Sloping drum

The rotary-tube dryers are used widely for coal drying in brown coal briquetting plants. They are also used for drying of hard coals. These dryers are indirect dryers heated by saturated steam at pressures of 0.15 to 0.55 MPa. This dryer (Figure 43.3) consists of a sloping drum (1), in which the perforated walls... 

The vessels will be pressurised up to 1,1 - 1,25 fold of the normal service pressure of the drums, within stress increments of 50 kPa (0,5 bar) and a constant and smooth slope of less than 10 kPa.min . During the complete test the data will be acquired, stored and analysed. 

The header is normally a 80 mm diameter pipe (50 mm may be adequate for small units) and is routed via an overhead pipe rack (which is generally sloped) to a non-condensible blowdown drum. 

Piping to Burners - First and second stage piping and headers, as well as the burner lines themselves, are sized to minimize pressure drop and velocity effects. Thus, maldistribution of flow to the burners will be minimized. The burner lines are fabricated from standard 1(X) mm pipe, and are arranged in a split grid layout with distribution headers and split feed lines on opposite sides, for both first and second stage burners. First and second stage headers must be sloped so that any condensate will drain back to the seal drums. However, the burner lines must be accurately installed in a horizontal plane. 

Ammonia receivers may have an oil drum pot, and the receiver will slope slightly down towards this. 

The three most common diffuser configurations are a vertical cylinder in which the semifluidized cossettes are scrolled upward (tower), a pair of upward-moving inclined twin-screw scrolls with cascading juices (slope), and a horizontal rotating drum equipped with offset compartments which allow the cossettes to fall forward as the drum turns (Raffinerie Tirlemontoise (RT) horizontal). Residence time within all of these diffusers is typically 45 to 60 minutes. 

Figure 4. Comparisons of two IMPROVEd DRUM samplers (12 LI min, three size cuts below 2.5 xm, and slit orifices) running side by side at Sacramento, California. The size range shown is for a particle diameter of 0.34 to 2.5 xm. Iron is used as a tracer of soil particles. The mean r2 for all stages less than 2.5 xm was 0.87 with a slope of 1.03.

With smaller logs a drum debarker is commonly used. This consists of a steel cylinder 3 m in diameter and 15-25 m long, placed on a slightly sloping axis, and capable of slow rotation on its axis. It is fitted with logtumbling baffles inside and has longitudinal slots cut into the periphery to allow bark fragments to fall out or be flushed out with water. Slow rotation of... 

Therefore, only closely sized agglomerates are produced. The slope of the drum can be adjusted/changed at point 5 and the drive is connected at point 6. The above considerations for sizing and scale-up must be modified and cannot be applied directly. 

The drum is essentially an inclined, cylindrical shell with a length to diameter ratio of 2.5-3.5, a retaining ring on the feed end, and a spiral discharge to obtain uniform distribution on the screen and optimal separation. The drum dimensions are adjusted for the required throughput rate. The slope is normally very small, e.g. 6° to the horizontal, and, in most cases, adjustable. 

Because in the normal drum which slopes down toward the discharge end no classification occurs, the output must be screened to remove undersized material and, sometimes, oversized agglomerates. Off-specification material is recirculated. 

Trommel efficiency is affected both by geometrical and operational factors, such as length, diameter, angle of slope, rotational speed, and feed rate. Rotational speed is the most crucial operational parameter, as it must be maintained at an optimum value. Optimum rotational speed occurs when the waste material tumbles in the drum forming a cascade, which means that waste material is partially carried up the interior wall of the rotating drum, reaches about the maximum height, and then falls back on the bottom. The optimum rotational... 

Drum agglomerators consist normally of a cylindrical steel tube with a slight (typically up to 10° from the horizontal) slope a toward the discharge end (see Fig. 7.18). Retaining rings are often fitted to the feed and discharge ends of the drum to avoid spill-back and, respectively, to increase the bed depth of material and/or its residence time. 

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