IMPROVE

THE U T I L I Z A T I O N

RAW-MATERIAL

RESOURCES

Ya.

and

G.

Sorkin

OF H Y D R O C A R B O N

Yuo I. B o k s e r m a n

UDC

665,6-403,004.8

The maximum conservation and prudent utilization of the light hydrocarbons present in as-produced crude oils represent a most important task in the national economy, As the cheapest and, in many chemical synthesis processes, an entirely irreplaceable raw-material source, light hydrocarbons and their resources to a certain extent determine the possibility and rate of growth of the c h e m ical and petrochemical industry. Whenlightliquid hydrocarbons are available in excess, they may be used for domestic and industrial purposes in cities, workers' housing projects, and agricultural areas and also for automotive fueI to replace gasoline, Such automotive use can give a considerable reduction in atmospheric pollul:ion, so as to improve the health conditions in cities, especially those that are saturated with automotive transporr In support of these statements the following data can be cited: In 1971, out of the total amount of hydrocarbon raw material used for pyrolysis and direct production of monomers by dehydration, about 48% consisted of light hydrocarbons, including pentane and isopentane. Hence, it is particularly important that losses of light hydrocarbons should not be allowed in regions of large oii fields, The concentration of large resources of light hydrocarbons in these regions makes it possible to organize the recovery of these hydrocarbons from the etudes in the oil fields, and to supply them to the areas of use by the most economical pipeline transport. This circumstance makes it possible, along with the reduction of transport costs, to build large petrochemical combines at the end points of such product pipelines, with blocks of large unit capacity for feedstock processing. This gives a considerable increase in the economic efficiency of such combines and reduces the cost of production. In the near future, districts of this type will include Western Siberia, where as early as 1975 the oii production should come to 125 million metric tons. Unfortunately, it must be stated that the scheme adopted by the Ministry of the Petroleum Industry for this district, that of degasification of the crude oil at the collection points at the dewatering temperature (cold separation) as the pressure is reduced in two or three stages to atmospheric, does not give complete conservation of lighthydrocarbon resources and may Iead to large losseso As can be seen from the data listed in Table !, in ~.he separation of Tyumen crudes at their dewatering temperature (20-40~ some 70~ of the light hydrocarbons through pentane remain in the crude. The separated crude contains about 15% of the ethane, 40% of the propane, 70~ of the n-butane, 65~ of the [sobu~.ane, 85~ of the isopentane, and 90-95% of the n-pentane, calculated on the initial contents of these hydrocarbons in the oil in place. Subsequently, during the transportation of the separated crude from the collection point in the oil field to the process unit of a refinery, along with terminal storage, losses are unavoidable; these are a conseqnence of loss of oil through leaks in equipment and pipelines and evaporation of light hydrocarbon~ from tanks, Any quantitative determination of these losses is extremely difficult since they depeud on many factors-the crude gravity and hydrocarbon composition, the climatic conditions at the tank farms, the tank design, the regime and time of pumping crude into the tanks, the regime of their operation, etc. It is an extremely complex problem to account simultaneously for the effects of all these factors; the most reliable information can be obtained only by a c c u m u Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 3, pp. 43-45, March, 1973.

9 1974 Consultants t~ureazz, a division of Plenum Publishing Corporation, 227 West 17th Street, New York, No Yo 10011~ No pa~ of this publication may be reproduced, stored in a retrieval system, or trc~nsmitted, in any form or by any me(ms, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission of the publisher~ A copy of this article is available from the publisher ]br $15.00.

219

TABLE 1. Residual Hydrocarbon Contents in Tyumen Crudes (Samotlor, Nizhnevartovskii) with Three-Stage Separation and Various Degassing Temperatures, % by Weight (from data of Giprotyumenneftegaz)

Separation temperature of crude oil in stage III Component 20

Ct

,

.

o

.

,

,

o

,

o

,

,

,

,

,

.

,

C2 . . . . . . . . . . . . . . . . C

8

.

iso-C

.

.

4

.

.

.

.

.

.

.

.

.

.

.

.

.

. . . . . . . . . . . . . . . . . . . . . . . . . .

n-C 4 iso-C 5 . . . . . . . . . . . . ,n-C 5. . . . . . . . . . . . . . . Recovery of Z Ct-C5 ResiduaIEC t C s in crude Vapor pressure after threestage separation, mm Hg at 38"C . . . . . . . . . . . .

~

0,3,~ 19,0 39,0 69,0 73,0 89,0 93,0 28 72

40 ~

70 ~

90 ~

0,25 10,0 37,0 64,0 72,0 87,0 90,0 31 69

0,0( 0,0t 16,0 45,0 48,0 75,0 84,0 49 51

0,00 0,00 10,0 27,0 35,0 59;0 66,0

1+ 38

latinga large volume of statistical and experimenta! data. Apparently, the complexity of setting up a longterm experiment explains the contradictions in data published [n various sources on the losses of oil and light fractions during storage in open tanks. Hence, we can name only certain average values for losses that have been obtained from analysis of the work of Nt[transneft [Scientific-Research Institute for Transport and Storage of Petroleum and Petroleum Products], VNIIUS, UFNII [Ufa Petroleum Scientific-Research Institute], Giprovostokneft [State Institute for Design of Installations of the Petroleum Industry of the Eastern and Southern Regions of the USSR], and individual authors. These losses together with transportation losses amount to 1.5-3.7% of the crude, depending on the degree of degassing and the vapor pressure (with tank storage times up to ,3 days).

