Project synthesisAugust 2026
Towngas · Public project synthesis
Two waste problems, one integrated process
Supercritical-water gasification and OXZEO light-olefin synthesis from a douzha-led regional feed portfolio and deliberately conditioned bauxite residue
Abstract
The design starts with the wastes rather than the reactor. Douzha supplies wet renewable carbon; bauxite residue is an alkaline treatment feed that must leave through controlled dealkalization and qualification. Ten isolatable hydrothermal trains merge only accepted gas into shared Rectisol, bi-reforming, and OXZEO units. The physical design basis is stable, while the corrected China utility basis strengthens the economics: current conversion remains fragile after ramp-up, but sustained 55% carbon efficiency plus contracted service value produces a materially stronger case.
Keywords
- SCWG
- Douzha
- Bauxite-residue conditioning
- Purposeful salt separation
- Bi-reforming
- OXZEO
- ISCC PLUS
Developed during a process engineering internship with the Green Fuels & Chemicals division of The Hong Kong and China Gas Company (Towngas), and its green-methanol venture VENEX, across Foshan, Guangdong and Jungar Banner, Inner Mongolia. A personal study. The analysis, the design decisions and any errors are the author's own, and it is not a Towngas or VENEX publication. The context image shows the affiliated Jungar Banner green-methanol facility, not the proposed SCWG complex.
01 · Design reasoning
The project begins with the wastes, not the reactor
The report is organised as a chain of engineering decisions. Each step answers a practical question, changes the design boundary, and creates evidence that must be obtained before the next commitment.
- 01
Question
What is the real starting problem?
Finding
Wet douzha is costly to dry and spoils quickly; bauxite residue is alkaline, mineral-rich, and difficult to release safely.
Design decision
Design one system around two engineered outlets: renewable-carbon conversion and residue conditioning.
- 02
Question
Which conversion platform fits wet, variable feeds?
Finding
SCWG uses the feed water as reaction medium and can accept qualified wet organics without a separate drying train.
Design decision
Select SCWG, but make pumpability, salt destination, and carbon closure—not nominal feed names—the acceptance criteria.
- 03
Question
What blend is both regional and operable?
Finding
The B1 recipe reaches 20.80 wt% solids and 8.649 wt% slurry carbon while keeping nitrogen and ash inside a controllable envelope.
Design decision
Use douzha as anchor; let cassava cake, clean pulp, liquor, and limited straw adjust carbon. Keep manure separate.
- 04
Question
Where can that recipe exist at scale?
Finding
Wet feed economics are dominated by moving water and spoilage risk; denser carbon and mineral feeds tolerate longer hauls.
Design decision
Screen the Qinzhou–Beihai–Fangchenggang corridor, then select a site from supplier-level annual delivered-cost data.
- 05
Question
How is common-mode failure contained?
Finding
Salt, fibrous slurry, and dirty heat recovery are train-specific risks; Rectisol, reforming, and OXZEO gain scale when shared.
Design decision
Build ten complete B1–B4 trains and merge only accepted raw gas into common B5–B7 facilities.
- 06
Question
What makes the project financeable?
Finding
Nearly one million tonnes per year of watery slurry support only 42–55 thousand tonnes per year of olefins.
Design decision
Treat the project as waste service plus certified carbon; require improved conversion, contracted fees, availability, and disciplined capital.
Renewable carbon + reaction water
Douzha
150t/day per train
- Starting problem
- Approximately 82.8 wt% water on the report basis, protein-rich, variable, and perishable.
- Use in the process
- The hydrated anchor matrix carries approved carbon co-feeds into the high-pressure system without a dedicated dryer.
- Defensible outlet
- Carbon is closed across gas, water, solids, purge, and olefin product.
Treatment feed + process aid
Bauxite residue
7t/day per train
- Starting problem
- Alkaline and mineral-rich; sodium, chloride, leaching, and destination performance govern release.
- Use in the process
- Iron and alkali surfaces may aid conversion while hydrothermal processing, B3 salt withdrawal, and B8 washing condition the residue.
- Defensible outlet
- Qualified product only; off-spec material receives a second wash or controlled retreatment.
- Hydrothermal architecture
- 10 × 300t/day trainsdesign basis
Each B1–B4 train is independently isolatable.
- Commercial throughput
- 3,000t/day gross slurrycalculated result
999,000 t/year at 333 operating days.
- Central blend
- B1balanced regional feeddesign basis
20.80 wt% solids and 25.947 t C/day per train.
- Light-olefin envelope
- 42.35–55.45kt/yearscreening assumption
42% current case to 55% financeability target.
- China Class 4 TCI
- ≈2.8RMB billionscreening assumption
Screening range approximately RMB 2.2–4.0 billion.
- Purchased-energy equivalent
- 260GJ/day per traincalculated result
After internal heat recovery and purge-fuel credit.
How to read the evidence labels
design basisSelected engineering basis for this screening design; not a vendor guarantee.
calculated resultArithmetic derived from the report's stated recipes, conversions, or economic assumptions.
screening assumptionA value suitable for comparing routes, but not yet demonstrated by continuous operation.
(needs testing)A load-bearing claim that must be retired with representative feed, equipment, or product testing.
contractual requirementValue exists only when supplier, certification, or offtake terms are binding.
base-case exclusionNo revenue or performance credit is taken until the claim is qualified.
02 · Feed platform
A balanced recipe, governed by properties rather than labels
Douzha is the anchor, but the platform remains flexible. Carbon density, pumpability, nitrogen, ash, salt, chloride, and a defined contaminant destination decide whether a regional co-feed belongs in the plant.
Central B1 recipe
One 300 t/day train
Every feed is metered into a controlled batch; new feed replaces an existing component rather than adding uncontrolled wet tonnes.
