Humidity and Liquid level help

Hi,

I need a little help and some advice. First I need to dry wood bio-mass to about 10% moisture content. The wood is being dried by blowing hot air at about 500 degrees C over it. I was thinking that I may be able to get some info by installing a humidity sensor and the inlet, one at the outlet and one outside the unit to measure ******t relative humidity. The dryer is about 5 feet long and 6 feet wide. Does this make any sense or would you recommend a different approach.

The second issue is that I have two tanks, about 4 feet in diameter and 6 feet high. A mixture of oil and water will pumped into the middle of the first tank. The tanks are connected together at the top through a 1 foot diameter pipe. The idea is that when the water and oil mixture is pumped into the middle of the tank, the oil will go to the bottom and the water will stay on top. I need to install a pressure or flow level switch that will instruct the pumps to turn on and remove the oil from one tank and the water from the other. What we don't want it the oil getting to high and transferring into the tank that is suppose to hold the water. What type of sensor or instrumentation would you recommend for this application.

I know there was a lot there and any help will be greatly appreciated.

Thanks

Richard

rvitrih said:

Hi,

I need a little help and some advice. First I need to dry wood bio-mass to about 10% moisture content. The wood is being dried by blowing hot air at about 500 degrees C over it. I was thinking that I may be able to get some info by installing a humidity sensor and the inlet, one at the outlet and one outside the unit to measure ******t relative humidity. The dryer is about 5 feet long and 6 feet wide. Does this make any sense or would you recommend a different approach.

The second issue is that I have two tanks, about 4 feet in diameter and 6 feet high. A mixture of oil and water will pumped into the middle of the first tank. The tanks are connected together at the top through a 1 foot diameter pipe. The idea is that when the water and oil mixture is pumped into the middle of the tank, the oil will go to the bottom and the water will stay on top. I need to install a pressure or flow level switch that will instruct the pumps to turn on and remove the oil from one tank and the water from the other. What we don't want it the oil getting to high and transferring into the tank that is suppose to hold the water. What type of sensor or instrumentation would you recommend for this application.

I know there was a lot there and any help will be greatly appreciated.

Thanks Richard

Click to expand...

FIRST did you type too many zeroes?? 500C is about 1000 F wood kindle temp is about 400. Do you want to dry it or burn it? Blowing air over it is identical to clothes dryer especially if you have some sort of agitation or tumbling. Should work like charm. Measuring inlet and outlet relative humidity should work OK
AFTER you correct for temperature.
Think I would measure water content of air and not RH.

SECOND Most oils float on water. Most oil water separators I have seen use barriers to ensure the oil goes out the top and the water out the bottom. I would use 3 tanks mixture in center tank and water on the "left" tank connect at the bottom
oil in right tank connected at top.

Dan Bentler

Thanks Dan,

The unit that I am working on is already semi built, actually almost built. As far as we can calculate the air blowing over the wood entering will be quite hot between 400 and 500 degrees C. The resonance time is the dryer will be on the order of seconds and I assume that they expect this wood to be fairly moist.

Also the oil that I am referring to is a bio-oil, it has a specific gravity significantly greater that water, so I am assuming that the water will float above this oil. Specific gravity of 1.30 for oil and 1.0 for water. This water and oil separation system is already all custom built from stainless steel and they are not going to give me money to redesign until I can prove that the existing design will not work very well.


Thank

Richard

If you were given a value of 260 deg, and assumed it was deg C, and calculated it, you would get a value of 500, now if the value had been deg F, it would calculate out to be 126 deg C.
Even then you are still dealing with steam as your discharge and Humidity tests may be difficult, as I believe Humidity is a measure of water in air not steam in air, ( I think )

500 deg C makes steel glow a dull red.

If the oil is from wood then you are talking about turpentine and like most oils its specific Gravity is near 0.86 of water, and the oil would float on water,
Then a condutivity probe could be used to determine when the water level reached the probe and start a water pump to remove excess water.

Specific gravity of 1.30 for oil and 1.0 for water.

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If the above values are reversed then you get a specific gravity of about 0.77

My sugestion is for you to confirm your values with the customer, as I am agreeing with Dan

rvitrih said:

Hi,
The wood is being dried by blowing hot air at about 500 degrees C over it. I was thinking that I may be able to get some info by installing a humidity sensor and the inlet, one at the outlet and one outside the unit to measure ******t relative humidity.

Richard

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Finding a humidity sensor that can survive these extremes might be a challenge. I'm suggesting you look at the "delta T" concept. http://lmgtfy.com/?q="delta+T"+wood+moisture

I'm also very suspicious of your numbers. Anything "bio" in todays politically correct environment would be using some sort of waste heat to dry the wood. 500 degrees C is high grade heat not waste heat.

Delta Controls makes a sensor that can detect differences in fluid composition. Check out their model 633 at http://www.deltacnt.com
This could be used to detect when the oil level reaches a certain point. And I would definitely double check the temperature spec...

Hi,

The numbers are correct. This is a bio-mass to biooil conversion unit. The duct work and dryer and all lined with 4 in refractory bricks, and I assume that the temp in drier might be even higher. The main heat source is producing heat in the order of 500 to 1000 degrees C. Also the specific gravity of this oil is approx 1.20, higher than water. I believe that water will float on top of this oil.

