ECONOMICS

INCREASING

THE ECONOMIC

EFFICIENCY

M. M. B u z o v k i n , K. K. B y k o v , L. F. M e r o n ' o - P e l i s e r , Y u . I. C h e r n y i a n d A. P . S h a f i r

O F REFINERY DESIGN UDC 66.013.5 : 665.63

The use of mathematical economics methods in the design and reconstruction of petroleum refineries makes it possible to investigate the influence of many factors on the schemes for development of existing and new refineries, and to obtain a solution that may be considered to be optimal under the conditions as defined [1]. Here we ar e presenting the principles of methodology of optimal design of schemes for the development and expansion of existing and new refineries. In developing an optimal flow plan for petroleum processing in a refinery, the following must be d e t e r mined: the fractional share of secondary refinery processes, with due regard to the given demand for p e t r o leum products with r es pe c t to product mix and quality; the optimal variant for compounding commercial p e troleum products; the dimensions of the commercial product tank farm for storing the in-transit r e s e r v e s of petroleum products, with due regard for seasonal variations in consumption; and the technoeconomic indices of petroleum refining as a whole in the plant during the plan period. As a result of interaction of a large number of factors affecting the petroleum processing flow plan, a region of freedom is formed, within which the individual param et ers in the refinery processing scheme may assume various values, thus giving r i s e to many variants in the prospective pla,~. The number of variants in the plAn~ is determined by the possibilities of change in structure of product output in the plant and by the possibility of using different variants and regimes in the rn~n,,facturing processes. The basic task of optimization is the development of the economically most effective scheme for p e t r o leum processing in the particular refinery being designed, while fulfilll-g requirements on production volume for all products of the assigned quality. Such a statement of the problem sets the sequence for determining the most effective refinery processing scheme. F i r s t Stage. The economic efficiency of various refining processes is determined in relation to the demand for petroleum products. The mathematical model describing the refinery process flow plan includes alternative p r o ce s s es that will produce the required q,mntity of commercial petroleum products and will fulfill the product quality requirements [2]. Also included in the mathematical model are limitations on r e s o u r c e s of production factors that a r e governed objectively by external or internal circumstances. The production factors that are satisfied without limitation in examining local problems and those that do not influence the refinery processing scheme a r e not considered at all in carrying out the calculations. As a result of the calculations in this f i r s t stage, the following must be obtained: the process scheme for petroleum refining in this particular refinery, with due regard to the assigneddemand for petroleum products with respect to product mix and quality during the planning period as a whole; the capacity of secondary processes included in the optimal plan; the basic teclmoeconomic indices for petroleum processing for the refinery as a whole during the planning period. Second Stage. The most effective petroleum processing flow plan is calculated with regard for variation in seasonal consumption of petroleum products. The seasonal variations reflect the actual economic activity and dynamics of petroleum product consumption. F o r example, in the spring and summer period (in comparison with fall and winter), we find an increase in gasoline consumption in connection with the g r e a t e r use of passenger automobiles; an increase in diesel fuel consumption in connection with the opening of r i v e r and sea navigation, sowing and harvesting operations in agriculture, etc; and a decrease in consumption of boiler fuel in boilers and electric power stations. The inclusion of a dynamic factor in the problem requires the application of appropriate m a t h e m a t i c a l economics models. F o r this purpose, the planning period is broken up into a number of seasons, and a model is constructed for each season. The models or blocks thus obtained are combined in an overall model b y m e a n s Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 5, pp. 22-26, May, 1979.

