SOP-001 · Rev 1.0
Raw Material Receipt & Incoming Quality Control
Procedure for receiving, sampling, testing, and accepting or rejecting all incoming raw materials: RHA, rice husk, NaOH lye, CaO, CTAB, and stearic acid.
1. Purpose & Scope
To ensure all raw materials meet specification before use, preventing out-of-spec inputs from causing product failures, equipment damage, or safety incidents. Applies to all materials entering the Fluxara site gate.
2. PPE Required
| Activity | Minimum PPE |
|---|---|
| NaOH lye sampling | Chemical splash goggles · nitrile gloves (min 0.4mm) · chemical-resistant apron · face shield |
| CaO / RHA sampling | P3 dust respirator · safety glasses · nitrile gloves · long sleeves |
| CTAB / stearic acid sampling | Safety glasses · nitrile gloves |
| Rice husk inspection | Dust mask (FFP2) · safety glasses |
3. Receiving Procedure
1
Verify delivery documents before unloading
Check: Purchase Order number matches · supplier name matches approved vendor list · delivery quantity matches PO · Certificate of Analysis (CoA) attached. STOP if CoA is missing — place vehicle in hold area.
2
Visual inspection before unloading
Check packaging integrity (no torn bags, leaking drums, damaged tanker). For NaOH: check tanker for corrosion, valve condition. For CaO: check bags for moisture exposure (CaO hydrates in wet bags — lumpy/hot CaO indicates partial slaking → reject). Record visual status in IMR-001.
3
Sampling — material-specific protocol below
Use clean, dry sampling tools only. Label sample immediately with: date, lot number, supplier, quantity. Two samples: one for QC testing, one retained as reference (sealed, labelled, stored 6 months).
4
Segregate pending QC — quarantine area
Place material in designated QUARANTINE zone (yellow floor marking). Do NOT mix with approved stock. Affix HOLD tag with lot number and date. Unloading may proceed into quarantine only.
5
Run QC tests per Table 1 below
Complete all mandatory tests. Target: results within 4 hours for RHA, CaO (dissolution test is 30 min). NaOH density test: 5 minutes. CTAB/stearic: CoA acceptance only (spot-check quarterly).
6
Accept or Reject decision
QC Officer signs acceptance on IMR-001 if all tests PASS. Affix GREEN ACCEPTED tag. Transfer to approved stock area. If ANY test fails: raise NCR (Non-Conformance Report), contact supplier, hold material. Plant Manager decision required for conditional use.
4. Acceptance Specifications by Material
| Material | Test | Method | Spec | Action on Fail |
|---|---|---|---|---|
| RHA (purchased) | SiO₂ by XRF | ED-XRF, 3 subsamples | ≥92% SiO₂ | REJECT entire lot |
| Dissolution proxy | 10% NaOH, 90°C, 30 min, filter | ≥85% dissolved | REJECT — crystallised | |
| LOI | Ignition 900°C, 30 min | <2% carbon | Reject if >5%; warn if 2–5% | |
| Colour | Visual | White to light grey | Reject if black/dark — unburned | |
| NaOH 48% lye | Density (concentration) | Hydrometer at 20°C | 1.50–1.52 g/mL (= 47–49%) | Reject or adjust billing |
| Iron content | Colorimetric (phenanthroline) | <10 ppm Fe | Warn — trace Fe contaminates product | |
| NaCl content | AgNO₃ titration | <1.5% NaCl | Reject — chloride causes scale | |
| CaO quicklime | Available CaO by XRF | ED-XRF or titration | ≥85% CaO | REJECT — stoichiometry fails |
| Slaking rate | Add 100g CaO to 400mL water, measure T rise at 1 min | T ≥45°C at 1 min | Reject if slow — dead burned | |
| MgO content | XRF | <5% MgO | High MgO = slow slaking | |
| Rice husk | Moisture | Moisture balance, 105°C | <15% moisture | Reject — high moisture drops NCV |
| Visual — no mould | Visual, smell | No black mould, no sour odour | Reject — combustion product unsafe | |
| CTAB | Purity per CoA | Supplier CoA acceptance | ≥99% pure CTAB | Reject if CoA missing |
| Appearance | Visual | White free-flowing powder | Reject if lumped/discoloured | |
| Stearic acid | Acid value per CoA | Supplier CoA | 195–210 mg KOH/g | Reject if out of range |
⛔ Critical Control Points
CCP-1: RHA dissolution test — NEVER bypass. Crystallised RHA batch will fail extraction, waste all downstream chemicals, and produce zero product from that batch. Cost of one failed batch ≈ ₹3–5L in NaOH alone.
CCP-2: CaO slaking rate test — Dead-burned lime (overheated) slakes very slowly, giving poor Ca(OH)₂ yield, reducing NaOH recovery, and increasing CaO consumption beyond budget by 20–30%.
CCP-3: NaOH concentration — Dilute lye (below 47%) means you are paying for water. Adjust billing by actual concentration and recalculate makeup quantities for that batch.
Received by (Storekeeper)
Name / Sign / Date
QC Tested by
Name / Sign / Date
Accepted / Rejected by (QC Officer)
Name / Sign / Date
SOP-002 · Rev 2.0
Furnace + Thermal Oil Heater (TOH) Startup, Operation & Temperature Control
Operating procedure for the 20 MT/day rice husk combustion furnace and Thermal Oil Heater (TOH) system. Covers startup, steady-state control, TOH oil circulation management, and safe shutdown. CEMS interlock management. Note: IBR boiler replaced by Thermal Oil Heater in DPR v16 — no IBR registration, no steam pressure hazard.
⚡
ABSOLUTE RULE: Furnace temperature must NEVER exceed 700°C. Above 700°C, amorphous silica crystallises into cristobalite — the RHA becomes chemically inert. CEMS auto-shutoff triggers at 720°C (20°C safety buffer). If auto-shutoff triggers, DO NOT RESTART without Shift Supervisor inspection and Plant Manager approval. Log the event in NCR system.
