Black Liquor Gasification Research Articles

System development and thermodynamic performance analysis of a system integrating supercritical water gasification of black liquor with direct-reduced iron process

Hydrogen metallurgy is an effective way to decarbonize the steel industry. In this study, a new system integrating biomass supercritical water gasification (SCWG) with hydrogen generation-shaft furnace-electric arc furnace (HSE) was proposed. The thermodynamic performance of SCWG-HSE system were analyzed and optimized. The results show that the gasification and energy efficiency of SCWG system increase with an increase in the gasification temperature. The carbon emission of the SCWG-HSE system are effectively reduced, and the product yield and energy efficiency of the system are improved by increasing gasification temperature and recovering furnace top gas. The energy and exergy efficiency of the SCWG-HSE system are 46.66% and 40.17%, respectively. The exergy destruction of SCWG gasifier and electric arc furnace are the major exergy damage sources of the SCWG-HSE system. The exergy efficiency of the ironmaking system reaches 51.60%, and the energy consumption and carbon emission per unit product are 18.49 GJ/t and 902.40 kg/t, respectively. Compared with the traditional Coking-Blast furnace ironmaking process, the energy consumption and carbon emission of this system are reduced by 7.32% and 40.84% respectively. This work is expected to open a new way for the application of biomass in the low-carbon steel industry.

Decarbonizing the Fertilizers Sector: An Alternative Pathway for Urea and Nitric Acid Production

Abstract In order to alleviate the environmental impact that nitrogen fertilizers production is responsible for, several efforts have been addressed to incentivize the partial or total decarbonization of the supply chains of ammonia and its derivatives. The decarbonization of the nitrogen fertilizers sector might help not only improve its carbon footprint, but also reduce its dependence on international market prices of natural gas. To this end, in this work, two fertilizers production plants, namely nitric acid and urea, are integrated into a kraft pulp mill via black liquor gasification to supply the renewable input required by the chemical processes. The performance of the proposed systems is assessed and compared in the light of thermodynamic, economic, and environmental indicators. The choice of the utility system has been driven by the interrelation of the market conditions, as well as the extent of the energy integration of the chemical plants. As a result, the exergy efficiency of the integrated plants remains competitive against the conventional kraft pulp mill thanks to the optimal selection of the operating conditions of the utility system. This efficiency indicator compares the exergy input with the minimum theoretical work needed to reversibly produce the chemicals out from the components in the environment. Furthermore, the overall CO2 emissions balance achieves negative values for some scenarios, pointing out the potential for atmospheric CO2 depletion when the integrated processes are implemented. The indirect emissions of the biomass supply chain proved to have a great impact on the CO2 balance. Finally, the findings suggest that both nitric acid and urea production have positive incremental net present values across the range of carbon taxes considered, indicating the economic viability of these integrated systems vis-à-vis the traditional standalone pulp and fertilizers production plants.

Process modeling and integration of hydrogen and synthetic natural gas production in a kraft pulp mill via black liquor gasification

The black liquor gasification integrated to chemical plants has shown potential for reducing the process irreversibility and promoting the decarbonization of this industrial sector. In the integrated chemical plants proposed in this work, the purpose is co-producing pulp and gaseous fuels, either hydrogen or synthetic natural gas, in order to expand the biorefinery product portfolio and, consequently, increase the plant revenues. However, due to additional equipment and utility demands, along with the uncertainty about the prices of the commodities; the benefits of the integrated setups must be thoroughly weighed by considering thermodynamic, economic and environmental indicators before the retrofit of the existing configuration is implemented. The exergy method is used along with the energy integration technique and other financial indicators to determine whether and in which scenarios the integrated biorefineries would be more attractive. The average exergy efficiency of the integrated chemical production plants is 44%, which is higher than that of the conventional case (40%). The balance of the overall CO2 emissions vary from 1.97 to −0.56 tCO2/tPulp, for the conventional and integrated setups, respectively. An incremental financial analysis under uncertainty also shows that the hydrogen production route with partial import of electricity and carbon taxations above 60 EUR/tCO2 outperforms the other scenarios. Therefore, the import of electricity from low-carbon grids and the upgrade of biorefinery residues arise as key factors for ensuring the sustainable production of traditionally fossil-based chemicals under more stringent environmental regulations.

