REACTION SECTION• Unit 111 – reaction section train I• Unit 112 – reaction section train II

OVERVIEW

Propane dehydrogenation reaction takes place at: low pressure (5 – 6 bar) high temperature (565 – 585 ˚C)

Steam is used in: decreasing partial pressure of the process gas converting most of the coke lay down on the catalyst to CO and CO2

controlling temperature

The main dehydrogenation reaction:Side reactions:

cracking hydrogenolysis hydrolysis coke conversion

Reactions in oxyreactor:

𝐶3 𝐻8↔𝐶3𝐻 6+𝐻2

𝐶3 𝐻8↔𝐶2𝐻 4+𝐶𝐻4

𝐶3 𝐻8+𝐻 2↔𝐶2𝐻 6+𝐶𝐻4

𝐶3 𝐻8+6 𝐻2𝑂↔3CO+10𝐻 2

𝐶+𝐻 2𝑂↔CO+𝐻2𝐶+2𝐻2𝑂↔𝐶𝑂2+2𝐻2

2𝐻2+𝑂2→2𝐻2𝑂

PROCESS CHEMISTRY

+124 kJ/mol

-242 kJ/mol

𝐶3 𝐻8+0 .5𝑂2→𝐶3𝐻 6+𝐻2𝑂 -118 kJ/mol

Propane conversion

Propylene selectivity

Propylene yield (per pass of reactor)

𝑋=𝑛𝑝𝑟𝑜𝑝𝑎𝑛𝑒 𝑖𝑛−𝑛𝑝𝑟𝑜𝑝𝑎𝑛𝑒 𝑜𝑢𝑡

𝑛𝑝𝑟𝑜𝑝𝑎𝑛𝑒 𝑖𝑛

𝑆𝑝𝑟𝑜𝑝𝑦𝑙𝑒𝑛𝑒=𝑛𝑝𝑟𝑜𝑝𝑦𝑙𝑒𝑛𝑒𝑜𝑢𝑡−𝑛𝑝𝑟𝑜𝑝𝑦𝑙𝑒𝑛𝑒 𝑖𝑛

𝑛𝑝𝑟𝑜𝑝𝑎𝑛𝑒𝑖𝑛−𝑛𝑝𝑟𝑜𝑝𝑎𝑛𝑒𝑜𝑢𝑡

𝑌 𝑝𝑟𝑜𝑝𝑦𝑙𝑒𝑛𝑒=𝑆𝑝𝑟𝑜𝑝𝑦𝑙𝑒𝑛𝑒 ∙𝑋

CALCULATIONS

Platinum promoted basic zinc/calcium aluminate, PtO2: pellets (cylindrical tablets) 24,410 kg per reformer 6,100 kg per oxyreactor

Properties: commercialized stable in presence of steam & oxygen at high T high selectivity at near equilibrium conversion its regeneration is simple and sustainable expected life time of more than 5 years as demonstrated in commercial unit available from a certified producer

CATALYST

FIRED HEATERS

Use the hot gases of combustion to raise the temperature of a feed flowing through coils of tubes aligned throughout the heater

Used throughout the hydrocarbon and chemical processing industries in places such as refineries, gas plants, petrochemicals, chemicals and synthetics, olefins, ammonia and fertilizer plants

FIRED HEATERS

Unit operations require fired heaters: Distillation Fluid Catalytic Cracking (FCC) Alkylation Catalytic Reforming Continuous Catalyst Regeneration (CCR) Thermal Cracking Coking Hydrocracking

FIRED HEATERS

Fired Reboiler: provides heat input to a distillation column by heating the column bottoms and vaporizing a portion of it

Cracking Furnace: converts larger molecules into smaller molecules, usually with a catalyst

Process Heater Vaporizer: used to heat and partially vaporize a charge prior to distillation

Process Heater: brings feed to the required temperature for the next reaction stage

Reformer Furnace: chemical conversion by adding steam and feed with catalyst Start-Up Heater: heating up a fluidized bed of catalyst before adding the charge Crude Oil Heater: heats crude oil prior to distillation

