UCIC Technical Reference
Full Operational Journey of Cement Manufacturing
United Cement Industrial Company (UCIC) - From Quarry to Dispatch
Quarrying & Raw Material Extraction
The cement manufacturing process begins at UCIC's seven active quarries distributed across the region. Each quarry supplies a specific raw material essential for clinker production: Othman Quarry (marble/limestone, 12,000 TPD, CaCO3 98%), Factory Quarry (marble, 10,000 TPD, CaCO3 96%), Al-Juhfa Quarry (gypsum, 3,000 TPD, CaSO4·2H2O 85%), Al-Jamoum Quarry (iron ore, 4,500 TPD, Fe2O3 55%), Al-Shumaisi Quarry (iron ore, 3,800 TPD, Fe2O3 52%), Umuq Quarry (iron ore, 4,000 TPD, Fe2O3 48%), and East Tufail Quarry (marble, 8,500 TPD, CaCO3 95%). The combined daily extraction exceeds 46,000 tonnes of raw material.
Extraction operations employ drilling and blasting techniques. Blast hole drilling uses rotary drills with 100-150 mm diameter bits, drilled to depths of 10-15 meters in a predetermined pattern. Each blast typically covers 10,000-20,000 tonnes of material, using ANFO (ammonium nitrate fuel oil) as the primary explosive with electronic detonators for precise timing. The blasted material is loaded into CAT 777 haul trucks (90-tonne capacity) by hydraulic excavators and transported to the primary crusher feed hopper. Haul distances range from 3.5 km (Othman) to 7.8 km (Al-Jamoum).
Quality control begins at the quarry face. Portable XRF analyzers provide real-time chemical analysis of the blasted material. Each haul truck is directed to either the primary crusher feed or a stockpile based on its chemical composition, ensuring consistent feed chemistry to the crusher. The target blend composition is: CaO 41-44%, SiO2 12.5-14.5%, Al2O3 2.5-4.0%, Fe2O3 1.5-3.0%, and MgO below 3.0%.
Primary & Secondary Crushing
The crushing circuit begins at the apron feeder, a heavy-duty chain-and-pan conveyor that extracts material from the 80-tonne dump hopper at a controlled rate. The apron feeder consists of overlapping manganese steel pans mounted on D6/D8 sealed roller chains, driven by a 30-75 kW motor through a VFD. The VFD modulates chain speed from 0 to 0.3 m/s based on crusher motor amp feedback, maintaining optimal crusher loading. The overlapping pan design prevents fine material leakage and provides a continuous, interlocking material bed.
From the apron feeder, material passes to the wobbler feeder, an elliptical-motion scalping device that removes 25-35% of the feed (material smaller than 60-100 mm) before it reaches the impact crusher. The wobbler feeder's eccentric shaft generates a 35-50 mm elliptical stroke at 400-600 RPM, causing material to stratify by particle size: fines settle to the bottom and pass through disc gaps, while oversize material travels forward to the crusher. This fines bypass reduces crusher power consumption by 15-20% and extends blow bar life proportionally.
The horizontal shaft impact crusher (HSI) performs primary size reduction. The rotor, weighing 8-15 tonnes with a moment of inertia of 15,000-40,000 kg·m2, stores 15-30 MJ of kinetic energy at 400-600 RPM. Four blow bars (each 150-300 kg, made from martensitic steel or chrome-iron with ceramic inserts, hardness 55-65 HRC) strike the feed material at 30-50 m/s tip speed. The impact generates a stress wave propagating at 4,000-6,000 m/s through the rock, causing instantaneous tensile fracture. Material is then thrown against adjustable breaker plates (impact curtains) at near-blow-bar velocity for secondary impact. The grinding path between rotor and breaker plates creates a multi-event impact zone where material cycles until reduced below the breaker plate gap setting (target ≤100 mm). The reduction ratio reaches 15:1 to 25:1, far exceeding jaw crushers at 4:1 to 8:1.
For the sticky clay fraction, a dedicated clay roller crusher handles material with moisture content exceeding 15%. Two counter-rotating rollers (800-1,200 mm diameter, each driven by a 200 kW motor delivering 13,000-25,000 Nm torque) create a nip angle of 16-24° that draws material into the crushing zone through friction. The roller gap of 50 mm is maintained by hydraulic cylinders with accumulator float protection. The 160-tonne hopper above the rollers provides 30 minutes of surge capacity.
