Wet kilns

Improvement of the energy efficiency in the pyroprocessing is reached by increasing the fuel efficiency of the kiln for example by replacing the wet kilns with preheater and precalciner systems, resulting in significant reduction of the CO2 emissions. 

By improving the heat recovery between the kiln flue gas and raw meal, the heat consumption was reduced by 30% with gas exit temperatures of 350°C and 400°C. With the reduction of the thermal consumption, the maximum production limit increased by 35-40% with respect to the long wet kiln. Looking to the process inside the kiln starting from the feed end, the various zones are as follows ... 

Borgholm, H E. A new heat recovery and desulphurization plant for4 wet kilns in Aalborg. 

These are shorter than wet kilns with lengths on the order of 90-120 m (about 300-400 ft). For long dry kilns, as with wet kilns, the drying, preheating, and calcination all occur in the one single vessel (Figure 1.6). 

Fuel Wet Kiln Long Diy Kiln I reheater Precalciner... 

The ABS polymer is recovered through coagulation of the ABS latex. Coagulation is usually achieved by the addition of an agent to the latex which destabilizes the emulsion. The resulting slurry can then be filtered or centrifuged to recover the ABS resin. The wet resin is dried to a low moisture content. A variety of dryers can be used for ABS, including tray, fluid bed, and rotary kiln type dryers. 

The time constants characterizing heat transfer in convection or radiation dominated rotary kilns are readily developed using less general heat-transfer models than that presented herein. These time constants define simple scaling laws which can be used to estimate the effects of fill fraction, kiln diameter, moisture, and rotation rate on the temperatures of the soHds. Criteria can also be estabHshed for estimating the relative importance of radiation and convection. In the following analysis, the kiln wall temperature, and the kiln gas temperature, T, are considered constant. Separate analyses are conducted for dry and wet conditions. 

Rotary kilns and, to a lesser extent, Fluo-SoHds kilns are used to calcine a wet precipitated calcium carbonate filter cake in the kraft or sulfate paper-pulp process (15). Lime is regenerated for use as a causticization reagent in recovering caustic soda for pulp digestion. Losses in lime recovery are replaced by purchased lime (see Paper Pulp). 

Cordierite [12182-53-5] Mg Al Si O g, is a ceramic made from talc (25%), kaolin (65%), and Al O (10%). It has the lowest thermal expansion coefficient of any commercial ceramic and thus tremendous thermal shock resistance. It has traditionally been used for kiln furniture and mote recently for automotive exhaust catalyst substrates. In the latter, the cordierite taw materials ate mixed as a wet paste, extmded into the honeycomb shape, then dried and fired. The finished part is coated with transition-metal catalysts in a separate process. 

Hours in kiln Dry-bulb temperature, °C Wet-bulb temperature, °C Relative humidity, %... 

Fig. 3. Temperatures and progress of reactions in a 132-meter wet-process kiln area B represents CaO in new compounds D, CaO as CaCO and E, free...

A blending system provides the kiln with a homogeneous raw feed. In the wet process the mill slurry is blended in a series of continuously agitated tanks in which the composition, usually the CaO content, is adjusted as required. These tanks may also serve as kiln feed tanks, or the slurry after agitation is pumped to large kiln feed basins. Dry-process blending is usually accompHshed in a silo with compressed air. 

Generally, a diy-feed kiln will have three zones of heating, and a wet-feed kiln will have four ... 

Rotary kilns operate at various temperatures throughout their length. A graph of approximate gas and charge temperatures for wet-process cement is shown in Fig. 12-67. The maximum charge temperature is 1700 to 1800 K for the gases, 1800 to 1925 K. Overall heat-transfer rates have been estimated to be in the range of 25 to 60 KJ/(s-m ) on the basis of total kiln volume. 

List the advantages and disadvantages of using a baghouse, wet scrubber, or LSI tor particulate collection from an asphalt plant drying kiln. The gases are at 250 X and contain 450 mg m of rock dust in the 0.1-10 /rm size range. Gas flow is 2000 min. Consider initial and operation cost, space requirement, ultimate disposal, etc,... 

Calcium oxide (lime) Rotary kilns, vertical and shaft kilns, fluidized bed furnaces Particulate matter Cyclones plus secondary collectors (baghouse, ESP, wet scrubbers, granular bed filters, wet cyclones)... 

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