A method of characterizing a mixed fuel flow period is provided. The method includes flowing a mixed fuel, the mixed fuel being comprised of at least a first fuel type and a second fuel type, the mixed fuel flow period being determined where the fuel is switched from the first fuel type to the second fuel type, determining a density of the first fuel type and a density of the second fuel type, and determining a total flow, the total flow being determined from the density of the first fuel type and the density of the second fuel type.

Described is a system for capturing and recovering carbon dioxide (CO.sub.2) from multiple distinct waste heat sources. The system includes an absorber for extracting CO.sub.2 from exhaust gas into a solvent stream selective for absorbing CO.sub.2 and creating a rich solvent stream. A solvent regenerator converts a first fraction of the rich solvent stream into a lean solvent stream and a crude CO.sub.2 vapor. A cross exchanger exchanges heat between lean and rich solvent streams. Several heat exchangers are associated with the solvent regenerator to transfer heat from multiple distinct waste heat sources into a second fraction of the rich solvent stream as well as recover waste heat from the multiple distinct waste heat sources. A compressor converts the crude CO.sub.2 vapor into a concentrated pressurized CO.sub.2 product, and a CO.sub.2 storage tank receives and stores the CO.sub.2 product.