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Open Discussion Forum

If you have a question we can place your inquiry in the open discussion forum and we will post responses from the industry. The industry pool of knowledge is far larger than any one person's experience. Please contact us with your inquiries and we will post the inquiry and the industry responses.

1. Please review the case histories in the DeMethanizer of an Ethylene Plant regarding studs / bolts failure along with best inspection practices / methods being followed for flanges / studs in cryogenic service? Ethylene Producer

2. We have five ethylene cracking furnaces in a Gas cracker plant. The furnaces have "W" configuration coils with inlet at tube number 1 and common outlet of two adjacent coils at tube number 4. The metallurgy of the coil has been upgraded with passage of time. At present, we are using HP40 micro alloy in four furnaces and a combination of HP40 (for cold passes) and 35Cr45Ni (for hot passes) in one furnace. Though we have successfully solved various furnace problems, coil bowing is a chronic problem, which we are struggling to deal with. To solve coil bowing, we have been regularly adjusting the variable spring hangers used to support the coil. However, significant improvement has not been observed. In addition to spring adjustment, we have been monitoring the elongation of tubes during cracking. Recently, we have decided to replace variable spring hangers with constant spring hangers. (Ethylene Producer)

3. We have 192 selas vortex K-9206 burners installed on the vertical walls of our ethylene cracking furnace. The walls are I.F. brick lined. Furnace tubes are vertically hung along the centre of the furnace. The burners are fired with natural gas. Coil outlet temperature (COT) of the furnace tube controls the gas flow to the burners. If the COT goes low, gas flow to burners would increase to increase the heat duty and vice versa. Over the years, COT has been increased to increase the ethylene margins. Due to this, the original tip opening of the burners has been increased from 3.3mm to 3.73 mm. this modification in the burner tip was carried out about one year ago. We are now observing high tube failures with indications of high surface temperatures on failed tubes. What is the groups experience with similar modification?

4. We are operating ethylene cracking furnaces of Selas and Lummus design. One of the important operating parameter is to restrict the tube metal temperature within metallurgical limits. For this purpose operators are required to record the tube temperatures by using optical pyrometers and recording it manually on a log sheet. To reduce the element of human error and omission, we would like to introduce some kind of data logging system which automatically records the temperature when the operator points it a tube and the readings could be afterward uploaded on a PC for analysis / corrective action. Appreciate if any one on the forum suggest any equipment, preferably tested one or any other idea to eliminate fudged reading from the log sheet.

5. Can you tell me your preferred way to measure differential pressure across a distillation column? Examples: Pressure transmitters at each point with a calculation in the D.C.S. A differential pressure transmitter located on top of the column.

6. We have an Ethane Cracker, where we face fouling in the Cracked Gas Compressor Intercoolers. The compressors are treated with a major anti-foulant program and are injecting with wash water. Wash oil is also injected intermittently. Each stage outlet temp is between 95-105 degrees C. The compressors themselves appear clean, since their polytrophic efficiency is steady. A black polymer deposit is however noticed on inlet tube sheet of the inter-stage coolers (process gas is on tube side). As a result pressure drop across the system increases causing plant shutdowns. We also notice that the inter-stage knock drums are inadequate causing liquid entrainment to compressors; can this result into fouling?

7. We have five ethylene cracking furnaces in a Gas cracker plant where we have a problem of tube leaks in convection bank, dilution steam section. What is the best way to repair the furnace tube leaks?

8. We have a gas cracker unit of capacity X MT per annum of Ethylene based on Ethane-Propane feed. We would like to share with you the problem of high differential pressure in water Quench Tower, we have been experiencing for more than last 2 -2 ½ years. We had inspected Quench Tower & oil water separator in the last shut down of July and observed that in QT, all primary / secondary quench water spray nozzles & pre-saturator section spray nozzles / splash baffles were intact and were also found clean. All 18 trays in the tower were also intact & clean this time as tower was opened after gasoline wash prior to shutdown.

However, We found good quantity of tar deposit in oil water separator 1st compartment which was partially cleaned as complete cleaning was not possible due to material being very hard & not coming out even by water hydro jetting. We restarted our plant on July 22, & we were puzzled to note that when we did not find any problem in tower / its internals then why Quench tower pressure drop is increasing over a period of just 1 ½ months and once again reached 0.189 kg/cm2 from 0.09 kg/cm2 at start of run during the month of Sept.

In the month of Nov, we did exhaustive cleaning of complete circuit (Quench tower + all QW exchangers + connected piping etc) with Pyrolysis gasoline. Subsequently during operation, we had kept a close watch & control on various Quench tower parameters and were able to sustain Quench tower operation for around 08 months. But again we have been facing problem of high differential pressure for last 15 days subsequent to start up of the plant after short shutdown in July, We have observed that the quantity of tar getting separated/ removed remains on lower side i.e. 10-15 kgs/day as against 100 kg/day used to be earlier and characteristic of tar is sometimes thick paste & sometimes powdery. (August)

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