Palm oil mill laboratory

Objective

- To carry out test

- To provide information to on the status of operation (process losses)

- To provide the information on on the status of product quality

- The data is used to control and monitor the process

- The data can assist engineer or mill manager to modify process or equipment to achieve greater efficiency

Instrument

Digital mass balance

Uv-vis spectrophotometer

Hot plate microwave

Moisture analyser

Thermostatic cabinet

Digital constant temperature tank (SOXHLET extraction apparatus)

Heating block nanocolor vario C2

Distillation apparatus

Air dry oven

Grinding machine

Losses

- Oil loss in EFB

- Oil loss in press fiber

- Oil loss in stork centrifuge

- Oil loss in sterilizer condensate

- Kernel losses in fiber cyclone, ripple mill, LTDS, hydrocyclone

Production oil

Test for moisture

1) Take approximately 10g sample.

2) Put in microwave for 4 minutes to heat it.

3) Weight the sample.

4) Get the difference of the weight after and before dried then divide by the sample weight to get the percentage of moisture of sample 

Test for FFA

1) Take approximately 3g sample.

2) Add 50ml isopropanol, 5 drops of phenolphthaen into a flask.

3) Add in few drops of sodium hydroxide into the mixture until it turns purple. 

4) Put the mixture on the hot plate and heat until bubbles appear.

5) Remove the mixture from the hot plate and add in sodium hydroxide until the mixture turn into red brown.

6) Record the amount of sodium hydroxide added.

7) Calculate the percentage of FFA by using the formula:

Amount of phenolpthaen added (ml) x normality (2.5600)/weight of the sample (g) = FFA

Crude oil tank, Gutther oil, VC underflow, crude oil tank

To test the oil content, moisture content and sludge content in the samples based on the visible layers.

1) Record the temperature for each of the equipment of which the sample are taken.

2) For VC underflow, the height of the crude oil in the clarifier need to be recorded.

3) Fill each sample in the test tube of 10ml. 

4) Put the sample in the centrifuge machine for 10 minutes.

5) The spinning the liquidat high speed will separate the content in the liquid by density. Visible layers will form after the spinning process finished.

6) Remove the sample from the machine and observe the layers formed on the sample

7) The top layer is oil layer, second layeris mixture of sludge, third layer is the water content and the bottom layer is the sludge. 

8) Record the volume of each layer and divide by the sample volume to get the percentage of the oil and moisture content.

Figure: centrifuge machine 

Figure 4: layer formation

Condensate, Sludge pit, Before stork

The sample from the condensate, sludge pit and before the stork will be taken once a day for daily process control. This sampling method usually takes few hours to 12 hours, so it can only do once a day. And the result usually only can be known on the next day.

Moisture test: 

1. Weight 48g of sample in a dish.

2. Heat the sample in the oven for 12 hours at103 degree Celsius.

3. Weight the sample.

4. Compare the weight to the initial weight of the sample, the difference is the moisture content.

Oil content test:

1. Use the dried sample from the moisture test and grind it into powder form.

2. Pure in 150ml of n-hexane and do the SOXHLET extraction for 4 hours.

3. Put the sample in the hour to dried for 2 hours under 103 degree Celsius.

4. Weight the sample and compare the difference in weight. 

Storage tank oil and dispatched CPO

The sample of storage tank oil will be taken in the morning everyday. The sample will be tested for the dobi, moisture content, impurities and FFA. The method of testing the moisture and FFA content is the same for sampling method the production oil. For the dispatch CPO, 4 samples will be taken, 2 of them will be given to the driver and another 2 will be used for testing in the lab. Same test with storage tank oil will be carry out on the dispatch CPO.

To test the dobi, uv-vis spectrophotometer will be using.

It measures the intensity of light passing through a sample, and compares it to the intensity of light before it passes through the sample. The ratio is called the transmittance, and is usually expressed as a percentage. The absorbance, is based on the transmittance. The spectrophotometer using in the lab is single beam spectrophotometer. 

