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) started on 1 May 2017. The Horizon 2020 project is being 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 for the first time from residual biomass (in this case sewage sludge).

Background and motivation

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

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

Starting point

• The EU aims to achieve a 60% reduction in transport-related greenhouse gas emissions by 2050 compared to 1990. 
• The share of low CO2-emitting sustainable aviation fuels should be 40%.
• First generation biofuels ("biodiesel") are environmentally and socially unsustainable because the cultivation of energy crops competes with food production
• The use of advanced biofuels based on lignocellulosic biomass from biogenic residues is not yet industrially available
• Biochemical processes such as fermentation are too slow and poorly suited to residues and wastes because they have a mixed composition and low cellulose content
• Thermochemical processes such as gasification and pyrolysis are more flexible with regard to the feedstocks, but so far can only be carried out cost-effectively in large central plants.

Objectives in the project

• Demonstration of the technical feasibility and cost competitiveness of a bioenergy value chain with a thermochemical core process (TCR process).
• Demonstration-scale production of green hydrogen and green diesel and petrol equivalents from sewage sludge.
• Validation of the feasibility of integrated small-scale hydrogen separation (by pressure swing adsorption) and on-site processing of TCR products compared to centralised petrochemical infrastructure
• Assessment of the potential contribution to EU renewable energy targets through validation of waste feedstocks for fuel production
• Showcase for future sustainable investment and economic growth
• Development of a business case, LCA and transfer of results

The core of the project is the development and operation of an integrated large-scale plant that can convert dried sewage sludge and other types of biomass waste into liquid fuels under standard conditions. These fuels should be able to be used in conventional engines and water fuel applications.  

The demonstration plant was built in the market town of Hohenburg (district of Amberg-Sulzbach, Upper Palatinate). The location offers the advantage of many years of experience in drying and handling sewage sludge. The quantities and quality of feedstock required in the project are available in Hohenburg. The groundbreaking ceremony at the Hohenburg industrial park took place on 7 November 2018.

The project will discuss the long-term benefits of the technology for the recycling of organic waste such as sewage sludge. In particular, it will be examined whether the products generated can be directly introduced into the existing petrochemical infrastructure and thus contribute to defossilisation.

In perspective, hundreds of decentralised plants in Europe could 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 EU-funded Fraunhofer UMSICHT project To-Syn-Fuel is nearing completion.

In front of the large-scale plant for the conversion of sewage sludge into fuel, the project team is filling a series production passenger car as a test vehicle. The vehicle will cover a distance of over 600 km with the sustainable, CO₂-neutral diesel. The following stops are planned along the route: Meeting with the German rally world champion Walter Röhrl at a race track in CZ, an appointment with the Bavarian Minister of Economic Affairs Hubert Aiwanger and a visit to Brussels. The car tour will end in week 38 with a final event at the large demonstrator in Hohenburg / Bavaria.

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 TCR process is the core of the To-Syn-Fuel demonstrator. The screw reactor, which is 12 metres long and weighs over 20 tonnes, was manufactured in Italy. It was installed in the pilot plant hall within a few hours using a gantry crane.

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.

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.