Softener under performing 1

[vij36]

Dear All,

We have installed a brand new water softener with two units each of 1000 liters resin capacity.
Our hardness of water is 250 ppm. So for a 50 ppm outlet hardness we expect the OBR need to be at least 2,00,000 liters for each unit.

After filling brine (150 kg each unit) and after a water flow of about 70,000 liters (each unit) hardness showed 6 ppm which is up to the mark. After flow of another 25,000 liters (total flow through softener is 70,000 + 25,000) the softener hardness is measured 180 ppm. For 95,000 liters flow itself the hardness is increased to 180 ppm from 6 ppm.

For 1000 liter resin tank when 900 liters actual capacity is considered the softener supposed to perform up to 2,00,000 liters of inflow.

Vendor says the water may not be passing through all over the resin tank area which may be one of the reason.

Could throw some light what may be the other reasons.

Thanks,

 

[vij36]

one reason the vendor is speculating is:

we are pumping softener output water to an over head tank. vendor says may be the back pressure from overhead tank preventing softening.

If that is the case then why for first 70,000 liters the softener output shown 6 ppm.

we are trying to find the actual reason

 

[PEDARRIN2]

Softeners need certain flow rates or the flow will channel through the resin and not contact the entire bed.

I always use 5-7 gpm/cf and 8-10 gpm/sf as guidelines

 

[bimr]

To ensure low hardness leakage, the water softener should be sized for 6 to 8 gpm/ft2 of bed area and 4 to 6 gpm/cubic feet of resin. Your regeneration should be using 10-12 lbs of salt per cubic feet of resin.

Why don't you post the diameter of the water softeners, the amount of resin in each water softener, the amount of salt used, the flow rates, and the intended use of the treated water.

 

[vij36]

Dear Sir,

There are two units of Pentair 3672 softener units cascaded .

I see two dimensions in the spec of 3672 Pentair spec.

36x72 and 760 mm x 1860 mm


Each unit data:
3672. Size 760 mm x 1860 mm.

Amount of resin 1000 liters. Effective area 900 liters

Salt 150 kg

Inlet to softener flow rate .
Max 7000 lph
Min 2000 lph

Purpose is general usage of water like bathing, cleaning, other than drinking purpose.

Please let me know if I miss any data.

Thanks,

 

[bimr]

My calculation shows the water softener should have a softening capacity of 250,000 liters per softening unit with the stated resin volume of 1000 liters.

Good design practice is to allow approximately 35% to 50% freeboard to allow room for the backwash bed expansion in a softening tank. For a tank with a 3 foot diameter and a straight side height of 6 foot, that equates to a volume of 1200 liters in the softening tank. If 50% freeboard was used, the tanks would only hold 600 liters of resin.

Confirm that the total volume of resin is in each tank. You can stick a ruler into the tank to measure the resin depth. Note that some of the tank depth may be taken up with a sand/gravel subfill under the water softener resin.

What is "OBR"?

If you want 50 mg/L hardness, you will have to bypass a portion of the flow.

Ask the water softener supplier for a copy of the water softener capacity calculations.

 

[PEDARRIN2]

At 8 gpm (sorry for the unit switch), your softener is way too big (36" diameter). You are likely channeling through the middle of the resin and getting hardness break through.

You do not indicated your daily flow volume, but since it seems to be domestic use, it is likely not a lot. Your hardness is not too excessive, I would recommend something like what is in the file I have attached (or similar manufacturer).

With these types of softeners, it is difficult to get less than nearly 0 hardness until you have hardness breakthrough. Mixing downstream gets tricky unless you have a consistent and/or constant flow rate.

 

[bimr]

Agree with PEDARRIN2 that if you are operating at 2000 lph, there may be channeling. However, it should work at the 7000 lph flow rate. If you plan to operate at the low flow rate, you can install a recirculation loop which will resolve the issue.

Are you operating both tanks at the same time?

