In the diesel engine system, pressures and temperatures both at the cylinder inlet and at the cylinder outlet are assumed to be fixed for convenience of analysis. When there is not enough energy to drive the turbocharger, TC, which is caused by the turbine expansion restriction to maintain the outlet temperature determined by the heat balance of the heat recovery boiler, aspirated air is additionally compressed by a booster, BC, which is driven by the main shaft.

Electricity for auxiliary power, such as power for CO₂ liquefaction and pumping the solution, is supplied by the generator, G, driven by the main shaft.

　

Fig. 3　Summary comparison between predicted and measured energies to strip CO₂ from the solutions

　

3.2　CO₂ Mass Transfer Model for CO₂ Separator

A calculation model of mass transfer of CO₂ between gas phase and liquid phase in a packed column using MEA solution is made according to the researches, that for absorption by Onda et al.⁽⁶⁾⁽⁷⁾ and that for stripping by Weiland et al.⁽⁸⁾ The model is based on the film theory and on two chemical reaction models： for the detail see the literature by lkame et al.⁽⁴⁾

The results calculated by the mass transfer calculation model are compared with authors' experimental results, which shows that the calculation model is in good accuracy. For example, the calculations of the energy necessary to strip CO² from the solutions are compared with the experimental results on various operating conditions in Fig. 2. The experiments were carried out both on absorbing and on stripping in a CO²-MEA system with packed columns, which were 54 mm in diameter and packed with nominal 6 mm ceramic Raschig rings to a height of 0.8 m.

　

3.3　Conditions for Calculation

The engine considered as a basis has shaft power of 10,000 kW with thermal efficiency of 50 % on LHV base. The air excess factor is 2.0; the air pressure at the cylinder inlet is 300 kPa; and at the outlet the gas temperature is 450 degree C and the pressure is 250 kPa. The efficiency of the turbine of the turbocharger is 85 % and that of compressors for the turbocharger and the booster is 80 %. On the assumption of perfect combustion of methanol, the engine discharges exhaust gas at a rate of 496 mols^-1 with CO₂ concentration of 6.3%.

The operating conditions of the CO₂ separator selected for calculation are listed in Table 1, and the figures with an asterisk stand for the reference calculation condition. The feed rates of the gas, the steam, and the solution are superficial values associated with the sectional area of the packed columns. The loading factor φ is the mole ratio of CO₂ to MEA in the solution, and the factor, 0.5, stands for stoichiometry.

　

Table 1　Calculation conditions for C0₂ separator

1.The figures with an asterisk stand for the reference calculation condition.

2.Both an absorber and a stripper are packed with ceramic Raschig rings.

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