BM-38|OPERATIONAL OPTIMIZATION GUIDE FOR AUTO-DUMPING POLISHING FILTERS IN ALUMINA REFINERY

Author | Rajendra Kunwar, Alumina Technology Specialist & Bayer Process Expert

1. Executive Summary & Process Context

In modern Alumina Refineries, polishing filtration represents a critical solid-liquid separation stage positioned after primary sedimentation/decantation. Transitioning from manual security filters to Auto-Dumping Vertical Leaf Pressure Filters has significantly enhanced operational automation, throughput capacity, and safety standard compliance. However, sustaining seamless performance requires strict adherence to operating parameters.

The polishing filtration system operates under two fundamental performance benchmarks:

·      Maximized Filtration Flux at Minimal Differential Pressure: Achieving high specific flow rates (m³/m²·h) while keeping operational head loss across the leaf media to a minimum.

·     Superior Filtrate Clarity (TSS ≤ 20 mg/L): Maintaining target clarity with suspended solids strictly controlled below threshold limits to avoid downstream trihydrate precipitation contamination and alumina quality degradation.

2. Standard Operating Cycle Sequence

Auto-dumping pressure leaf filters operate on a cyclic sequence governed by PLC/DCS automation. Each complete operational batch comprises five distinct phases:

Phase	Cycle Stage	Operational Objective & Description
1	First Filtrate Recirculation	Recirculate initial turbid liquor back to Feed Tank until a uniform precoat/filter cake layer is established on vertical leaf elements.
2	Liquor Filtration Mode	Main operational phase where pregnant liquor is filtered at optimum flow rate until terminal pressure drop (ΔP_max) or cycle timer is reached.
3	Filter Decompression	Depressurization of the vessel shell and displacement of residual liquor via back-pressure gas/steam to prepare for cake discharge.
4	Sludge / Cake Discharge	Automatic pneumatic/vibratory cake dumping into the sludge collection hopper/tank via bottom pneumatic discharge butterfly valve.
5	Cake Settling & Reset	Settling of discharged cake residue into the sludge tank followed by valve repositioning and vessel prefill for the next cycle.

3. Major Operational Disturbance & Corrective Action Matrix

During process fluctuations upstream, pressure leaf filters can exhibit severe operational anomalies. The table below outlines the root causes, process impacts, and recommended engineering countermeasures.

Operational Defect	Root Cause Analysis	Process Impact	Recommended Remedial Action
Fast Drop in Filtration Rate / Premature ΔP Spike	1. Excessive fines from over-grinding bauxite. 2. Inconsistent flocculant dosage/cooking in decanters. 3. Elevated liquor viscosity due to sub-optimal temperature in digestion blow-off.	Shortened cycle time, frequent backwashing, reduced plant throughput, high pump energy consumption.	• Optimize bauxite grinding particle size distribution (PSD). • Control digestor blow-off dilution to maintain target liquor temperature/viscosity profile. • Ensure proper flocculant hydration, cooking temperature, and steady metering.
Poor / Fluctuating Filtrate Clarity (TSS > 20 mg/L)	1. Inadequate or improper Filter Aid (TCA) dosing point (e.g., dosage into decanter instead of filter feed). 2. Pore blinding and scale build-up on leaf wire mesh. 3. High operating pressure forcing fines through media.	Liquor quality non-conformance, downstream hydrate contamination, premature cloth/leaf blinding.	• Continuous inline TCA dosing directly into filter feed pump suction header. • Maintain mass flow ratio: TCA Mass = 10 × TSS Mass in feed liquor. • Prepare Tricalcium Aluminate (TCA) at 80°C with 1-hour cooking time using quality burnt lime. • Perform periodic caustic chemical wash of leaf elements.

 

4. Engineering Guidelines & Preventive Practices

Key Engineering Rule of Thumb: Filter Aid (TCA) Dosing Standard Target Mass Flow Dosing Rate:   M_TCA (kg/h) = 10 × M_TSS (kg/h) • Critical Point of Dosing: Dosing TCA into Settler decanters causes it to act merely as a settling aid. Dosing MUST be targeted continuously into the suction line of the filter feed pumps. • Slurry Preparation Parameters: Slurry preparation must use high-grade active burnt lime, cooked at a target temperature of ~80°C for a minimum retention time of 60 minutes.

