Solids contact processes

Chemical Mixing, Flocculation and Solids Contact Processes... 

These processes depend on fluid shear for coagulant dispersal and for promoting particle contacts. Shear is most commonly introduced by mechanical mixing equipment. In certain solids contact processes shear results from fluid passage upward... 

Solids contact processes combine chemical mixing, flocculation and clarification in a single unit designed so that a large volume of previously formed floe is retained in the system. The floe volume may be as much as 100 times to in a "flow-through" system. This greatly increases the rate of agglomeration from particle contacts and may also speed up chemical destabilization reactions. 

Fluidization (ca. 1855) vt. A gas-sohd or liquid-solid contacting process in which a stream of fluid is passed upwards through a bed of small solid particles, causing them to lift, expand, and behave as a boiling liquid. The process is widely used in the chemical industry for performing reactions in which the solid is either a reactant or a catalyst. In the plastics industry, the main application is in fluidized-bed coating. 

In practical operations, maximum capacity of adsorbent cannot be fully utilized because of mass transfer effiects involved in actual fluid-solid contacting processes. In order to estimate practical or dynamic adsorption capacity, however, it is essential, first of all. to have information on adsorption equilibrium. Then kinetic analyses are conducted based on rate processes depending on types of contacting processes. The most typical of the rate steps in solid adsorbents is the intraparticle diffusion which is treated in the next chapter. 

Fig. 9.7, along with the solids contact process included in the process train for the effluent leaving the MFC. There are too many unknowns at this time to predict an energy balance for such a system, but presumably this process train would recover more energy directly as electricity and reduce the need for long detention time anaerobic digesters. The fate of the solids produced by the fermentation system, and those from the solids contact process, would need to be determined based on studying their characteristics in pilot scale tests of the proposed process train. 

As mentioned above, a solids contact process will likely be needed to further remove BOD from the MFC effluent. This process could be expected to improve the settling characteristics of the MFC biofilms. It is unknown at this point how well the SC reactor system would function. It is also possible that the solids from the primary clarifier could be used to augment the MFC solids or improve their settling characteristics, but primary clarifier solids can vary substantially in character and such a process has yet to be examined. 

Matasci, R.N., Kaempfer, C. and Heidman, J.A. (1986) Full scale studies of the trickling filter/solids contact process. J. Water Pollut. Control. Fed. 58(11), 1043-1049. 

Sulphur trioxide, SO3, m.p. 17 C, b.p. 49 C. Formed SO2 plus O2 over a catalyst (contact process - see sulphuric acid). The solid exists... 

In sintering, the green compact is placed on a wide-mesh belt and slowly moves through a controlled atmosphere furnace (Fig. 3). The parts are heated to below the melting point of the base metal, held at the sintering temperature, and cooled. Basically a solid-state process, sintering transforms mechanical bonds, ie, contact points, between the powder particles in the compact into metallurgical bonds which provide the primary functional properties of the part. 

FIG. 18-89 Reactor-clarifier of the high-rate solids-contact type. (EIMCO Process Equipment Co.)... 

The newer process uses a solid catalyst for reaction (19). Either finely divided platinum or vanadium pentoxide, V205, is effective. Because catalysis occurs where the gas contacts the surface of the catalyst, this process is called the contact process. 

In 1999, Luo and Domfeld [110] proposed that there are two typical contact modes in the CMP process, i.e., the hydro-dynamical contact mode and the solid-solid contact mode [110]. When the down pressure applied on the wafer surface is small and the relative velocity of the wafer is large, a thin fluid film with micro-scale thickness will be formed between the wafer and pad surface. The size of the abrasive particles is much smaller than the thickness of the slurry film, and therefore a lot of abrasive particles are inactive. Almost all material removals are due to three-body abrasion. When the down pressure applied on the wafer surface is large and the relative velocity of the wafer is small, the wafer and pad asperity contact each other and both two-body and three-body abrasion occurs, as is described as solid-solid contact mode in Fig. 44 [110]. In the two-body abrasion, the abrasive particles embedded in the pad asperities move to remove materials. Almost all effective material removals happen due to these abrasions. However, the abrasives not embedded in the pad are either inactive or act in three-body abrasion. Compared with the two-body abrasion happening in the wafer-pad contact area, the material removed by three-body abrasion is negligible. 

The oxidation of soot is a slow process, owing to its refractory character. Therefore, the soot particles are trapped in a filter, thus increasing the reaction time. However, catalysis is still required. The design of a catalytic filter is a challenge mainly because solid/solid contact is too poor for efficient catalysis [23]. Several ideas have been put forward. 

The equipment used to contact the solids with the solvent is usually a special designs to suit the type of solid being processed, and is to an extent unique to the particular industry. General details of leaching equipment are given in Volume 2, Chapter 10 and in Perry et al. (1997). 

The first and very simple solid contact polymeric sensors were proposed in the early 1970s by Cattrall and Freiser and comprised of a metal wire coated with an ion-selective polymeric membrane [94], These coated wire electrodes (CWEs) had similar sensitivity and selectivity and even somewhat better DLs than conventional ISEs, but suffered from severe potential drifts, resulting in poor reproducibility. The origin of the CWE potential instabilities is now believed to be the formation of a thin aqueous layer between membrane and metal [95], The dominating redox process in the layer is likely the reduction of dissolved oxygen, and the potential drift is mainly caused by pH and p02 changes in a sample. Additionally, the ionic composition of this layer may vary as a function of the sample composition, leading to additional potential instabilities. 

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