Techno-economical evaluations of decarbonized hydrogen production based on direct biogas conversion using thermo-chemical looping cycles

Hydrogen production by biogas conversion represent a promising solution for reduction of fossil CO₂ emissions. In this work, a detailed techno-economic analysis was performed for decarbonized hydrogen production based on biogas conversion using calcium and chemical looping cycles. All evaluated concepts generate 100,000 Nm³/h high purity hydrogen. As reference cases, the biogas steam reforming design without decarbonization and with CO₂ capture by gas-liquid chemical absorption were also considered. The results show that iron-based chemical looping design has higher energy efficiency compared with the gas-liquid absorption case by 2.3 net percentage points as well as a superior carbon capture rate (99% vs. 65%). The calcium looping case shows a lower efficiency than chemical scrubbing, with about 2.5 net percentage points, but the carbon capture rate is higher (95% vs. 65%). The hydrogen production cost increases with decarbonization, the calcium looping shows the most favourable situation (37.14 €/MWh) compared to the non-capture steam reforming case (33 €/MWh) and MDEA and iron looping cases (about 42 €/MWh). The calcium looping case has the lowest CO₂ avoidance cost (10 €/t) followed by iron looping (20 €/t) and MDEA (31 €/t) cases.     

Can simplified design methods for domestic rainwater harvesting systems produce realistic water‐saving and financial predictions?

Rainwater harvesting systems are a recognised approach for reducing reliance on potable mains supply. Many domestic systems are designed and assessed using simplified approaches that can be applied with little prior information. Oversimplification of the physical processes involved and ad hoc consideration of associated costs means that the results produced by these simplified methods are of questionable accuracy. This paper looks at three popular simplified approaches and compares the predicted water‐saving and financial performance with that of a more detailed simulation model, which includes explicit consideration of the physical processes and associated system costs. The simplified approaches predict significantly higher water and financial savings compared with the detailed model. Consequently it is recommended that simplified approaches should not be relied upon and greater preference should be given to the use of more detailed simulations that explicitly consider the important physical processes and include a thorough assessment of costs.     

Characterization and applications of a new composite material obtained by green synthesis,through deposition of zinc oxide onto calcium carbonate precipitated in green seaweeds extract

Zinc oxide was deposited onto calcium carbonate precipitated using a template of polysaccharides from Ulva lactuca green seaweeds (Black Sea). The resulted composite material was characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, UV–vis and FTIR spectroscopy. The therapeutic effect of prepared composite material was assessed in vivo as a topical application for the burns treatment and compared with that of ZnO. An increased antioxidant activity by combining zinc oxide with calcium carbonate capped with polysaccharides from green seaweeds extract in a composite material was demonstrated.     

Numerical comparison of LED directivity approximation functions for video displays

The approximation functions of the directivity of the light emitting diodes (LED) have been investigated. LEDs used in large scale LED video displays have been studied. LED directional properties among the other parameters define the video display image quality. The simplicity of an approximation function and ease of analytical handling have been targeted. These functions suppose to be used in display directivity engineering. Four candidate approximation functions were identified and their approximation performance analyzed. The evaluation is done on eight different type LEDs’ sample batches. These samples have been chosen to represent the variety of the main colors and the range of the most popular viewing angles used in large scale LED video displays design. The relative intensity approximation root mean square (RMS) error and approximation errors’ cross correlation have been used as performance estimation criteria. The radiometric intensity variation within a manufacturing lot was suggested as lower error bound. Approximation error variance was analyzed for various approximation ranges. Results of four candidate approximation functions’ performance on eight different type LEDs’ are presented.     

