Optimal Renewable Energy Distribution Between Gasifier and Electrolyzer for Syngas Generation in a Power and Biomass-to-Liquid Fuel Process

Abstract

By adding energy as hydrogen to the biomass-to-liquid (BtL) process, several published studies have shown that carbon efficiency can be increased substantially. Hydrogen can be produced from renewable electrical energy through the electrolysis of water or steam. Adding high-temperature thermal energy to the gasifier will also increase the overall carbon efficiency. Here, an economic criterion is applied to find the optimal distribution of adding electrical energy directly to the gasifier as opposed to the electrolysis unit. Three different technologies for electrolysis are applied: solid oxide steam electrolysis (SOEC), alkaline water electrolysis (AEL), and proton exchange membrane (PEM). It is shown that the addition of part of the renewable energy to the gasifier using electric heaters is always beneficial and that the electrolysis unit operating costs are a significant portion of the costs. With renewable electricity supplied at a cost of 50 USD/MWh and a capital cost of 1,500 USD/kW installed SOEC, the operating costs of electric heaters and SOEC account for more than 70% of the total costs. The energy efficiency of the electrolyzer is found to be more important than the capital cost. The optimal amount of energy added to the gasifier is about 37–39% of the energy in the biomass feed. A BtL process using renewable hydrogen imports at 2.5 USD/kg H2 or SOEC for hydrogen production at reduced electricity prices gives the best values for the economic objective.

Conceptual design and techno-economic analysis of biomass to liquid processes

“…The syncrude production is between 26.7 and 56.5 bbl/h for a biomass feed of 15.9 wtph. The syngas production increases with the addition of electrical energy in the SOEC, as suggested by a prior study (Putta et al, 2022). This also increases the total syncrude production and carbon efficiency as more carbon is retained in the syncrude.…”

“…The Norwegian law defines biofuels as fuel derived from the residues of agriculture, aquaculture, fisheries, and forestry (LOVDATA, 2022). The biomass feed considered in this study is forest residues identical to those used in the previous study by the same author (Putta et al, 2022). The ultimate and proximate analysis of the biomass feed is summarized in supporting information H.4.…”

“…The decomposition reaction is endothermic and is shown in Eq. 2 (Putta et al, 2022), where stoichiometric coefficients are calculated as ] i…”

Renewable-power-assisted production of hydrogen and liquid hydrocarbons from natural gas: techno-economic analysis

“…Putta et al investigated a similar optimization problem for the Biomass and Power to liquid process. 43 They found the optimal level of preheating to be about 37-39% of the energy in the biomass feed.…”

Assessment of electrified ethylene production via biomass gasification and electrochemical CO reduction

“…However, the direct electrification of PBtX routes is not as mature and has just recently gained more attention. Examples include the use of electrically heated gasifiers (Putta et al, 2022) or reformers (Melin et al, 2022), and electrochemical conditioning of syngas (Butera et al, 2021).…”