OK, it seems that among the many things thrown out as to why I am a partisan pathological liar on the subject of coal, one of the first items was a challenge to my assessment of the worthiness of the coal contained in the “monument” that Clinton reserved under the circumstances that don’t seem right and proper to myself. I was apparently asked why Wyoming PRB coal would not be just as good or better than the Kaiparowits Basin coal, and no counter-information or evidence was given as to why this other person thought this would be the case. So, having some rare spare time, I decided to go ahead and show my hand as to some of the steps I used to arrive at my judgement. Since some of my original work was left at my office (since I don’t carry this stuff with me, everywhere, since I am not usually challenged on my assessment of these issues with no counter-evidence given) I went ahead and did a new, mini analysis.
So, let’s do some analyses on the coal from the Kaiparowits basin to see how it stands up to Wyoming coal. I chose Black Thunder, since it is a very high-volume PRB coal, and is the basis for the OTC NYMEX PRB 8800 Btu coal future. I also chose Eagle Butte, since it is very representative of the OTC NYMEX PRB 8400 Btu coal future. In addition, I chose a Montana coal, Spring Creek, since it is another high-volume coal mined in close proximity to the Black Thunder and Eagle Butte coals.
The Kaiparowits basin samples I am using come from an average of qualities listed from Mono Power, recorded in 1983, and from Andalex, recorded in 1992. Since development of the region was very low to none at the time it was locked out, there is a large confidence in using samples from the same field taken so many years apart. The Black Thunder quality is Mine-Supplied for Year 2000 from ARCO Coal. The Eagle Butte quality is the average of 6576 samples taken by RAG Coal West from the Roland/Smith Seam. The Spring Creek quality, technically not a PRB coal but included for completeness from the region, and due to it’s high consumption by utilities, comes from a September 1999 analysis by Commercial Testing and Engineering, hired by Kennecott Energy.
So here are the coal quality properties of the Kaiparowits Basin coal and the others we will look at:
Kaiparowits Basin Black Thunder PRB Eagle Butte Spring Creek
Heating Value, Higher (Gross) : 10,800 Btu/lbm 8821 Btu/lbm 8350 Btu/lbm 9156 Btu/lbm
Proximate (Wet)
Moisture: 14.80% 27.31% 30.80% 25.92%
Ash: 7.00% 4.73% 4.70% 4.33%
Volatile Matter: 36.00% 34.16% 31.20% 30.58%
Fixed Carbon: 42.20% 33.80% 33.30% 39.17%
Ultimate (Wet)
Carbon: 61.60% 49.61% 48.50% 52.97%
Hydrogen: 4.33% 4.04% 3.30% 3.69%
Nitrogen: 0.83% 0.57% 0.70% 0.73%
Sulfur: 0.38% 0.24% 0.39% 0.36%
Chlorine: 0.02% 0.00% 0.00% 0.00%
Ash: 7.00% 4.73% 4.70% 4.33%
Moisture: 14.80% 27.31% 30.80% 25.92%
Oxygen: 11.04% 13.50% 11.60% 12.00%
(yes, these may not add to 100%. All undetermined or balance values go into oxygen,
since it is determined "by balance", after all)
Ash Mineral Analysis:
Silica: 55.40% 28.90% 27.70% 35.44%
Alumina: 17.80% 16.00% 14.60% 18.18%
Titania: 0.90% 1.23% 1.10% 1.11%
Iron Oxide: 5.00% 5.01% 5.50% 4.10%
Lime: 9.10% 23.60% 25.00% 14.65%
Magnesia: 2.00% 5.13% 6.10% 3.46%
Potassium: 0.60% 0.50% 0.20% 0.72%
Sodium: 1.50% 1.16% 1.70% 5.74%
Sulfur Trioxide: 6.90% 14.70% 15.70% 14.73%
Phosphorus Pentoxide: 0.20% 1.12% 0.60% 0.31%
Strontium: 0.00% 0.00% 0.00% 0.33%
Barium: 0.00% 0.56% 0.50% 1.22%
Manganese: 0.00% 0.02% 0.05% 0.01%
Undetermined: 0.50% 2.07% 1.20% 0.00%
Ash Fusion Temperatures
Initial Deformation, Minimum Reducing: 2200 F 2052 F 2221 F 2018 F
Softening, Reducing: 2300 F 2157 F 2230 F 2057 F
Hemispherical, Maximum Oxidizing: 2450 F 2192 F 2292 F 2293 F
Hardgrove Grindability: 47 53.2 58.5 46
Calculated Values (calculated by Una, not supplied):
Francis-Lloyd Heating Value verification:
(148.59*carbon + 530.3*hydrogen + 26.74*sulfur-55.378*oxygen)
10,848 Btu/lbm 8772 Btu/lbm 8324 Btu/lbm 9172 Btu/lbm
SO2 Loading, lbm/MBtu
0.702 0.543 0.933 0.785
Ash Loading, lbm/MBtu
6.48 5.36 5.63 4.73
Fuel Nitrogen Loading, lbm/MBtu
0.769 0.646 0.838 0.797
OK, enough of the simple stuff. Now, what I did next was I took all of these coal quality sets, and did an analysis on an actual power plant that was considered at one time to be a candidate for the coal from the Kaiparowits Region. This plant was originally designed to burn coals from typical New Mexico quality to Wyoming PRB type coals, so I’m not sandbagging the analysis by choosing a Virginia plant or anything. I did a detailed combustion and boiler heat transfer analysis, slagging and fouling tendency analysis, analysis of the effects on emissions, performance of steam generator auxiliary equipment, overall unit efficiency, and plant heat rate. Let’s summarize, since I can hear people clicking away already in boredom to head over to MPSIMS…
Overall Unit Heat Rate - AKA, unit thermal efficiency, measured in Btu/kWhr. This is essentially how much energy input from the coal is required to generate 1 kWhr of net electrical output from the plant. Thus, lower numbers are better. Note - thermal efficiency of the plant can be found by dividing the heat rate into 3413.
