HCL dosing

[chemEIT]

We are trying to install a HCL dosing system from HCL totes to our fumehoods. Can anyone suggest a good dosing system for such application.

 

[FiltrationEngineer]

It depends on the flow rate you need. You can use chemical metering pumps for small flows (LMI, Prominent, Neptune),

If the flows are higher than is practical for a chemical metering pump, try using a mag drive centrifugal pump (iwaki).

 

[chemEIT]

HCL liquid needs to be drawn in from a tote and delivered to the fumehood intermitantly. Will a chemical metering pump be capable of such suction and delivery pressures. What kind of control valves should be in place.

 

[FiltrationEngineer]

Yes. A chemical metering pump can draw liquid out of a tote. They are a positive displacement type pump that come with options such as manual or automatic speed control, and automatic on/off control. These are good for flow rates up from a small fraction of a gpm to about 1 gpm or so.

Its pretty typical to use them to draw liquid from a tote.

Here is an article:

http://www.chemicalprocessing.com/articles/2003/230.html

 

[chemEIT]

thanks for the inputs. I have one question regarding the outlet pressure from the metering pump. Will there be a pressure increase at the outlet of a running metering pump if the outlet is closed by a manual valve??

 

[cub3bead]

Sounds like a hazardous installation to me. If forced to put one in I would have a deadman switch at each hood which would open the delivery valve and start the pump. The system would deliver acid only as long as the deadman switch was held down at the hood. If you have multiple hoods I would interlock things so that acid could only be delivered to one hood at a time.

Positive displacement pumps usually have a built in relief valve to protect from over pressuring the discharge line. However, I would NOT leave the pump running all the time against a closed discharge. The relief valve could fail and you might not know it.

 

[pleckner]

Depending on the pump, a typical metering pump (positive displacement) can put out a huge pressure when deadheaded. The internal PSV is usually there (and sized) to protect the pump, not the dishcarge line (although you may get some arguments on this one). Nevertheless, you can't trust that PSV and should always put in a PSV to protect the discharge line. Pipe the PSV tail pipe back to the source vessel.

 

[FiltrationEngineer]

You don't want to deadhead a metering pump, or any PD pump. Something will break. In my experience, you don't put manual vavles on the metering pump lines. You just turn the pump on and off when you need flow.

I worked for a company that was sued because they used the polytubing that came with the pump. We were pumping 50% sodium hydroxide and the tubing popped out of the pushlock fitting and sprayed a guy with chemical. They lost the lawsuit. (It wasn't my project luckily).

 

[jeap]

Pleckner,

No arguments. Never, never!! install a positive dispacement pump without an external PSV. This PSV must be set below the design pressure of the discharge line. If you use a speed driver you barely can note if the pump is running when it goes at very low speed.

I suffered that some years ago, when somebody close the discharge valve and a cpcv line of caustic 32% expolded before my eyes. Furtunatelly, he and I used safety glasses and I just keep a little scare on my neck.

Internal PSV are designed to protect only the pump.

Regards

 

[pleckner]

Jeap: Glad you're OK.

 

[chemEIT]

Thanks guys for all the inputs. Does anyone knows of a deadman switch which can open/close a ball valve and switch on/off the metering pump at the same time.

 

[HEC]

Judging from the comments above, it sounds like a small PLC would suit the application.

Mark Hutton