The Nexus – Sustainability through integrated resource management

The Nexus approach in the process industry in times of energy turnaround

What is being implemented only slowly or only through the pressure of statutory regulations at local authority level has long since found its way into many production sites of process-oriented industries. Rising raw material prices and costs in wastewater disposal make the treatment and reuse of process water and process wastewater and the recovery of auxiliary and process materials an economically attractive challenge for companies.

In the wake of the energy revolution and the expansion of decentralized electricity production from renewable energies, the initial situation is changing: Whereas electrochemical processes – above all for the chemical synthesis of basic chemicals – were previously considered uneconomical because of their power requirements, they are gaining in importance in times when electricity from fluctuating sources (wind power and photovoltaics) which is not needed at the moment is driving down prices on the electricity exchanges.

Research facility with water.
© aaltair / shutterstock
Research facility with water.

Linking renewable power generation with industrial value creation: chemically storing or directly using excess electricity

It is crucial that electrochemical and electrophysical processes – just like the various energy storage systems – can contribute to grid stabilization as current collectors. “We therefore design our electrochemical and electrophysical cells to be as flexible as possible and implement them in a plant system in such a way that they can be operated as a function of the load on the power grid,” according to Egner’s explaination of the approach at IGB.

In addition to such flexible electricity utilization models (as well as batteries and pumped storages), sufficient long-term chemical storage facilities are required to balance the fluctuating generation of electricity from wind and solar energy. Biogas, purified into methane, can also play an important role in this context. It not only builds a bridge to the mobility sector but can also be fed into the natural gas grid as a long-term storage or converted into methanol as a material storage. Furthermore, new thermo-chemical sorption heat storage systems for the lossless long-term storage of heat developed at IGB make even the storage of electricity in this form efficient.

Resource efficiency through water reuse and resource recovery

© Rafael Krötz/Fraunhofer IGB
Free-flow electrophoresis prototype.

In contrast to municipal wastewater treatment, pollution in industrial process and wastewater is largely determined by the industry and the specific manufacturing process. In order to reuse process water in the sense of recycling, the impurities must be removed with as little energy and material expenditure as possible. “In addition to mass flow management and the selective detection of contaminations, this requires a tailor-made integrated process technology for the specific treatment of waste,” Egner explains.

For this purpose, Fraunhofer IGB has established various electrochemical and electrophoretic processes with which auxiliary material and resources contained in water can not only be removed, but also separated in a recyclable form. In this way, salts can be recovered by electrodialysis or capacitive deionization, and metal ions can be converted into high-purity fractions in the case of high yields using free-flow electrophoresis. The advantage of electrochemical and electrophoretic processes: They work without any additional chemicals.

Such production-integrated water recycling also makes it possible to achieve greater independence from natural water resources and therefore allows for production at locations with less water resources – right up to total independence from natural water resources through Zero Liquid Discharge.

Power-to-Chemicals – modular, flexible, energy-efficient

Fraunhofer IGB is developing catalysts and suitable membranes, processes and apparatus with current-controlled mode of operation for the electro-synthetic production of basic chemicals as an option for the direct compensation of an oversupply of electricity. In the Fraunhofer lighthouse project "Electricity as a raw material", for example, IGB is developing a single-stage process for the electrochemical production of ethene in just one process step. In the EU project Celbicon, methanol is produced from CO2 by electrocatalysis, which is used as a substrate for fermentation. An electrolysis cell, in which hydrogen peroxide can be produced only from water and air using electrical energy, is already available as a prototype at IGB.

© Fraunhofer IGB
Electrochemical cell for CO<sub>2</sub> reduction.