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Biofuels from Kraft Black Liquor: Pilot-Scale Gasification Development and Techno-Economic Evaluation of Industrially Relevant Biofuel Production Pathways
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.ORCID iD: 0000-0001-9208-1642
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Fuel combustion for transport was responsible for 24% of EU-28 greenhouse gas (GHG) emissions in 2016. Member states are expected to ensure that the share of renewable energy in the transport sector is at least 14% by 2030. Some countries, such as Sweden, have more ambitious targets. By 2030, GHG emissions from domestic transport are to be reduced by 70% relative to 2010 levels. A national emission reduction scheme launched in 2018 obliges suppliers of diesel and petrol to reduce their GHG footprints annually by a pre-determined amount, which could further stimulate demand for drop-in biofuels, and potentially even high blend alternatives. However, recent changes to Swedish domestic policy and the EU-wide RED sustainability criteria mean that biodiesel from some common crop-based biomaterials may no longer qualify for certain important tax benefits or count towards the 2030 renewables target. Given Sweden’s extensive forest products industry, woody residue and by-products, such as branches, toppings and black liquor (BL) are viewed as strategically important feedstock for the production of RED-compliant biofuels. Upgrading kraft BL to biofuels can also potentially help pulp mills expand their product base. Two conversion routes are seen as industrially relevant in the short-to-medium term: (a) gasification-catalytic synthesis, (b) liquefaction-hydrotreatment.

The production of methanol and dimethyl ether from kraft BL has been demonstrated extensively in a pilot facility, although a complete analysis of technical performance based on experimental measurements has not been performed previously. Since BL is not transportable, the biofuel production potential of a mill is effectively set by its pulp throughput, which limits potential economies-of-scale. BL is rich in catalytically active sodium compounds and blending it with other woody residue-based feedstock, such as pyrolysis oil (PO) before gasification allows the partial decoupling of biofuel production capacity from available black liquor volumes. Several commercial actors are currently testing the technical viability of using liquefaction-hydrotreatment for the production of renewable petrol and diesel blendstock from kraft lignin. The first step in both cases is co-located at a pulp mill. Depending on the desired end product and production route, subsequent upgrading and finishing may be carried out at a pulp mill or a crude oil refinery, with a resulting impact on both production economics and energetic performance that is complex and little studied. 

The main aim of this thesis is to evaluate the technical and economic viability of kraft liquor-based biofuel production pathways that are adjudged to be commercially relevant, that is they are seen as commercially deployable in the short-to-medium term at the present time. The catalytic co-gasification of PO and BL was studied in pilot-scale experiments, and resulting data were used to calculate key performance indicators. Blending BL with the more energy-rich PO led to an increase in cold gas efficiency without adversely affecting organic carbon conversion, which remained nearly complete at blend ratios of up to 20 wt.% PO. There were no signs of an increase in either soot or tar formation. Analyses of gas condensate samples found traces of unknown uncharged forms of sulfur and while sulfur reduction efficiencies were generally high, balance closures could not consistently be obtained owing to analytical difficulties. Further study appears warranted. Pilot-scale entrained-flow gasification experiments are expensive and time consuming. An alternative is thermodynamic equilibrium calculations, which were found to predict the flows of major syngas and slag constituents with a high degree of accuracy, subject to expected deviations in methane formation and sulfur distribution.

An analysis of production economics found nth-of-a-kind investments in gasification-based methanol and lignin liquefaction and hydrotreatment-based drop-in biofuels to be profitable for a range of sizes, although the latter pathway, which is currently prioritized for development in the short-run was at a lower level of technology maturity. In assessing the overall energetic performance of a pulp mill-integrated kraft BL-based biofuel production, explicit consideration of mill energy balance is needed to avoid misestimation. Modern market pulp mills with a large energy surplus, normally exported as electricity, are at an advantage. There are indications that relatively small gasification units of around 100 MW could potentially also be profitable, which means biofuel production facilities based on both principle conversion tracks could be used to debottleneck pulp production by relieving recovery boiler capacity constraints, although the viability of such an approach is mill specific and requires detailed investigation. While co-gasifying black liquor with pyrolysis oil or blending syngas from unblended black liquor with electrolysis hydrogen offers better carbon utilization, larger biofuel production potentials and a more diverse feedstock base, gasification of unblended black liquor comes out as the lowest cost option for producing drop-in biofuels from part-streams. 

