Depericarping station / nut and kernel plant

Depericarping Station

The depericarper station is a station that separates out the fibre, nut and stone. The station consist of few part:

- cake breaker conveyor

- nut polishing drum

- fibre cyclone air lock

- fibre cyclone fan

Introduction

When digested fruit is pressed to extract oil, a cake make up of nuts and fibre is produced. In this station, I can observe that the equipment is linked to each other and yet the complexity can still be understood. It involves CBC, separation column, distoner, fibre cyclone, fibre conveyor, fan, damper and so forth.

Cake breaker conveyor

The cake from the press become a dense well compacted mass that need to be broken up before separation. Here, the cake breaker conveyor functions to deliver the fibre and nut that has been squeezed from the press to the air separation column. It also functions to loosen the press cake to separate the nuts from the fibre.If the fibre and nut are not separate, the fibre will follow the nut to the drum can cause the machine to jam. The is a “L” shape paddles locate on the rotating shaft. The movement of the paddles opens up the fibre and loosen it from the nuts and keeps the fibre in a state of agitation so the conveyor needed to be cover on the side and the top to prevent spillage. A certain amount of moisture will be lost by evaporation as the loosened fibre passing along the cake breaker conveyor towards the nut separator. 

Figure: Depericaper                

Figure: Correct way to fit fibre cyclone

Nut and kernel plant

The nut and kernel plant is a station that runs the separation process of the nut, stone and sand. After that, the nut is obtained and broken down to separate kernel from the shell.

Figure: Flow of nut and fibre to kernel and shell

Polishing drum

After the fibre and nut is separate at the vertical column, the nut will then go into the polishing drum. Polishing drum function to remove the tiny pieces of EFB bunches and the fibre that is still attaching to the nut. The drum will be rotating while the nut will be rolling at the bottom of the drum and rub against each other and the drum surface to remove the fibre that are still attached to the nut. The polishing drum also helps to reduce the moisture content on the nut by evaporating the extra water content in the motion. There are holes on the drum to remove the sand and broken nut. The holes will become bigger near the end of the drum to allow the nut to fall into the incline nut conveyor and be transported to the destoner. The fibre and EFB bunches will fall out at the end of the drum.

Figure: Polishing drum

Destoner

The nut will then move to the destoner by nut conveyor. The function of destoner is to divide the nut from the stones and iron with the help from the destoner air lock and destoner fan. The stone and the iron such as screw, nut and etc need to be removed because it would cause damage to the ripple and the other components.

Figure: Destoner

Nut elevator

Nut elevator is used to lift the nut up to the nut silo. Nut elevator will only be used when the destoner couldn’t function. In nut elevator, the stones, iron and nut would not be separated, all of them will be transport to the nut silo. So it is not preferable to use nut elevator unless it is neccesary.

Nut silo

Nut silo is the place to retain the nut from the polishing drum for a period of time. The main function of nut silo is to reduce the moisture of the nut by allowing the nut to dry in the nut silo before go to ripple mill. In order to achieve high nut cracking efficiency, the kernels must be shrinked away from the shells by conditioning the nuts.

 Figure: Nut silo

Ripple mill

The ripple mill is a machine that functions to crack the nut for separation of the kernel and shell. Rotor is arranged horizontally and has number of rods at the outer layer. The outer perimeter of rotor is the ripple mill wall with rods. The nuts fed from top of ripple mill, and as the rotor rotates, nuts being crushed against rotor rods and stator and cracked.

Before work operation, the rod on the ripple mill need to be checked and ensure it can be used. After some time the rod will be thinned up and the spaces between the rods become larger. This will reduce the efficiency of cracking the nut so the rod need to be changed when the space between the rod is large. Make sure the magnet on the back of the inlet nut chute is functioning well. The magnet is used to attract the iron to prevent the iron fall into the ripple mill machine and damage the ripple mill. The throughput is 5 tonnes per hour for one ripple mill.

The cracking efficiency is set to be more than 98%. The number of broken kernel also need to be monitor here as it will also contribute to kernel losses.

Figure: diagram to show how ripple Mill works

            Figure: Rotor of mill ripple

Cracked mixture conveyor

Cracked mixture conveyor functions to transport the mixture of kernel and shell for winnowing to separate the light shell and kernel, and then sent to hydrocyclone pump. The conveyor need to be covered on the top because the tiny pieces of shell will spill out when moving.

Kernel grading drum

The function of the grading drum is to grade the kernel according to the size. But in this mill, it is used to filter out the stone and the uncracked nut. The uncracked nut will be send back to the CBC and then to nut silo then to be cracked in the ripple mill.

Winnowing column

Winnowing column functions to separate the shell and the kernel by flowing air current. The shell with some of the fibre in the mixture will be blow up by the flow of air and the kernel will fall down to the conveyor. There are 2 stages for the winnowing column to make more effective kernel and shell separation. The first stage is to remove the tiny fibre ad shell pieces, the 2^nd stage is to remove the shell and broken nut. The amount of broken kernel should be kept below 1%.

Hydrocyclone

The hydrocyclone functions to separate the kernel and shell by applying centrifugal force to the mixture in water to to separate the the component with different weight.

