Economic and environmental assessment of refinery oil sludge pyrolysis

Oil sludge generated during petroleum storage and refining presents persistent environmental and operational challenges in Bangladesh due to its heterogeneous composition and common reliance on long-term storage or low-value disposal routes. This study investigates fixed-bed pyrolysis as a waste-to-fuel strategy for tank-bottom sludge collected from Eastern Refinery Limited (ERL), Chittagong. The sludge was characterized using elemental analysis, thermogravimetric analysis, calorimetry, and FTIR to identify thermal decomposition behavior and dominant functional groups. Pyrolysis performance was evaluated at an optimum temperature of 450 °C, yielding 65.43 wt% liquid oil, 18.07 wt% non-condensable gas, and 16.50 wt% char. The recovered oil exhibited a density of 832.7 kg m⁻³ and a higher heating value of 42.4 MJ kg⁻¹, indicating suitability as an energy-rich product. A conceptual design for a small commercial facility sized to treat ∼15 t day⁻¹ of sludge was developed, and a comparative techno-economic assessment indicated a unit production cost of pyrolysis oil of ∼145 USD t⁻¹, with sensitivity to feedstock price and operating costs. A cradle-to-gate emission analysis (functional unit: 1 kg pyrolytic oil) using OpenLCA with ecoinvent 3.7.1 and ReCiPe Midpoint (H) suggested net climate benefits (GWP100: −2.90 kg CO₂-eq kg⁻¹ oil) under an avoided-burden assumption for sludge treatment. Overall, ERL sludge pyrolysis appears technically viable and potentially cost-competitive while offering measurable environmental advantages under the stated system boundary and assumptions.