Q & A > Question Details
We are interested in reducing treatment load on spent caustic treatment unit. Then we are going to idle visbreacker gasoline treatment process by feeding it to other units. At present we use sweetening process (washing with caustic and converting with Merox) for visbreacker gasoline product. The problem regarding to produced spent caustic as byproduct is unreliable spent caustic treatment process to meet the environmental specs. The alternatives are suggested as follows:
1- introducing to heavy naphtha hydrotreater unit (unifiner)
2- introducing to Kerosene/diesel hydrotreater unit
3- introducing to hydrocracker unit
4- sending to crude storage and refine it again
Would you please explain pros and cons about the abovementioned alternatives? What is the best alternative?
13/11/2017 A: Eric Hennings, Technip Stone & Webster, Eric.Hennings@technipFMC.com
Visbreaker naphtha is similar to coker naphtha and contains olefins . Downstream processing such as hydrotreating must address the increased heat of reaction (and H2 consumption) when hydrogenating these species. In addition, cracked naphthas contain diolefins which are susceptible to polymerization when mixed with O2-containing process streams. Air can ingress into process through atmospheric storage tanks. Note that even sat hydrocarbons can absorb air and later mix with cracked naphthas in the hydrotreating process, even when cracked naphthas are sent direct. Polymerization will increase fouling of the hydrotreater preheat exchangers and fired heater tubes. Olefins can also create issues in Alkylation under certain circumstances. If sat-butane stream is pre-fractionated in the presence of trace acid, then olefins will react prematurely. For this reason, cracked slop into the Crude Unit is avoided.
Best alternative is send direct to coker or FCC gas plant. Avoid sending any cracked naphtha to storage where it can absorb air.
10/11/2017 A: Sridhar Balakrishnan, Bharat Oman Refineries Limited , laksrid@yahoo.com
The best way is adopt one of three alternatives as suggested introducing to HNUU ( Unionfiner) , hydrocracker unit, Kerosene or Diesel hydrotreater unit. The disadvantages may be since visbreaker cracked gasoline contains lot of diolefins and heteroatoms , hydrogen consumption can increase. Catalyst cycle length can reduce . Sending it to crude oil storage would be , more than advantage , disadvantages are also there . Since being a cracked product during merox processing of kerosene , JFTOT failures can occur. The product needs to be hydrotreated , or else instability of the stream takes place.
08/11/2017 A: William Collings, Jacobs Consultancy, dave.collings@jacobs.com
1, 2, and 3 are all viable. 4 sounds like advice that could cause career problems. The idea that fits best depends on your current kit and capital constraints. You need a configuration study to choose the best option.