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渣浆泵运行工况的调节
添加时间:2020.03.01

渣浆泵运行工况的调节
    如果工作点流量大于或小于所需要的输送量,应设法改变工作点的位置。改变运转泵的工作点称为工况调节。既然泵的工作点为管路特性曲线与泵特性曲线的交点,因此,进行工况,调节有两种途径,即改变管路特性和改变泵的特性,下面分别加以论述。
1.改变管路特性

1)       管路节流调节

这是使管路特性变化的最简单、最常用的方法,即在排出管路上安装调节阀,开大或关小调节阀的开度,从而改变管路中局部阻力,管路特性系数k改变,使管路特性的斜率发生变化。在泵性能曲线不变的情况下,工作点发生变化,达到调节流量的目的。
    如图1- 52所示,当泵排出管路上调节阀全开时,设管路特性曲线为1.与泵H-Q性能曲线交点为M,对应的流量为Q1.随着调节阀逐渐关小,管路特性系数k逐渐变大,管路特性23相应地变陡,工作点变为M2M3,流量逐渐减少为Q2Q3,而泵的扬程从H1逐渐增大为H2H3。

由图1-52可以看出,当用关小调节阀使流量由Q1减小到Q2Q3时,泵的效率往往会有所下降,因为一般情况下总是按阀全开时所确定的工作点M来选泵的。至于功率,一般低、中比转速的离心泵,其功率性能曲线都是随流量减小而下有所下降的。但是从泵提供的能头利用程度来看,调节阀开度减小却增力加了附加阻力损失。设调节阀全开时,流量为Q1,管路特性系数为k1,则管路中流动损失为h=k1Q2;节流后,流大量变为Q2,总的流动损失为h=k2Q2,其中用于使液体在管路中进行输送时需要克服的流动损失仅为h=k,Qz 2,其余能头(k2 – k1)Qz 2则为节流调节损失。
    由此可见,用关小排出调节阀的方法改变管路特性来调节流量时,管路中局部阻力损失增加,需要泵提供更多的能头来克服附加的阻力损失,使整个装置效率不高,长期这样调节是不经济的。特别是对具有陡降扬程性能曲线的离心泵,采用这种方法调节就更不经济。但由于

该方法调节方法简单,且调节很方便,故仍被广泛的用于离心泵工况调节中。
2)旁路调书
    如图1-53所示,在泵出口设有旁路与吸液罐相连通。此管路上装一调节阀。离心泵在旁路调节装置上工作就如同在分支管路中一样,设h-Q1是主管路的管路特性,h-Q2是旁路
的管路特性,则并联后的管路特性为h-Q.当旁路调节阀完全关闭时,泵的性能曲线H-Q与主管管路特性h-Q1的交点为b1;旁路阀打开时,H-Q曲线与h -Q的交点为a。按分支管路中求各管中的流量方法,过a点作水平线交h-Qa1点,交h-Q2a2点,则通过主管的流量为Q.,旁路中流量为Qao由图可知,泵的流量变大,但主管中的流量比关闭旁路阀时主管中流量为小,所以流量得到了调节。
    这种调节方法也不经济,因为旁路中的流体浪费了功耗。若泵的轴功率随流量增加而减小,则用此方法调节较适宜。
    此外,当排液罐中液位变化时,也将使管路特性上下移动,工作点和流量均变化。

2.改变泵的特性

除上述利用泵串联、并联工作以改变性能曲线达到工况调节外,常见的改变泵性能曲线的方法还有改变工作转速、切割叶轮外径以及换叶轮调节等。
1)
改变工作转速
   
Hr。-42C2。mQ:=nD:b-E2C20可知,离心泵的场程和流量都和转速有关。当n增大时,由比例定律可知,流量和扬程相应地与转速近似地按次二次方的正比关系变化,即系的H-Q性能曲线向右上方移动:n减小时,H - Q性能曲线向左下方移动,如图1- 54所示、当管路特性h-Q不变时,就可得到不同的工作点,使流量改变。另外式(1-71)给出了调速的泵特性方程。
   
用变转速调节流量是比较经济的,因为它没有节流引起的附加能量损失。但是渣浆泵这种调节要求使用能改变转速的原动机来驱动,如直流电动机变频电动机和汽轮机等。目前广泛使用变频器与可变速交流电动机,或加液力联轴器驱动等方式。

Adjustment of operation condition of slurry pump

If the flow rate of the working point is greater than or less than the required conveying capacity, try to change the position of the working point. Changing the working point of the running pump is called condition regulation. Since the working point of the pump is the intersection of the pipeline characteristic curve and the pump characteristic curve, there are two ways to adjust the working condition, i.e. changing the pipeline characteristic and changing the pump characteristic, which are discussed respectively below.

