Measuring the level and high level alarm in the coke drum

The delayed coker is the only semi-continuous batch process in the refinery, with the feed continuously switched between two drums on a time-based cycle. The fresh feed, usually from the vacuum tower bottoms, is fed to the bottom of the coker fractionation tower to help pre-heat the feed and mix with the bottom hydrocarbons. This mixture is then passed to the heater to add the energy required to thermally crack the large hydrocarbon chains. After that, the heated resid is pumped into a large coke drum to allow for the cracking and expansion of the fluids, whereby the lighter cracked hydrocarbons are taken off the top of the drums to the fractionation tower, due to the high temperature. As the vapours escape the viscous liquid, they tend to create a foam layer. This foam layer can vary depending on many parameters such as operating temperature, pressure of the drum, type of crude, charging rate etc.

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Measuring the level of bottom liquids in the fractionator

Monitoring the level of tower bottom liquids in a delayed coker is among the most important measurements in a refinery. Due to the conditions in the coke drum and fractionator, a level measurement is very challenging. Where other measuring technologies tend to fail or end up being extremely unreliable, Berthold‘s radiometric level technology is ideal for monitoring the coke level due to its non-intrusive nature. Since large temperature variations through the whole operational cycle of a coke drum are a known issue to the operators, our patented automatic stabilization technology based on cosmic radiation has proven to be the most important feature to guarantee a stable and reliable level measurement without the need for recalibration. Separate level alarms ensure additional process safety. The same applies for the fractionator. Our level gauges are used to monitor the bottom liquid level – an important parameter for the efficient control of the complete coking cycle. The measurement is unaffected by surface turbulences, product falling down from the trays, different product densities and scaling/coking.

Customer benefits

  • Reliably prevents pump cavitation and improved utilization of drum capacity
  • Prevents of foam or liquid entering upper fractions
  • Uneffected by foaming, plugging, build-ups or changes in operational and/or product changes
  • Easy to install on existing columns – no process downtime
  • Non-intrusive and non-intrusive level measurement


  • Immune to interfering radiation with built in XIP, or continue measuring during weld inspections with RID
  • High level switch used to compensate continuous level for gas property changes in the coke drum
  • Highest sensitivity due to solid scintillators, leading to significantly lower source activities
  • Outstanding compensation functions (GPC and PBC) prevent falsification of measured values by process influences, such as wall build-ups or fluctuating gas properties

Whitepaper "Nuclear level devices on coke drums"

Global refiners are always seeking new techniques to optimize their refinery assets with the purpose of maximizing their profitability. Since delayed coking is one of the most profitable units in the refinery, many refiners are turning to this proven conversion technology. One of the most critical measurements in a DCU is the level measurement inside the drums. For a long time, neutron backscatter measurements were used for this purpose. In the meantime, this technology is complemented or even completely replaced by continuous gamma level measurement. The challenges of the level measurement as well as the advantages and disadvantages of these technologies, can be learned in this whitepaper.

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Berthold Webinar

Increase reliability and profitability in the delayed coking unit

LEARN FROM OUR EXPERTS how to increase reliability and profitability in the delayed coking unit with continuous level measurement. Our top minds take you through Berthold's solutions to the challenges faced when measuring level in a coke drum.

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SIL certification available

The SENSseries LB 480 series offers versions that are certified for use in SIL2 applications. SIL3 is achieved by adding an identical redundant SIL2 detector using the same source for homogenous redundancy. The certificate covers all measurement applications, from high level or low level alarms to continuous level. Thus the safe measurement of critical processes is guaranteed.

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Long-term stability

A reliable measurement, requiring no recalibration, is vital for the operation of the delayed coking unit, and is our highest priority. Berthold’s detectors offer stability in the face of changes in ambient temperature. Even drastic temperature shifts, e.g. from winter to summer do not cause measurement drift. Our patented method for detector stabilization compensates for temperature changes and aging.

Detector Stability

Gas Property Compensation (GPC)

Gas property fluctuations in large vessels can greatly impact the amount of gamma at the detector, and therefore impact the measured value, if Berthold's gas property compensation is not added. With GPC, a second detector monitors how much the gas properties are effecting gamma transmission. Based on this, the level detector compensates for changes in gas properties, providing a reliable level measurement. 

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TowerSENS detector for the best solution

TowerSENS Detector

TowerSENS detector with a maximum length of 8 m (cascaded to cover up to 32 m), this rod detector is designed to monitor long measuring ranges