High temperature induced draft fan

High Temperature Induced Draft Fan for 600 C Service

Product description: Induced draft fan for 600 C service: material selection, insulation and water-cooled bearing design, applicable processes and acceptance standards.
INQUIRY

Overview

600 C is firmly in heat resistant steel territory and usually comes with heavily dust laden gas. The main material is 12Cr1MoV, the bearing assembly is water cooled and the casing is lined with ceramic fibre, so temperature, wear and sealing are solved together.

Material Selection at 600 C

Pearlitic heat resistant steel provides the creep and oxidation performance needed at this level.

Location	Material / process	Basis
Impeller and casing	12Cr1MoV (GB/T 5310)	Good creep and oxidation resistance at 600 C
Welding consumables	Heat resistant electrodes (GB/T 5117)	Maintains weld strength at temperature
Bearing assembly	Water cooled bearing housing	Removes bearing heat positively
Insulation	50 mm ceramic fibre lining plus external insulation	Lowers metal wall temperature
Wear zones	Hardfacing on blades and liner plates	Combines temperature and abrasion resistance

Structural Measures at 600 C

Location	Material / process	Basis
Water cooled bearing housing	Jacket with circulating water and temperature monitoring	Keeps bearings within their limit
Expansion joints	Bellows joints in hot ducts (GB/T 12777)	Absorbs thermal displacement
Combined sealing	Labyrinth seal with graphite packing	Limits hot gas leakage
Welding procedure qualification	Qualified procedure with test coupon	Prevents weld cracking in service
Ceramic fibre anchoring	Anchors fixed to the casing	Stops the lining from collapsing

Applications

Typical duties are power plant boiler induced draft, cement kiln tail gas, coke oven gas and carbon rotary kilns.

Dust load is often high at this level, so wear resistance and temperature resistance have to be designed together.

Where dust load is high, a pre-collector ahead of the fan is recommended and the separation efficiency should be written into the technical agreement.

Acceptance and Verification

Standard	Title	Purpose
GB/T 5117	Covered electrodes for manual metal arc welding of non-alloy and fine grain steels	Welding consumable matching
GB/T 1236	Industrial fans - Performance testing using standardized airways	Air flow, pressure and efficiency testing
GB/T 12777	General specification for metal bellows expansion joints	Expansion compensation for hot ducts and casing
GB/T 9239.1 / ISO 21940-11	Mechanical vibration - Balance quality requirements for rigid rotors	Impeller balancing grade
GB/T 10178	Industrial fans - Performance testing in situ	On-site performance verification

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

FAQ

Does a water cooled bearing housing add failure points?

It adds cooling water management, but without water or forced cooling the bearing life at 600 C cannot normally be guaranteed. Water temperature, flow monitoring and a low flow alarm are recommended.

Does the impeller need hardfacing at 600 C?

For dust laden gas, yes. Hardfacing is normally applied to the wear prone areas and the rotor is re-balanced to G6.3 or tighter afterwards.

Why is welding procedure qualification emphasised?

Pearlitic heat resistant steels such as 12Cr1MoV are prone to hardening and cracking in the heat affected zone, and the risk grows during long term hot operation, so consumables, preheat and post weld treatment follow a written procedure.