4.0 HYDROCRACKER UNIT (HCU) 4.1 INTRODUCTION

Transcription

1 4.0 HYDROCRACKER UNIT (HCU) 4.1 INTRODUCTION PURPOSE The process objective of Hydrocracker unit (HCU) is to produce highest quality and quantity of High-speed Diesel and LPG products from gas oil feed stocks, while minimising the yields of Fuel Gas, Naphtha and Kerosene. The unit is designed for almost full conversion of the feedstock (97% conversion) with recycling of most of the unconverted oil back to the reactor UNIT CAPACITY The design capacity for the Hydrocracker is 1.7 MMTPA. The feed to the unit is a mixture of: Vacuum Gas Oil (VGO) from Vacuum distillation column. Heavy Coker Gas Oil (HCGO) from Delayed Coking unit. Heavy Gas Oil (HGO) from Atmospheric distillation column. Provision has been kept for processing both hot feed direct from source unit as well as cold feed from storage. The Crude mix considered for the design are: Arab Mix (50: 50 by weight) Kuwait Export The unit turn down ratio is 50% LICENSOR M/s Universal Oil Products (UOP), of USA is the licenser for this unit. The technology is designated as UOP Unicracking Process MAIN SECTIONS OF THE UNIT The Hydrocracker unit consists of following sections Reactor Section (High Pressure Section) Feed Charge Pumps & Feed Preheat section. Compressor Section Recycle Gas Furnace Reaction Section High Pressure Separators

2 Recycle Gas Amine Scrubber Fractionator Section (Low Pressure Section) Stripper Product Fractionator Feed Furnace Product Fractionator, debutanizer and De-Ethanizer LPG Amine Treatment 4.2 FEED CHARACTERISTICS The unit is designed for normal operation with 80 wt% Vacuum Gas Oil (VGO) from VDU and 20 wt% Heavy Coker Gas Oil (HCGO) from DCU. However the unit is alternately run on feed consisting of 72 wt% VGO (LVGO + HVGO) from VDU, 20 wt% HCGO and 8 wt% HGO from CDU. 4.3 PRODUCT PROPERTIES PRODUCT TEMP. CUT PROPERTY SPECIFICATION Vapour kg/cm² Max Vaporisation & % Min mm Hg Copper Strip Corrosion Not worse than 1 LIGHT NAPHTHA ⁰C Reid Vapour Pressure 0.4 kg/cm² Max S Content 5 ppmw max HEAVY NAPHTHA ⁰C S Content N Content 5 ppmw max 1 ppmw max

3 PRODUCT TEMP. CUT PROPERTY SPECIFICATION ASTM D86 Vol% 205⁰C / 300⁰C S Content 30 ppmw max KEROSENE ⁰C Freezing Pt/Flash Pt/Smoke Pt -51⁰C/40⁰C/21mm HSD ⁰C Cetane No. 56 Min S Content 50 ppmw max UNCONVERTED OIL 370 ⁰C+ S Content 50 ppmw max BLENDED DIESEL ASTM D86 Vol% Present : 350/370 Future : ---/340 POOL S Content 50 ppmw max (HN+KERO+HSD) Pour Point Summer/Winter 15/0 4.4 PROCESS DESCRIPTION In PREP Hydrocracker unit, a multiple catalyst fixed bed reactor system operates at elevated temperature (app.415 C) and pressure (approx. 170 kg/cm²) in a Hydrogen rich atmosphere, which promotes the removal of contaminants (Mainly Nitrogen metals and Sulphur) and the conversion of the feedstock to desired products. The incoming feed along with the recycle from Product Fractionator bottoms mixes with hydrogen rich recycle gas, coming from Recycle Gas Heater and enters the reactor section of the unit which comprises of two fixed, multiple bed reactors (Vendor-KOBE, JAPAN) in series, provided with demetallising, hydrotreating and hydrocracking catalysts. The incoming feed, in presence of these catalysts, is demetallised, hydro treated and further hydro cracked. After the reaction, the reactor effluent exchanges its heat with incoming feed in feed