- DouzhaAnchor wet matrix150 t/d
- Cassava cakeStarch-rich carbon60 t/d
- Fruit + vegetable pulpFlexible wet carbon20 t/d
- Organic liquorDissolved carbon trim10 t/d
- Milled strawDry carbon + C/N trim12 t/d
- Bauxite residueMineral treatment feed7 t/d
- WaterRheology adjustment41 t/d
Douzha control
Reference recipe
- Total solids
- 19.07%
- Feed carbon
- 23.688 t/d
- C/N screen
- 6.82
- Olefin envelope
- 38.66–50.62 kt/y
Balanced regional
Central commercial basis
- Total solids
- 20.80%
- Feed carbon
- 25.947 t/d
- C/N screen
- 10.97
- Olefin envelope
- 42.35–55.45 kt/y
High carbon
Upper pumpability screen
- Total solids
- 22.05%
- Feed carbon
- 27.864 t/d
- C/N screen
- 17.74
- Olefin envelope
- 45.47–59.55 kt/y
Manure campaign
Separate gate-fee trial
- Total solids
- 21.89%
- Feed carbon
- 26.848 t/d
- C/N screen
- 13.90
- Olefin envelope
- 43.82–57.38 kt/y
Compatible regional co-feeds
| Feed | Design dose / role | Function | Binding constraint |
|---|---|---|---|
| Douzha | 150 t/day B1 | Anchor wet carbon and slurry matrix | Nitrogen, spoilage, variable moisture |
| Cassava cake | 60 t/day B1 | Carbon-density control | Cyanogenic residues, sand, seasonality, gelation |
| Fruit + vegetable pulp | 20 t/day B1 | Flexible sugar/pectin/cellulose feed | Packaging, grit, chloride, rapid acidification |
| Organic liquor | 10 t/day B1 | Dissolved carbon replacing dilution water | Cleaning chemicals, conductivity, sulfur, refractory COD |
| Milled straw | 12 t/day B1 | Dry carbon and C/N trim | Rheology, bridging, char, erosion |
| Bagasse or cane trash | Alternate dry-fibre lane | Regional lignocellulosic carbon after milling | Silica, seasonal storage, fibrous rheology |
| Brewery / distillery residues | Alternate liquor or wet-pulp lane | Wet carbohydrate and soluble-organic carbon | Sulfate, cleaning chemicals, variable alcohol or acid |
| Manure cake | B3 only | Potential treatment-service revenue | Separate qualification for N, P, ash, chloride, pathogens |
Feed acceptance envelope
| Control | Normal target | Response outside target |
|---|---|---|
| Total solids | 18–22 wt% | Recalculate water and dry-fibre dose; hold batch if rheology remains outside the curve. |
| Particle size | Fibre D90 <0.5 mm; no hard grit >1 mm | Remill, screen, or reject; never rely on the high-pressure pump to comminute. |
| Yield stress / restart | Inside the qualified pump-loop envelope after 12 h hold | Reduce fibre or starch, add water, and repeat the restart test. |
| Feed carbon | 8.5–9.5 wt% gross slurry for B1/B2 | Adjust with qualified cassava, fibre, or liquor rather than adding uncontrolled wet tonnes. |
| Nitrogen, sulfur, ash, salts | Inside campaign-specific B4/B5/product limits | Segregate feed, adjust blend, increase purge, or move to a qualified campaign. |
| Chloride | Supplier, B1, B3, and recycle-water limits | Reject, prewash, segregate, or purge; do not recycle chloride indefinitely. |
03 · Regional sourcing
Why South China—and what the map does not decide
The Guangxi–Guangdong / Beibu Gulf corridor contains complementary wet-organic, dry-carbon, mineral, utility, and product-logistics opportunities. It is a first screen, not a selected plant site.
Wet feed
≈75 kmA practical first screen because haulage is mostly water and residence time affects spoilage.Dry / dense feed
150 km+Cassava solids, milled fibre, and mineral residue can tolerate a wider sourcing radius if delivered cost works.Decision variable
RMB/yearMinimise annual wet-water haul + dry-carbon haul + mineral transport + utilities + product logistics.Interactive siting screen
Qinzhou–Beihai–Fangchenggang corridor
Toggle feed and infrastructure layers. Candidate points compare screening logic only; supplier coordinates and volumes require verification.
Overlays
Alumina refineries. Shandong, Shanxi, Henan, Guangxi and Guizhou hold roughly 95% of Chinese capacity. Large, few, permanently sited point sources — the easy half of the problem.
Douzha is not a crushing by-product: ~90% of imported GM soybean is crushed for oil and meal, producing none. It arises only from soymilk and tofu manufacture on non-GM domestic beans. A few large beverage plants — clean point sources with single-supplier traceability.
Larger tonnage, harder supply chain. Thousands of small workshops sited close to consumption, so this follows population rather than capacity. This is where the ISCC risk lives — fragmented, self-declaring sources are exactly where feedstock integrity fails at audit.
China refines alumina largely from imported bauxite, which is why capacity clusters behind the northern terminals — Yantai, Longkou, Rizhao, Qingdao — and behind Fangchenggang. The same terminals land the imported soybean crushed at Rizhao, Nantong and Dongguan. The ports are where the bauxite arrives, and where the wrong soybean arrives.
Off by default. Soybean straw follows cultivation — Heilongjiang, Jilin, Liaoning. Heilongjiang is also the non-GM food-grade origin: where the beans start, not where the douzha appears.
Reading the marks
- Filled, sized by capacity. Only Fangchenggang (~2.4 Mt/y) has one — hence the single large mark.
- Hollow — capacity unverified, i.e. every other site.
- Dotted — neighbours and Taiwan, context only.
Haul-distance calculator
Great-circle distance to the nearest source in each active overlay.
04 · Process architecture
Ten dirty-service trains; one shared conversion island
B1–B4 contains the feed, salt, dirty heat-recovery, letdown, water, and solids risks inside independently isolatable trains. Only accepted raw gas crosses into shared B5–B7. B8 provides an explicit residue outlet and retreatment route.
B1–B4 complete hydrothermal trains
B5–B7 shared clean-gas conversion island
Release qualified residue or retreat
Read one dirty-service hydrothermal train from B1 to B4, then follow its accepted gas into the shared B5–B7 conversion island. B8 is an outlet-and-qualification route, not an indefinite recycle.
- Process stream
- Numbered stream tag
- Animated flow directionArrowhead flow direction
Receiving, blend preparation, and high-pressure feed
- Normal feed
- 300 t/day · 12.5 t/hour design basis
- Total solids
- 20.80 wt% B1 · 18–22 wt% envelope (needs testing)
- Discharge
- 25 MPa plus line losses design basis
Make a traceable, carbon-controlled slurry that can restart after settling and reach reactor pressure without bridging or excessive wear.
