I am interested in trying to recover heat from a pair of 75 hp Lamson blowers to hopefully add some degrees of heat to aeration tanks in the winter. Does anyone have any experience in this?

Is it feasible and effective to channel vented, heated air into the tanks? Currently, the heated air is released (wasted?)to the atmosphere.

Is it more feasible to use a collection system of copper tubing to capture heat from the in-building portion of the duct, then to use a vinyl/butyl tubing construct in the tank to heat the liquid, the heat carried by a circulating glycol-water mixture? 

Is there a heat transfer unit that could survive immersion that is not stainless steel?

Are covers (solar or pool-like covers) the more efficient way to keep heat in or heat aeration tanks?

I know these are several questions, but would appreciate any feedback. I'll check back tomorrow (Thursday, 12/6).

Thanks,

Mike

Great idea , but unfortunately the numbers don't add up. The amount of heat coming off your blowers is not enough to make any real difference. I can do the math if necessary to show this but in simple terms  i would suspect that the amount of heat given off 75 hp blowers would be no more than the equivalent of 10 hp or 7.5 kw. If you have an electric water heater in your house its probably in the range of 2.2 to 7kw (give or take a bit) and it heats maybe 100 gallons if that. I don't know how big your aeration tank is but with 75hp blowers i would think they could be 0.25 to 0.75 million gallon or more. Given the heat losses from the aeration tank is quite high by the constant mixing the amount of difference the heat from the blowers will make will be unnoticeable.

However it is great that you are thinking things through and looking for opportunities to improve. Afterall this is what the forum is about.

Regards

TerryF

Our WWTP is small @ 355,000 gallons (current flow about 170,000)...Aeration tanks = 8 times 20,400 gallons or 163,200, but I would looking at only 1/2 of that, one train of 4 or maybe just impacting a single tank. Still, I can understand the 100 gallons vs 20,400 gallon challenge in trying to raise a couple of degrees.

I actually started looking at some solar pool covers since the aeration tanks are open to the sky, when I got the idea of using wasted air from the blowers in conjunction with a winter cover. I figured that the increase might be incremental, but am not aware of loss via transfer, how to convert the BTU and temperature of the vented air to a quantitative view.

The current operation is 1 hour on and one hour off for the 75 hp blowers (good electric savings and seems to help the process), i.e., they are not constantly on, so I was already at a 50% point. Our smaller digester and surge/equalization tank blowers (25 hp) are on for 24/7.

So, I reckon that I will go back to researching covers. Thanks again.

Mike 

What is going to happen to the solar covers when the aeration starts up?

Further to my previous post , a substantial quantity of the heat generated by the blowers already go into the basin via the airflow through them. Try touching some of your aeration pipework.In fact many blowers have temperature , pressure, airflow limits on them designed to limit heat build up. Usually minimum airflows are specified to ensure adequate cooling.

Regards

TerryF

I agree that any cover cannot be tight, but my initial thought is that the evaporative surface area could be reduced, cutting the loss of heat.

I will continue to think and research some alternative approaches.

Mike 

I have not looked into floating balls, but will research them now.

Also, a more efficient method of keeping heat going to the basin by insulating the blower pipes leading to the aeration chamber is being considered.

Now all that is good for aeration tanks with blower air. If you have surface aerators they actually do not put any heat into the wastewater and a source of heat may be useful. Two small blowers would probably not significantly heat up your aeration tank. Get a chemical engineer to work out what the heat input divided by the flowrate of wastewater through the tank to give you an idea of the temperature rise. It should be able to be done on the back of an envelope.

Regards

Grant H

Thank you for your reply and suggestions. Some time has passed since I posed this question and my thoughts have gone to different possibilities.

I am now leaning towards finding some way to insulate the pipes or tubes that carry air to the diffusers. Although some of the piping is subterranean, some is above ground. My caution is actually due to the volume of the total aeration basins (two trains of 4) so I would at best hope to impact the first aeration basin in each train. Right now we are clipping 10 degrees (+ or - 1) C...things are a bit slow going until a warm up in the spring.

What do plants in the farther northern reaches do? Cover? Enclose?

Mike