How to calculate the fuel flow using the thrust specific fuel consumption?
As Peter Kämpf said, the units should be in kg per N per second/hour.
In your case assuming it's a typo, and assuming the formula is $\text{C}_\text{T}$ = 0.7 kg/h per Newton.

Then in static condition, 

Fuel flow $= 12 \cdot 10^3 \cdot 0.7 \cdot \frac{1}{60} \frac{kg}{s}$

gives 140 kg of fuel per second. Seems correct.

As a side note TSFC is not a fixed value but a variable of velocity as well. So have to make sure this CT is for static condition.