The loss of 1.5%refers to degassed crude with a vapor pressure on the order of 300-400 m m Hg at 38~ the loss of a.7%refers to crude with a higher Note: Separation pressures 6 k g / c m z for stage I, 2.5 vapor pressure. It follows that, if the crude produced k g / c m z for stage II, and 1.05 k g / c m z for stage IIL in the districts of Tyumen Oblast [Region] is separated at low temperatures, the losses during transport and storage before it gets to the refinery processing units will amount to about 3.7 million metric tons in 1975, up to 80% of this loss relating to light hydrocarbons, including 30% pentane. * 1470

230

375

270

The loss of such an amount of hydrocarbon raw material, particularly isoparaffinic hydrocarbons that are widely used in the synthesis of monomers, can lead to major expenditures if these monomers are obtained artificially by a route through isomerization and dehydration of normal paraffins or hydrocracking of straight-run naphtha fractions of the crude. According to data cited in [1], the cost of producing 1 metric ton of isoparaffinic hydrocarbons by isomerization of normal butane and pentane in high-temperature isomerizatton on alumina-platinum catalyst IP-62 comes to 43 rubies, and that by hydrocracking straight-run naphtha fractions is 3'7 rubies: in contrast, the cost of recovery from a wide-cut stabilizer overhead or a natural gasoline in central gas fractionating units ranges from 13 to 26 rubies. If it is assumed that, of the total quantity of light hydrocarbons lost during transport and storage of Tyumen crudes, the C4 and C s isoparaffins constitute 20 and 15%, respectively, the losses of these hydrocarbons in 1975 will amount to 1.a million tons. If such amounts of isoparaffins are to be obtained by hydrocracking straight-run naphthas, the additional expenditures (calculated according to cost) will amount to 19.5 million rubies per year; to produce these materials by isomerization of n-paraffins will cost 27 million rubies per year. To achieve any significant reduction of loss of light hydrocarbons, as can be seen from the data of Table 1, the crude must be hot-separated in the oil fields, heating it to 70-90r the separated products being directed to gas processing plants located in the oil fields. Such a scheme of crude oil pretreatment, apart from the significant curtailment of light-hydrocarbon losses, will make it possible to increase the raw-material resources for gas processing plants and will increase their profitability, increasing their charge rate; most important, as already pointed ,Jut, it will premit concentration of large masses of hydrocarbon raw material at a few points with transmission of this raw material to petrochemical corn*According to the data of [4], in the West Siberian crudes processed in 1971 at the Omsk Petroleum Refining Combine, the average content of C1-C4 hydrocarbons was 1.8%. From this value and from the data of Table 1 on degassing of Tyumen crudes it can be calculated that the losses of Ct-C 4 hydrocarbons en route from the oil fields to the combine will be 2 . 5 % b y weight, i.e~ close to the value of S%that we have assumed as the average value for losses. 220

bines via overland product pipelines. Moreover, separation of crude at elevated temperatures may give considerable simplification and cost reduction in desalting the crude oil; the question of the need for desalting in the oil fields has been raised repeatedly in our press [2, 3]. It is natural that the inclusion of a hot-separation stage in the flow plan for crude oit pretreatment in the oil fields will require additional capital investmen~ and the expenditure of material resources. However, the sum of these capital investments and incremental expenses will be far below the amount wasted in light-hydrocarbon losses if the present scheme is retained-that of cold degassing at the accepted temperatures for dewatering the crude oil The opponents of hot separation consider that, in order to avoid losses of light fractions during transport and storage of crude oils that have been degassed at low temperatures, all equipment must be tight along the route of movement of the crude oil-either by instalIing floating or pontoon-roof tanks at main pumping stations of the overland pipelines and at the refineries or by equiping the tank farms with gas-equalizing systems, gas holders, and compressor stations for the collection of hydrocarbon gases and vapors evolved from the crude by "breathing" of the tanks. There is no argument that the creation of such equipment would be a radical measure. However, it should be kept in view that the West-Siberian etudes will be processed largely in existing refineries, equipped with conventionat tankage. Replacing these tanks with ftoaKng-roof or pontoon-roof tanks would be time-consuming and would require large amounts of m e t a l It would be at least as expensive to equip the tank farms with gas-equalizing systems, with the construction of gas holders and compressor stations. Moreover, the additional quantity of light hydrocarbons entering with the crude oil will require a considerable expansion of the existing gas fractionation units in these refineries, or the construction of new units. SUMMARY 1. The scheme adopted for the development of oil fields in Western Siberia and Tyumen Oblast [Region], with crude oil degassing at the dewatering temperatures, does not ensure conservation of the light hydrocarbons remaining in the crude d~ing its subsequent transport from the oil field to the process units and storage in oil terminals. 2. For the utilization of light hydrocarbons a hot separation stage at temperatures on the order of 70-90~ must be included in the crude oil petreatment scheme. 3. The installation of a hot separation stage for the etudes will considerably curtail the losses of light hydrocarbons, will increase the profitability of gas processing plants, and will make it possible to concentrate at a few points major resources of hydrocarbon raw material, with pipeline transmission of this material to petrochemical combines. 4. The application of a hot separation stage in crude oil degassing will give a considerable simplification and cost reduction in crude oil pretreatment. LITERATURE CITED 1.

2, 3. 4, 5.

I. S. Vol'fson, A. M. Okruzhnov, M. P. Merechenko, et al., Ekonomika, Organizatsiya Upravlenie Neftepererab, Neftekhim. Prom., No. 6 (1970). Ya. G. Sorkin, Khim. i Tekhnol. Topliv i Masel, No. 3 (1968). Ya. I. Pankovsldi, V. Z. Abrosimov, and Ya. G. Sorkin, Khim. i TekhnoL, Topliv f Masel, No. 10 (1969). V. A.Ryabov, E. V. Yakimenko, et al,, Khim. i TekhnoL Topliv i MaseI, No. 2 (1972). O. A. Makhizabekov, Neftepromyslovo~ Strokel'stvo, No. 3 (1969).

221