TECHNIQUE TO REDUCE HEAT RECOVERY STEAM GENERATOR PURGE TIME UTILIZING SMART CONTROLS
Publication Date: 2014-Sep-03
The IP.com Prior Art Database
The present invention proposes a technique to perform a smarter purge of a heat recovery steam generator (HRSG) during a combined cycle power plant startup. The technique includes determining the purge duration. Determination of the purge duration is based on two embodiments. First embodiment includes a set of real time calculation that acquire account the temperature and corresponding volumes in the HRSG. Second embodiment includes a set of combustible detectors that identify potential hazardous areas volume in the HRSG. Calculation of the real time purging volume is based on operating temperature of the HRSG, which is above the auto ignition temperature of the fuel or focusing on specific volume detected by the combustible gas detector. This result the purge process involves performing required number of volume exchanges with that purge volume and performed in short time. The invention is applicable to all types of combined cycle power plants and to different purge scenario mainly during startups or at shutdown. The technique allows reducing and eliminating a HRSG purge utilizing temperature and/or combustible gas detector installed in the HRSG. By enabling reduction in the HRSG purge time, quenching and condensation is also reduced which results to reduce components life.
The present invention relates generally to a heat recovery steam generator (HRSG) and more particularly to a control scheme to determine in real time actual purge time in the HRSG.
Generally, the HRSG purge is performed at a low gas turbine speed, which is either during startup or after shutdown. During purge, the gas turbine is cranked up to a pre-determined speed and ambient air. This is acquired from the gas turbine inlet flow through the HRSG and purges residual hot gasses in the HRSG. As a result, purging allows removing any unburned present combustibles. Figure 1 depicts startup curve combined cycle power plant showing HRSG purge period.
Figure 1- Curve combined cycle showing HRSG purge period.
A conventional technique includes calculating duration of HRSG purge, which is based on number of volume exchanges required to remove residual gases and combustibles from the entire HRSG volume. As a result, air from the gas turbine sweeps entire HRSG volume for the pre-determine number of volume exchanges. However, the conventional technique requires long purge and results excessive cooling of the HRSG as entire HRSG volume is utilized for calculating duration of HRSG purge.
Another conventional technique includes estimating area of the HRSG, which is above auto ignition temperature of the fuel, and calculating the purge time based on performing a definite number of volume exchanges to purge that volume. However, the conventional technique does not acquire account of real time and transient condition in the HRSG. This results the actual purge time required is greater or smaller than that calculated.
Yet another conventional technique includes manual approach to calculate volume of the HRSG above the auto ignition temperature of the fuel. Area of the HRSG is above auto ignition temperature of the fuel is pre-designated and volume of the portion of this HRSG is calculated as a constant. Based on the volume the purge time is calculated to perform the required number of volume exchanges. However, the conventional technique does not include control scheme to calculate the purge time required during each start.
It would be desirable to have an efficient technique to determine actual purge time in the HRSG.
BRIEF DESCRIPTION OF THE DRAWING
Figure 1 depicts startup curve combined cycle power plant showing HRSG purge period.
Figure 2 depicts temperature distribution in the HRSG prior to a purge.
Figure 3 depicts first embodiment utilizing temperature feedback.
Figure 4 depicts temperature sensor array.
Figure 5 depicts flow chart in the process of first embodiment.
Figure 6 depicts second embodiment utilizing combustible detector feedback.
Figure 7 depicts Flow chart for the process in second embodiment.
Figure 8 depicts second embodiment utilizing combination of temperature and combustible detectors feedback.
The present invention proposes...