Chemical cleaning is widely used in power generation, petrochemical, oil and gas, and heat-exchange systems to remove scale, corrosion products, and organic deposits. Wastewater from these processes often contains high chemical oxygen demand, complex organic compounds, ammonia nitrogen, surfactants, corrosion inhibitors, and metal ions, making it difficult and costly to treat. Biological, adsorption, electrochemical, and advanced oxidation methods can remove pollutants effectively, but they often require complex facilities, high operating costs, or secondary treatment. Incineration offers a direct route for destroying organic contaminants, and co-combustion with pulverized coal is attractive because it uses existing high-temperature boiler environments. Yet OCW has high moisture content, low calorific value, and stable metal-chelate complexes, so its influence on coal ignition, burnout, and reaction kinetics must be clarified before engineering application.
A study (DOI: 10.48130/een-0026-0012) published in Energy & Environment Nexus on 30 June 2026 by Yaji Huang's team, Southeast University, reveals a coupled promotion–inhibition mechanism in which moderate OCW addition improves ignition and lowers activation energy, while excessive addition suppresses combustion intensity and delays burnout.
The researchers collected bituminous coal from the Dalyu coal mine in Shaanxi Province, China, and OCW from BaoSteel in Shanghai. The coal was dried, sieved to 100–150 mesh, and blended with OCW at 1, 3, 5, and 10 wt%, with pure coal used as the control. The OCW had a pH of 9.35 and contained high levels of chemical oxygen demand, Fe, Na, ammonia nitrogen, and total dissolved solids, reflecting its complex chemical composition. Combustion behavior was examined using non-isothermal thermogravimetric analysis from 30 to 1,000 °C under controlled gas flow. The team extracted ignition temperature, peak temperature, burnout temperature, maximum and average mass-loss rates, and combustion indices, including ignition, burnout, comprehensive combustion, and stability indices. They also applied Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose model-free kinetic methods to calculate apparent activation energy. The results showed that all samples underwent one main combustion stage between 400 and 650 °C. At 20 °C·min−1, increasing OCW reduced the maximum mass-loss rate from 9.38 to 7.89%·min−1 and the average mass-loss rate from 5.05 to 4.41%·min−1, indicating gentler combustion. At low heating rates, 1–5 wt% OCW lowered ignition temperature by about 15–25 °C compared with raw coal, suggesting that Fe/Na species and oxygen-containing organics promoted early oxidation. However, the comprehensive combustion index generally declined as OCW increased, especially at 20 and 40 °C·min−1, showing that moisture, ash, dilution, and diffusion resistance reduced overall reactivity. Kinetic analysis confirmed this balance: average activation energy decreased from 131.68 kJ·mol−1 for raw coal to 115.92 kJ·mol−1 at 5 wt% OCW, but rose to 122.77 kJ·mol−1 at 10 wt% OCW.
Overall, the study suggests that OCW can be disposed of through co-combustion with coal, but the blending ratio is critical. Moderate addition can lower ignition barriers and support more favorable reaction kinetics, while excessive addition can reduce combustion stability and delay final oxidation. These findings provide basic data and a scientific basis for the safe co-disposal of chemical cleaning wastewater in pulverized coal-fired boilers.
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References
DOI
10.48130/een-0026-0012
Origianl Source URL
https://doi.org/10.48130/een-0026-0012
Funding information
Funding was provided by the National Natural Science Foundation of China (Grant No. 52476108).
About Energy & Environment Nexus
Energy & Environment Nexus (e-ISSN 3070-0582) is a multidisciplinary journal for communicating advances in the science, technology and engineering of energy, environment and their Nexus.