Ammonia Separation Research Articles

Modeling of heat and mass transfer in vacuum membrane distillation for ammonia separation

Ammonia is both a contaminant and valuable commodity as chemical. The extraction of ammonia from wastewater was proven technically feasible using membrane distillation (MD). However, the fundamental separation mechanisms of ammonia in MD is not well understood, due to the complexity related to the binary transport and solution chemistry. This study aimed to develop a numerical model for the first time to describe the ammonia and vapour binary transport across hollow fibre membrane in single-stage vacuum membrane distillation (VMD). The key model constants were obtained based on measured membrane properties and unique ammonia chemistry. The modelling results indicated that the ammonia concentration factor into the permeate was strongly correlated with feed temperature at fixed pH but not sensitive to feed concentration. The trade-off between ammonia selectivity and membrane flux indicated a suitable temperature range of 40–45 °C for efficient extraction. The predicted gas pressure of ammonia-vapour mixture showed a slow increase of process driving force and membrane flux with feed temperature. While the averaged process driving force decreased as fibre length increased, indicating an optimal length for maximum permeate production. The predicted permeate gas and membrane surface temperatures were identical along fibre length, indicating minimal conductive heat loss and hence high thermal efficiency (>90%) for ammonia extraction.

Energy Use of Flux Salt Recovery Using Bipolar Membrane Electrodialysis for a CO2 Mineralisation Process.

Mineral carbonation routes have been extensively studied for almost two decades at Åbo Akademi University, focusing on the extraction of magnesium from magnesium silicates using ammonium sulfate (AS) and/or ammonium bisulfate (ABS) flux salt followed by carbonation. There is, however, a need for proper recovery and recirculation of chemicals involved. This study focused on the separation of AS, ABS and aqueous ammonia using different setups of bipolar membrane electrodialysis using both synthetic and rock-derived solutions. Bipolar membranes offer the possibility to split water, which in turn makes it possible to regenerate chemicals like acids and bases needed in mineral carbonation without excess gas formation. Tests were run in batch, continuous, and recirculating mode, and exergy (electricity) input during the tests was calculated. The results show that separation of ions was achieved, even if the solutions obtained were still too weak for use in the downstream process to control pH. Energy demand for separating 1 kg of NH4+ varied in the range 1.7, 3.4, 302 and 340 MJ/kg NH4+, depending on setup chosen. More work must hence be done in order to make the separation more efficient, such as narrowing the cell width.

Risk analysis for clean and sustainable production in a urea fertilizer industry

PurposeThe purpose of this paper is to develop a fuzzy methodology approaches based framework for carrying the risk analysis of a real industrial system of a urea fertilizer industry located in northern part of India.Design/methodology/approachPetri Net approach was applied for representing the series-parallel arrangement of the considered system. Various failure causes related to different subsystems or equipment of the considered system were listed under FMEA approach and their Risk Priority Number was tabulated. Further, to overcome the drawbacks of traditional FMEA approach in risk ranking fuzzy FMEA and grey relation analysis (GRA) approaches were applied within traditional FMEA approach and the ranking results were compared for better and effective decision making of risky components.FindingsThe proposed framework has overcome the drawbacks of tradition FMEA approach in an effective and efficient manner. Causes AC7, CL3, ST2, DR3 and NR3 of centrifugal compressor, hot heat exchanger, ammonia convertor reactor, cold condenser and ammonia separator have been identified as the most critical failure causes of the considered system.Originality/valueThe proposed framework has been tested with its application on an ammonia synthesis system of the considered process industry. The risk ranking results would be highly useful in developing a planned maintenance policy for the considered system which further results in improving the system availability.

Rates of Ammonia Absorption and Release in Calcium Chloride

After synthesis, ammonia can be selectively absorbed by calcium chloride; nitrogen and hydrogen are not absorbed. The kinetics of release seem to be diffusion controlled. The kinetics of absorption are consistent with a first-order reaction after an initial period of a higher-order reaction, which may indicate a nucleation event. At 225 °C, both absorption and release show half-lives of around 10 min if the ammonia partial pressure is swung from 2 to 1 bar, which allows design of an absorber for the periodic separation of ammonia. When this absorber replaces the ammonia condenser in a conventional ammonia synthesis, the ammonia production at low pressure can have the same rate as the conventional process operating at higher pressure.

