Development of FPS (fuel processing system) for ENE-FARMTokyo Gas is developing a fuel processing system for a residential fuel cell cogeneration system, ENE-FARM. A fuel processing system is a system for producing hydrogen from city gas to be used as fuel for fuel cells. It is made up of a desulfurizer, to remove the sulfur used as an odorant in city gas, and a fuel processor for producing and purifying hydrogen gas. By slimming down and reducing the cost of fuel processing systems via technologies that develop low-cost and high-performance desulfurizing agents, technologies that simplify the structure of fuel processors, and technologies that operate the catalyst optimally, we continue to contribute to wider adoption of our ENE-FARM system.
Background and Purpose
In an effort to help realize a low-carbon society, Tokyo Gas is promoting wider adoption of its ENE-FARM system. Important elements to achieve such expansion are lower costs and a reduction in the size of the system, and it is therefore necessary to examine all components individually. Positioned at the core of the ENE-FARM system, the fuel processing system discussed here produces hydrogen from city gas to be used as fuel for fuel cells. It is made up of a desulfurizer, which removes the sulfur used as an odorant in city gas, and a fuel processor for producing and purifying hydrogen.
We have accumulated desulfurization agent development technologies as well as fuel processing technologies for producing city gas from coal and petroleum. By leveraging these technologies to achieve cost and size reductions for fuel processing systems, we contribute to wider adoption of the ENE-FARM system.
〔ENE-FARM system structure〕
DesulfurizerThe natural gas that is the raw material for city gas is odorless. As a safety precaution, an odorant with a distinct odor is added to city gas to allow rapid detection of even the smallest gas leak. Although natural gas is a clean energy, the odorant added contains sulfur, and city gas therefore contains a small amount of sulfur. Introducing this sulfur component to the ENE-FARM system as-is would cause a reduction in the performance of the fuel processor and the PEFC stack. That is why a desulfurizer is used to completely remove the sulfur component from city gas.
Tokyo Gas develops desulfurizing agents used in desulfurizers and in 2001, we developed an agent that can easily remove odorants at room temperature. In 2011, a significant portion of this desulfurizing agent was replaced with lower-cost metal oxide and activated carbon, reducing the desulfurizing agent costs by two thirds. For our newest model, we look to further reduce costs by developing a new desulfurizing agent consisting of metal-impregnated activated carbon, and plan to utilize this in our ENE-FARM system going forward.
〔Changes in desulfurization agent costs〕
Fuel processorCity gas from which sulfur has been removed is introduced into the fuel processor, where the following three chemical reactions occur. Hydrogen is produced through the reaction of steam and methane, which is the main component of city gas, and the by-product, carbon monoxide, is reduced to 10ppm to prevent any damage to the PEFC stack.
- Reforming reaction: Decomposing the city gas to hydrogen and CO by reaction with water
CH4 + H2O → 3H2 + CO (400–650ºC)
- CO convert reaction: Removing CO to below 1%
CO + H2O → H2 + CO2 (200–450ºC)
- Selective oxidation reaction: Removing the small amount of remaining CO to the level of ppm
CO＋1/2O2 → CO2 (120–170ºC)
〔Fuel processing system structure〕
〔Fuel processor volume and production cost comparison〕
Tokyo Gas will continue to move forward with technology development aimed at further reducing the cost and size of fuel processing systems. In addition, the cost-reduction and streamlining technologies accumulated as part of the development of fuel processing system are also being put to use in solid oxide fuel cells (SOFC), and thus contributing to wider adoption of SOFC systems.