Place, publisher, year, edition, pages
Luleå University of Technology, 2019.
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keywords [en]
biofuels, black liquor, pyrolysis oil, gasification, drop-in, energy systems, techno-economic
National Category
Energy Systems Energy Engineering
Research subject
Energy Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-75787ISBN: 978-91-7790-433-5 (print)ISBN: 978-91-7790-434-2 (electronic)OAI: oai:DiVA.org:ltu-75787DiVA, id: diva2:1347225
Public defence
2019-10-11, E632, E Building, Luleå, 12:30 (English)
Opponent
Supervisors
Available from: 2019-09-02 Created: 2019-08-30 Last updated: 2019-09-13Bibliographically approved
List of papers
1. Performance of a Pilot-Scale Entrained-Flow Black Liquor Gasifier
Open this publication in new window or tab >>Performance of a Pilot-Scale Entrained-Flow Black Liquor Gasifier
2016 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 30, no 4, p. 3175-3185Article in journal (Refereed) Published
Abstract [en]

Pilot-scale entrained flow gasification experiments were carried out at the 3 MWth LTU Green Fuels black liquor gasification (BLG) plant, using ∼140 tons of Kraft black liquor (BL) with a dry solids content of ∼72.5%. Comprehensive mass and energy balances were performed to quantify process performance under varying pressure, load, and oxygen/fuel ratio. Carbon conversion efficiency of the BLG process was 98.3%–99.2% and did not vary systematically in response to process changes. The unconverted carbon is almost exclusively present as dissolved organic carbon in the green liquor (GL) stream. GL is an aqueous solution of sodium carbonate and sodium sulfide used to recover the inorganic pulping chemicals present in BL for reuse in the pulp mill. A small fraction of syngas CO is converted to formate ions dissolved in GL through reaction with hydroxide ions. Unconverted carbon present in GL solids is insignificant. Syngas produced is subsequently upgraded to methanol and dimethyl ether (DME) in an integrated fuel synthesis facility. Concentration of H2 in syngas is not significantly affected by operating point changes in the domain investigated, while CO and CO2 concentrations are. Syngas hydrocarbon concentration values are typically in the single-digit parts per million (ppm) with the exception of C6H6, which was present at 16–127 ppm. CH4 is present at 0.5%–1.2%, with lower concentrations at higher temperatures, and shows good correlation with C6H6. A quantity of 24%–27% of BL sulfur ended up in the syngas as 1.5%–1.7% H2S and 64–72 ppm COS. Cold gas efficiencies (CGEs) on a lower heating value (LHV) basis, when including syngas CH4, were 52%–55% and decreased at higher temperature. CGEs on an LHV basis, when considering only H2 and CO with a sulfur-free BL heating value relevant for catalytic syngas upgrading, were 58%–60% and showed the opposite temperature dependence. Good mass and energy balance closures show the figures presented to be reliable. The results obtained from this study demonstrate process stability at varying operating conditions and can be further used for techno-economic analysis and design purposes.

National Category
Energy Engineering
Research subject
Energy Engineering
Identifiers
urn:nbn:se:ltu:diva-6993 (URN)10.1021/acs.energyfuels.6b00349 (DOI)000374804400069 ()2-s2.0-84966351790 (Scopus ID)55470d2e-94b0-4bc5-af0e-20f0365821b0 (Local ID)55470d2e-94b0-4bc5-af0e-20f0365821b0 (Archive number)55470d2e-94b0-4bc5-af0e-20f0365821b0 (OAI)
Note
Validerad; 2016; Nivå 2; 20160404 (yawjaf)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2019-08-30Bibliographically approved
2. A study of black liquor and pyrolysis oil co-gasification in pilot scale
Open this publication in new window or tab >>A study of black liquor and pyrolysis oil co-gasification in pilot scale
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2018 (English)In: Biomass Conversion and Biorefinery, ISSN 2190-6815, E-ISSN 2190-6823, Vol. 8, no 1, p. 113-124Article in journal (Refereed) Published
Abstract [en]

The effect of the blend ratio and reactor temperature on the gasification characteristics of pyrolysis oil (PO) and black liquor (BL) blends with up to 20 wt% PO was studied in a pilot-scale entrained-flow gasifier. In addition to unblended BL, three blends with PO/BL ratios of 10/90, 15/85, and 20/80 wt% were gasified at a constant load of 2.75 MWth. The 15/85 PO/BL blend was used to investigate the effect of temperature in the range 1000–1100 °C. The decrease in fuel inorganic content with increasing PO fraction resulted in more dilute green liquor (GL), and a greater portion of the feedstock carbon ended up in syngas as CO. As a consequence, the cold gas efficiency increased by about 5%-units. Carbon conversion was in the range 98.8–99.5% and did not vary systematically with either fuel composition or temperature. Although the measured reactor temperatures increased slightly with increasing PO fraction, both unblended BL and the 15% PO blend exhibited largely similar behavior in response to temperature variations. The results from this study show that blending BL with the more energy-rich PO can increase the cold gas efficiency and improve the process carbon distribution without adversely affecting either carbon conversion or the general process performance.

