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Hi sirs
Sewage heat pump can save much energy and there're some project here in my country. I know there's no very special tech but I don't know what type heat exchanger is for the sewage water.
Who've done this kind of job would share us something,pls:)
regards
LC
Please explain what type of sewage it is, and how much solid is inside of it.
Hi LC,
The project I worked on used a simple shell & tube heat exchanger for the chiller and condenser (about 15 years ago).
The water that was flowing through the chiller was the grey water (I think this is the correct term) from the sewage treatment system. It is essentially clean water (all solids removed), but non-potable.
All of the solids and and other material were removed before the water flowed to the chiller.
Sounds like you were reclaiming heat from a clarified or treated effluent.
I remember a documentary with some footage from Sweden where they were talking about reclaiming heat from sewers.
Some documentary got into bio gas from manure as well.
Yep, the sewage was the clarified effluent discharge.
Sweden does have a very large heat pump system which uses centrifugal compressors in the heat pump. Basically, it is just a big centrifugal water chiller.
On the bio-gas system... Was this being used for co-generation and combustion turbines? There might be some refrigeration required to condition (dehumidify) the methane before it is used. Have worked on some of these too.:cool:
This system uses non-treated sewage water,only with two levels filter before entering heat exchanger. I'm not sure if the normal shell-tube HX is no problem.
regards
LC
Hi LC,
I would say the shell & tube exchanger is more forgiving in this application as the tubes would be easily cleaned. The project in Sweden does have shell & tube heat exchangers used on it I believe.
If there is a chance of minor particles or sediment, the tube velocity should be maintained at least 6 to 8 feet per second (1.8 to 2.4 meters per second) to provide a cleaning action on the tube ID.
The fouling factor should also be increased above the limits used for HVAC applications to also provide some additional run-time between cleanings too.
If the shell & tube exchanger is fabricated with channel heads and covers, the cover plate can be removed quickly to allow the tubes to be cleaned quickly.
The application of any heat exchanger is based on the application. If the fluid has solids or will accumulate material, then the system is dependent on the filters used. There are some centrifugal separators that can be blown down on a regular basis to maintain effectiveness of the seperators.
If filters are used, perhaps they should be provided with mechanical scrapers to keep the filters clean for longer periods of time.
Do you have any written material in English that may describe the heat pump you are thinking of?
Here are some links for more information:
http://www.stowa-selectedtechnologie...eat.Pumps.html
http://www.gryaab.se/admin/actions/u...2-10%20EGü.pdf
Hi, Mr Sze. I wish those links will be helpful. http://www.geoexchangebc.ca/pdf/Oslo...heat%20pump%22
http://www.georgiastrait.org/CAW/Res...heat%20pump%22
The Biogas was from manure on a large dairy farm maybe 3,000 head.Quote:
Originally Posted by US Iceman
It was treating the waste and producing the gas to replace propane. They seemed to find ways to use up as much of the biogas as they could but ended up burning a lot of it off.
They added greenhouses and heated with biogas, they ran stills made enthanol, but I do not rexall them generating electricity with it.
A starch plant in my hometown was forced to treat their effluent. They used an anerobic digestor to treat the waste and appease environmental concerns. It produced a substantial amount of gas, but it did not pay for itself. Was a smaller scale than 3000 crapping cows I guess.
If I recall this properly, methane is a bad greenhouse gas. Supposedly worse than CO2.
I wonder why cows were not legislated in the refrigerant protocols?:rolleyes:
It used to crack me up that the US tables of fouling factors started with distilled water (FF=0.0005 if I remember correctly) and went all the way up to "The Chicago Sanitary Canal" at 0.008 (imperial units). The second worst after the CSC according to the table was the East River, NYC - must be all the ex-mobsters swimming with the fishes in their concrete overshoes!Quote:
Originally Posted by US Iceman
Another laugh is that the Americans call imperial units "English units" - we've been blaming the English for all sorts of things for years!
