Bassey, Uwem
(2023)
Remediation of typical Nigerian crude oil contaminated soils using microwave heating.
EngD thesis, University of Nottingham.
Abstract
The Nigerian economy has received a boost from crude oil production since independence in 1960, with a daily crude oil production capacity of 2.5 million barrels per day and a reserve of 28.2 billion barrels. Over the years, exploration and transportation of raw and refined products have significantly impacted negatively on the environment. Most striking causes oil leakage and spillage is due to pipeline faults and sabotage. Over 11 million barriers of crude oil have been split into the environment. Oil spillage in Nigeria is a major issue, especially in the Niger Delta region, covering land mass of over 70,000 km2. This research work aims to apply microwave heating as a remediation technique for the treatment of different crude-oil-polluted soils (clay, loamy and sand). Conventional pyrolysis using a Gray-King (GK) retort provided a basis for comparison.
Batch scale microwave heating was carried out using different cavity power (0.8, 1, 2, and 3 kW), the results revealed that soil properties strongly influence oil removal. At various microwave power and optimum time, the percentage of oil removal is least for sand soil and similar levels for loamy A and loamy B soils contaminated soils. Results are consistent with the microwave properties of loamy A and loamy B soils. It has been shown that water in soil generally increases the dielectric constant and loss factor, which indicates that higher water content in soil is beneficial for microwave heating. Clay soil with higher water content gave best removal at all optimum treatment conditions. Percentage oil removal in soils increased with increasing MW power for 0.8, 1, 2 and 3 kW at equivalent treatment time and energy input. These results reveal that the remediation of crude oil contaminated soil by MW heating can be enhanced using higher microwave power inputs.
It was found that steam velocity increases when microwave power increases, improving the oil mass transfer rate out of the sample. This phenomenon is steam stripping and provides a more robust explanation of the power density and increasing soil water content effect on oil removal than has been previously suggested. The mass transfer correlation shows that steam velocity contributes to oil removal from clay and sandy soils than loamy soil. Oil removal through steam mechanism investigated in this work account for up to 20-40 % for clay, 2-7 % for loamy B and 4-26 % for sand soil. Oil removal increased with the steam velocity within the soil pores. Mass transfer models for clay and sand soils reveals that pore steam velocities impacts on the mass transfer coefficient
Conventional pyrolysis using a Gray-king (GK) retort provided a basis for comparison where complete oil removal was achieved at 500 oC with slow heating. For microwave heating, using 0.8 kW power and a treatment time of 400 seconds, close to 100 % oil removal was achieved for the clay soil, 80 to 90 % for the loamy soils, and less than 50 % for the sandy soil. The composition of recovered oil after microwave heating remains essentially unchanged, indicating thermal desorption is the primary mechanism for oil removal, compared to extensive cracking occur during conventional pyrolysis using a Gray-King furnace.
In conclusion, based on the findings, microwave heating can treat clay and loamy soil polluted by crude oil and can reduce treatment times compared to conventional pyrolysis.
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