1. Pre-Startup Checklist
TOH oil level in expansion tank: ½–¾ full (Therminol 55 / Dowtherm A)
TOH circulation pump: rotation checked, strainer clean, no oil leaks
TOH expansion tank nitrogen blanket: pressure 0.2–0.5 bar(g) confirmed
CEMS operational: CO₂, CO, temperature, PM sensors all showing green
Auto-shutoff interlock tested: confirm 720°C setpoint active
Husk conveyor belt inspected — no blockages, guards in place
Ash removal system operational (conveyor or manual handling route clear)
Fire suppression system: pressure OK, head inspection clear
All personnel briefed on emergency stop location
All TOH heat exchanger inlet/outlet valves: correct position (open)
2. Cold Startup Sequence
1
Start TOH oil circulation pump — cold oil loop
Start pump before lighting furnace. Cold oil (ambient temp) circulates through the furnace coil and all process heat exchangers. This prevents hot spots in the coil when the furnace heats up. Confirm oil flow at each HX outlet temperature sensor.
2
Ignite auxiliary burner (diesel or LPG) — warm furnace to 200°C
Use auxiliary burner to bring furnace to 200°C before introducing husk. This prevents incomplete combustion of the first husk load (cold furnace = unburned carbon, black ash). Oil outlet temperature will begin rising — monitor.
3
Begin husk feed at 25% of design rate (0.25 MT/hr)
Slowly increase husk feed over 2 hours. Monitor CEMS temperature continuously. Target furnace temperature: 550–650°C. If temperature climbs above 680°C, reduce feed rate immediately. Do NOT reduce air supply — reducing air causes CO formation. TOH oil outlet should reach 160–180°C within 90 minutes.
4
Increase feed rate to 50%, 75%, 100% (1-hour steps)
Each step: wait 60 minutes at new rate, confirm furnace temperature stable within 550–680°C, confirm TOH oil supply temperature 180–220°C, check RHA quality at ash output (white/light grey = good, black = incomplete combustion). Open process HX valves progressively as oil reaches setpoint.
5
Steady state: 1.0–1.4 MT/hr continuous feed
Normal operating: Furnace 580–660°C · TOH supply oil 180–220°C · TOH return oil 140–160°C. Log all parameters every 30 minutes in OPR-002 and OPR-002B.
3. Steady-State Operating Parameters
| Parameter | Normal Range | Warning | Alarm / Action |
|---|---|---|---|
| Furnace temperature | 550–660°C | 680°C — reduce feed | 720°C — auto-shutoff |
| TOH oil supply temp | 180–220°C | <170°C — check furnace feed rate | >230°C — reduce feed, check oil flow |
| TOH oil return temp | 140–165°C | — | >185°C — HX fouling, inspect |
| TOH system pressure | 0.2–0.6 bar(g) | — | >1.0 bar — check expansion tank, PRD |
| Feed rate | 1.0–1.4 MT/hr | — | <0.8 — check conveyor blockage |
| RHA colour (output) | White / light grey | Light brown — T too low | Black — unburned carbon, reduce feed |
| CO (CEMS) | <200 ppm | 200–500 ppm — check air supply | >500 ppm — incomplete combustion alarm |
| Stack PM (CEMS) | <50 mg/Nm³ | 50–100 mg | >150 mg/Nm³ — check ESP/cyclone |
4. RHA Collection and Transfer
1
Collect RHA from furnace ash outlet every 4 hours
RHA temperature at outlet: 150–250°C. Allow to cool in collection hopper to <80°C before transfer to RHA storage. HOT RHA transferred to wet bag can cause bag fire — mandatory cooldown.
2
Sample each RHA collection and record colour in OPR-002
White/grey = good. Light brown = furnace slightly cool (check feed rate). Black = unburned carbon — do NOT send to leach reactor, return for reburn or dispose.
3
Weekly dissolution test on bonus RHA
Even though this is own-furnace RHA, run dissolution test weekly to confirm temperature was maintained correctly. If dissolution <85%: review CEMS logs for temperature excursions.
5. Planned Shutdown Sequence
1
Reduce husk feed to zero, maintain air supply
Air supply must continue for 30 minutes after last husk load to ensure complete combustion of residual material. Shutting air before burnout causes CO formation and unburned carbon.
2
Continue TOH oil circulation until oil return temp drops below 100°C
Keep oil pump running throughout cooldown. Never stop the pump with hot oil in the furnace coil — static hot oil in the coil degrades rapidly and may coke. Close process HX valves progressively as temperature falls.
3
CEMS shutdown only after all combustion complete
CEMS must remain operating during entire cool-down. Regulators may inspect CEMS logs — gaps are a compliance issue.
⚠
TOH thermal oil condition monitoring: Check oil viscosity and acid number quarterly. Therminol 55 degrades above 250°C — ensure coil outlet temperature never exceeds 230°C. Replace oil if acid number >1 mg KOH/g or dark colour/sludge observed. Degraded oil loses heat transfer efficiency and can form deposits in the coil. No water treatment required (unlike steam boiler feedwater).
SOP-003 · Rev 1.0
NaOH Leaching Reactor Operation
Procedure for preparing NaOH solution, charging leach reactors with RHA, maintaining reaction conditions, and transferring sodium silicate solution to precipitation.
⛔
NaOH HAZARD — Corrosive: 10% NaOH at 90°C causes severe burns in under 5 seconds. Safety shower must be reachable in <10 seconds from any point in leach area. Gloves + face shield + apron MANDATORY for any reactor access. Never open a reactor under steam pressure.
