Gas stream processing:
- • CO2 in the vapour phase stream is removed using NaOH scrubber. Subsequently gas is dried to consist of only H2, CO, C1-C3 components only. This stream is then sent to a demethanizer which separates tail gas (CO + H2 + CH4) from a mixture of C1-C3 components. The C2-C3 + components enter a dethanizer which separates C2 from C3 components.
• Here C2 components refer to all kinds of C2s namely ethylene, acetylene etc. Similarly, C3 the excess of propylene, and propane.
• The C2 components then enter a C2 splitter which separates ethane from ethylene and acetylene.
• The ethylene and acetylene gas mixture is fed to absorption unit which is fed with an extracting solvent (such as N-methylpyrrolidinone) to extract Acetylene from a mixture of acetylene and ethylene.
• The extractant then goes to a stripper that generates acetylene by stripping. The regenerated solvent is fed back to the absorber.
• The ethylene stream is fed to a topping and tailing still to obtain high purity ethylene and a mixture of ethylene and acetylene as the top and bottom products. The mixture of ethylene and acetylene is sent back to the C2 splitter unit as its composition matches to that of the C2 splitter feed.
- • The liqiuid stream consists of C3,C4, aromatics and other heavy oil components is fed to a NaOH scrubber to remove CO2
• Eventually it is fed to a pre-fractionator. The pre-fractionator separates lighter components from the heavy components. The lighter components are mixed with the vapour phase stream and sent to the NaOH vapour phase scrubber unit.
• The pre-fractionator bottom product is mixed with the deethanizer bottom product.
• Eventually the liquid mixture enters a debutanizer that separates C3, C4 components from aromatics and fuel oil mixture. The bottom product eventually enters a distillation tower that separates aromatics and fuel oil as top and bottom products respectively.
• The top product then enters a depropanizer that separates C3s from C4 components.
• The C4 components then enter an extractive distillation unit that separates butane + butylenes from butadiene. The extractive distillation unit consists of a distillation column coupled to a solvent stripper. The solvent stripper produces butadiene and pure solvent which is sent to the distillation column.
• The C3 components enter a C3 splitter that separates propylene from propane + butane mixture. The saturates mixture is recycled to the saturates cracking furnace as a feed stream.