Helvellyn Group has received a significant endorsement for the use of its low impact coal replacement fuel, SERF, in the power generation sector.
The report confirms that Helvellyn’s alternative fuel 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.
The report highlights that the high renewable energy content can deliver significant economic benefits compared to firing coal without many of the drawback experienced with other alternative fuels. The economic benefit has been assessed at a range of coal and carbon price levels.
Helvellyn Group believes this could be a lifeline to operators of assets with a life expectancy that is longer than current or future legislation allows them to exploit.
As part of its ongoing assessment and refining of the product for the European market, Helvellyn Group commissioned a report to compare its fuel to coal at each stage in a power plant. The analysis, by Uniper Technologies, took account of
- Delivery, storage and handling
- Milling and delivery to boiler
- Combustion and boiler efficiency
- Boiler slagging, fowling, erosion and corrosion
- Primary emissions and flue gas cleaning
- Trace elements
- CO2 emissions
- Unit efficiency
The analysis looked at blends of SERF at 20% increments up to 100% substitution based on a 500MW boiler operating on a traditionally combusting a range of bituminous coal.
Delivery, storage and handling
SERF is specifically engineered to mimic the physical properties of coal and the report noted that individual plant arrangements would need to be taken into account, but in most cases SERF will be usable within existing ship/rail/road delivery and handling infrastructure. Importantly, SERF is water resistant, allowing for open air handling and the possibility of open stockpiles.
Milling and delivery to boiler
The report confirmed that SERF can be delivered to mills through the coal feeders and that no problems were expected in the milling process. Whilst it acknowledged that SERF may require a slightly more power to grind than coal, some benefits for milling plant are also noted
- Reduced likelihood of feeder plugging,
- Reduced air inlet temperature,
- Reduced likelihood of mill fires
The benefits increase as the substitution rate increases, but are immediately realisable at blends as low as 20%.
Unlike other alternative fuels, SERF does not generate 2-dimensional fibrous particles when milled, ensuring that, in a pulverised state, the fuel remains mobile and manageable.
Combustion and boiler efficiency
SERF is designed to mill to a slightly large particle size than coal in a pulverised state. This is to compensate for the higher volatile matter during combustion and ensure similar burnout time for coal and SERF in the boiler.
The report noted that despite the larger particle size, a higher burnout rate would exist, resulting in lower unburned carbon losses and an improvement in boiler efficiency.
Flue gas heat losses are predicted to remain the same as operating coal as an increase in hydrogen is counteracted by a decrease in carbon and a slightly lower mass flow of combustion air.
Boiler slagging, fouling, erosion and corrosion
The report acknowledges that coal-fired power plants vary widely in their propensity to suffer from slagging and fouling and the report highlights that the different ash composition of SERF means that these risks need to be evaluated 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 many factors including boiler design, operating regime, complementary coal quality and co-firing levels. Where such issues might arise, plant operators have a range of mitigation measures available to them.
The risk of boiler corrosion is low, principally as a result of 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.
Primary emissions and flue gas cleaning
Using SERF will lead to a reduction in SO2, NOx and particulate matter and, the higher the substitution rate, the lower the levels of each emission.
The use selective catalytic reduction may be eliminated at substitution rates of 40% and above as the NOx levels drop below 200 mg/Nm3. In addition, SO2 reduces incrementally with the increase in substitution, reducing reliance upon flue gas desulfurization, potentially to zero at 100% substitution.
Electrostatic precipitators are predicted to be more efficient due to a reduction in ash, a reduction in carbon-in-ash and an uplift in sodium-in-ash, reducing ash resistivity.
Firing SERF will reduce the quantity of fly ash and furnace bottom ash. Further testing is required to establish the ash suitability for further use within the confines of environmental rules.
Trace element emissions
Nearly all trace elements have lower concentrations in SERF than coal. In particular, mercury, fluorine (as HF) and chlorine (as HCl) emissions are expected to reduce proportionally as substitution rates increase.
The European specification for SERF includes a minimum 50% biogenic content. 100% substitution reduces fossil CO2 emissions from around 900 tonnes/GWh to around 400 tonnes/GWh
Substituting coal with SERF will give a higher boiler efficiency. At higher substitution rates, some turbine efficiency may be exchanged for increased soot blowing to avoid any risk of slagging and fouling. Attention should be paid to the rate of heat release in the boiler to ensure sufficient heat at the reheater to maintain turbine efficiency.
Auxiliary power demand will remain approximately the same, as SERF has similar (and generally slightly higher) calorific value to coal. A small increase in mill power consumption may be offset by reduced power demand for fans and flue gas cleaning systems.
Overall the substitution of SERF is expected to lift unit efficiency (on the unit modelled) from 36.7% on coal to 37.3% on 100% SERF.
Taking into account all of the benefits of adopting SERF at different blends up to 100% substitution and considering any potential downsides from higher blends, the report sought to establish a valuation of SERF on a break-even basis.
Using a range of prices for coal ($32-$64/t) and carbon (€20-€40/tCO2), the report sets out a range of break-even points for SERF in co-firing and 100% substitution scenarios. The data calculations are based on 40% biogenic content of SERF (Helvellyn’s non-EU specification), but the results were still extraordinary, showing a break-even point range from 123% of coal price to 150% of coal price.
Helvellyn Group is delighted by the results of the analysis which were beyond expectations. Frank Harris, CEO of Helvellyn Group, said “When we commissioned the report as part of our technical analysis of application and compliance for the European power generation sector, we had no idea that the modelling would be so thorough and highlight so many positive aspects of substitution, some of which we had not considered before.”
He went on “The overwhelming endorsement of this report combined with the legislative headwinds faced by the thermal power sector have led us to bring forward the European launch of our renewable coal alternative fuel, SERF, and we look forward to helping the owners and operators of generating assets find a way through the legislation and realise the full lifetime potential of their assets without significant capital investment.”