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THE CHEMICAL INDUSTRY, A NOVEL MARKET NICHE FOR FUEL CELLS?

G.P.J. Dijkemat, J. Grievink", C.P. Luteijn", M.P.C. Weijnen"

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

"Faculty of Chemical Engineering and Materials Science Julianalaan 136, 2628 BL Delft

Abstract

The chemical industry may be seen as a market for fuel cells. Fuel cells can be applied to upgrade by-product hydrogen. Fuel cell stacks may be fully integrated in the process system design to enhance the chemical process performance. In this case the arrangement of stacks is one of the unit operations which the chemical process is composed of. Finally trigeneration systems may be designed to produce chemicals, power and heat simultaneously, as equally important commercial products. Identification of novel market opportunities in the chemical industry can be done by a three-step method. The economic feasibility largely depends on stack lifetime and stack capital cost.

Introduction

The possibility to utilize low-BTU off-gases by implementing fuel cells on-site has been identified as a possible high value application in the fuel cell community [1]. In the chemical industry hydrogen-containing by-product streams are produced in a large number of processes. Also power and heat demand normally are large and on-site cogeneration systems are common in the industry. Thus the situation in the chemical industry seems to be promising for these kind of fuel cell applications.

In addition to by-product hydrogen utilisation ample opportunities for fuel-cell application of a different kind exist in the chemical industry, albeit not suitable for market-entry. These include process-integrated applications of fuel cell stacks [2] and trigeneration processes for the combined production of power, heat and chemicals [3,4], Below these categories are described and some examples are given for phosphor, methanol and ammonia plants. A general method to identify novel market opportunities for specific options for fuel cell integration in chemical plants and design of trigeneration processes is introduced [4], This is completed by an assesment of parameters which affect economic feasibility.

By-product hydrogen utilisation

The application of fuel cells to utilize hydrogen-rich process off-gases is rather obvious. Although a patent was issued to Haldor Topsoe for the use of ammonia synthesis off-gas as a fuel for an ER-MCFC [5] and the availability of hydrogen-rich off-gases has been investigated in the Netherlands, this concept has not been commercially applied. This may be attributed to the limited availability of commercial fuel cell stacks and the limited track-record of fuel cells in industrial service which hampers acceptance by the chemical industry as 'proven technology'. Also the development-track selected by the fuel cell companies has been focused on packaged systems for stand-alone power generation. More important however, the economics of upgrading by-product hydrogen by applying fuel cells apparently are not good enough. Lance et al. [6], who investigated the use of hydrogen gas released in chlorine electrolysis, concluded that economically there is no point in the use of fuel cells for energetic upgrading of hydrogen in'gas flows in the process industry. From a preliminary investigation of the use fuel cells in conventional ammonia production it was found that the application of a fuel cell to utilise off-gas is only attractive at a considerable electricity revenue and if a rather low cost of fuel cell equipment had been assumed [7]. In addition, pressure-swing-adsorption technology provides an economic solution for removal of the greater part of the hydrogen from the syntesis-loop off-gases, allowing the hydrogen to be recycled to the ammonia process. Also the use of phosporus-oven off-gas, which is rich in carbon-monoxide proved to be only slightly more competitive compared to the case where the gas is fired in a gasturbine cogeneration system [8].

Process integrated appplication of fuel cells

A fuel cell stack not only converts hydrogen into water by electrochemical reaction with oxygen for the purpose of production of DC-currentis, but it also acts as an active device for hydrogen-removal, oxygen depletion of air etc. [2, 3]. Thus a fuel cell can be viewed as a multi-fimctional unit operation which is available for inclusion in chemical process system design: at the process system level, a chemical plant usually is designed as an interconnected set of unit operations, i.e., reactors, separators, compressors, pumps etc. This is equivalent to the 'balance-of-plant' calculations around fuel cell stacks.

An example is the system option developed for the much applied ICI Low-Pressure methanol process, which is based on steam reforming of methane. In this process synthesis gas is produced containing excess hydrogen. By integration of a fuel cell the syngas composition may be corrected. Excess hydrogen is converted by the fuel cell, and the system efficiency increases [9]. This kind of system designs involve the complete integration of a fuel-cell stack in a chemical plant. Usually these require only a fraction of the cost of a stand-alone fuel cell system because the amount of auxiliaries is limited. Moreover, by improving the performance of the chemical plant (e.g. increased plant efficiency or increased plant capacity) an additional competitive edge compared to stand-alone fuel cell systems is realized.

Factors which indicate that process integrated application of fuel cells could be favourable are the availability of process-off gases or synthesis gas to be used for fuel, the availability of pure cathode reactants (oxygen, COj), a high process power-to-heat ratio and a large of DC-power consumption [2].

Table 1: Characteristics of MCFC-stack and the fuel cell auxiliary system
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