To test impurities:

1. Put a filter paper in a grooch crucible with a 20-25mm internal diameter base.

2. Rinse it with 10ml of n-hexane.

3. Dry the grooch crucible in the oven for 30 minutes at 103 degree Celsius. 

4. Cool down the grooch crucible in the desiccator.

5. Weight and record the grooch crucible with the filter paper.

6. Add in 20g of oil sample into a conical flask.

7. Add in 100ml of n-hexane.

8. Carefully filter the sample by vacuum.

9. Rinse the conical flask with n-hexane to ensure all of the sample are flow into grooch crucible.

10. Rinse the crucible with n-hexane and wipe it with a tissue paper.

11. Dry the crucible in the oven for 30-60 minutes at 103 degree Celsius.

12. Measure the weight of grooch crucible and we can get the weight of the impurities.

Control parameter:

FFA < 7%

DOBI > 2.7%

Moisture <0.2%

Impurities < 0.05%

Press cake fibre & EFB press

The fibres from the screw press machine will be collected as the sample to test the oil losses, moisture content and nut breakage in the fibre while the sample from EFB press will tested on moisture and oil content only. The sample will be collected every 2 hours until the mill process finished. 

If the oil content in the fibre is high, the oil losses will be high. So the adjustment need to make on the pressing machine ampere reading to get higher press force. In same way, if nut breakage is higher than control limit, the ampere control of the machine need to be reduced. Proper adjustment need to be made to achieve the balance of both oil and nut optimum extraction.

Control parameter for press cake fibre:

Nut breakage: < 10%

Oil content:  < 7.3%

Control parameter for EFB press fibre:

Oil content < 3%

Hard bunch and USB

100 sample will be taken at both of the thresher every 2 hours. The number of hard bunch will be calculated from the 100 sample. This sampling result is important to determine the performance of the sterilisers. Pressure, temperature and holding time are the factor that affect the bunches. If the hard bunch and USB is more than the control limit, the pressure and holding time need to be increase for the sterilizing condition.

Control parameter: 

1st thresher < 5%

2nd thresher < 3%

Nut and kernel station

Overall whole kernel: > 40%

Production quality: moisture (6-6.5%), dirt & shell(5-6%), FFA (<3%)

Despatch quality: moisture (<7%), dirt & shell(<6%), FFA (<5%)

Place for sample:

Fibre cyclone

- To determine the kernel loss through depericaper, if the losses is too high, the winds speed need to be adjusted by the opening damper. The amount of whole kernel, broken kernel, split nut, nut will be counted by weight. 

Control parameter:

Total kernel < 1%

Ripple mill

-To determine cracking efficiency. The amount of whole kernel, broken kernel, split nut, nut will be counted by weight. 

Control parameter:

Cracking efficiency > 98%

LTDS

-To determine the kernel loss through LTDS. The amount of kernel will be calculated by weight.

Control parameter:

1st stage: kernel < 2%

2nd stage: kernel < 1%

Hydrocyclone

-Kernel and shell sample will taken from the hydrocyclone.

Kernel: percentage of dirt to the sample will be calculated. The dirts are the nuts, split nuts, stone, free shell and broken kernels.

Control parameter: 

dirt < 5%

Shell:

Percentage of kernel contained in the sample will be calculated. The amount of whole kernel, broken kernel, split nut, nut will be counted by weight. 

Control parameter: kernel < 2% 

Wet kernel (before entering kernel silo)

The kernel sample will be collected from the top of the kernel silo. This is to test the moisture and dirt of the kernel before enter silo for drying. The dirts are, nuts, split nuts amd free shells.

Control parameter: dirt < 5%

Kernel silo

To determine the moisture and dirt of the kernels. Sample of dried kernel will be taken before sending to kernel bunker. The dirts are, nuts, split nuts amd free shells.

Control parameter: 

Moisture < 7%

Dirt < 5%

Dispatched kernel

Dispatched kernel will be tested on FFA, moisture content and dirt content. 

Control parameter: 

Moisture < 7%

Dirt < 6%

FFA < 5%

Kernel test:

There are few test on kernel including moisture content, shell and dirt content, broken kernel and split nut and FFA.

For shell and dirt, kernel and split nut, the test will be carry out by separating the nut, split nut, whole kernel, broken kernel, shell depend on the testing criteria. Then the amount of every separated contents will be weighted. 

Calculation: To calculate the amount of kernel, the weight of whole nut will be divided by 2 and the weight of split nut is divided by 3 and times 2. By this method, we are assuming the weight of the kernel is 1/2 of the nut weight and 2/3 of the split nut weight. The other method which is more accurate is by mashing the nut to remove the shell and weight the kernel. This method is not practising in the lab because it is time consuming.

