DM-XTech · DM-X CBM
DM-XTech · DM-X CBM
Proven anaerobic digestion, Pressurized Water Scrubbing, and high-pressure compression — nothing exotic, everything bankable.
Two of the 18 concrete cylindrical tanks (6 m diameter × 1 m deep) are being sealed and fitted with gas-collection infrastructure to operate as pilot anaerobic biodigesters. At commercial scale, purpose-built CSTR digesters of 100–200 m³ each are deployed.
High moisture content (~90%), soft cellular structure (no lignin to resist biological breakdown), and a favourable carbon-to-nitrogen ratio of approximately 10:1 — within the productive methanogenic range. The symbiotic Anabaena azollae cyanobacterium provides a nitrogen-rich substrate that supports robust microbial activity.
| Component | Concentration | Note |
|---|---|---|
| CH₄ (methane) | ~50% vol | Combustible fraction |
| CO₂ (carbon dioxide) | ~50% vol | Removed downstream by PWS |
| H₂S (hydrogen sulfide) | 200–2,000 ppm | Natural variation; partially retained as odorant |
| N₂, H₂O vapor | Trace | Minimal impact on downstream process |
| Parameter | Pilot Value | Commercial Scale |
|---|---|---|
| Number of digester tanks | 2 | 2–4 × 100–200 m³ CSTR |
| Tank dimensions (each) | 6 m Ø × 1 m deep | Engineered steel or RC vessels |
| Volume per tank | ~28.3 m³ | 100–200 m³ |
| Total active digester volume | ~56.6 m³ | 200–800 m³ |
| Operating temperature | Ambient (~28–34°C, mesophilic) | Mesophilic (30–38°C) |
| Hydraulic retention time | 25–30 days | 20–30 days |
| Organic loading rate | 1.5–2.0 kg VS/m³/day | 2.0–3.0 kg VS/m³/day |
| CH₄ yield (azolla) | ~220–280 L CH₄/kg VS | 250 L/kg VS (base case) |
| Estimated biogas output | ~40–80 Nm³/day | ~400–800 Nm³/day |
| Gas collection | HDPE ring manifold + dome seal | Gas holder + compressor suction |
| Digestate use | Liquid N-rich organic fertilizer | Solid/liquid separation → bagged + tanker |
The v3.5R financial model uses 250 L CH₄/kg VS as the base-case methane yield — the mid-range of peer-reviewed azolla digestion literature (220–280 L/kg VS). The upper bound of 280 L/kg VS is treated as an unmodelled upside. This conservatism absorbs feedstock variability, seasonal temperature effects, and digester start-up lag.
PWS exploits a simple physical fact: at 8 bar(g) pressure, CO₂ is approximately 26 times more soluble in water than methane. Pressurize raw biogas, wash it with cold water, and the CO₂ dissolves preferentially — leaving a gas stream enriched to ≥97% CH₄. No solvents. No membranes. No chemical regeneration.
The scrubbing water is continuously regenerated in a closed-loop system — no liquid waste is discharged to the environment.
| Tag | Service | Key Specification | Standard |
|---|---|---|---|
| D-101 | Anaerobic biodigester (CSTR) | Commercial 100–200 m³ · 25–30 d HRT · mesophilic | — |
| K-101 | Feed gas compressor | 2-stage oil-free recip. · 15 kW · 1→8 bar(g) | ASME B19.3 |
| T-101 | PWS absorption column | DN250 × 9.0 m · 5.0 m PP Pall rings · SS316L | ASME VIII Div.1 |
| V-104 | Twin-tower desiccant dryer | 4Å mol. sieve · −20°C dew point · 8-h auto cycle | — |
| K-102 | CBM compressor | 4-stage oil-free · 18.5 kW · 8→200 bar(g) · 50 Nm³/h | ASME B19.3 |
| V-103 | CBM cylinder filling manifold | 50-L Type-I steel · 200 bar · CNG thread (ISO 11439) | ISO 11439 / DOT-NGV |
| V-105 | Flash depressurization tank | DN600 × 2200 mm · 0.5 bar(g) | ASME VIII Div.1 |
| T-102 | Atmospheric air stripper | DN300 × 4500 mm · 2.0 m PP Pall rings | — |
| V-106 | Caustic scrubber (H₂S abatement) | DN250 × 2000 mm · 10% NaOH | — |
| P-101 A/B | Process water pumps (duty/standby) | 15 m³/h · 90 m head · 7.5 kW each · SS316L | ISO 5199 |
| E-102 | Process water cooler (PHE) | 50 kW duty · <20°C outlet · SS316L plates | — |
| XV-102 | H₂S bypass needle valve | Calibrated raw-biogas blend · ~50 ppm H₂S target | — |
PWS systems typically exhibit 1.5–2.5% methane slip — this is a well-characterized physical limitation of the technology, not a design flaw. Membrane upgrading can achieve lower slip (0.3–0.7%), but at higher CAPEX, greater sensitivity to H₂S, and membrane replacement costs. DM-XTech selected PWS for its robustness, zero chemical consumption, and 60+ years of commercial reference. The 2% slip is accounted for in the mass balance and carbon-credit calculations; residual CH₄ in the stripper off-gas is monitored but not recovered at Phase 1 scale.
