16对设计方法的快速检查

1、16quick check design methods对设 计方法的快速检查1 introduction 前言the design of pneumatic conveying systems is usually carried out on the basis of scaling data obtained from the pneumatic conveying of the material to be transported if previous experience of conveying a given material is not available, data is

2、 generally derived for the purpose by conveying the material through a test facility, as discussed in detail in the previous chapter most manufacturers of pneumatic conveying systems have such test facilities for this purpose.气力输送系统的设计通常是在从这种物料的 气力输送过程中获取的缩放数据的基础i】进行的。如果输送某种物料时没有以往经验可以利用，通常 耍在试验装置屮输

3、送这种物料以得到所需的数据，在前面的章节屮对此做了详细讨论。大多数气力输 送系统的制造商都有此等试验设施。if it is required to make a quick check on the potential of an existing system,or to provide a check on design proposals, there is little infoimation readily availablefor the engineer to use. pneumatic conveying does not lend itself to simple math

4、ematical analysis, and it is likely that many engineers would not be able to undertake such a task easily, particularly 讦 it were a low velocity dense phase system.如果需要对现冇系 统的潜力做快速检查，或提供冇关设计方案的检查，没有什么现成的资料可供工程师使用。气力 输送并不是容易的数学分析，很可能许多丁程师将无法腔任这样的工作，尤其对一个低速密相系 统。since pneumatic conveying systems tend

5、to have high power ratings, particularly for conveying in dilute phase suspension flow, it is useful to be able to obtain a rough estimate of air requirements at the feasibility stage of a project. most of the operating cost of a pneumatic conveying system is in the drive for the air mover if an est

6、imate can be made of the system air requirements, it is a simple matter to evaluate the operating cost in cents per ton conveyed to see if it is at an acceptable level before proceeding further.由于气力输送系统通常能耗高，特别是稀和悬浮流输送，在一个项冃的 可行性研究阶段能够获得空气需求的大略值是非常有用的。一个气力输送系统的大多数运行费用都是 花费在空气动力机械的驱动上。如果能估计出系统的空气要求，那

7、么算每吨输送的运行费用就简单了， 这样可以在进行下一步前看看它是否可以接受。1.1 methods presented b 前的方法a number of straightforward methods are presented that will allow a check to be made on the design of a pneumatic conveying system in a very short space of time, whether for a new or an existing system. horizontal and vertical section

8、s of pipeline and bends can all be accommodated, as well as dilute and dense phase conveying in some cases. for high pressure systems the influence of stepped pipelines can also be incorporated.现在冇一些简单的方法，可花费很少一点时间对气力输送系统的设计做个检 查，无论是新的还有已有的系统。水平和垂fi的管道部分以及弯头都可以容纳其小，某些情况下 稀相和密相输送都可以采川这些方法。対高压力系统，扩笛笛道

9、的影响也包括在莫中。three different methods are presented one is based on the value of the air only pressure drop for the pipeline, but this is strictly limited to dilute phase conveying only. another is based on the use of a universal set of conveying characteristics and the third uses the steady flow energy

10、 equation as a basis. both of these can be used for dilute and dense phase conveying, li而有三种不同的方法。一种是基丁管道的纯空 气压降值，但这严格限制为稀相输送。另-种是基于一套通用的输送特性，而第三种是以稳定流 动能量方程为基础。后面的两种既用于稀相输送，也可用于密和输送。1.2 potential accuracy潜在的准确度it must be emphasized that all three of these methods are strictly quick check methods an

11、d will provide only a first approximation solution. although some of the methods may appear to be mathematically correct, do not be killed into a false sense of security. there is no reference to conveyed material anywhere in any of the procedures in this respect reference to figures 4.16 and 4.18 w

12、ill bring any engineer back to reality with regard to the potential accuracy of these methods, whether for dilute or dense phase conveying.必须强调，所有这三种方法都是快速检查方法，只提 供一个近似的解决方案。虽然部分方法可能会显示出数学正确，但不要被虚假的安全所蒙蔽。这 些方法没冇在任何地方提及被输送的物料。在这方面，参考图4.16和图4.18,这将把任何工程师 带冋关于这些方法潜在准确性的现实，无论是稀相或密相输送。for a given materia

