ENK5-2001-30010 Hydrogen fuel gas from Supercritical Water Gasification of Wine Grape Residues

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Agricultural Residues : EESD (Energy, Environment and Sustainable Development)

Proposal No:	ENK5-2001-30010
Date Prepared:	February 2004
Source:	European Bio-Energy Projects (EUR 20808)

Introduction

The EU-15 wine production is 157 million hl resulting in a rest product of 4.7 million wet tons per year of trester with a moisture content of 70%. Utilisation as compost and fertiliser is limited due to the high moisture content, accumulation of pesticides and additives such as copper, boron and arsenic and labor intensive mulling practices. Combustion is difficult at the high moisture content and emissions of VOC's (ethanols) that exceed the TA Luft criteria. Landfilling is limited due to land shortages.

The EU aims at doubling the current share of renewable energies in the total energy demand of its member states from 6% to 12% by the year 2010. The largest contribution is to come from biomass based energy to be tripled by the year 2010 by adding 120 billion m³ natural gas equivalent capacity. The EU has an annual production potential of rest-biomass of 90 Mtoe. The quantity of CO₂ emission saved this way is 225 million tons per year or 6% of the total energy based CO ₂ emissions. Thus rest biomass use can replace fossil fuels and reduce external dependencies.

The first European working bench scale continuous flow SCWG unit was designed, constructed and operated by several of the partners. The present project continues this effort with a similar but more advanced 10 l/hr unit verified in a new 100 l/hr pilot unit.

Progress

The SCWG is carried out in both batch and continuous flow units. The organic laden water is pumped at 30 MPa through a heat exchanger into a 15 m long coiled tubular reactor. The coil inlet is at 500°C. This coil is located in a gas heated furnace where the slurry is heated to the reaction temperature of 600°C. During the coil passage the organics in the slurry are converted into hydrogen-rich fuel gas. By heat exchange with cold feed, the reactor product is cooled to ambient temperature, high pressure steam condenses and separates from the fuel gas in the 2 stage separator.

The produced CO₂ can be separated from the fuel gas by additional water scrubbing to generate a clean renewable CO₂ stream for commercial use. The condensate from the trester contains all the salts and metals from the original trester and most of these will crystallize and precipitate to be reused as fertiliser.

Near the critical temperature of 374°C water acts as hydrolysis agent for fatty esters, ethers, amines etc. At 600°C and above a critical density of 0.33 g/cm³ water becomes a strong oxidant resulting in the complete breakdown of the substrate structure by transfer of the oxygen from the water to the carbon atoms of the substrate.

Results show a thermal yield of higher than 70% even at water contents as high as 90% and up to 54 vol% H₂. Trester gasification showed 44 vol% H₂, 25 vol% CH₄, 2% vol CO, 22 vol% CO₂ and 8 vol% CH_2n.

Hardly any char formation was noted. Trester compost slurries were fluid up to DOM content of 20%, cucumber slurries even at DOM content of 35%. Fresh trester slurry ceased its fluidity at up to 8% DOM. The bioslurries showed Bingham fluid behavior and were suitable for high pressure pumping.

Impact

The operation of the SCWG process can be adjusted for different applications:

• fuel gas for the production of steam and heat for captive use (boiler concept). The high pressure steam can be expanded in staged turbines to produce electricity. The steam is further used for winery container sterilisation and distillations.
• combustion of fuel gas in a turbine with combined cycle for power and steam production.
• utilisation of the fuel gas for power production in a fuel cell, after removal of traces of H₂S and CO.
• production of pure hydrogen at high pressures for the market, after removal of CH₄, CO and CO₂.

It was estimated that hydrogen fuel gas can be produced at #7/GJ. This is strongly influenced by negative biomass gate value (as received at the entrance of the facility), compactness of the installation and short reaction times.

The EU estimates for biomass waste are 300 million tons (dry weight basis) of which only 27% is now recycled commercially. The fuel gas equivalent using SCWG is 150 billion m³ of natural gas produced and can prevent 6% of the total energy related CO₂ emission of the EU. Other sectors that can use the SCWG technology are waste treatment, sewage sludge handlers, bioindustries, vegetable processors etc.

The European rest biomass potential of 150,000 MW can lead to the construction of 150,000 small SCWG units of 1 MW each (similar to a large windmill) or 300 larger units of each 500 MW. The design, manufacturing and construction costs can amount to 150 billion Euros at 100% penetration or likely 15 billion at 10% penetration.