upgrade refinery residuals into valuable products

The MOL Plc Danube refinery in Szazhalombatta, Hungary, faced several operations challenges: 1) declining residual fuel-oil markets and 2) a need to

increase clean transportation distillates output. The refinery considered a residue upgrading project that would increase conversion of crude oil to distillates, eliminate residual fuel oil yields and improve refinery margins. After study-ing alternative paths, MOL selected delayed coking as the primary conversion process.

In 1997, the MOL board resolved to implement a resi-due upgrading project based on delayed coking. This proj-ect also included new facilities for a delayed coker, hydro-gen plant and sulfur recovery unit, as well as, revisions to the distillate hydrotreater and conversion of a vacuum gasoil (VGO) hydrotreater to a licensed mild hydrocracker.

Upgrade refinery residuals into value-added productsA European refiner effectively uses delayed coking to exit residual fuel-oil market

M. KOVAC and G. MOVIK, MOL Plc Danube Refinery, Szazhalombatta, Hungary; and J. D. ELLIOTT, Foster Wheeler USA Corp., Houston, Texas, US

Driving forces for change in refiningRefiners are under more pressure to improve profitability

while maintaining or increasing market share. Driving forces within the refining industry include:

• Increasing demand for clean, distillate transportation fuels

• Higher crude oil costs, especially for light, sweet crudes• Declining heavy residual fuel-oil markets.

Residual-oil conversion projects can be effectively used to meet these needs. Primary conversion processes commonly evaluated for such purposes are:

Noncatalytic • Visbreaking • Solvent deasphalting • Delayed coking • Flexicoking or fluid coking• Partial oxidation

Catalytic• Ebullated-bed hydrocracking• Slurry-phase hydrocracking• Residual fluid catalytic cracking.

All of these processes have good features and specific appli-cations. Thus, the refiner must evaluate these options and con-version routes, and select the best method for the refinery’s

specific situation. Delayed coking is the preferred choice for many residual conversion projects. This processing method offers several benefits:

• Complete conversion of residue feedstocks and elimina-tion of residual fuel-oil production. Demetallization is nearly 100%.

• Ability to process very heavy residue streams with high metals, carbon residue and asphaltenes

• Operational flexibility to handle a broad range of feed qualities and adjustable product specifications

• Ability to produce a broad range of liquid distillates that can easily be incorporated into the refinery processing scheme to produce clean distillate transportation fuels

• Moderate capital investment• The process has been commercialized for a long time and

is well supported by specialty equipment vendors, chemical suppliers and third-party consulting firms

• Byproduct fuel-grade coke is easily salable at positive net-back prices

• Modern delayed coker designs are proven to be energy efficient, environmentally friendly and intrinsically safe

• The semi-batch nature of the delayed coker facilitates easier operations and provides schedule flexibility due to equipment failures

• Operating and maintenance costs are reasonable, and peri-ods between turnarounds can be as long as five years.

The MOL Plc Danube refinery, Szazhalombatta, Hungary, with the new delayed coker complex.

FIG. 1

SPECIALREPORTJune 2006 issue, pgs 57 –62Used with permission.www.HydrocarbonProcessing.com

Reprinted from:

Article copyright © 2006 by Gulf Publishing Company. All rights reserved.

HYDROCARBON PROCESSING JUNE 2006

SPECIALREPORT PROCESS AND PLANT OPTIMIZATION

The project goals were:• Provide an exit from the uncertain heavy fuel-oil market• Strengthen competitiveness and increase crude conversion

level• Improve environmental conditions.Proposals from qualified delayed coker licensors were solic-

ited and evaluated. An experienced delayed coking technology licensor was selected. The technology licensor would provide the delayed-coker technology, supply the coker heater, and sup-port training and commissioning efforts for unit startup. Detail engineering and construction was to be provided by a local contractor with support from the technology licensor for coker-specific issues (Fig. 1).

Design basis coker. The coker was specified to process 3,250 m3/d (20,442 bpsd) of blended vacuum residue. In addition to vacuum residue, the coker was designed to process other extrane-ous streams:

• 7,000 metric ton/yr (mtpy) of refinery sludge on an intermittent basis

• 26,400 mtpy of propane/propylene from the FCC unit.

