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Guru
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Heating 14,000 Gallons of Water With No Added Equipment

12/15/2016 4:20 PM

I need your help solving a problem.

Problem definition:

  1. RO storage tank is 16.5 ft vertical wall x 12 ft diameter FRP light brown in color. Holds up to 14,000 gallons according to the tank stamp.
  2. Supply water to RO system (100-200 gpm) varies in temperature: Up to 28 C in summer (not a problem), and down to as low as 7-8 C in winter during the worst conditions we typically see. Thus, the RO system produces permeate at the prevailing temperature of the supply and sends this to the RO storage tank.
  3. RO storage tank supplies our 100-200 gpm CEDI system, that polishes the RO water to gas turbine/HRSG makeup specs. Not a problem, with one exception. The low temperatures in winter affect the CEDI stack impedance (voltage/current characteristic) so vastly, that it becomes questionable as to whether the system will produce water of sufficient quality, even if flow were decreased from 100 gpm per bank to 50 gpm.
  4. If you use a wind speed of 10 mph across the tank (about average), and consider that the tank is exposed to the south (so that sunlight could do at least part of the warming during the day if the tank were a dark color), and you are allowed to utilize the supply pumps to the CEDI system (with CEDI offline) to recirculate water from the RO tank through these pumps and back to the tank, at 200 gpm (normal rate for both pumps running in parallel), how long would it take to heat the tank to 30 °C at night, if the outside temperature is 2 °C?
  5. We are not allowed in this discussion to add such equipment as gas-fired or electrical heaters to the flow circuit. I am asking if the mechanical equivalent of heat can be utilized to help solve this issue at least partially. I realize it might be a silly question in appearance, but I am actually considering doing this if it will help the CEDI keep our plant in pure water during the winter months.
  6. We do have a steam heater (Pick) on another branch of the water supply line, but I suspect that without changing the piping arrangements to system booster pumps by way of installing a down regulator on the larger supply line (has less turns and less distance from main header of city supply), we can no longer expect much if any flow (in the correct direction) from the old line, without manually closing down the one manual blocking valve on the new line part way.
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Guru

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#1

Re: heating 14,000 gallons of water with no added equipment

12/15/2016 4:57 PM

Are you asking if you can warm the water 20C by pumping it around?

I don't think so. What is the power input to your pumps (amps x volts)? That's how much energy you have to work with.

If you figure the mass of water in the tank times the heat capacity of water, you can calculate the time the power to the pumps would take to warm the water by 1 deg C.

Time = Power/(mass of water) x (Heat Capacity)

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#13
In reply to #1

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 9:17 AM

I have not run a power draw study on the transfer pumps, but I know that at 90 gpm dilute flow with 5 gpm concentrate flow from the CEDI, the pressure input to the stacks is 60 psig. The motors are running on 480 3Ph, power, I will get back to you, but I think the motors are 15 HP only.

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#18
In reply to #13

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 9:44 AM

If 1000kW are needed to heat up that sort of flowrate from 7 to 30degC, then the pumps are undersized for the job by a factor of 90....

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#25
In reply to #18

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 10:05 AM

The pumps are correctly sized for the original job, but I must concur that attempting to warm up the tank by recirculating the contents through the existing pumps is a failed mission from the start. I am glad you gents can easily find the fallacy in my ideas, you are a real help, even if I forget to tell you.

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#34
In reply to #13

Re: heating 14,000 gallons of water with no added equipment

01/23/2017 4:43 PM

Your tank has 79 sq. metre surface area. 33mm approx thickness of expanded polystyrene equivalent thermal insulation passes 1 watt per sq.m per 'C (heat).

So 20 Celsius differential takes 79 x 20 = 1580 watts (steady state).

that's a lot less than the 10 kW output of your pump, so according to Richter's #26 calculation you can warm up the tank 20 degrees in a day or two by recirculation - so long as you lag the pipes. It might help to partially close a valve to increase pressure drop & energy lost in water

So it depends on how much water you draw off, bringing in cold water and how long it is too cold.

