Fcpp Application To Utilize Anaerobic Digester

Yoshio Nakayama Environment & Urban System Engineering Division

Toshiba Corporation 1-1 Shibaura 1-chome, Minato-ku, Tokyo 105, Japan

Nobuyuki Kusama Fuel Cell Systems Division Toshiba Corporation

Katsuya Wada Heavy Apparatus Eng. Laboratory Toshiba Corporation

1. INTRODUCTION

Toshiba and a municipal organization of Yokohama city are jointly conducting a program to utilize ADG (Anaerobic Digester Gas) more effectively. ADG which contains about 60% methane is produced by anaerobic digestion of waste water treatment sludge and has been used as an energy source for heating digestion tanks in sewage treatment plants and/or for combustion engine fuel. This program is focused on operating a commercial Phosphoric Acid Fuel Cell(PAFC) power plant on ADG because of its inherently high fuel efficiency and low emissions characteristics.

According to the following joint program, we have successfully demonstrated an ADG fueled FCPP. The success of this study promises that the ADG fueled FCPP, an environment-fnendly power generation system, will be added to the line-up of PC25™C applications.

The joint program consists of three phases as follows: Phase-1 (August, 1994 - October, 1995 )

- Evaluation of ADG composition

- Small scale verification tests of the ADG pretreatment system characteristics and Fuel Processor System(FPS) performance

Phase-2 (November, 1995 - March, 1996)

- Installation of demonstration plant

(a 200 kW FCPP and an ADG pretreatment unit) Phase-3 (April, 1996 - March, 1997 )

- Parametric tests on three cases of methane concentration (90%, 75% and 60%)

- Continuous operation on 60% methane

- Evaluation of capability to operate on 60% methane

- Definition of the optimum system for the ADG fueled FCPP application

2. EXPERIMENTAL PROGRAM

The system flow diagram for this study is shown in Figure 1. This system consists of a standard 200 kW FCPP designed to operate on pipeline natural gas and an ADG pretreatment unit which containing several sub-units as shown in Figure 1.

The desulfurizer operates at ambient temperature and pressure and reduces hydrogen sulfide (Fe203 + 3H,S —-Fe,S3 + 3Hp ). ADG contaminants are adsorbed by an activated carbon bed. A compressor is utilized to convey the ADG through a pressure swing adsorption unit ( PSA ) at the required pressure. The PSA consists of 2( two ) beds in series with automatically reversing capability.

The design also provides the capability to adsorb CO, (methane concentration) on one bed while the other bed is desorbing C02 by using a vacuum pump. The product gas .concentrated methane by the PSA, is delivered to the 200 kW fuel cell power plant .And the gas which is not concentrated methane ( removed only contaminants from the ADG feed gas ) is also usable by using the PSA by-pass line.

Digestion Tank

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