PH26273A - A method of preheating combustion air integrated in an improved combustion system - Google Patents

Description

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BACKGROUND OF THE INVENTION “4 F. | /

Field of the Invention oo

This invention relates in general to a heat transfer system but, more particularly to a method of preheating combustion air, through the heat of the burner flame or furnace heat transmitted through a heat exchanger means in an integrated combustion system. ‘ Description of the Prior Art

Because the waste flue gases of many industrial combustion operations contain considerable heat, it is logical to conserve fuel by recovering some of that heat, either in the process itself or in the waste product of combustion. Methods of recycling heat from combustion products can be grouped in three broad classes: 1. Pre-heating load: 2. Generating steam, hot water, or make up water or make up air: 3.

Preheating combustion air. Preheating combustion air is by far the most popular heat recovery system, probably because it requires the least rearrangement of the existing furnace and because it utilizes the rrecovered heat directly in the process where it vas released. This system reduces the flue gas loss from a furhace by transferring the heat from the hot flue gases to the cold combustion air. This results in a smaller portion of the heating value of the fuel being used in heating the air within the furnace and a larger portion of the air or heat in the fuel being available for useful heating. Because this increase in useful heat is achieved by using heat that would otherwise be thrown away in the unused hot flue gases, this process results in a gain in thermal efficiency.

The gain in thermal efficiency from use of preheated air could mean less fuel input required for the same load output or more load output obtainable from the same fuel input. By preheating combustion air between 600 to 2,200°F, savings in fuel with 10% excess air can be = .

achieved between 12% to as high as 80%. Preheating the air broadens the flammability limits, increase flame velocity, and raises flame temperature without necessarily showing marked changes in flame characteristics. The most notable difference is reduced fuel consumption and clean flue gases.

However, while the above features appear to be desirable, it cannot be generally achieved.

Depending upon the materials of construction, burners intended for use with cold air can usually be used with air preheated to 500 or 600°F , without damage to the burner accessories from the higher temperature levels. A few have been used with 800°F main air, often contrary to the recommendations of the burner manufacturer and sometimes with expensive added cooling arrangements.

With high temperature air passing through a burner, it needs a) an insulating refractory lining to protect the shell material from excess temperature and to reduce heat loss; b) special alloy or refractory materials for the internal components to repvent scaling and distortion that could affect performance and capacity: c) insulation protection for auxilliaries such as pilots; flame metering devices, observation ports, and valves; d) extra calculations in selecting the proper burner size because of the different air density. This latter factor can be quite complex when all of its ramifications throughout a complete system is considered.

Additionally, most fuels from petroleum based heavy oils to coal, (except gaseous fuels) have varying sizes and combustion characteristics. The lighter fractions for instance, will burn faster and the heavier fuel fractions will take longer to burn. Certainly for this reason, the fuel combustion particularly in factories having : purner facilities is incomplete and emits pollutants into the atmosphere due to the unburned hydrocarbons causing hazards to health

~~ 9Rowg and safety. The burner users also lose money due to the unburned and unused fuel which otherwise could also further improve productivity.

SUMMARY OF THE INVENTION

The present invention is therefore concerned with the ideal solution that would involve a series of fuel combustions adequate to burn cell of the hydrocarbons covering a wider and longer period of combustion.

It is therefore not only for environmental consideration but for practical business purposes as well that, a system be developed to preheat combustion air and utilize a system of successive combustion.

Hence, the primary object of the present invention is to provide a simpler method of recovering independent of and away from the burner defined by a tubular body having forced air inlet post and a heated air outlet that is so simple in construction that solves the disadvantages of the prior art.

Furthermore, the present invention does not damage any portion of the burner assembly of its accessories since it is past and away from the burner.

Moreover, the present invention can achieve much higher preheat air temperatures since it absorbs the heat of the flame and almost instantaneously convey the heated air to the successive open flames with easily achieving air temperatures of slightly below average flame temperatures.

Accordingly, it can mix heated air with the usually unburned and heavy fractions of the fuel located at the rich fuel zone at the center : of the flame more evenly and produce better fuel combustion zones.

This can be achieved by setting the main burner flame to a rich mixture.

Still the present invention has the flame type and quality that can also be substantially controlled by the location and size of the i»

device, the air pressure released, air velocity and air volume passing thru the device which can be controlled by manual or electronic means thru the use of air valves commercially available. Such controls can also be coupled to new burner systems.

