Operating FGD chimneys as “wet stacks”, without reheat, is economically attractive but it carries the risk of stack liquid discharge (SLD), also known as “spitting”. This phenomenon can be highly problematic, with acidic droplets raining down on the environment surrounding the power station. In serious cases, such SLD can damage private property such as cars and crops, as well as sensitive equipment within the power station itself.
According to the “EPRI Revised Wet Stack Design Guide”, chimneys lined with certain borosilicate lining systems can be operated safely, without spitting at velocities up to 18.3 m/s. The NTPC Barh Unit 1 power station in Bihar state will be using its existing chimney as an FGD Wet Stack after commissioning of its FGD system, being installed by BHEL. The flue gas velocity in this chimney however will be significantly higher than the recommended 18.3 m/s.
The supplier of the chimney lining system to BHEL, Hadek, offers a unique patented solution for this chimney, to safely handle the wet flue gas stream at these greater flue gas velocities. Hadek is the global supplier of the Pennguard lining system manufactured in USA and has supplied Pennguard linings to more than 142 power station chimneys worldwide. As per Mr Albert de Kreijj, Sales Director of Hadek, their unique lining system pattern has been tested for handling flue gas velocities up to 22.9 m/s and will help to prevent stack liquid discharge (“spitting”) from this chimney flue.