Fluxara Advanced
Renewables & Applications

Rice mills produce two waste streams: rice husk (the outer shell, ~20% of paddy weight) and the ash left after burning it (RHA — Rice Husk Ash). Both are abundant, cheap, and usually discarded. Fluxara converts them into two high-value industrial chemicals.

Precipitated Silica (PS) is the same white powder used in high-performance green tyres, toothpaste, food anti-caking, and industrial rubber. Global price: ₹26–95/kg depending on grade. It is made from the silicon dioxide (SiO₂) locked inside RHA — up to 92% of the ash is amorphous silica.

Nano-PCC (Precipitated Calcium Carbonate) is an obligatory co-product of the NaOH recovery step. When NaOH is recycled after silica extraction, it reacts with lime (CaO) and produces ultra-fine calcium carbonate — the same filler used in paints, plastics, silicone sealants, and paper. Price: ₹8–42/kg by grade.

The plant is thermally self-sufficient: rice husk is burned on-site to generate 199 GJ/day of heat. After running all processes (with MVR heat recovery), 83 GJ/day surplus remains — enough to power a Phase 1B expansion and a future Phase 2 line without buying any fuel.

Below 700°C, the silica in rice husk remains in an amorphous (non-crystalline) state — structurally disordered at the atomic level. This is essential: amorphous SiO₂ dissolves readily in NaOH, giving 88% extraction efficiency.

Above 700°C, silica undergoes crystallisation into cristobalite — a highly ordered crystal lattice. Cristobalite does NOT dissolve in NaOH at any practical concentration or temperature. The RHA becomes chemically inert and the entire batch is wasted. This is why a CEMS (Continuous Emissions Monitoring System) is wired to an auto-shutoff at 720°C — a 20°C safety buffer.

Na₂SiO₃ is a clear, viscous liquid used industrially in adhesives, cements, and detergents. At Fluxara it is an intermediate — it is never sold. Instead it is fed directly into Reaction 2 to precipitate silica. The "water glass" is essentially a dissolved form of silica with sodium attached — Reaction 2 removes the sodium by replacing it with CO₂.

The pH at which CO₂ is added controls when silica nucleates vs. grows. At higher pH (8–9), fewer nucleation sites form → larger particles → Standard grade (D50 ~20 µm). At lower pH (5.5–7), rapid nucleation creates many small particles → HDS grade (CTAB ≥175 mg/g, CIPD ≥80%). Dental grade requires additional washing to reduce lead below 1 ppm (Pb ≤1 ppm per FSSAI E551).

The CTAB surfactant added post-precipitation coats each silica particle. CTAB consumption — 0.289 MT/day (₹1,80,000/MT, imported) — is the primary driver of HDS premium. This is why CTAB supply chain (4-week buffer mandatory) is the highest supply-risk item in the BOM.

A mass balance is simply a material accounting statement: inputs = outputs + accumulation. For a continuous steady-state plant (no accumulation), every kilogram of raw material must appear somewhere in the outputs — either as product, by-product, waste, or atmospheric emission.

The key chain: RHA → SiO₂ extraction → Na₂SiO₃ → PS precipitation → Na₂CO₃ → NaOH recovery + Nano-PCC. The 12% of SiO₂ that is NOT extracted (100% − 88% = 12%) leaves as desilicated residue sold to brick kilns at ₹900/MT.

This surprises many people. The answer is stoichiometry: per mole of Na₂CO₃ converted, the CaCO₃ product has MW = 100.09 g/mol, but the NaOH "input equivalent" (2×NaOH = 80 g/mol) is lighter. Furthermore, Ca(OH)₂ (from CaO slaking) adds calcium mass to the product. So the PCC stream carries the weight of both the carbonate anion AND the calcium cation — it is inherently a heavier molecule per mole of sodium processed.

Combined with CaO purchased at 13.364 MT/day, the product PCC tonnage necessarily exceeds the silica tonnage. This is structural, not an error.

Net Calorific Value (NCV) is the energy released per kg of fuel burned, accounting for the energy lost evaporating moisture in the fuel. Rice husk has NCV ≈ 12,150 kJ/kg at 10% moisture. At 20 MT/day = 20,000 kg/day: gross thermal = 20,000 × 12,150 = 243,000,000 kJ/day = 243 GJ/day.

