Process simulation of hydrogen production through biomass gasification: Introduction of torrefaction pre-treatment

Torrefaction is a pretreatment method that converts biomass to a fuel-like substance that can replace coal for sustainable power generation. In this work, a thermodynamic-based process simulation model was developed to simulate the gasification of empty fruit bunch (EFB), with torrefaction as pretreatment, to determine the optimum conditions; equivalence ratio, reactor temperature, torrefaction medium concentration, steam-to-biomass (S/B) ratio and system configuration were studied to determine their influence on hydrogen concentration, higher heating value (HHV), syngas ratio and cold gas efficiency (CGE). The highest hydrogen yield was obtained at an S/B ratio of 1.3 at 800 °C, with a syngas ratio of 2.5 and a CGE of 84%. Concentration of torrefaction medium showed no effect on hydrogen concentration due to the simplicity of the model used, but work is in progress in this direction. Therefore, steam gasification is more suitable than air gasification in hydrogen production.     

Evaluation of pretreatment potential and hydrogen recovery from lignocellulosic biomass in an anoxic double-staged bioelectrochemical system

The possible impact of bio and electrochemical reactions during pretreatment of rice straw using solvents, sulphuric acid (SA), ammonia (AM), sodium hydroxide (NA), and distilled water (W) was investigated. The total volatile fatty acids (tVFAs) of 163.48 ± 10.49 mM in the electrochemical pre-treatment in the presence of sodium hydroxide (ENA) followed by sulfate-reducing bacteria (EBA) (140.88 ± 0.07 mM) indicating the involvement of electrolytic breakdown of lignocellulosic biomass. The hydrogen production of 0.224 ± 0.05 and 0.218 ± 0.10 mM/g of the substrate was found in the ENA and anoxic sodium hydroxide pre-treatment (CNA) respectively. There was no detectable gasification in SA and AM electrochemical pre-treatments. The major advantage of the electrochemical process is the formation of acetic acid at a lower temperature, whereas processes like autohydrolysis form it at high temperatures during stream explosion pretreatment. The hydrogen production of 1.26 mM/g was found from anoxic hydrolysate pretreated (ECP) rice straw. The SEM and FTIR analysis show distortion of outer layers of biomass in the electrochemical pretreatment (ECP) system, which improved its accessibility towards enzymes for value-added product recovery.     

A novel process simulation model for hydrogen production via reforming of biomass gasification tar

Process modeling and simulation are very important for new designs and estimation of operating variables. This study describes a new process for the production of hydrogen from lignocellulosic biomass gasification tars. The main focus of this research is to increase hydrogen production and improve the overall energy efficiency of the process. In this study, Aspen HYSYS software was used for simulation. The integration structure presented in this research includes sections like tar reforming and ash separation (Ash), combined heat and power cycle (CHP), hydrogen sulfide removal unit (HRU), water-gas shift (WGS) reactor, and gas compression as well as hydrogen separation from a mixture of gases in pressure swing adsorption (PSA). It was found that the addition of CHP cycle and the use of the plug flow reactor (PFR) model, firstly, increased the overall energy efficiency of the process by 63% compared to 29.2% of the base process. Secondly it increased the amount of hydrogen production by 0.518 kmol (H2)/kmol Tar as compared with 0.475 of the base process. Process analysis also demonstrated that the integrated process of hydrogen production from biomass gasification tars is carbon neutral.     

A novel integrated process for hydrogen production from biomass

A novel process, which integrated with biomass pyrolysis, gas–solid simultaneous gasification and catalytic reforming processes, was utilized to produce hydrogen. The effects of gasification temperature and reforming temperature on hydrogen yield and carbon conversion efficiency were investigated. The results showed that both higher gasification temperature and reforming temperature led to higher hydrogen yield and carbon conversion efficiency. Compared with the two-stage pyrolysis-catalytic reforming process, hydrogen yield and carbon conversion efficiency were greatly increased from 43.58 to 75.96 g H₂/kg biomass and 66.18%–82.20% in the integrated process.     

