Model-based partial letdown thrust balancing

摘要

A method, control system, and combined cycle power plant are disclosed herein, which enable balancing thrust between a high pressure (HP) section and an intermediate pressure (IP) section of an opposed flow steam turbine in a combined cycle power plant, including predicting or determining a presence or absence of a thrust imbalance between the HP section and the IP section based on steam flow, pressure, and temperature data at an HP section inlet; and based on the presence or absence of the thrust imbalance, adjusting an amount of steam that enters the HP section.

主权项

1. A combined cycle power plant comprising:
an opposed flow steam turbine having a high pressure (HP) section and an intermediate pressure (IP) section, and a rotor axially disposed between the HP section and the IP section; a heat recovery steam generator (HRSG); a high pressure (HP) steam line that conducts steam from the HRSG to an inlet on the HP section; an intermediate pressure (IP) steam line that conducts steam from the HRSG to an inlet of the IP section; a high pressure (HP) exhaust line that returns exhaust from the HP section to the HRSG; a district heating (DH) system line that provides steam from the HRSG to a DH system; a valved letdown line that provides a variable fraction of steam from the IP steam line to the DH system via the DH system line; and a valved cascaded bypass line including a valve, wherein the cascaded bypass line provides a variable fraction of steam to the HP exhaust line from the HP steam line, the variable fraction of steam thereby bypassing the HP section, wherein the variable fraction ranges from none of the steam in the HP line when the valve is closed to a fractional portion of the steam in the HP line when the valve is open, and wherein the valve is opened and the fractional portion of steam is provided in response to a condition in which the fraction of steam provided from the IP steam line to the DH system line causes a thrust imbalance on the rotor between the HP section and the IP section.