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#26
In reply to #1

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 10:06 AM

14000 gal = 53000 liters

53000 kCal required to raise temp 1 deg C

1 kCal = 4184 joules = 4184 watt sec = 1.162 watt hours

To raise temperature of 14000 gallons 1 C takes 61598 watt hours

30 hp = 22.4 kw

Time to raise temp 1C = 61.6 kwh/22.4 kw = 2.75 hours

This is best case, assuming motors deliver 15 hp each and no heat is lost to environment

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#27
In reply to #26

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 10:08 AM

That well proves the case that this scheme could work while the CEDI units are offline, but would never keep up with normal flow to one or both banks of stacks.

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#36
In reply to #26

Re: heating 14,000 gallons of water with no added equipment

01/24/2017 9:48 AM

In the meantime, we finally learned how to balance the system supply network, so that most of the time, more than 90% of the water passes through our steam heater. Works fine. During softener regeneration, we have to use more flow, so we open the auxiliary line a bit to raise header pressure to 40 psig, this allows 70% through the heater, and 30% unheated passes right into service lines.

So there we go. We were never going to be able to keep up using other schemes to heat the RO tank contents.

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#2

Re: heating 14,000 gallons of water with no added equipment

12/15/2016 5:10 PM

Sounds like it's time to go to the local building supply center and buy some insulation and good heavy tarps and just let the incoming water heat keep the tank up to temp.

Around here we can keep a 400 BBl (~17,000 gallon) fresh water tanks on oil rig sites from freezing in -20F temps with that method.

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#14
In reply to #2

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 9:22 AM

Freezing the lines is not the issue, or the contents of the tank, typically.

Cold water affects how well the CEDI units operate. They do not tolerate cold water much at all. RO system inlet pressure increases with cold water, since temperature affects the water transport coefficient, but this hurdle is not usually an issue if the membranes are clean and essentially at factory specs.

I agree that some insulation would be a plus on the coldest days (around -10 to -20 °C is worst case here in Lubbock, although I think the record in Texas is lower than that).

The thought of using geothermal heat storage during the summer and heat recovery during the winter has occurred to me, but I am pretty sure that management will not fork over the money for it. It would be cheaper to install a natural gas fired heating system for the CEDI feed, and so far, they will not bite on that either.

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#28
In reply to #14

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 1:04 PM

After reading the other posts it sounds like you are one of those guys I see over on the electronics forums who think that going with powered heating systems under light clothing is somehow better than just spending the time and money to get the right clothes for the weather!

Given your mild climate low end temperatures and limited times you need to keep the tanks warm enough to work I cant see how anything other than simple insulation would be more long term cost effective.

As Lyn said, have the tanks polyurethane insulation sprayed, along with any other major heat loss points, and it's done. No other external power or equipment needed. just keep the heat from escaping in the first place. If nothing is lost there is nothing to make up.

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#29
In reply to #28

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 1:12 PM

What? You didn't like the tea cup warmers?

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#31
In reply to #29

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 3:35 PM

Something a little more oomph please? I am about ready to follow Tcmtech's advice and put a giant tent over the tank and burn tires in barrels around it. I am sure the homeless will be then found crawling under the concertina wire.

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#30
In reply to #28

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 3:33 PM

You still do not apparently get that the source water is getting colder than what the CEDI will tolerate. All the blankets in the world do nothing to help with that. I respect your advice, but it will not work this time.

My fall back option:

  1. block in the new larger capacity header
  2. use the "old" header that still has a steam (Pick) heater in circuit
  3. cut-back the feed to the RO system to produce a final permeate (product) with a flow rate of about 80-85 gpm, as long as 25-30 °C can be reached (there is a steam flow controller unit). The Pick heater is just undersized for 100% flow.
  4. Only operate the CEDI on a warmer tank by starting up when possible on low tank level, matching CEDI total feed to final product flow off the RO. We still have to draw from the RO tank, since there is no provision for direct feed here.