Segregated receipt, fine milling, high-shear blending, batch release, and two 100% positive-displacement pumps per train.
Testing focus: Full-scale cold and hot pump/restart loop using seasonal supplier blends.
Source basis: §5.1, Tables 2.3–2.4, Appendix D.1
Inlet streams
| Tag | Stream | Phase | Components | Quantity |
|---|---|---|---|---|
| 1 | Douzha + wet co-feeds | Slurry | Douzha, cassava cake, pulp, and organic liquor | — |
| 2 | Milled straw | Solid | Qualified fine fibre; D90 below 0.5 mm | — |
| 3 | Bauxite residue | Slurry | Assayed mineral treatment feed | — |
| 4 | Blend water | Liquid | Make-up or qualified recycle water | — |
Outlet streams
| Tag | Stream | Phase | Components | Quantity |
|---|---|---|---|---|
| 5 | Released HP slurry | Slurry | 300 t/day carbon-controlled B1 feed | — |
Note
Main equipment
Segregated shared receiving and train day tanks; Fibre mill and grit removal; High-shear blend/restart loop; 20 total P-101 A/B high-pressure pumps
Warning
Critical design risk
Fibre bridging, starch gelation, grit wear, mineral settling, and a failed restart after hold.
Supercritical-water gasification
- Temperature
- 625 °C (needs testing)
- Pressure
- 25 MPa (needs testing)
- Residence screen
- 30–90 seconds (needs testing)
Convert wet organic carbon to methane-rich raw gas while exposing bauxite residue to hydrothermal conditioning.
Rapid near-critical heat-up and 30–90 second residence promote hydrolysis and gasification. Methane suppression remains an optimisation—not a basis for deleting B6.
Testing focus: Continuous carbon closure across gas, water, and solids, followed by an integrated 1,000-hour mixed-feed campaign.
Source basis: §5.2 and Appendix D.1
Inlet streams
| Tag | Stream | Phase | Components | Quantity |
|---|---|---|---|---|
| 5 | Released HP slurry | Slurry | Wet organic and mineral feed | — |
Outlet streams
| Tag | Stream | Phase | Components | Quantity |
|---|---|---|---|---|
| 6 | SCWG effluent | Supercritical | Methane-rich gas, water, salts, and mineral solids | — |
Note
Main equipment
R-201 externally heated reactor; H-101 dirty-service feed/effluent exchanger; Trim heater and water quench; Online gas analysis and full liquid/solid sampling
Warning
Critical design risk
Char, wall deposition, corrosion, heat-flux excursions, and uncertain mixed-feed carbon-to-gas efficiency.
Purposeful hot-salt precipitation and separation
- Configuration
- Twin lead/lag per train design basis
- Service
- Hot, high-pressure, before H-101 design basis
- Annual concentrate
- 10,656 t/year site calculated result
Make salts leave through a controlled underflow instead of attaching to the reactor, heat exchanger, or pressure boundary.
Twin lead/lag hot separators use controlled nucleation, continuous dense-underflow withdrawal, switch-over, and flush recovery.
Testing focus: Mixed-feed hot loop proving underflow mass, wall deposition, pressure-drop recovery, and repeated separator switching.
Source basis: §5.3, Table 5.2 and Appendix B-03
Inlet streams
| Tag | Stream | Phase | Components | Quantity |
|---|---|---|---|---|
| 6 | SCWG effluent | Supercritical | Gas, water, precipitating salts, and mineral solids | — |
Outlet streams
| Tag | Stream | Phase | Components | Quantity |
|---|---|---|---|---|
| 7 | Salt-depleted effluent | Supercritical | Gas/water/mineral stream to heat recovery | — |
| 8 | B3 concentrate | Mixed | Na/K/P/S/Cl-bearing controlled product or purge | — |
Note
Main equipment
Twin continuous hot separators; Underflow cooling and flash; Flush and switch-over system; Concentrate quarantine and release tanks
Warning
Critical design risk
A salt bridge or ineffective underflow forces a train outage and erodes the commercial availability case.
Heat recovery, letdown, and three-phase separation
- Heat recovery
- 555 GJ/day per train screening assumption
- Raw gas
- 55.80 t/day per train calculated result
- Aqueous stream
- 233.75 t/day per train calculated result
Recover sensible heat, reduce pressure safely, and separate accepted gas from aqueous and mineral outlets before trains merge.
H-101 transfers heat to incoming slurry, staged sacrificial trims reduce pressure, then primary/secondary vessels split gas, water, and solids. Ammonia recovery and controlled purge prevent indefinite nitrogen and chloride recycle.
Source basis: §5.4 and Tables 6.2, 7.1–7.2
Inlet streams
| Tag | Stream | Phase | Components | Quantity |
|---|---|---|---|---|
| 7 | Salt-depleted effluent | Supercritical | Hot gas, water, and mineral solids | — |
Outlet streams
| Tag | Stream | Phase | Components | Quantity |
|---|---|---|---|---|
| 9 | Accepted wet raw gas | Gas | CH₄, CO₂, H₂, CO, and acid-gas traces | — |
| 10 | Aqueous treatment stream | Liquid | Water, ammonia equivalent, organics, and ions | — |
| 11 | Separated mineral solids | Solid | Conditioned solids routed to B8 | — |
Note
Main equipment
Modular H-101 exchanger; Staged hard-faced letdown trims; Primary and secondary separators; Ammonia recovery, water polishing, and chloride purge
Warning
Critical design risk
Residual fines can foul H-101; two-phase letdown can erode trims; liquid carryover can contaminate the common gas island.
Shared acid-gas removal and catalyst protection
- Feed
- Up to 558 t/day wet raw-gas screen screening assumption
- Sulfur guard target
- <0.1 ppmv total S screen screening assumption
- Architecture
- Shared · N+1 critical auxiliaries design basis
Remove sulfur and control carbon-dioxide routing before reforming and OXZEO synthesis.
A shared Rectisol system removes bulk acid gas and water; hydrolysis/COS management and a ZnO guard protect downstream catalysts.
