The May 2016 issue of Trains Magazine features an excellent article by Hayley Enoch outlining the difficulties facing the U.S. railroad preservation industry in procuring quality coal, especially given the recent decline in supply due in large part to coal-fired utilities switching to cleaner, more affordable natural gas. The article explains nicely the varieties of coal available and the way each type of locomotive burns said variety. It also alludes specifically to struggles coal-fired steam locomotive operators face procuring consistent fuel.
To combat this struggle, many operators already have found significant benefit in converting coal-fired locomotives to oil. The engines can be refueled from a standard oil pumper truck, the fireman’s job is made less labor intensive, and there is no ashpan to empty or fire to rake. This in turn cuts down labor associated with operation.
That said, even with coal at $200/ton and diesel at $2/gallon, it is still roughly half the cost to fuel a locomotive on coal than oil ($7.69 per MMBTU vs $15.60 per MMBTU).
All that aside, we as preservationists have a duty to keep steam locomotives and historic rail equipment operating well into the 21st Century. Already, the changing public perception associated with coal consumption is beginning to have an impact.
Consider, for instance, the Durango & Silverton Railroad – it faced criticism from local residents regarding smoke coming from the engine house associated with hostling the locomotives overnight. The solution agreed to by all parties was to burn compressed wood pellets in the engines overnight, a fuel that burns more cleanly than coal and with less odor. This measure was also combined with use of emissions scrubbers on the roof of the engine facility.
It is not too much of a stretch to anticipate this type of concern impacting other railroad preservation groups. While photographers may enjoy a large plume of smoke, it is neither responsible of the fireman or the railroad to tolerate that under most circumstances. Every steam railroad was concerned about smoke - couching it "back in the day" from a perspective of inefficiency and economics.
Today, preservationists have a responsibility to use locomotives efficiently and with an eye to avoid criticism from an ever-changing riding public.
Another Alternative in Solid Biofuel?
We at the Coalition for Sustainable Rail have been working with the University of Minnesota’s Natural Resources Research Institute to develop a solid biofuel alternative to coal for use in all manner of boilers – including steam locomotives.
The fuel is made from woody biomass (e.g. sustainably-harvested forest, used railroad ties, etc.) in a process known as “torrefaction.” Known as torrefied biomass (or biocoal), the fuel conversion process is a derivative of coffee roasting technology originally designed in the early 20th century in France (torrefaction = "to roast" in French).
This is not just coffee roasting technology anymore. Raw biomass is heated up in a sealed, oxygenless environment to between 250 and 300 degrees Celsius, a process known as partial pyrolysis. At this temperature, many of the volatiles in the woody biomass begin to decompose and part of the sappy lignin that binds the material together breaks down and vaporizes. This gas is captured in the sealed vessel, then returned to the original heat source to add to the combustion heat and increase the thermal efficiency of the reaction system. Research has shown that the fuel conversion process is up to 96% thermally efficient.
Test Burn of Torrefied Biomass Pellets
The briquetted pucks produced by torrefaction are analogous to coal, except that they are renewable, have no heavy metals, burn cleaner, smoke less, and smell a bit like BBQ in their unburned state. The GIF above shows torrefied biomass pellets created by NRRI during an open-air test burn, and the following table compares torrefied biomass with other regularly-available fuels.
CHARACTERISTICS OF SOLID FUELS COMPARED TO TORREFIED BIOMASS
|Characteristic||Wood||Wood Pellets||Torrefied Biomass||Charcoal||Coal|
|Moisture Content (% wt)||30-40||7-10||1-5||1-5||10-15|
|Calorific Value (BTu/lb)||3,850-5,100||6,450-6,850||8,600-11,000||8,000-9,500||8,600-14,000|
|Volatiles (% db)||70-75||70-75||55-65||10-12||15-30|
|Fixed Carbon (% db)||20-25||20-25||28-35||85-87||50-55|
|Bulk Density (lb/cu.ft.)||12.5-15.6||34.3-46.8||46.8-53.1||12.5||49.9-53.1|
|Vol/ Density (BTU/cu.ft.)||53.7-80.5||201.3-279.1||402.6-501.9||161.0-171.8||493.8-638.8|
Unlike other alternatives on the market for replacing coal, torrefied biomass is about as close as one can get to the original “black diamonds.” It can be shoveled or stoker-fired into a boiler, it burns in the same way as coal, and the fuel shares the same handling equipment. Just as outlined in Ms. Enoch's original Trains Magazine article, however, solid fuels require unique loading systems (clamshell bucket, loader, etc.).
High-end torrefied fuel is approximately 11,000 BTU/lb, while optimal bituminous coal is approximately 13,000 BTU/lb. While it is easy to assume that it would take 15% more torrefied biomass to equate the same heat output of bituminous coal (since it is 15% less energy dense), the reality is a bit more nuanced.
The ash content of torrefied biomass fuel is generally at or below 5%, whereas typical bituminous coal is around 10% ash content (Kentucky-sourced). Likewise torrefied biomass fuel is generally around 1% moisture, while the same bituminous coal is 8%. This means the torrefied fuel will light and burn much easier, and the combustion will be much more efficient (heating ash and water does nothing to improve the fire but consume energy). Therefore, a locomotive boiler may require slightly more biocoal by weight than coal to boil the same amount of water, but not the aforementioned 15%.
When CSR first announced its project in 2012, NRRI was able to make a few pounds of torrefied biomass per hour. In the coming few months, however, it will finalize commissioning of a one-of-a-kind, 28,000 pound-per-day reactor capable of making quantities of fuel sufficient to fill steam engine tenders for testing.
We are currently in talks with a few steam locomotive operators to undertake testing with the fuel to see how it performs in traditional fireboxes, both burned alone and blended with coal. Our group is aiming to get ahead of the curve in finding a readily-available, drop-in replacement fuel for coal.
To quote Ms. Enoch: "Will a day come when tourist railroads may be forced to move away from coal if their operations are to continue? It seems unfathomable, but nothing is out of the question. For the moment, though, that day is still on the horizon."
We agree that the day is still on the horizon, but we are working to be prepared in case that day does come. Our research is focusing in part on ways to keep the traditions of hand and stoker firing alive, regardless of whether the locomotive burns coal or a wood-based alternative.