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Project manager: Prof. Dr.-Ing. Carlowitz
Funding period: 03/2015 - 09/2017
Funding body: DBU
Objective and reason for the project
To ensure the best possible image depth and brilliance and thus high quality standards, organic solvents (mainly ethyl acetate and ethanol) are predominantly used in flexographic packaging printing today. These evaporate after the ink has been applied and are fed to a downstream treatment system as waste gas (exhaust air) together with ambient air drawn in. From solvent mass flows of one ton per hour, it is now economically viable to adsorptively remove the organic substances from the exhaust air, desorb them with water vapor and condense them. After a costly reprocessing process - due to the high water load - it can then be used again. Below a solvent mass flow of 1 t/h, the use of regenerative thermal post-combustion plants, which oxidize the solvents to predominantly carbon dioxide and water and thus detoxify them, is state of the art today.
The aim of this project is to develop a recovery process for solvent mass flows of less than 1 t/h (mass flow range 0.2...0.8 t/h), which on the one hand is economically interesting for flexographic packaging printing companies and on the other hand significantly reduces total carbon dioxide emissions. It should be noted that the production of one kilogram of ethyl acetate, for example, generates just under 2.9 kg ofCO2 plus around 2 kg ofCO2 during oxidation in a regenerative thermal post-combustion plant, so that a considerable reduction in carbon dioxide emissions can be expected if the solvents are recovered.
The novel concentration process, which is to be developed for the relatively high solvent loads in the exhaust air from flexographic packaging printing and is not yet state of the art, is based on scrubbing the exhaust air using high boilers (Genosorb 1843) and desorption
- either up to 130 °C using inert gas at ambient pressure or
- at a lower temperature and negative pressure,
so that the high temperatures of > 200 °C required in the case of an adsorption process (using zeolites or activated carbons) for inert gas desorption (without water vapor!) are avoided and increased acetic acid formation (from ethyl acetate) is largely prevented, even under the influence of catalytic effects by the adsorbent. The subsequent condensation is planned in three stages: Firstly, it is cooled to around 50 °C and Genosorb is separated and returned to desorption. Then water entrained during absorption (origin: ambient air) is separated with lower solvent proportions at temperatures above the freezing point of water. Finally, the condensation of mainly organic solvents with very low water content takes place at sub-zero temperatures. The water-rich fraction is planned to be processed by distillation with subsequent membrane drying, while the predominantly solvent-containing fraction only requires membrane drying. The recovered solvents are then to be used (again) to adjust the viscosity of the printing inks.
Presentation of the work steps and the methods used
The challenge of the project lies mainly in the relatively complex system technology of the overall process, for the experimental validation of which the pilot plant created as part of a preliminary R&D project (aim: development of an efficient washing stage with a powerful demister) is to be supplemented in terms of plant technology, designed to be transportable and tested in a flexo packaging printing plant in the bypass in order to obtain meaningful findings for the project planning of main designs.
With regard to the methods, an investigation with standard analytics (temperature, FID, particle measurement technology) will be carried out to evaluate the separation performance of the new module. Further analyses are planned to analyze the quality of the recovered solvents (GC analyses).
The NALF project is a DBU-funded third-party project with the companies AWS Group AG, Clausthaler Umwelttechnik-Institut GmbH, Labor Ilgen and Arwed Löseke Papierverarbeitung und Druckerei GmbH.