燃烧学讲义（14燃烧技术）

科技与论语 MACROBUTTON MTEditEquationSection2 Equation Chapter 1 Section 1 错误！未找到图形项目。 0.​ 绪论 1.​ 燃料 2.​ 燃料的燃烧计算 MACROBUTTON MTEditEquationSection2 Equation Chapter (Next) Section 1 3.​ 输运现象 MACROBUTTON MTEditEquationSection2 Equation Chapter (Next) Section 1 REF _Ref224634539 \r \h [5] REF _Ref224654757 \r \h [7][10] 输运什么呢？质量、动量、能量。The subject of transport phenomena includes three closely 4.​ 化学动力学基础 MACROBUTTON MTEditEquationSection2 Equation Chapter (Next) Section 1 5.​ 燃烧学基本方程 MACROBUTTON MTEditEquationSection2 Equation Chapter (Next) Section 1 任何一门成熟的学科都有它自己的数学模型体系，它能够在数学上描述这门学科所涉及的所有特征。人们通过解方程就可以预测这门学科所涉及的所有现象，比如在天体力学中通过解经典力学方程，就能确定行星（如海王星）的轨道；在分子物理中通过解薛定谔方程，就可以确定分子光谱。 这章介绍燃烧学基本方程。它是在流体力学方程基础上得到的。The dynamics and thermodynamics of a chemically reacting flow are governed by the conservation laws of mass, momentum, energy, and the concentration of the individual species. In this chapter, we shall first present a derivation of these conservation equations based on control volume considerations. 6.​  7.​ 预混可燃气着火理论 MACROBUTTON MTEditEquationSection2 Equation Chapter (Next) Section 1 8.​ 层流预混可燃气火焰传播理论 MACROBUTTON MTEditEquationSection2 Equation Chapter (Next) Section 1 9.​ 非预混燃烧 MACROBUTTON MTEditEquationSection2 Equation Chapter (Next) Section 1 10.​ 火焰稳定 MACROBUTTON MTEditEquationSection2 Equation Chapter (Next) Section 1 这一章与第6章的着火相对，考虑熄火问题。 11.​ 湍流燃烧 MACROBUTTON MTEditEquationSection2 Equation Chapter (Next) Section 1 12.​ 液体燃料燃烧 MACROBUTTON MTEditEquationSection2 Equation Chapter (Next) Section 1 remains unknown. 13.​ 固体燃料燃烧 MACROBUTTON MTEditEquationSection2 Equation Chapter (Next) Section 1 人类燃烧燃料的历史： 木材→煤炭→石油→煤炭→生物质。 14.​ 燃烧污染 15.​ 燃烧技术、燃烧装置 15.1.​ Overview[15] A burner is a device for safely controlling the combustion reaction. It is typically part of a larger enclosure known as a furnace. A process heater is any device that makes use of a flame and hot combustion products to produce some product or prepare a feed stream for later reaction. Examples of such processes are the heating of crude oil in a crude unit, the production of hydrogen in a steam–methane catalytic reformer, and the production of ethylene in an ethylene cracking unit. A boiler is a device that makes use of a flame or hot combustion products to produce steam. The furnace is the portion of the process unit or boiler encompassing the flame. The radiant section comprises the furnace and process tubes with a view of the flame. In contrast, the convection section is the portion of the furnace that extracts heat to the process without a line of sight to the flame[15]. 15.1.1.​ The Burner[15] 图 14‑1A typical industrial burner. The typical industrial burner has many features, which can be classified in the following groups: air metering, fuel metering, flame stabilization, and emissions control. A burner is a device for safely controlling the combustion reaction. Diffusion burners supply most of the heating duty in refinery and boiler applications; therefore, we discuss them first. 图 14‑1 shows the main features for accomplishing this. The particular version of burner shown in 图 14‑1 is a natural draft burner. That is, a slight vacuum in the furnace (termed draft — 0.5 in. water column below atmospheric pressure is a typical figure) and a relatively large opening (burner throat) allow enough air to enter the combustion zone to support the full firing capacity. The diffusion burner comprises a fuel manifold, risers, tips, orifices, tile, plenum, throat restriction, and damper. Each diffusion burner type may differ in detailed construction, but all will possess these main functional parts. We discuss each in turn. The Fuel System About Fuels Fuel Metering Turndown Burners operate best at their maximum capacity. One measure of the flame stability of a burner design is the turndown ratio. The turndown ratio is the ratio of the full firing capacity to the actual firing capacity. The maximum turndown ratio is the max/min firing ratio. The turndown ratio is