13、l to be conveyed it is possible that the accuracy of some of these quick check methods could be improved quite considerably. if conveying data is available for a particular material, fine tuning could be undertaken. constants relating to individual pipeline features such as bends, vertical lift and

14、pipeline bore could be changed or added once again it must be emphasized that the resulting models would only provide more reliable system design and checking information for the material being considered, and only for that particular grade of the material.对于一种给定的被输送物料,有町能在和当程度上提高这些快速检查方法的准确性。 如果能得到

15、特定物料的输送数据，可在此基础上进行微调。与单一管道特征，如弯头，垂直提升 和管径筹有关的常量可以更改或添加。必须再次强调，结果模型只会提供更可靠的系统设计和检 查所考虑物料的信息，并只能用于特定等级的物料。2 air only pressure drop method纯空气压降方法this method uses the value of the air only pressure drop for a pipeline as a basis for evaluating its conveying potential. this resistance due to the air is r

16、elated to the additional resistance resulting from the conveying of material. the pressure drop due to the air can be readily measured, or simply calculated for any pipeline by means of the equations presented in chapter 6.此方法以-条管道的纯空气压降为基础來评估英输 送潜力。由于空气导致的阻力与输送物料产牛的附加阻力有关。由于空气导致的压降易于测量, 或者根据第6章屮的公式

17、町对任何管道进行简单的计算。2.1 basic equations基础公式the ideal gas law relates the volumetric flow rate of the air to the pressure and temperature of the air, as considered in chapter 5. the volumetric flow rate can also be expressed in terms of the conveying line inlet air velocity and the pipelinebore. in most co

18、nveying situations the volume occupied by the conveyed materialcan be neglected in comparison with that of the air.如第5章介绍，理想气体定律显示了空气体积流 量与空气的压力和温度的关系。体积流量可川输送线入口气速和管径來表示。在大多数输送情况 下，被输送物料占用的体积与空气的体积相比可以忽略。these models, therefore, can be used quite reliably in gassolid flow situations.material flow r

19、ate can be introduced in terms of the solids loading ratio ofthe conveyed material. the solids loading ratio is a parameter that is often known approximately, and in these cases quite simple equations can be derived equating the variables.因此，这些模式可相当可靠的用于气-固流动情况。物料流量采用被输送物料固气比 的形式。人家都知道固气比是一个估计的参数，在这

20、些场合中，可从各种变量的等式中推导出很 简单的公式。2. 1.1 solids loading ratio固气比solids loading ratio, , is defined as the ratio of the mass flow rate of the material conveyed, to the mass flow rate of the air used to convey the material and this was first presented at equation 4.5:固气比c|)定义为被输送物料的质最流最与输送物料所用空气的质量 流量z比，第一次列出

21、是在公式4. 5中：(p = (dimensionless) (i)where nip = mass flow rate of material - ib/hand niv = mass flow rate of air lb/h这里加“=物料质量流量lb/hhia二空气质量流量-lb/hit is a dimensionless ratio and is a particularly useful parameter since its value remains constant along the length of a pipeline, regardless of the air p

22、ressure and conveying air velocity.这是无量纲的比值，也是一个特别有用的参数，i大1为沿管长这个值不变, 而不管空气压力或输送气速怎么变化。2.7.2 ideal gas law理想气体眾律air mass flow rate is not always a convenient parameter with which to work, and air flow rate is more usually expressed in volumetric terms. from the ideal gas law, for a steady flow situa

23、tion, however, one can readily be evaluated from the other, as first illustrated at equation 5.4:空气质量流量这个参数有的时候使用起來不方便，空气流 量更多的是川体积流量來农示。但是，根据理想气体圮律，在稳沁流动状态下，人们可以很容易 地在两者间进行换算，公式5.4首次阐明了理想气体定律：144 p v = m(i r twhere p = absolute pressure of gas ibf/in? v = volumetric flow rate ofgas at pressure ;p -

24、 fvyminnia - mass flow rate of gas - ib/minr = characteristic gas constant ft ibf/lb r and t = absolute temperature of gas 一 r =/°f + 4602.1.3 volumetric flow rule 体积流量这里p二气体绝对压力lbf/in2v=压力p下的气体体积流量-ft"/min=气体质量流量-lb/minr =气体常数ft lbf/lb r气体绝对温度r=r°f + 460volumetric flow rate is given

