I was extremely interested to read the article on the Severnside works (NCE 5 July), having just been through a similar enhancement process on an overseas project.
Mouchel designed and managed the complete rehabilitation of a similar sized and aged Prill tower at a fertiliser plant in the Middle East. Here the inside of the tower had been attacked by the ammonium nitrate. Also the external faces had suffered from a combination of harsh environmental conditions and higher than predicted imposed stresses from thermal loading.
Many large cracks were full depth allowing ammonium nitrate to visibly escape .
Our solution included breaking out the corroded sections and repairing with sprayed concrete. To strengthen the tower against imposed thermal loading - and in many areas to reinstate structural integrity - Mouchel devised a solution of bonding carbon fibre plates around the periphery of the tower.
The repair was successfully carried out during a 25 day annual shutdown. The tower is now being painted externally to further enhance long term durability.
Steve Godman, project manager, Mouchel Consulting, West Hall, Parvis Road, West Byfleet, Surrey, KT14 6EZ