Conversion of sewage sludge into fuel and hydrogen

The EU project »The Demonstration of Waste Biomass to Synthetic Fuels and Green Hydrogen« (acronym: TO-SYN-FUEL) was launched on 01 May 2017. The Horizon 2020 project is led by Fraunhofer UMSICHT Sulzbach-Rosenberg, Department of Energy Technology, together with other partners.

The project has a total volume of over 14 million euros and a duration of 48 months. The project aims to show how liquid synthetic fuels and hydrogen can be produced decentrally from residual biomass (in this case sewage sludge) for the first time.

Background and motivation

Millions of tonnes of organic waste (biogenic residual and waste materials) from various sectors are today landfilled or incinerated worldwide. This leads to significant amounts of greenhouse gas emissions and corresponding air, soil and water pollution.

In the TO-SYN-FUEL project, such waste materials from biomass (e.g. organic waste such as biowaste, anaerobic digestate and dried sewage sludge) are to be disposed of and used with the help of a combination of different technologies. In a newly developed large-scale plant they will be converted into sustainable biofuels, green hydrogen and biochar.

Starting point

energy from renewable sources is the key to mitigating climate change

EU target: 10 percent of energy used in transport should come from renewable sources

First-generation biofuels ("biodiesel") are ecologically and socially unsustainable because the cultivation of energy crops competes with food production

There is a need for the market introduction of advanced biofuels using lignocellulosic biomass

Biochemical processes such as fermentation are too slow and are poorly suited for residual and waste materials because they have a mixed composition and low cellulose content

Thermochemical processes such as gasification and pyrolysis are more flexible in terms of the feedstock, but can so far only be carried out cost-effectively in large central plants

Objectives in the project

Demonstration of the technical feasibility and cost competitiveness of the bioenergy value chains TCR-> PSA-> HDO

Production of green hydrogen and green diesel and gasoline equivalents from sewage sludge

Validation of the logistical advantages of integrated small-scale hydrogen separation and purification (PSA) and HDO modules with the TCR unit compared to the central petrochemical infrastructure.

Contribution to the objectives of the Renewable Energy Directive for renewable energies by validating waste raw materials for the production of fuels.

Showcase for future sustainable investment and economic growth across Europe

Development of a business case, LCA and dissemination of the results

The final part of the project consists in the development and implementation of a large-scale technology aimed at converting dried sewage sludge and other types of biomass waste under standard conditions into liquid fuels that can be used in conventional combustion engines and green hydrogen.  

The fuel production plants will be built in the market of Hohenburg (district of Amberg-Sulzbach, Upper Palatinate). The location offers numerous advantages: on site, there is years of experience in drying and handling sewage sludge. The quantities and quality of input material required in the project are available in Hohenburg. The ground-breaking ceremony in the Hohenburg Industrial Park took place on 7 November 2018.

The large-scale production of the To-Syn-Fuel demonstration plant will represent a real business advantage. It offers a long-term opportunity for converting organic waste into renewable fuels. These can then be fed directly into the existing oil infrastructure. Hundreds of such plants, which could be installed across Europe, would be sufficient to convert up to 32 million tonnes of organic waste per year into sustainable products and biofuels. This would mean up to 35 million tonnes of greenhouse gas savings per year. In terms of socio-economic development, 100 plants would create at least 5,000 skilled jobs.

The current phase of the To-Syn-Fuel project is the integrated operation of the systems and the production of liquid fuels and green hydrogen from sewage sludge. The first test campaigns with the TCR total system showed very satisfactory performance. In over 500 hours of operation, more than 200 tonnes of dried sewage sludge were converted into over 20,000 litres of TCR® oil. The yield and quality of the products obtained is as expected.

In the following months, further campaigns are planned to process 12 tonnes of dried sewage sludge per day and to gain further long-term experience with the technology. In addition to the production of the fuel, extensive engine testing will be carried out to determine whether the drop-in fuels have comparable engine performance and emissions to fossil-derived fuels.  At the end of the project, the technology combination TCR®/PSA/HDO will be validated at TRL-7 (system prototype demonstration in operational environment) including a life cycle assessment of the overall system.

The pilot plant hall for the To-Syn-Fuel demonstration plant has been completed and the first components such as the hydrogen storage tank and the combined heat and power plant are already on site. By the summer of this year, the main plant components of the TCR technology will gradually be set up and gradually commissioned.

In the To-Syn-Fuel plant, sewage sludge is converted in Fraunhofers Thermo-catalytic reforming (TCR) system into valuable solid, liquid and gas fractions. The produced liquid bio-oil is refined to suitable fuels using the hydrogen from the produced TCR gas fraction. This hydrogen will need to be purified first. Hydrogen is separated from other species, like carbon monoxide, carbon dioxide  and methane using one of project partner HyGear’s key technologies: Pressure Swing Adsorption (PSA).  The separation is based on variation of adsorption capacity of an adsorbent as function of operating pressure. The cleaned hydrogen is compressed and redirected to the hydrodeoxygenation (HDO) reactors or can be used for other applications, like fuel cells. The required purity of the hydrogen can be controlled by the PSA settings.

The existing PSA technology has been modified to meet the specification of the TCR gas combined with recycled hydrogen out of the HDO part of the TSF plant. Several technology improvements have been implemented to reduce size and cost of the PSA. 

Mid June 2020, the PSA the construction was finalized, the software loaded and the container ready for shipment to the To-Syn-Fuel plant in Hohenburg in Bavaria, Germany. The system will be installed during the summer. It is expected the first TCR gas will be cleaned in September 2020.