HPCL IT DHDS Block Overview

1

Specification BS-I BS-II Euro-III

Sulfur, ppmw max 2500 500 350

Cetane number, min 48 48 51

Polyaromatics % max No spec No spec 11

Density, kg/m3 820 - 860 820 - 860 820 845

Distillation

T 85 max 350 350 No spec

T 95 max 370 370 360

SPECIFICATIONS OF DIESEL

DHDS Block Diagram

Sweet Diesel to Tanks

PDS FDS Reformer PSA

DHDS Amine Section

Naphtha

Hydrogen

Sour Diesel H2S rich H2

Lean Amine

from D-SRU

Rich Amine to D-SRU

Sour Water to D-SRU

Purge Gas

H2

Hydrogen Production

Hydrogen Plant is designed to produce 2296 Kg/hr (25000 NM3/hr) of pure hydrogen (99.98%) using Steam Reforming of Naphtha with further enrichment in shift converter & purification in PSA.

Process Steps

Feed (Naphtha) Pre-desulphurisation

Final desulphurisation

Steam Naphtha Reforming (Reforming +Steam Generation)

CO HT shift conversion

H2 purification (PSA)

Pre - Desulphurization Section

To remove Sulphur from Naphtha which is poison to reformer catalyst (Sulphur reduction from 1000PPM to 10PPM).

Naphtha and recycle H2 are heated and sent to Reactor where Sulphur compounds are converted to H2S over Cobalt-Molybdenum based catalyst

RSH + H2 RH + H2S (Exothermic Reaction)

T=3400C & P =24.5 Kg/cm2g

Other Side Reactions

O2+H2 2H2O ( Exothermic Reaction)

CnH2n+H2 CO+H2O (Exothermic Reaction)

CO2+H2 CO+H2O (Endothermic Reaction)

Process Description(PDS)

LC001

PC003A/B

FC327 Sour Naphtha

Fuel Naphtha to

Reformer

Recycle H2

R01

60-F-01

To E02

FC003 FC002

P01A/B

P13A/B

E01 61D01

To Flare


Naphtha from

E01

BFW

SWS

SWR LC062

Sour Water

to D-SRU

FC059

FC058

E02 D02

D04

K01A/B

PC058 Naphtha

from C01

Bottom

Naphtha to

C01

Recycle Gas to E01

E03A/B E06

SWS

SWR

Sweet Naphtha

to storage

Naphtha to D11 LC079A/B


Naphtha from D02

Sweet Naphtha

FC076

Sour

Water

Purge Gas

from D02

E04

D07

E05

SWS SWR

D03

P02A/B

Flare Flare

PC084 PC080A/B

FC075

Steam

Final Desulphurisation

To reduce the Sulphur content of Naphtha from 10 ppm to < 0.5 ppm.

Naphtha and H2 are heated and processed in reactor(R11) to convert S

compounds to H2S over Cobalt-Molybdenum based catalyst.

R - SH + H2 R - H + H2S

C2H5Cl + H2 C2H6 + HCl

T=390oC & P= 30.8 Kg/cm2g

Chloride Removal in R12A/B by sodium aluminate

2HCl+2NaAlO2 Al2O3 + 2NaCl +H2O

The H2S generated in R11 is absorbed in ZnO reactor(R12A/B)

ZnO + H2S ZnS + H2O

DHDS Refresher,2011

Process Description (FDS)

Process Gas

from 61R13

Feed+H2

to 61CE15 To 61E13A/B

Sweet Naphtha

from Tk186

Hydrogen

From MGC

61D11

61P11A/B

61E11

PC111A

LC101

FFC101

PC117A

XV102

PC111B

DHDS Refresher,2011

Feed + H2

from 61CE15

61AM12

Naphtha

to 61D11

61PC117B

Process Description (FDS)

61R11

R12A

R12B

SWS

SWR

LC116

PC116A/B

Steam Reforming

Desulfurised Naphtha is mixed with steam and passed through a Nickel

catalyst packed in vertical narrow 104 tubes (34 Ni - 25 Cr) mounted in the

reformer at high temperature

Top Catalyst :Ni +dispersed Potash to suppress coke formation

CnHm + nH2O nCO + (n+m/2)H2 (endothermic)

CH4 + H2O CO + 3H2 (endothermic)

C + H2O CO + H2 (endothermic)

Outlet T= 860oC & P=24.6 kg/cm2g

Process is endothermic and heat is supplied by fuel firing with 40 top fired

burners.