Place, publisher, year, edition, pages
Springer, 2018
National Category
Energy Engineering
Research subject
Energy Engineering
Identifiers
urn:nbn:se:ltu:diva-61518 (URN)10.1007/s13399-016-0235-5 (DOI)000425594800011 ()2-s2.0-85042226433 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-02-20 (rokbeg)

Available from: 2017-01-18 Created: 2017-01-18 Last updated: 2019-08-30Bibliographically approved
3. Thermodynamic equilibrium analysis of entrained flow gasification of spent pulping liquors
Open this publication in new window or tab >>Thermodynamic equilibrium analysis of entrained flow gasification of spent pulping liquors
2018 (English)In: Biomass Conversion and Biorefinery, ISSN 2190-6815, E-ISSN 2190-6823, Vol. 8, no 1, p. 19-31Article in journal (Refereed) Published
Abstract [en]

he main goal of this work is to investigate if thermodynamic equilibrium calculations can be useful for understanding and predicting process performance and product composition for entrained flow gasification of spent pulping liquors, such as black liquor. Model sensitivity to input data is studied and model results are compared to published pilot plant data. The high temperature and the catalytic activity of feedstock alkali make thermodynamic equilibrium a better predictor of product composition than for many other types of biomass and gasification technologies. Thermodynamic equilibrium calculations can predict the flows of the main syngas and slag products with high accuracy as shown by comparison with experimental data with small measurement errors. The main process deviations from equilibrium are methane formation and sulfur distribution between gas and slag. In order to study real process deviations from equilibrium, it is very important to use consistent experimental data. Relatively small errors in the model input, primarily related to fuel composition, can lead to grossly erroneous conclusions. The model sensitivity to fuel composition also shows that the gasification process is sensitive to naturally occurring feedstock variations. Simulations of a commercial-scale gasification process show that cold gas efficiency on sulfur-free basis can reach over 80 % and that greatly improved efficiency can be obtained by reducing ballast present in the form of water or inorganics.

Place, publisher, year, edition, pages
Springer, 2018
National Category
Energy Engineering
Research subject
Energy Engineering
Identifiers
urn:nbn:se:ltu:diva-60579 (URN)10.1007/s13399-016-0225-7 (DOI)000425594800003 ()2-s2.0-85042227019 (Scopus ID)
Funder
Swedish Energy Agency, 38026-1
Note

Validerad;2018;Nivå 2;2018-02-20 (rokbeg)

Available from: 2016-11-21 Created: 2016-11-21 Last updated: 2019-08-30Bibliographically approved
4. Multi-aspect evaluation of integrated forest-based biofuel production pathways: Part 1. Product yields & energetic performance
Open this publication in new window or tab >>Multi-aspect evaluation of integrated forest-based biofuel production pathways: Part 1. Product yields & energetic performance
Show others...
2019 (English)In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 166, p. 401-413Article in journal (Refereed) Published
Abstract [en]

Forest-based biofuels are strategically important in forest-rich countries like Sweden but the technical performance of several promising production pathways is poorly documented. This study examines product yields and energy efficiencies in six commercially relevant forest-based “drop-in” and “high blend” biofuel production pathways by developing detailed spreadsheet energy balance models. The models are in turn based on pilot-scale performance data from the literature, supplemented with input from technology developers and experts. In most pathways, biofuel production is integrated with a market pulp mill and/or a crude oil refinery. Initial conversion is by pyrolysis, gasification or lignin depolymerization and intermediate products are upgraded by hydrotreatment or catalytic synthesis.

While lignin oil (LO) hydrodeoxygenation had the highest expanded system efficiency, considerable uncertainty surrounds product yields owing to absence of suitable experimental data on LO upgrading. Co-feeding vacuum gas oil and fast pyrolysis oil in a fluidized catalytic cracker has a complex and uncertain effect on fossil yields, which requires further investigation. Co-locating bio-oil hydrotreatment at the refinery improves heat utilization, leading to higher system efficiencies. Explicit consideration of mill type and energy requirements is required to avoid performance misestimation as an assumption of energy surplus can confer a definite advantage.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Biofuels, Pyrolysis, Gasification, Lignin oil, Energy efficiencies, Product yields
National Category
Energy Engineering
Research subject
Energy Engineering
Identifiers
urn:nbn:se:ltu:diva-71274 (URN)10.1016/j.energy.2018.10.008 (DOI)000455694300035 ()2-s2.0-85056190528 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-11-07 (inah)