Molecular simulation of methane steam reforming reaction for hydrogen production

By means of advanced techniques of molecular simulations, we have studied the chemical equilibrium of methane steam reforming reaction. We have computed the conversion of CH₄, yield and selectivity of H₂, etc. in the gas phase by reactive canonical Monte Carlo (RCMC) method and compared with those from Gibbs energy of formation method. The consistency of the two methods encourages us to use the RCMC method to optimize the operating conditions. We found that under low pressure 0.1 MPa, high temperature 1073 K and high water-gas ratio H₂O/CH₄ = 5, the CH₄ conversion, H₂ yield and selectivity were the highest, with the values of 99.93%, 3.51 mol/molCH₄ and 99.98%, respectively. In addition, the pore size of activated carbon significantly affects the chemical equilibrium composition in the pores. Since low pressure and high temperature are not conducive to the adsorption of reactive components by activated carbon, the chemical balance in the pores cannot be improved. At 773 K, 3.0 MPa and pore width is less than 2 nm, the pores are mainly occupied by CH₄ and H₂O reactant molecules. Further increasing the temperature can increase the H₂ content in the pores, but the adsorption capacity in the pores will decrease. We use activated carbon to adsorb and separate CO and H₂ (CO:H₂ = 1:3), the main components after the gas phase reaction reaches equilibrium. At 298 K, 7.5 MPa and the optimal pore width of 0.76 nm, the CO/H₂ selectivity is 28.3 and the CO adsorption capacity is 8.45 mmol/cm³.     

Challenges for renewable hydrogen production from biomass

The increasing demand for H₂ for heavy oil upgrading, desulfurization and upgrading of conventional petroleum, and for production of ammonium, in addition to the projected demand for H₂ as a transportation fuel and portable power, will require H₂ production on a massive scale. Increased production of H₂ by current technologies will consume greater amounts of conventional hydrocarbons (primarily natural gas), which in turn will generate greater greenhouse gas emissions. Production of H₂ from renewable sources derived from agricultural or other waste streams offers the possibility to contribute to the production capacity with lower or no net greenhouse gas emissions (without carbon sequestration technologies), increasing the flexibility and improving the economics of distributed and semi-centralized reforming. Electrolysis, thermocatalytic, and biological production can be easily adapted to on-site decentralized production of H₂, circumventing the need to establish a large and costly distribution infrastructure. Each of these H₂ production technologies, however, faces technical challenges, including conversion efficiencies, feedstock type, and the need to safely integrate H₂ production systems with H₂ purification and storage technologies.     

Pretreatment of lignocellulosic biomass for enhanced biogas production

Lignocellulosic biomass is an abundant organic material that can be used for sustainable production of bioenergy and biofuels such as biogas (about 50–75% CH₄ and 25–50% CO₂). Out of all bioconversion technologies for biofuel and bioenergy production, anaerobic digestion (AD) is a most cost-effective bioconversion technology that has been implemented worldwide for commercial production of electricity, heat, and compressed natural gas (CNG) from organic materials. However, the utilization of lignocellulosic biomass for biogas production via anaerobic digestion has not been widely adopted because the complicated structure of the plant cell wall makes it resistant to microbial attack. Pretreatment of recalcitrant lignocellulosic biomass is essential to achieve high biogas yield in the AD process. A number of different pretreatment techniques involving physical, chemical, and biological approaches have been investigated over the past few decades, but there is no report that systematically compares the performance of these pretreatment methods for application on lignocellulosic biomass for biogas production. This paper reviews the methods that have been studied for pretreatment of lignocellulosic biomass for conversion to biogas. It describes the AD process, structural and compositional properties of lignocellulosic biomass, and various pretreatment techniques, including the pretreatment process, parameters, performance, and advantages vs. drawbacks. This paper concludes with the current status and future research perspectives of pretreatment.     

