Solid Recovered Fuel (SRF) - Heavy Line

Five Percent of Residual Waste Could Power 700,000 U.S. Homes

RDF, SRF, Waste-to-Energy

Five Percent of Residual Waste Could Power 700,000 U.S. Homes (Waste-to-Energy)

If 5% of residual waste from recycling facilities were diverted to energy recovery, it would generate enough power for around 700,000 American homes annually, according to a new study carried out by the University of Texas at Austin.The study found that while single-stream recycling has helped divert millions of tons of waste from landfills in the U.S. – where recycling rates for municipal solid waste are currently over 30% – Material Recycling Facilities (MRFs) currently landfill between 5% and 15% of total processed of the material treated as residue.  According to the researchers this residue is primarily composed of high energy content non-recycled plastics and fibre.

Waste to Energy

Waste to Energy

The report proposed that one possible end-of-life solution for these energy dense materials is to process the residue into Solid Recovered Fuel (SRF) that can be used as an alternative energy source capable of replacing or supplementing fuel sources such as coal, natural gas, petroleum coke, or biomass in many industrial and power production processes.The research – completed by Michael Webber, Ph.D, and his team of university researchers – was part funded by the American Chemistry Council (ACC).MethodologyThis project consisted of four components:

1) a global literature search of SRF projects, experiments, and production companies;

2) site visits to various MRFs, an SRF production facility, and a cement kiln;

3) a pilot project involving the manufacture and test burn of residue-derived SRF; and

4) a life-cycle analysis of SRF production and use.

 

The authors said that the SRF used was a blend of 60% MRF residue and 40% post-industrial waste products producing an estimated 60% plastic and 40% fibrous material mixture. A sample was sent to a lab for a third party elemental analysis and to calculate the energy value of the fuel. The SRF was fed into the kiln at 1 ton/hr (910 kg/hr) for 24 hours and then 2 ton/hr for the following 48 hours.The emissions data recorded in the experimental test burn were used to inform the life-cycle analysis portion of this study.

Findings

The report, titled ‘Residue-Derived Solid Recovered Fuel for Use in Cement Kilns‘, showed that fuel engineered from waste could serve as valuable fuel for not only cement kilns, but potentially for other energy intensive commercial and industrial operations.

The key findings of the report were:

  • The experimental test was successful on a technical basis and proved that refuse- derived SRF can be used as an alternative fuel at a cement kiln.
  • The experimental data and independent testing showed an average SRF heating value of about 12,500 Btu/lb (8.08 kWh/kg), which is comparable to the bituminous coal the cement kiln uses.
  • Emissions data for sulfur dioxide (SO2) from the cement kiln indicated that the use of SRF reduced the SO2 emissions rate by roughly 50% compared to the Reference Case using coal alone. Results from the life-cycle analysis portion of the study revealed that the use of SRF at 1 ton/hour reduces SO2 emissions by 19% – 44%.
  • The nitrogen oxides (NOX) emissions rate increased by 25% when the SRF was used at 1 ton/hour and by 93% during the 2 ton/hour feed rate period compared to the Reference Case using coal. The total emissions were 40%, 50%, and 75% of the total permitted levels for the non-SRF, 1 ton/hour, and 2 ton/hour test periods, respectively. Results from the life-cycle analysis portion of the study revealed that the use of SRF at 1 ton/hour increased NOX emissions by 16% – 24%.
However, follow-up discussions with cement kiln operators suggest that the spike in NOX was likely due to the lack of an efficient feeding system for the experimental fuel and that plant operators would normally adjust burn conditions to more effectively control combustion. No adjustments were made during this limited test run.
  • The analysis showed that CO2 emissions were reduced by about 1.5% in the SRF Case compared to the Reference Case – or around 13,780 tons/year (13,780 tonnes/year) in absolute reductions.
  • The analysis concluded that the fuel use at the cement kilns o set by using SRF significantly outweighs the energy requirements of producing and transporting SRF. The production and transportation used 1% – 11% of the heating value of the SRF.

Conclusions

According to the ACC, Webber’s research reaffirms the benefits of waste to energy.

The research team found that if only 5% of unusable materials from recycling facilities were diverted from landfills to energy recovery, it would generate enough energy to power approximately 700,000 American homes annually.

At the same time, the reductions in carbon emissions as compared to coal would be equivalent to removing one millions cars from U.S. roads, and there would be significant reductions in sulfur emissions. “In this case, one person’s trash truly is another person’s treasure. Americans send tons of waste to landfills each and every day, meaning that one of America’s most abundant and affordable sources of energy ends up buried in landfills,” commented Cal Dooley, president and CEO of ACC. “It’s time we got smart and made energy recovery a central part of America’s energy strategy,” he added. Meanwhile Dr. Webber added: “The findings from our study demonstrate how engineered fuels can make a meaningful contribution to our nation’s strategy while reducing carbon and sulfur emissions compared to some forms of energy,”

“The combination of environmental benefits, emerging science and economic opportunity make recovering energy from waste an opportunity that we can’t afford to ignore,” concluded the doctor.