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循环流化床锅炉原理讲义提要翻译版

循环流化床锅炉原理讲义

Work Guidance Book of Principle of CFB

boiler

第一章、概述

Chapter 1 General

第一节什么叫循环流化床

Section 1: what is the circulating fluidized bed boiler?

采用循环流化床燃烧技术，燃用固体燃料的锅炉就是循环流化床锅炉。固体颗粒（燃料、底渣、循环灰、石灰石、砂子等）在炉膛内以流态化的方式运动，被流化风带走的部分颗粒经分离器分离，送回炉膛循环燃烧。炉膛内的颗粒浓度高，燃烧、传质、传热剧烈，温度分布均匀。

The circulating fluidized bed boiler (CFB boiler) is a kind of boiler which utilizes the combustion technology of circulating fluidized bed, which is to fire the solid fuel. The solid particles (fuel, bottom ash, circulating ash, limestone, sand, ect.) are moving in the way of fluidized state in the furnace. The partial particles taken away by fluidized air are separated by separators, and then return back to the furnace for circulating combustion. In the furnace, particle density is high, the distribution of temperature is proper, and combustion, heat transfer, and material circulation are good.

循环流化床锅炉的工作过程大致为：燃料及石灰石脱硫剂经破碎至合适粒度后，由给煤机和给料机从流化床燃烧室布风板上部给入，与燃烧室内炽热的沸腾物料混合，被迅速加热，燃料迅速着火燃烧、石灰石则与燃料燃烧生成的SO2反应生成CaS04(石膏)，从而起到脱硫作用。燃烧室温度控制在850℃左右。在较高气流速度的作用下，燃烧充满整个炉膛，并有大量固体颗粒被携带出燃烧室，经高温旋风分离器分离后，一部分热炉料直接送回流化床燃烧室继续参与燃烧；另—部分则送至外置床换热器，在外置床换热器中与受热面和空气进行热交换，被冷却至400～600℃后，经送灰器送回燃烧室或

排出炉外。经旋风分离器导出的高温烟气，在尾部烟道与对流受热面换热后，通过布袋除尘器或静电除尘器，由烟囱排出。

Generally, the working process of CFB boiler is that after fuel and limestone desulphurizer are crushed into proper particle sizes, they are conveyed to the combustion chamber by coal feeders and material feeders from the upper part of air distributor, and then they are mixed with red-hot boiling material to be heated up rapidly. Thus, fuel catches fire quickly and burns, limestone reacts with SO2, which fuel burns with limestone and generates, to produce CaS04 that can have the desulphurizing function. The temperature of combustion chamber should be controlled to about 850℃. Under the influence of higher air flow, the combustion is full in the whole furnace, and a lot of solid particles have been carried out of the combustion chamber and are separated by high temperature cyclone separator. And then one part of heated boiler material is directly returned to the combustion chamber to continuously burn, and the other part is sent to the heat exchanger of external bed and exchanges heat with the heating surface and air in the external bed heat exchanger, where it is cooled to 400～600℃, and then through the ash conveyer it is sent back to the combustion chamber or is discharged outside the boiler. After the high temperature flue gas emitted by the cyclone separator exchanges the heat with convection heating surface at the backpass, it is emitted from the stack by the bag filter and the electrostatic precipitator.

第二节循环流化床一些基本名称术语

Section 2: some basic technical terms of the CFB boiler 床料bed material

锅炉运行过程中，在炉膛及循环系统（分离器，立管，回料系统等）内燃烧或载热的固体颗粒，称为物料。

During running of the boiler, the solid particles, which carry over heat or burn in furnace or in the circulating system (separators, upright pipes, and material-returning system, etc.), are called the bed material.

● 堆积密度和颗粒密度

Tapping /bulk/pack density and particle density

将固体颗粒不加约束的自然堆放时单位体积的质量称为颗粒的堆积密度，用d

ρ来表示，单位为3/kg m ；单个颗粒的质量与其体积的比值称为颗粒密度或真实密度，用

p ρ表示，单位为3/kg m 。

When the particles are heaped naturally and unrestrictedly, the mass of the unit-volume is called particle tapping density, which is expressed by d ρ, and its unit is 3/kg m . The ratio of the mass of unit particle and its volume is called the particle consistence or actual consistence, which is expressed by

p ρ, and its unit is 3/kg m . 比例: proportion 比值 ratio 比

率：rate

● 密相区

Dense region

在流化床锅炉下部，颗粒浓度较大，这部分区域称为密相区，密相区内沿高度方向浓度逐渐降低。循环流化床锅炉中，一般定义密相区低于二次风喷口高度，密相区的空隙率为0.7左右。比电阻 resistivity

At the lower part of the CFB boiler, the particle density is high. So this area is called the dense region. The density in the dense region is slowly reduced along the height. In the CFB boiler, generally the dense region is defined below the height of the secondary air spout. The gap rate of dense region is about 0.7.

