Reducing stranded asset risk in off-grid renewable mine sites by including hydrogen production

Mine sites are an ideal candidate to be decarbonised through the installation of variable renewables and storage. However, the operation of mine sites is dependent on many factors, including mineral price, which can vary significantly, leading to periods of inactivity. Therefore, for sites that have invested in renewable generation and storage, there exists a potential of stranded assets, which negatively impact their business case, potentially reducing investment in such equipment and, therefore, decarbonisation potential. The current study therefore has investigated the potential of using variable renewable energy coupled with thermal energy storage and biodiesel to supply heat to a mine site. With the base case established, the economic impact of lower or no mine operations on the net present value were evaluated. To reduce the impact of mine turndown, the potential of installing a hydrogen production facility in an effort to utilise the stranded assets was also undertaken. Preliminary results show the base case to be very economical with a net present cost of $151.4 M after 30 operational years. This value was reduced to $45.7 M and -$81.1 M if the mine only operated at half capacity or did not operate at all, respectively. The addition of hydrogen production powered by the installed variable renewable generation resulted in a slightly better net present value of $174.7 M if the mine operated as normal for 30 years. For the two other cases, the installation of an electrolyser resulted in significantly better results than if it had not been installed for the half capacity and no operation cases with net present costs of $90.9 M and -$7.1 M, respectively. A sensitivity analysis on these results show that while the hydrogen production only plays a minor role in site savings, a price of between $1.1/kg to $2.0/kg is necessary for the system to be economically justifiable. Therefore, the current study shows that the addition of an electrolyser can significantly reduce the risk of stranded assets in fully renewable mine sites by providing an additional revenue stream during mine turndown events.     

Performance analysis of a novel solar PTC integrated system for multi-generation with hydrogen production

The performance analysis of a novel multi-generation (MG) system that is developed for electricity, cooling, hot water and hydrogen production is presented in this study. MG systems in literature are predominantly built on a gas cycle, integrated with other thermodynamic cycles. The aim of this study is to achieve better thermodynamic (energy and exergy) performance using a MG system (without a gas cycle) that produces hydrogen. A proton exchange membrane (PEM) utilizes some of the electricity generated by the MG system to produce hydrogen. Two Rankine cycles with regeneration and reheat principles are used in the MG configuration. Double effect and single effect absorption cycles are also used to produce cooling. The electricity, hot water, cooling effect, and hydrogen production from the multi-generation are 1027 kW, 188.5 kW, 11.23 kg/s and 0.9785 kg/h respectively. An overall energy and exergy efficiency of 71.6% and 24.5% respectively is achieved considering the solar parabolic trough collector (PTC) input and this can increase to 93.3% and 31.9% if the input source is 100% efficient. The greenhouse gas emission reduction of this MG system is also analyzed.     

Environmental sustainability assessment of large-scale hydrogen production using prospective life cycle analysis

The need for a rapid transformation to low-carbon economies has rekindled hydrogen as a promising energy carrier. Yet, the full range of environmental consequences of large-scale hydrogen production remains unclear. Here, prospective life cycle analysis is used to compare different options to produce 500 Mt/yr of hydrogen, including scenarios that consider likely changes to future supply chains. The resulting environmental and human health impacts of such production levels are further put into context with the Planetary Boundaries framework, known human health burdens, the impacts of the world economy, and the externality-priced production costs that embody the environmental impact. The results indicate that climate change impacts of projected production levels are 3.3–5.4 times higher than the allocated planetary boundary, with only green hydrogen from wind energy staying below the boundary. Human health impacts and other environmental impacts are less severe in comparison but metal depletion and ecotoxicity impacts of green hydrogen deserve further attention. Priced-in environmental damages increase the cost most strongly for blue hydrogen (from ～2 to ～5 USD/kg hydrogen), while such true costs drop most strongly for green hydrogen from solar photovoltaic (from ～7 to ～3 USD/kg hydrogen) when applying prospective life cycle analysis. This perspective helps to evaluate potentially unintended consequences and contributes to the debate about blue and green hydrogen.     