Source basis: §5.5 and Appendix D.2
Inlet streams
| Tag | Stream | Phase | Components | Quantity |
|---|---|---|---|---|
| 9 | Ten-train raw-gas header | Gas | Accepted B4 gas only; up to 558 t/day screen | — |
Outlet streams
| Tag | Stream | Phase | Components | Quantity |
|---|---|---|---|---|
| 12 | Clean methane-rich gas | Gas | Sulfur-protected reformer feed | — |
| 13 | Controlled CO₂ split | Gas | Bi-reformer ratio-control feed or export | — |
| 14 | Recovered sulfur | Solid | Qualified sulfur outlet | — |
Note
Main equipment
Common gas header with train acceptance; Rectisol absorption/regeneration; COS hydrolysis as required; Duty/standby ZnO guard beds
Warning
Critical design risk
One wet or sulfur-rich train can contaminate the shared conversion island.
Shared steam/CO₂ bi-reforming
- Outlet screen
- ≈850 °C screening assumption
- Pressure
- ≈2.8 MPa design basis
- Duty
- 290 GJ/day per train equivalent screening assumption
Convert methane-rich SCWG gas into the CO/H₂ ratio required by the OXZEO island.
Steam and dry reforming are combined in a fired tubular reactor. The step is strongly endothermic and remains necessary because the B2 gas is methane-rich.
Source basis: §5.6, §7.3 and Appendix D.2
Inlet streams
| Tag | Stream | Phase | Components | Quantity |
|---|---|---|---|---|
| 12 | Clean methane-rich gas | Gas | Rectisol/ZnO-protected SCWG gas | — |
| 13 | Controlled CO₂ split | Gas | Dry-reforming contribution | — |
| 15 | Reforming steam | Gas | Recovered/generated steam | — |
Outlet streams
| Tag | Stream | Phase | Components | Quantity |
|---|---|---|---|---|
| 16 | Ratio-controlled syngas | Gas | CO and H₂ for OXZEO | — |
Note
Main equipment
Fired tubular bi-reformer; Steam and CO2 ratio control; Syngas waste-heat boiler; Flue-gas heat recovery
Warning
Critical design risk
The methane round-trip consumes high-grade heat and exposes tubes/catalyst to real-gas impurities and carbon formation.
Shared OXZEO synthesis and product recovery
- Temperature screen
- ≈400 °C (needs testing)
- Pressure
- 2–3 MPa design basis
- Carbon efficiency
- 42% current · 55% target (needs testing)
Convert conditioned synthesis gas into C₂–C₄ light olefins and separate product, recycle, and purge.
Oxygenate synthesis and zeolite conversion are represented as cooled fixed beds with recycle and staged condensation/fractionation; website chemistry is intentionally simplified.
Testing focus: Licensed real-gas conversion, selectivity, life, regeneration, turndown, and product-separation guarantees.
Source basis: §5.7, Tables 6.3–6.4 and 10.5
Inlet streams
| Tag | Stream | Phase | Components | Quantity |
|---|---|---|---|---|
| 16 | Ratio-controlled syngas | Gas | Sulfur-free CO and H₂ | — |
| 17 | Qualified recycle gas | Gas | Unconverted synthesis-loop return | — |
Outlet streams
| Tag | Stream | Phase | Components | Quantity |
|---|---|---|---|---|
| 18 | Light-olefin product | Gas | Recovered C₂–C₄ olefins | — |
| 17 | Qualified recycle gas | Gas | Unconverted loop return | — |
| 19 | Water, oxygenates, and purge | Mixed | Condensed coproducts and controlled fuel purge | — |
Note
Main equipment
Cooled OXZEO reactor beds; Interstage heat removal; Recycle compressor and purge; Condensation and C2–C4 product separation
Warning
Critical design risk
Real-gas catalyst life, hot spots, selectivity, and product-recovery losses directly control financeability.
Residue washing, qualification, and retreatment
- Annual wet-screen solids
- 24,143 t/year calculated result
- Release basis
- Destination-specific Na/Cl, leaching, XRF/XRD contractual requirement
- Recycle policy
- No indefinite mineral recycle design basis
Create a defensible outlet for the mineral phase without claiming that one pass always makes a saleable product.
Counter-current washing lowers soluble alkali and chloride. Each batch is released to a destination specification or sent to a second wash/controlled retreatment.
Testing focus: Representative B8 wash trials plus buyer-specific performance, Na/Cl, leaching, phase, and legal-status qualification.
Source basis: §5.8, Appendix B-04 and Appendix D.3
Inlet streams
| Tag | Stream | Phase | Components | Quantity |
|---|---|---|---|---|
| 11 | Separated mineral solids | Solid | B4 mineral phase | — |
Outlet streams
| Tag | Stream | Phase | Components | Quantity |
|---|---|---|---|---|
| 20 | Qualified residue | Solid | Destination-specific conditioned mineral product | — |
| 21 | Off-spec retreatment | Slurry | Second wash or controlled treatment; no indefinite recycle | — |
Note
Main equipment
Counter-current wash/filtration; Product and quarantine storage; XRF/XRD and leach testing; Second-wash/retreatment route
Warning
Critical design risk
Residue composition is source-dependent; overclaiming product status creates environmental and commercial liability.
Operating windows
How each train enters, changes, recovers, and leaves service
≈9 active train-equivalents. Ten independent hydrothermal modules averaging 90% uncorrelated availability; the shared back end must remain stable at eight-train turndown.
Start on clean water
Establish pump pressure, heat the circuit through the critical region, and prove both B3 separator paths before introducing organics, residue, or dry fibre.
Train gas stays outside the shared header until B4 carryover, B5 inlet composition, and sulfur are within specification.
Move recipes at constant gross flow
Correct wet-feed variability with trim water first, then adjust qualified carbon co-feed only inside solids, rheology, nitrogen, ash, salt, and chloride limits.
A complete batch certificate prevents alternating supplier slugs from reaching B2.
Recover a fouling separator without losing the train
Increase B3 underflow, reduce organic/mineral feed while maintaining water, pressure-match the standby vessel, then isolate and flush the fouled separator.
Restart requires recovered baseline differential pressure and a confirmed open underflow—not completion of a timed wash.
Remove feed before heat and pressure
Isolate B7 fresh syngas, cool on recycle, retain B6 steam, then remove bauxite residue, fibre, and wet organics in that order while clean water sweeps the train.
Unverified transient gas never enters the common OXZEO loop.