1. NaOH Solution Preparation
Why we use 10% NaOH by weight
We receive 48% NaOH lye. To make 10% solution: dilute with process water. Ratio: for every 1 kg 48% lye, add 3.8 kg water → gives ~4.8 kg of 10% NaOH. The dilution is exothermic (NaOH dissolution heat = −44.5 kJ/mol) — always add lye to water, never water to lye (steam explosion risk).
1
Fill dilution tank with calculated volume of process water first
Never reverse this order. Water first, then lye. Use metering pump to add lye slowly (not in one shot). Monitor temperature — if solution exceeds 60°C, slow lye addition, increase cooling.
2
Mix recovered NaOH from causticisation with fresh makeup
Recovered NaOH (from SOP-007) is the primary source. Fresh 48% lye is only the makeup (4.375 MT/day at Ph1A). Mix both in the NaOH day tank. Measure final pH (target: 12.5–13.5) and concentration (density check).
2. Reactor Charging and Reaction
1
Confirm reactor is clean and PP lining intact
Visual inspection before each batch: check PP lining for cracks, blistering, delamination. Any damage → take reactor out of service, do NOT use until repaired. NaOH in contact with bare SS316 at 90°C will cause corrosion and Fe contamination.
2
Charge RHA: weighed batch per production plan
Phase 1A: 15.032 MT/day total RHA split across 3 reactors = ~5.01 MT per reactor per day, or ~1.67 MT per batch (at ~3 batches/day/reactor). Weigh on hopper scale — record actual weight in OPR-003.
3
Fill with 10% NaOH solution to target solid:liquid ratio (1:8 by weight)
For 1.67 MT RHA: add 13.4 MT NaOH solution (10%). This gives ~1.67 MT NaOH solution per 167 kg SiO₂ available per batch. Start agitator before adding NaOH to ensure mixing.
4
Heat to 90°C using steam jacket, maintain 2 hours
Open steam valve slowly. Temperature ramp: allow 20–30 minutes to reach 90°C. Maintain 88–92°C for exactly 2 hours (set timer). Log temperature every 30 minutes. Agitator speed: 30–40 rpm continuously.
5
Check extraction (optional in-process — mandatory for new RHA supplier)
Take 50 mL sample at 2-hour mark. Filter. Measure silicate concentration (sodium silicate) by titration or refractometer. Expected Na₂SiO₃ concentration: 60–90 g/L. Low silicate = poor extraction → extend by 30 minutes and recheck.
6
Drain sodium silicate solution to holding tank
Open bottom valve slowly. Allow gravity drain (do not pressurize). Transfer to Na₂SiO₃ holding tank — feed to precipitation within 4 hours to prevent partial silicate polymerisation (gelling) that clogs filters.
3. Residue Handling
1
Wash reactor residue with hot water (80°C) × 2 washes
Wash water goes to evaporator (contains dissolved NaOH — recover it). Do not discard wash water — it contains ₹8–12/kg of NaOH value.
2
Transfer desilicated residue to residue holding tank
Residue is the 12% of SiO₂ that was not extracted plus the non-SiO₂ ash components. Volume: ~2.862 MT/day (Ph1A). Transfer to desilicated residue pond, allow to dry, sell to brick kilns @ ₹900/MT.
⛔ Critical Control Points
CCP-1: Temperature must be 90°C ±2°C for full 2 hours. Below 85°C: extraction drops to <75%. Above 95°C: excessive NaOH vapour, scaling, and risk of foaming that can block vent lines.
CCP-2: PP lining inspection BEFORE every batch. A cracked lining means corrosion and Fe contamination that will fail product QC tests (Fe content in silica product).
CCP-3: RHA must be from SOP-001 ACCEPTED stock only. Never use HOLD or REJECT material regardless of production pressure.
SOP-004 · Rev 1.0
Silica Precipitation — Grade-Specific Operation
Procedure for precipitating precipitated silica from sodium silicate solution using CO₂, with grade-specific pH profiles for Standard, HDS, and Dental grades.
1. Grade-Specific pH Profiles
Standard Grade
HDS Grade
Dental / Food
| Grade | Start pH | Reaction pH | End pH | CO₂ Rate | Temp | CTAB Added? |
|---|---|---|---|---|---|---|
| Standard | ~12 (silicate) | Slow drop 12→8.5 | 8.0–9.0 | Slow, controlled | 60–70°C | No |
| HDS | ~12 | Moderate drop 12→6.5 | 6.0–8.0 | Moderate (mass flow control) | 55–65°C | Yes — at end |
| Dental / Food | ~12 | Fast drop 12→6.0 | 5.5–7.0 | Fast initial, slow final | 50–60°C | No (no CTAB for food) |
2. Standard Precipitation Procedure (HDS Grade — Primary Production)
1
Pre-heat precipitation vessel to target temperature
HDS: 55–65°C. Use steam-jacket or hot water coil. Add process water to vessel first (50% fill). Start agitator (40–50 rpm).
2
Transfer Na₂SiO₃ solution from holding tank
Fill vessel to operating level. Confirm pH: should be 11.5–12.5. If pH <11: silicate is partially neutralised — check for CO₂ contamination in holding tank (open vents).
3
Initiate CO₂ feed via mass flow meter
CO₂ from furnace flue via absorption/compression unit. Confirm CO₂ purity ≥95% (check CEMS). Set mass flow controller to profile per grade. CO₂ sparge point: below liquid surface, agitator zone. Monitor pH in real time (in-line probe).
4
pH endpoint control — the most critical step
HDS: when pH reaches 7.0–8.0, SLOW CO₂ rate by 50%, continue until pH 6.5–7.0 stable for 10 minutes. Record exact endpoint pH in OPR-004. If pH drops below 6.0: STOP CO₂ immediately — acidified silica dissolves back slightly, losing product. Add small amount of Na₂SiO₃ to recover to 6.5.
5
Add CTAB solution (HDS only)
CTAB dissolved in hot water (40°C): 5% CTAB solution. Add via metered pump to stirred precipitation vessel over 20 minutes. Rate: 0.289 MT/day total CTAB for Phase 1A ÷ batches per day. Agitate 30 minutes after CTAB addition before filtering.