TYPICAL HEATERS

plays a critical role in industrial combustion processes

heat is transferred from the hot combustion products to some type of load

radiation is often the dominant mechanism

convection also plays an important function

HEAT TRANSFER IN FIRED HEATERS

MOODS OF HEAT TRANSFER

CONDUCTION

The process of heat transfer through the material due to the temperature difference

Heat flow from high to low temperature Affected by:

thermal conductivity (Material)

temperature difference between the metal surfaces

area of heat transfer material thickness

CONVECTION

Heat transferred between solid surface and adjacent liquid or gas in motion

Two types: Forced convection Natural convection

RADIATION

Energy emitted by matter in the form of electromagnetic waves

Heat transfer without contact Unlike conduction and convections, does not require

a medium Thermal radiation emitted by bodies due to their

temperatures

COMBUSTION

COMBUSTION

Combustion: a chemical reaction that produces heat

It requires: fuel, oxygen, and a source of ignition

Two types of combustion reaction: Complete Incomplete

Complete Combustion Incomplete Combustion

• CH4 + 2 O2 → CO2 + 2 H2O + Heat

• Happens with enough oxygen

• One pound of carbon releases 14,100 BTU’s

• If oxygen is not enough, some of the carbon atoms unite with one atom of oxygen to form carbon monoxide (CO) instead of carbon dioxide (CO2)

• One pound of carbon releases 4,000 BTU’s

• Generate unburned fuel which poses fire, or explosion hazard in the furnace

COMPLETE VS. INCOMPLETE COMBUSTION

COMBUSTION

Excess air:

important for complete combustion to occur

provides enough oxygen to react with fuel

if extra oxygen is supplied, it must be heated to

maintain the proper furnace temperature, so it

actually wastes energy

DRAFT SYSTEMS

DRAFT SYSTEMS

Draft: buoyant energy created by hot gases as they rise through the furnaceDraft systems:

a. Natural Draftb. Forced Draftc. Induced Draftd. Balanced Draft

Natural Draft Forced Draft Induced Draft Balanced Draft

• Maintained by the natural, upward flow of hot gases

• Flue gases are replaced with cool air

• Draft is controlled by the damper’s position

• Combustion air is supplied by a fan

• Permits steady control of the air at the burners

• Draft is produced by discharging the flue gas with a fan

• The fan is located between the convection section and the stack

• Two fans

• One fan (forced) supplies air to the burners

• Other fan (induced) discharges flue gas from the burners

• Allows greater control

DRAFT SYSTEMS

Natural draft Forced draft Induced draft Balanced draft

FURNACE COMPONENTS

FURNACE

Furnace walls, floor, and ceiling are lined with a material that reduces heat losses and reflects heat back to the tubes (refractory lining)

Inside the stack is a damper which controls the flow of flue gases out of the furnace, thus controls the furnace draft

Radiation section bulk of the total heat transferred occurs

Convection section surface area required is controlled by film resistance of the flue-gas

sideTubes

carry the process fluid, or flow through the furnaceBurners

where combustion occurs

COMPONENTS

PDH FIRED HEATERS

Convection section (1st, 2nd convection)

Radiation section 6 bottom burners

PREHEATER

Catalyst filled tubes 10 rows, 68 tube per row

Top fired burners 11 rows, 17 burner per row

Tubes connected to manifolds top and bottom

Flue gas duct, balance burner and stack

STAR REFORMER

PROCESS DESCRIPTION

Reaction is performed in two identical parallel trains

Propane feed is purified in Depropanizer before entering both trains

Each train consists of: Preheater Reformer Oxyreactor Heat Recovery

Feed to Depropanizer is vaporized by the process gas

Heavier components (butane and heavier) are drawn off as bottom product

Recycle propane from fractionation section is sent to the tower to be reused as feedstock

Remaining propane feed is drawn off as overhead product

DEPROPANIZER (FEED PREPARATION)

Number of trays: 40

Type of trays: valve tray

Typical overall efficiency: 70 – 80%

Tower pressure: 13.9 kg/cm2

Tower temperature: 90˚C

Tower pressure difference: 0.30 – 0.50 kg/cm2

DEPROPANIZER (FEED PREPARATION)

