Microporous Insulation for Hot Blast Ducts

The hot blast system is where a blast furnace’s energy efficiency is quietly won or lost. Stoves preheat the combustion air to well over 1000 °C, and ducts carry that blast to the tuyeres under pressure. Every degree lost through the stove shell and duct walls is a degree that has to be made up by burning more coke in the furnace. Nano microporous boards, layered inside the duct and behind the stove lining, keep more of that heat where it belongs.

Why Blast Temperature Is So Valuable

Hot blast temperature is one of the strongest levers on coke rate and furnace productivity. Higher blast temperature means the furnace needs less coke to reach the same tuyere-raceway conditions, which lowers fuel cost and raises output per tonne of hot metal. The practical limit is how much heat the stoves and ducts can hold on to — and that is where insulation quality decides the ceiling.

How the Insulation Is Applied

In hot blast ducts, several layers of microporous board strip are applied inside the duct shell, then the refractory layer is installed over them. In the stove itself, the boards serve as a backup layer behind the working refractory on the dome and the combustion chamber walls.

Prepare the duct or stove shell interior.
Layer microporous boards or strips against the shell, closing joints to form a continuous barrier.
Install the refractory working layer over the boards.
Use flexible sheet for the duct bends and transitions where rigid board is hard to fit.

Because the board is only millimetres thick for a given thermal resistance, it fits inside ducts without meaningfully reducing the gas cross-section — a real advantage over bulky ceramic-fibre or insulating-brick packs.

The Efficiency Gain

Lower heat loss from the stove shell and duct walls.
Higher blast temperature delivered to the tuyeres.
Reduced coke rate for the same furnace output.
Cooler duct and shell surfaces, which improves working conditions and shell life.

On the efficiency side, the same microporous backup approach that lifts blast-furnace hot-blast efficiency by roughly 10% in field comparisons against conventional backup insulation is what makes the layer worth specifying. The board’s thermal conductivity — down to 0.021 W/m·K at 200 °C — is the reason it outperforms ceramic fibre of far greater thickness.

Board Selection for Hot Blast Systems

Hot blast systems run at high interface temperatures, so grade selection matters. Grade 1000 (1000 °C) is used where the board sits well behind the hot face; Grade 1100 (1100 °C) is specified where the layer sits closer to the blast temperature. A layer-by-layer thermal calculation confirms that the board never exceeds its continuous-use rating.

Property	Grade 1000	Grade 1100
Classification temperature	1000 °C	1100 °C
Density	220–280 kg/m³	220–280 kg/m³
Thermal conductivity, 200 °C	0.021 W/m·K	0.021 W/m·K
Thermal conductivity, 800 °C	0.034 W/m·K	0.034 W/m·K
Form	Board, strip, flexible sheet	Board, strip, flexible sheet

For duct bends and the stove dome, flexible sheet and custom-shaped boards follow the geometry without the gaps that flat boards leave on a curve.

Recommended products for this application: standard boards for the stove, flexible sheet for duct bends, and custom-shaped boards for transitions.

Frequently Asked Questions

Does the board restrict blast flow?

No. Because the board achieves its insulation in millimetres, it adds far less wall thickness than ceramic fibre or insulating brick, so the duct cross-section stays essentially unchanged.

Can the boards take the hot blast pressure?

The board is a backup insulator behind the refractory layer; the refractory carries the gas pressure and abrasion. The board’s job is thermal, not structural.

How do you verify the temperature rating is safe?

By layer-by-layer thermal calculation. Each layer’s conductivity and thickness are assigned, and the interface temperature at the board is checked against its continuous-use rating before the design is finalised.

How is the board fixed inside the duct?

The boards are layered against the duct shell and held by the refractory layer applied over them. On curved transitions, flexible sheet wraps the profile and is secured before the refractory goes on, so there is no sag or gap during service.

Holding blast temperature is holding margin. Contact us for a hot-blast-specific board and thickness recommendation, or review our standard board range. Contact us to get started.