CHALLENGES FACING EUROPEAN REFINERS TODAY

Stefan G. Petrov, Lukoil Neftochim Bourgas AD

Antony M. Donov, Lukoil Neftochim Bourgas AD

Dicho S. Stratiev , Lukoil Neftochim Bourgas AD

 Received: 25.10.03; Cited: 05.12.03

Abstract:

The main refiners concern today is environmental legislation impact on their productivity and profitability. In May 2001, the proposals for Auto Oil II are finalized. These directives stated that the sulfur level in both gasoline and diesel fuels is to be 50 ppm by the year 2005, with some availability of 10 ppm sulfur fuel.

The 10 ppm sulfur level will become mandatory in 2011. It is estimated, that significant efforts and capital investments will be required in future to meet the directive for 10 ppm sulfur fuels.

The production of motor gasolines and diesel fuels is very dynamic process, strongly impacted by different factors as price, market, demand, environmental requirements and etc.  All these factors reflect on the quantity, quality and product range.  The persisting increase of need for  fuel qualities, dictated  by automobile industry and environmental requirements for atmosphere free of toxic components create serious problems for the refiners and their profits.

During  last ten years the public expectations for environmental clean fuels  have been maintained by continuous research on the total impact of fuels on environment. The governments in Europe and USA responded to these expectations by establishing  of stringent specifications for motor fuels. The current specification for sulphur content in diesel fuel for Europe is 350 ppm.

Diesel fuel with sulphur content of 50 ppm is defined as a diesel fuel with ultra low sulphur level (ULSD).   From year 2005  the whole diesel fuel in europe will be ULSD. Furthermore now in Europe there is process of implementation of specification for 10 ppm sulphur, which fuel is defined as diesel fuel, having sulphur content near to zero (NZSD). On May, 11^th 2001 EC Commission has accepted the submission for revision of Directive 98/70/EC concerning environmentally friendly specifications for gasoline and diesel fuel with 10 ppm sulphur in all EC member countries, starting from January, 1^st 2005. The main objective of this act is to reach sulphur level which will define the whole diesel fuel as NZSD. In October 2001 there was a suggestion,  made by the so called "green lobby" in European Parlament  to get down this starting date  to  year 2008. The present developments regarding this issue in USA are similar,  though  the objective there is 15 ppm sulphur. [1]

In UK the  transition to ULSD is already a fact. This was  accomplished by stimulating taxation, i.e. there was different taxation on ULSD and standard diesel fuel grade EN 590 (sulphur level 0f 350 ppm). In 1998  the rate of taxation for standard diesel fuel has been increased by 5 USD/barrel and in the beginning of 1999 by 7.5 USD/barrel. Therefore it is easy to explain why since the summer of 1999  all refiners  in UK are producing only ULSD.

Germany  will go  one step ahead of other European countries  by gradual  reduction  of sulphur content in diesel fuel to 10 ppm. This will be accomplished by imposing of stimulating tax of 2.5 USD/barrel, starting from November 1^st, 2001 for diesel fuel, containing 50 ppm sulphur.   The more important fact is that from January 1^st, 2003 this tax rate will be transferred on the diesel fuel with sulphur content of 10 ppm. There is no doubt that this pattern will be followed by the remaining European countries. The result from this activity  will be alteration of   50  ppm standard sulphur content  in diesel fuel  to 10 ppm after year of 2005.

Having started once,  the initiative  to reach the limit of 10 ppm sulphur content in fuels for a certain region  will  spread all over the total fuel market,  due to logistic difficulties for supply of the region with fuels, having  different sulphur content. There are expectations for  a high price to reach this level, particularly for  diesel fuels, where this  price  will be  presumably two times higher than the one for gasolines.  This problem will  be intensified also due to the expected  defficiency of diesel fuel and kerosene in the European market. 

In respect to the other  properties of diesel fuel, the requirements, established since January 1^st, 2000 are still in full validity:

- density at 15 °C                                                  not higher than 0.845 g/cm³;

- cetane number                                                    not lower than 51;

- boiling point of 95 % by volume                            not higher than 360° C;

- polycyclic aromatic hydrocarbons  content             not more than 11 %               

Now Lukoil Neftochim Bourgas is producing diesel fuel for export with sulphur content of 350 ppm, which is relevant to EN 590.  The coming new specifications  require immediate proceedings towards providing  for  production of new components for ultra clean fuels.