Automatic pressure-assisted dual-headspace gas-liquid microextraction. Lab-in-syringe platform for membraneless gas separation of ammonia coupled with fluorimetric sequential injection analysis

A novel pressure-assisted dual-headspace lab-in-syringe microextraction technique is presented as an alternative approach for automatic on-line membraneless gas separation of volatile compounds. The developed gas-liquid microextraction procedure is based on the lab-in-syringe (LIS) concept by using two independent micro-syringe pumps which are connected to each other for the application of negative and positive pressure inside the common headspace area of the syringe barrels. The adoption of reduced and increased pressure conditions is facilitated by the programmable LIS strategy resulting in increased extraction rates. The analytical process includes the in-situ ammonia vapor generation in the headspace of the first microsyringe, under reduced pressure environment, and its subsequent transportation into the headspace of the second microsyringe. Then, positive pressure is applied inside the second microsyringe enabling the ammonia vapor dissolution into the extraction solution to produce a fluorescent product (isoindol-1-sulfonat). The reaction is time and temperature affected, thus after an optimized time of delay inside the thermostated syringe barrel at 60 °C, it is delivered into the flow-cell of the miniSIA system where it is quantified at 425 nm (excitation wavelength, 365 nm). The proposed preconcentration system has been fully tested and optimized regarding the relevant parameters affecting the generation of gaseous ammonia, its effective transportation into the headspace of the second syringe barrel and its quantitative dissolution and reaction with the extraction solution. For a sample volume of 3000 μL, the sample frequency is 8 h−1, the precision expressed as relative standard deviation (RSD) is 3.6 (at 5.0 μg L−1) and a detection limit (3s) of 0.05 μg L−1 for ammonium is obtained. The detection is linear in the concentration range of 0.15 and 10.0 μg L−1 with a correlation coefficient of 0.9987. The accuracy of the proposed method has been evaluated by analyzing a standard reference material (relative error: 3.8%) as well as using the Certified Method (relative error < 5.5%) for ammonium determination. The potential of this novel schema has been demonstrated for ammonia determination in natural water samples.

Process simulation of ammonia synthesis over optimized Ru/C catalyst and multibed Fe + Ru configurations

Ammonia synthesis over different iron- and ruthenium-based catalysts was modelled with appropriate rate models, used for the simulation of the process under different configurations and conditions. The kinetic models have been simulated and validated against experimental data. A scaled up reactor has been designed, at first with a once through configuration. On this model reactor we performed a sensitivity analysis to optimise the reaction conditions. Then, the sizing of an ammonia separation unit and the optimisation of the recycle loop allowed to compare different possible configurations.A multibed catalytic reactor with intercooling was then designed, using the same catalyst or different catalyst types properly to maximise the ammonia productivity. In particular, Fe-based catalysts were followed by the Ru/C one, in order to push the ammonia productivity towards the equilibrium value.The goal of the work is the design of an ammonia synthesis loop which couples different catalysts towards the optimisation of productivity and cost of operation and installation.

Anaerobic digestion of chicken manure by a leach-bed process coupled with side-stream membrane ammonia separation

This study pioneered the use of a single-stage methanogenic leach bed reactor (LBR) for high-solids (total solid content: 14%–16%) anaerobic mono-digestion of chicken manure. Chicken manure was loaded into the LBR in cloth sachets without adding any bulking agents. Ammonia was separated and recovered by placing a hydrophobic gas diffusion membrane in a leachate collection chamber. Methane production in the membrane-integrated LBR was 0.272 m3/kgVS and 2.3 times higher than that in the control LBR. The results revealed that using membrane-integrated LBR for anaerobic digestion is a simple and cost-efficient technology for the mono-digestion of chicken manure and ammonia removal.

Self-Optimizing Control in Chemical Recycle Processes

An engineer always has to make assumptions about the system boundary. In this paper, the impact of neglected dependencies of manipulated variables on the disturbance variables as example for said assumptions is investigated in the context of self-optimizing control. The feedback through dependent disturbances influences both the optimal operating point and the combination of measurements. As a case study, we consider an ammonia synthesis reactor with a simplified model for the ammonia separation and the recycle. The disturbance dependency changes the optimal selection matrices through the recycle. However, we find that it is possible to neglect the recycle in the selection of the controlled variables for this example if the setpoint is adjusted.

