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渣漿泵的工作特性及工況調(diào)節(jié)
在石油及其產(chǎn)品的儲(chǔ)存與運(yùn)輸過(guò)程中.泵與管道閥門(mén)、儀表等其他管件組成一個(gè)輸送系統(tǒng)。在這個(gè)輸送系統(tǒng)中,泵為流體提供壓力能頭.流體流經(jīng)管路、閥門(mén)和管件等要克服摩擦阻力損失而消耗能量.其間要遵循質(zhì)量守恒和能量守恒這兩個(gè)基本定律.即泵排出的流量等于管路中的流量(嚴(yán)格說(shuō)是質(zhì)量流量在不考慮液體可壓縮性的情況下，通常取體積流量相等),單位質(zhì)量流體所獲得的能頭等于流體沿管路輸送所消耗的能頭.這樣才會(huì)穩(wěn)定運(yùn)行。泵和管路任何一方的特性發(fā)生變化，都會(huì)引起整個(gè)系統(tǒng)工作參數(shù)的變化。本節(jié)主要介紹離心泵、管路及整個(gè)輸送系統(tǒng)的特性,并分析影響裝置特性的各種因素及工況調(diào)節(jié)。
--、離心泵的工作特性
1.固定轉(zhuǎn)速離心泵的工作特性
在恒定轉(zhuǎn)速下,泵的揚(yáng)程與流量(H-Q)的變化關(guān)系稱(chēng)為泵的工作特性。此外，泵的工作特性還包括功率與流量(P - Q)特性以及效率與流量(η- Q)特性。泵所輸出的流量Q和提供的揚(yáng)程H之間的關(guān)系，可以用H= f(Q)之間的數(shù)學(xué)關(guān)系式或曲線來(lái)表示。
對(duì)固定轉(zhuǎn)速的離心泵，可以由實(shí)測(cè)或泵特性曲線上取點(diǎn)得到的幾組揚(yáng)程、流量數(shù)據(jù)，利用最小二乘法回歸得到泵機(jī)組的特性方程H= f(Q),表示為:
式中H-- 離心泵揚(yáng) 程,m;
Q--離心泵 排量,m3 /h;
a.b---常 數(shù),由實(shí)測(cè)或泵特性曲線上得到的n組(Q ,H)數(shù)據(jù)回歸得到;、
m----流態(tài)指數(shù),層流m=1,水力光滑區(qū)m=0. 25，混合摩擦區(qū)m=0. 123,祖糙區(qū)m=0。
2.葉輪直徑變化后泵的工作特性
在相同轉(zhuǎn)速下,采用不同的葉輪直徑，可以得到不同的泵特性。根據(jù)離心泵的切割定律，葉輪直徑變化后的泵特性方程為:
式中D0、D---變化前、后的葉輪直徑，mm；
a、b----對(duì)應(yīng)葉輪直徑 D0時(shí)泵特性 方程(1-68)中的兩個(gè)常數(shù)。
3. 變轉(zhuǎn)速泵的工作特性
轉(zhuǎn)速變化后的泵特性可用下式描述:
式中n---- 調(diào)速后 架的轉(zhuǎn)速.r/mim;
N0----調(diào)速前 架的轉(zhuǎn)速.r/mim;
a、b----對(duì)應(yīng)于轉(zhuǎn)速n0時(shí)泵特性方程(1-68)中的兩個(gè)常數(shù)。
在輸油管道工藝設(shè)計(jì)中將(1-68). 式(1-70).式(1- 71)統(tǒng)一寫(xiě)為：
式中A.B----對(duì)應(yīng)于式(1- 68)、式(1-70).式(1- 71)中的兩個(gè)常數(shù)，
同)輸送液體時(shí)，所需能頭大小可由伯努利方程來(lái)表示，
h=Pb- PA/pg+ (Hb+ HA)+hw
式中h---裝置所需 能頭,m;
PA、PB---吸液罐和排液罐液面上的壓力,Pa;
ρ---液體密度,kg/m2;
HA、Hp----吸液罐和排液罐液面至泵軸中心線的距離,m;
hw----克服單位質(zhì)量液體流經(jīng)吸 人管路與排出管路總的流動(dòng)損失所需水頭,m。
在上式中，當(dāng)液體升高的高度和排灌與吸液罐內(nèi)液面上壓頭差不變時(shí)，它們是常數(shù)，且與管路中流量Q無(wú)關(guān)，故稱(chēng)為靜揚(yáng)程，而吸入管路與排出管路中液體的沿程阻力損失和局部阻力損失之和，則與管路中液體流速平方成正比，即與流量的平方成正比。由流體力學(xué)可知:
式(1-73)便是離心泵在単根管路上輸送液體吋的管路特性方程.它表示管路中流量與克服液體流經(jīng)管路吋流動(dòng)損失所需的能頭之同的關(guān)系。用曲殘表示這一關(guān)系吋.它是一條拋物線，h-Q曲線稱(chēng)為管路特性，如困1-41所示。在Q=0肘.方程中H= (H』+ H)+Pa-PA.
pg決定了拋物線的起點(diǎn)位畳。
2.裝置系統(tǒng)的エ作點(diǎn)
1) 圏解法
在由離心泵、管路等組成的系統(tǒng)中,汞串咲在管路中,渣漿泵所提供的能頭H與管路裝置所需要的能頭h相等,即二者必然會(huì)保持能量供求平衡的關(guān)系;管路中輸送的流量等于汞所排出的流量，這時(shí)泵一管路系統(tǒng)處于穏定的工作狀態(tài)。 將泵的性能曲線H -Q與管路特性曲線h - Q畫(huà)在一形圖上.稱(chēng)カ裝置特性。而兩條性能曲線的交點(diǎn)M即為泵的エ作點(diǎn)·也是裝畳系統(tǒng)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.