Thanks for the memories
Cheers
Andy P
GWP of CO2 is 1 by definition of GWPQuote:
Originally Posted by US Iceman
GWP of CH4 (methane) is 23
GWP of R134a is 1300
GWP =global warming potential
Supposedly the worst greenhouse gas is water vapour, when you consider how much there is
I've seen similar tables as to the one you describe. If I remember right, they date back to about the 1950's or 60's. And, they were very, very conservative.Quote:
Originally Posted by Andy P
I guess I'm a little curious about the comment though. Do you think I was in error by suggesting a slightly higher fouling factor to allow for increased run-time between cleanings?
It is common practice to make allowances for differentiating between the fouling factors used for open and closed loop systems and potential fluid contamination on process systems.
I suppose I would like to hear more about your concerns Andy.
Maybe ODP is more concernedQuote:
GWP of CO2 is 1 by definition of GWP
GWP of CH4 (methane) is 23
GWP of R134a is 1300
GWP =global warming potential
CH4 ODP = 0
R134a =0
R22 = 0.034
ODP = ozone depleting potential
No, you were not in error. A customer once ordered a seawater/water chiller, so we made it with a special condenser.Quote:
Originally Posted by US Iceman
They called us soon after it was commissioned, because it was not working. At first glance we put the blame on the condenser.
We removed and opened it.
We found toilet paper and algaes inside.
At the end of the day we discovered that, yes it was sea water, but pumped from a busy harbour without any gross filtration.
I believe that was the point in the old fouling factor tables mentioned previously. I think the message here is, water is not always clean. Even closed circuit piping systems.Quote:
Originally Posted by NoNickName
I also believe the importance of the fouling recommendations is not the absolute value specified, but that an investigation should take place to determine the exact condition of the water.
At the very least, some questions should be asked.
Sometimes we learn this the hard way. Some separate processes may require higher fouling factors to increase the run-time between cleaning.
This issue of fouling factors is very interesting. They do add expensive heat transfer surface and make the exchanger larger. In a competetive situation, it works against you trying to sell the equipment. Especially if the other companies do not do this.
That is why I think it is important to explain why you are adding it (fouling factor) and what benefit it adds.
Thanks for the feedback NoNickName. I would like to hear from others on this too.
Hi Iceman - thanks for the comment. This is a tricky subject and I'm no more expert than average. In general I totally agree that river water, harbour water and "waste water" should be assumed to be dirty and the design should include an allowance for fouling. However all that the allowance achieves is a lower figure for overall heat transfer coefficient than you would otherwise have, and hence as you said, a bigger surface area. At first this is clean so the heat transfer is actually better than design and the evap temperature will be a bit higher - then as the cr*p builds up the TD on the heat exchanger widens because the performance diminishes. You are spot on: this does not eliminate the need for cleaning just makes the time interval between cleans a bit longer. However in a bad situation that might mean once every eight days insted of once every seven day!Quote:
Originally Posted by US Iceman
My concerns about this approach are:
1) as the surface fouls and roughens I suspect that the rate of build up increases so paying large amounts for a lot of extra surface might only buy you a little extra time.
2) keeping the tube velocity up is also good practice, but the combination of higher velocity and particulates in the water could lead to rapid erosion. If you're going to do this then use a tougher tube material such as cupronickel or admiralty brass rather than copper (for *****s) or stainless steel rather than carbon steel (for ammonia)
3) one problem of increasing fouling factor and getting a bigger heat exchanger is that the flow area probably went up for the revised selection, and unless the number of passes increased the tube velocity would therefore go down.
4) for me the best approach is good filtration upstream, with tough tubes and fairly high velocity. Unfortunately the filters probably cost more than the increased surface. Ideally a pair of filters with an alternate automatic backflush arrangement to avoid the need for manual cleaning. With this arrangement I'd go for a moderate fouling factor of 0.002 hr.ft2.F/BTU (0.00036 m2K/W) or so
Cheers
Andy P
And: who's going to clean the cr*p out of the fouled damned shell and tube?
