5 kWe + 5 kWt PEMFC generator from bioethanol: a demonstrative project

A power unit constituted by a reforming section, a H2 purification section and a fuel cell is being tested in the framework of a demonstrative project. The system size allows to cogenerate 5 kWe + 5 kWt (hot water at 65°C) as peak output. The integrated fuel processor consists of six reactors connected in series, as sketched below. Bioethanol is transformed into syngas in the pre-reforming and reforming reactors. The reformate is purified from CO by means of two water gas shift reactors operating at high and low temperature (HT and LT-WGS), respectively, and by two methanation reactors connected in series. The goals of the present project are to test the integrated fuel processor, to check the effectiveness of the proposed technology and to suggest possible adequate improvements. Indeed, in spite of the research efforts to improve hydrogen yield during ethanol steam reforming, from a practical point of view it is compulsory to test the real efficiency of the whole energy conversion technology, from H2 production and purification to power and heat output. Other key points for market penetration are system durability, reliability and flexibility. However, only a few reports on fuel processors, and even fewer on integrated systems, can be found in the literature. Therefore, we started the present demonstrative experimentation on an assembled reformer-H2 purification system, whose size is suitable for small houses (ca. 5 kWe + 5 kWt). Bioethanol from marc, the widespread byproduct of wine production, diluted to 96.0 vol% was used to feed the unit. A heat exchange reactor (shell and tubes) is used, containing both the steam reforming catalyst and a commercial combustion catalyst. After evaporation ethanol is mixed with air for feeding the combustion side and with steam to feed the hydrogen production line. A pressure relief valve allows to set the reformate discharge pressure so to match the FC requirement and gas sampling points are available after each reactor. Typical gas composition is reported in the following Table as vol% on a dry basis. No significant amount of by-products was detected and ethanol conversion was 100% after the first reactor. Compound Prereformer Reformer HT-WGS LT-WGS H2 59 73 73 74 CO 1 10 1.5 0.4 CO2 21 17 24 24.4 CH4 19 - 1.5 1.2 H2 concentration was ca. 60% after the pre-reforming stage, as expected since a high methane yield was achieved by ethanol decomposition, but reaction temperature was too low to achieve its full reformation. The latter was accomplished in the subsequent reforming reactor. CO concentration was kept below 2 vol% after the former WGS stage and below 0.5 vol% after the latter. Such a purity level is suitable to feed the newly developed PEMFC operating at 160-180°C. The further purification required to meet the higher H2 purity demand of low temperature PEMFC (CO<20 ppm), is accomplished by the two selective methanation reactors. CO concentration decreased from 0.4 vol% after the LT-WGS stage, to ca. 15 and 10 ppmv, respectively, after the first and second methanation reactors. Therefore, the present fuel processor showed fully suitable for the selected power size and for H2 production with enough purity for both a LT-PEMFC (CO < 20 ppmv) and a newly developed HT-PEMFC. However, the system requires a long start-up time (ca. 3.5 h), making it applicable to continuous operations and stationary applications, only. Ackowledgements Linea Energia S.p.A., Parco Tecnologico Padano, Provincia di Lodi, Italy and Università degli Studi di Milano are gratefully acknowledged for financial support.