Study on performance comparison of different fin combinations of catalyst filled plate fin heat exchanger for hydrogen liquefaction

A mathematical model of catalyst filled plate fin heat exchanger (CFPFHE) is established to compare different fin models and analyze fin performance of different fin combinations. The results show that the single-layer fin model inadequately reflects the double-layers fin model from flow distribution and fin performance. The indexes of ortho-para hydrogen conversion (YY_pH2) of different fin combinations are all about 0.95, meeting the requirement of the CFPFHE. The plain_serrated fin has the best fin performance among four fin combinations. Compared with the plain_plain, the Colburn heat transfer factor (j factor) and thermal enhancement factor (TEF) of cool and hot sides of the plain_serrated fin are increased by 68.0～51.0% and 28.5～13.6%, 8.5～6.1% and 8.4%～6.1% at Re_hot = 500～1500, respectively. Further, the fin combinations of high-efficiency fin and plain respectively used in cool and hot sides have excellent overall fin performance, which provides a theoretical guidance for fin selection of the CFPFHE.     

Design of a sustainable and reliable hydrogen supply chain network under mixed uncertainties: A case study

In the recent decade, the design of green hydrogen supply chains has been highlighted by researchers. Although, nowadays, responsiveness and social responsibility of networks could also be regarded as important measures that could attract more consumers to use hydrogen. Accordingly, this paper aims to improve the reliability and social responsibility of a hydrogen supply chain along with its economic and environmental aspects. To ensure the network's responsiveness, a new objective function is extended that maximizes the reliability of products' delivery. Also, a novel reliability approach is developed to immune the network against disruptions. As a new sustainability indicator, social factors are considered in the design of the hydrogen supply chain. Finally, a mixed possibilistic flexible programming method is proposed to assure the outputs' reliability. The results illustrate that by 28.4% enhancement in cost objective, the value of environmental, social, and reliability objectives are desirably improved 39.2%, 45.6%, and 24.1%, respectively.     

Economic valuation of green hydrogen charging compared to gray hydrogen charging: The case of South Korea

The South Korean government promotes hydrogen-powered vehicles to reduce greenhouse gas (GHG) emissions but these vehicles use gray hydrogen while charging, which causes GHG emissions. Therefore, converting this fuel into green hydrogen is necessary to help reduce GHG emissions, which will incur investment costs of approximately USD 20 billion over a decade. In this study, a contingent valuation method is applied in an analysis to examine the extent to which consumers are willing to pay for green hydrogen charging compared to gray hydrogen charging. The results indicate that the monthly mean of willingness to pay per driver is 51,674 KRW (USD 45.85), equivalent to 4302 KRW per kg (USD 3.82). Additionally, consumers accept a 28.5% increase in the monthly average fuel expenses when converting to green hydrogen. These findings can be used in the development of pricing and energy use plans to finance the expansion of green hydrogen infrastructure.     

Hydrofluoroolefin-based mixed refrigerant for enhanced performance of hydrogen liquefaction process

Hydrogen has the highest gravimetric energy density of all fuels; however, it has a low volumetric energy density, unfavorable for storage and transportation. Hydrogen is usually liquefied to meet the bulk transportation needs. The exothermic interconversion of its spin isomers is an additional activity to an already energy-intensive process. The most significant temperature drop occurs in the precooling cycle (between ?150 °C and up to ?180 °C) and consumes more than 50% of the required energy. To reduce the energy consumption and improve the exergy efficiency of the hydrogen liquefaction process, a new high-boiling component, Hydrofluoroolefin (HFO-1234yf), is added to the precooled mixed refrigerant. As a result, the specific energy consumption of precooling cycle reduces by 41.8%, from 10.15 kWh/kg_LH2 to 5.90 kWh/kg_LH2, for the overall process. The exergy efficiency of the proposed case increases by 43.7%; however, the total equipment cost is also the highest. The inflated cost is primarily due to the added ortho-to-para hydrogen conversion reactor, boosting the para-hydrogen concentration. From the perspective of bulk storage and transportation of liquid hydrogen, the simplicity of design and low energy consumption build a convincing case for considering the commercialization of the process.     

Avenues to the financial viability of microbial electrolysis cells [MEC] for domestic wastewater treatment and hydrogen production

We propose targets, based on real world data, necessary to design a financially viable microbial electrolysis cell (MEC) for the treatment of domestic wastewater. By reducing the cost of the anode and current collecting materials by 90%, a viable organic loading rate would be between 800 and 1,400g-COD/m³/d (2–3A/m²). The anode and current collector materials account for 94% of the total material costs; consequently, cost savings in any other material are moot. If the bioanode can be reused after 20 years, further, significant savings could be achieved. To develop targets we used real world data, for the first time, to evaluate the financial viability of MECs against the current predominant method of wastewater treatment: activated sludge. We modelled net present values for eight potential scenarios and the performances required for MECs to break-even.     

