Design integrates delayed coking, needle coke production processes

Ted Moon
LaunchPad Writing + Research
Houston

Amid steadily increasing global demand for needle coke, Turkmenistan’s state-owned Turkmenbashi Complex of Oil Refineries (TCOR) in 2019 launched preliminary investigations into implementing needle coke production at the Turkmenbashi portion of its 10-million tonnes/year (tpy) integrated Turkmenbashi-Seydi refining system.

Following its 2018 award of a contract to Westport Trading Europe Ltd. (WTL) to deliver engineering, procurement, and construction (EPC) for a grassroots 900,000-tpy delayed coking unit (DCU) and 500,000-tpy solvent deasphalting unit (SDA) at the Turkmenbashi refinery, TCOR approached the service provider to execute a scoping and technology design study for the potential integration of the needle coke production unit into the DCU (OGJ Online, Aug. 3, 2020).

By using existing equipment from the complex and incorporating other process efficiencies, WTL’s preliminary design study for the proposed needle coke-DCU integration project presented TCOR a cost-efficient system for ensuring production of low-sulfur, low-ash needle coke product according to the operator’s specifications.

In addition to providing a brief overview of the needle coke market, this article presents WTL’s novel design for the integrated needle coke production unit and discusses quality specifications of the planned needle coke.

Market overview

Produced during the processing of petroleum residues, petroleum coke serves as a feedstock for a variety of industrial processes and products, including the production of graphite electrodes for arc furnaces, anodes for smelting aluminum and producing lithium-ion batteries, reducing agents in chemical processing, sulfidizers in the extraction of nonferrous metals from their ores, and structural material in manufacturing of corrosion-resistant equipment used to produce glass, paint, and fertilizers. Two types of coke are produced for specialty end uses, each suited as an appropriate feedstock based on its physical, chemical, and operational properties.

Obtained by coking residual straight-run and secondary products from the basic refining process, anode-grade coke is used to produce carbon anodes consumed in aluminum refining. Needle coke—named for the elongated, needle-like structure of its fibers—is produced in DCUs from low-sulfur thermal cracking residues, catalytic cracking gas oils, extracts, or pyrolysis resins. Because needle coke is used in the production of carbon products for the defense and nuclear industries, its availability has become a matter of national security and industrial safety in many countries, prompting steadily rising global demand for the product.

Needle coke is also important to the steel industry, where it is used to make the ultra-high-power (UHP) graphitized electrodes for electric arc furnaces in the steelmaking process. In recent years, increased demand for high-quality steel and growing adoption of the electric arc furnace manufacturing process have led to a sharp rise in needle coke consumption. Due to an increasing share of smelted electric steel in electric arc furnaces, as well as its expanding use in the lithium-ion battery, nuclear power, and aerospace markets, needle coke production is poised to grow 5.5% annually through 2025, with corresponding market revenues to reach more than $4 billion during the same timeframe, according to Transparency Market Research.

The global manufacturing base for needle coke, however, remains highly monopolized. While primary manufacturers are in the US, UK, and Japan, about 60% of the needle coke consumed in the world is sold on the free market, which, when combined with increased global consumption, has encouraged emergence of new needle coke producers in countries such as South Korea, China, and Turkmenistan.

Project background

Commissioned in 1943, TCOR’s integrated refining complex has since undergone a series of upgrades to keep pace with Turkmenistan’s growing demand for transportation fuels (Fig. 1). The refinery also has a history of needle coke production, the pilot batch of which was produced in 1969 from low-sulfur Turkmen crude oil. In the late 1980’s, Turkmen Petroleum Co.—Turkmenistan’s national oil concern and a trading arm of TCOR—decided to build a 120,000-tpy DCU and calcining unit to establish permanent production of needle coke at the complex. While construction of feedstock pretreater was initiated, the project ended with the collapse of the former Soviet Union in 1991.

With development of the refinery’s new DCU-SDA in 2019, TCOR resumed plans to implement needle coke production at the site, enlisting WTL to carry out a scoping and technology design study for the proposed production unit to be built as an integral part of the DCU-SDA complex.

Proposed system design

WTL’s preliminary design of the integrated DCU-needle coke production unit includes a combination of John Wood Group PLC subsidiary Amec Foster Wheeler’s proprietary delayed coking technology and WTL’s own process, which entails applying catalytic cracking technologies to optimize production of high-quality needle coke while still allowing for production of ordinary—or green—coke.

Configured to process up to 200,000 tpy of feedstock and produce up to 40,000 tpy of needle coke, the integrated unit’s design hinges on strict feedstock specifications required to achieve TCOR’s desired quality of needle coke production. The unit is designed to receive feedstock with:

Maximum sulfur content of 0.5 wt %.
Maximum nitrogen content of 0.2 wt %.
Minimum aromatics content of 69 wt %.
Minimum density of 1.03 g/cu m.

