Browsing by Author "Luqmani, Benjamin A."

Now showing 1 - 12 of 12
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    Ammonia recovery and utilisation for biogas upgrading in membrane contactors.
    (Cranfield University, 2023-07) Luqmani, Benjamin A.; McAdam, Ewan; Pidou, Marc
    This thesis has developed an innovative system for biogas upgrading using hollow fibre membrane contactors (HFMC) whilst recovering ammonia from wastewater as a reactive solvent to intensify CO₂ absorption. An expanded two- phase region for ammonia-water separation was identified and exploited to foster selective, low energy recovery of concentrated gas-phase ammonia from wastewater by vacuum thermal stripping. Selective stripping was translated to a gas-liquid contacting column which demonstrated mass transfer rates analogous to commercially established stripping processes. Investment in selective ammonia recovery from anaerobic digester centrate represents a cost saving over a 20-year economic lifetime relative to biological nitrogen removal. During physical CO₂ absorption in HFMC, solvent chilling and gas pressurisation were observed to increase flux and selectivity, thereby reducing membrane area and path length for biogas upgrading. Chilled conditions will promote wetting resilience to favour the application of microporous membranes, which are low- cost and technologically mature. Translation to recovered ammonia solvents will further intensify CO₂ absorption, but can result in gas-side reactions within the ternary CO₂-NH₃-H₂O system which reduce process stability. In a positive synergy, chilled, pressurised conditions could limit ammonia ‘slip’ and maintain the system below a critical threshold to prevent gas-side reactions and improve process resilience. Pressurised, reactive crystallisation in HFMC during CO₂ absorption by ammonia solvents was demonstrated for the first time, and observed to occur at a consistent supersaturation level. Consequently, ammonium bicarbonate crystals exhibited consistent characteristics independent of pressure which supports simplified online control and solids recovery for scale- up. The integrated system proposed in this thesis presents a cost effective, circular economy solution for ammonia recovery and biogas upgrading which is closely aligned to net zero ambitions within the water sector and wider society.
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    Ammonia recovery from brines originating from a municipal wastewater ion exchange process and valorization of recovered nitrogen into microbial protein
    (Elsevier, 2021-06-18) Guida, Samuela; Van Peteghem, Lotte; Luqmani, Benjamin A. ; Sakarika, Myrsini; McLeod, Andrew J.; McAdam, Ewan J.; Jefferson, Bruce; Rabaey, Korneel; Soares, Ana
    A hollow fibre membrane contactor (HFMC), and two vacuum thermal stripping processes, a rotary evaporator (VTS) and multi-component system (MVTS) were compared for their ability to recover ammonia (NH3) from ion exchange (IEX) regeneration brines. The IEX was a 10 m3/day demonstration scale plant fed with secondary municipal wastewater. The 10% potassium chloride regeneration brine was used multiple times leading to ammonium (NH4+-N) saturation (up to 890 mg N/L). When treating the saturated IEX brine, the highest NH3 mass transfer coefficient for the HFMC, MVTS and VTS were 0.6, 0.7 and 0.1 h−1, respectively, compared to values between 1.7 and 3.5 h−1, when treating a synthetic solution. The highest NH3 recovery was obtained with the HFMC (99.8%) and the ammonium sulphate produced was characterised for impurities, presenting high quality. Concentrated ammonium (NH4+-N) solutions (0.5–3.1 g N/L) were obtained from the MVTS and VTS processes. To further valorise the recovered NH4+-N solution produced from the MVTS process, this was used as a substrate for microbial protein (MP) production. Limited differences were observed for production rate (specific growth rate 0.092–0.40 h−1), protein yield (0.021–0.18 g protein/g acetate-CODconsumed) and protein content (0.073–0.87 g protein/g cell dry weight) between recovered and commercial nitrogen (N) sources, indicating that recovered N from IEX can serve as a substrate for MP production. This study demonstrates a comprehensive N management solution for wastewater applications, leading to a range recovered products. These combined technologies can contribute to the local economy, whilst delivering to the ambitious NET-ZERO and circular economy targets.
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    CO2 absorption into aqueous ammonia using membrane contactors: Role of solvent chemistry and pore size on solids formation for low energy solvent regeneration
    (Elsevier, 2022-03-16) Bavarella, Salvatore; Luqmani, Benjamin A. ; Thomas, Navya; Brookes, Adam; Moore, Andrew; Vale, Peter C. J.; Pidou, Marc; McAdam, Ewan J.
