potential heat, mine water
Last Post 03 Feb 2008 11:14 AM by dmaceld. 11 Replies.
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hedgehogUser is Offline
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26 Jan 2008 07:46 PM
i work in a potash mine, my work is in the shaft and headframe, our headframe has a natural gas fired infloor heat system that is not very effective. our mine has a brine inflow, we pump the water up the 3200' shaft, the 2 8" lines come out of the shaft and then outside the headframe, there is approx 1500 gpm @ 25 degrees celcius in each line. the water is saturated with salt. could a geothermal system be used to capitalize on this endless supply of heat? and if so how much or how large of system?
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26 Jan 2008 11:32 PM
Posted By hedgehog on 01/26/2008 7:46 PM
our mine has a brine inflow,
I know this is way off topic but I'm curious. Where is the brine coming from? Hopefully it's coming from a salt water aquifer or ocean water. If not, has your company studied the implications of that much water flowing in? If it's ground water somewhere above your mine then it's coming through a salt layer. Fresh water moving through salt will dissolve it creating a larger and larger void that eventually will cave in. Having big holes in the earth above your mine doesn't sound too reassuring to me.

I worked at the Strategic Petroleum Reserve in Louisiana where we store crude oil in salt caverns. We abandoned our only mechanically mined cavern (a former Morton salt mine) when we discovered water entering it from above. This was different from your situation because the mine was in a salt dome and only about 400' below ground. We pumped the oil out, filled it with brine, sealed it up, and walked away.


Now, to your heating question. Given the fact you have brine at 77F you have a huge thermal supply but probably not quite as hot as you need. You could use a heat pump to pull the heat out of the brine using a heat exchanger and use that to heat the floor medium. Because of the corrosiveness of brine you'll need to look at a stainless steel exchanger, or maybe even zirconium.

In what way is the current floor system not effective? How warm are you wanting to heat the building? Do you have electrical equipment in the building, such as motors? Maybe all you need to do is insulate and seal the building. You may have enough heat source already to keep it warm if it's properly sealed and insulated.




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dmaceldUser is Offline
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26 Jan 2008 11:38 PM
Another thing you'll have to pay attention to with respect to the brine. Is it 100% saturated? If so you won't be able to suck heat out of it without diluting it with fresh water. The reason is the capacity of water to hold salt increases with temperature, and of course drops as the temperature drops. If it's saturated brine and you cool it down you will have salt precipitating out in the pipes, eventually clogging them, kind of like clogged arteries!


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27 Jan 2008 12:12 AM
our mine has 2 shafts approx 10 miles apart, ours is the updraft shaft, we currently dont have much for insulation in the headframe, it is sheeted in, however not well sealed. because this is the updraft shaft there is a lot of humidity, apparently in the past they tried sealing it up and insulating it, pretty much made a rain forest. the heat is totaly expendable, just to make it comfortable on the main level, keep our air lines from freezing up. this is south east saskatchewan, temps in the winter frequently get to -30C even -40C. cost for a system isnt really an object as we get a capital budget that we have to spend, ie: we can spend 5 million to save 100g's annually. as for adding fresh water to prevent salt precipitation, that can be done.
as for your curiosity, our mining is done in the prairie evaporite salt formation, we are approx 3200 feet underground, back in 1986 we had a water break out, some poor mining practices were exercised in the previous years, leaving a unstable area in the mine, we now have water coming in from above us. it originates in the dawson bay formation, a limestone/shale/brine layer that is about 100 feet above normal mining. the water comes in normaly around 3000gpm. there have been several occassions where it will break out and come in at 12,000gpm, last year it broke out at 25,000gpm, this created a bit of panic. we can control and even stop the inflow by drilling into the dawson bay close to a specific inflow and injecting calcium chloride, this reacts with the brine and forms gypsum, sealing off the inflow. through painful experience it has been learned its best to maintain a inflow of 2000 to 3000. this keeps the dawson bay pressure around 900psi, its normal static pressure before we had any leaks was over 1200psi, in the past they managed to seal off the inflow, the pressure rose and eventualy busts out and makes a major inflow.
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27 Jan 2008 10:47 AM
I'm not sure what's available on the net about the cavern I mentioned but you might look for it. Weeks Island, Strategic Petroleum Reserve, and sinkhole. What we did was drilled a series of wells in a circle around the sinkhole and circulated cold calcium chloride, I think, brine through loops in the wells. This froze a cylinder around the sinkhole to keep fresh groundwater from entering. We then pumped the brine from below the oil in the cavern and dumped it back into the sinkhole. By recirculating brine we cut down significantly the salt erosion above the cavern. This bought us plenty of time to get the oil out and seal up the cavern.

Don't know if any of this approach would have value for your operation but thought I would mention it anyway.

If you want contact info down there PM me and I'll give you a couple of names and numbers.


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28 Jan 2008 12:05 PM
Hedgehog, I would think that you need is a heat exchanger of similar design to the drain heat recovery units (see http://www.eere.energy.gov/consumer/your_home/water_heating/index.cfm/mytopic=13040 ) to avoid scale buildup. A larger industrial verison of this might work well. Perhaps you can just affix a coil around your existing pipe? A typical water sourced heat pump should work to extract enough heat.
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02 Feb 2008 05:53 PM
how much potential heat would i have here? like i said 3000gpm @ 25degrees celcius
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02 Feb 2008 07:57 PM
heat pumps need flow of 3 GPM per ton at 50°. 2 GPM at 70°. So you could supply heat to 1500 tons of heat pump equipment. So in theory you could supply 1,200,000 BTUh of heat.
Dewayne Dean

<br>www.PalaceGeothermal.com<br>Why settle for 90% when you can have 400%<br>We heat and cool with dirt!<br>visit- http://welserver.com/WEL0114/- to see my system
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02 Feb 2008 08:30 PM
Posted By hedgehog on 02/02/2008 5:53 PM
how much potential heat would i have here? like i said 3000gpm @ 25degrees celcius

A lot!!!!