● 稀相区 Dilute region

在流化床锅炉炉膛上部，气流中粒子浓度较低，空隙率为0.85~0.99，称为稀相区，稀相区内颗粒浓度比较均匀，沿炉膛高度颗粒浓度变化比较缓慢。循环流化床锅炉中，一般定义稀相区为锅炉下部锥段以上直段500mm 以上为稀相区。

At the upper part of the furnace of CFB boiler, the particle density is low in the airflow, and the gap rate is 0.85~0.99. So this area is called the dilute region where the particle

consistence is comparatively even. The changes of the particle density along the height of furnace are slow. In CFB boiler, generally the dilute region is defined that it locates at above 500mm of straight section which is above conical section at the lower part of boiler.

● 过渡区

Transition region

在流化床锅炉密相区和稀相区之间，颗粒浓度处于沿高度快速变化状态，存在比较大的扬析与夹带现象，称为过渡区。

The particle density between the dense and the dilute region of CFB boiler is in the rapid changing state with the height, and there exist phenomena of obvious elutriation and carrying over in this area where is called the transition region.

● 流化速度

● Fluidization speed

流化速度一般是指假设床内没有床料时空气通过炉膛的速度，因此也叫空塔速度或表观速度。用

0u 表示，单位为/m s ，即： 0Q

u A = （1－7）

式中，Q 为空气或烟气体积流量，3/m s 。A 为炉膛截面积，2m 。

Generally, assuming that there is no material on the bed, fluidization speed is the speed which air passes through the furnace. Therefore it is also called the empty tower velocity or the apparent speed. It is expressed by

0u , and the unit is /m s , that is : 0Q

u A = （1－7）

In above formula, Q is the volume-flow of air or fuel gas, 3/m s .A is the cross-section

of the furnace.,2

m .

第三节循环流化床技术的特点

Section 3: technical characters of CFB

●燃烧特点

●Combustion characters

1）低温动力控制燃烧

1) Low temperature dynamical control combustion

2）高速度、高浓度、高通量的固体物料流态化循环过程

2) C irculating process of solid material fluidized state with high speed, high density,

and high flux.

3）高强度的热量、质量和动量传递过程

3) The transfer process of high intensity heat, mass and momentum

●优点

●Advantages

1）燃料适应性广

1)the wide applicability

2)燃烧效率高the high efficiency of combustion

2）高效脱硫the high efficiency of desulphurization

3）NOx排放量低the low emission of NOx

4）调峰性能好the good performance of peak adjustment

5）燃料制备、给煤系统简单the easy preparations for fuel and the simple feeding coal system

此外，CFB锅炉还具有传热系数高、可以压火运行、不存在炉内和受热面结渣、

不会灭火放炮等优点，其它污染物如CO、HCl、HF等的排放量也很低。

In addition, CFB boiler have the advantages of the high coefficient of heat transfer, banking fire running, no slagging inside the boiler and at the heating surface, no flameout and explosion, etc. the low emission of other contaminations, such as: CO、HCl、HF etc.

●缺点

●Disadvantages

1）烟风阻力大，厂用电率高 the strong resistance of fuel gas and air, the high power consumption of the auxiliary power

2）N

2O排放较高 the high emission of N

3）需大量敷设耐磨耐火浇筑料 A lot of wear-resistant and refractory material is needed to be used.

●一些新问题some new following problems:

1）由于设计和施工工艺不当导致的磨损问题 the abrasion problems caused by improper design and construction workmanship (wear and tear 指

金属磨损)

2）飞灰含碳量高的问题 the high carbon content of fly ash

3）底渣冷却系统的问题 the bottom ash cooling system

4）炉膛、分离器以及回料系统及其之间的膨胀和密封问题

The expansion problem and sealing problem among the furnace, separator, material returning system

5）炉膛温度偏高以及石灰石选择不合理导致的脱硫效率降低问题

The desulphurization efficiency is reduced because of improper limestone selection and high furnace temperature.