The reduction of sulphur content  in fuels can be achieved by different methods. In most cases these methods demand a certain way of hydrotreatment.   Usually this is accomplished via improvement of the operation of hydrotreatment and hydrocracking units mainly by means  of catalysts elaboration  and units revamping. [2]

At present time the emphasize is laid on policies, leading to lower capital investments,  i.e. increase of capacity and desulphurisation at minimum costs. At the same, in purpose to reach the Directive of 10 ppm sulphur in the fuels time we recognize the need of substantial capital investments.   The  persisting necessity of hydrotreatment, hydrocracking and dearomatization lead to extended hydrogen consumption. In many refineries the shortage of hydrogen  will become  а factual problem.

Notwithstanding of the imposed severe environmental restrictions  the main requirement is only  for sulphur reduction.   The suggestions for future regulations does not provide for mandatory change in the other parameters as cetane index, density, T 90 and total aromatics.  This is of great importance for the refiners, because the processes, used for sulphur reduction are may be the "cheapest ones".  

In conclusion,  one can say that regardless  the fact that there are existing  commercial technologies for production of diesel fuel with ultra low sulphur content, the final decision for the most adequate approach  or combination of those is very specific for each refinery.

Because of the unique combinations  of feedstocks, operating plants and demands in different markets it is not possible to point out a single approach, which is   the most appropriate  for a certain plant that can be the same for another one.

Table 1 shows a comparison between the different commercial   processes for production of diesel fuels, having sulphur content below 15 ppm. [3]

Table 1  Comparison between different commercial processes for production of diesel fuel with sulphur content below 15 ppm.

  * 1= Most efficient, 5 = most inefficient

**1= Easiest way, 5=Most difficult way

***1= cheapest, 5= most expensive

 In purpose to be able to select the optimum approach  for transition to diesel fuel with ultra low sulphur level, each refiner should find  solutions of the following particular issues:

1) Is it possible to revamp or modify  the existing plant equipment in purpose to meet the forthcoming specifications for diesel fuel  or it will be necessary to build a new plant ?

2) Will  be the modifications, realized today,  sufficient to meet the possible future specifications ?

3) Is there possibility for capital investment in  several stages  and to what extent ?

4)  What effect will have and the achievement of requirements for low sulphur content on the improvement of other important parameters of diesel fuel  and to what extent ?

Before considering the specific issues of the revamp it is essential  to review the process parameters, affecting the hydrodesulphurisation of diesel fuel  and main technologies or improvements, required for the production of ULSD.  The most important of these parameters  are the following [4 - 7]:

1) Application  of catalysts with higher activity  - Тhe employment of the most active hydrotreating catalysts or catalytic systems  can improve considerably  the desulphurisation performance of the existing hydrotreating units. For example  there is information  that  catalysts, developed by Akzo Nobel (KF757, KF848), Haldor Topco (TK573, TK 574) or Criterian, series "Century" and "Sentinel" has desulphurizing  activity higher  by 25 -75 %, compared to the ones, used in the second half  of  years of 1990.  Only the application  of better catalysts can reduce the existing 359 ppm of sulphur to 100 - 250, which is quite distant of the forthcoming  levels of 10 - 15 ppm.

2) Adjustment of the feed or final boiling point  - At first sight the most simple alternative seems to be the transition to crude with lower sulphur content, but one approach like this can lead to opposing results, due to higher concentration of sulphur compounds, having lower reactivity  in hydrotreated fractions. One of the most efficient way for production of ULSD is to use "easier feeds", as straight distillation kerosine or light gas oil. Many of the existing units can produce ULSD by means of "cutting off" of the sulphur compounds with lowest reactivity (for example dibenzothiofenes), contained in  feeds with higher final  boiling points  and in feeds with high aromatic level (as catalytic gasoil  from FCC). To be able to perform this it will be necessary to use  higher activity catalysts.

3) Operating temperature rising - The increase of  reactor operating temperature will have  direct impact  on the desulphurization ability  on existing unit.  This alternative  has  quite limited efficiency and requires additional costs due to the shorter cycle between  catalyst regenerations at higher temperatures.

