Performance analysis of ammonia-water absorption/compression combined refrigeration cycle

In view of different compressor adding ways in the ammonia-water absorption/compression combined refrigeration AWA /CCR cycle combining the Schulz state equation of the ammonia-water solution the theoretical analysis and calculations on two combination ways by adding the compressor in the high-pressure area and in the low-pressure area are conducted respectively.The effects of several factors including the evaporation temperature Te heat-source temperature Th as well as the cooling water temperature Tw on the equivalent heat consumption in compression qCW heat consumption in absorption qG and the system coefficient of performance COP are analyzed under the two combination configurations.The results show that the effect of the equivalent heat consumption in compression on the COP is less than that of the heat consumption in absorption.Besides the compressor set in the high-pressure area uses more energy than that in the low-pressure area. Moreover the compressor in the low-pressure area is superior to that in the high-pressure area with respect to the COP. Under the given intermediate pressure there is an optimum heat-source temperature corresponding to the maximum COP of the AWA/CCR cycle.

Thermodynamic analysis of simplified dual-pressure ammonia-water absorption power cycle

A simplified dual-pressure ammonia-water absorption power cycle(DPAPC-a) using low grade energy resources is presented and analyzed.This cycle uses turbine exhaust heat to distill the basic solution for desorption.The structure of the cycle is simple which comprises evaporator,turbine,regenerator(desorber),absorber,pump and throttle valves for both diluted solution and vapor.And it is of high efficiency,because the working medium has large temperature difference in evaporation and small temperature difference in absorptive condensation,which can match the sensible exothermal heat resource and the cooling water simultaneously.Orthogonal calculation was made to investigate the influence of the working concentration,the basic concentration and the circulation multiple on the cycle performance,with 85-110 ℃ heat resource and 20-32 ℃ cooling water.An optimum scheme was given in the condition of 110 ℃ sensitive heat resource and 20 ℃ cooling water,with the working concentration of 0.6,basic concentration of 0.385,and circulation multiple of 5.The thermal efficiency and the power recovery efficiency are 8.06 % and 6.66%,respectively.The power recovery efficiency of the DPAPC-a is 28.8% higher than that of the steam Rankine cycle(SRC) and 12.7% higher than that of ORC(R134a) under the optimized situation.

Influence factors on thermal conductivity of ammonia-water nanofluids

In order to investigate the mechanism of nanoparticles enhancing the heat and mass transfer of the ammonia-water absorption process,several types of binary nanofluids were prepared by mixing Al2O3 nanoparticles with polyacrylic acid(PAA),TiO2 with polyethylene glycol(PEG 1000),and TiN,SiC,hydroxyapatite(noodle-like) with PEG 10000 to ammonia-water solution,respectively.The thermal conductivities were measured by using a KD2 Pro thermal properties analyzer.The influences of surfactant and ammonia on the dispersion stabilities of the binary nanofluids were investigated by the light absorbency ratio index methods.The results show that the type,content and size of nanoparticles,the temperature as well as the dispersion stability are the key parameters that affect the thermal conductivity of nanofluids.For the given nanoparticle material and the base fluid,the thermal conductivity ratio of the nanofluid to the ammonia-water liquid increases as the nanoparticle content and the temperature are increased,and the diameter of nanoparticle is decreased.Furthermore,the thermal conductivity ratio increases significantly by improving the stabilities of nanofluids,which is achieved by adding surfactants or performing the proper ammonia content in the fluid.

Thermodynamic and Experimental Analysis of an Ammonia-Water Absorption Chiller

A single stage ammonia-water absorption chiller with complete condensation is designed, built and tested. The apparatus is designed for a cooling capacity of 2814 W, which is obtained using electric heater as heating source. The thermodynamic models have been derived using the First and Second Laws. Calculated results are compared with experimental data. The results show that the cooling capacity of experimental apparatus is found between 1900 and 2200 W with the actual coefficient of performance (COP) between 0.32 and 0.36. The contribution of the components to internal entropy production is analyzed. It shows that the larger irreversibility is caused by spanning the largest temperature and dissipated thermal energy by heat transfer losses at the generator and evaporator. In the experimentation, the low pressure is lower than the designed value. This is a consequence of a large capacity in the falling film absorber which performs as expected. This decreases the evaporation pressure, and the evaporating temperature could be reduced to the designed value.

