H2/oil ratio

Typical operating conditions were 450°C, 30 bar total pressure, a hydrogen/oil ratio of 900 Nl/kg and a weight hourly space velocity (WHSV) of 1.5 kg/(kg h) for a period of 200 h. It was checked that at these conditions at the reactor inlet the criteria for wetting and plug flow for trickle-bed reactors [3,4] were met. Extreme conditions (higher temperatures and H2/oil ratios) led to extensive evaporation of the VGO such that the criteria mentioned were no longer adhered to. 

Figure 1. The effects of a series of Mo/AljOj catalysts with varying Mo loading (0-10%(m/m)) on the coke selectivity and the hydrodesulfurization activity. The HDS activity has been expressed as a second-order rate constant ( hds)< Process conditions temperature 450 C, pressure 30 bar, H2/oil ratio 900 Nl/kg, WHSV 1.3 kg/(kg h) and run length 180 h.

The effect of the H2/oil ratio on the coke content of a NtV/SiOj catalyst (low HDS activity, thermal coke predominates) is shown in Figure 6. The distinct maximum of the coke deposited with the H2/oil ratio is apparent from both experiment and theory. Detailed analysis of the model output indicates that at low gas rates the VGO feedstock is mainly in the liquid phase throughout the reactor, whilst at the highest gas rates the reactor is operated in the gas phase already at the reactor inlet. In both limits the amount of coke deposited is modest. Intermediate gas rates (1000 Nl/kg), however, lead to much higher rates of coke... 

Figure 2. Catalyst hydrodenitrogenation activity response. Feed FMC oil catalyst BD pressure 1500 psig H2/oil ratio 7500 scf/bbl space time 2.99 hr (LVHST). (O), 371°C (700°F) (U), 427°C (800°F) (A),...

HDT is carried out under a wide range of operating conditions. The severity of the process is adjusted depending on the properties of the feed and required product composition. The main process variables are pressure, temperature, hydrogen-to-oil (H2/oil) ratio, and space velocity. Each variable affects the process in different ways therefore, the set of operating conditions must be carefully adjusted to achieve an efficient operation. 

An accurate selection of the set of operating conditions ensures the best process performance. The main process variables (temperature, pressure, space velocity, and H2/oil ratio) are adjusted according to the specific HDT application. Table 13.3 shows typical operating conditions of various processes [59, 60]. Most of these processes are generally carried out in fixed-bed units, with the exception of ebullated-bed residue HCR. Naturally, the severity of the process increases with the heaviness of the feedstock. Distillate HDT is carried out at relatively mild conditions compared to residue HDT. HCR processes require more severe conditions than HDT and are much more demanding in terms of hydrogen supply. A brief discussion on the effect of these variables is presented later. 

H2/oil ratio is a standard measure of the voliune of hydrogen circulating through the reaction system with respect to the volume of liquid feed. It is defined by the following relationship ... 

One relevant aspect of gas recycling is its effect on the gas-liquid equilibrium in the reactor [61]. It is typical for most HOT units to operate with partially vaporized hydrocarbon feed. This effect alters gas composition and reaction rates. Increasing the H2/oil ratio can be useful for concentrating the heaviest and most refractory compounds (e.g., dibenzothio-phenes in gas oil feeds) in the liquid phase, providing them more contact time with the catalyst. However, special care must be taken with excess recycle rates because some of the species in the vaporized fraction may not have access to the active sites of the catalyst particle. 

The evaluation was carried out under the following operating conditions LHSV of 0.25 h", initial temperature of380°C, pressure of 9.81 MPa, and H2/oil ratio of 891 std m /m . The mass balance runs were performed consecutively by recovering the products every 12 h. Inter-reactor samples were taken every 24 h in order to monitor the behavior of the first reactor. The sample size was kept at less than -2% of the total feed rate so as to reduce the disturbance of the system. This small amount was sufficient enough to carry out some analyses, particularly to determine metals content in the products for estimating the metals uptake in the first reactor. 

Figure 13.28 H2/oil ratio and superficial gas velocity profiles. Simulated (—) 380°C. (—) 400°C ( ) experimental.

Figure 13.34 presents one possible reactor configuration and the simulation of reactor temperature, H2/oil ratio, and conversion of the chemical lumps. In order to limit the sharp temperature rise caused by the hydroprocessing reactions, the total catalyst volume was divided into six catalyst beds. Ri required four beds as a result of the large heat release in this section ( 72°C), whereas R2 required only two beds. Bed inlet temperatures and delta-Ts for each reactor were adjusted to be more or less equal in order to match the average temperature... 

Figure 13.34 Simulation of the proposed industrial reactor configuration. Evolution of reactor temperature, H2/oil ratio, and concentration of the chemical...

The H2/Oil ratios are for units in which off-gas from the high-pressure separator is recycled. For once-through naphtha hydrotreaters associated with catalytic reformers, the H2/Oil ratio can be much higher than 350 scf bbl (60 m /w ). For units that treat olefinic cracked stocks from FCC or coking units, H2/Oil ratios are higher to control the extra heat released by olefin saturation. 

However, the diesel yield is maximized at a certain temperature and then decreases as a result of higher conversions achieved at higher temperatures (RENEW, 2008). Moreover, it was shown that the yield of gasoline and diesel in the product decreases as the H2/oil ratio decreases and so does the conversion. The diesel... 

Figure 6.68 H2/oil ratios and the corresponding values of H2 partial pressure.

Figure 6.70 Effects of the H2/oil ratio on H2 consumption and catalyst life.

The HDT catalyst is typically a CoMo/NiMo alumina supported catalyst, whose composition and textural properties vary according to the different purposes. The severity of the operating conditions depends on the type of feed and the quality of the flnal product. In general, the process is carried out at high pressure and temperature typical commercial units operate at 2-20 MPa, 320°C-440°C, H2/oil ratio of 350-1800 N-mVm and liquid hourly space velocity (LHSV) between 0.2 and 8h (Satterheld, 1975). 

Inside the reactor, H2/oil ratio decreases along each catalyst bed as a result of hydrogen consumption. Interbed hydrogen quenching acts as a make-up source producing a step increase at the entrance of the following catalyst bed. The H2/oil profile along the reactor usually has the inverse shape of axial temperature, as it will be demonstrated in the simulations presented in the next section. 

Reaction temperature and H2/oil ratio are other two process variables that favor catalyst wetting efficiency and are not considered explicitly in the partial wetting model. The theoretical curve of Figure 8.20 is valid only for specific conditions of reaction temperature and H2/oil ratio. Increasing any of these variables, particularly reaction temperature, will displace upward the zone in which catalyst wetting efficiency is a strong function of liquid velocity. 

The reactor model was applied to design and simulate the commercial-scale reactors of the IMP heavy oil upgrading process, keeping in mind the aforementioned criteria. It was considered that the reactors operate at the following average conditions overall LHSV of 0.25 h, temperature of 380°C, H2/oil ratio of 890 std mVm, ... 

Figure 8.23 is a histogram plotting the average H2/oil ratio in both reactors as a function of the number of hydrogen quenches. The analysis indicates that two... 

In addition, deeper physicochemical knowledge is required to establish a proper deactivation function however, if reacting conditions in laboratory (pressure, temperature, H2/oil ratio, space velocity) are similar to those at pilot or industrial scale, then a time-dependent deactivation rate is useful to model the reaction kinetics. On the other hand, this deactivation function cannot be extrapolated to different operating conditions and, consequently, new deactivation function parameters should be proposed for each different operating condition. 

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