Development Of Advanced Concepts For Dirmcfc Cogeneration Applications In The European Market

Peter J. Kortbeek, Ron G. Ottervanger1 and Andrew L. Dicks2

'Dutch Fuel Cell Corporation (BCN) PO Box 1093,1940 EB Beverwijk, The Netherlands Tel nr. 31-251-279200; Fax: 31-251-223887; E-mail: [email protected]

2British Gas pic, Research and Technology Division Ashby Road, Loughborough, Leicestershire LEI 1 3QU, United Kingdom Tel: 44-1509-282818; Fax: 44-1509-283144; E-mail: [email protected]

Introduction

Early 1996 a three year (1996 - 1998) joint European project was launched under the name 'Advanced DIR-MCFC Development", aiming at the development of Direct Internal Reforming (DIR) Molten Carbonate Fuel Cell (MCFC) systems for «generation applications for the European market. In this project participate: Brandstofcel Nederland BV (BCN)» British Gas pic (BG), Gaz de France (GDF), Netherlands Energy Research foundation (ECN)» Stork, Royal Schelde and Sydkraft AB. The European Fuel Cell User Group (EFCUG) supports the project as an advisory board. Whereas the US and Japanese programmes are aimed at large-scale demonstrations of the MCFC technology, this project focusses on the development of concepts and technology, required for MCFC systems that will be competative on the cogeneration market. The project partners provide the essential expertise: from end-user, system engineering, stack development up to fundamental material research.

The 'Advanced DIR-MCFC Development' project

The project involves three levels: 1/ cogeneration market analysis, 2/ system development and 3/ stack and material development. The market analysis provides the essential guidance for system concept studies and MCFC technology development Tasks at the different levels are carried out in parallel and with strong interaction. The project development plan is shown in the figure below.

Figure 1: development plan

1/ Analysis of the European cogeneration market

The market analysis, based on in-house expertise, literature surveys and enquiries during the first half of 1996, has revealed important information with respect to the European market demands and the specific end-user requirements for cogeneration systems. This analysis is not a simple task since, within the 15 member countries of the European Union (EU), there exists an enormous diversity both in the structure of the energy market and the availability and usage of primary fuels. To make the situation even more complex, in many countries the energy market is undergoing fundamental changes, which, in general, will transform the structure from strict monopolies to a more open market situation. The diversity in the energy market is also reflected in the market penetration of cogeneration systems. On average, cogeneration accounts for about 7% of the electricity produced in Europe. Penetration of cogeneration in most European countries is in the 1-4% range whereas in a few (the Netherlands, Denmark and Finland) this is substantially higher (30% or above). Although it is generally accepted that cogeneration increases the overall efficiency of energy use substantially, and therefore contributes to lowering the environmental impact of energy production, many barriers prevent its acceptance. Eliminating these barriers will require the efforts of many, both in the markets, institutions and political fields.

This project focuses on the European market for medium sized (0.5-10 MWe), natural gas fuelled, cogeneration systems. Typical technologies that have already penetrated this market segment are gas-engines and gas-turbines which, in general, replace central power/steam boiler systems. Emerging technologies on this market are other fuel cell types like PAFC, SPFC and SOFC. Applications that are attractive for medium sized MCFC systems are: 1

- light process industry, eg. food processing

- residential applications

- hotels

- hospitals

Particularly attractive features of the hotel and hospital niche market are the steady demand of both power and heat over the year and the consumption of steam for air conditioning.

Other important aspects covered in the present study are 'standards' and 'regulations.' It is considered of vital importance that the system design complies with European, national and local standards and regulations.

Based on the market analysis and user requirements, cogeneration applications will be selected where MCFC systems offer positive benefits compared with competing technologies.

2/ System development

Fuel cell systems are expected to have the benefits of high efficiency at full and part load, high quality of heat, flexibility in heat-to-power ratio and an extremely low environmental impact

However, these benefits are so far only demonstrated by the 'first generation' demonstration installations, which typically are very complex, voluminous, and expensive. To improve the economics of MCFC systems, the present high capital cost has to be reduced.

Cost reduction of the system is one of the main driving forces for the system design studies carried out in this project. Compared with External Reforming (ER) systems, Internal Reforming (IR) MCFC systems allow for a simpler system layout and lower parasitic power losses associated with stack cooling. Compared with Indirect Internal Reforming (IIR), Direct Internal Reforming (DIR) gives advantages in terms of a simpler design and lower stack cost.

Over the past decade, tools have been developed to model MCFC systems both under steady-state and dynamic conditions. These tools are used in the present project for trade-off studies taking into account a wide variety of system concepts (based on ER and IR stacks), with and without process flow recycling under ambient or pressurised conditions, for the application selected in the market study. From these studies one system concept will be selected, for which a preliminary design will be made, including a cost and economic analysis.

First results show that DIR systems operating at atmospheric pressure in the range up to several MW are more cost effective and have a wider operational window than pressurised systems.