higher if one modulates the air in proportion to the fuel. If the air dampers are manually controlled, then one is interested in the maximum unmodulated turndown ratio, because this is the more conservative case. A typical maximum turndown ratio for premix burners is 3:1. Diffusion burners often have turndown ratios of 5:1 without damper modulation, i.e., leaving the damper fully open despite lower fuel flow. One typically achieves 10:1 turndown ratios with automatic damper and fuel modulation. Multiple burner furnaces usually require a turndown ratio of somewhere between 3:1 and 5:1 with the air dampers fully open. To achieve greater turndown for the unit as a whole, one isolates some of the burners (fuel off, dampers closed). Turndown is easiest for a single fuel composition. Multiple fuel compositions always reduce the available pressure for some fuels and reduce the maximum turndown ratio. The Air System The Flame Holder Stabilizing and Shaping the Flame Controlling Emissions 15.1.2.​ Archetypical Burners When taxonomists classify things, they speak of slots and filler. Slots are the classes or categories, and filler is the stuff that populates the class. With respect to major considerations that affect burner design, we shall list five: • Fuel state: – Gas – Liquid – Solid • Flame shape: – Round – Flat • Fuel–air mixing strategy: – Fuel and air premixed (premix burner) – Separately metered fuel and air (diffusion burner) • Firing orientation – Upfired (the burner fires from the floor upward) – Downfired (the burner fires from the roof downward) – Side-fired (the burner fires from the wall sideway) • Emissions – The burner design reduces combustion-related emissions. – The burner design has no special features for reducing combustion related emissions. 表 14‑1Burner Sampling for One Manufacturer These five characteristics generally fix the burner design, and they will define an archetypical burner. Neglecting solid-fired burners for now (e.g., wood, municipal solid waste, pulverized coal, etc.), each of the above categories has two possibilities, except for firing orientation, which has three. This leads to 24·3 = 48 different slots. However, as is typical, not every slot has a filler, and some burner models fill more than one slot. For our purposes, about a dozen burner types are of importance. We should add that there are many kinds of esoteric designs for special reactions, but as regards traditional fuel–air combustion, these categories will do. Table 2.1 shows the slots and how one burner manufacturer has chosen to fill them. Round-Flame Gas Diffusion Burners Round-Flame Gas Premix Burners 图 14‑2A gas premix floor burner. (Courtesy of the American Petroleum Institute, Washington, DC.) Flat-Flame Gas Diffusion Burners Flat-Flame Premix Burners Flashback Use of Secondary Fuel and Air Round Combination Burners In some facilities, fuel oil can be a significant fuel stream. Normally, a refinery will want to burn as heavy a fuel as possible because other liquid fuels have greater value (e.g., transportation fuels for automobiles, trucks, and aviation). When sold commercially, fuel oils are widely available and graded as either number 2 or 6, with intermediates formed by blending. Fuel oil 2 is similar to automotive diesel. Fuel oil 6 is much heavier (also called residual fuel oil or, archaically, Bunker C oil). Marine and stationary boilers and some process heaters burn this fuel. Sometimes, the liquid fuel comprises rejected oil from other processes (waste oil) in whole or part. One can also burn pitch — a nondescript fuel from a variety of sources that is solid at room temperature. One must heat these fuels to reduce their viscosity in order for them to burn efficiently. Heavy liquid fuels do not atomize well even under pressure (so-called mechanical atomization), so fuel guns make use of pressurized steam to produce the requisite atomization. Mechanical atomization is sufficient for light oils such as fuel oil 2. Sometimes, light liquid fuels use compressed air for atomization. This is the case if steam atomization could be detrimental or there is insufficient fuel oil pressure for mechanical atomization. For example, light naphtha fractions can prevaporize in the fuel oil gun. Prevaporization is unwanted because it leads to slug flow in the fuel gun, that is, alternate slugs of liquid and gaseous fuel going to the burner. This causes erratic flow and performance. 