Weidou Ni

A partial least squares and wavelet-transform hybrid model to analyze carbon content in coal using laser-induced breakdown spectroscopy.

A partial least squares (PLS) and wavelet transform hybrid model are proposed to analyze the carbon content of coal by using laser-induced breakdown spectroscopy (LIBS). The hybrid model is composed of two steps of wavelet analysis procedures, which include environmental denoising and background noise reduction, to pretreat the LIBS spectrum. The processed wavelet coefficients, which contain the discrete line information of the spectra, were taken as inputs for the PLS model for calibration and prediction of carbon element. A higher signal-to-noise ratio of carbon line was obtained after environmental denoising, and the best decomposition level was determined after background noise reduction. The hybrid model resulted in a significant improvement over the conventional PLS method under different ambient environments, which include air, argon, and helium. The average relative error of carbon decreased from 2.74 to 1.67% under an ambient helium environment, which indicated a significantly improved accuracy in the measurement of carbon in coal. The best results obtained under an ambient helium environment could be partly attributed to the smallest interference by noise after wavelet denoising. A similar improvement was observed in ambient air and argon environments, thereby proving the applicability of the hybrid model under different experimental conditions.

Combination of cylindrical confinement and spark discharge for signal improvement using laser induced breakdown spectroscopy

Spark discharge has been proved to be an effective way to enhance the LIBS signal while moderate cylindrical confinement is able to increase the signal repeatability with limited signal enhancement effects. In the present work, these two methods were combined together not only to improve the pulse-to-pulse signal repeatability but also to simultaneously and significantly enhance the signal as well as SNR. Plasma images showed that the confinement stabilized the morphology of the plasma, especially for the discharge assisted process, which explained the improvement of the signal repeatability.

Application of a spectrum standardization method for carbon analysis in coal using laser-induced breakdown spectroscopy (LIBS).

Measurement of coal carbon content using laser-induced breakdown spectroscopy (LIBS) is limited by its low precision and accuracy. A modified spectrum standardization method was proposed to achieve both reproducible and accurate results for the quantitative analysis of carbon content in coal using LIBS. The proposed method used the molecular emissions of diatomic carbon (C2) and cyanide (CN) to compensate for the diminution of atomic carbon emissions in high volatile content coal samples caused by matrix effect. The compensated carbon line intensities were further converted into an assumed standard state with standard plasma temperature, electron number density, and total number density of carbon, under which the carbon line intensity is proportional to its concentration in the coal samples. To obtain better compensation for fluctuations of total carbon number density, the segmental spectral area was used and an iterative algorithm was applied that is different from our previous spectrum standardization calculations. The modified spectrum standardization model was applied to the measurement of carbon content in 24 bituminous coal samples. The results demonstrate that the proposed method has superior performance over the generally applied normalization methods. The average relative standard deviation was 3.21%, the coefficient of determination was 0.90, the root mean square error of prediction was 2.24%, and the average maximum relative error for the modified model was 12.18%, showing an overall improvement over the corresponding values for the normalization with segmental spectrum area, 6.00%, 0.75, 3.77%, and 15.40%, respectively.

Economic assessment of a distributed energy system in a new residential area with existing grid coverage in China

Abstract A distributed energy system refers to an energy system where energy production is close to end use, typically relying on various small-scale energy generation, conversion and storage technologies. The Chinese government has recently expressed interest in promoting this type of energy system. The paper develops an optimization model to evaluate the economic feasibility of adopting a distributed energy system in a new residential community in Beijing, where grid coverage is already well developed and accessible. The economic implications of adopting different grid connection regimes are also assessed. Results show that compared to the more conventional approach of relying entirely on the grid for electricity supplies, a distributed energy system is cheaper when a connection to the power grid can still be used to draw some electricity during periods of peak demand. Additionally, the economic benefits of electricity buy-back provisions for the distributed energy system are found to be minimal.

