secondary circulating system to extract portions of the gaseous atmosphere in said primary circulating system and feed the gaseous atmosphere into said burner means for consumption of oxygen therein, dehumidifier means connected between said secondary blower means and said burner means to extract moisture from at least a portion of the gaseous medium and control the temperature level of the hot gaseous atmosphere supplied by said burner means; means connected into a portion at least of said secondary circulating system and defining an auxiliary flow circuit in said apparatus to initially condition the gaseous atmosphere for oxygen deficient levels, said last means including a circulating blower connected into said secondar circulating system across said burner means a cooling hum| ifier connected between said burner and said secondary circulating system in advance of said burner; and control means in said apparatus selectively operable to render said auxiliary flow circuit operable and inoperable.

9. ln apparatus for reducing raw material in an oxygen deficient gaseous medium to a final product, the apparatus having raw material reducing means, a separator, a blower, conduit means connected to and providing a circulation system for the gaseous medium between said reducing means, said separator and said blower for transporting reduced material to said separator for separation from the gaseous medium, a furnace providing a source of heated oxygen deficient gaseous medium connected into said conduit system, and a recirculation conduit system connected between said conduit means and said furnace to extract portions of the circulating gaseous medium from said conduit means and return it to said furnace, the improvement of: means to obtain an initial oxygen defi cient gaseous medium in said conduit means comprising:

l. a first connection between said furnace and said recirculation conduit system,

2. water spray means in said first connection to cool the hot gaseous medium from said furnace,

3, dehumidifier means upstream of said furnace to extract the water therefrom and return to said furnace dried hot gaseous medium and gaseous medium from said circulation system, and

4. means to conduct a portion of the dried oxygen deficient gaseous medium of said recirculation conduit system directly into said circulation system ahead of said reducing means.

10. Apparatus for reducing raw material in an oxygen deficient atmosphere comprising: a first system of a material reducer, a blower and a separator connected by conduits to have the blower force the atmosphere in the conduits through the reducer to the separator; a furnace and means supplying to the furnace fuel and combustion air, and conduit means lead ing from said furnace into said first system to supply oxygen deficient hot products of combustion thereto; a second system including conduits connected from said first system to said furnace to move a portion of the atmosphere out of said first system and feed it into said furnace to consume oxygen therein before returning it to said first system; and means to control the fuel and combustion air supply to said furnace including oxygen analyzing means in said second system connected to the furnace fuel supply, and temperature responsive means in said first system connected to the combustion air supply, said control means varying the ratio of fuel and combustion air to said furnace to consume oxygen and prevent unburned fuel carryover from said furnace to said receiver.

Claims

2. The improvement set forth in claim 1 wherein said auxiliary means to reduce the oxygen in the primary flow circuit includes a flow connection between said secondary flow circuit and said oxygen burner such that part of the gaseous medium in said secondary flow circuit is substantially oxygen depleted.
2. water spray means in said first connection to cool the hot gaseous medium from said furnace,
3. dehumidifier means upstream of said furnace to extract the water therefrom and return to said furnace dried hot gaseous medium and gaseous medium from said circulation system, and
3. The improvement set forth in claim 1 wherein said auxiliary means includes a connection in parallel with said oxygen burner to pass oxygen deficient gaseous medium into said primary flow circuit.
4. The improvement set forth in claim 1 wherein said auxiliary means includes control means operable to exclude the latter from connection to said primary and secondary flow circuits.
4. means to conduct a portion of the dried oxygen deficient gaseous medium of said recirculation conduit system directly into said circulation system ahead of said reducing means.
5. In apparatus for reducing raw material in a gaseous medium conditioned to inhibit explosion and fire, the improved combination of raw material reducing means, a separator, blower means, first conduit system connecting said reducing means, separator and blower in series to move said reduced material from said reducing means to said separator to separate said gaseous medium for return to said reducing means; burner means to supply hot oxygen deficient gaseous medium into said first conduit system adjacent said reducing means; second conduit system connected into said first conduit system downstream of said blower and to said burner means to extract a portion of the gaseous medium from said first conduit system, third conduit system connected into said first and second conduit systems in bypass of said burner means, fourth conduit system connected across said second conduit system from downstream of said burner means, valve means in said conduit systems controllable to recirculate portions of the gaseous medium through said burner means and back to said second conduit system and to return other portions of the gaseous medium to said first conduit system, means in said fourth conduit system to humidify and cool and the hot gaseous medium flow therein, and means in said second conduit system upstream of said burner means to dehumidify the gaseous flow.
6. The improved combination of claim 5 and including fuel supply means connected to said burner mans, a source of combustion air supply connected to said burner means, and control means in the apparatus to regulate the amount of fuel and combustion aiR supplied to said burner means at a variable ratio that consumes oxygen in said first and second conduit systems.
7. The improved combination of claim 6 wherein said control means includes oxygen analyzer and temperature responsive units, said oxygen analyzer unit being disposed in one of said conduit systems, and said temperature responsive unit being located to sense temperature at said raw material reducing means.
8. In apparatus to reduce raw material to a final product in an oxygen deficient gaseous atmosphere; raw material reducing means, a separator having a final product discharge from the gaseous atmosphere, a gaseous atmosphere primary blower means, and conduits connected between said reducing means, separator and blower to define a primary gaseous atmosphere circulating system; burner means connected into said primary circulating system to supply dried oxygen deficient hot gases thereto; a secondary blower connected into said primary circulating system conduit downstream from said primary blower means and into said burner means in a secondary circulating system to extract portions of the gaseous atmosphere in said primary circulating system and feed the gaseous atmosphere into said burner means for consumption of oxygen therein, dehumidifier means connected between said secondary blower means and said burner means to extract moisture from at least a portion of the gaseous medium and control the temperature level of the hot gaseous atmosphere supplied by said burner means; means connected into a portion at least of said secondary circulating system and defining an auxiliary flow circuit in said apparatus to initially condition the gaseous atmosphere for oxygen deficient levels, said last means including a circulating blower connected into said secondary circulating system across said burner means, a cooling humidifier connected between said burner and said secondary circulating system in advance of said burner; and control means in said apparatus selectively operable to render said auxiliary flow circuit operable and inoperable.
9. In apparatus for reducing raw material in an oxygen deficient gaseous medium to a final product, the apparatus having raw material reducing means, a separator, a blower, conduit means connected to and providing a circulation system for the gaseous medium between said reducing means, said separator and said blower for transporting reduced material to said separator for separation from the gaseous medium, a furnace providing a source of heated oxygen deficient gaseous medium connected into said conduit system, and a recirculation conduit system connected between said conduit means and said furnace to extract portions of the circulating gaseous medium from said conduit means and return it to said furnace, the improvement of: means to obtain an initial oxygen deficient gaseous medium in said conduit means comprising:
10. Apparatus for reducing raw material in an oxygen deficient atmosphere comprising: a first system of a material reducer, a blower and a separator connected by conduits to have the blower force the atmosphere in the conduits through the reducer to the separator; a furnace and means supplying to the furnace fuel and combustion air, and conduit means leading from said furnace into said first system to supply oxygen deficient hot products of combustion thereto; a second system including conduits connected from said first system to said furnace to move a portion of the atmosphere out of said first system and feed it into said furnace to consume oxygen therein before returning it to said first system; and means to control the fuel and combustion air supply to said furnace including oxygen analyzing means in said second system connected to the furnace fuel supply, and temperature responsive means in said first system connected to the combustion air supply, said control means varying the ratio of fuel and combustion air to said furnace to consume oxygen and prevent unburned fuel carryover from said furnace to said receiver.