PTQ Q2 2023 Issue

WGFR

46,000

Constant overhead receiver temperature = 130 ˚F RX yield constant 13.1 wt% C3=

44,000

42,000

32,000 34,000 40,000 36,000 38,000

40,000

38,000

36,000

Constant overhead receiver temperature = 130 ˚F Constant overhead receiver pressure = 3.5 psig Constant C2 minus

34,000

30,000 32,000

30,000

28,000

7.5 wt%

10.3 wt%

13.1 wt%

3.5 psig

6.5 psig

9.5 psig

Reactor C3=

Receiver pressure

Figure 8 WGC ICFM flow changes with higher reactor LPG

Figure 9 Receiver pressure optimisation

P1 = Suction pressure, psia P 2 = Discharge pressure, psia

system pressure drop and increase receiver pressure. Figure 9 shows the WGFR reduction when receiver pressure is increased from 3.5 to 9.5 psig for a 13.1 wt% C3= reactor yield, fixed dry gas, and 130°F receiver temperature. Using the Figure 6 curve, the WGCFR can be reduced by increas - ing pressure to stay within the compressor stable operating range. Sometimes WGC suction pressure can be increased enough to maintain maximum absorber operating pressure. Reducing MC overhead receiver temperature also decreases WGCFR. This can be accomplished with several potential modifications depending on the specific process and equipment constraints. Adding fin-fan or CW con - denser capacity or higher CW flow rate all reduces receiver temperature. Decreasing MC reflux rate by adding a new top pumparound or increasing lower MC pumparound duties also reduces receiver temperature. Figure 10 shows the effect of receiver temperature on WGFR at fixed receiver pressure varying reactor wt% C3= yield. Ultimately the WGFR must be maintained between the surge point and stonewall on the WGC polytropic head/ICFM curve. During pre-conceptual and conceptual process work, the most cost-effective means of controlling the WGFR needs to be found. MC overhead system changes often affect both temperature and pressure concurrently. Figure 11 shows how receiver temperature and pressure influence WGFR for a 13.1 wt% C3= yield at constant dry gas yield.

WGC performance curves Increasing reactor LPG yield raises the WGFR unless oper - ating changes counteract it. Raising WGC suction pressure and lowering temperature reduces the WGFR. The WGFR is always the actual flow conditions at compressor inlet and can be calculated by using WGC low stage discharge flow meter in standard units corrected to inlet conditions. WGC inlet flow meters are not needed and generate para - sitic pressure drop even when using a venturi meter. WGC curves as shown in Figures 6 and 7 allow the impact of any potential upstream pressure and temperature changes to be quantified. Managing WGCFR WGCFR must be managed when increasing reactor C3/C4 yields. Figure 8 shows how the WGFR varies for a fixed MC overhead receiver pressure and temperature at reactor C₃= yields of 7.5, 10.3, and 13.1 wt% assuming a constant C2 minus yield. WGFR increases with higher reactor LPG yields unless the pressure and/or temperature is changed. Assuming Figure 6 is the low stage WGC curve, WGFR quickly exceeds the maximum capacity and must be reduced to stay within the stable operating range of the compressor. MC overhead receiver temperature and pressure needs to be managed through cost-effective process or equipment changes. Table 1 shows potential modifications to reduce

WGFR

28,000 26,000 24,000 30,000 32,000 34,000 40,000 36,000 38,000 44,000 42,000 48,000 46,000

Constant overhead receiver pressure = 3.5 psig Constant C2 minus

Modifications to reduce pressure drop

ΔP reduction, psi

Eliminate feed nozzle coke Main column trays to packing CW trim cooler bundles Additional CW flow rate Replace high ΔP piping Eliminate wet gas flow meter Air fin-fan bundles

2-4 2-4 2-5

Varies Varies Varies

130 ˚F 115 ˚F 100 ˚F

1-2

7.5 wt%

10.3 wt%

13.1 wt%

Reduce condensing load-additional PA cooling

Varies

Reactor C3=

Figure 10 Receiver temperature optimisation

Table 1

PTQ Q2 2023