Biomass to liquid

BtL ( Biomass to Liquid, German: biomass liquefaction) are synthetic fuels ( XtL fuels) that are produced from biomass. The procedures for BtL production are still in development and not yet competitive.

• 5.1 cultivation
• 5.2 Use

• 6.1 advantages
• 6.2 disadvantages

Principle and Application

The main steps of the manufacturing method are the most common gasification of biomass, in which the so-called synthesis gas is produced and the subsequent synthesis of the Fischer- Tropsch process or the methanol - to-gasoline process (MTG). The end product of fuels can be produced chemically differ somewhat from conventional fuels like gasoline or diesel, but also in gasoline or diesel engines can be used. BtL fuels are second generation biofuels. This means that they have a wider range of raw materials can be used as biodiesel or bioethanol and, for example, cellulose- rich biomass such as straw and wood. The fuel yield per hectare of arable land could thus be increased.

Some other fuels, which are also produced by a biomass liquefaction are not allocated to the BtL fuels in general. These are, for example, be produced by bioconversion of sugar, starch or cellulose bioethanol fuels and cellulosic ethanol and Furanics. In a pyrolytic liquefaction of biomass pyrolysis oil directly it can be converted to fuel after preparation.

Several steps are necessary in the production of BtL fuels:

Providing the raw materials differs from the other XTL fuels that are produced from gas or coal. The steps of the gasification and gas cleaning also differ significantly from the GTL manufacturing process, but are partly similar to the CTL - manufacturing process. The synthesis can, however, occur at all XtL fabrications equal if the same method is used (eg, Fischer- Tropsch synthesis).

While the process for the production of CTL and GTL fuels are established, the method are for BTL -fuel production is still under development or in an early stage of practical trials. Mainly is currently being studied in the production of BtL diesel fuels.

Historical Background

CTL fuels have already been manufactured in the 1940s in the German Reich and the Second World War to the present day in South Africa on a large scale. The production of GTL fuels has been established since the 1990s. In the course of the energy turnaround advanced renewable energy, and therefore biofuels such as biodiesel, bioethanol and BtL into focus. In the context of climate change and because of the limited and thus increasing price of oil large capacity for the first-generation biofuels (such as biodiesel, bioethanol ) were set up in the industrial countries. BtL fuels are politically heavily promoted as second-generation biofuels, especially in Europe.

Production

Provision of raw materials and processing

The production of BtL usually begins in order to dry the highly water -containing biomass. The starting material can be used both biomass wastes such as straw or wood residue as well as grown specifically for fuel production crops ( energy crops, such as short rotation coppice ). After a required depending on the process and equipment technology shredding and cleaning of the parts of plants is gasification. It should be noted that often only the calorific values ​​of the substances used are considered. Since these are however determined by mass, the density of the different materials, for example, to be transported in straw significantly larger and leads to processing volume of material, in the consideration remains largely ignored. So beech and spruce have indeed almost the same calorific value of about 15 MJ / kg, but the density ( volume) is significantly different: 0.77 and 0.44 kg/dm.sup.3. Taking into account the large necessarily to be transported and processed volumes is the processing of waste materials, fast-growing biomass or straw to be considered critically.

Gasification

The first step is to varying degrees completed thermal cracking, pyrolysis in dealing with these synthesis methods. At temperatures of about 200 ° C to about 1000 ° C, the physical and chemical structure of the biomass is converted. Long molecular chains are cleaved by the influence of heat. He painted numerous different liquid and gaseous hydrocarbons with shorter chain length and with progressive course also increases carbon monoxide, carbon dioxide, carbon and water. While the complete oxidation to carbon dioxide and water is prevented by (air ) oxygen deficiency, can the other characteristics of the pyrolysis products in addition to the primary process conditions of temperature, pressure and residence time affect also supplied chemical reactants and catalysts in the reactor. Other variants of gasification are possible. If the reaction is carried out in a liquid solution that is reactants simultaneously, one also speaks of a solvolysis, in a hydrogen atmosphere, however, by a hydrogenolysis.

Carbo - V process

This particular method is based on a two step process, where first at 400-500 ° C, the particulate biomass in coke ( biochar ) and containing tar carbonization is broken. During the biochar is discharged, takes place at about 1500 ° C, a entrained flow gasification of low-temperature carbonization, so that the longer-chain hydrocarbons can be broken down into simple molecules and thus in a tar-free synthesis gas. The high temperature of this gas is then used to gasify the removed and crushed biochar at 900 ° C now also. The raw material can be more fully utilized than with other methods. Thus the resulting raw gas is tar-free and after dedusting and washing of similar quality to natural gas produced from the synthesis gas.

Liquefaction

The pyrolysis is less complete, is formed instead of a gas, a liquid product, which is also referred to as pyrolysis. This method could be used, for example, to increase the transport- for raw materials with low density, such as straw. Can be followed by gasification of the BtL production plant.

Synthesis

The subsequent step is the step of the synthesis, in which the fission products are prepared by chemical reaction to the BTL fuel in the synthesis gas. Most takes place ajar to the Fischer- Tropsch synthesis process to produce the BtL fuels.

This technique was used in the pilot plant of the choirs Industries GmbH. Here, the carbonate -V A method for the production of biogas with developed by Shell Shell Middle Distillate Synthesis, a refined Fischer- Tropsch process has been combined. Shell produces so on an industrial scale in the Malaysian Bintulu already GTL fuel from natural gas and mixes it his "V- Power" Fuel at.

Another plant in the preliminary smaller scale, the plant in Güssing ( Austria ). This synthesis gas is produced with a wooden fluidized bed gasification, which is currently still burned in an engine. At the installation of a Fischer- Tropsch plant is working. As of spring 2007, there will be gaseous fuel at a gas station. Liquid fuels are to be offered as from autumn 2007.