A review on the non-thermal plasma-assisted ammonia synthesis technologies

Abstract Ammonia has been intensively studied as a clean, sustainable fuel source and an efficient energy storage medium due to its effectiveness as a hydrogen carrier molecule. However, the current method of ammonia synthesis, known as the Haber-Bosch process, requires a large fossil fuel input, high temperatures and pressures, as well as a significant capital investment. These volatile conditions and high operating costs prevent decentralized and small-scale ammonia production at the level of small farms and local communities. This article provides systematic review of the plasma-assisted ammonia synthesis under low temperature and pressure conditions. Non-thermal plasma technology represents a promising alternative method of clean ammonia synthesis, as it circumvents the volatile operating conditions, fossil fuel use, and high capital costs of the Haber-Bosch process. This technology could be beneficial to the ammonia industry, through its potential to promote localized and environmentally friendly energy production and storage. The opportunities of the non-thermal plasma technology lie with providing an avenue towards a cleaner ammonia industry, including a renewable pathway that incorporates this technology with other renewable energy approaches. However, the two most critical challenges of this technology are the fixation of nitrogen gas and back reactions. To overcome these challenges, researchers could work to further develop catalysts with stronger plasma synergistic activities, and optimizing reactor designs for rapid separation of ammonia after being synthesized.

Relating water vapor transfer to ammonia recovery from biogas slurry by vacuum membrane distillation

Abstract As the byproduct of biogas production, biogas slurry with high content of ammonia nitrogen may cause serious environmental problems (e.g. eutrophication). Ammonia recovery from biogas slurry is of great importance in minimizing the environmental impacts and maximizing the benefits. This study explores the role of water vapor transfer in ammonia recovery from biogas slurry by vacuum membrane distillation. The overall mass transfer coefficients, ammonia separation factors and ammonia fluxes are used to evaluate ammonia separation performance. Effects of various operating parameters including the feed temperature, flow rate, initial pH of biogas slurry and vacuum pressure on ammonia separation performance are investigated and discussed. Ammonia separation performance is dominated by the initial pH of biogas slurry. Optimizing operational parameters can effectively increase the overall mass transfer coefficient, but does not necessarily improve the ammonia separation factor. Water flux has an important impact on the overall ammonia transfer coefficient. An interesting S curve logistic model can well fit the relationship between the water flux and the overall ammonia transfer coefficient, suggesting that there is an optimal water flux. A relatively high concentration aqueous ammonia (up to 1.0 mol-N/L, much higher than the value in feed biogas slurry

Dry anaerobic digestion of chicken manure coupled with membrane separation of ammonia

In this study, the anaerobic digestion of egg-laying hen manure combined with membrane-based ammonia separation was investigated. Long-term continuous experiments with and without ammonia separation were performed by increasing the organic loading rate (OLR). Although the control digester was completely inhibited at an OLR and influent total Kjeldahl nitrogen (TKN) concentration of 3.85kgVS/m3·d and 8.2g/l, respectively, an average methane yield of 0.30±0.02m3/kgVS was achieved with a membrane-integrated digester at an OLR and influent TKN concentration of 6.0kgVS/m3·d and 15g/l, respectively. When the ammonia concentration increased above 4000mg/l, hydrogenotrophic methanogens Methanoculleus bourgensis and Methanobrevibacter sp. performed methane production via syntrophic acetate oxidation.

Once-through CO2 absorption for simultaneous biogas upgrading and fertilizer production

A new process is developed for biogas upgrading using the total ammonia nitrogen (TAN) in biogas slurry as a renewable absorbent. TAN in biogas slurry can be transferred into free ammonia by adding NaOH to increase the solution pH. Increasing the pH of biogas slurry to 10 causes that >90% TAN transfers into free ammonia, leading to high TAN removal ratios. However, further increasing the pH of biogas slurry has limited effects. Vacuum membrane distillation (VMD) has higher kinetics constants and thus is a more effective way to recover and enrich ammonia from biogas slurry compared with thermal or air stripping. After VMD, the recovered aqueous ammonia solution with high TAN concentrations and the enhanced biogas slurry can be used as “once-through” CO2 absorbents. With alkaline addition, VMD does not increase the CO2 absorption capacity, but significantly minimizes the phytotoxicity of biogas slurry. When NaOH dosage is below 0.25M, superior ammonia separation performance with high kinetics constants and low phytotoxicity can be achieved. The recovered aqueous ammonia solution also has excellent CO2 absorption performance for biogas upgrading and can help obtain high content of methane. This study provides an effective process for biogas upgrading with low costs and generation of valuable products, including high purity bio-methane, low phytotoxicity biogas slurry for agricultural application and high concentration NH4HCO3 as a fertilizer.

