ARDS

Feedstock and products of the ARDS

ARDS unit has been commercially recognized since the mid-1960s

Feedstock vary from relatively light residues like the "Arabian light" all the way to the heavy residues

S%=4.5%

API=12.5

ARDS capacity

Increasing demand of lighter, low-sulfur, and high-quality liquid products

Cost effective

ARDS sections

01.

Removal %

95% sulfur & metals

70% carbon residue

60% nitrogen

60% conversion of vacuum residue

reduces S, N, metals & residual carbon in presence of Hydrogen

Reaction section

02.

Fractionation section

Obtain lighter and more valuable products: LPG, Naphtha and low-sulfur fuel oil

Reactor type in ARDS

Catalytic Fixed bed reactor

• Found to have an optimal economic value.
• Converts 20% of the feedstock to diesel and increase the production of gasoline .

Temperature and pressure ranges: 285-400oC

900-20000 kPa

High purity excess hydrogen is recycled and used to minimize cock formation.

• Usually multiple trains with each train containing a number of series reactors with a guard reactor

Catalysts

CoMo Sulfur removal

NiMo Nitrogen removal and aromatic ring saturation

The most common combination of active elements in hydrotreating catalysts are the CoMo, NiW and NiMo promoters on alumina base.

Demetallization is achieved in the first and second reactors while the desulfurization is achieved in the third and fourth reactors

Guard reactor has 7% of the total catalyst volume while the other three reactors have 31% each

CoMo

Catalyst's deactivation

Residues have high potential for coke formation because of the low hydrogen/carbon ratio that causes quick catalyst deactivation

Using excess hydrogen through the recycle is required to reduce coke formation.

To avoid catalyst deactivation due to metal deposition, contaminated catalyst should be removed continuously under operation.

Models

Effect of reaction parameters in ARDS

Feed specifications

Up to a temperature of 400oC and a pressure of 2000 psi

Heavier feed requires more severe conditions (higher Temperature and Pressure)

Effect of reaction parameters in ARDS

Temperature

Hydrogen pressure

Effect of reaction parameters in ARDS

Catalyst

Surface area and pore volume losses are highest for the catalyst in the last reactor and lowest for the catalyst in the first reactor

Aromaticity and degree of condensation in the product asphaltenes is higher for the hydrodemetallization (HDM) catalysts than for hydrodesulfurization (HDS) catalysts.

MAB

1X65,900 BPD

ARDS in Kuwait

MAA

4X42,000 BPD

1 common fractionator

Al Zour new refinery will be designed to process 615,000 BPD of Kuwait export crude and will include 3 ARDS units

The primary objective of the units is to reduce the sulfur content of atmospheric residue to 0.5%

Recent Development

Improving feed characteristics and catalysts combination

Using appropriate catalyst combination prevents pressure-drop increase

Improving liquid distribution in the ARDS unit's catalyst bed prevents the formation of hot spots (Uniform distribution)

Ebullated reactor