Feed rate, cost effects

The circulating catalyst in the FCC unit is called equilibrium catalyst, or simply E-cat. Periodically, quantities of equilibrium catalyst are withdrawn and stored in the E-cat hopper for future disposal. A refinery that processes residue feedstocks can use good-quality F-cat from a refinery that processes light sweet feed. Residue feedstocks contain large quantities of impurities, such as metals and requires high rates of fresh catalyst. The use of a good-quality E-cat in conjunction with fresh catalyst can be cost-effective in maintaining low catahst costs. 

Controlling Quality of Two Products Where the two products have similar values, or where heating and cooling costs are comparable to product losses, the compositions of both products should be controlled. This introduces the possibility of strong interaction between the two composition loops, as they tend to have similar speeds of response. Interaction in most columns can be minimized by controlling distillate composition with reflux ratio and bottom composition with boil-up, or preferably boil-up/bottom flow ratio. These loops are insensitive to variations in feed rate, eliminating the need for feedforward control, and they also reject heat balance upsets quite effectively. 

Comparison of Examples 2.1 and 2.2. Table 2.4 gives a measure of the effect of nonoptimum feed point on the column in this example, Table 2,4 shows that V and V, and therefore reboiler and condenser duties, increase by about 3 to 4 percent in Example 2.2. This roughly corresponds to a 3 to 4 percent increase in energy consumption and operat-mg costs. If the column or its heat exchangers are at a maximum capacity limit, the column feed rate will need to be reduced by 3 to 4 percent. If these consequences can be tolerated, a shutdown to change the column feed nozzle will be unnecessary. Note that in this example, the effect of nonoptimum feed was quite mild. In other casas, it may be far more detrimental,... 

As a general rule, gas separation by membranes is most attractive in applications where a product purity of 95% or lower is acceptable or the feed flow-rate is not too high. As the required purity approaches 100%, the membranes become less cost effective than other separation processes. This is particularly true with single-stage units. For more stringent applications, some traditional separation processes are preferred or required to integrate with the membrane system. 

This effect is illustrated in Figures 10 and 11, for systems with an unenriched air RFSG and a UGETC. In each case, the system has a rotary cascade dryer with integral burner, a biomass feed rate of I.S dt/h, a biomass cost of 30/dt and a moisture content to the gasifier of 10%. 

Figure 12 shows the effect of biomass feed rate on CoE for sy ems with an unoiriched air RFSG and a UGETC. The systm has a rotary cascade dryar with integral burner, a biomass moisture content to and frcsn the dry of 7S% and 10%, and a biomass cost of 630/dt. 

The effect of feed rate on fjo is minimal. The effect of feed rate on CoE on the other hand is major, with CoE felling sharply as feed rate increases, particularly at low feed rates. A quadrupling of feed rate results in a halving of CoE. The trends are repeated at other biomass costs and initial moisture contents, and also for systems with the band conveyor dryer. 

A vapor-recompression evaporator is to concentrate a very dilute aqueous solution. The feed rate is to be 30,000 Ib/h the evaporation rate will be 20,000 Ib/h. The evaporator will operate at atmospheric pressure, with the vapor mechanically compressed as shown in Fig. 16.12 except that a natural-circulation calandria will be used. If steam costs 8 per 1000 lb, electricity costs 3 cents per kilowatthour, and heat-transfer surface in the heater costs 70 per square foot, calculate the optimum pressure to which the vapor should be compressed. The overall compressor efficiency is 72 percent. Assume all other costs are independent of the pressure of the compressed vapor. To how many effects will this evaporator be equivalent ... 

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