6
Transfer silica slurry to filter press feed tank
pH should be 6.5–7.5 in feed tank. Check slurry density (refractometer or density meter). Target 8–12% solids by weight. Too thick: filtration too slow. Too dilute: filter press capacity wasted.
3. CO₂ Supply Management
Furnace CO₂ vs. bottled CO₂ — what to do during furnace downtime
Primary CO₂ source: furnace flue gas via absorber/scrubber system. During planned furnace maintenance (<4 hours), buffer CO₂ storage (compressed cylinders, minimum 3-day stock = ~28 MT CO₂) covers precipitation. During extended furnace shutdown (>8 hours): reduce leaching rate to match CO₂ availability. NEVER use food-grade CO₂ for industrial precipitation (cost prohibitive). Budget: maintain 3-day CO₂ cylinder buffer at all times.
| Phase | CO₂ Used/day | Buffer needed (3 days) | Cylinder inventory |
|---|---|---|---|
| Phase 1A | 9.36 MT/day | 28.1 MT | ~281 × 50L cylinders (at 100 bar, 5 kg/cylinder) |
| Phase 1B | 12.2 MT/day | 36.6 MT | ~732 × 50L cylinders |
ℹ
CO₂ from furnace contains N₂, SO₂ trace, and particulates. The absorption/scrubbing system removes PM and SO₂. Confirm CO₂ purity ≥95% before use. Impure CO₂ can introduce sulfur contamination into silica — unacceptable for dental grade.
⛔ Critical Control Points
CCP-1 (GRADE CRITICAL): pH endpoint. Wrong endpoint = wrong grade. A batch targeting HDS (pH 6.5–7.5) that ends at pH 8.5 is Standard grade (₹26/kg vs ₹45/kg). Revenue loss: ~₹19/kg. Label batch with actual endpoint pH — QC decision for upgrade/downgrade.
CCP-2: Temperature during precipitation. Above 75°C: silica particles undergo Ostwald ripening (small particles dissolve, large grow) — product coarsens, BET drops. Below 40°C: slow kinetics, agglomeration. Maintain 55–65°C for HDS.
CCP-3: CTAB addition timing. Add AFTER pH endpoint is reached, not during. CTAB added to high-pH (alkaline) solution partially hydrolyses — reduces coating efficiency.
SOP-005 · Rev 1.0
Filter Press Operation & Cake Washing
Operating procedure for plate-and-frame filter presses separating precipitated silica from Na₂CO₃ filtrate, including cake washing requirements by grade.
1. Operating Cycle
1
Plate inspection before each cycle
Check filter cloth: no tears, holes, blinding (clogged pores). Blinded cloth: soak in 5% NaOH solution for 30 minutes, rinse with water — usually clears blockage. Torn cloth: replace immediately (silica will pass through). Replace cloths every 200–300 cycles or when filtrate appears milky.
2
FILL: Pump slurry at 3–5 bar (increasing to 6–8 bar as cake builds)
Slurry pump starts at low pressure. As cake builds, resistance increases, pressure rises automatically (centrifugal pump characteristic). When pump pressure reaches design maximum (8–10 bar) with minimal flow: filling is complete. Typical fill time: 20–30 min.
3
FILTRATION: Hold at pressure until filtrate flow drops to <10% initial rate
Na₂CO₃ filtrate goes to causticisation tank. Confirm filtrate clarity: should be clear yellow/colorless. Turbid filtrate means cloth damage — divert to recovery. Duration: 20–30 min.
4
WASHING: Push hot water (70–80°C) through cake — number of washes per grade
Standard grade: 2 washes (each wash volume = 50% of cake void volume)
HDS grade: 3 washes (Na₂O spec <1%)
Dental grade: 5 washes (Na₂O <0.3%, Pb concentration reduction)
Wash water goes to evaporator (contains dissolved Na₂CO₃ — recover it, do not discard).
HDS grade: 3 washes (Na₂O spec <1%)
Dental grade: 5 washes (Na₂O <0.3%, Pb concentration reduction)
Wash water goes to evaporator (contains dissolved Na₂CO₃ — recover it, do not discard).
5
OPEN: Release pressure, separate plates, collect cake
Cake drops into slurry tank for reslurrying before spray drying. If cake too wet (>65% moisture): add one more filtration cycle. If cake too dry (<45% moisture): it may crack in spray dryer — add small water wash before opening.
2. Cake Wash Quality Test (Dental Grade — Mandatory)
| Wash # | Expected Na₂O content (approx.) | pH of washwater | Action |
|---|---|---|---|
| Before washing | ~5–8% | 10–11 | — |
| After wash 1 | ~1–2% | 9–10 | Continue |
| After wash 2 | ~0.5–1% | 8–9 | Continue |
| After wash 3 | ~0.2–0.4% | 7–8 | Continue if dental grade |
| After wash 4–5 | <0.15% | ~7 | ACCEPT for dental |
⚠
Dental grade Pb removal: Lead (Pb) in the final silica must be <1 ppm (FSSAI E551). Pb is removed primarily by thorough washing. Each wash reduces Pb ~80%. After 4 washes, Pb is typically <0.3 ppm. Confirm by XRF on final product — not on the cake (XRF on wet cake is inaccurate).
SOP-006 · Rev 1.0
Triple-Effect Evaporator & MVR Operation
Operating procedure for the triple-effect evaporator with MVR compressor, concentrating the NaOH/Na₂CO₃ circuit from ~5% to 15–20% solids before causticisation.
⚡
MVR must be running before evaporator steam feed is opened. Without MVR: evaporation requires 167 GJ/day — exceeds available steam by 25.6 GJ/day. Operating evaporator without MVR = thermal deficit = leach reactor temperatures will drop = extraction falls = production loss. If MVR fails: immediately throttle evaporation rate and alert Plant Manager.