Products obtained from the delayed coker included:• Treated coker fuel gas (FG)• Propylene (99.5% purity)• Propane• Treated C4 LPG• Light coker naphtha (LCN)• Heavy coker naphtha (HCN)

New delayed coker, side view.FIG. 2

��

��

��

Product yields of the delayed coker-design vs. actual.FIG. 3

��

��

��

Variance in sulfur levels of coker products-design vs. actual.

FIG. 4

��

��

��

Specific gravities of coker products-design vs. actual.FIG. 5



• Light coker gasoil (LCGO)• Heavy coker gasoil (HCGO)• Fuel-grade coke.

Features of delayed coker design. Processing objectives dictated that the delayed coker operating conditions be configured for low coking pressure at 1.03 BarG in the coke drum and ultra-low recycle ratio at 5% liquid volume to produce maximum clean distillates and minimize fuel-grade coke production (Fig. 2). With this style of operation, coke production was limited to 230,000 mtpy. The green coke was slated for sale to the local power and cement industries. Table 1 summarizes the design features for the delayed coker.

During detail design, MOL elected to add several features:• Advanced hydraulically operated coke drum unheading

systems• Advanced coke cutting system with hydraulically operated

motors for the drilling system• Enclosed coke transport and storage using environmentally

friendly tubular conveyors and a coke storage “barn”• Advanced process control and operator simulation through

the DCS. Commissioning and startup. The preparation for startup

involved a team effort between MOL and technology licensor in various activities.

Operating guidelines. The licensed package was supplied with operating guidelines from which MOL was able to develop their operating instructions.

Training. During the summer of 2000, MOL was provided with classroom training and additional third-party training at an existing delayed coking facility.

Precommissioning and commissioning. In May 2001, the tech-nology licensor’s lead operations advisor was sent to Szazhalombatta

to provide assistance with precommissioning, unit checks, vendor coordination, onsite training and operating instruction support. In mid-summer, he was joined by three additional operations advisors and an instrument engineer to complete the commis-sioning effort.

Unit startup and test run. Following strong client-licensor teamwork in preparing for the startup, the unit was started up on Oct. 6, 2001, without incident at 80% capacity. The unit capacity was increased to 100% on October 10 with all products “on spec.” About three weeks later, the coke-drum switch valve experienced an unforeseen and unusual metallurgical failure. While the valve was repaired by the vendor on an expedited basis, the unit was idled for two weeks and restarted on November 14. A capacity test at 110% was completed on November 22. The performance guarantee test was done on December 6, 7 and 8. All guarantees were met.

Delayed coker performance. During evaluation, it was determined that the coker feedstock was higher in carbon residue than the design feed. Table 2 summarizes the variance of the feed and change in quality.

A comparison of the design and evaluation yields is shown in Fig. 3. The design yields and product properties were based on a proprietary model for delayed coking. Pilot-plant runs were not required. The resulting yields and product properties had small variances from the general model after feed differences are considered.

Regarding the actual operating yields, note the higher coke yield as a function of the heavier-than-design feedstock. One comment on the yield pattern was a displacement of light coker gasoil for heavy coker naphtha experiences with this feedstock. This pattern was investigated and has subsequently been incorpo-rated into the proprietary delayed coker yield models.

Fig. 4 shows a relative comparison of the expected sulfur dis-tribution and actual values. The variances were acceptable to the

TABLE 4. Refinery products before and after coker project

Before After coker, % coker, %

Gasoline 22.4 24.0

Naphtha 6.8 8.4

LPG 4.5 5.3

Middle distillates 37.7 42.7

Heavy fuel oil 14.6 1.2

Coke 3.4

Other 14.0 15.0

100.0 100.0

TABLE 1. Design features of the delayed coker

• Advanced coke drum design for optimum life. Specifications included drum plate chemistry and thickness and fabrication instructions.

• Side-wall double-fired coker heater fitted for online spalling. This design provides long heater run length by minimizing reaction time in the heater.

