Sludge Depth Level Sensor For Slurry Pit

[ericvd]

Hi,

On the site I am curretly working we have the requirement to measure the sludge depth in our bottom ashing slurry pit. The arrangement as follows:

- The inflowing slurry is mixture of approx (70% water, 20% sand and 10% large ash klinker rocks). Ash clusters up to 50mm diameter.
- The slurry is mixed with water, but it enters the slrry pit allready mixed with the ash, so its about as clear as coffee.
- The pit is located below surface, so no entry from the sides. Its about 6m below surface and the slurry level is about 1m below surface, i.e. the range of measurement is about 5m.
- The pit is tapered downwards in order to collet the slurry at the suction.
- 3 large suction pipes and other stuctrures at the bottom of the pit.

We have doubts of the effectiveness of an ultrasonic device as the slurry will be fairly agitated, so particles will be floating around. Also, the shape of the pit and all the pipes at the bottom might scramble sound waves. Also, the fact that we might drop water level below the instrument might further render it ineffective.

We have also looked into a "smart-dive" system that actually does ultrasonic density measurement, by moving up and down and as such can see density changes. It seems nice idea, but we are concerned about driving the thing into a bed of settled sand and rocks.

Accuracy is not our most important factor, more reliability and robustness. so we were thinking in the lines of a bobbing device that is dipped into the pit and stops when it hits the sand bed, but not sure how to go abouts building something like this, or whether there is something on the market perhaps.

Oh and lastly, the idea behind the installaion is to detect sand buildup in the pit that occasionally cause our pumps and pipes to block up.

Thanks in advance

 

[RaRo]

Level measurement may not be the only way around your pumping issue.
Would the apparent density of the slurry be correlated to the sand buildup? If it is, you may be able to simply use a vibrating blade density probe upstream the pump in the pipe if the speed is enough to prevent clogging the blades.

 

[Compositepro]

You can make a type of density meter with a differential pressure transmitter. Connect the D/P cell to two dip tubes that are purged with a low flow of pure water. One tube terminates near the bottom of the sump and the other near the fluid surface level. The differential pressure reads zero with no slurry and will increase as the slurry level increases.

 

[ericvd]

Thanks for the ideas. There is problems with a DP level measurement:

- we dont have access to the very bottom for the pit (its in the ground)
- the density of the solids varies as differnt areas is ashed, i.e. fine sand if the mills is ashed, course ash and rocks if the boiler is ashed and also a combination of the two streams.
- even if the two factors above didnt exist, I think there will still be an issue with measuring the hydroulic pressure of the sand/rocks, as sand is not liquid, I think you'll pretty much measure the water pressure.

The density cannot (easily) be related to the sand buildup. We have allready considered density measurement for this but it wont be usefull as fistly, we'll have to get the slurry mixture homogenous to give us a good measurement, which is not the easiest thing to do...think lots of sand and rocks in a swimming pool...and secondly even if we could, we dont really know what density is acceptable at this stage (however, it could probably be established in a lab or by costly trail and error). The other issue with putting the probe in the pipe is the fact that it will probably last few days if you consider what we are pumping....rocks up to 80mm dia, mixed with sand and water. Another problem is that we would like to detect sand buildup prior to switching on the pumps, otherwise we might end up detecting sand after the pipe has been blocked, or in the process of blocking up, which almost defeats the purpose.


Any other ideas perhaps?

Thanks

 

[RaRo]

Going,
there exist weighted level 'floaters' for level or liquid/liquid level measurement. Those use either articulated arms (I would not recommend those) or piston/telescopic rods.
Our supplier is Bilfinger Berger Industrial Services. Their devices are specifically made to the service (length and weight adjustments).

 

[PersonalProfile]

I am familiar with device which may be of use: "jumping monkey" which is used to measure the level in ore passes (have also seen it used to measure the level in arduous environment such as a kiln), however I could not find any information online.

It consists of a mass which is lifted up and down via a winch where the line tension is measured - a slack line indicates the level!

Regards,
Lyle