Partial oxidation, heavy residue

This most widely used black pigment is also in the top 50 chemicals. About 4.0 billion lb of carbon black were made in 2001. Commercial value was 1.4 billion at 35C/lb, but 93% of this is used for reinforcement of elastomers. Only 7% is used in paints and inks. Carbon black is made by the partial oxidation of residual hydrocarbons from crude oil. See Chapter 6, Section 7.2. The hydrocarbons are usually the heavy by-product residues from petroleum cracking, ideally high in aromatic content and low in sulfur and ash, bp around 260°C. 

Here again, this is not a refining process, properly speaking. Partial oxidation is one of the processes for the ultimate conversion of heavy residues, asphalts, coke and even coal. 

Heavy Hydrocarbon-Based Partial Oxidation Processes. Two major partial oxidation processes are commercially available, the SheU process (38) and the Texaco process (39). Operating conditions in the gas generator vary from 1200°C to 1370°C and from 3100 kPa to 8270 kPa (450—1200 psig). Generally, heavy oils are the hydrocarbon feeds however, the process can also accommodate feeds from natural gas to residual oils. 

There are different sources for obtaining synthesis gas. It can be produced by steam reforming or partial oxidation of any hydrocarbon ranging from natural gas (methane) to heavy petroleum residues. It can also... 

The catalytic conversion of heavy hydrocarbons, such as heavy oil or sulphurous organic residues, from the oil industry via steam reforming is not feasible because solid carbon starts to be deposited at temperatures above 800 °C, which renders the catalyst inactive in a short period of time and, furthermore, blocks the gas flow in the reactor. Heavy hydrocarbons are, therefore, converted to hydrogen using partial oxidation (POX). Note that in refineries the term gasification is more commonly used partial oxidation is the scientific terminology. 

Partial oxidation has practically no restrictions regarding the nature of the hydrocarbon and the sulfur content. Natural gas, refinery gases, LPG, naphtha, heavy fuel, vacuum residue, visbreaker oil, asphalt, and tar can be used as feedstock. As the investment costs for partial oxidation are higher than for steam reforming, mainly because of the cyrogenic air separation, it is usually not a choice for the lighter hydrocarbons, but heavy feedstocks from fuel oil to asphalt, when favorably priced, can be a competitive option for various locations and circumstances. In some special cases, where the primary reformer is a bottleneck for a capacity increase, a small parallel partial oxidation unit based on natural gas could be installed, if a surplus of... 

Natural gas will remain the preferred feedstock of present ammonia production technology in the medium term (15-20 years) as may be assumed from the world energy balance shown in Table 47. Partial oxidation of heavy hydrocarbon residues will be limited to special cases and coal gasification might not play a major role in this period. 

C. Higmann, Perspectives and Experience with Partial Oxidation of Heavy Residues, Lurgi company brochure. 

Partial oxidation units may operate with feedstock, ranging from natural gas to heavy oil fractions such as asphalt. Heavy feedstock may contain large amounts of both sulfur and heavy metals. In many cases these compounds are removed from the raw syngas downstream the POX reactors. Some residual carbon or soot may be formed in the combustion chamber of the reactor.To avoid the carbon lay-down in the heat exchanger downstream the POX reactor, special coils and high gas velocity are used. The carbon may be removed downstream the heat exchanger in a suitable water wash or scrubbing system. ... 

Higman, C. Perspectives and Experience with Partial Oxidation of Heavy Residues. L Hydrogene, Maillon Essentiel du Raffinage de Demain, L Association Frangaise des Techniques du Petrol, Paris, 28 June 1994. http //www.higman.de/ gasification/paris.pdf. 

A non-catalytic partial oxidation process based on the above reactions has been largely used for the past five decades for a wide variety of feedstocks, in particular heavy fractions of refinery, such as naphtha, vacuum fuel oil, asphalt residual fuel oil, or even whole cmde oil. The absence of catalysts implies that the operation of the production unit is simpler (decreased desulfurization requirement) but the working temperatures results higher than 1200°C. The high values of this parameter permit satisfactory yield to H2 and CO to be obtained without using a selective catalyst. 

Another variation of the partial-oxidation process is one in which a heavy-oil fraction is cracked in the presence of an inert solid and a hydrogen-rich gas under conditions which result in the saturation of olehns and diolefms. During the process some coke and residual material depoats on the inert solid. The latter then flows by gravity to a combustion aone where the coke is burned off the solid in the presence of oxygen and steam to produce the hydrogen-rich gas used in the cracking cycle. ... 

As mentioned above in Section 2.3, partial oxidation is an alternative process to steam reforming for producing hydrogen from methane. It is also applicable to a wide range of liquid hydrocarbons that include heavy oils found in low-value refinery residues (refinery bottoms ) and to the gasification of coal see Section 2.7. In general terms, the process may be expressed as ... 

The production of hydrogen by steam-reforming of methane or by partial oxidation of heavy residues (POX) inevitably leads to an increase in self-consumption and additional emissions of CO2. 

The reaction is performed with a burner in a brick-lined reactor at a temperature close to 1400 C Afterwards, reaction products are cooled down and liquid condensates containing mostly tar and heavy oil are recovered while off-gases are scrubbed in order to remove the deleterious impurities (i.e., H S, COS, and CO ). Hydrogen is later separated from CO and used as-is for the synthesis of ammonia or purified. Theoretically, all hydrocarbons can be used as feedstocks for partial oxidation but for economical reasons only low-sulfur heavy residues from the petrochemical industries are used. 

Partial oxidation Hydrocarbons including heavy fuel residues H O, 0. None 1200-1500°C 30-80atm CO, H, (CH, CO,)... 

Two processes are commercially established for heavy oil gasification, the Shell and the Texaco process (Figures 6.2.27 and 6.2.28) but the main steps of both processes are practically identical [see Supp (1978, 1997) for details). Besides partial oxidation of natural gas and residue oil, this process has been developed further for coal slurries (Table 6.2.6). Oxygen, pre-heated heavy oil, and steam are fed to the refractory-lined reactor where the oil is sprayed into the reactor. The reaction starts in a water-cooled burner, which also houses the atomizing gun and the oxygen and steam inlets. 

Natural gas is catalytically converted with steam, it can be easily desulfurized, and in contrast to coal and heavy oils other impurities like metal compounds or inorganic matter leading to a catalyst deactivation are not present. This process is called steam reforming, and is followed by autothermic reforming where the residual methane of the syngas is converted with air/oxygen by catalytic partial oxidation. 

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