334

0009-3092/79/0506-0334 $07.50 9

Plenum Publishing Corporation

TABLE 1. E x a m p l e of E n t r i e s in Data B!~nk for Process, Unit Des/gna~on af ml~

Ualt number

D ~ c d a a of pcoduct ~flization

Dedgaa~on of lncomtng mean~

Ovcr~dl for plan(

cut

Hydml~e~ing

03

r

~30-350"C

cul

8

2 l.~'4gl

~

=

"" i

Nc,c n b ~ ~f/ncon'dng ~ e , ams

Numbex of ~dt

I1 .oo t.t0., IOllO21

1.1.1 1o41o61

l~

I~176 I

I

NumbcBc/"incomb~

oo

IoII121

I-I~

54

5S

55

..o

55

1221291

Dedgna~ion

F ~

Hyd,rosen-l~chga~

"c2 I-~176

1 I

230,-350"C c~'l

__1_2t

_111 --|

Naphtha (ove/head)

- - I --I

I i --I

Hyd~'o~en ~d,~d c

i0 ~

J 0

Payloll

Capital/nve~nenz

pu~pl~g c~pacit7

o3o5

I o.o551

-!~ io. , i 0

03PR

~

i

~

I1,, _•

of a number of linking r e s t r i c t i o n s . In o r d e r to account for s e a s o n a l variations in consumption of petroleum products, we m a y c o n s i d e r either a t h r e e - p e r i o d s y s t e m (such as winter, s u m m e r , and winter) or a t w o period s y s t e m (such as winter and s u m m e r ) with a t r a d e - o f f of r e s e r v e s of p e t r o l e u m products between the periods [3]. The s e a s o n a l consumption of p e t r o l e u m products c a u s e s underloading or idle time for p r o c e s s units in certain periods and m a k e s it n e c e s s a r y to s e t up an additional c o m m e r c i a l product tank farm to s t o r e r e s e r v e products c a r r i e d o v e r f r o m one period to the other. The optimal p e t r o l e u m p r o c e s s i n g s c h e m e m a k e s it p o s s i b l e to account for the s e a s o n a l variations in p e t r o l e u m product consumption. Coordination of the solutions in both s t a g e s is achieved by a s s i g n m e n t of limitations for the second stage with r e s p e c t to petroleum p r o c e s s i n g capacities f o r the plnnning period as obtained in the first stage. A s a result of the s e c o n d - s t a g e calculations, the following should be obtained: a rational flow plan for p e t r o l e u m p r o c e s s i n g in the r e f i n e r y in the different periods in which it is functioning, with due regard to the given demand for p e t r o l e u m products with r e s p e c t to product m i x and q , ~ l i t y during the individual periods; the loading of the s e c o n d a r y p r o c e s s units in each period and as a whole, without regard to integral change in their capacities; variants in compounding of components to obtain c o m m e r c i a l products in each of the periods being examined; the optimal s i z e of the c o m m e r c i a l tank f a r m f o r storage of r e s e r v e p e troleum products c a r r i e d o v e r f r o m one period to the other; m o r e p r e c i s e l y defined t e c h n o e c o n o m i c indices with r e s p e c t to p e t r o l e u m p r o c e s s i n g for the plant during the planning period. On the b a s i s of the r e s u l t s obtained, the p r e v i o u s l y obtained optimal flow plan for the refinery is now c o r r e c t e d and adjusted. C o m p u t e r i z e d calculations a r e aimed at finding an effective p r o c e s s flow plan for petroleum refining under the conditions of satisfying all limitations with r e s p e c t to f e e d s t o c k r e s o u r c e s and the structure and quality of the p e t r o l e u m products manufactured. A s a c r i t e r i o n of e f f e c t i v e n e s s it is n e c e s s a r y to u s e a m a x i mum in the effect (savings) obtained. Under conditions of limited r e s o u r c e s of crude oil, growing consumption volume, and i n c r e a s e d production v o l u m e s , w e may also adopt as such a criterion the m a x i m i z a t i o n of output of that p e t r o l e u m product for which utilization is the m o s t favorable. However, the application of such a c r i t e r i o n is difficult at p r e s e n t b e c a u s e of the lack of any index for total efficiency in utilizing manufactured petroleum products in the national e c o n o m y . Hence, as a c r i t e r i o n of efficiency in the proposed t w o - s t a g e method w e used a m i n i m u m in prorated c o s t s for p e t r o l e u m p r o c e s s i n g . By this m e a n s w e achieve c o n f o r mance of this particular and s p e c i a l c r i t e r i o n of the p r o c e s s flow plan in the r e f i n e r y being designed and the o v e r a l l c r i t e r i o n for growth and siting of the petroleum refining industry in the country as a whole.

