New steam turbine operational mode for a gas turbine combine cycle bottoming cycle system. (5th November 2021)

• Record Type: Journal Article
• Authors: Zhong, Zaixi; Huo, Zhaoyi; Wang, Xin; Liu, Feng; Pan, Yuhua
• Is Part Of: Applied thermal engineering. Volume 198(2021)
• Publication Date: 2021-11-05
• Subjects: The off-design model -- Bottom cycle system -- Triple-pressure reheat HRSG -- Off-design characteristic -- Operating reliability; Heat engineering -- Periodicals; Heating -- Equipment and supplies -- Periodicals; Periodicals; 621.40205
• DOI: 10.1016/j.applthermaleng.2021.117451
• Languages: English
• ISSNs: 1359-4311

Abstract

Highlights: A new solving method for the off-design model of bottom cycle system is provided. High pressure approach point temperature difference was found to be key factor for the bottom cycle system safe operation. Fixing steam pressure obviously increases the irreversible loss of bottom cycle system. A new steam turbine operational mode is proposed. Abstract: The gas combine cycle are widely used in generating electricity and recovering byproduct gas due to its high thermal efficiency, low pollution emission, and excellent regulation capacity. The highly dynamic nature of power demand and byproduct gas forces it to often run at off-design conditions, which in turn reducing the operating reliability of the bottom cycle system. A new steam turbine operational mode is proposed in this paper to ensure the safe operation of the bottom cycle system. Base on the new solving method proposed in Section 3 of this paper, the off-design model consisting of heat recovery generator (HRSG), steam turbine, condenser and water pump is established in MATLAB, and the refropm9.0 and LAPWS-95 are used for obtaining the physical properties of flue gas and steam/water. Then, the off-design characteristic of the bottom cycle system with different steam turbine operational mode is analyzed in detail. The result shows that as the gas turbine load decreases, the bottom cycle system has the best thermal performance under sliding pressure operational mode. However, its high pressure (HP) approach point temperature difference for the sliding pressure operational mode has a significant drop and is less than 2 ℃ below 74.21% load. The constant HP operational mode can obviously elevate the HP approach point temperature difference, however, the irreversible loss of the bottom cycle system is also increased. After the new steam turbine operational mode considering both sliding pressure and fixed HP is adopted, the HP approach point temperature difference is equaled to 2 ℃ bellow 74.21% load, while the thermal performance is better than that for the constant HP operational mode. As the gas turbine load decreases, the thermal efficiency and output power of the bottom cycle system decrease to 26.47% and 71.23 MW at 40% load, which are 0.53% and 1.45 MW higher than that for the constant HP operational mode. By reasonably regulating the HP steam pressure, the new steam turbine operational mode ensure the safe operation of the bottoming cycle at a cost of minimal thermal performance loss.