I agree with all of this and the methodology completely.Quote:
Originally Posted by Andy P
I think you will agree this is a tricky situation. The harder tubes (and/or possibly greater wall thickness) increases the wall resistance + the increased fouling factor will increase the exchanger cost.
Personally, I think I would investigate a prime surface ID for ease of cleaning and perhaps an exterior tube surface enhancement to decrease the exchanger size. However, this would all be based on the exact nature of the resulting film coefficients and the penalty forced by the increase in resistance of the other "corrections" (wall thickness & material conductivity).
This would make an interesting review of various tubes, materials, and surface enhancements, in an attempt to have the film coefficient ratios (inside to outside) be approx. equal to the surface ratio (inside to outside).
Even with the design methods used, the continued good operation of this would be predicated upon a regular periodic inspection and possible cleaning of the tubes.
This type of application, while a chiller, is a long way from the usual field of HVAC systems.
Well... That is part of the issue. Knowing the tubes have a high potential for excess fouling, as a designer you can only do so much.Quote:
Originally Posted by NoNickName
Brushes that can be cycled through the tubes can be purchased. Filters can be installed.
However, the owner has to ensure the equipment is maintained and operating correctly as the designer intended.
I would rather over-design a system and tell the owner why, than explain why it doesn't work after it has failed.
Wall thickness: that's true for st steel vs carbon steel, but not such a big deal for cupronickel as far as I remember.Quote:
Originally Posted by US Iceman
Another thing to be wary of when using higher fouling factors is the particularly bad effect of fouling on enhanced tubes. The enhancement gives greatly improved performance when the tube is clean - but the higher up you are, the further you have to fall. If using internally enhanced tubes (eg rifled or wavy) I would put a much heavier fouling factor on (maybe three times as much) - which of course cancels out the benefit of enhancement in heat exchanger size. Better to stick to plain tubes if fouling is a concern
Cheers
Andy P
And another thing....(I really ought to go to bed!) We had a seawater condenser fail on a quayside job in Norway. When it was opened up we found severe erosion plus a relatively fine grit, which turned out to be the remains of seashells which had gone through the seawater pumps and been smashed up. A fine filter wouldn't have caught them after the pump, but a rough basket upstream would have prevented the problem. They were incredibly abrasive, and really ripped the tubes. You can imagine the rest of the story....
Cheers
Andy P
You said it better than I tried to. It's been too long since I have really had to do this sort of work.Quote:
Originally Posted by Andy P
That's probably about the best advice a person can get for this type of service.Quote:
Originally Posted by Andy P
Have you ever used the HiTran inserts from CalGavin? These little inserts look like paperclips in a string. I have heard they tend to provide a self-cleaning action in the tube ID. I would be interested to learn the experiences of others on this item.
That is another example of how things go wrong with a perfectly good installation. Details, details, details...Quote:
They were incredibly abrasive, and really ripped the tubes.
Did the tube erosion occur only at the tube entrance, or along the entire tube length? I suspect the majority of it was at the tube entrance and decreased to a lesser amount down the tube.
Here are some links I was trying to find.
http://www.friotherm.com/
http://www.caddet.org/public/uploads...ter/972_03.pdf
Hi Iceman,Quote:
Originally Posted by US Iceman
From what I remember there was some erosion on the tube ends, but the burst was part way down a tube and the heavy erosion was quite localised. I concluded at the time that there had probably been something partly blocking the tube which pushed the velocity up even higher at that point. Of course by the time we cut into the condenser the blockage was long gone. Possibly seaweed or plastic or somesuch.
Regarding Calgavin - we looked at the insert as a possible addition to DX ammonia aircooler tubes a while back, but the pressure drop penalty was too high so it never went ahead. For brine chillers I think they would be most appropriate for viscous fluid, such as glycol at low temperature, but they really push the pressure drop up, so you pay something in pump power. Do you think there would be a risk of erosion if they were used with dirty water? (possible localised high velocity)
Cheers
Andy P
Just joined this thread.
There was some 13 to 15 years ago a contest here in Belgium for the most environment saving house and I gave some ideas how I saw it.
