年产50万吨合成氨原料气制备的工艺筛选设计方案学士学位论文.doc

年产50万吨合成氨原料气制备的工艺筛选设计方案摘要：本设计是年产能力为50万吨合成氨造气工段（合成氨所需原料-CO+CO2）的初步工艺设计。以焦炉气为原料，焦炉气经脱硫、压缩、精脱硫、富氧转化、中串低变换、改良热钾碱脱碳、甲烷化、合成气压缩、氨合成。工艺技术成熟可靠，产品纯度高，消耗定额低，生产成本低。从工艺设计、节能降耗及实际案例等方面比较了上述工艺；结果表明：不论是哪种净化、精制工艺，关键的工艺控制点是：将CO+CO2净化精制至微量级，降低有效氢的损耗，降低生产消耗。关键词：焦炉气、低耗、合成氨、净化、精制1、焦炉气配煤造气制合成氨的必要性焦炉气生产合成氨类似天然气生产合成氨，焦炉煤气自身的特点是氢多碳少，C/H低，焦炉气成分如表1。单独用于合成氨生产时，原料气耗量大，弛放气排放量多，单位产品能耗高。必须补碳。综合考虑，我国煤炭资源丰富，价格便宜，宜采用煤制气补碳，煤制气有效成分（H2+CO）高，可以把合成气调整合理，最大限度地利用原料气。因此，要想取得好的经济效益，合理地利用原料资源，采用煤、焦、化一体化的联合流程，不仅将能源和环境保护结合起来，而且将传统的焦化工业与化学工业及化肥工业有机地结合起来，生产大宗支农产品尿素，是新一代焦炉气综合利用的好途径。2、工艺生产路线概述将来自焦化厂净化后的剩余焦炉煤气，进入气柜进行混合、缓冲，然后通过罗茨鼓风机升压，湿法脱硫装置脱除焦炉气中的H2S，再加压至2.3 MPa，送干法脱硫装置，将气体中的总硫脱至7 mg/m3以下，利用深冷空分装置送来的富氧，混入蒸汽进行催化部分氧化转化，将气体中的甲烷及少量其他烃转化为CO和H2，转化后的高温气体经废锅回收热量降温后，补加蒸汽进入变换工序的中变炉，进行CO变换反应，调整CO含量至3%，然后进入ZnO 精脱硫槽，将气体中的总硫脱至（13）106，再进入装有铜锌催化剂的低温变换炉，控制变换气中CO含量为0.3%。 灰熔聚粉煤气化炉生产的煤气，单独进行压缩、净化、中温变换，之后也进入ZnO 精脱硫槽，与转化后的中变气混合，一起进入低温变换炉，进行深度变换。变换后的低变气进入脱碳装置脱除CO2，控制脱碳气中CO2含量0.2%，再经甲烷化装置精制，使气体中的COCO2 20106，合格的氢氮气经合成气压缩机组，加压至31.4 MPa送往氨合成装置。氨合成采用31.4 MPa的高压合成工艺。流程示意如图1。氨合成产生的放空气净氨后，作为转化装置预热炉的燃料气。图1 工艺技术路线方框图3、合成氨工艺的选择3.1焦炉气的转化焦炉气转化制氨合成气有以下两种方案。方案一 蒸汽转化 本方法通过蒸汽转化，将焦炉气中的甲烷转化为H2、CO、CO2，以降低合成气中的惰性气体含量，同时增加CO、CO2量，该法制得的合成气中氢含量高，H2/N2在补N2时调节。缺点是：蒸汽转化炉投资较高，能耗较高，致使生产成本偏高。方案二 富氧蒸汽转化的方法采用本方法的特点是转化所需热量通过转化炉内焦炉气的燃烧提供，燃烧后的尾气没有外排而是直接进入合成原料气中，生产合成气的H2/N2比例由加氮量控制。该法比以天然气为原料的蒸汽转化生产合成氨过程简单，流程简短，易于控制。虽然到目前为止，利用焦炉气生产合成氨的厂家还为数不多，但可以认为是工业应用中成熟的国产化技术。为节省空分装置的氧气用量，保证转化炉操作的稳定性和安全可靠性，流程中设置了蒸焦预热炉和富氧软水预热炉。综合各方面的因素，由于本装置的主要目的是利用富余的焦炉气生产合成氨，使焦炉气得到最大限度的利用。因此，采用富氧蒸汽转化比较合理。3.2 煤造气本装置造气采用常压灰熔聚流化床气化炉，净化加压后，在变换工序补入系统。用3台3600 mm常压灰融聚流化床气化炉，两开一备，以粉煤为原料生产煤气，煤气经湿法脱硫，加压至2.3Mpa后，再经ZnO干法脱硫和中温变换，在ZnO精脱硫工序补入系统。工艺流程主要包括进料、供气、气化、除尘、废热回收等工序。3.3 净化3.3.1脱硫工艺（1）湿法脱硫分为物理吸收法、化学吸收法与直接氧化法三类。目前运用较为广泛且性能较好的脱硫方法有PDS法、改良ADA法，栲胶法、茶灰法、MSQ法、改良对苯二酚法、KCA法。经过综合比较，栲胶脱硫和改良ADA脱硫都是本装置可以采用的脱硫工艺，但考虑到现有装置采用的是改良ADA工艺，且使用效果良好，工人操作熟练，因此，本装置拟采用“改良ADAPDS”工艺。对再生后硫泡沫的处理，采用连续熔硫工艺，主要设备熔硫釜，选用邯钢化肥公司开发的、获国家专利的“连续进行硫回收的金属釜”。同时，设溶液回收装置。该工艺具有如下特点：设备台数少、不建厂房、投资较省；操作简单易掌握，生产安全；生产弹性大，可根据负荷间断或连续运行；操作人员少，维修量小，运行费用低；生产过程中没有废气、废渣、废液产生，操作环境好。（2）干法脱硫湿法脱硫后，焦炉气中仍含无机硫20mg/m3,有机硫约250 mg/m3，硫是转化、变换、甲烷化和合成催化剂的毒物，为降低消耗，延长催化剂使用寿命，采用干法脱硫。干法脱硫主要有氧化铁法、铁钼锰矿法、活性炭法、钴-钼加氢法、氧化锌法等。无机硫的脱除相对容易，有机硫则不易直接脱除，一般先转化为无机硫，再进行脱除。加氢转化反应属可逆反应，故转化前先进行无机硫的脱除，以保证加氢反应彻底。焦炉气中硫的形态复杂，且含有较难转化的噻吩，用铁钼加氢串氧化锰法比较合适。该法在焦炉气制合成氨工艺中已运行多年，效果良好。因此，本装置选择此方法，并在氧化锰槽后串中温氧化锌槽把关，以确保总硫小于（13）106。3.3.2 变换工艺变换系统按照热利用方式，分为换热式流程和饱和热水塔流程两种。换热式流程一次性投资省，占地少，操作稳定，蒸汽消耗较高；而饱和热水塔流程可以多回收部分反应热，提高气体的温度和湿含量，减少外加蒸汽量，降低能耗，但装置投资费用较高。本装置变换操作压力高，由饱和塔带出的水蒸气量相对于中、小型氮肥厂的低压变换为低，因此本装置采用换热式中串低变换工艺，流程中设置废热锅炉回收变换反应热，副产的中压蒸汽用于本系统。3.3.3 脱碳工艺目前合成氨厂采用的脱碳方法，大致可分为三类，即化学吸收法、物理吸收法和物理化学吸收法。化学吸收法适合于CO2分压低的气体净化，此法净化率高，但脱碳溶液溶剂再生时需加热，能耗高，热钾碱法属于此类方法。物理吸收法适合于CO2分压高、处理量大的气体净化，脱碳溶剂再生采用降压工艺，不需加热，但净化率略低于化学吸收法。