Feedwater Preheating in Combined Cycle Power Plants
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Solution Overview
Problem
In combined cycle power plants using fuel gas/oil with high sulfur content, the existing methods to prevent corrosion in heat recovery steam generators by maintaining feedwater temperature above the acid dew point are inadequate, especially when a booster pump configuration is used, as they only effectively address a small portion of the feedwater, leaving a major portion at risk of acid condensation.
Innovation Solution
A method involving a preheating system that monitors condensate temperature and directs it through a series of heating exchanges using fluids from intermediate and hot sources within the heat recovery steam generator's economizer, ensuring the feedwater is heated above the acid dew point, utilizing control valves and recirculation pumps to manage the heating process effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a booster pump configuration is used to pump feedwater directly into the high-pressure economizer, then the feedwater flow rate is increased, but the feedwater temperature drops below the acid dew point causing corrosion
Solution Approach 1:
The patent applies preliminary action by preheating the feedwater in the low-pressure economizer before it enters the high-pressure economizer. The feedwater is heated to a temperature above the acid dew point in advance, so that when it is pumped directly into the high-pressure economizer, it does not cause acid condensation corrosion. This resolves the contradiction by preparing the feedwater in advance to withstand the harsh conditions in the high-pressure section.
Solution Approach 2:
The patent segments the feedwater heating process into two distinct stages: first heating in the low-pressure economizer to reach a safe temperature, then pumping into the high-pressure economizer. This segmentation allows the feedwater to be heated in a controlled manner before entering the high-pressure section, resolving the contradiction between high flow rate and corrosion prevention.
2Object-affected harmful factors
If feedwater is bypassed to the low-pressure evaporator drum to avoid acid condensation, then corrosion is prevented, but the feedwater temperature may still be insufficient when using booster pumps
Solution Approach 1:
The patent applies preliminary action by preheating the feedwater in the low-pressure economizer before it enters the high-pressure economizer. The feedwater is heated to a temperature above the acid dew point in advance, so that when it is pumped directly into the high-pressure economizer, it does not cause acid condensation corrosion. This resolves the contradiction by preparing the feedwater in advance to withstand the harsh conditions in the high-pressure section.
3Object-affected harmful factors
If the feedwater temperature is maintained above the acid dew point, then corrosion is prevented, but additional heating equipment and control systems are required
Solution Approach 1:
The patent applies multi-functionality by using the low-pressure economizer to serve dual purposes: it acts as both a heat exchange device and a preheating chamber for the feedwater. The low-pressure economizer heats the feedwater to a temperature above the acid dew point before it enters the high-pressure economizer, eliminating the need for separate heating equipment. This resolves the contradiction by making existing equipment perform multiple functions.
Solution Approach 2:
The patent applies self-service by using the waste heat from the exhaust gas in the low-pressure economizer to preheat the feedwater. The system uses its own waste heat resources to achieve the preheating function, eliminating the need for external heating equipment. This resolves the contradiction by making the system self-sufficient and reducing additional device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach ensures that the majority of the feedwater is heated above the acid dew point, effectively preventing corrosion in the heat recovery steam generator, enhancing the operational reliability and efficiency of the combined cycle power plant while minimizing capital costs.
Implementation Method 1
directing a first fluid from an intermediate source of the low-pressure economizer to heat the condensate
Implementation Method 2
heating exchange between the first fluid from the intermediate source and the condensate
Implementation Method 3
generating steam in the heat recovery steam generator
Implementation Method 4
exhaust heat of the gas turbine is used to generate steam by passing it through the heat recovery steam generator
Implementation Method 5
the produced steam can be used to drive the steam turbine
Data Source
AI summary
A method for operating a combined cycle power plant includes transferring exhaust gas from a gas turbine to a heat recovery steam generator. Further, the method includes preheating condensate before being fed as feedwater to the heat recovery steam generator. Moreover, the method includes reheating the feedwater in the heat recovery steam generator. The method also includes generating steam in the heat recovery steam generator for a steam turbine, wherein preheating the condensate includes monitoring a temperature of the condensate: if the temperature of the condensate is equal to or above a preset temperature, directing the condensate to a low-pressure economizer of the heat recovery steam generator; if the temperature of the condensate is lower than the preset temperature: directing a first fluid from an intermediate source of the low-pressure economizer to heat the condensate.