High Temperature Induced Draft Fan for 900 C Service

Overview

900 C approaches the scaling limit of conventional austenitic stainless steel. Grade 310S or 253MA is used with an aluminium diffusion and pre-oxidation treatment, while the drive moves to a circulating oil unit so that water cooling and forced lubrication keep the bearings within range.

Material Selection at 900 C

At this level surface treatment and cooling design matter as much as the base grade.

Location	Material / process	Basis
Impeller and casing	06Cr25Ni20 or 253MA type heat resistant stainless	Higher creep and scaling resistance required
Surface treatment	Aluminium diffusion followed by pre-oxidation	Extends the scaling life
Bearing assembly	Water cooled housing with oil circulation unit	Positive cooling and stable lubrication
Insulation	100 mm ceramic fibre with composite lining	Brings wall temperature within the material limit
Instrumentation	Thermocouples at inlet and casing	Enables over-temperature alarm and interlock

Structural Measures at 900 C

Location	Material / process	Basis
Composite lining	Ceramic fibre with lightweight insulating brick	Better insulation and anchor protection
Shaft thermal sleeve	Insulation sleeve, cooling medium if required	Controls the temperature gradient
Expansion joints and sliding feet	Sized for the full 900 C growth	Releases thermal stress
Infrared inspection	Periodic measurement during operation	Finds local hot spots and lining damage
Over-temperature interlock	Alarm and trip settings	Protects the fan from process upsets

Applications

Typical duties are yellow phosphorus tail gas, carbon roasting furnaces, submerged arc furnace gas and lime kilns.

Yellow phosphorus tail gas is hot and carries phosphorus and fluorine compounds, so material and lining must address high temperature and chemical attack together.

An over-temperature alarm and interlock, with sensors at the fan inlet and in the casing hot zone, allows abnormal conditions to be found early.

Acceptance and Verification

Standard	Title	Purpose
GB/T 20878	Stainless and heat-resisting steels - Designation and chemical composition	High temperature and corrosion resistant grades
GB/T 3003	Refractory fibres and products	High temperature lining material and acceptance
GB/T 12777	General specification for metal bellows expansion joints	Expansion compensation for hot ducts and casing
GB/T 1236	Industrial fans - Performance testing using standardized airways	Air flow, pressure and efficiency testing
GB/T 9239.1 / ISO 21940-11	Mechanical vibration - Balance quality requirements for rigid rotors	Impeller balancing grade

Please provide gas composition, temperature, dust load and air flow. Fan size and motor power are calculated for the actual duty.

FAQ

Can 310S still be used continuously at 900 C?

Yes, but the oxide layer grows faster. Aluminium diffusion and pre-oxidation extend the scaling life, and inspection intervals should be shortened accordingly.

Are both an oil unit and water cooling needed?

Under the radiant load at 900 C, grease lubrication alone is not stable. The oil circulation unit handles lubrication and heat removal while water cooling isolates the heat source.

What is special about yellow phosphorus tail gas?

The gas is hot and its composition differs from ordinary flue gas, combining high temperature oxidation with specific chemical attack. Material and lining must be evaluated for the actual gas composition rather than copied from another industry.

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