Industrial equipment such as boilers, pipelines, and heat exchangers must be chemically cleaned to remove scale, corrosion products, and organic deposits. However, this maintenance process generates organic cleaning wastewater containing high concentrations of organic compounds, ammonia, dissolved salts, and metal ions. Because this wastewater is difficult and costly to treat, researchers are exploring whether it can be safely destroyed in existing coal-fired boilers.
A new study published in Energy & Environment Nexus shows that blending a controlled amount of organic cleaning wastewater with bituminous coal may support its thermal disposal while maintaining acceptable combustion behavior.
The researchers found that adding 1% to 5% organic cleaning wastewater could lower the temperature required for coal ignition and reduce the apparent activation energy of combustion. However, increasing the wastewater proportion to 10% introduced stronger inhibitory effects.
"Our results show that organic cleaning wastewater does not simply promote or suppress coal combustion. Its effects depend strongly on the blending ratio and result from a balance between catalytic substances and components that absorb heat or restrict oxygen transfer," said corresponding author Yaji Huang of Southeast University. "A moderate addition may provide a practical balance between easier ignition and stable combustion, but excessive loading should be avoided."
The wastewater examined in the study was produced during industrial chemical cleaning and contained ethylenediaminetetraacetic acid, commonly known as EDTA, along with substantial concentrations of iron, sodium, ammonia nitrogen, and dissolved solids.
The team blended the wastewater with bituminous coal at proportions of 1%, 3%, 5%, and 10% by weight. They then used non-isothermal thermogravimetric analysis to track ignition, mass loss, burnout, and reaction kinetics at different heating rates.
At a heating rate of 10 °C per minute, adding wastewater reduced the coal ignition temperature from 411.6 °C to as low as 390.6 °C. The researchers attributed this improvement to oxygen-containing organic compounds and iron and sodium species in the wastewater. These substances may promote early oxidation reactions and facilitate the decomposition of oxygen-containing functional groups.
Kinetic calculations produced a similar result. The average apparent activation energy decreased from 131.68 kJ per mole for untreated coal to 115.92 kJ per mole for coal containing 5% wastewater. The 10% blend had an average activation energy of 122.77 kJ per mole.
Among the tested conditions, the 5% blend showed the lowest average activation energy, suggesting that moderate wastewater addition made the combustion reaction easier to initiate and sustain.
The benefits were accompanied by tradeoffs. As the wastewater proportion increased, the maximum and average mass-loss rates generally declined. Overall combustion indices also decreased by approximately 4% to 15% under several test conditions.
The researchers explained that the wastewater's high moisture content absorbs heat, while its ash and inorganic components dilute combustible material. At higher proportions, mineral residues may also form a dense layer around coal particles, limiting oxygen diffusion and delaying the final burnout stage.
At 10% wastewater addition, these negative effects became more pronounced. Burnout temperatures increased at heating rates of 20 and 40 °C per minute, indicating that complete combustion required higher temperatures.
The findings reveal a dual effect: small additions can support ignition through catalytic activity, while excessive additions reduce combustion intensity through moisture-related heat absorption, fuel dilution, and ash-related diffusion resistance.
The study provides laboratory evidence supporting the controlled co-disposal of organic cleaning wastewater in pulverized coal-fired boilers. Such an approach could use existing high-temperature infrastructure to destroy hazardous organic compounds while reducing the need for separate treatment facilities.
The authors emphasize that the findings are based on thermogravimetric experiments. Further pilot-scale and full-scale studies will be needed to assess pollutant emissions, ash behavior, boiler corrosion, and long-term operational safety before widespread industrial adoption.
===
Journal reference: Zhang J, Huang Y, Qiu Y, Jiang X, Zhang L, et al. 2026. Combustion characteristics and thermokinetics of coal blended with organic cleaning wastewater. Energy & Environment Nexus 2: e018 doi: 10.48130/een-0026-0012
https://www.maxapress.com/article/doi/10.48130/een-0026-0012
===
About Energy & Environment Nexus :
Energy & Environment Nexus (e-ISSN 3070-0582) is an open-access journal publishing high-quality research on the interplay between energy systems and environmental sustainability, including renewable energy, carbon mitigation, and green technologies.
