Processing of Municipal Solid Waste before Anaerobic Digestion – Qualities, CAPEX and OPEX of Case Studies
Langen, M.1, and Mitchinson, J.2, 1HTP Ingenieurgesellschaft PartG, 2MWH UK Ltd
(free)
Abstract:
Processing of Municipal Solid Waste (MSW) before Anaerobic Digestion (AD) incurs a significant cost both in terms of capital expenditure (CAPEX) and operational expenditure (OPEX). This paper determines different process options like “Standard” and “Advanced BioSolids” and characterizes the process options. The “Standard“ option is relatively simple and comprises only a few process steps. The “Advanced BioSolids” option is more complex and refines the biosolid fraction by segregating inorganic items and other non-digestibles in a multi-stage dry refining process.
Model calculation of mass balance and product quality is based on a typical composition of MSW in western urban settlements, this is e.g. 41 mass-% of digestible biomass. The quality of digestible biomass going from pre-processing to digestion is increased from 71,2 %, achieved by a “Standard” process to, 93,9 %, achieved by an “AdvancedBioSolid” process.
The calculation of CAPEX is undertaken for annual capacities of 180.000 t/y and of 310.000 t/y. As a result CAPEX for mechanical equipment for pre-processing is 15 to 30% of CAPEX for total mechanical equipment, this means pre-processing plus digestion, combined-heat and power (CHP) and emission reduction installation. Calculation of OPEX is done by summarizing all operational costs deriving from the pre-processing plus digestion, CHP and emission reduction. As a result higher CAPEX for pre-processing installation leads to lower OPEX. OPEX as a function of CAPEX for pre-processing can be seen as a graph of different gradient.
The paper finalizes with a draft of a catalogue of pre-processing steps and their relevance for product quality and yield. Decision makers of authorities and companies get a hint of what is relevant in terms of process evaluation and meeting the targeted figures of OPEX.
