Waste heat recovery sytem

Hi,

I am unable to see discussions about recovering the waste heat energy at prime-mover's exhaust. May be, I missed such a thread or it is not feasible for boats. Please comment.

Syed

 

Already done see:
http://www.polarpowerinc.com/products/heat_exchanger/heat_exchanger.htm

Read http://www.polarpowerinc.com/products/heat_exchanger/heat_exchanger.htm#Safety Notes too.

 

you can also tap into the engine (FWC/Intercooler types only) for Hydronic heating (usually baseboard type) w/ "hot water" rated gate or ball valves to shut it off when not needed.

a bit of common sense & some engine coolant flow knowledge w/ suction and pressure ports (theres always extra plugs on eng & WP) on the engine and water pump and it's a go.

personally, I would make it non-thermostat (just close down the gate valve to regulate) due to elec. selonoids needed and extra places that could leak.

 

Hi Dears,
Thank you indeed for the valuable information. I have some idea about the waste heat recovery systems, practiced in industry. Their usefulness / practicability on boats was my prime concern. Specially for the boat sizes, mostly discussed in this forum.
Regards,
Syed

 

"Specially for the boat sizes, mostly discussed in this forum."

Most of the boats discussed here are yachts that frequently chose to dump the exhaust at the transome and use excess sea water from cooling the engines heat exchanger to cool the exhaust.

This prevents the FG from catching fire , but doesnt leavre much heat in the exhaust to use.

A dry stack is usually seen on comercial work boats , along with keel cooling. This cuts down on the maint and boosts the relibality , but is hard to accomidate with pleasure interiors.

Dry stack could have somthing as simple as tubing coiled arround the stack to recover heat for heating or?

FAST FRED

 

that's how a "Steam Jenny" (steam cleaner) or "Hot water pressure washer" works.


you could take a stack type exhaust and go up 1 size, i.e. 4" to 5" to allow for the internal tubing (more efficient). the number of coils would determine how hot (BTU's) it could get.


soft copper tubing could be used but custom wound Stainless steel would be better. fill the tubing w/ fine sand to lessen any kinks in the tubing then blow it out w/ air and then flush it well w/ water.

 

Hi, just reading through some posts as I am interested in diesel engine design espescially the turbo and charge air cooler aspect of the engine. I work for a company that design and manufacture charge air coolers for large diesel engines called Vestas aircoil.
I welcome this subject to be opened again, I know that waste heat recovery is used and should be explored deeper.

 

Boats with a dry stack will frequently have the stack built into a clothes locker to dry and warm foul weather gear.

Commercial head boats will use the engine coolant to heat the rail where the pax can warm their hands.

 

Very roughly, engine heat energy in the fuel goes to four places, 30% to shaft power, 30% to engine cooling liquid, 30% to exhaust gas, and 10% to ambient heat loss (lube oil coolers, engine compartment heat,etc.

Using engine waste heat has been done for many years. Closed cooling water (or antifreeze) circulating systems provide plenty of heat. Back in the 1960s US Army boats used square structural tubing to support the steel decks, and engine coolant was run thru the tubing to keep ice off the decks.

Exhaust heat recovery boilers are common on many large diesel ships, providing steam and hot water for all kinds of applications. As mentioned earlier, wet exhaust systems on smaller boats loose most of their heat energy to the water that is injected into the exhaust, so pleasure boats do not need to deal with very hot exhaust pipes. Still plenty of heat available in the engine coolant system, just like the heater in an automobile.

 

I think the problem with these systems on smaller, recreation oriented boats is that the entire effort is contrary to the direction of small engine development. Machinery to take advantage of low quality energy is necessarily bigger and heavier on a per watt basis than machinery that uses high quality sources. Given the same budget, space, and weight allowance as a heat recovery system, you could get the same benefit from reengineering the prime mover to be more efficient.

Once you are dealing with heavy commercial duty or continuous duty at reasonably steady power output, then it begins to make more sense. For stationary applications, it also makes more sense.

The one area I think might be worth looking at is coupling exhaust heat recovery to RO watermakers. A fifty degree C feedwater increase could about double production from a given membrane.

http://msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_0036/0901b803800362e9.pdf?filepath=liquidseps/pdfs/noreg/609-02057.pdf&fromPage=GetDoc

I think pretty much everything else has been done as far as servicing appliances with heat where the size and weight and complexity isn't a deal breaker.

 

Temperature Correction Factor

The Dow paper you reference gives a Temperature Correction Factor (TCF) as a function of deviation from 25C (77F).

The TCF at 25C is 1.00000, and a 50C increase (to 75C = 167F) gives a TCF of only 1.000482. This is a very small increase in performance as far as I understand, nowhere near double performance.

Please help me understand what is the basis of your statement?

 

the quantity in the brackets = 0.00026

times 2640 = 0.686

this is the x in e^x written as EXP(x)

e^0.686 = about 2

 

RO Membrane Equations

philSweet, Now I see the errors, both yours and mine. Your original statement:

"A fifty degree C feedwater increase could about double production from a given membrane."

What you actually intended should be the statement: "A 25 degree C feedwater increase from 25C to 50C could about double production from a given membrane." That gives a TCF of 1.98, very nearly 2x that you stated.

My error is neglecting the 2640 multiplier on the exponential. Correctly evaluating the function, with a 50C increase (25C to 75C) the TCF increases by a factor of 3.57

HOWEVER the Filmtec membranes are rated only to 35C, (higher operating temperature voids the warrantee for the membranes) The increase in temperature from 25C to 35C gives a TCF of only 1.33

 

yes, I plugged in 50C, which is the temp, not the differential. The differential is only 25C since the TCF it is referenced to std conditions.

 

If you want to get real anal about this recovery thing, how about using the exhaust heat to warm the hot side of a displacement engine, which can be employed to drive a generator (or whatever). You can cool the other end of the piston with sea water/keel cooler, etc. for a wide thermal variance. Starting is always and issue with these puppies, but once she's hot and running . . .