Just for reference in the US in 2022 there were 4 different types of coal.
From
https://www.eia.gov/energyexplained/coal/
Anthracite contains 86%–97% carbon and generally has the highest heating value of all ranks of coal. Anthracite accounted for less than 1% of the coal mined in the United States in 2022. All anthracite mines in the United States are in northeastern Pennsylvania.
Bituminous coal contains 45%–86% carbon. Bituminous coal is the most abundant rank of coal found in the United States, and it accounted for about 46% of total U.S. coal production in 2022. Bituminous coal is used to generate electricity and is an important fuel and raw material for making
coking coal for the iron and steel industry. Bituminous coal was produced in at least 16 states in 2022, but five states accounted for about 78% of total bituminous production. The top five bituminous producing states and their percentage share of total U.S. bituminous production in 2022 were:
- West Virginia—31%
- Illinois—14%
- Pennsylvania—14%
- Kentucky—11%
- Indiana—9%
Subbituminous coal typically contains 35%–45% carbon, and it has a lower heating value than bituminous coal. In 2022, subbituminous coal accounted for about 46% of total U.S. coal production. The five subbituminous producing states and their percentage share of total U.S. subbituminous production in 2022 were:
- Wyoming—89%
- Montana—8%
- New Mexico—2%
- Colorado—2%
- Alaska—<1%
Lignite contains 25%–35% carbon and has the lowest energy content of all coal ranks. Lignite is crumbly and has high moisture content, which contributes to its low heating value. In 2022, five states produced lignite, which accounted for 8% of total U.S. coal production. The five lignite-producing states and their percentage share of total U.S. lignite production in 2022 were:
- North Dakota—56%
- Texas—36%
- Mississippi—7%
- Louisiana—1%
- Montana—<1%
Note the lack of cross over of types of coal from region to region. Also note the huge difference between high grade Bituminous and low grade Bituminous You might need around 50-60% more tons of low grade Bituminous than you do high grade, even cutting off the extremes.
Yes you can design fire boxes and boilers to use different types of coal. But to run well they have to use a somewhat consistent type of coal. BTW in many older books/magazines some US Railroads than were using engines running on subbituminous were described as burning lignite.
View attachment 813842
Northern Pacific was one RR that burned low grade fuel (Subbituminous/lignite) using a rather large fire box/grate. Apparently true lignite is rather crumbly and needs a bigger firebox/grate area, closer spaced grate rods and smaller inlet air hole in the bottom. Larger/standard airholes tend to blow the smaller coal pieces up out of the fire box, through the boiler tubes and out the stack. True lignite was mostly used in stationary power plants.
"Like all NP Northerns, the A-2s burned Rosebud coal, a fuel with 22-28% moisture content and 7-9% percent ash. Compared to more typical locomotive coal, which were rated at 11,000-15,000 BTU/pound, Rosebud generated 8,750 BTU. Such low-grade brown stuff was laid by a Standard modified type B stoker on a large grate. Firebox heating surface area included 62.6 sq ft " This is for the class right after the one in the photo. The stoker was a mechanical stoker to move the quantity of fuel per hour than these big locomotives needed.
Granted a much small boiler could be hand fired.
Low grade fuels (solid or liquid) should be used in rear areas were it is easy to replenish fuel due to short trips. Using low grade fuel for moving long distance can mean doubling the amount (tonnage) of fuel used for long distance traveled which means less cargo actually moved (might be only 1-2 coal wagons per trip?).