Step 3: Reclaimer & Material Handling
After crushing, the ≤10 cm material is transported by conveyor belts to either circular or longitudinal reclaimer systems. These systems build and maintain long-term stockpiles that decouple quarry and crushing operations from the raw mill, ensuring a continuous, homogenized feed despite upstream disruptions. Two stacking methods are used: chevron stacking, where the stacker boom deposits material along the centerline creating triangular cross-sections that naturally blend coarse and fine fractions during reclaiming; and windrow stacking, where material is deposited in parallel layers across the full pile width for horizontally homogeneous feed, typically paired with longitudinal reclaimers.
Circular reclaimers consist of a boom mounted on a central pivot rotating 360 degrees around a circular stockpile. The scraper or bucket chain cuts into the chevron-stacked pile and deposits material into a central hopper for transport to the raw mill. The rotating design blends coarse and fine material naturally. Longitudinal reclaimers travel along a straight rail track parallel to a long rectangular stockpile, with the boom swinging across the pile face. Conveyor belts (1,200-1,800 mm wide, 2-4 m/s, up to 1,000 TPH capacity) are the primary transport infrastructure, each equipped with pull cords, sway switches, and zero-speed sensors as mandatory safety interlocks. A strict SOP start-up sequence governs the entire material handling system: visual inspection, pull cord reset check, sway switch check, warning horn activation, sequential belt start, and controlled gate opening only after all belts are confirmed running.
Raw Mill Grinding (Vertical Roller Mill)
Crushed material from storage is proportioned into five feed bins: two marble sources (Othman, East Tufail), one iron ore blend (Al-Jamoum, Al-Shumaisi, Umuq), one gypsum (Al-Juhfa), and one corrective material (Factory Quarry). Each bin discharges through a weight feeder that precisely controls the feed rate. The blend passes through a metal detector before entering the raw mill.
The vertical roller mill (VRM) is the centerpiece of the raw grinding circuit. The grinding table (4.0-5.6 m diameter) rotates at 20-30 RPM, driven by a 2,500-4,500 kW motor through a bevel-planetary gear reducer. Four rollers, each applying 1,500-3,500 kN of force through a hydraulic-pneumatic system pressurized to 120-160 bar, press material against the table. The grinding bed thickness is maintained at 30-80 mm. Material fed onto the center of the table is carried outward by centrifugal force and passes under the rollers, where size reduction occurs through combined compression and shear.
The mill is air-swept: hot gas from the kiln preheater (300-400°C) enters through the ring nozzle at 80-120 m/s throat velocity. This high-velocity gas stream lifts ground material upward while simultaneously drying the raw material from 8-15% moisture to below 0.5%. Coarse particles exceeding 200 µm have terminal velocities exceeding the upward gas velocity in the expanded zone and fall back to the grinding table for re-grinding, creating an internal circulating load of 200-400%. Fine particles enter the dynamic classifier rotor (40-120 RPM), where centrifugal force rejects oversize (above the d50 cut point of 40-60 µm) back to the table, while product-size fines pass through and exit with the gas stream to the baghouse. The final raw meal has a Blaine fineness of 3,200-3,800 cm2/g with a residue on 90 µm (R90) of 12-18%.
Preheater Tower & Rotary Kiln
Raw meal from the silo is fed into the top of the 5-stage cyclone preheater tower, where it cascades downward through stages 1-5, exchanging heat with hot gases rising from the kiln and calciner. Each stage consists of a gas duct where meal is injected into the hot gas stream, a cyclone where gas-solid separation occurs, and a discharge pipe directing meal to the next stage. The gas temperature gradient across the stages is: Stage 1 exit at 280-350°C, Stage 2 at approximately 500°C, Stage 3 at 700°C, Stage 4 at 850°C, and the calciner at 900-950°C. Raw meal particles (mean diameter 40-60 µm, specific surface area 5,000-8,000 m2/kg) reach thermal equilibrium with the surrounding gas in 0.1-0.3 seconds.
The calciner fires 55-65% of the total kiln fuel (pulverized coal or pet coke), raising the temperature to 900-950°C and achieving approximately 95% calcination. The calcination reaction (CaCO3 → CaO + CO2) requires approximately 425 kcal/kg of clinker - roughly 60% of the total thermal energy. By performing the majority of calcination in the calciner rather than the kiln, the kiln length can be reduced and its primary function shifts to final clinkering.
