SECTION A: PREFACE
The principal objective of an operating manual is to describe relevant operating procedures, instructions and process safety information in an orderly manner for use by operating personnel for safe and efficient operation of a plant facility. These operating procedures and instructions shall be up-to-date reflecting changes in plant hardware and operating practices carried out from time to time. The Crude and Vacuum Distillation Unit-II was commissioned under the Visakh Refinery Expansion Project-I (VREP-I) to enhance the crude refining capacity of VR by 3.0 MMTPA. CDU-II is equipped with the latest technology. Its design provides for energy conservation; operational flexibility and maximization of product recoveries.
The original edition of operating manual of Crude Distillation Unit-II (CDU-II) was prepared prior to the commissioning of the unit in the year 1985 by M/s EIL. It was later updated in July 2008, based on the standard operating manual and process package provided by EIL. Plant Standing Instructions (PSI) issued from time to time based on operating experience and learning are available separately in field room.
Primary purpose of this revised operating manual is to integrate all the scattered operating procedures and instructions into a single operating manual while simultaneously fulfilling the requirements under Process Safety Management System (PSM) of Visakh Refinery. PSM-PR-04, which is based on OSHA-1910.119 standard, specifies the methodology and the format to be followed and the contents to be included in the preparation of an operating manual. Some of the new subjects that are incorporated in the manual due to PSM format are:
• Operating Limits and Consequence Deviations • Upset Conditions and Stabilization
• Avoiding Deviations and Plant Upsets • Temporary Operations
• Process Safety Information • Special or Unique Hazards
Efforts have been made to include the relevant information in a concise, step-by-step, easy-to-read format so that they are within the comprehension of the readers. The users of this manual are encouraged to suggest ideas for further refinement and highlight typographical errors if any, to improve the overall quality of the manual.
Operating procedures & conditions given in this manual are indicative. These should be treated as general guide only for routine start-up and operation of the unit. The actual operating parameters and procedures may require minor modifications/changes from those contained in this manual as more experience is gained in operation of the Plant. For detailed specifications and operating procedures of specific equipment, corresponding Vendor's operating manuals/instructions need to be referred to.
Approved by
Signature
Name G S JOSHI
SECTION B: TABLE OF CONTENTS CHAPTER No: TITLE FROM PAGE NO LATEST REV NO. REV DATE
1 Administrative Requirements of the Manual
Section A : Foreword
Section B : Table of Contents
Section C : Annual Certificate of Validity and accuracy
Section D : Document control
Section E : Procedure for revision of the Manual
Section F : List of Abbreviations Section G : List of Copy Holders Section H : Record of Revisions to the Manual
Section I : List of Standing Instructions
1
0
31-03-2012
2 Introduction 17 0 31-03-2012
3 Basis of Design 20 0 31-03-2012
4 Feed and Product Characteristics 38 0 31-03-2012 5 Brief Process Description & Process
Chemistry
46 0 31-03-2012
6 Detailed Description of Configuration and Process
60 0 31-03-2012
7 Description of critical control schemes 127 0 31-03-2012 8 Description of Distributed control System
(DCS)
136 0 31-03-2012
9 Description of Advanced Process control 138 0 31-03-2012 10 Pre-commissioning Activities 161 0 31-03-2012 11 Preparatory Operations & Activities for
Commissioning
168 0 31-03-2012
12 Initial Start up Procedure 171 0 31-03-2012 13 Start up Procedure after T&I 195 0 31-03-2012 14 Operating Limits & Consequences of
Deviations
199 0 31-03-2012
CHAPTER No: TITLE FROM PAGE NO LATEST REV NO. REV DATE
16 Major equipment description and operating Procedure
224 0 31-03-2012
17 Upset Conditions & Stabilization. 270 0 31-03-2012 18 Avoiding Deviations and Plant Upsets 283 0 31-03-2012 19 Emergency Procedures and Shutdowns. 287 0 31-03-2012 20 Re-Startup after Emergency Shutdowns 301 0 31-03-2012
21 Normal Shutdown Procedure 304 0 31-03-2012
22 Temporary Operations 324 0 31-03-2012
23 Process Safety Information
a. ‘Information on Deviation From the Design Limits of Major Equipment and Minimum Consequence’-(PSM/FR/2.6) b. ‘Information of plant Relief System’- (PSM/FR/2.7)
c. ‘List of Process System Interlocks and Trips’ -(PSM/FR/2.10)
d. ‘List of Enclosed Facilities’- (PSM/FR2.8)
e. ‘Information on Plant Holdups’- (PSM/FR/2.5)
f. ‘Design Codes and Standards Employed’-(PSM/FR/2.9)
325 0 31-03-2012
24 Sampling requirement and Sampling Procedures
326 0 31-03-2012
25 List of Plant Equipment 338 0 31-03-2012
26 Plant Chemicals a. Withdrawal management
b. Max Storage allowable in the Plant c. Storage precautions
d. Loading procedures e. Empty container disposal f. Handling Precautions
g. Description of Chemical dosing system.
347 0 31-03-2012
27 Occupational Safety & Health a. Chemical Hazards (MSDS)
CHAPTER No: TITLE FROM PAGE NO LATEST REV NO. REV DATE
b. First aid Procedures
c. PPE requirements, type and Usage d. Fire Fighting System 0& equipment e. Spill Handling
28 Plant Drainage System Description 379 0 31-03-2012 29 Environmental Management
a. Effluent Generation and Control b. Plant Emissions
c. Solid Waste
382 0
31-03-2012
30 Special or Unique Hazards 390 0 31-03-2012
31 Safe Work Practices a. Work Permit Procedures.
b. Confined Space Entry procedure c. Procedure for Opening Process equipment and
Piping
d. Lockout/ Tag out Procedures e. Electrical isolation procedure
f. Procedure for entry, presence, access and exit
control in the Plant
404 0 31-03-2012
32 Standard Operating Procedures of Process Equipment.
444 0 31-03-2012
33 Chemical/HC spillage Handling Procedure
478 0 31-03-2012
34 List of Annexures :
a) Unit master blind list
b) Individual equipment blind list c) List of Vendor manuals
d) Start – up & Shutdown check lists e) LEL detectors status
f) Instrument air fail to open control valves
g) DCP cylinders, First aid fire hose
CHAPTER No: TITLE FROM PAGE NO LATEST REV NO. REV DATE
reels and safety showers h) Auto ignition temperatures i) Corrosion probes, coupons and
FSM technology.
35 Description of Utility systems 540 0 31-03-2012 36 Instrumentation Tags Description 549 0 31-03-2012
Approved by
Signature
Name P N VARA PRASAD
Designation DIVISION HEAD- PRODUCTION
CERTIFICATE OF AUTHENTIFICATION
This is to certify that this Operating Manual is current and accurate.
DATE
SECTION D: DOCUMENT CONTROL
1. The administrative sections (Chapter 1 of PSM/GL/4.1) are approved by Division Head- Operations.
2. The original operating manual in file and tab format is maintained with the Division Head.
3. Three hard bound copies of the manual are issued as “Controlled Copy” to the respective plants- one for plant Manager, one for DCS and one for Field room. Controlled copy stamping is done on the following pages: “Title Page”, “Table of Contents” and First Page of every chapter.
4. Uncontrolled hard bound copies are made available to the plant personnel, Section Head, “Disaster Control Room” (formerly “Central Control Centre”), Refinery Engineering Documentation, Technical Department , HOD-Operations & YSF as training copies. The training copies are marked as “Training Copy”
5. In case of any doubt regarding the latest revision, the Original Copy is the reference document for confirmation.
6. All obsolete sections/chapters are removed by the Respective Division Heads. Revisions & additions are managed by way of “Plant Standing Instructions” which are annually integrated with the manual.
Approved By Sign
Name P N VARA PRASAD
Designation DIVISION HEAD- PRODUCTION BLOCK
SECTION E : REVISION OF THE OPERATING MANUAL
1. This Operating Manual is revised for the following :
• Change in Operating practice in any part of the Plant short and long duration.
• Implementation of changes in Hardware and/or software systems of the Plant which have impact on procedure.
• Change in Chemicals. • Changes in Safety systems.
2. The revision of the Operating Manual is done in two stages :
• Managing changes in the Operating Manual within one year cycle. • Updating Operating Manual annually.