1. Startup Sequence
1
Start MVR compressor — confirm running before steam
Start compressor motor. Wait for compressor to reach operating speed (2–3 minutes). Confirm discharge pressure: 1.5–2.0 bar above first-effect pressure. Confirm compressor outlet temperature: 115–125°C. ONLY THEN open steam to first effect.
2
Open feed to first effect, start at 50% design flow
Feed: dilute Na₂CO₃ / wash water / spent NaOH solution mixture. Start at 50% to allow evaporator to reach thermal equilibrium (30–45 minutes). Then increase to 100%.
3
Monitor concentration of product stream (conductivity or density)
Target density at outlet of third effect: 1.18–1.22 g/mL (= 15–20% Na₂CO₃). Use inline density meter or manual hydrometer check every 2 hours. Too dilute: reduce feed rate. Too concentrated: risk of crystallisation in effect 3 — increase feed slightly.
2. Critical Operating Parameters
| Parameter | Effect 1 | Effect 2 | Effect 3 | Action if Deviation |
|---|---|---|---|---|
| Temperature | 120–130°C | 90–100°C | 70–80°C | Check steam supply, check inter-effect valves |
| Pressure | ~2 bar(g) | ~0.5 bar(g) | Vacuum (−0.6 bar) | Check vacuum pump, condenser cooling |
| MVR discharge | 115–125°C / 2.0–2.5 bar(g) | If low: MVR motor fault, check VFD | ||
| Product density | 1.18–1.22 g/mL | Adjust feed rate | ||
| Non-condensable purge | Open vent once per hour | Non-condensables accumulate, reduce HTC | ||
3. Scaling Prevention
Why scaling is the primary maintenance issue in evaporators
As Na₂CO₃ solution concentrates, it approaches saturation. CaCO₃ (if carried over from causticisation) is extremely insoluble and deposits on heat transfer surfaces as hard scale, reducing heat transfer coefficient (HTC) over time. Signs of scaling: evaporation rate drops at same steam input, product temperature deviates, pressure drops across effects change.
Prevention: (1) Ensure CaCO₃ is fully separated in filter press before sending liquid to evaporator. (2) Weekly acid clean (5% citric acid or HCl) dissolves CaCO₃ scale: circulate for 2 hours, drain, rinse with water. (3) Monitor HTC monthly — if drops >15% from baseline, schedule cleaning.
SOP-007 · Rev 1.0
CaO Slaking & Causticisation (NaOH Recovery)
Procedure for on-site CaO slaking to produce Ca(OH)₂ slurry and causticisation of Na₂CO₃ solution to recover NaOH. Produces Nano-PCC as obligatory co-product.
🔥
CaO HAZARD: CaO + water is strongly exothermic. Rapid slaking of large CaO charge can raise slurry temperature above 100°C — steam flash hazard. NEVER add large CaO charges at once. Add continuously via screw feeder at controlled rate. Slaker must have functioning cooling water jacket and temperature alarm (alarm at 95°C, shutoff at 100°C).
1. CaO Slaking
1
Check slaker cooling water — confirm flow before starting CaO feed
Cooling water flow to slaker jacket: confirm open and flowing. Temperature of cooling water inlet: <35°C. Do NOT start CaO feed if cooling water is off — temperature will exceed 100°C rapidly.
2
Add process water to slaker vessel first (water first, CaO second)
Water:CaO ratio = 3:1 by mass (to ensure excess water for complete slaking and manageable heat). Never add CaO to a dry vessel — exotherm is concentrated, causing hot spots.
3
Start CaO screw feeder at 50% rate, monitor temperature
CaO feed rate: 13,364 kg/day ÷ 24 hours = 557 kg/hr design rate. Start at 280 kg/hr. Slaker temperature should rise to 70–90°C — GOOD sign (confirms slaking is occurring). If temperature doesn't rise: CaO may be dead-burned (poor reactivity) — check SOP-001 CaO slaking test.
4
Increase to full rate (557 kg/hr) when temperature stabilises 75–90°C
Hold slaker at 80–90°C for 30 minutes at design rate to confirm complete slaking. Sample slaker output: filter, check residue — if white lumps remain, slaking incomplete. Ca(OH)₂ slurry should be smooth, white, milky consistency.
5
Transfer Ca(OH)₂ slurry to causticisation vessel
Ca(OH)₂ slurry must be used within 4 hours — it slowly carbonates in air (absorbs CO₂) and loses reactivity. Keep covered or under N₂ blanket if holding >2 hours.
2. Causticisation
1
Add concentrated Na₂CO₃ solution to causticisation vessel
Na₂CO₃ from evaporator (15–20% concentration). Pre-heat vessel to 80°C. Volume: calculated from daily Na₂CO₃ production. Start agitator (30 rpm) before adding anything.
2
Add Ca(OH)₂ slurry slowly over 30 minutes
Stoichiometric: 0.699 kg Ca(OH)₂ per kg Na₂CO₃. Add 10% excess Ca(OH)₂ (to drive conversion to completion). Agitate throughout. Temperature: maintain 80–90°C using steam jacket.
3
React for 2 hours at 80–85°C
CaCO₃ precipitates as fine white particles (this is your Nano-PCC product). NaOH remains in solution. Agitation speed: increase to 50 rpm during first 30 minutes to prevent CaCO₃ agglomeration, then reduce to 30 rpm.
4
Measure NaOH recovery efficiency (weekly or new process conditions)
Filter a 100 mL sample. Titrate filtrate with HCl to measure NaOH + Na₂CO₃ content. Calculate: NaOH recovered ÷ theoretical NaOH from stoichiometry. Target ≥80%. If <75%: investigate — check Ca(OH)₂ quality, Na₂CO₃ concentration, temperature. Log in OPR-007.