Magnetic Field Enhancement in Ammonia-Water Absorption Refrigeration Systems

Absorption enhancement has been considered as an effective way of improving coefficient of performance (COP) of refrigeration systems and magnetic enhancement is one of these methods. A model of magnetic field enhancement in ammonia-water absorption systems is presented in this paper. A numerical model using finite difference scheme was developed based on the conservation equations and mass transport relationship. Macroscopic magnetic field force was introduced in the momentum equation. The model was validated using data obtained from the literature. Changes in the physical properties of ammonia solution while absorbing both in the direction of falling film and across its thickness were investigated. The magnetic field was found to have some positive effect on the ammonia-water falling film absorption. The results indicate that absorption performance enhancement increased with magnetic intensity. The COP of simple ammonia solution absorption refrigeration system increased by 1.9% and 3.6% for magnetic induction of 1.4 and 3.0 Tesla respectively.

Computer Simulation of an Ammonia-Water Absorption Cycle for Refrigeration: Using a Distillation Tower to Replace the Generator

By using a distillation tower as the regenerator, the coefficient of performance (COP) of the ammonia-water absorption refrigeration cycle is calculated in this work. Two types of distillation towers, namely an equilibrium-stage tower with a total condenser and a packed-bed tower with a partial condenser, are used in the cycle. From the simulation results, it is found that both types of distillation towers can successfully increase the COP of the cycle due to increased ammonia concentration in the vapor phase of the ammonia-water refrigerant. It was also found that the tower equipped with a partial condenser provides higher COP than that of the tower equipped with a total condenser. The value of COP can be further increased when the generator is replaced by the packed-bed tower in this water-ammonia absorption cycle. The effects of the mass flow rate ratio of NH3/H2O, stage number, reflux ratio and energy duty of the tower on the COP of the cycle are also studied in the present paper.

Thermodynamic Modelling of a 10-kW Ammonia-Water Absorption Machine

Absorption chillers are cooling units usually powered by renewable energy or waste heat.Their performance generally depends on the temperatures of the heat source,the ambient and the medium to be cooled.The present work deals with the thermodynamic study of a 10 kW NH3/H2O absorption machine in order to find the COP(coefficient of performance).The first and second laws of thermodynamics were used for the operating conditions.The thermodynamic properties of the NH3/H2O mixture were determined using the EES(Engineering Equation Solver)software.The results of the simulation of the machine were validated with the results of the literature.After validation,the program was used to simulate a 10-kW NH3/H2O absorption machine for milk conservation/cold storage in northern Senegal.The simulation results of the 10-kW ammonia-water absorption machine give an acceptable COP of 0.521 with a milk storage temperature of 4°C.

Theoretical and experimental investigation on a liquid-gas ejector power cycle using ammonia-water

The purpose of this paper is to investigate a novel power cycle using low-temperature heat sources such as oceanic-thermal, biomass as well as industrial waste heat. Both a reheater and a liquid-gas ejector are used in this ammonia-water based cycle. Energy analysis and parametric analysis are performed to guide the theoretical performance and experimental investigation is done to verify the theoretical results. The results show that the generator pressure, heating source temperature and turbine outlet depressurization made by the ejector can affect the cycle performances. Besides, the experimental thermal efficiency is much lower than the theoretical one on account of the heat losses and irreversibility. Moreover, the performance of liquid-gas ejector is affected by primary flow pressure and temperature.

Transportation of low-grade thermal energy over long distance by ammonia-water absorption

This paper presents the importance and the cycle choice for long-distance transportation of low-grade thermal energy, and the thermodynamic and hydrodynamic feasibility of single-effect ammonia-water absorption system for heat or cold transportation over long distance are also involved. A model of a long-distance thermal energy transportation system is built and analyzed, which shows satisfactory and attractive results. When a steam heat source at 120℃ is available, the user site can get hot water output at about 55℃ with the thermal COP of about 0.6 and the electric COP of about 100 in winter, and cold water output at about 10℃ with the thermal COP of about 0.5 and the electric COP of 50 in summer. A small-size prototype is built to verify the performance analysis. Basically the experimental data show good accordance with the analysis results. The ammonia-water absorption system is a potential pro-spective solution for the heat or cold transportation over long distance.