3. The revisions are issued as ‘Standing Instructions’. The list of Standing Instructions is maintained in Section I of Chapter 1-Administrative Requirements of the Manual’.
4. The Standing Instructions are backward integrated into the Operating Manual once in a year.
5. The chapters which get revised at the time of revising operating manual, the Revision number of the Chapter which is revised is increased by “1”. The Chapters which are not revised retain the same Revision Number.
Approved By Sign
Name P N VARA PRASAD
II. SECTION F : LIST OF ABBREVIATIONS
ABBREVIATION EXPANSION
ATF Aviation Turbine Fuel ATP Additional Tank age Project BARC Bhabha Atomic Research Centre
BA Breathing Apparatus
BCW Bearing Cooling Water
BFW Boiler Feed Water
CCR Continuous Catalytic Reformer
CAS Chemical Abstracts Service
CBD Closed Blow Down
CISF Central Industrial Security Force CPP Captive Power Plant
CPWD Central Public Works Department DAF Dissolved Air Floatation
DCP Dry Chemical Powder
DOB Daily Order Book
DMP De-Mineralization Plant
DRN Disposal Requirement Notice
DCN Design Change Note
EPM Environmental Procedures Manual ESA External Safety Audit
EHS Environment Health Safety ETP Effluent Treatment Plant ELCB Earth Leakage Circuit Breaker
EMS Environmental Management System
EDMS Engineering Document Management System E&P Economics & Planning FCCU Fluid Catalytic Cracking Unit
HLPH High Lift Pump House HSD High Speed Diesel
ABBREVIATION EXPANSION ISA Internal Safety Audit
IWL Inspection Work List
IFO Internal Fuel Oil JBO Jute Batching Oil
KOD Knock Out Drum
LLPH Low Lift Pump House LSHS Low Sulfur Heavy Stock MOC Management of Change
MSIHC Rules Manufacture, Storage , Import of Hazardous Chemical Rules
MSDS Material Safety Data Sheet
MEROX Mercaptan Oxidation
MES Mechanical Engineering Services
MS Motor Spirit
NDT Non-Destructive Test
NHT Naphtha Hydro-Treater
NRV Non return Valve
OISD Oil Industry Safety Directorate
OCP Operational Control Procedure
OSTT Off Shore Tanker Terminal PDI Plant Daily Instructions
P&ID Piping & Instrumentation Diagram PFD Process Flow Diagram
PLC Programmable Logic Control
PPM Parts Per Million
PSI Process Safety Information PS&E Process Safety & Environment
PSV Pressure Safety Valve PHA Process Hazard Analysis PAD Process Analysis & Design
PPE Personnel Protective Equipment PMS Project Management System
ABBREVIATION EXPANSION PSMS Process safety management system
PA Paging Announcement
PSSR Pre- Start Up Safety Review
PESO Petroleum & Explosives Safety Organization PIR Project Initiation Request
QAP Quality Assurance Plan QRA Quantitative Risk Analysis RCA Root Cause Analysis
RCW Recirculating Cooling Water
RCR Ramsbottom Carbon Residue ROV Remote Operated Valve
RED Refinery Engineering Documentation STEL Short Term Exposure Limit
SSA Surprise Safety Audit SRU Sulfur Recovery Unit
SWP Safe Work Practice
SMPV Static & Mobile Pressure Vessels SKO Superior Kerosene Oil
SAC Strong Acidic Cations SBA Strong Basic Anions SRN Straight Run Naphtha
SR Short Residue
T&I Turnaround & Inspection TLV Threshold Lower Value
TSV Thermal Safety Valve
TC Turnaround Cycle
TOB Turnover Book
TBP True Boiling Point UEL Upper Explosive Limit
VRCFP Visakh Refinery Clean Fuels Project
VGO Vacuum Gas Oil
ABBREVIATION EXPANSION VREP Visakh Refinery Expansion Project
VD Vacuum Diesel
YSF Yard Shift Foreman
Approved By
Sign
Name P N VARA PRASAD
Designation DIVISION HEAD- PRODUCTION BLOCK
SECTION G: LIST OF COPY HOLDERS
List of the Controlled Copy holders are as given below:
S.NO COPY TYPE DESIGNATION OF THE COPY HOLDER
1 Original Division Head-Production Block
2 Controlled Copy
Unit Manager, CDU II Unit DCS, Field room 3 Training Copy
(Hard Copy)
HOD-Operations HOD-F&S Technical Services
Refinery Engineering Documentation. All Plant Personnel
YSF
Note:
1. “Controlled Copy” means that the Plant Division Head will monitor it for its status, incorporate changes as & when required, ensure its applicability and accessibility.
2. Training copy will be available in soft as well as hard copies.
Approved By
Sign
Name P N VARA PRASAD
SECTION
H:
R
ECORD OFR
EVISIONS TO THEM
ANUAL1. The revisions to the Operating Manual are made through issue of Standing Instruction. 2. The Standing Instructions are issued either to revise the existing operating procedure in
the Operating Manual in part or as an addendum.
3. The Standing Instructions are issued by the Respective Division Head-Operations.
4. The Standing Instructions for respective plants are filed in a separate File with tab separators and kept as records.
5. List of Standing Instructions issued are recorded and maintained in Chapter 1, Section I of the respective operating manual.
6. The Standing Instructions which describes recurring operational activity are identified among the standing instructions issued and incorporated in the corresponding chapter of the Operating Manual.
7. The revision of the Operating Manual is carried out annually to ensure the operating procedures are current and accurate.
8. The record of the Standing Instructions issued is retained long term in Operations Department.
Approved
By Sign
Name P N VARA PRASAD
Designation DIVISION HEAD-PRODUCTION BLOCK
SECTION I: PART-I:
STANDING INSTRUCTIONS - IN USE
SL. NO STANDING INSTRUCTION NO. STANDING INSTRUCTION TITLE DATE OF ISSUE 1. ADM/OPRN/PRODN/ SI/003Equipment draining Aug 2000 Standing Instructions Incorporated in Operations Manual Chapter-28 2. ADM/OPRN/PRODN/
SI/008
CDU-II startup Check-List March 2000 Standing Instructions Incorporated in Operations Manual Chapter-34 3. ADM/OPRN/ PROD /SI/07
CDU-II Desalter Online De-sludging
Feb’ 2002 Standing Instructions Incorporated in Operations Manual Chapter-16 4. OPRN/PROD/SI/011 Process Units Effluent
Monitoring
Nov’ 2001 Standing Instructions incorporated in Operations Manual Chapter-28 5. ADM/OPRN/ PROD
/SI/012
VREP I/ VREP- II –OWS System
Aug’ 2001 Procedure incorporated in Operations manual Chapter-28
6. ADM/OPRN/ PROD /SI/016
Refinery Fuel Gas System Management and Control
Feb’ 2005 Standing Instructions incorporated in Operations Manual Chapter-15 7. ADM/OPNRN/OM&S/ SI/017 11-E-40A/B commissioning procedure
May’2005 Standing Instructions incorporated in Operations Manual Chapter-.16 8. OPRN/ADMN/SI/20 Standing Instructions on feed
tank change over
Dec’ 2005 Incorporated in Operations Manual Chapter-15 9. ADM/OPRN/PRODN/
SI/23
Empty oil & chemical drums collection for washing in CDU block March’ 2006 Standing Instructions incorporated in Operations Manual Chapter-26. 10. ADM/OPRN/PROD/SI /30
Standing Instruction for Improving Aesthetics of MOI Control Room
May’ 2010 Standing Instructions incorporated in Operations Manual Chapter-8
11. ADM/OPRN/PRODN/ SI/32
procedure for monitoring online ER probes, PIN matrixes and corrosion coupons for high acid crudes in CDU-II
Dec’2010 Standing Instructions incorporated in Operations Manual Chapter-.34 12. ADM/OPRN/PRODN/
SI/34
Procedure for commissioning of PFD in CDU-II
April’ 2011 Standing Instructions incorporated in Operations Manual Chapter-.16
13. ADM/OPRN/PRODN/ SI/035
Avoid congealing of Heavy oil R/D lines from CDU-2
May 2011 Standing Instructions incorporated in Operations Manual Chapter-.15 14. ADM/OPRN/PRODN/
SI/036
APH water washing procedure July 2011 Standing Instructions incorporated in Operations Manual Chapter-.06 15. ADM/OPRN/PRODN/
SI/037
To apprise Merox DCS shift-In-charge in case of fluctuation in sour water flow.
