In terms of efficiency and environmental impacts, fuel cells have advantages over conventional technologies. PEi looks at an interesting installation in Japan.
With the control of greenhouse gas emissions now an international issue of growing importance, the fuel cell power plant (FCPP) is increasingly being viewed as one of the most promising new technologies of the future. Indeed FCPPs are beginning to see their first commercial applications in industrial plants aimed at increasing overall energy efficiency while minimizing impact on the environment.
One interesting installation is being carried out at a manufacturing plant owned by Seiko Epson, Japan. Toshiba has installed a waste-methanol fuelled FCPP based on phosphoric acid fuel cell (PAFC) technology at the company’s Toyoshina Works.
The installation of the FCPP is in line with a strict environmental policy which Seiko Epson has put in place. The company’s environmental policies include:
- Create and offer environmentally sound products and build environmentally sound manufacturing processes.
- Prevent pollution by maintaining and raising the environmental management level.
- Contribute to the environmental efforts of both the local and the international community.
Seiko Epson has established environmental policies and group-wide activity guidelines as a means of ensuring uniformly high-quality environmental activities. Seiko Epson has also put together a variety of cross-divisional organizations, beginning with an Environmental Affairs Committee which examines the issues and steers company-wide activities.
This promotion organization covers all divisions, plants and affiliated companies, and an expert committee is also set up for each individual theme. The mobility and flexibility of this organization enable the company to immediately respond to developments around the world.
Group-wide activity guidelines at Seiko Epson are shown in Table 1.
PAFC power plant development
Toshiba has been aggressively promoting the 200 kW plant “PC25TMC” since its introduction. It was developed as a commercial phosphoric acid FCPP in cooperation with IFC/ONSI and was awarded the “minister of MITI Prize” at New Energy Vanguard 21 campaign in 1997 in Japan. Toshiba believes that PC25TMC is the leader in commercial PAFC power plants. The standard specification, which is used for cogeneration, runs on city gas.
Figure 1. View of an FCPP unit
At present, a total of 113 PC25TMC FCPP units have been delivered by IFC/ONSI or Toshiba to various locations around the world. The installations have been achieving excellent operating results. This operating experience demonstrates that IFC/ONSI and Toshiba have developed a reliable technology and can manufacture, maintain and support 200 kW on-site FCPPs.
Figure 2. The Seiko Epson plant uses two PC25C units
To expand new markets while making full use of the advantages and flexibility of the FCPP, Toshiba is developing various applications for the on-site power plant. It has already developed the following systems which are applicable to various industrial fields. Applications that use industrial waste for fuel are being watched with great interest because of the energy saving and environmental protection aspects.
Applications for Toshiba’s on-site power plant include:
- Back-up fuel systems: During cut-off of a main fuel supply such as in an emergency, the FCPP would continue operation by automatically changing to stored back-up fuel and provide electricity, heat and portable water.
- Premium power supply system: The FCPP can act as a premium power supply for important loads, providing constant voltage and constant frequency
- DC power supply system
- Available fuel sources: FCPPs can use natural gas and propane (LPG), waste- methanol, ADG (Anaerobic Digester Gas), biogas and by-product hydrogen.
- Dual fuel system: two kinds of fuel are available simultaneously.
Traditionally, waste methanol, which contains about 55 per cent methanol and about 45 per cent water, is discharged from the product washing process at the Seiko Epson plant. This waste-methanol was treated as chargeable industrial waste and burned.
With a view to reducing industrial waste and promoting recycling, in line with its group-wide activity guidelines, Seiko Epson wanted a way of using this waste-methanol effectively as an energy source. Thus, waste-methanol fuelled FCPP was developed by Toshiba and installed at the Toyoshina Works in March 1999. The project was carried out under a subsidy based on the “New Energy Law” which is the support programme by MITI/NEDO, Japan.
The view and system flow diagram are shown in Figure 1 and 3 respectively. The system combines two PC25 TMC FCPPs and a waste-methanol pretreatment unit which consists of two storage tanks (one is a new methanol tank and the other is a waste-methanol tank), an adsorption bed to remove contaminants and a methanol vaporizer.