氨型碱性水化学对690TT腐蚀特性的影响

为探索氨型碱性水化学对传热管材料690TT腐蚀行为的影响,开展传热管材料690TT合金在B-Li-NH_4OH和NH_4OH两种水质下的腐蚀特性研究,分析690TT腐蚀产物释放特性,综合评价氨型碱性水质对690TT腐蚀特性的影响。研究结果表明,690TT材料与两种氨型碱性水质均具有较好的相容性。690TT在两种水质中均形成了致密的氧化膜,氧化膜由NiFe_(2)O_(4)尖晶石氧化物和少量的铁氧化物Fe_(2)O_(3)组成,相对而言690TT在NH_(4)OH型水质条件下的总腐蚀失重量、总腐蚀产物释放量略低于在B-Li-NH_(4)OH水质下,但690TT向水质释放的Ni元素总量与上述规律相反,这可能与Ni元素和氨形成络合物[Ni(NH_(3))_(m)]^(2+)有关,Ni元素释放量增加对反应堆一回路辐照场控制有不利影响。本研究结果可为氨型碱性水化学技术的设计和应用提供数据支撑。

热泵精馏耦合吸收处理含盐氨水

针对含盐氨水的回收与处理,利用蒸发除盐、精馏脱氨并耦合吸收制备一定浓度的氨水。采用一系列节能技术对蒸发和精馏进行计算优化,即双效蒸发与塔顶蒸汽直接压缩热泵精馏耦合吸收工艺(SchemeⅠ)、热泵蒸发与塔顶蒸汽直接压缩热泵精馏耦合吸收工艺(SchemeⅡ)和热泵蒸发与塔底闪蒸再压缩热泵精馏耦合吸收工艺(SchemeⅢ)。选用ELECNRTL电解质模型计算物系的热力学数据和相平衡数据,并以年总费用、综合能耗和热力学效率等作为工艺评价指标,对提出的以上3种处理工艺进行模拟与优化。研究结果表明,与SchemeⅠ相比,SchemeⅡ和SchemeⅢ可分别节省年总费用22.18%和31.66%;节约能耗47.56%和57.87%;而热力学效率则分别提高了8.59%和2.28%。显然,SchemeⅢ在年总费用与能耗方面更具优势,SchemeⅡ在热力学效率方面更具优势。

气化装置外排废水氨氮高分析与处理

气化装置外排灰水中氨氮含量较高会造成水处理装置SBR活性污泥失活,造成分公司水处理装置处理气化废水难度增加,为了实现水处理装置长周期平稳运行,气化装置外排灰水量需要降低。从而加剧气化系统水的恶性循环,水质逐渐变差,最终影响气化装置的长周期平稳运行。文章通过分析外排废水中氨氮高的形成原因,针对性的进行生产优化调整,减少外排废水氨氮含量,保障装置平稳运行。

电解制氢合成氨技术综述与展望

随着可再生能源技术的飞速发展,电解制氢合成氨的工艺路径受到越来越多的关注。自1920年代发展至今,电解制氢合成氨已经有100多年的历史,历经了水力发电合成氨到当前风光发电驱动下的合成氨。本文旨在全面回顾合成氨工业的发展历程,深入剖析化石能源合成氨、风光发电制氢合成氨和网电制氢合成氨的技术发展和特点。在此基础上,细致分析了国内电解制氢合成氨的当前态势,预测了我国未来合成氨的产业规模,预计2030年国内合成氨行业产值达到3173亿元,预计2050年达到7900亿元。针对合成氨行业的发展路径,本文提出了深刻的思考与策略建议,指出两条可行的发展路线:其一,在可再生能源资源丰富且电价相对低廉的地区,氨可作为有效的电力储存与消纳手段,促进能源体系的灵活性与可持续性;其二,对现有合成氨装置实施绿色转型,通过部分采用绿氢替代化石原料,逐步释放并扩大合成氨的产能与环保效益。

鄱阳湖季节性氨氮水生生物生态风险评估

基于生态环境部颁布的《淡水水生生物水质基准—氨氮》提供的有限离散基准值,对鄱阳湖内6个测站在2018年的氨氮水生生物生态风险(RQ)进行量化评估,进一步讨论了水温和pH值对氨氮水生生物毒性的影响,提出了一种《淡水水生生物水质基准—氨氮》的运用思路,对鄱阳湖地区氨氮的治理提供了数据支撑和经验借鉴。结果表明:氨氮平均浓度最高出现在冬季,平均浓度最低出现在秋季;鄱阳湖夏季的短期水生生物水质基准(SWQC)和长期水生生物水质基准(LWQC)最低,春季的SWQC和LWQC最高;鄱阳湖夏季的长期水生生物生态风险LRQ>1,表明在夏季鄱阳湖的氨氮长期水生生物生态风险超过环境容许值;鄱阳湖夏季存在因水温和pH值的升高导致SWQC和LWQC降低,进而引发水生生物生态风险提高的问题。加强对鄱阳湖的pH值监控和预警应作为水资源管理的重点。

