Calculations

CO2 Capture and Compression Calculations, Step by Step

A worked walkthrough of the five formulas that run a capture and compression skid, from capture efficiency to compressor power, with real units and inputs.

Five calculations carry most of the engineering load on a capture and compression skid: capture efficiency, regeneration heat load, compressor power, absorber pressure drop, and solvent or sorbent consumption. Each uses flue gas flow, CO2 concentration, and temperature as shared inputs, so pull those from your continuous emissions monitor and gas analyzer first. A typical post-combustion train treats 50,000 to 500,000 Nm3/h of flue gas at 3 to 14 percent CO2 by volume. Get the mass balance right and the Capture Efficiency, Regeneration Heat Load, and CO2 Compressor Power calculators all line up. This guide works each number end to end.

Capture efficiency is CO2 in minus CO2 out, divided by CO2 in, on a mass basis. Take 100,000 Nm3/h of flue gas at 12 percent CO2. CO2 density at normal conditions is 1.964 kg/Nm3, so inlet CO2 is 12,000 Nm3/h times 1.964, or 23,568 kg/h. If the treated stack reads 1.2 percent CO2 on roughly 88,800 Nm3/h of remaining flow, outlet CO2 is about 2,093 kg/h. Efficiency is 23,568 minus 2,093, divided by 23,568, or 91.1 percent. The Capture Efficiency calculator runs wet or dry basis; keep both streams on the same basis or you overstate performance by 2 to 4 points.

Regeneration heat load is the reboiler duty that strips CO2 from rich solvent, and it dominates operating energy. Compute it as capture rate times specific reboiler duty. Standard 30 percent MEA needs 3.5 to 4.0 GJ per tonne CO2; advanced solvents like piperazine or CESAR1 run 2.4 to 2.8 GJ per tonne. At 21.5 t/h captured and 3.6 GJ/t, duty is 77.4 GJ/h, about 21.5 MW thermal. Convert to low pressure steam at 3.5 bar with latent heat near 2,148 kJ/kg and you need roughly 36 t/h of steam. The Regeneration Heat Load calculator ties the solvent's specific duty to your capture rate directly.

Compressor power moves captured CO2 from near atmospheric to pipeline pressure of 110 to 150 bar. Use polytropic head per stage: H equals Z times R times T1 divided by molar mass, times n over n minus 1, times the bracket of pressure ratio raised to n minus 1 over n, minus 1. With Z near 0.95, R at 8.314 kJ/kmol K, M of 44, T1 of 313 K, and five stages at a ratio of 2.5, total specific work lands near 95 to 110 kWh per tonne CO2. For 21.5 t/h that is about 2.2 MW electrical. The CO2 Compressor Power calculator handles the stage stacking and intercooling.

Absorber pressure drop sets blower energy, since flue gas must be pushed up through the packing. Structured packing drops 15 to 25 mbar per meter at design gas load; a 20 meter absorber with liquid distributors and demister totals 120 to 180 mbar. Blower shaft power is volumetric flow times pressure rise divided by efficiency. At 100,000 Nm3/h, about 30.6 actual m3/s at inlet, and 15,000 Pa across a blower at 0.72 efficiency, power is 30.6 times 15,000 divided by 0.72, or 638 kW. Run the Absorber Pressure Drop calculator first, then feed its result straight into Blower Energy Cost.

Consumables close the balance. Liquid amine plants lose solvent to degradation and volatilization at 1.2 to 1.8 kg MEA per tonne CO2; at 21.5 t/h that is roughly 26 to 39 kg/h of makeup, which the Solvent Makeup Cost calculator prices. Solid sorbent systems instead track working capacity, typically 1.5 to 2.5 mmol CO2 per gram, so capturing 21.5 t/h at 2.0 mmol/g cycled needs a large sorbent inventory and a defined replacement fraction per year. The Sorbent Consumption calculator converts working capacity and cycle count into annual mass. Both numbers feed back into the skid mass balance.

Close with throughput. Skid Throughput ties captured tonnes per hour to the limiting unit, usually absorber flooding or compressor inlet volume. Check that your captured 21.5 t/h matches 91 percent of the 23.6 t/h inlet CO2, that the compressor swallows the resulting suction volume, and that regeneration steam is actually available. When one calculator's output becomes another's input, unit consistency is everything: keep flows in Nm3/h, mass in kg/h or t/h, energy in GJ/h and kWh/t. The Heat Exchanger Fouling Loss and CO2 Leak Loss calculators then quantify the small but real gaps between these ideal numbers and field data.

Published 2026-07-02.