Resco Products has been serving cement plants and rotary cement kilns for decades. Our experts are well-versed in the best practices for refractory product selection and rotary cement kiln installation: charging, calcining, burning, and discharge zones.
The raw materials for cement production are principally limestone and clay, along with other minor additives. These materials are ground and blended in a raw mill to produce kiln feed. Years ago, the majority of cement plants operated wet process kilns. Since the industry modernized over the past 30 years, almost all cement produced in North America today is made in dry-process kilns, including kilns with preheater towers.
Rotary Cement Kiln Process
Kiln feed for a wet process kiln has a water content of approximately 40%. In the charging zone of a wet process kiln, steel chains are used as heat exchangers in the drying process. Chains extract heat from the kiln’s hot exhaust gases to dry the slurry feed. Since the kiln feed ends must contain high temperatures, refractory linings are used in the chain sections. High strength castables and gunning mixes are the preferred refractory lining materials for the chain section. Long dry-process kilns may also use chain systems, but most modern dry-process kilns have preheater towers.
Rotary Cement Kiln Preheaters
Preheater towers are structures composed of a series of hot gas ducts and cyclones, in which the raw mix is suspended in the kiln exhaust gas, transferring heat that dries and preheats the raw mix. Most preheater towers also have a precalciner vessel where fuel is introduced to support the calcination process. Linings in the preheater tower are constructed from brick and monolithic refractories based on fireclay or medium alumina-content raw materials. The partially-calcined mix is fed to the rotary kiln at the bottom of the tower.
Cement kilns with preheater towers have three major refractory zones: the calcining zone, the burning zone (sintering zone) and the discharge. The calcining zone brick lining can exhibit alkali spalling; Seneca 60 P addresses that condition with superior resistance. On the other hand, the calcining zone refractories require higher alumina content for greater thermal resistance; Rescal 70D and Alumex P-8 are often best for this service.
Rotary Cement Kiln Burning Zone
The burning zone requires basic refractory for chemical compatibility with the clinker. Resco's basic brick plant was a North American pioneer in the manufacturing of magnesite-spinel brick. Rescomag 85 is our standard magnesite-spinel brick offering for this zone. Rescomag 92 FMS is best for the most severe conditions. Z-DOL is Resco's offering for burned dolomite brick burning zones.
Rotary Cement Kiln Discharge Zone
Brick refractories in the discharge zone require abrasion and thermal shock resistance. Rescal 70D is our standard offering. For improved brick life especially when used against a retainer ring, Alumex P-7 and Alumex P-8 are favored selections du to their higher strengths. Low-cement castables, including Kricon 32-70, QuikTurn 32-70, and the R-Max product family, offer exceptional service for the castable nose ring.
Cement clinker is discharged from the kiln into the clinker cooler. The clinker is moved from the cooler inlet to the discharge by the reciprocating motion of perforated grates. In the cooler, air is blown through the bed of hot clinker, cooling it back to near-ambient temperatures. Cooler linings are preferable medium to high alumina castables, preferably low-cement types with good abrasion resistance.
For all rotary cement kiln questions, get in touch with Resco Products.