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07_Chap_Wang.qxd  05/05/2004  4:20 pm  Page 342
                    342                                                    Lawrence K. Wang et al.

                       Solution

                                               θ= tan −1  (88.2/U ) = 65.6°
                                                             flg
                    Example 3

                       Determine the flare height assuming the following system data are known for a steam-
                       assisted elevated flare system (see Fig. 1):
                          Flare gas flow rate = 36,200 scfm
                          Flare gas heat content = 300 Btu/scf
                          Flare tip diameter = 60 in.
                          Flare gas exit velocity = 40 ft/s
                       Solution

                       Using Eq. (7)
                                                                  −3
                                 H = (0.02185)(Q  × h ) 1/2  − (6.05 × 10 )(D )(U )(cos θ)
                                              flg  flg                tip  flg
                                                                    −3
                                 H = (0.02185)(36,200 × 300) 1/2  − (6.05 × 10 )(60)(40)(cos 65.6°)
                                 H = 66 ft
                    Example 4

                       Determine the flare cost (FC), the purchased equipment cost (PEC), the total capital cost
                       (TCC), and annual cost of the steam-assisted elevated flare system illustrated in Fig. 1 and
                       analyzed in Example 3. Assume that the March 1990 site preparation cost (SP) and building
                       cost (Bldg.) are $50,000 and $100,000, respectively.
                       Solution

                       1.  Determine the flare cost (FC) using Eq. (9) because H is between 30 and 100 ft.
                                H = 66 ft.
                               FC = [78 + 9.14 (D ) + 0.749 (H)] 2
                                               tip
                               FC = [78 + 9.14 (54) + 0.749 (66)] 2
                               FC = $386,000 March 1990 cost


                       2.  Determine the purchased equipment cost (PEC). Assume auxiliary equipment costs (i.e.,
                          ductwork, dampers, and fans) estimated from another chapter of this handbook series
                          (22) are $10,000. The equipment cost EC is then $386,000 + $10,000 = $396,000. Next,
                          use Table 4 to obtain the purchased equipment cost, PEC, as shown follows.
                                      The equipment cost (EC) = flare cost (FC) + auxiliary equipment cost
                                                           = $386,000 + $10,000
                                                           = $396,000 March 1990 cost.


                            The purchased equipment cost (PEC) = EC + 0.1 EC (instrumentation)
                                                               + 0.03 EC (sales taxes)
                                                               + 0.05 EC (freight)
                                                           = 1.18 EC
                                                           = 1.18 ($396,000)
                                                           = $467,000 March 1990 cost
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