碳酸丙烯酯脱碳法（简称PC），聚乙二醇二甲醚脱碳法（简称NHD法）均属此类方法。物理化学吸收法处理量大，净化率高，生产操作稳定，但脱碳溶剂的再生需加热，蒸汽耗量较大，N-甲基二乙醇胺加少量活化剂组成的脱碳溶剂（简称改良MDEA），其脱碳机理就属物理化学吸收法。该法兼具物理及化学吸收法的特点，溶液再生通过减压闪蒸和加热汽提共同完成，该法溶液稳定，操作简单，净化度较高，但仍需要消耗一定的热能，其再生热能消耗以CO2计约为1880 kJ/m3。改良热钾碱法脱碳工艺尽管热能消耗较高，但配转化流程，在天然气制合成氨厂广泛采用，且气体净化度和CO2回收率高。非常适合本装置转化后变换气中CO2含量较低、系统操作压力不高的工况，可以弥补焦炉气中CO2不足的缺点。故项目采用改良热钾碱法脱碳工艺。具体流程为三段吸收、双塔变压再生的先进工艺，进一步降低溶液再生能耗。3.4 合成3.4.1压缩机的选择压缩工序是合成氨系统的心脏部分，压缩机是合成氨生产的关键设备。目前，国内外大中型合成氨厂压缩一般采用离心式和往复式压缩机。国内外许多气头和油头的大中型合成氨厂均采用离心式压缩机。但离心式压缩机有以下不足之处：（1）使用条件要求高，要求原料气体不含油、尘；（2）排气压力较低；（3）离心式压缩机整机或主要部件需引进，投资高；（4）采用汽轮机驱动时，热动与工艺联合，相互影响，稳定性差。本装置以焦炉气为原料生产合成氨，由于焦炉煤气中氢含量较高，使得气体分子量很小，且焦炉气中含有尘和焦油，这些因素都给使用离心式压缩机造成困难，故不宜采用离心式压缩机。而往复式压缩机与离心式压缩机相比尽管有不足之处，但有运行平稳可靠，排气压力高，系国内制造、使用经验丰富的优点。为此本可研选择往复式压缩机，采用低压段和高压段分开的压缩方案。3.4.2 精制 CO和CO2都是氨合成催化剂的毒物，经初步净化后的气体，进入合成系统之前，必须再行精制，使COCO2的含量低于20106，并清除残留的O2和H2S。通常采用两种方法处理：一种是借助于镍催化剂将微量的CO和CO2转化为惰性的甲烷，即甲烷化；另外一种方法是用适当的溶剂将残余CO和CO2吸收掉，即铜氨液洗涤法。采用甲烷化的方法，由于合成气中的氢含量高，甲烷化反应比较彻底，其中的CO和CO2含量可以降至106数量级，其工艺流程简单，设备较少，操作费用低。适用于各种合成氨配套产品的生产流程，操作压力随所配产品流程不同而有差异，但此过程消耗掉数倍于一氧化碳和二氧化碳含量的氢气，而且还生成一些无用的甲烷气体，使得合成气中的惰性组分含量增加，合成系统放空量增加，损失加大，能耗增高。铜氨液洗涤法技术较成熟,醋酸亚铜氨液稳定性好，气体净化度高。但此种方法不仅能耗高，工艺条件要求比较严格，而且由于废液中含有重金属“铜”，存在环境污染的问题。上述两种方法相比，甲烷化法具有流程简单、操作方便、设备和操作费用低等明显优点，故本工程推荐采用甲烷化精制工艺。3.4.3 氨的合成对于氨合成来说，传统的反应压力为31.4 MPa。近年来合成压力有逐渐下降的趋势，16 MPa的氨合成装置已在一些中大型氨厂运行。合成的压力高，压缩功高，但有利于反应平衡，设备相对缩小。合成的压力低，压缩功相对低，但设备相对增大。压力高低各有利弊。本工程按31.4 MPa氨合成设计。选用先进可靠、技术成熟的1800 mm合成塔内件及与之相配套的高效分离内件、后置式废热锅炉（热回收系统）。具有塔阻力小，氨净值高，使用寿命长，操作稳定简单，投资少的特点。设置废热锅炉回收反应热，副产蒸汽。3.4.4 氨氢回收氨回收是合成氨厂节能降耗的主要措施之一，设置等压回收塔，用尿素深度解吸液洗涤回收氨罐弛放气和合成放空气中的氨，得到的稀氨水送尿素车间解吸，降低氨耗。洗涤后的尾气送转化加热炉作为燃料气燃烧，减少燃料焦炉气的消耗。由于本装置转化消耗燃料气，故不设氢回收装置。4、环保和节能（1）环保合成放空气主要有害物为CH4、NH3，放空气经洗涤NH3后，减压后送转化加热炉燃烧，得到的稀氨水，送往尿素解吸、水解系统回收利用。本装置在建设中，对生产过程中排放的“三废”，均采取了有效的治理措施，保证污染物达标排放，符合国家推行的清洁生产要求。（2）节能本着降低能耗、提高经济效益、改善环境的目的，采用了如下节能技术措施：充分利用变换气余热，作为脱碳再生塔煮沸器的热源，既节省蒸汽，又节省冷却水。转化、变换、甲烷化、氨合成等采用新型催化剂，提高转化效率，降低能量消耗。脱碳采用涡轮泵回收能量，吨氨节电19.2 kWh。气化工艺采用常压灰融聚工艺，以烟煤为原料，符合中国节能技术政策大纲。本装置合成氨的单位能耗为48282.8 MJ，折标煤为1647 kg，优于现阶段（2004年底）我国平均水平（吨氨耗标煤1700 kg），但与国际先进水平（1000 kg）相比，相差了647 kg。在今后设计及生产中将采取更先进的节能措施，以便更好地节约能源。5、结语本项目以焦炉气为原料，焦炉气经脱硫、压缩、精脱硫、富氧转化、中串低变换、改良热钾碱脱碳、甲烷化、合成气压缩、氨合成。工艺技术成熟可靠，产品纯度高，消耗定额低，生产成本低。合成氨的生产主要是以焦炉气为原料，有明显的价格和成本优势，在市场竞争中具有较强的竞争力，符合国家的能源政策、产业政策和环保政策以及地区的发展规划，是焦炉剩余煤气综合利用的新方向。参考文献【1】陈德祥 陈秀等编 .煤化工工艺学. 煤炭工业出版社出版1998.2【2】钟蕴英、关梦嫔、崔开仁、王惠中编 .煤化学. 中国矿业大学出版社出版，1988.7【3】煤炭加压气化. 中国建筑工业出版社出版，1981.3【4】郭树才编 .煤化工工艺学. 化学工业出版社出版，1991.3【5】沙兴中、杨南星编 .煤的气化与应用. 华东理工大学出版社出版，【6】张成芳编 .合成氨厂工艺技术与节能. 华东化工学院出版社出版。1990.4【7】梅安华主编 .小合成氨厂工艺技术与设计手册.（上册）化学工业出版社出版【8】李永恒主编 .造气动技术问答. 化工部上海化工研究院，化工部化肥工业科技情报中心站出版，1993（上、下），天津科学技术出版社 1999请删除以下内容，O(_)O谢谢！