图 14‑3A flat-flame diffusion burner. Radial orifices admit fuel through the center pipe, while combustion air flows through the outer pipe. Unlike premix designs, this radiant wall burner cannot flash back. The design accommodates high forced draft air preheat applications. 图 14‑4Wall-fired diffusion burners in operation. The photo shows an ethylene cracking furnace equipped with John Zink Model FPMR burners. The process tubes (right) are receiving heat radiated from the burner firing along the wall. (Photo courtesy of John Zink LLC, Tulsa, OK.) 图 14‑5 A flat-flame premix burner. The flame heats the refractory, which in turn radiates heat to the process tubes inside the furnace. Secondary air allows for a higher capacity, as the eductor need not inspirate all of the combustion air. Also shown is a secondary fuel nozzle at the burner tip. Some burners do not have all these features. 图 14‑6Venturi section of a premix burner. The Venturi (more generically, an eductor) comprises an inlet bell, throat, and expansion section. The fuel jet induces a low-pressure zone along the jet surface. The surrounding atmospheric pressure pushes air into the low-pressure zone. The fuel and air mix and exit the venturi toward the tip outlet. 图 14‑7 An oil gun. Steam vaporizes oil droplets allowing for uniform combustion. Practitioners use the term oil gun to refer to the liquid fuel delivery and atomization assembly. 图 14‑7 shows a typical design. Very often, one burns fuel oil and gas together (in so-called combination burners). This is sometimes to add fuel flexibility — perhaps the gas and the liquid fuel are available in different seasons. However, the more typical practice is to use the less expensive heavy oil with the gas fuel serving to make up the required process heat. Thus, both fuels fire simultaneously. A combination burner is a gas-fired burner augmented with a fuel oil gun. 图 14‑8shows one common arrangement. The typical combustion scenario is a single fuel oil gun in the center of the burner with gas firing at the periphery. When both fuels fire at once, flame lengths tend to be longer than when either fires alone. This is due to the peripheral combusting gas reducing the available oxygen for the fuel oil stream. To minimize (but not eliminate) this effect, separate air registers provide individualized airflow to each zone. 图 14‑8 A combination burner. John Zink Model PLNC combination gas–oil burner. One may fire the burner on gas only, oil only, or both. (Rendering courtesy of John Zink LLC, Tulsa, OK.) Burner Orientations Upfired Downfired Side-Fired Balcony Fired Combination Side and Floor Firing 15.2.​ Archetypical Process Units[15] Boilers, process heaters, and reactors comprise three main categories of process units. One may further differentiate among them as follows. 15.2.1.​ Boilers A boiler is a device for generating steam. There are two main configurations for fired units: firetube and watertube. 15.3.​ 气体燃料燃烧技术及实验装置 15.4.​ 液体燃料燃烧技术及实验装置 15.4.1.​ 燃油喷嘴 15.4.2.​ 配风器 15.4.3.​ 加力燃烧室 燃烧室和加力燃烧室. http://www.hudong.com/wiki/%E5%8A%A0%E5%8A%9B%E7%87%83%E7%83%A7%E5%AE%A4 在加力发动机上向燃气或风扇后气流喷油点火燃烧以提高气流温度用以短期内增大发动机推力的部件。加力燃烧室由扩压器、点火器、喷嘴、火焰稳定器、防振隔热屏和筒体组成。进入加力燃烧室的气体首先在扩压器中减速，然后与喷嘴喷入的燃油掺混形成油气混合气。为使燃油浓度在整个加力燃烧室中有良好的分布，一般采用几十个或几百个离心式或直流式喷嘴喷油。这些喷嘴装在几个供油圈上。油气混合气流过火焰稳定器（一般采用V形槽式）后,形成回流区，使局部气流流速降低以利于燃烧，同时另一部分燃油直接喷到火焰稳定器附近，以便在火焰稳定器后产生富油区，提高燃烧的稳定性。流过火焰稳定器的油气混合气经点火器点着形成稳定的点火源，用以点燃火焰稳定器附近的混合气。接着已燃的灼热燃气向前回流，点燃后续的油气混合气。因此加力燃烧室内的油气混合气，一经点燃后，点火器即可停止工作。只要气流的压力、流速、温度和油气比配合得当，燃烧就能循环稳定地进行下去。油气比过大或过小，均能造成加力燃烧室熄火。