Product preparation

The product of the synthesis is a mixture of various hydrocarbons. A use as a fuel to provide a treatment is necessary, the method of on of the crude oil refining accesses (for example, distillation, rectification ), for example. For example, the extraction is carried out by BTL and BTL diesel fuel from the synthesis product. In a limited framework can control the synthesis, so that, for example, a preferred production of BtL diesel is possible.

Other methods of preparation

A production of BtL fuel can also be done with other methods, but the distinction usually have a unique name. In part, as an intermediate synthesis gas but not a liquid ( pyrolysis oil ) before:

• Flash pyrolysis with very short residence times in the reactor, the
• Catalytic direct liquefaction, in which the pyrolysis takes place in an oil sump with the catalyst addition and the
• Hydrogenated direct liquefaction, resulting from the stable by (pressure) of hydrogen during pyrolysis product hydrocarbons.

In these methods will create a product liquid ( or Biorohöl biocrude Oil called ) are primarily lipophilic ( water insoluble ) may contain substances. In a further step, the processing into biofuel with the help of established petrochemical processes takes place.

Appropriate facilities currently exist at various locations in Germany, including the " Department of Process Engineering" HAW Hamburg ( pilot plant scale ), as well as some commercial operators ( "HP- DoS " process, production precursor).

At other institutions working on the development of manufacturing processes, such as at the Forschungszentrum Karlsruhe with the bioliq process.

Also, a microbiological production is possible. Thus, researchers have the bacterium Escherichia coli genetically manipulated at the University of Exeter, that it can be prepared by adding fatty acids depending on Genausstattung alkanes and alkenes of different lengths. Depending on the composition Kraftstoffreplika can then be generated.

Fuel properties

There are currently only measurements from pilot plants. Fischer- Tropsch fuels will have a 7 % lower volumetric energy content than diesel, a lower viscosity and a much higher cetane number.

Emissions from BtL fuel are lower than for fossil fuel ( see paragraph environmental impact ). BtL diesel or gasoline can be used without extensive conversion in the standard diesel or petrol engines ( gasoline engines ).

Environmental impact

The environmental impact can be made between the effects of biomass production and the emissions from the use by combustion of BtL. For an overall assessment, however, the complete process including the elaborate production to consider.

Cultivation

The environmental impact of the production of BtL fuel depend mainly on the type of biomass used. As with other biofuels also, the use of waste or forest wood to rather lower environmental impact. The use of energy crops, the harm to the environment and higher greenhouse gas savings are lower. Another important criterion is the degree of conversion, which also depends on whether electricity and heat still to be produced in the process. There is thus a trade-off between high fuel yields per surface on one side and minimal environmental impact on the other side.

Approximately 5 to 10 kilograms of wood are required to produce 1 kg of BtL. First optimistic estimates should be on an acre of farmland to grow as much biomass that from about 4000 liters of BtL fuel can be produced annually. Recent calculations in a European research project yielded a maximum of 2300 kg BtL fuel per hectare in the use of short rotation wood. The degrees of conversion and yields per hectare vary, depending on the method and type of biomass.

Use

Theoretically, any diesel engine can be operated with BtL fuel. In practice, the first measurement is a reduced emission of ( unburned ) hydrocarbons ( 40 %) and carbon monoxide and particulate matter found in the combustion. Reason is that, unlike fossil fuels, lack of aromatic compounds. Since no sulfur compounds are present, emissions are reduced here. However, a slight loss of power had to be accepted. For a full review, but also the additional emissions of these pollutants must be considered in the production of fuel, which outweigh this loss of emissions from the combustion part.

Pros and Cons

Benefits

• Improve the balance of trade in many countries dependent on oil imports, by reducing oil imports.
• BtL fuels have similar benefits to other renewable energy sources, such as Reduction of fossil CO2 emissions
• Conservation of fossil resources
• Greater independence from energy imports
• Strengthening the regional economy

Disadvantages

• The potential of previously unused biomass is limited. A comprehensive development of BtL production would thus also lead to increased competition for land and uses as agricultural and forestry land would have to be increasingly used for this purpose.
• The production costs for BTL are highly regarded, so that competitiveness with conventional fuels appears possible with the current manufacturing process only in financial support.
• Another biofuel, which is located in the development, is cellulosic ethanol. For its production, similar raw materials would be required as for BTL. It is unclear which method is more appropriate.
• During the thermal conversion lost depending on the process and by-products (electricity, heat, naphtha ) 30 to 60 % of the stored energy in the biomass. The fuel yield per hectare is therefore not necessarily higher than other biofuels and, depending on the starting material and procedures vary greatly. In addition, the cost of harvesting, transporting, shredding and otherwise taken into account.
• Since the energy density of the proposed starting materials (straw, reed, bamboo, fast growing trees, ...) is low, the volume to be processed compared to fossil fuels, but also to slow-growing hardwoods are significantly larger.
• The limited catchment areas for the large volume raw materials (transport costs ) require smaller generator units with resulting in reduced efficiency.

Production and market introduction

2005 agreed to build choirs Industries with the Shell oil company, the world's first commercial-scale manufacturing plant for 18 million liters of BtL fuel a year. On 6 July 2011, the provisional insolvency administration was placed over the assets of the choirs Industries. Developed by choirs Industries biomass gasification process Carbo V was acquired by Linde AG by the insolvency administrator and developed.

As a general importance of the industrial policy framework are considered, such as far pledged only to 2015 as part of the Energy Tax Act tax incentives for particularly consider eligible biofuels such as BtL, cellulosic ethanol and biomethane.