Eff of Cogeneration & Absorption Machine

[stellabella]

We have a 600 kW NG CoGen plant and all heat produced (H2O and exhaust) is wasted. We also run a NG direct fired absorption unit for chilled water. We are looking into the feasibility of retiring the existing unit and installing another absorption unit that can run off of the waste heat. Does anyone know about the efficiency of the units? In other words, BTUs of Cooling Out vs. BTUS of Hot Water IN.

 

[KiwiMace]

If you are dumping the exhaust heat... how is this a cogen?

This depends on the quality of the waste heat.. temp mostly. See a chiller vendor for details.

 

[willard3]

He didn't mean cogen, he meant electrical generation.

I just did a project with cogen waste heat and the new absorption units run at highest efficiency at 175F waste water temp, very much lower than the old ones that required 210-220F.

Given that you're paying for the NG absorption and not for the recovered heat absorption, the efficiency increase is 100%. Other than this, efficiencies are vendor-specific; speak to a salesman.

 

[ChrisConley]

How relevant is the efficiency of the chiller given that you are using waste heat from a 600kW cogen?

If the efficiency is 1/2 Btu/hr per 1 Btu/hr input, you are still ahead of the game as the input is waste.

If you plant is a cogen, would that imply you are using exhaust gas to produce steam to produce electricity through a steam boiler? If so, low grade steam would work well in an absorption chiller, likely better than exhaust gas.

 

[stellabella]

The reason for inquiring about the efficiency of the proposed absorption machine is thatthe existing machine, which it would replace, is a direct fired NG machine. Therefore, although the waste heat is free, there will be a capital expenditure for the purchasing of a new absorption machine that can use the waste heat from the CoGen unit,

 

[willard3]

Put a meter on the NG absorption unit and record usage.

With NG at $6-10/million btu, capital paydown without regard to efficiency will probably be less than 3 yrs.

 

[Core4Guy]

I know this is an old tread but in general there are absorbers that claim run about 16,000 btu's per ton at 160° there are other that state worse more reasonable performance. There is even an "ad" Adsorption unit installed at one of the wineries in my area running off the waste heat from a couple of Capstone Micro turbines. Check with manufactures.