Of course, DX ground source heatpump, heat reclaim on mechanical ventilation (mechanical ventilation has become an obligation in every Belgium house), heat reclaim on the fridge and the sewage heat pump.
How I saw it? Collecting all the grey water from the house during the day in a small isolated storage tank and retract during the night on cheaper rates the heat out of it with a small compressor. Then let if flow afterwards its normal way to the drain.
I received a letter that my project was chosen together with 4 others and that they should decide which project was the best. I gave them a call that I hadn't building plans but that it were only some ideas how I saw it in case I should build a house.
Hi Andy,
My first guess was the tube erosion was more dominant within the first few centimeters of the tube entrance. The entrance losses and velocity profile would have been the worse here before the flow was fully developed in the tubes.Quote:
Originally Posted by Andy P
But then... I have been known to be wrong before too.:)
I have a friend who tried this and said it works great for the first pass of the circuit. He tried these on some liquid overfeed air-cooling evaporators to help break up the liquid refrigerant so that it had better wall contact with the first pass tubes. Sort of a first pass spray system if you will.Quote:
Originally Posted by AndyP
That's for sure... Instead of heat transfer enhancements, it might be more prudent to spend the time looking for a better heat transfer fluid with better properties.Quote:
Originally Posted by Andy P
There have to be some new fluids available with better low temperature viscosities and conductivities. That would provide better Reynolds numbers and film coefficients, and lower pressure losses. Unfortunately, I bet the fluids can tend to be a little expensive.
Going from memory I seem to remember the inserts would flex under flow conditions. That was one of the selling features to help keep the tubes clean. You have probably heard all of the other selling points too.Quote:
Originally Posted by Andy P
In short, I'm not sure what would happen. If the particles were somewhat soluble with water, the inserts may be fine. If the particles are abrasive as your project encountered, it may erode the inserts too.
That is part of the problem with designing equipment and systems. There are so many variables, anyone of which can come back and haunt you.:o
Best Regards,
US Iceman
Hi Peter,
That is really interesting Peter. With this idea it might be possible to build a single packaged system for the house for heating and cooling. A coil could be submerged in the storage tank to pull heat out.Quote:
Originally Posted by Peter
One coil for the refrigerator, one coil for air conditioning, one coil for other heat recovery. This starts to look like a little supermarket refrigeration system.
One refrigeration system with multiple evaporators.:cool:
That was in fact the idea: only a copper coil in the unit so that you don’t need any pumps.
A little bit like the ice bin beer coolers.
The unit is then installed inside the storage tank and the discharge lines are going inside the building or the unit is inside the building and the lines going to the tank are he suction lines.
The fact that you have +/- 8 hours to retract the heat makes that you don’t need a big compressor.
Pure theoretically seen, this device can foresee all the heating or at least the pre-heating of all the domestic hot water because all this wasted energy could be retracted.
Plastic valves are commercially available. The only problem I could think of was that the valve could block due to the dirt/debris.
My wife measured for some weeks the flow and the outlet temperature of her fume hood and I calculated that this energy was capable of heating +/- 10 l water a day, just enough to wash the dishes.
My fridge is now for more then 10 years connected to a timer which bridges the thermostat during the cheap night rates. This Real Time Clock can in fact very easy and cheap be foreseen on the PCB’s already available in most new modern fridges. Via a push-button on the front panel the user then can select eventually this option.
A client of mine with a big freezer of +/- 15 x 15 x 10 m, stacekd full with vegetables runs his freezer from Friday evening till Monday morning. They’re only in standby during the remaining days.
Cooling the house: well, if you can pump water coming from the underground in a closed circuit, then you even don't need compressors to cool your house, at least not in our countries. Only a pump.
Just using the energy of the underground and preheat it for teh winter seson where you can use preheated soil.
Well, as you see, many ideas, only finding time to make and test this all.
I understand. We still have to work to feed the family.;)Quote:
Originally Posted by Peter
i believe good ideas is the premise of the new product.
Peter can apply for a patent:)
regards
LC