Recirculation loops

The reaction is initiated with nickel carbonyl. The feeds are adjusted to give the bulk of the carbonyl from carbon monoxide. The reaction takes place continuously in an agitated reactor with a Hquid recirculation loop. The reaction is mn at about atmospheric pressure and at about 40°C with an acetylene carbon monoxide mole ratio of 1.1 1 in the presence of 20% excess alcohol. The reactor effluent is washed with nickel chloride brine to remove excess alcohol and nickel salts and the brine—alcohol mixture is stripped to recover alcohol for recycle. The stripped brine is again used as extractant, but with a bleed stream returned to the nickel carbonyl conversion unit. The neutralized cmde monomer is purified by a series of continuous, low pressure distillations. 

Catalytic cathodes in membrane cell operations exhibit a voltage savings of 100—200 mV and a life of about 2 + yr using ultrapure brine. However, trace impurities such as iron from the caustic recirculation loop can deposit on the cathode and poison the coating, thereby reducing its economic life. 

Fig. 7. Flow diagram of a BWR direct-cycle system. The deminerali2ers, heaters, and one recirculation loop are omitted.

Pharmaceutical Industry. In the pharmaceutical industry, sterility of deionized water systems is maintained by using an ozone residual. The ozone residual concentration is maintained at >0.3 ppm ppm in the water recirculation loop. Prior to product compounding, the ozone residual is removed by contact with uvirradiaton for <1 s. Ozone also is used to oxidize pyrogens from distilled water destined for intravenous solutions. 

Continuous polymerization systems offer the possibiUty of several advantages including better heat transfer and cooling capacity, reduction in downtime, more uniform products, and less raw material handling (59,60). In some continuous emulsion homopolymerization processes, materials are added continuously to a first ketde and partially polymerized, then passed into a second reactor where, with additional initiator, the reaction is concluded. Continuous emulsion copolymerizations of vinyl acetate with ethylene have been described (61—64). Recirculating loop reactors which have high heat-transfer rates have found use for the manufacture of latexes for paint appHcations (59). 

Another version of a fluidized-bed reactor has been introduced by Vogelbusch (Austria). This reactor has an internal recirculation loop set up by means of a high flow impeller. The system utilises porous glass beads for immobilizing the cells. However, glass beads may not work with all types of cells. 

Loop Reactors For some gas-hquid-solid processes, a recirculating loop can be an effective reactor. These involve a relatively high horsepower pumping system and various kinds of nozzles, baffles, and turbulence generators in the loop system. These have power levels... 

MF and UF systems can be designed to operate in various process configurations. A common configuration is one in which the feedwater is pumped with a cross-flow tangential to the membrane. The only pretreatment usually provided is a crude prescreening (usually 50 to 300 / m). The water that permeates the membrane is clean. The water that does not permeate is recirculated as concentrate and blended with additional feedwater just after the preliminary filter. To control the concentration of the solids in the recirculation loop, some of the concentrate is discharged at a specified rate. 

Adding a recirculating loop to the transport reactor, a well-mixed condition is achieved provided the recirculation rate is large with... 

HAZOP focuses on study nodes, process sections, and operating steps. The number of nodes depending on the team leader and study objectives. Conservative studies consider e er line and vessel. An experienced HAZOP leader may combine nodes. For example, the cooling looser . .ater chlorination system may be divided into a) chlorine supply to venturi, b) recirculation loop, and e) to .er water basin. Alternatively, two study nodes may be used a) recirculation loop and tower water basin, and b) chlorine supply to venturi. Or one study node for the entire process. 

BWRs do not operate with dissolved boron like a PWR but use pure, demineralized water with a continuous water quality control system. The reactivity is controlled by the large number of control rods (>100) containing burnable neutron poisons, and by varying the flow rate through the reactor for normal, fine control. Two recirculation loops using variable speed recirculation pumps inject water into the jet pumps inside of the reactor vessel to increase the flow rate by several times over that in the recirculation loops. The steam bubble formation reduces the moderator density and... 

A flow diagram of a simple cross-flow system is shown in Figure 16.12. This is the system likely to be used for batch processing or development rigs it is in essence a basic pump recirculation loop. The process feed is concentrated by pumping it from the tank and across the membrane in the module at an appropriate velocity. The partly concentrated retentate is recycled into the tank for further processing while the permeate is stored or discarded as required. In cross-flow filtration applications, product washing is frequently necessary and... 