Material enters the rotary kiln (60-80 m long, 4.0-4.8 m diameter, 3-4% slope, 2.5-4.0 RPM) at approximately 900°C and 95% calcined. Over 30-45 minutes residence time, material travels through five thermal zones: transition (950-1,100°C, 8-12 m), upper sintering (1,100-1,300°C, 10-15 m) where liquid phase appears, burning zone (1,300-1,450°C, 10-15 m) where C3S formation peaks and clinker nodules grow to 5-25 mm, lower sintering (1,450-1,350°C, 5-8 m), and cooling (1,350-1,200°C, 5-10 m). The main burner produces a flame temperature of 1,800-2,000°C with a flame length of 12-20 m.
Clinker exits the kiln at 1,200-1,400°C and enters the grate cooler where it is rapidly quenched to 100-150°C over 20-30 minutes. Rapid cooling prevents conversion of β-C2S to γ-C2S and fixes the liquid phase as reactive glass. The cooler recuperates heat at 65-75% efficiency into secondary air for kiln combustion and tertiary air for calciner combustion.
Clinker Chemistry & Mineralogy
Portland cement clinker consists of four major mineralogical phases. Tricalcium silicate (C3S, alite) comprises 50-70% of clinker and is responsible for early strength development (1-28 days) with a heat of hydration of 500 J/g. It reacts rapidly with water, forming C-S-H gel and calcium hydroxide. Dicalcium silicate (C2S, belite) comprises 15-30% and contributes to late strength development (beyond 28 days) with a lower heat of hydration of 250 J/g, making it beneficial for mass concrete applications.
Tricalcium aluminate (C3A) comprises 5-10% and has the highest heat of hydration (865 J/g). Without gypsum addition, C3A causes flash set upon mixing with water. Gypsum is added during cement grinding to form ettringite (3CaO·Al2O3·3CaSO4·32H2O), which forms a protective barrier around C3A grains. Sulfate resistance decreases with higher C3A content. Tetracalcium aluminoferrite (C4AF, ferrite) comprises 5-15% and acts as a fluxing agent, lowering the eutectic temperature in the kiln from 1,338°C to approximately 1,260°C, and controls cement color.
Three burnability indices control clinker quality. The Lime Saturation Factor (LSF = CaO / (2.8SiO2 + 1.2Al2O3 + 0.65Fe2O3)), target 92-98%, controls the maximum theoretical C3S content. The Silica Ratio (SR = SiO2 / (Al2O3 + Fe2O3)), target 2.0-3.0, controls liquid phase quantity. The Alumina Ratio (AR = Al2O3 / Fe2O3), target 1.0-2.5, controls liquid phase viscosity. Free lime (uncombined CaO) is the primary daily quality control parameter, targeted below 1.5%. High free lime (above 2.0%) causes unsound cement with expansion risk.
Cement Grinding (Ball Mill)
Clinker from the storage silo is fed into the ball mill along with gypsum (3-5% by weight, from Al-Juhfa Quarry) for setting time control. The ball mill is a two-chamber tube mill 4.0-5.2 m in diameter and 13-17 m long, rotating at 14-16 RPM (65-75% of critical speed, Nc = 42.3/√D = 18-22 RPM). The mill is driven by a 3,000-7,000 kW motor through a girth gear and pinion.
Chamber 1 occupies 30-40% of the mill length and is optimized for impact grinding (cataracting). It is charged with large 90-60 mm steel balls (30-35% of total ball weight) and lined with aggressive lifter bars 80-120 mm high spaced at 200-300 mm intervals. These lifters carry the ball charge above 60% of mill diameter, from which the balls fall in a parabolic trajectory, striking the clinker at the toe of the charge at 3-6 m/s. The high-energy impact fractures clinker from 1-25 mm to 500-1,000 µm. Ball wear is 150-300 g per tonne of cement, and specific power is 15-25 kWh/t.
Material passes through the diaphragm (6-12 mm slotted steel casting, tapered to prevent blinding) into Chamber 2, which occupies 60-70% of the mill length and is optimized for fine grinding by attrition (cascading). It is charged with smaller 40-15 mm balls (65-70% of ball weight) and lined with classifying liners whose lifter height decreases toward the discharge end. This gradient directs smaller balls toward the discharge for fine grinding. Material enters at 500-1,000 µm and exits at 15-45 µm (Blaine 3,000-5,000 cm2/g). Specific power is 25-35 kWh/t. Mill ventilation (0.5-1.5 m/s) maintains outlet gas at 80-110°C to prevent gypsum dehydration.
Air Separator & Classification
The air separator operates on the precise balance of two opposing forces: centrifugal force (Fc = m × ω2 × r) from the rotating rotor cage, and drag force (Fd = ½ × Cd × ρ × A × v2) from the inward air flow. Particles larger than the cut size (d50, typically 40-60 µm) experience Fc > Fd and are thrown outward to the rejects cone for return to the mill. Particles smaller than d50 experience Fd > Fc and pass inward through the rotor blades as finished product.
