Mingjiang Ni

Predicting coal ash fusion temperature with a back-propagation neural network model

A novel technique, the back-propagation (BP) neural network, is presented for predicting the ash fusion temperature from ash compositions for some Chinese coals instead of the traditional techniques, such as the ternary equilibrium phase diagrams and regression relationships. In the applications of the BP networks, some modifications to the original BP algorithm are adopted to speed up the BP learning algorithm, and some useful advice is put forward for the choice of some key parameters in the BP model. Compared to the traditional techniques, the BP neural network method is much more convenient and direct, and can always achieve a much better prediction effect.

Gasification characteristics of MSW and an ANN prediction model

Gasification characteristics make up the important parts of municipal solid waste (MSW) gasification and melting technology. These characteristics are closely related to the composition of MSW, which alters with climates and seasons. It is important to find a practical way to predict gasification characteristics. In this paper, five typical kinds of organic components (wood, paper, kitchen garbage, plastic, and textile) and three representative types of simulated MSW are gasified in a fluidized-bed at 400-800 degrees C with the equivalence ratio (ER) in the range of 0.2-0.6. The lower heating value (LHV) of gas, gasification products, and gas yield are reported. The results indicate that gasification characteristics are different from sample to sample. Based on the experimental data, an artificial neural networks (ANN) model is developed to predict gasification characteristics. The training and validating relative errors are within +/-15% and +/-20%, respectively, and predicting relative errors of an industrial sample are below +/-25%. This indicates that it is acceptable to predict gasification characteristics via ANN model.

The fragmentation of coal particles during the coal combustion in a fluidized bed

Abstract This paper presents an experimental method for studying the fragmentation of coal particles during coal combustion in a fluidized bed and the quantitative fragmentation indexes of 10 typical Chinese coal ranks. The influences of a variety of factors such as the bed temperature, the size of coal particles, the coal rank and the fluidizing medium on the fragmentation index of coal particles are also studied. The research results show that the main reason for the fragmentation of coal particles is the primary fragmentation, and that the volatile matter can drastically influence the degree of fragmentation of coal particles.

Non-Thermal Plasmas for VOCs Abatement

Volatile organic compounds (VOCs) are some of the most common air pollutants emitted from commercial and industrial processes; VOCs may also reduce indoor air quality. Increased environmental awareness, however, has resulted in stringent regulations controlling VOCs emission and has motivated researchers to develop various kinds of treatment. Non-thermal plasma (NTP) processes are regarded as promising methods for VOCs abatement. This paper reviews the state of the art and achievements of NTP for VOCs abatement and includes a description of several reactor configurations based on different discharge principles. Of particular interest are NTP-catalytic systems, characterized by higher energy efficiencies and lower byproduct production than the NTP-alone systems. Physical–chemical effects of NTP-catalytic systems occurring during plasma catalytic processes are discussed. The NTP decomposition mechanisms for toluene, naphthalene and trichloroethylene are discussed in detail. Influences of various processing parameters are summarized, and comments are given based on removal efficiencies and operational costs.

The research on the estimation for the NOx emissive concentration of the pulverized coal boiler by the flame image processing technique

Abstract In this paper, flame image processing technique is used to estimate NOx emissive concentration of the pulverized coal boiler. According to the brightness value of flame image pixels, the temperature distribution of the flame is calculated. The combustion characteristic parameters are picked up from the flame image. Based on the back propagation neural network, the model to estimate the NOx concentration in the gas released from the power plant boiler has been developed. The experiments on the furnace flame monitor system of a power plant have testified that this estimation model can get the satisfying results.

Combustion and inorganic bromine emission of waste printed circuit boards in a high temperature furnace

High temperature combustion experiments of waste printed circuit boards (PCBs) were conducted using a lab-scale system featuring a continuously-fed drop tube furnace. Combustion efficiency and the occurrence of inorganic bromine (HBr and Br(2)) were systematically studied by monitoring the main combustion products continuously. The influence of furnace temperature (T) was studied from 800 to 1400°C, the excess air factor (EAF) was varied from 1.2 to 1.9 and the residence time in the high temperature zone (RT(HT)) was set at 0.25, 0.5, or 0.75 s. Combustion efficiency depends on temperature, EAF and RT(HT); temperature has the most significant effect. Conversion of organic bromine from flame retardants into HBr and Br(2) depends on temperature and EAF. Temperature has crucial influence over the ratio of HBr to Br(2), whereas oxygen partial pressure plays a minor role. The two forms of inorganic bromine seem substantially to reach thermodynamic equilibrium within 0.25s. High temperature is required to improve the combustion performance: at 1200°C or higher, an EAF of 1.3 or more, and a RT(HT) exceeding 0.75 s, combustion is quite complete, the CO concentration in flue gas and remained carbon in ash are sufficiently low, and organobrominated compounds are successfully decomposed (more than 99.9%). According to these results, incineration of waste PCBs without preliminary separation and without additives would perform very well under certain conditions; the potential precursors for brominated dioxins formation could be destroyed efficiently. Increasing temperature could decrease the volume percentage ratio of Br(2)/HBr in flue gas greatly.

