渣浆泵的工作特性及工况调节

在石油及其产品的储存与运输过程中.泵与管道阀门、仪表等其他管件组成一个输送系统。在这个输送系统中,泵为流体提供压力能头.流体流经管路、阀门和管件等要克服摩擦阻力损失而消耗能量.其间要遵循质量守恒和能量守恒这两个基本定律.即泵排出的流量等于管路中的流量(严格说是质量流量在不考虑液体可压缩性的情况下，通常取体积流量相等),单位质量流体所获得的能头等于流体沿管路输送所消耗的能头.这样才会稳定运行。泵和管路任何一方的特性发生变化，都会引起整个系统工作参数的变化。本节主要介绍离心泵、管路及整个输送系统的特性,并分析影响装置特性的各种因素及工况调节。
--、离心泵的工作特性
1.固定转速离心泵的工作特性
    在恒定转速下,泵的扬程与流量(H-Q)的变化关系称为泵的工作特性。此外，泵的工作特性还包括功率与流量(P - Q)特性以及效率与流量(η- Q)特性。泵所输出的流量Q和提供的扬程H之间的关系，可以用H= f(Q)之间的数学关系式或曲线来表示。
    对固定转速的离心泵，可以由实测或泵特性曲线上取点得到的几组扬程、流量数据，利用最小二乘法回归得到泵机组的特性方程H= f(Q),表示为:

式中H-- 离心泵扬 程,m;

Q--离心泵 排量,m3 /h;

a.b---常 数,由实测或泵特性曲线上得到的n组(Q ,H)数据回归得到;、

m----流态指数,层流m=1,水力光滑区m=0. 25，混合摩擦区m=0. 123,祖糙区m=0。
2.叶轮直径变化后泵的工作特性
    在相同转速下,采用不同的叶轮直径，可以得到不同的泵特性。根据离心泵的切割定律，叶轮直径变化后的泵特性方程为:
式中D0、D---变化前、后的叶轮直径，mm；
      a、b----对应叶轮直径 D0时泵特性 方程(1-68)中的两个常数。

3. 变转速泵的工作特性
转速变化后的泵特性可用下式描述:
式中n---- 调速后 架的转速.r/mim;

N0----调速前 架的转速.r/mim;

a、b----对应于转速n0时泵特性方程(1-68)中的两个常数。
在输油管道工艺设计中将(1-68). 式(1-70).式(1- 71)统一写为：
式中A.B----对应于式(1- 68)、式(1-70).式(1- 71)中的两个常数，

同)输送液体时，所需能头大小可由伯努利方程来表示，

h=Pb- PA/pg+ (Hb+ HA)+hw
式中h---装置所需 能头,m;
PA、PB---吸液罐和排液罐液面上的压力,Pa;

ρ---液体密度,kg/m2;
HA、Hp----吸液罐和排液罐液面至泵轴中心线的距离,m;
hw----克服单位质量液体流经吸 人管路与排出管路总的流动损失所需水头,m。

在上式中，当液体升高的高度和排灌与吸液罐内液面上压头差不变时，它们是常数，且与管路中流量Q无关，故称为静扬程，而吸入管路与排出管路中液体的沿程阻力损失和局部阻力损失之和，则与管路中液体流速平方成正比，即与流量的平方成正比。由流体力学可知:

式(1-73)便是离心泵在単根管路上输送液体吋的管路特性方程.它表示管路中流量与克服液体流经管路吋流动損失所需的能头之同的关系。用曲残表示这一关系吋.它是一条抛物线，h-Q曲线称为管路特性，如困1-41所示。在Q=0肘.方程中H= (H』+ H)+Pa-PA.
pg决定了抛物线的起点位畳。
2.装置系統的エ作点

1) 圏解法

在由离心泵、管路等組成的系統中,汞串咲在管路中,渣浆泵所提供的能头H与管路装置所需要的能头h相等,即二者必然会保持能量供求平衡的关系;管路中輸送的流量等于汞所排出的流量，这时泵一管路系統处于穏定的工作状态。 将泵的性能曲线H -Q与管路特性曲线h - Q画在一形图上.称カ装置特性。而两条性能曲线的交点M即为泵的エ作点·也是装畳系統的。

