Heating furnaces are used in petroleum, chemical, metallurgy, machinery, building materials and other industries. The seven commonly used refractory castables for heating furnaces are: low cement, alumina cement, phosphate, mullite, lightweight, anti-dry slag, self-leveling castables. Other refractory materials include refractory fibers and plastics.
(1) Low cement castable
It is suitable for the high and medium temperature zones of heating furnaces, and its operating temperature is between 1400~1500℃. Low cement castable is a castable made of micro powder as binder, aluminate cement as accelerator, and some coal preventive agent and water reducer. Its main features are: moderate solidification speed, good thermal shock resistance, high load softening temperature, strong slag resistance, high refractoriness, etc.
(2) Self-leveling castable
It is suitable for parts of heating furnaces with complex structures that cannot be vibrated manually. The maximum operating temperature is 1500℃. Its characteristics are good thermal shock resistance, high refractoriness, simple construction, and almost no need for vibration.
(4) Phosphate castable
It is suitable for the bottom of heating furnaces and other parts that are seriously affected by material friction and hot air erosion. Its operating temperature is between 1000~1600℃. It is a castable made of phosphoric acid or phosphate as binder, alumina cement and magnesia as accelerator. Its characteristics are high refractoriness, good thermal shock resistance, high compressive strength, strong erosion and impact resistance, and good wear resistance (better if a small amount of steel fiber is added).
(5) Mullite castables
Due to the high thermal shock resistance, erosion resistance, good erosion resistance, good volume stability and high operating temperature of mullite castables, it is generally used in key parts such as the furnace wall, furnace roof and pressure beam of the heating furnace, or used to prefabricate burner bricks.
(6) Anti-dry slag castables
Suitable for the bottom of the heating furnace and the parts where iron oxide slag is deposited. The maximum operating temperature can reach 1600℃. Its main characteristics are: high refractoriness, good thermal shock resistance, and good resistance to the erosion of iron oxide slag in the heating furnace.
(7) Lightweight castables
Suitable for thermal insulation layers of furnace walls, furnace roofs, flues and other parts. High-strength lightweight castables can also be used as working linings for exhaust systems and hot air ducts. Its characteristics are low bulk density, low rate of change of reburning line (good thermal stability), low thermal conductivity, and certain refractoriness. It combines the advantages of refractory materials and thermal insulation materials.
(8) Refractory fiber materials
Refractory fiber materials (felt, board, brick, block and blanket, etc.) have been widely promoted and used in various furnaces since they were applied in my country in the early 1980s. In recent years, refractory fiber spray coatings and refractory fiber castables have also been widely used. This is mainly because when refractory fiber is used as furnace wall material, the furnace wall is light, the furnace body has a fast heating and cooling speed, and good thermal stability. When used as the thermal insulation layer of the furnace, it has good sealing performance and significant energy-saving effect. When refractory fiber spray coating (or refractory fiber castable) is used as the furnace lining, mechanized construction can be adopted to shorten the construction period.
- 1) Refractory fiber bricks. Refractory fiber bricks can be used as thermal insulation linings for furnaces and kilns. They feature low thermal conductivity, low heat capacity, high strength, and excellent thermal shock resistance.
- 2) Refractory fiberboard. Refractory fiberboard offers superior mechanical and structural strength, low thermal conductivity, low shrinkage, and resistance to airflow erosion. Its flat surface makes it easy to install.
- 3) Refractory fiber wool (blanket). Refractory fiber wool (blanket) features low thermal conductivity, low heat storage, and excellent thermal insulation properties. It also exhibits excellent resistance to thermal shock, erosion, and crystallization. It also offers excellent sound insulation and mechanical strength. Its fibers exhibit good elasticity and minimal shrinkage at high temperatures, making it easy to process and install.
(9) Refractory plastics
In the past decade, in my country’s newly built large-scale heating furnaces, plastics have been widely used to replace traditional refractory brick linings and refractory castables. Its advantages are: integral ramming without gaps, strong integrity, good airtightness, low heat loss, and energy saving; high high temperature strength, good thermal shock resistance, strong spalling resistance, and good mechanical vibration resistance, which can extend the life of the furnace and reduce production costs. Plastics can be used for the working surface of the furnace roof and furnace wall of the heating furnace. The heating furnace lining also utilizes a variety of shaped refractory products (such as high-alumina bricks, clay bricks, and magnesia bricks) and shaped insulating refractory products (such as clay insulating refractory bricks, high-alumina insulating refractory bricks, and diatomaceous earth insulating refractory bricks). These refractory materials are manufactured, inspected, and used in accordance with national refractory material standards.
They are suitable for use in the high and medium temperature zones of heating furnaces, operating between 1400°C and 1500°C. Low-cement castables are manufactured using micronized powder as a binder, aluminate cement as a setting accelerator, and some coal retarder and water reducer additives. Their key features include moderate setting speed, excellent thermal shock resistance, high refractoriness under load, strong slag resistance, and high refractoriness.
