Level measurement for the oil and gas industry

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Refining


Catalytic cracking unit

The Fluid Catalytic Cracker (FCC) unit upgrades heavier fractions into lighter, more valuable products. This unit takes a large hydrocarbon and partially inserts it inside a zeolite catalyst. The hydrocarbon cracks into pieces, one of which is in the gasoline range. During the process, catalyst is continually moving and being regenerated. The reaction happens in the riser, as the catalyst and hydrocarbon are lifted to the top of the unit with steam. The cracked hydrocarbons and catalyst are separated in the cyclones and catalyst descends into the "dip legs". Catalyst is sent to the regenerator where excess carbon is burned off the catalyst. The regenerated catalyst is sent back to the riser to begin the process again.


Coking

The coking unit (coker) takes the heaviest oil, typically resid, and cracks it. This results in some naphtha (gasoline) and coke. The coker is a batch process consisting of an even number of coke drums that are constantly being filled with coke or emptied by cutting the coke out with water jets. Most cokers are delayed cokers, but there are also specialty cokers that make different grades and types of coke for sale to specific industries.


Column reboilers

A heat exchanger positioned near the bottom of the distillation column re-heats and vaporizes liquid and reintroduces the vapor several trays higher. This improves separation by introducing more heat into the column. For effective functioning of the re-boiling process, level monitoring of the reboiler is required. In some steam reboilers, the level must be controlled so that only a percentage of tubes are covered. This allows a control scheme to regulate the heat transfer in the reboiler by controlling the percentage of the reboiler tubes covered by liquid. This is a critical control loop as heat transfer into the liquid is a strong function of the percentage of tubes covered.


Crude desalting

Salt in the crude stream presents serious corrosion and scaling problems and must be removed. Salt is dissolved within the remnant brine of the crude oil. Desalting removes both salt and the residual free water. Though the refinery is the most economical place for desalting, pipeline requirements often necessitate field desalting. Level instrumentation is integral to single and two-stage desalting systems, multiple orifice plate mixers, and the settler tank of a chemical desalter. Interface level control keeps free water from hitting the desalter electrodes and prevents expensive damage. The Interface level should be kept constant otherwise electrical field changes will disturb electrical coalescence.


Crude dewatering

Level instrumentation is integral to single and two-stage desalting systems, multiple orifice plate mixers, and the settler tank of a chemical desalter. Interface level control keeps free water from hitting the desalter electrodes and prevents expensive damage. The Interface level should be kept constant otherwise electrical field changes will disturb electrical coalescence. Level controls designed for interface detection will sense the beginning of the oil/water interface during dewatering procedures and provide feedback to a control system which will terminate water draw-off when appropriate.


Crude storage

Upon arrival at the refinery terminal, crude oil is pumped into above-ground storage tanks with capacities of thousands to millions of gallons. Raw crude is stored in floating-or fixed-roof tanks field-built to API standards. Tank level measurement by non-contact radar has gained share over mechanical float type and servo gauges due to its accuracy, low maintenance, no moving parts and fast set-up. Tank level is maintained by valve actuation. By triggering an emergency cutoff, level controls prevent overflows and shut down pumps when level falls below low level. Safety certified controls may be necessary due to crude’s low flash point.


Diesel fuel

Diesel-powered engine-generator sets provide emergency power to operate critical nuclear plant systems in the event of a loss of station service power. The main diesel fuel storage tank provides a fuel capacity for one to seven days of full-load generator operation. Main storage tanks typically require a fuel level indicator with a remote indication transmitter. Sensors actuating electrical pumps connected to the main tank continuously monitor day tank fuel level. Day tank high-level alarms can lock out supply pumps until a system reset. Low levels and critical low-levels actuate alarms and the system will display the low-level conditions.


Sulfur recovery

The sulfur recovery unit (SRU) is made up of an oxidizer and a number of fixed bed catalyst reactors (claus reactors). The exact process flow varies among several different styles of sulfur recovery units. A high H2S feed stream coming from the amine unit is the feed stock for the SRU. A tail gas unit may be added to improve efficiency. The SRU converts H2S to molten sulfur in several steps. There is no furnace in the sulfur recover unit because the oxidizer itself is a large burner.


Amine unit

The amine unit has two major parts - the contactor column and the stripper column. There is no furnace in the amine unit. The contactor removes acid gases (H2S or CO2) from process gas streams by contacting it with Amine. The amine is heated as it absorbs the acid gas (heat of absorption). Monitoring the height of the heat of absorption in the tower is important for good energy efficiency. The stripper column uses heat to regenerate the amine by releasing the acid gas. Generally this goes to a down stream unit such as the sulfur recovery unit (SRU).


Hydro treater & cracker

The hydrotreater (HTU) is a fixed bed reactor with many functions, but mainly it produces low sulfur road fuel. Detecting channeling and mal-distribution is key in the hydrotreater to ensure long run times and efficiency while minimum interference of process is required to meet the latest low sulfur regulations. The hydrocracker (HCU) takes heavy oil and cracks it to produce lighter fractions. Hydrocrackers are high pressure, fixed-bed reactors. Early detection of temperature change is critical because HCU's are susceptible to runaway.


Isomerization

Isomerization units contain a fixed bed catalyst reactor generally for changing straight-chain, normal molecules into branched molecules. These units may be found in the refinery or in petrochemical facilities. Detecting channeling and mal-distribution is essential to efficient running of the isomerization unit as well as prolonging catalyst life.


Midstream

  • Well steam separation
  • Amine unit
  • Compressors
  • Refrigeration unit for butane/ propane
  • Glycol chillers

  • Gas Dehydration skids

  • Fuel Scrubbers
  • Propane / Butane Storage
  • Flare KO
  • Vapor recovery


Upstream land-based

  • API Tanks
  • Heater Treater
  • 3 phase separators
  • Chemical injection
  • Flare KO

 

Upstream offshore

  • MEG Skid
  • Test Separator
  • 3 phase separators LP/MP/HP
  • Boiler room
  • Fuel storage
  • Water tanks
  • Flare KO
  • Dolly ride positioning
  • Ballast tanks
  • Sea level wave height
  • Chemical injection skid
  • Skimmers

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