335

Evidence was presented in [4] for the convergence of calculated r e s u l t s when using multistage models, a special case of which is the proposed complex. The operating and capital costs a r e calculated on the basis of existing p r o c e d u r e s used by our i n d u s t r y - b r a n c h design and s c i e n t i f i c - r e s e a r c h institutes. The input data f o r construction of the m a t h e m a t i c a l - e c o n o m i c s model a r e as follows: 1) D i s t r i c t o r a r e a in which r e f i n e r y construction is planned. 2) Refinery capacity, overall product mix during the planning period, and seasonal product mix. 3) Quality of crude or mixture of e t u d e s entering the r e f i n e r y f o r processing. 4) Quality of basic products manufactured at the s t a r t of r e f i n e r y construction, and possible changes in quality r e q u i r e m e n t s in the future. These data, in the s y s t e m s approach to optimization of r e f i n e r y flow plans, axe the r e s u l t of o p t i m i z a tion of the plan for growth and siting of the petroleum refining industry for the country as a whole. In o r d e r to construct the model, the following a r e also n e c e s s a r y : 5) An approximate p r o c e s s flow plan, Including all possible manufacturing p r o c e s s e s needed to produce the given product mix, r e p r e s e n t e d in s e v e r a l variants and r e g i m e s . 6) Material balances for all p r o c e s s units included in the original s c h e m e for the r e f i n e r y being designed, applicable to different types of crude oil being p r o c e s s e d . Material balances and indices with r e s p e c t to new manufacturing p r o c e s s e s a r e assumed on the basis of p r e l i m i n a r y s c i e n t i f i c - r e s e a r c h development, design data, o r information f r o m the l i t e r a t u r e . 7 7) Standard or specification r e q u i r e m e n t s on quality indices of components and principal c o m m e r c i a l products obtained by compounding. H e r e we r e f e r in the case of gasoline to a knock r e s i s t a n c e , distillation curve, sulfur content, and lead and a r o m a t i c hydrocarbon contents; for diesel fuel we r e f e r to the cetane n u m ber, distillation curve, sulfur content, and viscosity; for boiler fuel, we r e f e r to the v i s c o s i t y and sulfur content. In the case of o t h e r petroleum products OCt fuels, coke, ete), which a r e not produced by blending diff e r e n t components, the standard or specification r e q u i r e m e n t s on quality a r e not taken into account, since they must be fulfilled by starting with r e q u i r e m e n t s on the feedstock quality and p r o c e s s technology. When taking into account the influence of seasonal variations in petroleum product consumption on the s c h e m e of petroleum processing, data a r e needed on cb.nge in product quality as a r e s u l t of storage. 8) Technoeeonomlc Indices with r e s p e c t to all p r o c e s s e s included in the r e f i n e r y flow pl.n; calculated per unit of feedstock f o r the corresponding p r o c e s s unit when operating on different feedstocks and under different conditions. H e r e we r e f e r to the consumption of the following m a t e r i a l and e n e r g y r e s o u r c e s p e r ton of f e e d stock p r o c e s s e d : e l e c t r i c e n e r g y (kW-h); fuel (tons); steam and hot w a t e r (Gcal); f r e s h and r e c y c l e d water (mS); catalysts, reagents, and basic and auxiliary m a t e r i a l s (rubles); cost for i n t r a - p l a n t pumping (rubles). In addition, the following a r e used as technoecenomic indices: a) N o r m s for amortization and routine maintenance that a r e applicable in a c c o r d a n c e with the existing i n d u s t r y - b r a n c h n o r m s (in fractions of the value of capital assets). The l a t t e r a r e d e t e r m i n e d f r o m the calculated capital costs for the unit and an average percentage of the nonvolume costs c h a r a c t e r i z i n g the given plant. b) Costs involved in underutilization of c o m m e r c i a l tank f a r m (rubles). c) Operating, p r o r a t e d and capital costs f o r p r o c e s s equipment and g e n e r a l plant facilities f o r the r e f i n e r y as a whole during the planning period a r e calculated on the basis of the listed information. The d e p a r t m e n t a l and offsite costs a r e also calculated from the average p e r c e n t a g e of total costs f o r p r o cessing, without the value of feedstocks and reagents. 9) Typical capacities of the units for s e c o n d a r y p r o c e s s e s in petroleum refining. F o r effective utilization of this methodolo~] of optimal design of p r o c e s s i n g s c h e m e s in the development of existing and new r e f i n e r i e s , it is proposed to use a computer software s y s t e m consisting of the following p a r t s : p r o c e s s data bl~nk; packets of p r o g r a m s of linear p r o g r a m m i n g L P - 4 0 0 entering into the software of the ICL computer o r a packct of applied p r o g r a m s of mathematical p r o g r a m m i n g entering into the software of a r e g u l a r - s e r i e s computer; p r o g r a m s for setting up accounts according to the r e s u l t s of the computerized calculation. The p r o c e s s data blank is intended for r e c o r d i n g information on the p r o c e s s units and the units for

