Zone 2 - Capacity, specification & price ranges
Seven Zone 2 digestion equipment items for a 10 TPD CBG plant — digester tanks, agitators, biogas storage dome, heating coils, blower, and safety fittings — with capacity specifications and indicative Indian supplier price ranges.
| Equipment | Capacity / Size | Key Specifications | Price Range (Approx. INR) |
| CSTR Digester Tank | 1,200 - 1,500 m^3 | RCC or Glass-Fused-to-Steel; Leak-proof | ₹40,00,000 – ₹70,00,000 |
| Plug Flow Reactor | 800 - 1,000 m^3 | Horizontal design for high-solids waste | ₹50,00,000 – ₹85,00,000 |
| Submersible Agitators | 2 to 4 Units | 5 - 10 HP; ATEX/Flameproof; SS 304 | ₹8,00,000 – ₹15,00,000 |
| Double Membrane Dome | Tank Diameter size | UV-resistant PVC; Dual-layer "Lung" | ₹12,00,000 – ₹20,00,000 |
| Internal Heating Coils | ~100 kW heat duty | SS 316L (Acid resistant); Hot water circulation | ₹6,00,000 – ₹10,00,000 |
| Biogas Blower | 50 - 80 m^3/hr | Centrifugal; Flameproof; VFD included | ₹2,50,000 – ₹4,50,000 |
| Flame Arrestor & PRV | 4" - 6" diameter | SS Mesh; Prevents flash-back; Safety relief | ₹1,50,000 – ₹3,00,000 |
Beyond definitions
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How to read this table
- Equipment is listed in Zone 2 system order — from the main vessel through safety fittings.
- Price ranges are indicative ex-works procurement costs from Indian suppliers for 10 TPD scale. Civil construction and installation are not included.
- CSTR Digester Tank and Plug Flow Reactor are alternative choices — select one based on your feedstock's TS% (see the Reactor Types table).
- ATEX / Flameproof ratings on agitators and blowers are mandatory for equipment inside the biogas production zone — non-rated motors are a safety and insurance risk.
- GFS = Glass-Fused-to-Steel; RCC = Reinforced Cement Concrete; SS 316L = low-carbon stainless steel grade with improved acid resistance; VFD = Variable Frequency Drive; PRV = Pressure Relief Valve.
About this table
Zone 2 of a Compressed Biogas (CBG) plant is where anaerobic digestion actually occurs — inside the reactor tank. This table covers the seven principal equipment items required for Zone 2 at a 10 TPD plant scale: the reactor vessel itself, the agitation system, the biogas storage membrane, the heating system, and the critical safety components that prevent flammable gas incidents.
The reactor tank — either a CSTR Digester (1,200–1,500 m³) or Plug Flow Reactor (800–1,000 m³) depending on feedstock — is typically constructed in Reinforced Cement Concrete (RCC) or Glass-Fused-to-Steel (GFS). RCC is lower-cost but requires precise waterproofing; GFS panels are factory-coated, corrosion-resistant, and faster to erect on site. The size difference (CSTR larger than Plug Flow for the same throughput) reflects the higher water dilution required by CSTR designs — Plug Flow handles denser feedstock in a smaller volume. Submersible Agitators (2–4 units, ATEX/flameproof rated for explosive gas environments) maintain the feedstock in suspension inside a CSTR, preventing sedimentation and ensuring uniform temperature distribution across the tank volume.
The Double Membrane Dome sits on top of the reactor and serves as the primary biogas storage buffer. Its dual-layer UV-resistant PVC construction — an inner gas-holding bladder and an outer protective shell — allows the dome to expand and contract as gas accumulates and is drawn off, acting as a pressure buffer between gas production and the downstream compressor. This dome typically stores 30–60 minutes of gas production, preventing compressor starvation during variable production periods. Internal Heating Coils (SS 316L, 100 kW heat duty) circulate hot water through the reactor to maintain mesophilic temperature (35–40°C) year-round — critical in northern Indian winters when ambient temperatures can drop below 10°C and unheated digesters lose 30–50% of methane yield.
The Biogas Blower moves gas from the dome to the Zone 3 upgrading unit at controlled pressure, while the Flame Arrestor and Pressure Relief Valve (PRV) are mandatory safety fittings that prevent flash-back ignition from travelling back to the reactor in the event of a downstream fire or over-pressure event. Both are required under PESO and CCOE inspection criteria.
Key insights
- The Double Membrane Dome is a pressure buffer, not just a cover — its 30–60 minute gas storage capacity is critical for stable compressor operation in Zone 4.
- ATEX/Flameproof ratings on all electrical equipment inside the digester zone are a non-negotiable safety requirement under PESO rules — standard industrial motors cannot be substituted.
- SS 316L (rather than standard SS 304) is specified for heating coils because the slightly acidic digester liquid at 35–40°C causes pitting corrosion in 304-grade steel over time.
- Heating the digester to 35–40°C through winter using the internal coil system is the single most important operational measure for maintaining consistent year-round CBG output in northern India.
Methodology & sources
Equipment sizes and specifications are typical for Indian-fabricated equipment at 10 TPD plant scale as of 2024. The 100 kW heat duty figure for heating coils is an indicative design basis for mesophilic digestion in a winter climate; actual heat load depends on reactor insulation quality, ground temperature, and inlet feedstock temperature. Price ranges are ex-works estimates excluding GST, installation, and civil works.
Related data tables
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