• Safety interlock systems for coke drum isolation, coke cutting system and heater operation. An enclosed operator shelter was specified for the decoking operation on the top deck of the coke drum structure.

• The heater was supplied with air preheat and low NOx features

• Enclosed blowdown system for recovering unconverted oils and vapors without impacting the environment. Result: No scheduled flaring due to drum switching and turnover

• Decoking water systems designed for 100% recovery and recycling of water

• Sludge injection system to process refinery sludges and convert them to product

• Gas plant with 90%+ recovery of C3 streams; amine scrubbing of coker product gas prior to refinery export and fuel use in the coker heater; amine treating of the C3/C4 LPG stream and a naphtha splitter

• Licensed sections from others include a C3/C4 LPG caustic treater and propane-propylene splitter

TABLE 2. Feed quality variance

Specific gravity –.0085

Carbon residue, wt% +2.3

TABLE 3. Coke quality — design vs. actual

Design feed prediction Actual feed operation

VCM, wt% 8 –11 10.2

Ni+V ppmw 1,026 1,195

Heating value, kJ/kg 35,674 35,800

HGI 50– 80 64

Moisture, wt% 12– 15 9.3



hydrotreating units. The actual sulfur distribution is considered environmentally favorable. Fig. 5 illustrates the differing gravities of the liquid products. Table 3 lists the design estimate for coke quality with the actual coke.

Coke disposal is 30% to local steel and cement industries and 70% export to purchasers in Europe. After accounting for vari-ances in operation and feed quality, the design basis for yields and product quality was confirmed by the operating data.

Impact of coker on operations and profitability. As a result of the coker project, the MOL Szazhalombatta refinery was able to effectively exit the heavy fuel-oil market. Table 4 lists the percentage shift in refinery products before and after the coker project.

The profitability of the delayed coker is high. In the second-quarter 2002 statement of financials, MOL stated:

“The operating profit of the refining and marketing segment increased by 9% to HUF 21.1 billion compared to the second quarter last year, in spite of the lower crack spreads and reduced Brent-Ural differential. . . The start of the delayed coker increased further the efficiency of the refining process and contributed HUF 3.1 billion to group performance.”

Based on the currency exchange at the time, this is equivalent to €140,000/day (US$129,000/day).

Outlook. MOL has executed a very successful coker project at the Szazhalombatta Refinery. The delayed coker is the center-piece of the projects and has achieved the processing targets set

during the design phase. This project is profitable and allowed MOL to economically reach its goals of exiting the uncertain heavy fuel-oil market, improving competitiveness and improving environmental conditions. The success of the coker operation is due to an effective teamwork between refiner and licensor to define the design, control the execution and start up the unit without incident. HP

Miroslav Kovac is a supervisor of the delayed coker unit in MOL Plc’s Danube Refinery. He has 12 years of experience in petroleum refining in the fields of process engineering and opera-tion. Previously, he worked as a research fellow at the University of Veszprem. He holds an MS degree in chemical engineering from

the University of Veszprem.

Gabor Movik is a process engineer of the residue processing area in MOL Plc’s Danube Refinery. He has seven years of experi-ence in petroleum refining in the field of process engineering. He holds an MS degree in chemical engineering from the University of Veszprem.

John D. Elliott is director, refining and coking, for Foster Wheeler USA Corp., Houston, Texas. He joined Foster Wheeler in 1967 and has over 30 years’ total experience in refining process engineering. He is recognized as a leading authority on heavy oil. Mr. Elliott’s assignments have involved process design and operating

follow-up on a number of refining units, including over 50 major delayed coker proj-ects. Mr. Elliott has presented many papers on heavy oils processing and, in particular, delayed coking, at major industry seminars globally. He holds a BS degree in chemical engineering from Pennsylvania State University, and is a member of AIChE.

2020 Dairy AshfordHouston, Texas 77077

Phone 281.597.3000Fax 281.597.3028

Email [email protected]

Article copyright © 2006 by Gulf Publishing Company. All rights reserved. Printed in U.S.A.Not to be distributed in electronic or printed form, or posted on a website, without express written permission of copyright holder.

upgrade refinery residuals into valuable products

Documents