In a series of experiments on the flow of flocculated kaolin suspensions in laboratory and industrial scale pipelines(26-27-2Sl, measurements of pressure drop were made as a function of flowrate. Results were obtained using a laboratory capillary-tube viscometer, and pipelines of 42 mm and 205 mm diameter arranged in a recirculating loop. The rheology of all of the suspensions was described by the power-law model with a power law index less than unity, that is they were all shear-thinning. The behaviour in the laminar region can be described by the equation ... 

Phase-averaged values of 4 in a plane midway between two baffles of a stirred tank have been plotted in Fig. 1 (from Hartmann et al., 2004a) for two different SGS models (Smagorinsky and Voke, respectively) in LES carried out in a LB approach. The highest values, i.e., the strongest deviations from isotropy, occur in the impeller zone, in the boundary layers along wall and bottom of the tank, and at the separation points at the vessel wall from which the anisotropy is advected into the bulk flow. In the recirculation loops, the turbulent flow is more or less isotropic. 

The progress of the hydrolysis reaction was monitored by periodic sampling and analysis of the hydrolysate and by continuous monitoring of the gases evolved. Sixteen 42-ml samples of the hydrolysate were collected during each run. The sampling system attached to the recirculation loop comprised an insulated cabinet with an ice or dry ice bath in which the... 

The SOFC module is set (sized) to operate at 0.69 volts per cell. The spent fuel and air effluents of the SOFC are combusted within the module to supply heat for oxidant preheating. Unlike the natural gas case, the fuel does not require a pre-reformer with only 0.3% methane along with 36% hydrogen and 43% carbon monoxide. The carbon monoxide will be either water gas shifted to hydrogen or utilized directly within the fuel cell. A gas recirculation loop for the... 

The use of a multichannel support made of a sintered oxide carrying a separation layer deposited on the surface of the channels was not a new concept. This was described in the patent literature as far back as the 1960s (Manjikian 1966). The multichannel geometry is particularly attractive in terms of its sturdiness, lower production cost compared to the single tube or tube-bundle geometry and lower energy requirement in the cross-flow recirculation loop. However, Ceraver was the first company to industrially produce multichannel membranes. Since 1984 these membranes, which have 19 channels per element with a 4 mm channel diameter are sold under the trademark Membralox. ... 

This process has a classical on-line instrumentation gathering measurements of liquid flow rates (at the input of the reactor and in the recirculation loop), temperature and pH in the reactor and biogas flow rate and composition i.e., CO2, CH4 and H2 content in the biogas) [30]. In addition, the following sensors were installed over the years a TOC analyzer, a titrimetric sensor [3] and a FT-IR spectrometer [29]. Since 1998, this instrumentation provides us with the following on-line measurements in the liquid phase every... 

Flue gas recirculation Flue gas recirculation, alone or in combination with other modifications, can significantly reduce thermal NO,. Recirculated flue gas is a diluent that reduces flame temperatures. External and internal recirculation paths have been applied internal recirculation can be accomplished by jet entrainment using either combustion air or fuel jet energy external recirculation requires a fan or a jet pump (driven by the combustion air). When combined with staged-air or staged-fuel methods, NO emissions from gas-fired burners can be reduced by 50 to 90 percent. In some applications, external flue-gas recirculation can decrease thermal efficiency. Condensation in the recirculation loop can cause operating problems and increase maintenance requirements. 

For the case of impossible 3-D reactor or vessel sampling, this upward-flowing pipeline sampler should be implemented with the reactor in a recirculation loop configuration, as shown in Figure 3.20. The only new requirement is a low-power pump, to be operated full-time for all systems where this is feasible. 

Figure. 3.20 Colocation of correct upstream sampler and PAT sensor, shown here for a recirculation loop configuration (right). The PAT sensor is deployed in upstream small-diameter piping with a field of view matching as best possible the same stream segment which is being sampled for reference analysis. This setup allows for reliable multivariate calibration because of the colocated [X, f] modalities.

The self-mixing up-streaming recirculation loop ranks as the prime example of the SUO lot transformation in which a 3-D lot (reactor) has been turned into an easy to sample 1-D configuration (pipeline). 

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