Thanks

maybe presure mesurement can help indentify how much of the tank volume consists of oil? If presure is above presure than tank full of water then it is clear that presure excess will tell you how much there is oil, if that oil is heavier than water. But u must know fluid level of the tank and precisely calculate presure.

rvitrih said:

the oil will go to the bottom and the water will stay on top. I need to install a pressure or flow level switch that will instruct the pumps to turn on and remove the oil from one tank and the water from the other. What we don't want it the oil getting to high and transferring into the tank that is suppose to hold the water. What type of sensor or instrumentation would you recommend for this application.

Click to expand...

You will need two analog devices. One to measure the top of the liquid level. One to measure the pressure at the bottom of the tank. The pressure will change with oil level, even if the level of the combined liquids stay the same. It will be a combination of pressure and liquid level that determines where the boundary is.

One problem will be if the two are still mixed.

The pressure sensor needs to be kept as far from any outlets or inlets as possible to keep the readings accurate.

danw might be the guy to ask what sensor would be best for your application.

OK so he has had two people ask him if he has his numbers right. He has said yes twice so he must be sure of what he is doing - he is the on scene guy after all. I bet in the near future he will get darn tired of explaining his sinking oil. Come to think of it PCBs also sink.

How soluble in water is the oil? What happens if oil contaminated water goes to sewer? Is this a big EPA thing?

I think relying on good old gravimetric will do the job. I would start with just this and not worry about instrumentation at initial stage. I find myself having to put my mind in reverse ie taking oil off bottom and water off top.
How many gallons per day of mixture are you thinking of doing
AND of that mix
how many gallons of oil and how many of water?
Will this concentration be fairly consistant?
Have you run a lab bench top simulation of this? I sure would.
What will be allowable water content of finished product?

Oil water separators I have seen used several steps not just one or two as is proposed here.

For wood drying
I think I would talk with Vasaila they make a variety of humidity sensors.

At this "high" temperature I envision fire problems.

With 15 years field experience in safety and health I have seen several and read of many dust explosions / fires in several industries and processes. Grain handling, plywood and particle board plants, aluminum scrap handling and dust collectors at Boeing. That gives me enough knowledge to ask the question and I am NOT the goto answer guy on this issue. A fire protection engineer comes to mind. Pay close attention to Hazardous Location electrical criteria. Grounding and bonding for conveyer belts may be needed.

If the chip size is consistant and large maybe not much problem. If there is a mix of chips and sawdust or worse yet sanding dust I think a fire will be a higher probability. Exhaust ducts are known to explode in plywood and particle board plants becuase of sanding dust. Static on conveyer belts was enough to cause the roofs to blow in a couple of Oregon USA particle board plants. The whole issue here will depend on particle size air velocity and whether or not the particles can get airborne in sufficient concentration to cause explosion. Wood is an insulator and will be prone to static problems.
Dust explosions are violent - just look at grain handling.

Doncha just hate it - ask a simple question and get all these dang problems??

Dan Bentler

Humidity

Hi

Okay here we go, the unit will in theory produce 25000 gallons of oil per day, the amount of water that will be used to condense is still unknown, but I should have some calculations done soon. Some water will mix with the oil, we might have to put in separators down line of the initial separation process. Once up and running the concentration will be very uniform.Simulations have only been theoretical, this will be a try and adjust process. Allowable water content in finished product is 30%, bearing in mind that the oil already contains some water do to the extraction process even before it gets condensed.

For the drying, it is assumed that the wood chunks, not chips or sawdust will be roughly the same size, this size will be determined from testing once this is up and running. I am under the impression that the wood will be fairly fresh and have a high moisture content. The dryer used very high temps and a very short resonance time in the dryer.

I did not design any of this, I have however been tasked with making it work.

Cheers

Thank for all the help

Richard.

I am also wondering if anyone here has any experience with direct injection spray in rapid condensors. If you do please send me a pm it would be greatly appreciated

rvitrih said:

I did not design any of this, I have however been tasked with making it work.

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Keep in mind the fellow in this thread, he is trying to move an object at a constant speed back and forth. His object is connected to a crank. While this makes for smooth direction transitions. The object is always accelerating and decelerating and never at a constant speed.

http://www.plctalk.net/qanda/showthread.php?t=45976

Correct me where I am wrong
1. You are making this oil by some kind of distillation process
2. You are condensing this oil by water spray
3. You are then separating water from oil

In essance you are using one of the better methods to get a pure product then contaminating it with water to get it to condense.
What is crossover temp on the still?
Instead of condensing with water spray can you take an oil to air heat exchanger and preheat air to your wood dryer. I would not use water spray to condense I would use a water jacketed heat exchanger as final condensor.

You are the guy who did not get included on the design
1. You are now entering one of the better schools ie school of hard knocks (aka experience)
2. You have my sympathy
3. Sounds like the outfit I last worked for. Thank God I am gone.

Dan Bentler

leitmotif said:

school of hard knocks (aka experience)

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"Experience is that marvelous thing that enables you to recognize a mistake when you make it again."

-- Franklin P. Jones

Very often I find myself fixing mechanical problems with electrical solutions.