Olah, G. A., Goeppert, A., and Prakash, G. K. S., 2006, “Beyond Oil and Gas: The Methanol Economy,” Wiley-VCH.
2001, “Feasibility of Methanol as Gas Turbine Fuel,” GE Position Paper.
Choi, Y. and Stenger, H., 2002, “Kinetics of Methanol Decomposition and Water Gas Shift Reaction on a Commercial Cu-ZnO/Al2O3 Catalyst,” Fuel Chemistry Division Preprints,47(2), pp. 723-724
Brown, J., C., and Gulari, E., 2004, “Hydrogen Production from Methanol Decomposition over Pt/ Al2O3 and ceria Promoted Pt/Al2O3 Catalysts,” Catlysis Communications, 5, pp. 431-436.
Topsoe, H., 1998, “Process for Generating Power in a Gas Turbine Cycle,” United States Patent No.: 5,819,522.
Janda, G., F., Kuechler, K., H., Guide, J.,J, Mittricker, F., F., and Roberto, F., R., 1999, “High Efficiency Reformed Methanol Gas Turbine Power Plants,” Pub. No.: WO/1999/009301.
Jin, H., Hui, H., and Cai, R., 2006, “A Chemically Intercooled Gas Turbine Cycle for Recovery of Low-temperature Thermal Energy,” Energy, 31, pp. 1554-1566
Jin, H., and Ishida, M., 2000, “A Novel Gas Turbine Cycle with Hydrogen-fueled Chemical-looping Combustion,” International Journal of Hydrogen Energy, 25, pp. 1209–1215.
Ishida, M., and Kawamura, K., 1982, “Energy and Exergy Analysis of A Chemical Process System with Distributed Parameters based on The Energy-direction Factor Diagram,” Ind Eng Chem Proc DD, 21, pp. 690–695.
Chen, C., 2005, “A Technical and Economic Assessment of CO2 Capture Technology for IGCC Power Plants,” PhD dissertation of Carnegie Mellon University
Pfaff, I., Oexmann, J., and Kather, A., 2010, “Optimized Integration of Post-combustion CO2 Capture Process in Greenfield Power Plants,” Energy, 35, pp. 4030-4041.
Atkinson, J. and Zachary, J., 2010, “Design Challenges for Combined Cycles with Post-combustion CO2 Capture,” Proceedings of Power Gen International 2010, Orlando, FL.
1 Introduction The methanol economy has been advocated since the 1990s. Methanol has been suggested as a potential replacement for fossil fuels in energy storage, as fuel and as raw material for synthetic hydrocarbons and their products. Methanol price also could be potentially lower than distillate when it is produced based on coal gasification .
One of the fuel uses for methanol is to produce power through gas turbines (GTs). Tests have shown that, with minor system modifications, methanol is readily fired and fully feasible as a gas turbine fuel. Effective utilization of methanol as a fuel in power systems will become an important issue in the future .
Methanol indirect combustion typically includes two kinds of chemical reactions: methanol decomposition (dry methanol cracking) and methanol steam reforming. Gaseous methanol can be catalytically decomposed to carbon monoxide and hydrogen according to the reaction:
CH3OH = CO + 2 H2 Equation 1
/> This takes place rapidly with respect to temperature. Pressure hinders the decomposition process so that a higher temperature is required when pressure increases.
The chemical reaction, whereby methanol is catalytically steam-reformed, is the following:
CH3OH + H2O = CO2 + 3 H2 Equation 2
This reaction takes place through a catalyst being active above 200°C and at the same time, the catalyst is not active for the reverse reforming reaction (methanation). It is possible to achieve full conversion at relatively low temperature [3, 4].
There is an assortment of techniques that take advantage of the methanol indirect combustion, resulting in a variety of power cycle configurations. [5-7].
In recent years, concerns about global warming have driven the potential for imposing limits on greenhouse gas emissions from conventional fossil fuel power plants. However, greenhouse gas issues for methanol fueled power systems are not addressed in the noted studies.
This paper develops two advanced combined-cycle systems based on methanol indirect combustion:
Methanol decomposition combined-cycle system without CO2 capture
Pre-combustion CO2 capture combined-cycle system based on methanol steam reforming
This study is based on process modeling using Aspen Plus and GTPro software tools. In order to carry out a comprehensive study, two conventional combined-cycle configurations with/without CO2 capture are modeled and compared. Based on the simulation results, exergy analysis is carried out to identify advantages of the new systems.
2 Methanol indirect combustion combined cycle 2.1 System description Figure 1 shows a flow schematic of a methanol decomposition combined-cycle system. The liquid methanol as a fuel, at pressure above 22 bar, is first heated and converted into gas through 3 stages (preheating, evaporation and superheating) to a temperature of 220°C. The superheated methanol proceeds to an endothermic reaction with a catalyst in the reactor. The reaction takes place at constant temperature of 220°C, and the majority of the methanol gas is decomposed into syngas (CO and H2) as per Equation 1 . The sources for methanol heating and decomposition are:
Intermediate pressure (IP) steam from high pressure (HP) steam turbine exhaust, cold reheat steam
Low pressure (LP) steam from IP turbine
The combined cycle in Figure 1 consists of a gas turbine, HRSG and steam turbine generator. The minor differences from conventional combined-cycle configurations are: