Thermodynamic and Economic Evaluation of an IGCC Plant Based on the Graz Cycle for CO2 Capture

Abstract

The IEA World Energy Outlook 2009 predicts a considerable growth of the world's primary energy demand and states that fossil fuels will remain the dominant source of primary energy. Among them coal will increase its share because of its vast reserves, its relatively even global distribution and its low prices compared to oil and gas. On the other hand the burning of coal emits larger quantities of CO 2 than oil and gas. As CO 2 is the leading cause for global warming, the use of coal for power generation demands a clean coal technology with carbon capture and storage (CCS).Therefore in this work it is suggested to combine a coal gasification unit with a Graz Cycle power plant, an oxy-fuel technology of highest efficiency. The firing of the syngas from coal gasification with pure oxygen avoids the expensive precombustion CO 2 sequestration and leads to a working fluid of CO 2 and steam, where CO 2 is captured by simple steam condensation. In contrast to this, the more conventional technology is to send the syngas to a water-shift reactor and a CO 2 scrubber so that a fuel containing mainly hydrogen is obtained which can be fired in a conventional combined cycle plant.In order to evaluate these two competing technologies a thermodynamic simulation as well as an economic cost analysis of both power cycles is performed. It turns out that the achievable efficiency of the Graz Cycle plant is -despite of the increased oxygen demand -far higher than that of a plant of conventional capture technology due to the avoidance of shift reaction and scrubbing. The following economic analysis shows mitigation costs of 22.5 €/ton CO 2 avoided for the Graz Cycle plant compared to 33 €/ton for an IGCC plant with CO 2 capture.

Oxyfuel combustion for CO2 capture in power plants

“…Jericha et al (2008) present an advanced 600 MW e cycle with increased pressure ratio of 50 and combustor outlet temperature of 1500 • C with a net efficiency of 54.4%. Sanz et al (2010) present an IGCC Graz cycle claiming 45% net efficiency compared to 39% for a pre-combustion plant.…”

Oxy-fuel combustion technology: current status, applications, and trends

“…Accordingly, it was concluded that the choice of technology development might be needed based on other factors besides the efficiency. In their investigation on coal syngas with coal gasification, Sanz et al described the thermos‐economic performance of Graz cycle. They compared their findings with those of an IGCC system using water‐gas shift for hydrogen production from syngas integrated with pressurized amine scrubbing for carbon dioxide capturing.…”

Novel cycles: oxy-combustion turbine cycle systems

“…Figure 6.5 presents yet another oxy-fuel cycle confi guration, typically referred to as the Graz cycle. This power cycle uses a mixture of CO 2 and water vapor as the working fl uid and has been extensively analyzed with several improvements suggested in a series of papers (Jericha and Fesharaki, 1995 ;Jericha and Göttlich, 2002;Jericha et al ., 2004Jericha et al ., , 2006Jericha et al ., , 2008Sanz et al ., 2005aSanz et al ., , 2005bSanz et al ., , 2007Sanz et al ., , 2010. The novelty of the cycle shown in Fig.…”