Feeds, multiple

The optimum number of stages and feed locations can be determined graphically 

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Dense phase systems are at cost disadvantage when multiple feed points are required, or when incremental compressed air for conveying is not available from existing sources. In the latter instance, the entire investment cost of an air compressor and associated auxiUaries must be allocated to the cost of the conveying system. 

Predemethanization. The conventional design employs a single-step multiple feed tower. Utilization of a second tower upstream of the existing primary tower reduces the load on the primary tower. This reduces the propylene refrigeration power and reduces the propylene chilling loads. This approach is typically uneconomical with low pressure demethanizers, but has been combined with high pressure demethanizer systems by some Hcensors. 

Demethanizer Overhead Expander and Multifeed Fractionation. Incorporation of an expander into the conventional high pressure demethanizer system eliminates bottlenecks in the refrigeration system, the demethanizer condenser, and charge gas compressor. It reduces the cost by lowering the refrigeration power. Multiple feed deethanization and ethylene fractionation debottlenecks the deethanizer, ethylene fractionator, and the refrigeration systems, thereby reducing power consumption. 

Since the belt is wrapped snugly around the material, it moves with the belt and is not subject to any form of internal movement except at feed and discharge. In addition, the belt can operate in many planes, with twists and turns to meet almost any layout condition within the fixed hmit of curvature placed on the loaded belt. It can convey and elevate with only a single drive multiple feed and discharge points are relatively easy to arrange. 

Multiple feeds to Eliminate interconnections single machine,, Interlock feed valves so only one can be open two feeds open at once. Incompati- 1 " three-way valve ble materials come Implement appropriate operating procedures in contact, possi- and training bly leading to runaway reaction. CCPS G-f5 CCPS G-32... 

Kister [94, 95] examines binary distillation systems with multiple feeds, one or more side products, one or more points of heat removal or addition, and various combinations. 

These devices have gas and liquid streams which merge, i.e. are fed into each other, e.g. by special dual-feed, triple-feed or multiple-feed arrangements. Both phases are then passed in the same encasing, e.g. the same micro channel. From there, fragmentation of the gas stream occurs, forming a dispersion. 

Figure 11.1. Distillation column (a) Basic column (b) Multiple feeds and side streams...

The McCabe-Thiele method can be used for the design of columns with side streams and multiple feeds. The liquid and vapour flows in the sections between the feed and take-off points are calculated and operating lines drawn for each section. 

In general, the Lewis-Matheson method has not been found to be an efficient procedure for computer solutions, other than for relatively straightforward problems. It is not suitable for problems involving multiple feeds, and side-streams, or where more than one column is needed. 

The Ni/Re on carbon catalyst was also evaluated in a 1700 hour continuous reactor test to determine the stability of the catalyst. This test was performed with a different model compound than xylitol. Shown in Figure 5, the results from the lifetime test of the Ni/Re catalyst operated at constant process conditions sampled intermittently for 1700 hours. This shows that for a similar aqueous hydrogenation reaction deliberately operated to near completion, the catalyst retained its activity and product selectivity even in the face of multiple feed and H2 interruptions. We feel that this data readily suggests that the Ni/Re catalyst will retain its activity for xylitol hydrogenolysis. 

Multiple feeds, e.g., pond feeds, sludge, biomass, industrial waste... 

Viswanathan, J. and I. E. Grossmann. Optimal Feed Locations and Number of Trays for Distillation Columns with Multiple Feeds. Ind Eng Chem Res 32 2942-2949 (1993). 

The IEM model is easily extended to treat multiple feed streams and time-dependent feed rates (Fox and Villermaux 1990b). 

Multi-environment presumed PDF models can also be easily extended to treat cases with more than two feed streams. For example, a four-environment model for a flow with three feed streams is shown in Fig. 5.24. For this flow, the mixture-fraction vector will have two components, 2 and 22- The micromixing functions should thus be selected to agree with the variance transport equations for both components. However, in comparison with multi-variable presumed PDF methods for the mixture-fraction vector (see Section 5.3), the implementation of multi-environment presumed PDF models in CFD calculations of chemical reactors with multiple feed streams is much simpler. 

Figure 11.21. Column with multiple feeds and sidestreams...

The Ponchon-Savarit method, using an enthalpy-composition diagram, may also be used to handle sidestreams and multiple feeds, though only for binary systems. This is dealt with in Section 11.5. 

The enthalpy-composition approach may also be used for multiple feeds and sidestreams for binary systems. For the condition of constant molar overflow, each additional sidestream or feed adds a further operating line and pole point to the system. 

For the case of multiple feeds, the procedure is similar and may be followed by reference to Figure 11.31. 

Multiple feeds, both liquid and vapor, and sidestream drawoffs, both liquid and vapor, are permitted. A general nth tray is sketehed in Fig. 3.13. Nomenela-ture is summarized in Table 3.1. The equations deseribing this tray are ... 

The biomass is fed overbed through multiple feed chutes using air jets to help distribute the fuel over the surface of the bed. Variable-speed screw conveyors are usually used to meter the fuel feed rate and control steam output. Feedstocks such as bark and waste wood are chipped to a top size of 25 mm (1 in) to ensure complete combustion. The bed usually consists of sand around 1 m (3 ft) deep. This serves to retain the fuel in the furnace, extending its in-furnace residence time and increasing combustion efficiency. It also provides a heat sink to help maintain bed temperature during periods of fluctuating fuel moisture content. 

Figure 5.1-5. Tubular reactor with multiple feed. E, fresh ethylene I, initiator.

In the multiple-feed process an initiator mix is used to obtain a smooth temperature profile and low initiator consumption. The initiator mix consists of three or four organic peroxides from Table 5.1-2 differing in activity. To cover the range of lower temperatures, dicyclohexyl peroxy dicarbonate, /-butylperoxy neodecanoate, or /-butylperoxy pivalate are used. The peroxide for moderately high temperatures is frequently /-butylperoxy 2-ethylhexanoate or /-butylperoxy benzoate. The high-temperature initiator in the mix is di(/-butyl)peroxide. 

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