Conceptual design and analysis of a novel system based on ash agglomerating fluidized bed gasification for co-production of hydrogen and electricity

In this paper, a novel system with ash agglomerating fluidized bed gasification and CO₂ capture to produce hydrogen and electricity is firstly designed in Aspen Plus. The newly-proposed system is composed of eight subsystems, namely air separation unit, gasification unit, water gas shift unit, Rectisol unit, CO₂ compression unit, Claus unit, pressure swing adsorption unit, gas and steam turbine unit. The thermodynamic performance and hydrogen to coal ratio of the new proposed system are investigated. The results demonstrate that the hydrogen to coal ratio, energy efficiency, net electricity power and exergy efficiency of the overall system for Yangcheng anthracite are 0.096 kg/kg, 46.52%, 1.71 MW and 43.92%, respectively. Additionally, the exergy destruction ratio and exergy efficiency of each subsystem are researched. More importantly, the influences of the oxygen to coal ratio, steam to coal ratio and coal types on the hydrogen to coal ratio, energy efficiency and exergy efficiency are also studied.     

Techno-economic analysis of adiabatic four-stage CO2 methanation process for optimization and evaluation of power-to-gas technology

Owing to increasing demands for clean energy, caused by global warming, renewable energy sources have attracted significant attention. However, these sources can affect the reliability of electrical grids owing to their intermittency. Power-to-gas technology is expected to help address this issue. In this study, the CO₂ methanation process, which yields synthetic natural gas (SNG) via the synthesis of CO₂ and H₂ through proton exchange membrane (PEM) water electrolysis using surplus electricity generated from renewable energy, was evaluated and optimized based on techno-economic analyses. Requirements for the introduction of SNG produced through CO₂ methanation in domestic natural gas markets are presented by considering various scenarios. Results indicate that, even if the electricity costs, including system marginal price and renewable energy costs, are minimal, the costs for PEM water electrolysis and CO₂ methanation must be reduced by ~$550/kW and 25%, respectively, relative to current levels for the viable introduction of SNG in domestic markets.     

循环流化床锅炉灰平衡和循环倍率计算方法探讨

目前，国内的循环流化床锅炉存在不少问题，就性能问题而言，主要是两大问题，一是不能定量地确定循环倍率，导致燃烧性能的计算不准确，二是不正确的灰平衡计算导致传热性能的计算不准确。所以，正确地确定循环流化床锅炉的循环倍率和灰平衡计算方法不仅是必需的，而且是迫切的。本文从灰平衡的基本要素出发，对循环倍率和农平衡的计算方法进行探讨．     

Hydrogen production through the sulfur–iodine cycle using a steam boiler heat source for risk and techno-socio-economic cost (RSTEC) reduction

A modified sulfur-iodine cycle with a non-nuclear heat source is proposed to enhance the economics and reduce risk and damage to society in terms of cost. A modified sulfur cycle employs a steam boiler as a heat source. The modified sulfur iodine cycle is composed of fewer reactions than the original. Thermodynamic feasibility analysis, economic evaluation, risk assessment, and socio-economic analysis are carried out on both the sulfur-iodine cycle and modified sulfur-iodine cycle, and the results are compared. 50.9 kJ/mol of steam was required for the minimum entropy range without the violation of the second law. The results show that the modified process is thermodynamically feasible with a positive entropy region at operating temperatures. The capital cost and operating cost are reduced by 40% and 29% for 1 kmol/h hydrogen production, respectively. The failure rate in the modified process is reduced by 64% compared to that of the original. The social health cost in the modified cycle is reduced by 41% compared to that of the original.     

循环流化床锅炉在我国的现状和发展

可以燃用高硫、低灰熔点、低挥发分的低质煤的循环流化床锅炉，本文介绍其在我国应用的现状、存在问题、改进措施和展望。     

China׳s precarious synthetic natural gas demonstration

In 2013, China׳s national government abandoned its previous cautious policy and started to promote large-scale deployment of coal-based synthetic natural gas (SNG). Coal-based SNG is both carbon-intensive and very water-intensive. Driven by a smog crisis and the recession of coal industry, China׳s 2013 policy change is major setback in its long-term efforts in carbon mitigation and water conservation. The government of China made the policy change before the commercial commencement of China׳s first SNG demonstration plant. Since the commencement of China׳s SNG demonstration plant, many problems have started to appear. In this article, I discuss the nature of demonstration project and explain the danger in starting a crash program without evaluating the demonstration comprehensively and transparently.     

Ash effects during combustion of lignite/biomass blends in fluidized bed

Aiming at investigating the role of minerals in evaluating co-firing applications of low rank coals and biomass materials, agricultural residues characteristic of the Mediterranean countries, one lignite and their blends with biomass proportions up to 20% wt, were burned in a lab-scale fluidized bed facility. Fly ashes and bed material were characterized in terms of mineralogical, chemical and morphological analyses and the slagging/fouling and agglomeration propensities were determined.The results showed that combustion of each fuel alone could provoke medium or high deposition problems. Combustion of raw fuels produced fly ashes rich in Ca, Si and Fe minerals, as well as K and Na minerals in the case of biomass samples. However, blending of the fuels resulted in a reduction of Ca, Fe, K and Na, while an increase of Si and Al elements in the fly ashes as compared to lignite combustion, suggesting lower deposition and corrosion problems in boilers firing these mixtures. The use of bauxite as an additive enriched bottom ash in calcium compounds. Under the conditions of the combustion tests, no signs of ash deposition or bed agglomeration were noticed.     

Effect of the type of gasifying agent on gas composition in a bubbling fluidized bed reactor

It is commonly accepted that gasification of coal has a high potential for a more sustainable and clean way of coal utilization. In recent years, research and development in coal gasification areas are mainly focused on the synthetic raw gas production, raw gas cleaning and, utilization of synthesis gas for different areas such as electricity, liquid fuels and chemicals productions within the concept of poly-generation applications. The most important parameter in the design phase of the gasification process is the quality of the synthetic raw gas that depends on various parameters such as gasifier reactor itself, type of gasification agent and operational conditions. In this work, coal gasification has been investigated in a laboratory scale atmospheric pressure bubbling fluidized bed reactor, with a focus on the influence of the gasification agents on the gas composition in the synthesis raw gas. Several tests were performed at continuous coal feeding of several kg/h. Gas quality (contents in H₂, CO, CO₂, CH₄, O₂) was analyzed by using online gas analyzer through experiments. Coal was crushed to a size below 1 mm. It was found that the gas produced through experiments had a maximum energy content of 5.28 MJ/Nm³ at a bed temperature of approximately 800 °C, with the equivalence ratio at 0.23 based on air as a gasification agent for the coal feedstock. Furthermore, with the addition of steam, the yield of hydrogen increases in the synthesis gas with respect to the water–gas shift reaction. It was also found that the gas produced through experiments had a maximum energy content of 9.21 MJ/Nm³ at a bed temperature range of approximately 800–950 °C, with the equivalence ratio at 0.21 based on steam and oxygen mixtures as gasification agents for the coal feedstock. The influence of gasification agents, operational conditions of gasifier, etc. on the quality of synthetic raw gas, gas production efficiency of gasifier and coal conversion ratio are discussed in details.     

热脏发生炉煤气的工业应用

从多年的经验出发,介绍了热脏发生炉煤气的使用背景和现状。分析亍热脏煤气的性能,重点介绍了热脏煤气系统中的各种设备及其使用注意事项,最后介绍了流化床煤气发生炉。     

煤泥循环流化床锅炉NOx排放特性研究

为有针对性地进行CFB(循环流化床锅炉)锅炉设计以及优化锅炉运行参数,需了解煤泥CFB燃烧NO_x排放特性及其影响因素。本文通过对一台20 t煤泥循环流化床锅炉进行相应的测试分析,得到NO_x排放浓度随床温和氧量的变化规律。研究结果表明,维持锅炉炉膛过量空气系数1.2,下料层床温由800℃升到935℃的过程中,NO_x浓度由296 mg/m~3上升到341 mg/m~3;维持下料层床温905℃,烟囱中部烟气氧含量由9.3%升到10.5%的过程中,NO_x排放浓度由285 mg/m~3上升至377 mg/m~3。在控制下料层床温和炉膛氧含量这两个参数条件下,可使得烟囱中部NO_x排放浓度水平整体降低,平均排放不高于250 mg/m~3,整体保持在300 mg/m~3以下,符合限定地区污染物排放要求。在一定运行参数范围内,NO_x排放浓度随下料层床温升高而增大,随氧量升高而增大。     

Coal hydrogasification: Entrained flow bed design-operation and experimental study of hydrogasification characteristics

Coal hydrogasification processes including wire-mesh grid reactor, batch reactor, curie-point pyrolyzer, fixed bed reactor and so on were utilized or developed in laboratory researches. Although the experimental results could help to understand the basic behavior of coal hydrogasification, it was difficult to directly utilize such data for devising a new hydrogasifier. This paper designed a continuous entrained flow bed facility and described the hydrogasification characteristics. This device (15–30 kg/d) mainly consisted of a high-H₂ pressure feed system, a high-temperature tube reactor. The capabilities were shown as follows: the temperature from 700 °C to 850 °C, H₂ pressure from 0.1 MPa to 3.0 MPa, isothermal zone 300–600 mm, feeding rate from 15 to 30 kg/d and water yield was easy to obtained by tar-water separation. The good mass balance on the carbon and weight basis was established by analyzing the product distribution in detail. The results showed the yields of CH₄ and light aromatic hydrocarbons increased through hydrogenation of tar and volatiles, hydrogasification of coal char. Although the small pilot plant had high heat loss through refractory with increasing H₂ pressure, the typical results obtained from the continuous stable operation of the entrained flow bed reactor confirmed the design of new large-scale hydrogasification process was technical feasibility.     

Biogas to high purity hydrogen by methane dry reforming in TZFBR+MB and exhaustion by Steam-Iron Process. Techno–economic assessment

A techno-economic study has been carried out with the aim of analyzing the performance (product distribution and energy yields) and estimating the production costs of high purity hydrogen obtained from biogas. For such purpose and taking advantage of empirical data developed in our laboratory, it has been proposed a system consisting of a two-zone fluidized bed reactor aided by a system of permselective (Pd/Ag) metallic membranes inserted in the fluidized bed (TZFBR+MB), and a battery of several fixed bed reactors operating cycles of reduction and oxidation (Steam-Iron Process -SIP-). The feed has always been an equimolar mixture of CH₄ and CO₂ simulating a sweetened biogas. The first reactor (TZFBR+MB) can produce a stream of pure hydrogen (i.e. PEMFC quality) as permeated flow through the MB, and a retentate stream rich in all species resulting from the methane dry reforming reaction (MDR) and the water gas shift equilibrium (WGS). The singularity of this kind of complex reactors is that regeneration of the catalyst is performed in the same reactor and simultaneously to the MDR reaction because of the two-zone. Due to the reductive behavior of the retentate stream, it can be fed to a bed of solid where up to two different oxygen carriers (iron oxide with additives and cobalt ferrite) can be reduced to their metallic state. Once the solid has been completely reduced, it can be reoxidized with steam releasing a high purity hydrogen stream. Both reactors (i.e. TZFBR+MB and SIP) have been coupled in different degrees. A performance (hydrogen and energy yields) as well as costs analysis (fixed assets and operating costs) have been performed with the aid of Aspen HYSYS v9.0, used for dimensioning the equipment needed to process up to 1350 kg/h of biogas. On this way, the integrated process enhances the efficiencies of every single process allowing pure hydrogen yields up to 68% at 575 °C in the TZFBR+MB and an overall energy efficiency greater than 45%. Production costs have been found to be in the range from 4 to 15 €/kg, still high but not so far away from the target of DOE fixed in 2 $/kg by 2020.     

降低流化床锅炉排烟温度提高锅炉效率的研究

南屯电力分公司5#锅炉投产运行后,实际运行排烟温度高于设计温度。分析了产生这种现象的影响因素,介绍了改造后的省煤器实际运行效果。     

Technical assessment of synthetic natural gas （SNG） production from agricul- ture residuals

This paper presents thermodynamic evaluations of the agriculture residual-to-SNG process by thermochemical conversion, which mainly consists of the interconnected fluidized beds, hot gas cleaning, fluidized bed methanation reactor and Selexol absorption unit. The process was modeled using Aspen Plus software. The process performances, i.e., CH 4 content in SNG, higher heating value and yield of SNG, exergy efficiencies with and without heat recovery, unit power consumption, were evaluated firstly. The results indicate that when the other parameters remain unchanged, the steam-to-biomass ratio at carbon boundary point is the optimal value for the process. Improving the preheating temperatures of air and gasifying agent is beneficial for the SNG yield and exergy efficiencies. Due to the effects of CO 2 removal efficiency, there are two optimization objectives for the SNG production process: (I) to maximize CH 4 content in SNG, or (II) to maximize SNG yield. Further, the comparison among different feedstocks indicates that the decreasing order of SNG yield is: corn stalk > wheat straw > rice straw. The evaluation on the potential of agriculture-based SNG shows that the potential annual production of agriculture residual-based SNG could be between 555×10 8～611×10 8 m 3 with utilization of 100% of the available unexplored resources. The agriculture residual-based SNG could play a significant role on solving the big shortfall of China’s natural gas supply in future.     

国内煤泥燃烧循环流化床锅炉研究现状

文中重点阐述了国内煤泥循环流化床锅炉的研究进展及现状,并结合煤泥在循环流化床锅炉中的燃烧特性,分析了煤泥的主要给料燃烧方式以及纯烧煤泥的循环流化床锅炉的技术特点,对我国纯烧煤泥的循环流化床锅炉的大型化具有一定的指导意义。     

氧量对天然焦蒸汽气化特性的影响研究

在小型流化床(50mm、高1600mm)实验装置上对沛城煤矿天然焦-蒸汽气化反应进行实验研究,考察蒸汽中掺入氧气,共同作为气化介质对气化反应产气量、碳转化率、煤气热值和煤气组分等因素的影响,同时与ASPENPLUS软件对其气化过程的模拟结果进行了对比。实验中,天然焦试样量0.2kg/h,蒸汽量1.05kg/h,气化温度900℃,实验结果表明:气化介质中氧量明显影响天然焦蒸汽气化特性。随着氧含量的增加,初始阶段(0～0.2L/min)煤气产量提高了1.76倍,碳转化率提高了1.94倍,两者均显著增加;随着氧量的进一步增加(0.2～1.0L/min),其增加幅度趋缓,产气量增加1.16倍,碳转化率增加1.34倍。煤气中有效气体(H2+CO+CH4)的体积分数和煤气热值均持续减少,有效气体份额从76.9%下降到54.3%,煤气热值从9.01MJ/m3减少到6.34MJ/m3,而CO2体积分数增加明显,从23.1%增加到37.3%。Aspen模拟结果与实验结果基本一致,具有实际指导意义。     

掺烧煤气对循环流化床锅炉的影响及设计对策

混烧煤气会对循环流化床锅炉产生一定的影响；循环流化床锅炉如要求混烧煤气，在整体设计中应当考虑工况的变化，并消除其带来的不良影响。     

循环流化床烟气脱硫床料的质量平衡和化学成份的变化

对循环流化床内脱硫过程中床料的质量、化学成份的变化进行了理论分析,发现当选定循环倍率5－50后,只要分离器的效率达到83％－98％,床内就可以维持质量平衡。当操作参数变化引起床内物料质量改变时,改变离开床的床料量可以很快达到平衡;而化学成份的动态是不平衡的,它的过渡过程与床内的床料量、反应产物的产率以及相关参数的变化幅度等有关。     

无烟煤沸腾床锅炉掺烧煤矸石的分析

对沸腾床锅炉中无烟煤掺合矸石燃烧时混合燃料粒径的合理分布情况、掺矸比例和因之产生的料层厚度、风室静压及除尘脱硫等问题进行分析,对高硫无烟煤矿小装机容量火电站的资源综合利用有一定借鉴意义。