25、by:体积流量可用卜式计算:velocity，areaand for a circular pipe 对于圜管八c x鳥讪n .where c = conveying air velocity - ft/min 这里 c =输送气速-ft/minand d = pipe bore 一 ind =管径 -inthis is the actual volumetric flow rate. since air and other gases are compressible, volumetric flow rate will change with both pressure and tempe

26、rature 1( also means that the conveying air velocity will vary along the length of a pipeline a full explanation and analysis of this was included in chapter 5 on air requirements 这是实际体积流 量。由于空气和其他气体是町压缩的，体积流量将随压力和温度而变化。这也意味着沿管长输送气速 将有所不同。在第5章的“空气需求”中对此有完整的解释和分析。2.2 working relationships工作关系the thre

27、e equations presented above are exact equations, and so any combination of these equations will similarly produce precise relationships. although these equations include all the basic parameters in pneumatic conveying, they will not produce design relationships this is because they do not include th

28、e necessary fundamental relationships between material flow rate, pressure drop and conveying air velocily. combinations of equations 1 to 3, however, will produce equations that can be usefully used to check system designs. they will also provide a good basis for the inclusion of design relationshi

29、ps.上面介绍的三个公式是严格的等式，所以任意组合这些公 式都同样会产牛准确的关系。虽然这些公式包括了气力输送的所有基本参数，但它们不能提出设计关 系。这是因为它们没有包括必要的物料流址，压降和输送空气流速z间的基本关系。但是，将公式1 到3组合起來所生成的公式，可以有效地用來检查系统设计。他们还对设计关系的包摄捉供一个良好 基础。2.2.7 material flow rale物料流量by substituting equation 3 into 2 to eliminate v, making ma the subject of the equation and substituting

30、this into equation gives:将公式3代入公式2以消去v,使加成为公式的主项并 将其代入公式1,可得：山龙d匚p cm n = (p x x 1l11p4 rtby putting r 二 53.3 ft ibf/lb r for air gives:空气的r = 533 ft ibf/lb r,代入上式可得:p c “(4)m n =0 x ib/h卩679 t2.2.2 pipeline bore 管径for a given material flow rate and conveying conditions, the diameter of the pipeline

31、is generally required. an alternative arrangement of the equations gives:对给定的物料流量和输送条件,通 常需要知道管道的直径。对公式重新排列后，可得：0-5in(5)2.2.3 conveying line pressure drop输送线压降an alternative arrangement, in terms of the pressure required to convey the material gives:重新组合后，也可表示为输送物料所需的压力：m p t,p = 67*9 ibf/it? abs (6

32、)cd1 02.2.3.1 reference conditions参考条件the variables in these equations can be taken at any point along the pipeline in the case of air pressure and velocity, however, these are generally only known, with any degree of accuracy, at the very start and end of a pipeline since the conveying line inlet a

33、ir velocity is probably the most critical parameter in system design it is generally conditions at the material feed point, at the start of the pipeline, that arc used for this purpose.在这些方程中的变量可按这条管道的任意点來取。但是，不管准确度如 何，通常唯一已知的是，管道一开始和管道末尾处的空气压力和速度。输送线入口气速可能是系统设 计中最关键的参数，它通常规定为在管道起始端、喂料点处的气速。2.3 empi

34、rical relationships以经验为依据的关系it will be seen from equations 4 to 6 that, for a given material and pipeline, there are six variables relating the main conveying parameters of these, the conveying air temperature will be known; solids loading ratio is a function of the conveying air velocity, pipeline

35、bore and material flow rate; and either the material flow rate required, pipeline bore to be used, or conveying line pressure drop available will be specified this means that there are three basic variables in each of these equations. 从式4至06 可以看 出，对于给定的物料和管道，在输送的主要参数中有6个变量。当然，其中输送气温是已知的；固气 比是输送气速、管径

36、和物料流量的函数；并且无论是所盂的物料流量，所用的管道口径，还是可用的 输送线压降都会被指定。这意味着，在这些公式中只有三个基本变量了。it will be possible to provide solutions to equations 4 to 6, therefore,讦 two further relationships can be provided these will, by necessity, be empirical, and so the accuracy of any expressions developed will ultimately depend upon