Sustainable aviation fuels – Options for negative emissions and high carbon efficiency

Mitigating the climate impact from aviation remains one of the tougher challenges in adapting society to fulfill stated climate targets. Long-range aviation cannot be electrified for the foreseeable future and the effects of combusting fuel at high altitude increase the climate impact compared to emissions of green-house gasses only, which further limits the range of sustainable fuel alternatives. We investigate seven different pathways for producing aviation biofuels coupled with either bio-energy carbon capture and storage (BECCS), or bio-energy carbon capture and utilization (BECCU). Both options allow for increased efficiency regarding utilization of feedstock carbon. Our analysis uses process-level carbon- and energy balances, with carbon efficiency, climate impact and levelized cost of production (LCOP) as primary performance indicators.The results show that CCS can achieve a negative carbon footprint for four out of the seven pathways, at a lower cost of GHG reduction than the base process option. Conversely, as a consequence of the electricity-intensive CO2 upgrading process, the CCU option shows less encouraging results with higher production costs, carbon footprints and costs of GHG reduction. Overall, pathways with large amounts of vented CO2, e.g., gasification of black liquor or bark, as well as fermentation of forest residues, reach a low GHG reduction cost for the CCS option. These are also pathways with a larger feedstock and corresponding production potential. Our results enable a differentiated comparison of the suitability of various alternatives for BECCS or BECCU in combination with aviation biofuel production. By quantifying the relative strengths and weaknesses of BECCS and BECCU and by highlighting cost, climate and carbon-efficient pathways, these results can be a source of support for both policymakers and the industry.

Sulfur transformation mechanism during supercritical water gasification of black liquor

Supercritical water gasification (SCWG) was a promising technology to treat black liquor harmlessly and recycle energy efficiently, while the sulfur transformation of black liquor during SCWG process remained unknow. Herein, the effects of different parameters on gasification and sulfur transformation was determined in a batch reactor. The results showed that reaction temperature played the most important role. H2 was the most important gaseous product with the maximum yields of 19.01 mol·kg−1, simultaneously achieving the highest carbon gasification efficiency (95.16 %), COD removal rate (99.98 %) and the pH of 8.5 at 700 °C, 30 min and 25 MPa. After SCWG treatment, most of sulfur existed in the form of sulfide (H2S/S2−), and the maximum proportion of which was up to 90.51 % at 700 °C, 30 min and 25 MPa. With the increase in temperature, the organic sulfur (thiol/thioether, sulfone and thiophene) and inorganic sulfur (sulfate and thiosulfate) were transformed into sulfide (H2S/S2−). Finally, the sulfur transformation mechanisms of black liquor in SCWG were proposed. This work provided a basis for resource utilization of black liquor and a promising method for sodium sulfide production.

Performance comparison of black liquor gasification and oxidation in supercritical water from thermodynamic, environmental, and techno-economic perspectives

The black liquor poses a great threat to the environment and it is also a kind of available biomass resources. By the supercritical water gasification (SCWG) and supercritical water oxidation (SCWO) technology, the black liquid with high water content can be converted into hydrogen-rich gas or heat energy. In this study, a pulp mill integrated with black liquor SCWG and SCWO subsystems, which have a processing capacity of 11.2 t/h of black liquor with a concentration of 15.2 wt%, is designed. The thermodynamic analysis, techno-economic analysis (TEA), and life cycle assessment on the system are conducted. The gasification characteristics and thermodynamic performance of the SCWG and SCWO systems under different working conditions are studied. The thermodynamic analysis shows that the highest energy efficiencies of SCWG and SCWO systems are 41.53 % and 19.89 %, respectively. The lowest processing cost of black liquor is 398.68 RMB/t, which is obtained in the SCWO system at 600 °C. At 800 °C, the minimum hydrogen production cost of SCWG system is 23.28 RMB/kg H2. The LCA results show that the environmental benefits of SCW system at high temperatures are significantly better than those of integrated black liquor combustion systems. Finally, a multi-attribute decision making results of the SCWG and SCWO systems show that the optimal reaction temperature is 800 °C.

