Technical Papers
CO2 Recovery from Diesel Engines in a Solar-Hydrogen-Methanol Energy System*
Katsuhide Hiraoka**, Masaru Ikame**, Susumu Kan**, Takanao Kumakura**
Concept of a solar-hydrogen-methanol energy system 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 to be used in the methanol energy system, the effects of CO2 recovery parameters such as gas and liquid flow rates, liquid concentration, and stripping temperature 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. Heat rejected from the engine is used for CO2 recovery, but reduction in the engine output power is not avoidable, which is mainly caused by shortage in power for the turbocharger and requirement for supplemental supercharging power. Both the attainable maximum CO2 recovery ratio and the net output power depend on the ratio of the stripping steam feed rate to the flow rate of the exhaust gas.
1. Introduction
The world is facing the controversial issue of the greenhouse effect caused by the increase of CO2 concentration in the atmosphere which is assumed mainly to be caused by increase of fossil fuel consumption in the world. And the problem of eventual depletion of the fossil fuel still remains. In order to meet these difficult problems, several hydrogen energy systems are proposed such as PORSHE, EQHHPP and WE-NET, in which systems, overseas natural energy sources are assumed to be utilized.(1) The authors also proposed a solar hydrogen energy system for the transportation sector of Japan to supply hydrogen by utilizing solar energy as a substitute of the present petroleum fuel and their evaluation of the system indicated the possibility of the system.(2)(3)
Concept of a solar-hydrogen-methanol energy system is a kind of the solar hydrogen energy system for the transportation sector of Japan; methanol is delivered as a substitute fuel and it is produced with CO2 recycled and H2 produced by electrolysis with photovoltaic power. The authors have been doing researches on CO2 recovery from diesel engines for ship propulsion which are assumed to be used under the solar-hydrogen-methanol energy system.
* Translated from Journal of MESJ Vol.33, No. 1 (Manuscript received Aug.22, 1997) Lectured May 15, 1997
** Ship Research Institute (Shinkawa, Mitaka City)
Technology of CO2 absorbing and removing from industrial gas streams is already applied to commercial utilization. Literatures on it are published and are mostly for large-scale plants to clear CO2 to very small concentration. In view of application to CO2 recovery from heat engines exhaust, smaller plants are preferred and absorption in alkaline solution seems to be suitable because of its high absorption capacity. Monoethanolamine (MEA) aqueous solution is one of the most widely used because of its high absorption capacity and regenerative character.
The authors carried out fundamental experiments of CO2 absorbing and stripping with a packed column using MEA solutions to acquire data for heat engines CO2 recovery design.(4) Further, they made a calculation model of mass transfer between gas phase and liquid phase in the packed column of CO2 separator on the basis of the experimental results.(4)
Since thermal energy between 120 degree C and 150 degree C is necessary to recover CO2 with MEA solution, utilization of the rejected heat of diesel engines seems to be effective to recover CO2, from diesel engines exhaust. In this research, sensitivity of operating conditions of the CO2 recovery equipment to net output power of diesel engines, CO2 recovery ratio and volume of the packed columns is analyzed with the mass transfer calculation model.
This paper provides an outline of concept of a solar-hydrogen-methanol energy system for the transportation sector of Japan and results of analysis of CO2 recovery from methanol fueled marine diesel engine assumed to be used in the solar-hydrogen-methanol energy system.
