Alloy for Pyrolysis Reactor 1

[Mohsen_81]

Hi all,

In Waste Plastic Pyrolysis, we faced severe corrosion problems in our Pyrolysis Reactor.

Operating condition:

-Feed: Mix of waste plastic​

-Temperaure: up to max 850°C​

-5hours Pyrolysis, 2-3 hours regeneration (combusion+deckocking)​

-Time by time cool down to room temperature for maintenance.​

Material:

-Shell and pipes alloy: Incoloy Alloy 800H Severe corroded​

-Sintered plate: Hastelloy X Corroded​

Do you have any idea/experience which material can be replaced to solve the corrosion problem?
Thank you

 

[MJCronin]

WOW ----- Waste Plastics (high chloride) at 950 C (1562 F) ???

Corrosion on Incoloy 800H and Hastelloy C ????

You have run out of materials .... My guess is pure NICKEL - ???? - It will not be cheap .....

This is what happens when Chemical Engineers Design processes without regard to limitations of modern metallic materials ....

MJCronin
Sr. Process Engineer

 

[Compositepro]

Refractory linings are often used in such applications.

 

[EdStainless]

Look up what is used in medical waste incinerators. Typically C type alloys (C22, 686) is used where cooler and refractories used in hotter sections.
Controlling the moisture, oxygen, and temperature is critical. And what you are adding to assist emissions control.
You also have to prevent any deposits from forming.
This is all combustion control.
I have seen C22 weld overlay work well, until things get out of balance and then the overlay gets destroyed in a single run.
There is no easy fix.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

EdS,

You are correct, everything critically depends on combustion control.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[davefitz]

similar corrosion occurred on many MSW combustion furnaces in the 1990's- they originally used carbon steel furnace waterwalls, but they corroded to paper thin and failed within 2 yrs. They had the tubes replaced with a weld overlay of inconel, but the key factors in reducing the corrosion involved understanding the ash chemistry of the molten material on the walls. Maintaining the wall surface temperature below ( 500 F ?) and preventing an alternating oxidizing/reducing environment via better combustion control and improved pre-combustion mixing of waste feed solved the problem. The use of high temperature O2 probes to better control combustion and improving the removal of lead or aluminum debris in the waste feed helps as well, but in order to maintain the wall surface temp below ( 500 F) it is neccesary to limit the boiler's drum operating pressure. This limits the steam cycle efficiency. As I recall the wall molten ash was a lead- chloride mixture, and of course all ash in the convection pass was laced with dioxin- nasty stuff.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

 

[isoca]

as i understood, corrosion problems are in the side that is in contact with the polymer mix. If this is the case, do you have any information about the atmosphere composition? I agree that C22 could be a good alternative but I have some doubts regarding the service temperature (850ºC)

 

[Mohsen_81]

@EdStainless
Thanks for your reply.
In the second line, you mentioned moisture and oxygen control. What is the problem with moisture at this high temperature? And what should be controlled regarding oxygen?
It is not also possible to prevent deposit formation. We remove that by decocking.
And what do you mean by "things get out of balance" in the last line?

Thank you so much.

 

[blacksmith37]

Be careful with decoking; steam air decoking can overheat about anything. Is it known if the main damage occurs during the process or decoking ? Is the reactor a single vessel or several tubes ? Recycles plastics sounds like chloride from PVC.