 

4.1 Filter Leaf Maintenance & Chemical Wash Protocol 

Accumulation of hard aluminosilicate scale and embedded fines leads to leaf hardening. Hardened leaves cause an abrupt increase in filtration differential pressure, driving fine suspended solids through the pore matrix into the filtrate stream. A scheduled caustic washing program using hot caustic liquor at 85–90°C must be integrated into routine maintenance schedules to dissolve scale and restore mesh porosity.

CETI ENTERPRISES, INDIA

CETI Enterprises supports alumina industry professionals through technical training, process audits, calcination performance assessment, energy optimization, process troubleshooting, equipment design review, debottlenecking and refinery improvement programmes. For further details please visit our website at https://ceti.co.in

About the Author: Rajendra Kunwar is Bayer Process & Alumina Technology Specialist. Through CETI Enterprises, he offers expert technical consultancy in customized online / onsite team training, process for production of specialty grade ATH & Alumina, efficiency enhancement, quality improvement, energy reduction, cost reduction, troubleshooting and plant debottlenecking. To explore how we can support your plant operations or upcoming expansion, please contact us at rajendra@ceti.com.

 

BM-037 | Process Engineering Approach to Maximise Alumina Extraction in Alumina Refinery

Author: Rajendra Kunwar, Alumina Technology Specialist & Bayer Process Expert

 

1. Introduction

Alumina extraction efficiency is one of the most important performance indicators of the Bayer digestion circuit. It directly influences bauxite consumption, residue generation, caustic soda utilisation, digestion energy requirements and the overall production cost of alumina. 

The primary objective of digestion is to dissolve the available alumina minerals in bauxite into caustic liquor under controlled temperature, pressure, concentration and residence-time conditions. However, achieving high extraction is not simply a matter of increasing digestion temperature or caustic concentration. It requires an integrated understanding of bauxite mineralogy, dissolution kinetics, liquor chemistry, slurry hydraulics, equipment performance and downstream reaction behaviour.

A poorly optimised digestion circuit can leave valuable alumina in the residue, increase soda losses and reduce the economic value of the refinery's bauxite resources.

The engineering objective is to maximise the extraction of available alumina consistently and economically.

2. Definition and Measurement of Extraction Efficiency

Extraction efficiency represents the proportion of alumina entering with the bauxite that is transferred into the dissolved phase under the defined process conditions.

A simplified mass-balance expression is:

Extraction efficiency (%) = (Mass of alumina extracted into liquor ÷ Mass of alumina in bauxite feed) × 100

Two different performance indicators should be distinguished:

• Total-alumina extraction: Alumina transferred to the liquor relative to total Al₂O₃ entering with the bauxite.
• Available-alumina extraction: Alumina extracted relative to the alumina determined to be available under the specified digestion conditions. 

The plant must define which indicator it reports and maintains that basis consistently.

Where dissolved alumina subsequently precipitates or is incorporated into desilication products, the dissolved alumina measured in blow-off liquor may be lower than the gross amount initially dissolved. Therefore, extraction calculations should be supported by representative sampling, accurate flow measurements and a properly closed material balance. 

3. Major Factors Affecting Alumina Extraction 

3.1 Bauxite Mineralogy and Available Alumina 

Bauxite mineralogy establishes the fundamental digestibility of the feed. Gibbsite, boehmite and diaspore exhibit different dissolution characteristics. Gibbsite generally dissolves under less severe digestion conditions, while boehmite and diaspore typically require higher temperatures and more demanding conditions. The following parameters should be established during bauxite characterisation:

• Mineralogical distribution of gibbsite, boehmite and diaspore.
• Total and available Al₂O₃.
• Reactive and total silica.
• Iron oxide, titania and other mineral impurities.
• Organic matter, moisture and feed variability.

Engineering implication: The digestion temperature, caustic concentration and residence time must be selected according to the mineralogical composition of the actual bauxite blend. A digestion regime suitable for predominantly gibbsitic bauxite may not provide adequate extraction from a boehmitic feed. 

