How a tonne is counted
A removal is a mass of carbon dioxide that came out of the air and went somewhere it will stay, minus everything it took to put it there. Both halves are measured here and the second half is not small.
What is metered
A Coriolis mass flow meter on the collection line, downstream of the drier, logs every desorption step. One cycle on one column is 4.06 kg and 6.86 cycles a day. Nothing is inferred from the loading model: the model plans the cycle, the meter counts the tonne, and where they disagree the meter is right.
Inlet and outlet CO2 are logged continuously by non-dispersive infrared analysers, calibrated fortnightly against two reference gases. The blank column runs the same schedule with no sorbent in it, and its recovered mass is the instrument's own answer to the question of whether the meters are reading something that is not there. It has never exceeded 0.4 kg in a month.
What is deducted
| Line | t CO2 a year | Basis |
|---|---|---|
| Gross removal, metered | 40.7 | Collection line, four production columns. |
| Electricity, fans and vacuum pumps | −5.9 | Metered at the board, at the grid intensity published for the half hour. |
| Heat for regeneration | −2.7 | Waste heat from the neighbouring dryer, charged at its own carbon intensity rather than at zero. |
| Sorbent manufacture and change-out | −1.2 | Amortised over the measured life of a charge, 82 kg a column. |
| Drying, compression, transport, injection | −2.4 | Third-party invoices and their own emissions factors. |
| Net removal, sold | 28.5 | 70 per cent of gross. |
The ratio is the number worth arguing about, and it is the first one we publish. A plant that reports gross tonnes is reporting the easy half.
Who checks it
- Meter data is written to an append-only log at the plant and copied nightly.
- An independent verifier audits four weeks a year, chosen by them and not by us, and re-derives the net figure from raw logs.
- Injection receipts come from the storage operator and carry their own monitoring obligations.
- Tonnes are retired against a serial number, and the serial is on your invoice.
If you want the raw logs before you buy, ask for them. We have sent them to every buyer who has asked, and to two who were auditing us for someone else.