Pipestill

Figure 1 shows a simplified flow plan for a typical hydroskimming refinery. The atmospheric pipestill performs the initial distillation of crude oil into gas, naphtha, distillates, and residuum. The naphtha may be separated into gasoline blending stock, solvents, and Powerformer feed. The distillates include kerosene, jet fuel, heating oil and diesel oil. The residuum is blended for use as bunker fuel oil. 

Light ends recovery and fractionating equipment is necessary after the Powerformer and on the pipestill overhead stream to separate the effluent mixtures into the desired boiling range cuts. 

Figure 2 shows a simplified flow plan for a typical conversion type refinery. The atmospheric P/S residuum can be fed to a vacuum pipestill. The vacuum tower enables the refiner to cut deeper into the crude, at the same time avoiding high temperatures (above about 750 °F) which cause thermal cracking with resultant deposition of coke and tarry residues in the equipment. 

The tendency is greatest, however, where pressures are close to atmospheric and "superheat" relative to atmosphere is least. Pipestill atmospheric towers and cat unit fractionators tend to fall in this category. Some operators consider that the likelihood is great that calculated condensation (dew) will coalesce to droplets which will gravitate (rain) when the partial pressure of condensibles at the dew point exceeds 1/3 atmosphere. With this factor and environmental protection in mind, some plants have diverted such releases into closed systems. Generally, however, this has not been of sufficient concern, and such releases have been treated as though they were all vapor. 

Where the acid condensate is corrosive, neutralisers, e.g. ammonia or neutralising amines, can be injected into the vapour stream to cocondense with the acid vapour. This is the practice with the overheads of a crude oil pipestill (Fig. 9.4). 

Pipestill gas the most volatile fraction that contains most of the gases that are generally dissolved in the crude. Also known as pipestill light ends. 

Pipestill A furnace containing a series of pipes through which oil is pumped and heated. During heating, the oil is vaporized prior to introduction into the distillation unit or thermal cracking unit. 

Pipestill furnaces vary greatly in size, shape, and interior arrangement and can accommodate 25,000 bbl or more of crude petroleum per day. The walls and... 

Figure 7-10 A pipestill furnace (heater) and a bubble (distillation) tower.

Pipe still (pipestill) a still in which heat is applied to the oil while being pumped through a coil or pipe arranged in a suitable firebox the distillation tower in a refinery. 

Next came the use of pipestills and bubble towers where the vapor in the tower bubbles through the liquid on the plates in the tower. Bubble towers allow fractionation to take place while a mixture of rising vapor is scrubbed by a stream of falling oil. Bubble towers are used in topping plants, rerun operations, cracking plants and natural gas stabilization. 

To provide raw material for this comparative study of untreated and heat-treated oils, asphaltenes from Cold Lake crude (crude asphaltenes) and from Cold Lake vacuum residuum (residuum asphaltenes) were prepared by n-heptane precipitation as described in the Experimental section. The Cold Lake residuum fraction was prepared by Imperial Oil Enterprises, Ltd. at Sarnia, Ontario, Canada. The distillation history of this bottoms fraction indicates that the pot material was subjected to temperatures as high as 314-318°C during atmospheric and vacuum distillation. The length of time at 300°C or higher was about two hours. This is well in excess of what would be experienced in a pipestill and should have provided ample time for any decomposition. It should be noted, however, that since it was possible to maintain the system vacuum at 0.35 mm, the maximum temperature experienced by the residuum was not quite as high as it might be during refinery distillation (e.g. ca 350°C). 

The thermal history of these particular residuum asphaltenes is much more severe in terms of heating time than would ordinarily be the case for a refinery product from a pipestill since, in the present instance, a pot distillation was used. It therefore seems likely that refinery asphaltenes should be even less different from their respective crude asphaltenes than in this investigation, assuming that pipestill temperatures would be kept below the decomposition temperatures for the asphaltenes,... 

Achieves low viscosity and volatility using efficiently fractionated solvent neutrals from the lubes vacuum pipestill via one base stock per feed. 

In this formulation of the Newton-Raphson method, the equations for each column of the system are solved simultaneously.19 To demonstrate this approach, the pipestill example is used see Fig. 4-6. To solve problems involving... 

The pipestill problem solved herein was originally solved by Cecchetti et al.8 by use of the original 0 method of convergence which is described in Chap. 3. This problem is based on data from field tests which were made on the pipestill shown in Fig. 4-6. The 6 method for distillation columns may fail to converge for some absorber-type problems, such as the pipestill. The pipestill is classified as an absorber-type problem because the main column has a condenser but no reboiler the first sidestripper has a reboiler but no condenser and all of the remaining strippers are of the conventional type. 

Figure 4-6 Actual stage numbers in the main column and the side strippers of the pipestill. [Hess et al, Hydrocarbon Process.. 56(5) 241 (1977), by courtesy Hydrocarbon Processing.]...

The pipestill shown in Fig. 4-7 is used for the purpose of separating the hydrocarbon feed Fj into seven fractions (Vl9 Wj, W2, W4, Ws, L28). The remain-... 

Table 4-13 Composition of the feed stream F and other specifications for the pipestill, Example 4-11 (Taken from ReJ. 13 by courtesy Hydrocarbon Process.)...

For the general case of any stage j in which a single-liquid phase is in equilibrium with the vapor phase, there exist two independent variables per stage, Oj (or QCj or Qpj) and 7 for a total of 2N independent variables. The total of 2N + 1 independent variables for the pipestill results from the existence of two liquid phases in the accumulator, which give rise to three independent variables [0 , 0i (or Qcil T,] for stage 1. 

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