conduction, transfer of heat or electricity through a substance, resulting from a difference in temperature between different parts of the substance, in the case of heat, or from a difference in electric potential, in the case of electricity. Since heat is energy associated with the motions of the particles making up the substance, it is transferred by such motions, shifting from regions of higher temperature, where the particles are more energetic, to regions of lower temperature. The rate of heat flow between two regions is proportional to the temperature difference between them and the heat conductivity of the substance. In solids, the molecules themselves are bound and contribute to conduction of heat mainly by vibrating against neighboring molecules; a more important mechanism, however, is the migration of energetic free electrons through the solid. Metals, which have a high free-electron density, are good conductors of heat, while nonmetals, such as wood or glass, have few free electrons and do not conduct as well. Especially poor conductors, such as asbestos, have been used as insulators to impede heat flow (see insulation). Liquids and gases have their molecules farther apart and are generally poor conductors of heat. Conduction of electricity consists of the flow of charges as a result of an electromotive force, or potential difference. The rate of flow, i.e., the electric current, is proportional to the potential difference and to the electrical conductivity of the substance, which in turn depends on the nature of the substance, its cross-sectional area, and its temperature. In solids, electric current consists of a flow of electrons; as in the case of heat conduction, metals are better conductors of electricity because of their greater free-electron density, while nonmetals, such as rubber, are poor conductors and may be used as electrical insulators, or dielectrics. Increasing the cross-sectional area of a given conductor will increase the current because more electrons will be available for conduction. Increasing the temperature will inhibit conduction in a metal because the increased thermal motions of the electrons will tend to interfere with their regular flow in an electric current; in a nonmetal, however, an increase in temperature improves conduction because it frees more electrons. In liquids and gases, current consists not only in the flow of electrons but also in that of ions. A highly ionized liquid solution, e.g., saltwater, is a good conductor. Gases at high temperatures tend to become ionized and thus become good conductors (see plasma), although at ordinary temperatures they tend to be poor conductors. See electrochemistry; electrolysis; superconductivity. Almost everyone has experienced the Doppler effect, though perhaps without knowing what causes it. For example, if one is standing on a street corner