The hydrocyclone is a closed vessel designed to convert incoming liquid velocity into rotary motion. It does this by directing inflow tangentially near the top of a vertical cylinder. This spins the entire contents of the cylinder, creating centrifugal force in the liquid. Heavy components move outward toward the wall of the cylinder where they agglomerate and spiral down the wall to the outlet at the bottom of the vessel. Light components move toward the axis of the hydrocyclone where they move up toward the outlet at the top of the vessel.

The shell and kernel in the water flow to the pump to be pumped into the hydrocyclone. There are 2 plate at the middle, which is also known as overflow tube. The top one close the upper part of the cylinder and forms a lids. The height of the plate is adjustable to allow the amount of water to flow into the upper part of the cylinder. The exit pipe is situated near the top of the cylinder. The higher the plate, the more shell will move to the upper part with the kernel. There is a rotating drum connected to the upper part exit tube of the hydrocyclone. The function of the rotating drum is to filter out the kernel from the water. The rotating drum will drain away the water from the kernel by the rotating motion. A rotating shaft is place near the top of the rotating drum to stablelise the rotation of the drum.

There are 3 hydrocyclone, the first 2 are for the kernel and another one is for the shell. For the first one, the overflow tube height is the highest to allow more kernel and some part of shell flow out to the rotating drum. The remaining will flow into the second hydrocyclone. In the second cylinder, the overflow tube height is lower to achieve less shell from flowing out of the exit tube. The remaining of this hydrocyclone now should contain most of the shells and the least number of the kernels. The remaining will being pumped to the third hydrocyclone. For this hydrocyclone, the substances from exit tube at the bottom of the cylinder will be flow out to the rotating drum. The exit tube at the upper part of the cylinder connect to the second hydrocyclone to allow the kernel to flow back to the second hydrocyclone and out to the rotating drum.

In this part, the kernel sample will be taken every 2 hour to make sure the percentage of the dirt (shell, nut and split nut) contained in the kernel is below 5%. The number of shell containned in the hydrocyclone of this mill is achieved at below 1% and the line 2(B2) of hydrocyclone contain less dirt than the line 1. For the wet shell, the number of kernel loss (kernel, broken kernel, nut, split nut) also set at below 1% and the line 2 always contain more kernel than the line 1.

Figure: The flow of nut and kernel mixture with water in hydrocyclone       

Figure: 3 hydrocyclone

Kernel silo

Kernel lifted from hydrocyclone by kernel elevator to kernel silo for drying process. Kernel need to be dried so that the moisture is below 7%. This is because wet kernel will become rotten quickly and the FFA will increase rapidly. The kernel silo will blow hot air into the kernel silo for the drying process of kernel. Steam will be flowing through to heat the air. The temperature of the hot air is kept below 80 degree celcius. Too much heat will affect the colour of the kernel oil and cause the kernel to dry too fast on the surface while inside still wet. The kernel have to stay in the silo for more than 8 hours for complete drying process. Then the silo will be opened for half an hour to remove the dried kernel.

There will be spot checks every hour on every silo on the kernel from the top. The amount of dirt (nut, split nut, shell) is controlled below 5%.

The spot check on the dried nut will be taken from the bottom outlet of the kernel silo. Dirt (nut, split nut, shell) and moisture content is kept below 5% and 7%.

Figure: Kernel silo      

Figure: Inside view from top  

 Kernel bunker

After drying process, kernel will be sent from kernel silo to be stored in the kernel bunker. The moisture of kernel bunker should be kept below 7% and the dirt should be kept below 6%. There is a pipe at the bottom of the bunker to drain away the excess water in the bunker. First In First Out (FIFO) system should be practised so that the kernel quality and condition is well maintained.

Fibre conveyor

The fibre from the depericaper, winnowing column are all send to boiler to be used as fuel by fibre conveyor. The conveyor needed to be covered so that to prevent the foreign object ike wood and steel do not enter the conveyor. This could cause damage to the boiler.

Process that cause kernel losses

1. Sterilisation

Ineffective sterilisation will lead to USB and Hard bunch after threshing. The fruit that is still attached to the bunches will lead not only to oil losses, but also kernel losses.

2. Screw press

Too much cone pressure (high amp) will cause broken nut.

3. Depericarper

Wind velocity control. Control the wind speed at appropriate level to prevent the kernel from being lifted with the fibre. Control the damper can fine tune the wind velocity in the column.

The distance from CBC to polishing drum should around 3.5 to 4 meter.

4. Winowing column

Inappropriate wind speed. The control of wind speed can be made by controling the opening of the damper.

5. Ripple mill

Need to make sure the speed of the ripple mill is suitable to prevent broken nut. The worn-off rods and wall should be replaced. The wall can be adjusted to required gap against the rod for optimum cracking efficiency and broken kernel.

6. Hydrocyclone

The flow rate of pump does not meet the suitable rate for the separate of shell and kernel in the cylinder. The hole of the cone wear out after used and increase in the diameter. The vortex lining also will wear out after some time and need to be replaced if necessary.