由于加力燃烧室内气流的压力低、流速高，点燃的混合气要在较长的筒体内才能完成燃烧过程，现代加力燃烧室中燃油的含热量只有85％～90％可以转变为有用的热能，其余部分或因燃油雾滴来不及燃烧而排出发动机，或通过筒体散热而损失掉，因此提高加力燃烧效率对于降低耗油率有重要的意义。此外，加力燃烧室中的气流还会出现强烈的压力振荡，这种现象称为振荡燃烧。振荡燃烧会引起结构零件振动、筒体过热熄火，甚至加力燃烧室损坏等。因此通常需要在加力燃烧室上采取防止燃烧振荡的措施，如安装多孔波纹形的防振隔热屏等。加力燃烧室中的零件均用耐高温合金制成。 15.5.​ 固体燃料燃烧技术及实验装置 15.5.1.​ 锅炉 15.6.​ 旋流燃烧 图 14‑9 Schematic diagram of processing leading to CRZ formation [1]: (1) tangential velocity profile creates a centrifugal pressure gradient and sub-atmospheric pressure near the central axis; (2) axial decay of tangential velocity causes decay of radial distribution of centrifugal pressure gradient in axial direction; (3) thus, an axial pressure gradient is set up in the central region towards the swirl burner, causing reverse flow.[20] The use of swirl-stabilised combustion is widespread, including power station burners, gas turbine combustors, internal combustion engines, refinery and process burners [1]. The mechanisms and benefits of swirl stabilised combustion are well documented and depend in most instances on the formation of a central toroidal recirculation zone（CRZ） which recirculates heat and active chemical species to the root of the flame, allows flame stabilisation and flame establishment to occur in regions of relative low velocity where flow and the turbulent flame velocity can be matched, aided by the recirculation of heat and active chemical species [1,2]. The situation can be explained based on the momentum balance in the radial direction as follows where fc denotes the centrifugal force and w the azimuthal velocity.These processes are illustrated in 图 14‑9and arise as follows: – Swirling flow generates a natural radial pressure gradient due to the term w2/r. – Expansion through a nozzle causes axial decay of tangential velocity and hence radial pressure gradient. – This in turn causes a negative axial pressure gradient to be set up in the vicinity of the axis, which in turn induces reverse flow and the formation of a CRZ. – Where the tangential velocity distribution is of Rankine form [1] (i.e. free/forced vortex combination), the central vortex core can become unstable, giving rise to the PVC phenomena. – The formation of the CRZ is thus dependent on the decay of swirl velocity as swirling flow expands. 15.6.1.​ 旋流强度 通常用旋流强度(又称旋流数)来表征流体旋转强弱的程度，用无量纲数 s 来表示。旋流强度定义为切向旋转动量矩M 和轴向动量I与特征尺寸 r0 乘积之比，即： MACROBUTTON MTPlaceRef \* MERGEFORMAT (8.72) 其中切向旋转动量矩为 MACROBUTTON MTPlaceRef \* MERGEFORMAT (8.73) 轴向动量I 等于 MACROBUTTON MTPlaceRef \* MERGEFORMAT (8.74) 式中 和 为任意横断面的轴向速度和切向速度； p为任意横断面的静压力； R为喷嘴出口半径。 使气流旋转的主要有三种：使气流(或部分气流)切向进入圆柱形通道，在轴向管流中放置导向叶片，用转动叶片\叶栅等机械装置使气流旋转。 15.6.2.​ 旋转射流扩散火焰 根据旋转射流流场的特征，旋转射流扩散火焰可以分为两类：弱旋转射流扩散火焰，强旋转射流扩散火焰。 当旋流强度小于一定值时，轴向速度到处为正值，不会出现轴向逆流，即不存在回流区的旋转射流叫做弱旋转射流，在这种条件下产生的火焰称为弱旋转射流扩散火焰。弱旋转射流根据轴向速度分布有两种形式，一种是旋流强度很小，轴向速度分布与自由射流相仿，呈高斯型，并具有相似性；另一种是当旋流强度增加到某一值时，轴向速度最大值离开射流轴线，而形成双峰形速度分布，如果再增加旋流强度，就会开始产生回流。 弱旋转射流扩散火焰几乎在整个火焰长度上，均有比较冷的核心区存在，而反应区处于冷核心区和环境空气流之间的某区域内。弱旋转射流扩散火焰的应用范围并不广，因为它没有稳定火焰的特征。 当旋转射流的旋流强度增加时，沿轴向的反向压力梯度大到足以发生反向流动，并建立起内部回流区，这时的旋转射流叫做强旋转射流。所产生的火焰称为强旋转射流扩散火焰。这种具有回流区的旋转射流在稳定火焰方面起着重要作用，在燃烧技术中应用很广。右图为s =1.57时的强旋转射流流线图。回流区长度、宽度随旋流强度的增加而增大。 强旋转射流的轴向u和径向速度v 按1/x衰减，切向速度w 按1/x2规律衰减，压力p按1/x4规律衰减。而弱旋转射流轴向u的衰减随旋流强度的增加而加快，切向速度w的衰减与旋流强度没有显著的关系。 由实验得出，大多数情况下对强旋转射流，当x/d0 > 20时旋转运动基本消失，而对弱旋转射流，当x/d0 > 10时旋转运动就已基本消失。 研究表明，附加的扩口和喷嘴的阻塞结构（圆管或圆盘）对旋转射流的流动结构有较大的影响。喷嘴加装扩张段后，可以增加回流区尺寸和回流量。 旋转射流扩散火焰大体上有三种形式：（1）旋流强度很低的扩散火焰。外形与自由射流扩散火焰类似；火焰在喷口一定距离处稳定；由于气流旋转，射流膨胀，卷吸空气混合加强，使燃烧速度加快；与自由射流扩散火焰相比，旋转射流火焰长度要短一些，宽一些；火焰前沿面呈波动状，随着湍流强度的增加，与自由射流火焰的差异明显增大。（2）中等或高的旋流强度下，由于产生了回流区，增加了火焰的稳定性，使着火点靠近喷口，甚至在扩张段内就形成了火焰。由于旋流强度大，射流扩张相应加大，卷吸量增加，混合更强烈，燃烧强度更高，结果形成更短、更宽的火焰。（3）旋流强度更高，并具有扩张段时，火焰将贴在扩张段及炉壁上，呈平面火焰；此时喷口的几何形状对径向贴壁流动的影响很大；如果采用喇叭形、大张角、短长度、发散型喷嘴，甚至在中等的旋流强度水平下，就能产生平面火焰。 