(187b) Techno-Economic Evaluation of Manure Pre-Treatment Strategies for the Production of Biogas | AIChE

(187b) Techno-Economic Evaluation of Manure Pre-Treatment Strategies for the Production of Biogas


Zavala, V. M. - Presenter, University of Wisconsin-Madison
Hu, Y., University of Wisconsin-Madison
Kim, J., University of Wisconsin-Madison
Karthikeyan, K., University of Wisconsin-Madison
Sustainable resources are playing an increasingly important role in energy generation. Previous research has shown that biomass is suitable for producing electricity through technologies such as anaerobic digestion (AD) [1]. AD is currently being applied to stabilize organic matter in animal manure, to recover energy (in the form of biogas), and to reduce environmental impact of manure application (e.g., reduction of greenhouse gas emissions) [2,3]. On the other hand, AD systems in the US face financial barriers, mainly due to high uncertainty in investment and operations, as well as the relatively low price of output products in current markets [4,5]. Studies have presented various ways to strengthen the competitiveness of AD, including co-digestion [6,7], policy incentives [8], addition of biochar [9], and pretreatment of waste [10]. Recent experimental results have shown that proper AD pretreatment methods can enhance the fermentation process of dairy manure and double the biogas yield [11]. To identify the economic feasibility of the novel pretreatment methods, techno-economic analysis needs to be conducted to quantify the trade-off between increased revenue and potential additional equipment and operational expenses.

In this work, we considered 5 different pretreatment scenarios of dairy manure, including (a) no pretreatment, (b) 2% HCl (acid), (c) 10% NaOH (alkaline), (d) 5% NaOH and 10% H2O2 (AHP), and (e) 2.5% H2SO4 and 6.0% Na2SO3 with irradiation (SPORL). For each of these scenarios, a conceptual process design and techno-economic analysis was conducted, and the corresponding mass and energy balance was estimated using a combination of experimental and simulation data. Our analysis computed capital investment and annual production cost of AD, desulphurization, combined heat and power unit, and biogas upgrading unit [12,13]. We also used a supply chain optimization framework to test the impact of logistical issues and calculated the breakeven price of derived products (electricity and biomethane) in the State of Wisconsin [14]. It was found that, while pretreatment yields a significant increase in biogas yields, the AD systems are in general not profitable. The pretreatment method (b) and (c) have the best economic performance and can reduce the breakeven price of derived products by 20-30%, while the pretreatment method (d) and (e) increase the breakeven price due to high chemical and equipment costs. A series of sensitivity analyzes were conducted to inspect process bottlenecks; we found that, surprisingly, the biogas cleaning unit is the main economic bottleneck. This cleaning unit is responsible for removing trace contaminants generated during the AD process (such as H2S). We thus conclude that research should be centered not only on increasing biogas yield but also on suppressing trace contaminants.


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