1。 Change pipeline characteristics

1) Pipeline throttling regulation

This is the simplest and most commonly used method to change the characteristics of the pipeline, that is, install a regulating valve on the discharge pipeline, open or close the opening of the regulating valve, so as to change the local resistance in the pipeline, change the coefficient K of the pipeline characteristics, and change the slope of the pipeline characteristics。 When the performance curve of the pump is constant, the working point changes to adjust the flow。

As shown in Figure 1-52, when the regulating valve on the discharge pipeline of the pump is fully open, the pipeline characteristic curve is set as 1. The intersection point with the H-Q performance curve of the pump is m, and the corresponding flow is Q1. As the regulating valve is gradually closed, the pipeline characteristic coefficient K is gradually increased, the pipeline characteristics 2 and 3 are correspondingly steeper, the working points are m2 and M3, the flow is gradually reduced to Q2 and Q3, and the pump lift is gradually increased from H1 to H2 and H3.

It can be seen from figure 1-52 that when the flow is reduced from Q1 to Q2 or Q3 by turning down the regulating valve, the efficiency of the pump will often be reduced, because in general, the pump is always selected according to the working point m determined when the valve is fully open. As for the power, the power performance curve of low and medium specific speed centrifugal pump decreases with the decrease of flow rate. However, from the utilization degree of the energy head provided by the pump, the reduction of the opening of the regulating valve increases the force and the additional resistance loss. When the regulating valve is set to be fully open, the flow rate is Q1, and the characteristic coefficient of the pipeline is K1, then the flow loss in the pipeline is h = K1q2; after throttling, the flow becomes Q2, and the total flow loss is h = k2q2, among which the flow loss to be overcome when the liquid is transported in the pipeline is only h = k, QZ2, and the other energy head (K2 – K1) QZ2 is throttling regulation loss.

It can be seen that when the pipeline characteristics are changed to regulate the flow by turning down the discharge regulating valve, the local resistance loss in the pipeline increases, and the pump is required to provide more energy head to overcome the additional resistance loss, so that the efficiency of the whole device is not high, and it is uneconomical to adjust in this way for a long time。 Especially for the centrifugal pump with steep drop head performance curve, it is more uneconomical to adjust by this method。 But because of

This method is simple and convenient to adjust, so it is still widely used in the condition adjustment of centrifugal pump.

2) Bypass Book Adjustment

As shown in Figure 1-53, a bypass is set at the pump outlet to connect with the liquid suction tank. A regulating valve is installed on the pipeline. The centrifugal pump works on the bypass regulating device as in the branch pipeline. H-q1 is the pipeline characteristic of the main pipeline, and h-q2 is the bypass

When the bypass control valve is completely closed, the intersection point of the pump performance curve H-Q and the main pipeline characteristic h-q1 is B1; when the bypass valve is opened, the intersection point of the H-Q curve and H-Q is a. According to the method of calculating the flow in each pipe in the branch pipeline, the flow through the main pipe is Q and the flow through the main pipe is qao when crossing point a as the horizontal line and point A1 and point A2 as the h-q2. It can be seen from the figure that the flow of the pump increases, but the flow in the main pipe is smaller than that in the main pipe when the bypass valve is closed, so the flow is regulated.

This method of regulation is also uneconomical because the fluid in the bypass wastes power. If the axial power of the pump decreases with the increase of the flow rate, this method is suitable for regulating.

In addition, when the liquid level in the drain tank changes, the pipeline characteristics will move up and down, and the working point and flow will change.

安徽快3开奖结果2. Change pump characteristics

安徽快3开奖结果In addition to the above-mentioned use of pumps in series and parallel operation to change the performance curve to achieve the condition regulation, the common methods to change the pump performance curve include changing the working speed, cutting the outer diameter of impeller and changing the impeller regulation。

1) Change the working speed

It can be seen from HR. - 42c2. M and Q: = Nd: b-e2c20 that the field path and flow rate of centrifugal pump are related to the rotating speed. When n increases, it can be seen from the proportional law that the flow rate and head change in proportion to the rotational speed approximately according to the quadratic power, i.e. the H-Q performance curve of the system moves up and to the right: when n decreases, the H-Q performance curve moves down and to the left, as shown in figure 1-54, when the pipeline characteristic H-Q remains unchanged, different working points can be obtained to change the flow rate. In addition, equation (1-71) gives the pump characteristic equation of speed regulation.

It is more economical to adjust the flow with variable speed because it has no additional energy loss caused by throttling. However, the adjustment of slurry pump requires the use of prime mover which can change the speed to drive, such as DC motor frequency conversion motor and steam turbine. At present, frequency converter and variable speed AC motor are widely used, or with hydraulic coupling drive.





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