5
Transfer to CaCO₃/NaOH separation (filter press or wash thickener)
Separate CaCO₃ (Nano-PCC) from NaOH liquor. NaOH liquor → recycled to leach reactors. CaCO₃ slurry → classification and coating (SOP-009). Wash CaCO₃ cake × 3 to recover entrained NaOH (wash goes back to causticisation).
⛔ Critical Control Points
CCP-1: CaO quality (from SOP-001). Dead-burned CaO gives <60% slaking efficiency — NaOH recovery crashes. Never use CaO that failed slaking rate test.
CCP-2: Na₂CO₃ concentration going in. Below 10%: reaction is slow and inefficient. Above 25%: risk of Na₂CO₃ crystallisation in causticiser, which blocks pipes and vessel.
CCP-3: Wash all CaCO₃ cake — every wash recovers ~₹800–1200 of NaOH value. Skipping washes is equivalent to throwing money away.
SOP-008 · Rev 1.0
Spray Dryer Operation
Procedure for spray drying the precipitated silica filter cake slurry to produce finished powder at <6% moisture, maintaining grade integrity through temperature control.
1. Slurry Preparation for Feed
1
Reslurry filter cake to 20–30% solids
Add filter cake to reslurry tank with hot water (60°C). Mix with high-shear agitator to break up cake lumps (5 minutes at 200 rpm). Target: smooth, pumpable slurry with no lumps >2mm. Lumps cause nozzle blockage.
2
For HDS grade: confirm CTAB content in slurry
CTAB should already be in slurry from precipitation. Take 10 mL sample, filter, measure CTAB in filtrate (UV-Vis at 254nm). If CTAB is entirely on silica surface (none in filtrate): good — coating is complete. If high free CTAB in filtrate: slurry over-dosed — reduce next batch CTAB by 5%.
2. Spray Dryer Temperature Control by Grade
| Grade | Inlet Air Temp | Outlet Air Temp | Reason |
|---|---|---|---|
| Standard | 170–200°C | 80–95°C | High throughput; no surface sensitivity |
| HDS | 150–170°C | 70–85°C | CTAB begins to degrade at >180°C |
| Dental / Food | 130–155°C | 65–80°C | Gentle — preserves silanol groups for thickening function; no browning |
⚠
CTAB thermal stability: CTAB quaternary ammonium compound decomposes above 180°C, producing trimethylamine (fishy odour) and altering surface chemistry. HDS grade MUST use inlet T ≤170°C. If dryer runs too hot: product will have strong odour AND CTAB surface area will be reduced — batch may fail CTAB test.
3. Product Collection and Packaging
1
Cyclone separator primary collection — check efficiency daily
Cyclone captures 95–98% of dried silica. Fines exit with exhaust air → captured by bag filter. Combined cyclone + bag filter product is mixed and goes to product silo. Monitor bag filter differential pressure — if >200 Pa: clean bags (pulse jet).
2
Sample every 2 hours from product silo — moisture check
Moisture analyser test: 2g sample at 105°C, 10 minutes. Target <6%. If moisture 6–8%: increase inlet temperature by 10°C or reduce feed rate 10%. If moisture >8%: stop production, investigate feed slurry density (may be too thick).
3
Pack into 25 kg woven PP bags or 500 kg jumbo bags
Confirm grade label matches production record. Seal bag immediately after filling — silica absorbs moisture from air (hygroscopic). Jumbo bags for domestic bulk; 25 kg labelled bags for domestic retail and export samples. Print batch number, date, grade, and key specs on label.
SOP-009 · Rev 1.0
PCC Hydrocyclone Classification & Surface Coating
Procedure for classifying nano-PCC from causticisation by particle size using hydrocyclones and applying stearic acid or OCC coating to produce sealant and plastics grades.
1. Hydrocyclone Classification Principle
How hydrocyclones separate by particle size
A hydrocyclone has no moving parts — it uses centrifugal force created by the tangential inlet to separate particles by size. The slurry enters tangentially at the top, spins rapidly. Large/heavy particles migrate to the wall (centrifugal force) and exit at the bottom (underflow = coarse fraction). Fine particles move toward the centre (lower pressure zone) and exit at the top (overflow = fine fraction).
Cut point (d50) of the hydrocyclone depends on: inlet pressure, cyclone diameter, vortex finder length, and slurry density. Smaller diameter cyclones = finer cut point. For 0.5 µm PCC (plastics grade), multi-stage classification with small-diameter cyclones (25–50 mm) is needed.
| PCC Grade | Target d50 | Cyclone Stage | Coating | ₹/kg |
|---|---|---|---|---|
| Coatings / Bulk | 2.0 µm | Single stage | None (uncoated) | ₹8–15 |
| Sealant Grade | 0.7 µm | Two-stage | Stearic acid 1.8–2.2% | ₹26 |
| Plastics Grade | 0.5 µm | Three-stage + fine screen | OCC (oleic acid / coupling agent) | ₹42 |
2. Stearic Acid Coating Procedure (Sealant Grade)
1
Prepare stearic acid solution: dissolve in hot water (85°C) at 3% concentration
Stearic acid melts at 69°C. Above 80°C it dissolves readily in hot water (with mild agitation). Prepare daily batch based on PCC production plan. Stearic acid must be food-grade (vegetable-derived) for any PCC that may contact food-contact polymers.
2
Mix stearic acid solution into classified PCC slurry (0.7 µm fraction)
Target coating level: 1.8–2.2% stearic acid on dry PCC weight. Add stearic solution slowly over 20 minutes with agitation. The stearic acid molecules bind to the CaCO₃ surface (carboxylate head bonds to Ca²⁺, tail points outward). Maintain temperature 70–80°C during coating.
