Life cycle perspective of bio-oil and biochar production from hardwood biomass; what is the optimum mix and what to do with it?

Abstract

Many studies identified the optimum temperature to maximise bio-oil/biochar yield using fast pyrolysis from woody biomass. However, the optimum mix of biochar and bio-oil production and their final utilisation to achieve optimal environmental and economic benefits are yet to be investigated. Hence, the aim of this study was to identify the optimum mix and utilisation using life cycle assessment and costing approach. Two utilisation scenarios were analysed: Scenario 1 considered terrestrial carbon sequestration through spreading biochar in corn fields while Scenario 2 assumed the co-combustion of biochar to displace coal in a coal-fired power station. In both scenarios, bio-oil was assumed to substitute heavy fuel oil in an industrial boiler. The functional unit used in the study was 1 Mg of green thinned logs from hardwood plantations. Scenario 1 showed outstanding greenhouse gas emissions offset (1,680 kg-CO 2-eq per function unit). However, this scenario lagged behind when considering other environmental impacts. Scenario 2 delivered more modest greenhouse gas offset, but it had better overall environmental and economic performance. The results indicated that the overall environmental performance of Scenario 2 decreased with increasing pyrolysis temperature due to the decline in biochar yield as well as the increased energy consumption during the pyrolysis process. Meanwhile, lifecycle cost reduced when the pyrolysis temperature increased because of the increased bio-oil production, which has higher economic value than biochar. Assuming equal weights for the environmental and economic functions, the optimal performance of Scenario 2 is likely to be achieved when the pyrolysis process is run at 500 ˚C with the bio-oil and biochar yields being 64% and 22%, respectively. Monte Carlo Analysis revealed that for balanced environmental and economic weights (30%-70%) the solution is robust. The Monte Carlo Analysis results suggested that under the optimal conditions, there is 97.5% likelihood that Scenario 2 would achieve 1,050 kg-CO 2-eq greenhouse gas emissions offset and realise $25.8 life cycle cost savings per functional unit. This study demonstrates an easy method to incorporate life cycle assessment and costing into an optimisation decision making framework. Thus, allowing a more comprehensive assessment of policies incorporating multiple environmental impacts (criteria). It contributes to the debate about the economic and environmental validity of using forestry by-products, as well as other low cost woody biomass as a renewable energy source.

Engineered Biochar Production and Its Potential Benefits in a Closed-Loop Water-Reuse Agriculture System

“…To further improve the economic feasibility of biochar and agricultural coproduction, pyrolysis units should be installed and operated for biochar production near feedstock sources, thus reducing the high cost of long-distance transportation of low-energy-density biomass [60]. The crude oil generated during pyrolysis can be transported to nearby refineries (economically feasible if <500 km) to further increase biochar's commercial values (i.e., marketability) for its applications in agriculture [24,61].…”

The Eco-Friendly Biochar and Valuable Bio-Oil from Caragana korshinskii: Pyrolysis Preparation, Characterization, and Adsorption Applications

“…The bio-oil also contains a certain amount of high-value chemicals, such as Guaiacol (Phenol, 2-methoxy-) and α-D-glucose (1,4:3,6-Dianhydro-α-D-glucopyranose). The Guaiacol (relative content 5.08%) is an important fine chemical intermediate and widely used in the synthesis of medicines, spices and dyes [58]. The α-D-glucopyranose (relative content 2.63%), which is mainly used in medical liver function test or medicine, is rarely synthesized artificially considering its cost.…”

“…Interestingly, the bio-oil contains α-D-glucopyranose and thus can be a valuable product obtained by pyrolysis biomass, which usually exists in the form of black-brown organic liquid mixture. Discussing with some related literature reports [56][57][58], the bio-oil of Caragana korshinskii biomass has the advantages of wide raw material sources, abundant reserves, renewable, high energy density, and easy transportation and storage. Khuenkaeo et al [57] and Lu et al [58] also believed the bio-oil is a potential source of liquid fuel and chemical raw materials.…”

“…Discussing with some related literature reports [56][57][58], the bio-oil of Caragana korshinskii biomass has the advantages of wide raw material sources, abundant reserves, renewable, high energy density, and easy transportation and storage. Khuenkaeo et al [57] and Lu et al [58] also believed the bio-oil is a potential source of liquid fuel and chemical raw materials. Therefore, biomass pyrolysis is an important technical method for solving fossil energy problems in the future, and many scholars have reached consensus on this point [56][57][58].…”

Techno-economic and environmental analysis of bio-oil production from forest residues via non-catalytic and catalytic pyrolysis processes

“…Allocation by mass was chosen for both scenarios. Biochar has a significant economic value as a co-product, which is not suitable for allocation by economic value when bio-oil is the main product (Lu & El Hanandeh, 2019). Furthermore, the economic value of bio-oil is not fixed but determined through the profitability analysis, where several assumptions were made.…”