3.2 Bauxite Particle-Size Distribution 

Grinding increases the exposed mineral surface area and reduces the diffusion distance for dissolution. Finer particles generally dissolve faster, provided that the mineral phases are accessible and the process conditions are suitable. However, excessive grinding can increase power consumption and generate fine residue particles that adversely affect settling, washing and filtration. The optimum particle-size distribution must balance:

• Alumina dissolution kinetics.
• Grinding energy consumption.
• Mineral liberation.
• Residue settling characteristics.
• Downstream filtration capacity and liquor clarity.

A criterion such as 80% passing 147 µm may serve as an initial reference for certain bauxites, but it should not be treated as a universal design standard. The optimum grind must be confirmed through representative laboratory tests and plant trials. 

3.3 Digestion Temperature 

Temperature is a major determinant of dissolution kinetics. Increasing temperature generally accelerates the dissolution of alumina minerals, but the benefit depends on mineralogy, liquor composition and residence time.

The principal considerations are:

• Actual slurry temperature rather than the steam-header temperature.
• Temperature uniformity across parallel digestion trains.
• Heat-transfer performance and fouling.
• Temperature fluctuations during changes in feed rate.
• Potential reversion or precipitation of dissolved alumina under unfavourable conditions.

For predominantly gibbsitic bauxite, excessive digestion severity may be unnecessary and economically disadvantageous. For boehmitic bauxite, higher temperatures may be essential.

Recommendation: Establish the optimum temperature through digestion test work and verify it against extraction, steam consumption, reversion and downstream performance.

3.4 Caustic Concentration and Alumina-to-Caustic Ratio

The dissolving capacity of the digestion liquor depends on following critical parameters:

• Effective caustic concentration.
• Alumina-to-caustic ratio.
• Carbonate concentration.
• Liquor dilution.
• Bauxite-to-liquor ratio.
• Temperature.

Stable liquor preparation and accurate dosing of fresh caustic and spent liquor are essential for maintaining consistent digestion conditions. 

3.5 Slurry Density and Bauxite-to-Liquor Ratio 

Slurry concentration affects the interaction between bauxite and digestion liquor, equipment hydraulics, viscosity, heat transfer and effective residence time.

The optimum slurry density should be established by considering:

• Bauxite characteristics and particle-size distribution.
• Liquor composition and temperature.
• Agitator capacity.
• Digester working volume.
• Pumping and pressure-drop limitations.
• Steam consumption and production rate.

Slurry density should therefore be controlled as a critical process variable rather than treated solely as a feed-preparation parameter.

3.6 Effective Residence Time

Adequate residence time is necessary for the dissolution reactions to approach the required level of completion investigating following factors:

• Effective working volume.
• Flow distribution between digesters.
• Short-circuiting and dead zones.
• Agitator performance.
• Slurry accumulation and solids suspension.
• Variation in throughput and slurry density.

The objective is to establish the optimum residence-time for the selected bauxite and digestion conditions.

3.7 Reactive Silica and Desilication Products

Reactive silica reacts with dissolved sodium aluminate under Bayer process conditions to form desilication products (DSP). The principal control measures are:

• Accurate characterisation of reactive silica in the bauxite.
• Appropriate pre-desilication,
• Control of desilication conditions.
• Monitoring of silica loading and DSP formation.
• Assessment of alumina and soda associated with the solid residue. 

3.8 Lime Addition and Liquor Chemistry

Lime is used in Bayer circuits for specific chemical-control objectives, including causticisation of sodium carbonate under suitable conditions. Its effects depend on the liquor composition, bauxite impurities and overall circuit configuration.

The dosage must be optimised against:

• Carbonate concentration and causticisation performance.
• Soda recovery.
• Oxalate and impurity behaviour.
• Formation of calcium-bearing solids.
• Scaling and residue-handling implications. 

Lime dosage should be based on liquor analyses, process objectives and demonstrated plant performance. 

3.9 Digester Agitation and Hydrodynamics 

Effective agitation promotes uniform temperature, solids suspension and contact between the bauxite particles and caustic liquor. Inadequate mixing may create local variations in temperature and liquor composition, reduce effective reaction time and encourage solids accumulation. Performance assessments should cover:

• Impeller condition and configuration.
• Agitator speed and power input.
• Slurry rheology and solids concentration.
• Suspension of coarse particles.
• Dead zones and short-circuiting.
• Mechanical wear and internal equipment condition.