An overview on cell and enzyme immobilization for enhanced biohydrogen production from lignocellulosic biomass

Hydrogen gas, a carbon-free energy carrier, can be produced via fossil fuel reforming, coal gasification, water electrolysis, photocatalysis, or biological process. Biohydrogen production from lignocellulosic biomass (LCB) in this regard, appears as an environmental benign, sustainable, non-food competing second generation fuel. LCB serves as the largest potential carbon source for sustainable biohydrogen production with an enormous global annual capacity of more than one trillion tons. Enzymes in this case, are widely used to hydrolyse the LCB into fermentable sugars, and subsequent hydrogen production is carried out by dark fermentation. However, the untapped non-food competing LCB is currently impeded by several critical bottlenecks including sensitivity of cells and enzymes to numerous denaturing conditions, recyclability, and high cost of enzyme. Low productivity of hydrolysis and hydrogen production in this regard, lead to a larger bioreactor and capital expenditures (CAPEX) requirement, which in turn, making this approach to be less competitive in commercial application. These bottlenecks can be overcome by immobilization technique, which enables the recyclability, improves stability and productivity of the enzyme and cells. Current review accommodates for the important outlook and critical insights into the immobilization techniques, providing important guidelines for the operation of immobilization techniques to elevate commercial competitiveness of biohydrogen production from LCB in the future. The effect of geometry, surface charges, and wettability of different type of carriers for cell immobilization to enhance biohydrogen production are discussed. The critical aspects of the immobilization parameters, such as temperature, pH, and duration which could significantly affect the properties of immobilized enzymes are thoroughly examined in this review. Suggestions and future directions of this field are provided to assist the development of an efficient, economic, and sustainable hydrogen production process.     

Aqueous-phase reforming of biomass using various types of supported precious metal and raney-nickel catalysts for hydrogen production

Aqueous-phase reforming (APR) of real biomass was studied for production of hydrogen gas. Wheat straw, an abundant by-product from wheat production was used as representative lignocellulosic biomass. Wheat straw was hydrolyzed in an environmentally benign-sub critical water condition. APR experiments of wheat straw hydrolysates were performed using commercial catalysts which were made of Pt, Pd and Ru doped on carbon, activated carbon and alumina supports for production of hydrogen rich gas mixture. The activity and selectivity of two commercial raney-nickel catalysts were also monitored in terms of hydrogen production.     

Green synthesis of magnetite nanoparticle and its regulatory effect on fermentative hydrogen production from lignocellulosic hydrolysate by Klebsiella sp.

This study describes the synthesis and characterization of magnetite nanoparticles (NPs) from water hyacinth (WH) extract and its regulatory effect on fermentative hydrogen production from lignocellulosic hydrolysate by Klebsiella sp. Characterization of WH-magnetite-NP revealed that it was a pure magnetite NP in a spherical shape with an average particle size of 13.5 ± 3.7 nm. The maximum cumulative hydrogen production with an increment of 23.49% and an optimum Y(H₂/S) of 83.20 ± 2.19 mL/g_substrate was obtained with WH-magnetite-NP at 20 mg/L. Monitoring of key node metabolites further established the potential of WH-magnetite-NP to increase the flux distribution of the hydrogen synthesis pathway. The hydrogenase activity was enhanced via WH-magnetite-NP addition, with peak value 2.1 times of the control. The expression of functional genes in key pathways assessed via RT-PCR highlighted the effect of WH-magnetite-NP on the evident promotion of hydrogenase and formate-hydrogen lyase. This is the first attempt to detect the expression of multiple functional genes in key metabolic pathways to explain the regulatory mechanism upon NP addition.     

