7 replies to this topic

[jamesnzx]

Hi,
Can someone kindly suggest me some methods of controlling upstream pressure as well as downstream pressure, whereby the upstream pressure should be keep at about 50 to 60bar (reject from reverse osmosis unit) and downstream pressure at 20bar maximum since the downstream equipment is sensitive to pressure.
Thanks in advance

[Zauberberg]

Control valve should be sufficient. It is commonly employed for pressure regulation.

[fallah]

You mean simultaneously controlling upstream/downstream pressures?

[jamesnzx]

yup, the reject of the RO unit is used as the feed to another equipment (NF unit) which it has to maintain at 20bar(downstream pressure) and the reject of the RO unit(upstream pressure) to be maintain at 50-60bars

One of the idea which i have come out with is to have a back-pressure regulator at the reject of the RO unit and a pressure regulator just before the NF unit, thus, regulating both the pressure upstream and downstream. However, in between this section of pipes, it results in an discharge line with another backpressure regulator and compromising the feed flowrate into NF unit. Any other better suggestions or constructive feedbacks are welcome. Thanks

[Zauberberg]

We used to operate a few RO units in Bioko Island and I can't recall any kind of flow/pressure regulation problems. Normally the Reject stream line is equipped with a back-pressure regulator so as to maintain the RO unit pressure at desired value. By controlling the Permeate flow, the flow of Reject stream is automatically predetermined and the control valve downstream of the back-pressure valve cannot affect the Reject stream flow from the RO unit. So you can resolve the pressure letdown issue by installing a PC valve upstream of the NF Unit - unless we are missing some information.

[Zauberberg]

These units are normally fully packaged, standalone skids (I remember "Metito" being the supplier in EG) so one of the options you have is to contact these people and make them aware of your concerns regarding the interconnecting system. Although I remember "Metito" technical support service as extremely poor one - they almost wanted to charge every single sentence they used to send by e-mail. Rubbish.

If nothing else, you can post a sketch here (include all the existing regulation loops) and I'm sure we can resolve the problem.

Good luck,

[djack77494]

A sketch is always a good idea. In general, you cannot control two independent variables (like upstream and downstream pressures) with a single control loop and, similarly, you should not attempt to use two active control loops to control a single variable. It sure sounds like you are wanting to independently control two variables, so plan on two control loops.

[Padmakar Katre]

Hi,
Can someone kindly suggest me some methods of controlling upstream pressure as well as downstream pressure, whereby the upstream pressure should be keep at about 50 to 60bar (reject from reverse osmosis unit) and downstream pressure at 20bar maximum since the downstream equipment is sensitive to pressure.
Thanks in advance

Dear,
As specified by that the limit for downstream pressure of 20 bar can be maintained by a PIC taking pressure signal from downstream PT. Now in case of upstream pressure could you tell us what develops this much of the pressure of 50-60 bar? You problem is quite similar to PRDS where the downstream steam headers' pressures are maintained on PIC and upstream excess pressure is vented through a silencer. So in your case the if the upstream pressure goes higher as the downstream is maintained at 20 bar then you need other option to relieve it through an upstream PT signal. Again you have issue when an upstream pressure falls down the downstream PIC will open wide to maintain 20 bar in the downstream. It's bit complicated. Provide us a sketch and little description of the system so that we can comment.