The objective is to achieve effective mixing at an appropriate energy cost. 

3.10 Digestion Pressure, Steam Supply and Heat Transfer 

In pressurised digestion, pressure supports operation at the required temperature and controls boiling behaviour within the system. Extraction can be adversely affected by unstable pressure, inadequate steam availability, heat-transfer deterioration or inappropriate operating conditions. The following parameters should be monitored:

• Digester pressure and temperature.
• Steam pressure, quality and availability.
• Heat-exchanger performance, where applicable.
• Fouling and scale formation.
• Heating-system stability.
• Flash-system performance and associated temperature changes. 

These variables are particularly important when production rate increases or the bauxite blend changes. 

3.11 Feed Stability and Circuit Configuration 

A digestion circuit should be evaluated as an integrated system rather than as a collection of individual vessels.

Fluctuations in bauxite feed, caustic concentration, slurry density, steam supply and production rate can prevent the circuit from reaching a stable operating condition.

The investigation should include:

• Consistency of feed distribution.
• Operation of parallel digestion trains.
• Digester working levels and flow paths.
• Recycle and bypass arrangements.
• Instrument calibration.
• Reliability of control valves and flow measurements.

Stable operating conditions are essential for achieving consistently high extraction rather than intermittent high readings. 

3.12 Reversion and Secondary Reactions 

Dissolved alumina may be lost from the liquid phase through reversion, precipitation or incorporation into secondary solid phases. These mechanisms are influenced by liquor composition, temperature, residence time, mineral surfaces and downstream cooling conditions.

The assessment should distinguish between:

• Incomplete dissolution of alumina minerals.
• Alumina dissolved and subsequently precipitated.
• Alumina incorporated into DSP.
• Analytical discrepancies between liquor and residue measurements.

This distinction is fundamental to selecting the correct corrective action. 

3.13 Instrumentation, Sampling and Material-Balance Accuracy 

An extraction-efficiency figure is only as reliable as the underlying measurements.

The following data will validate the extraction efficiency:

• Dry bauxite feed rate.
• Bauxite total and available Al₂O₃.
• Blow-off liquor flow rate.
• Dissolved Al₂O₃ and caustic concentration.
• Liquor density and sampling conditions.
• Suspended solids in liquor samples.
• Residue quantity and residual alumina.
• Relevant recycle and bypass streams.

A sudden apparent improvement in extraction should be verified against feed variability, liquor analyses and residue data before it is attributed to a process change.

4. Practical Troubleshooting Matrix

Observed problem	Potential causes to investigate	Recommended first action
Low extraction with stable temperature	Coarse grind, resistant mineral phases, insufficient effective residence time	Review mineralogy, particle-size distribution and digestion test results
Low extraction with fluctuating temperature	Steam instability, fouling, poor control	Validate temperature profiles and heating-system performance
Low extraction after a bauxite blend change	Higher boehmite content, lower available alumina, increased reactive silica	Conduct feed characterisation and reassess digestion conditions
High soda consumption with increased residue alumina	DSP formation, liquor losses, incomplete washing or other circuit losses	Perform soda and alumina balances across digestion and residue handling
Deteriorating settling and filtration	Excessive fines, altered residue mineralogy, DSP or organic effects	Review grinding, residue characteristics and downstream separation
Extraction results inconsistent with residue analyses	Sampling errors, flow-meter inaccuracies, inconsistent analytical basis	Reconcile the alumina mass balance and validate sampling procedures
Extraction deteriorates at higher throughput	Reduced effective residence time, mixing limitations or heating constraints	Review hydraulic capacity, temperature stability and vessel utilisation

These are diagnostic starting points to confirm using plant data and targeted tests.

5. Recommended Process-Control Strategy

For sustained improvement, the refinery should establish a structured extraction-efficiency monitoring programme. 

Daily monitoring

• Bauxite feed rate and mineralogical variability, where data are available.
• Particle-size distribution.
• Digestion temperature and pressure profiles.
• Liquor caustic concentration and alumina-to-caustic ratio.
• Slurry density and throughput.
• Blow-off liquor analyses.