and an ambulance approaches with its siren blaring, the sound of the siren steadily gains in pitch as it comes closer. Then, as it passes, the pitch suddenly lowers perceptibly. This is an example of the Doppler effect: the change in the observed frequency of a wave when the source of the wave is moving with respect to the observer. The Doppler effect, which occurs both in sound and electromagnetic wavesincluding light waveshas a number of applications. Astronomers use it, for instance, to gauge the movement of stars relative to Earth. Closer to home, principles relating to the Doppler effect find application in radar technology. Doppler radar provides information concerning weather patterns, but some people experience it in a less pleasant way: when a police officer uses it to measure their driving speed before writing a ticket. Sound and light are both examples of energy, and both are carried on waves. Wave motion is a type of harmonic motion that carries energy from one place to another without actually moving any matter. It is related to oscillation, a type of harmonic motion in one or more dimensions. Oscillation involves no net movement, only movement in place; yet individual points in the wave medium are oscillating even as the overall wave pattern moves. The term periodic motion, or movement repeated at regular intervals called periods, describes the behavior of periodic waveswaves in which a uniform series of crests and troughs follow each other in regular succession. A period (represented by the symbol T ) is the amount of time required to complete one full cycle of the wave, from trough to crest and back to trough. Period is mathematically related to several other aspects of wave motion, including wave speed, frequency, and wavelength. Frequency (abbreviated f ) is the number of waves passing through a given point during the interval of one second. It is measured in Hertz (Hz), named after nineteenth-century German physicist Heinrich Rudolf Hertz (1857-1894), and a Hertz is equal to one cycle of oscillation per second. Higher frequencies are expressed in terms of kilohertz (kHz; 103 or 1,000 cycles per second); megahertz (MHz; 106 or 1 million cycles per second); and gigahertz (GHz; 109 or 1 billion cycles per second.) Wavelength (represented by the symbol , the Greek letter lambda) is the distance between a crest and the adjacent crest, or a trough and an adjacent trough, of a wave. The higher the frequency, the shorter the wavelength. Amplitude, though mathematically independent from the parameters discussed, is critical to the understanding of sound. Defined as the maximum displacement of a vibrating material, amplitude is the size of a wave. The greater the amplitude, the