4) Addition of reactor volume - The addition of reactor volume is another simple alternative,  requiring  moderate costs to improve the desulphurization ability of existing unit.  The  additional volume  can be implemented in series or in parallel  to the existing one.  The main considerations are hydraulic resistance of the system, space availability, additional piping and instrumentation,  all of which  can happen to  be a serious problem for adding of reactor volume.  The dense catalyst charging  can lead to increase of the quantity in the same volume by 15 % , but this, from other side can cause higher initial differential pressure in the reactor.

5) Increase of the hydrogen / feed ratio -  The increase of circulating gas  will have positive impact on the  catalyst activity. This will reduce the inhibiting action of H₂S and  NH_3.  and will increase the desulphurization  catalyst activity.  This impact is  too low. For example,  the increase of H₂/ feed ratio  with 50 %  can provide profit of only 5 - 8 °C  in catalyst activity.  It is necessary to emphasize that H₂/ feed ration depends on the compressor  hydraulics and capacity. 

6) Circulating  gas  H₂S removal - The installation of H₂S scrubber has two advantages.  First of all this increases the partial pressure of H₂ by means of H₂S removal. Furthermore, since H₂S inhibits  some hydrodesulphurization reactions, the scrubber improves the catalytic activity.

7) Operating pressure increase  - The total operating pressure  is defined by design pressure and very often it is not possible to increase it substantially.

8) Increase of H₂ partial pressure -  Whether total operating pressure in the reactor can not be increased, the expansion of  H₂ partial pressure is one efficient way for improvement of operation. This can be accomplished by  gas scrubbing  or improvement of fresh gas quality.  The fresh gas purity can be maximized by addition of PSA to the hydrogen source. 

9) Installation of two-stage reactor system  - One of the ways to reduce necessity of catalyst volume  is to install  second stage to the existing one stage hydrotreater. The second stage shall consist of second reactor and  scrubber or hot stripper  for removal or essential reduction of  H₂S and NH₃ levels in the treating gas to the second reactor. The catalytic system can be optimized (for example by employment of catalyst with precious  metal in the second reactor)  to improve of other  diesel fuel properties (cetane number, aromatic hydrocarbons).  In this case it will be  necessary careful consideration and comparison of the costs  for this alternative  and  the one, required for a new unit, or combination of other options.

10) Building a new unit -the most efficient, but the most expensive  solution. 

Several companies have developed processes for deep desulphurization and dearomatization of diesel fractions.

SYN- Technology - SYN/SAT license - result of the join efforts of Lummus Global Ins. and Criterion Catalyst Co. [8]

SYN/SAT [9] technology - for solving of hydrotreating problems by application of different catalysts and reaction technology of high efficiency. With this technology are solved problems from deep desulphurization to deep dearomatization  and cetane index improvement.

SYN SHIFT [9] technology - selective introduction of hydrogen in hetero-atoms, opening of rings and saturation of aromatic (mainly polar) hydrocarbons, and consequently reduction of final boiling point. The opening of rings leads to reduction of sulphur and nitrogen content.

The process SYN/SAT and SYN SHIFT combines  the technology of ABB Lummus Global Ins. for direct or counter-current contact of gas or liquid in reactors with several catalysts beds, using special SYN/SAT catalyst by Criterion Catalyst Co. [9]

In case of  HDS mode  there is production of diesel fuel with sulphur content below 0.05 % ,  but in HDS/HAD (hydrosesulphurization /hydrodearomatization)  mode the diesel fuel is with sulphur  of 10 ppm and 5% aromatic hydrocarbons.

Operating conditions.  Feed and product quality in SYN/SAT Unit 

Table 2

Feed and product quality in SYN SHIFT

Table 3 

Process HALDOR TOPSOE [8] -   Two-stage  (HDS/HDA) process for production for distilled products with low content of aromatic hydrocarbons.  This process provides for production of diesel fuel with content of aromatic hydrocarbons of </- 10 % by weight.