Common-mode warning: Supplier, recycle-water, or shared-control failures can correlate outages. Segregated feed tanks, traceable water, and independent permissives are economic safeguards.
Chemistry in practical terms
Why the methane-rich gas still needs B6
Three process transformations; the full licensed kinetics remain a vendor and pilot workstream.
- 01
SCWG
Wet organic carbon → CH₄-rich gas + CO₂ + H₂B2 converts the wet feed; methane formation is expected on the central basis. - 02
Bi-reforming
CH₄ + H₂O/CO₂ + heat → CO + H₂B6 spends high-grade heat to create the synthesis-gas ratio OXZEO needs. - 03
OXZEO
CO + H₂ → oxygenate intermediate → C₂–C₄ olefinsB7 performance is expressed as integrated feed-carbon-to-olefin efficiency.
05 · Mass, carbon + energy
Nearly one million tonnes of slurry support tens of thousands of tonnes of olefins
The balances make the central design tension visible: water and mineral handling size the high-pressure plant, while only the renewable carbon fraction becomes saleable hydrocarbon product.
One B1 train · 300 t/day
300 t/day in- Raw gas to B555.80 t/dContains 90% of feed carbon on the screen
- B3 salt concentrate3.20 t/dControlled salt product or purge
- B8 washed solids7.25 t/dQualified destination or retreatment
- B4 aqueous stream233.75 t/dNitrogen recovery, polishing, recycle, and purge
Current performance
42.35 kt/year olefins
- Olefin carbon
- 10.898 t C/day/train
- Purge carbon
- 7.398 t C/day/train
Financeability target
55.45 kt/year olefins
- Olefin carbon
- 14.271 t C/day/train
- Purge carbon
- 4.024 t C/day/train
Heat-integration cascade
1,060 gross → 260 purchased GJ/day per train
Purchased-energy equivalent includes 205 GJ/day thermal and 55 GJ/day shaft/electric work.
Gross duties
Slurry heating+690
SCWG reaction + loss+55
B6 reforming + furnace+290
B4/B5 regeneration+25
Recovery + credit
H-101 feed/effluent−555
Reformer + flue gas−150
OXZEO heat−45
Hot water + solids−25
Purge-fuel credit−60
Site result
Purchased equivalent260
Purchased thermal682,650 GJ/year · ≈23.7 MW
Electricity≈50.9 GWh/year · ≈6.36 MW
Potential ammonium sulfateUp to ≈27.9 kt/year after qualification
06 · Equipment + assurance
The process is released by measurements, not by equipment names
The public report carries the equipment quantities, chloride inventory controls, preliminary HAZOP, and analytical release plan into the website. These controls connect supplier acceptance to metallurgy, train isolation, product quality, and safe shutdown.
Major equipment and confirmation programme
| Area / equipment | Quantity | Screening duty | Critical confirmation |
|---|---|---|---|
| B1 receiving trains | Shared receipt + train day tanks | 3,000 t/day complex | Supplier variability, storage, odour and metering |
| P-101 A/B high-pressure pumps | 20 total | 12.5 t/hour per duty pump | Wear, check-valve life and restart on the B1 slurry |
| H-101 feed / effluent recovery | 10 modular train systems | 555 GJ/day per train | Deposit control, thermal stress, cleanability and tube-failure isolation |
| R-201 SCWG reactors | 10 | ≈2.3 m³ gross per train screen | Residence time, heat flux, alloy, fatigue and char behaviour |
| V-301 A/B hot-salt separators | 20 | ≈10 m³ gross each screen | Mixed-salt settling, wall adhesion and continuous underflow |
| B5 Rectisol / ZnO | 1 shared train with spared pumps and beds | 558 t/day wet raw-gas screen | Gas load, refrigeration and sulfur speciation |
| B6 reformer | 1 shared system in multiple boxes | ≈2,900 GJ/day gross equivalent | Tube metallurgy, catalyst, firing and decoking |
| B7 OXZEO | Licensed multi-bed system | 42–55 kt/year olefin envelope | Real-gas performance, catalyst life and product specification |
| B8 + nitrogen recovery | Shared and source-traceable | 72.5 t/day solids · 2,337.5 t/day aqueous | Product quality and water / chloride closure |
Plant-wide chloride control
| Location | Measurement | Control response |
|---|---|---|
| Supplier unloading | Chloride, conductivity, Na/K and source history | Reject, segregate or allocate prewash |
| B1 final blend | Batch chloride and conductivity | Prevent high-pressure-feed release above the campaign limit |
| B3 underflow | Chloride mass and mineral / salt phase | Confirm that the intended salt-removal route is working |
| B4 recycle water | Continuous conductivity plus frequent ion chromatography | Increase controlled purge or stop recycle |
| B8 product and wash | Soluble and total chloride | Second wash or alternate destination |
| Corrosion coupons | Metal loss, pitting and cracking evidence | Revise the chemistry limit, alloy or inspection interval |
Preliminary HAZOP register
| Deviation | Consequence | Safeguard / response |
|---|---|---|
| Low B1 flow with heat | Wall overheating, char and a pressure / temperature excursion | Independent flow trip cuts firing and organics, maintains water and uses local blowdown |
| High B3 differential pressure | Reactor backpressure and a blocked outlet | Twin-separator switch, feed reduction, water flush and independent relief |
| Letdown erosion or failure | Loss of containment or downstream high level | Staged sacrificial trims, condition monitoring and a closed receiver |
| Liquid carryover to the gas header | Rectisol / reformer upset and common-mode contamination | Independent high-high level closes double block; knockout and coalescer remain in service |
| Sulfur breakthrough | B6 / B7 catalyst poisoning | Lead / lag beds, analyser voting and immediate off-spec diversion |
| Low B6 steam-to-carbon ratio | Reformer coking and tube overheating | Hard permissive, feed cut, steam purge and decoking provision |
| High B7 temperature | Selectivity loss, catalyst damage and pressure rise | Multipoint temperature trip, fresh-gas cut and recycle / inert cooling |
| Methanol release | Fire, toxicity and environmental release | Closed drains, detection, bunding, classified equipment and remote isolation |
| High chloride inventory | Pitting, stress-corrosion cracking and off-spec residue | Inventory alarm, stop recycle, increase purge and quarantine the source |
Analytical release plan
| Location | Online measurements | Laboratory / periodic measurements |
|---|---|---|
| Supplier + B1 | Mass, density, pH, conductivity and tank temperature | Total solids, rheology, particle size, CHNS, ash, ions, metals and excluded contaminants |
| B2 outlet | Temperature, pressure, flow and H₂ / CH₄ / CO / CO₂ GC | Aqueous TOC, solid carbon and full C / N / S / mineral closure |
| B3 | Differential pressure, underflow flow / density and wall temperature | Ion balance, crystal / mineral phase, organics and leachability |
| B4 | Levels, water carryover, conductivity and ammonia proxy | NH₃ / NH₄⁺, TOC / COD, ions, metals and purge / recycle release |
| B5 + B6 | Total sulfur, H₂S / COS, water, gas composition and tube skin | Methanol carryover, catalyst poisons and carbon deposition |
| B7 | Bed temperature / pressure drop, conversion, selectivity and recycle flow | Full product specification, oxygenates, catalyst deposition and activity trend |
| B8 | Moisture and process pH | XRF / XRD, Na / Cl, carbon, metals, leachability and destination performance |
Relief philosophy: each hydrothermal train depressurises to its own water-filled quench / blowdown receiver. Dirty salt-bearing relief remains separated from the clean B5–B7 syngas and hydrocarbon relief system until composition and hydraulic studies justify any shared boundary.
