I am a final year engineering student and doing my industrial project in pulp and paper industry. My project involves the level measurement of slurry (95% water and 5% pulp) and in industry they use capacitance based DPT level measuring technique. my doubt here is DPT is completely dependent on density of the fluids or solids inside the tank, but how come they use this to measure the level of slurry which has diff. density or SG?

Plz help me towards it.....

 

You are mixing two completely different technologies
Capacitance and DPT which I assume is Differential Pressure do not go together.

Perhaps you mean Capacitance or DPT.

The differential pressure would be effected slightly by the change in density but not enough to offset the simplicity and reliability advantages. The percentage of pulp is likely to be fairly constant for a given tank.

Roy

 

> I am a final year engineering student and doing my industrial project in pulp and paper industry. My project involves
> the level measurement of slurry (95% water and 5% pulp) and in industry they use capacitance based DPT level

I should say it's a long time since I worked at a pulp mill. on further thought, Is it possible they are using the capacitance to correct for the DP level? they could also be using the difference between the two readings to back calculate the pulp to water ratio.

I think you will find a great variation between pulp mills on how they measure levels.

Hopefully a tech with current mill experience will pipe up.

Roy

 

Hello sir,

Thank you for your reply post.

As you worked in paper industry as per your words, can you please share what kind of measuring technique is suitable to measure the De-inked pulp level based upon your experience.

In DPT,the level is measured based on the formula,
Level=(S.G or density)*(diff. Pressure).

As we know the pulp consistency is 5% and remaining 95% water. can we just measure the diff. Pressure and take 5% of it, multiply it by pulp density and remaining 95% by water density and then add up both?

My next ques. Is can we use capacitance type level measurement where the agitator spins all the time inside the tank?

 

Sorry, when I said it's a long time I mean over 30 years, I don't want to steer you in the wrong direction. I think you have your formula transposed or perhaps I just miss understand
Differential Pressure = Level * Density
Therefor Level = Differential Pressure / Density

Pulp mills have a few terms peculiar to that industry
What do they mean by %, percent of Volume or percent of Mass

I thought you were telling me they do use capacitance.
I was a bit surprised by that, it wouldn't be my choice for an agitated tank, I recall from working in an engineering office they used mostly DP.
but things have changed a lot in 20 years, I would think they use all sorts of different technologies now.

All you Pulp & Paper guys feel free to jump in and enlighten us

 

I understand that 30 years is a very long gap and a big THANKS to you for helping me out eventhough......
Sorry for my mistake on the level calculation formula and your way is the correct one
Level=DP/ S.G or Density.

Prior to my knowledge the % indicates the volume of pulp.

For instance the volume of the tank is 50m^3 and when i mean 5% of pulp consistency, the pulp must be of 0.25m^3 and remaining of water inside the tank.

 

Pulp density varies with consistency. But for the purposes of measuring a tank level then near enough is good enough. Assume a density of 1.013. If the tank overflows at 100 % then get an instrument tech to re-range the DP transmitter.

Realistically, exact accuracy is not required. You only need to know if the tank is empty, somewhere in the middle or about to spill over into the sump.

Rob
www(.)lymac.co.nz

 

Sir,

Hope i am getting the exact answer now with your help..thank you....let me post new thread if i have further doubts of it....

 

We use this technique to measure the level of juice (with pulp) in big tanks at the plant where i work. The reason we use this is technique is that the density wont diff much between different batches. Even if it diff. it wont be more than 0,5%. We also use vibrating forks for high and low level signals so the level doesn't have to be exact. I just started a project for calibrating the sensors properly and if you are accurate with your settings you will reach a precision of 0,5%.