Blasch Precision Ceramics

CONFIDENTIAL © 2019 Blasch Precision Ceramics

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Blasch Precision Ceramics Answering the Right Questions

A Different Perspective on Designing with Refractory Materials


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The Question

People have been asking the tough

questions for millennia…

‒ Like, “How do we design this

thing so the stone beams

won’t crack and fall on our

heads, thus killing us?”


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The Answer

People have been answering those questions

since the beginning of time…

‒ This is sometimes referred to as the Brute

Force approach, and while it is effective, it

has significant limitations…

‒ You reach a point of diminishing

returns.

‒ You remain limited by the parameters

of the original design.


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The Right Question

The right question should not be how to make

the existing design work better, but how to

best achieve the aims that the existing system

was designed to address…

‒ Like, “How can we span greater lengths

and support more weight?”


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The Right Answer

The right answer almost always starts with a

fresh look at the problem and a blank sheet

of paper.

‒ And it can sometimes yield solutions

that are great leaps forward…


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The Right Answer

And, sometimes, asking the right question makes all the difference in the world…


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The Right Answer

So, what does this have to do with refractories in process plants? We’re not building cathedrals here…

‒ You’d be surprised how many process vessels contain free-standing brick structures, or tons of

monolithic refractory, for example…


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The Right Answer

Why is that?

‒ Refractory can be difficult to form into complex shapes, and brick and monolithic refractories are

simple and cheap to produce.

‒ Brick and monolithic have been used since the earliest days of metal and chemical processing.


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Types of Ceramic Materials

Ceramic products are usually divided into four sectors:

Structural – Including bricks, pipes, floor and roof tiles.

Refractory – Kiln linings, gas fire radiants, steel and glass making crucibles.

Whiteware – Tableware, wall tiles, pottery products and sanitary ware.

Technical – Also known as Engineering, Advanced, Special, and in Japan, Fine Ceramics. Such

items include tiles used in the Space Shuttle program, gas burner nozzles, ballistic protection,

bio-medical implants, jet engine turbine blades and missile nose cones. Frequently the raw

materials do not include clays.


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re·frac·to·ry (/rəˈfrakt(ə)rē/)

adj.

‒ 1. Obstinately resistant to authority or control. See Synonyms at unruly.

‒ 2. Difficult to melt or work; resistant to heat: a refractory material such as silica.

‒ 3. Resistant to treatment: a refractory case of acne.

n. pl. re·frac·to·ries

‒ 1. One that is refractory.

‒ 2. Material that has a high melting point.

Definition of “Refractory”


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Refractories can tolerate high temperatures (1,750 °C for common materials), and are capable of

repeated thermal cycling. This is due to a coarse grained, non-fully dense body with a unique

bond phase. This makes it easier for the body to react to changes in temperature without

generating fatal stresses. The vast majority of materials used in the process plants are

refractories.

Chemical resistance varies, generally depending on the bond phase.

Refractories in general wear fairly well, but not nearly as well as a fully dense technical ceramic.

This too is directly related to the composition of the bond phase and the fact that it is generally

much softer than the particulate that makes up the body.

Characteristics of Refractory Ceramics


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Technical ceramics are generally very fine grained, fully dense, sintered bodies with no bond

phase. In this respect they resemble metals, except that for their hardness and temperature

capabilities, they cannot be melted and poured (so make that PM parts).

Technical ceramics have much better abrasion resistance than refractory grade materials

because their dense, uniphase configuration.

Technical ceramics are difficult to form in any size and complexity, as pressing and slip casting

yield generally simple shapes, and extensive machining is required for more complicated

geometries.

Characteristics of Technical Ceramics


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Modulus of Rupture

‒ ASTM C133 Standard Test Methods for

Cold Crushing Strength and Modulus of

Rupture of Refractories.

‒ MOR measures breaking strength of a bar

with an unsupported span.

Relevant Properties of Refractories


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Creep

MOR properties change significantly with

temperature.

Refractory will exhibit creep at temperatures

approaching its maximum use limit.



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Temperature Differentials

Differential in temperature across sample greatly

increase stress.


Static Stress

‒ FEA of 9”X9”X42” Slab

‒ Constant 1900 ºF

temperature

‒ 10 psi max stress

Thermal Stress

‒ FEA of 9”X9”X42” Slab

‒ 10 ºF temperature

variation

‒ 1500 psi stress


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Mortar does not “glue” things together

Mortar weakens precipitously at temperatures

above 1,600 °F.

Thermal cycling causes shearing.

Really cannot be considered a high temperature

adhesive.



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Reversible linear thermal expansion (and contraction)

Refractories expand as they heat up and contract as they cool down.

