The aim of the project was about using the waste heat content of the exhaust air from an installed steam boiler within a complex steam generation system: an aged two (2) steps heat recovery system for boiler feed water and warm water was installed but not corresponding to best efficiency expected. Some pitting corrosion occurred also, which let to high operational costs and several maintenance unexpected failures, sometime equipment shutdowns, where the heat recovery was not in use. There was a decrease of the heat exchange surface and therefore a high decrease of the overall system efficiency.
The main pitting damage occurred around condensation temperature of HCl at approx. 110°C, which caused very high pitting corrosion and damage to the 2nd step of heat exchangers in the old system - with heat exchange from 120°C down to 80°C exhaust gas temperature. The new system was designed and installed with a single step concept: an inlet temperature of 205°C, using the total heat exchange down to 120°C for boiler feed water without condensation of HCl. The higher exhaust gas temperature currently leads to a much better corrosion resistance with lower operational cost and much more efficient heat recovery. The picture below visualizes the energy saved with heat recovery comparing the old system against the new installed single step mode.
The exchange of the old steam boiler economizer with a state of the art economizer reduced energy consumption by approximately 1%, reduced CO2 emissions by 400t/year. Yearly cost saving of natural gas was also decreased by a significant amount in favor of reduced operational cost for the Client on site.