第四节 CFB锅炉系统及其组成

Section 4 CFB boiler systems and its constitution

循环流化床锅炉系统主要包括锅炉本体系统和锅炉辅助系统两部分。锅炉本体系统主要包括燃烧系统与汽水系统等。锅炉辅助系统包括煤与石灰石系统、烟风系统、灰处理系统、锅炉控制系统、点火系统等。下图为循环流化床锅炉系统及其组成示意图。

CFB boiler system includes mainly two parts, that is, boiler proper system and its auxiliary system. The boiler proper system mainly includes combustion system and steam & water systems. The boiler auxiliary system mainly includes coal and limestone systems, fuel gas and air systems, ash handling system, boiler control system, ignition system, etc. The following figure is CFB boiler system and its schematic diagram:

图循环流化床锅炉系统及其组成示意图

Figure 4 CFB boiler system and its schematic diagram

1、煤仓；

2、炉膛；

3、分离器尾部烟道；

4、返料器；

5、外置式热交换器；

6、给煤机；

7、冷渣器；

8、石灰石仓；9、流化风室；10、汽包；11、对流过热器；12、省煤器；13、空气预热器；14、电除尘器；15、引风机；16、烟囱；17、一次风；18、下二次风；19、上二次风；20、石灰石风机

1. Coal bunker

2. Furnace

3. Backpass of separators

4. Material-returning device

5. External heat exchanger

6. Coal feeder

7. Slag cooler

8. Limestone silo;

9. Fluidized air chamber; 10. steam Drum; 11. convection superheater 12.Economizer; 13. Air preheater; 14. Electrostatic precipitator (ESP); 15. I.D. fan; 16. Stack 17. Primary air;

18. Lower secondary air; 19. Upper secondary air; 20. Limestone fan;

1）、炉膛。也叫流化床燃烧室，是供燃料燃烧的地方。由炉墙和水冷壁围成的空间，燃料在其内呈现流化状态燃烧。炉膛包括下部锥段和上部直段两部分，分为密相区、过渡区和稀相区。流化床燃烧室是流化床燃烧系统的主体,完成大约50％燃料释热量的

传递吸收过程。它既是一个燃烧设备，也是一个热交换器和脱硫、脱氮装置，集流化过程、燃烧、传热与脱硫、脱硝反应于一体。Membrane(膜试)

1). Furnace. It is also called the fluidized bed combustion chamber where the fuel burns. The fuel burns in the fluidized state in the chamber surrounded by the boiler walls and water wall. The furnace includes the lower conical section and the upper straight section, which are divided into t he dense region, transition region and dilute region. The CFB combustion chamber is the main part of CFB combustion system, and about 50% of heat release rate of the transferring and absorbing process of fuel finish in here. It is not only a combustion device, but also a heat exchanger, desulphurized and denitrogened device, and it integrates with the desulphurization process, combustion, heat transfer, desulphurization, and denitration.

炉膛底部是布风板，布风板上嵌有大量的风帽，风帽上开有许多小孔。布风板下

面是风室。布风板一方面保证一次风穿过布风板进入炉膛对炉内物料进行均匀流化，另

一方面将固体颗粒限制在炉膛布风板以上，将物料与风分隔开来，并对固体颗粒（床内

物料）起支撑作用。下图是典型的布风板结构图。

The bottom of furnace is an air-distributor on which a lot of air nozzles are embedded. There are many orifices opened on the air nozzles. An air chamber is under the air-distributor. The air-distributor not only makes the primary air pass through it and enter into the furnace to evenly fluidize material, but also restricts the solid particle to the upper air-distributor, separate the material from air, and have the support function to the solid particles (material within bed).The following figure is a typical structure of the air-distributor:

1—内管2—外罩3—环形底板

1—inner pipe 2---- external cover 3---annular base plate

图水冷布风板及钟罩式风帽

Figure Water-cooled distributor and bell glass air cap 风帽是保证床内物料正常流化和隔绝固体颗粒向风室倒流的关键部件，主要通过特殊的风帽及风帽小孔结构设计来实现。布风板及风帽设计的好坏直接影响床内颗粒的流化情况，它应当有一定的阻力以保证整个床面流化的均匀同时应尽量控制阻力不致过大以减小阻力损失，同时，风帽设计还特别强调防止炉膛内向风室的漏渣。从风帽的功能出发，实际采用的风帽有多种型式，如钟罩型、蘑菇型、猪尾型、T型、Γ型定向风帽等，目前应用最广泛效果相对较好的是钟罩型风帽（钟罩型风帽具体结构型式及尺寸还有许多差别和变种）。