115E001

119E002

1. Propane is mixed with MP steam to the 1st convection section of

the preheater

2. MP steam and process condensate are mixed with the

Feed/Steam mixture to the 2nd convection section then enters

the radiation section

3. Superheated Feed/Steam mixture is admitted to the tubes of

STAR reformer then mixed with MP steam before entering

oxyreactorPROCESS FLOW

4. Steam is added with oxygen to the distributors in oxyreactor

5. Heat available from effluent gas is used to generate HP steam

and preheat BFW

6. Process gas is further cooled for maximum heat recovery

7. Flue gases of the reformer are additional heat source for the

generation and superheating of HP steam

PROCESS FLOW

NORMAL OPERATION

Propane is fed from: UGDC tank farm

Before entering the reaction section, propane feed is prepared and preheated by:

feed vaporizer depropanizer feed superheater preheater

PROCESS FLOW

CONVERSION VS. SELECTIVITY

Liquid Hourly Space Velocity (LHSV)

Pressure (Pout) Temperature (Tout) Steam to Hydrocarbon Ratio (ST/HC)

OPERATING PARAMETER VARIATION FOR REFORMER

LIQUID HOURLY SPACE VELOCITY (LHSV)

OUTLET PRESSURE

OUTLET TEMPERATURE

STEAM TO HYDROCARBON RATIO (ST/HC)

OPERATING PARAMETER VARIATION SUMMARY

Parameter Variation Effect Remark++ selectivity- conversion-- selectivity+ conversion-- conversion-- selectivity++ conversion++ selectivity++ conversion done already from- selectivity SOC to EOC-- conversion+ selectivity+ conversion higher energy cons.+ selectivity limited by aux boiler- conversion- selectivity

limited by EQ size

loss of propane

limited by Compr. Suction pressure

increase

decrease

increase

decrease

increase

decrease

increase

decrease

LHSV

Pout

Tout

STHC

REGENERATION

Minor reactions that occur during the propane dehydrogenation reaction are cracking

Cracking is primary thermal and results in formation of small amounts of coke

This requires regular regeneration of the catalyst

REGENERATION

Coke formation is lowered by: presence of steam

REGENERATION

𝐶+𝐻 2𝑂↔CO+𝐻2

𝐶+2𝐻2𝑂↔𝐶𝑂2+2𝐻2

Coke formation is promoted by: high temperatures low St/HC ratio high olefin content of the process gas

REGENERATION

RGN takes place within 1 hour: Cut feed to reaction section Purge with steam Regenerate with steam & air Purge with steam Reestablish feed to reactor

STAR process regeneration: No chemical addition for catalyst Buffering of product upstream of fractionation → 100% continuous

production

REGENERATION

1 2 3 4 5 6 7 8RXN Train I O O O R O O O O

RXN Train II O O O O O O O R

O = normal operation, R = regeneration

1st purge: 7 mins removing any HC traces present before introducing air for RGN

1st burn: 6 or 8 mins burn off the coke deposit on the catalyst

2nd burn: 33 or 35 mins oxidize the active component of the catalyst PtO + ½ O2 ↔ PtO2

2nd purge: 5 mins purge the oxygen out of the reactor system

REGENERATION

Unit 115 Reduction of process gas to 50%

Unit 116

Reduction of process gas to 50%

Raw Gas Compressor in kickback

Unit 117

Solvent circulation flow is constant at 100%

Stripper reboiler duty slightly decrease

EFFECT OF RGN ON PDH PLANT

Unit 118

Reduction of process gas to 50%

Dethanizer feed is constant (liquid buffer)

Drier feed reduces to 50%

Cold box feed from Drier reduces to 50%

Cold box feed from Deethanizer top is constant

C3-Splitter feed is constant

Depropanizer feed and reflux reduce to 50%

EFFECT OF RGN ON PDH PLANT

Unit 119 Consumers cooling is reduced by 50%

Unit 157

Fuel gas demand from reaction section reduces

Fuel gas demand from Aux. Boiler increases

C4+ production reduces

C2- from Dethanizer is kept constant

Natural gas import increases by approximately 35%

Fuel gas composition changes

EFFECT OF RGN ON PDH PLANT

Unit 183

HP steam to BFW turbine nearly constant

HP steam to RGC turbine at approximately 86%

HP steam to Heat Pump compressor is constant

Unit 190 Process condensate amount slightly decrease

EFFECT OF RGN ON PDH PLANT