Elimination of waste in flexographic colour printing

An innovative system for the treatment of wash water from the flexo printing process was introduced in a corrugated board plant. Evaporation is used to separate the water from the solids. The purified water is then used in the production of corrugated board.

Initial situation

The Delmenhorst plant belonging to Klingele produces corrugated board from paper which is then used to make packaging material.

Once the corrugated board has been printed, the flexographic printing press needs to be cleaned of any residual ink. The resulting wastewater contains substances such as copper, petroleum hydrocarbons and adsorbable organic halogens (AOX), and is therefore classified as waste requiring special supervision. The liquid waste was originally disposed of by a waste management company, a costly process due to the large quantities of water involved.

The aim of the project was to introduce a process with which the ink wastewater generated during printing could be treated internally.

The new process was required to meet the following criteria:

• The purified wastewater was to be reused in the production process
• No chemicals were to be used
• Energy consumption was to be as low as possible
• The wastewater treatment was to be economically viable

Technical solution

The ink wastewater treatment selected was developed by Jaske & Wolf Verfahrenstechnik, originally for another area of application.

The water is separated from the ink wastewater by evaporation, leaving behind industrial water and a solid. The energy used is recovered during the process and reused several times.

The ink wastewater treatment facility was adapted to the Delmenhorst plant standards when first put into operation and then refined until it was ready for series production.

Findings

The new process has reduced the quantity of ink wastewater requiring disposal at the Delmenhorst plant by 4,000 m³ a^-1.

The purified water is fed back into the production process and used in its entirety to make the glue used in the production of corrugated board.

Supplying hot water to the glue manufacturing process reduces the amount of electrical energy required to heat the water.

The resulting solid matter has a high calorific value and is currently fed into a waste incineration unit, where it is used to generate thermal energy. The high calorific value significantly reduces the cost of disposal.

It was possible to reduce the chemicals required to a small amount of defoaming agent only.

Conclusions
The process is of interest to any paper mill with similar wastewater problems, and to printing plants and paint shops.

Source: Final report

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