Designing heat exchanger for enhancing heat transfer of slurries in biogas plants

• Heat transfer geometries with enhanced performance for the slurries with high viscosity can improve the net raw biogas production in bio-methane process. In this study, the rheological properties of different slurries were tested, correlated and implemented to computational fluid dynamics (CFD). CFD was then used to screen a new geometry based on the twisted tube combined with mechanism study, and experimental testing was conducted for verification. It shows that the twisted hexagonal tube (THT) has the highest performance. The mechanism for enhancing the heat transfer with THT was mainly due to the effective shear rate. Furthermore, the waste-heat recovery with the THT heat exchanger in biogas production was estimated quantitatively and compared with the normal heat exchanger and scraped-surface heat exchanger (SSHE). Compared to the normal heat exchanger, for THT, the increase of net raw biogas production δNRBP can be up to 17%, while it is only up to 8.53% for SSHE. Besides, the external heating up processes with THT and normal heat exchanger were studied to estimate the heating time for different temperature fluctuations and power requirements of boiler. It is found that the process with THT can save 25-38% heating time for the anaerobic reactor compared to the normal heat exchanger. Therefore, designed THT heat exchanger is promising, and the developed methods can also be beneficial for studying other heat transfer processes.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Energiteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Energy Engineering (hsv//eng)

Nyckelord

rheological properties

CFD

twisted hexagonal tube

scraped-surfaced heat exchanger

waste-heat recovery

external heating

Energiteknik

Energy Engineering

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