07 · Certification + market position
Four claims, four separate evidence chains
Product footprint, certified attribution, residue treatment, and price premium are related but not interchangeable. The design keeps each claim narrow enough to audit and refuses value where contracts or measured performance do not yet exist.
ISO 14067 product carbon footprint
Meter utilities, logistics, conversion losses, gas, water, solids, and product by accounting period.
Waste status does not automatically create a zero footprint.
ISCC PLUS chain of custody
Track supplier, point of origin, wet/dry mass, eligible category, conversion factor, losses, and outgoing attribution.
Mass balance does not mean every product molecule is physically traced to one waste batch.
EU product premium
A certified circular/bio attribution and lower verified footprint may support differentiated offtake.
The 20% premium is a scenario only; it must be written into price and volume terms.
EU CBAM and China carbon value
Track policy interfaces separately from product qualification and waste-treatment performance.
Light olefins are not currently treated as CBAM goods, and no China ETS/CCER value is credited in the base case.
08 · China economics
Capital dilution—not catalyst price—is the financial problem
The high-pressure and salt-resistant plant is sized by 999,000 t/year of slurry, but its saleable olefin output is only 42.35–55.45 kt/year. Commercial success therefore requires a stack of operational and contractual improvements.
Main cost driver
RMB 2.814bn TCI
Ten high-pressure feed, reactor, heat-recovery, and salt-separation trains process almost one million tonnes of watery slurry each year.
| Input | Project quantity | Public unit basis | Annual treatment |
|---|---|---|---|
| Electricity | ≈50.9 GWh/year | RMB 0.40/kWh | RMB 20.4m/year |
| Biomass thermal energy | ≈682,650 GJ/year | RMB 650/t pellets · 16.5 GJ/t LHV · 80% useful heat | RMB 33.6m/year |
| Purchased water | Closed by the site water balance | RMB 20/t | Included in the water OPEX line |
| Provisional operating tax | Saleable light-olefin output | RMB 35/t product | RMB 1.9m/year at 55% conversion |
CAPEX by area RMB million
- B1 feed preparation140
- B2 ten-train SCWG island880
- B3/B4 salt, heat, letdown + water330
- B5 Rectisol + sulfur protection250
- B6 bi-reforming260
- B7 OXZEO + recovery390
- B8 residue finishing150
- Utilities + offsites260
- Buildings / EPCM / owner154
Cash OPEX RMB million/year · public planning basis
- Electricity20.4
- Biomass thermal energy33.6
- Maintenance and inspection70.0
- Labour and site services32.0
- Catalysts, ZnO, methanol and chemicals32.0
- Water, purge treatment and disposal15.0
- Insurance, administration and certification15.0
- Operating tax at 55% product case1.9
42% → 55% carbon efficiency
Where the additional olefin carbon comes from
Efficiency is olefin carbon divided by the 25.947 t C/day entering one B1 train.
| Carbon destination | 42% case | 55% target | Change |
|---|---|---|---|
| Olefin product | 10.898 | 14.271 | +3.373 |
| Synthesis-loop purge | 7.398 | 4.024 | −3.374 |
| Aqueous organic loss | 1.297 | 1.297 | — |
| Solid / char loss | 1.297 | 1.297 | — |
| CO₂ loss | 5.057 | 5.057 | — |
Primary lever
OXZEO conversion, recycle, and recovery
Increase single-pass conversion and olefin selectivity, recover more unconverted CO/H₂, separate recycle gas more cleanly, and reduce the minimum stable purge without accumulating inerts.
Primary lever
Bi-reformer conversion and ratio control
Convert more methane, reduce CH₄ slip, and hold the CO/H₂ ratio inside the B7 catalyst window so carbon reaches the synthesis loop in a usable form.
Secondary opportunity
SCWG gas yield
Reduce char and aqueous-organic formation while maintaining 90% carbon transfer to raw gas. This could improve beyond the report's 55% case, which holds upstream losses constant.
Carbon protection
Separation and clean-gas recovery
Limit hydrocarbon carry-under into water, liquid carryover, Rectisol co-absorption losses, and off-spec gas rejection while still protecting the reformer and OXZEO catalysts.
Operability enabler
Stable feed and salt management
Keep carbon density, pumpability, residence time, and separator availability stable. These sections protect achieved efficiency but do not create the modelled 42%→55% increase directly.
Evidence required: The 55% value is a financeability target, not measured performance. Confirm it with real-gas reformer/OXZEO trials, catalyst-life and recycle-loop modelling, product-recovery tests, and a continuous full-plant carbon balance.
Current-performance commodity
Can the present technical case work as an ordinary commodity-olefin plant?
20-year NPV−RMB 1223.8m
- Olefin
- 42.35 kt/y
- Revenue
- RMB 406.2m/y
- Cash OPEX
- RMB 219.5m/y
- EBITDA
- RMB 186.8m/y
- IRR / payback
- 2.9% · 15.1 y
- NPV after 70% / 90% ramp
- −RMB 1331.8m
Nothing is upgraded. This is the reference case against which the other three scenarios are compared.
