Understanding refractory failures

Gary J. Bases, BRIL Inc.

Pages: 1 2 3 4

Refractory is an integral part of boilers. In the steam-generating industry, refractory materials are used to fill gaps and openings (to help keep the fire inside the firebox), to line wet and dry hoppers for collecting ash and slag, and to protect the lower furnace wall tubes inside fluidized-bed and cyclone-fired boilers and boilers fired by refuse-derived fuels.

Refractory failure is a major cause of boiler energy losses as well as a major contributor to boiler outages. Understanding why a refractory material fails requires a complex analysis of many interrelated factors: materials that don't match the operating environment, incompatibility with the by-products of fuel combustion, and improper installation techniques (Figures 1 and 2).

Courtesy: BRIL Inc.

1. Ash me no questions. Flyash inside a penthouse between the screen, superheater, and reheater.

Courtesy: BRIL Inc.

2. Unprotected section. A wet bottom-ash hopper with areas of missing refractory.

Diagnosing a refractory failure can be described as a series of steps leading to discovery of the root cause.

Step 1: Begin the discovery process

The process begins with the collection of basic technical information about the failure, followed by interviews of plant and installation personnel. Document the following:

Material samples and data sheets of the existing brick or refractory lining.
Material samples of ash clinkers and slag.
Chemical analysis of the fuel being burned.
Where and for how long the refractory material was stored prior to installation.
When it was manufactured.
Its condition at the time of installation.
How much material was installed.
How it was installed or applied (pneumatically, toweled, poured, shotcrete, etc.).
How it was cured and/or dried, using which procedures.