Selection of flue gas treatment equipment in an automotive factory using the critic and multimoora methods

Industrialization, urbanization, and rapid population growth have intensified air pollution into one of the most critical global environmental challenges. Among high energy- and material-intensive industries, the automotive sector warrants particular scrutiny for its environmental footprint. In this context, exhaust emissions originating from paint-shop oven lines—especially stacks releasing volatile organic compounds (VOCs) and hazardous air pollutants (HAPs)—pose significant risks to environmental quality and human health. The primary aim of this study is to identify, through a rigorous scientific framework, the most suitable flue gas treatment technology for mitigating these emissions. Within the scope of an automotive manufacturing facility, multiple end-of-pipe abatement alternatives were assessed using a multi-criteria decision-making (MCDM) framework that combines the CRITIC method for objective weighting of criteria and the MultiMoora method for ranking alternatives. Fourteen performance criteria spanning technical, environmental, and economic dimensions were considered, including cost, energy efficiency, carbon footprint, VOC removal efficiency, operational simplicity, maintenance requirements, and system reliability. Criteria weights were derived objectively via CRITIC, and alternatives were ranked with MultiMoora. The evaluation set, constructed through expert judgment, vendor technical catalogs, and literature synthesis, was scored by a panel of six specialists (five mechanical and one electrical-electronics engineer). The findings demonstrate that the "Electric Thermal Oxidation Reactor (TAR) with Heat Recovery" emerges as the most suitable alternative under baseline weightings. Sensitivity analyses with two divergent scenarios—cost-focused and green production–focused—reveal that the decision outcome is contingent on strategic priorities: the green production scenario reconfirms the heat-recovery electric TAR as optimal, whereas the cost-dominant scenario elevates the "Natural-Gas-Fired TAR." Overall, the study evidences the applicability of MCDM techniques to technology selection in automotive flue gas treatment and contributes to the structured, evidence-based design of decisions grounded in environmental sustainability. In addition, it underscores how technology choice can be systematically optimized within the broader ambitions of energy efficiency, carbon mitigation, and green production policy. Expanding upon this foundation, the study first delineates the public health and ecological stakes of air pollution, framing industrial emissions not only as regulatory and technical matters but also as determinants of morbidity, mortality, and long-term environmental integrity. Synthesizing authoritative sources, the analysis reiterates that ambient air pollution contributes to millions of premature deaths annually, with particulate matter (PM2.5), nitrogen dioxide (NO2), sulfur dioxide (SO2), ozone (O3), and carbon monoxide (CO) constituting core pollutants. HAPs—such as benzene, formaldehyde, and various chlorinated or aromatic organics—exert severe toxicological effects even at low concentrations, with credible links to cancer, neurological impairment, and reproductive harm. Against this epidemiological and toxicological backdrop, automotive paint operations (encompassing surface preparation, primer and color applications, clear coat/varnish, and thermal curing) are identified as major emission sources of VOCs and selected HAPs. Particularly during drying and curing, solvents volatilize under elevated temperatures, demanding robust, continuously reliable abatement systems that harmonize regulatory compliance, worker protection, environmental stewardship, and cost-effectiveness. The study situates the automotive paint-shop context within evolving regulatory architectures. It references European and Turkish regulatory frameworks that impose stringent emission limits and require best available techniques (BAT), with specific emphasis on VOC directives and industrial emissions legislation. Within these regimes, several abatement classes are recognized as mainstream: thermal oxidation (direct-fired thermal oxidizers; recuperative and regenerative thermal oxidizers), catalytic oxidation, adsorption (typically activated carbon), and condensation-based auxiliaries. Each technology exhibits performance envelopes conditioned by the inlet concentration of VOCs, gas temperature, volumetric flow, humidity, co-contaminants, and opportunities for heat integration. Thermal oxidation technologies, in particular, deliver very high destruction efficiencies for VOCs (commonly 98–99.9%), but their energy intensity necessitates careful integration with heat recovery (e.g., high-effectiveness ceramic beds in RTOs) or upstream concentration systems to improve fuel economy. Catalytic oxidation enables lower reaction temperatures and reduced energy consumption but is sensitive to catalyst poisoning and requires vigilant maintenance regimes. Adsorption performs well at relatively low concentrations and temperatures, often as a polishing or recovery step, albeit with regeneration logistics