    Solids formation can substanitally reduce the energy penalty for ammonia solvent regeneration in carbon capture and storage (CCS), but has been demonstrated in the literature to be difficult to control. This study examines the use of hollow fibre membrane contactors, as this indirect contact mediated between liquid and gas phases in this geometry could improve the regulation of solids formation. Under conditions comparable to existing literature, NH4HCO3 was evidenced to primarily crystallise in the gas-phase (lumen-side of the membrane) due to the high vapour pressure of ammonia, which promotes gaseous transmission from the solvent. Investigation of solvent reactivity demonstrated how equilibria dependent reactions controlled the onset of NH4HCO3 nucleation in the solvent, and limited ‘slip’ through transfomation of ammonia into its protonated form which occurs prior to the phase change. Crystallisation in the solvent was also dependent upon ammonia concentration, where sufficient supersaturation must develop to overcome the activation energy for nucleation. However, this has to be complemented with a reduction in solvent temperature to offset vapour pressure and limit the risk of gas-phase crystallisation. While changes to the solvent chemistry were sufficient to shift from gas-phase to liquid phase crystallisation, wetting was observed immediately after nucleation in the solvent. This was explained by a local region of supersaturation within the coarse membrane pores that promoted a high nucleation rate, altering the material contact angle of the membrane sufficient for solvent to breakthrough into the gas phase. Adoption of a narrower pore size membrane was shown to dissipate wetting after crystallisation in the solvent, illustrating membrane contactors as a stable platform for the sustained separation of CO2 coupled with its simultaneous transformation into a solid. Through resolving previous challenges experienced with solids formation in multiple reactor configurations, the cost benefit of using ammonia as a solvent can be realised, which is critical to enabling economically viable CCS for the transition to net zero, and can be exploited within hollow fibre membrane contactors, eliciting considerable process intensification over existing reactor designs for CCS.
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    Data related to "Examining disruptive gas-phase reactions during CO2 capture in membrane contactors: CO2-NH3-H2O as a model ternary system"
    (Cranfield University, 2024-05-23 17:10) Luqmani, Benjamin A. ; Pidou, Marc; McAdam, Ewan
    Data related to figures for "Examining disruptive gas-phase reactions during CO2 capture in membrane contactors: CO2-NH3-H2O as a model ternary system"
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    Data related to "The role of solvent temperature and gas pressure on CO2 mass transfer during biogas upgrading within porous and dense-skin hollow fibre membrane contactors"
    (Cranfield University, 2023-04-14 14:37) Luqmani, Benjamin A. ; McAdam, Ewan; Pidou, Marc
    Source data for published works: 'The role of solvent temperature and gas pressure on CO2 mass transfer during biogas upgrading within porous and dense-skin hollow fibre membrane contactors'.
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    Data related to figures from "Transitioning through the vapour-liquid equilibrium for low energy thermal stripping of ammonia from wastewater..."
    (Cranfield University, 2023-04-21 14:29) Luqmani, Benjamin A. ; Pidou, Marc; McAdam, Ewan
    Supporting dataset related to figures in the following work : "Transitioning through the vapour-liquid equilibrium for low energy thermal stripping of ammonia from wastewater...".
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    Data supporting the publication "Transforming wastewater ammonia to carbon free energy: Integrating fuel cell technology with ammonia stripping for direct power production"
    (Cranfield University, 2022-03-08 09:18) Davey, Christopher J.; Luqmani, Benjamin A. ; Thomas, Navya; McAdam, Ewan
    Data File supporting article titled "Transforming ammonia to carbon free energy: Integrating fuel cell technology with ammonia stripping for direct power production"
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    Data supporting: 'CO2 absorption into aqueous ammonia using membrane contactors: Role of solvent chemistry and pore size on solids formation for low energy solvent regeneration'
    (Cranfield University, 2022-10-13 16:42) Bavarella, Salvatore; Luqmani, Benjamin A.; Thomas, Navya; Brookes, Adam; Moore, Andrew; Vale, Peter C. J.; Pidou, Marc; McAdam, Ewan
    Solids formation can substantially reduce the energy penalty for ammonia solvent regeneration in carbon capture and storage (CCS), but has been demonstrated in the literature to be difficult to control. This study examines the use of hollow fibre membrane contactors, as this indirect contact mediated between liquid and gas phases in this geometry could improve the regulation of solids formation. Adoption of a narrower pore size membrane was shown to dissipate wetting after crystallisation in the solvent, illustrating membrane contactors as a stable platform for the sustained separation of CO2 coupled with its simultaneous transformation into a solid. Through resolving previous challenges experienced with solids formation in multiple reactor configurations, the cost benefit of using ammonia as a solvent can be realised, which is critical to enabling economically viable CCS for the transition to net zero, and can be exploited within hollow fibre membrane contactors, eliciting considerable process intensification over existing reactor designs for CCS.