25C = 77F. You can extract 1 Btu from every pound of water for every degree F you lower the temp. This is assuming the specific heat of the brine is the same as water, which it isn't on a pound basis but should be close on a gallon basis.

3000 gpm x 8.54 lbs/gal x 60 min/hr x 1°F = 1,537,200 Btuh for every 1°F you drop the temp.

When you walk up to the brine pipes do you feel warmth radiating from them? If so they may be warm enough as is. 77 certainly isn't hot, but neither is it cool. If you're not looking to keep the shed particularly warm maybe you could build a radiator overhead, along the walls, or along the work areas, using something like 1" pipes and divert some of the brine through it. Blow air past it slowly and you could possibly keep the shed at 60F+. Or, if you can pour another layer of concrete on the floor install a labrynth of PEX tubing in a slab. I would think you'd want to make a lot of short parallel runs connected to headers so you can run lots of brine volume and drop it's temp by maybe only 1/10 of a degree. You'll have to verify if PEX is compatible with brine. You could consider poly tubing also.

This approach would save the hassle of installing a heat pump system.

I think it's a project worth pursuing! Good luck.
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02 Feb 2008 08:37 PM
I just reread some of your earlier posts. Is there any way you can pass the updraft air from the shaft through a radiator as it enters the building? What temperature is it coming from the mine? I would think it would be fairly warm. Does it pass through the building now, or is it just exhausted directly outdoors? I gather from your earlier post at least some of it must be coming through the building.



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hedgehogUser is Offline
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03 Feb 2008 10:32 AM
i like the idea of the wrap aound heat exchanger, we dont want to impede the flow of this water at all, first of they want every gpm we can squeeze out of the system, secondly, remember this water just come up a 8" pipe and 3200' of verticle rise, so we have some pretty high head pressures at the mine level, 1385psi static pressure alone, this pipe is in 20' sections connected with Vic couplers, there is quite a bit of maintainance associated with this piping system as it is so we dont want to increase the pressure any more than we have to. as for the updraft air coming up from underground, there is a ventilation tunnel just underneath the 'collar' and 2 large vent vans pulling the air from the shaft and blowing it into the atmosphere. we try and prevent the air from entering the head frame, especially in the winter, the air is coming from a area of high barometric pressure and very high humidity, letting it come in to our cold, low pressure head frame creates copious amounts of condensation, quite literally the headframe becomes a rain forrest, not good for us or all the equipment inside. the fans suck hard enough that the headframe has a negative pressure compared to outside. i realize this doesnt help our heating problem but thats just the way it is. i guess the efficiency of a wrap around heat enchanger would depend on how long it is and possibly if they is any way to increase turbulance inside the pipe. remember this is saturated brine, at -40 we still dont have any ice in the pond this water dumps into. so our heat extraction doesnt have to stop and the normal freezing point of water. i'd like to thank you all for your input and great ideas, and some very good questions. although i dont personally sell or install geothermal systems i have been a very big advocate of them in my area and have let dozens of people tour my basement and get some education on how geo really works.
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03 Feb 2008 11:14 AM
Posted By hedgehog on 02/03/2008 10:32 AM
i like the idea of the wrap aound heat exchanger, 
Yep, probably the best approach all things considered.

the fans suck hard enough that the headframe has a negative pressure compared to outside. i realize this doesnt help our heating problem but thats just the way it is.
I suppose you've looked at ways to reduce the fans' propensity to suck air out of the head frame building. That would be a worthwhile place to look again I would think. I really didn't think you'd be blowing the mine air through the building but wanted to be sure.

i guess the efficiency of a wrap around heat enchanger would depend on how long it is and possibly if they is any way to increase turbulance inside the pipe.
I think more critical than length will be the conductance path from the pipe wall to the heat tube. It'll be a challenge to keep from having gaps between the two. You may want to look at embedding the heat tube in a grout or concrete coating on the pipe. I really doubt you'll have a problem with too little turbulence in the pipe. The conductance path will be a greater influence. How about making essentially a shell and tube exchanger? Put the brine pipe inside a larger pipe and run the heating water through the annulus.

remember this is saturated brine, at -40 we still dont have any ice in the pond this water dumps into.
I'll bet you've got a healthy layer of precipitated salt at the bottom of the pond though! Since the brine is saturated you will have an issue with it precipitating onto the walls of the pipe where you drop its temperature by heat extraction. At the SPR when they inject oil into a cavern and push brine out, salt precipitates out in the brine pipe as it comes through the earth and cools down as it approaches ground level. I don't remember the temp drop but it's not more than about 5 to 10F. That's at flow rates about 10x what you have. During oil fill they have to reverse flow in the brine string and pump fresh water for about a half-hour every 12 to 24 hours. Oil flow doesn't stop because oil is compressible and for a few hours they can pump oil and water both into the cavern!

Even a retired engineer can build a house successfully w/ GBT help!
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