A comprehensive review on lignocellulosic biomass biorefinery for sustainable biofuel production

The increasingly severe environmental pollution and energy shortage issues have demanded the production of renewable and sustainable biofuels to replace conventional fossil fuels. Lignocellulosic (LC) biomass as an abundant feedstock for second-generation biofuel production can help overcome the shortcomings of first-generation biofuels related to the “food versus fuel” debate and feedstock availability. Embracing the “circular bioeconomy” concept, an integrated biorefinery platform of LC biomass can be performed by employing different conversion technologies to obtain multiple valuable products. This review provides an overview of the principles and applications of thermochemical processes (pyrolysis, torrefaction, hydrothermal liquefaction, and gasification) and biochemical processes (pretreatment technologies, enzyme hydrolysis, biochemical conversion processes) involved in LC biomass biorefinery for potential biofuel applications. The engineering perspective of LC biofuel production on separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), simultaneous saccharification and co-fermentation (SSCF), and consolidated bioprocessing (CBP) were also discussed.     

A review on current trends in potential use of metal-organic framework for hydrogen storage

Hydrogen can be a promising clean energy carrier for the replenishment of non-renewable fossil fuels. The set back of hydrogen as an alternative fuel is due to its difficulties in feasible storage and safety concerns. Current hydrogen adsorption technologies, such as cryo-compressed and liquefied storage, are costly for practical applications. Metal-organic frameworks (MOFs) are crystalline materials that have structural versatility, high porosity and surface area, which can adsorb hydrogen efficiently. Hydrogen is adsorbed by physisorption on the MOFs through weak van der Waals force of attraction which can be easily desorbed by applying suitable heat or pressure. The strategies to improve the MOFs surface area, hydrogen uptake capacities and parameters affecting them are studied. Hydrogen spill over mechanism is found to provide high-density storage when compared to other mechanisms. MOFs can be used as proton exchange membranes to convert the stored hydrogen into electricity and can be used as electrodes for the fuel cells. In this review, we addressed the key strategies that could improve hydrogen storage properties for utilizing hydrogen as fuel and opportunities for further growth to meet energy demands.     

Exergetic analysis of hydrogen utilisation pathways – Part 1: Energy supply in buildings

This article analyses exergy losses along hydrogen utilisation pathways recently discussed in Germany and other countries. As a renewable fuel hydrogen will be an important part of sustainable future economies. Hydrogen can be used in all sectors, especially in buildings, for mobility and in industry, e.g. in steel production or ammonia synthesis. However, hydrogen has to be produced in a sustainable way. The most promising production is via water electrolysis using renewable electricity. In the first part of this work, exergy analysis is made for the complete hydrogen pathways from production until final utilisation for energy supply in buildings. The second part will focus on pathways for mobility. In the third part, the results are compared with available alternatives to hydrogen such as direct use of electricity in building supply or mobility. The results for building energy supply show that firstly transportation in pipelines (mixture with natural gas and pure hydrogen) is very efficient. Secondly, major exergy losses are caused by the electrolyser. Thirdly, combustion of renewable hydrogen for room heating in common boilers cause the highest exergy losses, but the use of combined heat and power (CHP) units or fuel cells can improve the exergy efficiency substantially.     

Performance evaluation of a solarized gas turbine system integrated to a high temperature electrolyzer for hydrogen production

In this paper, the performance of a solar gas turbine (SGT) system integrated to a high temperature electrolyzer (HTE) to generate hybrid electrical power and hydrogen fuel is analyzed. The idea behind this design is to mitigate the losses in the electrical power transmission and use the enthalpy of exhaust gases released from the gas turbine (GT) to make steam for the HTE. In this context, a GT system is coupled with a solar tower including heliostat solar field and central receiver to generate electrical power. To make steam for the HTE, a flameless boiler is integrated to the SGT system applying the SGT extremely high temperature exhaust gases as the oxidizer. The results indicate that by increasing the solar receiver outlet temperature from 800 K to 1300 K, the solar share increases from 22.1% to 42.38% and the overall fuel consumption of the plant reduces from 7 kg/s to 2.7 kg/s. Furthermore, flameless mode is achievable in the boiler while the turbine inlet temperature (TIT) is maintained at the temperatures higher than 1314 K. Using constant amounts of the SGT electrical power, the HTE voltage decreases by enhancing the HTE steam temperature which result in the augmentation of the overall hydrogen production. To increase the HTE steam temperature from 950 K to 1350 K, the rate of fuel consumption in the flameless boiler increases from 0.1 m/s to 0.8 m/s; however, since the HTE hydrogen production increases from 4.24 mol/s to 16 mol/s it can be interpreted that the higher steam temperatures would be affordable. The presented hybrid system in this paper can be employed to perform more thermochemical analyses to achieve insightful understanding of the hybrid electrical power-hydrogen production systems.     

