Scraped reactor

When the product of a reaction is purified and isolated, some of it is inevitably lost during the collection process. Gases may escape while being pumped out of a reactor. Liquids adhere to glass surfaces, making it impossible to transfer every drop of a liquid product. Likewise, it is impossible to scrape every trace of a solid material from a reaction vessel. 

After each growth cycle, the reactors must be opened, the wafers removed, and the lower portion of the reactor physically cleaned. The lower quartz reactor and the bottom plate (base plate) are scraped clean using a metal tool, and the particulate material (mixture of GaAs, GaAsP, arsenic oxides and phosphorus oxides) is collected in a metal container positioned below the vertical reactor. 

A second method involves the installation of cooling cylinders and wall scrapers (Figure 9). On large reactors this is complex and expensive. Great problems will ensue if the scraped-off material remains stuck to the scraper blades. Cleaning and dismanteling are extremely difficult. 

Theoretical estimates of the erosion of the first wall and plasma contamination due to sputtering requires a knowledge of particle and photon fluxes to the wall, as well as data on the erosion yields. Sputtering will be discussed in a later part of this chapter. Here we shall briefly summarize some of the calculations done on primary fluxes in future fusion reactors. The calculations are rather uncertain because of the poor understanding of various parameters such as divertor efficiency, refueling, neutral beam heating, plasma temperature and density profiles, including the scrape-off layer in the case of divertor operated Tokamaks. 

In another US patent, [47], polyolefins and tires scrapes mixture is fed to the batch reactor equipped with a special mixer. A screw extruder or other device is used for feed... 

In the next reactor design [48] mixer arms have exactly the same dimensions and shape as the internal reactor part and in the course of the run coke residue is scraped by mixer arms from the heated reactor walls. Scraped coke falls down and is collected at the bottom of the reactor and removed with part of the reaction mixture by a suction pipe. The main process products are the gas fraction (used for heating purpose), gasoline and light gas oil and paraffin fractions. 

A batch-type reactor equipped with a screw feeder and mixer is offered by US patent [49]. A special grate is mounted inside the reactor, above the cracked melted waste plastics mixture. Scraped waste plastics which are submitted to the cracking reactor melt at the grate and fall down to the reaction mixture. As in the case of previous patent description, in the course of cracking process a mixer of a special construction scrapes coke form the reactor walls and then coke is removed from the specially shaped reactor bottom by a screw transporter. The process temperature attains level of 450° C. 

Scraped surface heat exchangers (SSHE) have been used as tubular reactors for plastics pyrolysis. SSHE overcome coking and carbon deposits forming on heat exchanging surfaces when the plastic pyrolyzes to hot gases. A tubular reactor with a special internal screw mixer has been developed in Poland [5]. The purpose of the specially shaped internal mixer is to mix the molten plastic and to scrape coke from the internal surface... 

The possible heavy impurities that may remain in the receiving channel of the reactor are periodically scraped by a traditional mechanical apparatus and are collected in a container prepared for the purpose of evacuating them easily. 

Step 7. The CPVC slurry flows to the reactor centrifuge, a spinning horizontal drum. The solids are forced against the circular drum wall and are compressed there. Liquid hydrochloric acid (waste liquor) collects in the drum and overflows through an opening at one end. and the wetcake retained on the wall, which contains 90 wt% CPVC resin and 10% hydrochloric acid, is scraped out by a large interior screw conveyor. 

The batch scale rotative reactor was developed and used as a tool to validate the new heat transfer model [4, 6]. The batch reactor consists of a well insulated tank which contains molten salt and is equipped with heating elements in order to be able to heat the salt to the set point temperature. A second well insulated tank can be placed in the salt bath. The feedstock enters the reactor through the feedpipe. The same agitation blades as those found in the industrial reactor are used. The stirring mechanism transports and agitates the feedstock in a circular manner. The center of the reservoir is kept free of feedstock by a scraping mechanism. The diameter of the feedstock tank is 107 cm and the effective heat transfer area is 0.82 m [6]. 

The nucleoside along with (Boc)20 and catalyst DMAP (amounts as stated below) were placed in the ball mill with 9-mm Pyrex beads. For small scale reactions (ca. 100-300 mg) 16-20 beads were used on gram-scale reactions as many as 25-30 were used. The mixture was ground (ca. 120-140 rpm) until the reaction was complete, as judged by TLC analysis of small aliquots scraped from the reactor and dissolved in a suitable solvent. On completion the thick oily product was washed from the apparatus using several small portions of a suitable solvent. The solvent was then evaporated and the residue was applied to a short column of silica gel. 

Packed column, trickle-bed reactor, film reactors (falling film, agitated film, scraped/wiped film), rotating disk (or rotating... 

In U.S. plants hydrofluorination is carried out in two stirred fluidized-bed reactors in series, with counterflow of solids and gases. The bed to which UO2 is fed and from which exhaust gases are discharged runs at 300°C, partially converts UO2 to UF4, and reduces the HF content of the effluent gases to around 15 percent. The bed to which anhydrous HF and the partially converted UO2 are fed runs at 500°C and converts more than 95 percent of the UO2 to UF4. To prevent caking of the fluidized beds, it has been found necessary to provide each reactor with a vertical-shaft, slow-speed stirrer to scrape the reactor walls. Production rates around 700 to 900 kg/h are obtained in 0.75-m-diameter reactors. Effluent gases are filtered to remove entrained solids, cooled to condense aqueous HF, and scrubbed to remove the last traces of HF. 

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