Impact on energy savings and CO 2 emissions on heat exchangers used in Study A * **
300
OHTC plain tube OHTC with Turbotal
250
With Turbotal
Gain on energy recovery (Gcal/yr) Gain on energy recovery (TOE/yr)
18,200
200
1820
Energy savings
1092 k€ 5,460 546 k€
150
Gain on CO2 emissions (tons first yr)
Reduction in CO 2 emissions
100
Table 4
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0 100
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300
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700
Day
days for bare tubes to 820 days with the rotating device. The fouling mitigation allowed improved fouling rate con- trol and, consequently, control of heat exchanger perfor- mance and pressure drop related to the fouling layer, even though no direct pressure drop measurement was available on these four exchangers. A payback analysis was done on this application to evalu - ate the energy gains (see Table 4 ) compared to the Turbotal cost installation, which was in the range of €130,000. The payback calculated by considering only the cost of energy and the gain on CO2 emissions was about one month. However, some other sources of savings should also be considered, such as reduction of maintenance cost (avoid- ance of mechanical cleaning) and production losses (reduc- tion of throughput during partial shutdown for cleaning). Case B results The trend presented in Figure 5 shows successive runs during which the duty (blue trend) was plotted. The refer - ence run, bare tubes, started in November 2014. The aver - age duty from 30/11 to 22/04 was roughly 36 GJ/h. The duty then decreased from roughly 36 GJ/h to 22 GJ/h by 28 November 2015, for an average of 30 GJ/h over the entire reference run. The drop in duty was about 40% in one year, even though the flow rates on tube and shell sides remained very sta - ble and close to the design case. The flow rate across the heat exchangers remained close to the design value, which
Figure 4 Trend of OHTC for both cases with (red) and without Turbotal (blue) in the same flow conditions
a shutdown and mechanical cleaning were required to recover heat transfer on these exchangers. The comparison of the first six months with the Turbotal rotating device highlighted the direct benefits that are sum - marised in Table 4 on heat recovery in the range of 1,092 k€. There was also a significant reduction in the CO2 emis- sions from the furnace, about 560 tons of CO2 . Depending on the location, these emissions can be subjected to taxes at different rates over the world (CO2 emissions are being taxed at 100 €/ton in Western Europe.) In comparison, the run with the rotating device lasted 820 days of continuous operation. The SOR was typically with an OHTC of 270 kcal/h.m² °C, which dropped slowly to 150 kcal/h.m² °C within 300 days and remained in the range of 150 to 200 kcal/h.m² °C depending on the flow conditions. This phenomenon is due to the fouling mitigation during the run. The Turbotal rotating device significantly reduces the fouling rate but cannot prevent fouling deposition from occurring. Some previous work identified that fouling resist - ance with the rotating device ends up with an asymptotic profile corresponding to the distance between the tube wall and the rotating device. 4 Run lengths were multiplied by a factor of four, from 183
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Spirelf installation
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Duty design as per datasheet
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01/11/2014 10
0
28/08/2015
23/06/2016
13/02/2018
19/04/2017
Figure 5 Trend of exchanger duty (blue) equipped with Spirelf vs crude flow rate (red) and bottom pumparound flow rate (green)
44
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