Energy saving with tube inserts for heat exchangers When it comes to fouling in crude oil preheat trains, tube inserts can maximise heat transfer and reduce heat exchanger fouling, with an average six-month payback
Nicolas Aubin Petroval
R efiners face the challenge of continuously improv - ing energy efficiency and reducing CO2 emissions. The energy efficiency of refinery and petrochemical plants is strongly influenced by the efficiency of their heat exchangers. The achievable level of heat recovery that can be reached represents significant margins estimated during the plant design phase. However, reality may be completely different once fouling occurs at any stage of the process. Fouling will lead to loss of heat recovery, pressure drop increase, and throughput reduction until a maintenance shutdown becomes mandatory. The benefits of using tube insert technologies are already demonstrated in terms of increased heat transfer coeffi - cient, reduced fouling rate, and stability of pressure drop. Against this backdrop, fouling in crude oil preheat trains caused by asphaltene deposition and/or coke formation on hot surfaces will be examined in detail. In tests performed for crude oil preheat train fouling, heat exchangers forming part of preheat trains at two refineries were equipped with the proprietary Turbotal technology inserts for Study A, and the proprietary Spirelf technology inserts were equipped for Study B. Their performance was monitored over different periods, depending on the case, between two and four years and compared to the previous run durations at similar process conditions. Study A – Heat transfer enhancement and fouling mitigation with Turbotal inserts Turbotal technology is a rotating device hooked on a fixed head and attached to the tube end on the inlet side (see
Figure 1 Turbotal technology device in a glass tube
Figure 1 ). These inserts incorporate a continuous online cleaning device whose purpose is to reduce the fouling layer at the tube walls by means of mechanical effect. The technology uses the energy of the flow running in the tubes to effect a rotation of the device within the range of 1,000 rpm during the whole run duration with a limited impact on pressure drop. The final pair of heat exchangers before the furnace were experiencing severe fouling over less than one year. The four heat exchangers were equipped with the inserts and oper - ated in the same range of process conditions as previously discussed (see Table 1 ). The monitoring of the performance was then compared with the previous data. The comparative trend of the outlet temperature is presented in Figure 2 . The trend presented in Figure 2 shows an increased out - let temperature at SOR of 3°C (in clean condition). This gain is related to the extra turbulence generated by the rotation
260.0
Loss of 0.9˚C/month
250.0
With Turbotal
Heat exchangers design and operating conditions
y=-0.0276x + 246.52 R =0.6703
240.0
Position in the train
Just before the furnace 2 branches of 2 bundles
230.0
Bundle number
Bare Tube = without Turbotal
Tube number/bundle
1,164
220.0
Loss of 2.5˚C/month
Tube length
6,100 mm
y=-0.0925x + 239.94 R =0.9311
OD/BWG
1in/12
210.0
Product tube/shell side Flow rate (tube side) Flow velocity (tube side)
Crude/atmospheric residue
200.0
580/830/920 t/h
0
100
200
300
400
500
1.2 to 2.2 m/s
Number of days
Tube insert
Proprietary Turbotal technology
Replacement frequency
Every 2 years
Figure 2 Trend of feed outlet temperatures with Turbotal inserts compared to previous run with bare tubes
Table 1
93
PTQ Q2 2023
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