Today, we attempted one more run of H105B CEDI (Ionpure stacks), but current draw was down to 0.3-0.4 A per stack at 570 Volts. Not optimal. For the RO water being sourced, minimal current should be at least over 1 ampere. Voltage applied is maxed out. Unit start had "normal" rinse in quality to allow capture of high purity water, criterion is only <0.4 μS/cm. After less than 10 minutes the feed went to 12.2 °C, and H105B output was no longer meeting criterion, and water was being discarded. Too many days running on high stack impedance (cold water), and the stacks simply cannot regenerate fast enough to keep up with throughput. Also, I add that these stacks are nearing the end of their serviceable life expectancy...

System was placed in lay-up condition until the fall back plan is implemented.

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#32
In reply to #30

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 10:07 PM

I have yet to read anything that was definitive about where the heat is being lost from.

Maybe I overlooked it but so far from what I have read it seems the tank has been the focus of the thermal issues.

If that's not where the heat is being lost from then I have no answer to give that relates to it.

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#33
In reply to #32

Re: heating 14,000 gallons of water with no added equipment

12/17/2016 6:41 PM

Yes, the water is cold on arrival in our plant.

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#3

Re: heating 14,000 gallons of water with no added equipment

12/15/2016 5:20 PM

..."The theoretical temperature rise of the water within the pump at steady state conditions assuming that all the heat generated remains in the fluid.

dT = H / (778*Cp*n)
dT = Temperature rise of fluid, deg-F
H = Pump head, Feet
Cp = Specific Heat of the liquid, Btu/(lb-deg F)
n = Pump efficiency, decimal value

http://www.eng-tips.com/viewthread.cfm?qid=277335

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#5
In reply to #3

Re: heating 14,000 gallons of water with no added equipment

12/15/2016 5:51 PM
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#19
In reply to #5

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 9:44 AM

Thank you, good link.

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#15
In reply to #3

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 9:25 AM

Thank you for the clear way to calculate it. I knew it was approximately along those lines. One question: I thought pump efficiency would run against the production of heat in the fluid being pumped, shows you what I know. I remember the old mechanical equivalent of heat experiment in physics lab, where one turned a paddle in a pot of water X times and then calculated the energy input, and measured the temperature rise. The paddles in water did not seem particularly efficient.

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#4

Re: heating 14,000 gallons of water with no added equipment

12/15/2016 5:40 PM

After painstaking analysis of your dilemma, I have calculated that by using 11,831 of these devices you can heat your water to the desired temperature in two hours, if the tank is painted black after the application of 2.4 inches of polyurethane foam.Hope this helps!

See other posts for suggestions.

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#16
In reply to #4

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 9:26 AM

Heck Lyn, you can do better than that. How many Gebo's livestock tank heaters does it take?

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#6

Re: heating 14,000 gallons of water with no added equipment

12/15/2016 7:38 PM

Do you have live steam available, and if so how much.

What I'm getting at is direct steam inject.

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#20
In reply to #6

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 9:49 AM

We do have steam in the plant. Steam is available at Pick heater, but new problem emerged with header pressures being unsuitable between old header where Pick heater is installed, and new one where there is no heater. The Pick heater was undersized for the job in the first place, so maybe move the existing one, and buy another one.

Problem with that is steam is only available when the combined cycle is dispatched, and there are times we would like to operate water system even when CC if offline. That is not the worst obstacle to have, though. Plan for that would be to extend the live steam at 600 psig (small diameter line probably 1") out to the water processing building, put the old heater inline with RO feed, and install another suitable heater to heat the RO storage tank contents directly with its own controller when steam is available. I don't know if management will bite on that one either.

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#7

Re: heating 14,000 gallons of water with no added equipment

12/15/2016 8:27 PM

Run a loop over to that GT with the clogged HX tubes? That sounds like a heat recovery scheme ripe for the plucking.

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#21
In reply to #7

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 9:51 AM

Obviously, some heat could be pulled from cooling system water return header also, but again, that requires a new heat exchanger to be installed $$, and no leaks could ever be tolerated or the CEDI bites the dust majorly.