Air nozzle is a critical part which ensures the normal material fluidization inside the bed and isolates the solid particles from flowing

reversal to the air chamber. This function is mainly realized through structure designs which have a special air nozzles and orifices on it. The design of air distributor and air nozzle influences directly the fluidized status inside the bed. Therefore, it should have some resistance to ensure the even fluidization of the whole bed surface and avoid increasing the resistance to reduce resistance loss. What’s more important, the design of air nozzle emphasizes to prevent from leaking slag from furnace to air chamber. The air nozzles applied are different types based on their functions, such as bell,mushroom type, pigtail type, T type, Γtype oriented air nozzle. Nowadays, the most widely used of air nozzles with the best effect are bell type (the specific structure and sizes of air nozzles with bell type have many difference and other types.) 大型CFB锅炉布风板及其下的风室往往由水冷壁管弯制而成，形成水冷风室和水冷布风板结构，以防止其高温变形（尤其是采用床下点火方式时）。

The air distributor of large-sized CFB boiler and the air chamber below it are often made by water wall tube bending. The structure of water wall air chamber and water-cooled air distributor are formed to prevent deformation in high temperature (especially when use below-bed ignition).

炉膛内燃料的燃烧以二次风入口为界分为两个区。二次风入口以下为大粒子还原气氛燃烧区，二次风入口以上为小粒子氧化气氛燃烧区。燃料的燃烧过程、脱硫过程、O的生成及分解过程主要在燃烧室内完成。炉膛下部锥段以下及炉内其它易磨NOx和N

损部位敷设耐火浇筑料，以保护受热面。

The combustion of fuels inside the furnace is divided into two zones with the boundary line of secondary air input. Below the secondary air input is reducing atmosphere combustion zone for big particle. Above the secondary air input is oxidizing atmosphere combustion zone for fine particle. The process of combustion, desulphurization, formation and decomposition of NOx and N2O is mainly finished in combustion chamber. The below part of conical section in the under part of furnace and other abrasion sections are covered with refractory to protect the heating surface.

炉膛上部一般还悬挂部分受热面（水冷壁、过热壁或再热壁），也有采用其它结构的受热面（Ω管、分隔墙）等，以吸收炉膛内燃烧释放的部分热量。

Some heating surfaces (water wall, superheated wall or reheated wall) are hanged on the upper side of furnace. There are also some heating surfaces that are other structures(Ω pipe, separating wall) to absorb partial heat released by furnace.

2）、分离器。有多种形式，常见的是高温绝热旋风分离器及汽（水）冷旋风分离器。它将被烟气从炉膛带出的未燃尽的燃料分离下来，让回料系统将其送回炉膛继续燃烧。

2) Separator. There is many types of separator. The most common are high temperature heat insulation cyclone separator and steam (water)-cooled cyclone separator. It separates big particle of the fuels which are not burnt out of flue gas from furnace and makes big particle sent back into furnace by material returning system to combust again.

分离器是循环流化床燃烧系统的关键部件之一。它的形式决定了燃烧系统和锅炉整体布置的形式和紧凑性，其性能对燃烧室的空气动力特性、传热特性、物料循环、燃烧效率、锅炉出力和蒸汽参数，对石灰石的脱硫效率和利用率，对负荷的调节范围和锅炉启动所需时间以及散热损失和维修费用等均有重要影响。国内外目前普遍采用的分离器有高温耐火材料内砌的绝热旋风分离器、水冷或汽冷旋风分离器。旋风分离器分离效率高，阻力较大，燃烧系统布置欠紧凑。早期CFB锅炉发展中曾出现过各种形式的惯性分离器，如百叶窗分离器、U型分离器、异型惯性分离器等，但经过实践证明，惯性分

离器由于分离效率低，虽然具有阻力小、燃烧系统布置紧凑的优点，用于CFB锅炉，会带来带负荷能力差、燃烧效率低、尾部受热面磨损大等重大缺陷，已经逐渐被淘汰。其它还有方形分离器、下排气旋风分离器等等对旋风分离器的不同变种型式，但最成熟可靠的仍然是传统结构的旋风分离器。

