Sustainability and lifecycle assessment of pyrolysis oil production and application

Sustainability assessment

Sustainability means that the needs of the present generation are met without compromising the ability of future generations to meet their own needs. The concept of sustainability is made tangible by definition of sustainability principles, criteria and measurable indicators. If bioliquids like pyrolysis liquid and biofuels like pyrolysis diesel are counted towards European renewable energy targets and/or receive renewable energy subsidies, they need to comply with a minimum set of European sustainability criteria as defined in the Renewable Energy Directive (RED). Within the Residue2heat project, VTT (2017)[1] has checked the potential emission reductions of pyrolysis oil using the method of the Renewable Energy Directive and its proposed successor (RED II), resulting in the emission reductions from the application of pyrolysis oil for residential heating, using forest residues (89% reduction), bark (94%), straw (90%), and Miscanthus (80%); the latter being somewhat lower due to the use of artificial fertilisers.

Figure 1: Photograph of miscanthus stalk harvesting (source = http://www.sieverdingbeck-agrar.de/miscanthus/bilder/ernte/)

 Lifecycle assessment

Within this project BTG has carried out a Life Cycle Assessment, using two impact methods (IPCC 2013 & ReCiPe 2016 methods), which resulted in marginally higher emissions per MJ pyrolysis oil than the RED, mainly because residues are allocated part of the environmental impacts associating with growing the crop, while in the RED this allocation is not applied. See Table 1. Outlier is Miscanthus with a better performance using the LCA methods, because differences in the assumed use of fertilisers.

Table 1. Comparison of the GHG emissions of FPBO in g CO2 eq/MJ FPBO using three different calculation methods.

ReCiPe 2016 has a much broader scope than GHG emission reduction as it contains 17 midpoint impact categories that can be merged into three endpoint categories: damage to human health, ecosystems and resource availability. ReCiPe 2016 is a commonly used LCA impact assessment method. The method is described in detail in Huijbrechts et al (2016)[2].

Figure 2: The Endpoint scores of the ReCiPe 2016 impact assessment for the production of 17.8 GJ heat from natural gas, heating oil, wood pellets, and pyrolysis oil from five different biomass sources.

Figure 2 shows the endpoint impacts of 17.8 GJ of heat, which is the average per capita domestic energy consumption for heating and hot water within the EU, using oil, natural gas pellets and pyrolysis oil produced from a number of feedstocks. The feedstock “pellet wood”, a typical mixture of biomass sources used for the production of pellets, was added to be able to compare wood pellets with pyrolysis oil.

Overall, the heating options using fast pyrolysis bio-oil score better than the fossil fuel heating options. In both endpoints damage to human health and damage to resources, bioenergy has a lower impact than fossil fuel heating options. In the damage to ecosystems endpoint, bioenergy has a similar impact, either slightly higher or slightly lower, depending on the allocation of the biomass. However, this impact is of a different origin, where fossil heating causes the damage to ecosystems by global warming, the bioenergy options receive an impact from the occupation of land by forests and crop land.

Please contact Martijn Vis (BTG) for more information on this subject.

 

[1] https://www.residue2heat.eu/wp-content/uploads/2017/07/D6_1_Sustainable_Chain_Evaluation_1.1_VTT_20170706.pdf

[2] Huijbrechts, M. et al. (2016) ReCiPe 2016, a harmonized lifecycle impact assessment method at midpoint and endpoint level. Report I: characterization.