Carbon Return

The fuel cell’s exhaust isn’t ordinary flue gas — because it’s produced electrochemically rather than by combustion in open air, it comes out already about half carbon dioxide by volume (see Energy & Power). That concentration is what makes capture cheap here: roughly $15–25 a tonne, mostly drying and compressing a stream that’s already mostly what you want, rather than the $50–100 a tonne typical of stripping CO₂ out of a normal 4–15%-concentration flue gas.

Capture is the easy part. What follows is genuine infrastructure: the CO₂ is piped back down the same trench as the incoming gas line — one 6-inch pipe in, one 4–6-inch pipe carrying supercritical CO₂ out — and injected into the depleted side of the same gas field it came from, never into a compartment still being actively produced. A depleted field always has more than half its pore volume still open once the gas is gone, since CO₂ is far denser at reservoir conditions than the methane it replaces. One real precedent anchors the sizing: the Illinois Basin’s Decatur Project injected roughly 1,000 tonnes a day through a single well for three years. A community’s own return, at 749 tonnes a day, is a fraction of what one well of that kind can handle — so the design calls for two or three injection wells plus a spare, not a field of them.

Transport and storage cost more than capture, purely because the flow is small relative to the pipeline: $15–37 a tonne to move it, $10–20 to store it, for a total return cost of roughly $40–80 a tonne — adding $2.10–4.25 to every million Btu of gas, 60–125% on top of wellhead price. The 45Q federal tax credit, at $85 a tonne for geologic storage, covers that entire range and then some for twelve years. But the design is explicit that the obligation to return the carbon doesn’t depend on the credit existing — only whether doing so costs the community money or turns a small profit.

Where this stops being one building’s problem

None of this — the wells, the pipeline, the field itself — belongs to a single building or even a single community. A regional body called the Council of Fifty coordinates well sites and pipeline routes across fifty communities and roughly five million people, but coordination isn’t ownership: every well and every ten-mile pipeline segment is titled to a specific community and leased out to an operating business, the same title/custody split that governs everything else in this system. At that fifty-community scale, sharing one trunk pipeline drops the transport cost to $6–11 a tonne — a real economy of scale, but one that only exists once several communities’ gas fields and pipelines are coordinated together, not something a single community can capture alone.

One figure worth flagging plainly: earlier project materials state 94 tonnes a day as a community-wide total, but that figure covers only the 24 public buildings. The corrected, full community-wide total — all 1,986 buildings — runs closer to ten times that.

Governed by Bureau 23.