Aug 2011 Standing Instructions incorporated in Operations Manual Chapter-15 16. ADM/OPRN/PRODN/
SI/038
Procedure for fuel oil gun cleaning
Sept’2011 Standing Instructions incorporated in Operations Manual Chapter-15 17. ADM/OPRN/PRODN/
SI/042
Car seals Management Dec 2011 Standing Instructions incorporated in Operations Manual Chapter-15
PART-II:
RECORD OF STANDING INSTRUCTIONS CANCELLED
SL. NO STANDING INSTRUCTION NO. STANDING INSTRUCTION TITLE DATE RE V. EXPIRED/ INCORPORATED 1. ADM/OPRN/PROD N/SI/002
Effluent Monitoring Aug 2000 0 EXPIRED 2. ADM/OPRN/PROD
N/SI/013
Work Permit System in the Units
Sep 2000 0 Invalid. New work permit system Procedure
incorporated in Operations Manual Chapter-31 3. ADM/OPRN/PROD
N/SI/014
Safety Job Card (Red Job Card System)
Oct 2000 0 Invalid. New work request Procedure incorporated in Operations Manual Chapter-31
Approved By
Sign
Name P N VARA PRASAD
Designation DIVISION HEAD- PRODUCTION BLOCK
INTRODUCTION
The Crude and Vacuum Distillation Unit-II was commissioned under the VISAKH Refinery Expansion Project-I (VREP-I) to enhance the crude refining capacity by 3.0 MMTPA.
The facilities put up under VREP-I are listed below:
i) Grass-root Crude and Vacuum Unit of 3.0 MMTPA capacity designed to process Basrah crude.
ii) Grass-root Fluidized Catalytic Cracking Unit of 0.6 MMTPA
iii) Bitumen Blowing Unit which was later revamped to 225 TMTPA unit in VREP–II with a new Biturox reactor
iv) VREP-I BCW system.
v) Capacity augmentation of the existing utilities and offsite facilities to meet the additional requirements.
CDU / VDU-II have a design capacity to process 3.0 MMTPA of crude oil. The crude processing capacity was enhanced to 3.2 MMTPA by installing Pre-Flash Drum in 1996.The design feed stocks for the unit are Basrah and Bombay High (BH). In addition, two check cases have been considered for the unit design, namely Kuwait and Heavy Arabian Mix crudes. The unit was designed based on 330 on-stream days per annum. The CDU is designed to produce Liquefied Petroleum Gas (LPG), Straight Run Naphtha,(SRN), Heavy Naphtha (HN), Superior Kerosene Oil (SKO), High Speed Diesel (HSD),and Reduced Crude Oil (RCO). The unit is also designed for special product Aviation Turbine Fuel (ATF)
The CDU also comprises the Naphtha Stabilizer section and the SRN Caustic and Water Wash sections.
The VDU is designed to process RCO from CDU and to produce Light Vacuum Gas Oil (LVGO), Heavy Vacuum Gas Oil (HVGO), Slop cut and Short Residue (SR). CDU / VDU are designed to operate in conjunction and independent operation of either of these units is not considered.
The crude oil is pumped from the off-site storage tanks to the Crude Distillation Unit. The various stages of operation it undergoes are as follows:
Crude Pre-heating in process heat exchangers and desalting of crude in Desalter. Again preheating the desalted crude in process heat exchangers.
Heating of pre-heated crude oil in Atmospheric Fired Heaters. Fractionation in Atmospheric Distillation Column.
Stabilization of Straight run naphtha in Stabilizer unit & Caustic - Water wash Treatment. Products steam stripping (Heavy Naphtha, Kero and Diesel) and routing to designated Product tanks or treatment facilities (in case of special products like ATF, Bitumen etc.). Heating of Atmospheric Column bottoms (Reduced Crude Oil) in Vacuum Heater. Fractionation of RCO in Vacuum Distillation Column.
Routing of products (VGO, Slop Cut, and Vacuum Residue) to designated tanks/units. The products from CDU can be routed as follows:-
1) Stabilizer off Gas to FCCU-II
2) LPG to the Amine Treating Unit (ATU) 3) Stabilized Naphtha to
a. Stabilized Naphtha storage tanks b. MS tanks
c. 6” T/o downstream of 11-E-19for giving hook-up to VRCFP. 4) Heavy Naphtha to
a. ATP diesel line
b. Heavy naphtha intermediate tank c. Stabilized naphtha rundown line d. Storage
e. Slop
f. 4”line hook-up given to route HN to VRCFP (NHT-CCR). 5) Kerosene to
a. Storage
b. Diesel Header c. ATP Diesel Header d. FO Blend
e. MEROX when on ATF regulation f. Slop.
6) DSL to
a) Sour diesel storage tanks b) ATP diesel header c) FO blend to HFO header d) FO blend to RFO header e) LDO blend header f) To FCCU-2
g) To DHDS upstream of 11-E-23 h) To CDU-3 for flushing oil. i) Slop
The VDU products are routed as follows:- 1. Hot well oil to TK 17.
2. VGO to
(a) FCCU-I/FCCU-II as hot feed (b) VGO storage tanks
(c) Slop
(d) LDO header. 3. Slop Cut to
(a) Vacuum furnace along with RCO (As recycle stream)
(b) As product rundown, second part gets mixed with SR product up stream to 12-E-01 A/B/C. (provision also there to mix with SR down-stream of 12-E-12-E-01A/B/C). (c) To CDU-I cooler box.
(d) To FCCU-II via recycle control valve. 4. SR to
a) VBU storage b) Direct VBU feed. c) To HFO line d) To RFO line e) To BBU feed f) Slop header
g) 10” startup line/circulation line back to crude inlet line to Preheat train – I. h) LDO header.
DESIGN BASIS
The Crude Distillation Column has been designed to process 3 MMTPA. Design of all the equipments other than crude column was based on Basrah crude. Crude column design was based on Kirkuk crude for both Kerosene (SKO) and Aviation Turbine Fuel (ATF) operations.
The unit was designed to process the crudes of API 31.3 ° to 36 ° API with marginal shortfalls in throughput. All the exchangers are specified to process Basrah crude only.
Modifications, under the “BH Conversion Project”, have been done in the plant to process 3 MMTPA of Bombay High crude also.
3.1.1 ELECTRICAL DESALTER: a) Design feed:
Crude Basrah Bombay high
Kg/ hr 367647 367647 Sp. Gravity @ 15 °C 0.848 0.8284 API @16 °C 33.6 39.2 Total Sulfur, wt % 1.9 0.15 Wax content wt% 6.0 14.7 RVP @ 100 °F, psi 7-9 5.5
H2S content Nil Nil
Viscosity @ 20 °C 9.0 cst -
Viscosity @ 37.8 °C 5.9 cst -
Pour point °C -15 +30
Conradson carbon residue, wt% 4.3 -
Characterization factor 11.9 -
Water &sediments, vol % 0.15 0.05
Salt content, (ptb) 3.0 5.0 Vanadium, ppm 18.0 4.24 Nickel, ppm 5.4 6.2 Iron, ppm 1.0 7.14 TBP distillation, wt% wt% IBP-150 °C 19 24.5 150- 250 °C 16.7 19.6 250-370 °C 19.8 23.2 370 °C plus 45.5 32.7 b) Design product:
3.1.2 DISTILLATION UNIT:
a) Design feed:
The design feed for the unit is BASRAH crude oil with the characteristics indicated in the table 1.
b) Design products:
i. Product battery limit conditions:
Atmos section:
Product TBP cut range °C Temperature °C Pressure, Kg/cm2A LPG C3-C4 40 8.0 Stabilized naphtha C5-130 43 5.0 Heavy Naphtha 130-160 43 5.0 Kerosene/ATF 160-270/160-230 43 5.0 Diesel 270-380/230-380 43 5.0 RCO 380+ 343 14.4 Vac section:
Product TBP cut range °C Temperature °C Pressure, Kg/cm2A
Light vacuum gas oil 380-400 70/213 5.0
Heavy vacuum gas oil 400-530 70/240 5.0
Slop distillate 530-550 90 9.0
Vacuum residue 550+ 90 9.0
Vacuum residue(bitumen unit feed)
3.2 Equipment Design Basis:
3.2.1 ELECTRIC DESALTER :
Design inlet chloride as NaCl 85.601 mg/l Design outlet chloride as NaCl 5 mg/l Required process water 5 vol, % Insoluble water in desalted crude 0.2 vol.% Oil content of effluent brine 100 ppm Max.