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    The role of solvent temperature and gas pressure on CO2 mass transfer during biogas upgrading within porous and dense-skin hollow fibre membrane contactors
    (Elsevier, 2023-08-02) Luqmani, Benjamin A. ; Brookes, A.; Moore, Andrew; Vale, Peter C. J.; Pidou, Marc; McAdam, Ewan
    Biogas upgrading uniquely requires pressurisation of hollow fibre membrane contactors (HFMC) to be competitive with classical water absorption, and when complemented with an ambient industrial temperature range, these conditions will determine CO2 mass transport phenomena that are distinct dependent upon whether microporous or nonporous membranes are used. This study therefore examines the independent and concomitant role of temperature and pressure in determining CO2 mass transport, and selectivity, within microporous and nonporous HFMC. At low solvent temperatures, higher CO2 flux was achieved which indicates that solvent solubility is more critical than CO2 diffusivity to enhancing mass transport. Low temperatures also favoured mass transfer within the microporous membrane, explained by the reduction in solvent vapour pressure which limited pore wetting by condensation. In contrast, the nonporous membrane exhibited poorer mass transfer at low temperatures due to a decline in dense polymer permeability. Crucially in this study, neither wetting of the microporous membrane or plasticisation of the nonporous membrane were observed following pressurisation. Consequently, CO2 flux increased in proportion to the applied pressure for both membrane types, emphasising the critical role of pressurisation in augmenting process intensification for biogas upgrading which is typically facilitated at pressures of 7–10 bar. Resistance-in-series analysis illustrated how pressurisation reduced gas-phase resistance, and subsequently enhanced selectivity. Consequently, an outlet gas quality of 98% methane could be achieved within a single microporous module at 4.5 bar, meeting the industrial standard for biomethane whilst reducing solvent requirements, separation energy and methane losses. Comparable behaviour was observed during pressurisation of the nonporous membrane, but with a less significant benefit to CO2 mass transfer and selectivity, ostensibly due to the resistance imparted by the dense polymer. When considered collectively, low solvent temperature and high gas pressure enhance process intensification subsequently reducing process size (e.g., membrane area) and separation energy, while also advancing selectivity to deliver a gas product at the composition required for biomethane with minimum methane losses, which are critical factors in demonstrating microporous HFMC as an industrially competitive solution for biogas upgrading.
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    The use of ammonia recovered from wastewater as a zero-carbon energy vector to decarbonise heat, power and transport – a review
    (Elsevier, 2025-01-01) Powders, Mark Thomas; Luqmani, Benjamin A.; Pidou, Marc; Zhu, Mingming; McAdam, Ewan J.
    Ammonia (NH3) is an energy vector with an emerging role in decarbonising heat, power and transport through its direct use as a fuel, or indirectly as a hydrogen carrier. Global ammonia production is having to grow to enable the exploitation of NH3 for energy decarbonisation, which it is projected will consume >50 % of manufacturing capacity by 2050. Ammonia recovered from wastewater can be directly exploited as a sustainable source of ammonia, to reduce the demand for ammonia produced through the energy intensive Haber-Bosch process, while fostering a triple carbon benefit to the water sector, by: (i) avoiding the energy required for aeration of biological processes; (ii) reducing nitrous oxide emissions associated with ammonia oxidation, which is a potent greenhouse gas; and (iii) producing a zero-carbon energy source that can decarbonise energy use. While previous reviews have described technologies relevant for ammonia recovery, to produce ammonia as a zero-carbon fuel or hydrogen carrier, wastewater ammonia must be transformed into the relevant concentration, phase and achieve the product quality demanded for zero carbon heat, power and transport applications, which are distinct from those demanded for more conventional exploitation routes (e.g. agricultural). This review therefore presents a synthesis of established and emerging technologies for the extraction and concentration of ammonia from wastewater, with specific emphasis on enabling the production of ammonia in a form that can be directly exploited for zero carbon energy generation. A précis of technologies for the valorisation of ammonia as a clean energy or hydrogen resource is also introduced, together with discussion of their relevancy and applicability to the water sector including implications to energy, carbon emissions and financial return. The exploitation of ammonia recovered from wastewater as a zero carbon energy source is shown to offer a critical contemporary response for the water sector that seeks to rapidly decarbonise existing infrastructure, while responding to ever stricter nitrogen discharge limits.