A hybrid quantification model and its application for coal analysis using laser induced breakdown spectroscopy

The low sample-to-sample reproducibility of laser induced breakdown spectroscopy (LIBS) is the most critical obstacle to wide commercialization of the technology. Averaging multi-pulse normalized spectra is the only applied method to improve the sample-to-sample reproducibility; however, the method can only improve the reproducibility to some extent because the averaging process can only eliminate random noise and has no effect on non-random noise, and because normalization can only partially and indirectly remove the signal fluctuations. In addition, the measurement accuracy of LIBS is also limited due to matrix effects as well as signal uncertainty. In this work, we propose a set method to improve both precision (sample-to-sample reproducibility) and accuracy for LIBS quantification. The method includes three steps: (1) the intensities of all spectral lines from every single pulse are converted to a standard state value using a “spectrum standardization” method to reduce the measurement uncertainties to acceptable levels; (2) the standardized spectra are compared with a large spectral database to check whether the current sample is a new sample or is already in the database with known composition/property information; and (3) if the sample is found to be a new sample, a dominant factor based partial least square (PLS) model is applied to provide quantitative analytical results, and the new standardized spectral information and analytical results are inserted into the spectrum database, making the database self-adaptable for future measurements; while if the sample is found to be already in the database, the analytical results are directly obtained from the database. The proposed method was applied for coal analysis. The results showed that the relative standard deviation (RSD) of carbon for different measurements of the same sample is 0.3%, proving that LIBS is able to provide high reproducibility, at least for coal analysis applications. The average measurement errors for carbon, hydrogen, volatiles, ash and heat values are 0.42%, 0.05%, 0.07%, 0.17% and 0.07 MJ kg−1, respectively, and all of these measurement accuracies fully meet the requirements of the national standard for coal analyses using traditional chemical processing methods. This is the first quantitative application of LIBS with real industrial requirements, and the present work proves the feasibility of LIBS for accurate quantification from a technical point of view.

Application of spatial confinement for gas analysis using laser-induced breakdown spectroscopy to improve signal stability

The quantitative analysis of gaseous samples using laser induced breakdown spectroscopy (LIBS) is limited due to its relatively lower signal reproducibility compared with that of solid samples. In this study, a cylindrical spatial confinement was first applied to reduce the signal fluctuations in the analysis of ambient air using LIBS. With the aid of plasma image analysis, bowl-shaped confinements were further designed to reduce the signal fluctuations. The location and the size of the confinements were also optimized to achieve the best effect. Results show that a cylindrical confinement reduces the signal fluctuations to some extent. Compared with using the cylindrical confinement, the shape and position of the plasma are better stabilized and spectral fluctuations are further reduced by using a bowl-shaped confinement. Simply using the traditional spectral area normalization method to alleviate the influence of the variance in plasma energy, the pulse-to-pulse relative standard deviations (RSDs) can be reduced to 2.94% for nitrogen and 3.97% for oxygen, which are comparable to RSDs found in the analysis of solid samples.

A Multi-Criteria Model for the Optimal Design of Distributed Energy Systems

The optimal design of distributed energy systems can significantly improve the performance of such systems. A multi-criteria modeling approach for the optimal design of distributed energy systems is presented in this paper. The total annual cost and greenhouse gas emissions are selected as the objectives to optimize simultaneously. The model is applied to a hypothetic hotel in Beijing, China. Optimal total annual cost and greenhouse gas emissions are presented in the form of a Pareto-frontier, on which a decision maker can pick up any point according to their specific design criteria or interest.

Coal Gasification Based Solid Oxide Fuel Cell Power Generation with CO2 Capture

As environment regulations for coal-fired power plants becomes more and more stringent in the future carbon-constrained world, the combination of solid oxide fuel cell (SOFC) and coal gasification provides a promising solution. The goal of this study was to integrate SOFC with coal gasification in the context of carbon capture. System modeling and simulation were performed with the aim at assessing and comparing different system configurations. The various candidate concepts were put into two categories: pre-SOFC-capture and post-SOFC-capture. The impacts of different oxidize agents (air fed or oxygen fed) and different re-circulation arrangements of air and fuel loops were investigated. Results show that air fed post-SOFC-capture systems have advantages over pre-capture systems in both power output and efficiency Among post-SOFC-capture concepts, air fed with recirculation of both air and fuel seems to be the most promising configuration. Overall efficiency of above 50% could be achieved with such a configuration due to the better utilization of high temperature streams at SOFC outlet.