PTQ Q2 2023 Issue

Wet gas compressor

Flue gas

Wet gas

Regen.

Reactor

Main column

LIQUID to absorber

Oil feed

Pressure

Air blower

Air

Figure 1 Air blower to WGC inlet PFD

of the essential tools used to debottleneck when increas- ing LPG production. Lower pressure drop helps increase the WGC gas handling capacity because it raises suction pres- sure and reduces the actual gas volume. Reactor temperature and catalyst formulation changes increase WGFR, which must stay within the stable operat- ing range of the compressor while compressing the gas to maximum gas plant operating pressure. The air blower to WGC inlet is a single complex hydraulic system with many potential cost-effective modifications to allow higher LPG yield without replacing the WGC and/or driver. For instance, eliminating coke formation in the MC inlet nozzle (see Figure 2 ) can save 2-5 psi, which allows higher MC receiver pres- sure, thereby reducing WGFR. 3 This is often ignored, yet it can help debottleneck the WGC. Finding lower-cost opportunities Replacing the WGC, its driver or paralleling operations are high-cost outcomes when increasing LPG yield. Although, this may be necessary when unit feed rate and LPG yield have increased over the years. Identifying opportunities

to reduce system pressure drop starts with detailed pres- sure surveys, which isolate the various piping segments and equipment that generate pressure drop (see Figure 3 ). These measurements augment normal engineering tool cal- culations and are more accurate than any calculation tool result. The measured pressure profile helps to quickly iden - tify debottlenecking options early in the work process. Even today, when technology allows such things as ‘digital twins’, old-school field measurements still have value. Once the wet gas is compressed, the C 3 = plus must be condensed, absorbed, and stripped to allow further down- stream processing. As more naphtha (gasoline) is converted to C 3/C₄, condensing duty moves from the MC overhead to compressor inter-stage condensers, high pressure (HP) condensers, absorber inter-coolers, and debutanised gaso- line recycle coolers (see Figure 4 ). Debutaniser gasoline recycle must be processed through the stripper and debu- taniser, then cooled in fin-fan and/or cooling water (CW) exchangers. Operating pressure and temperatures are important variables affecting condensing and recovery. For example,

Driver

WGC

Main column

Reactor euent

Overhead receiver

Pressure

Figure 2 Main column (MC) inlet nozzle coke ring

Figure 3 MC to WGC pressure survey

PTQ Q2 2023