High temperature induced draft fan

High Temperature Induced Draft Fan for 800 C Service

Product description: Induced draft fan for 800 C service: material selection, insulation and water-cooled bearing design, applicable processes and acceptance standards.
INQUIRY

Overview

800 C calls for grade 310S. Its 25 percent chromium and 20 percent nickel form a stable oxide film in strongly oxidising gas, and a ceramic fibre lining behind the casing keeps the metal wall temperature down. Lining anchors and expansion joints decide whether the lining survives.

Material Selection at 800 C

High chromium and nickel content is what makes 310S suitable for strongly oxidising gas at this level.

Location	Material / process	Basis
Impeller and casing	06Cr25Ni20 (GB/T 4237, GB/T 20878)	Good scaling and creep resistance at 800 C
Welding consumables	Heat resistant stainless filler (ER310 type)	Prevents high temperature cracking
Bearing assembly	Water cooled housing with forced circulation	Maintains bearing temperature
Insulation	80 mm ceramic fibre with anchors	Lowers wall temperature and heat loss
Expansion joints	Bellows joints (GB/T 12777)	Absorbs duct and casing movement

Structural Measures at 800 C

Location	Material / process	Basis
Anchored lining	Stainless anchors secure the ceramic fibre	Prevents lining from blocking the flow path
Expansion joints in the lining	Divided according to thermal growth	Stops the lining cracking on heat up
Sliding supports	Guided sliding structure	Releases large casing expansion
Weld inspection	Penetrant testing on critical welds	Finds crack initiation sites
Bake-out procedure	Controlled heating curve to remove moisture	Protects the lining on first start

Applications

Applications include sintering machine gas, roasting furnaces, glass furnace off gas and metallurgical cooling circuits.

This temperature band usually involves strongly oxidising gas, which is what the 25 percent chromium and 20 percent nickel content of 310S is designed for.

Where the duty involves frequent starting and stopping, the moisture removal schedule for the lining should be written into the operating procedure.

Acceptance and Verification

Standard	Title	Purpose
GB/T 4237	Hot rolled stainless steel plate, sheet and strip	Stainless impeller and casing material
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 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

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

FAQ

What is the difference between 310S and 253MA?

Both are used above 800 C. 310S relies on high nickel and chromium for scaling resistance, while 253MA adds silicon, rare earths and nitrogen for better creep and thermal fatigue performance at higher cost.

Can the ceramic fibre lining be blown away?

Under high velocity dust laden flow it can detach. Stainless anchors are used to hold the fibre, an anti-erosion layer is added at bends and castable material may be used where impact is severe.

Why are expansion joints in the lining so important?

Steel grows considerably between ambient temperature and 800 C. Without expansion joints the lining cracks on the first heat up and the crack grows with each cycle.