Marine auxiliary boiler convection bank design platform

Abstract

The invention discloses a marine auxiliary boiler convection bank design platform, and belongs to the technical field of marine boiler design. In order to solve the problems that an existing design method depends on experience and multi-objective optimization cannot be achieved, the system comprises a tube bundle thermal performance obtaining module, a heat exchange tube bundle thermal performance obtaining module, a heat exchange tube bundle thermal performance obtaining module and a heat exchange tube bundle thermal performance obtaining module, the external constraint and demand input module is used for setting structural parameter constraints and multiple targets such as boiler efficiency, weight, volume and cost; the boiler performance calculation module is used for checking the comprehensive performance of the design scheme; and the structure parameter optimization module is used for converting a multi-objective optimization problem into a single-objective problem to solve by adopting a main objective method, and automatically outputting tube bundle structure parameters which meet constraints and have optimal performance. According to the method, rapid, automatic and global optimization design of the convection bank of the marine auxiliary boiler is realized.

Description

Technical Field

[0001] This invention relates to the field of marine auxiliary boiler equipment technology, and in particular to a design platform for convection tube bundles in marine auxiliary boilers. Background Technology

[0002] Driven by environmental regulations and low-carbon demands, the shipping industry's green transformation and ship replacement cycles have jointly created an urgent need for auxiliary boilers using green fuels such as methanol and ammonia. However, the calorific value of these fuels is significantly lower than that of traditional fuel oil, resulting in a decrease in boiler furnace flame temperature and radiative heat transfer. To ensure boiler efficiency, convective heat transfer must be significantly increased, but the strict size and weight limitations of marine auxiliary boilers preclude the possibility of achieving this goal by simply increasing the number of bare tubes.

[0003] Currently, although various finned tubes are used to enhance heat transfer, traditional design methods have fundamental limitations due to the complexity and diversity of their structural parameters. This method follows a "trial and error" cycle: pre-assuming the structural parameters of the enhanced heat transfer tube, calculating the heat transfer through simulation or existing correlations, and then substituting the results into a thermodynamic program to check the efficiency; if the requirements are not met, the parameters are re-assumed and the cycle repeats. This method has a long design cycle, heavily relies on experience, and the resulting solution can only barely meet the thermal efficiency requirement, without optimization in key performance aspects such as volume, weight, and cost, leaving significant room for improvement. Therefore, this invention provides an integrated design platform for convection tube bundles that can rapidly and synergistically optimize multiple performance aspects. Summary of the Invention

[0004] To address the above technical problems, this invention aims to overcome the shortcomings of existing marine auxiliary boiler convection tube bundle design methods, and solve the technical problems of relying on experience, long design cycles, and only being able to meet thermal efficiency requirements without being able to perform synergistic optimization under multiple objectives such as volume, weight, and cost.

[0005] To address the aforementioned technical problems, this invention provides a design platform for convection tube bundles in marine auxiliary boilers, comprising: a tube bundle thermal performance acquisition module for acquiring thermal performance correlations of enhanced heat transfer tube bundles; an external constraint and demand input module for determining the constraints and objective function for optimization calculations; a boiler performance calculation module for verifying various performance parameters of the auxiliary boiler when using enhanced heat transfer tube bundles with specific structural parameters; and a structural parameter optimization module for calculating the optimal structural parameters of the enhanced heat transfer tube bundles based on the thermal performance correlations, constraints, and objective function.

[0006] The tube bundle thermal performance acquisition module is used to obtain general thermal performance correlations for enhanced heat transfer tube bundles. This module constructs a high-precision model through a combination of experimental testing, simulation, and data fitting. First, heat transfer and pressure drop data of a specific tube bundle under different operating conditions are obtained through experimental setups. Second, a fluid simulation model is established and validated based on the experimental data, and this model is used for large-scale parameter sweep calculations. Finally, the calculation results are converted into dimensionless criterion numbers such as the Nusselt number (Nu) and drag coefficient (f), and regression analysis is used to fit a heat transfer and flow resistance correlation applicable to a wide range of operating conditions.

[0007] External Constraints and Demand Input Module: Used to define the boundary conditions and optimization objectives for the optimization design. The constraints mainly include the range of structural parameters such as pipe wall thickness, pipe diameter, and fin size, as defined by classification society specifications and industry standards; the objective function includes one or more performance indicators such as boiler efficiency, system weight, total volume, and manufacturing cost.

[0008] Boiler Performance Calculation Module: This module is used to verify the overall performance of the entire boiler system after adopting enhanced heat exchange tube bundles with specific structural parameters. It integrates functions such as thermodynamic calculation, hydrodynamic calculation, flue gas resistance calculation, strength calculation, weight and volume estimation, and cost analysis, enabling a comprehensive evaluation of the technical and economic feasibility of the design scheme. In the thermodynamic calculation, the convective heat transfer is directly calculated using the correlation formulas provided by the tube bundle thermal performance acquisition module.

[0009] The structural parameter optimization module performs multi-objective optimization calculations to search for optimal tube bundle structural parameters. This module employs a primary objective method, transforming multiple optimization objectives into a single primary objective function and multiple constraints, thus converting the multi-objective problem into a single-objective problem for solution. If a feasible solution cannot be obtained during the solution process, the system can prompt the user to relax the constraints of secondary objectives.

[0010] Furthermore, the tube bundle thermal performance acquisition module includes: a tube bundle simulation unit, used to establish and correct the simulation model of the enhanced heat transfer tube bundle, and perform large-scale simulation calculations to obtain convective heat transfer coefficient and pressure drop data; and a correlation fitting calculation unit, used to obtain the dimensionless correlation of convective heat transfer and drag pressure drop of the enhanced heat transfer tube bundle based on the convective heat transfer coefficient and pressure drop data through a multiple linear regression method.

