Hydroprocessing

Question 1

Hydroprocessing

Answer 1

Used to treat bottom of the barrel, Atmospheric Resid Crude and Vacuum Resid Crude. but mostly for ARC.
ARC is better used as feedstock for catalysed processes due to low viscosity, better operations and better impurity reduction.

Can be performed by fixed bed, moving bed, expanded bed or reduced FCC.
The main functions are to
- Reduce boiling point range
- Remove most impurities like metal and nitrogen and sulphur
- For Preparing the feed for processes like FCC
- Increase H/C ratio

Question 2

Functions of guard reactor and main reactor

Answer 2

Guard reactor is there to remove metals which can poison the catalyst in the main reactor.
The main reactor then removes S and N compounds while also cracking the hydrocarbons with hydrogen present so astro increase H/C ratio

Question 3

Fixed Bed Process

Answer 3

The feed is passes through a filter to remove particle more than 25 armstong. It is the mixed with heated hydrogen. The mixture is added to the guard reactor from the top where the suspended solids are deposited. In the guard reactor fixed bed, the metals are then deposited on the catalysts (silica alumina with cobalt and molybdenum). The metal reduced product is them passed through three or four series fixed bed reactors where S and N reduction take place along with the cracking process to make hydrocarbons with a lower boiling point. The resultant product is the n passed though a high pressure and low pressure separators where the gas and liquids are separated. The liquid is taken for fractionation to extract naphtha, fuel gas, distillates and heavy oil.
The H2 and Hs2 gas are separated using an H2S scrubber which extracts H2s with amine while the H2 gas goes back as a recycle to the feed.

Question 4

Expanded/Ebullated Bed

Answer 4

LC-Fining method
The pre heated feed is added/mixed with the hydrogen see as added to the first reactor at from the bottom. the gas and liquid then travel up the reactor hence ebullating/ expanding the catalyst bed. The product from the first reactor is sent to the second reactor for further conversion. The product from the last reactor then goes through a set pf separators in order to separate the gas and liquid fractions. The high pressure separator is first used t remove gas and then the low pressure separator takes the liquid from the high pressure separator for the removal of more gas. The liquid product is then taken to the fractionator for processing to the required product.

• —> the effluent is always recycled to
• to prevent channelling
• ensure that the bed is always expanded
• to control reaction rate
• to keep the heat release due to exothermic reaction at as sate rate

Question 5

Advantages and Disadvantages of Expanded Bed

Answer 5

Advantages

• The reaction is always at equilibrium
• Can add or remove catalysts during operation hence, catalytic activity is constant
• no chance of solid settling

Disadvantages

• Backmixing dilutes reactants
• slower reaction rate than fixed bed
• requires about 3 times more catalyst than fixed bed for same amount of conversion