42% feed-carbon-to-olefin efficiency; 42.35 kt/year product; RMB 7,500/t commodity netback; base waste-service fees; no certified EU premium.
The plant produces positive annual EBITDA, but not enough to repay the roughly RMB 2.8bn capital base within the project horizon. This is the report's clearest evidence that commodity olefins alone are not the business model.
Current performance + EU 20%
Can stronger service contracts and a 20% EU premium rescue current conversion performance?
20-year NPV+RMB 150.2m
- Olefin
- 42.35 kt/y
- Revenue
- RMB 589.6m/y
- Cash OPEX
- RMB 241.5m/y
- EBITDA
- RMB 348.2m/y
- IRR / payback
- 10.8% · 8.1 y
- NPV after 70% / 90% ramp
- −RMB 15.1m
Technical performance stays at 42%; annual service fees increase from the base to the contracted portfolio, and the model adds a certified 20% price premium plus its export/compliance allowance.
42.35 kt/year product; contracted circular-service fees of RMB 203.5m/year; RMB 9,000/t netback; source-aligned utilities; no benefit from reaching the 55% target.
The level annual case crosses zero, but its NPV becomes slightly negative after a 70%/90% two-year ramp. Commercial rescue at current conversion is therefore possible only narrowly, with little tolerance for capital overrun or lost availability.
Improved conversion + contracts
Can better carbon conversion and contracted waste-service income work without a green premium?
20-year NPV+RMB 629.8m
- Olefin
- 55.45 kt/y
- Revenue
- RMB 624.4m/y
- Cash OPEX
- RMB 219.9m/y
- EBITDA
- RMB 404.5m/y
- IRR / payback
- 13.2% · 7.0 y
- NPV after 70% / 90% ramp
- +RMB 444.4m
Carbon efficiency rises from 42% to 55%, while eligible waste streams move onto contracted circular-service fees. Product remains at the commodity netback.
55.45 kt/year product; RMB 7,500/t netback; improved integrated conversion; contracted circular fees; no EU premium or speculative carbon/scandium credit.
This is a more robust commercial bridge than Scenario B. It remains positive after the two-year ramp and shows that sustained carbon recovery plus binding supplier contracts matter more than premium marketing alone.
Improved + EU 20%
What is the upside if technical, contractual, and certified-market improvements all arrive together?
20-year NPV+RMB 1150.6m
- Olefin
- 55.45 kt/y
- Revenue
- RMB 707.6m/y
- Cash OPEX
- RMB 241.9m/y
- EBITDA
- RMB 465.7m/y
- IRR / payback
- 15.6% · 6.0 y
- NPV after 70% / 90% ramp
- +RMB 943.5m
Scenario 3's 55% conversion and contracted service fees are retained, then the model adds the 20% certified EU premium and its associated allowance.
55.45 kt/year product; improved conversion and availability; contracted circular fees; certified 20% premium; no China carbon-market, CBAM, or scandium value.
This is the strongest central upside case, not the base forecast. It offers the best return, but only if the plant, suppliers, certifier, and product buyer all deliver their respective parts of the value stack.
| Premium | Netback RMB/t | Break-even product | Break-even C efficiency | NPV at 55% |
|---|---|---|---|---|
| 0% | 7,500 | 45.54 kt/y | 45.2% | +RMB 630m |
| 10% | 8,250 | 43.82 kt/y | 43.5% | +RMB 814m |
| 20% | 9,000 | 40.38 kt/y | 40.0% | +RMB 1151m |
| 30% | 9,750 | 37.57 kt/y | 37.3% | +RMB 1479m |
TCI rises to RMB 4.0bn
−RMB 1.186bn NPVDestroys the improved + premium case.
Availability falls 10%
≈−RMB 0.5–0.7bn NPVSalt separation and train turnaround are commercial variables.
Netback falls RMB 1,000/t
≈−RMB 472m NPVOfftake quality and market positioning matter at 55.45 kt/year.
Waste fee falls RMB 100/t
≈−RMB 680m NPVThe waste-service contract is more valuable than a cosmetic by-product credit.
Qualified ammonium sulfate adds RMB 30m/y net
+RMB 255m NPVUseful upside after product qualification, but insufficient to rescue the 42% commodity case alone.
Route decision
OXZEO, methanol, or renewable methane
The design includes two fallback routes. They are complete battery-limit alternatives, not shortcuts that automatically remove the hydrothermal or gas-cleanup systems.
OXZEO light olefins
Retain B1–B6 and the full B7 synthesis, recycle, and C₂–C₄ recovery island.
55.45 kt/year at the 55% feed-carbon target
Highest screened product value and strongest differentiation for certified chemical markets.
Highest catalyst, scale-up, reformer-duty, and product-separation risk.
Renewable methanol
Retain B1–B6, replace OXZEO and deep olefin fractionation with a mature methanol loop and distillation.
138.2 kt/year screen at 60% carbon efficiency on the same B1 feed
Mature synthesis, liquid storage, and established chemical/marine logistics.
Lower value density; B6 usually remains because B2 gas is methane-rich. Vendor battery-limit economics are still required.
Renewable methane
Retain B1–B5, then replace most of B6/B7 with CO₂ removal, drying, compression, and grid or LNG conditioning.
Capacity depends on measured B2 gas composition and methane recovery
Lowest downstream complexity and avoids the endothermic methane round-trip.
Requires a firm gas offtake or premium; methane slip becomes a critical greenhouse-gas control.
09 · Final design position
Technically coherent; commercially conditional
The design now states what is fixed, what is a controlled fallback, and what still needs evidence. These are the decisions that define the next development programme.
Final conclusion
The process is technically coherent and can become commercially credible, but only as an integrated waste-service and certified-carbon project. It should not be presented as a commodity-olefin plant that happens to use waste.
Feed
Douzha remains the anchor. Cassava, clean pulp/liquor, and controlled straw adjust carbon; manure is a separate qualified campaign.
Location
The Guangxi–Guangdong / Beibu Gulf corridor is an opportunity, not a selected site. Decide from supplier-level delivered-cost data.