336

blending p e t r o l e u m products, and also f o r information on the connection between units. In Table 1 we show an example of filling in the p r o c e s s b l . n k in the c a s e of the unit f o r h y d r o t r e a t i n g a d i e s e l fuel cut in a r e f i n e r y c u r r e n t l y being designed, p r o c e s s i n g c r u d e of oil of the S a m o t l o r type. The columns of the p r o c e s s data blank a r e divided into s e c t i o n s with c e r t a i n designations: the s t r e a m s of p e t r o l e u m p r o d u c t s obtained in the unit (in our example, 03) f r o m other units in the p r o c e s s i n g s c h e m e (section I); units and p r o d u c t s w h e r e the p r o d u c t s manufactured in the given unit can b e used (section ID. In the f i r s t two lines of the c h a r t ' c o d e s of columns," with the designations " n u m b e r of unit" and " n u m b e r s of incoming s t r e a m s , " t h e r e a r e s y m b o l s signifying the following: the n u m b e r of the unit under c o n s i d e r a t i o n (03) and the n u m b e r of the incoming s t r e a m of p e t r o l e u m product entering f r o m other p r o c e s s units (for section 1); and the n u m b e r of the unit f o r c o m m e r c i a l product to which the product manufactured in the unit u n d e r c o n s i d e r a t i o n is directed, and the n u m b e r of this product in that unit in which it is produced (for section H). In the two o t h e r lines of column codes " n u m b e r of unit ~ and " n u m b e r s of output s t r e a m s " t h e r e a r e s y m b o l s with the following r e s p e c t i v e meanings: n u m b e r s of the units f r o m which the v a r i o u s types of feedstock e n t e r the unit under consideration (03), and n u m b e r s of the s t r e a m s of p e t r o l e u m p r o d u c t s under which they a r e designated in those units (for section I); and the n u m b e r s of the unit under consideration and the output s t r e a m of p e t r o l e u m product obtained in this unit (for section I1). The n u m b e r entered in the f i r s t column in section I does not c a r r y any i n f o r m a t i o n on the connection with o t h e r units, since in the model this column is a v a r i a b l e d e t e r m i n i n g the sum of feedstock of the unit. In the example under consideration, the f i r s t two s y m b o l s 03 show that this column p e r t a i n s to a unit with the n u m b e r 03. The other six s y m b o l s a r e a r b i t r a r y ; in our example, five of t h e m a r e zero, and the l a s t symbol, C, ifidicates that the column is a s u m m a t i o n . In the lines of this column a r e written the coefficients of the m a t r i x model showing the f r a c t i o n s of r e a g e n t s r e l a t i v e to the total feedstock, which is taken as unity, f o r the section "entering," and in the lines of the sections "obtained," they indicate the f r a c t i o n s of the output p r o d u c t s of the unit. The f r a c t i o n s of the input s t r e a m s a r e written with a m i n u s - s i g n , and the f r a c t i o n s of the output p r o d u c t s a r e written with a p l u s - sign. The codes of the lines consist of four symbols, of which the f i r s t two indicate that the line p e r t a i n s to the given unit (in the example, 03). The last two s y m b o l s f o r the section "entering" a r e a r b i t r a r y , and