that affect life-cycle costs and operational complexity. Condensation and other emerging methods—such as advanced membranes or photocatalysis—play ancillary roles or remain at pilot scale pending further scale-up evidence. A further conceptual thread in the study is the articulation of a "green production factor," aggregating criteria associated with energy recuperation, carbon footprint reduction, eligibility for and integration with renewable energy (e.g., photovoltaic coupling for electrified reactors), and overall environmental performance. This concept informs both the baseline assessment and sensitivity analyses, clarifying how different corporate strategies or policy incentives (e.g., carbon pricing, renewable credits) can pivot the preferred technology. The work highlights that heat recovery is a principal lever for reconciling high removal efficiencies with economic viability; recuperative and especially regenerative designs substantially reduce net energy consumption, while electrified oxidation units can eliminate on-site combustion-derived CO2 and simplify utility infrastructure, thereby aligning with decarbonization roadmaps. Methodologically, the research employs a transparent and replicable MCDM design. First, a decision matrix is compiled for candidate technologies sized for a representative plant: a Marmara-region automotive factory with 250,000 vehicles/year capacity, paint lines operating at a line speed of 45 vehicles per hour, and a representative oven exhaust of approximately 10,000 Nm3/h. This establishes a realistic basis for comparing alternatives at scale. Fourteen criteria capture a balanced set of performance outcomes, and the data feeding each criterion draw from vendor documentation, literature benchmarks, and structured expert scoring. Objective weighting through CRITIC proceeds by normalizing the decision matrix, calculating standard deviations and inter-criteria correlations, and deriving information content (Cj) for each criterion. Criteria with higher variability and lower redundancy (correlation) are assigned greater weights, reducing subjective bias and guarding against overweighting criteria that move in lockstep. Subsequently, MultiMoora is applied to rank alternatives using three complementary perspectives—ratio method,reference point, and full multiplicative form—followed by a dominance-based synthesis to form the final ordering. This multi-pronged approach offers robustness because it triangulates results, mitigating artifacts attributable to any single method's assumptions. Empirically, the heat-recovery electric thermal oxidation reactor (electric TAR with integrated heat recovery) outperforms under the baseline weighting scheme. This outcome reflects a superior combined score across VOC removal efficacy, high potential for energy recuperation, reduced local carbon externalities (particularly when electricity supply is decarbonized or coupled with on-site renewables), operational reliability, and manageable maintenance profile. Importantly, the electric TAR design simplifies fuel logistics by eliminating the need for natural gas infrastructure and associated combustion controls, while enabling factory acceptance testing under controlled conditions prior to installation. In operational environments where uptime and repeatability are paramount, such integration and pre-commissioning advantages can translate into lower commissioning risk and smoother ramp-up. The sensitivity analysis is central to the study's decision-science contribution. When the weighting vector is re-oriented toward cost predominance—substantially increasing the relative importance of capital expenditure, maintenance cost, and operating cost—natural-gas-fired TAR becomes the top-ranked option. This pivot underscores that at higher energy prices for electricity, in markets with carbon externalities not fully internalized into power tariffs, and where fuel infrastructure already exists, a well-engineered gas-fired TAR can minimize total cost of ownership while maintaining high abatement performance. In contrast, when the weighting elevates the green production factor—giving preeminence to energy recovery, renewable compatibility, carbon footprint, and VOC destruction— the heat-recovery electric TAR is reconfirmed as optimal. This alignment with sustainability priorities emphasizes that technology selection is sensitive to governance models (ESG metrics, Science-Based Targets, internal carbon pricing), corporate strategy (net-zero pathways), and local grid carbon intensity. The study's dual-scenario design thus functions as a practical guide for decision-makers to map alternative futures: it clarifies which technology is favored under distinct policy, price, and sustainability regimes, thereby reducing regret in long-lived capital investments. From an implementation standpoint, the plant-scale assumptions provide an illustrative anchor for engineering and procurement. The decision space presumes stable production rates and consistent coating thicknesses across the planning horizon and abstracts away site-specific constructability constraints such as building geometry or tie-in complexities—reasonable simplifications for the comparative phase. The experts' scoring