Note that this is a Discussion article more than being conclusive. Feel free to engage – mail us at barnie@pbe-projects.com
I should also say that I think the interweb has enough material addressing generic issues and explanations, so I wish to be a bit more specific. Here I address two very specific matters.
1. Expired insulating materials in a dual layer linings and
2. Thermocouple placement.
It may seems an odd pairing, but it formed part of an interesting discussion and manner of thinking which I found interesting.
Expired material:
Assuming a hydraulic bond L.W AL2O3-SiO2 insulating backing lining is expired and expiration motivated by time/deterioration:
In this case we are dealing with a 20% CaO content material with a density of 0.73gr/cm3. And following API 936 section “7.2.4 Shelf Life” … +3 months past expiration test were done. But a further 3 months has passed. Besides the obvious fact that it is out of it *best before date, setting times were a natural consequence and it is worth saying that in spite of optimal storage conditions, inherent deterioration is inevitable. Herewith some detail a the point where the material was 6 months past is Best before date!:
- Forms were originally removed 12 – 24 hours after final pour – depending on thickness and geometry. But with the aged material days later a 6mm welding rod could be pressed into it about 25% deep and come out damp.
- Client: “…it’s all we have and we have to use it, besides it’s the backing lining and the high density hot-face lining has no curing issues.”
The Questions then becomes:
- What is the impact on insulating value when LW insulating material does not cure optimally?
- Will the insulating material have sufficient strength to avoid crumbling between the casing and the dense lining under the inherent pressure it is exposed to a) during dry out and b) in process conditions.
- If curing of an insulating (or any for that matter) lining does not occur optimally; does it affect the amount of moisture retained in hydrate and chemical phases?
- Does the excess free water cause concern…. these are questions one should not be asking but here I am.
- With a high porosity material one could likely assume “excess liquid” will evaporate – but I’m trying to better understand the impact of residual liquid that did not bond? Does it mean the amount of free water that has to be released at +-100deg C increases?
- Lastly, does it dictate an extended dry out?
- Assuming and extended dry out is necessary, at which temperature(s) should Holds be prolonged?
- Needless to say but I guess necessary is that – Inevitably the owner takes the risk if they decide to continue using expired material.
Thats about it for the subject above, feel free to share your comments.
Now for Thermocouple placement:
Not “where” in terms of keeping it out of a sump that may fill up with condensate, or a cold spot…but instead whether it should be flush or raised form the linings surface, one may even debate wheterit should be within the lining, but for the sake of this conversation I am not going to:
API says 13mm above the surface of the refractory, but various articles and specialists says – on the surface. With a understanding that gas vs surface temps differ significantly.
So, which is the correct way?
13mm of the surface or tight to the surface?
The way I see it, API has gathered the best minds in the inductry to guide us, and there should be no reason to question them – but naturally we do. Lets consider these 3 points in favor of the half an inch of the surface principle.
- Vapor may cool the Thermocouple as it is released.
- Heat capacity of the lining implies various material based on density and mineral composition will transfer heat to the Thermocouple diferently.
- Hold times and slow curves – or heat up strategies.
That’s relay all I want ot say about dry outs now, in a next discusion I may elaborate on winter vs “normal” fuels, and types of fuel considering stoichiometry, carbon depsosition on intermediate lining dry outs and using gas instead to avoid that.