4 effluent exchangers and then it gets separated into liquid and gaseous fractions in the HP separator. The recovered gaseous stream is recycled to the unit's reactor section by the Recycle Gas Compressor. Make up Hydrogen from make up Gas compressors joins at the discharge of the Recycle Gas Compressor. The recovered liquid stream goes to the Fractionation Section where it is separated into Gas, LPG, Naphtha, Naphtha, Kerosene, Diesel and Unconverted Oil. Part of the Unconverted Oil is sent back to Reaction Section as Recycle Oil. Following is a section wise brief process description of the PREP Hydrocracker unit REACTION SECTION The Cold Feed (Normally VGO ex storage; Provision is also made for taking HCGO ex storage) after getting preheated in a MP steam heater, is mixed with Hot Feed (HCGO ex DCU and VGO ex AVU) and the Recycle Oil coming from Fractionation Section. This mixed stream is filtered in an automatic backwash filter system (Vendor: RONNINGEN PETTER, USA) to remove any suspended particles. The filtrate is then collected in a vertical feed surge drum & is routed to the first reactor. On its way to the reactor, feed exchanges heat against hot reactor effluent in the feed/effluent exchanger, and mixed with the hot H2 rich recycle gas stream pre-heated in recycle gas heater. In the first reactor, which has three beds, predominantly feed demetallising and hydrotreating reactions take place and in the second reactor, which is having two beds, predominantly feed hydrocracking reactions take place. In order to minimise the catalyst temperature rise due to heat generated during the exothermic reactions, a provision has been given to introduce cool hydrogenrich quench gas between catalyst beds. The hot reactor effluent, after exchanging heat in feed preheat and Recycle gas preheat exchangers, will flow to the high pressure Hot Separator. The Liquid portion will then go to Hot Flash drum via Charge Pump (Vendor: EBARA, JAPAN) Power Recovery Turbine. The Liquid ex Hot Flash drum goes as feed to the stripper column in Fractionation section. The vapours ex Hot Flash drum are condensed in an air cooler and flow to Cold Flash Drum. The vapours

5 from Hot Separator, exchange heat with recycle gas and cold flash drum liquid, get cooled in an air cooler and then enter HP Cold Separator. The gases from the Cold Separator are treated in an amine scrubber and then flow to a turbine-driven, centrifugal Recycle Gas Compressor (RGC) (Vendor- BHEL). Compressed recycle gas combines with make up hydrogen, exchanges heat with reactor effluent and recycled to the Recycle Gas Heater. The liquid portion ex Cold Separator flows to the Cold Flash Drum along with the condensed vapours from Hot Flash Drum. The sour water after separation in Cold Flash Drum is sent to Sour Water Stripper, via Sour Water Degassing Drum in the Fractionation Section. The hydrocarbon liquid ex Cold Flash Drum, after getting preheated with Hot Separator vapour goes as feed to the Stripper column in Fractionation Section. The gases separated in Cold Flash Drum are sent to DHDT for amine treatment and then to Refinery Fuel Gas Header. The Reaction Section also contains three numbers of, electrical motor drive reciprocating type, Make Up Gas Compressors (MUG) (Vendor: THOMASSE I NETHERLANDS). These MUG compressors compress the make up hydrogen coming from Hydrogen Generation Unit. The compressed hydrogen joins the recycle gas at the Recycle gas Compressor discharge FRACTIONATION SECTION The liquid hydrocarbons recovered in Hot and Cold Flash drums of the Reaction section are steam stripped of their light gaseous components in the Stripper Column. The vapours recovered in the Stripper flow to a Sponge Absorber Column where heavier hydrocarbons would be absorbed in the lean oil coming from Debutanizer column. The rich oil from Sponge Absorber goes back to the Debutanizer column. The gases from the Sponge Absorber are routed to Refinery Fuel Gas Header after Amine treatment. The liquid stream from the bottom of the Stripper column is preheated with Product Fractionator bottoms and then in the Product Fractionator Feed Heater before it enters the flash zone of the steam stripped Product Fractionator. Overhead vapours leaving the Product Fractionator are partially condensed before they enter the overhead receiver, where, sour water and Naphtha are