Periodic performance assessment

• Laboratory digestion tests on representative bauxite samples.
• Review of available alumina and residual alumina in residue.
• Evaluation of reactive silica and DSP formation.
• Verification of flow-meter and laboratory performance.
• Review of heat-transfer deterioration and agitation effectiveness.
• Reconciliation of alumina and soda mass balances.

6. Conclusion

Alumina extraction efficiency is governed by the interaction of bauxite mineralogy, particle size, liquor chemistry, digestion temperature, residence time, slurry concentration, pressure, agitation and the performance of the overall digestion circuit.

Successful optimisation requires identifying the dominant limitation for the specific bauxite and process configuration, validating the diagnosis through plant data and laboratory testing, and implementing corrective measures with measurable performance targets.

The ultimate objective is to maximise the economically recoverable alumina from each tonne of bauxite while controlling soda losses, energy consumption, residue generation and downstream process stability.

CETI ENTERPRISES, INDIA

CETI Enterprises supports alumina industry professionals through technical training, process audits, calcination performance assessment, energy optimization, process troubleshooting, equipment design review, debottlenecking and refinery improvement programmes. For further details please visit our website at https://ceti.co.in

About the Author: Rajendra Kunwar is Bayer Process & Alumina Technology Specialist. Through CETI Enterprises, he offers expert technical consultancy in customized online / onsite team training, process for production of specialty grade ATH & Alumina, efficiency enhancement, quality improvement, energy reduction, cost reduction, troubleshooting and plant debottlenecking. To explore how we can support your plant operations or upcoming expansion, please contact us at rajendra@ceti.com.

 

 

BM-057 | CONCEPTUAL DESIGN OF 50,000 TPA SPECIALTY GRADE ATH PLANT

Comprehensive Feasibility Study, Four-Grade Product Mix, Process Flowsheet, Capex, Opex & Financial Appraisal

Author: Rajendra Kunwar, Bayer Process Expert

Project Identification:	BM-057 (Specialty Chemical Facility)
Nominal Plant Capacity:	50,000 Metric Tonnes Per Annum (tpa)
Target Product Slate:	1. Dry Chemical | 2. Fire Retardant | 3. Toothpaste | 4. High Purity
Document Status & Date:	Final Feasibility & Conceptual Design Report | November 2026

Executive Summary 

This document presents the detailed technical and commercial conceptual design for project BM-057, a modern 50,000 metric tonne per annum (tpa) specialty Aluminium Trihydrate (ATH / Alumina Trihydrate / Al(OH)3) manufacturing facility. Designed to process wet alumina hydrate cake from refinery precipitation into four high-value specialty grades, the plant delivers robust product flexibility, superior energy efficiency, and strict zero liquid discharge (ZLD) environmental compliance. 

The plant design addresses four primary market segments: (1) Dry Chemical Grade for aluminium chemical synthesis, (2) Fire Retardant Filler Grade for polymer compounding and flame-proof cable jackets, (3) Toothpaste Grade for dentifrice polishing abrasives, and (4) High Purity Grade for catalyst carriers and electronic glass formulations.

Project Highlights: Key Financial & Operating Benchmarks:

·      Total Plant Capacity: 50,000 tpa total capacity across 330 operational days/year (151.5 tpd nominal rate). 

·   Total Capital Investment (CAPEX): $25.00 Million USD (approx. ₹207.5 Crore INR) including complete equipment, civil works, utilities, and EPCM. 

·    Operating Expenditure (OPEX): $404.40 per tonne of blended output ($18.20 Million USD at 90% operating capacity).

·      Projected Annual Revenue: $29.50 Million USD at 90% capacity, yielding an EBITDA of $11.30 Million USD (38.3% EBITDA margin). 

·      Financial Viability: Internal Rate of Return (IRR) of 26.4%, Net Present Value (NPV @ 10%) of $24.80 Million USD, and a Simple Payback Period of 3.6 Years.

