Method of smoldering combustion for the treatment of oil sludge-contaminated soil.

There is an urgent need to globally remediate oil sludge-contaminated soil (OSS). Smoldering combustion is a new low-energy approach for the treatment of organic waste. Therefore, the feasibility of smoldering combustion for the treatment of OSS was investigated in this study using a series of laboratory-scale experiments. The effective remediation of OSS was found to be achievable when the mass ratio of oil sludge in the sample reached 1/12 and above. Experimental results showed that smoldering at peak temperatures above 500 °C was found to completely remove petroleum hydrocarbons from the samples. The mass ratio of oil sludge in the sample had little effect on the distribution of the major elements (Si, Al, and Ca) in the smoldering products, and most of the minerals in the oil sludge adhered to the surface of the soil particles after smoldering. The smoldering heating environment is detrimental to the reusability of the soil, increases soil pH and available phosphorus content, and decreases organic carbon and total nitrogen content. Moreover, the influence of the airflow rate and material height on smoldering characteristics was investigated. Matching the appropriate airflow rate can help maintain optimal smoldering conditions, and smoldering remains stable with increasing material height. The addition of recovered oil to a sample with a low mass ratio of oil sludge can help with smoldering ignition and improve the removal efficiency of petroleum hydrocarbons. This study has confirmed that smoldering can be used to treat OSS within a broad range of oil sludge concentrations without pretreatment.

Method of smoldering combustion for refinery oil sludge treatment.

Refinery oil sludge is a type of hazardous waste generated during petroleum refining. Smoldering combustion has been studied in waste treatment but has not been applied to refinery oil sludge treatment. This work verified the feasibility of smoldering combustion for refinery oil sludge treatment through bench-scale experiments. Experimental result showed that the solid residue that remained from smoldering combustion of oil sludge was odorless, granular, and brick-red. The mass and volume of the residue were much smaller than those of the original oil sludge. The typical substances in the oil sludge (i.e., petroleum hydrocarbons [C10-C40]) were not found in the residue, thereby indicating the good performance of smoldering combustion in treating oil sludge. Water and oil were recovered by condensing the off-gas. The composition of the recovered oil was similar to coking diesel. The calorific value of the recovered oil was higher than that of kerosene, thereby demonstrating the possibility of reutilization. The components of noncondensable off-gas contained a small amount of SO2 and NOx and a large amount of H2, CO, and H2S, which need to be further purified. Three factors influencing the smoldering performance of oil sludge, including moisture content, filler to oil sludge ratio, and airflow rate, were explored.

Comparative study on the characteristics of condensable particulate matter emitted from three kinds of coal.

Condensable particulate matter (CPM) is quickly formed by several gaseous substances in flue gas after emission and belongs to primary particulate matter emitted into the atmosphere by stationary sources. Many studies have shown that current CPM emissions from coal-fired stationary sources far exceed filterable particulate matter, and the issue of CPM emissions has attracted widespread attention. The current research on CPM mainly focuses on its emission characteristics in stationary sources and its migration characteristics in pollutant-controlled equipment, lacking the characteristics of CPM directly generated by fuel combustion. In this study, a one-dimensional flame furnace is used as a stable source of flue gas in the laboratory. The concentration (including inorganic and organic components) and chemical composition (including water-soluble ions, metal elements, and organic matters) of CPM are obtained by the combustion of three kinds of coal (Inner Mongolia lignite, Jinjie bitumite, and Ningxia anthracite) that China consumes in large amounts. The characteristics of CPM including emission factors obtained from different kinds of coal under various experimental conditions are comparatively analyzed. Moreover, a scanning electron microscope-energy-dispersive spectrometer is used to observe the morphology and elemental composition of CPM collected on the filter membrane after the combustion of different kinds of coal. Results show that CPM is mainly in the form of droplets or spheres, and heavy metal elements such as Hg, As, Se, and Sb are detected. These valuable data will enrich people's understanding of the characteristics of CPM generated by coal combustion and can provide data references for evaluating the influence of CPM on the environment.