in the example a r e designated as CI, C2, and C3; f o r the section , o b tained," t h e s e two s y m b o l s a r e sequence n u m b e r s of the output products and the c o s t indices of the unit. The line " c a p a c i t y " is coded in the e x a m p l e as 03PR (where 03 is the n u m b e r of the unit, and PR is an a b b r e v i a t i o n of the word "productivity"). The line " l o s s e s " does not have any s y m b o l e n t r y defining a p p l i cability to the unit under the n u m b e r 03, since this line is c o m m o n f o r all units of the r e f i n e r y , and its code c o n s i s t s of six Latin l e t t e r s making up the word " P o t e r i . " * Thus, the p r o c e s s data blank r e p r e s e n t s the m a t h e m a t i c a l model of the unit and m a k e s it p o s s i b l e to unify all information on the manufacturing p r o c e s s e s in a c c o r d a n c e with a single principle, thus reducing the l a b o r r e q u i r e d in setting up a m a t h e m a t i c a l model f o r a r e f i n e r y p r o c e s s i n g s c h e m e . The p r o g r a m for f o r mulating the accounts in a c c o r d a n c e with the r e s u l t s of the calculation p r o v i d e s f o r output of data in the f o r m of tables in a c c o r d a n c e with the f o r m adopted in setting up the technoeconomie b a s i s of the s c h e m e f o r d e velopment of r e f i n e r i e s in the design or r e c o n s t r u c t i o n stage. The s o f t w a r e f o r computational investigations in selecting the o p t i m a l p r o c e s s s c h e m e f o r r e f i n e r i e s has been worked out in a n u m b e r of p r a c t i c a l e x a m p l e s . According to p r a c t i c a l data, the l a b o r costs in setting up a m a t h e m a t i c a l model f o r the calculation of m a t e r i a l balance, plus checkout of the p r o g r a m in a cemputer, when c o m p l e t e information is available with r e s p e c t to the plant under study, amounts to about 20 m a n - d a y s for a l a r g e r e f i n e r y ; the l a b o r cost in c a r r y i n g out a c o m p u t e r i z e d calculation in a c c o r d a n c e with a m a t h e m a t i c a l model that has a l r e a d y been checked out is about 1 m a n - d a y . Here, with a single run, s e v e r a l v a r i a n t s can be calculated for the r e f i n e r y flow plan that is being modeled. The d i r e c t computing t i m e in a t h i r d generation c o m p u t e r in which the software s y s t e m has a l r e a d y been calculated is 1 0 - 1 5 min. Thus, the e f ficiency in u s e of a c o m p u t e r to r e d u c e l a b o r c o s t s in calculating m a t e r i a l b a l a n c e s in l a r g e r e f i n e r i e s is quite evident. M o r e o v e r , the u s e of this set of m a t h e m a t i c a l - e c o n o m i c s models, along with a c o m p u t e r , m a k e s it p o s sible to obtain an o p t i m a l solution of the p r o b l e m as it is s e t up, in a c c o r d a n c e with a c r i t e r i o n that is s e lected in advance; this is actually i m p o s s i b l e when using t r a d i t i o n a l methods of calculation. *Codes entered in the c o m p u t e r c o n s i s t s solely of n u m b e r s and L a t i n - a l p h a b e t l e t t e r s . is a t r a n s l i t e r a t i o n of the R u s s i a n word meaning " l o s s e s ' - T r a n s l a t o r . ]

[The word "poteri"

337

LITERATURE .

2. 3. 4.