Biorefineries in Kraft pulp mills for biofuels production: A critical review

AbstractKraft pulp production generates residues and by‐products of significant importance to the mill. Solid residues from forestry activities are commonly used to generate steam in power boilers. In the recovery cycle, black liquor generates steam (and subsequently energy) by burning in the Tomlinson boiler, while white liquor is regenerated. Well‐developed alternative technologies can use these residues and by‐products to generate different types of biofuels. This review addresses the use of such technologies integrated with Kraft mills, in the concept of biorefineries, showing advantages, disadvantages, and successful examples. Solid residues from forestry can be used to produce bio‐oil through processes such as fast pyrolysis and hydrothermal liquefaction. Bio‐oils are currently used for heating through combustion in commercial/industrial boilers, but greater appreciation occurs if used as biofuels, which is done through catalytic upgrading processes. Black liquor gasification generates synthesis gas, which can be burned for energy co‐generation, used to produce synthetic fuels, or as a hydrogenating agent for bio‐oil or crude tall oil catalytic upgrading. Kraft biorefineries are gradually being implemented, justifying efforts to improve existing and new biomass conversion technologies.

The impact of technology availability on the transition to net-zero industry in Sweden

There is great uncertainty about what technologies will be available in time to meet Sweden's 2045 net-zero emission target for the industrial sector. This study therefore investigated how the availability of innovative technologies affects cost-effective pathways to meeting this target. The investigation employed scenario analyses using TIMES-Sweden with a new techno-economic database of industrial technologies. The scenarios varied according to how the net-zero target was defined and which technologies could be used to meet the target. Technology readiness levels (TRLs) were used to define which and when new technologies were available for investments. Based on the scenario results, a technology prioritisation pattern was identified, indicating the conditions under which technology options generated cost-efficient solutions from a systems perspective. If carbon offsetting was allowed, then carbon capture and storage (CCS) was promoted, using biofuels as a supplement. When carbon offsetting was restricted, technologies using biofuels and/or electrification options were preferred. In all scenarios, the use of heat pumps and the integration of biofuel production in the forest industry, for example, strengthened sector coupling and were favoured for the efficient use of biomass. The results also revealed that a net-zero industry with restricted use of carbon offsetting relies on technologies with a TRL of 6 (on a scale of 9) to become available; in such cases, hydrogen electrolysis and black liquor gasification were key. When carbon offsetting was unrestricted, CCS technologies combined with low-cost negative emissions provided the most cost-efficient solution, but it led to fossil fuel lock-in. For Sweden, the local availability of biomass provides a competitive advantage when the use and production of biofuels both reduces the need for using more costly power-to-fuel solutions in industry and makes available low-cost negative emissions.

Catalytic supercritical water gasification of black liquor along with lignocellulosic biomass