3
Filter and dry coated PCC
Filter press to <50% moisture. Dry at 110°C (fluid bed dryer or spray dryer) — stearic acid does not degrade at 110°C (decomposes >250°C). Check coating by dispersibility test: drop 1g coated PCC on water surface — hydrophobic coated PCC floats. Uncoated PCC sinks immediately.
4
Verify coating % by TGA (weekly)
TGA: heat 50 mg coated PCC from RT to 600°C under N₂. Weight loss from 200–450°C = stearic acid (organic coating). Target 1.8–2.2% weight loss. Below 1.5%: product is under-coated — may not disperse in polymer. Above 2.5%: over-coated — wasted reagent, possible stickiness.
SOP-010 · Rev 1.0
QC Testing Procedures — PS & PCC
Standard methods for testing precipitated silica and nano-PCC product quality including BET surface area, CTAB value, particle size, moisture, pH, and XRF elemental analysis.
1. BET Surface Area (N₂ Adsorption)
1
Degass sample: 200°C, vacuum, 2 hours
Remove adsorbed water and organics from silica surface. DO NOT exceed 250°C — CTAB degrades. Use BET instrument degassing port (standard SS tube). Sample weight: 150–300 mg. If BET instrument has heating limitation, use separate Schlenk line.
2
Run BET measurement: N₂ adsorption at −196°C (liquid N₂)
Multi-point BET: 5–7 pressure points between P/P₀ = 0.05–0.35. Plot BET straight line, derive surface area from slope and intercept. Typical values: Standard 140–165 m²/g · HDS 160–180 m²/g · Dental 100–140 m²/g.
3
Report and compare to spec — three replicates per batch
CV (coefficient of variation) between replicates should be <3%. If CV >5%: sample not homogeneous, resample. Report mean ± standard deviation in CoA.
ℹ
BET calibration: Use certified reference material (e.g., Cabot Cab-O-Sil M5, certified BET ~200 m²/g) monthly to verify instrument accuracy. Record calibration check in calibration log. If reference value deviates >5%: recalibrate instrument per manufacturer procedure.
2. CTAB Surface Area (HDS Grade — Mandatory)
1
Prepare CTAB standard solution: 11 g/L in deionised water
Accurately weigh 11.00 g CTAB (≥99% pure). Dissolve in 1L deionised water at 40°C (CTAB dissolves slowly at room temperature). Standardise solution concentration by conductimetry or UV-Vis.
2
Add 300 mg dry silica to 100 mL CTAB solution, agitate 1 hour at 25°C
Silica must be dry (<0.5% moisture) — moisture dilutes CTAB solution and gives high apparent CTAB value. Use orbital shaker at 150 rpm. Temperature control important — CTAB adsorption is temperature-sensitive.
3
Filter and measure residual CTAB in filtrate by UV-Vis at 254 nm
CTAB absorbs UV at 254 nm. Prepare calibration curve (5 standards: 0, 2, 4, 6, 8 g/L). Read absorbance of filtrate. Calculate CTAB adsorbed = (initial − final) concentration × volume ÷ silica mass. Target HDS: ≥175 mg CTAB/g silica.
3. Particle Size Distribution (Laser Diffraction)
1
Disperse 0.5g silica in 100 mL water with 1% Triton X-100 surfactant
Triton X-100 prevents agglomeration during measurement. Sonicate for 2 minutes (probe sonicator, 50W). Without proper dispersion, agglomerates read as large particles — you'll get D50 of agglomerates, not primary particles.
2
Add to laser diffraction cell, measure at obscuration 5–15%
Obscuration <5%: too few particles, poor statistics. >15%: multiple scattering, inaccurate. Run 3 cycles per sample. Record D10, D50, D90, D99. Compare to grade spec.
| Grade | D50 Spec | D90 Spec | Action if OOS |
|---|---|---|---|
| Standard | ≤20 µm | ≤45 µm | Downgrade — no action |
| HDS | ≤15 µm | ≤35 µm | Check precipitation pH — may have drifted |
| Dental | ≤12 µm | ≤25 µm | Do NOT release — return to precipitation review |
4. XRF Elemental Analysis (Dental Grade — Every Batch)
1
Prepare fused bead or pressed pellet per instrument method
Fused bead (lithium borate fusion): destroys matrix effects, most accurate. Pressed pellet: faster, adequate for most elements. For Pb at <1 ppm: ED-XRF pressed pellet is adequate (LOD typically 0.2 ppm for Pb).
2
Run semi-quantitative scan first, then quantify elements of concern
Dental grade elements: SiO₂ ≥99%, Fe <50 ppm, Pb ≤1 ppm, As ≤1 ppm, heavy metals total ≤20 ppm. Any exceedance: HOLD batch, investigate — check RHA supplier, leach reactor lining, wash efficiency.
5. CoA Template (Certificate of Analysis)
What every CoA must contain for export
Customer-facing CoA must include: Product name + grade · Batch number · Date of manufacture · Physical appearance · Moisture % · BET surface area (m²/g) · CTAB (for HDS) · D50 (µm) · SiO₂ content % · pH of 5% aqueous suspension · Heavy metals (if dental) · Packaging details · Testing standard reference · QC Officer signature + company stamp. Export customers also require: HS Code (2811.22.00 for precipitated silica) · Country of origin declaration.
SOP-011 · Rev 1.0
ETP & ZLD System Operation
Operation of the effluent treatment plant and zero liquid discharge system. Mandatory Day 1 compliance requirement. No liquid effluent may exit site boundary.
