Advanced alkaline water electrolysis using inorganic membrane electrolyte (I.M.E.) technology

The Belgian Hydrogen Research Programme, aiming at the development of a new concept in advanced alkaline water electrolysis has resulted in demonstration projects with prototype electrolyser units.The new concept, named I.M.E. technology (inorganic membrane electrolyte) produces hydrogen under pressure (0.5–4.0 MPa) at current densities up to 12500 Am^?2 and temperatures not exceeding 120°C.Electrocatalysts based on non-noble metals are deposited on perforated nickel plates. These electrodes are pressed against an inorganic ion-exchanger membrane based on polyantimonic acid.Circular cells (surface area up to 0.2 m²) are assembled in a filter-press type manner.Prototype electrolysers, having hydrogen production rate from 2.5 Nm³h^?1 to 25 Nm³h^?1 have been constructed and tested.Multicell performances (up to 60 unit cells) at 2000 Am^?2 are 1.6 V at 90°C and even 1.5 V at 120°C.At a 5 times higher current density (10000 Am^?2) cell voltages only increase with 0.3 V at 90°C and 0.2 V at 120°C.Since 100% Coulombic efficiency has been measured in these 60 unit cell stacks the electrical power consumption (at 2000 Am^?2) per normal cubic meter of hydrogen produced is 3.81 kWh at 90°C and 3.65 kWh at 120°C.A techno-economic analysis was performed to quantify the cost of hydrogen as a function of design parameters such as module cost and module performance capability.     

Optimal adaptive control of (bio)chemical reactors: past, present and future

In this paper an overview of optimal adaptive control of (bio)chemical reactors is presented. Following the paradigm of the Minimum Principle of Pontryagin the derivation of optimal control sequences for fed-batch production processes is briefly revisited. Next, it is illustrated how the obtained optimal profiles can be exploited in the characterization of nearly optimal control sequences in terms of the qualitative behavior of the specific growth and production rates as function of the limiting substrates. Implementing this knowledge leads in a natural way to the design of (nearly) optimal adaptive feedback controllers. Special emphasis will lie on the potential of on-line biomass measurements (obtained with the Biomass Monitor) in the estimation algorithm of the growth kinetics being the adaptive component of the controller. Extensions towards fermentation processes with (i) multiple substrates and (ii) non-monotonic kinetics are also included. Finally, perspectives towards optimal adaptive control of not perfectly mixed (bio)chemical reactor systems, such as chemical tubular reactors, are outlined.     

Non-strict Interventionism: The Case Of Right-Nested Counterfactuals

Journal of Logic, Language and Information - The paper focuses on a recent challenge brought forward against the interventionist approach to the meaning of counterfactual conditionals. According to...     

Biomass characteristics in three sequencing batch reactors treating a wastewater containing synthetic organic chemicals

The physical and biochemical characteristics of the biomass in three lab-scale sequencing batch reactors (SBR) treating a synthetic wastewater at a 20-day target solids retention time (SRT) were investigated. The synthetic wastewater feed contained biogenic compounds and 22 organic priming compounds, chosen to represent a wide variety of chemical structures with different N, P and S functional groups. At a two-day hydraulic retention time (HRT), the oxidation-reduction potential (ORP) cycled between -100 (anoxic) and 100 mV (aerobic) in the anoxic/aerobic SBR, while it remained in a range of 126+/-18 and 249+/-18 mV in the aerobic sequencing batch biofilm reactor (SBBR) and the aerobic SBR reactor, respectively. A granular activated sludge with excellent settleability (SVI=98+/-31 L mg(-1)) developed only in the anoxic/aerobic SBR, compared to a bulky sludge with poor settling characteristics in the aerobic SBR and SBBR. While all reactors had very good COD removal (>90%) and displayed nitrification, substantial nitrogen removal (74%) was only achieved in the anoxic/aerobic SBR. During the entire operational period, benzoate, theophylline and 4-chlorophenol were completely removed in all reactors. In contrast, effluent 3-nitrobenzoate was recorded when its influent concentration was increased to 5 mg L(-1) and dropped only to below 1 mg L(-1) after 300 days of operation. The competent (active) biomass fractions for these compounds were between 0.04% and 5.52% of the total biomass inferred from substrate-specific microbial enumerations. The measured competent biomass fractions for 4-chlorophenol and 3-nitrobenzoate degradation were significantly lower than the influent COD fractions of these compounds. Correspondent to the highest competent biomass fraction for benzoate degradation among the test SOCs, benzoate oxidation could be quantified with an extant respirometric technique, with the highest specific oxygen uptake rate (SOUR(benzoate), 0.026 g O2 h(-1) g(-1) XCOD) in the anoxic/aerobic SBR. These combined results suggest that operating SBRs with alternative anoxic/aerobic cycles might facilitate the formation of granular sludge with good settleability, and retain comparable removal of nitrogen and synthetic organic compounds. Hence, the practice of anoxic/aerobic cycling should be considered in wastewater treatment systems whenever possible.     