Thermo-economic process model for thermochemical production of Synthetic Natural Gas (SNG) from lignocellulosic biomass

A detailed thermo-economic model considering different technological alternatives for thermochemical production of Synthetic Natural Gas (SNG) from lignocellulosic biomass is presented. First, candidate technology for processes based on biomass gasification and subsequent methanation is discussed and assembled in a general superstructure. Both energetic and economic models for biomass drying with air or steam, thermal pretreatment by torrefaction or pyrolysis, indirectly and directly heated gasification, methane synthesis and carbon dioxide removal by physical absorption, pressure swing adsorption and polymeric membranes are then developed. Performance computations for the different process steps and some exemplary technology scenarios of integrated plants are carried out, and overall energy and exergy efficiencies in the range of 69–76% and 63–69%, respectively, are assessed. For these scenarios, the production cost of SNG including the investment depreciation is estimated to 76–107 € MWh⁻¹_SNG for a plant capacity of 20 MW_th,biomass, whereas 59–97 € MWh⁻¹_SNG might be reached at scales of 150 MW_th,biomass and above. Based on this work, a future thermo-economic optimisation will allow for determining the most promising options for the polygeneration of fuel, power and heat.     

Fermentative hydrogen production from lipid-extracted microalgal biomass residues

The conversion of lipid-extracted microalgal biomass residues (LMBRs) into hydrogen plays the dual role in renewable energy production and sustainable development of microalgal biodiesel industry. An anaerobic fermentation process to covert LMBRs into hydrogen was investigated in this work. Using batch experiments, the effects of pretreatment of inoculum (by acid, base, heat, and chloroform, respectively), initial pH (5.0–7.0), inoculum concentrations at 0.59–2.94 g VSS/l (volatile suspended solids, VSS) and substrate concentrations at 4.5–45 g VS/l (volatile solids, VS) were investigated, respectively. The results showed that the most effective hydrogen production was obtained from fermentation of LMBRs with a concentration of 36 g VS/l at the initial pH 6.0–6.5 using the heat-treated anaerobic digested sludge as inoculum. Acetate, propionate and butyrate were the main fermentation byproducts in the conversion of LMBRs into hydrogen.     

Performance of a water gas shift pilot plant processing product gas from an industrial scale biomass steam gasification plant

In this paper, the performance of a commercial Fe/Cr based catalyst for the water gas shift reaction was investigated. The catalyst was used in a water gas shift pilot plant which processed real product gas from a commercial biomass steam gasification plant with two different qualities: extracted before and extracted after scrubbing with a rapeseed methyl ester gas scrubber. The performance of the WGS pilot plant regarding these two different gas qualities was investigated. For this reason, extensive chemical analyses were carried out. CO, CO₂, CH₄, N₂, O₂, C₂H₆, C₂H₄, and C₂H₂ and H₂S, COS, and C₄H₄ S were measured. In addition, GCMS tar and NH₃ analyses were performed. Furthermore, the catalyst's activity was observed by measuring the temperature profiles along the reactors of the water gas shift pilot plant. During the 200 h of operation with both product gas qualities, no catalyst deactivation could be observed. A CO conversion up to 93% as well as a GCMS tar reduction (about 28%) along the water gas shift pilot plant was obtained. Furthermore, a specific H₂ production of 63 g H₂ per kg biomass (dry and ash free) was reached with both product gas qualities. No significant performance difference could be observed.     

Enhanced hydrogen production from lipid-extracted microalgal biomass residues through pretreatment

Energy recovery from lipid-extracted microalgal biomass residues (LMBRs) plays a significant role in the sustainable development of the microalgal biodiesel industry. Different methods were used to pretreat LMBRs to improve their solubilization and anaerobic hydrogen production abilities. The pretreatment methods studied included thermal (100 °C and 121 °C), alkaline and thermo-alkaline pretreatments (combinations of alkaline and thermal pretreatments). The results showed that thermo-alkaline pretreatments resulted in remarkable improvements of LMBR solubilization, which led to an increase in hydrogen yield. The highest hydrogen yield of 45.54 mL/g-volatile solid (VS) was achieved from LMBRs pretreated by the thermo-alkaline pretreatment at 100 °C, which was approximately three-fold higher than the yield from untreated LMBRs. The results of this study proved that thermo-alkaline pretreatment at 100 °C is an effective method to improve LMBR solubilization and increase the hydrogen production from LMBRs.     

