2 replies to this topic

[iplan]

This is regarding wash water injection at the reactor downstream of hydrotreating / unifiner / hydrocracker reactors. We are using condensate water for wash water injection and prior to injection , the condensate is cooled by cooling water. If the exchanger leaks then cooling water leaking into this wash water would cause chloride ingress in the wash water that would be supplied to proces units and cause problem in steel used in process units.

I would like to know

Is it okay to use cooling water to cool this wash water
How the risk is mitigated.

Many thanks
iplan

[S. Biswas]

From design point, if chloride content in cooling water is less than 50 ppm, corrosion is not an issue - regular CS material is okay. In case it is more than 50 ppm, it calls for a special requirement on metallurgy.

Secondly, cooling water operating pressure is generally lower than wash water pressure. If so, cooling water can not go into wash water side in case of tube leakage or rupture.

Thanks,
Sahajamal Biswas

This is regarding wash water injection at the reactor downstream of hydrotreating / unifiner / hydrocracker reactors. We are using condensate water for wash water injection and prior to injection , the condensate is cooled by cooling water. If the exchanger leaks then cooling water leaking into this wash water would cause chloride ingress in the wash water that would be supplied to proces units and cause problem in steel used in process units.

I would like to know

Is it okay to use cooling water to cool this wash water
How the risk is mitigated.

Many thanks
iplan

[Zauberberg]

Cooling water supply pressure usually ranges between 5-8bar, and it's hard to imagine that you have lower pressure on the wash-water side - unless there is a booster pump downstream of condensate cooler.

What is the purpose of cooling the condensate? If I understood your application correctly, the idea of injecting condensate is to maintain some liquid water at the inlet nozzle of heat transfer equipment in order to prevent corrosion and fouling. So you have calculated the amount or water which is going to be injected until you reach such conditions (water vapor pressure) when the water will stop evaporating and some part of it will remain as liquid, providing continuous equipment washing. Is that your application? I have seen similar (continous or intermittent) services in CDU/FCC tower overhead system, also in Naphtha Reformer units.

Injected condensate is going to evaporate anyway till you reach the conditions when some ammounts of condensate have to remain as liquid, simply driven by phase equilibrium at injection point (pressure, temperature, water dew point). The only difference in these two cases - injecting warm or cold condensate - is in the relative amount of condensate which needs to be injected, and the difference is calculated and expressed by sensible heat content difference between warm and cold condensate. In simple words, if you use warm condensate, you will have to inject it a little bit more than if you are using cold condensate. But this difference is usually very small, since the main contributor to temperature reduction of process stream comes from the condensate evaporation (latent heat), rather than heating it up to its boiling point (sensible heat).