Time-averaged concentration calculations in pulse electrochemical machining, spectral approach

Simulation of the species concentrations during the pulse electrochemical machining (PECM) process can provide information on system design and guidelines for practical use. In detailed numerical calculations, the concentrations will be calculated simultaneously with the temperature due to mutual dependencies. The pulses that are applied to the PECM system have to be described on a timescale that can be orders of magnitude smaller than the physical timescales in the system. If the full detail of the applied pulses has to be taken into account, the time accurate calculation of the variable distributions' evolutions in PECM can become a computationally very expensive procedure. A different approach is used by time averaging the pulses applied to the system. Performing this, the timesteps used during the calculations are no longer dictated by the pulse characteristics. Using this approach is computationally very cheap, yet satisfying results can be obtained. In the previous study of the authors (Smets et al., J Appl Electrochem 37(11):1345–1355, 2007 [8]), the hybrid calculation and the quasi-steady-state shortcut (QSSSC) were introduced. These methods introduce errors, however, which were quantified using analytical solutions and found to be acceptable. The results applied only to rectangular pulses. In this study, the more general case of arbitrary pulse forms is considered using a spectral approach. The concentration and the temperature calculation have different requirements for optimal approximated calculations, and a compromise has to be found between them. An analysis is performed on a simplified model, which provides useful guidelines during simulations.     

Derivation of generic optimal reference temperature profiles for steady-state exothermic jacketed tubular reactors

Despite the existence of advanced controllers for jacketed tubular reactors, generic optimal steady-state reference temperature profiles are rather scarce. In this paper, optimal (infinite dimensional) temperature profiles are derived by exploiting a combination of analytical and numerical optimal control techniques for two cost criteria which both involve a trade-off between a conversion and an energy cost. Hereby, the following results are obtained: (i) a more complex model which also incorporates heat transfer, yields more valuable references than a simple model which only takes the reaction into account, (ii) the analytical approach allows to extract generic features in the reference profiles, enhancing the robustness against model mismatch, and (iii) the performance loss due to practical implementation hardware, i.e., the availability of only a finite number of isothermal jacket elements, is quantified.     

Ageing of EUROBITUM bituminised radioactive waste: An ATR-FTIR spectroscopy study

The extent of the physico-chemical processes of concern in the study of the acceptability of Eurobitum bituminised radioactive waste for underground disposal (water uptake by hygroscopic NaNO₃ - swelling - pressure build-up - NaNO₃ leaching) will depend on the degree of ageing of the bituminous matrix. In the work reported here, the ageing behaviour was studied by comparing the characteristics of 25 years old radioactive Eurobitum with those of 25 years old non-radioactive Eurobitum samples that were heated or gamma-irradiated in the presence or absence of oxygen. Chemical changes in the bitumen structure were followed in the mid-infrared region with Attenuated Total Reflectance Fourier Transform InfraRed Spectroscopy (ATR-FTIR) by measuring the evolution of the band heights at 1700 cm⁻¹ (CO functional groups) and 1600 cm⁻¹ (CC double bonds). Needle penetration depths and ring and ball softening points were determined for some samples. Oxidation of bitumen in the presence of oxygen results in a distinct increase of both the number of CO and CC functionalities, with a positive linear relationship existing between the two groups. The production of CO functional groups seems to promote the generation of CC double bonds. Heating at 130 °C is much more efficient than gamma irradiation at low to moderate dose rates (20-140 Gy/h) to oxidise the bitumen. As the oxygen concentration decreases, for instance by diffusion limitation deeper inside the bitumen, the number of CO and CC functionalities formed per unit of time decreases. A similar behaviour was observed for 25 years old radioactive Eurobitum. In absence of oxygen, gamma irradiation still results in a small increase of the number of CO functional groups, probably by oxygen still adsorbed on the bitumen, and in a relatively higher amount of CC double bonds. The surface layer (<5 cm) of 25 years old radioactive Eurobitum was heavily oxidised. The material had become very hard and brittle, and was full of small fissures. Due to these fissures, radio-oxidation processes took also place deeper inside the waste. The consequences of these observations for the long-term behaviour of Eurobitum in underground disposal conditions are discussed.