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#8

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 2:10 AM

Of course you can achieve this heating by circulating water, calulate the energy/power required to do it and that power must be consumed (at least) by the circulators.

I can tell you that it is going to be a ridiculous exercise.

Why is adding heaters not allowed?

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#22
In reply to #8

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 9:51 AM

It is allowed, the problem is getting management to take action, really.

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#9

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 3:10 AM

It is not possible to answer the question with the information given. Nothing has been stated, for example, about the amount of lagging around the pipes and the ambient temperatures through which that particular stream passes. Nothing has been stated about the power input to the pumps.

Rather than start heating the tank up from cold, it would be better to introduce heat to the tank make-up stream, and lag everything to within an inch of its life.

  1. Be aware that without antibacterial resilience provided by chemical treatment, a tank full of lukewarm water is an ideal breeding ground for bacteria.
  2. The only purpose of a tank is to allow level to go up and down. Look at ways of getting rid of the tank from the process with the local Process Engineer.
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#23
In reply to #9

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 9:55 AM

While I have seen systems similar to ours with no buffer tank, there can exist a big mismatch between RO system output and allowable feed to CEDI system due to stack impedance, such that CEDI flow has to be reduced to match with current draw demand.

It is not feasible to turn down the RO system to a similar extent without upsetting the system parameters too far from the design point (too much flux on some membranes, not enough flow velocity over others).

I will look at this option some more.

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#10

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 4:42 AM

150usgpm of water from 7 to 30degC requires around 100kW of heat.

  • If 100kW is applied instantly to 150usgpm at 7degC going through an incoming stream heat exchanger, the effect is more-or-less instant.
  • If 100kW is applied to static 14000usg at 7degC then it will take around 37 minutes to get to 30degC.
  • If 100kW is applied to a tank of 14000usg initially at 7deg C with 150usgpm coming in at 7degC and 150usgpm going out then it will take over 3h to get to 30degC
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#11
In reply to #10

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 5:48 AM
  • Correction 1000kW.
  • Correction 100min.
  • Correction 8.3h.

Explanation: low temperatures in the calculator's battery.

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#12
In reply to #10

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 6:12 AM

"150usgpm of water from 7 to 30degC requires around 100kW of heating."

I make that about 873 kW: where am I going wrong?

150 US gallons is 8X150 lb = 1200 lb / minute about 9 Kg/s

mass/s * Temp diff * specific heat capacity

9 * 23 * 4.186 = 866.5

EDIT--Hey that's not fair you sneaked in a correction whilst I was being perplexed.

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#24
In reply to #10

Re: heating 14,000 gallons of water with no added equipment

12/16/2016 10:01 AM

Good points, well taken. I agree a line heater (or 4 line heaters of 250 kW would do better). I also see that having 20 °C feed to the CEDI is better than 10 °C, although I would love to see 30 °C as a control point year round.

Obviously, line heaters would be the most easily controlled since they are electric heaters. They do not introduce anything into the water, (very slight metal loss???), and I expect that experience with that would provide guidance on any emerging issue with it. The only thing with line heaters that I can conceive of as a disadvantage is the need to shut down the heater prior to taking the CEDI offline, but even that can be built into the PLC that controls the system, so operator merely clicks on the disable button, and the shutdown sequence takes over, right?

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#35
In reply to #24

Re: heating 14,000 gallons of water with no added equipment

01/23/2017 6:27 PM

I am not clear about your problem with HRSG feed water - you have not stated how long you need 200 usg/min. Do you need that per minute of HRSG operation (which seems a lot) or just for time to run a batch (x how many minutes?) through a treatment plant & how often?

Without that data there seems just 1 MW of electric power to heat 200 usg/min incoming water as a solution and that does not allow for heat loss from tank in cold wind if outdoor & not thermally insulated.

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#17

Re: Heating 14,000 Gallons of Water with No Added Equipment

12/16/2016 9:32 AM

I did not read the question but please change the color of the tank!

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