Figure 3. Flow diagram of the plant
Waste-methanol and methanol are mixed and contaminants are adsorbed by an adsorption bed. The mixed methanol is vaporized by the steam supplied from the FCPP. The design also provides the capability of vaporizing methanol using the process steam in the Works. The plant uses 90 kg/h methanol steam per one FCPP for an operating electrical output of 200 kW (40 per cent LHV) and a 176 Mcal/h thermal output (41 per cent LHV). The plant is optimized for thermal output,. Three types of outputs are available at the Works:
- Steam (17% LHV) directly used for product process
- Hot water (12% LHV) used for heat source of absorption refrigerator
- Warm water (12% LHV) used for preheat source of boiler feed water
Load operation started in July 1999 at 400 kW electrical output and has continuously operated at this output. The electrical and thermal outputs are completely used in the Works. The installation has been a success in that it shown excellent performance in the reduction and recycling of industrial waste with minimum impact to environment. The plant has demonstrated a reduction of 14.5 per cent in terms of CO2 emission and an energy saving (calculated in terms of raw petroleum) of 337 kilo-litres per year.
Toshiba’s fuel cell technology has a bright future in Japan. In addition to waste-methanol fuelled FCPPs the company has delivered ADG (Anaerobic Digester Gas) fuelled FCPPs and biogas fuelled FCPPs in Japan. ADG and biogas are low-calorie methane gases. They have a similar composition to gas produced from industrial waste but the contaminants are different. These systems are attractive since their operating cost is cheaper than the standard city gas fuelled FCPP.
For customers who cannot generate sufficient methane from their industrial waste, dual fuel systems can be installed. In a dual fuel system, ADG or biogas is mixed with city gas to generate the standard 200 kW. For example, a biogas and city gas fuelled FCPP was installed at Japanese brewery, Sapporo Breweries Ltd. which has operated continuously at 200 kW.
This ADG technology can also be used at facilities which treat animal excrement. Toshiba plans to aggressively introduce these applications at sewage and/or excrement disposal sites, water treatment facilities or garbage treatment facilities.
With a growing number of examples in Japan, Toshiba believes that more business enterprises will introduce FCPPs. With their energy efficiency and compatibility with the environment FCPP technology is one of the key technologies for energy saving and environmental protection in the 21st century.
Fuel cell technology
Fuel cells are electrochemical devices that convert the chemical energy directly into electrical energy. In a typical fuel cell, gaseous fuel is fed continuously to the anode (negative electrode) compartment and an oxidant (i.e., oxygen from air) is fed continuously to the cathode (positive electrode) compartment. The electrochemical reactions take place at the electrodes to produce an electric current.
A fuel cell, although having similar components and characteristics, differs from a typical battery in several respects. A battery is an energy storage device i.e. the maximum energy available is determined by the amount of chemical reactants stored within the battery itself. Thus, the battery will cease to produce electrical energy when the chemical reactants are consumed. In a secondary battery, the reactants are regenerated by recharging, which involves putting energy into the battery from an external source.
The fuel cell, on the other hand, is an energy conversion device which theoretically has the capability of producing electrical energy for as long as the fuel and oxidant are supplied to the electrodes.
A variety of fuel cells are in various stages of development. These are usually classified according to the type of electrolyte used in the cells such as alkaline fuel cell (AFC), phosphoric acid fuel cell (PAFC), molten carbonated fuel cell (MCFC), solid oxide fuel cell (SOFC) and polymer electrolyte fuel cell (PEFC).
The PAFC power plant which is already commercially available, and has a number of applications to make full use of its advantageous characteristics.
A fuel cell power plant embodies more than the above fuel cell stack. In general, fuel cell power plant consists of a fuel processor, fuel cell power section, power conditioner, and potentially a co-generation or bottoming cycle in order to utilize the rejected heat. Fuel processing system depends on the fuel. At natural gas fuelled FCPP, fuel processor includes desulphurizer to remove sulphur containing odorants for leak detection and steam reforming reactor which convert natural gas into H2-rich gas. Power conditioning for a fuel cell power plant includes power consolidation, current control, AC to DC inversion, and stepping the voltage up through a transformer.