1. Broad Market Scenario & Demand Drivers 

The global Aluminium Trihydrate (ATH) market is valued at approximately $1.85 Billion USD in 2026 and is projected to expand at a Compound Annual Growth Rate (CAGR) of 5.8% through 2032. ATH (CAS No. 21645-51-2) represents the world's most widely utilized eco-friendly, halogen-free flame retardant and functional inorganic filler.

1.1  Key Market Drivers by Segment

·       Flame Retardant & Polymer Compounds: Stringent building codes, automotive electrification (EV battery pack enclosures), and electrical insulation requirements (UL 94 V-0 standards) drive demand for ultrafine (D50 < 3.5 µm) and surface-modified ATH fillers. When heated above 220°C, ATH undergoes endothermic decomposition, releasing 34.6% of its weight as water vapor, which dilutes combustible gases and cools the substrate without liberating toxic smoke. 

·      Toothpaste & Oral Care: Modern dentifrice formulations favor precipitated ATH due to its controlled Relative Dentin Abrasiveness (RDA 40–60), high refractive index compatibility with sorbitol (1.57), and excellent fluorine compatibility compared to silica or calcium carbonate. 

·   Chemical Intermediates & Water Treatment: Essential raw material for manufacturing high-purity aluminium chemicals including Aluminium Sulphate (alum), Polyaluminium Chloride (PAC) for municipal water purification, Synthetic Zeolites, and Aluminium Fluoride (AlF3) for aluminium smelting. 

·    High Purity Specialty Applications: High-purity grades (Al(OH)3 > 99.9%, Na2O < 0.05%) are increasingly specified for petroleum refining catalyst substrates, specialty glass, and ceramic micro-substrates.

Figure: BM-057 Product-Mix Allocation and Annual Tonnage Breakdown

2. Detailed Technical Specifications of Target ATH Grades

Project BM-057 is configured to produce four distinct commercial grades of ATH. Each grade requires rigorous control over particle size distribution (PSD), whiteness index, total/soluble soda (Na2O), iron content, and oil absorption.

2.1 Master Technical Specifications Matrix

 

Parameter / Test Method	Grade 1: Dry Chem.	Grade 2: Flame Ret.	Grade 3: Toothpaste	Grade 4: High Purity
Al(OH)3 Content (%)	≥ 99.2%	≥ 99.6%	≥ 99.6%	≥ 99.9%
Al2O3 Content (%)	≥ 64.5%	≥ 65.0%	≥ 65.0%	≥ 65.2%
Fe2O3 Content (%)	≤ 0.020%	≤ 0.012%	≤ 0.008%	≤ 0.003%
Total Na2O Content (%)	≤ 0.35%	≤ 0.20%	≤ 0.10%	≤ 0.04%
SiO2 Content (%)	≤ 0.025%	≤ 0.015%	≤ 0.010%	≤ 0.005%
Moisture at 105°C (%)	≤ 0.30%	≤ 0.20%	≤ 0.25%	≤ 0.15%
Loss on Ignition (1000°C)	34.2 – 34.8%	34.4 – 34.8%	34.5 – 34.8%	34.6 – 34.8%
Particle Size D50 (µm)	45.0 – 75.0 µm	1.5 – 4.5 µm	8.0 – 12.0 µm	1.0 – 3.0 µm
Whiteness Index (Hunter L)	≥ 92.0%	≥ 96.5%	≥ 97.5%	≥ 98.5%
Special Attribute / Functional	Coarse Free Flow	Silane Coated	Low RDA (40-60)	Low Trace Metal

2.2 Grade-by-Grade Technical Descriptions

Grade 1: Dry Chemical Grade ATH — A coarse, free-flowing white crystalline powder produced by direct flash drying of washed precipitation cake. Designed for rapid dissolution in sulphuric acid or caustic liquor to produce alum, PAC, and aluminium fluoride.

Grade 2: Fire Retardant Filler Grade ATH — An ultrafine, micronized, high-whiteness powder subjected to fluid energy milling and optional surface modification with vinyl-silane or stearic acid (0.8–1.2 wt%). Provides excellent fire suppression, smoke mitigation, and low viscosity build-up in PVC cables, epoxy resins, and SMC/DMC automotive parts.

