Conversion of Residual Biomass into Liquid Transportation Fuel: An Energy Analysis

Abstract

An energy balance, in broad outline, is presented for the production of a high-quality liquid transportation fuel from residual crop biomass. The particular process considered is comprised of (1) harvesting surplus biomass (such as crop residue); (2) locally pyrolyzing the biomass into pyrolysis oil (PO), char, and noncondensable gas (NCG); (3) transporting the PO to a remote central processing facility; (4) converting the PO at this facility by autothermal reforming (ATR) into synthesis gas (CO and H2); followed by, at the same facility, (5) Fischer–Tropsch (FT) synthesis of the syngas into diesel fuel. In carrying out our calculations, we have made several assumptions about the values of the process parameters. These parameters, of course, can be modified as better input data become available. The material and energy balance has been incorporated into an Excel spreadsheet. The scope and our approach to the energy budget using a widely available spreadsheet hopefully provides greater transparency, as well as ease of scenario manipulation than has generally been found in the literature. The estimated energy efficiencies computed with the spreadsheet are comparable to those obtained with Aspen software. A spreadsheet is offered as a tool for further analysis of the energy budget of this and related processes. The Excel spreadsheet can be used as a nimble scouting tool to indicate promising avenues of study in advance of using a more comprehensive analysis such as that afforded by Aspen software. The process considered, in which a portion of the char and noncondensable gas are used to supply heat to the drying and pyrolysis steps and under the assumptions made, was found to have an energy efficiency to liquid fuel on the order of 40%. That is, 40% of the initial energy in the biomass will be found in the final liquid fuel after subtracting out external energy supplied for complete processing, including transportation as well as material losses. If the energy of the remaining char and NCG is added to that in the product diesel oil, the total recovered energy is estimated to be ∼50% of the initial energy content of the biomass. If char and NCG are not used as a heat source in the process, the energy efficiency of the produced diesel drops from 40% to 15%. It must be realized that the distribution of energy content among the fast pyrolysis products PO, char, and NCG is ∼69%, ∼27%, and ∼4%, respectively. Therefore, using char and NCG to provide fuel for the drying and pyrolysis steps is very critical in maintaining high energy efficiency of the product fuel. The weight of diesel fuel produced is estimated to be ∼13% of the initial weight of biomass, implying that 1 t of biomass (30% moisture) will produce 1.0 barrels of diesel oil. The pyrolysis of biomass to PO, char, and NCG is estimated to have an intrinsic energy efficiency of ∼90%. For the model considered, trucking biomass to a central facility without first converting it to PO is estimated to reduce energy efficiency by ∼1%.

Review of recent developments to improve storage and transportation stability of bio-oil

“…Considerable efforts during the last five to ten years have contributed to the development of measuring standards and methods of bio-oil stability so that improvements in the storage and transportation stability of bio-oil can be quantified [20,21]. So far, extensive studies have been focused on the upgrading of bio-oil into advanced bioproducts and/or biofuels, and the state-of-art of bio-oil upgrading has been critically reviewed [22,23]. However, only limited information is available on the comprehensive understanding of bio-oil stability, including the mechanisms leading to instability, methods to quantitatively measure stability, the difference between stabilization and upgrading of bio-oil, and recent developments in techniques and methods to improve the storage and transportation stability of bio-oil.…”

Energetic assessment of air-steam gasification of sewage sludge and of the integration of sewage sludge pyrolysis and air-steam gasification of char

“…This value is lower than the decomposition heats found in the literature for other types of biomass. For example, a decomposition heat of 0.3 MJ kg À1 has been reported for pyrolysis of crop residues [29]. The higher ash content in sewage sludge, which is not decomposed during the process, can explain this difference.…”

Modeling of soot formation during partial oxidation of producer gas

“…Liquid fuels in this area can be for instance ethanol, methanol and bio-diesel produced from different types of biomass using various methods. Fischer-Tropsch diesel produced from synthesis gas (CO and H 2 ) derived from renewable resources is a growing area of research [1][2][3][4]. Traditionally the synthesis gas used for the Fischer-Tropsch process was produced via coal gasification.…”

“…Traditionally the synthesis gas used for the Fischer-Tropsch process was produced via coal gasification. Lately research has been focused on how to produce synthesis gas by utilizing gas produced via biomass gasification [4][5][6][7][8][9][10]. The gas produced by the gasifier is often referred to as producer gas.…”

“…The gas produced by the gasifier is often referred to as producer gas. The producer gas contains CO, CO 2 , H 2 and H 2 O as well as CH 4 and higher hydrocarbons, including some tar compounds. There are also small amounts of contaminants present in the syngas, such as NH 3 , H 2 S, COS and HCN.…”