Developing a control system and converting pounds per min. to gallons per min.

I am developing a moisture control system.I will start by explaining what I have at the moment.I am weighing material on a belt with a belt scale and it is anywhere from 32 - 36 tons per hour. I am also measuring the moisture in the material that is between 2 - 4%. For example , I am taking 32 TPH *2000= 64,000 lbs an hour. I am taking 64,000 *.02 ( for 2%)and determining that 1,280 lbs of this weight is water. We make our product at about 10% moisture , so the operator would select an additional 8% of water that would be an additional 5,120 lbs of water per hour. Divide this by 60 and we have 85.3 pounds a minute. This is what I would like to convert to gallons per minute and send that to a water valve. The flow valve is set for gallons per minute.

My question is, that I need to convert Pounds of water a minute to Gallons of water a minute. I weighed a gallon of water and it weighs 8.616 lbs. I am using a ControlLogix plc , and I was wondering which instructions and methods would
be best to use. I think I have everything working like I want it to, but I am stuck on this issue. But please feel free to let me know if something else does not make sense.

Thanks in advance , and have a great weekend.

I would use the Divide instruction.

GPM = 8.616 LBS/Min / Pounds of Water per Minute.

You may want to weigh several samples over a 2-week period, then calcuate an average weight for a gallon of water. It will vary depending on mineral content, air content, and temperature. You may even need to add a temperature correction factor to your equation, if the water temperature varies.

Standard weight for water is 8.33 pound per gallon at STP.
I first think at 8.6 I would check my scales - oops - DEDUCT weight of container.

Since you are desiring weight and volume calculations you must allow for temperature. A pound of water at 40F will NOT weigh same as at 80F

Dan Bentler

I think you mean a Gallon of water @ 40 Degf. won't weight the same at 80 degf. Of a pound of water will weigh a pound at any temperature.

Wouldn't you have to use a meter that measures the moisture content of water first.

Mark Buskell said:

Wouldn't you have to use a meter that measures the moisture content of water first.

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My guess is that it's pretty wet.

Yes, I am checking that before the scale. Thanks for all your responses.

Does the material on the belt have the same density as water? If it doesn't, your calculation for finding the weight of water in the product is not going to be accurate.

My guess is that it's pretty wet.

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Every time I checked, it read 100% moisture.

Standard weight for water is 8.33 pound per gallon at STP.

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Many errors are introduced by using the "standard" this or "standard" that. If you think about it, the only thing that matters is how much the water Rob is USING actually weighs. It really doesn't matter if the average water around the world weighs XX lbs/gallon. Water does not weight the same unless it is pure water, and that rarely gets used for process water (too expensive).

Most natural water has mineral content, so it weighs significantly more than pure water. In some mountain areas, the utility water is almost pure rainwater or snow-melt, but where the water comes out of lowland rivers, it is not close to pure. In Maryland, it could be either, but probably is mineral-laden river water.

Does the material on the belt have the same density as water? If it doesn't, your calculation for finding the weight of water in the product is not going to be accurate.

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Vic, Robs question was not how to find the weight of water in the product, but how to convert LBS/MIN of water to GALS/MIN.

My question is, that I need to convert Pounds of water a minute to Gallons of water a minute.

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I see that I wrote the terms reversed. It should have been:

Gallons Per Minute = Pounds of Water per Minute divided by 8.616 LBS/Gallon

I am thinking that if I simply have 64,000 Pounds Per Hour ( 32 TPH) at 3 % moisture I have 1,920 lbs of water per hour , and if I have 72,000 Pounds Per Hour ( 36 TPH) at 3% then I have 2,160 lbs of water per hour. Would this thinking get me close ?
I get this figure by taking a certain amout of dirt , weighing it , putting it on a burner , or just let it dry out for a few days , weigh it again and come up with a percentage using the subtracted moisture thru the drying process.

The difference between the weight of water at 40F vrs. 80F is only .0275 pounds and that is using pure water. I will have to check how much effect there is when you using water that contains minerals. Here is the link about water density.
http://www.engineeringtoolbox.com/water-density-specific-weight-d_595.html
I was wondering how many would catch my water moisture content post.

Would this thinking get me close ?

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Yes, exactly correct.

I get this figure by taking a certain amout of dirt , weighing it , putting it on a burner , or just let it dry out for a few days , weigh it again and come up with a percentage using the subtracted moisture thru the drying process.

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Does your process not have a built-in real-time moisture sensor on the conveyor belt somewhere? The moisture content seems to be a critical factor for your process, and it would most likely pay to have a moisture sensor and meter, giving a continuous reading of the mositure content.

Yes it does , I just did this in the lab and used this data to build on.

Great. You are good to go.