Viscosity Refinery Residues

The Mizushima Oil Refinery of Japan Energy Corporation first implemented an operation of vacuum residue hydrodesulfiirization in the conventional fixed bed reactor system in 1980. We have also conducted a high conversion operation to produce more middle distillates as well as lower the viscosity of the product fuel oil to save valuable gas oil which is used to adjust the viscosity. Vacuum residue hydrodesulfurization in fixed bed reactors mvolves the characteristic problems such as hot spot occurrence and pressure-drop build-up. There has been very little literature available discussing these problems based on commercial results. JafiFe analyzed hot spot phenomena in a gas phase fixed bed reactor mathematically, assuming an existence of the local flow disturbance region [1]. However, no cause of flow disturbance was discussed. To seek for appropriate solutions, we postulated causes ofhot spot occurrence and pressure-drop build-up by conducting process data analysis, chemical analysis of the used catalysts, and cold flow model tests. This paper describes our solutions to these problems, which have been demonstrated in the commercial operations. 

Notes Asphaltenes IC7, heptane insoluble IC5, pentane insoluble refinery residues AR, atmospheric residue VR, vacuum residue. HV Vickars microhardncs.s measurement for solidification tempara-ture. If LMO occurrence is obtained by Fourier transform infirared (FUR), electron spin resonance (ESR), reflectance, or viscosity measirrements, an asterisk ( ) is used. 

Since its introduction in 1939, visbreaking process has been extensively used for upgrading refinery residues (atmospheric or vacuum residues) and other heavy streams to produce gas, naphtha, distillates, and visbroken residue. The term visbreaking comes from the words viscosity and breaking. ... 

Visbreaking is a mild thermal cracking process that reduces the viscosity of heavy fuel oils and reduces the amount of low-viscosity blending stocks that must be added to the heavy residuals to meet viscosity specifications of the specific heavy fuel oil. The amount of heavy fuel oil production by a refinery is reduced by 20—30 percent if a visbreaker is used. The refinery profitability is improved with visbreaker operation, because heavy fuel oils are low value products. 

Devolatilizers Devolatilization systems are liquid-limited due to the combination of high liquid viscosity and removal of a component with high relative volatility. Simpson and Lynn [AlChE J., 23 (5), 666-673 (1977)] reported oxygen stripping from water at 98 percent complete, in less than 1 ft of contact. The concept has been employed for residual devolatilization in refineries. 

In the present context, heavy oils and residua can also be assessed in terms of sulfur content, carbon residue, nitrogen content, and metals content. Properties such as the API gravity and viscosity also help the refinery operator to gain an understanding of the nature of the material that is to be processed. The products from high-sulfur feedstocks often require extensive treatment to remove (or change) the corrosive sulfur compounds. Nitrogen compounds and the various metals that occur in crude oils will cause serious loss of catalyst life. The carbon residue presents an indication of the amount of thermal coke that may be formed to the detriment of the liquid products. 

The Mizushima Oil Refinery of Japan Energy Corporation first implemented a high conversion operation of vacuum residue, versus a constant desulfurization operation, in the commercial residue hydrodesulfurization unit equipped with fixed-bed reactors, to produce more middle distillates as well as fuel oil with lower viscosity. The catalysts will be replaced when the sulfur content in the product oil reaches the allowable limit. Since we have believed that an increase in the residue conversion decreases the catalyst activity by coke deposition, we have been interested in controlling the coke deactivation to maximize the residue conversion during a scheduled operating period. 

Gebauer et al. [38] suggest visbreaking of waste plastics with vacuum residue. This is a thermal process, applied in refineries in order to convert partially atmospheric vacuum residue and decrease viscosity and melting temperature. According to the authors, addition of 5% of waste plastics in laboratory tests does not influence noticeably the process parameters and final products properties. As in the case of LCO and VGO fractions the application of vacuum residue and mixture of waste plastics is applicable in refineries. 

A principal source of the heaviest lube base stocks is vacuum-reduced crude (vacuum residuum). The primary application of the deasphalting process is to reduce the Conradson carbon residue (CCR), metals (Ni, V, etc.) content and viscosity of a vacuum residuum in order to produce an acceptable quality heavy lube base stock. The CCR content of a refinery stream is determined in an ASTM analytical test that involves... 

There are two major types of VDU ojjerations in a modem refinery -feedstock preparation and lubricant production. Feedstock preparation is the most common ojjeration that recovers gas oU from the atmospheric residue as a feed to the downstream conversion units (e.g. FCC and hydrocracking units), which converts the gas oil into more valuable liquid products such as gasoline and diesel. Lubricant production is designed to extract petroleum fractions from the atmospheric residue to produce luboil with desirable viscosity and other related properties. 

Since the d and for residual fuel oil, a low-value product, continues to decrease, visbreaking has become an important process in a refinery due to its capacity to reduce the amount of residual fuel. The produced visbroken residue has a reduced viscosity, which needs less diluent (middle distillates) to bring its viscosity down to a marketable level, so that the middle distillate saved can be used for producing other more valuable refinery products. 

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