Failure analysis and solution for WH-800 centrifuge

Shanxi Xinlin Steel Co., Ltd. Coking Plant Li Dong

In our gas purification ammonium sulfate section, a WH-800 horizontal single-stage piston pusher and continuous filter centrifuge (WH-800 centrifuge) appeared a fault shutdown. The fault manifested as: the fuel pump was not pushed after the oil pump was started. The pressure indication of the pusher and oil gauge is zero. The so-called non-pushing is that the pusher tray of the centrifuge cannot reciprocate, so that the centrifuge loses the function of automatic unloading.

1 How the centrifuge works

As shown in Figure 1, when the composite cylinder is driven by the pulley connected to it, the cylinder is connected to one end of the cylinder, and the other end of the cylinder is connected to the drum to drive the drum together for full-speed rotary motion; The piston and the composite cylinder wall are connected by a guide key, the piston can be connected with one end, and the other end is connected with the pusher plate, which pushes the pusher plate and the drum synchronously at full speed, and has a set of control in the piston. The piston reciprocates by itself. Under the hydraulic drive, when the piston reciprocates in the composite cylinder, the pusher disc can reciprocate in the drum.

After the pulley rotates the drum at full speed, the suspension can be continuously introduced into the conical cloth bucket mounted on the pusher tray by the feeding tube. Under the action of centrifugal force, the suspension is evenly smashed onto the screen along the circumference of the large end of the cloth bucket. Most of the liquid phase is swept out of the drum through the gap of the screen and the small hole of the drum wall, and is collected in the middle casing and discharged by the drain pipe. The solid phase is trapped on the screen to form an annular filter residue layer. As the piston progresses, the pusher plate can move the filter residue layer forward along the drum axis for a distance, and when the piston returns, the pusher tray also returns. At the time, the surface of the vacant screen forms a new layer of filter residue.

As the piston drives the pusher disc to reciprocate, the above process is repeated, and the filter residue is pushed forward one by one. In the process, the filter residue is further dried, and finally the filter residue is pushed out of the drum and discharged through the front casing discharge port.

It can be seen from Fig. 1 that the hydraulic system consists of a power device - an oil pump, a control regulator - a double throttle valve (composed of a throttle valve, a pressure reducing valve, a pressure regulating valve); an actuator - a composite cylinder; an auxiliary device - - fuel tank, pipeline, oil pressure gauge, etc.; working medium - oil consists of five parts. When the pressure regulating three-way cock is in the working position, the oil passage B and the oil passage C are penetrated and cut off from the oil passage A. At the pressure regulating position, the oil passage C and the oil passage A are penetrated and the oil passage B is cut.

2 failure analysis

2.1 Causes the centrifuge to “do not push the material”

The pusher operation of the centrifuge is driven by hydraulic pressure, and there are two reasons why the centrifuge does not push the material. First, the pusher tray is blocked by the material; second, the hydraulic system fails.

2.1.1 Push tray is blocked by material

During the pushing operation, the ammonium sulphate crystallization slag is too thick or too dry or the sulphate crystals, acid tar and other impurities accumulated in the drum after the pushing of the material are adhered to the screen to cause coalescence. Reciprocating operation creates greater resistance. When this resistance is too large and it is difficult to overcome under hydraulic drive, the pushing operation will stop. At this time, the hydraulic system oil pressure gauge indication value should be large to reach the hydraulic system setting value.

2.1.2 Hydraulic system failure

The hydraulic system is a transmission carrier that converts mechanical energy into oil pressure energy through an oil pump, and converts the pressure energy of the oil into a mechanical energy of reciprocating motion of the piston through a composite cylinder to promote the movement of the load. When the following failures occur in the system, the push tray will not push.

(1) Loss of pressure: The hydraulic system does not have pressure energy. There are two reasons for the pressure loss of the hydraulic system: one is that the oil pump is not supplied with oil; the other is that the hydraulic oil circuit has a short-circuit fault, such as the pressure regulating valve of the pressure regulating valve is broken, the pipe is broken, and the like. The oil pump does not supply oil, the hydraulic system oil can not obtain pressure energy; and the "short circuit" phenomenon occurs, even if the oil obtains pressure energy, it will also be lost due to "short circuit" pressure relief, so the centrifuge will lose The driving force of the pushing operation, and thus the function of pushing the work. At this time, the oil gauge pressure indication is zero.

(2) Under-pressure: The hydraulic system does not rise in oil pressure and the oil pressure is low. Since the system oil pressure is low, the friction resistance of the pushing system during the pushing operation can not be overcome, and the pushing operation is stopped. The main causes of the underpressure of the hydraulic system are: the pressure setting value on the pressure regulating valve is too low, the matching clearance between the hydraulic components is too large, and the oil is too thin. At this time, the hydraulic pressure indication value is low.