Supercritical water gasification (SCWG) is a novel technology for environmental pollution management and hydrogen production from biomass and wastes. In this study, the SCWG of black liquor (BL) which is high-potential biomass and rich in alkalis was investigated. The experiments were conducted in a batch reactor at 350–400 °C, reaction time of 1–60 min, and constant concentration of 9 wt% of BL in the absence and presence of heterogeneous catalysts (3–5 wt%), lignocellulosic biomass, and formic acid (5 and 7 wt %) in three parts. First, the SCWG of BL was performed without any additive. The experimental results showed that the maximum production of H2, CO2, and CH4 was obtained at the highest temperature and reaction time; 400 °C and 60 min. The hydrogen yield was also enhanced by increasing the temperature, and reached 3.51 mol H2/kg dry ash free-black liquor (DAF-BL) at 400 °C. Reaction time increment improved the gas product and gasification efficiency up to 28.03 mmol and 21.73%, respectively. Subsequently, three heterogeneous catalysts (MnO2, CuO, and TiO2) were used, however 5 wt% of MnO2 was the best catalyst, significantly improving the hydrogen yield compared to the same condition of BL gasification without a catalyst. Hydrogen yield reached 5.09 mol H2/kg (DAF-BL) at 400 °C and the reaction time of 10 min. Finally, BL with poplar wood residue as a lignocellulosic biomass and formic acid was gasified separately and the highest hydrogen yield was obtained in the case of 5 wt% of formic acid (10.79 mol H2/kg (DAF-BL)). Overally, SCWG dramatically reduced the chemical oxygen demand of BL to 76% using 5 wt% of formic acid.

Extraction of phenolic compounds from sulfur-free black liquor thanks to hydrothermal treatment before the production of syngas for biofuels

Nowadays, black liquor, the liquid residue from cooking step in pulp industry is burnt to produce energy for the plant. But as the pulp mills have energy in excess, higher added values applications for black liquor may be looked for. Hydrothermal treatment offers a good opportunity as it is well suited for this kind of wet feedstock. It may be used to depolymerize organic compounds or produce syngas for biofuels applications. The objective of this study is to combine phenols and biofuel production by extracting the small organic molecules formed at moderate temperature prior to complete gasification of black liquor. Hydrothermal experiments from 225 °C to 600 °C have been performed on sulfur-free black liquor in batch reactor. At 280 °C phenol, guaiacol and syringol were found in their highest quantity: 5% of the initial lignin (which represented 6 wt% of the liquid black liquor) could be converted into these three compounds.

Technology Readiness Level Assessment of Formalin Production Pathways

Formalin is among the highest production volume chemicals and can be obtained by several production pathways, though there are several potential production pathways in earlier development stages. To evaluate the maturity level of formalin production technologies, assessment is performed according to Technology Readiness Levels (TRL). TRL is a method used to describe the maturity of technologies, and assign them a TRL level or a range of levels from 1 to 9, with TRL 9 indicating the most mature technologic systems. Formalin is most synthesized from methanol produced via syngas which is obtained by steam reforming of natural gas. Other production pathways are formalin produced from biogas, through gasification of biomass, coal, black liquor and other, through methanol produced by direct hydrogenation of CO2 or via reverse water gas shift reaction, also known as the CAMERE process. Finally, emerging technologies such as direct conversion of methane, syngas or CO2 to formalin were considered. This work will contribute to a wider understanding of the various technologies used in the formalin production field.

Black liquor gasification with calcium looping for carbon-negative pulp and paper industry

Although considered one of the major energy-intensive industries (EIIs), the pulp and paper industry has also the potential for energy production from an industrial waste, black liquor. This study proposes black liquor gasification (BLG) coupled with calcium looping (CaL) as a CO2 capture route for the pulp and paper industry. BLG with H2 production (BLG-CaL-H2), BLG with gas turbine combined cycle (BLG-CaL-GT) or with solid oxide fuel cell (BLG-CaL-SOFC) were considered. The dependence of carbon capture and storage (CCS) cost on the natural gas, limestone, electricity imported and H2 sale prices aside the expenditures related with BLG-CaL were evaluated. The CCS route, based on CaL retrofitted to the pulp and paper plant, was found to have a lower cost of CO2 avoided (39.0 €/tCO2) when compared with BLG-CaL (48.8–57.1 €/tCO2). Between the BLG-CaL scenarios, BLG-CaL-H2 presented the lowest cost of CO2 avoided (48.8 €/tCO2) but the highest energy penalty. Based on the thermodynamic performance, it was shown that CaL retrofit and BLG-CaL-SOFC presented the best overall performance, turning the electricity importer reference plant into electricity exporter. The economic sensitivity showed that the capital requirement of BLG-CaL has a strong effect on the cost of CO2 avoided for all alternatives. The H2 production is also strongly affected by the H2 sale price while BLG-CaL-SOFC and BLG-CaL-GT are strongly dependent on natural gas price.