Grade 3: Toothpaste Grade ATH — A specialized precipitated grade engineered with a controlled, narrow particle size distribution (D50 ~ 8–12 µm) and smooth particle morphology. Provides soft dentin cleaning without tooth enamel abrasion (RDA 40–60), high fluoride retention due to ultra-low soluble soda (Na2O < 0.05%), and clean taste profile.

Grade 4: High Purity Grade ATH — An ultra-pure grade manufactured via multi-stage deionized water washing and chemical purification. Trace transition metals (Fe, Cu, Cr) are kept below 30 ppm, making it ideal for pharmaceutical antacids, catalyst carriers, and high-transmission optical glass.

Figure: Particle Size D50 and Whiteness Comparison Across Target ATH Grades

3. Process Technology & Conceptual Flowsheet Design

The BM-057 facility adopts an integrated hydro-metallurgical Bayer process route followed by controlled liquor decomposition / neutralization precipitation with high-efficiency filtration, drying, micronization, and surface coating adopting a few key unit operations as described hereunder. 

3.1 Key Unit Operations

·  Unit 100 — Seeded Crystallization: Purified sodium aluminate liquor is fed into stirred precipitation tanks where temperature, seed concentration, and agitation rate are precisely controlled to establish target particle nucleation.

 

·   Unit 200 — Filtration & Counter-Current Washing: The slurry is transferred to horizontal vacuum belt filters equipped with multi-stage counter-current deionized water wash headers to reduce residual soda (Na2O) below 0.10%.

 

·     Unit 300 — Flash Drying: Washed filter cake (12–15% moisture) is processed through a gas-fired spin-flash dryer operating at 140–160°C inlet temperature to yield dry coarse ATH powder (<0.2% moisture).

 

·     Unit 400 — Air Jet Milling & Classification: For Fire Retardant and High Purity grades, dried powder is fed into fluid energy air-jet mills integrated with dynamic air classifiers to achieve sub-micron and micronized distributions without iron contamination.

·    Unit 500 — Surface Coating & Packaging: Micronized FR powder is fed into a continuous high-speed pin mixer where silane coupling agent or stearic acid is atomized and coated onto particle surfaces at 80°C.

Figure: BM-057 Conceptual Process Flow Diagram (50,000 tpa Plant)

4. Product-Mix & Operational Strategy

To maximize gross margin while maintaining continuous plant utilization, the 50,000 tpa capacity is allocated across the four grades based on market demand and contribution margins. 

Grade Name	Share (%)	Annual (tpa)	Daily Rate (tpd)	Primary Packaging
Dry Chemical Grade	40.0%	20,000 tpa	60.6 tpd	1000kg Jumbo FIBC
Fire Retardant Filler Grade	36.0%	18,000 tpa	54.5 tpd	25kg Paper Bags / FIBC
Toothpaste Grade	14.0%	7,000 tpa	21.2 tpd	25kg Valve Bags
High Purity Grade	10.0%	5,000 tpa	15.2 tpd	25kg Sealed Fiber Drums
TOTAL PLANT OUTPUT	100.0%	50,000 tpa	151.5 tpd	Integrated Warehouse

5. Capital Expenditure (CAPEX) Estimate

The total estimated capital cost for project BM-057 is $25.00 Million USD (approx. ₹207.5 Crore INR). The estimate has been prepared to Class 3 feasibility accuracy (±15%).

Item	Cost Center Description	Cost ($M USD)	Cost (₹ Crore)
1.0	Major Process Equipment (Precipitation, Filters, Flash Dryers)	$10.80 M	₹ 89.64 Cr
2.0	Micronization, Air Jet Milling & Surface Coating Package	$3.80 M	₹ 31.54 Cr
3.0	Civil Works, Factory Buildings & Steel Structures	$3.50 M	₹ 29.05 Cr
4.0	Utilities (Boiler, Compressed Air, RO Water, ZLD ETP)	$2.60 M	₹ 21.58 Cr
5.0	Electrical Substation, MCC & DCS/PLC Automation	$1.80 M	₹ 14.94 Cr
6.0	Engineering, EPCM, Pre-operative & Contingencies	$2.50 M	₹ 20.75 Cr
TOTAL	TOTAL ESTIMATED PROJECT CAPEX	$25.00 M	₹ 207.50 Cr

6. Operating Expenditure (OPEX) Estimate

Operating costs are modeled based on continuous processing at 90% capacity utilization (45,000 tpa output). The blended average cost of production is $404.40 per tonne of finished ATH. 

