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Hydrocarbons from sustainable Sources

1 SUSTAINABLE DEVELOPMENT IS..

Meeting the needs of the present without compromising the ability of future generations to meet their needs (economic, social, environmental) U.N. 1987

2 OBJECTIVE

Great quantities of hydrocarbon fuels will be needed for the future, even if electricity based energy carriers begin to partially replace liquid hydrocarbons in the transportation sector. Fossil fuels and biomass are the most common feedstocks for production of hydrocarbon fuels.

However, using renewable or nuclear energy, carbon dioxide and water can be recycled into sustainable hydrocarbon fuels in non-biological processes which remove oxygen from CO2 and H2O (the reverse of fuel combustion). Capture of CO2 from the atmosphere would enable a closed-loop carbon-neutral fuel cycle.

A process based on high temperature co-electrolysis of CO2 and H2O to produce syngas (CO/H2 mixture) is identified as a promising method. High temperature electrolysis makes very efficient use of electricity and heat (near-100% electricity-to-syngas efficiency), provides high reaction rates, and the syngas produced can be catalytically converted to hydrocarbons in well-known fuel synthesis reactors (e.g. Fischer-Tropsch).

From Graves thesis

3 WHY WE NEED THIS PROJECT

CO2 is a greenhouse gas which occurs naturally in the earth’s atmosphere through a process known as the carbon cycle.

Every time we burn gas, oil and coal (fossil fuels) to create energy sources, such as electricity and petrol, more CO2 is released into the atmosphere. The effect of all this extra CO2 in the atmosphere is that it traps more heat from the sun than is needed; this is known as the greenhouse effect or global warming, causing the earth’s average temperature to increase at a greater rate than it would naturally.

However, due to our constant demand for energy, the CO2 in the atmosphere has now increased to unnatural levels, by more than 35%.

3.1 EFFECTS

While the average global temperature keeps increasing, on a day-to-day level the climate is changing in unpredictable ways. We are already experiencing more extreme heat waves and drought, and with the warmer conditions causing glaciers and sea ice to melt, this leads to rising sea levels and more frequent and severe flooding around the world.

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Natural disasters such as those caused by global warming will also effect our food supplies. More frequent cases of flooding and drought will wipe out harvests leading to large hikes in world food prices, as well as shortages.

From,

http://www.lbhf.gov.uk/Directory/Environment_and_Planning/Carbon_reduction/CO2_and_why_we_need_to_reduce_it/175453_CO2_and_why_we_need_to_reduce_it.asp

4 INDUSTRIAL UTILIZATION OF CO2 INTO VALUABLE PRODUCTS

Industrial techniques for utilization of co2:

Few promising physical and chemical technologies for the utilization and conversion of CO2 from a power plant into viable economic products. Various existing and future utilization technologies were explored in this project for optimum CO2 utilization.

4.1 CHEMICAL UTILIZATION

4.1.1 Carbon dioxide fixation into organic compounds

4.1.2 Electrochemical utilization of carbon dioxide

4.1.3 Carbon dioxide reforming of methane

4.1.4 Solid oxide fuel cell – gas turbine combined cycle

4.2 CARBON CAPTURE AND STORAGE (CCS) Carbon capture and sequestration is the process of capturing waste carbon dioxide (CO2) from large point sources, such as fossil fuel power plants, transporting it to a storage site, and depositing it where it will not enter the atmosphere, normally an underground geological formation.

The precursors carbon dioxide (CO2) and water (H2O) are used in combination with electrical energy from regenerative sources to produce process gas which is subsequently synthesized into hydrocarbons.

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5 PROCESS OVERVIEW:

Process have 4 steps:

5.1 CAPTURING CO2 FROM AIR The Climeworks CO2 capture technology is based on a cyclic adsorption / desorption process on a novel filter material (“sorbent”).

5.2 SOLID OXIDE ELECTROLYSIS (SOEC)

1ST STEP IN PROCESS. USING ELECTRICAL ENERGY, STEAM (H20) IS SPLIT INTO HYDROGEN (H2) AND OXYGEN (02)- CHEMICAL REACTION 3H2O—»3H2+1.5O2

5.3 CONVERSION REACTOR

Within the 2"“ step hydrogen is mixed with carbon dioxide (C02) and fed into the conversion reactor to produce carbon monoxide (CO) and hence syngas (H2 + CO).