Assessment of black liquor hydrothermal treatment under sub- and supercritical conditions: Products distribution and economic perspectives

This study reports an alternative method for black liquor treatment with potential for energy and process savings in the paper and pulp industry. Gasification of black liquor was carried out under sub- and supercritical conditions, varying the black liquor feed composition (0.10, 2.55 and 5.00 wb%) and temperature (350, 425 and 500 °C). Liquid products were identified by high resolution mass spectrometry (FT-Orbitrap MS) and compounds belonging to classes O3 and O4 were found to be the most representative in the products of reactions performed at 500 °C. The mass spectra results also revealed the overall selectivity of reactions, where decarboxylation and demethoxylation reactions were favored under subcritical and supercritical conditions, respectively. Among the gaseous products, hydrogen and methane were produced with maximum of 69.04 and 28.75 mol%, respectively, at 2.55 wb% and 425 °C. The proposed thermodynamic modelling of the reaction system satisfactorily predicted the gas phase behavior of the system. In the economic analysis, the simulated conditions indicated that the main energy requirements for a scaled-up black liquor gasification process are related to the necessary heat exchangers and pressurizing of the black liquor solution. Furthermore, the cost of the black liquor gasification is around 0.06 US$ per kg of feed stream. Liquid and gaseous products from gasification could be obtained at a cost of 56.64 US$ and 3.35 US$ per tonne of stream, respectively. Therefore, black liquor gasification is an interesting route for obtaining combustible gases and value-added bioproducts.

Sulfur Recovery from Syngas in Pulp Mills with Integrated Black Liquor Gasification

Research Highlights: As to fill the current knowledge gap and to deliver important findings to the scientific community, efficient sulfur recovery from black liquor gasifier syngas, comprising both gas cleaning and returning sulfur to the pulping process, was modeled and assessed from a techno-economic viewpoint. This manuscript proves that the associated investment and operational costs cannot be neglected and that they impact the black liquor gasification feasibility significantly. To prove its gasification as a sustainable and more efficient processing route over its combustion in recovery boilers, a substantial process efficiency improvement and operating costs reduction must be targeted in future research. Background and Objectives: Sulfur compounds found in black liquor partly turn into hydrogen sulfide during gasification and exit the gasifier in the syngas. Their efficient recovery in their sulfidic form to the pulping process is of utmost importance. Current studies focus on black liquor gasifier syngas desulfurization only. Materials and Methods: A mathematical model of two H2S absorption units from a 66.7 tDS/h (1600 tons dry solids per day) black liquor gasification process to 20 ppm H2S content in cleaned syngas using either white liquor plus NaOH or N-methyldiethanolamine (MDEA) was created using the Aspen Plus simulation software. Results: The results show that CO2 co-absorption significantly increases the lime kiln load: +20% in the MDEA alternative and +100% in the other one. The MDEA alternative requires almost the same investment costs but by around USD 9.7 million (>50%) lower annual operating costs compared to the other one. Economic evaluation was based on the assumed discount rate of 5% and on the expected plant operation time of 25 years. The estimated total investment cost of the whole plant is around USD 170 million for both alternatives. The whole plant including this alternative exhibits a positive net present value (over USD 19 million), an internal rate of return of 5% and a profitability index of 1.12, whereas that with the other alternative is economically infeasible. Conclusions: The MDEA-based syngas cleaning technology represents a more efficient and economically feasible option of sulfur recovery. A major drawback of both modeled syngas cleaning technologies is that their estimated annual operating costs significantly reduce the expected profit margin of gasification over the traditional black liquor combustion in a recovery boiler. Syngas cleaning and sulfur recovery have to be further optimized to reach a significant cut down in operational costs to improve the economic feasibility of black liquor gasification.

