This invention relates to a combustion system and method and, more particularly, to a combustion system and method utilizing heated air from an enclosure which is to be heated to form a combustible mixture for heating the enclosure.
Both liquid and gaseous fuel systems are widely used in industry for the heating of processing chambers, such as drying and curing ovens. These systems generally fall into one of two broad categories. One category includes the nozzle mixing systems in which the fuel is introduced through the burner tip where it is then mixed at the burner with air supplied from a separate source, such as a blower, to form a combustible mixture which ignites at the burner. The second category is the premix type of system in which a combustible mixture of air or other oxidizing gas is mixed with the fuel before reaching the burner and this mixture is pressurized and discharged from the burner where it ignites. Burners such as infrared burners are within the last category, as is the present invention.
Several premix systems have been employed in the past which utilize liquid fuels, such as No. 1 and No. 2 fuel oils. One such system includes an oil superheating device which includes a tank having liquid fuel oil therein. An auxiliary burner is located in the tank to heat the oil and form oil vapors. The vapors are drawn from the tank by a Venturi or other vacuum mixing device and cold air, at ambient room temperature, is blown through the Venturi where the vaporized oil and air are mixed to form the combustible mixture. This mixture is then conducted to the burners where it is burned.
That system suffers several disadvantages. One disadvantage is that the room temperature air in the combustible mixture consumes sensible heat upon ignition of the mixture, thus resulting in low efficiency and economy. Another disadvantage is that the system is cumbersome and requires the provision of substantial quantities of auxiliary equipment which is both expensive and space consuming. Another significant disadvantage is that of safety, since the auxiliary burners which are employed to heat the oil to vaporize it always present the possibility of explosion of the vapors. In addition, since the vapors are mixed with air which is only at ambient temperature, condensation of the oil may occur in the piping and at the burners which produces soot. Such soot requires frequent cleaning, reduces efficiency and may damage the articles being treated in the oven. Moreover, the condensation of the oil prevents the use of infrared burners which are only operable with gaseous fuels and frequently necessitates a change of burners where both liquid and gaseous fuels must be used on different occasions.
Another system employs an air heating chamber which also contains an auxiliary burner. Air at ambient room temperature is injected under pressure into the air heating chamber where its temperature is elevated by the auxiliary burner to a temperature substantially in excess of the dew point of the liquid fuel. This heated air is then brought into contact with atomized liquid fuel to vaporize the fuel and form a combustible mixture which is burned at the burners.
Although the latter system, to a major extent, solves the safety and condensation and sooting problems encountered in the first described system, it is essentially still as uneconomical, cumbersome and space consuming as the first described system. In addition, special burners are needed in the air heating chamber because of the elevated pressures in that chamber.
Systems have also been employed in the past in an attempt to improve economy. These systems, by and large, have utilized economizers or heat exchangers for transferring some of the sensible heat from the flue gases escaping from the oven or enclosure to the air which forms the combustible mixture. Although such economizers or heat exchangers do improve the economy of the system, they are cumbersome, expensive, and space consuming.
The present invention overcomes each of the above mentioned disadvantages. The present invention is economical, not only from the standpoint of improved heat-to-fuel ratios, but also from the standpoint of reduced initial capital expenditure, reduction of auxiliary equipment and reduction in space comsumption. The present invention may be readily adapted to the dual use of alternate fuels of different kinds and phase states in the event that one of the fuels becomes unavailable and the need for shutdown or changing burners, such as infrared burners, which are otherwise not compatible with both gas and liquid fuels is avoided. The combustion system and method of the present invention are safe and minimize explosion hazard. Specially designed auxiliary burners need not be employed in the present invention, since the auxiliary burners need not discharge against a back-pressure. Finally, the present invention may be easily retrofited on existing installations.
In one principal aspect of the present invention, a combustion system which is adapted to heat an enclosure includes combustion burner means for supplying heat to the enclosure, conduit means connected to the burner means for supplying a combustible mixture of an oxidizing gas and a fuel to the burner means, injection means for discharging a finely atomized liquid fuel to the conduit means, second conduit means between the enclosure and the first conduit means for supplying heated oxidizing gas from the enclosure to the first conduit means adjacent the injection means, and control means for controlling the temperature and quantity of the oxidizing gas supplied from the enclosure such that the oxidizing gas vaporizes the liquid fuel atomized by the injection means and forms a combustible mixture.
In another principal aspect of the present invention, a method of heating an enclosure includes the steps of elevating the temperature of the enclosure, forming an atomized liquid fuel, removing a portion of an oxidizing gas from the heated enclosure, contacting the atomized liquid fuel with the heated oxidizing gas, controlling the quantity and temperature of the gas removed from the enclosure so as to form a combustible mixture with the fuel and vaporize the atomized liquid, and burning the mixture to heat the enclosure.
These and other objects, features and advantages of the present invention will be more clearly understood through a consideration of the following detailed description.