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Deactivation of one or several LP Turbine(s) for low and minimum load case operation

IP.com Disclosure Number: IPCOM000247370D
Publication Date: 2016-Aug-29
Document File: 2 page(s) / 562K

Publishing Venue

The IP.com Prior Art Database

Abstract

The idea of this invention is to increase the flexibility concerning part, low and minimum load of existing and new steam power plants by adapting the number of active LP turbines to the required load case and the resulting steam flow through the LP turbines. With the optimized steam flow to exit diameter ratio the expansion through the active LP turbine(s) is improved and there is a pressure difference to be released via the last LP stages remaining so that windage is prevented. In case of an existing power plant the idea is to block the steam flow from the intermediate pressure (IP) turbine to one (or several) LP turbine(s) using a shut-off device (e .g. a shut-off flap, compare Figure 1). Globe valves at the extractions of the inactive LP turbine avoid extraction steam coming from the active LP turbine(s) to enter the inactive turbine(s). Non-return valves at the inactive LP turbine exit(s) block the entry of exit steam coming from an active LP turbine and allow the condenser to keep the inactive turbine(s) up to the shut-off flap evacuated. In this case the turbine blades of the inactive turbine(s) are still rotating. But as the blading of this turbine meets quasi vacuum in the casing the blades are not harmed by windage.

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Deactivation of one or several LP Turbine(s) for low and minimum load case operation

Background

Nowadays steam power plants have to be flexible in load change and low load operation to react to fluctuation in power generation of renewable power plants such as solar and wind . Concerning low or minimal load operation windage in the last low pressure (LP) turbine stages is a critical topic. For low load operation the turbines, especially the LP turbines, are massively over dimensioned. Consequently no or very little pressure difference remains to be reduced over the last turbine stages and the exit stages effect as propellers increasing the energy content of the steam instead of reducing it. This leads to increased exit temperatures and a reduced energy output. As long as certain temperatures in and downstream the LP turbines are within limitations the effect of windage can be accepted. But with the reduced power output often a notable loss in the cycle efficiency is taken. During low or minimal load operation the power plant often meets other undesirable effects, such as strongly reduced live steam- and hot reheat- temperatures. Measures to counteract are often limited by occurring windage.

As long the temperatures are in limits windage and the resulting loss in efficiency is generally accepted. Often there are spray systems installed to cool the last stages in case the steam temperatures at the last stages or at the LP turbine exit exceed set values. As the water droplets increase the risk of erosion massively it is not recommendable to use the spray system in continuous operation.

Invention

The idea of this invention is to increase the flexibility concerning part, low and minimum load of existing and new steam power plants by adapting the number of active LP turbines to the required load case and the resulting steam flow through the LP turbines. With the optimized steam flow to exit diameter ratio the expansion through the active LP turbine(s) is improved and there is a pressure difference to be released via the last LP stages remaining so that windage is prevented. In case of an existing power plant the idea is to block the steam flow from the intermediate pressure (IP) turbine to one (or several) LP turbine(s) using a shut-off device (e .g. a shut-off flap, compare Figure 1). Globe valves at the extractions of the inactive LP turbine avoid extraction steam coming from the...