Working characteristics and condition regulation of slurry pump
In the process of storage and transportation of petroleum and its products, pumps, pipeline valves, instruments and other pipe fittings form a transportation system. In this transportation system, the pump provides the pressure head for the fluid. When the fluid flows through the pipeline, valve and pipe fitting, it needs to overcome the friction resistance loss and consume energy. The two basic laws of mass conservation and energy conservation should be followed. That is, the flow discharged by the pump is equal to the flow in the pipeline (strictly speaking, the mass flow is equal to the volume flow without considering the compressibility of the liquid), and the single flow The energy head obtained by the potential mass fluid is equal to the energy head consumed by the fluid transportation along the pipeline, so as to operate stably. The change of the characteristics of either pump or pipeline will cause the change of the working parameters of the whole system. This section mainly introduces the characteristics of centrifugal pump, pipeline and the whole conveying system, and analyzes various factors affecting the characteristics of the device and the condition regulation.
--Working characteristics of centrifugal pump
1. Working characteristics of fixed speed centrifugal pump
At a constant speed, the relationship between the head and the flow (H-Q) of the pump is called the working characteristics of the pump. In addition, the working characteristics of the pump also include power and flow (P-Q) characteristics and efficiency and flow (η - Q) characteristics. The relationship between the output flow Q of the pump and the provided lift h can be expressed by the mathematical relationship or curve between H = f (q).
For the centrifugal pump with fixed speed, several groups of head and flow data can be obtained from the measured data or points on the pump characteristic curve, and the characteristic equation H = f (q) of the pump unit can be obtained by least square regression, which is expressed as:
Where, h -- lift of centrifugal pump, m;
Q -- discharge capacity of centrifugal pump, m3 / h;
a. B --- constant, obtained by regression of N group (Q, H) data obtained from actual measurement or pump characteristic curve
M ---- flow regime index, laminar flow M = 1, hydraulic smooth area m = 0.25, mixed friction area m = 0.123, Zu rough area m = 0.
2. Working characteristics of the pump after the impeller diameter changes
At the same speed, different impeller diameters can be used to obtain different pump characteristics. According to the cutting law of centrifugal pump, the characteristic equation of the pump after the impeller diameter changes is as follows:
Where d0, D --- impeller diameter before and after change, mm;
a. B ---- two constants in the pump characteristic equation (1-68) corresponding to impeller diameter d0.
3. Working characteristics of variable speed pump
The pump characteristics after speed change can be described as follows:
Where n is the rotation speed of the speed regulating rear frame. R / MIM;
N0 - speed of speed regulating front frame. R / MIM;
a. B ---- two constants in the pump characteristic equation (1-68) corresponding to the speed N0.
In the process design of oil pipeline, formula (1-68), formula (1-70) and formula (1-71) are uniformly written as follows:
Where A.B ---- corresponds to formula (1-68), formula (1-70). Two constants in formula (1-71),
(the same as) when conveying liquid, the required energy head size can be expressed by Bernoulli equation,
h=Pb- PA/pg+ (Hb+ HA)+hw
Where h is the energy head required by the device, m;
PA, Pb -- pressure on liquid level of suction tank and drain tank, PA;
ρ - liquid density, kg / m2;
Ha, HP ---- distance from liquid level of suction tank and drain tank to the center line of pump shaft, m;
HW ---- water head required to overcome the total flow loss of unit mass liquid flowing through suction pipe and discharge pipe, M.
In the above formula, when the height of liquid rise and the pressure head difference between the drainage and filling and the liquid level in the suction tank remain unchanged, they are constant and have nothing to do with the flow Q in the pipeline, so they are called static head. The sum of the resistance loss along the pipeline and the local resistance loss in the discharge pipeline is directly proportional to the square of the liquid flow rate in the pipeline, that is, the sum of the resistance loss along the pipeline and the local resistance loss is directly proportional to the square of the flow rate in the pipeline. According to hydrodynamics:
Equation (1-73) is the pipeline characteristic equation of centrifugal pump when delivering liquid on the pipeline. It represents the same relationship between the flow rate in the pipeline and the energy head required to overcome the flow loss when the liquid flows through the pipeline. It is a parabola, and the H-Q curve is called the pipeline characteristic, as shown in Fig. 1-41. In the equation, H = (H] + H) + PA PA
PG determines the starting point of the parabola.
2. Operation point of device system
1) solution method
In the system composed of centrifugal pump and pipeline, the mercury is in the pipeline, and the energy head h provided by slurry pump is equal to the energy head h required by pipeline device, that is to say, they will maintain the balance of energy supply and demand; the flow delivered in the pipeline is equal to the flow discharged by mercury, which means the pump pipeline system is in stable working state. Draw the performance curve H-Q of the pump and the characteristic curve H-Q of the pipeline on a graph, and call the characteristics of the device. And the intersection point m of the two performance curves is the pump's working point, which is also installed in the system.