Recycled carbon fuels
Definition from RED II:
(35) ‘recycled carbon fuels’ means liquid and gaseous fuels that are produced from liquid or solid waste streams of non- renewable origin which are not suitable for material recovery in accordance with Article 4 of Directive 2008/98/EC, or from waste processing gas and exhaust gas of non-renewable origin which are produced as an unavoidable and unintentional consequence of the production process in industrial installations;
The feedstock for these processes is a variety of industrial waste gases that are today flared or used for energy (power and/or heat) production in excess of what is used for the internal needs of the process from which they are emanating. Examples of such gases are coke oven gas, blast furnace gas and basic oxygen converter gas in the steel industry, converter gas from production of alloying metals and refinery off-gases. While coke oven gas and refinery fuel gases are rich in methane and other hydrocarbons, the other gases are very rich in CO but have low hydrocarbon content.
Such gases can be used to produce FT hydrocarbons or methanol after generating a gas similar to synthesis gas, see PVC1: Transport fuels via gasification. Gases with high hydrocarbon content are treated by steam reforming or partial oxidation to generate synthesis gas. The catalytic conversion of CO rich gases requires that H2 is available in the synthesis gas in the correct proportions, which can be accomplished by a water gas shift reaction step consuming CO to produce H2. The gases are then cleaned to synthesis gas quality by similar processes and then converted to fuels by the same type of catalytic reactions as was described in the cited section. There is one example of methanol production from coke oven gas in China.
Another option is gas fermentation that can utilize gas streams with a wide range of CO and H2 compositions directly to produce ethanol, as the acetogenic microbes used are also capable of an efficient biological water gas shift reaction. Furthermore, the gas purity requirements are less strict than for chemical catalysis. The ethanol produced is then separated by distillation and dehydration as described in PVC5: Alcohol fuels from cellulosic sugars and EVC3: Sugar and starch fermentation to ethanol. A tail gas, including any hydrocarbons in the feed, unreacted CO and H2 not converted as well as CO2 leaves the process. Some of the energy in the feed gas is consumed to build microbial biomass in the system. The excess biomass can be used to produce biogas via anaerobic digestion, see Section 22.214.171.124. The biogas together with the tail gas can be used to cover process energy needs.
There are some industrial scale developments in this area. Lanzatech have developed technology at TRL 7, approaching TRL 8, for CO or synthesis gas fermentation which is being demonstrated at industrial scale, 45 000 tonnes ethanol/year (29 000 toe/year) in a steel mill in China using CO-rich BOF gas. A second plant is under construction in Belgium using a mixture of BOF and blast furnace gas at a capacity of 65 000 tonnes ethanol/year (42 000 toe/year), and there are also a number of other project being pursued, e.g. with Aemetis , for ferroalloy off-gas in South Africa and for refinery gas in India.
Waste plastics, non-biogenic fraction of RDF etc. can, separated or together with biogenic fractions, be processed by thermal conversion and upgrading methods already described above such as gasification, pyrolysis and HTL, and thus being at the same TRL level. The Enerkem gasification developments were already described above in PVC1: Transport fuels via gasificationp.
One specific type of processing which has recently received a lot of attentions is the processing of separated plastic waste streams via pyrolysis or HTL systems. The pyrolysis of waste plastics, mostly fractions or mixed fractions of polyethene (polyethylene), polypropene (polypropylene) and polystyrene, is mostly performed by slow pyrolysis at 400 °C in kilns or other types of furnaces to render a mixed oil fraction, char and some gases, the latter used internally as a fuel. The oil fraction from pyrolysis or from HTL processing can then be fractionated by distillation to yield conventional hydrocarbon fuel fractions, in particular a diesel fraction. This is mostly done as an integrated part of the process due to legal requirements in the EU, but could also be done in a refinery. Any liquid residue is recycled, or used for energy in the process.
There are a number of such developments in the USA and the EU at a scale of 10 000- 40 000 tonnes/year. Some examples of developers with industrial scale plants in operation and/or construction are (IGE Solutions (NL), JBI (USA), Klean Industries (JP), Nexus Fuels (CN), Plastic Energy (UK), Quantafuel (NO), Recycling Technologies (UK), ReNew ELP (UK), Remondis (DE), Renewology (USA), VADXX (USA).
 SGAB Technology status and reliability of the value chains: 2018 Update. 28 December 2018. Ed. I Landälv, L Waldheim, K Maniatis. artfuelsforum.eu/news-articles/updated-sgab-report-technology-status-and-reliability-of-the-value-chains/