Mutual effects of porosity and reactivity in char oxidation

The motivation for this review is the need to understand the interdependence of porous structure and reactivity of highly porous carbonaceous materials during oxidation. These materials can be oxidized in three regimes: regime I, kinetically controlled conditions; regime II, partial diffusion-controlled conditions; regime III, diffusion controlled conditions. Since the emphasis here is on the porous structure and its influence on reactivity, conditions where transport processes are dominant were not included for they mask the view of interest. Therefore, the review discusses only physicochemical processes occurring during oxidation of highly porous chars in regime I. Furthermore, reactivity is influenced by many factors, such as catalysis, volatile matter, and water content. To avoid the effect of these factors, highly porous synthetic chars with nothing but elemental carbon and residual hydrogen and oxygen was chosen. Mainly, we discuss a commercial product known as Spherocarb which consists of spherical particles with specific surface area of about 1000 m² g⁻¹ and porosity of about 0.6. These particles are well defined and reproducible in their properties. They serve well as model materials for various synthetic chars, coal chars, and other carbonaceous materials. The review presents in a systematic manner macroscopic properties and processes that shed light on different aspects of porosity and reactivity. These are presented both from experimental observation as well as modeling view. An attempt was made to present a porous structure model that can reconstruct all available experimental data on these particles during oxidation. In the review the following processes and properties are discussed: shrinkage, fragmentation, and porosity. All are directly connected to porous structure and reactivity.     

Hardness and carbonate effects on the reactivity of zero-valent iron for Cr(VI) removal

Zero-valent iron (Fe0) was used to remove hexavalent chromium, Cr(VI), in groundwater via a coupled reduction-oxidation reaction. Nine columns were set up under various groundwater geochemistry to investigate the effects of hardness and carbonate on Cr(VI) removal. The Cr(VI) removal capacity of Fe0 was found to be about 4 mgCr/g Fe0 in the control column (i.e., column 1). A slight decrease in the Cr(VI) removal capacity was found in the presence of calcium hardness. However, there was a 17% drop in the Cr(VI) removal capacity when magnesium hardness was present at low to moderately hard level. Results also revealed that carbonate changed the morphology of the Fe0 by formation of pale green precipitates on the iron filings. Furthermore, there was a 33% decrease in the Cr(VI) removal capacity of Fe0 when both carbonate and hardness ions were present. In general, the presence of hardness ions and carbonate in groundwater have great impact on the Fe0 by formation of passivated precipitates, such as CaCO3, on the Fe0 surface resulting in a diminished lifespan of the Fe0 by blocking electron transfer.     

Novel approach to solving the inverse equation of point kinetics by the Bernoulli number generalisation method

ABSTRACT

A new approach to solve the inverse equation of point kinetics is presented. The neutron density history can be considered as a series of infinite Bernoulli numbers. In order to simplify the problem, the proposed method uses an approximation which considers only two derivatives of the neutron population density. The reactivity is calculated for different forms of neutron population density and for different time steps. Due to its high precision, the results obtained suggest that the proposed method can be used in a real-time digital reactivity meter.     

Design & construction of a digital real time reactivity meter for Tehran research reactor

Reactivity measurement is one of the challenges of monitoring, control and investigation of nuclear reactors. In this paper design and construction of a reactivity meter for continuous monitoring of reactivity in research reactors are described. The device receives amplified output of the fission chamber, which is in mA range, as the input. Using amplifier circuits, this current is converted to voltage and then digitalized with a microcontroller to be sent to serial port of computer. The device itself consists of software, which is a MATLAB real time programming for the computation of reactivity by the solution of neutron kinetic equations. After data processing the reactivity is calculated and presented using LCD. Tehran research reactor is selected to test the reactivity meter device. The results of applying this reactivity meter in Tehran research reactor (TRR) are compared with the experimental data of control rod worth, void coefficient of reactivity and reactivity changes during approach to full power. The maximum relative error in several experiments is calculated to be 13%.     

