Practical applications and optimum gas flowrate for maximum power saving

6 Practical applications and optimum gas flowrate for maximum power saving 

Drag reduction offers the possibility of lowering both the pressure drop and the power requirements in slmry pipelines. Air injection can be used, in practice, 

Air injection can also be beneficial because it may be easier to re-start pumping after a shutdown as the pipe will not be completely full of slurry. On the other hand, if the pipeline follows an undulating topography, difficulties can arise ftom air collecting at the high points. 

However, additional energy will be required to compress the air to a pressure in excess of the upstream pressure. Thus, the circumstances under which there will be a net saving of power for pmnping will be strongly dependent on the relative elficiences of the slurry pirnip and the gas compressor, and on the specific plant layout. Dziubinski and Richardson [1985] have addressed this problem and the salient features of their study are siunmarised here. They introduced a power saving coefficient, defined as 

Air is injected into a 50 m long horizontal pipeline (of 42 mm diameter) carrying a china clay slurry of density 1452 kg/m. The rheological behaviour of the slurry follows 

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