Barry B. Pruden

Economics of hydrogen recovery processes for the purification of hydroprocessor purge and off-gases

Abstract Pressure swing adsorption, membranes and countercurrent gas-liquid contacting were evaluated for the purification of hydrocracker and hydrotreater purge and off-gases. Industrial cases relevant to upgrading and refining were examined, and the most economic and technically suitable options were determined. For pressure swing adsorption (PSA), surprisingly, the best economics were at lower recoveries, when tail gas met fuel gas pressure requirements. This eliminated tail gas compression which is relatively expensive. Membranes were marginally better than PSA at higher feed pressures (∼7.0 MPa), and there was no advantage in combining these processes due to loss of economies of scale. Countercurrent gas-liquid contacting, which recovers hydrogen near feed pressure, has an advantage over both PSA and membrane when the feed pressure is high. A sensitivity analysis indicated that high feed gas capacity, high purity, and a low fuel gas price favor hydrogen recovery processes. The impact of increased recovery and purity on the economics of hydrogen recovery was negligible compared to the effect of unit sizes (economy of scale).

Economics of thermal dissociation of H2S to produce hydrogen

Abstract Two process schemes for the thermal decomposition of H 2 S were studied and their economics evaluated. The first scheme involved the recycling of H 2 S through a modified steam methane reforming type furnace so that all of the possible hydrogen could be extracted. In the second scheme, H 2 S was passed once-through a decomposition/heat exchanger type reactor then on to a conventional Claus sulphur recovery plant. A model incorporating the influence of heat transfer on the thermal decomposition predicted H 2 S conversions from 22 to 26%. The cost of producing hydrogen is significantly greater for the second scheme because only 22% of the available hydrogen is recovered. The cost of producing hydrogen using the first scheme is greater than that from conventional steam methane reforming, but with improvements in heat transfer and separations the process should become more competitive.

Fluidized-bed steam methane reforming with oxygen input

Abstract A study was undertaken to determine whether oxygen could be added directly to a fluidized bed of catalyst to provide all of the endothermic heat for the reforming reaction. It is shown that oxygen can be successfully introduced onto a reforming reactor to provide for the endothermic heat of reforming reactions. The methane conversion increased with increasing reactor temperature, oxygen input flow rate and steam–methane ratio and decreased with increasing reactor pressure as expected. Methane conversion and hydrogen yield are compared to those expected at equilibrium. There was 100% conversion of oxygen under all conditions. Most experimental runs reached and maintained autothermal conditions. The hydrogen yield increased with increasing temperature and steam–methane ratio. The hydrogen yield decreased minimally with increasing reactor pressure and oxygen flowrate.

Asphaltene precipitation : detection using heat transfer analysis, and inhibition using chemical additives

Experimental temperature data for a new precipitation detection technique based on heat transfer through a precipitate layer are presented. The fully automated technique requires only 39 h to determine the solvent/bitumen ratio at which asphaltene precipitation begins. Precipitation of n-heptane asphaltenes from Cold Lake bitumen was found to begin at a solvent/bitumen ratio of 1.5. Using this detection technique, a number of aromatic compounds, compounds with N, S and O heteroatoms and hydrogen donor solvents, chosen for their similarity to resins, were tested for their ability to delay the onset of asphaltene precipitation. Phenanthrene was found to be the most effective additive, and the compounds containing nitrogen the least effective.

Flow loop apparatus to study the effect of solvent, temperature and additives on asphaltene precipitation

A detection technique was developed for the onset of asphaltene precipitation based on the measurement of pressure drop across an in-line filter. An in-line filter of a nominal size of 60 μm was used to capture the precipitate and thus detect the onset, which was indicated by a dramatic increase in the pressure drop across the filter. Experimental runs required only 4 h to complete and the apparatus is capable of testing opaque samples at high temperatures and pressures. The effects of solvent type and temperature on the onset of precipitation were investigated for Athabasca and Cold Lake bitumens. For both bitumens, the qualitative behavior of the onsets with solvent type (carbon number) and temperature were similar, displaying an increase in the onsets at lower carbon number and temperature values and decrease at the higher values. To identify the effectiveness of resin type compounds to dissolve asphaltenes, 20 g of various aromatic, hydrogen donor, heteroatom and surfactant compounds were added to 100 g samples of Athabasca and Cold Lake bitumens. It was found that aromatic and hydrogen donor compounds increased the onset ratio by a slight to moderate degree, heteroatom compounds increased the onset ratio by a moderate degree, whereas surfactants increased the onset ratio by the highest degree.

