A global printer had excessive energy use and as a result suffered the negative cost and environmental impact. The factory has multiple printing lines where solvent-based inks are dried using warm air dryers. Exhausts from the dryers are destroyed in a regenerative thermal oxidiser protecting the environment.
Benchmarking – The existing printing process and drying systems were analysed and mapped to build a picture of how the solvent loading, airflows and energy interacted. The existing gas burner heating systems, dryer setup and balance were all evaluated. To quantify the analysis, site measurements of airflows and solvents were taken.
Solution
Due to the complexity of the system the solution was multi-dimensional.
Process Optimisation – Firstly, the print dryers air balance was optimised, and heat source switched to an indirect thermal oil system. This optimisation reduced the quantity of fumes sent to the oxidiser by 60%, reducing operating costs at the oxidiser. By reducing the air volumes, the solvent concentration was increased, enabling the thermal oxidiser to operate without support fuel, and providing the added benefit of waste gas heat recovery.
Optimisation of the dryers cut natural gas use by 1.1 million kWh/year
Energy savings at the thermal oxidiser saved 2.5 million kWh/year
Heat Recovery – The excess heat from the thermal oxidiser was captured, through the installation of an indirect thermal oil heat recovery system. The thermal oil system was then used to heat the print dryers, delivering further savings.
Heat recovery from the thermal oil system saved 320,000kWh/year
The total solution reduced carbon emissions by 752 tonnes of CO2e.