XtL fuel
As XtL fuels (also: Fischer-Tropsch Fuels ), various synthetic fuels referred to, which are for converting a solid or gaseous energy carrier is in a liquid at normal temperature and pressure carbonaceous fuel. The "X" represents a variable and is replaced by an abbreviation of the original energy source, while "tL" stands for the English "to liquid". The abbreviations GtL ( gas-to-liquid ) when using natural gas or biogas , BtL ( biomass-to-liquid ) when using biomass and CtL ( coal-to-liquid ) when using coal are currently in use as an initial energy source.
XtL process
Regardless of the original energy source, the XtL process for all forms of XtL fuels consists of four phases:
- Gasification: The original energy source is converted into a usable synthesis gas.
- Gas cleaning and gas conditioning: preparation of the synthesis gas for the subsequent synthesis
- Hydrocarbon synthesis : Synthesis of the gas in a Fischer-Tropsch synthesis to more complex hydrocarbons, which serve as fuel raw products. This creates paraffins, oleofins and oxygen compounds. The chain length of the mostly straight hydrocarbons ranges from gaseous methane (one carbon atom) to solid waxes (20 and more carbon atoms).
- Processing: The hydrocarbons are processed into the finished fuel, whereby they can be adapted as synthetic fuels to later requirements.
history
In 1925, at what was then the Kaiser Wilhelm Institute for Coal Research in Mülheim an der Ruhr, the Fischer-Tropsch synthesis was developed to liquefy coal , the central process step in XtL fuels.
Beginnings: striving for self-sufficiency in Germany
In the course of the efforts of the German Reich before the Second World War , a number of systems were built to produce fuel from the coal, which was available in large quantities, but these were mainly based on the Bergius-Pier process developed in 1913, while for the Fischer-Tropsch synthesis only small capacities were built up. In total, capacities for 4.275 million t / a according to the Bergius-Pier process and 1.55 million t / a according to the Fischer-Tropsch synthesis had been built up by the end of the Second World War. Compared to petroleum-based fuels, however, both processes were not competitive, so that they were almost completely abandoned after the war.
Expansion of CtL plants in South Africa
In the Republic of South Africa, which also had sufficient coal resources and had to import crude oil, the first modern CtL plant in South Africa was put into operation in 1955 for political reasons. It was built by Suid Afrikaanse Steenkool en Olie (Sasol) with the participation of the German Lurgi AG . The Sasol 1 pilot plant was designed for around 6,000 barrels of fuel per day. From 1980 the capacities were expanded significantly, due to the political development in South Africa.
In 1980 and 1982 Sasol II and Sasol III were put into operation, with a total capacity of 104,000 barrels / day available. With the political opening, the program was expanded to include natural gas as a raw material source and in 1995 and 1998 additional capacities for 124,000 barrels / day of CtL and GtL fuel were created.
GtL as a modern fuel
Sasol became world market leader in XtL technologies thanks to the South African developments and in 2006 built a modern GtL plant in Qatar with a capacity of 34,000 barrels / day. Together with Foster Wheeler , Sasol is also planning a plant in China with an annual capacity of 60,000 barrels / year. Fischer-Tropsch processes are followed in both plants: a high-temperature process with process temperatures of 350 ° C (Synthol and Advanced Synthol), in which petrol and alkenes are produced as platform chemicals , and a low-temperature process at 250 ° C for the production of diesel fuel and waxes .
In 1993, the mineral oil company Royal Dutch Shell also put its first GTL plant into operation. The plant in Bintulu in Malaysia has a capacity of 12,000 barrels / day and is operated in a specially developed Fischer-Tropsch process, the Shell Middle Distillate Synthesis (SMDS process). At the end of 2009, the Pearl GtL plant in Qatar, which was built by Shell, went into operation. This is currently the world's largest plant and produces 120,000 barrels / day.
Second generation biofuels: BtL
In the course of the raw material turnaround, biofuels in particular have moved into the focus of fuel production in recent years . Large international capacities have been built up for the so-called first-generation biofuels, biodiesel and bioethanol . With further development, the Fischer-Tropsch synthesis also increasingly moved into the focus of research and development, BtL fuels are strongly promoted as second-generation biofuels, especially in Europe. There is currently no large-scale industrial BtL production - but pilot projects are ongoing and Choren Industries has set up a first plant in Freiberg , Saxony, for the BtL fuel they call SunFuel and SunDiesel.