Reformer Feed from

61CE12

Process Gas to

61E12

61FC212

61KM12A/B

Blow down

from 61D15

E16

TC134

Water /Steam to 61D15

61CE17

61CE16B

61CE16A STACK

Process Description (Reformer)

CE11

CE12

CE13

CE14

CE15

Water from D15

Desulphurised

Feed from

61R12A/B

Feed to F11

Short Loop

Nitrogen

XV152 FC152 FC151

Feed+H2

from 61E11 Feed +H2

to R11

Water from D15

Water/Steam

TC153

Ammonia PC152A

Export

Steam

Steam from

D15

Water from D15

Water/Steam


Export Steam

To F11

61D15 LC171

TC153

PC152B

Steam to

Silencer

61E12

TC181 Water/Steam

from CE14

Water/

Steam

from

CE17

Blow

down

to

E16

Water

to

CE14

BFW

from

61E13

Process Gas from F11 Process Gas to HT Shift Reactor

Water to

CE17

Water to

CE11


Water/

Steam

from

CE11

CE-13

Steam Reforming

Parameters influencing design and operation

Pressure - favored by low pressure.

Steam carbon ratio:

Defined as moles of steam per atom of carbon in the HC feed.

CARBON FORMATION

2CO C + CO2

Sufficient steam is required to avoid carbon lay down in the catalyst

Temperature :

Conversion favored by high temperature.


FC181 FC182

LC181

LC191

PC191

DM Water

from Header

Condensate to Degassifier

BFW from Degassifier

BFW to steam

drum

DM Water to Degassifier

Naphtha + H2

Naphtha+H2 to

CE15

AM11A/B

61E15

Syn Gas from Reformer

R13

CO Shift Conversion

Process:

HT shift reaction converts the carbon monoxide present in the reformer

gas to Carbon dioxide producing additional H2.

CO + H2 CO2 +H2 (exothermic)

Iron oxide catalyst is used.

Improve PSA performance by reducing CO load.

The Catalyst should be operated at the minimum practical inlet

temperature giving the desired conversion of CO.

As the Catalyst ages it is necessary to increase the converter inlet

temperature in order to maintain a satisfactory exit CO level.

Importance of Recycle Hydrogen

Predominantly Catalytic

Cracking Reactions &

Olefin Saturation

Predominantly Reforming Reactions

thus generation of H2

Generated Hydrogen Keeps the

catalyst of this portion in

reduced state.

Recycle H2 of FDS section keeps this

portion of catalyst in reduced state.

H2 molecules

Process Gas from D13 H2 to B.L

Flare

H2 to PDS

Purge Gas to

Burners

Flare


PSA(Pressure Swing Adsorption)

Adsorption is the preferential partitioning of substances from the gaseous

or liquid phase onto the surface of a solid.

Adsorbent : solid substrate Adsorbate : adsorbing phase

PSA unit works on the principle that the adsorbent attracts and retains the

impurities at higher pressure and releases them at lower pressure.

4 Basic steps carried out by automatic PLC controlled control valves

1. Adsorption

2. Depressurization

3. Purging

4. Re-Pressurisation

Adsorption

05

10

15

20

25

0 100 200 300 400 500 600 700 800 900

SubCycle Time : 165 Second ( 2.75 Minute)

Cycle Time : 825 Second ( 13.75 Minute)

Process Description (PSA)

Adsorption,165

P-Equalisation,70

Providing Purge,95 Dump,75

Purge,95

Isolation-II,95

R-Equalisation,30

Repressurization, 130

Isolation-I, 30

DHDS Unit

DHDS Unit designed to supply High Speed Diesel with 0.25 % wt. sulfur

content with a capacity of 5400 TPD. After revamp its capacity increased to

7290 TPD, and it can achieve 0.002 % wt. sulfur (Max).

DHDS Major Section

DHDS Reaction Section ( High Pressure Section )

Amine Absorption Section (High and Low pressure Section)

Stripping Section (Low Pressure Section)

Naphtha Stabilization Section (Low Pressure Section)

DHDS Process Description

Sour Diesel

Recycle H2

E01/02/34

F01 R01

R02

HP Separator

Cold Separator

H2S rich Gas to HP

amine absorber

Steam

Stripper

Stabilizer

Stab. Naphtha Sweet Diesel

E06

E03

Wash Water

H2 from PSA

E05A/B FC1801

60K01A/B/C

E12A/B

60K02

60FC1902 Recycle Gas from HP

Amine absorber Recycle Gas to

E01

To Quenches

Compressor Section

DHDS Relatives

Cold Feed from Tanks

CDUs LD/HD/VD/VBN

FCCUs LCO/HCO

Fuel Gas

H2 to VRCFP

H2 from VRCFP

Sweet Diesel to

Tanks

Stabilizer Naphtha to MS

Tank / CDU-III Run down

Sour Water to

D-SRU/Merox/VRCFP

AAG to D-SRU

DHDS

Diesel Composition

Diesel composition : ( 9-23 Carbon atoms )

