I agree, the algae is going to use up CO2 whether you pipe it in or not. That just seems like a waste of money, unless the accelerated algal growth (and thus, the yield over time) is worth the expense of the infrastructure.
You know what “carbon sequestration” is? And how the eco-nuts love it?
They Valcent add this to their algae proposals to generate more interest. Of course it can be done in a laboratory and it probably accelerates algae growth. But this sounds impractical on an industrial scale.