Effluents hydrocracking

Reformer charge Reformer effluent Hydrocracker charge effluent Recycle gas... 

In the two-stage operation, the feed is hydrodesulfurized in the first reactor with partial hydrocracking. Reactor effluent goes to a high-pressure separator to separate the hydrogen-rich gas, which is recycled and mixed with the fresh feed. The liquid portion from the separator is fractionated, and the bottoms of the fractionator are sent to the second stage reactor. 

The melt used in this work was prepared from the residue of hydrogen-donor extraction of Colstrip coal with tetralin solvent in such a way as to simulate the composition of an actual spent melt. The extraction was conducted in the continuous bench-scale unit previously described (17) at 412°C and 50 min residence time. The residue used was the solvent-free underflow from continuous settling (17) of the extractor effluent. The residue was then precarbonized to 675°C in a muffle furnace. The melts were blended to simulate the composition of a spent melt from the direct hydrocracking of the Colstrip coal by blending together in a melt pot zinc chloride, zinc sulfide, and ammonium chloride, ammonia, and the carbonized residue in appropriate proportions. Analysis of the feed melt used in this work is given in Table I. 

Many processes of gas absorption with chemical reaction are set up at high pressures, result of technical and/or economical requirements. That is, for example, processes of hydrocracking and hydrorefining of heavy oils and processes of oxydation of liquid effluents. However, if many chemical systems are found to determine the mass transfer parameters in an industrial reactor at atmospheric pressure by using the chemical method, they become scarce at elevated pressures. Several physical and chemical methods have been proposed chemical methods present some severe drawbacks, since one has to replace the gas-liquid system of interest by another one, presenting different physical properties (specially a different coalescence behaviour). 

Reprinted with permission from "Corrosion by Sulfide Containing Condensate in Hydrocracker Effluent Coolers, API Division of Refining, May 1968, American Petroleum Institute, Washington, D.C.)... 

The liquid phase of the separator/finisher, which contains hydrotreated feed plus unconverted effluent from the hydrocracking reactor, is recycled to the... 

These fouling phenomena are believed to be due to the precipitation of asphaltenes from hydrocracked, effluent streams. Fragmentation reactions decrease the solubility power of effluent maltenes and the solubility of asphaltene micelles, thus facilitating precipitation [1]. 

Sour water (hydrogen sulfide in water) is also obtained as aqueous condensate from the fractionation of the volatile products of refinery operations, such as the fluid catalytic cracker (FCC), hydrotreater, hydrocracker, or coker. In fact, in a refinery, which is endeavoring to minimize water use, sour waters may make up as much as 25% of the total aqueous effluent discharged. 

The reactor effluent leaving the air cooler is separated into hydrogen-rich recycle gas, a sour water stream, and a hydrocarbon liquid stream in the high-pressure separator. The sour water effluent stream is often sent to a plant for ammonia recovery and for purification so water can be recycled back to the hydrocracker. The hydrocarbon rich stream is pressure reduced and fed to the distillation section after light products are flashed off in a low-pressure separator. 

It is evident that the above approach was followed to arrive at a high selectivity towards middle distillates, the prerequisite being a second stage which can convert the heavy wax fraction in the HPS effluent very selectively into middle distillates, the Heavy Paraffin Conversion (HPC) stage (see Fig. 2). In the HPC the waxy product of the HPS is hydro-isomerized and hydrocracked to give the maximum yield of middle distillates. 

Dehydrogenation of this fraction was carried out for 262 hours without any significant fall in initial catalyst activity. The aromatic content of the product (mainly toluene) was 36-40 %. It is interesting that the catalyst, in spite of the rather high temperature at which the reaction took place, caused practically no hydrocracking of the hydrocarbons, the effluent gas consisting of 99% hydrogen. Sulfur compound present in small amounts... 

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