Wastewater heat reclaim 1

[m2e]

Hi, I've previously posted this question in the energy forum, but I wanted to also post it here because nowadays HVAC engineers deal a lot with this kind of project too. I thought I might find some valuable advise here.

I'm working on a project where we would like to harvest the heat in the wastewater in a wastewater treatment plant. We're thinking to use water-water heat pump to get the heat for a number of other purposes, such as providing heat for the building, domestic hot water, the wastewater treatment processes, etc.

1. Do think think it's feasible?
2. What would be your approaches to this project, and what type of equipment are you thinking of using?
3. Is it possible to use the heat for building cooling too? (Absorption chiller? or using the sewer as a heat sink for water-air heat pump?)

Thanks.

Thank you.

 

[ChrisConley]

Where are you in the world? What temperatures does your wastestream run at? Do you have a use for heat year-round or just seasonally? What kinda of flows does your plant see, typically?

Couple of thoughts.. sewage is hard on heat exchangers, and there isn't a pile of data. I know an engineer who has spent a large amount of time pumping pig manure around, and he complains constantly about the lack of data.

A heat pump has potential, provided you can find a heat exchanger to pump the wastewater through. You could do a 'water source heat pump' with a closed loop coil in the waste... I see issues with fouling.

Absorption chilling would be a challenge in that you generally require fairly high grade heat, and most heat pumps work less efficiently the higher the grade of heat you are producing. McQuay has a scroll Templifier that does have some capabilities to do higher discharge temperatures.

Cost would be the other issue, as you end up stacking equipment on top of equipment (Sewage to HX, HX to Heat Pump, Heat Pump to Chiller).

Another energy/CO2 concept would be to capture the methane produced by the waste (typically flared) and run it through a CHP.

Just some thoughts, interesting project.

 

[GMcD]

You also need some "bio-engineering" as the question of "what happens to a cooled watewater stream" needs to be answered- the bacteria and digestive processes of the waste stream breakdown needs to be addressed. I'm familiar with some Swiss technology that imbeds polyethylene pipe in precast concrete sewer pipes to connect to a water to water heat pump to extract the low grade waste heat from sanitary sewer waste piping, but I haven't seen any definitive study or commentary on what happens to the sewage treatment process by cooling off that waste during part of the digestion and breakdown period?

The only other small scale sewer waste heat reclaim that is out there is the GFX residential/commercial drain pipe heat recovery thingy- basically a whole whack of copper tubing wrapped around the outgoing sanitary sewer drain to pre-heat the cold water being routed into the domestic hot water heater.

 

[JimFischbeck]

I am the Executive Director at the Washington County Wastewater Treatment Plant in Ft Edward, NY. We just started up a treated effluent powered heat pump [Water Furnace, 6 Ton capacity] on November 4, 2008, to heat our new 2000 sq ft maintenance building. Seems to be working great. We will be tracking efficency over the winter to see if biological fouling becomes a problem.

 

[JimFischbeck]

BTW..On the advice of the provider of the Water Furnace, we have no heat exchanger. We did install a 50 mesh y-strainer on the effluent supply line. Uses ~12 gpm. Pump and dump. Coldest the eff. ever gets is ~ 9C. The plant is 2 mgd avg. Dead of winter, flow drops to 1.3 mgd. Coldest air temps are -20F. Delta T target is 4-5C. Effluent is 30/30mg/l BOD/SS. Unit uses 16 amps x 217 volts x 1.73 [3-phase] = 6KW. Heat rise thru machine is ~45F.

 

[m2e]

At the moment, I don't have much detailed information yet, because we're just on the conceptual and feasibility study stage. Thanks for all your input, and I'll take the ideas and do some study, and hopefully this project can go ahead, and I'll post some update here.

 

[JimFischbeck]

We initially were looking at dunking a "Slim Jim" plate type heat exchanger in a clarifier, but things got real expensive real fast. A spiral hx [for sewage/coolant exchange] was available was available for ~$800 but was dispensed with as unnecessasary since our effluent is not corrosive.

 

[JimFischbeck]

We have been using the effluent powered heat pump all winter without a heat exchanger. It is working great so far.

 

[m2e]

Thanks for your update, Jim.