Relation between pH and MOL (Milk Of Lime)

@anu-sekar-0vMhfV • Oct 23, 2024

Oct 23, 2024

1.4K

I have undergone an industrial visit to Sugar industry. In Sulphitation area ( In sugar industry), Sugar juice is mixed with SO2 gas. But if it is mixed directly, the sugar juice becomes acid. So to avoid this, MOL (Milk Of Lime), which is pH Booster is added with juice before adding SO2. After adding MOL, pH should be maintained around 8.9 or 9. According to the pH value we should maintain the flow of MOL. Now my question is, " Is there any relation already existing between the flow of MOL and pH value?"
for example, if i want to increase 1 pH value, what should be the flow rate of MOL?

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Ramani Aswath

@ramani-VR4O43 • Jul 22, 2013

There are a large number of variants of sugar refining process. SO2 can be added before, together with or post MOL addition. Control can be manual or automatic. If the pH is too acidic inversion of sugar takes place.
MoL has a pH about 12.3. Obviously the quantity of MoL will depend upon the SO2 in the liquor.
This document gives some general info on the various processes in use:
<a href="https://www.sugartech.co.za/sulphitation/" target="_blank" rel="nofollow noopener noreferrer">Sugar Engineers</a>

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ANU SEKAR

@anu-sekar-0vMhfV • Jul 22, 2013

A.V.Ramani
There are a large number of variants of sugar refining process. SO2 can be added before, together with or post MOL addition. Control can be manual or automatic. If the pH is too acidic inversion of sugar takes place.
MoL has a pH about 12.3. Obviously the quantity of MoL will depend upon the SO2 in the liquor.
This document gives some general info on the various processes in use:
<a href="https://www.sugartech.co.za/sulphitation/" target="_blank" rel="nofollow noopener noreferrer">Sugar Engineers</a>
In the industry I have visited, the pH control is manual. I have decided to do automation. can you please suggest me some ways to carry out this project.

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Ramani Aswath

@ramani-VR4O43 • Jul 23, 2013

On-Off controls work satisfactorily where large masses are involved. There are are many pH sensors available in the market. Use one of these and a set point control that switches a MoL feed pump or solenoid valve if gravity feed is used. MoS is a mild alkali. There will be no wild swings of pH if excess is added.
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ANU SEKAR

@anu-sekar-0vMhfV • Jul 23, 2013

I have read in an IEEE paper that "pH is a non linear parameter and conventional P, PI cannot be used" In that paper they used Adaptive non linear controller.
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Ramani Aswath

@ramani-VR4O43 • Jul 23, 2013

If the mass is large, the rate of change of a parameter is slow. On-Off control is best in such situations. This is true about temperature also, even though accurate sensors are available.
In the case of sulphitisation, there is no great accuracy needed, since manual controls are often used.
Adaptive non linear control can be used. However, is it needed?
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madhu27

@madhu27-Yq7VLh • Jul 23, 2013

Sir, On-off control is used for manual operation. But for automation, is it enough?
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Ramani Aswath

@ramani-VR4O43 • Jul 23, 2013

Manual control is where an operator reads a pH meter and adjusts by hand a valve or a pump to put in more MoL till the value needed is reached.
In On-Off auto control the variable is converted into a voltage (or current), compared with a set value and the pump or valve actuated depending on the value.

I am using an on/off control with a microprocessor to regulate the temperature in a sterilizer. The processor is used for monitoring various parameters and abnormal conditions.
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madhu27

@madhu27-Yq7VLh • Jul 26, 2013

Sir, for a batch process it works good. But it is a continuous process. By using on off control only 100% open or 100% close is possible. How can it be used for continuous flow?
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Ramani Aswath

@ramani-VR4O43 • Jul 27, 2013

Can you put up a sketch or a line diagram of the process? Are you having just a pipe through which the cane juice flows without any tank in line? Are you talking about regular sugar manufacturing or some other industry?
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ANU SEKAR

@anu-sekar-0vMhfV • Jul 27, 2013

A.V.Ramani
Can you put up a sketch or a line diagram of the process? Are you having just a pipe through which the cane juice flows without any tank in line? Are you talking about regular sugar manufacturing or some other industry?
Sir, Myself and Madhu27 are batchmates doing the same project. we are talking about the regular sugar industry. In the industry we visited, they dont have any seperate mixing tank for juice and MOL. It gets mixed in the Line. After mixing the pH should be around 8.9 or 9.This pH can be maintained by controlling the flow of MOL. And this mixture when mixed with SO2, the pH should be maintained around 7.3 or 7.4. For maintaining this pH value, we should adjust the flow of SO2. The primary controlled variable is MOL. Only if the final pH is not 7.3 or 7.4 (after Sulphitation) we should control the flow of SO2, since SO2 is costly than MOL.
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Ramani Aswath

@ramani-VR4O43 • Jul 27, 2013

Where does the mix go after all this is done? What is the next process?
Where are you people located? What exactly is the project that you are working on? If it is a course related project that is already configured, it is better that you concentrate on the execution of the proposal rather than scouting around.

If some kind of control scheme has already been though of then let us look at how to go forward with that instead of starting from scratch.
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ANU SEKAR

@anu-sekar-0vMhfV • Jul 27, 2013

A.V.Ramani
Where does the mix go after all this is done? What is the next process?
Where are you people located? What exactly is the project that you are working on? If it is a course related project that is already configured, it is better that you concentrate on the execution of the proposal rather than scouting around.

If some kind of control scheme has already been though of then let us look at how to go forward with that instead of starting from scratch.

It goes to clarifier in sugar process. we are located in Coimbatore,Tamil Nadu, India. Our project is pH Automation in sugar industries. Now we have to design or choose suitable Controller Which can effectively control pH.
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Ramani Aswath

@ramani-VR4O43 • Jul 27, 2013

I assume that the limed syrup is delivered directly to the clarifier where the precipitation of the sulfite and impurities take place.
I still feel that pH in the clarifier should be monitored and lime added. Since the clarifier volume will be fairly large, an on-off control would work. If you are very particular, a less than needed MoL flow can be set in a constant supply and the on-off controller only adds the extra needed to control the pH.
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