Comparative assessment for mechanical vapour recompression and multi-effect evaporation technology in palm oil mill effluent elimination

Abstract

Due to the alarming methane emission from anaerobic palm oil mill effluent (POME) treatment practices in palm oil mills, POME elimination strategy is considered as an alternative zero waste solution towards methane mitigation apart from biogas recovery. By dewatering the effluent, POME evaporation technology provides opportunities in water recycling, oil recovery, effluent elimination and process integration with downstream refinery. One of the challenges for implementing POME evaporation is the extensive thermal energy use, which threatens energy efficiency and carbon footprint of palm oil mill. Advanced technologies such as multi-effect evaporation (MEE) and mechanical vapour recompression (MVR) can be considered to reduce steam demand for POME evaporation. Recently, electrical-driven MVR evaporator emerges as a popular solution for solution concentration and food powder production. In MVR systems, evaporated vapour is recompressed by power-consuming mechanical energy to enable steam reuse and reduction in fresh steam demand. In this paper, MEE and MVR evaporation systems are considered for POME dewatering in the integrated palm-oil based complex (POBC) optimisation. A fuzzy multi-objective optimisation model was developed to evaluate the trade-offs of economic benefits, energy consumption and environmental impacts between thermal and electrical driven evaporation techniques for sustainable POBC design. MEE was selected in the fuzzy optimal POBC with aggregate satisfaction of four objectives and improved the EP and GHG reduction of baseline study by 12 % and 61 %. Single-effect MVR POME evaporator contributed to 64 % thermal cost savings with overall 1.5 % reduction in POBC profitability. The optimal results and electricity-to-steam (ETS) price analysis have provided critical insights into the feasibility of MEE and MVR evaporation in POMs. Reducing electricity tariff to achieve ETS ratio below 1.27 could increase the economic favourability of MVR-implemented POBC.