Separator is one of the essential parts in CFB boiler combustion system. Its formation totally influences the forms and cohesion of combustion system and the whole structure of boiler. Its performance has great influence on air dynamic characteristics ,heat transfer characteristics, material circulation, combustion efficiency, boiler rating and steam parameter, desulphurization efficiency and availability, adjusting scope of load, start-up time of boiler, heat elimination loss and maintenance expense. The separators used widely now in and abroad are heat proof cyclone separator, steam cooled or water cooled cyclone separator with high temperature fire proof material set inside. Cyclone separator has high separation efficiency, strong resistance, and its combustion structure needs more cohesion. There existed various inertial separators in the early stages of boiler development, such as dry screen, U type separator and bastard inertial separator, but it’s been proved that inertial separators, although with small resistance and coherent structure, have been fallen into disuse because of low separation efficiency which will bring bad load capability, low combustion efficiency and huge abrasion surface at the back end to the CFB boiler. Other variation types of separators are squareness separator, lower row cyclone separator, etc, but the most mature and reliable type is still cyclone separator with traditional structure.

3）、回料系统。布置在分离器下面，它的作用是将分离下来的燃料送回炉膛中继续燃烧，并保证流化内的高温烟气不经过返料装置短路流入分离器。返料装置既是一个物料回送器，也是一个锁气器。

3) Material returning system. It is installed below the separator and its effect is to send the separated fuel back to the furnace to be combusted again. It guarantees that fluidized hot fuel gas doesn’t flow into separator through material returning equipment. Material returning equipment is both material returning device and air lock device.

回料系统的正常运行对燃烧过程的可控性、对锅炉的负荷调节性能起决定性作用。如果回料系统作用失常，物料的循环燃烧过程建立不起来，锅炉炉膛内将失去大型循环灰对热量的携带和均匀分配功能，燃料释放的热量会大量集中在炉膛下部，造成运行床温超温，燃烧室内的燃烧工况变差，炉内受热面传热系数下降，难以吸收到额定负荷下需要的热量，锅炉将达不到设计蒸发出力。因此，回料系统的合理设计和运行是非常重要的。

The normal operation of material returning system plays a decisive role on controllability of combustion process and load adjusting performance of

boiler. If material returning system doesn’t effect normally, then the circulating combustion process can’t be established and the heat entrainment and uniform assignment of large sized circulating ash will be lost in furnace. The heat released by fuel will gather under part of furnace, leading to the over temperature of operation bed temperature, bad combustion condition in combustion chamber, descending of heat transfer coefficient of heating surface in furnace. Then the necessary heat in nominal load can’t be absorbed and the boiler can’t reach evaporative rating.

Therefore, the reasonable design and operation of material returning system is very important.

流化床燃烧系统中常用的返料装置是非机械式的。设计中采用的返料器主要有两种类型：一种是自动调整型返料器，如流化密封返料器；另一种是阀型返料器，如"L”阀等。自动调整型返料器能随锅炉负荷的变化，自动改变返料量，不需调整返料风量。阀型返料器要改变返料量则必须调整返料风量，也就是说，随锅炉负荷的变化必须调整返料风量。

Material returning equipment often used in CFB combustion system is not mechanical. There are mainly two types of material returning device: one is adjustment automatically, such as fluidized seal device, the other is Valve type material returning device, such as “L”. The automatic adjusting material returning device can change the amount of returning material with the changes of boiler load. It is unnecessary to adjust air flow of returning material. Valve type material returning device has to adjust air flow of returning material to change the amount of returning material. That’s to say, it needs to adjust the air flow of returning material with the changes of boiler load.

4）外置式换热器。

循环流化床锅炉可以带有外置换热器也可以不带外置换热器，国内135MW级以下容量的CFB锅炉均不带外置换热器。随着锅炉容量的增大和参数的提高，炉内需要布置更大比例的过热、再热受热面，而同时炉膛比表面积相对减小。因此，对于200MW及以下容量等级CFB锅炉，可以选择不采用外置热交换器结构而在炉内布置屏式受热面或采

用外置热交换器设计结构。对于200MW~300MW级CFB锅炉，如果不带外置热交换器，炉内受热面将布置大量的屏式受热面，磨损的风险增大；而对于更大容量（如600MW级超临界）CFB锅炉，则必须采用外置热交换器以布置更多比例的过热、再热受热面。

