Analysis Supports Coal-Like Fuel for Power Plants

The post Analysis Supports Coal-Like Fuel for Power Plants appeared first on POWER Magazine.

A British company that manufactures a fuel that it says mimics coal said it has received a significant endorsement" for the use of its product in the power generation sector. An analysis by Uniper Technologies said Helvellyn Group's alternative fuel, known as 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."

Research has been done for years on finding substitutes with similar characteristics for coal, specifically metallurgical or coking coal, which is used in steelmaking. Research and development also has focused on woody biomass, with projects aimed at transforming the product into dense, compact forms that have low ash content to minimize the risk of fire, and that can be easily transported, are water-repellent, and can be stored outdoors for long periods. That process, known as torrefaction, produces briquettes that can be burned like coal in existing coal-fired plants. Biomass plants, such as the Boardman plant in Oregon, have shown promise but also have been challenged by the same market forces that have disadvantaged coal-fired units in recent years, particularly low prices for natural gas and now renewable energy.

Helvellyn has said SERF is specifically engineered to mimic the physical properties of coal," with an ability to burn more efficiently and with fewer greenhouse gas emissions. The Uniper analysis, detailed in a report not yet publicly released but with some information provided to POWER, said individual power plant characteristics would need to be taken into account, but in most cases SERF will be usable within existing ship/rail/road delivery and handling infrastructure." The fuel is water-resistant, which means it can be handled and stored in open-air stockpiles.

Our process is able to take a wide range of carbonaceous feedstocks [including low grade coal, sludges, wastes, and/or biomass] and produce fuels to a precise specification consistently," Frank Harris, Helvellyn's CEO, told POWER on June 18. 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."

Lifeline' for Coal Plant Operators

The Uniper analysis looked at blends of SERF at 20% increments, up to 100% substitution, based on a 500-MW boiler that would traditionally burn a range of bituminous coal. Harris told POWER that the endorsement from Uniper is a significant moment for EU [European Union] power plants that are facing early closure due to legislation against coal." The group has said the coal substitute could be a lifeline to operators of assets with a life expectancy that is longer than current or future legislation allows them to exploit."

Helvellyn has said its product allows operators to maintain their existing alternative fuel mix while, in most instances, adding Helvellyn fuel as a direct drop-in replacement for coal from the point of delivery through pre-combustion processing and in combustion." The group has produced a document that details the company's process and provides information about the fuel and its ash specifications.

Helvellyn's plan is to help coal plant operators extend the life of their units through the use of a substitute fuel that mimics coal, but with fewer emissions. Courtesy: Helvellyn Group

Our notional plan is to build out 1.2 mtpa [millon tons per annum, or year] of production in the UK, but we are not constrained in ambition and see a strategic partnership with someone in the power sector might provide the synergies to roll out plants across Europe, to support a phased fuel switch and allow the continued operation of thermal power plants that will otherwise be legislated out of business way before their natural end of lifecycle," said Harris.

Helvellyn in February launched a direct coal replacement product for the cement industry. The group's solid fuels are designed to meet the needs of hard to adapt large industrial plants that are seeking to reduce, or even eliminate, their reliance on coal," the company said. Harris told POWER: We launched the product to the EU cement vertical in February and have some negotiations ongoing for supply to three European kilns."

Product Valuation

Helvellyn commissioned the Uniper report as part of its ongoing assessment and refining of the coal substitute product for the European market. The Uniper analysis looked at several things, including delivery, storage, and handling; milling and delivery to boiler; combustion and boiler efficiency; and boiler slagging, fowling, erosion, and corrosion.

Said Harris: 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 modeling would be so thorough and highlight so many positive aspects of substitution, some of which we had not considered before.

The Uniper report really caught us off guard, as the remit was pretty technical, but to get to the full technical analysis, they had to model the fuel throughout the entire power plant journey," Harris said, noting Uniper does that for a great many plants looking to change coal spec or improve assets." Harris said modeling the coal substitute across its use in a power plant was [the] assessment that produced the headlines, not the rather dry data on process chemical analysis compared to burning coal," which Harris said also showed that SERF is less environmentally damaging than coal on every measure."

Uniper studied SERF's characteristics for primary emissions and flue gas cleaning; by-products; trace elements; emissions of carbon dioxide (CO₂); and unit efficiency. The analysis considered the adoption of SERF at different blends up to 100% substitution. The report detailed benefits and potential downsides, particularly from higher blends, and sought to establish a valuation of SERF on a break-even basis.

Using a range of prices for coal ($32-$64/ton) and carbon (20-40/tCO₂), the report established 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). Harris called the results extraordinary," noting they showed a break-even range from 123% of coal price to 150% of coal price.

Said Harris: 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 [SERF] renewable coal alternative fuel ... 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."

Core Principles

The Helvellyn fuel for cement production is based on four core principles: high energy, low moisture, low chlorine, and ease of handling. The company said exact fuel specification and presentation can be fine-tuned to meet the specific needs of a given plant, though typically, it 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%; sulphur <0.2%; and nitrogen <0.4%.

The Uniper report said that SERF can be delivered to mills through existing coal feeders, and said no problems were expected in the milling process." The report noted that SERF could need more power to grind than coal, but the benefits of SERF for a milling plant include a reduced likelihood of feeder plugging, a lower air inlet temperature, and a lower risk of mill fires. The report said those benefits increase as the substitution rate moves higher, and can be immediately realized at blends as low as 20%."

Helvellyn said that unlike other alternative fuels, SERF does not generate 2-dimensional fibrous particles when milled, which ensures that in a pulverized state the fuel remains mobile and manageable. SERF is designed to mill to a slightly larger particle size than coal in a pulverized state, to compensate for the higher volatile matter during combustion, and ensure similar burnout time for coal and SERF in the boiler.

The Uniper 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. The report said flue gas heat losses are expected 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 Uniper 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 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 using SERF will lead to a reduction in SO₂, NO_x, and particulate matter, noting that the higher the substitution rate, the lower the levels of each emission. The use of selective catalytic reduction may be eliminated at substitution rates of 40% and above, as the NO_x 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. The use of electrostatic precipitators is 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 also will reduce the quantity of fly ash and furnace bottom ash. Harris said more testing is required to establish the ash suitability for further use within the confines of environmental rules.

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, and substituting SERF for coal at 100% reduces CO₂ emissions from about 900 tonnes/GWh to about 400 tonnes/GWh

Unit Efficiency

Substituting coal with SERF also provides increased boiler efficiency. At higher substitution rates, some turbine efficiency may be exchanged for increased sootblowing to avoid the risk of slagging and fouling. Helvellyn has said 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. Helvellyn said that overall, the substitution of SERF is expected to lift unit efficiency (on the unit modeled) from 36.7% on coal to 37.3% on 100% SERF.

Harris said the company is working on a new manufacturing site in Yorkshire, with a plan to resume that project in early July after it was halted due to the coronavirus pandemic. He said Helvellyn also has a number of other potential future sites under review."

-Darrell Proctor is associate editor for POWER (@DarrellProctor1, @POWERmagazine).

The post Analysis Supports Coal-Like Fuel for Power Plants appeared first on POWER Magazine.