Kaiparowits Basin: 10,051 Btu/kWhr
Black Thunder: 10,463 Btu/kWhr
Eagle Butte: 10,578 Btu/kWhr
Spring Creek: 10, 354 Btu/kWhr
This is an enormous increase in unit efficiency when compared to these other coals from the Wyoming/Montana region. But why is the efficiency so much higher? Well, the Unit Heat rate can be expressed as:
NUHR, Btu/kWhr = (Net Turbine Heat Rate, Btu/kWhr) / ((Boiler efficiency)( 1 - auxiliary electrical energy/gross electrical energy))
(net turbine heat rate is turbine efficiency, which was assumed to be constant for this quick analysis. In reality, differential steam requirements of sootblowers, air preheat coils, and flue gas reheat; and differential superheater and reheater spray flow volumes might very well change this. But let’s keep this quick and dirty, OK? 
)
Since it’s obvious by inspection (well, to me anyhow) that boiler efficiency should be the key factor, let’s look at how that fell out for the coals:
Kaiparowits Basin: 88.13%
Black Thunder: 84.65%
Eagle Butte: 83.79%
Spring Creek: 85.69%
Wow - big difference in boiler efficiency. Why did this happen? Well, lets look at some of the boiler efficiency losses, expressed in terms of latent, sensible, and unburned combustible losses (ignore variations in radiation/convection from boiler enclosure, ash pit losses, pulverizer heat credit, etc, etc)
Latent heat losses are losses of heat due to the vaporization of the moisture contained inherently in the coal, and the vaporization of moisture produced by the combustion of the hydrogen contained within the coal. Since this heat of vaporization cannot be realistically recovered in a steam generator, it is considered an efficiency loss.
Kaiparowits Basin: 5.23%
Black Thunder: 7.58%
Eagle Butte: 7.61%
Spring Creek: 6.79%
Big difference again, and pretty obvious to me by inspection of the original coal quality. Now, let’s look also at sensible heat losses. These are losses that can be “sensed”, which are essentially stack energy losses (although the boundary drawn by ASME typically is at the air heater gas outlet, not the stack). Let’s see how these losses compare:
Kaiparowits Basin: 3.87%
Black Thunder: 4.17%
Eagle Butte: 4.29%
Spring Creek: 4.07%
But why is there a difference in the sensible loss? Well, two reasons. First, the high calcium content (lime) of the ash of the 3 Wyoming and Montana coals causes the formation of a reflective ash layer on the furnace water walls, thus reducing the radiation heat transfer and increasing the gas outlet temperature of the boiler. And this increased temperature means increased heat loss. Second, the ash mineral constituents of the Wyoming and Montana coals was predicted to cause greatly increased slagging in the furnace and fouling of the radiative tubes in the furnace, thus decreasing heat transfer further relative to the Kaiparowits Basin coal. These two effects combined created an increased furnace, boiler economizer, and air heater gas outlet temperature:
Kaiparowits Basin: 2219 F / 776 F / 298 F
Black Thunder: 2234 F / 787 F / 313 F
Eagle Butte: 2260 F / 793 F / 315 F
Spring Creek: 2183 F / 780 F / 310 F
Note that while the Kaiparowits coal had a higher furnace exit gas temperature than the Spring Creek coal, it was predicted to suffer from less convective pass tube fouling, and thus ended up with a lower economizer gas outlet temperature, and thus a lower air heater gas outlet temperature. Also, less air heater fouling was predicted as well for the Kaiparowits coal.