Simultaneous glucose and xylose utilization for improved ethanol production from lignocellulosic biomass through SSFF with encapsulated yeast

Simultaneous glucose and xylose uptake was investigated for ethanol production using the simultaneous saccharification, filtration and fermentation (SSFF) process with pretreated wheat straw as a xylose-rich lignocellulosic biomass. A genetically engineered strain of Saccharomyces cerevisiae (T0936) with the ability to ferment xylose was used for the fermentations. SSFF was compared with a conventional method of simultaneous saccharification and fermentation (SSF) for glucose and xylose uptake, ethanol production, and cell viability on 10% and 12% suspended solids (SS) basis. With 10% SS, an ethanol yield of 90% of the theoretical level was obtained during SSFF with 80% xylose uptake while only 53% ethanol yield was observed during the SSF process. Increasing the solid load to 12% resulted in an ethanol yield of 77% of the theoretical value and 36% xylose uptake during SSFF while only 27% ethanol yield and no xylose uptake was observed during the corresponding SSF process. The SSFF process preserved the viability of the genetically engineered yeast throughout the fermentation, even when reused for 2 consecutive cultivations. The results show that the SSFF process does not only enhance effective cell performance but also facilitates simultaneous glucose and xylose utilization, which is important for broad range of biomass utilization for lignocellulosic ethanol production.     

Energy consumption analysis of integrated flowsheets for production of fuel ethanol from lignocellulosic biomass

Fuel ethanol is considered one of the most important renewable fuels due to the economic and environmental benefits of its use. Lignocellulosic biomass is the most promising feedstock for producing bioethanol due to its global availability and to the energy gain that can be obtained when non-fermentable materials from biomass are used for cogeneration of heat and power. In this work, several process configurations for fuel ethanol production from lignocellulosic biomass were studied through process simulation using Aspen Plus. Some flowsheets considering the possibilities of reaction–reaction integration were taken into account among the studied process routes. The flowsheet variants were analyzed from the energy point of view utilizing as comparison criterion the energy consumption needed to produce 1 L of anhydrous ethanol. Simultaneous saccharification and cofermentation process with water recycling showed the best results accounting an energy consumption of 41.96 MJ/L EtOH. If pervaporation is used as dehydration method instead of azeotropic distillation, further energy savings can be obtained. In addition, energy balance was estimated using the results from the simulation and literature data. A net energy value of 17.65–18.93 MJ/L EtOH was calculated indicating the energy efficiency of the lignocellulosic ethanol.     

Modeling & optimization of renewable hydrogen production from biomass via anaerobic digestion & dry reformation

There is a growing interest in the usage of hydrogen as an environmentally cleaner form of energy for end users. However, hydrogen does not occur naturally and needs to be produced through energy intensive processes, such as steam reformation. In order to be truly renewable, hydrogen must be produced through processes that do not lead to direct or indirect carbon dioxide emissions. Dry reformation of methane is a route that consumes carbon dioxide to produce hydrogen. This work describes the production of hydrogen from biomass via anaerobic digestion of waste biomass and dry reformation of biogas. This process consumes carbon dioxide instead of releasing it and uses only renewable feed materials for hydrogen production. An end-to-end simulation of this process is developed primarily using Aspen HYSYS® and consists of steady state models for anaerobic digestion of biomass, dry reformation of biogas in a fixed-bed catalytic reactor containing Ni–Co/Al₂O₃ catalyst, and a custom-model for hydrogen separation using a hollow fibre membrane separator. A mixture-process variable design is used to simultaneously optimize feed composition and process conditions for the process. It is identified that if biogas containing 52 mol% methane, 38 mol% carbon dioxide, and 10 mol% water (or steam) is used for hydrogen production by dry reformation at a temperature of 837.5 °C and a pressure of 101.3 kPa; optimal values of 89.9% methane conversion, 99.99% carbon dioxide conversion and hydrogen selectivity 1.21 can be obtained.     