Economics and simulation of fluidized bed membrane reforming

Abstract In this study a Fluidized Bed Membrane Reforming (FBMR) process has been proposed and enhancements to improve the economics of the Steam Methane Reforming (SMR) process for production of hydrogen have been incorporated. Separation of the product hydrogen using membrane technology to drive the reaction beyond its thermodynamic equilibrium and the use of high flux palladium coated niobium/tantalum membranes have been studied. Capital and operating costs were estimated, and supply cost economics determined for comparison to a conventional Steam Methane Reforming plant. The study identified that Fluidized Bed Membrane Reforming has an increase in conversion over conventional technology at comparable operating temperature and pressure. Direct firing of fluidized bed reactors located in the radiant section of a reformer type furnace is the most efficient scheme to transfer the heat of reaction compared to the condensing sodium vapor type of heat transfer. The configuration with high flux membranes has a lower estimated capital and operating cost than conventional SMR.

Asphaltene precipitation from cold lake and athabasca bitumens

ABSTRACT The onset of asphaitene precipitation from Cold Lake and Athabasca bitumens was studied using a heat transfer technique. The onset for these two types of bitumen was at a n-heptane to bitumen volume ratio of 1.4 to 1.7. Since it is important to suppress the onset of precipitation, a number of additives (aromatics; hydrogen donor solvents, solvents with the heteroatoms nitrogen, sulphur, and oxygen; and surfactants) were tested for their ability to delay the onset of asphaitene precipitation from Cold Lake bitumen. Phenanthrene, an aromatic, and the surfactant nonyl-phenol were found to be most effective. Cold Lake bitumen maltenes were found to be as effective as the aromatic chemical additives in delaying the onset of asphaitene precipitation. As the maltenes fraction contains saturates, the resins fraction alone should be even more effective at delaying precipitation.

Formation of coke during thermal hydrocracking of Athabasca bitumen

Abstract The formation of two structurally different cokes during thermal hydrocracking of Athabasca bitumen is attributed to differences in coking properties of the asphaltenes and the deasphalted heavy oils. The grain-mosaic coke structure formed from the asphaltenes may be ascribed to the presence of crosslinkage groups derived from the phenolic character of this fraction of the bitumen. Carbonization of the deasphalted heavy oils of the bitumen results in a flow-type coke structure. These two cokes appear to form independently of each other and can therefore be readily identified in samples collected from the reactor.

The Development of an Onset-of-Precipitation Detection Technique Using Heat Transfer Analysis

ABSTRACT Presently, no definitive technique has been reported that measures the onset-of-precipitation of asphaltenes from a hydrocracker product at process conditions. In the present paper, a detection technique utilizing heat transfer analysis is presented. The method is suitable for the high temperature and pressure conditions in upgrading and is based on a heat transfer analysis of the precipitated layer. The modeling of the technique is provided, as well as details of the heat transfer vessel. Results from glycerol and corn oil model fluid experiments and simulations demonstrate the validity of the method Preliminary experimental results for Cold Lake bitumen are presented along with recommendations on how the method will be further improved.

Microscopic changes in the coal-based catalysts used in the hydrocracking of Athabasca bitumens

Abstract Conventional catalysts are rapidly fouled with coke and metal deposits when used to hydrocrack residual oils. This work is part of a study in which a slurry of coal particles coated with catalyst was used in the hydrocracking of Athabasca bitumen in a continuous-flow pilot plant operated on the scale of one barrel (159 litres) per day. The fusinite and semi-fusinite macerals were unreacted after passing through the reactor and served as sites for coke and mineral-matter deposition. Unoxidized vitrinite macerals were converted to gas and oil and gradually disappeared, but oxidized vitrinite remained visible. This oxidized vitrinite, which had an oxidation rim around the periphery of the maceral, was coked in the interior. It is presumed that the gases and liquids evolved passed through fractures in the oxidation rim. The semi-coke-like structure resulting from partially oxidized vitrinite then behaved like the other coal inerts and served as a site for deposition of coke and mineral matter from the bitumen.