Level Control for Conversion Applications in the Petroleum Refining Process

The safety and efficiency of every aspect of the petroleum refining process is dependent on accurate level measurement. Reliable instrumentation is especially important in the extreme temperature and pressure environments that are often a part of the process. This blog post explores level instrumentation for conversion applications in the petroleum refining process. This is the third in Magnetrol’s series on level control for petroleum refining. Be sure to check out the previous two posts, from May 26 on treatment applications and from June 9 on separation applications.

CATALYTIC CRACKER

petroleum_refining_process_1The Fluid Catalytic Cracking Unit (FCCU) cracks heavy, low-value feedstocks into high-value, lighter molecular weight hydrocarbons which are blended to finished products. A cracker can produce a wide variety of yield patterns by operating in either Gasoline, Distillate or LPG modes.
Challenges: Catalytic crackers utilize a reactor and a catalyst regenerator with connecting risers where the reactions take place. Level controllers are often positioned on the first stage regenerator and at the top of the reactor. Level measurements involve fluidized solids levels at high temperatures. Conventional measurement techniques can be subject to plugging.
Level Instrumentation:
Continuous Level: E3 Modulevel® Displacer-Actuated Transmitter

CATALYTIC STRIPPER

Variations in cat cracking include Selective Component Cracking (SCC) for polypropylene production, a two-vessel and external-reactor design for processing heavy residue feeds, and a UOP process for converting gas oils and resid feedstocks. All crackers employ a petroleum_refining_processsteam stripper to remove hydrocarbons entrained in the spent catalyst.
Challenges: Stripper level control allows sufficient residence time for stripping steam to displace hydrocarbons for recovery. It also maintains sufficient pressure to keep air in the regenerator from reverse flow into the reaction system, thereby causing a hazard. A waste heat recovery steam drum would also require monitoring.
Level Instrumentation:
Point Level:
Series 3 Float- Actuated External Cage Level Switch or B40 Float-Actuated Level Switch
Continuous Level: E3 MODULEVEL Displacer Transmitter or Eclipse® Model 706 Guided Wave Radar Transmitter
Visual Indication: Orion® Instruments Atlas™ or Aurora® Magnetic Level Indicators

HYDROCRACKING

Heavier feedstock difficult to process by cat cracking or reforming can be converted by hydrocracking. By combining catalytic cracking and hydrogenation to crack feedstock in the presence of hydrogen, hydrocracking produces gasoline and distillate blending streams. About a dozen different hydrocracking process schemes are in current use.
petroleum_refining_process_3Challenges: Level controls for the catalyst stripper, separator liquid and flash drum liquid must contend with severe process conditions to maintain optimum operation of the hydrocracker. These conditions include elevated temperatures and pressures, the presence of steam and high pressure hydrogen, and aggressive corrosives.
Level Instrumentation:
Point Level:
Series 3 Float-Actuated External Cage Level Switch or Model B40 Float- Actuated Level Switch
Continuous Level: E3 MODULEVEL Displacer-Actuated Transmitter or ECLIPSE Model 706 Guided Wave Radar Transmitter
Visual Indication: ORION INSTRUMENTS ATLAS or AURORA Magnetic Level Indicators

ACID SETTLING TANKS

Alkylation is a combining process that creates alkylate, a premium, high-octane blending petroleum_refining_process_4stock. A large acid settler tank within the unit allows for separation of the acid/hydrocarbon emulsion created in the reactor. Sight glasses have traditionally measured settler level, but these are susceptible to plugging and require diligent flushing at regular intervals.
Challenges: Interface level control of the settler is required. Product/acid cross-contamination causes overall efficiency problems and can result in hazardous conditions. Inaccurate settler level indication is a frequent cause of physical acid carryover in the reactor effluent. Release of acid can cause extreme hazards to both process and personnel.
Level Instrumentation:
Point Level: Model A15 Displacer- Actuated Level Switch
Continuous Level: E3 MODULEVEL Displacer-Actuated Transmitter or ECLIPSE Model 706 Guided Wave Radar Transmitter
Visual Indication: ORION INSTRUMENTS ATLAS or AURORA Magnetic Level Indicators

