Case 2: Nigeria Impurities/Pre-Cleaning Case

Turning Dirty Paddy into Export-Grade Rice in Nigeria: The Double-Layer Filtration Playbook

The situation: rocks, straw, and a CM-LG30 pushed past its limits

A West African customer running a CM-LG30 huller battled high impurity loads—stones, straw, field debris—that hammered screens (an average of 17 damaged screens/month) and produced finished rice that exceeded impurity thresholds by ~30%. Starlight retrofitted a double-layer filtration system (upper vibrating screen + lower high-speed airflow separation) and upgraded screen materials to a corrosion-resistant alloy. The outcomes: screen life tripled (replacement cycle from 1 → 3 months), impurity rate met international standards (≤1.5%), and processing stabilized at ~500 tons/day (previously sagging to ~300 on failure days).

Why West African paddy needs aggressive pre-cleaning

Nigeria’s supply chains blend paddy from multiple smallholders. Field drying on tarpaulins and roadside transport introduces stones and silica dust. In this context, a line that relies on a single coarse screen or a basic aspirator will overfeed huskers with trash, accelerating wear and forcing frequent stoppages. West Africa’s rapid mechanization efforts are expanding output but also concentrating flows—so mills must lift pre-cleaning capacity to keep downstream equipment in its design window. (Regional market realities from your research.)

The Starlight flow: separate heavy, light, and fibrous contaminants before the husker

Layer 1: Vibrating screen deck removes coarse overs (sticks, straw clumps) and fines (dust) with two mesh stages.
Layer 2: Airflow separation strips light contaminants (chaff, leaf) and helps redistribute density before the destoner.
Destoner (recommended): if not already installed, a gravity-type destoner after the air channel removes high-SG stones without clipping head rice.
Magnet traps: at least two points (pre-husker and pre-whitener) to catch tramp metal that would scar polishers.
Optional color sorter (downstream): mops up discoloration that slipped through mechanical separation.

Screen metallurgy and life-cycle cost

Upgrading to corrosion-resistant alloy screens matters in humid, dusty environments. The triple-life outcome in this case was driven by:

  • Hardness and abrasion resistance: resists silica scoring from sandy paddy.

  • Dimensional stability: mesh holds spec under thermal cycling, keeping cut-size consistent.

  • Edge treatment and fastening: reinforced edges reduce tear-out during high-G vibration.
    The result isn’t just fewer purchases—it’s fewer line stops, tighter cut control, and steadier husker load.

Commissioning and tuning checklist you can re-use

  • Feed uniformity: oscillating feeders or spreaders prevent screen blinding and stratify the bed.

  • Mesh selection: start with empirical cut sizes from historical debris audits; refine after 72 hours by checking rejects.

  • Air velocity setpoint (for airflow separation): measure pressure differential; target a velocity that lifts chaff without entraining kernels.

  • Destoner bed angle: adjust until stone discharge is continuous with minimal head rice loss.

  • Dust control: bag filters/cyclones to keep visibility and bearings safe; dust explosions are rare in rice but good housekeeping is cheap insurance.

Quality gains that multiply downstream

Husker roll life extends when grit is under control. Whiteners see smoother current draw curves, and polishing media lasts longer. Color sorters reject less because there is less damage and contamination entering them. That compounding effect is what took this line from sporadic 300-TPD days on failure events back to a stable 500-TPD cadence.

Starlight’s “Dirty Paddy Kit” for West Africa

For Nigeria and neighbors where impurity load is high, we standardize:

  • Double-deck vibratory screens with changeable meshes and robust tensioning.

  • High-speed aspiration channels with adjustable vanes and inspection doors.

  • Gravity destoners sized for actual mass flow (not nameplate).

  • Alloy screen media with at-least-3× service life in humid/dusty conditions.

  • Operator SOPs, including a 2×/shift sieve inspection and a weekly debris audit log (what did you catch, and how much?).

  • Spare sets: one full mesh set and bearing kit on site reduces reactive downtime to hours, not days.

Making the business case to owners and lenders

  • Compliance and export readiness: hitting ≤1.5% impurities aligns with common international specs and raises sale options.

  • OPEX reduction: screens last 3× longer; labor hours shift from emergency maintenance to planned checks.

  • Throughput stability: consistent 500-TPD makes labor scheduling and trucking predictable, which lenders like.

  • Safety and ESG: cleaner air from better aspiration and dust capture improves worker conditions, which supports certifications.

What Starlight learned—and applies elsewhere

  1. Pre-cleaning is a system, not a part. Sizing, air handling, metallurgy, and SOPs matter as much as the first machine you buy. 2) Local paddy profiles vary—we start every West African engagement with a debris assay (five 20-kg samples) before we fix mesh sizes. 3) Training locks in the gains—when operators understand why they do a daily debris log, cut-size drift gets caught before it becomes a quality crisis. (Regional approach grounded in your market brief.)