Ammoniakabscheidung in neuartigen Biofiltern

Currently used bio filters are suited for odor reduction in livestock keeping but not for ammonia separation. Therefore it was the objective to develop a novel bio filter system which was able to ensure a high and long-lasting ammonia separation. This novel bio filter, which is equipped with a pH control in a water swamp beneath the filter layer and a conductivity control for water discharge, was investigated in terms of ammonia separation and nitrogen disposition over several months under practical conditions. The results show a stable ammonia separation of more than 88 % if certain consecutively described operating conditions are kept.

Ammonia Synthesis at Reduced Pressure via Reactive Separation

Ammonia is normally made at high temperature and pressure using a promoted iron catalyst. High temperatures are needed to get fast kinetics; the high pressure is used to ensure high conversion. Alternatively, ammonia can be made at high temperature but lower pressure if the product ammonia is rapidly separated. Here, we have systematically studied the effect of temperature and pressure on the rates of reaction. We then have qualitatively investigated the absorptive separation of ammonia using calcium chloride in a reaction–separation process. Rapid separation reduces the constraint of reversible reaction and enables us to obtain appropriate reaction rates at relatively lower pressure. The effect of different operating conditions—reaction temperature, pressure, absorption temperature, and gas transport—on production rates is carefully measured, and this elucidates the potential and the limits of this type of low-pressure ammonia synthesis.

Pervaporation of ammonia solution with γ-alumina supported organosilica membranes

In this work, pervaporation of ammonia-solution using c-alumina supported organosilica membrane (HybSi , Pervatech) was explored to understand ammonia removal performance and material stability in this unique high pH environment. During the testing of synthetic ammonia solution of 50 mg/L at 45 C (pH 10), the hybrid silica membrane showed a preference towards ammonia transport over water, with an ammonia separation factor up to 12 and flux of 4.3 kg m 2 h 1 stable in a continuous testing period of 7 h. At an ammonia concentration of 1000 mg/L (pH 11), the membrane initially exhibited separation preference towards ammonia at 45 C, then gradually reversed to water selective after increasing to 70 C, where a significant flux decline was observed. The membrane degradation was investigated by FTIR, porosimetry, SEM and XRD. Only slight change in organosilica chemistry and structure was evident, however more significant degradation was observed in the supporting c-alumina layer. The changes in crystalline alumina structure, porous properties and physical structure undermined the functional silica separation layer. Therefore while the organosilica membrane appeared stable in the high pH aqueous ammonia environment, membranes for ammonia pervaporation applications should consider alternative supporting layers to c-alumina.

Performance of a Small-Scale Haber Process

This work identifies a benchmark for the performance of a small-scale ammonia synthesis plant powered by wind energy. The energy used is stranded, far from urban centers but near locations of fertilizer demand. The wind energy drives the pressure swing absorption of air to make nitrogen and the electrolysis of water to make hydrogen. These are combined in the small-scale continuous Haber process to synthesize ammonia. The analysis of runs of the small plant presented in this article permits an assessment of how the current production rate is controlled by three resistances: catalytic reaction, ammonia separation by condensation, and recycling of unreacted gas. The measured catalytic reaction rates are consistent with separate experiments on chemical kinetics and with published reaction mechanisms. The condensation rates predicted are comparable with literature correlations. These rate constants now supply a rigorous strategy for optimizing this scaled-down, distributed ammonia plant. Moreover, this method...