ALKYLATION TANKS

Storage and wash vessels in the alkylation unit include those for fresh and depleted acid and water, an acid analyzer settling pot, and a number of wash tanks. Caustic washes petroleum_refining_process_5neutralize free acid carried over from the reaction zone and neutralize alkyl sulfates in the net effluent. Water washes decompose remaining esters and remove caustic and salt that might have carried over from the caustic wash.
Challenges: Interface level control in caustic and water washes prevents corrosion and fouling of the deisobutanizer and other downstream units. Levels rising above high set points can cause carryover of caustic or water, while too low levels can cause hydrocarbon carryunder.
Level Instrumentation:
Point Level:
Series 3 Float- Actuated External Cage Level Switch
Continuous Level: E3 MODULEVEL Displacer- Actuated Transmitter or ECLIPSE Model 706 Guided Wave Radar Transmitter or Pulsar® Model RX5 Pulse Burst Transmitter
Visual Indication: ORION INSTRUMENTS ATLAS or AURORA Magnetic Level Indicators

CATALYTIC REFORMER

Catalytic reforming upgrades low-octane naphthas into high-octane gasoline blending components called reformates. Using heat and pressure with platinum catalysts to petroleum_refining_process_6rearrange hydrocarbon molecules, this process converts low-octane gasoline fractions into petrochemical feedstocks and higher octane stocks suitable for finished gasoline blending.
Challenges: A hydrogen-rich gas stream is removed from the separator for recycling. Liquid product monitored for level at the bottom of the separator is sent to a stabilizer. Where stabilizer fouling has occurred due to the formation of ammonium chloride and iron salts, a monitored water wash system should also be included.
Level Instrumentation:
Point Level:
Series 3 Float- Actuated External Cage Level Switch
Continuous Level: E3 MODULEVEL Displacer- Actuated Transmitter or ECLIPSE Model 706 Guided Wave Radar Transmitter or PULSAR Model RX5 Pulse Burst Transmitter
Visual Indication: ORION INSTRUMENTS ATLAS or AURORA Magnetic Level Indicators

COKING OPERATIONS

Coking is the final means of converting the heaviest products of atmospheric and vacuum distillation. Feed is heated and cracked into light gases, gasoline blendstocks, distillates, and gas oil. Level applications for delayed and continuous (contact or fluid) coking include petroleum_refining_process_7the fractionator, light gas oil stripper, steam, condensate, blowdown and settling drums, and vent gas knockout drums.
Challenges: Process conditions that level instrumentation must contend with include high temperatures, high pressures, foaming, and steam. An interface level gauge in drums that are susceptible to foaming will help avoid foam-over and increase coke drum output.
Level Instrumentation:
Point Level: Series 3 Float- Actuated External Cage Level Switch or B40 Float- Actuated Level Switch
Continuous Level: E3 MODULEVEL Displacer-Actuated Transmitter or ECLIPSE Model 706 Guided Wave Radar Transmitter
Visual Indication: ORION INSTRUMENTS ATLAS or AURORA Magnetic Level Indicators

ISOMERIZATION

petroleum_refining_process_8Isomerization in a variety of process configurations alters the arrangement of atoms to convert normal butane into isobutane, and normal pentane and hexane into high-octane gasoline components. Isomerization is similar to catalytic reforming in that the hydrocarbon molecules are rearranged, though isomerization only converts normal paraffins to isoparaffins.
Challenges: Near the end of the process, reactor effluent is cooled and separated into the liquid product isomerate and a recycle hydrogen-gas stream. Isomerate is caustic-washed and water-washed, acid stripped, and stabilized before going to storage. Stabilizer bottoms and wash tanks require level monitoring.
Level Instrumentation:
Point Level:
Model A15 Displacer- Actuated Level Switch
Continuous Level: E3 MODULEVEL Displacer-Actuated Transmitter; or ECLIPSE Model 706 Guided Wave Radar Transmitter
Visual Indication: ORION INSTRUMENTS ATLAS or AURORA Magnetic Level Indicators

Petroleum Refining Process Applications

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