For moisture test, the sample of the kernel will be grind into smaller pieces with diameter less than 2mm. Then add in approximately 10g of grind kernel sample and heat in the oven for 4 hours. Then the weight different after heated and the initial weight of the sample is the moisture content. Divide it by the total sample weight to get the percentage of the moisture. The moisture content needed to be control under 7%. High moisture content will lead to increase in FFA and cause to kernel to be rotten quickly.

For FFA test, put the grind kernel to a filter paper that folded into a cone shape and put on a beaker. Add in n-hexane to extract the oil from the kernel. After that the steps to test the FFA in the oil extracted is the same as testing FFA in production. FFA is free fatty acid. The amount of FFA need to be as low as possible to ensure the good quality of the kernel. 

Boiler test

1. Boiler water

-Total hardness test

-Hydrate alkalinity

-Sulphite

-Phosphate

-Chloride

-Silica

-Total dissolved solids

2. Softener

-Total alkalinity

-Chloride

3. Feed water

-Total hardness

-Total iron test kit

-Chloride

-Total dissolve solids

Effluent test

There are total of 5 stages in effluent pond, holding pond, cooling pond, acidification pond, anaerobic pond, irrigation pond. Each effluent sample will be test on 3 tests, COD, BOD and pH. 

COD test

1) Insert 0.2ml of the sample into a test tube slowly to prevent the mixing of 2 layer.

2) Close the test tube and shake it.

3) Put the test tube in the heating block for 2 hours under 148 degree Celsius

4) Shake the tube after 10 minute removed from the heating block.

5) Put the test tube into cell compartment and press M.

BOD test

Initial preparation:

A) Aerated dilution water preparation

1. Fill a 10 litre bottle to 3/4 full. 

2. Induce air flow into the bottle for 6 hours using an air pump.

B) BOD nutrient mixture preparation

1) Prepare 2 bottle of BOD3 nutrient mixture powder and label with R1 and R2.

2) Pour 10ml of Aerated dilution water into the BOD3 mixture.

C) Preparation for control and sample.

- control:

1) Pour 500ml of aerated dilution water into a bottle.

2) Pour in 1.25ml nutrient mixture R1 and R@ into the bottle.

3) Shake the bottle to homogenized the mixture.

- sample:

1) Pour in the nutrient mixture and aerated dilution water according to table 1.

D) Preparation for BOD3 testing end reading.

1) Prepare 2 bottle and label it as C2 and S2.

2) Fill in the C2 bottle with the “control” bottle until full and S2 bottle with the “sample” bottle. Keep both of the bottles in the incubator BOD for 3 days.

E) Preparation for BOD3 testing initial reading

-Blank:

Take 1 test tube and pour in the the mixture from the “control” bottle and label as C1.

-Sample: 

Take 1 test tube and pour in the the mixture from the “sample” bottle and label as S1.

* Prevent the formation of air column in the test tube, fill the test tube until the mixture spill out.

F) Determination of BOD3 value.

1. Insert 2 drops of BOD3 R1 and R2 to C1 and S1.

2. Shake each test tube to make sure they mixed well.

3. Close the test tube for 2 minutes       Figure 9: Device to insert the effluent into test tube

4. Fill in 5 drops of BOD3 R3 mixture. Prevent the formation of air column

5. Set the method on the photometer PF-12 with 822.

6. Pour in C1 into the photometer PF-12 and press M button.

7. Record the reading of C1.

8. Repeat step 7 & 8 to determine the S1 reading.

BOD calculation:

C0 = C1 - C2

S0 = S1 - S2

BOD3 = D x (S0-C0) + C0

* refer the table 1 for the value of D.  Figure 10: Insert the sample to the test tube

 

  

Table 1

Discussion

Laboratory result is very important to monitor the performances of the process of the mill. Operator and assistance manager use test result from laboratory to control the process to achieve maximum OER and KER. Hence, the laboratory test must be precise and accurate all the time.

There are several common error happen during the lab test such as parallax error, zero error, handling method. Human emotional also can affect the handling of the sample and affect the test result. This is unavoidable, but monitoring of the lab test by the management should be done once a while to ensure the operator in the lab is caring out the test properly.

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.