系统中水含量对锂介导合成氨的性能影响

针对锂介导合成氨(LM-NRR)过程中存在的水污染问题,通过对比实验及扫描电子显微镜(SEM)、X射线衍射仪(XRD)、X射线光电子能谱仪(XPS)等表征手段,探讨了含水量对LM-NRR体系的性能影响及其在反应界面中的作用机理。结果表明,无水条件下的LM-NRR体系具有较好的氨合成性能,在反应时间为120 min、N2流速为4 m L·min^(-1)、电流密度为3 m A·cm^(-2)条件下的氨合成速率可达0.0124μg·s^(-1)·cm^(-2),法拉第效率为7.05%。含水量对LM-NRR体系的影响显著,会极大地降低体系的氨合成速率及法拉第效率。这主要是由于反应界面上的水会加剧竞争性析氢反应(HER)、促进电解质中Li BF_(4)的水解以及钝化表面活性锂位点,进而降低了体系的氨反应活性。

海水养殖尾水中NH_(4)^(+)-N去除技术的机理与工艺研究进展

总结了海水养殖尾水中NH_(4)^(+)-N的来源及特点,NH_(4)^(+)-N去除技术的机理与功能微生物、工艺应用及其微生物分布等,重点对海水养殖尾水中NH_(4)^(+)-N去除技术的机理与工艺应用进行了阐述。好氧氨氧化微生物主要包括氨氧化细菌(AOB)、氨氧化古菌(AOA)及全程硝化菌(comammox),厌氧氨氧化微生物主要包括厌氧氨氧化细菌(AnAOB)。基于好氧氨氧化微生物原理去除NH_(4)^(+)-N的主要工艺技术包括移动床生物膜反应器(MBBR)、曝气生物滤池(BAF)、人工湿地和生态塘等;基于厌氧氨氧化菌处理海水养殖尾水的主要工艺技术有厌氧流化床、厌氧固定床等。指出工艺应用与微生物种群结构之间关系的研究不足。富集氨氧化微生物从而实现经济高效脱氮是未来工艺研究的重点方向。

不同改性生物炭对稻田氮素损失及产量的影响

为进一步挖掘稻田生态系统生物炭增效、节肥和减排潜力,以无生物炭为对照(CK),设置玉米秸秆生物炭(B)、酸化生物炭(B_(pH))、氮负载生物炭(B_(NH_(4)))、铁改性生物炭(B_(Fe))和钙改性生物炭(B_(Ca))6个处理,通过2a试验,对生物炭阳离子交换量(CEC)、含氧官能团以及其处理下水稻产量、氮素提取、氨挥发、氮素淋失和土壤氮残余等进行了研究.结果表明:与B相比,B_(pH)、B_(NH_(4))和B_(Fe)分别显著提升生物炭CEC(53.9%、29.6%和28.2%),且4种改性处理均可显著提升生物炭-COOH、-OH、C=O、O-H等含氧官能团浓度,增强生物炭吸氮能力.全生育期累积氨挥发在9.1~19.9kg/hm^(2)(2021)和8.5~13.7kg/hm^(2)(2022)之间,除B_(NH_(4))降氨效果明显(44.6%)外,其他处理第1年对氨挥发无显著影响;而B_(Ca)、B_(NH_(4))和B_(Fe)在第2a均显著降低氨挥发,较CK分别降低33.5%、37.5%和37.8%.4种改性生物炭连续2a,较CK降低氮素淋失19.0%和35.2%(B_(pH))、15.0%和21.0%(B_(Ca))、11.3%和28.7%(B_(NH_(4)))、12.6%和29.0%(B_(Fe)).B在第1年对产量无显著影响,但老化1年后增产显著(8.8%);B_(pH)和B_(NH_(4))连续2a分别增产19.7%和12.2%(2021年),11.5%和5.8%(2022年).B_(pH)、B_(Ca)和B_(NH_(4))在2a均显著降低了活性氮排放,降幅为23.4%、21.8%和42.3%(2021年)和23.5%、30.5%和35.5%(2022年).不同生物炭处理第1a土壤矿化氮残余无显著差异;但B_(Ca)、B_(NH_(4))和B_(Fe)第2a增效显著.同时考虑增产、活性氮减排和矿化氮可持续性,B_(NH_(4))综合效果最佳,同CK相比,2021和2022年分别可降低氨挥发42.3%和35.5%,铵态氮淋失10.6%和29.0%,硝态氮淋失14.7%和23.4%,氮素积累提高13.4%和4.3%以及矿化氮残余提高15.0%和17.9%,最终增产19.7%和5.7%.

