Abstract
Based on the Paris Agreement compiled at COP21, many nations are now obligated to have penalties for CO2 emission reductions.
As a result, many companies are working to reduce CO2 emissions to ensure their survival.
We in the liquor, soft drinks, and food industries are no exception, and all members are working to reduce CO2 emissions, but it is believed that existing technologies alone will not allow them to achieve zero CO2 emissions while continuing their operations.
Asahi Quality and Innovations, Ltd. , where I work, is an independent research subsidiary of Asahi Group Holdings, Ltd. and is currently working on a number of technological developments to create a new model for medium- to long-term CO2 emissions reduction at the 212 companies and 70 plants that manufacture and sell Asahi Group beer, liquor, soft drinks and food products sold around the world.
This time, we report on one of those technological development items, the successful development of a technology for acquiring carbon-neutral electricity using SOFC, and its contents and results.
Asahi Breweries, Ltd. and Asahi Soft Drinks, Ltd. under the Asahi Group began introducing anaerobic wastewater treatment processes in their factories from 1988, and all of their factories in Japan are now operating stably on a daily basis.
The anaerobic wastewater treatment process uses methane fermentation as the main reaction, which produces methane gas as a byproduct. This methane gas is defined as carbon-neutral methane gas because they are from beer or beverage production derived from agricultural crops. This methane gas has been combusted in boilers and recovered as thermal energy.
However, it was confirmed that converting methane gas into electricity using fuel cells, rather than burning it to convert it into thermal energy, has significant cost advantages and reduces CO2 emissions. Therefore, we decided to change the use of methane gas from boiler fuel to fuel for electricity power generation, and to implement power generation using SOFC.
However, although many challenges to fuel cell power generation using biomethane gas had been implemented, there were no reports of successful power generation exceeding 10,000 hours. The most significant reason for this was thought to be the presence of poisoned substances in the methane gas.
The poisoned substances present in the fuel will constantly attack the electrodes during power generation and the electrodes become inactive and eventually lose their ability to generate power as a fuel cell.
Since highly purified fuel is the key to long-term power generation, the goal of this R&D was to improve the purification accuracy to below the detection limit for all poisoned substances.
Based on the results of these studies, we aimed to develop a technology that would enable stable long-term continuous SOFC power generation for more than 10,000 hours by highly purifying biomethane gas, a byproduct of the anaerobic wastewater treatment process.
Development goals:
1. Remove poisoned substances to below than the detection limit (less than 10 ppb).
2. Fuel cell degradation rate of less than 1% after start of power generation
(challenge target: less than 0.5%)
We analyzed the biomethane gas comprehensively and identified hydrogen sulfide and sulfur compounds as the poisoned substances to be dealt with, aiming to reduce them to below the detection limit.
The research was conducted by transporting gas purified in a small bench-scale purification system installed in our brewery to the Kyushu University Next-Generation Fuel Cell Research Center for power generation tests. (manufactured by Mitsubishi Heavy Industries, Ltd.).
As a result, continuous power generation for 10,000 hours was successfully achieved. The power generation time was 10,650 hours. Degradation throughout the period was 0.3%, an extremely low result.
Based on these results, a hybrid SOFC demonstration power plant that combines an in-house designed biomethane refining facility and a 200kW stationary SOFC power generator, backed up by biomethane gas with city gas, was constructed in our brewery with supported from the Japanese Ministry of the Environment. The plant started its automatic continuous power generation in the fall of 2021. As a result, the total operating hours reached 10,676 hours, and 3,408 hours for biomethane gas alone (end of October,2022). Degradation during this period was less than 0.5%/1,000 hours, and automatic operation is still ongoing.
This paper reports the results of this 200 kW biomethane gas SOFC demonstration power plant operation and the key points of the design for practical use.
Figure 1