37、 the accuracy of the empirical relationships used the first of these is a relationship or suggested value for conveying line inlet air vclocity. the second is a relationship for solids loading ratio and this is in terms of conveying line pressure drop pnramelers因此，如果再进一步 提供两个关系式，就可以对公式4到6求解。这些关系式当然是

38、以经验为依据的，因此任何表达式的准 确性将最终取决于所用经验关系的准确度。其中第一个是输送线入口气速的关系或建议值。第二个是 固气比的关系，这与输送线压降参数有关。2.3.1 conveying line inlet air veloc迥输送线入 口气速the conveying line inlet air velocity to be employed depends upon the minimum conveying air velocity at which the material can be successfully conveyed this depends very muc

39、h upon the material to be conveyed and the solids loading ratio at which it is to be conveyed.采用的输送线入口气速収决于安全输送物料所需的最低输送气速。这与被输送 的物料及输送固气比冇很大关系。a graphical representation of this relationship between minimum conveyingair velocity and solids loading ratio for typical powdered and granular materials i

40、spresented in figure 16.1. these relationships for different materials were first introducedin chapters典型粉体和颗粒料的绘低输送气速与固气比乙间关系用图形农达在图16中。不同物料的这些 关系最早是在第4章中介绍。for a material that is capable of being conveyed in dense phase, such as amaterial having good air retention properties like barite, fine fly

41、ash or cement, theconveying limits are defined approximately by:对有密相输送能力的物料,如有良好存气性的重晶石,细飞灰 或水泥等，其输送极限可近似地由卜式确定：c伽=2300for < 10cmm = (7330 0 ° - 1370) for 10 < 0 v 80 ft/min - (7)=600for 0 > 80where cmin = minimum conveying air velocity - ft/minand 4> = solids loading ratio -这甲-gn加二

42、最低输送气速ft/mine -固气比-三£4=二刁 tv mumuauoo lunluq一solids loading ratiofigure 16.1 relationship between minimum conveying air velocity and solids loadingratio for different materials.不同物料最低输送气速和固气比z间的关系。for a material that is not capable of being conveyed in dense phase, such asgranular materials hav

43、ing both poor air retention and poor permeability, the conveyinglimits arc defined approximately by:对不能以密相输送的物料，如存气性和透气性都差的颗粒料，戏输 送极限可近似地由下式确定：cnun = 2300 to 3200 ft/min (for all 0)(8)a graphical representation, for typical materials, of these relationships betweenminimum conveying air velocity and

44、solids loading ratio is also included onfigure 16.1. for most purposes, the use of this graph probably provides the quickestmeans of determining the necessary value, but for anyone wanting to programthe analysis, equations 7 and 8 arc offered for this purpose.图 16.1 中也包含了对于典型的物料的故低输 送气速和固气比之间关系的图示。对

45、于大多数的目的，这张图可能是确定必要数值最快的i种手段， 但想要对分析编写程序，可使用公式7和8。design would generally be based on a conveying line inlet air velocity, ch20% greater than the minimum conveying air velocity, c,”加:设计时，通常取输送线入口气速c/比最低输送 空气流速c伽大20% o(9)cl =1 -2 cmin ft/min2.3.2 solids 厶oading rulio固气比an approximate relationship betwe

46、en pressure drop and solids loading ratio, fordilute phase conveying, is presented in figure 16.2. the relationship is based uponthe assumption that the curves on figure 16.2 are equi-spaced with respect to conveyingline pressure drop for many materials conveyed in dilute phase this is areasonable a

47、pproximation.稀和输送时，压降和固气比z间的近似关系显示在图16.2中。这种关系是是: 以假设图16.2曲线代表的输送线压降为平均间隔为基础。对于许多以稀相输送的物料，这是一个合理 的近似。air flow rate vofigure 16.2 influence of solids loading ratio and air flow rate on conveying line pressuredrop for dilute phase suspension how.稀相悬浮流动时，固气比和空气流屋对输送线压降的影响。(10)-lbf/in2-lbf/in2a mathemat

