Exergy Destruction

[ermorgan]

Is there a way to get COCO to calculate exergy destruction around a unit op? For example, if I had a compressor I know the heat loss, but I don't necessarily have a way to tell the information calculator what the entropy of the I/O streams is. Any thoughts?

Thanks,

Eric

[jasper]

Entropy can now be measured using the MeasureUnit. Update is available via COCO Update (CUP). Hope that helps.

[ermorgan]

Wow. Thanks a lot. I'm amazed at your dedication to this project. Some commercial software isn't this good.

Eric

[ermorgan]

Hello again,

I'm attempting to calculate the heat flow out of a plug-flow reactor. I'm not sure if there's a simple way to do this. The reactor is a small methanol reactor. I'm measuring the rates of the two reactions at the beginning of the reactor and then using the heats of the reactions to get a total "heat out" term. (I'm incorporating the catalyst, etc to get dimensions of J/s.) The problem is, the rates change throughout the reactor. Is there a way to get the total reaction in the reactor (integration?). My next attempt will probably use the average of three points...

Thanks,

eric

[jasper]

Is this the COUSCOUS PFR? Or another PFR? The COUSCOUS PFR accumulates the heat simply in what flows through the reactor, so it will give you the total heat balance, unless you are running it isothermally. Can you give more details?

[ermorgan]

I believe it's a COUSCOUS PFR, it's from the Insert-->Unit Operation in the COFE menu. I can get an energy balance on the report, and by going to the "Balance" tab on the reactor menu. But I'm attempting to access the heat loss through the information streams, which proves more difficult. Right now, I'm getting the enthalpy flow across the reactor using the info streams and measurement device. It doesn't appear to include the heat of reaction, but maybe I'm wrong (I'm using heat of RXN in the solve routine). Under this assumption, I accessed the reaction rates for each reaction and manually calculated the heat rate inside the reactor. Seemed to work pretty well, and I got reasonable answers. I have no heat duty or cooling tubes, so perhaps if I add those in, the heat duty will be calculated automatically. I attached the (very messy) sheet, if you'd like to have a look.

Thanks for your help.

Eric

[jasper]

You can get the heat duty on an information stream as follows. The heat duty is exposed as a parameter. Each parameter in COFE can be turned into a virtual information stream. Double click the unit, go to the ports tab. On the Port Operations drop down, select Add Virtual Information Port. Select output, heat duty.

Let me know if this is what you were looking for.

edit: there was no attachment.

[jasper]

Note that the heats transferred to cooling tubes and external wall are available separately by connecting the (thermal) energy ports.

[ermorgan]

I tried the heat duty virtual port approach, but the answer was 0 watts, which is not the correct answer. Since I'm not using any tubes, etc I can't use that approach at present. I could conceivably add those features to the reactor and then compute the heat duty. From an exergetic perspective, the energy is wasted either way (tubes vs. air). The attachment extension fsd is not allowed. Hmm.

Eric

[jasper]

I can get an energy balance on the report, and by going to the "Balance" tab on the reactor menu.

These balances simply give product minus feed enthalpy. You can get this on an information stream by measuring these and subtraction using the information calculator.

I tried the heat duty virtual port approach, but the answer was 0 watts,

Sorry about that - this is the heat input, not output.

I'm measuring the rates of the two reactions at the beginning of the reactor and then using the heats of the reactions to get a total "heat out" term. (I'm incorporating the catalyst, etc to get dimensions of J/s.) The problem is, the rates change throughout the reactor. Is there a way to get the total reaction in the reactor (integration?).

I am not entirely clear on which heat you are looking for. Are you looking for the total enthalpy change of the unit? Measure EnthalpyF before and after the unit and subtract. Are there any effects you want to exclude from this enthalpy difference, such as changes in temperature and pressure (you mention you want to obtain the total heat of reaction which presumably is at standard conditions)? In this case, use a couple of units, start in standard conditions, change T and P to reactor inlet conditions, then the reactor, and bring the product back to standard conditions. Measure the EthalpyF change over the whole.

If you are looking for the total amount of reaction that has occured, you can simply look at the difference in flow rates of one of the reactants or products?