Energy Utilization in EDC Cracking

Abstract

The exergy losses in the thermal cracking of 1,2-dichloroethane (EDC) have been investigated for the EDC cracker in INEOS' vinyl chloride monomer (VCM) plant at Rafnes in Norway. This process section is the most energy demanding section in the plant, and an overview of the distribution of exergy losses was desired as part of the work for reducing energy consumption.

The investigations were based on the results of established mass and energy balances for the process section in Aspen Plus. Calculations were done in a spreadsheet.

Exergy balances were computed for a base case simulation. Different tests that were developed to investigate different modification's effect on exergy losses.

The total exergy losses in the EDC cracking section were found to be 59.5 MW, or 3362 kJ/kg VCM. The largest exergy losses in the process section were located in the cracker unit. The internal losses in the cracker dominated and accounted for 75 % of all the internal exergy losses in the process section. The rest of the noticeable exergy losses were discovered in the heat exchangers in the top system.

Preheating the EDC feed and the combustion air was found to give the largest reductions in the cracker exergy losses. This test shows a reduction in fuel gas needs of 6.6 %. Reduction in excess combustion air on the other hand showed no noticeable reductions. Fouling in H1406 and unnecessarily large amounts of excess air under normal conditions both result in large increases in exergy losses, and should be avoided if possible.