Pyrolysis Fuel Oil

IRB 7, N-234, Ensaco250 Used to rubber industry PFO Pyrolysis fuel oil 4. Conclusion... 

Description Feeds are sent to USC cracking furnaces (1). Contaminants removal may be installed upstream. A portion of the cracking heat may be supplied by gas turbine exhaust. Pyrolysis occurs within the temperature-time requirements specific to the feedstock and product requirements. Rapid quenching preserves high-olefin yield and the waste heat generates high-pressure steam. Lower temperature waste heat is recovered in the downstream quench oil and quench water towers (2) and used in the recovery process. Pyrolysis fuel oil and gaso-... 

Gas oil produees similar yields of ethylene and propylene to fun range naphtha but there is a large inerease in the production of pyrolysis fuel oil (b.p. >200°C). 

Vacuum gas oil produces less olefins but relatively more propylene. The major products are pyrolysis gasoline and pyrolysis fuel oil. 

LSWR is finding increasing use in cracking operations, particularly those configured to crack gas oil. The high wax content, indicative of linear paraffins, generates a good ethylene yield and the pyrolysis fuel oil is low in sulphur and used to produce carbon black. 

If the fuel oil uses as the feedstock is low in sulphur, i.e. LSWR, then the pyrolysis fuel oil produced will also be low in sulphur and this makes the product attractive for the production of carbon black. 

Feedstock (after pre-treatment if necessary) is passed along with steam to the pyrolysis furnace. This cracks the compounds in the naphtha, producing a full range of products which are extremely complex. As with gas feedstock, heavier products are produced, but in increased volumes. After quenching a primary fractionator (not present in gas crackers) separates the heavy pyrolysis fuel oil from the cracked gases. 

Gas oil cracking has all of the characteristics of naphtha cracking. The typical statistics are given in Table 9.4. Relative to naphtha, the gas oil cracking requires considerably more feed for the same ethylene output (500 kt/y) and at the same time produces increased volumes of pyrolysis gasoline and more particularly pyrolysis fuel oil. This requires an increase in the fixed capital to naphtha for the same scale of operation. 

In general, with decreasing hydrocarbon partial pressure, unsaturated components such as acetylene, ethylene, propylene, and butadiene increase whereas BTX, pyrolysis fuel oil, and saturated components such as methane, ethane, and propane decrease. Low hydrocarbon partial pressure can be attained either by high steam dilution or by low absolute pressure in the cracking coil, which is determined by furnace outlet pressure and pressure drop in the cracking coil. For each specific case there is an optimum steam dilution. Reduction of steam dilution influences yields, utilities, running times and, in the case of a new ethylene plant, of course, investment costs—but in different ways, either positive or negative. Thus, an optimization has to be carried out to identify the most economic steam dilution. 

Residence Time. The influence of residence time on yields is similar to that of hydrocarbon partial pressure, but smaller. In principle, unsaturated components increase slightly with shorter residence time, depending on the cracking severity. At the same time, saturated components and pyrolysis fuel oil (PFO) decrease. The quality of pyrolysis fuel oil also is influenced by residence time. For constant P E, the ratio of carbon to hydrogen in PFO becomes smaller with decreasing residence time, which has a positive effect on coking tendency besides other parameters. 

Figure 3d. Pyrolysis fuel oil yields as a function of molecular collision parameter. Feedstock naphtha.

Figure 4. Ethylene and pyrolysis fuel oil yields from thermal, cracked hydroconverter residue (S).

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