Management of Fouling in Crude Oil Preheat Trains
of a PHT in Figure 3A, which features three parallel crude streams and three hot streams initially providing a heat recovery of 28MW. The crude flow splits can be varied and this needs to be included in simulation tools investigating different cleaning schedules, as the heat loads need to be adjusted in order to compensate for an exchanger being offline for cleaning. Simulators such as smartPM™ include this facility. Figure 3B compares the performance of the network, with dynamic fouling, for the base case (no cleaning, no modification) and three mitigation options. In the absence of mitigation, the CIT drops
over 30K over three years, with increased CO2 emissions from the furnace of 10,000 tonnes.
Figure 3B shows that cleaning units A and B every six months gives an improvement in performance. When an exchanger is taken off-stream for cleaning, the CIT drops. This drop can be minimised by controlling the flow splits. Fouling in these units is still severe and this remains the case even when the cleaning schedule is optimised. The optimal schedule requires extended simulation, but this can now be performed on a desktop PC.5
The repeated drops in CIT for
this case indicate regular cleaning, which is unlikely to be attractive to the refinery operator and highlights the need to reduce the
1.
IHS ESDU, Energy, Emissions, and Efficiency: How to address heat exchanger fouling to reduce energy and maintenance costs while improving plant performance, PennEnergy, Webcast, 2011. Available at:
www.pennenergy.com/index/research-and_data/ webcasts/webcast-display/4560536008/ webcasts/pennenergy/live-events/
energy_-emissions.html (accessed 25 May 2011). 2. 3. 4.
rate of fouling in the prime actors; units A and B. Investigation of the design of these units indicated that they were designed with pinch technology approaches; the crude flowed on the shell-side with low velocities and high surface temperatures. Modelling the units reconfigured with the crude on the tube-side indicated that the original performance could be met by the modification shown in Figure 3C. The simulated performance shown in Figure 3B is superior to the other options and this case can be taken forwards for comparison with the remaining option, namely the use of antifouling chemicals.
Conclusions
It is unlikely that fouling can be eliminated from crude oil distillation unit PHTs, particularly given the ‘dirtier’ nature of crudes being processed. Managing fouling in these networks requires a working knowledge of their fouling behaviour: data reconciliation of plant operating data can be used to construct a fouling map of the system and generate information on fouling rates. This information can be used in the software tools which have been developed to identify and compare optimal mitigation options such as cleaning or heat exchanger redesign. n
Yeap BL, Wilson DI, Polley GT, Pugh SJ, Retrofitting crude oil refinery heat exchanger networks to minimise fouling while maximising heat recovery, Heat Tran Eng, 2005;26(1):23–34.
Wiehe IA, Kennedy RJ, The oil compatibility model and crude oil incompatibility, Energ Fuel, 2000;14(1):56–9.
Joshi HM, Shilpi NB, Agarwal A, Relate crude oil fouling research to field fouling observations, Presented at: the 8th International Conference of Heat Exchanger Fouling and
Cleaning, Schladming, Austria, 14–19 June 2009.
5. Ishiyama EM, Paterson WR, Wilson DI, et al., Scheduling cleaning in a crude oil preheat train subject to fouling: incorporating desalter control, Appl Therm Eng, 2010;30(13):1852–62.
6.
Ishiyama EM, Pugh SJ, Paterson WR, et al., Management of crude preheat trains subject to fouling, Presented at: Heat Exchanger Fouling and Cleaning IX, Fodele Beach, Crete, 5–10 June, 2011.
Mission Critical Equipment
Air Cooled Heat Exchangers, Cold Boxes, and Brazed Aluminum Heat Exchangers for the gas processing industry.
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