Required pH 7.0-8.5
Operating temperature 120-130 °C. 3.2.2 ATMOSPHERIC DISTILLATION COLUMN:
The crude distillation column has been designed to handle KIRKUK crude at capacity of 3 million tons/yr. the crude distillation column has been processed various other crudes like Kirkuk, Kuwait and 50:50 light heavy Arabian crudes with the same heat removal at the circulation reflux exchangers as for designed for Basrah crude.
3.2.2.1 Pressure:
The atmospheric column reflux drum operating pressure was set to 2.6 Kg/cm2 abs. in order to obtain total condensation of the over head product at 45 °C. Accordingly the flash zone pressure has been fixed at 3.2 Kg/cm2.
3.2.2.2 Over flash and bottom stripping steam:
Over flash (6 vol % on crude) and bottom stripping steam rate (28 kg/m3 of reduced crude) have been fixed to produce reduced crude containing not more than 10 volume per cent of gas oil boiling below 380 °C.
3.2.2.3 Heat removal:
The location and amounts of heat removal by the various circulating refluxes are selected to balance the tower loading and also to make it possible to recover heat in reboiler. The heat removal from the column is as below:
Diesel CR 5.0 MM K.cal/hr Kerosene CR 11.0 MM K.cal/hr Top pump around 7.4 MM K.cal/hr 50 °C temperature drop is taken for circulating reflux.
3.2.2.4 Top Reflux:
The design reflux is selected to give an overhead temperature which prevents condensation of water at the top of the tower.
3.2.3 NAPHTHA STABILISER:
The stabilizer has been designed to make a naphtha bottom product of RVP 10 max. and top overhead product of LPG contains not more than 1 mol. %. Mol. % C5.
3.2.4 NAPHTHA CAUSTIC/ WATER WASH SYSTEM:
The caustic wash system is designed to remove all hydrogen sulphide in naphtha and reduce the mercaptan content to 10 ppm. A circulation rate of 25 % of naphtha is taken for caustic and water circulation. The caustic hold has been fixed to give a batch time of 6 days.
3.2.5 VACUUM DISTILLATION COLUMN:
3.2.5.1 Number of stages:
A single stage dry vacuum distillation system is provided for FCC feed preparation. 3.2.5.2 Flash zone temperature:
The flash zone temperature is set at 395 °C to achieve the desired vaporization at the pressure in the flash zone.
3.2.5.3 Tower pressure:
The operating pressure is selected such that there is no requirement of steam to achieve the desired vaporization and the tower diameter is minimized. A pressure of 24 mm Hg at flash zone ensures that the ejector system suction pressure will be 5 mm Hg. Abs.
3.2.5.4 Column internals:
Packed column has been provided for achieving low pressure drop. Glitsch grid has been provided in the wash zone. Chimney trays are provided for the draw off of the side stream products. Demister pads are provided above the wash zone to prevent carryover of asphaltenes and at the top of the tower (to minimize carryover of hydrocarbons into the ejectors system).
3.2.5.5 Recycle:
The vacuum column is designed with a recycle rate equal to 6 v% of the tower feed in order to ensure satisfactory product quality.
3.2.5.6 Pump Around:
Pump around locations and duties are chosen to balance the column internal loading while maximizing the crude preheat.
3.2.5.7 Bottom Quench:
The tower bottom temperature is kept at 350 °C to reduce possible cracking during hold up in the tower. The quenching is achieved by returning a quench streams to the tower at a temperature of 250 °C after heat exchange between vacuum residue and crude.
3.3 Material Balance (design case):
3.3.1.1 Atmospheric Distillation column: (Basrah Crude) i.) SKO operation:
ii.) ATF operation:
3.3.1.2 Naphtha Stabilizer Material Balance for Basrah crude:
3.3.2.1 Crude Distillation Column Material Balance for Bombay High crude:
*ATF cannot be produced from BH crude due to high Aromatics in it 3.3.2.2 Naphtha Stabilizer Material Balance for Bombay High crude:
3.3.2.3 Vacuum Distillation Column Material Balance for Bombay High crude:
The performance of the above design has further been checked even for the following cases. The material balance has been tabulated given as under.
a) Crude Distillation Column Material Balance for Basrah crude SKO operation without Heavy Naphtha production
b) Crude Distillation Column Material Balance for Basrah crude ATF operation without Heavy Naphtha production
3.3.3.2 Vacuum Distillation Column Material Balance for Kuwait crude:
3.3.4.2 Vacuum Distillation Column Material Balance for Kirkuk crude:
3.3.5.1 Crude Distillation Column Material Balance for 50:50 Light: Heavy Arabian crude SKO operation:
3.3.5.2 Vacuum Distillation Column Material Balance for 50:50 Light: Heavy Arabian crude:
3.4 FEED/ PRODUCT BATTERY LIMIT CONDITION
FEED STOCK: CRUDE (@ 1.0 kg/cm2 & 30 oC)
PRODUCT Pressure (kg/cm2) Temp (OC)
LPG 8.0 40 Stabilized Naphtha 5.0 43 Heavy Naphtha 5.0 43 Kerosene/ATF 5.0 43 Diesel 5.0 45 RCO 14.4 343 LVGO 5.0 *213/70 HVGO 5.0 *240/70 (Slop/RFO/HFO) 9.0 90
Short Residue(BBU feed) 9.0 250
Short Residue 9.0 90
3.5 UTILITIES CONDITIONS AT UNIT BATTERY LIMIT:
Utilities And Their Specifications: 3.5.1 LP Steam:
Minimum Normal Maximum Mech. Design
Pressure (Kg/cm2 ) 3.5 4.0 5.0 6.5
Temperature (°C) Saturated 150 170 190
3.5.2 MP steam:
Minimum Normal Maximum Mech. Design
Pressure (Kg/cm2 ) 10.0 11.0 12.0 13.5
Temperature (°C) Saturated 250 280 300
3.5.3 HP steam:
Minimum Normal Maximum Mech. Design
Pressure (Kg/cm2 ) 34 36
Temperature (°C) Saturated 370 390 3.5.4 Instrument Air:
Minimum Normal Maximum Mech. Design
Pressure (Kg/cm2 ) 5.0 6.0 7.0 9.5
Dew Point (°C) at 1.0 Kg/cm2 -40°C -40°C -40°C -40°C
Oil Content (ppm) 0.0 0.0 0.0 0.0
Temperature (°C) 30 40 45 65
3.5.5 Plant air:
Minimum Normal Maximum Mech. Design
Pressure (Kg/cm2 ) 4.0 5.0 6.0 9.5
Dew Point (°C) No Free Moisture - No Free Moisture - Oil Content (ppm) 0.0 0.0 0.0 0.0 Temperature (°C) 30 40 45 65
3.5.6 Raw Water:
Turbidity (ppm) 15
M. Alkalinity as CaCO3 (ppm) 50-192
Ca Hardness as CaCO3 (ppm) 30-150
Total Hardness as CaCO3 (ppm) 22-300
Silica as SiO2 (ppm) 50 (max)
Chlorides as Cl ((ppm) 30-200 Sulfates as SO4 (ppm) 80-
Iron as Fe (ppm) 0.25
TDS as CaCO3 (ppm) 700
Total Suspended Solids (ppm) 23
pH 7.0-9.0 Conductivity at 250C micro mho/cm approx 5.0
Pressure Kg/cm2 Operating =3.5, Mech. Design = 7.0 Temperature 0C Operating =32, Mech. Design = 65
3.5.7 Cooling water:
Unboosted Boosted Mech. Design
Pressure Kg/cm2 2.0 3.5
Temperature 0C 33 44 65
3.5.8 Boiler feed Water (MP):
Supply Mech. Design
Pressure Kg/cm2 5.2
Temperature 0C 120 150
3.5.9 DM feed water:
Turbidity (ppm) Nil
Hardness as CaCO3 (ppm) Nil
Silica as SiO2 (ppm) 0.05
Chlorides as NaCl ((ppm) 0.05
Iron as Fe (ppm) Nil
pH 6.5-8.0 Pressure (Kg/cm2 )at grade 3.0
Temperature 0C Ambient
Mech. Design Pressure (Kg/cm2 ) 7.0
Mech. Design Temperature (0C) 65
3.5.10 LP condensate:
Maximum Mech. Design
Pressure (Kg/cm2 ) 4.5 6.5
Temperature 0C 147 170
Oil Content 15 15
Conductivity micro mho/cm 1.0 1.0
3.5.11 Fuel oil at unit Battery Limit:
Minimum Normal Maximum Mech. Design
Pressure (Kg/cm2 ) 8.0 10.0 11.0 18.0 Temperature 0C 110 130 200 200 Fuel Oil LSHS Specific Gravity @ 150C 0.959 0.9756 Viscosity, cst at 82 0C 100 39.4 Viscosity, cst at 100 0C 45 23.6 Sulfur content (wt.%) 4.5 0.7
Ash Content (ppm) - 0.1 (max)
Sediment (ppm) - 0.25(max)
Flash Point 0C >93 >93
Pour Point 0C +30 +51
Heating Value (Kcal/kg gross) 10,200 10,200
Net H/C ratio 9480 9480
Normally LSHS only will be used. However FO will be used for short duration when LSHS is not available.