Paraffin ( straight chain Hydrocarbons) -- Olefins

Naphthenes (Cyclic Hydrocarbons)

Aromatic Compounds ( benzene Rings like structures)

DHDS Reactions

Desirable Reactions

Elimination of Sulphur

Elimination of Nitrogen and oxygen

Elimination of metals

Saturation of olefins/ di-olefin & Aromatics

Undesirable Reactions

Hydro cracking

coking

Desulphurisation

Mercaptans , sulfides and disulfides react easily leading to saturated and aromatic compounds.

Sulphur combined into cycles of aromatic structure is difficult to eliminate.

Desulphurization reaction is exothermic, consume hydrogen and produce H2S.

2 to 3 molecules of hydrogen are consumed for every atom of sulphur removal.

DHDS Reactions

+ 6H2 H2S + + Heat

S

Elimination of Nitrogen

C

N

+ 5H2 C5H12 + NH3 + Heat C

C

C

C

Nitrogen removal is desired to improve feed stock color & color stability.

De-nitrification rate is lower than the desulphurization rate.

Reactions are exothermic.

On average 4 molecules of H2 are consumed per atom of nitrogen

DHDS Reactions

Hydrogenation

Hydrogenations occur of olefinic and aromatic compounds.

The reactions are highly exothermic and decreases the number of reacting

molecules.

C-C=C-C-C-C + H2 C-C-C-C-C-C

Demetalization:

The organo metal compounds ( As, Pb, Cu, Ni, V) are cracked and the metals are

trapped on the catalyst.

Undesirable Reactions : Hydro cracking

Cracking of Hydrocarbon in presence of hydrogen

* Consumes hydrogen * Reduces product yield * Hydrogen purity of recycle gas.

DHDS Reactions

Undesirable Reactions :Coking

Heavy molecules are adsorbed on the active sites of the catalyst, it may get

condensed and polymerize on the catalyst and form coke.

Catalyst Pores Catalyst Active Sites

DHDS Reactions

Effect of Temperature

Temperature

Aromatic/Olefin Saturation

Coking

Hydrodesulphurization De-nitrification

Rate

of

Reacti

on

Effect of Pressure

Pressure

Hydrodesulphurization Aromatic/Olefin Saturation

Coking

Rate

of

Reacti

on

Amine Section

Lean Amine from

D-SRU

H2S rich gas from

Reflux Drum

Rich Amine to D-SRU

H2S rich recycle gas from 60D02

Flare or Fuel Gas

Header

Recycle Gas to RGC

suction

Rich Amine to LP Amine

absorber

Fuel Gas or Flare

Header

HP Amine absorber

LP Amine

absorber

HPAA bypass

HC 1701

Chemistry of Amine Section

H2S is a weak acid & ionizes in water to form hydrogen ion & sulfide ion.

H2S + H2O H3O+ + HS-

Di ethanolamine is a weak base and ionizes in water to form amine ion and

hydroxyl ion

(HOCH2CH2)2NH + H2O (HOCH2CH2)2NH2+ + OH-

When H2S dissolves into the solution containing the amine ion, it reacts to form

a weakly bonded salt of the acid & the base

(HOCH2CH2)2NH2+ + HS- (HOCH2CH2)2NH2SH

The sulphide ion is thus absorbed by the amine solution.

(HOCH2CH2)2NH + H2S (HOCH2CH2)2NH2SH

Absorption independent variables

Temperature Lower Temperature favors the absorption. However lean amine temperature

should be maintained 7 to 13oC higher than the gas temperature to avoid the

condensation.

Acid gas loading Absorption depends on restricting the H2S loading in the rich amine to

favour the forward direction of the reaction given in equation. The H2S loading

of the amine solution is controlled by adjustment of the amine circulation rate.

Amine concentration Practical and economical considerations, confirmed by field experience, have

generally shown that the optimum amine concentration for this unit is 25% wt

DEA. This is based on the lowest heat requirement for the desired H2S removal,

the lowest chemical losses, and the fewest operational problems.

Documents

HPCL IT DHDS Block Overview