Evaluation of XtL fuels
An advantage of all XtL fuel types is the lower dependence on petroleum. It is often emphasized that the fuel properties can be controlled in a targeted manner during the synthesis and that this enables a slightly higher efficiency of the vehicle engines. On the other hand, there is a very high expenditure of energy in the gasification and synthesis steps. Since XtL fuels do not contain cyclic compounds or sulfur, combustion is cleaner than petroleum-based fuels. Since very different raw materials are used for the various XtL fuels, their respective advantages and disadvantages must be assessed differently.
CtL
The global oil production maximum is expected in the next few decades . Since the range of coal reserves is significantly greater, CtL fuels could secure the fuel supply in the future. However, the CO 2 balance of the CtL synthesis is very poor. Coal naturally contains little hydrogen. For the Fischer-Tropsch synthesis , however, the synthesis gas requires a hydrogen-to-carbon monoxide ratio of 2: 1. The missing elemental hydrogen is generated by the water-gas shift reaction . A lot of carbon dioxide is released. The climate balance is therefore worse than with GtL, BtL and conventional petroleum-based fuels. However, there are ways out here too. Since the carbon dioxide is obtained in concentrated form, a carbon dioxide sequestration can be carried out very easily. Another way out is to add regeneratively produced hydrogen to the synthesis gas. This method is also discussed under the keyword power-to-liquid . However, electricity or hydrogen generated from renewable sources is expensive.
GtL
Since global natural gas supplies are limited, GtL fuels are not a long-term alternative, but rather a supplement to petroleum-based fuels. The CO 2 balance of GtL fuels is significantly worse than for gas that is used in natural gas vehicles . However, if natural gas occurs as a by-product of oil production in areas remote from the market, transport is often not worthwhile, which is why the gas is flared. By converting the natural gas into GtL, the energy density is greatly increased and transport is economical. An alternative to GTL production is the conversion to liquefied natural gas (LNG liquefied natural gas), thus also increasing the transportability by a greater energy density. Both variants are currently gaining in importance and, due to the use of a waste product, can be assessed as ecologically positive. Depending on the price of oil , the promotion of natural gas for GTL production is also worthwhile. Large deposits, such as in the Middle East , can be developed. For example, Qatar is currently building a GtL plant in a consortium with Royal Dutch Shell and Qatar Petroleum , which is expected to produce 140,000 barrels a day from 2009 onwards. In this case, the CO 2 balance is negative and, due to the complex GtL synthesis, also significantly worse than with natural gas extracted near the market, which is used without prior chemical conversion.
BtL
The CO 2 balance of BtL is better than that of fossil fuels, since the BtL combustion only releases the amount of CO 2 that was previously absorbed by the plant. The need for large areas is criticized in order to make a significant contribution to the fuel supply. For Germany, maximum potentials of 20 to 25% of the demand are given. However, these values are to be regarded as clearly too high, since other uses of the agricultural area, such as food and feed production, substrate provision from biogas plants and the cultivation of renewable raw materials for the chemical industry, compete for these areas. In the course of climate protection, it is planned to significantly increase the proportion of biofuels in Germany by increasing the existing minimum quotas. Another point of criticism is that the costs per ton of CO 2 equivalent saved are higher for biofuels than, for example, for energy efficiency measures or renewable energies such as electricity from wind and water power and biomass cogeneration plants .
PtL
PtL ( Power-to-Liquid or Power-to-Liquids) is a process for converting CO 2 into various synthetic fuels such as gasoline, diesel, kerosene and methanol.
Individual evidence
- ↑ Martin Kaltschmitt, Hans Hartmann and Hermann Hofbauer (eds.), 2009: Energy from biomass. Basics, techniques and procedures. Springer Verlag, 2nd edition, p. 656, ISBN 9783540850946 .
- ↑ - Handelsblatt report on the construction of a GtL plant in Qatar
- ↑ - Description of the Power to Liquids process of Sunfire GmbH, Dresden
literature
- Georg Schaub and Dominik Unruh: Synthetic hydrocarbon fuels and the reduction of fossil CO 2 emissions In: VDI reports 1704 Innovative vehicle drives , VDI-Verlag 2002, Düsseldorf; Principle of the XtL generation; Differences between CtL, GtL and BtL production; Estimates of CO 2 emissions