Separation of ammonia from radioactive wastewater by hydrophobic membrane contactor

The radioactive wastewater produced in the manufacturing process of UO2 kernel for high temperature gas-cooled reactor (HTR) contains high concentration of ammonia. The ammonia has to be removed effectively for further treatment of the wastewater. In this study, the hydrophobic membrane contactor (HMC) was adopted to remove and recover the ammonia from radioactive wastewater at room temperature. The operating parameters such as feed velocity and initial ammonia concentration were determined. In addition, the effect of wastewater composition on ammonia separation was studied. The experiment results showed that ammonia removal efficiency could reach above 90% after 120 min operation when pH was not adjusted. While the initial pH of wastewater was adjusted to 12.0, ammonia removal efficiency could reach above 95%. The ammonia mass transfer coefficient increased with increase of feed velocity and tended to an asymptotic value when the feed velocity reached 0.049 m/s. When the initial ammonia concentration was 2211.6 mg/L, 5864.6 mg/L and 23,898.7 mg/L, the ammonia removal efficiency was 95.0%, 94.2% and 94.1%, respectively after 120 min operation, i.e. the initial concentration of ammonia in wastewater had almost no effect on ammonia separation. In addition, the coexisting substances, such as urea and tetrahydrofurfuryl alcohol (THFA), also had no effect on ammonia separation. The HMC is a promising way to separate ammonia from radioactive wastewater.

Experimental Study on CO2 Absorption into Aqueous Ammonia-based Blended Absorbents

A crucial problem for the promising absorbent aqueous ammonia (NH3) is the low CO2 absorption rate and high ammonia volatile loss rate. This work investigated the effect of potential promoters for CO2 absorption into aqueous ammonia solutions on a wetted wall column. Monoethanolamine, sarcosinate, taurinate, glycinate, piperazine and 1-methyl piperazine were introduced to NH3 solutions as promoters. We found sarcosinate, piperazine and 1-methyl piperazine could increase the mass transfer coefficient of CO2 into the ammonia-based solutions significantly. We further undertook a detailed mass transfer study of CO2 into ammonia based blended solutions to investigate the effects of temperature and additive concentration. Besides, a novel ammonia separation method from low concentration ammonia solution by membrane vacuum regeneration was developed which could recover more than 80% of ammonia gas from low concentration ammonia.

Anaerobic digestion for methane generation and ammonia reforming for hydrogen production: A thermodynamic energy balance of a model system to demonstrate net energy feasibility

During anaerobic digestion, organic matter is converted to carbon dioxide and methane, and organic nitrogen is converted to ammonia. Generally, ammonia is recycled as a fertilizer or removed via nitrification–denitrification in treatment systems; alternatively it could be recovered and catalytically converted to hydrogen, thus supplying additional fuel. To provide a basis for further investigation, a theoretical energy balance for a model system that incorporates anaerobic digestion, ammonia separation and recovery, and conversion of the ammonia to hydrogen is reported. The model Anaerobic Digestion-Bioammonia to Hydrogen (ADBH) system energy demands including heating, pumping, mixing, and ammonia reforming were subtracted from the total energy output from methane and hydrogen to create an overall energy balance. The energy balance was examined for the ADBH system operating with a fixed feedstock loading rate with C:N ratios (gC/gN) ranging from 136 to 3 which imposed corresponding total ammonia nitrogen (TAN) concentrations of 20–10,000 mg/L. Normalizing total energy potential to the methane potential alone indicated that at a C:N ratio of 17, the energy output was greater for the ADBH system than from anaerobic digestion generating only methane. Decreasing the C:N ratio increased the methane content of the biogas comprising primarily methane to >80% and increased the ammonia stripping energy demand. The system required 23–34% of the total energy generated as parasitic losses with no energy integration, but when internally produced heat and pressure differentials were recovered, parasitic losses were reduced to between 8 and 17%.

Analysis of ammonia separation from purge gases in microporous hollow fiber membrane contactors

In this study, a mathematical model was developed to analyze the separation of ammonia from the purge gas of ammonia plants using microporous hollow fiber membrane contactors. A numerical procedure was proposed to solve the simultaneous linear and non linear partial differential equations in the liquid, membrane and gas phases for non-wetted or partially wetted conditions. An equation of state was applied in the model instead of Henry's law because of high solubility of ammonia in water. The experimental data of CO2–water system in the literature was used to validate the model due to the lack of data for ammonia–water system. The model showed that the membrane contactor can separate ammonia very effectively and with recoveries higher than 99%. SEM images demonstrated that ammonia caused some micro-cracks on the surfaces of polypropylene fibers, which could be an indication of partial wetting of membrane in long term applications. However, the model results revealed that the membrane wetting did not have significant effect on the absorption of ammonia because of very high solubility of ammonia in water. It was also found that the effect of gas velocity on the absorption flux was much more than the effect of liquid velocity.