Desander

1. Denomination

Example: STC 60 2 – 100

STC     -Super Twin Cyclone

60         - 60 mt FFB/hr

2          - 2 cyclone

100       - Diameter of cyclones (mm)

The bigger diameter cone (150mm) is recommended to be installed immediately after the

Crude Oil Tank or Clarification Tank to remove sand and abrassive material from the process

medium. This we termed as first stage desanding system.

The second stage desander system has smaller cone diameter (100mm) to remove fine

sands and impurities carried over after the first stage.

The primary function of an Alfa Laval Precleaner Sandcyclone is to trap sand particles present

in the Crude Palm Oil or Sludge. The removal of sand particles reduces the wear and tear of

the bowl components in all Alfa laval Centrifugal Machines and Decanters.

2. PRESSURE DROP

The most important requirement for efficient sand removal in any desanding system, is the

pressure drop. This is the pressure difference between the inlet and outlet of the desander.

The recommended pessure for the desander is:

Inlet pressure : 3.5 barg

Outlet pressure : 1.5 barg

The outlet pressure mainly depends on the static height of the receiving tank. If the tank is

located at a low position, the outlet pressure need not be high and a lower inlet pressure can be

used. A lower inlet pressure is preferred to minimise the wear and tear of the equipment.

The maximum inlet pressure should not exceed 4.5 barg. The separating efficiency does not

increase propotionally with high inlet pressure.

The modular cyclone will be supplied with one (1) pressure gauge for the inlet and another for the outlet. It is recommended to install the gauges about 300 mm to the inlet and 300 mm after the

outlet. The pressure gauges supplied is a bolted diaphragm construction and can be easily

dismantled for periodic cleaning. It is recommended that the pressure gauge should not be exposed

directly to the line pressure all the time because of the pulsating pressure from the pump. It should

be installed with a valve, to be opened only during reading. A needle valve is preferred to avoid any

pressure surge during opening. This will prolong the life of the pressure gauge.

3. OPERATION PROCEDURE

3.1 Automatic Mode

In switching Selector Switch (CS) to AUTO, the whole system is in automatic operation

i.e. all the valves (top, bottom and water valves) are in automatic sequence of operation

according to pre-programmed mode as Sequence 1 to 2.

Sequence No. 1

TOP VALVE CLOSE

BOTTOM VALVE OPEN

WATER VALVE OPEN

This mode of operation is pre-adjusted to 10 sec. (or other duration as determined by

individual Mill). This operation is to open the BOTTOM VALVE to drain off any sediment of

sand as accumulated from the previous precleaner sandcyclone effect. At the same time,

The WATER VALVE is also opened to wash down any sediment in the sand receiver.

Sequence No. 2

TOP VALVE OPEN

BOTTOM VALVE CLOSE

WATER VALVE CLOSE

This mode of operation is pre-adjusted to 15 min. (or other duration as determined by

individual mill).

This operation is to open the TOP VALVES while the other BOTTOM VALVE and WATER

VALVE are closed. The desanding is achieved by a combination of centrifugal and

gravitational action. The sludge is introduced tangentially at high velocity into the cyclone

head or top cylinder from where it descends on a helical path. The circular motion

provides a sizeable centrifugal acceleration causing the sand particles to be impelled

towards the wall and discharged at the bottom of the cone settling in the sand receiver.

The residual liquid ascend in axial direction and leave the system through the centre of the

head or top cylinder. It requires a minimum pressure drop of 2 bar, usually provided by a

centrifugal pump.

4.0 MAINTENANCE MANUAL

4.1 Electrical Defects

STEP 1 : System does not operate, check the following :

1. If there is any 220V AC supply.

2. If fuse burnt, change a new 2a fuse.

3. If selector switch (CS) does not work, adjust

contacts or clean up contacts or change a new switch.

STEP 2 : Turn selector switch (CS) to AUTO mode,

1. Check if timers are faulty, change a new timer.

2. Turn selector switch (CS) to MAN mode, if BOTTOM VALVE,

TOP VALVE or WATER VALVE does not operate, check if

Relay is faulty, change a new Relay.

STEP 3 : Turn system to OFF mode, i.e. at neither AUTO nor MAN mode.

1. Take off all timer, check if timer coil burnt.

2. Take off all relay, check if relay coil burnt.

3. Isolate all electric solenoid valve, check if

coil burnt.

4.2 Pneumatic Defects

STEP 4 : System does not operate, check the following :

1. If there is any air supply at 80 psig.

2. If supply air line clogged up.

3. If supply air line leakage.

STEP 5 : Turn system to MAN mode, if system does not work, check the following :

1. If no air supply to Pneumatic Actuator, solenoid valve is jammed or air line clogged.

2. If there is air supply to Pneumatic Actuator, the Actuator is jammed, then, dismantle

actuator and check seals for leakage.

3. If there is air supply to Pneumatic Actuator, the ball valve is jammed, then dismantle

ball valve and check if valve clogged or worn out. Replace ball valve if necessary.