氨水强化超临界二氧化碳地质埋存方法

为提高二氧化碳捕集、利用与封存(CO_(2) capture,utilization and storage,CCUS)末期CO_(2)地质埋存能力,提出氨水强化CO_(2)埋存方法,向储层注入氨水,利用氨水与CO_(2)发生化学反应提高CO_(2)埋存量。通过高温高压物理模拟装置和岩心驱替装置,选定实验参数范围为20 MPa、40~80℃、氨水浓度6%~26%,选取高渗岩心进行实验,明确了氨水与CO_(2)的反应规律和岩心中氨水强化CO_(2)埋存效果。结果表明,氨水吸收CO_(2)的量与氨水浓度呈正比,与温度呈反比,但低温会析出碳酸氢铵晶体,减少氨水吸收CO_(2)的量;氨的吸收能力与氨水浓度呈负相关,与温度没有明显的线性相关性;在60℃条件下,6%浓度的氨水表现出最佳的CO_(2)吸收效果;与饱和地层水相比,饱和6%浓度氨水可使岩心的CO_(2)埋存量提高7.5倍;岩心迂曲度每增加0.5,氨水强化埋存的单位岩石孔隙体积CO_(2)埋存量可以增加200 mL,而地层水埋存的单位岩石孔隙体积CO_(2)埋存量仅增加11 mL。该研究首次提出了一种新的二氧化碳埋存模式并开展实验研究,为CCUS项目强化二氧化碳地质埋存提供了一种新思路和新途径。

重溶水解法制备高纯氧化铍试验研究

针对高氟铀铍矿提铀过程中,利用所得BeSO_(4)溶液制备氢氧化铍时存在杂质较高问题,研究了采用重溶水解法处理高Fe、Al杂质的粗氢氧化铍沉淀,考察了粗Be(OH)_(2)沉淀方式、NaOH用量、重溶温度对粗Be(OH)_(2)重溶效果的影响。结果表明:采用重溶水解法能使Be与SO_(4)^(2-)高效分离,大幅降低产品中Fe、Al含量;将所得纯度较高Be(OH)_(2)进行焙烧可制备符合工业标准的高纯BeO产品。

N_(2)气氛下氨水溶液γ辐射分解行为

某些压水堆中使用氨及其分解产生的H_(2)抑制H_(2)O_(2)、O_(2)和·OH等氧化性物种的浓度,在保持一回路的还原性化学环境的同时调节冷却剂pH,以减轻结构材料的腐蚀。本工作为了研究脱氧氨水溶液在辐射场中的分解行为,针对其在γ场中的辐解过程进行了实验研究,重点考察了N_(2)压强、气相与液相体积之比和温度对氨水溶液辐解的影响,测定了剩余氨、H_(2)和氮氧化物(NO_(2)^(-)和NO_(3)^(-))的浓度及溶液的pH。结果表明:N_(2)压强(0.5~5.0 MPa)及气液体积比的变化未对氨的分解和氮氧化物的生成造成影响,吸收剂量为28.8 kGy时,辐解产生的氮氧化物浓度约为1 mg/L,但N_(2)压强和气液体积比的增加会显著降低H_(2)的浓度。温度由25℃升至200℃时,氨的分解过程将大幅放缓,吸收剂量为14.4 kGy时,30 mg/L氨水中氨的分解比例由26.5%降至8.4%,高温有利于抑制氨的分解速率,但同时导致NO_(2)^(-)和NO_(3)^(-)的浓度分别升高34和3倍左右。此外,本工作中还建立了含氨冷却剂的辐解模型并对其可靠性进行了验证,不同温度下实验数据与模型预测结果的最大相对误差仅为4.1%。随后利用该模型计算了不同初始浓度的含氨冷却剂辐解过程中剩余氨的浓度变化,结果表明较高的初始浓度有利于体系中氨的保持,连续辐照的情况下单独使用氨抑制氧化性物种时需要及时对其进行补充。