Environmental impact of the excess electricity conversion into methanol

In this work, the impact on the environment of a renewable methanol production in combination with a wastewater treatment plant (WWTP) was analysed. Carbon dioxide from biogas and hydrogen from water electrolysis were used as resources for methanol synthesis. Additionally, it was decided to use the available excess of electricity and it was prepared for a small city in North-West of Germany (Emden) to have a realistic scenario. As a consequence, methanol plant was simulated with the use of ASPEN Plus software in order to calculate the mass balance and energy requirement. Subsequently a comparative life cycle assessment (cradle-to-gate) was conducted in order to compare renewable methanol with conventional process and also with methanol produced from biomass. In order to evaluate possible impact on the environment, 11 common impact categories were selected. Results showed that enough excess electricity was already available to utilize the whole CO2 from WWTP in Emden. Subsequently it was found that the production of renewable methanol, without emissions related to windmill construction, has much lower impact on the environment than conventional production according to all impact categories. Furthermore, the combination of power-to-methanol plant with WWTP allowed utilization of the biogenic carbon dioxide and application of the produced via electrolysis oxygen. Therefore, thanks to substitution of air with produced oxygen, a reduction in electricity consumption for the aeration system could be possible. However, taking into account the emissions related to wind electricity, renewable methanol would cause lower emissions according to 5 impact categories (acidification potential, climate change, ozone layer depletion, photochemical oxidation, and primary energy demand from non-renewable resources) than natural gas or biomass based methanol. (C) 2018 Elsevier Ltd. All rights reserved.