Research on mechanism of ammonia escaping and control in the process of CO2 capture using ammonia solution

As CO₂ is the major greenhouse gas, reducing its emission has become an attentive problem in the whole world. It is very important to develop CO₂ capture technology for coal-fired power plants. Using ammonia solution to absorb CO₂ from the flue gas, which is expected to have advantages of low cost, high efficiency and high absorption load, has become an emerging, hot research area in recent years. However, this technology faces a troublesome problem of ammonia escape. This paper analyzes the mechanism of escaping ammonia; it is also shown the main existing methods to control the escape of ammonia. By comparison, it is concluded that controlling the source of ammonia is feasible. It is also shown that adding some organic additives can inhibit the escape of ammonia and enhance the CO₂ removal to some extent at the same time.     

聚乙二醇二甲醚抑制脱碳吸收剂中氨逃逸的实验及原理分析

CO₂作为主要的温室气体,其减排问题引起全球范围的广泛关注,开展适合我国国情的燃煤电厂CO₂减排技术研究至关重要。氨法脱除电厂烟气中CO₂具有低成本、高脱除效率等特点,但该技术面临的一个很大问题是氨的逃逸。针对氨法脱碳过程中氨逃逸问题展开实验研究,采用鼓泡吸收反应器研究了聚乙二醇二甲醚（NHD）对氨逃逸的抑制效果以及氨水和NHD浓度对氨逃逸的影响,并分析了NHD抑制氨逃逸的机理。结果表明,NHD对氨逃逸具有一定的抑制作用,同时在一定程度上提高了脱碳效率。添加5%NHD后,氨逃逸量降低24.86%,CO₂的脱除效率增加10%左右。研究结果对进一步开展氨法捕集CO₂研究有较大的参考价值。     

氨法捕碳技术再生过程无机添加剂效应研究进展

近年来,二氧化碳等温室气体的过量排放已成为全球气候变化的主要原因,为达到“碳达峰、碳中和”的目标,中国积极参与国际社会碳减排行动,主动顺应全球绿色低碳发展潮流。由于中国正处于新旧能源结构交替的过渡期,二氧化碳重要来源是以化石燃料燃烧为主的火电厂排放的烟气,因此减少烟气排放并进行二氧化碳捕集仍是碳减排的关键。碳捕集与封存（Carbon Capture and Storage,CCS）技术中的氨法碳捕集技术具有众多优点,成为目前研究热点之一。通过类比氨法脱碳过程中添加剂对氨逃逸与二氧化碳脱除效果的影响,重点分析了无机添加剂对富液解吸的影响,对国内外的研究进展进行了综述,对该技术未来发展方向进行了展望,包括再生机理、再生能耗、氨逸出、添加剂与吸收剂的循环利用与过渡金属氧化物的尝试等。     

氨法脱碳过程中氨逃逸规律及其抑制

近年来随着环境保护的不断深入,控制温室气体排放逐渐成为研究重点,而火力发电作为CO₂最大的集中排放源,对其实施碳捕集是必要的。氨法脱碳优点众多,但氨逃逸问题始终没有得到很好解决。通过实验研究明晰了CO₂浓度、氨水吸收剂浓度、吸收反应温度对氨逃逸的影响规律,基于金属离子的络合效果探讨了几种金属离子对氨逃逸的抑制效果,发现Ni²⁺对氨逃逸有较好的抑制效果,并通过紫外分光光谱推测了其抑氨机理。本研究成果可对氨逃逸问题的解决提供一定的参考。     

氨法碳捕集过程中氨逃逸控制

本研究致力于解决再生氨法碳捕集过程中氨的逃逸问题。根据实验室前期研究结果,分别选取抑制效果较好的丙三醇和Co（Ⅱ）进行实验研究。详细分析了其抑制氨逃逸机制,并通过IR、XRD等对物种进行分析。同时探究其对再生氨法碳捕集过程CO₂脱除效率和解吸效果的影响。实验结果表明,丙三醇和Co（Ⅱ）对氨逃逸均有较好的抑制效果,平均抑氨效率在40%以上。二者的引入对吸收过程均无显著影响,且Co（Ⅱ）能使CO₂解吸比例提高。     

两种强化低碳化度氨水结晶的新型氨法脱碳工艺

针对目前氨法二氧化碳捕集技术中存在的氨逃逸、再生能耗高、反应后期吸收率低等问题, 提出了两种基于溶析法强化结晶的工艺, 分别为混合吸收剂法以及溶析法强化低碳化度氨水结晶工艺。低碳化度氨水结晶可以使吸收过程维持在较高的吸收速率, 采用晶体产物解析既可以实现再生能耗的降低又可以解除再生能耗对于氨水浓度的限制, 因此可选低浓度氨水作为吸收剂, 在一定程度上解决当前氨法脱碳中存在的问题。两种工艺均采用以晶体产物再生代替富液循环的再生方法, 大大降低再生过程中的能耗。两种新工艺均是采用半连续鼓泡反应系统进行的基础研究, 并从工艺路线、吸收效率、结晶收率、晶体产物特性等方面进行对比。     

强化结晶氨法脱碳实验研究

针对目前氨法二氧化碳捕集技术中存在的氨逃逸、再生能耗高、反应后期吸收率低等问题提出了强化结晶氨法捕碳工艺,采用氨水乙醇组成的混合吸收液,利用半连续鼓泡反应系统研究了实验过程中吸收液组成、吸收温度、烟气流量及烟气中CO₂体积分数对吸收及结晶规律的影响。实验结果表明,混合吸收液中选用高比例乙醇、较低的吸收温度、较高的烟气流量以及较大的CO₂体积分数有利于吸收液中晶体出现时间提前,有利于强化结晶过程,晶体含氨量占初始氨总量的分数可达38.75%,并且混合吸收液的CO₂吸收能力较纯氨水工况明显提高。创新之处在于:提出了一种强化结晶氨法捕碳工艺,对氨水乙醇混合吸收液的吸收及结晶规律进行研究,给出了能够改善吸收效果并利于结晶过程的有利工况。为接下来新工艺的进一步研究提供基础数据和参考。     

氨氮和林可霉素对有机物厌氧消化的抑制效应

以含高蛋白质和抗生素的林可霉素生产残渣产沼利用为背景,通过中温厌氧消化批式实验,研究不同的氨氮浓度(300～4500 mg·L<'-1>)和林可霉素浓度(0～100 mg·L<'-1>)对含氮含抗生素类生物质废物的厌氧消化产甲烷能力的抑制作用.结果表明,氨氮和林可霉素浓度均与累积产甲烷量显著负相关.经过240 h的培养...     

水泥生料中氨含量检测方法研究探索

本文主要探究了氯化钾溶液提取法和纳氏试剂法两种方法在水泥生料中氨含量检测的适应性和准确性，并进行了第三方检测验证。研究结果表明，氯化钾溶液提取法适用于0~50 mg/kg浓度的氨含量检测，而纳氏试剂法适用于20~100 mg/kg浓度的氨含量检测，本研究为水泥生料中氨含量检测提供指引和参考，对水泥工业实现氮氧化物超低排放，确保氨逃逸合格有着重要意义。     

Volatilization of ammonia from urea-ammonium nitrate solutions as influenced by organic and inorganic additives

Fertilizers containing urea can suffer from nitrogen (N) loss through ammonia volatilization, resulting in reduced effectiveness of the fertilizers. The loss of N may be reduced by use of organic or inorganic additives.Laboratory experiments were conducted on surface soil samples (0–15 cm) from two agricultural soils (St. Bernard and Ste. Sophie) to determine the impact of ammonium thiosulfate (ATS), boric acid, and a humic substance from leonardite, on NH₃ losses from surface-applied urea-ammonium nitrate (UAN) solutions. Experiments were carried out using moist soil samples in closed containers. Evolved NH₃ was carried out of the containers and trapped in boric acid solution using an ammonia-free humidified air flow.Total NH₃ losses in these experiments ranged from 12.1 to 21.3% of the N applied. The reduction in NH₃ volatilization (expressed as % of added N) due to additives ranged from 13.6 to 38.5% and 3 to 36.3% in St. Bernard and Ste. Sophie soils, respectively. More NH₃ volatilized from the boric acid or humic treated UAN solutions than from ATS-UAN solutions.Boric acid, ATS, and the humic substance, all significantly reduced urea hydrolysis in both soils in comparison to the untreated UAN solution. Further, the humic substance and boric acid treatment induced significant reduction in NO₃-formation. The results suggest that humic substance and to a lesser extent boric acid may function as urease and/or nitrification inhibitors. ATS treatment, particularly at higher levels increased NO₃-formation in both soils. The reason for this increase in nitrate formation is not clear.     

可逆气态膜-多效膜蒸馏-精馏过程脱除水相氨氮副产氨水

可逆气态膜-多效膜蒸馏-精馏耦合工艺可用于脱除料液或废水中的氨氮并得到高纯浓氨水。考察了磷酸二氢铵为可逆吸收剂时气态膜法脱氨效果和多效膜蒸馏-精馏法吸收完成液再生效果。实验结果表明:可逆气态膜总传质系数K和单程氨氮脱除率η分别可达13.9 μm·s^-1和97.5%,废水氨氮值可降至5 mg·L^-1以下;吸收完成液经多效膜蒸馏预浓缩后再经精馏再生可同时得到浓度为5%～18%的氨水。该耦合过程电耗极小的同时蒸汽耗量为28~40 kg·m^-3废水,约为单纯精馏过程的1/5。此外气态膜脱氨和多效膜蒸馏预浓缩过程有效地阻止了废水中挥发性杂质进入浓氨水产品。该过程对气态膜和膜蒸馏用微孔疏水膜组件的稳定性要求苛刻,长期操作试验显示聚四氟乙烯膜能够满足此要求。     

氨法吸收烟气中二氧化碳与脱碳后溶液解吸研究进展

氨法碳捕集因具有脱除效率高、低成本、高吸收容量等特点,而成为目前CO2捕集的研究热点之一。本文阐述了氨法吸收CO2与脱碳后溶液解吸的主要机理,综述了国内外该法的研究进展,分析了影响该技术应用的几个方面问题,比如机理研究、氨逃逸、解吸能耗等,提出今后应开展氨法碳捕集的工业化试验以及联合脱硫脱碳方面研究,尽快使该工艺得以工业化应用。     

燃煤烟气中SO2对氨法脱碳的影响

利用湿壁塔实验台对燃煤烟气中SO₂对氨水溶液［1%～7%(质量）］吸收CO₂的影响进行了实验研究,具体分析了不同反应温度（20～80℃）和CO₂体积分数（5%～20%）条件下,CO₂传质通量及传质系数随SO₂浓度和SO₂负载量的变化规律。结果表明, SO₂浓度由0增至11428 mg·m^-3,CO₂传质通量及传质系数均有一半左右降幅,而SO₂负载量［0.1～0.4 mol SO₂·（mol NH₃）^-1］的增加,同样导致CO₂传质通量及传质系数明显减小。氨水浓度及反应温度增加可有效提高CO₂传质通量和传质系数,相对降低SO₂对CO₂传质的影响。CO₂浓度的增加可明显提高其传质通量,但是CO₂的传质系数有所降低。     

Exclusion of CO and CO2 from ammonia synthesis gas by an electrocatalytic process

A new exclusion process for CO and CO₂ from ammonia synthesis gas has been proposed: this takes place at room temperature and atmospheric pressure. The process is based on the electrochemical reduction of CO and CO₂ to methanol proceeding at a mediated electrode via homogeneous catalysis. The maximum percentages of CO and CO₂ excluded from the initial gas were about 1.5 and 4.1%, respectively, with a mediated electrode of 82.8 cm² area in a reaction time of 5 h. The amount of excluded CO and CO₂ was equivalent to the sum of moles of methanol formed and gases dissolved into the solution alone. The electroreduction of CO and CO₂ was more efficient at three-phase (electrode/solution/gas) and at two-phase (electrode/solution) interfaces, respectively.     

Viscosity-prediction models of ammonia water nanofluids based on various dispersion types

This paper intends to apply the techniques that nano-particles enhance the heat and mass transfer to the ammonia water absorption refrigeration. Three types of nanofluids were obtained by adding the mixture of carbon black with emulsifier OP-10, ZnFe₂O₄ with sodium dodecyl benzene sulfonate (SDBS), and Fe₂O₃ with SDBS to the ammonia water solution, respectively. A series of experiments was performed to investigate the viscosities of the three kinds of nanofluids. The results show that, the content of surfactant and nano-particles, the interaction between surfactant and nano-particles, and the dispersion type are the key parameters that affect the viscosity of ammonia water nanofluid. Based on Einstein model and considering the solvation effect, two models to estimate the viscosity of ammonia water nanofluids were proposed in this paper. One is to analyze monolayer adsorption without considering the decrease of “free” surfactant content in ammonia water basefluid. The other model is to analyze electric double layer (EDL) adsorption, while taking the change of “free” surfactant content in ammonia water basefluid into account. The presented models and other theoretical models have been compared with experimental data. The comparison results show the presented models, in general, have higher accuracies and precisions.     

Application of an electrochemical-ion exchange reactor for ammonia removal

A new concept for ammonia removal from aqueous solution by zeolites followed by electrochemical oxidation/regeneration was studied in this work. In the first mode, (NH₄)₂SO₄ solution is passed through an ion exchange column where ammonium is concentrated in the zeolite. During the second mode (electrochemical oxidation/regeneration), the absorbed ammonia is harmlessly removed by electrochemical oxidation in the presence of sodium chloride (NaCl) and simultaneously the zeolite is regenerated. Continuous experiments were carried out for 172 h with five loading and four regeneration cycles without finding the loss of ammonia removal capacity of the zeolite. With electrochemical oxidation/regeneration, the conversion rate of ammonia adsorbed by the zeolites into nitrogen gas was more that 98%, and the conversion rate to nitrate was less than 2%; no ammonia or nitrite was detected in the regenerated solution. The regeneration solution can be repeatedly reused over a long period of time with 2.0 g/L NaCl added to the regeneration solution, saving both water resources and the chemical reagent. Moreover, approximately five times less energy was consumed with the present method than that of the direct electrochemical oxidation of ammonia.     