1. ETP Process Flow
| Stage | Unit | Purpose | Key Parameter |
|---|---|---|---|
| 1 | Collection sump + equalization | Buffer flow variability, pH averaging | Retain 6–8 hours |
| 2 | pH neutralisation | Adjust pH 6–9 (TSPCB limit) | pH 7–8 target; use HCl or lime |
| 3 | Chemical precipitation | Remove Ca, Mg, heavy metals | Add Na₂CO₃ or lime; settle 2 hours |
| 4 | Lamella clarifier | Settle suspended solids | Effluent TSS <100 mg/L |
| 5 | MBR (Membrane Bioreactor) | Remove residual organics (CTAB, stearic) | COD <250 mg/L output |
| 6 | RO (Reverse Osmosis) | Desalinate — 80% permeate recovery | Permeate TDS <500 mg/L → recycle |
| 7 | MEE (Multiple Effect Evaporator) | Concentrate RO reject to solid | Solid cake for disposal |
2. Daily Monitoring Requirements
Collection sump level — below 75% (if above: reduce process water use or increase ETP throughput)
pH of equalized effluent (before treatment): record, target 7–10 (alkaline from NaOH, lime)
MBR differential pressure — if >0.5 bar: membrane fouling, backwash required
RO permeate TDS: <500 mg/L (conductivity meter). If above: check RO membranes for scaling
RO recovery rate: measure inlet flow vs. permeate flow. Target: 80% recovery
MEE — solid cake volume: record and arrange disposal (lined landfill or hazmat contractor)
Confirm NO liquid discharge at site boundary (visual inspection of drain outlets)
⛔
ZLD compliance is non-negotiable. Any liquid discharge detected at site boundary is a TSPCB violation — immediate notice, potential closure order. If ZLD system fails: STOP production immediately and draw down surge tank. Do NOT bypass ZLD even for short periods. Notify Plant Manager + TSPCB within 24 hours of any system failure (as per consent conditions).
SOP-012 · Rev 1.0
Emergency Response Procedures
Response procedures for the primary emergency scenarios at Fluxara: NaOH spill, furnace temperature excursion, fire, CO₂ asphyxiation, CaO burn, and TOH thermal oil system emergency.
Emergency 1 — NaOH Spill / Skin Contact
!
IMMEDIATE: Remove contaminated clothing, flush with water for 15+ minutes
Do not stop flushing to assess injury — time matters. Safety shower location: within 10 seconds of any NaOH work area. Shout for help immediately.
!
Eye contact: eyewash for 15 minutes continuously
Hold eyelids open. Flush from inner to outer corner. Seek medical attention immediately after flushing — even if pain has subsided. NaOH eye exposure can cause permanent damage if not treated.
!
Large spill: evacuate area, neutralise with citric acid or vinegar (dilute)
Absorb with dry sand/vermiculite. Do NOT flush NaOH to drain — it is an alkaline effluent. Collect in drums for ETP. Notify TSPCB if spill reaches drainage.
Emergency 2 — Furnace Temperature Excursion (>700°C)
⚡
CEMS auto-shutoff triggers at 720°C — confirm husk feed stopped
CEMS should auto-cut husk conveyor. If it doesn't (manual intervention): hit EMERGENCY STOP on furnace feed conveyor. Do NOT reduce air supply — this causes CO formation and fire risk.
2
Collect RHA from that session separately — do NOT mix with normal RHA
Over-temperature RHA is partially crystallised and will fail extraction. Label it "HOLD — Over-Temp," run dissolution test. If <75% dissolution: dispose, do not use in production.
3
Investigate cause before restart: review CEMS log, check feed rate, check air supply
Common causes: feed rate spike (conveyor blockage cleared all at once → surge), air supply reduction (damper fault), fuel moisture change. Fix root cause. Plant Manager sign-off required before restart.
Emergency 3 — Husk Storage Fire
🔥
Activate fire alarm, call 101, evacuate non-essential personnel to assembly point
Do not attempt to fight large husk fires manually — husk pile fires can be deep-seated and reignite. Evacuate first.
2
Activate sprinkler system in husk storage area
Sprinkler manual override valve location: [marked on site map]. Do not enter burning husk storage.
3
Isolate furnace husk feed immediately
Prevent fire from traveling via conveyor to furnace building. Cut conveyor power at main panel.
3
Notify TSPCB and insurance within 24 hours
Requirement under factory license and insurance policy. Document with photos, CEMS log extract.
Emergency 4 — CO₂ Asphyxiation (Precipitation Area)
!
CO₂ alarm: evacuate immediately, do not re-enter without SCBA
CO₂ at >5% is immediately dangerous. Person found unconscious in CO₂ area: DO NOT ENTER without Self-Contained Breathing Apparatus (SCBA). Two-person rescue rule — never enter alone.
2
Move casualty to fresh air, call 108 ambulance
If breathing: recovery position. If not breathing: start CPR. CO₂ asphyxiation — once in fresh air, most people recover rapidly if treated quickly.
3
Locate CO₂ leak — check precipitation vessel vent valves, supply line flanges
Increase ventilation fans. Re-enter only after CO₂ monitor reads <1%. Fix leak before resuming production.
Emergency 5 — TOH System Overpressure / Pressure Relief Device (PRD) Lift
!
PRD lifts (hot oil vapour release): clear area, do not approach — hot oil hazard
Therminol 55 vapour at >210°C is flammable. PRD discharge is to a safe vent — confirm vent is unobstructed. Do NOT approach PRD outlet area. PRD will reseat when pressure drops below setpoint.
2
Reduce husk feed immediately, shut furnace air damper to reduce combustion
Reducing furnace output will lower TOH oil temperature and pressure. Continue oil circulation — do NOT stop the pump. Monitor TOH supply pressure and temperature from control room.
3
If pressure still rising: shut TOH oil circuit isolation valve, let system cool
This disconnects the furnace coil from the process. TOH oil in the furnace will cool via radiation. Record all data. Do not restart until Plant Manager and TOH vendor have reviewed. No regulatory notification required (TOH is not an IBR boiler).
✓
Quarterly drill schedule: Q1: NaOH spill + eyewash test · Q2: Fire drill + assembly point headcount · Q3: CO₂ scenario + SCBA fitting · Q4: Combined emergency evacuation. Record drill, participants, and any corrective actions in Safety Register (SAF-012).