Rotor speed (40-120 RPM) is the primary fineness control. Doubling rotor speed increases centrifugal force by a factor of four (Fc ∝ ω2), shifting the d50 to approximately half its previous value. This allows precise control from Blaine 3,000 cm2/g (coarse cement, ~60 µm d50) to Blaine 5,000 cm2/g (fine cement, ~25 µm d50). Air flow rate provides secondary control.
Separation performance is quantified by the Tromp curve. The sharpness index (SI = d25/d75) measures curve steepness at the cut point: values above 0.8 indicate excellent separation. The bypass fraction (short-circuit particles) should be below 15%. The circulating load (CL = rejects flow / product flow × 100) typically ranges from 200-400%. A high CL with low bypass indicates efficient classification; a high CL with high bypass indicates wasted grinding energy.
Product Storage & Dispatch
Finished cement is conveyed to four storage silos: Silo A (OPC, 30,000 MT), Silo B (SRC, 25,000 MT), Silo C (Blended/Composite, 20,000 MT), and Silo D (Bulk Loading Station, 15,000 MT). Each silo has level monitoring, aerated discharge cones, and fluidizing pads. Total storage capacity is 90,000 MT (15-20 days of production).
Dispatch occurs through bulk loading (pneumatic spouts at 100-200 TPH with dust collection) and bagged cement (6-spout rotary packers filling 50 kg bags at 2,000-3,000 bags per hour, automatically palletized and shrink-wrapped). Supporting utility systems include screw compressors for instrument air, cooling tower and raw water supply, steam boiler for process heating, and a 132 kV substation with backup diesel generators.
Central Control Room (CCR) & DCS Operations
The entire plant is monitored and controlled from the Central Control Room using two DCS platforms: Siemens PCS7 for process control and ABB 800xA for plant automation, with SCADA for remote monitoring. The DCS manages over 5,000 control loops across all plant sections. Each loop consists of field sensors (temperature, pressure, flow, level, vibration), final control elements (VFDs, control valves, dampers), and PID control algorithms.
Gas analyzers at critical locations monitor: O2 at the kiln inlet and outlet (managed at 2.0-4.0% excess), CO at the preheater exit (below 0.1% for safety), NOx and SO2 at the stack (NOx below 600 mg/Nm3, SO2 below 200 mg/Nm3), and CO2 for emission reporting. Analyzer data feeds directly into the DCS for automatic combustion optimization.
Safety interlock systems provide hard-wired safety functions independent of the DCS. E-Stop pull cords run the full length of all conveyors, crushers, and mills. Gas detection sensors (CO, CH4, H2S) are installed in confined spaces, coal mill areas, and the kiln feed platform. Fire suppression systems (FM-200 for electrical rooms, water deluge for conveyors and mills) activate automatically. Bearing temperature monitoring trips equipment above 85°C (alarm at 80°C), and vibration cutoff sensors protect against mechanical failure.
Maintenance Strategies & Reliability
UCIC employs combined preventive and predictive maintenance. Preventive maintenance follows a fixed schedule: daily lubrication and visual inspection of all rotating equipment; weekly belt alignment and bolt torque checks; monthly oil analysis and vibration monitoring on mills and kiln drive; quarterly refractory inspection; and yearly major overhaul. PM compliance rate target: 95%.
Predictive maintenance covers 120 vibration measurement points (ISO 10816: below 1.8 mm/s RMS = good; 4.5-11.2 mm/s = plan repair within 1 month; 11.2-28 mm/s = repair within 1 week; above 28 mm/s = immediate shutdown). FFT spectrum analysis identifies unbalance, misalignment, bearing wear, and gear mesh faults. Infrared thermography covers 80 points (motor bearings max 90°C, kiln shell max 400°C, electrical panels max 65°C). Oil analysis on 45 points monitors wear metals, viscosity, and water content.
Lockout/Tagout (LOTO) follows a six-step procedure: (1) notify affected personnel; (2) shutdown via DCS; (3) full energy isolation (electrical MCC, mechanical coupling, gravity blocking, hydraulic/pneumatic lockout and bleed, thermal cooldown); (4) personal lock and tag application (group LOTO boxes for crew work); (5) zero energy verification (button test, voltage measurement, rotation check); (6) controlled release by the original lock holder only. Tag colors: red = danger, yellow = caution, green = isolated, orange = group LOTO.