Operating pressure dependence of the pressurized oxy-fuel combustion power cycle

Oxy-fuel combustion technology is an attractive option for capturing carbon dioxide (CO2) in power generation systems utilizing hydrocarbon fuels. However, conventional atmospheric oxy-fuel combustion systems require substantial parasitic energy in the compression step within the air separation unit (ASU), the flue gas recirculation system and the carbon dioxide purification and compression unit (CPU). Moreover, a large amount of flue gas latent enthalpy, which has high water concentration, is wasted. Both lower the overall cycle efficiency. Pressurized oxy-fuel combustion power cycles have been investigated as alternatives. Our previous study showed the importance of operating pressure for these cycles. In this paper, as the extended work of our previous study, we perform a pressure sensitivity analysis to determine the optimal combustor operating pressure for the pressurized oxy-fuel combustion power cycle. We calculate the energy requirements of the ASU and the CPU, which vary in opposite directions as the combustor operating pressure is increased. We also determine the pressure dependence of the water-condensing thermal energy recovery and its relation to the gross power output. The paper presents a detailed study on the variation of the thermal energy recovery rate, the overall compression power demand, the gross power output and the overall net efficiency.Aspen Technology, Inc.Thermoflow Inc.ENEL (Firm

Analysis of oxy-fuel combustion power cycle utilizing a pressurized coal combustor

Growing concerns over greenhouse gas emissions have driven extensive research into new power generation cycles that enable carbon dioxide capture and sequestration. In this regard, oxy-fuel combustion is a promising new technology in which fuels are burned in an environment of oxygen and recycled combustion gases. In this paper, an oxy-fuel combustion power cycle that utilizes a pressurized coal combustor is analyzed. We show that this approach recovers more thermal energy from the flue gases because the elevated flue gas pressure raises the dew point and the available latent enthalpy in the flue gases. The high-pressure water-condensing flue gas thermal energy recovery system reduces steam bleeding which is typically used in conventional steam cycles and enables the cycle to achieve higher efficiency. The pressurized combustion process provides the purification and compression unit with a concentrated carbon dioxide stream. For the purpose of our analysis, a flue gas purification and compression process including de-SO[subscript x], de-NO[subscript x], and low temperature flash unit is examined. We compare a case in which the combustor operates at 1.1 bars with a base case in which the combustor operates at 10 bars. Results show nearly 3% point increase in the net efficiency for the latter case.Aspen Technology, Inc.Thermoflow Inc

Modeling the slag layer in solid fuel gasification and combustion -- Formulation and sensitivity analysis

A steady-state model has been developed to describe the flow and heat transfer characteristics of the slag layer in solid fuel gasification and combustion. The model incorporates a number of sub-models including one for particle capture, and takes into consideration the temperature and composition dependent properties of slag, the contribution of momentum of captured particles and the possibility of slag resolidification. An equally important issue is the interaction of the particles colliding with the slag layer. High inertia particles tend to rebound whereas slower particles are trapped in the slag layer. Since only trapped particles are relevant to the slag layer build-up, a particle capture criterion for colliding particles is introduced. The model predicts the local thickness of the molten and the solid slag layers, the average slag velocity, the temperature distribution across the layer and the heat flux to the coolant, taking into account the influence of molten and resolidified slag layers coating the combustor or reactor wall.ENEL Ingegneria e Innovazione S.p.

Production planning with hot section life prediction for optimum gas turbine management

The power production planning problem has been deeply investigated. Maintenance management and load allocation problems have been assumed as crucial aspects for achieving maximum plant profitability. Modeling of life consumption of hot section components has been considered as one of the key feature necessary to simulate the plant behaviour. The approach takes market scenarios, as well as actual status and performance of plant components into account. A supervisor algorithm provides the operating parameters needed to establish each plant loading. Economic implications related to maintenance strategies including postponement or anticipation of maintenance interventions are investigated and results obtained by the numerical simulation are presented and widely discussed. © 2008 Gas Turbine Society of Japan