It is imperative to compartmentalize and limit this effect to the local area.

Cool down is more damaging because the shrinking cool face is pulling the hot face into tension.


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Examples of Traditional Refractory Design

Sulfur Recovery Unit Reaction Furnace Checkerwalls.

Spent Acid Regeneration Furnace Baffles.

Precast Boiler Tube Ferrule Systems.

Top Fired Steam Methane Reformers Flue Gas Tunnels.

Coreless Induction Furnace Linings.


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SRU Reaction Furnace Checkerwalls


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Flat spans invite creep.

Mortar is extremely weak at temperature.

Use the lesson of the arch.

Use mechanical engagement rather than

mortar to retain/contain assembly.



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Spent Acid Regen Furnace Baffles


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Not tied into full circumference of the furnace.

Relies on mortar for structural integrity.



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Precast Boiler Tube Ferrule Systems


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For many decades simple round ferrules

embedded in a monolithic refractory have been

the standard for high temperature waste heat

boiler tubesheet protection.



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Reliability of a round ferrule installation is

strongly influenced by:

‒ Selection of refractory.

‒ Type of anchors used.

‒ Skill of the installers.

‒ Care of the cure out.



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If concrete requires expansion joints to survive

100 °C temperature swings over periods of many

months, how can one expect refractory to

survive 1,700 °C swings in days without them?



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Ferrules are specifically designed to fit each

application’s tubesheet and unique set of

operating conditions.

Each ferrule is impacted only by those around it.

Particularly compatible with systems that use

oxygen enrichment and those with very large

tubesheets, where stresses can be quite large.



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No castable is required between the ferrules.

During installation, some castable would be

needed around the perimeter of the ferrules, but

the amount needed would be quite small in

comparison to a conventional installation. This

system can typically be installed in about one third

of the time it would take to do a conventional

installation. Additionally, refractory cure times can

often be reduced during startup.



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Replacement costs are quite low. If the plant

owner wishes to inspect the tubesheet, they

would typically need to remove the ferrules. For a

conventional installation this is time consuming

and costly because the castable must be removed

and the ferrules cannot be reused. For precast

ferrules, such activities are simpler; typically only

small fraction of the ferrules need to be replaced,

which substantially reduces maintenance costs

and downtime.


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Top Fired SMR Flue Gas Tunnels


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Coreless Induction Furnace Linings


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The basic furnace consists of a metal structure

(furnace box), water cooled alternating current

coil operating at very specific currents and

frequencies. The coil produces a magnetic field

which causes eddy currents to flow within the

charge. Resistance heating from this induced

current within the metal heats the charge raising

the temperature to its molten point.



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This thermal gradient is what gives the lining its stopping power. The difference in expansion associated

with the temperature gradient results in a strain proportional to this gradient. This strain adds to the stress

state of the lining.


HEAT


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Thermal Expansion

Because of the high temperature, there is

thermal expansion in the ceramic shown here

both in the vertical and horizontal directions.



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For a reference scale, in our example we will look at a 3 ton

lining heated to 1,600 °F.

The “green” color is shown the starting size, while the light red

color shows its expanded size after heating.

The lining is constrained in the bottom, this vertical expansion

goes up from the base.

The height of this lining will expand as much as 7mm.

The ID expansion is proportionally greater than the OD.

expansion because of the thermal gradient through the lining

wall. This constraint results in stress.



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One Piece Lining

The FEA results show the ID of the lining

experiencing a higher stress than the OD,

which occurs because of non-uniform

thermal expansion. This stress will weaken

the ceramic causing cracks.

The cracking of the lining results in a series

of smaller pieces which reduce stress.



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Mortared Brick Assembly

The max stress seen by the ID of the

mortared brick lining is similar to the stress

seen by the monolithic rammed lining. This

is expected, since the mortared brick will

act as a singular body, up until the point

where the thermal stress causes the

weakest portion of the system (the mortar)

to break.



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Failure (cracks) Due to Thermal Stresses



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Segmented Interlocking Brick Assembly

What if we reduced the assembly into non-

mortared interlocking bricks? In order to

best accommodate thermal growth, every

block now manages its own thermal

expansion and the entire system must be

mortar free, but for stability reasons must

be completely interconnected.



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The Interlocking T&G system provides mechanical advantages to deal with the adverse temperatures

required with molten metal melting.

Mortared Brick One Piece Interlocking T&G


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Interlocking T&G Lining


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Keep material in compression.

Do not confuse mass with stability.

Protect from point loading.

Isolate from impact and vibration.

Work with thermal cycling, not against it.

Decouple stresses, do not magnify them.

Smaller components working together work better.

Design Guidelines to Keep in Mind


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Thank You

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