Bc

Figure 4 ¿ko thermal coupling ■■ BRuc-na's scheme

Figure 4 ¿ko thermal coupling ■■ BRuc-na's scheme

FIG'JRE 4.11(d) THERnftL COUPLING

SCHEnE

FIGURE 4.12 RNRL/TICflL DiftGftAM 0F THE

PETlyuK/STüPlN THERMñl COüPUNG

SC'rl&riE

4.2.9 Other Common Heat Integrations

DIFFERENT COLUMNS One of the most straight-forward energy saving schemes is thdt of direct heat integration between different columns. Such a scheme can be implemented whenever one column rejects energy at a temperature sufficiently high to be utilized for heatir.c in another column. Figure 4.13 shows a typical example. Energy can be rejected at the overhead condenser, an intercondenser, a feed precooler or a product cooler, and can be utilized in a reboiler, interreboiler or feed preheater. Some examples were discussed by Rathore (30). Some application guidelines are as follows:

(i) In most cases, the heat rejection duty differs from heat demand by the user, and there is a need to use a trim cooler/heater. Such an exchanger is also important to ensure good control in case of variations in one of the duries, and often to enable system startup.

(ii) Sometimes when the temperature difference between the heat-rejecting fluid and the potential user is not sufficiently high, a change in pressure in one or both columns can raise the heat-rejecting fluid temperature or lower the potential user temperature sufficiently to achieve an adequate temperature difference.

(iii) The consequences of a possible exchanger leakage must be studied carefully when using this technique, especially if any of the fluids is hazardous.

(iv) When the columns are a large distance apart ( > 200 feet, Reference 30), the above technique is unlikely to be attractive. In such cases, the hot liquid belt technique (4.2.3) is often preferred.

SAME COLUMN One arrangement commonly used in gas-plant demethanizer is that of column feed providing reboil and/or interreboil to the column. This saves refrigeration energy.

Demethanizer

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