QRB=mEXrw(Gs/Ls)/(GA/LA) (3)
where mEX stands for mass flow of exhaust gas and rw for latent heat of water.
The ratio of the gas-to-liquid feed rate ratio in Eq. 3, (Gs/Ls)/(GA/LA), reduces to the ratio of the steam flow rate of stripper to the exhaust gas flow rate： since mass flow of solution is the same between the absorber and the stripper, saying that Ss stands for sectional area of the stripper and SA for that of the absorber, the ratio, (Gs/Ls)/(GA/LA), is equal to (Gs/Ss)/(GA/SA), which means the ratio of the steam flow rate of stripper to the exhaust gas flow rate.
The reboiler uses about three quarters of the steam generated by the heat recovery boiler, therefore the ratio in Eq. 3, (Gs/Ls)/(GA/LA), that is, the ratio of the steam flow rate of stripper to the exhaust gas flow rate, affects the heat load of the heat recovery boiler and resultantly does the net output power.
The net output powers at the attainable maximum CO2 recovery ratios in Fig. 4 to Fig. 7 are organized in Fig. 15. It is shown that as far as the effect of the gas and liquid feed rate in absorber and stripper, the net output power and the attainable maximum CO2 recovery ratio depend on the gas-to-liquid feed ratio, (Gs/Ls)/(GA/LA), that is, the ratio of the steam flow rate of stripper to the exhaust gas flow rate
6. Conclusion
Concept of a solar-hydrogen-methanol energy system to deliver methanol as a substitute fuel of petroleum for the transportation sector in Japan is outlined. In the system, methanol is produced with CO2 recycled and H2 produced by electrolysis with photovoltaic power.
Concerning CO2 recovery from the exhaust gas of a 10,000 kW diesel engine with a thermal efficiency of 50 % to be used in the methanol energy system, the effects of CO2 separator operating parameters on the engine performance and the attainable CO2 recovery ratio are analyzed on the basis of a mass transfer calculation model for a packed column with aqueous monoethanolamine solution.
Primary results are as follows.
1) When heat rejected from the engine is used for the CO2 recovery, reduction in the engine output power is not avoidable, while the attainable CO2 recovery ratio is limited by allowable power reduction. Output power reduction is mainly caused by shortage in exhaust gas energy for turbocharger, which requires the supplemental supercharging power.
2) Both the maximum attainable CO2 recovery ratio and the net output power depend on the gas-to-liquid feed ratio, (Gs/Ls)/(GA/LA), which reduces to the ratio of the steam flow rate of stripper to the exhaust gas flow rate.
3) The stripping temperature, the MEA concentration, and the loading factor of the solution have little effect on the net output power at a certain gas and liquid feed rate, but higher maximum CO2 recovery ratio is obtained as they are higher, respectively.
4) The volume of packed column of absorber and stripper increases as CO2 recovery ratio increases and it steeply increases in the vicinity of the attainable maximum CO2, recovery ratio.
Smaller nominal size of the packing, smaller the total volume of the packed columns.
References
1) Tokio Ohta Edited, High Technology of Hydrogen Energy (suisoenerugi-saisentan-gijutu), NTS, 1995, (in Japanese)
2) K.Hiraoka et al., Int. J. Hydrogen Energy, Vol.16, No.9, (1991), pp631-638, and Vol. 16, No.11, (1991), pp755-764
3) K.Hiraoka et al., Proc. 10th World Hydrogen Energy Conf., (1994), pp.339-348
4) M.Ikame et al., Report of Ship Research Institute, Vol.33, No.6, (1997),(in Japanese)
5) Statistics of Energy in Transportation Sector (unyu- kankei-enerugi-yoran), Information Administration Division, Ministry of Transport, 1996, (in Japanese)
6) K.Onda, H.Takeuchi, E. Soda, J. Chem. Eng. Jpn, Vol.1, No.1, (1968), pp.62-66
7) K.Onda, H.Takeuchi, Y.Okumoto, J. Chem. Eng. Jpn, Vol.1, No.1, (1968), pp.56-62
8) R.H.Weiland, M.Rawal, R.G.Rice, AIChE Journal, Vol.28, No.6, (1982), pp.963-973
