Pyrolysis biochar systems for recovering biodegradable materials: A life cycle carbon assessment

Energy Policy, 2011

Life cycle assessment (LCA) of slow pyrolysis biochar systems (PBS) in the UK for small, medium and large scale process chains and ten feedstocks was performed, assessing carbon abatement and electricity production. Pyrolysis biochar systems appear to offer greater carbon abatement than other bioenergy systems. Carbon abatement of 0.7-1.3 t CO 2 equivalent per oven dry tonne of feedstock processed was found. In terms of delivered energy, medium to large scale PBS abates 1.4-1.9 t CO 2 e/MWh, which compares to average carbon emissions of 0.05-0.30 t CO 2 e/MWh for other bioenergy systems. The largest contribution to PBS carbon abatement is from the feedstock carbon stabilised in biochar (40-50%), followed by the less certain indirect effects of biochar in the soil (25-40%)-mainly due to increase in soil organic carbon levels. Change in soil organic carbon levels was found to be a key sensitivity. Electricity production off-setting emissions from fossil fuels accounted for 10-25% of carbon abatement. The LCA suggests that provided 43% of the carbon in the biochar remains stable, PBS will out-perform direct combustion of biomass at 33% efficiency in terms of carbon abatement, even if there is no beneficial effect upon soil organic carbon levels from biochar application.

This study aimed to investigate the extent to which it is possible to marry the two seemingly opposing concepts of heat and/or power production from biomass with carbon sequestration in the form of biochar. To do this, we investigated the effects of feedstock, highest heating temperature (HTT), residence time at HTT and carrier gas flow rate on the distribution of pyrolysis co-products and their energy content, as well as the carbon sequestration potential of biochar. Biochar was produced from wood pellets (WP) and straw pellets (SP) at two temperatures (350 and 650 °C), with three residence times (10, 20 and 40 min) and three carrier gas flow rates (0, 0.33 and 0.66 l min−1). The energy balance of the system was determined experimentally by quantifying the energy contained within pyrolysis co-products. Biochar was also analysed for physicochemical and soil functional properties, namely environmentally stable-C and labile-C content. Residence time showed no considerable effect on any of the measured properties. Increased HTT resulted in higher concentrations of fixed C, total C and stable-C in biochar, as well as higher heating value (HHV) due to the increased release of volatile compounds. Increased carrier gas flow rate resulted in decreased biochar yields and reduced biochar stable-C and labile-C content. Pyrolysis at 650 °C showed an increased stable-C yield as well as a decreased proportion of energy stored in the biochar fraction but increased stored energy in the liquid and gas co-products. Carrier gas flow rate was also seen to be influential in determining the proportion of energy stored in the gas phase. Understanding the influence of production conditions on long term biochar stability in addition to the energy content of the co-products obtained from pyrolysis is critical for the development of specifically engineered biochar, be it for agricultural use, carbon storage, energy generation or combinations of the three.

IntechOpen, 2019

Organic matter derived from plants and animals are known as biomass. It has a great potential to be used as an alternate source of energy by employing ther-mochemical conversion techniques. Among the available techniques, pyrolysis is considered to be the most efficient technique used for the conversion of biomass-based waste into value-added solid, liquid and gaseous products through heating in an oxygen-limited environment. Biochar (solid fuel) is a carbonaceous material and has multiple applications in various fields such as soil health, climate stability, water resource, energy efficiency and conservation. The yield of biochar depends on organic constituents of biomass and the pyrolytic process parameters such as temperature, time, heating rate, purging gas, particle size, catalyst, flow rate, pressure and types of pyrolysis reactors. Suitable conditions for biochar production were observed to be slow pyrolysis, low carrier gas flow rate, acid-catalysed biomass or biomass mixed with some inorganic salts, low heating rate, large particle size, high pressure, longer residence time, low temperature, feedstocks with high lignin content and pyrolysis reactors with lower bed height. Thermal conversion of biomass could be a possible sustainable alternative to provide economically viable, clean and eco-friendly solid fuel.

Environmental Science & Technology, 2010

Biomass pyrolysis with biochar returned to soil is a possible strategy for climate change mitigation and reducing fossil fuel consumption. Pyrolysis with biochar applied to soils results in four coproducts: long-term carbon (C) sequestration from stable C in the biochar, renewable energy generation, biochar as a soil amendment, and biomass waste management. Life cycle assessment was used to estimate the energy and climate change impacts and the economics of biochar systems. The feedstocks analyzed represent agricultural residues (corn stover), yard waste, and switchgrass energy crops. The net energy of the system is greatest with switchgrass (4899 MJ t -1 dry feedstock). The net greenhouse gas (GHG) emissions for both stover and yard waste are negative, at -864 and -885 kg CO 2 equivalent (CO 2 e) emissions reductions per tonne dry feedstock, respectively. Of these total reductions, 62-66% are realized from C sequestration in the biochar. The switchgrass biochar-pyrolysis system can be a net GHG emitter (+36 kg CO 2 e t -1 dry feedstock), depending on the accounting method for indirect land-use change impacts. The economic viability of the pyrolysis-biochar system is largely dependent on the costs of feedstock production, pyrolysis, and the value of C offsets. Biomass sources that have a need for waste management such as yard waste have the highest potential for economic profitability (+$69 t -1 dry feedstock when CO 2 e emission reductions are valued at $80 t -1 CO 2 e). The transportation distance for feedstock creates a significant hurdle to the economic profitability of biochar-pyrolysis systems. Biochar may at present only deliver climate change mitigation benefits and be financially viable as a distributed system using waste biomass.