greater the energy the wave contains: amplitude indicates intensity, which, in the case of sound waves, is manifested as what people commonly call volume. Similarly, the amplitude of a light wave determines the intensity of the light. electromagnetic radiation,energy radiated in the form of a wave as a result of the motion of electric charges. A moving charge gives rise to a magnetic field, and if the motion is changing (accelerated), then the magnetic field varies and in turn produces an electric field. These interacting electric and magnetic fields are at right angles to one another and also to the direction of propagation of the energy. Thus, an electromagnetic wave is a transverse wave. If the direction of the electric field is constant, the wave is said to be polarized (see polarization of light). Electromagnetic radiation does not require a material medium and can travel through a vacuum. The theory of electromagnetic radiation was developed by James Clerk Maxwell and published in 1865. He showed that the speed of propagation of electromagnetic radiation should be identical with that of light, about 186,000 mi (300,000 km) per sec. Subsequent experiments by Heinrich Hertz verified Maxwells prediction through the discovery of radio waves, also known as hertzian waves. Light is a type of electromagnetic radiation, occupying only a small portion of the possible spectrum of this energy. The various types of electromagnetic radiation differ only in wavelength and frequency; they are alike in all other respects. The possible sources of electromagnetic radiation are directly related to wavelength: long radio waves are produced by large antennas such as those used by broadcasting stations; much shorter visible light waves are produced by the motions of charges within atoms; the shortest waves, those of gamma radiation, result from changes within the nucleus of the atom. In order of decreasing wavelength and increasing frequency, various types of electromagnetic radiation include: electric waves, radio waves (including AM, FM, TV, and shortwaves), microwaves, infrared radiation, visible light, ultraviolet radiation, X rays, and gamma radiation. According to the quantum theory, light and other forms of electromagnetic radiation may at times exhibit properties like those of particles in their interaction with matter. (Conversely, particles sometimes exhibit wavelike properties.) The individual quantum of electromagnetic radiation is known as the photon and is symbolized by the Greek letter gamma. Quantum effects are most pronounced for the higher frequencies, such as gamma rays, and are usually negligible for radio waves at the long-wavelength, low-frequency end of the spectrum.