FYI, the overall average of 15 industry-standard coal slagging indices (10 of which were applicable, we want to be scientifically valid here), and 5 industry-standard coal ash fouling indices were:
Slagging
Kaiparowits Basin: Low/Medium
Black Thunder: Medium
Eagle Butte: Medium
Spring Creek: Medium
Fouling
Kaiparowits Basin: Medium
Black Thunder: Medium/High
Eagle Butte: High
Spring Creek: High
However, if we want to examine just two of the most representative indices, I would have to choose the Battelle Western Index and the Western Base-to-Acid Ratio Index for slagging:
Batelle Western Index - Base/Acid * (Steam Flow per Waterwall Area / 32,000)
Kaiparowits Basin: Low
Black Thunder: High/Severe
Eagle Butte: High/Severe
Spring Creek: Medium
Western Base-to-Acid Ratio Index - (Base/Acid)
Kaiparowits Basin: Low
Black Thunder: Medium
Eagle Butte: Medium
Spring Creek: Medium
Of course, the Battelle Western Index really seems to very heavily favor the Kaiparowits coal - to an unreasonable extreme. Whereas if one just looked at the Western Base/Acid Ratio, one might conclude there was not a great difference. Since I am not partisan in coal matters, I therefore feel it is better to take the average of the 10 applicable indexes of the 15 standard indexes that are typically used. These fifteen are, of course, the Battelle Western and Eastern Indexes, the AEP Slagging Factor, the Western and Eastern Base-to-Acid Ratio Indexes, the Silica Factor, Iron/Calcium Ratio, Attig & Duzy, Ash Fusion Temperatures Index, Multi-Viscosity, Watt & Fereday, Hoy & Roberts, BCURA, Dolomite Index, and Babcock & Wilcox slagging index.
(Wanna guess which ones are applicable or not to these coal cases? Extra credit points…)
I will not go into the details of the fouling analysis at this time, to spare you more boredom.
And as for the last boiler efficiency component we will look at, we see another interesting thing. Due to the very favorable combustion characteristics predicted for the Kaiparowits coal, it was predicted to have by far the least unburned carbon heat loss of any of the coals:
Kaiparowits Basin: 1.16%
Black Thunder: 1.99%
Eagle Butte: 2.69%
Spring Creek: 1.87%
True, in all fairness, this unit has control problems that give it an inordinately high unburned carbon loss. It is possible if they can increase their excess air and grind fineness they can reduce this loss considerably, and thus also reduce the differential efficiency losses between each coal. Of course, by changing their excess air and grind fineness, NO[sub]x[/sub] emissions may be adversely affected…but I won’t go into that.
Now, let’s look at some emissions figures - namely, annual emissions. Well, on this unit I assumed a base-load profile demand curve with a 68% capacity factor for one year note: gross basis, not net). Below are the annual SO[sub]2[/sub], NO[sub]x[/sub], and CO[sub]2[/sub] emissions predicted for each coal (note - this unit has a wet flue gas desulfurization system, with an emissions limit of 0.8 lbm/MBtu).
SO[sub]2[/sub] Emissions, ton/year
Kaiparowits Basin: 7971 tons
Black Thunder: 6370 tons
Eagle Butte: 10,990 tons
Spring Creek: 9122 tons
NO[sub]x[/sub] Emissions, ton/year
Kaiparowits Basin: 10,222 tons
Black Thunder: 9435 tons
Eagle Butte: 10922 tons
Spring Creek: 10324 tons
CO[sub]2[/sub] Emissions, Mton/year
Kaiparowits Basin: 2.373 Mton
Black Thunder: 2.416 Mton
Eagle Butte: 2.508 Mton
Spring Creek: 2.463 Mton
Well, these are some general quick-and-dirty calculations that I did. We can see that there are many factors here that, at least from a technical standpoint, tend to favor the Kaiparowits coal over these particular common coals from the PRB and nearby Montana Basin region. Of course, since coal quality can vary a bit, one can always come up with coal quality for any of these coals which is better or worse than what I analyzed - that is the nature of the science. I hope that the samples I chose were very representative and proper. You, gentle reader who made it this far, will just have to take my word for it that I tried to find the most representative samples from these particular mines and regions from the information I have available. Or else call me a partisan liar. I would suggest if one is going to do that, they perform their own study and get back to me on what they find.
I also have not even touched maintenacen and availability considerations, boiler erosion differences, coal handlability issues, supply issues, stockpile problems, fire suppresion for PRB coals, etc. Does anyone want to hear it? I’m guessing…no.
But then again, I may not know what the hell I am talking about. Well, this one point has been discussed by myself at least. Perhaps we can cover more specific points later?