3.5.12 Fuel gas at unit Battery limit:
Minimum Normal Maximum Mech. Design
Pressure (Kg/cm2 ) 3.5 4.0 4.5 7.0
Temperature 0C 30 40-50 60 70
3.5.13 Electricity supply to unit:
Volts Phases Cycles
Lighting 230 1 5C CPS
Emergency power for instruments
110 1 50
For interlocks 110 DC 3.6 UTILITY CONSUMPTION: Utility consumption rate:-
Utility Consumption
L.P Steam (Kg/hr) 1800
M.P Steam (Kg/hr) 17260-10000
H.P Steam (Kg/hr) *21100
Cooling Sea Water (m3/hr) 3257 (*3606)
D.M Water (m3/hr) 27* Service Water (m3/hr) 17.4* Fuel Oil (T/hr) 6.54 Fuel Gas (T/hr) 5.45 1. (*) When FCC is down 2. * intermittent Generation 3.7 CHEMICAL CONSUMPTION
Chemical Chemical name Average consumption(w.r.t crude feed rate) Neutralizer Ammonia 2 PPM *
Filmer EC1021A 1.4 PPM
Demulsifier EC2040A 5 PPM
caustic ---- 5 PPM max.
3.8 EQUIPMENTS DESIGN CONSIDERATION: 3.8.1 Roto-dynamics Machinery:
All roto-dynamic machines are over designed to 120% of limiting design flow. All the pumps are motor driven and following pumps however will have a turbine driven spare: crude charger, crude booster (presently for PFD), atmos col. Reflux and KERO CR.
3.8.2 Heat Exchangers:
All the coolers, condensers and other heat exchangers are over designed to 110% of limiting design on flow and duty. Condensers must have 20% spare philosophy, i.e., 20% overdesign on flow and duty (ex. Trim condenser (2+1) each of 60% duty. There are no spares available for other exchangers. For air fin coolers, extent of cooling can be maximized up to 42°C. Preheat exchangers are for obtaining maximum possible preheat and each exchanger has block and bypass valves. Stacked exchangers are not more than two or three.
3.8.3 Heaters:
The combination burner firing as well as individual burner firing facility is there. Either FO or FG can take the full load if required. Turn down ratio of heater is 50%. Turndown ratio of burners for oil firing is 1:3 and for gas firing is 1:5. Atomizing steam is MP steam at pressure of 11.5 Kg\cm2. Stack height has to be maximum of 60 meters and the diameter has to be such that flue gas exit velocity shall be more than 20meters/sec at turndown condition. Soot blowers operating with electric motors for 11-F-01 and for 12-F-01 inst. Air operated with pneumatic and retractable soot blowers. Both heaters are provided with air pre-heater.
3.8.4 Instruments:
All the instruments are under Centralized (Distributed Digital Control) Automatic Computerized control and pneumatically controlled. There are no local controls on instruments. All instruments have power supply of 110V, 50Hz. Safety valves have 100% spares and they are all provided with block valves and bypass valves. All control valves must have isolation and bypass valves. All field junction box have to be explosion proof. All the pressure gauges and dial thermometers should have 6” diameter.
3.8.5 Atmospheric Column:
The material of construction is Carbon steel with SS410 cladding up to light diesel and Monel clad is present up to tray#4 from top. Trays are SS410 except top four trays which are made up of Monel. The trays are valve trays except the chimney trays at draw-off. Overhead condenser shell is Monel clad 3mm over CS. Tubes are of titanium (and before 2010 T&I tubes are made of copper and nickel (70:30)). Channel section is of Monel clad 3mm thick. Overhead drum has to be 100% cement lined.
3.8.6 Vacuum Column:
The column has structured packing and the material of construction is CS with SS410 clad up to 250°C limit during T&I material is upgraded to SS316 2.5 Mo (min) metallurgy. The top section and the overhead vapor line are of only CS. Surface condenser is floating head type and its shell is made up of CS + Monel clad 3mm. Tubes are made up of Cu & Ni and upgraded to titanium tubes. Channel section also has 3 mm Monel clad and the drum needs 100% cement lining. The associated lines to drum are of CS. Surface condensers are floating head type and only 12-E-07A having back flushing facility.
3.8.7 Stabilizer:
The stabilizer also has valve trays and internals are of SS410. Overhead vapor line is made of CS. Condensers shell is of CS with Monel lining and tubes are of Cu & Ni in ratio (70:30). Channel section is having Monel clad of 3 mm. Drum has 100% cement lining and re-boiling is provided by KERO CR stream
FEED AND PRODUCT CHARACTERISTICS
4.1 FEED SPECIFICATIONS AND INLET BATTERY LIMIT CONDITIONS
4.1.1 Feed Characteristics:
• The Crude Distillation Column has been designed to process 3 MMTPA of Basrah crude for both Kerosene (SKO) and Aviation Turbine Fuel (ATF) operations. Modifications, under the “BH Conversion Project”, have been done in the plant to process 3 MMTPA of Bombay High crude also.
•
Property Basrah Bombay high
SP.GR 0.848 0.8284 API @ 16 °C 35.4 39.2 RVP@38 0C psi 5.8 5.5 Pour point , 0C -15 +30 Wax Content % Wt 6.0 14.7 Total Sulfur % Wt 1.9 0.15 Salt content (ptb) 3.0 5.0 Viscosity 9.0 cst @ 20°C 2.876 KV @ 40 °C 5.9 cst @ 37.8°C 2.404 KV @ 50 °C Asphaltenes (wt %) 1.0 0.05
Total light ends (wt%) 5.02 2.62
4.1.2 Feed at battery limit Conditions:
Feed Stocks Pressure Temperature Source
Crude oil 1.0 Kg/cm2 Ambient (300C) Storage tank
4.1.3 TBP Distillation: Temperature, °C Basrah (wt%) BH (wt%) IBP-150 19.0 24.5 150-250 16.7 19.6 250-370 19.8 23.2 370 Plus 45.5 32.7
4.1.4 Metal content weight ppm:
Metal Basrah Bombay high
Vanadium 18.0 4.24
Iron 1.0 7.14 Nickel 5.4 6.2
Sodium - -
4.2 PRODUCT SPECIFICATIONS AND OUTLET BATTERY LIMIT CONDITIONS:
4.2.1 Products TBP at ranges for crude and vacuum unit are as follows: Product PG Case (0C) BH Case (0C)
Overheads IBP-130 IBP-110
Heavy Naphtha 130-160 110-140 ATF/KERO 160-230/160-270 140-240 /140-270 Diesel 230-380/270-380 240-380/270-380 LVGO 380-400 IBP-410 HVGO 400-530 400-510 Slop 530-550 510-550 Short Residue (VR) 550+ 550+
4.2.2 Liquefied Petroleum Gas (LPG) (As per IS-4576 standards)
Property Basrah Bombay High
Yield tones/annum 68075 62100
Sp. Gravity at 15/4 °C 0.554 0.549
Vapor Pressure at 65 0C 16.87 Kg\Cm2 16.88
Sulphur wt% <0.003 -
H2S Wt% 0.45* -
Dryness no free entrained water no free entrained water
Volatility: evaporation 2 2
Weathering 95% Vaporization by volume at 760 mm HG pressure
95% Vaporization by volume at 760 mm HG pressure * LPG for further treatment.