Processes of UOP [10] - One  and two-stage hydrotreating of diesel fuel in purpose to reduce  the level of sulphur and aromatic hydrocarbons. AR-10 - one-stage hydrogenation. AR-10/2 - two-stage hydrogenation (Table 4)

 Diesel fuel  quality by alternatives AR-10 and AR-10/2

Table 4

The two-stage diagram has been designed particularly for saturation of aromatics hydrocarbons (Figure 1). In the first stage the operating conditions  provides for feedstocks with sulphur content,  suitable  for the second stage,  where precious metal catalyst is used.  The hydrogen consumption rates are significant.

Technology of Linde Process Plants, Ins/ Process Dynamics, Ins [11]

This is new technology for production of diesel fuel with ultra low sulphur content (Figure 2). It is expected that this new process will be installed  as preliminary treatment of the feedstock for existing hydrotreating unit. In case of configurations, intended for  preliminary treatment stage the main objective  is more efficient utilization of hydrogen. In this case the existing conventional reactor  will have very little work and it's main function will be final treatment.  The new technology employ completely new approach  for introduction of hydrogen in the reactor. This approach permits much higher space velocities, compared  with the conventional hydrotreating reactors.  The process will be  with  conventionally used catalysts.  The investigations shows  sulphur content of 8 ppm  in the produced  hydrotreated diesel product, at sulphur content in the feed  1-2 % by weight.

This new technology is  with several advantages:

 ·       Low capital cost

·       No substantial modifications in the operation of existing HDS units, whenis installed as preliminary treatment stage.

·       Improvement of cetane index

·       Increase of capacity without modification of existing equipment

There is another significant issue in regard to emissions of  motor flue gases. This issue nowadays is subject of very severe requirements.

The question  for solving problems to reduce the smoke of the flue gases is under discussions.  Consideration  are given to  many different possibilities, which will be applied independently or in combination:

·       Modification of motors;

·       Employment of desulphurization and dearomatization in the refineries;

·       Use of fuel additives;

·       Improvement of lubricating oils quality.

Since we are producers of diesel fuels  we are interested in the methods for solving the problems, related to the  emmissions of flue gases from diesel motors.

 - Reduction of sulphur content - there are requirements for hydrodesulphurisation and improvements of the catalytic systems.

  - Density reduction  - this can be achieved  by reduction of final boiling point  of diesel cut, but this is related to lower yield of light oil products, on the account of the heavier ones.  It obvious that  the economy of the refineries  will suffer in case of reduction of density.

    - Cetane number increase  - information, provided by Ethyl shows that the addition of 0.1 % of additive for cetane number  "HITEC4103" will rise the cetane number with 4 units.

We are interested in the additives for diesel fuel. The market offers the following type of diesel fuel additives:

            - additives to increase the cetane number;

            - additives to improve the combustion process  in diesel  motors;

            - antioxidants;

            - corrosion inhibitors;

            - demulsifiers (preventing turbidity, caused by presence of moisture);

            - deactivators mor metals;

            - additives, improving the lubricating properties;

            - additives to ensure easy  flowing  at lower temperatures;

            - biostatic additives;

            - deodorizing additives;

            - antifoam additives;

            - detergents dispersion additives;

Usually  in the market are available  ready packages, containing components, that improve several fuel properties.

 Table 5 shows several additives for solving some problems, related to handling,  storage and distribution of diesel fuel.

Technologies for additives application

Table 5

The main chracteristic of the motor fuels properties is their tendency toward self- ignition, which usually happens in the period of self ignition  detention, i.e.  the time from the moment of fuel injection  to it's ignition. The generally accepted parameter for diesel fuel  igniton is the cetane number.

It is necessary to emphasize the favorable  influence of the additives, improving cetane number on the environmental characteristic  of diesel fuel. There are several companies, offering cetane number additives as Adibis ADX743, Ethyl - HITEC 4103 and others. This types of additives reduce the flue gases emissions, the white smoke, noise and at the same time improves the motor starting at low temperatures, the time, required for motor heating and etc.

(Figure 3). The measurements indicates reduction in  hydrocarbons, CO, NOX and particles emissions. The nitrogen oxides NOX can be reduced by decrease of aromatic compounds  or by increase of cetane number. The calculations shows, that the approach with cetane number improvement can be ten times more profitable. The particles reduction can be three times pore economical with cetane number additive.