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Application Of Hydraulic Coupler In Power Plant Induced Draft Fan
Oct 20, 2017

Induction fan conveying medium is dusty and high temperature flue gas. In addition to considering the fan size, weight, efficiency and regulation performance, but also requires wear resistance, the adaptability of dust to ensure the safe operation in the specified maintenance cycle. At present, there are three types of induced draft fans for coal-fired power plants: adjustable axial fans, adjustable axial fans and centrifugal fans.


  

       1, fan selection in the main consideration of several elements

       1.1 Fan wear resistance

In the case of the same external flue gas conditions, the fan wheel wear and the square of the speed is proportional to. Under the same conditions, the rotational speed of the axial fan is the highest, which is generally higher than that of the static fan and the centrifugal fan. Centrifugal fan speed is low, the blade for the plate, and the surface can be done anti-wear treatment, good wear resistance.

       In the domestic early dust concentration higher flue gas system, the centrifugal fan pressure coefficient is larger, to achieve the same indenter required impeller peripheral speed is small, the corresponding speed can be lower, better anti-wear performance; axial fan pressure Coefficient is small, the same pressure under the high speed, then under the same conditions, wear resistance worse. Adjust the axial fan of the moving blade can be in the same hub by a simple way to replace several times, the impeller group life is also very long. In addition, due to the static blade adjustment axial fan of all components, the most easy to wear is the rear guide vane. And the guide vanes can be designed to be detachable, bolted to the diffuser, if found to wear, even in the operation can also be extracted to check or replace, so it is more suitable for use in poor conditions on the boiler fan.

    1.2 fan regulation performance and efficient range

     The performance of different types of fans is compared, and the equivalence curves of three kinds of fans are analyzed. Centrifugal fan equivalent curve similar to the ellipse, the short axis is almost parallel with the resistance characteristic curve, in the low load regulation efficiency can only be reduced and decreased faster. Adjusting the axial flow fan blades can change the angle through the hydraulic system to change the characteristic curve of the fan. It can maintain a high fan efficiency within a certain load range. The equivalent elliptical long axis is almost parallel to the resistance characteristic curve , To the low load regulation efficiency slow down. And the static axis of the axial fan is fixed on the hub can not change the angle, you can adjust the impeller before the static guide leaf angle to change the fan performance curve, the equivalent curve of the approximate oval long axis and resistance characteristics of the curve was an angle, When the load is adjusted, the efficiency reduction is faster than the axial adjustment of the axial flow fan, and the structure is relatively simple.

       The design of the boiler induced draft TB point relative to the BMCR point of the margin is relatively large, the draft fan is selected in accordance with the TB point design, and the actual work is long-term operation between the TMCR to BMCR point near.

Adjustable axial flow fan is basically on the equivalent curve, which means that the efficiency of the adjustment process is very small, so the adjustment of a wide range of efficiency. In the selection, it is possible to make the boiler design point, that is, TB point and BMCR point at the same time fall in the efficient area of the fan. The characteristics of the centrifugal fan determines the maximum operating conditions under the constant speed conditions are not the most efficient point, the actual operating point efficiency is low, according to the boiler BMCR point design parameters, the fan efficiency is generally not more than 70%. From the energy point of view, can increase the speed control device. Based on the cost of variable frequency speed is much higher than the hydraulic speed, so we can use the night coupler to improve the centrifugal fan regulation performance, so that in various conditions, the centrifugal fan can be in efficient area operation. From the fan to adjust the efficiency aspects of consideration, double-action adjustable axial fan of the highest efficiency, followed by static control axial fan, centrifugal fan the worst.

     1.3 Maintenance and reliability

Centrifugal fan structure is simple, less moving parts, the flue gas dust content of the adaptability is better, easy to maintain, high reliability. For the centrifugal fan bearing is located outside the fan, easy maintenance. With the recent years of research and improvement of axial fans, the current axial fan reliability is also high. In the maintenance, the adjustable shaft fan flow more than the other two, maintenance process than the latter two high.

     2. Application of Hydraulic Coupler in Centrifugal Fan

     2. 1 hydraulic coupling works

Hydraulic coupler, also known as hydraulic coupling, is a liquid for the work of the intermediary

Quality, the use of liquid kinetic energy changes to pass the energy of the blade drive

Institutions, with no-load start motor, smooth stepless speed and so on. For the fan speed adjustment, can optimize the boiler air conditioning system. The speed-type hydraulic coupler is mainly composed of pump wheel, turbine, spoon tube and so on. When the driving shaft drives the pump wheel to rotate, the working oil will gain energy and inertia under the action of the blade and cavity in the pump wheel Centrifugal force is sent to the outer circumference of the pump wheel to form a high-speed oil flow, the pump on the outer circumference of the high-speed oil flow and the radial relative velocity and the pump wheel export speed of the composition of the joint speed, into the turbine The radial runner is introduced and the turbine is rotated along the radial flow path of the turbine through the change in the flow moment of the oil. The oil flow to the turbine outlet is combined with the radial velocity at the turbine outlet and the peripheral speed at the turbine outlet. , Into the radial flow path of the pump wheel, and regain energy in the pump wheel. In this process, when the pump wheel drives the working oil cycle, the mechanical energy of the prime mover is converted into the kinetic energy and the potential energy of the working oil, and the working oil is formed by the circulation of the working oil in the pump wheel and the turbine. After entering the turbine, the mechanical energy carried by the turbine is able to work on the turbine when the turbine is rotated and then converted into the mechanical energy of the output shaft, which is transmitted to the fan, thus realizing the flexible transmission of the motor shaft power.

