Pyrolysis gas

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Pyrolysis gas is a flammable gas that is mainly obtained from the volatile components by pyrolysis of biomass (including biogenic and other waste such as plastic or sewage sludge) at temperatures below 500 to 1500 ° C.

process

The biomass is split into solid, liquid and gaseous components by pyrolysis. Among other things, pyrolysis coke (wood or activated charcoal) is obtained as solid constituents, the liquid phase is condensed and can be used, for example, as bio- pyrolysis oil as fuel. The components that do not condense at operating pressure are hydrogen , carbon monoxide and dioxide as well as methane and higher hydrocarbons .

Depending on the process conditions, there are considerable differences in the proportions of solid, liquid and gaseous products. For example, under the conditions of "slow pyrolysis" at temperatures between 150 and 600 ° C, around 81% pyrolysis gas, around 14% coke and up to 5% pyrolysis oil are produced in "flash pyrolysis" (also known as rapid or flash pyrolysis) If the pyrolysis gases generated at 475 ° C are cooled very quickly, the yield of pyrolysis oil is increased to up to 75%, so that only 15–20% are used as pyrolysis gas.

composition

Pyrolysis gas consists of the following typical components, whereby the composition can vary greatly depending on the input materials and process conditions. The values ​​given are guide values ​​for pyrolysis gas made of wood. Also, the calorific value is highly dependent on the process conditions and the starting materials, it is in a range from 4000 to 8000 kJ / m N ³.

component proportion of
Nitrogen, carbon dioxide up to approx. 60%
hydrogen up to approx. 5%
Carbon monoxide up to approx. 35%
higher hydrocarbons up to approx. 10%

Manufacturing

In pyrolysis with the aim of producing liquid or solid energy sources (e.g. charcoal production , torrefaction ), pyrolysis gas is produced as a usable by-product. In biomass gasification , pyrolysis is followed by oxidation and reduction as further conversion steps. Energy-rich product gases ( synthetic natural gas ) are generated, which include pyrolysis gas as well as gaseous products from the latter processes.

Applications

There are various options for further processing the pyrolysis gas. In addition to the energetic use for electricity and / or heat generation, the use as a raw material source for chemical applications is possible. Before further processing, the pyrolysis gas is usually subjected to washing in order to remove individual components or dust.

Chemical processing

The pyrolysis gas can be further processed into carbon monoxide and hydrogen by steam reforming with steam. This gas can be converted into chemical products in various technical processes.

Energetic use

The pyrolysis gas can be used directly in the pyrolysis as an energy supplier and thus replace fossil fuels in the provision of the required process heat . It can also be used as a heating component in gas turbines to generate electricity.

Gases from pyrolysis processes

Other gaseous products from pyrolysis processes with special or non-biogenic raw materials are also sometimes referred to as pyrolysis gases.

Depending on the type and origin of the fuel and the pyrolysis process, a distinction is made:

From the pyrolysis of fossil fuels:

From the pyrolysis of waste, for example in the Hamburg process :

  • generally the main component of pyrolysis gases: carbon monoxide (carbon monoxide, CO)

In many cases, the higher volatile constituents contained in pyrolysis gases ( tar , pitch , benzene , phenols , ammonia , ...) are separated out as raw materials for material use, while the actual gas is used for energetic use (combustion).

swell

  • Fachagentur Nachwachsende Rohstoffe ev, 2006: Analysis and evaluation of the thermo-chemical gasification of biomass. Series of Renewable Raw Materials, Volume 29. Landwirtschaftsverlag, Münster. ( pdf ) ISBN 9783784334332

Individual evidence

  1. ↑ Frank Behrend: Direct Liquefaction of Biomass - An Overview ( Memento of the original from January 6, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 1.4 MB), lecture “Direct liquefaction of biomass and plastics” on November 29, 2007, p. 16, accessed on May 5, 2013 and January 6, 2016. @1@ 2Template: Webachiv / IABot / www.mlu.sachsen-anhalt.de
  2. ↑ guten-aufarbeiten.de: sewage sludge pyrolysis (PDF; 65 kB).

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