Design and computational analysis of a metal hydride hydrogen storage system with hexagonal honeycomb based heat transfer enhancements-part A

In this study, design and performance analysis is carried out for a 10 kWh metal hydride based hydrogen storage system. The system is equipped with distinctive aluminium hexagonal honeycomb based heat transfer enhancements (HTE) having higher surface area to volume ratio for effective heat transfer combined with low system weight addition. The system performance was studied under different operating conditions. The optimum absorption condition was achieved at 35 bar with water at room temperature as heat transfer fluid where up to 90% absorption was completed in 7200 s. The performance of the reactor was observed to significantly improve upon the addition of the HTE network at a minimal system weight penalty.     

Refueling-station costs for metal hydride storage tanks on board hydrogen fuel cell vehicles

Refueling costs account for much of the fuel cost for light-duty hydrogen fuel-cell electric vehicles. We estimate cost savings for hydrogen dispensing if metal hydride (MH) storage tanks are used on board instead of 700-bar tanks. We consider a low-temperature, low-enthalpy scenario and a high-temperature, high-enthalpy scenario to bracket the design space. The refueling costs are insensitive to most uncertainties. Uncertainties associated with the cooling duty, coolant pump pressure, heat exchanger (HX) fan, and HX operating time have little effect on cost. The largest sensitivities are to tank pressure and station labor. The cost of a full-service attendant, if the refueling interconnect were to prevent self-service, is the single largest cost uncertainty. MH scenarios achieve $0.71–$0.75/kg-H₂ savings by reducing compressor costs without incurring the cryogenics costs associated with cold-storage alternatives. Practical refueling station considerations are likely to affect the choice of the MH and tank design.     

Comparative techno-economic study of typically combustion-less hydrogen production alternatives

A techno-economic study is performed for a large scale combustion-less hydrogen production process based on Steam Methane Reforming (SMR). Two process versions relying on different renewable heat sources are compared: (1) direct solar heating from a concentrated solar power system, and (2) radiation from resistive electrical heaters (electric SMR). Both processes are developed around an integrated micro-reactor technology, incorporating in a monolithic block most sub-processes needed to perform SMR. A baseline techno-economic scenario with low-cost feedstock and electricity, priced at $4/MMBtu and $0.04/kWh respectively, results in an LCOH of $2.31/kg_H2 for solar SMR and $1.59/kg_H2 for electric SMR. Results further show that solar SMR is currently more attractive economically than electric SMR coupled with distributed wind power systems, but electric SMR is more favourable in the long term due to the expected future improvements in the LCOE and capacity factor of wind power systems.     

Improving inter-plant integration of syngas production technologies by the recycling of CO2 and by-product of the Fischer-Tropsch process

This paper deals with the emission reduction in synthesis-gas production by better integration and increasing the energy efficiency of a high-temperature co-electrolysis unit combined with the Fischer-Tropsch process. The investigated process utilises the by-product of Fischer-Tropsch, as an energy source and carbon dioxide as a feedstock for synthesis gas production. The proposed approach is based on adjusting process streams temperatures with the further synthesis of a new heat exchangers network and optimisation of the utility system. The potential of secondary energy resources was determined using plus/minus principles and simulation of a high-temperature co-electrolysis unit. The proposed technique maximises the economic and environmental benefits of inter-unit integration. Two scenarios were considered for sharing the high-temperature co-electrolysis and the Fischer-Tropsch process. In the first scenario, by-products from the Fischer-Tropsch process were used as fuel for a high-temperature co-electrolysis. Optimisation of secondary energy sources and the synthesis of a new heat exchanger network reduce fuel consumption by 47% and electricity by 11%. An additional environmental benefit is reflected in emission reduction by 25,145 tCO₂/y. The second scenario uses fossil fuel as a primary energy source. The new exchanger network for the high-temperature co-electrolysis was built for different energy sources. The use of natural gas resulted in total annual costs of the heat exchanger network to 1,388,034 USD/y, which is 1%, 14%, 116% less than for coal, fuel oil and LPG, respectively. The use of natural gas as a fuel has the lowest carbon footprint of 7288 tCO₂/y. On the other hand, coal as an energy source has commensurable economic indicators that produce 2 times more CO₂, which can be used as a feedstock for a high-temperature co-electrolysis. This work shows how in-depth preliminary analysis can optimise the use of primary and secondary energy resources during inter-plant integration.     