Available from: 2018-10-18 Created: 2018-10-18 Last updated: 2019-08-30Bibliographically approved
5. Multi-aspect evaluation of integrated forest-based biofuel production pathways: Part 2, economics, GHG emissions, technology maturity and production potentials
Open this publication in new window or tab >>Multi-aspect evaluation of integrated forest-based biofuel production pathways: Part 2, economics, GHG emissions, technology maturity and production potentials
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2019 (English)In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 172, p. 1312-1328Article in journal (Refereed) Published
Abstract [en]

Promoting the deployment of forest-based drop-in and high blend biofuels is considered strategically important in Sweden but many aspects of the overall performance of the foremost production technologies are as yet unexamined. This paper evaluates the technology maturity, profitability, investment requirements, GHG performance and Swedish biofuel production potential of six commercially interesting forest-based biofuel production pathways.

Significant heterogeneity in technology maturity was observed. Lack of technical demonstration in industrially representative scales renders the liquefaction-hydrotreatment route for drop-in biofuels less mature than its gasification-catalytic upgrading counterpart. It is a paradox that short-term priority being accorded to pathways with the lowest technology maturity. Nth-of-a-kind investments in (a) gasification-based methanol, (b) hydropyrolysis-based petrol/diesel, and (c) lignin depolymerization-based petrol/diesel were profitable for a range of plant sizes. The profitability of pulp mill-integrated small gasification units (<100 MW) goes against the common perception of gasification being economically feasible only in large scales. New low-cost options for debottlenecking production at recovery boiler-limited kraft mills appear worth investigating. GHG emission reductions ranged from 66 to 95%; a penalty was incurred for high consumption of natural gas-based hydrogen. Swedish biofuel production potentials ranged from 4 to 27 TWh/y but a more feasible upper limit is 12–15 TWh/y.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Biofuels, Gasification, Lignin oil, Pyrolysis oil, Black liquor, Forest residues
National Category
Energy Engineering
Research subject
Energy Engineering
Identifiers
urn:nbn:se:ltu:diva-73052 (URN)10.1016/j.energy.2019.02.036 (DOI)000464488100107 ()2-s2.0-85063629405 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-04-11 (johcin)

Available from: 2019-02-27 Created: 2019-02-27 Last updated: 2019-09-13Bibliographically approved
6. Combining Expansion in Pulp Capacity with Production of Sustainable Biofuels – Techno-economic and GHG emission assessment of Drop-in Fuels from Black Liquor Part-Streams
Open this publication in new window or tab >>Combining Expansion in Pulp Capacity with Production of Sustainable Biofuels – Techno-economic and GHG emission assessment of Drop-in Fuels from Black Liquor Part-Streams
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Drop-in biofuels produced from forestry by-products such as black liquor (BL) can help achieve deep reductions in transport GHG emissions. Upgrading kraft BL to drop-in biofuels can also help pulp mills increase pulp production and expand their product base, especially if the technical and economic risk associated with recovery boiler replacement can be mitigated. The economic and GHG performance of two lignin-based pathways and three gasification-based pathways is examined. All of these pathways can be used to debottleneck recovery boiler-limited pulp mills by converting black liquor part-stream to drop-in biofuels, with final processing in crude oil refineries, which is poorly investigated in the literature. Process modelling was carried out using best available technical data to estimate biofuel yields, estimate GHG footprints and determine biofuel production costs.

Results show that the lignin route and the gasification have comparable production costs of ∼ 80 EUR2017 in the best case. One yields diesel as the primary biofuel product, while the other produces petrol and LPG. Mill that have an energy surplus that is normally exported as electricity have an advantage as biofuel integration sites over mills with no or negative surplus. All of the examined pathways can meet or exceed RED II criteria for GHG emission savings from new plants. Within the lignin route, the use of natural gas as hydrogen source represents the cheaper option by some margin, but GHG savings from the electrolysis-hydrogen alternative are considerably greater. The use of pyrolysis oil and electrolysis hydrogen as secondary feeds can improve the efficiency of biofuel production and generate larger biofuel yields from the same amount of black liquor. However, the high price of pyrolysis oil and the high investment cost of PEM electrolysis makes the BLG+electrolysis and BLG+pyrolysis alternatives more expensive than the gasification of unblended black liquor.

National Category
Energy Systems
Research subject
Energy Engineering
Identifiers
urn:nbn:se:ltu:diva-75785 (URN)
Available from: 2019-08-30 Created: 2019-08-30 Last updated: 2019-08-30

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