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Coal Substitute Fuel Gets a Boost from Report

image credit: Image courtesy of Helvellyn Group
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  • Jun 23, 2020

London-based Helvellyn Group is a manufacturer of a low environmental impact direct coal replacement fuel for industrial and power generation applications called SERF.

Their fuel is specifically designed to mimic the characteristics of coal, allowing for use of the same fuel delivery, preparation and combustion infrastructure, without modification and resulting in the same combustion characteristics, but with a substantial CO2 emissions reduction.

Although coal substitutes have been used in the past, and currently some power plants are using wood pellets in place of coal, the dirtiest fossil fuel has been essential to not just power generation but industrial processes such as steel making, which makes decarbonizing a headache.

The issue at stake is can coal-fired assets continue to the end of their life-cycle, or will utilities have to decommission them prematurely, because of new environment legislation? That would result in economic losses, so any method of life extension would be welcomed by power suppliers.

SERF is used in place of bituminous coal, with up to 100% substitution. Normal transport and handling processes can be used, and the fuel is water-resistant so it can be stored in external stockpiles.

An analysis by highly-respected consultants Uniper Technologies said Helvellyn Group’s SERF, “is technically suitable for use in large scale thermal power plants in a blend, and potentially up to full substitution, with little or no capital outlay and delivering a net reduction in operating costs.”

Frank Harris, Helvellyn’s CEO, explains how SERF is produced, “Our process is able to take a wide range of carbonaceous feedstocks, including low grade coal, sludges, wastes, and biomass, and produce fuels to a precise specification consistently,” He continues, “We knew that the fuel would work in large-scale powergen, and now we have independent analysis from one of the most experienced companies in the sector, to back that up, emphatically.”

The fuel is normally supplied in 50mm lumps, as shown above, but it can also be purchased as pellets, logs or ground into a fine gravel-like substance.

The company notes that exact fuel specification and presentation can be fine-tuned to meet the specific needs of a given plant. Normally SERF is presented as 50 mm hard, hydrophobic lumps with the following properties: energy >25 kJ/kg (10,750 Btu/lb, 5.97 kcal/kg); ash content <6%; moisture <2%; chlorine <0.07%; carbon >60%; sulfur <0.2%; and nitrogen <0.4%.

The Uniper analysis acknowledges that coal-fired power plants vary considerably in their tendency to suffer from slagging and fouling, and the report highlights that the different ash composition of SERF means that these risks need to be assessed on a case-by-case basis. SERF contains higher levels of calcium and sodium, which increases risks of some types of boiler ash deposition, but it also contains low levels of iron, which is beneficial.

Risks are also dependent on factors including boiler design, operating regime, complementary coal quality, and co-firing levels. Helvellyn has said that plant operators have a range of mitigation measures available should issues arise. The company said the risk of boiler corrosion is low, primarily due to the low chlorine level in SERF, and erosion risks are expected to be reduced as a result of lower ash content and lower flue gas flow rates.

Harris said that using SERF will lead to a reduction in SO2, NOx, and particulate matter, noting that the higher the substitution rate, the lower the levels of each emission. SERF is expected to produce higher boiler efficiencies, together with lower ash remnants.

Whether this technology will succeed in replacing the oldest of the fossil fuels remains to be seen, but it looks promising.

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Carl Bozzuto's picture
Carl Bozzuto on Jun 24, 2020

While it is clear that emissions of SO2, NOx, and particulate will be reduced, I am not sure about the reduction in CO2 emissions.  Of course a complete fuel analysis is not given.  However, the ranges given in the post seem to indicate that the fuel is at least 60% carbon.  The other constituents add up to less than 10%.  The HHV is noted to be greater than 10750 BTU/lb.  This information begs the question of what the remainder of the 30% is.  An Indiana coal with the following composition has an HHV of 10720 BTU/lb...C - 58.5%, H - 4.0%, S - 4.3%, O - 7.2%, N - 0.9%, ash - 11.0%, moisture - 14.1%.  The products of combustion at 20% excess air (typical for coal firing) would give 1007.6 lb/MMBTU fired of which 58.36 lb/MMBTU would be water and 9.13 lb/MMBTU would be ash.  The CO2 mole concentration would be 13.3% by volume.  I took a guess at the composition for the SERF fuel with an HHV of 10750 BTU/lb.....C - 60.0%, H - 6.4%, S - 0.2%, O - 25%, N - 0.4%, ash - 6.0%, moisture - 2.0%.  I raised the hydrogen content somewhat as there is less water and ash.  The remainder was assumed to be oxygen on the basis of the description of the origins of the material (ie waste sludges, biomass, etc.).  If the remaining amount of matter were attributed to hydrogen instead of oxygen, the heating value of the fuel would be way too high.  Natural gas (methane) is 25% hydrogen and the HHV is 23,100 BTU/lb.  The products of combustion for this assumed fuel gave 1007.1 lb/MMBTU fired, or only slightly less than the Indiana coal.  However, 66.863 lb/MMBTU would be water and only 9 lb/MMBTU would be ash.  The increase in water would detract from the boiler efficiency.  The CO2 concentration would be 13.5% on a volume basis.  From this analysis, there is no reduction in CO2 emissions and even, perhaps a slight increase.  With the above information, I estimated the boiler efficiency for the 2 fuels assuming 20% excess air and 300 F exit gas temperature.  The Indiana coal showed an estimated 88.06% boiler efficiency, while the assumed fuel showed an estimate 87.05% boiler efficiency.  I then assumed that the produced fuel might be easier to burn for some reason.  I changed the excess air to 15% and the exit gas temperature to 285 F.  The boiler efficiency came out 87.6%, still lower than the Indiana coal.  From this analysis, it is hard for me to see how the produced fuel reduces CO2 emissions.  Of course, I had to make assumptions about the composition and heating value of this fuel, since only ranges were given.  Perhaps the writer can provide that kind of information so that a better analysis can be made.

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