4) External heat-exchanger

CFB boiler can be either accompanied with external heat-exchanger or not. None of the CFB boiler less than the capacity of 135MW in our country is accompanied with external heat-exchanger. With the increase of boiler’s capacity and parameters, super heated surface and reheated surface with larger proportions need to be installed inside the furnace. At the same time, specific surface area reduces relatively.So, to the boiler of 200MW or less than external heat-exchanger structure is not adopted here, but platen/pendant heating surface is installed. To the 200MW~300MW CFB boiler, abundant platen heating surfaces are installed on heating surface inside furnace if without external heat-exchanger. This will increase the risk of abrasion. While to the CFB boiler of larger capacity (600MW super critical), external heat-exchanger must be installed to assign more super heated and reheated surfaces.

外置式换热器的作用是，使分离下来的物料部分或全部（取决于锅炉的运行工况和蒸汽参数）通过其内布置的受热面，并将高温灰冷却到500℃左右，然后通过返料器送至床内再燃烧。外置换热器内可布置省煤器、蒸发器、过热器、再热器等受热面。外置换热器的实质是一个细粒子鼓泡流化床热交换器，流化速度0.3～0.45m/s,具有传热系数高、磨损小的优点。

The effect of external heat-exchanger is to make part or all separated material(depends on the operation condition of boiler and steam parameter) pass through the heating surface installed inside it and cools the high temperature ash to be around 500℃.Then send them back to bed to combust again through loop seal device. Some heating surface, like economizer, evaporator, super heater and reheater, can be installed inside the external heat-exchanger. The essential of external heat-exchanger is fine-grained bubbling fluidized bed heat-exchanger with fluidized speed 0.3～0.45m/s.Its advantages are high heat

exchanges coefficient and low abrasion.

采用外置换热器的优点如下：①可解决大型循环流化床锅炉床内受热面布置不下的困难；②为过热蒸汽温度和再热蒸汽温度的调节提供了很好的手段；③增加循环流化床锅炉的负荷调节范围；④增加同一台锅炉对燃料的适应性；⑤节约锅炉受热面的金属消耗量。

The advantages of adopting external heat-exchanger are as follows: 1. Solve the problem that there is not enough space of heating surface in large sized CFB boiler. 2. Provide good methods to super heated and reheated evaporative temperature adjustment.3.Increase the load adjustment scope of CFB boiler.4.Increase adaptability of the same boiler to different fuels.5.Reduce the metal consumption of boiler heating surface.

5）、CFB锅炉辅助系统

5) Auxiliary system of boiler

包括煤与石灰石制备与输送系统、烟风系统、灰渣处理系统、锅炉控制系统、

点火系统等

It includes preparation and transportation system of coal and limestone, flue gas system, ash slag handling system, boiler control system and ignition system.

第二章、CFB锅炉基本原理

Chapter 2 Basic Theory of CFB Boiler

固体颗粒的特性

Section 1 Characteristics of Solid Particle

1．颗粒平均粒径Average particle size of particles

对于宽筛分的颗粒群，如流化床锅炉入炉燃料、石灰石、床内物料、底渣、循环灰、飞灰等均是由大小不同形状各异的颗粒所组成的宽筛分颗粒，不同物料的破碎特性与破碎方式不同，成灰特性和分离器分离性能差异等，也会形成不同的颗粒群粒度构成。由于有关流化床的试验资料与计算公式中，颗粒尺寸往往是需要首先确定的重要参数，这就需要确定出一个能够在大小和性能上代表这些大小不同、形状各异、为数众多的宽筛分颗粒的平均直径。As to the coarse screening particle groups, such as CFB boiler fuel, limestone, material inside the bed, bottom slag, circulating ash, fly ash, etc., which are coarse screening particles constituted by particles with different sizes and shapes, because they are different in crushing characteristics and methods, ash formation characteristics and separating performance of separators,etc., can also form different granularity construction of particle groups. Due to the fact that particle size is always an important parameter needed to be defined firstly in test data and computational formula related to fluidized bed, it is necessary to make certain an average diameter which can represent these major coarse screening particles with different sizes and shapes in size and performance。

工程上一般由筛分确定固体颗粒的粒度分布并由此确定颗粒群的平均直径。主要有以下几种：In project, usually the granularity distribution of solid particle is defined by screening and the average diameter of particle groups is also defined in this way. Here are the main categories:

重量平均直径v d是各档粒径i d (所处相邻筛分孔径i d '

和1i

的平均值)与其重量

份额乘积的总和，即：Weight mean diameter v d is the product sum of each shelve

particle size i d (the mean value of surrounding screening mesh diameter i d ' and 1i d +' ) and its weight share,i.e.