Combining expansion in pulp capacity with production of sustainable biofuels – Techno-economic and greenhouse gas emissions assessment of drop-in fuels from black liquor part-streams

Drop-in biofuels from forest by-products such as black liquor can help deliver deep reductions in transport greenhouse gas emissions by replacing fossil fuels in our vehicle fleet. Black liquor is produced at pulp mills that can increase their pulping capacity by upgrading some of it to drop-in biofuels but this is not well-studied. We evaluate the techno-economic and greenhouse gas performance of five drop-in biofuel pathways based on BL lignin separation with hydrotreatment or black liquor gasification with catalytic synthesis. We also assess how integrated biofuel production impacts different types of pulp mills and a petroleum refinery by using energy and material balances assembled from experimental data supplemented by expert input. Our results indicate that drop-in biofuels from black liquor part-streams can be produced for ~80 EUR2017/MWh, which puts black liquor on the same footing (or better) as comparable forest residue-based alternatives. The best pathways in both production routes have comparable costs and their principal biofuel products (petrol for black liquor gasification and diesel for lignin hydrotreatment) complement each other. All pathways surpass European Union’s sustainability criteria for greenhouse gas savings from new plants. Supplementing black liquor with pyrolysis oil or electrolysis hydrogen can improve biofuel production potentials and feedstock diversity, but better economic performance does not accompany these benefits. Fossil hydrogen represents the cheaper option for lignin hydrotreatment by some margin, but greenhouse gas savings from renewable hydrogen are nearly twice as great. Research on lignin upgrading in industrial conditions is recommended for reducing the presently significant performance uncertainties.

Integrated chemical looping combustion in pulp mill for high energy efficiency and low carbon emission

Pulp making is a high-energy-consumption process that obtains its energy by directly combusting coal and black liquor in boiler, which is low efficiency and high emission. Mini-sulfide sulfite anthraquinone (MSSAQ) pulp making technology can reach 55%–66% pulping yield but suffers from bad economic performance. The combination of black liquor gasification (BLG) and chemical cycle combustion (CLC) can achieve high pulp production and clean production and has better economic performance. This research proposes an integrated CLC-BLG-MSSAQ pulp making process. Compared with conventional Kraft and MSSAQ processes, the CLC-BLG-MSSAQ process improves the energy efficiency by 6.2% and 12.2%, decreases carbon emissions by 0.62 t/ADt and 0.17 t/ADt. The economic analysis shows that under the scenario of USD 20/t CO2-eq or above, the CLC-BLG-MSSAQ process, which has higher combustion efficiency and lower carbon emission, will cost the least compared with Kraft and MSSAQ processes.

Hydrogen production from supercritical water gasification of soda black liquor with various metal oxides

Supercritical water gasification is an innovative handling method of black liquor, which can also produce hydrogen-rich gases. In this study, the catalytic activity of 14 common metal oxides on SCWG of black liquor were investigated and the catalytic mechanism was studied through X-ray photoelectron spectroscopy (XPS) analysis. All the tested oxides improved the gasification efficiency and V2O5, WO3 and Co2O3 showed the highest performance. The H2 yields of 21.67 and 21.03 mol/kg were achieved with the presence of Co2O3 and ZnO respectively. The gasification efficiency increased with the increasing V2O5 amount, but the H2 fraction increased firstly and then decreased. The highest H2 fraction of 44.59% was obtained with V2O5 loading amount of 45 wt%. The increase of reaction time improved the CE, but the further prolongation had little influence. The XPS analysis of CuO and Fe2O3 showed some of them were reduced to metal (Cu) or lower-valence oxides (Cu2O, FeO). The metal oxides probably promoted black liquor decomposition by introducing reactive oxygen, and the generated metal also catalyzed the gasification. Accordingly, an oxidation reactor could be introduced to recycle the metal oxides, which may help to realize the complete gasification of black liquor or other refractory wastes at milder temperatures.

