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Heat Pump Powered Thermal Water Softener

Removing dissolved solids without messing around with resins and salt
  [vote for,

Fresh water as supplied to homes, business etc. varies in its composition widely across the globe. Where I grew up, the water is extremely soft (~25mg/litre) due to a combination of near constant rain and favorable flora & geology. Conversely, the south east of England has very hard water (~300 mg/l) probably because they deserve it. The situation is similar in most of the USA. Such water made "hard" by the presence of dissolved minerals, largely calcium carbonate, creates numerous problems. Soaps & detergents form calcium salts with hard water meaning much more has to be used. Calcium carbonates also precipitate out when heated, meaning any device that heats water is susceptible to "scaling". Calcium carbonate precipitating out due to heat can be seen in numerous thermal springs around the world. Conversely coastlines in the very northerly/southerly latitudes don't have sandy beaches since the cool waters dissolve away all the calcium carbonate sea shell fragments.

The standard solution to this problem is a water softener. This works by passing the water through an ion-exchange resin. The surface of this material is covered with negatively charged regions, occupied by sodium (Na+) ions. When dissolved calcium (Ca2+) passes through the resin, Ca2+ binds to the resin, displacing Na+ ions which move into the water. Eventually, the resin is saturated with Calcium and needs to be "recharged" by temporarily soaking the resin in high-concentration sodium chloride (NaCl) solution to knock all the Ca2+ ions off to be discarded.

This system works, but isn't perfect since it consumes salt and inevitably makes the water a little salty. To solve it, let's use heat. Our water softener is a two-chambered device, one chamber will be heated and one cooled by a heat pump. Pick your favorite type. Water from the standard domestic supply flows into chamber 1 where it is heated. Calcium carbonate is ~4x less soluble at 50C vs 15C <link>. So, in these conditions it will slowly begin to precipitate out. The chamber should be large enough to have enough dwell time for this to happen. The water then passes through a filter. This can be a simple particulate filter, or perhaps somewhat more sophisticated continuous flow device e.g. radial flow separator. The point is, solid calcium carbonate is removed.

The water then flows into a second chamber where it is cooled to normal temperatures by the heat pump, this recovers most of the energy used to heat it in the first place. The water then goes into the conventional water supply distribution of the house etc. with a much lower hardness.

bs0u0155, Jul 18 2022

Calcium carbonate solubility https://upload.wiki...20px-CaCO3-Temp.gif
[bs0u0155, Jul 18 2022]

Includes a heater/heat exchanger, but still using resin. https://patents.goo...tent/US7390413B2/en
[bs0u0155, Jul 19 2022]


pocmloc, Jul 18 2022

       //they deserve it//   

       Can't argue with that, really.
pertinax, Jul 18 2022

       [+] but this seems to clever to have not been thought of, have you done a patent search?
doctorremulac3, Jul 19 2022

       ////they deserve it//   

       Can't argue with that, really.//   

       I'm trying out my new "Karmic consequences" theory of how the world is the way it is. California used to be lovely, beaches, great weather, mountains, lakes etc. Now it's an expensive gridlocked homeless shelter built on a fault line that's on fire a lot. Well, that's punishment, for hosting evil big tech and inventing pet psychics or something, not sure yet. I haven't worked out what Rwanda has done to deserve its lot, but it's clearly something.   

       Conversely Britain is largely free of earthquakes, tornados, hurricanes, baseball, floods, landslides, derechos, ice storms, sand storms, dust storms, famines & mosquitos because we don't deserve them. We just have 2 days of hot weather to remind us to light a fire under the current political representatives.
bs0u0155, Jul 19 2022

       (re link) Yea, that's different allright. Well dang B, I think you should pursue this.
doctorremulac3, Jul 21 2022


       <learning... and we're learning>   

       Wouldn't a heat exchanger be far simpler? You can recover something like 80-90% of the heat with a contraflow system.
Selky, Jul 21 2022

       Calcium carbonate and other interesting mineral deposits currently accrue at the bottom of your average home hot water heater. Add a filter to solve for that, ahead of (above) the bypass valve that sends the now-softer water through the attached heat exchanger on its way to your cold tap. A three-for-one deal, no?
Sgt Teacup, Jul 22 2022

       //Wouldn't a heat exchanger be far simpler? You can recover something like 80-90% of the heat with a contraflow system.//   

       What heat? There's no heater. I'm essentially using the heat pump to heat the water, and recovering the same heat from the same water, just later on. It won't be 100% efficient, the water leaving the softener will be a little warmer than the water entering it, but given the gradients are very small it should be 80-90% efficient given enough insulation.
bs0u0155, Jul 22 2022


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