resulted in a lower coil inlet temperature (CIT) at the fur- nace and extra consumption of fuel to compensate for this loss of preheat. The Spirelf vibrating devices were implemented during a cleaning shutdown, and the performance of the exchangers was represented on the same trend. After the installation on 29/11/2015, the average duty was 37 GJ/h, and it was perfectly maintained at this level until 19/04/2018, the date of the turnaround of the unit after 872 days in operation. Over the entire run with the vibrating devices, the crude flow rate was at design value. However, the performance of the heat exchangers was limited by the regulation of the unit operating on the shell side flow (specifically the bottom pumparound flow rate). A few unit upsets occurred, but the exchangers were never opened, and performances ben- efited from occasional unit recirculation, such as October 2017. The implementation of Spirelf in these heat exchangers considerably increased the run length from one year to two-and-a-half years. Additionally, there was a significant increase in duty, averaging at 25% and equivalent to the firing of more than 100 tons of fuel gas per month. The savings on fuel consumption over the first year amounted to 872 k€, and the benefit related to avoided CO 2 emissions was in the range of 436 k€, as summarised in Table 5 . Case C results The trend presented in Figure 6 shows a reference run from November 2016 to October 2020. From November 2020, a new run started, and the OHTC of the six exchangers, including the three equipped with Fixotal (red), was plotted. The trend in blue is the OHTC of the train’s first six heat
Impact on energy savings and CO 2 emissions on heat exchangers used in Study B * **
With Spirelf
Gain on energy recovery (Gcal/yr) Gain on energy recovery (TOE/yr)
14,500 1,450 872 k€ 4,350 436 k€
Energy savings
Gain on CO 2 emissions (tons first yr)
Reduction in CO 2 emissions
Table 5
exchangers (HXs), and the green trend is the crude flow of the unit showing operating condition sustainability. The trend presented in Figure 7 shows the duty comparison between the last six HXs (red) and the first six HXs (blue) between the two consecutive runs. • SOR : From the reference run, it was identified that within six months, the OHTC of the last six HXs (red) dropped to the level or below the first six HXs (blue), showing the large impact of fouling on the performance of the exchangers. The implementation of Fixotal tube inserts to promote shear stress in the last three HXs was visible from the SOR, with an OHTC 26% higher than the reference run over the first three months. This was a consequence of the higher turbulence generated on the tube side, which is visible in the duty exchanged in Figure 7 , with a +8.3% increase compared to the reference run. • Until chemical cleaning: From the reference run, after six months, the performance of the last six HXs contin - ued declining to an OHTC of 200kJ/h.m² °K until a chem - ical cleaning (vertical dotted line) was performed in late October 2018 (two years of operation). The comparison with the Fixotal run showed that the
SOR Nov 2016
SOR Nov 2020
1600.00
600.00
1400.00
500.00
Chemical cleaning
1200.00
Chemical cleaning
400.00
1000.00
FIXOTAL installation
800.00
300.00
600.00
200.00
400.00
100.00
200.00
0.00
0.00
Date
A-F heat transfer rate kJ/)hr.m .K)
G-L heat transfer rate kJ/)hr.m .K)
CRD charge kL/h
Figure 6 Trend of OHTC with Fixotal equipment on half of the exchangers (red) Study C
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PTQ Q1 2025
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