Nobrainer’s Think Tank

[EDIT: I received an email from Kent Hawkins informing me that I correctly identified a mistake and that he has since corrected the problem in his calculator. Thanks, Kent. Sorry for the sarcasm here.]

I began Part 6 by saying that “one of my new favorite blogs” is “MasterResource”. I’ve since edited that post because I ended up publishing it several weeks after I wrote it and, in that time, realized that the blog isn’t that great.

Case in point: Poster Kent Hawkins has created a CO2 savings calculator. He seems very proud of it. He’s even made updates to it!

The model relies on this graph. It uses a percent reduction in efficiency due to required turndown and applies a corresponding CO2 penalty.

The model seems reasonable; reductions in efficiency lead to CO2 rate (the amount of CO2 released per unit of electricity) penalties.

Seems.

But the model is wrong. As are the outputs, which frankly don’t pass the sanity check.

First, let’s consider the sanity check. Based of the initial post, there’s a chart showing fuel reduction for a given scenario (the scenario is has major flaws, but that’s not the point of this post).

Then we see that for the scenario, despite fuel savings, we can actually have CO2 emission increases.

Let’s sanity check that. The model assumes all the fuel is natural gas. The model reports that less natural gas is being used. And the model reports that more CO2 is being emitted. In other words, the CO2 per unit of natural gas is increasing. The model says that natural gas is a variable carbon content fuel. That is insane. Thus, the sanity check fails.

Going back to the initial graph, we see that for a given efficiency and fuel type (i.e. any spot on a curve) there’s a corresponding CO2 rate. For proper analysis, Kent should not be assigning a pre-defined penalty based on some efficiency change. Rather he need only pick the CO2 rate of the curve that corresponds the efficiency in question and thence proceed.

I’ve re-created the given graph for natural gas fired plants.

You can create a similar graph for heat rate (the amount of fuel burned to product a unit of electricity). This is another way of viewing efficiency.

The heat rate and CO2 rate graphs are very similar you’ll notice.

So similar, that if you plot heat rate VS CO2 rate, you get a straight line!

Let me change the values on the y-axis.

It’s still a straight line, and the coefficient is 117.08 lb/MWh… exactly what the EIA says it is. And why is that? Because that’s how you properly convert. I multiplied the heat rate by the CO2 coefficient. The CO2 coefficient for a fuel is not going to change based on plant efficiency. The change in CO2 has to be directly proportional to the change in quantity fuel used.

Here’s the data for my charts:

Kent Hawkins should have used the above graph in the model. If he had, then he wouldn’t have created variable carbon content fuel. He should also have sanity checked his work. Hopefully he and the others at MasterResource will approve my comment, notice it, correct their model and their faulty conclusions.