Based on swirl number, the swirl flows are classified into weak, medium and strong swirl. If swirl number is less than 0.3 it is usually classified as weak swirl and if it is between 0.3 and 0.6 it is called medium swirl and if the swirl number is greater than 0.6, it is called strong swirl [9]. The recirculation zone geometry is a direct function of swirl number [3]. Study on the effect of various parameters on flow development behind vane swirlers. International Journal of Thermal Sciences 47 (2008) 1204–1225 It is known that the inner recirculation zone is well defined for swirl numbers exceeding 0.6. In typical industrial combustors, the swirl number is generally chosen close to this value P. Palies, D. Durox, T. Schuller, S. Candel. The combined dynamics of swirler and turbulent premixed swirling flames. Combustion and Flame 157 (2010) 1698–1717 However, because the Bragg criterion says that the primary zone should be as short as possible, S' between 0.6 and 1.0 would appear to be optimal. Because the hub-to-tip ratio of the axial swirler will likely be in the range 0.7-0.9, it can be estimated from Eq. (9.48) that, for a swirl number S' = 0.6-1.0, a vane angle in the range 35 to 50 deg will be required. Jack D. Mattingly, William H. Heiser, David T. Pratt. Aircraft Engine Design. Second Edition. AIAA EDUCATION SERIES J. S. Przemieniecki Series Editor-in-Chief.American Institute of Aeronautics and Astronautics, Inc.2002 15.6.3.​ 涡核进动（Precessing Vortex Core） 15.7.​ 内燃机 15.7.1.​ 汽油机 15.7.2.​ 柴油机 15.8.​ Gas turbine(燃气透平) combustor[17][18] An important distinction of gas-power engines used for classification purposes is whether they operate utilizing intermittent or continuous combustion. Continuous fluid flow machines such as the basic gas turbine unit shown in Figure 12.1 consist of separate compressor-combustor-turbine components. Windmills are considered by many to be forerunners of today's gas power turbomachines. Historically, windmills were used by different cultures throughout the world, including that of ancient China. Hero of Alexandria, Greece, constructed a steam turbine device that was driven by hot flue gases rising from an open fire. The idea of an efficient power-generating gas turbine machine was envisioned during the Age of Steam, but the earliest recorded patent for a gas turbine was filed by the Englishman John Barber in 1791. By the late 1930s, successful elements needed for an economical gas turbine began to become available. Useful propulsion machinery has resulted from an availability and compatibility of both suitable fuels and engines, a thesis repeatedly stated throughout this text. In addition, an application or need for a particular fuel-engine combination often will exist; manned flight provided an impetus for gas turbine engine development. The first practical aircraft gas turbine engines appeared during the 1940s, although experimental machinery was operated a decade earlier. Work begun in the early 1930s resulted in his Wl, a flying engine that operated in 1941 and produced 634 N (859 ft) of thrust. His original unit was built by Rover but, by 1943, Rover was taken over by Rolls-Royce. Several American and German companies also developed and built early jet engines; however, only a few were operational by the end of World War II. Military use of jet engine aircraft was common by the end of the Korean War, and the first commercial use of a jet engine occurred in 1953. It was not until the 1960s, however, that jet engines entered into satisfactory commercial use. After the 1970s, aircraft-derivative gas turbines began to find a variety of new applications, including marinized aircraft designs for ship propulsion, hovercraft applications, and industrialized designs for stationary power generation. Many factors helped to slow development of a reliable gas turbine, including the low compressor and turbine component efficiencies of early designs, lack of suitable materials able to withstand locally high temperatures developed in hot sections resulting from continuous combustion, and unacceptably large total stagnation pressure loss across the combustor. Worldwide gas turbine industries today manufacture civilian as well as military power plants for air, land, and sea applications