SOLETAIR process aims for 100% renewable solution, which combines CO2 from air and electricity from sun into sustainable consumer products. Our demonstration facility includes a solar field and three mobile container units: electrolyzer for hydrogen production, direct air capture for CO2 production and intensified synthesis reactors for hydrocarbon production. Our ambition is to integrate these units successfully and demonstrate that 100% renewable future is possible
Solar photovoltaic (PV) electricity is used as a renewable energy source in our SOLETAIR system to produce electricity especially to the hydrogen unit that is the most energy intensive part in the system.
Renewable energy plant consists of flat roof, carport, wall, 2-axis tracking, and manual tracking solar PV installations. The total installed power is 206.5 kWp. The panels of the fixed systems are mainly faced to south, but one wall mounting is faced to west. The slope degree in the all systems is 15° despite of the wall mounting systems. The size of the flat roof system is 56.5 kWp, carports 108 kWp, walls 36.8 kWp (18.4 kWp to south, 18.4 kWp to west), 2-axis tracking 5 kWp, and manual tracking 250 Wp. West wall installation can be seen from the site of the SOLETAIR demonstration plant. The total solar PV panel area is about 1500 m2 and it includes totally 827 panels.
Renewable energy plant includes different solar PV panel technology based on silicon. Both mono- (mono-Si) and poly-crystalline (poly-Si) panels are used. In addition, part of the panels are manufactured by back-contacted metal wrap through module technology, in which all the contacts are on the rear side of the cell. Conventional technology is H-pattern. All the panel strings are connected to string inverters instead of the manual tracking system that has a micro inverter.
Renewable energy production is measured by the automation system and the data is stored to a database. Real time measurements of renewable energy production are available for each single solar PV power plant. The production numbers can be found from the webpages; real time renewable energy production and renewable energy production history data. The SOLETAIR site is connected to the solar PV power plant through the internal electricity grid.
Proton exchange membrane (PEM) water electrolysis process is used in hydrogen production. The system produces high-purity hydrogen gas at elevated pressures. Hydrogen is used with recycled carbon dioxide to produce renewable fuels, raw materials, and chemicals in MOBSU. The hydrogen gas can also be used as a chemical energy storage and can later be reconverted into electricity in a fuel cell, albeit with an additional penalty in terms of losses in conversion.
A hydrogen production system is built in a standard shipping container and virtually connected to a renewable energy source, the 206.5 kWp solar PV power plant at LUT. In other words, the water electrolysis process can be selected to be operated according the instantaneous solar PV production or according to recorded solar PV production figures.
The process in the hydrogen production system is the following: Water can be stored in a 1 m3 buffer tank and then supplied to a reverse-osmosis unit. The purified water is further deionized in order to decrease the conductivity of the water in order to preserve the lifetime of the electrolysis unit. The 5 kW proton exchange membrane electrolyser splits the water molecules into hydrogen and oxygen gas, when DC current is supplied to the electrodes. Hydrogen is formed at the cathode and oxygen at the anode side of the electrolyser.
Due to the compact design of the proton exchange membrane electrolyser, the cathode compartment pressure can be adjusted to a much higher pressure compared to the anode compartment pressure. The PEM electrolyser at LUT can produce hydrogen at a maximum outlet pressure of 50 bar, while the oxygen outlet pressure is kept at 2 bar. Operating temperature of the electrolysis unit is controlled to 70 °C by water cooling. The hydrogen production unit is produced by a Danish company EWII, but modified to enable the adjustment of both gas outlet pressures by back-pressure valves.
The hydrogen gas produced by the proton exchange membrane electrolyser is processed in a hydrogen gas drying unit to decrease the dewpoint down to −70 °C. Minimizing the water content in the hydrogen gas outlet prevents the gas from freezing in Nordic winter conditions, when the gas is supplied to outdoor gas storage. The produced dry hydrogen gas is stored into two 350 l composite cylinders. From the gas storage, the hydrogen can be supplied to the MOBSU synthesis unit or a PEM fuel cell located in the hydrogen production container.
Direct air capture (DAC) is the carbon source of the SOLETAIR project. DAC falls under the class of carbon sequestration technologies. However, direct air capture is the only carbon capture technology that can directly capture CO2 previously emitted in the atmosphere. When surplus renewable energy drives the unit, DAC has the potential of being 100% negative carbon emission technology.
The current DAC unit is a modified version of air-scrubbing units for civil shelters. The main principle for collecting carbon dioxide is adsorption/desorption process using solid amine sorbents. The sorbents used in the direct air capture unit are amine-functionalized polystyrene spherical beads.
Direct air capture of carbon is as follows: (1) Ambient air is introduced to the resin bed by fans. As air passes through the bed, CO2 reacts with the amine in the resin via chemisorption. In parallel water is also physically adsorbed. N2 and O2, major components of air, pass the bed unabsorbed. (2) Next is purging, pneumatic valves are closed and high vacuum is applied to remove air in the bed. (3) The bed is then heated to 80°C, to reverse the adsorption reaction and produce gas (CO2, H2O) in bed. (4) Finally, heating and vacuuming is continuously applied for two hours to collect the product CO2. Water is removed via air-cooled heat exchanger.
The current direct air capture set-up is modular with dimension 340 cm (L) x 220 cm (W) + 242 cm (H). This allows the unit to be deployed easily as part of a power-to-gas / power-to-liquid /power-to-X system or as a standalone decentralized carbon source for CO2 utilization. The DAC is designed to produce 3800 g/day of CO2. It can be operated manually or via time based automation using Siemens Simatic system.