4.2.3 Stabilized Naphtha (SRN):
Property Basrah Bombay High
Rate tones/annum 401423 356950 Pour point °C 0.69 - Sulfur mercaptans, PPM 10 27 Sp.Gravity@400C NA 0.726 RVP (max) Psi 10 7.0 E.O.N clear 53.4 Paraffins vol % 77.8 60.9 Naphthenes, vol % 16.9 29.2 Aromatics, vol % 5.3 9.9 ASTM-distillation Temperature IBP - 49 10% 51.5 70 30% 65.5 83 50% 84 94 70 % 96 105 90% 111.5 120 FBP 118 138
4.2.4 Heavy Naphtha (HN) Product:
Property Basrah Bombay High
Rate tones/annum 153000 192600
Sp.Gravity@150C 0.7723 0.747
ASTM D-86(Vol. %) Temperature 0C
IBP 118 126 10% 136 138 30% 141 143 50% 144 149 70% 148 153 90% 156 161 FBP 177 177 Viscosity 20°C CST NA NA Sulfur wt% 0.016 48 ppm Paraffins vol % 65.8 52.7
Naphthenes, vol % 19.5 30.0
Aromatics, vol % 14.7 17.2
Flash point °C 20 20
4.2.5 Kerosene Product:
Property Basrah Bombay high
Flash point 0C 45 48 Smoke point mm. 25 Rate tones/annum 549600 770400 Sp.Gravity@150C 0.8104 0.803 Sulfur Wt % 0.158 0.25 Viscosity Cst @ 20° C 2.2 1.32 Viscosity Cst @37.8 °C 1.5 1.30 Diesel index 68.7 33
ASTM D-86(VOL %) Temperature 0C
IBP 148 143 10% 175 177 30% 192.2 195 50% 206 208 70% 221 222 90% 251 241 FBP 291.9 260 4.2.6 ATF product:
Property Basrah Bombay high
Flash point 0C 43 Smoke point mm. 25 Rate tones/annum 350700 578400 Sp.Gravity@150C 0.7886 0.791 Sulfur Wt % 0.098 0.013 Viscosity Cst @ 20° C 1.6 0.93 Viscosity Cst @37.8 °C 1.2 0.95 Freezing point, °C -50 -47 Diesel index 71
IBP 150 110 10% 170 149 30% 182 161 50% 190 171 70% 199 183 90% 218 202 FBP 249.6 240 4.2.7 Diesel (DSL):
Property Basrah Bombay high
Flash point 0C 115 Smoke point mm. NA Rate tones/annum 539099 639000 Sp.Gravity@150C 0.8527 0.855 Sulfur Wt % 1.6 0.129 Viscosity Cst 8.7 Viscosity Cst @37.8 0C 5.2 N2 NA 52 mg/l
ASTM D-86(VOL %) Temperature 0C
IBP 236.9 241 10% 272 269 30% 293 284 50% 307 300 70% 323 322 90% <366 366 4.2.8 Diesel (DSL): (during ATF regulation)
Property Basrah Bombay high
Flash point 0C 94 Smoke point mm. NA Rate tones/annum 737999 831000 Sp.Gravity@150C 0.8525 0.852 Sulfur Wt % 1.32 0.129 Viscosity Cst @ 20 °C NA 3.74 Viscosity Cst @37.8 0C 4.0 3.2
ASTM D-86(VOL %) Temperature 0C IBP 213.5 175 10% 246 224 30% 270.5 246 50% 289.5 264 70% 311.5 289 90% <366 348 4.2.9 Light Vacuum Gas Oil (LVGO):
Property Basrah Bombay high
Flash point 0C 79 Rate tones/yr 93309 125830 Sp.Gravity@150C 0.891 0.861 Sulfur Wt % 2.45 0.174 Viscosity Cst @ 20 °C 34 17.3 Viscosity Cst @ 37.8 °C 16 12.5 Metal Content NA 96% distillate 400 467
4.2.10 FCCU FEED : (LVGO + HVGO)
Property Basrah Bombay high
Pour point 0C +48 +30 Sulfur Wt % 3.5 0.19 Rate Kg/hr 50980 Sp.Gravity@150C 0.933 0.90 Viscosity Cp 1.12@2460C NA [email protected] NA Metal Content NA
ASTM D-86 (VOL %) Temperature 0C
5% 410.1 379
10% 422.0 395
30% 444.7 425
70% 480.0 467
90% 511.4 512
95% 529.2 538
4.2.12 Slop Distillate:
Property Basrah Bombay high
Flash point 0C NA Pour point 0C +55 +34 Rate Kg/hr 4831 9950 Sp.Gravity@150C 0.961 0.93 Sulfur Wt % 6.0 0.35 Viscosity Cp [email protected] NA Metal Content NA
ASTM D-86(VOL %) Temperature 0C
5% 469.1 425 10% 486.7 448 30% 511.3 505 50% 525.3 549 70% 546.4 - 90% 573.8 - 95% 599.0 - 4.2.13 Vacuum Residue (VR/SR):
Property Basrah Bombay high
Pour point 0C +60 NA Rate Kg/hr 91931 Sp.Gravity@150C 10.56 0.99 Sulfur Wt % 5.50 0.68 Viscosity Cp 3.0@3820C NA 37.2@2200C NA Metal Content NA
ASTM D-86(VOL %) Temperature 0C
5% 513.1 464
10% 526.5 520
50% 616.2 641
70% 661.2 702
90% 711.5 794
95% 713.7 819
4.3 PRODUCT’S BATTERY LIMIT CONDITIONS:
Products Pressure Kg/cm2 Temperature0C Destination Stabilizer off
Gas
8.1 35 FCCU-2/FG header
LPG 16.0 40 MEROX
Light Naphtha 5.5 40 storage tank
Heavy Naphtha 5.5 40 into Diesel
Kerosene/ATF 5.5 44 storage tank
Diesel(DSL) 5.5 44 storage tank
VGO 7.0 70/140 Storage tank/FCCU
Vacuum Residue 9.0 90/250/160 Storage
BRIEF PROCESS CHEMISTRY & PROCESS DESCRIPTION
CRUDE CHEMISTRYCrude oil is one of the two major fossil fuels on earth, the other being coal. It is the major and a cost effective energy source today; though efforts are on to discover other means. Crude oils vary widely in appearance and consistency from country to country and from field to field. However, all crude oils consist essentially of hydrocarbons.
Hydrocarbons:
Organic compounds of carbon and hydrogen are known collectively by the name hydrocarbons. As carbon has a valency of four and hydrogen is monovalent, it can normally be expected that carbon should form only one tetra-hydride by combining with four atoms of hydrogen. Such a compound known as methane or CH4 does exist, but as carbon can also combine with itself and can also leave some of its valencies unsatisfied by getting involved in unsaturated bonds or linkages, the number of hydrocarbons is truly myriad.
Saturated and Unsaturated Hydrocarbon Compounds:
In any compound made up of carbon and hydrogen the carbon atoms behave as though they had four arms and the hydrogen atoms behave as though each had only one arm. Each arm of the carbon atom must always be occupied, that is, it must be holding something, either a hydrogen atom or another carbon atom. When all the carbon arms or bonds are used to hold other atoms, the compound is said to be “saturated”. Similarly, a compound which does not have all the carbon arms or bonds taken up by other atoms is said to be “unsaturated”. There are millions of different ways in which carbon and hydrogen atoms can be connected together to form hydrocarbon molecules. To help describe these in a systematic way, Science has classified hydrocarbons into various families depending on their molecular structure. In petroleum chemistry, hydrocarbons are classified primarily into four groups
Type of Hydrocarbon Group:
Type of Hydrocarbon Group
Paraffins Saturates
Naphthenes Cyclic saturates
Olefins Unsaturated Aromatics Unsaturated
Paraffinic Family:
The first family of hydrocarbons is Paraffins. They are saturated hydrocarbons with the general formula CnH2n+2.
