Comparative Exergy and Environmental Assessment of the Residual Biomass Gasification Routes for Hydrogen and Ammonia Production

Abstract

The need to reduce the dependency of chemicals on fossil fuels has recently motivated the adoption of renewable energies in those sectors. In addition, due to a growing population, the treatment and disposition of residual biomass from agricultural processes, such as sugar cane and orange bagasse, or even from human waste, such as sewage sludge, will be a challenge for the next generation. These residual biomasses can be an attractive alternative for the production of environmentally friendly fuels and make the economy more circular and efficient. However, these raw materials have been hitherto widely used as fuel for boilers or disposed of in sanitary landfills, losing their capacity to generate other by-products in addition to contributing to the emissions of gases that promote global warming. For this reason, this work analyzes and optimizes the biomass-based routes of biochemical production (namely, hydrogen and ammonia) using the gasification of residual biomasses. Moreover, the capture of biogenic CO₂ aims to reduce the environmental burden, leading to negative emissions in the overall energy system. In this context, the chemical plants were designed, modeled, and simulated using Aspen plus™ software. The energy integration and optimization were performed using the OSMOSE Lua Platform. The exergy destruction, exergy efficiency, and general balance of the CO₂ emissions were evaluated. As a result, the irreversibility generated by the gasification unit has a relevant influence on the exergy efficiency of the entire plant. On the other hand, an overall negative emission balance of -5.95 kg_CO2/kg_H2 in the hydrogen production route and -1.615 kg_CO2/kg_NH3 in the ammonia production route can be achieved, thus removing from the atmosphere 0.901 t_CO2/t_biomass and 1.096 t_CO2/t_biomass, respectively.

Keywords: biomass gasification; bioproducts; decarbonization; energy integration; exergy analysis.

Figure 1

Flowsheet of the biomass pre-treatment and gasification unit. See Supplementary Material for numbered stream properties. Flow properties (1–8) can be found in the Supplementary Material, Tables S1–S3.

Figure 2

Flowsheet of the syngas conditioning unit for hydrogen production. Flow properties (1–4) can be found in the Supplementary Material, Tables S4–S6.

Figure 3

Flowsheet of the syngas treatment unit for ammonia production. Flow properties (1–8) can be found in the Supplementary Material, Tables S7–S9.

Figure 4

Flowsheet of the syngas purification unit for the ammonia production route. Flow properties (1–4) can be found in the Supplementary Material, Tables S10–S12.

Figure 5

Flowsheet of the syngas purification unit for hydrogen production. Flow properties (1–3) can be found in the Supplementary Material, Tables S13–S15.

Figure 6

Flowsheet of the pressure swing adsorption for hydrogen recovery and purge gas combustion. Flow properties (1–5) can be found in the Supplementary Material, Tables S16–S18.

Figure 7

Flowsheet of the ammonia synthesis loop. Flow properties (1–9) can be found in the Supplementary Material, Tables S19–S21.

Figure 8

Flowcharts of the hydrogen production route from residual biomass.

Figure 9

Flowcharts of the ammonia production route from residual biomass.

Figure 10

Comparison of the biomass gasification modeling results between the simulation in this work and the literature data reported by Marcantonio et al. [41] for walnut husk.

Figure 11

Cold gas efficiency (CGE) and carbon conversion efficiency (CCE) in the gasification process of biomass residues.

Figure 12

Comparison of the exergy efficiencies of (a) hydrogen and (b) ammonia production routes using different types of residual biomass.

Figure 13

Cold and hot composite curves for different waste biomass conversion processes exhibiting no need for external heating requirements, but showing the need for further cooling requirements: (a) sugarcane bagasse to hydrogen; (b) sugarcane bagasse to ammonia; (c) sewage sludge to hydrogen; (d) sewage sludge to ammonia; (e) orange bagasse to hydrogen; (f) orange bagasse to ammonia.

Figure 14

Grand composite curves for different waste biomass conversion processes exhibiting no need for external heating requirements, but showing the need for further cooling requirements: (a) sugarcane bagasse to hydrogen; (b) sugarcane bagasse to ammonia; (c) sewage sludge to hydrogen; (d) sewage sludge to ammonia; (e) orange bagasse to hydrogen; (f) orange bagasse to ammonia.

Figure 15

General and detailed emissions (biogenic and fossil, emitted directly, indirectly, and avoided) for the conversion process of (a) hydrogen and (b) ammonia for different types of selected biomass.