3/ Stack development

A system dedicated internally manifolded DIR stack design is under development in the project. Verification of the design will be carried out in stacks of 0.1 m2 area up to 2kW output. Improvements with respect to state-of-the-art ECN technology concern the following key issues:

- thermo-hydraulic management

- cell sealing for sustained large differential pressures across the stack

- verification of lifetime to 25,000 hours

In a DIR stack, about 60% of the heat from the electrochemical reaction is absorbed by the endothermic steam reforming reaction. Disadvantages that are often encountered when the heat from an ER stack is removed by the process gas do not occur. On the other hand, in a DIR stack, flow and thermal distribution are more strongly coupled than in the ER case. Modelling of the thermo-hydraulic behaviour is essential for the development of DIR stack design. A 3-dimensional model has been developed in which the main process parameters are taken into account The model has been validated with experimental data obtained from ER and DIR stack tests.

In the 'first generation' MCFC installations, pressure control was achieved by using hot valves. Such valves are expensive. These valves can be omitted if the stack can sustain differential pressures of the order of200 mbar. Seals are currently under development to reach this target

The target for the service life of the stack under system operating conditions is 25,000 hours. This target is a severe challenge for state-of-the-art technology in several areas: cathode dissolution, separator corrosion, reforming catalyst activity and electrolyte management An improved cathode (based on LiCo02) and separator coating is currently being developed.

Electrolyte evaporation is reduced by switching the carbonate composition from lithium-potassium to lithium-sodium. Issues affecting the catalyst lifetime are also being studied.

Acknowledgement

The project is funded by the partners, by the European Commission (under JOULE III contract) and, for the Dutch part, by the Dutch Ministry of Economic Affairs and the Dutch Agency for Energy and Environment (NOVEM BV).

AMMONIA SYNTHESIS AND ER-MCFC-TECHNOLOGY -A PROFITABLE COMBINATION?

G.P.J. Dijkema', J. Vervoort, R.J.E. Daniels, C.P. Luteijn"

Delft University of Technology 'Faculty of Systems Engineering, Policy Analysis and Management ''Faculty of Chemical Engineering and Materials Science Jaffalaan 5, 2628 BX Delft The Netherlands

Similar to stand-alone ER-MCFC power systems industrial ammonia production facilities include hydrogen-rich synthesis-gas production. Therefore, integration of ER-MCFC stacks in a conventional industrial ammonia plant was investigated. By preliminary process design calculations three promising process structures were evaluated:

1. ER-MCFC is fed by the ammonia plant's steam-reformer; anode off-gas to firing

2. similar to structure 1; in this case the anode off-gas is redirected to the ammonia process

3. ER-MCFC is fed by ammonia-synthesis purge gas

The results indicate that for options 1 and 3 a return-on-investment for the ER-MCFC of around 8 % is achievable at a stack cost of $250/kW and a revenue of 7c/kWh. Option 2 is not profitable, because of the associated reduction in ammonia production. The degree of hydrogen-utilization in the ER-MCFC to be selected for maximum profit varies with the process structure and indicates that there is scope for ER-MCFC stacks which operate at low hydrogen-utilization.

Introduction

External Reforming Molten Carbonate Fuel Cell (ER-MCFC) systems research is primarily focused on the development of stand-alone power systems where an extensive amount of capital-intensive equipment is required in addition to the ER-MCFC-stack. As a consequence the competitiveness of ER-MCFC power systems still remains doubtful, also because economy-of-scale effects are limited compared to «¡generation systems. Incorporation of the MCFC-stack in chemical production processes may offer a market where its potential is fully utilized. More in particular the combination of ammonia production and ER-MCFC technology may be promising for fuel cell technology because industrial ammonia production facilities include hydrogen-rich synthesis-gas production and because ammonia is the world's largest chemical produced.

Ammonia plant description

An industrial ammonia plant based on conventional steam-reforming operated on natural gas comprises [1]:

- a catalytic steam reformer operated at 20-30 bar, and TexiI=780°C., producing synthesis gas (a mixture of CO, H2, and COj), with a significant amount of unconverted methane;

- secondary reforming with air. By catalytic partial oxidation of the unconverted methane using air the remainder of the feed is reformed autothermally, and the nitrogen required for the ammonia synthesis is fed to the process;

- CO-shift, C02 removal and methanation of residual CO;

- ammonia synthesis loop (P = 100-200bar) composed of a reactor, separator make-up gas and recycle compressor.

Conversion in the two-stage ammonia reactor is 21% per pass. The liquid product is essentially free of impurities and may be sent to storage. The reactor off-gas is recycled. Although stoechiometric for ammonia synthesis, the syngas from the secondary reformer contains some inerts (methane, noble gases); thus a purge from the synthesis-loop is required, which may amount to as much as 5% of the amount of hydrogen produced in the plant, which after hydrogen-recovery is normally fired in the reformer furnace.

Process structures for combinations of ER-MCFC and ammonia technology In process system design an ER-MCFC-stack may be considered to be a multifunctional unit operation [2], Besides producing DC-power and heat at high temperature, the MCFC acts as a H2- and CO-consumer. It also may add C02 to the process gas (by CO-shift and the active transport of C02 from anode to cathode), and supply power and heat. The full potential of an ER-MCFC in an ammonia plant is utilized if all these functions are applied for the benefit of the process. Furthermore, the ammonia plant should perform as many of the functions of the ER-MCFC stand-alone power system [2], viz. generation of a hydrogen-rich feed gas, supply of compressed air and C02 and utilization of anode-off gas and heat generated.

CH4 K J reformer H2 (3) aHir°(02/N2) ' " ~T---------- H2/CO (1-2)

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