A boiler cannot capture 100% — efficiency is typically 80–85%. At 82%: useful heat = 243 × 0.82 = 199.3 GJ/day. This is the energy available for process use.

MVR (Mechanical Vapour Recompression) is a heat pump for evaporators. Instead of using fresh steam to evaporate water from the sodium silicate solution, MVR compresses the vapour produced and reuses it as the heat source. At 65% energy saving on evaporation: MVR saves 0.65 × 167.1 = 108.6 GJ/day. Without this saving, process heat demand (224.9 GJ/day) would exceed supply (199.3 GJ/day) by 25.6 GJ/day — the plant cannot operate at design throughput.

DSCR = (EBITDA − Income Tax on PBT) ÷ (Principal Repayment + Interest). It answers: "For every ₹1 of debt service due this year, how many rupees of operating cash does the plant generate?" Banks require DSCR ≥ 1.25× as the loan covenant. A DSCR of 2× means the plant generates twice the cash needed to service debt — very comfortable. A DSCR of 0.27× (Year 1) means the plant cannot service debt from operations — the promoter's bridging WC of ₹1.55 Cr covers the gap. Year 1 is the moratorium period; no principal repayment is due, only interest.

Y1/Y2 DSCR uses EBITDA/DS directly (minimal tax because EBITDA is low or moratorium applies). Y3/Y4+ include 25.17% income tax on PBT after depreciation. The exact tax figure requires the depreciation schedule annexure (pending for v16).

The jump is not just utilisation (60%→75% adds only ~25% volume). The key driver is product qualification: HDS (High Dispersibility Silica) for green tyres qualifies in Y2. HDS commands ₹45–50/kg domestic vs. ₹26/kg standard — a 73–92% premium. Once the first tyre manufacturer qualifies the batch (typically 3–6 month trial + approval cycle), the entire HDS volume shifts to premium pricing. Revenue per MT effectively doubles for the HDS portion. Similarly, Y3's FSSAI dental certification unlocks ₹90–95/kg pricing (3.5× standard).

CTAB (cetyltrimethylammonium bromide) surface area is the standard test for measuring the silica surface accessible to polymer chains in a rubber compound. The CTAB surface area (mg/g) directly correlates with how well the silica disperses in the tyre rubber matrix — hence "High Dispersibility Silica."

A CTAB ≥175 mg/g with CIPD (CTAB-based In-rubber Performance Descriptor) ≥80% means the silica is engineered for low rolling resistance (better fuel economy) — the defining performance claim of green tyres. This specification requires precise pH control during precipitation, strict particle size control, and CTAB surface treatment post-filter.

CIPD is calculated from dynamic mechanical analysis of the rubber compound — tyre manufacturers run this test in-house as part of supplier qualification. This is why HDS qualification takes 3–6 months and requires supplying samples before any order.

Raw (uncoated) CaCO₃ is hydrophilic — it attracts water and clumps in polymer matrices, causing weak spots. Stearic acid coating makes each particle surface hydrophobic (oil-loving), allowing it to disperse uniformly in silicone or polymer matrices without agglomeration. The coating adds minimal cost (₹1,20,000/MT stearic acid at 0.162 MT/day) but commands a 50–100% price premium over uncoated bulk PCC.

Particle size (d50 = median diameter) is controlled via hydrocyclone classifiers. The plastics grade at 0.5 µm requires tighter classification and more passes — hence highest price at ₹42/kg.

Phase 1A leaves 83 GJ/day thermal surplus. Phase 1B only requires ~9 GJ/day to process an additional 4.568 MT/day of purchased RHA. The binding constraint is equipment throughput, not heat. A second filter press, a second spray dryer, an extra leach reactor, plus piping — totalling ₹1.50 Cr — unlocks this capacity.

At ₹9.29 Cr/yr incremental EBITDA from ₹1.50 Cr investment, the payback is under 2 months. This is why Phase 1B is funded from Year 1 accruals, never from bank debt. Installing it at Month 18 (mid-Year 2) allows the first year of cash to accumulate before the investment.