Fischer-Tropsch synthesis is used in our newly designed Mobile Synthesis Unit (MOBSU) to combine carbon and hydrogen and produce valuable gas, liquid and solid products for various uses.
We are currently working on two different production lines which are tailored for either natural gases or liquid and wax component production. These units are positioned side by side inside the Mobile Synthesis Unit.
The methanation production line produces synthetic natural gas (i.e. methane) from CO2 and H2 by using Sabatier reaction. Synthetic natural gas can replace traditional, fossil-derived natural gas without any problems. The reactor will be VTT in-house design with a nickel-based catalyst. Operating temperature for the methane production is around 300 °C in mildly elevated pressure. (not presented in the animation)
The Fischer-Tropsch production line has two major steps. First, we will alter CO2 to a more useful component, CO. This is done by reverse water gas shift reaction (rWGS) in which a gas mixture of CO, CO2, H2 and H2O is balanced at high temperature of 800 °C with the help of a precious metal catalyst. The reactor operates at the same pressure as the following Fischer-Tropsch synthesis in order to avoid compression between process steps. The design of rWGS reactor and the catalyst is VTT in-house know-how.
Secondly, carbon monoxide and hydrogen are reacting to hydrocarbons in the Fischer-Tropsch reactor. Our project partner, IneraTec GmbH, has designed and manufactured this ultra-compact and efficient reactor. Fischer-Tropsch reaction produces a wide range of products from light hydrocarbon gases like methane, to liquid components like diesel and up to more solid wax components.
The main parts of Fischer-Tropsch module are the intensified reactor, a hot trap to condense the wax products, and a cold trap to condense the liquid products. Our Fischer-Tropsch unit has a cobalt catalyst in a novel compact reactor with integrated water evaporation cooling cycle.
Mobile Synthesis Unit is positioned in 2.5 x 9.1 x 3 m sea container and easily transportable. It contains both Fischer-Tropsch and methanation reactors together with a sophisticated control room.
The renewable product stream from the Mobile Synthesis Unit is a mixture of hydrocarbons ranging from light gaseous products to liquids and even solid paraffin waxes. The share of each type of product varies a lot depending on the reaction conditions and the catalyst used in the Fischer-Tropsch reaction. It is essential to utilize all of these products fully to make an economically feasible process.
The renewable product that is in gaseous form at room temperature consists of methane, the main component of natural gas, and other light hydrocarbons. It is easy to separate the gaseous fraction from the liquid and solid products. In larger refineries light olefins – ethylene, propylene and butenes – are separated from this fraction. These basic petrochemicals form the basis for the manufacture of a wide range of plastics and other products. On the other hand, the light paraffins generally known as Liquefied Petroleum Gas, are sold to customers to be used for instance in stoves, grills and refrigerators. In smaller scale such as in the case of the Mobile Synthesis Unit, the preferred use of the gaseous fraction is for energy.
The liquid product can be fractioned by distillation to renewable gasoline and middle-distillate hydrocarbons. The gasoline fraction is further hydrotreated and reformed over a platinum catalyst in order to increase its octane number and to improve other characteristics for motor use. The middle-distillate fraction is also hydrotreated and thereafter distilled to renewable jet-fuel and/or diesel.
There is only limited use for the wax fraction in special applications such as candles or white oils for consumer products. However, it is possible to hydrocrack the waxes to diesel and jet-fuel and to lesser extent to gasoline. These products can then be combined with the distilled liquid products.
The wide range of Fischer-Tropsch products offers a lot of flexibility in tailoring the product. For instance, instead of motor fuel, the Fischer-Tropsch products can be refined to renewable petrochemicals such as olefins or aromatics and the further upgraded to isocyanates, which are the building blocks for polyurethane foams.
SOLETAIR project aims to demonstrate a process that would bind CO2 emissions and surplus electricity into everyday renewable consumer products. Depending on the chosen synthesis unit (methanation or Fischer-Tropsch) and following upgrading process, the ultimate product can be something as simple as synthetic natural gas or complicated petrochemical compounds like polyurethane.
In the case of gaseous products, synthetic natural gas is easy to utilize as such. The product quality is very high and therefore the gas can be directly injected into natural gas grid. Natural gas is widely used by consumers in Europe for heating, cooking and fueling vehicles. In Finland, natural gas is predominantly used in the combined heat and power production1. The renewable synthetic natural gas from SOLETAIR process can be used in cars and domestic appliances also in Finland, to increase the share of renewable in the natural gas consumption.
When the SOLETAIR process is operated in the Fischer-Tropsch mode, the main part of the renewable consumer product is liquid fuels: gasoline, kerosene and diesel. These fuels are high quality, they can be mixed with fossil-based fuels and used in the vehicles. The combustion of the fuel in an engine releases CO2 emissions, which can be again utilized by the SOLETAIR process creating a closed CO2 loop.
If the renewable hydrocarbons are refined to olefins and aromatics instead of fuels, wide range of possible renewable consumer products exists. The simplest and cheapest olefin-based product is polyethylene which is the most common plastic. However, SOLETAIR process is aiming for the higher-value products, which are based on three aromatic compounds: benzene, toluene and xylene. These are building blocks for complicated and valuable polymers, such as polyurethane, which is used in the soft and elastic foam of sneakers. Renewable plastic products like polyurethane sequestrate CO2 unlike fuels, which release CO2 back to atmosphere. Therefore, every renewable consumer product, every pair of sneakers with SOLETAIR components removes CO2 permanently from the atmosphere with purely renewable process.
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