Absorption kinetics of carbon dioxide into aqueous ammonia solution: Addition of hydroxyl groups for suppression of vaporization

Aqueous ammonia can act as an alternative absorbent for CO₂ removal, but it has high volatility and reduces the ammonia concentration. We analyzed the hydroxyl additives 2-amino-2-methyl-1-propanol (AMP), ethylene glycol, and glycerol to reduce the vapor pressure of ammonia solutions. In addition, absorption efficiency groups of aqueous ammonia solutions containing hydroxyl additives were investigated. The results show that the addition of AMP, ethylene glycol, or glycerol to NH₃ reduced the vapor pressure of the absorbent by 14.0%, 22.7%, and 75.2%, respectively. The reaction rate constants of aqueous NH3 containing AMP, ethylene glycol, and glycerol additives at 293, 303, 313 and 323 K are given by $k_{2,NH_3 /AMP} = 4.565 \times 10^5 \exp ( - 1396.5/T)$ , $k_{2,NH_3 /ehylene glycol} = 1.499 \times 10^6 \exp ( - 1978.7/T)$ and $k_{2,NH_3 /glycerol} = 7.078 \times 10^6 \exp ( - 2413.3/T)$ , respectively.     

Introducing trace Co to molybdenum carbide catalyst for efficient ammonia synthesis

Development of the cost-effective catalysts with excellent catalytic performance is highly demanded for ammonia synthesis, and the strong adsorption of ammonia greatly hinders the design of cost-effective and high-performance ammonia synthesis catalysts. Herein, we report that the addition of a small amount of Co species (0.1 wt%) into Mo₂C catalyst, which can provide electrons to Mo₂C, not only leads to improvement of the adsorption and migration of hydrogen, but also facilitates the adsorption and desorption of ammonia. Consequently, Mo₂C catalyst with 0.1 wt%Co offers a 40% higher ammonia synthesis activity and a lower negative reaction order with respect to NH₃ in comparison to Mo₂C. This work stresses the importance of the minor components in improving the ammonia synthesis activity by accelerating the migration of reactants over the catalyst surface and the escape of products from the catalyst.     

Thermodynamic Simulation of CO2 Capture for an IGCC Power Plant using the Calcium Looping Cycle

A CO₂ capture process for an integrated gasification combined cycle (IGCC) power plant using the calcium looping cycle was proposed. The CO₂ capture process using natural and modified limestone was simulated and investigated with the software package Aspen Plus. It incorporated a fresh feed of sorbent to compensate for the decay in CO₂ capture activity during long‐term cycles. The sorbent flow ratios have significant effect on the CO₂ capture efficiency and net efficiency of the CO₂ capture system. The IGCC power plant, using the modified limestone, exhibits higher CO₂ capture efficiency than that using the natural limetone at the same sorbent flow ratios. The system net efficiency using the natural and modified limestones achieves 41.7 % and 43.1 %, respectively, at the CO₂ capture efficiency of 90 % without the effect of sulfation.     

The influence of formula modifications and additives on ammonia loses from surface-applied urea-ammonium nitrate solutions

Urea-ammonium nitrate (UAN) solution fertilizers are subject to N loss through ammonia (NH₃) volatilization. This loss may be reduced by manipulation of the proportion of urea and by use of additives to reduce urea hydrolysis or increase fertilizer solution acidity. This research was design to study the effect of urea proportion in UAN solutions, added ammonium thiosulfate (ATS), and aquechem liquor (an industry by-product) on NH₃ loss from N solutions surface-applied to a range of agricultural soils.NH₃ volatilization from urea (U), ammonium nitrate (AN), and UAN solutions surface-applied on six eastern Canadian soils was investigated. Ammonia loss from urea solutions ranged from 23 to 55% of the applied N. Increased AN-N in UAN solutions caused a reduction of NH₃ loss greater than the reduction in urea. Less volatilization was observed with N solutions of higher acidity. This effect was more pronounced on a sandy soil than on clay soil.When ATS was added to UAN solution, a further reduction of NH₃ losses was observed. This reduction ranged from 12 to 23.5% in Dalhousie clay and Ste. Sophie sand soils, respectively. Addition of aquachem liquor (AqL) to the UAN solution did not consistently reduce NH₃ loss.Supported by a grant from the Natural Sciences and Engineering Research Council of Canada, and Nitrochem Inc., Canada.