    2. 2 Economical analysis of the hydraulic coupler

    2. 2. 1 slip ratio of the coupler S

In the actual operation of the coupler, the pump wheel speed (in n tables

) Must be slightly larger than the turbine speed (in n1), the only way in the circulation circle pump wheel outlet oil pressure can be higher than the turbine inlet

Oil pressure, thus completing the torque transmission. Pump wheel and turbine speed difference

And the ratio of the pump wheel speed is called the hydraulic coupler slip, with S said, that is:

                      S = (n - n1) / n = 1 - n1 / (1)

From (1) can be seen in n1 / n exactly two rounds of the transmission ratio, with i said. On the brand name of the coupler, the concept of the rated slip rate is the percentage of the coupler passing the rated load multiplied by 100%, expressed as S%.

     2. 2. 2 Coupler drive efficiency η

The energy loss of the hydraulic coupler during the working process is mainly the loss of flow of the liquid in the working chamber and the impact loss at the inlet of the working wheel, the loss of the working wheel and the air friction, and the mechanical loss of the bearing, seal, Therefore, the output power N2 of the hydraulic coupler is always smaller than the input power N1, and the ratio of the two is the transmission efficiency η of the hydraulic coupler,

                     η = N2 / N1 = η1 × η2 × η3 (2)

Where: η1, η2, η3, respectively, volumetric efficiency, mechanical efficiency, hydraulic efficiency. Most of the working fluid flowing from the pump wheel enters the turbine and has a small portion flowing directly to the pump inlet through the axial clearance between the working wheels and a small portion of the turbine between the turbine and the rotating housing The gap flows out and fails to flow into the turbine, which causes the volume loss, but this amount is usually small. If this flow loss is ignored, η1 = 1. 0

      Mechanical efficiency η2 is the output wheel output torque and input torque ratio:

ηB = MBY / MB

ηW = MW / MYW

Where: η2 - pump wheel mechanical efficiency

MBY - Pump torque on the action of the liquid

MB - The input torque of the prime mover on the pump wheel

ηW-turbine mechanical efficiency

MW-turbine output torque

MYW - Liquid input torque to the turbine

The influence of the hydraulic efficiency of the coupler η is to consider the various hydraulic losses, including the internal friction loss during liquid flow, the friction loss between the liquid and the working wheel surface, the impact loss of the liquid entering the inlet of the working wheel,


       η = N2 / N1 = (MW × n1) / (MB × n) = (MYW × ηW × η1) / ((MBY × n) / ηB)

Control (2), (3) can be seen: η1 = MYW / MBY

η2 = ηW × ηB

η3 = n1 / n

If η1 ≈1.0, η2 ≈1.0 can be η = n1 / n = i


When n1 / n is 1, the efficiency η = 0, this is because the coupler in the high rotation ratio, the pump wheel, turbine speed is very close, work

The circulating fluid flow in the cavity is obviously weakened, the effective torque of the transmission is extremely small, and the proportion of the friction loss is relatively increased, so the efficiency value

Significantly lower than the gear ratio. The ratio of n1 / n is about 0.97 to 0.99, and the maximum value of η is increased, and then increases with the increase of the turbine speed n1,

But soon fell to zero. This shows that η = n1 / n relationship is not applicable at this time, but also shows the efficiency of the hydraulic coupler never

Can reach 1.

When the speed ratio is small, the total power of the hydraulic coupler is very small, but the power of the fan is the same as that of the fan. The shaft power required is smaller than the shaft power when the baffle is throttled

More, so the slip loss of power than the throttle loss power is much smaller.

2. 3 Advantages of hydraulic coupler

        Speed control type hydraulic coupler for centrifugal fan speed adjustment has the following advantages:

(1) stepless speed regulation: in the hydraulic coupler input speed of the same circumstances, you can output a continuous, stepless, changing speed;

(2) work smoothly: can be balanced to start, accelerate, slow down and stop;

(3) no-load start: motor can load or light load start,

It can choose the most economical motor and electronic control equipment, reduce the start of electricity

Flow, saving energy;

(4) Isolation vibration: There is no mechanical connection between the pump wheel of the hydraulic coupler and the turbine. The torque is transmitted through the working fluid and is flexible. When the drive shaft has periodic vibration, it will not reach the driven shaft

, With a good vibration isolation effect, can reduce the impact load, extend the motor and fan mechanical life;

(5) overload protection: the hydraulic coupler is a flexible drive, the pump wheel and the turbine between the speed difference, so when the driven shaft resistance torque increases, the slip increases, and even brake, and the prime mover Still continue to run, but not burn the motor, while the fan has also been protected;

(6) no mechanical wear: There is no direct machine between the pump and the turbine

Mechanical contact, so the work of reliable, long-term maintenance without maintenance, long life;

(7) easy to control: hydraulic coupler is stepless speed change, it is easy to achieve automatic control for the servo system control;

(8) energy saving: Compared with the baffle adjustment, energy saving effect is remarkable

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