Particle feed rate

Figure 6-12 Typical integral charge spectrum (Min, 1965). Length of channel = 1.37 m, air velocity = 10.7 m/sec, particle feed rate = 0.000147 kg/sec. (Reproduced with permission of K. Min.)...

The non-isothermal erosion rigs are easy to fabricate but they fail to simulate the erosion conditions. Hence, such rigs presently are not popular. In contrast, isothermal type erosion rigs can simulate erosion conditions but are difficult to fabricate. A schematic diagram of one such erosion rig fabricated by the author at DMRL is shown in Fig. 6.2a. The unique feature of this rig is its ability to alter the particle feed rate by over 100 times. Its particle feeding system is a miniaturized conveyer belt system and the particle feed rate is controlled by controlling the speed of the motor of the system. A further description of this rig is available elsewhere [14]. 

The effect of particle feed rate on erosion rate... 

The influence of particle feed rate on the erosion rate of 304 and 430 SS over a large temperature range was investigated by Zhou and Bahadur [51], The... 

The above discussion clearly brings out certain features of the elevated temperature erosion of metallic materials. Almost all metallic materials exhibit ductile erosion response at room temperature, whereas at elevated temperature both brittle and ductile erosion responses are established [41,46,47]. The velocity exponents for metallic materials are around 2.5 during ambient temperature erosion. At elevated temperatures, the velocity exponents of metals and alloys vary over a wide range from 0.9 to more than 3.0 [41 3]. It is found that the erosion rate at room temperature increases with increase of particle size up to 50 pm, beyond which the particle size has no effect on the erosion rate. The reported literature indicates that the erosion rate increases with increase of particle size at high temperatures [39,40,44,49]. At ambient temperature, changing the particle shape from angular to spherical alters the erosion response from brittle to ductile [60,61], while at elevated temperatures, brittle to ductile response is noted irrespective of the particle shape [39,40, 47]. The particle feed rate has a negligible effect on the room temperature erosion rate [62-64]. A remarkable effect of the particle feed rate has been noted at elevated temperatures [39]. The mechanical properties of the erodent have a nominal influence on room temperature erosion behaviour [65-73]. However, at elevated temperature this aspect has yet to be explored. 

Occidental Petroleum Coal Conversion Process. Garrett R D Co. (now the Occidental Research Co.) developed the Oxy Coal Conversion process based on mathematical simulation for heating coal particles in the pyrolysis unit. It was estimated that coal particles of 100-mm diameter could be heated throughout their volumes to decomposition temperature (450—540°C) within 0.1 s. A large pilot faciUty was constmcted at LaVeme, California, in 1971. This unit was reported to operate successfully at feed rates up to 136 kg/h (3.2 t/d). 

In the most common production method, the semibatch process, about 10% of the preemulsified monomer is added to the deionised water in the reactor. A shot of initiator is added to the reactor to create the seed. Some manufacturers use master batches of seed to avoid variation in this step. Having set the number of particles in the pot, the remaining monomer and, in some cases, additional initiator are added over time. Typical feed times ate 1—4 h. Lengthening the feeds tempers heat generation and provides for uniform comonomer sequence distributions (67). Sometimes skewed monomer feeds are used to offset differences in monomer reactivity ratios. In some cases a second monomer charge is made to produce core—shell latices. At the end of the process pH adjustments are often made. The product is then pumped to a prefilter tank, filtered, and pumped to a post-filter tank where additional processing can occur. When the feed rate of monomer during semibatch production is very low, the reactor is said to be monomer starved. Under these... 

Particle Size Distribution. Almost every feed slurry is a mixture of fine and coarse particles. Performance depends on the frequency of distribution of particle size ia the feed. Figure 5 shows that whereas all of the coarse particles having a diameter greater than some are separated, fewer of the very fine particles are, at any given feed rate. The size distribution frequency of particles ia feed and centrate for a fine and coarse feed are quite different. More coarse particles separate out than fine ones. Classification of soHds by size is often done by centrifugal sedimentation. 

Abrasion, a serious problem in some appHcations, requires the addition of hard-surfacing materials to points exposed to abrasive wear (12). The severity of wear depends on the nature, size, hardness, and shape of particles as well as the frequency of contact, the force exerted against the wearing parts, and sohds loading as related to feed rate and soflds concentration. 

Media Si. Media are suppHed in several size grades and the grade used varies at each plant. The finer grades improve media stabiUty, but finer particles are more difficult to recover and the feed rate of these finer-grade slurries should be reduced by a factor of 0.5—0.75 to maintain magnetic recovery. A typical size analysis as used in various heavy-media separation plants treating coal (qv) is given in Table 4. 

The devolatilized coal particles are transported to a direct-fired multihearth furnace where they are activated by holding the temperature of the furnace at about 1000°C. Product quaUty is maintained by controlling coal feed rate and bed temperature. As before, dust particles in the furnace off-gas are combusted in an afterburner before discharge of the gas to the atmosphere. Finally, the granular product is screened to provide the desired particle size. A typical yield of activated carbon is about 30—35% by weight based on the raw coal. 

The physical properties of spray-dried materials are subject to considerable variation, depending on the direction of flow of the inlet gas and its temperature, the degree and uniformity of atomization, the solids content of the feed, the temperature of the feed, and the degree of aeration of the feed. The properties of the product usually of greatest interest are (1) particle size, (2) bulk density, and (3) dustiness. The particle size is a function of atomizer-operating conditions and also of the solids content, liquid viscosity, liquid density, and feed rate. In general, particle size increases with solids content, viscosity, density, and feed rate. 

Rake-Lifting Mechanisms These should be provided when abnormal thickener operation is probable. Abnormal thickener operation or excessive torque may result from insufficient underflow pumping, surges in the solids feed rate, excessive amounts of large particles, sloughing of solids accumulated between the rakes and the bottom of... 

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