Closing second chimney pipe

[Harv]

I have a chimney with 2 flues, one is used for a fireplace on the main floor. In my basement, the back side of the second flue has a 6" clay pipe which been used as a vent for a clothes dryer. (I have now re-routed the dryer vent and hired a certified chimney cleaner to remove all lint from this flue.) On the front side of the chimney wall in the basement the builder created a second 6" clay pipe in this same flue about 12" lower than the pipe for the old clothes dryer vent, This lower pipe is ideally situated for a wood stove on a cement floor against a cement block wall in the basement. I would like to close this upper 6" pipe and install a wood stove in the basement using the lower 6" clay pipe. What is the safest and most cost effective means of blocking this upper clay pipe?

 

[bholler]

I have a chimney with 2 flues, one is used for a fireplace on the main floor. In my basement, the back side of the second flue has a 6" clay pipe which been used as a vent for a clothes dryer. (I have now re-routed the dryer vent and hired a certified chimney cleaner to remove all lint from this flue.) On the front side of the chimney wall in the basement the builder created a second 6" clay pipe in this same flue about 12" lower than the pipe for the old clothes dryer vent, This lower pipe is ideally situated for a wood stove on a cement floor against a cement block wall in the basement. I would like to close this upper 6" pipe and install a wood stove in the basement using the lower 6" clay pipe. What is the safest and most cost effective means of blocking this upper clay pipe?

Firebrick and refractory mortar.