Chemical Reaction

3H2+CO2—>2H2+CO+H2O

5.4 FISCHER-TROPSCH REACTOR

Syngas (H2 + CO) from step two is fed into the Fischer-Tropsch reactor to be polymerized to long chains of hydrocarbons (-CH2-).

Chemical Reaction

2 H2 + C0 —> -CH2- + H20

Steam from cooling is recycled to the SOEC to increase the overall efficiency from approx.

50 to 70 % (compared to a standard water electrolysis).

5.5 DISTIILATION COLUMN

Within the distillation column the mix of hydrocarbons is separated into three fractions:

Waxes

Diesel

Naphtha

Residual gases are fed back to the Fischer-Tropsch and conversion reactor. This increases the rate of carbon utilization to min. 95 %.

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6 DETAILED DESCRIPTION

6.1 SOEC(SOLID OXIDE ELECTROLYSIS) Electrolysis of water is the decomposition of water (H2O) into oxygen

(O2) and hydrogen gas (H2) due to an electric current being passed through the water.

PrincipleAn electrical power source is connected to two electrodes, or two plates (typically made from some inert metal such as platinum, stainless steel or iridium) which are placed in the water. Hydrogen will appear at the cathode (the negatively charged electrode, where electrons enter the water), and oxygen will appear at the anode (the positively charged electrode).Electrolysis of pure water requires excess energy in the form of overpotential to overcome various activation barriers. Without the excess energy the electrolysis of pure water occurs very slowly or not at all.

EquationsIn pure water at the negatively charged cathode, a reduction reaction takes place, with electrons (e−) from the cathode being given to hydrogen cations to form hydrogen gas (the half reaction balanced with acid):Reduction at cathode: 2H+(aq) + 2e− → H2(g)At the positively charged anode, an oxidation reaction occurs, generating oxygen gas and giving electrons to the anode to complete the circuit:Oxidation at anode: 2H2O(l) → O2(g) + 4H+(aq) +4e−

The same half reactions can also be balanced with base as listed below. Not all half reactions must be balanced with acid or base. Many do, like the oxidation or reduction of water listed here. To add half reactions they must both be balanced with either acid or base.Cathode (reduction): 2H2O(l) + 2e− → H2(g) + 2 OH−(aq)

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Anode (oxidation): 4OH−(aq) → O2(g) + 2 H2O(l) + 4 e−Combining either half reaction pair yields the same overall decomposition of water into oxygen and hydrogen:Overall reaction: 2H2O(l) → 2 H2(g) + O2(g)

High pressureHigh pressure electrolysis is the electrolysis of water with a compressed hydrogen output around 120-200 Bar(1740-2900 psi).[8] By pressurising the hydrogen in the electrolyser the need for an external hydrogen compressor is eliminated, the average energy consumption for internal compression is around 3%.

High-temperatureHigh-temperature electrolysis (also HTE or steam electrolysis) is a method currently being investigated for water electrolysis with a heat engine. High temperature electrolysis may be preferable to traditional room-temperature electrolysis because some of the energy is supplied as heat, which is cheaper than electricity, and because the electrolysis reaction is more efficient at higher temperatures.

Solid Oxide Electrolysis Cells (SOEC) are expected to provide the highest efficiency of electrolytic hydrogen production, because the applied voltage can be reduced due to favourable thermodynamic and kinetics conditions. Another advantage of SOECs is that they can operate reversibly as Solid Oxide Fuel Cells (SOFC) producing electricity with a high efficiency by consuming the stored hydrogen.

At present, electrolysis technology is centred on low temperature alkaline and PEM electrolysers.The problem with the low temperature technology is that >2/3 of the cost of electrolysis is due to electricity demand:G = H - T SG = n F e where e is the electrical potential which decreases with temperature.The high temperatures required for SOEC operation lead to a lower theoretical decomposition temperature for steam and lower electrode polarization losses compared to those associated with liquid water.

SOECs are effectively reverse solid oxide fuel cells. Where a fuel cell is also capable of being used as an electrolyser cell it is referred to as a Solid Oxide Regenerative Fuel Cell (SORFC).Oxide ion conducting SOECs produce a gaseous mixture of hydrogen and water vapour at the cathode supplying power and H2O to the cell.