(3) The piston of the composite cylinder loses the automatic commutation function. The compound cylinder has a set of self-reciprocating mechanism for controlling the piston. It consists of inner and outer valve stems, two reversing valve stems and some oil passage holes. When the reversing valve stem and the outer valve stem sliding failure are stuck, the hydraulic oil passage in the piston is blocked. Since the oil passage is blocked, the pressurized oil cannot alternately enter the cylinder piston sides to push the piston to reciprocate. The pusher plate connected to the piston by the push rod also appears to be pushed. At this time, due to the high pressure of the hydraulic system, the gauge indication of the oil pressure gauge is large, and the set pressure value of the hydraulic system can be reached.

2.2 Possible causes of “hydraulic pressure indication is zero”

1 The oil pressure gauge is damaged; 2 The hydraulic system is out of pressure.

If the hydraulic pressure gauge loses the pressure indicating function due to its own damage, the cause of the "pushing tray not pushing" fault may involve various situations of the above fault analysis; if the oil pressure gauge is not damaged, the indication is normal, but the indication is normal, but The pressure indication after starting the oil pump is zero, indicating that there is a “loss of pressure” phenomenon in the hydraulic system, and this “loss of pressure” phenomenon is the direct cause of “do not push the material”.

3 fault judgment and search

3.1 Check if the oil pressure gauge is normal

After the hydraulic gauge is removed, it is installed on another spare unit for testing. The test result is as follows: the pointer of the oil pressure gauge is flexible and works normally. It shows that the oil pressure gauge is not damaged, and the hydraulic system does have a “loss of pressure” phenomenon.

3.2 Check if the oil supply of the oil pump is normal

Reload the inspected pressure gauge to the faulty centrifuge, and then rotate the pressure regulating cock (used when setting the hydraulic system pressure) set on the double throttle valve from the "working position" to the "pressure regulating position". In Figure 1, the oil passage "C" and the oil passage "B" are cut off to make it penetrate with the oil passage "A", and then the throttle valve handle on the counter is rotated counterclockwise from the "set opening" position to " The slowest opening position. After starting the oil pump, the indicator of the oil pressure gauge was immediately indicated to 2.2 MPa - the hydraulic system pressure set point. This indicates that the oil pump supply and pressure regulating valve are working properly. At the same time, it is stated that the “loss of pressure” phenomenon of the hydraulic system is not caused by the oil pump not supplying oil, but by the “short circuit” of the oil circuit.

3.3 Check and judge the “short circuit” of the hydraulic system

Stop the oil pump and rotate the throttle valve handle on the double throttle valve clockwise from the “slowest opening” position to the “set opening” position, and then press the pressure regulating three-way cock on the “pressure adjustment position”. Rotate to the "working position", that is, cut off the oil passages "C" and "A" to make it penetrate with the oil passage "B". After that, the oil pump is started and the sealing of each hydraulic component is checked. The results of the inspection were as follows: the power unit – the oil pump, the control section – the compound throttle, and the connecting pipes (including the passage from the double throttle to the composite cylinder) showed no signs of oil leakage. This shows that the short circuit relief phenomenon can only appear inside the composite cylinder. The schematic diagram of the compound cylinder oil circuit is shown in Figure 2.

At this time, the piston is at the leftmost position of the cylinder, and the annular groove of the right reversing valve stem is just in communication with the a hole. The pressure oil entering the annular oil groove of the piston passes through the a hole to the upper end oil groove of the outer valve stem, and then the outer valve stem is pressed down. . At this time, the central annular oil groove 0 communicates with the annular oil groove 1, and the annular groove 4 communicates with the annular groove 3. Therefore, the pressure oil entering the central annular groove 0 enters the left cavity of the oil cylinder through the annular oil groove 1 and the nail hole, thereby pushing the piston to the right. The oil in the right chamber of the cylinder is returned to the tank through the hole of the cylinder through the hole B, the annular groove 3 and the annular oil groove 4.

4 overhaul

We dismantled the composite cylinder and found that the gland fastening screw at the lower end of the outer stem of the piston (as shown in Figure 2) was broken and the gland was broken. In this way, the downward sliding of the outer valve stem in the valve stem hole loses the limit position, and when the outer valve stem slides downward in the valve stem hole, the central annular oil groove 0 of the valve stem hole and the valve stem hole lead to the cylinder wall hole. When the annular oil groove 2 of the return oil tank is penetrated, the pressure oil entering the annular oil groove 0 at the center of the valve stem hole will directly return to the oil tank, and a "loss of pressure" phenomenon will occur in the composite oil cylinder.

Due to the broken screw, the inner wall of the cylinder and the surface of the piston were severely scratched, which was difficult to repair at one time. For this reason, we replaced a new cylinder and piston device. After overhaul, the WH-800 centrifuge resumed the pushing operation, and the inspection effect was obvious.