process integrates long-horizon maintenance insights—such as catalyst replacement windows, bed fouling risks in RTOs at variable solvent loads, and the trade-offs between high-effectiveness heat recovery and pressure drop penalties— with operability considerations including control system sophistication, diagnostic capabilities, and safety interlocks. This fosters a holistic value function rather than a narrow focus on headline efficiency or single-point operating conditions. The study also situates process-integrated measures as complementary to end-of-pipe controls. Upstream interventions—electrostatic application to raise transfer efficiency, closed-loop booths, robotic coating for consistency, and the use of waterborne or reformulated low-VOC coatings where process-critical properties permit—can materially reduce the inlet load to abatement systems. While powder coatings can nearly eliminate VOCs, their limited adoption for exterior Class-A automotive finishes reflects current performance and aesthetic constraints; nonetheless, they remain attractive for wheels, frames, and ancillary parts. In the ovens themselves, the thermally driven volatilization of solvents is unavoidable; hence, abatement stages remain indispensable, and optimization focuses on heat integration and destruction efficiency. The integration of heat recovery, whether via recuperative exchangers or regenerative beds, becomes a decisive factor in reconciling environmental performance with production economics. A noteworthy triangulation in the results is the concordance between MCDM outcomes and vendor-experiential rankings. The authorized supplier's recommended installation order for facilities of similar scale—placing the heat-recovery electric TAR at the top, followed by electric TAR, natural-gas-fired TAR, electric RTO, heat-recovery natural-gas RTO, conventional natural-gas RTO, rotary RTO, and finally direct-fired thermal oxidizer—mirrors the dominance inferred by the CRITIC–MultiMoora synthesis. Such convergence between analytical modeling and field-proven practice increases confidence in the recommended choice and suggests that the criteria set, weightings, and performance data effectively capture the salient decision drivers. In terms of broader implications, the study demonstrates the practical usefulness of integrating CRITIC with MultiMoora for environmental technology selection problems characterized by multiple, sometimes competing objectives. By combining objective weight derivation with a robust multi-perspective ranking, the framework minimizes subjective bias while preserving expert knowledge where quantitative data are sparse (e.g., for qualitative operability or reliability indicators). The approach is transferable to adjacent industrial decisions—thermal vs. catalytic abatement in different sectors, solvent recovery vs. destruction trade-offs, or hybrid configurations that stage concentration, oxidation, and polishing. Moreover, the framework can be extended by incorporating life-cycle assessment (LCA) to capture embodied carbon and materials impacts, probabilistic sensitivity analyses to reflect uncertainty in energy prices and production volumes, and real options reasoning to value flexibility under evolving policy and market conditions. The study's conclusions underscore a set of actionable recommendations for automotive manufacturers and environmental engineers: Prioritize heat recovery integration irrespective of the chosen oxidation technology; energy recuperation is the single most powerful lever to reduce operating costs and carbon intensity without sacrificing removal performance. Consider electrified oxidation where grid carbon intensity is declining or where on-site renewables and storage can be deployed; the elimination of combustion CO2, simplified utilities, and enhanced pre-commissioning can create a compelling total value case. Use structured MCDM to align technology choice with strategic priorities; explicitly test cost-dominant and sustainability-dominant scenarios to future-proof the selection and clarify triggers for switching preferences. Continue upstream VOC minimization in paint application and material selection to lower inlet loads, stabilize abatement system operation, and defer capacity expansions. Engage with vendors to validate design envelopes, pressure drops, thermal efficiencies, and control philosophies under site-specific duty cycles; reconcile MCDM outcomes with field experience to derisk procurement. In conclusion, by demonstrating that the heat-recovery electric TAR is the preferred option under balanced and sustainability-leaning priorities, and that the natural-gas-fired TAR becomes optimal under stringent cost emphasis, the study provides a calibrated decision compass for automotive paint-shop emission control. It advances an academically rigorous yet practical pathway for technology selection that harmonizes regulatory compliance, environmental performance, and economic feasibility. Future work that augments the present framework with LCA, stochastic modeling of market and policy variables, and dynamic optimization of integrated energy systems would further strengthen the robustness of investment decisions in the decarbonizing industrial landscape.