Forced Flow Steam Generator Wall Heating Surface and Ferritic Steel
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Solution Overview
Problem
Forced flow steam generators operating in the oxyfuel process face high production, maintenance, and operational costs due to the need for heat-resistant materials like martensitic steel alloys and nickel-based materials, and increasing recirculated flue gas proportion is energy-intensive and costly, reducing plant efficiency.
Innovation Solution
A forced flow steam generator design using ferritic steel alloys with a chromium proportion of 1.9-2.6 wt% for the combustion and surrounding walls, combined with a wall heating surface arrangement that extracts thermal energy from flue gas to limit heat absorption and prevent excessive heating of the operating medium, allowing for reduced oxygen consumption and lower operational costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If martensitic steel alloys or nickel-based materials are used for combustion chamber wall and surrounding wall, then the walls can withstand high temperatures and dissipate large amounts of heat, but the construction and maintenance costs become very high due to required postheat treatment after welding
Solution Approach 1:
The patent changes the material parameter from martensitic steel or nickel-based alloys to ferritic steel alloy with specific chromium content (1.9-2.6 wt%). This material substitution eliminates the need for postheat treatment after welding, significantly reducing construction and maintenance costs while still enabling the walls to withstand the required high temperatures in the oxyfuel process
Solution Approach 2:
The patent employs a less expensive ferritic steel alloy that can be welded without costly postheat treatment, effectively replacing expensive heat-resistant alloys. This approach accepts the use of a lower-cost material that achieves the necessary performance without the additional manufacturing complexity and cost of post-weld heat treatment processes
2Temperature
If the recirculation proportion of cooler flue gas is increased to reduce combustion chamber temperature, then the temperature in the combustion chamber and heat absorption in wall tubes are reduced, but a larger amount of oxygen must be used to maintain predetermined oxygen proportion
Solution Approach 1:
The patent changes the material parameter of the combustion chamber wall and surrounding wall to ferritic steel alloy with 1.9-2.6 wt% chromium. This material change enables the walls to withstand higher temperatures without requiring excessive recirculation of flue gas, thereby maintaining efficient combustion with lower oxygen consumption while still protecting the wall tubes from excessive heat absorption
3Temperature
If recirculated flue gas proportion is increased to cool walls, then wall temperatures are reduced, but plant efficiency decreases from operational economy perspective
Solution Approach 1:
The patent changes the material composition to ferritic steel alloy with specific chromium content, which provides adequate heat resistance. This allows the plant to operate with lower flue gas recirculation proportions, maintaining wall temperature control while preserving plant efficiency and operational economy
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
The use of ferritic steel alloys and a wall heating surface arrangement effectively reduces the operating medium's temperature, minimizing the need for costly heat-resistant materials and reducing oxygen consumption, leading to a more economical and efficient operation of the steam generator.
Implementation Method 1
a wall heating surface arrangement 36 which extracts thermal energy from the flue gas for this purpose
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
The invention refers to a forced flow steam generator (10) and to a method for its operation. The forced flow steam generator (10) has a combustion chamber (1 1) with a burner arrangement (20). A fuel (B) and a mixture (G) consisting of pure oxygen and flue gas (R) are fed into the combustion chamber (1 1) or to the burner arrangement (20) for combusting. A flue gas duct (27) is connected to the combustion chamber (11) in the flow direction (S) of the flue gas (R), and a flue gas passage (26) is connected to the flue gas duct. The flue gas (R) for the oxygen-flue gas mixture (G) is fed back from the flue gas passage (26) via a flue gas recirculation line (28). The forced flow steam generator (10) is operated in the so-called oxyfuel process. A plurality of auxiliary heating surfaces (35) are arranged in the flue gas duct (27) downstream of the burner arrangement (20). Between the burner arrangement (20) and the auxiliary heating surfaces (35), provision is made for a wall heating surface arrangement (36) which at least partially covers a combustion chamber wall section (38) of the combustion chamber wall (12) which delimits the combustion chamber (11). For this purpose, the wall heating surface arrangement (36) has a plurality of wall heating surfaces (37) which butt against the respectively associated segment of the combustion chamber wall section (38). The operating medium (A) flows through the wall heating surface arrangement (36) and in this way thermal energy is dissipated from the flue gas (R) in order to limit the heating of the operating medium (A) in the combustion chamber wall tubes (13) and therefore to limit wall tube temperatures in the upper section of the boiler.