And yet the device is easy to install or dismantle, service, or completely replaces even on relatively frequent intervals due to high rates of fuel cost, maintenance cost savings, and even the ease and quick replacement of the entire unit, should that be so necessary.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE 1 is a section view of the heat recovery device which covers the major components of the system;

FIGURE 2 is the sectional view of the boiler furnace showing the successive combustion system;

Referring now to the drawings in detail wherein like numerals designate same parts throughout, there is shown in Figs. 1 and 2 a heat recovery system in accordance with the present invention generally designated as 10 comprising a heat induction tubing 11 disposed within a heated air transmission tubing 12 and transversely protruding therefrom, an air blower 13 juxtaposely disposed to said heated air transmission tubing 12, and an air control valve 13 regulating the flow

Qu of forced aif Econ said blower 13.

As shown in Fig. 2 is a sectional view of a boiler furnace showing the heat recovery system 10 installed. Such a boiler furnace includes a boiler 14, a furnace 15 and a conventional burner 16. A plurality of said air transmission tubing 12 are positioned inside the combustion chamber and exposed to the radiated and convection heat of the flame F from said burner 16. Said tubing 12 is made out of metal and may be optionally coated with a thin layer of heat resistant castables. . The induction tubing 11 is located inside the combustion chamber

. ¢ 2 6 27 3 : Hi but a short distance away from the firewall 17 where the burner 16 is ’ positioned. Said induction tubing 11 is attached to the air transmission tubing 12 and is so positioned that the other end of said induction tubing 11 is facing the opposite direction of the forced air from the blower 13.

The method of preheating the combustion air integrated in this heat recovery system 10 commences by allowing the forced air A (as shown in dotted lines) as provided by the blower 13 to pass through said heated air transmission tubing 12. The amount of such air A is regulated by said air control valve 137 disposed within said transmission tubing 12. As the — fired at the furnace 15, a small portion of the furnace/kiln heated flue gas G is sucked by the protruding portion 16” of said induction tubing 11. The air A passing thru the induction 11 causes a sucking action involving the venturi effect and draws the hot flue gas from the combustion chamber which the heated flue gas mixes with air A from the blower 13 and the diluted air

D becomes heated. And since the air tubes 12 are positioned inside the combustion chamber and exposed to the radiated and convection heat of the flame from the burner 16, it transmits the heat to the air inside the transmission tubing 12 which further raised the already flue gas diluted air d to further enhance the heat of the combustion air.

The heated air A from the air tubes 12 are then spacedly infused into the path of the burner flame to achieve a mere efficient and controlled combustion. The conventional burner 16 is then adjusted to burn a rich mixture M either reducing the primary air input to the normal amount of fuel being fed into the burner or increasing the fuel feeding means without increasing the primary air.

The resulting rich mixture M will produce a long, lazy and dull redish flame which initially has a poor combustibility, burning mostly the light fractions of the fuel. The heavier fractions of the fuel fre

DER) remain partially unburned. 2 0 2 ( 9)

The size of the multiple air and induction tubes and their corresponding air valves are fabricated and installed in accordance with the type of application, capacity of burner, dimensions of the combustion chamber, the amount of heat and its desired manner of heat distribution within the combustion chamber and the rate of infusion of free flowing air into the flame path from the burner 16 either thru single or multiple, tangentially directed air exit means, of the directed orifice sizes, and at such heated air exit points facing the flame path to facilitate the intimate mixture of the heated air into the rich flame. The multiple and spacedly infused heated air in various points in the flame path, can vastly improve the subsequent and succesive heat relase of the initially rich burner flame by providing a collective and controlled combustion that can achieve very high efficiencies.

The ideal flame quality can be achieved the concerted and integrated adjustments of said air valves 12, with the burner fuel feed rate of the conventional burner, the primary air adjustments, and the synchronization thereof of all the stated instruments.

The flame quality can be further monitored by the use of optical pyrometers 18 inserted thru the conventional furnace peep holes, or monitoring the temperature of the exit flue gas and making necessary changes as described above to achieve ideal adjustments. For instance. an ideal adjustment would involve the lowest exit flue gas heat, and coupled with a low percentage of excess air, and suitable operation and production outputs.

However, flame qualities, have to be adjusted to the use and } application. Various flame types may have to be produced in accordance with the subject application, such as the oxidizing and reduction process and other tempering means.

Claims (1)

1. : : Ce , t TT Cram 0 6 27 3 A method of preheating combustion air in a burner furnace for improving the combustion system comprising the steps of | : : heating the burner furnace by burner means,

   conveying some amount of the hot flue gases to conduits provided within the furnace at a distance from the burner means,

   directing the conveyed flue gases to air tubes provided within the inner surface of the furnace, introducing air to the air tubes, allowing the flue gases to mix with the air within the air tubes producing preheated combustion air, and infusing the preheated combustion air to the furnace on the path of the burner means producing an enriched air-fuel mixture increasing the combustion efficiency of ’ the burner furnace. fw ; Inventor