Fuel cell CHP using biogas from brewery effluent
by the CADDET Japanese National Team

An unusual fuel cell combined heat and power (CHP) system, using biogas generated from a brewery's organic wastewater, began operating at Chiba Brewery, Japan, in June 1998. This 200 kWe plant will reduce the total energy consumption of the brewery by 4% ­ a saving equivalent to 663 kl/year of oil.

The fuel CHP plant at Chiba Brewery.

Introduction

Fuel cell power generation systems have low emissions of nitrogen oxides and other pollutants and produce very little noise and vibration. They can achieve high power generation efficiency and heat recovery rates with relatively small-scale facilities, thus they constitute environmentally-friendly CHP systems. The use in fuel cells of biogas generated from organic wastes instead of fossil fuel gases (city gas, LPG) can further mitigate environmental damage. Japan's "Special Law Concerning the Promotion of the Widespread Use etc of New Energy" designates fuel cell power generation as one of several new energy technologies that will be supported by investment grants up to one third of the total investment. This law was executed in June 1997 to encourage energy users and producers to tackle global environmental problems more positively.

The Chiba Brewery

Sapporo Breweries Ltd's Chiba Brewery is located in an industrial park in Funabashi, Chiba Prefecture. The brewery effluent is combined with waste from other food companies in the park and aerobically treated by an activated sludge process in the park's wastewater treatment plant. The wastewater treatment charges to each company depend on the quality and the volume of effluent to be treated. The activated sludge process is commonly used for wastewater treatment in the food industry, but it uses large amounts of power for aeration and the sludge produced is difficult to dispose of in large quantities. As the volume of beer production has grown, the volume of effluent discharged from the Chiba Brewery has increased. Consequently, the brewery's wastewater treatment costs have risen considerably.

 

Flow chart of fuel cell CHP system using biogas.

Organic wastewater from breweries consists of low-concentration effluent, from washing bottles, cans, tanks and pipes; and high-concentration effluent, comprising waste liquids such as those squeezed out of spent grains and tank residues. Anaerobic pre-treatment of the high-concentration effluent can reduce significantly both the power required for aeration and the volume of sludge produced. The brewery therefore decided to install a pre-treatment plant to reduce its treatment costs.

Sapporo Breweries has been committed to environmental protection for many years. In this anaerobic effluent pre-treatment project, the company looked for more effective utilisation of biogas generated by methane fermentation (65­75% methane; 25­35% carbon dioxide), rather than burning the gas in steam boilers as is usually done. As a result, the company decided to install a fuel cell CHP system, which can utilise 80% of the energy content of biogas as electricity and heat, cuts down carbon dioxide emissions and emits very small amounts of nitrogen oxides and sulphur oxide. World-wide, there are very few commercial fuel cell systems using biogas from wastewater treatment facilities.

Results of performance verification test for gas pre-treatment system

 Biogas contents

 At inlet of pre-treatment system

  At outlet of pre-treatment system

 Methane

 65 - 75% volume

 > 90%

 Carbon dioxide

 25 - 35% volume

 < 10%

 Sulphur component

 maximum 5,000 ppm

 < 6 ppm

 Ammonia

 < 1 ppm

 < 0.05 ppm

 Salt

 maximum 30 ppm

 < 0.05 ppm

Biogas pre-treatment

High-concentration organic effluent from the brewery is first pre-treated in an acid fermentation tank and then fed, under nearly-neutral pH conditions, to an anaerobic reactor where the effluent generates biogas through methane fermentation. This biogas contains sulphur components and other impurities harmful to fuel cell operations, and these must be removed by a gas pre-treatment system. The quantities of these minor components differ significantly between different sources of biogas. Hence, the pre-treatment equipment must be optimally designed according to the biogas source. The system consists of four main constituents: a desulphuriser, an ammonia/salt removal unit, a buffer tank and a gas analyser. These pre-treatment processes not only remove impurities but also absorb carbon dioxide from biogas, thereby increasing the concentration of methane in the gas.

Fuel cell power plant

The CHP plant uses Toshiba's 200 kWe phosphoric acid fuel cell, PC25TMC &shy; the commercial fuel cell with the largest number of installations in Japan. Methane-enriched biogas from the gas pre-treatment system is fed to the fuel cell unit and converted to hydrogen through an ordinary fuel reformation process. The union of this hydrogen and air in the cell generates electricity.

The total investment cost of the fuel cell CHP plant, excluding the cost of the anaerobic wastewater treatment installation, was JPY230 million (where JPY is the Japanese yen). One-third of this sum was subsidised by a grant under the "Special Law" for the promotion of new energy.

Performance

The system has an output of 200 kWe and 205 kWth; it will generate 1,728 MWh/year of electric power and recover 1,768 MWh/year of waste heat. The amount of power purchased and fuel required to manufacture 1 kilolitre of beer will be reduced by about 6% and 2% respectively, and the brewery will save about 4% of its total energy consumption &shy; a saving equivalent to 663 kl/year of oil. These savings are worth about JPY 30 million/year.

Performance verification testing has shown that the gas pre-treatment system is effectively removing impurities from the biogas (see the Table above), and the fuel cell plant operates with no problems.

As brewing conditions change, for example, in terms of production volume and beer type, the volume and composition of the biogas produced from the brewery effluent vary significantly. The most important task remaining to be carried out is, therefore, to cope with these fluctuations in biogas production and establish the most efficient and comprehensive way of operating the total system, including the effluent treatment installation and the fuel cell plant.

For more information contact the CADDET Japanese National Team in Tokyo.

The CADDET Renewable Energy Newsletter is a quarterly magazine published by the CADDET Centre for Renewable Energy at ETSU, UK.

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