PTQ Q2 2023 Issue

Figure 3 Spirelf technology device in a cut tube

of the device, leading to an 80% increased heat transfer coefficient on the tube side compared to bare tubes. The slope of the preheat decrease is almost three times slower with Turbotal technology compared to bare tubes. This phenomenon is due to the fouling mitigation during the run. The technology significantly reduces the fouling rate but cannot eliminate the fouling deposition from occur - ring. Previous studies detected that the fouling resistance generates an asymptotic profile corresponding to the dis - tance between the tube wall and the device. A payback analysis has been performed on this applica - tion to evaluate the energy gains compared to the cost of the device and installation. An average gain of more than 10°C was achieved during the first year, leading to a gain in energy of €1.4 million to compare with an investment in the range of €100,000.

Exchanger bundle with Turbotal

The calculated payback is in the range of one month when factoring only the cost of energy. However, other cost sources would have to be considered, such as reduced maintenance cost (avoided mechanical cleaning), production losses (throughput reduction during partial shutdown for cleaning), and CO 2 emissions costs from the furnaces (around 100 €/t today in Europe). Factoring in these additional cost reduc - tions results in an actual payback period of less than one month vs just from energy savings at the furnace.

Heat exchangers design and operating conditions

Performance of the heat exchangers improved considerably and stabilised

Position in the train

Just before the furnace 1 branch of 2 bundles

Bundle number

Tube number/bundle

710

Tube length

9,144 mm

OD/BWG

3/4in/14

conditions compared to before the installation of Spirelf technology

Product tube/shell side Flow rate (tube side) Flow velocity (tube side)

Crude/atmospheric residue

309 t/h 1.7 m/s

Tube insert

Proprietary Spirelf technology

Replacement frequency

Every 3 years

Study B – Extensive run duration with Spirelf technology Spirelf technology is a vibrating device fixed on both tube ends by a fixing wire (see Figure 3 ). This system is also a continuous online cleaning device whose purpose is to reduce the fouling layer on the tube walls by means of mechanical effect. The technology uses the energy of the flow running in the tubes to convert it to vibrations of the device both radially and longitudinally. The extra pressure drop from the Spirelf is minimal and allows for a potential run duration of up to six years. The last pair of heat exchangers just before the furnace was experiencing severe fouling over less than one year. The two heat exchangers were equipped with Spirelf tech - nology and operated in the same range of original process conditions from Table 2 . The monitoring of the performance was then compared with the previous data; the compara - tive trends of the heat transfer coefficients of each tube bundle and the crude flow rate can be seen in the results section (see Figure 4 ).

Table 2

600

U Clean as per design

Spirelf installation

500

400

300

Throughput as per design

U Clean

U E12A U E12B

Crude feed

2000 400 600 800 1000 1200 1400 1600 1800 0 200 Days 200

Figure 4 Trend of crude feed and OHTC for both tube bundles compared to previous run with bare tubes

94

PTQ Q2 2023

www.digitalrefining.com

Powered by