48、ical expression for this is:其数学表达式为:pawhere conveying line pressure drop 一 lbf/in2 这里输送线be 降 andair only pressure drop - lbf/in2/?妒 纯空气压降2.3.3 material flow rule 物料流量now from equation 1 :现在根据公式 1 ：0 -性directly equating these two expressions for solids loading ratio gives:直接将两个固气比的表达式相等,可 得到：if air m

49、ass flow rale, ma, is not a convenient parameter, equation 11 can be expressed in an alternative form, in terms of air pressure, p, and velocity, c, by substituting a combination of equations 3 and 5 to give:如果空气质量流量加“用起来不方便,将公式3和公 式5代入后，町到用空气压力八速度c表示的另一种表达形式：lb/hanother alternative is to substitute

50、 solids loading ratio, from equation 10into equation 4, which gives:将山公式10表示的固气比/代入公式4,p c d267 9 tlb/h町得到另一种表达式:- (12)pipeline inlet conditions are the most convenient to use here这里管道入 i i 条件是最便于使用的。 2.3.3a negative pressure systems负压系统for vacuum systems the pressure, p9 will be atmospheric.对真空系统,压

51、力p将是大气压。2.3.3.2 positive pressure systems正压系统for positive pressure systems the pressure, /?, in equation 12 will be equal to theconveying line pressure drop, a/?c, plus atmospheric pressure, which is:对正压系统,公式 12里的压力p将 等于输送线压降"加上大气压力，即：几+几伽where 几=输送线压降lbf/in2 这里尸输送线压降-lbf/in2and patm = atmosphe

52、ric pressure ibf7in2 patm = 大气压力 ibf7in22. 3. 4 pipeline bore 管径by substituting the solids loading ratio, (/)9 from equation 10 into equation 5, theexpression can be in terms of the pipeline bore required:将由公式10表示的固气比代入公式5,可得到所 需管径的表达式：82405(13)inthe situation for both positive and negative pressure

53、 systems is the same as above.上jfri的公式对正压和负压系统都适用。2.3.5 a ir supply pvessuye 供气压力alternatively, the expression can be in terms of the pressure required to convey the material. substituting the solids loading ratio, 0, from equation 10 into equation 6 gives:另外，也看表示为输送物料所需的压力的形式。将由公式10表示的固气比4)代入公式6,可得

54、:67-9 x'pacd2 仏-如)lbt7in2 abs(14)pipeline inlet conditions are again the most convenient to use.这里管道入 i 丨条件也是故便于使用的2.3.5.1 negative pressure systems负压系统for negative pressure systems the pressure, p, will be atmospheric and hence ap(can be determined, which is the value required in this case re-a

55、rranging equation14 and expressing in terms of pipeline inlet conditions for this case gives:对负压系统，压力将是人气压, 因此可以确定这种情况下所需的几。重新排列公式14,并用这种情况下管道入口条件來表示：(15) pa 67 9 _j+ 1 ibf7in2ld palm 丿23.5.2 positive pressure systems正压系统for a positive pressure system汉寸正压系统：、pcpalmsubstituting this into equation 14

56、and expressing in terms of pipeline inlet conditions gives:将z代入公式14,并用管道入口条件來表示：“/力-（皿+m）67-9this is a quadratic equation, the solution to which is:这是一个二次方程，解决问题的办法是:palm +、pa("a”(16)note:注意：this will give the coitcct root.这将给hl止确的根。2.3.6 air only pressure drop纯空气压降since the air only pressure d

57、rop, 內 / features prominently in all of these models, a convenient expression for this pressure drop is required. an expression that will give the air only pressure drop in terms of conveying line inlet, or exit, air velocity is needed. these models were derived in detail in chapter 6 on the air onl

58、y datum.曲 丁所有这些模型 中纯空气压降皿都占有很重要的位置，这个压降需耍有一个方便的衣达形式。纯空气压降川输 送线入口气速或出口气速的形式來表示。在笫6章“纯空气基准”中详细推导了这些模型。23.6.1 negative pressure systems负压系统for negative pressure systems the expression also needs to be in terms of the inletair pressure, p/, since this is generally known (usually atmospheric). such an expressionwas developed at equation 6.20 and is:对负压系统，这个表达式也盂要用入口空气压力来农示，因为 这个压力通常是己知的(常为人气压)。对公式6.20推导得到的表达式为：(17)ibpirr2.3