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Energy Efficient Coil Coating Process

Periodic Reporting for period 3 - ECCO (Energy Efficient Coil Coating Process)

Berichtszeitraum: 2021-04-01 bis 2022-07-31

Coil coating is a continuous process for providing coating to a metal strip. In this process, a paint, mainly consisting of pigments, chemical crosslinkers and solvents, is applied. The paint is afterwards dried while the solvents evaporate. In the conventional process the required heat is provided through convective heat transfer using hot air. In order to prevent the creation of an explosive atmosphere in the process, operation at a solvent concentration below the lower explosion limit by using an excess amount of air is inevitable. Prevention of VOC emission entails recovery or thermal decomposition of the solvents, which is technically complex and expensive.
In the ECCO project the proof of concept of a novel curing oven has been performed in a pilot scale coil coating line. In ECCO, the curing oven is operated at elevated solvent concentration which allows the direct utilization of solvents as a fuel for heat generation. The oven system is separated in two sections: The radiant burner section, where intense radiation in the IR-spectrum is emitted at high temperatures resulting from combustion inside of a ceramic porous structure, and the curing oven section which is operated over the upper explosion limit or, in other words, below a critical oxygen concentration. The prevention of a thermal decomposition of the solvent loaded atmosphere at high temperatures is ensured through separation of the two oven sections by an IR-transmissive material. Starting from previous activities at TRL 4, an interdisciplinary approach was followed, based on advanced-materials, combustion technology and prediction tools for system design/optimization, with active participation of key industrial stakeholders, to achieve TRL 6 and realize a prototype curing oven at industrially relevant size and environment. ECCO proposes an oven concept which leads to a drastically reduced size and increased energy efficiency as we as well a higher production flexibility due to a fuel-flexible, modular and potentially energetically self-sustainable process. In comparison to existing conventional convective curing systems, ECCO presents a less energy demanding, environment-friendly and economical technical curing oven concept.
The novel curing oven system allowing safe operation with an oven atmosphere below the limiting oxygen concentration is the core development of the ECCO-project. In this context several solutions have been developed which can be categorized into technical solutions for components and materials.
The solution for the operation below the limiting oxygen concentration is part of the developed ECCO concept. In this concept flue gas from the radiant burners is directed into the curing oven where it is mixed with solvent vapors. The gaseous mixture is extracted from the curing oven section and fed to the burners where the solvent vapors are used as fuel. The flue gas extracted from the curing oven allows to operate the porous burners with less excess air without overheating resulting in a reduced oxygen concentration in the flue gas. On the component level, besides the radiant burner section and the curing oven section, the technical solution for the prevention of the curing oven section from ambient air entrainment based on pre- and post-inertisation chambers utilizing the flue gases from the burners and an active suction system have been developed.
The developed material solution for separating the ECCO curing oven in a radiant burner section and curing oven section bases on IR-transmissive glasses. For the glass separation different materials have been deeply investigated regarding their capability to maximize the transmissivity of the IR-radiation and withstand the thermal stresses during start-up, operation and shut-off in the oven environment. Catalytic coatings avoiding the deposition of carbonaceous substances on the IR-transmissive material at high temperatures have been developed. For the porous burners, advanced SiC based composite materials have been developed and tested under operating conditions exceeding the maximum operating temperature of current products. Detailed chemical kinetic reaction mechanism based on surrogate fuels for the simulation of solvent combustion is developed and validated. An experimental facility for the characterization of solvent combustion in structured porous media is developed.
The ECCO oven has been fabricated and been implemented into a demo scale batchwise processing coil coating line. Several Coil have been coated with primer, top- and back coating formulations. The results show comparative results to existing technologies. ECCO sucessfully provides the proof of concept of a novel technology for drying and curing in steel coil coating.
The ECCO solution significantly reduces the equipment size to production-capacity ratio. In comparison to the conventional system and assuming the same production-capacity, the ECCO process allows for a volume reduction of 70% for the curing oven. As a consequence of the equipment size to production-capacity ratio improvement, there is substantially positive impact on the compactness and modularity of the system.
The ECCO concept results to this drastic reduction in energy consumption of significantly over 50% in comparison to average even new installations and 40% in comparison to the best installations. The reduction in energy consumption is proportionally associated to a reduction in the natural gas resources consumption. Additionally, the total recovery of solvent vapours from the drying/curing process demonstrates a potential for reduction of waste production of 100%, since the solvent vapours are efficiently used as fuel.
The ECCO process shows significant benefits concerning a reduction in Capex and Opex costs. The ECCO process results in a Capex reduction of at least 40% and an Opex reduction of at least 40% and in most cases significantly over 50% for the curing oven operation pending on the type of conventional technology to be compared with. Concerning the reduction of operating costs, these are mostly associated to the energy consumption of the curing oven in comparison to conventional curing ovens operating with thermal or recuperative incinerations and over 40% for curing ovens operating with thermally integrated regenerative thermal oxidization systems.
As a positive environmental impact of the ECCO process, the reduction of natural gas consumption is directly associated to a reduction of CO2 emissions. Additionally, the complete and clean combustion of the solvent vapours without VOC emissions can be also regarded as environmentally positive.
The technological solutions considered in the ECCO process have a strong potential for retrofitting existing coil coating production lines by increasing their compactness, modularity and flexibility.
In terms of compactness and modularity, the ECCO curing oven presents a much smaller size and avoids additional infrastructures for the incinerator system installation. In terms of process flexibility, the ECCO curing oven operation also presents strong advantages. On one hand, the
radiant porous burners can be fuelled with either solvent vapours or natural gas (or a mixture of both), which leads to a fuel-flexible process operation. On the other hand, the burner system operation concept allows for an adjustable positioning of the burner batteries, containing sets of porous burners that can be locally switched on or off.

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