Enhanced hydrogen storage performance of Cu3(BTC)2 in situ inserted with few-layer silicon-based nanosheets

Silicon-based nanosheets (SNS) were synthesised via a mild (60 °C) and time-saving (8 h) modified topochemical method. Then, Cu₃(BTC)₂ and SNS@Cu₃(BTC)₂ were successfully synthesised by microwave irradiation, and their characteristics and hydrogen storage performance were analysed by multiple techniques. The accordion-like SNS exhibited void spaces, a unique low buckled structure, and ultrathin, almost transparent, loosely stacked layers with a high specific surface area (362 m²/g). After in-situ synthesis with Cu₃(BTC)₂, the SNS compound achieved a high specific surface area (1526 m²/g), outstanding hydrogen storage performance (5.6 wt%), and a desirable hydrogen diffusion coefficient (10^?7). Thus, SNS doping improved the hydrogen storage performance of Cu₃(BTC)₂ by 64% through electron transfer reactions with Cu enabled by the unique composite nanostructure of SNS@Cu₃(BTC)₂. This study presents a promising method of synthesising SNS and porous composite materials for hydrogen storage.     

Enhanced methane production using pretreated sludge in MEC-AD system: Performance,microbial activity,and implications at different applied voltages

Although various pretreatment methods are employed to promote sludge hydrolysis and thereby promoting methane production in the subsequent microbial electrolysis cell assisted anaerobic digestion (MEC-AD) system, the questions arise are, “which pretreatment method on waste activated sludge (WAS) maximises the sludge hydrolysis and what is the optimal applied voltage on anaerobic digestion (AD) to stimulates the direct interspecies electron transfer (DIET) performance and thereby accelerating the methane production fed with pretreated WAS?” was still unanswered. Herein, firstly, a series of pretreatment methods to hydrolyse and mineralise the organic matter of WAS was performed to evaluate solubilization efficiency and thereafter, the influence of different applied voltages (0.3 V, 0.6 V, and 0.9 V) on coupled MEC-AD reactors fed with pretreated WAS was investigated to apprehend the DIET promotion for methane production. The results indicated that in MEC-AD reactors, the methane yield increased by 27.2%, 44.8%, and 37.3% when the applied voltages were 0.3 V, 0.6 V, and 0.9 V, respectively. Therefore, the alkaline-thermal pretreatment (ATP) enhanced the sludge hydrolysis in WAS, followed by an applied voltage of 0.6 V in the MEC-AD reactor fed with pretreated WAS, enhanced methane production under DIET stimulation induced by the increased abundance of electroactive microorganisms (EAM) and the advanced electron transfer. Besides, the energy balance estimation validates that with an applied voltage of 0.6 V in MEC-AD could achieve higher net energy input.     

A techno-economic study for a hydrogen storage system in a microgrid located in baja California,Mexico. Levelized cost of energy for power to gas to power scenarios

In this work a techno economic feasibility study is carried out to implement a Hydrogen based Power to Gas to Power (P2G2P) in a Microgrid, located in a rural area in Baja California, Mexico. The study aims to define the feasibility to store energy throughout seasons with this novel alternative using an electrolyzer to produce green hydrogen from excess renewable energy in winter, to store it during months and re inject it to the grid as electricity by a fuel cell in the high energy demanding season. The Microgrid was modeled in Homer software and simulations of the P2G2P lead to Levelized Cost of Energy data to compare between the P2G2P scenarios and the current diesel-battery based solution to complete the high demand by the community. This study shows that using hydrogen and fuel cells to substitute diesel generators it is possible to reduce CO₂ emissions up to a 27% and that in order for the P2G2P to be cost competitive, the fuel cell should reduce its cost in 50%; confirming that, in the medium to long term, the hydrogen storage system is a coherent alternative towards decarbonization of the distributed energy generation.