6 separated. The recovered naphtha stream is partially recycle back and partially sent for storage, along with the Debutanizer bottoms after cooling in trim cooler. Heavy Naphtha, Kerosene and Diesel are taken out from the Product Fractionator as side streams. These are stripped in respective side cut strippers and sent to storage after trim cooling. The bottom product fro Product Fractionator is the unconverted oil. Most of this product is recycled back to Reaction section, after heat exchange, at the inlet of the feed filter. A small portion of the unconverted oil is sent to storage after heat exchange and trim cooling. This is mainly used as a blend for IFO and it can also be used as a feed for FCC unit. The overheads from Debutanizer receiver are partly routed back to the Debutanizer as reflux and partly taken to LPG amine Scrubber. The stream from LPG Amine Scrubber is taken through sand filter to De-ethanizer. The overhead gases from De-ethanizer are routed to Refinery Fuel Gas Header. LPG from Deethanizer bottom is routed to storage. 4.5 SAILENT FRATURES OF HYDROCRACKER Almost complete conversion of the feed stock into valuable products (97 % conversion) by adopting recycle technology. Maximization of Diesel product. Unit is designed to produce Euro-III & IV Diesel. The blend components will be Diesel, Kerosene and Heavy Naphtha. Designed to handle high sulphur feed stock. (Feed Sulphur may be as high as 3.7 wt%). Designed to handle maximum hot feed. (Normal operation- 80% hot feed). Designed to handle Heavy Coker Gas Oil as feed (up to 30% of the total feed). Common spillback control strategy for the Make Up Gas Compressors, which is simpler and more economical in terms of number of High-Pressure equipments and joints. Dry Gas Seal for the Recycle Gas Compressor. Amine washing of recycle gas.

7 Two numbers of High Pressure Separators (Hot and Cold). PREP Central Fuel gas Mixing Drum is located in HCU B/L. Amine treated fuel gas from DHDT, DCU and existing Refinery Fuel gas mix together in this drum. Fuel gas from this drum is sent to Central Fuel Gas KO Drum in PREP AVU for supply and distribution of sweet fuel gas to entire PREP. 4.5 ENERGY CONSERVATION MEASURES Power generation to the tune of nearly 1630 kw in two numbers of Power Recovery Turbines. Pre heating DM water by using some of the hot streams, thus avoiding extra cooling by air and water. Steam Traps Condensate Collection and Recovery System Using MP steam as the reboiling medium for the Stripper column instead of a dedicated furnace. Designed to utilize stripped sour water as wash water. Common stack and APH for two numbers of furnaces viz, Recycle Gas Furnace and Product Fractionator Feed Heater. Designed to handle MDEA (Methyl Di Ethanol Amine) in place of DEA (Di- Ethanol Amine) for scrubbing LPG, Off gases and the Recycle Gas. >- Use of dedicated Pump bearing Cooling Water System for cooling of glands, bearings and bridle for Pumps and Compressors, in place of cooling water. The return water from these Pumps and Compressors will be collected in a sump at the battery limit and it will be routed to cooling water return header. Two-stage high-pressure separation system (Hot & Cold separators) for Reactor effluents has been provided to reduce the load on air fin coolers 4.6 COMPARISON BETWEEN PR & PREP HCU PR PREP FIELD HYDROCRACKER HYDROCRACKER PROCESS Once Through Recycle Mode

8 FIELD PR PREP HYDROCRACKER HYDROCRACKER CONVERSION 60% Full Conversion (97%) FEED QUALITY VGO VGO+HCGO HOT FEED PROVISION No YES UNIT CAPACITY (MMTPA) 1.5 on HS VGO 1.7 On LS VGO 1.7 on VGO+HCGO NO.OF REACTORS 3 2 CATALYST OPERATING CYCLE HYDROTREATING CATALYST HYDROCRACKING CATALYST HIGH PRESSURE SEPARATORS RECYCLE GAS AMINE TREATMENT STRIPPER COLUMN HEAT SOURCE VACUUM COLUMN AND VACUUM FURNACE POWER RECOVERY TURBINE MUG COMPRESSOR SPILLBACK CONTROL MUC SUCTION KNOCKOUT DRUMS 18 Months 24 Months HC-K HC-T HC-22 DHC No Yes Reboiler Furnace MP Steam Direct Injection Yes No 1 on Charge Pump 1 on Charge Pump and 1 on Lean Amine Pump Individual Stage Common For each Stage and For the first Stage and each Compressor common for all Comp.

9 RGC FIELD PR PREP HYDROCRACKER HYDROCRACKER STEAM Fully Condensing Back Pressure Type TURBINE (HP Steam Supply) (HP to LP Steam) SEAL Oil Seal Dry Gas Seal MUG Suction of Recycle Discharge of Recycle JOINING Gas Compressor Gas Compressor AT BUFFER GAS COMPRESSOR Yes No PRODUCT YIELD PATTERN COMPARISON PRODUCTS PR PREP HYDROCRACKER HYDROCRACKER GAS LPG LIGHT NAPHTHA HEAVY NAPHTHA KEROSENE DIESEL UNCONVERTED OIL