In the case of lifecycle analyses, pyrolysis biochar systems have all integrated treatment and usage systems for any products resulting from the carbonisation of biomass. These systems require biomass ingredients as an input material source, which is a fuel available in many forms, f.e. forestry by-products, sewage waste, animal manure, etc. These materials are put into the pyrolysis process, where the produced biochar (active coal) is fed into the soil, where the circulation of the coal restarts. The biochar system is a complex system which requires multiple components and details to be taken into consideration to allow for a proper lifecycle assessment, in order to make the proper decisions.

Biomass is considered to have potential to be used as an alternative energy source. High carbon content present in biomass converts it into high energy biochar on thermochemical treatment. Among few well established thermochemical technologies for the treatment of biomass and biogenic waste to produce high energy char along with oil and gaseous yield, pyrolysis is the most studied and discussed technique in the recent past. A comparison between the existing techniques is established in the present work. Production of char from the biomass and biogenic wastes is reviewed and it was found that yield of the biochar depends upon the biomass composition like moisture content and presence of cellulose or lignin. Pyrolysis product distribution and their quality strongly depend upon the process parameters. Different biomasses which can be used as raw material in pyrolysis are also reviewed and categorized depending upon their source. Pyrolysis process parameters such as temperature, heating rate, residence time etc. also influence the biochar yield. This study discusses the effect of these process parameters on the production of biochar through pyrolysis of biomass.

Detritus, 2021

The pyrolysis of sewage sludge is an alternative method to recycle the contained nutrients, such as phosphorus, by material use of the resulting biochar. However, the ecological effects of pyrolysis are not easy to evaluate. Therefore, a life cycle assessment (LCA) was carried out to determine the environmental impact of sewage sludge pyrolysis and to compare it with the common method of sewage sludge incineration. In order to identify the most sustainable applications of the resulting biochar, four different scenarios were analyzed. The modeled life cycles include dewatering, drying and pyrolysis of digested sewage sludge and utilization paths of the by-products as well as various applications of the produced biochar and associated transports. The life cycle impact assessment was carried out using the ReCiPe midpoint method. The best scenario in terms of global warming potential (GWP) was the use of biochar in horticulture with net emissions of 2 g CO2 eq./kg sewage sludge. This sc...

Journal of Analytical and Applied Pyrolysis, 2020

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Renewable Energy, 2020

The aim of this work was to analyse the influence of the pyrolysis temperature and feedstock composition on biochar yield and physicochemical properties. The raw materials to be pyrolyzed were characterized, and an experimental design was applied to carry out a statistical study. Three operating temperatures (673, 773 and 873 K) and two bio-wastes (nut and almond shells) were used. Several correlations linking the values of different physicochemical properties of the biochar with the two variables were proposed. On the basis of these correlations, it was found that almost all physicochemical characteristics of both almond and nut shell-based biochars depended on both the pyrolysis temperature and bio-waste composition, and an interaction of the two variables was observed in our experiments. Only the biochar yield did not exhibit an interaction between these two variables. The biochars presented H/C and O/C ratios and higher heating values similar to those of bituminous coal, confirming their potential as solid bio-fuels. They also presented high K and Ca contents. The obtained values for the aromaticity factor, stable C mass fraction and recalcitrance potential, indicated that the biochars could also be used for soil amendments, especially as acidic or basic compounds, according to their pH values.

Biochar, 2020

Various studies have established that feedstock choice, pyrolysis temperature, and pyrolysis type influence final biochar physicochemical characteristics. However, overarching analyses of pre-biochar creation choices and correlations to biochar characteristics are severely lacking. Thus, the objective of this work was to help researchers, biochar-stakeholders, and practitioners make more well-informed choices in terms of how these three major parameters influence the final biochar product. Utilizing approximately 5400 peer-reviewed journal articles and over 50,800 individual data points, herein we elucidate the selections that influence final biochar physical and chemical properties, total nutrient content, and perhaps more importantly tools one can use to predict biochar’s nutrient availability. Based on the large dataset collected, it appears that pyrolysis type (fast or slow) plays a minor role in biochar physico- (inorganic) chemical characteristics; few differences were evident...