In this work we show how two different catalyst layer fabrication techniques can improve the PEM fuel cell performance by introducing macro porosities in the layer. In the first technique, a template with 4 μm diameter pillars made using photo lithography is pressed against the cathode side of Gore® Primea® MEA to create evenly distributed macro pores/channels. In the other technique, mono-dispersed polystyrene particles with 1 μm diameter were used as pore formers to obtain homogeneously distributed macropores in the cathode catalyst layer. These MEAs were made in-house with the cathode catalyst layer thicknesses of about 1 μm. Fuel cell testing carried out on these two types of modified MEA structures with lower Pt utilization show a reasonable improvement in the cell performance at higher current densities. The improved performance at high current densities could be attributed to the presence of macro porosities in the catalyst layer, which enhance the mass transport properties of the catalyst layer.

This paper describes design and optimization of a Waste Heat Recovery Unit (WHRU) for a power cycle which uses CO2 as a working fluid. This system is designed for offshore installation to increase gas turbine efficiency by recovering waste heat from the exhaust for production of additional power. Due to severe constraints on weight and space in an offshore setting, it is essential to reduce size and weight of the equipment to a minimum. Process simulations are performed to optimize the geometry of the WHRU using different objective functions and thermal-hydraulic models. The underlying heat exchanger model used in the simulations is an in-house model that includes the calculation of weight and volume for frame and structure for the casing in addition to the thermal-hydraulic performance of the heat exchanger core. The results show that the for a set of given process constraints, optimization with respect to minimum total weight or minimum core weight shown similar results for the total installed weight, although the design of heat exchanger differs. The applied method also shows how the WHRU geometry can be optimized for different material combinations.

In the present work, previous studies carried out by the Norwegian aluminium industry and research centres with the aim of recovering heat from aluminium production off-gas, are reviewed. The main challenge in improving heat recovery is the fouling phenomena, which is due to the presence of particulate matter and corrosive gases in the off-gas. Fouling can occur due to particle deposition, condensation of corrosive acids and scaling reactions, which in turn can build up hard layers, particularly, on heat exchanger surfaces. The review focuses primarily on fundamental studies (theoretical and experimental), which address off-gas composition characterization, particle size distribution and particle deposition phenomena in laboratory and industrial environments. Moreover, it presents commercial concepts already implemented in industry applications. Upcoming activities in regards to the scaling phenomena, which include the design of a cold-finger for laboratory and industrial measurements, as well as mathematical modelling using CFD, are also discussed.

A cylindrical fouling probe or "cold-finger" has been used to investigate fouling from aluminium production offgas. The probe was located upstream from the off-gas cleaning system. Surface deposits have been collected for further analysis by EPMA and XRD, and compared with off-gas dust and old scale samples collected in the same experimental site. Cross-section micrographs of the deposit surfaces have been obtained to highlight the differences in surface structures formed on the upstream and downstream faces of the cold-finger. Strongly adhered hard scale formed after only two days in the upstream face of the probe. Loosely attached deposits accumulated downstream, which consisted of distinguishable particles of Al2O3, spherical Cryolitic bath condensates and Ni-S phases. The hard scale was rich in small bath condensates (NaAlF4) that form a tight network keeping together the larger particles. The deposition of those particles is suggested to be a key in scale formation.

Hard grey scale (HGS) is a strongly adhering fouling material forming on solid surfaces impinged by off-gas generated in the pot cells of primary aluminium production plants. Even though associated maintenance costs have a significant economic impact, the mechanisms behind HGS formation are not well understood. In the present work, a cooled fouling probe or “cold finger” placed in the off-gas duct, upstream of the gas treatment centre (GTC), at a Norwegian aluminium production site was used to study the formation mechanisms of HGS. Fouling experiments were performed with durations ranging from a few hours to several months. HGS formed on the windward side of the probe, whereas dusty and loosely attached deposits accumulated on the leeward side. The chemical composition and crystal phase evolution of the different deposits and off-gas particle samples were analysed by electron probe micro-analyser equipped with an energy-dispersive spectrometer (EPMA-EDS), quantitative x-ray diffraction (Q-XRD), LECO-C and transmission electron microscopy (TEM). Moreover, image analysis (IA) was used to investigate the particle size distribution and deposition properties of particles with different compositions. Inertial deposition of atmolite (NaAlF4) nanoparticles, produced by pot cell electrolyte vapour condensation, has been identified as the key mechanism in the formation of HGS.