Evaluation

When the compressor was brought down to install the polymer seals, the only work performed that would affect efficiency was the installation of the upgraded seals. This allowed the efficiency change to be attributed solely to the thermoplastic seals. After the upgrade, the plant personnel determined the compressor flow increased 3.1% and the steam turbine driver steam consumption was reduced 2.7%. Based upon this, the plant easily decided to upgrade the other six candidate compressors that would be opened during the major turnaround in March of 1999. The compressors upgraded include: the first two cases of the charge gas train (first three compression stages, figure 3), the two propylene compressors, the ethylene compressor, and the purge propylene compressor.

Three compressors not upgraded at that time where the last stage of the charge gas, which had abradable seals running against rotating teeth, and the two methane compressors that were being considered for replacement or major rerates. Based upon the success of all of the other compressors upgraded and considering some issues experienced by DuPont in the past with the abradable seals in the 4th stage charge gas compressor; the plant decided to go ahead and remove the teeth off the last charge gas compressor and upgrade with thermoplastic seals. These seals were installed in July of 2005 and spares supplied in January of 2006.

Results

Often it is difficult to accurately determine the true impact of a seal upgrade project. However, by carefully analysing all factors DuPont was able to estimate the following (attributed to the thermoplastic seal upgrade project):

• 7% reduction in steam flow to the ethylene driver.
• 17% increase in head coupled with a 5% gas flow increase accompanied by a 5% increase in motor power consumption with the purge propylene train. Overall an efficiency gain even though the motor draw did increase.
• 9 to 16% increase in flow with the propylene compressor coupled with an 8% speed increase and a 4% steam flow increase. (Note: due to the seal problem mentioned earlier only a fraction of the seals were upgraded.)
• 14% flow increase in the charge gas train with a 5% steam flow increase.

Experience to date

As outlined above DuPont installed Duratron PAI seals in the charge gas booster compressor in 1997. Based on this success, DuPont installed Duratron PAI seals in the 1st, 2nd and 3rd stage charge gas compressors, the high case and low case propylene compressors, the ethylene and the purge propylene compressors during the 1999 turn around (TA).