Cooling zones, densities

In the absence of calcium hydroxide, quicklime only reacts with carbon dioxide at temperatures above about 300 °C and below 800 °C. This reaction can occur in the cooling zone of lime kilns under abnormal conditions. It results in carbonation of quicklime at the surface of the pores, and can give abnormally low reactivities for a given mean apparent density. 

The heart of a furnace black production plant is the furnace in which the carbon black is formed. The feedstock is injected, usually as an atomized spray, into a high-temperature and high-energy density zone, which is achieved by burning a fuel (natural gas or oil) with air. The oxygen, which is in excess with respect to the fuel, is not sufficient for the complete combustion of the feedstock, which therefore is, for the most part, pyrolyzed to form carbon black at temperatures of 1200-1900 °C. After the reaction mixture is quenched with water and further cooled in heat exchangers, the carbon black is collected from the tail gas by using a filter system. 

Fig. 2 Schematic diagram of the pulsed supersonic nozzle used to generate carbon cluster beams. The integrating cup can be removed at the indicated line. The vaporization laser beam (30-40 mJ at 532 nm in a 5-ns pulse) is focused through the nozzle, striking a graphite disk which is rotated slowly to produce a smooth vaporization surface. The pulsed nozzle passes high-density helium over this vaporization zone. This helium carrier gas provides the thermalizing collisions necessary to cool, react and cluster the species in the vaporized graphite plasma, and the wind necessary to carry the cluster products through the remainder of the nozzle. Free expansion of this cluster-laden gas at the end of the nozzle forms a supersonic beam which is probed 1.3 m downstream with a time-of-flight mass spectrometer.

The thermal stagnation zone can happen in the lower part of the droplet layer, over which t(z) has almost reached its possible limit, and so there is no cooling of droplets over the lower part of their trajectories. This means that the density of droplets is too high, and the efficiency of the cooling system can be improved by arranging the spraying nozzles to reach a lesser density of droplets. 

---