Scale
Ten 300 t/day B1–B4 trains merge after B4 into shared B5–B7 units; common critical equipment uses N+1 redundancy.
Salt
Salt precipitation is desired at B3 and is the principal availability risk; prove twin continuous withdrawal, switching, and flush recovery.
Residue
Target one-pass conditioning with a second-wash/retreatment fallback. Do not claim guaranteed product status or indefinite recycle.
Nitrogen + chloride
Recover ammonia after qualification and maintain explicit supplier limits, wash, recycle-water monitoring, and controlled purge.
Bi-reforming
Retain B6 because central SCWG gas is methane-rich. Treat methane suppression as an optimisation rather than a design assumption.
Certification
Keep PCF, ISCC, waste treatment, and product claims separate. Treat EU premium as contractual and take no CBAM credit.
Economics
The 42% commodity case remains negative. At current conversion, contracts plus a 20% premium are only marginally positive after ramp-up; 55% conversion with contracted service value is materially more robust.
Fallback route
If salt availability, carbon conversion, or offtake cannot be demonstrated, compare complete methanol and renewable-methane packages on the same feed and contract basis rather than adding more slurry capacity.
Next decision gate
Load-bearing claims to retire
Commercial FEED follows representative evidence and contracts; it is not the current project status.
- B-01B1 is pumpable and restartable at 20.8 wt% solids.
Full-scale cold and hot pump/restart loop on seasonal supplier blends.
- B-0290% of feed carbon reaches B4 raw gas.
Continuous carbon closure including gas, water, solids, and purge.
- B-03B3 withdraws salt continuously.
Representative mixed-feed hot loop with underflow, wall-deposition, switch, and flush recovery.
- B-04B8 residue meets a destination specification.
Wash trials, XRF/XRD, Na/Cl, leaching, legal status, and customer performance.
- B-05B4 can recover 75% of feed nitrogen.
Real-liquor removal, acid demand, impurity profile, and ammonium-sulfate product registration.
- B-06B5 can hold total sulfur below 0.1 ppmv.
Rectisol/ZnO licensor guarantee across start-up, train switching, and off-spec transients.
- B-07B6 can meet the 290 GJ/day-per-train-equivalent duty screen.
Rigorous real-gas equilibrium plus vendor furnace, tube-life, steam, and decoking balance.
- B-08The integrated plant can sustain 42–55% feed-carbon efficiency.
Long-duration B7 real-gas balance including recycle, purge, catalyst cycle, and product recovery.
- B-09Total capital can remain near RMB 2.8 billion.
Chinese vendor budget quotations and project-specific construction and contingency factors.
- B-10The contracted organic service-fee case is available.
Binding supplier terms after logistics, moisture/carbon adjustment, contamination liability, and competing-use review.
- B-11A certified 10–30% product premium is bankable.
Binding certified-volume offtake and delivered-cost schedule.
- B-12The twenty-year operating convention is realistic.
Ramp-up, catalyst cycle, major-turnaround, correlated-outage, and asset-life plan.
Financing depends on conversion, contracts, and capital discipline
The design is capital-intensive and cannot rely on commodity product sales alone. A credible financing case emerges only when higher verified carbon conversion, dependable plant availability, contracted waste-service income, and certified product value are delivered together.
The weaker configuration struggles to recover the infrastructure investment, while the improved configuration can support an investable case. Even then, the project has limited tolerance for construction overruns, slow ramp-up, unreliable salt handling, or a product premium that is not secured by contract.
The public website reproduces the report's stated Class 4 capital estimate, rounded public utility assumptions, project OPEX allowances, and twenty-year scenario results. These remain screening inputs, not supplier quotations or guarantees.
The public website may reproduce every technical and commercial planning value stated in the downloadable public report. Only the private reference-plant methanol cost breakdown and the underlying identities and detailed descriptions of References 36–46 remain available through the dedicated Towngas project login.
Source basis
Report sections used on this page
- 01
Towngas SCWG–OXZEO Process Design — public project reportAuthoritative disclosure boundary for this public website; August 2026
- 02
Operating windows and train management§5.10 and Table 5.6
- 03
Closed mass, carbon, and production balances§6 and Tables 6.1–6.8
- 04
Energy balance and heat recovery§7 and Tables 7.1–7.4
- 05
Equipment, materials, chloride control, safety, and analysis§8 and Tables 8.1–8.6
- 06
Certification and market positioning§9 and public claim-control ledger
- 07
China CAPEX, OPEX, route comparisons, and 20-year evaluation§10 and Tables 10.1–10.12; private methanol component breakdown omitted
Public descriptions of References 36–46
36 · Restricted commercial benchmark. Source identity, original document title, facility attribution, and detailed source description are withheld from the public edition. Technical values are reproduced only where authorised.
37 · Industrial technical reference a. Source identity, original document title, facility attribution, and detailed source description are withheld from the public edition. Technical values are reproduced only where authorised.
38 · Industrial technical reference b. Source identity, original document title, facility attribution, and detailed source description are withheld from the public edition. Technical values are reproduced only where authorised.
39 · Industrial technical reference c. Source identity, original document title, facility attribution, and detailed source description are withheld from the public edition. Technical values are reproduced only where authorised.
40 · Industrial technical reference d. Source identity, original document title, facility attribution, and detailed source description are withheld from the public edition. Technical values are reproduced only where authorised.
41 · Industrial technical reference e. Source identity, original document title, facility attribution, and detailed source description are withheld from the public edition. Technical values are reproduced only where authorised.
42 · Industrial technical reference f. Source identity, original document title, facility attribution, and detailed source description are withheld from the public edition. Technical values are reproduced only where authorised.
43 · Industrial technical reference g. Source identity, original document title, facility attribution, and detailed source description are withheld from the public edition. Technical values are reproduced only where authorised.
44 · Industrial technical reference h. Source identity, original document title, facility attribution, and detailed source description are withheld from the public edition. Technical values are reproduced only where authorised.
45 · Industrial technical reference i. Source identity, original document title, facility attribution, and detailed source description are withheld from the public edition. Technical values are reproduced only where authorised.
46 · Industrial technical reference j. Source identity, original document title, facility attribution, and detailed source description are withheld from the public edition. Technical values are reproduced only where authorised.