Cost Component	Specific Consumption	Unit Rate	$/Tonne Out	Annual ($M)
Raw Hydrate Cake / Feed	1.02 t / t ATH	$230 / tonne	$234.60	$10.56 M
Power & Utilities	110 kWh / t	$0.09 / kWh	$62.50	$2.81 M
Natural Gas (Drying)	38 Nm³ / t	$0.45 / Nm³	$17.10	$0.77 M
Silane / Coating Chemicals	Weighted Blend	Market Rate	$28.00	$1.26 M
Direct Labour & Overhead	75 Personnel	Loaded Rate	$26.20	$1.18 M
Maintenance & Spare Parts	3% Equipment	Annual	$16.00	$0.72 M
Packaging & Logistics	Bags & FIBCs	Standard	$20.00	$0.90 M

7. Indicative Financial Appraisal & Viability Metrics

Financial evaluation assumes a 10-year operating horizon, 70:30 Debt-to-Equity financing structure at 8.5% interest rate, and a 10% Weighted Average Cost of Capital (WACC) discount rate.

7.1 Revenue Realization & Margin Matrix

Grade Description	Volume @ 90%	Selling Price	Annual Revenue	EBITDA Margin
Dry Chemical Grade	18,000 tpa	$360 / tonne	$6.48 Million	22.5%
Fire Retardant Filler Grade	16,200 tpa	$720 / tonne	$11.66 Million	43.0%
Toothpaste Grade	6,300 tpa	$820 / tonne	$5.17 Million	48.2%
High Purity Grade	4,500 tpa	$1,380 / tonne	$6.21 Million	61.5%
BLENDED TOTAL	45,000 tpa	$655.50 / t avg	$29.52 Million	38.3% avg

 

7.2 Key Financial Performance Metrics

 

Financial Indicator	Project Benchmark	Feasibility Assessment
Project Internal Rate of Return (IRR)	26.4%	Highly Attractive (>15% Hurdle)
Net Present Value (NPV @ 10%)	$24.80 Million USD	Strong Value Creation
Simple Payback Period	3.6 Years	Rapid Capital Recovery
Break-Even Capacity Utilization	41.5%	High Safety Margin against Downturns
Average Debt Service Coverage (DSCR)	2.45x	Excellent Bankability & Debt Capacity

 

Figure: Financial Snapshot of Project BM-057 (At 90% Operating Capacity)

8. Conclusion & Strategic Next Steps

The conceptual design for BM-057 confirms that establishing a 50,000 tpa four-grade specialty ATH facility is highly viable technically, environmentally, and commercially. The high proportion of specialty Fire Retardant, Toothpaste and High Purity grades provides strong margin insulation against commoditized alumina chemical cycles.

Strategic Recommendations:

 

1. Pilot Validation: Commission detailed pilot-scale crystallization trials to firm up particle morphology and soda leaching parameters for Toothpaste and High Purity grades. 

2.  Feedstock Security: Establish long-term raw alumina hydrate cake supply contracts with regional bauxite refineries to hedge against feedstock price volatility. 

3. EPCM Execution: Proceed to Front-End Engineering Design (FEED) and initiate environmental permitting for the Zero Liquid Discharge (ZLD) effluent treatment plant.

 

CETI ENTERPRISES, INDIA

CETI Enterprises supports alumina industry professionals through technical training, process audits, calcination performance assessment, energy optimization, process troubleshooting, equipment design review, debottlenecking and refinery improvement programs. For further details please visit our website at https://ceti.co.in

About the Author: Rajendra Kunwar is Bayer Process & Alumina Technology Specialist. Through CETI Enterprises, he offers expert technical consultancy in customized online / onsite team training, process for production of specialty grade ATH & Alumina, efficiency enhancement, quality improvement, energy reduction, cost reduction, troubleshooting and plant debottlenecking. To explore how we can support your plant operations or upcoming expansion, please contact us at rajendra@ceti.co.in