Car-bottom furnaces

Car-bottom furnaces differ from standard types in that the charge is placed upon movable cars for running into the furnace enclosure. The top oi the car is refractory-lined and forms the furnace hearth. The top only is exposed to heat, the lower metal structure being pro-tec ted by the hearth brick, sand, and water seals at the sides and ends and by the circulation of cooling air around the car structure below the hearth. For use where floor space is hmited elevator furnaces serve similar purposes. 

Side-fired box and car-bottom furnaces are ideally fired with main burners on 2.5-ft to 4.5-ft (0.6 m to 1.4 m) centers along the top on one side, and small pumping high-velocity burners on the opposite bottom side. (See fig. 6.1.) The main burners should have ATP technology so that the temperature can be controlled to a flat profile with the T-sensors located at the level of the top of the load through each of the two long sidewalls. 

A natural-gas-fired car-bottom furnace is to be built for heating 175 000 pounds of steel ingots from 50 F to 2150 F in 16 hr. Using formulas and data from this book and References 51 and 52 as well as from refractory suppliers data, select hearth, sidewall, and roof construction. Then calculate heat loss, heat storage, and coldface temperatures for the selected hearth, wall, and roof. 

Side view of a batch car-hearth furnace with top-firing, bottom-fiuing. 

Fig. 1.18 Car-hearth heat treat furnace with piers for better exposure of bottom side of loads. The spaces between the piers can be used for enhanced heating with small high-velocity burners. (See chap. 7.) Automatic furnace pressure control allows roof flues without nonuniformity problems and without high fuel cost.

Fig. 3.4. Car-hearth heat treat furnace with piers, ceramic fiber waiis, and high-veiocity burners top left and bottom right). Courtesy of Horsburgh and Scott Co.. Cieveiand, OH.

Fig. 6.1. Side-fired in-and-out furnace (with car-hearth), 18 wide x 12 deep x 8 high iD. Adjustabie fiame burners give uniform heating width-wise/depth-wise double-stacked piers help bottom uniformity. (See also figs. 3.26 and 6.23.)...

Finish sinter and coke are stored in the blast furnace trestle bins. These bins are loaded with bottom dump rail cars. From the trestle bins, the sinter and coke are transported by conveyor belt to the blast furnace charge bins. The coke (typically 8 to 10% of total charge) and sinter are discharged with vibratory feeders from the charge bins, and are weighed on scale belts. From the scale belts, the sinter and coke are transported by a series of conveyor belts to a... 

A measured mix of sinter and coke is delivered into a weighed transfer hopper from separate feed bins and the contents are dumped into the top of the furnace. Some furnaces can be fitted with fixed feed hoppers and others use rail-mounted bottom dump transfer cars. 

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