CITED

B. P. Suvorova (ed.), Mathematical Methods and Models in planning for the Petroleum Refining Industry [in Russian], Nanka, Moscow (1967). L. F. M e r o n ' o - P e l i s e r and Yu. L Chernyi, l~kon. Organiz. Uprav. Neftepererab. Neftekhim. Promst., No. 9, 14-16 (1973). L. F. M e r o n ' o - P e l i s e r and Yu. I. Chernyi, Avtomat. Kontrol.-Izmer. Pribory, No. 11, 2-6 (1975). I. Ya. Vakhutinskii and L. M. Dudkin, Izv. Sib. Otd. Akad. Nauk SSSR, Set. Obshchestv. Nauki, Issue 3, No. 11, 47-53 (1973).

ECONOMIC

EFFICIENCY

TERT-BUTYL

ETHER

AUTOMOTIVE

GASOLINE

OF UTILIZATION

AS A C O M P O N E N T

OF M E T H Y L OF H I G H - O C T A N E

L. M. N o r e i k o , S. A. F e i g i n , E. D. R a d c h e n k o , A. V. A g a f o n o v , a n d G. P . K l i s h i n a

UDC 62.- 632.001.4

It is well known that isoparaffinic hydrocarbons (isopentane, and, more importantly alkylate) play a major role in the production of high- octane automotive gasolines, i.e., those with octane numbers of 93 and up by the r e s e a r c h method. The largest q~j.ntities of these hydrocarbons are required for the production of unleaded gasolines. However, the raw material r e s o u r c e s for alkylate production are inadequate, particularly the r e s o u r c e s of Imtylenes. In view of this shortage, along with the increased emphasis on environmental protection and the petroleum shortage, it has been proposed that alcohols and ethers that can be obtained from nonpetroleum raw materials should be used as high-octane components of automotive gasolines. These products have high octane numbers, with particularly high blending octane numbers (115-120), so that high-octane gasolines can be produced without ethyl fluid; also, the emission of toxic gases to the atmosphere can be curtailed considerably. In a number of countries, methyl alcohol and methyl t e r t - b u t y l ether (MTBE) have been proposed as gasoline components. Tests on gasolines with methyl alcohol contents up to 15% have shown that the specific consumption when using such blends is some 8-10% higher than with traditional gasolines. Also, such gasoline will separate into layers. These shortcomings present a considerable b a r r i e r to the widespread application of alcohols. Tests on MTBE as a gasoline component, both in the USSR and in other countries, have demonstrated that this product has considerable promise. The specific consumption of gasoline blended with MTBE is the same as that of ordinary gasolines. The MTBE mixes readily with t h e o t h e r components of gasoline in any proportions and is almost insoluble in water, so that MTBE-blended gasolines do not separate into layers when water is present. They a r e stable during storage, and give higher efficiencies than conventional gasolines at low speeds, as well as good c ol d -st art i ng characteristics. When such blends are used, no vapor lock is encountered, no icing takes place, and corrosion is absent. In some countries, MTBE is already being used as a gasoline component [1]. In the USSR, extensive tests a r e being performed on gasolines blended with ethers [2, 3]. In the present article we a r e reviewing results of economic studies in the field of the production and utilization of MTBE and e t h e r - containing gasolines of the AI- 93 grade. The demand for MTBE is defined by its use as a replacement for alkylate and isopentane in producing AI-93 gasolines, and also for increasing the output of unleaded AI-93 gasoline; the future demand for MTBE can be estimated in t e r m s of millions of tons. Such a demand can be satisfied after organizing MTBE production in process units with high individual p r o duetion capacities. The raw materials for the production of MTBE are isobutylene and methanol Isobutylene is present in butane-butylene fractions from gas fractionation units and in the b u t y l e n e - isobutylene fraction obtained in Translated from Khimiya i TekhnologiyaTopliv i Masel, No. 5, pp. 26-28, May, 1979. 338

0009- 3092/79/0506-0338 $07.50 9 1980 Plenum Publishing Corporation