Pellet length

The first task was to produce carriers from different recipes and in different shapes as shown schematically in Fig. 8. The raw materials diatomaceous earth, water and various binders are mixed to a paste, which is subsequently extruded through a shaped nozzle and cut off to wet pellets. The wet pellets are finally dried and heated in a furnace in an oxidising atmosphere (calcination). The nozzle geometry determines the cross section of the pellet (cf. Fig. 3) and the pellet length is controlled by adjusting the cut-off device. Important parameters in the extrusion process are the dry matter content and the viscosity of the paste. The pore volume distribution of the carriers is measured by Hg porosimetry, in which the penetration of Hg into the pores of the carrier is measured as a function of applied pressure, and the surface area is measured by the BET method, which is based on adsorption of nitrogen on the carrier surface [1]. 

The ability to predict volatiles release rate and composition is of interest for furnace simulations ( 1). Fig. 2 presents calculated volatiles flux as a function of time in dimensional form for three pellet lengths using the experimentally determined time-dependent surface flux of 3-4 cal/cm /s and a single reaction to describe weight loss. This figure is to be compared to the... 

Figure 2. Calculated volatile flux from devolatilizing pellet vs. time for three pellet lengths, 0.5 cm (----------------------------------) 1.0 cm (-----) and 1.5 cm (--------).

Fig. 3 presents the experimental CO yield versus time for the same 3 pellet lengths. Two peaks also occur for CH, and H O (22). The gas species yield variations with pellet length are similar to those for CO. The initial experimental maximum is less distinct in the experiment than in model predictions owing to the requisite time between 2 successive GC samples. Fig. 4 shows product distribution as a function of time resulting from devolatilization of the 1.5 cm pellet (the larger pellet gives greater sensitivity concentration measurements). Water-free tar is the major product and its production increases with particle size. 

In order to assess whether secondary reactions to form CO could be responsible for the experimental CO versus time curve shape, a series-parallel kinetic mechanism was added to the model. Tar and gas are produced in the initial weight loss reaction, but the tar also reacts to form gas. The rate coefficients used are similar to hydrocarbon cracking reactions. Fig. 5 presents the model predictions for a single pellet length. It is observed that the second volatiles maximum is enhanced. For other pellet lengths, the time of the second peak follows the same trends as in the experiments. While the physical model might be improved by the inclusion of finite rates of mass transfer, the porosity is quite large and Lee, et al have verified volatiles outflow is... 

Figure 3. Experimental CO yield vs. time for three pellet lengths, 0.5 cm (-) 1.0 cm (-...

During the 2-1/2 year investigation and production period, the d-RDF was characterized by measuring moisture, ash, pellet and bulk densities, pellet length, content of fines and integrity, properties chosen because of their probable relationship to the use of d-RDF as a stoker fuel. The values of these properties, and the relation to corresponding values for coal, are necessary to predict and understand results when d-RDF is transported, mixed, and fired. 

The pellet lengths were limited by the position of the breaker plate installed on the interior surface of the cover of the die. However, the centrifugal force from the rotating die and impacts from loose pellets within the shell cover of the die, cause the pellets to break off at random lengths. Also, included pieces of plastics and textiles form planes of weakness and the pellets break shorter. 

Figure 4. Pellet length distribution sample A (V2 in. diameter—2 drops)...

Densification is accomplished by a 300 HP California Pellet Mill Model 7162-3. The pellets are formed by extrusion through nominally 3/8 inch diameter radial holes in a cylindrical die. Pressure is exerted on a "pad" of the material to be densified by rolls which have fixed shafts. The pellet die rotates about the pressure rolls. Pellet length is controlled by a "cut-off" knife positioned to clip the pellets as they exit the rotating die. The exiting material stream from the pellet mill is mechanically lifted to a pellet cooler, which discharges to a screen to remove under-size pellet pieces and fines. The fines and pieces are recycled to the pellet mill infeed system. Finished pellets are conveyed by high pressure air system to tank storage. 

Tests with 0.068- and 0.096-in. (0.173- and 0.244-cm) -diam detonators, summarized in Figure 15, showed that the weight is more important than the pellet length in initiating RDX [8,18], primarily due to increased radial losses in smaller diameters. As a result of the data in Figure 16, a minimum of 51 mg oflead azide was chosen for a 0.136-in. diam. 

However, to obtain uniform pellet quality, minimize pellet length variations, avoid uneven die wear, and ascertain constant power demand, it is necessary to distribute the feed evenly across the entire working width (= perforated area) of the die. Since the particulate feed can only enter the operational area of the machine from the open front of the die ring and, additionally, the interior is to a large extent occupied by the press rollers, this requirement is not easily met. 

An increase in the linear heat generation rate by an amount directly proportional to the decrease in pellet length... 

Number of sub-assemblies per fuel element Number of fuel pins per sub-assembly Pin outer diameter, mm Clad thickness (min.), mm Pin overall length, mm Fuel pellet diameter mm Fuel pellet length, mm Fuel pellet density (min.), g/cm- Mean mass of uranium dioxide per pin, kg... 

Porous, cylindrical-shaped pellets are used as catalyst for the reaction A products, in a packed bed. We wish to model the steady-state diffusion-reaction processes within the particle. When the pellet length to diameter ratio (L/2R) > 3, flux to the particle end caps can be ignored. Assume the surface composition is and that reaction kinetics is controlled by a linear rate expression = kC (mole/volume time), and diffusive flux obeys = -D dC /dr. 

The fuel pellet length-to-diameter ratio is decreased from 2 1 to 1 1, which reduces ridging. 

Optimization of the chamfer shape, pellet length-to-diameter ratio (L/D), and pellet dish. The chamfer shape at the ends of the pellets influences the size of the interpellet, circumferential sheath ridges, as does the L/D ratio. The chamfer, as well as the dishes at the pellet ends, also provide space to accommodate fission gas release. 

Longfiber reinforced granulates Ft>er length = pellet length 8-25 nm... 

The global rate is the measured rate, which is the rate averaged over the pellet length L or the flux at the pellet surface divided by L. If dimensionless variables are used, the equation can be rewritten as ... 

Does an increase in the Thiele modulus result in an increase, decrease, or no change in the internal and external concentration and temperature differences Answer the question when the increase is due to an increase in pellet length, a decrease in effective diffusivity, or an increase in temperature. 

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