The use of U3Si2 dispersed fuel in Low-Power Research Reactors

The use of U₃Si₂ as a Low Enriched Uranium (LEU) dispersed fuel in Low-Power Research Reactors is investigated in this paper. The fuel proves to be usable if some of the original fuel rods (HEU UAl₄–Al fuel) are still simultaneously employed (mixed core) without changing the structure of the actual core. About 3.5712 mk Initial Excess Reactivity (IER) is procured. Although the worths of both the control rod and the reactivity devices decrease, the safety of these reactors is higher in the case of the new LEU fuel. If the dimensions of the meat and/or the clad are allowed to change these reactors can be run with a meat 2.15 mm outer radius, and a clad 0.58 mm thickness. The IER will then be 4.1537 mk, and both the control rod (CR) worth and the safety margins decrease.     

Change of pyrolysis characteristics and structure of woody biomass due to steam explosion pretreatment

Steam explosion (SE) pretreatment has been implemented for the production of wood pellet. This paper investigated changes in biomass structure due to implication of steam explosion process by its pyrolysis behavior/characteristics. Salix wood chip was treated by SE at different pretreatment conditions, and then pyrolysis characteristic was examined by thermogravimetric analyzer (TGA) at heating rate of 10 K/min. Both pyrolysis characteristics and structure of biomass were altered due to SE pretreatment. Hemicellulose decomposition region shifted to low temperature range due to the depolymerization caused by SE pretreatment. The peak intensities of cellulose decreased at mild pretreatment condition while they increased at severe conditions. Lignin reactivity also increased due to SE pretreatment. However, severe pretreatment condition resulted in reduction of lignin reactivity due to condensation and re-polymerization reaction. In summary, higher pretreatment temperature provided more active biomass compared with milder pretreatment conditions.     

不同煤阶煤焦炭显微结构与热性质的研究

采用模拟焦炭反应性和反应后强度,研究了不同变质程度单种煤焦炭显微结构与热性质之间的关系。中等变质阶段的焦煤、肥煤和瘦煤所制焦炭有较高的各向异性,低变质程度的气煤、1/3焦煤以及高变质程度的贫煤所制焦炭各向异性程度较低。焦炭的热性质与焦炭的各向异性有很好的相关性,焦炭反应性随各向异性程度的增大而减小,反应后强度则随各向异性的增大而增大。     

焦炭热强度影响因素的研究

利用试验焦炉（SCO）对梅山常用11种单种强粘煤进行了试验,研究了炼焦煤的性质对焦炭热强度影响。研究结果表明,炼焦强粘结煤的粘结性、变质程度和碱度指数是对焦炭热强度的关键影响因素,焦炭的机械强度和碱度指数是内在因素。     

A study on the effect of the CO2/steam mixtures and the addition of natural minerals on the reactivity of Adaro coal gasification

The synergetic effect in reactivity and gas yield on the various ratio of CO₂/steam mixtures was investigated. The isothermal gasification was conducted at three different temperatures. The synergy effect was evaluated on the ratio of CO₂/steam mixtures and reaction temperatures. In order to analyze the synergy quantitively, two reaction indexes were calculated from carbon conversion. The effect of natural minerals like Dolomite and Kaolin was investigated as well. The influence of synergy was varied upon the ratio of CO₂/steam mixtures and the optimal synergy was observed when the ratio of CO₂/steam mixtures was 1:2. The best synergy in reactivity and gas yield was shown at 800 °C and at 900 °C, respectively. By adding Dolomite, the synergetic effect in both reactivity and H₂ yield was promoted at 800 °C. Conclusively, the ratio of CO₂/steam mixtures and Dolomite played an important role to facilitate the synergy in the coal gasification.     

猪瘟病毒E2蛋白4重复抗原表位的构建及抗原活性研究

利用PCR方法获得4次重复的猪瘟病毒E2蛋白中和性抗原表位基因，将其克隆到pGEM-5ZF( )载体，测序正确后亚克隆到pGEX-3X载体构建得到重组质粒pGEX-3X-4P。重组质粒在大肠杆菌中诱导表达了含4重复抗原表位的融合蛋白。该蛋白经纯化后，利用间接ELISA检测其与血清的反应性，结果表明，纯化的融合蛋白与兔抗CSFV E2血清有很强的反应性，与兔抗BVDV E2血清不反应，说明该重复抗原表位在鉴别诊断CSFV与猪的BVDV感染方面具有潜在的应用价值。