Along with my previous comments, this appears to be an odd arrangement and not economical for you.

 

[vij36]

Dear Sirs,

What is "OBR"?

Output between regeneration. Softener output flow between two regeneration.

Are you operating both tanks at the same time?

Yes

I would send a softener schematic setup and Softener spec soon. We are diving the flow to two units separately.
Meanwhile here are some more details:

Softener unit (3672 Pentair )total volume is 1000 liters. Out of which 900 liters is resin. May be 70 liters is free board. For softener resin should be almost full so that softening happens properly is the vendor opinion.

Pre covid our water requirement was about 3,50,000 liters per day.
Source of water is external water tankers which has Total Hardness of 470 ppm and Ca as CaCo3 is 325 ppm.
So we thought of doing 50% softening and blend it with raw water. And softener designed accordingly. 2 units of 3672 with each having 900 liters of 220 na resin type.

At present water consumption is reduced from 3,50,000 to 2,50,000 liters per day. And raw water hardness is only 225 ppm since source of water is internal drilled bore wells.

When a pump and three bore wells run in the campus, the pressure at each softener unit shows 4.5 kg with flow 7,000 to 8,000 LPH.

When only bore wells run and softener unit pressure shows 2 KG pressure with flow 1.5 to 2,000 LPH.

Water demand profiling we do not know since water demand varies with number of parameters such as weekends, special events etc.,

There is separate inlet to each softener unit.

So as you both pointed, low inlet flow rate of 2,000 LPH to Softener is causing hardness break through. I will work out on the re-circulation loop after understanding the water demand profile in a day.

Will the Softener spec shows what is the minimum inlet flow required to avoid hardness breakthrough?

Yesterday the vendor tried to do 1200 liters brine regeneration but it is taking only 250 to 300 liters and remaining coming back to brine tank. He is suspecting back pressure from overhead tank not allowing brine to enter softener unit and forcing back to brine tank.. He always says Overhead tank pressure is the issue. Overhead Tank height 17 meters. He is planning to make an air release valve on top of Softener unit so that any air in Softener to over head tank will be vent out.

Now can we conclude that because the softener is not taking brine fully and giving 75% back to brine tank, that is the reason the softening not happening ?

I shall come back with schematic, softener spec.

Thanks,

 

[bimr]

Not sure that is the problem. The water softener outlet is usually shut off during regeneration.

 

[PEDARRIN2]

Your initial post said hardness is 250 ppm. Now you are saying 470 ppm. That is almost double. You could definitely be having hardness breakthrough due to channeling.

I have never had good success blending domestic water downstream to get less than 0 gpg. The flows are too variable (bathroom sink running at 0.5 gpm and toilet flushing at 25 gpm). It can be done with some rather elaborate controls, but typically not inexpensive and maintenance intensive.

 

[bimr]

I don't believe that a water softener is a good recommendation for your facility as the hardness is too high. The water will end up being corrosive as well.

You will be better off with what is known as a Low Pressure RO also known as a Nanofilter.

Low Pressure RO

 

[PEDARRIN2]

https://wcponline.com/2019/03/15/water-softeners-and-corrosion/

 

[bimr]

https://wcponline.com/2019/03/15/water-softeners-a...

Have to take exception to that extremely poor technical article written by a recent graduate nurse and a chemist, both of whom appear to know very little about water chemistry. The water quality association is a trade group that promotes water softeners. The chemist is also a promoter of electrochemical water treatment gadgets that are totally worthless.

The article doesn't mention the Langelier Saturation Index which is the most widely used predictor of water corrosion.

Langelier Calculator

The premise of the article is that water softeners don't increase the corrosivity of water. That would obviously make the funders of the water quality association happy.

However, if you look at the LSI of the raw water and remove the hardness, you can observe that the softened water is much more corrosive. It changes the water from being slightly corrosive to being seriously corrosive. The poster did not reveal the water quality parameters so I assumed a pH of 7.7, conductivity of 500 mg/L, HCO3 of 100, and a water temperature of 25.

