For some difficult TBM project, we may get somewhere we do not like, too much solids, too high mud density, then the dewatering unit is not working so efficienly. Though filter press is a good option, here we can have some improvent. To make the dewatering unit working as we wanted.
If you add a smaller decanter centrifuge (Let's say 40m3/h) to treat the drilling mud without polymer before feeding to the exisiting centrifuge with poleyer, it can reduce the mud density from 1.7 SG to around 1.2 SG
Then you treat the 1.2 SG mud with your exisiting centrifuge to get clean water which is around 1.0 SG. From our engineers experience, you can get the centrifuge capacity from 8 m3/h to around 20 m3/h for getting clean water in this case, maybe more by increasing the speed and differential speed. And you can save a lot on the volume of the polymer.
Normally, for geting clean water, our client will treat the mud by mechanical method first to get the desity down, that means to get most of the solids out from the mud, for the ultra fine solids, they use polymer to do dewatering.
Since the mud is still heavy with 1.7 SG after the desander treatment. So we suggest to put a centrifuge to reduce the density of the mud to around 1.2 SG before feeding to the decanter centrifuge with polymer.
That means, first phase is mechnical only, second phase is chemically enhanced centrifuge treatment. This way will increase the total capacity of the system to at least double capcity of existing unit.
And also you can save the polymer and chemicals.
Moreover, the mechanical treatment centrifuge, you only need to use a small centrifuge with cheap price, not the big bowl, to match the chemical enhanced phase separation.
Another way is to increase the mixing time of the chemical with the mud by extend the outside feeding tube of the centrifuge before feeding to the centrifuge.
And also increase the bowl speed to around 1800- 2000RPM and increase the differential speed to around 30 RPM, anyway, it should be within the limit of the centrifuge not to get the centrifuge overload.
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Published: 01 February 2015