The product retains approximately 50 ppm H₂S via a calibrated bypass blend. While this provides a natural "rotten egg" odorant for leak detection, it is higher than the synthetic THT/mercaptan odorization used in LPG (~5–15 ppm equivalent). H₂S is corrosive, toxic at sustained exposure (OSHA TWA 10 ppm), and combusts to SO₂. The 50 ppm level is acceptable in the product stream but requires:
The plant is engineered to fail safely at every stage. Every hazardous area is zone-classified per IECEx / PNS IEC 60079; every pressure vessel has independent pressure relief; every compressor has an emergency shutdown (ESD) tied to gas detection.
| Hazard | Consequence | Engineered Mitigation |
|---|---|---|
| Over-pressure of T-101 | Vessel rupture, gas release | Dual-redundant PSVs at 9.5 bar(g); rupture disc at 10.5 bar; pressure transmitter on DCS trip |
| Biogas leak in digester area | Flammable cloud formation | Continuous LEL monitoring; Ex-rated equipment; forced ventilation; ESD on 25% LEL |
| H₂S exposure to operators | Asphyxiation / toxicity | Fixed + portable H₂S monitors; 10 ppm TWA alarm; SCBA for confined space entry |
| Compressor seal failure (K-102) | High-pressure CBM release | Seal gas monitoring; vibration trip (ISO 10816-3 Zone B); automatic isolation |
| Cylinder over-fill | Cylinder rupture | Mass flow meter + pressure transmitter redundant fill control; 10% over-pressure rupture disc |
| Water contamination in product | Downstream corrosion, low quality | V-104 twin-tower dryer; on-line dew point analyzer; ≥−20°C dew point spec |
| Power failure during operation | Loss of ventilation, ESD systems | UPS on DCS and gas detection (30 min); fail-safe SDVs; emergency vent on depressurization |
| Digester overload (shock feeding) | Foam-over, pH crash, production loss | Gradual feed ramp-up; pH + VFA monitoring; controlled feed pumps on DCS |
The plant is engineered to Philippine Nuclear Research Institute / DOE / DENR safety standards for industrial gas installations. Cylinder handling follows PNS Philippine National Standards harmonized with ISO 11439 / DOT-NGV. No element of the plant design depends on operator perfect vigilance — the engineered safeguards are layered and independent.
At steady-state operation (50 Nm³/h nameplate, 82% utilization):
| Stream | Rate | Basis |
|---|---|---|
| Fresh azolla input | 47.6 kg per Nm³ CBM | Derived: 1/(0.10×0.75×0.250)÷0.98 PWS recovery |
| Dry matter (DM) | 10% of fresh | Standard azolla value |
| Volatile solids (VS) | 75% of DM | Standard herbaceous biomass |
| Methane produced | 250 L CH₄/kg VS (base case) | Conservative mesophilic yield |
| Raw biogas volume | ~2× methane volume (50% CH₄) | Typical for fresh herbaceous substrate |
| CBM product (after PWS) | 98% CH₄ recovery | 2% CH₄ slip accounted |
| CBM mass | 0.717 kg/Nm³ at STP | Standard biomethane density |
| LPG equivalent displaced | 0.797 kg LPG per Nm³ CBM | BTU parity basis |
| Compression electricity | ~1.0 kWh/Nm³ | K-101 + K-102 combined |
| Make-up water | ~5% of circulation | Closed-loop PWS system |
| Digestate (organic fertilizer) | ~90% of fresh weight | N-rich liquid + solid fraction |