Networks (experimental)
Glossary & symbols
Definitions of network terminology, key symbols with units and reference values, and the relevant source files.
Experimental feature. Networks mode is under active development. Some technical aspects are still being validated with domain researchers. If you find results that don’t make sense, please open a GitHub issue or email co2gis.support@gmail.com.
Glossary
| Term | Definition |
|---|---|
| Source | A CO₂ emitter; a network terminal with an emission flow (Mt/yr). |
| Sink | A storage/injection site; a terminal with an injection capacity (Mt/yr). |
| Spur | A feeder pipe from a source toward the network (lower flow). |
| Trunk | A shared, higher-flow pipe carrying the sum of the flows that merged into it. |
| Junction | A node where two or more upstream paths merge. In the heuristic: a cell with ≥2 predecessors. In the MILP: a candidate pass-through node. Flows combine here to form trunks. |
| Capture target | The minimum total CO₂ (Mt/yr) the MILP network must transport. The optimiser selects the cheapest subset of sources meeting it. |
| Candidate graph | The discrete graph the MILP optimises over: nodes are sources, sinks, and a grid of junction candidates; arcs are a k-nearest-neighbour pruned set, each carrying a COMET-weighted cost. |
| Steiner node | A junction candidate with no flow or capacity. The optimiser uses some and ignores the rest — trunks form at the ones it keeps. |
| Pressure segment | A piece of a pipe no longer than the booster spacing. A pipe splits into several segments only when it exceeds that length. |
| Booster spacing | The maximum pipe length between compressors (≈150 km at reference parameters: Δp_total / (Δp/km)). |
| Spacing booster | A compressor at a pressure-segment boundary, recovering one segment’s pressure drop. |
| Junction booster | An extra compressor where two source or sink hubs connect (hub-to-hub rule); sized for the merged downstream flow. |
| COMET formula | The per-cell cost blend Fc · Fs · [Flu(1 − 0.1N) + 0.1N · Fci] used for both routing and pricing. |
| r.cost / r.drain | GRASS tools: r.cost accumulates least-cost distance from origins; r.drain traces the least-cost path back from a destination. |
| PuLP | Python library used to build the MILP linear/integer program. |
| HiGHS | Open-source (MIT) MIP solver that PuLP calls to solve the model. |
Key symbols
These parameters are shared with the single-pipeline tool — they are not specific to Networks mode. They are set in the plugin’s Price Estimation engineering inputs. For a detailed explanation of how each is used, see Pipeline diameter (Darcy–Weisbach) and Segments & booster stations.
| Symbol | Meaning | Units | Reference value |
|---|---|---|---|
| λ | Darcy friction factor | — | 0.015 |
| ρ | CO₂ density | kg/m³ | 827 |
| Δp/km | admissible pressure gradient | MPa/km | 0.02 |
| Δp_total | pressure budget per booster | MPa | 3 |
| D | pipe inner diameter | m | 0.2 – 1.0 (MILP classes) |
| M | CO₂ mass flow | kg/s | per pipe |
| B_c | pipe unit cost | €/m² | 1357 |
| α | booster cost, linear term | M€/MW | 0.547 |
| β | booster cost, fixed term | M€ | 0.42 |
| B_eff | booster efficiency | — | 0.75 |