Normal (Straight Chain) Paraffins & Isomers:
There are two ways in which carbon and hydrogen can be combined in butane
In the normal butane, the chain is straight where as in the iso-butane, the chain is branched, although both compounds have the same number of carbon and hydrogen atoms. For heavier hydrocarbons there can be more isomers.
Properties of Paraffins:
1) Good natural stability. However, high reactivity in presence of oxygen or under the influence of heat.
2) Low effect of temperature on viscosity. Highly paraffinic lubricants have high viscosity index.
3) At a sufficiently high molecular weight they form waxy solids. Paraffinic crudes are good sources of waxes.
4) Paraffinic hydrocarbons in the gasoline range burn too readily and lead to the ‘knocking’ phenomenon. They are poor components in gasoline blends.
5) In lubricants they lead to high pour points.
Properties of Iso-Paraffins:
1) For the same carbon number (number of carbon atoms in the hydrocarbon molecule), iso-paraffins have lower boiling points than iso-paraffins.
2) They make better components in gasoline blends; they have better (higher) octane rating. Naphthenic Family:
Naphthenic hydrocarbons have fewer hydrogen atoms per molecule than paraffins. This is because they have a closed or ring structure. Naphthene molecules with one ring have the general formula CnH2n. They are also known as cyclo-paraffins. While rings can be small (3, 4 carbon atoms) or large (above 6) many naphthenes in petroleum have 5 or 6 membered rings.
Properties of Naphthenes:
1) Naphthenes in motor oils form soft fluffy carbon deposits
2) Viscosity is affected more by temperature change. Viscosity index is lower for naphthenic lubricants for paraffinic ones.
3) Naphthenic lubricants have low pour points.
4) Naphthenes in gasoline improve its octane rating e.g. n-heptane has 0 octane and methyl cyclo-hexane, 78octane number.
Olefin Family:
Olefinic are unsaturated hydrocarbons with the general formula CnH2n. While olefins as such are not normally found in natural crude oil, they are produced by cracking reactions. The simplest member of this family is ethylene. Like paraffins, the higher members of the olefinic family can exist in straight chain (normal) or branch (iso) structure. The location of the double bond can vary, leading to different isomeric compounds.
Properties of Olefins:
1) Olefins are highly reactive. Thus their presence in gasoline or lubricating oils leads to interaction with oxygen to form sludge, gum and varnish.
2) In gasoline the presence of some olefins does improve octane rating (anti –knock properties). However, anti-oxidants will have to be added to suppress oxidation tendencies. Aromatic Family:
Aromatics are unsaturated ring type hydrocarbons of a special chemical category. In these structures, alternating double and single bonds having a property known as resonance confer some stability and other special characteristics.
Aromatic streams from a refinery normally contain benzene or its derivatives, condensed aromatic hydrocarbons like naphthalene or their derivatives.
Properties of Aromatics:
1) In view of the property of electronic resonance, benzene hydrocarbons are quite stable. 2) High octane values render aromatics excellent blended components.
3) Have high solvency power. They make good commercial solvents. 4) They are poor viscosity index components in lubricating oils. 5) Aromatics in kerosene produce smoky flames (low smoke point).
Crude Oil:
Various systems of classification have been attempted since the early production of crude oil from the last century. Based on the nature of hydrocarbons present in Crude Oils, they are broadly classified into
Paraffin Based Crude Oils: These consist mainly of paraffinic hydrocarbons and little / no Asphaltenes matter. They usually give good yields of paraffinic wax, high grade SKO and high grade lubricating oils.
Asphaltene Based Crude Oils: They contain little / no paraffin wax but Asphaltene material is usually present in large proportions. They consist of mostly Naphthenes. Lube
Oils of these crude oils are more sensitive to temperature. These crude oils give high quality Gasoline.
Mixed Base Crude Oils: These crude oils exhibit considerable overlapping of the both types described above. A majority of the crude oils are of this type.
Recent classifications are based on their API gravity (calculated from specific gravity) and sulphur content. Generally the higher the API gravity (or lighter the crude) the more distillate products it contains and the higher is its value.
Sulphur is a significant factor in the crude cost as it is an impurity. The sulphur content in the petroleum products is restricted by product specifications. High sulphur crudes also have to be processed after all, but the investment and operational costs are high. Sulphur in crude occurs in different forms like free Sulphur, Hydrogen Sulphide, Mercaptans, etc.
Nitrogen is also present in crude oils in very minute quantities in the form of Indoles, Pyridines, Quinolines, etc. Nitrogen compounds create problems while processing and to the stability of the products. Catalyst deactivation or poisoning, gum formation are some of the offshoots of Nitrogen.
Pour point is also important factor to the extent of handling the crude oil. Crude oils with high pour point require special handling facilities such as heat tracing and tank heating coils. Sometimes pour depressing additives are also used. Pour point is an indication of-wax content in crude oil.
Low Sulfur crudes:
Crude Origin API gravity Sulfur (Wt %)
Tapis Malaysia 47.6 0.05
Skua Australia 40.6 0.09
Bombay High India 39.2 0.15
Qua Iboe Nigeria 36.1 0.26
Ratna India 35.2 0.26 Ravva India 35.13 <0.1
Labuan Malaysia 33.2 0.09
Mirri Light Malaysia 29.19 0.23
High Sulphur crudes:
Crude Origin API gravity Sulfur (Wt %)
Kuwait Kuwait 31.2 2.53
Dubai UAE 31.05 2.0
Kirkuk Iran 35.6 1.99
Basrah Iraq 33.6 1.9
Umm Shalf UAE 35.77 1.39
Upper Zakum UAE 33.9 1.05
RANGE OF PRODUCTS MADE FROM CRUDE OIL Propylene
Liquefied Petroleum Gas - LPG Gasoline (Petrol)/SRN
Naphtha
Aviation Turbine Fuel (ATF) Mineral Turpentine Oil (MTO) Kerosene
Diesel Oils Jute Batching Oil Lube Oils
LSHS / Fuel Oils Asphalt
Sulphur
The Crude Distillation Unit of Visakh Refinery Expansion Project consists of Atmospheric and vacuum Distillation Sections. The unit was originally de-signed to process 3.0MMPTA of Basrah crude. It is also capable of processing other feed stocks like Kuwait (31.3 API), Kirkuk (36 API) and 50:50 light / heavy Arabian mix crudes. Besides the unit is also capable of processing Bombay High crude (39.2 API) at 90% design capacity without any change in unit configuration or equipments and for capacities higher than 90%, the following constraints are encountered.
Low preheat and consequent overloading of Atmospheric Furnace. High product rundown temperatures
Stabilizer Re-boiler duty.
The main equipment of the unit include an electrostatic Desalter, an Atmospheric
Distillation Column (ADU), strippers, furnaces, Vacuum Distillation Column (VDU),ejectors, pumps, exchangers, etc. The plant produces straight run products as well as Heavy Vacuum Gas Oil (HVGO) the feed stock for FCC units and Vacuum Residue (VR), the feed stock for Bitumen Blowing Unit (BBU).
From 1991 with the non-availability of Basrah crude, the unit processed mostly BH crude with reduced throughputs due to the above mentioned constraints. To overcome these constraints, the unit was modified in two stages in 1991 and 1993 to process BH crude (or similar crudes) at 100% capacity.
BRIEF PROCESS DESCRIPTION
The unit process can be classified into two sections as given under. 5.1 ATMOSPHERIC SECTION
Crude oil from the off-site tanks is supplied as feed to the unit. In the Atmospheric Section, crude is preheated in a series of preheat- exchangers. The sensible heat of various products and circulating refluxes (CRs) is used for this purpose. After the crude attains a preheat of 125 oC, it is sent into a Desalter for removal of water, salts, metals, sludge and any other impurity. This is achieved by controlled addition of water to the crude to form an emulsion and the separation of the emulsified water from the crude under an electric field. The water thus injected into the crude extracts the salts in the crude. After desalting, the crude is boosted to a higher pressure and is split into two streams. One stream is preheated by the Atmospheric Distillation Column products and the other by the Vacuum Distillation Column products and refluxes .After passing through the preheat exchangers, crude from both the streams is combined and sent into a Pre-Flash Drum (PFD), which facilitates the removal of lighter products from the preheated crude. This works on the principle of flashing. The bottoms of the PFD are then boosted again in a turbine driven pump and sent into an exchanger for further preheat gain in the form of sensible heat of Circulating Oil from FCCU-II. There is also a provision to route crude to the PFD downstream of the Circulating Oil exchanger. The outlet of this exchanger is routed to the Atmospheric Furnace for further heat gain. Once the crude attains the required coil outlet temperature, which is dependent on the crude being processed, it is sent into the flash zone of the Atmospheric Distillation Column.