Use the LSI calculator and see for yourself.

 

[PEDARRIN2]

BIMR,

OP did not indicate all the water quality parameters, and what was indicated changed. Totally agree that LSI needs to be determined which requires good water analysis. But what was the basis for your assumptions? Would other, just as reasonable, assumptions push the LSI into less corrosive nature?

I use WQA information with a grain of salt (pun not intended). They are a trade group and some of their members do promote unusual (snake oil) means of treating water. But as a trade organization, I would assume they have installed many softening systems and have some tribal knowledge which, while not necessarily empirical, should not be neglected. If their installations were producing corrosive downstream water, I would assume some of those situations would cause a certain lack of customer appreciation which would result in lower future sales - something no salesman wants. So, I also take their "opinions" into account.

I have also designed many commercial systems with softeners with high(er) hardness levels and have yet to have a client come back 5, 10, 20 years later and complain about their piping leaking due to corrosive water. Maybe the water chemistry just worked for me.

I know all this is anecdotal and not empirical - but it is real.

 

[bimr]

OP did not indicate all the water quality parameters, and what was indicated changed. Totally agree that LSI needs to be determined which requires good water analysis. But what was the basis for your assumptions? Would other, just as reasonable, assumptions push the LSI into less corrosive nature?

The assumptions are reasonable. What makes this water corrosive is the removal of the extreme hardness. Ion exchange softening of waters with moderate or less hardness is not generally problematic.

 

[vij36]

Dear Sirs,

Sorry for the confusion created in hardness number of inlet.

Actually the hardness is 375 when were sourcing water from out side of our campus.
Now the hardness is 250, the source of water is our inside campus bore wells.

The fluctuation in hardness become my nightmare. The day the brine recharge happens the softener output hardness will be below 10 ppm after 1 day or so it increases up to 150.

We have two sump pumps and 4 bore wells.
Based on some some complex logic in the overhead tank level the pumps will be switching on.
We want to blend raw water with softener outlet water so that hardness is maintained near to 100 ppm.

Now the issue is flow fluctuations at softener inlet.
Some times the flow becomes up to 8,000 LPH with pressure 3.5 to 4 bar which I can see at each softener gauge and on multi port valve. And some times the flow goes below upto 1,000 LPH with pressure 1.5 Kg/ cm2.

The vendor says he needs constant pressure and flow at each softener unit. His concern is if flow is too low during brine recharge then the salt intake don't happen to softener and will go back to brine tank.

Softener spec is:
minimum working pressure 1.8 bar
max working pressure 3.5 bar
max flow rate 14,000 LPH.

Our target hardness after blending is 100 mg/ L since our management don't want very low hardness.

Attached schematic of our Softener setup. One more vendor objection is the output of softener directly goes to over head tank which is at 15 meter height which he says creating back pressure.

Kindly give advice to overcome the hardness fluctuations.

Sincerely,

 

[bimr]

As PEDARRIN2 (Mechanical) observed, your water softeners are oversized for the application. The minimum flow (to prevent channeling through the resin) through a 36-Inch diameter water softener should be approximately 1 liter per sec.

If you want it to work correctly, install recirculation loops around each water softener. Size the recirculation pumps for 1 liter per sec. One pump per water softener. Add isolation valves and a non-return check valve on the recirculation loops (not shown on the sketch).

You will need a pump like this for the application. Capacity 1 liter per sec @1.4 bar.

Link

 

[vij36]

Dear Sirs,

I apologize in advance if the below concern raised by our plumber and softener vendor does not make sense.
The water simply will remain in loop and don't get lifted to Over head tank at 15 m height.

 

[bimr]

The recirculating loop provides pressure to recirculate only. The incoming pressure from the borehole will lift the fluid to the overhead tank. The same incoming pressure that is lifting the fluid now.