Hydrogen production by supercritical water gasification of black liquor: Use of high temperatures and short residence times in a continuous reactor

The Supercritical Water Gasification (SCWG) of black liquor (BL) to obtain hydrogen and dispose of organic waste simultaneously has been studied in a continuous reactor employing short residence times. The experiments were conducted at 600–700 °C, with times between 24.5–29.1 s, at 23 MPa and feedstock was diluted to different concentration levels (0.81–2.43 wt.%). Furthermore, different NaOH concentrations (0–1.2 wt.%) were added to maintain a basic medium and avoid the polymerization of the compounds. Hydrogen production and COD removal was conducted with short residence times. The best results regarding hydrogen yield were achieved at 700 °C, 24.5 s residence time and 0.9 wt.% NaOH concentration, with a production of 38.68 mol H2/kgsample. In contrast, and regarding COD removal, the best results were obtained at 700 °C, with 24.5 s residence time and the highest feed COD concentration used (2.43 wt.%). The COD removal levels reached were between 65–90 %.

Techno-economic feasibility of supercritical water gasification of black liquor

The objective of this study is to investigate the techno-economic feasibility of supercritical water gasification (SCWG) of black liquor integrated to a Kraft pulp mill. The process simulations have been performed through Aspen Plus software. The assessment includes five integration scenarios: stainless steel 316 or Inconel 625 as the reactor materials and hydrogen or combined heat and power (CHP) as the target products. The results illustrates that Inconel reactor is more profitable for CHP production than stainless steel as well as providing lower production cost of hydrogen. Inconel is also more robust against loss of pulping chemicals and changes in the energy price. However, the assessment uses the experimental yields even though surface-to-volume ratio of the reactor will reduce in the industrial scale. Therefore, the results should be validated in pilot scale as well before implementation. Nevertheless, a special reactor configuration can increase surface area. The techno-economic results can be improved by comprehensive investigations of process conditions including also residence time, the concentration of reactor inlet and heterogeneous catalyst. In addition, the SCWG process integrated to a pulp mill can also receive feedstocks from other biomass sectors. This would improve the economic and environmental performances of those sectors as well.

Life cycle and decision analysis of electricity production from biomass – Portugal case study

The present study aims to endow decision-makers with an evaluation of the different ways to produce electricity from biomass considering their life cycle impact and energy efficiency, in order to highlight the most sustainable options. A model was developed based on a life cycle approach complemented by a sensitivity analysis, and supported by a posterior decision analysis, having the criteria of used energy per 1 MJ of electricity produced and as well as emissions of carbon dioxide, methane, nitrous oxide and solid particles. The decision analysis methods on LCA studies show to be useful in selecting the best solutions in multiple criteria decision, demonstrating particular importance in complementing the sensitivity analysis within an overall comparison between pathways. The considered technologies include wood gasification, Rankine's cycle, co-firing, black liquor gasification, biogas engine and combined cycle gas turbine, using as feedstock farmed wood, forest residues, black liquor, manure and municipal waste, in a total of eleven ways were studied. The results show that no solution have better results in all criteria comparatively, yet the proposed decision methods suggested that the best “global” pathways were the ones using manure, combined cycle using municipal waste as feedstock and forest residues gasification. The pathway that consumes less energy to produce 1 MJ of electrical energy is the cofiring using forest residues. The emissions of PM10 and PM2.5 are minimized in the pathways of Rankine cycle and IGCC with forest residue as feedstock, respectively. The sensibility analysis indicates that input values chosen can affect considerably the final results, together with the quality of the biomass.