Crude when it enters the Column is partly converted into vapor phase, which travels up in the Column (enriching section). The balance crude oil which is in the liquid form travels to the bottom section (stripping section) of the column. Stripping steam is introduced at the bottom of the column to strip off the lighter fractions in the bottom product. This also helps in the vaporization of hydrocarbons by lowering of partial pressure† (Dalton’s law of pressures). The vapors in the enriching section are separated into four fractions namely the overhead fractions and three side draw-offs. The overhead fraction is condensed totally in the overhead condensers and is collected in the reflux drum. To control the top temperature of the column, a part of the above condensed vapors, known as Unstabilized Naphtha, is sent to the column as top reflux. The balance is used as a feed to Naphtha Stabilizer. The stripping steam used in the Atmospheric column gets condensed along with the overhead vapors and is accumulated in the boot of the reflux drum. This condensate, known as Sour water, can either be used for
Desalter wash water injection, or can be routed to the Sour Water Stripping Unit (SWSU) for treatment.
Heavy Naphtha, Kerosene / ATF and Diesel are the three side draw-offs. They are further steam stripped† (importance of steam stripping) in strippers to meet the product specifications. Three Circulating Refluxes (CR’s) Top Pump Around, Middle Pump Around (Kerosene CR) and Bottom Pump Around (Diesel CR) are also drawn separately; their sensible heat is removed and then they are returned to the column to maintain the temperature profile inside the column .Unstabilized Naphtha, which is a mixture of Naphtha and LPG, from the overhead reflux drum, is sent to the Stabilizer. The process in the Stabilizer is a simple two-component distillation with a reboiler and overhead condensers. Unstabilized Naphtha is preheated in an exchanger, which extracts the sensible heat from Stabilized Naphtha, and sent into the Stabilizer. The heat input to maintain the bottom temperature of the Stabilizer is provided by a reboiler, which uses Middle Pump Around (Kero CR) as the heating medium. The overhead vapors from the Stabilizer are condensed in the overhead condensers and collected in the reflux drum. To maintain the top temperature, a part of the above condensed liquid i.e., LPG is sent as reflux to the Stabilizer. The balance LPG is routed to MEROX for further treatment. The Stabilized Naphtha or Straight Run Naphtha (SRN) from the Stabilizer bottom is routed to the Caustic Wash Section for the removal of mercaptans and H2S present in it by washing it with caustic solution. The outlet of the Caustic Wash Section is then routed to the Water Wash Section where the caustic treated SRN is washed with water to remove any caustic carry-over in SRN. The outlet of this section is routed to storage tank.
The bottom product of the Atmospheric Distillation Column, known as the Reduced Crude Oil is sent to the Vacuum Distillation Column for further processing.
5.2 VACUUM SECTION
The Reduced Crude Oil from the Atmospheric Distillation Column is mixed with Slop-Cut Distillate Recycle, heated and partially vaporized in the Vacuum Furnace and is introduced into the flash zone of the Vacuum Distillation Column. The liquid portion of the feed drops into the bottom section of the Column and is withdrawn as Short residue. The vaporized portion rises up in the tower and is fractionated into three side stream products. The Short Residue is partially routed back to the Vacuum Distillation Column bottom as quench after transferring some of its sensible heat to the crude oil. The balance can be routed either as feed to the Bitumen Blowing Unit, or the Vis-Breaker Unit or can be sent to Fuel Oil storage
tanks. Slop-Cut Distillate is withdrawn as the first side draw-off from the Wash Zone of the Vacuum Distillation Column. The vapors rising from the Wash Zone pass through the demister pad to ensure the removal of entrained Asphaltenes and metals to achieve the quality of FCCU feed. A slip stream of Slop Distillate, known as Slop-cut Recycle, can be routed to the Reduced Crude Oil stream which is then routed to the Vacuum Furnace.
The Slop-Cut Distillate is mixed with the Short Residue and sent to the Fuel Oil pool. In case the Short Residue is being regulated for Bitumen directly from the column, then there is a provision to route the Slop Distillate to a Cooler Box in CDU-I. The hydrocarbon vapor from the Wash Zone is condensed in the HVGO and LVGO sections. HVGO is drawn off as the second side stream along with the Internal Reflux and the Circulating Reflux. Internal Reflux (Wash Oil) is a hot HVGO stream from the pump discharge routed to the Column below the HVGO bed to avoid coke formation in the Wash Zone. Circulating Reflux is used to preheat the crude, generate steam and then returned to the Vacuum Column at the top of the HVGO section. The product can be routed either as hot feed to FCCU-II or to the storage tank. LVGO is the third side stream drawn along with the Circulating Reflux and Internal Reflux to the HVGO packing. Circulating Reflux is used to preheat the crude and is cooled further before returning to the Vacuum Column at the top of the LVGO section.
Vacuum is maintained by a three-stage ejector system, with three ejectors in each stage, and surface condensers. The Vacuum Column overhead vapor flows through the 1st stage ejectors. The discharge from the 1st stage ejectors goes to the primary condenser. The non-condensable in this condenser are drawn by the 2nd stage ejectors, whose outlet is again routed to a secondary condenser. The non-condensable of the secondary condenser are drawn by the 3rd stage ejectors. The discharge of the 3rd stage ejectors goes to an after-condenser and non-condensable vapors are routed to atmos Heater (hot well off gas burners) or vented to the Atmosphere through the Hotwell Drum. The condensate from all the condensers is routed to the Hotwell Drum through dip legs. Water and oil carry over in the condensate are separated in the Hotwell Drum. Water can be used for Desalter wash water injection or can be routed to the Sour Water Stripping Unit. Oil which is carried over along with the tower overheads and enters the Hotwell is pumped to the Hotwell Oil intermediate storage tank or the slop oil tank.
5.3 CHEMICAL INJECTIONS i. De-emulsifier
De-emulsifier solution is added to the crude at the feed pump suction to break the water-crude emulsion. De-emulsifiers are surface activating agents and act on the interfacial surface tension of crude and water emulsion.
ii. Caustic
Caustic solution is injected either at the feed pump suction or at the suction of the feed booster pump. Caustic is injected to remove the hydrolysable salts, which if not removed, can get converted into HCl and cause corrosion in the system.
iii. Neutralizer
Neutralizer solution is injected to the overhead vapour line and top reflux line of Atmospheric Column and the Vacuum Column overhead system. This helps in maintaining a stable pH at the column overhead area, which is very essential for a good Corrosion control.
iv. Corrosion Inhibitor
Corrosion Inhibitor solution is injected into the overhead vapour line and the Top Reflux line of the Atmospheric Distillation Column and in the overhead vapour line of the Vacuum Distillation Column. This helps in preventing the contact of corrosive water and acids with the shell of the column. It acts by forming a film on the surface of the shell in the overhead area. This film is impervious to the acids formed.
5.4 DISTILLATION
The Chemical Engineering operation used in the Crude / Vacuum Distillation Unit to process crude oil (or range of hydrocarbons) into a range of products is Distillation. Distillation technique is employed to separate various product cuts from the crude petroleum in this primary distillation unit.
Distillation is one of the many separation processes employed in chemical industry. It is a physical process (not necessarily involving chemical reactions) where separation is achieved using differences in their boiling points or, in other words, difference in volatility. The application of this technique ranges from the simplest binary distillation to the most complex distillations like azeotropic or extractive distillations.
5.4.1 PRINCIPLE
If solution of two components with different boiling points is allowed to flash in a vessel, the liquid and vapour portions separate and after sufficient time attain equilibrium. The vapors will be richer in lighter components and the liquid residue therefore leaner. Suppose the vapours are condensed and flashed again, the resulting vapours will be richer in the lighter components. By repeating the procedure, we will reach a stage when vapours will be full of the lighter components (ideally). Similarly, by repeatedly heating and flashing the liquid portion, we will eventually end up with a liquid which is hundred per cent the heavier component. The same principle is used in a distillation column with an integration of the above process and each step where the heavier component in the vapours is condensed and