Mineral oils: processes and products – Miscellaneous
Reexamination Certificate
2000-08-08
2003-06-24
Norton, Nadine G. (Department: 1764)
Mineral oils: processes and products
Miscellaneous
C137S013000, C585S899000
Reexamination Certificate
active
06582591
ABSTRACT:
The invention relates to exhortation of naphtha in a crude oil pipeline.
Naphtha is one of the products from the refining of oil, the distillation range of which lies in the 50-180° C. region. It is predominantly composed of normal paraffins and isoparaffins and to a lesser extent of naphthenics (cycloparaffins). Olefinic and aromatic products are minor constituents of it. In schemes for the refining and upgrading of crude oil, this naphtha cut is conventionally intended:
for reforming, in which operation paraffins and naphthenics are converted into aromatics with high octane numbers suitable for use in the formulation of premium-grade gasolines;
for steam cracking, a key operation for the production of basic chemicals in which naphtha is cracked in the presence of steam at approximately 750-850° C. to yield ethylene, propylene, butadiene, butenes, benzene and other less desired products. This operation is described in detail in the book by A. Chauvel et al., Procédés de Pétrochimie, Volume 1, page 131, published by Technip (1985).
The steam cracker is composed essentially of a “cold part”, in which the products resulting from the cracking reaction are separated by distillation and purified, and of a “hot part”, in which the cracking reactions take place. This hot part comprises:
a convection region, in which the products are preheated from 120° C. to approximately 550° C. by recovery of the sensible heat of the furnaces;
a radiation region, in which the temperature is raised from 550° C. to 750-850° C., where the cracking proper takes place;
a quenching region, in which the temperature of the cracking products is suddenly lowered from 750-850° C. to approximately 350-400° C. by means of exchangers operating with steam.
The naphtha which feeds the steam cracker must not comprise heavy products or products which cannot be distilled, or else the convection region will rapidly become fouled or the quenching region will become coked, episodes which result in the unit being shut down for cleaning or decoking. In view of the very large size of these units (amounts of naphtha treated of greater than 1.5 million tonnes per year), such shutdowns constitute major disadvantages from an economic viewpoint.
The transportation of naphtha and more generally the transportation of refined petroleum products takes place in pipelines known as “white product pipelines”. The same pipeline is used for the transportation of different products which are injected sequentially therein batchwise. A mixing region is formed at each interface between different batches, which region, on arrival, corresponds to a contaminated product known as “contaminate” which, in principle, has to be reprocessed before it is used. This contaminate represents on average 5 to 10% of the total batch conveyed in the pipeline.
Pipeline operators know of and properly control this phenomenon. Thus, in order to reduce the volumes of contaminates or to minimize the reprocessing thereof, it is possible, for example:
to avoid pumping shutdowns, which result in pipeline surges;
to rinse the pumping stations, in order to prevent the products present in the “cutoffs” from mixing with the main product;
to make batches as big as possible;
to take care that two batches which succeed one another do not have very different viscosities;
to group together batches with similar qualities, so as to minimize the reprocessing operations: thus, the contaminate between a batch of LSC (low sulphur content) fuel oil and a batch of HSC (high sulphur content) fuel oil can be allocated to the HSC fuel oil without reprocessing. Likewise, the contaminate between a batch of kerosene and a batch of gas oil will be allocated to the gas oil.
A much more complex problem to be solved is the transportation of refined products in a crude oil pipeline. Crude oil pipelines generally have larger diameters than “white product” pipelines and thus have much greater transportation capacities, generally over greater distances. The transportation of refined products in a crude oil pipeline thus takes place at a much lower cost in comparison with the cost with regard to white product pipelines. Furthermore, over certain routes, white product pipelines do not always exist and the use of a crude oil pipeline then makes it possible to save on a considerable investment. The use of crude oil pipelines for the transportation of refined products is thus a very important economic issue, which is why these pipelines are sometimes used for this purpose despite the difficult problems of contamination which have to be solved.
Thus, in order to avoid or minimize contamination at the interfaces between batches of refined products or between crude oil and refined products, it is advisable to take the precautions already listed in the description of the sequential transportation of refined products in a white product pipeline.
However, crude oil comprises highly coloured products, long-chain paraffins which can precipitate out, insoluble asphaltenes and mineral loads, all factors which, over time, result in a deposit on the walls of the pipeline. This deposit can release impurities during the passage of a batch of refined product, which constitutes a fresh source of contamination which this time affects the core of the batch. The article entitled “Batching, treating keys to moving refined products in crude-oil line” in “
Oil and Gas Journal
” of Oct. 5, 1998, page 49, gives a very good account of the whole problem and of the precautions which it is advisable to take in order to minimize the contamination at the interfaces and at the cores of the batches. In particular, the use of “scrapers”, which are generally moved along in the pipeline with the crude oil in order to periodically clean the walls, is to be prohibited during the transportation of refined products, as it enhances the turbulence and increases the level of contamination in the batches.
This article shows a typical sequence of batches of refined products which can be transported in a crude oil pipeline: Crude oil—Diesel oil—Premium-grade petrol—Methyl tert-butyl ether (MTBE)—Premium-grade petrol—Aviation fuel (Jet A)—Diesel oil—Crude oil.
Once all the precautions have been taken to minimize contamination, each of the interfaces of the various batches is detected on arrival by ultrasound and colorimetry. The whole of each batch is distilled, treated over zinc oxide and conveyed to the corresponding finished product tank. The interfaces are themselves also distilled, treated over ZnO and conveyed to downrated product tanks while awaiting reprocessing.
The transportation of batches of naphtha is, however, not at all envisaged in this
Oil & Gas Journal
article.
The Applicant has now discovered that the transportation of naphtha between two batches of condensates in a crude oil pipeline makes it possible to collect, on arrival, a batch of naphtha which shows very little contamination and which is suitable for directly feeding a steam cracker without any processing and in particular without predistillation.
In contrast to the case of the transportation of the products which is described in the above-mentioned article in
Oil & Gas Journal
, where the said products are systematically redistilled on arrival in order to remove the contamination contributed by the crude oil, the Applicant has found that, surprisingly, the batches of naphtha transported between two batches of condensates did not need to be redistilled before feeding the steam cracker.
A subject-matter of the present invention is therefore a process for conveying a batch of naphtha in a pipeline, the prime purpose of which is to transport crude oil, characterized in that the said batch of naphtha, bracketed by batches of condensates, namely a head batch of condensate and a tail batch of condensate, is conveyed in the pipeline and, on arrival, the batch of naphtha is recovered between a point in time at the earliest at the end or substantially at the end of the passage of the head condensate
aphtha interface region and a point in time at the latest at the beginning or
Jaubert Jean-Marc
Niklaus Alain
Atofina
Millen White Zelano & Branigan P.C.
Norton Nadine G.
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