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    Transforming wastewater ammonia to carbon free energy: Integrating fuel cell technology with ammonia stripping for direct power production
    (Elsevier, 2022-03-07) Davey, Christopher J.; Luqmani, Benjamin A. ; Thomas, Navya; McAdam, Ewan J.
    The transformation of ammonia from pollutant to energy rich carbon free fuel presents an opportunity for the transition of wastewater services to net zero. However, there is only limited knowledge of how the product quality of ammonia recovered from real wastewater might impact on its downstream exploitation in fuel cells. This study therefore exploited vacuum stripping to produce an aqueous ammonia concentrate from real wastewater that was then evaluated within a direct ammonia fuel cell, as a reference technology for energy generation. A 17 g L−1 aqueous ammonia product was created by vacuum stripping centrate from a full-scale anaerobic digester (2 gN L−1). The pH of the product was lower than expected due to the mild-acidification of solution by the co-transport of low MW volatile organic compounds. This reduced power density in the fuel cell, due to the incomplete deprotonation of ammonia (lowering oxidation potential at the fuel cell anode) and a decrease in [OH–] which is required for complete electrochemical conversion. We propose that improved vacuum stripping design can increase the distillate ammonia concentration and produce a more alkaline product, yielding markedly higher fuel cell power density by enhancing ammonia oxidation at the anode (through concentration and deprotonation) and reducing [OH–] mass transfer limitations. As the separation energy for ammonia is dominated by the latent heat demand of water vapour, a synergy exists between creation of a concentrated ammonia product (that improves power density) and reducing the energy demand for separation. The energy balance from this research evidences that despite the high latent heat demand for separation, the low cost of heat coupled with the power produced from ammonia yield a favourable economic return when compared to conventional biological treatment. This study also identifies that revaluing ammonia as a carbon free fuel can help reposition wastewater treatment for a zero-carbon future.
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    Transitioning through the vapour-liquid equilibrium for low energy thermal stripping of ammonia from wastewater: enabling transformation of NH3 into a zero-carbon fuel
    (Elsevier, 2023-11-17) Luqmani, Benjamin A. ; Brookes, A.; Moore, Andrew; Vale, Peter C. J.; Pidou, Marc; McAdam, Ewan
    Vacuum thermal stripping permits the recovery of ammonia from wastewater in a concentrated form, which is key to its exploitation in the circular economy, but the latent heat demand for thermal separation remains a critical barrier to exploitation. In this study, we investigate the vapor-liquid equilibrium (VLE) for ammonia-water as a mechanism to enhance recovered ammonia quality and minimise the thermal energy required for ammonia separation. Below the dew point (65 °C at 0.25 bar) a two-phase region of the VLE exists where 48 %wt gas-phase ammonia could be produced (61 °C) compared to only 2 %wt within the stripping region adopted widely in the literature. This was complemented by a 98 % reduction in thermal separation energy, since limited water vaporization can occur when the feed is maintained below the activation energy threshold for bulk evaporation. Operation within this practically unexplored region of the ammonia-water VLE fosters a gas-phase product suitable for energy generation in gas turbines or solid oxide fuel cells. Comparable product quality was achieved using concentrated wastewater, which validated the VLE for design in the presence of a broad range of dissolved gases and volatile inorganic compounds. Rapid desorption of CO2 occurred during vacuum stripping, subsequently increasing pH >9 without the requirement for alkali addition to shift the ammonia-ammonium equilibrium in favor of gaseous ammonia. Consequently, the two-phase region of the VLE defined for vacuum thermal stripping provides a synergistic strategy to mitigate chemical demand, minimise separation energy and recover gas-phase ammonia for zero carbon energy generation, constituting a significant advancement toward the net zero ambitions of the water sector.