A review of catalytic hydrogen production processes from biomass

Hydrogen is believed to be critical for the energy and environmental sustainability. Hydrogen is a clean energy carrier which can be used for transportation and stationary power generation. However, hydrogen is not readily available in sufficient quantities and the production cost is still high for transportation purpose. The technical challenges to achieve a stable hydrogen economy include improving process efficiencies, lowering the cost of production and harnessing renewable sources for hydrogen production. Lignocellulosic biomass is one of the most abundant forms of renewable resource available. Currently there are not many commercial technologies able to produce hydrogen from biomass. This review focuses on the available technologies and recent developments in biomass conversion to hydrogen. Hydrogen production from biomass is discussed as a two stage process – in the first stage raw biomass is converted to hydrogen substrate in either gas, liquid or solid phase. In the second stage these substrates are catalytically converted to hydrogen.     

Conceptual net energy output for biofuel production from lignocellulosic biomass through biorefining

There is a lack of comprehensive information in the retrievable literature on pilot scale process and energy data using promising process technologies and commercially scalable and available capital equipment for lignocellulosic biomass biorefining. This study conducted a comprehensive review of the energy efficiency of selected sugar platform biorefinery process concepts for biofuel production from lignocelluloses. The process data from approximately a dozen studies that represent state-of-the-art in cellulosic biofuel production concepts, along with literature energy input data for agriculture operations, were analyzed to provide estimates of net energy production. It was found that proper allocation of energy input for fertilizer and pesticides to lignocellulosic biomass and major agriculture or forestry products, such as corn and lumber in corn farming and lumber plantations, respectively, were critical. The significant discrepancies in literature data suggest studies are needed to determine energy inputs for fuel in farming and farm machinery. Increasing solids loading in pretreatment to at least 25% is critical to reducing energy input in a biorefinery. Post thermo-chemical pretreatment size reduction approach should be adopted for energy efficient woody biomass processing. When appropriate pretreatment technologies are used, woody biomass can be processed as efficiently as herbaceous biomass and agricultural residues. Net energy output for cellulosic ethanol was estimated to range approximately from −500–2000 MJ/ton biomass (HHV base); indicating that the energy input/output ratio is approximately 1:1 for cellulosic ethanol. However, net energy can reach approximately 4000–7000 MJ/ton of biomass when energy from lignin is included.     

Life cycle assessment of hydrogen production from biomass gasification systems

In this study, a Life Cycle Assessment (LCA) of biomass-based hydrogen production is performed for a period from biomass production to the use of the produced hydrogen in Proton Exchange Membrane (PEM) fuel cell vehicles. The system considered is divided into three subsections as pre-treatment of biomass, hydrogen production plant and usage of hydrogen produced. Two different gasification systems, a Downdraft Gasifier (DG) and a Circulating Fluidized Bed Gasifier (CFBG), are considered and analyzed for hydrogen production using actual data taken from the literature. Fossil energy consumption rate and Green House Gas Emissions (GHG) are defined and indicated first. Next, the LCA results of DG and CFBG systems are compared for 1 MJ/s hydrogen production to compare with each other as well as with other hydrogen production systems. While the fossil energy consumption rate and emissions are calculated as 0.088 MJ/s and 6.27 CO₂ eqv. g/s in the DG system, they are 0.175 MJ/s and 17.13 CO₂ eqv. g/s in the CFBG system, respectively. The Coefficient of Hydrogen Production Performance (CHPP) (newly defined as a ratio of energy content of hydrogen produced from the system to the total energy content of fossil fuels used) of the CFBG and DG systems are then determined to be 5.71 and 11.36, respectively. Thus, the effects of some parameters, such as energy efficiency, ratio of cost of hydrogen, on natural gas and capital investments efficiency are investigated. Finally, the costs of GHG emissions reduction are calculated to be 0.0172 and 0.24 $/g for the DG and CFBG systems, respectively.