*Polymer-Based Membranes for C3+ Hydrocarbon Removal from Natural Gas DOI: http://dx.doi.org/10.5772/intechopen.103903*

#### **Figure 5.**

*Schematic of the NGL recovery process: (A) without membrane; (B) utilizing rubbery membrane to divert NAG stream to feed LRU.*

**Figure 6.** *Schematic of the cascaded-refrigeration process to recover C2+ NGL from natural gas.*

gas leaving the third cooling stage is recycled back to exchange heat with gas feeding each stage and leaving the first stage at around 450 psi (referred to as high pressure (HP) residue gas). The liquids collected in the three stages are fed to the demethanizer, which is operating at lower pressure. The C2+ NGL product is obtained as the bottom product, while the top gas product from the demethanizer (low pressure (LP) residue gas) is consolidated with HP residue stream and sent to SG network. This LRU process is ideally designed to process AG stream, which is C2 <sup>+</sup> rich and free of or very lean in nitrogen. However, under certain situations of higher demand for C2+ NGL, the LRU is designed or operated with feed that is composed partially of NAG. As noted in **Table 4**, the N2 content of NAG stream is higher, and the C2+ content is considerably lower, than in AG stream.

**Table 5** compares the performance of the NGL process when 140 MMSCFD of the NAG stream is diverted to mix with the 500 MMSCFD AG stream. In reference (base case), **Table 5** provides the performance of the NGL process when only AG stream is fed to the LRU. When portion of NAG is let down directly to mix with AG, the condensability of the feed stream to LRU is reduced, as indicated by the increase in N2 content and reduction in the C2+ content. Nevertheless, the C3+ NGL liquids production has increased as a direct result of the increase in feed to LRU, while liquid C2 production has decreased in almost similar rate rendering the cascaded-refrigeration NGL recovery process not sensitive to the increase in the flow of C2+ to LRU. On the other hand, diverting part of the NAG selectively through membrane has resulted in increasing the condensability of the feed to LRU. As a result of enhancing the