Based on the predesign study, the integrated needle coke production unit—which will use a feedstock of decant oil, extracts, and low-sulfur thermal cracking residues to produce needle coke as well as recycle gas (to be returned via piping to the DCU), naphtha, light coking gas oil, and heavy coking gas oil—will consist of the following:

Fractionator.
Cube-residue formation column.
Separate heat exchangers—or furnaces—for cube residue and the decant oil-distillate cracking residue mixture.
Thermal cracking furnace.
Evaporator and separator.
Separate coking chambers for green and needle coke.

Fig. 2 shows the flow scheme for the integrated DCU-needle coke production unit.

Production processes

The proposed integration project will equip the Turkmenbashi refinery to produce both green and needle coke.

Green coke production. After initial heating, tar and asphalt produced by the DCU enter the lower part of the fractionator along with coking products returned from the green and needle coking chambers, where contact results in heat and mass exchange. The tar-asphalt mixture is enriched with high-boiling fractions of coking products and also forms secondary raw materials known as cube residue. Once formed, the cube residue passes to its designated furnace for heating at coking temperatures between 480-510° C., after which it enters the coking chamber for production of green coke.

Needle coke production. After heating in a designated furnace, decant oil from the refinery’s catalytic cracking unit enters the cube residue formation column, where it mixes with distillate-cracked residue received from the bottom of the evaporator. This distillated-cracked residue is obtained from a mixture of heavy coking gas oil from the fractionator and extract that is thermally cracked at temperatures between 480-530° C. and subsequently cooled with light gas oil and degassing in the evaporator. Low-boiling fractions of this process remaining at the evaporator’s top are sent to the overhead line of the green and needle coke chambers for recycle to the fractionator. The resulting mixture of decant oil with distillate-cracked residue from the cube residue formation column next passes to a designated furnace to be heated at temperatures of 480-510° С., after which it enters the coking chamber for production of needle coke.

Incorporating existing equipment

In addition to new equipment for processing light oil products generated at the needle coke production unit, WTL’s design incorporates use of several pieces of existing equipment in the DCU-SDA complex. This equipment includes the complex’s:

Block for steaming and cooling coke ovens.
Gas cleaning unit.
LPG treating unit for mercaptans removal and regeneration of spent alkali.
Booster compressor for coke oven gases.
Gasoline stabilization column.

WTL’s proposed design also includes addition of the following associated equipment and structures:

High-rise metal structures for the coke drilling system.
Drilling booth.
Elevator shaft for lifting to the reactor block, including exit platforms.
Reactor site with bridge crane.
Conveyor galleries, conveyors.
Coke crushing area.
Coke shop.
Coke railway loading system.
Shunting device, railway track, railway scales.

Quality, safety, cost benefits

WTL’s proposed integrated system design is configured to produce high-quality needle coke meeting the following specifications:

A maximum volatile substances content of 9.0 wt %.
A maximum sulfur content of 0.5 wt %.
A maximum ash content of 0.2 wt %.
A minimum microstructure score of 5.5.

Alongside complying with Turkmenistan’s ecological safety standards, WTL’s integrated design also adheres to all legislative requirements and applicable rules regarding industrial safety for equipment, technical devices, buildings, and structures.

While terms of TCOR’s nondisclosure agreement prevent release of detailed cost estimates for works related to the DCU-needle coke integration plan, WTL’s study confirmed the project is economically feasible. Because the design includes use of the DCU-SDA complex’s existing equipment, the proposed design also accommodates ongoing increased efficiency of needle coke production at the site. By using WTL’s design, TCOR anticipates an estimated 4-year payback period on its overall capital investment in the integration project.

Project status

In late-July 2021, the government of Turkmenistan confirmed TCOR and contractor WTL remain on schedule to complete construction of Turkmenbashi’s new DCU-SDA unit in 2022. A final investment decision on the needle coke production integration project will follow thereafter.

The author

Ted Moon ([email protected]) is founder and principal of LaunchPad Writing + Research, a technical writing and market research firm in Houston serving the petroleum industry. Contracted by Westport Trading Europe Ltd. to document the service provider’s work on the Turkmenbashi needle coke integration project for the current article, Moon previously held roles as a technology editor for JPT Online—the website for the Society of Petroleum Engineers’ Journal of Petroleum Technology—and Endeavor Business Media Inc.’s Offshore Magazine. He holds a PhD (1999) in chemical engineering from Pennsylvania State University and a BS (1992) in chemistry from California University of Pennsylvania.