Investigations on the influence of surfactant in morphology and optical properties of zinc oxide nanopowders for dye-sensitized solar cells applications

We studied the influence of the synthesis route on the morphology and optical properties of zinc oxide (ZnO), with applications in dye-sensitized solar cells (DSSCs). For this purpose, we obtained surfactant capped ZnO nanopowders, in the presence of non-ionic surfactants with different structures, and demonstrated their behavior as semiconductors in DSSCs. The ZnO nanopowders and films (obtained from nanopowders using the doctor blading method) were analyzed by transmission electron microscopy (TEM), high resolution TEM (HRTEM), and selected area electron diffraction (SAED). The optical properties were examined by UV, visible spectroscopy, and the band gap energies were calculated using the Tauc equation. The values obtained for DSSCs efficiencies were in good agreement with the characteristics of ZnO, both powders and films, and can be correlated with the synthesis route. The highest efficiency (1.19%) was achieved using ZnO nanopowder capped with Triton X-100, having a mean diameter of ～19 nm. We find that the use of capped ZnO nanoparticles is favorable for DSSCs, possibly because of the good porosity of the film and better dye adsorption. Moreover, the efficiency of the cells is influenced by the surfactant structure, due to the particle morphology.     

A review of principles and methods applied to the optimum calculation and design of externally-pressurized bearings: Part 2: Moderate/high-speed bearings

This paper in the second of two parts¹, and is a review of the characteristic aspects of optimizing hybrid bearings and the possibilities of applying mathematical programming methods. The most important physical implications of the high relative speed between the two bearing surfaces are briefly presented: non-laminar flow, thermal effects, film rupture. The flow graph representations of lubricant flow in the bearing are also given. Finally, elements are provided for the application of nonlinear programming in the externally-pressurized bearing (epb) optimization. The conclusions show the nonlinear programming processes to be superior and recommendable. The final section of the paper deals with the solving methodology based on the epb optimizing nonlinear programming.     

Review of principles and methods applied to the optimum calculation and design of externally-pressurized bearings: Part 1: Low/moderate speed bearings

A review is presented of the main calculations, design principles and methods for optimization of externally-pressurized bearings (EPBs). Several EPB optimizing aspects are presented followed by a brief presentation of various author's approaches to this problem. To permit more systematic use of the available information an overall classification of the possible solutions to the problem is given. Starting from the speed criterion, the differences in calculation and optimization between low-speed and high-speed bearings respectively are presented by means of the concept of the hybrid bearing. This paper treats only the problem of low/moderate-speed bearings, using classical methods. The recommended values are given comparatively as optimum for the main geometric and functional parameters.     

Subsample interpolation bias error in time of flight estimation by direct correlation in digital domain

This work presents an investigation of the bias error introduced in time of flight estimation realized by subsample interpolation in digital domain. The time of flight estimation is accomplished based on the evaluation of the peak position of the cross correlation function. In order to cope with the discrete nature of the cross-correlation function, subsample estimation exploits three time domain interpolation techniques: parabolic, cosine, Gaussian and frequency domain interpolation using phase angle. An empirical equation relating the maximum value of the bias error to sampling frequency and signal parameters (center frequency and envelope bandwidth) has been derived. It is found that the maximum value of the bias error is in inverse cubic relation to sampling frequency and in quadratic relation envelope bandwidth for cosine interpolation. The maximum value of the bias error is in inverse cubic relation to sampling frequency and in quadratic relation to center frequency and envelope bandwidth for parabolic interpolation. The coefficients related to the approximation technique are given. Results can be applied for bias errors estimation or correction when fast subsample interpolation is used and application of phase domain interpolation is unacceptable due to processing speed limitations. The equations for minimum required sampling frequency are derived by balancing the interpolation error against Cramer–Rao lower bound.     

Angle Encoding Disk Surface Parameters Evaluation Using Conventional Laser Head: Initial Study

Surface quality is one of the most important parameters in mechanical treatment. In recent years a great number of contact and non-contact surface quality measurement methods have been created. This article covers a non-contact laser method of surface parameter evaluation, intended for the evaluation of the surface quality of an angle encoder disk. For such a measurement, this paper proposes using a conventional compact disc laser-reading unit. The proposed system is relatively simple and inexpensive. The device allows measuring unevenness in the surface thickness of an encoder disk, as well as its surface roughness and profile details. The structure of the measurement system, the static and dynamic calibration results and the experimental surface measurement results for an angle encoder disc are presented.