Temperature-Interval TI Method

Returning to Example 10.1, the temperature-interval (TI) method is used for the calculation of MER 

The first step in the TI method is to adjust the source and target temperatures using Ar i . Somewhat arbitrarily, this is accomplished by reducing the temperatures of the hot streams by Ar, i , while leaving the temperatures of the cold streams untouched as follows  

It is noted that initially, no energy is assumed to enter this interval from a hot utility, such as steam ati higher temperature that is, Ssteam = 0. Hence, 30 x 10 Btu/hr arc available and flow down as aieskl ual, R, into the next lowest interval 2 that is, /J = 30 X 10 Btu/hr. Interval 2 involves streams HI, H2, and C2 between 235°F and 240°F AT = 5 F), and hence, the enthalpy difference is 

When this is added to the residual from interval 1, / this makes the residual from interval 2, k, = 32.5 X 10 Btu/hr. Note that no temperature violations of Ar ,i occur when the streams are mabhedin interval 2 because the hot stream temperatures are reduced by AT. Interval 3, 180 F to 235T (AT= 55°F), involves aU four streams, and hence, the enthalpy difference is —82.5 X 10 Btu/hr as detailed in Table 10.1, making the residual from interval 3 equal to (32.5 — 82.5) x 1(X = —50 X 10 Btn/h. Similarly, the enthalpy differences in intervals 4 and 5 are 75 X Kf and —15 X Kf Btu/hr, respectively, with the residuals leaving these intervals being 25 x 10 and 10 X 10 Btu/hr. Note that fcr 

Energy Flows between Intervals Initial Pass Final Pass 

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A closer examination of the temperature-interval (TI) method shows that the minimum hut and cold utilities can be calculated by creating and solving a linear programming (LP) problem, as discussed in Section 18.4. This approach is illustrated in the example that follows. 

Be able to determine the minimum cooling and heating utilities (MER targets) for a network of heat exchangers using the temperature-interval (TI) method, the composite-curve method, or the formulation and solution of a linear program (LP). 

A different approach consists of stepwise changing the adsorbent temperature and keeping it constant at each of the prefixed values Tx, Ts,. . ., Tn for a certain time interval (e.g. 10 sec), thereby yielding the so-called step desorption spectra s(81-85). The advantage of this method lies in a long interval (in terms of the flash desorption technique) for which the individual temperatures Ti are kept constant so that possible surface rearrangements can take place (81-83). Furthermore, an exact evaluation of the rate constant kd is amenable as well as a better resolution of superimposed peaks on a desorption curve (see Section VI). What is questionable is how closely an instantaneous change in the adsorbent temperature can be attained. This method has been rarely used as yet. 

The second cleaning method, specific to TSDC measurements and which may be apphed in our case, is due to Bucci et al. [23]. It consists of first polarizing the material at a temperature T, such that T 2 and removing the field at temperature Td such that [Pg.34]

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