A mathematical model for a circulating fluidized bed (CFB) boiler

In developing a mathematical model for a CFB boiler we use earlier work. Our model includes mathematical descriptions of the underlying physical and chemical processes. It has been applied to simulation of a 12 MW CFB boiler. The calculations agree well with test results.

A review on black carbon emissions, worldwide and in China

Black carbon (BC) produced from open burning (OB) and controlled combustion (CC) is a range of carbonaceous products of incomplete combustion of biomass and fossil fuel, and is deemed as one of the major contributors to impact global environment and human health. BC has a strong relationship with POPs, in waste combustion, BC promotes the formation of POPs, and then the transport of POPs in the environment is highly influenced by BC. However less is known about BC formation, measurement and emissions estimation especially in developing countries such as China. Different forms of BC are produced both in CC and OB. BC emission characteristics and combustion parameters which determine BC emissions from CC and OB are discussed. Recent studies showed a lack of common methodology and the resulting data for describing the mechanisms related to BC formation during combustion processes. Because BC is a continuum carbonaceous combustion product, different sampling and measuring methods are used for measuring their emissions with great quantitative uncertainty. We discuss the commonly used BC sampling and measuring methods along with the causes for uncertainty and measures to minimizing the uncertainty. Then, we discuss the estimations of BC emission factors and emission inventory for CC and OB sources. The total emissions of BC from CC and OB in China are also estimated and compared with previous BC emission inventories in this review and we find the inventories tend to be overestimated. As China becomes the largest contributor to global BC emissions, studies for characterizing BC emissions from OB and CC sources are absent in China. Finally, we comment on the current state of BC emission research and identify major deficiencies that need to overcome. Moreover, the advancement in research tools, measuring technique in particular, as discussed in this review is critical for researchers in developing countries to improve their capability to study BC emissions for addressing the growing climate change and public health concerns.

Co-destruction of organic pollutants in municipal solid waste leachate and dioxins in fly ash under supercritical water using H2O2 as oxidant.

Supercritical water oxidation (SCWO), with hydrogen peroxide as oxidant, is applied to the co-disposal of two distinct waste streams: municipal solid waste leachate and incineration fly ash. The chemical oxygen demand (COD) removal efficiency increases rapidly with rising temperature and excess oxygen. Rising residence time from 1 to 2 min has surprisingly little effect. The addition of fly ash accelerates COD conversion markedly and also polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs, dioxins) in the original fly ash are efficiently destroyed. High-chlorinated PCDD/Fs are more likely to be destroyed than low-chlorinated PCDD/Fs, at all experimental conditions. In addition, PCDDs are much more reactive than PCDFs, since the PCDDs/PCDFs ratio declines from 0.17 to 0.12 as excess oxygen rises from 0% to 300%.

Ozone-enhanced oxidation of PCDD/Fs over V2O5-TiO2-based catalyst

The catalytic oxidation of PCDD/Fs (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans) vapors was studied in a temperature range of 180-220°C on a honeycomb V2O5-TiO2-based catalyst, in the presence and the absence of ozone. A stable dioxin-generating system was established to support the experimental program and this system could adjust the concentration of PCDD/Fs by injecting appropriate mother liquors. At 220°C the removal efficiency(1) (RE) of PCDD/Fs reaches up to 97% and the degradation efficiency (DE) up to 90%. Both values diminish at lower operating temperatures. In the presence of ozone, however, these values rise to 99% and 98% at 220°C. Especially at low temperatures the effect of ozone is obvious. Catalytic oxidation with ozone thus offers a low-temperature solution to achieve higher rates and low activation energies. The morphology and microstructure of the catalysts changes after ozone treatment and some of their characteristics seem closely related with DE-values.