Heat Recovery Steam Generator Segmentation for Auxiliary Fuel Operation
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Solution Overview
Problem
In integrated gasification combined cycles, when the gasifier is stopped for an extended period due to malfunctions or maintenance, the use of auxiliary fuel in the gas turbine equipment leads to a significant reduction in steam flow through the heat recovery steam generator, resulting in decreased heat recovery efficiency.
Innovation Solution
The system incorporates a circulation line unit that switches between different heat exchangers based on whether combustible gas or auxiliary fuel is being used, forming serial or separate heat exchange lines to maintain optimal flue gas temperature and heat recovery efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gasifier is stopped for maintenance or due to abnormality and auxiliary fuel is used in the gas turbine equipment, then the gas turbine can continue to generate power, but the steam flow through the heat recovery steam generator becomes markedly less than design flow rate, causing excessive steam temperature rise and decreased heat recovery efficiency
Solution Approach 1:
The heat recovery steam generator is divided into multiple independent heat exchangers (first heat exchanger, second heat exchanger, third heat exchanger) that can operate independently or in combination. This segmentation allows the system to maintain heat recovery efficiency by routing flue gas through different heat exchanger configurations depending on whether combustible gas or auxiliary fuel is being used.
Solution Approach 2:
The circulation line unit dynamically switches between different heat exchanger configurations based on the fuel type being used. When auxiliary fuel is used, the system activates a different heat exchange pathway compared to when combustible gas is used, allowing the heat recovery system to adapt to varying steam flow conditions and maintain optimal heat recovery efficiency.
2Temperature
If steam bypasses at least one of the plurality of superheaters to prevent excessive temperature rise, then steam temperature is controlled, but the heat recovery efficiency of the heat recovery steam generator further decreases
Solution Approach 1:
The superheater system is segmented into multiple independent superheaters that can be selectively activated or bypassed. When auxiliary fuel is used, the system can bypass certain superheaters to control steam temperature while still maintaining heat recovery efficiency by routing flue gas through alternative heat exchangers that are optimized for low steam flow conditions.
Solution Approach 2:
Different heat exchangers and superheaters are designed with different local characteristics optimized for different operating conditions. The first, second, and third heat exchangers have different heat transfer characteristics, allowing the system to select the most appropriate heat exchange pathway for the current fuel type, thereby maintaining both temperature control and heat recovery efficiency.
3Loss of energy
If the cooling water flow rate is increased to maintain heat recovery efficiency, then heat recovery efficiency is maintained, but the steam temperature rises excessively
Solution Approach 1:
The system dynamically adjusts both the cooling water flow rate and the heat exchanger configuration based on fuel type. When auxiliary fuel is used, the system routes flue gas through heat exchangers optimized for low steam flow conditions and adjusts cooling water flow accordingly, maintaining heat recovery efficiency without causing excessive steam temperature rise.
Solution Approach 2:
Different heat exchangers are designed with different local heat transfer characteristics. The first heat exchanger, second heat exchanger, and third heat exchanger have different surface areas, heat transfer coefficients, and flow characteristics, allowing the system to select the most appropriate heat exchange pathway for the current operating conditions, thereby decoupling heat recovery efficiency from steam temperature rise.
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 configuration allows for sustained heat recovery efficiency even when auxiliary fuel is used, preventing excessive steam temperature rise and ensuring efficient power generation.
Implementation Method 1
a gas cooler that generates steam from cooling water by heat exchange between the combustible gas generated by the gasifier, and the cooling water
Implementation Method 2
a heat recovery steam generator that recovers the quantity of heat of flue gas discharged from the gas turbine equipment, and generates steam
Data Source
AI summary
Provided is an integrated coal gasification combined cycle equipped with: a gasifier that generates combustible gas from pulverized coal; a gas cooler; gas turbine equipment; an auxiliary fuel supply unit that supplies an auxiliary fuel to the gas turbine equipment; a heat recovery steam generator; steam turbine equipment; generators; and a circulation line unit that circulates cooling water. The heat recovery steam generator has a first medium-pressure coal economizer and a second medium-pressure coal economizer. When the combustible gas generated from the pulverized coal is burned, a serial heat exchange line is formed wherein cooling water passes through the first medium-pressure coal economizer, the second medium-pressure coal economizer, and the gas cooler. When the auxiliary fuel is burned, separate heat exchange lines are formed, wherein the cooling water separately passes through the first medium-pressure coal economizer and the second medium-pressure coal economizer.