1n v i i i d X d +==∑

其中，i X 是某一筛上残留物料的重量份额；i d 是该残留物所在筛孔直径与上一级筛孔

直径的算术平均值，1('')/2i i i d d d +=+

或i d =i d 是标准筛层数。Thereinto ,i X

is weight share of residue on a certain screen; i d is the arithmetic mean of screening mesh

diameter of this residue and the screening mesh diameter at the last grade , 1('')/2i i i d d d +=+

i d =i d is standard screening layer numbers.

当颗粒的比表面积（颗粒表面积与体积的比值）起重要作用时，可以采用比表面积平均粒径S d 。假设宽筛分颗粒各筛分档的颗粒球形度相同，可以推出：When the specific surface area of particle plays the main role, the mean particle size S d of specific surface area can be applied. Suppose the particle sphericity in deferent screening classifications of coarse screening particle is the same, we can conclude:

/S n i i i d X d +==∑

其含义是，利用此比表面积平均粒径S d 计算的颗粒群平均比表面积（,6/s v av p S d =Φ）与具有相同数值直径与球形度的单颗粒比表面积相等（

6/v p s S d =Φ）。It means, the mean specific surface area （,6/s v av p S d =Φ）of particle groups,

calculated by using this mean particle size S d of specific surface area, is equal to specific surface area of single particle with same diameter and spherical degree. （6/v p s S d =Φ）

工程应用中还常常用颗粒的中位径（

50d ）来衡量宽筛分颗粒群的粗细程度，其定义是，

假定有一筛网，颗粒利用其过筛时，筛上残留物与筛下物质量正好相等（即各占50％），

此筛网的筛孔直径即为颗粒的中位径。颗粒中位径的测定可以通过确定颗粒的粒度分布

d） of particles 后作图或拟合插值求得。In project usage, the median diameter（50

is often used to measure degree of finess of broad screening particle groups, its definition is , suppose there is a screen cloth, when particles passing through it, if the residue on the screen rightly is equal to the matter below the screen in quality(or each accounts for 50％), the screening mesh diameter of this screen cloth is the median diameter of particles. The measurement and definess to particle median diameter can be obtained via drawing diagrams or fitting interpolation after defining the particle granularity distribution.

2．颗粒的分类Classification of particles

根据固体颗粒在气体流化介子作用下流化特性不同，Geldart[1]将颗粒分为A、B、C、D四类，这种分类方法主要考虑了颗粒的粒径dp、颗粒密度ρs与气体密度ρg的密度差两种因素对流态化特性的影响，目前这种分类方法被流化床研究者广泛采用，错误！未找到引用源。为根据颗粒粒径和密度差进行的颗粒分类。科学的颗粒分类方法对了解颗粒的流态化特性行为有重要作用，因为对于不同类的颗粒，相同的流化条件可能得到完全不同的颗粒运动特性。错误！未找到引用源。列出了不同类型颗粒的特点。According to different fluidization characteristics of solid particle affected by gas fluidized meson, Geldart[2] classifies particle into four categories: A,B,C,D. This classification mainly considers the influence of the two factors as particle size dp,the density difference between particle density ρs and gas density ρg on fluidization characteristics and at present, it is widely applied by fluidized bed researchers. Table 1 is the particle classification in accordance with particle size and density difference. The scientific method of particle classification plays very important role in understanding the fluidization characteristics of particle, because to different kinds of particles, they may have completely different motion characteristics under the same fluidization condition. Table 1 also lists the characteristics of different kinds of particles.

表 1 A、B、C、D四类粒子的特点

Table 1 characteristics of the four kinds A、B、C、D of particle

粒度分布较宽的煤颗粒同时具有A颗粒和B颗粒的属性。气速较低时，它充分表现B颗粒的鼓泡特征；气速高时，煤颗粒中细粉特征占主导地位，它也可以是下部鼓泡流态化，而上部为湍流或快速流态化。The coal particles distributing quite widely have the properties of both particle A and particle B at the same time. When the air velocity is low, the bubbling features of particle B is fully displayed; and when the air velocity is high, the fine powder characteristics in coal particle will be dominant, it can be the under part bubbling fluidization, while the upper part is onflow or high velocity fluidization.