Cold air firing

Corresponding fuel savings compared to cold-air firing will vary approximately from 30 to 70 percent. 

The air/fuel ratio is not as critical as with recuperators and cold air firing, provided that all of the fuel is burned completely. An increase of 50% excess air at 2400 F (1316 C) furnace temperature with air preheated to 2000 F (1093 C) reduces the efficiency only 2%. 

Example (b) In a pit with bottom control of temperature opposite the burner wall, the top-to-bottom temperature difference will be 20°F (11°C) with cold-air firing, 40°F (22°C) with hot-air firing, and over 75°F (42°C) with oxy-fuel firing. 

Example 6.6 A pit fiirnace is being fired with natural gas and 10% excess air, and has a 2400 F (1589 C) flue gas exit temperature. The wall, hearth, and roof losses are calculated to be 1.55 kkBtu/hr. With cold air firing, there is a40°F (22°C) temperature difference from top to bottom of the ingots. Predict the corresponding temperature difference when using 1300 F (704 C) combustion air, and when using oxy-fuel firing. 

If cold air firing has a 40°F (22°C) temperature drop from top to bottom of the pit, the same pit with 1300 F combustion air would have a temperature drop of... 

Secondary smoke is produced mosdy by the condensation of water in humid or cold air. The presence of hydrogen chloride or hydrogen fluoride in the combustion products increases the extent and rate of condensation. Composition modifications to reduce primary smoke may reduce secondary smoke to some extent, but complete elimination is unlikely. The relatively small amount of smoke produced in gun firings by modem nitrocellulose propellants, although undesirable, is acceptable (102—109). 

In another building, gusting winds caused transient increases in pressure that tripped the ventilation fans. The problem was overcome by increasing the fan speeds. Unfortunately the increased flow of cold air through a doorway cooled a fire water main so much that it froze and cracked [21 ]. 

When thou takest any earthen, or glass vessel from the fire, expose it not to the cold aire too suddenly for fear it should break. 

FOR MORE THAN A THOUSAND YEARS PHILOSOPHERS INSISTED THAT AIL SUBSTANCES WERE MADE UP OF FOUR ELEMENTS FIRE THAT WAS DRY AND HOT, EARTH THAT WAS HOT AND MOIST, WATER THAT WAS MOIST AND COLD, AIR THAT WAS COLD AND DRY. WE KNOW BETTER NOWI... 

Just for practice, let us suppose we have a stack temperature of 600°F, ambient air is 100°F, the convective section has 10 percent 02, and the firebox has 6 percent 02 measured just below the shock tubes. What percentage of fuel fired (AF in our equation) is being wasted by cold air leaking into the convective section ... 

The first stage of form, Aristotle believed, was found in the four elements of Earth, Air, Fire, and Water. The elements, while distinguished from each other, are also related by four qualities. These qualities are dry, moist, hot, and cold. Each element possesses two qualities, of which one predominates, and each element is linked to two other elements by the quality... 

Like almost every Western scientist and philosopher up to the 17th century, alchemists unquestioningly accepted Aristotle s theory of the Universe. According to him, all material things in the world were composed of varying proportions of the four elements of Earth, Air, Fire, and Water. But substances could be altered into other substances by the appropriate application of one of the four qualities of wetness, dryness, cold, or heat. This idea of change was fundamental to Ae alchemist s belief that base metals could be transmuted into gold. 

One method consists in firing an inclined panel of coal 650 to 1,000 feet long. It is surrounded by fire-proof corridors to prevent fire from breaking into other parts of the mine. The coal is ignited by remote control and at first the fire is fanned by cold air. 

Aiistotie s theory rested upon the supposed existence of four elementary properties or qualities. These formed two pairs of opposites hot and cold, wet and dry. When combined pairwise, as represented in the appended diagram (Fig. i), they gave rise to the four fundamental simple bodies, or elements earth, air, fire and water. All kinds of matter were held to be composed of these four elements, assodated in different proportions. Further, according to Aristotle, die four elements were also incorporated with a prima materia this had no material existence until it became... 

A comparison of the combustion temperatures in flame- and in FLOX -mode should clearly show the reduction of the temperature peaks. Figure 23.13 shows, in the upper diagram, the temperature field of a 400 kW burner in a furnace at 1200°C fired with cold air in flame mode. In the second diagram, the same burner is operated with air at 600°C, but the fuel input is reduced to 245 kW to take into account the preheating and thereby keeping the net heat input constant. The temperature field of a 200 kW FLOX burner using preheated air at 950°C is represented in the bottom diagram. 

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