Cement kiln calcination + CO2 liquefaction

Preheated limestone (CaCO3) enters an indirectly-heated rotary kiln that calcines it toward CaO, releasing a CO2-rich off-gas; the gas is knocked free of moisture, then compressed and cooled to liquefy the CO2 for transport/storage. Honesty notes: (1) this specific kiln model (rotary_kiln) heats via an indirect utility-temperature wall duty (an NTU model), not a simulated internal flame, so no combustion stoichiometry runs inside it here — real oxy-fuel combustion IS modeled elsewhere in this codebase (fired_heater's oxidant="oxy_co2" mode: near-pure-O2 combustion diluted by a recycled-CO2 stream instead of air's nitrogen), see allam-fetvedt-cycle for a real working example of it; (2) the calcination conversion shown (~21%) is the real, kinetically-limited result of this model's validated Arrhenius parameters at this residence time/temperature, not a claim of complete calcination — a real cement plant's preheater-tower-plus-kiln train achieves far higher calcination degree than one rotary-kiln unit alone models here; (3) CO2 must be compressed above roughly 5.2 atm before it can be liquefied by cooling at all (it has no liquid phase at 1 atm at any temperature), which the compressor stage here reflects.