[0011] Furthermore, the tube bundle thermal performance acquisition module also acquires data through a tube bundle thermal performance testing device; the testing device is used to measure the heat transfer and pressure drop of an enhanced heat transfer tube bundle with fixed structural parameters but varying number of tube rows at different Reynolds numbers, in order to correct the simulation model established by the tube bundle simulation unit.

[0012] Furthermore, in the external constraint and demand input module, the constraint conditions include strengthening the structural parameter range constraint of the heat exchange tube, and the objective function includes one or more indicators based on boiler performance.

[0013] Furthermore, the structural parameter range constraints include the specified ranges for pipe wall thickness, pipe diameter, and fin size.

[0014] Furthermore, the objective function includes at least one of boiler efficiency, weight, volume, and manufacturing cost; wherein, when multiple objective functions exist, the module is configured to identify one as the primary objective function and convert the remaining objective functions into constraints.

[0015] Furthermore, the performance parameters used by the boiler performance calculation module for verification include at least one of the following: thermal efficiency, flue gas resistance, volume, weight, and manufacturing cost of the convective heating surface.

[0016] Furthermore, the performance parameters verified by the boiler performance calculation module correspond to the objective function set in the external constraint and demand input module.

[0017] Furthermore, the structural parameter optimization module is configured to perform the following operations: transform the multi-objective optimization problem into a single-objective optimization problem, wherein a primary objective function from the external constraint and demand input module is used as the optimization objective, and the remaining secondary objective functions are used as constraints; and call an optimization algorithm to solve the single-objective optimization problem to obtain the optimal structural parameters of the enhanced heat exchange tube bundle.

[0018] The present invention has the following beneficial effects: (1) Standardization and automation of the design process: By establishing a precise thermal performance correlation and an automated optimization process, the over-reliance on the personal experience of designers is overcome, and the design efficiency and consistency of results are significantly improved; (2) Global optimal design scheme: By adopting a multi-objective optimization method, the optimal solution for the main performance indicators can be found under the premise of satisfying all hard constraints, avoiding the drawback that the traditional trial and error method can only obtain "feasible solutions" rather than "optimal solutions"; (3) Accumulation and insight of design knowledge: The system can output the optimal parameter combination and its performance comparison under different requirements, which helps designers to deeply understand the intrinsic relationship between structural parameters and system performance, accelerate talent training and stimulate innovative design. Attached Figure Description

[0019] Reference numerals: 1-Upper boiler drum; 2-Convection heat exchange surface; 3-Lower boiler drum; 4-Deck; 5-Lower header; 6-Burner; 7-Upper header; 8-Chimney.

[0020] Figure 1 This is a schematic block diagram of the marine auxiliary boiler convection tube bundle optimization design platform of the present invention.

[0021] Figure 2 This is a schematic diagram of a marine D-type methanol dual-fuel auxiliary boiler according to an embodiment of the present invention.

[0022] Figure 3 This is a schematic diagram of a marine needle tube according to an embodiment of the present invention. Detailed Implementation

[0023] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0024] Example: Figures 1-3 The diagram illustrates a convection tube bundle design platform for a marine auxiliary boiler. The following description, in conjunction with the accompanying drawings, further illustrates an embodiment of the invention: An existing marine type D oil-fired auxiliary boiler with an operating pressure of 2 MPa and an evaporation capacity of 45 t / h needs to be converted into a methanol / oil dual-fuel auxiliary boiler with the same load. The boiler volume must remain unchanged, the total weight must not exceed the original weight, the thermal efficiency when burning methanol must not be less than 80%, and the flue gas resistance must not exceed the original fan discharge head. A simplified diagram of the boiler structure is shown below. Figure 2 , Figure 2 The flue gas flow direction is indicated in the diagram. A steam outlet is located above the upper drum, and the boiler must meet the requirements of the CCS classification society. Since methanol combustion temperature is lower than fuel oil, radiative heat transfer is reduced. To maintain a thermal efficiency of at least equal to or higher than that of fuel oil before modification, convective heat transfer needs to be increased. Here, needle-shaped tubes are used to replace the original bare tubes in the boiler, enhancing convective heating surface heat transfer and improving boiler thermal efficiency. The task is: based on the requirements, use a reverse design platform to reverse calculate the optimized needle-shaped tube structure parameters that meet the requirements. The needle-shaped tube structure is shown in [reference needed]. Figure 3 .

[0025] First, a needle-shaped tube with defined parameters was selected, and test specimens were fabricated with three tube bundles per single row, arranged in 3, 5, and 9 rows (in parallel). The heat transfer Q and drag pressure drop Δp of the three specimens under different wind velocities were measured using a hot air tunnel test device. The data was saved for comparison and verification with the simulation model results. After the experiment, a simulation calculation model was established according to the experimental conditions. The following turbulence models were selected: standard k-ε, RNG k-ε, standard k-ω, k-ω SST model, and large eddy simulation model. The simulation results were compared with the experimental results; the error should be less than 10%. If the error exceeds 10%, the computational grid and modifiable calculation parameters in the turbulence model were adjusted until the error meets the requirements. After obtaining a reliable simulation model, the arrangement was set to parallel. Following the orthogonal experimental principle, the outer diameter D of the tube, the tube length, the needle diameter d, the needle length l, the needle spacing t, the number of needle rows n, the needle circumference angle α, and the Nusselt number Nu and drag factor corresponding to different numbers of tube rows N were calculated. The thermal dimensionless calculation correlation for needle tube bundles is obtained using a correlation fitting calculation program, as shown in the following equation:

[0026]

[0027]

[0028] In the formula, x1~x8 and y1~y7 are fitting coefficients, and Cs and Cz are the correction coefficients for the tube bundle geometry arrangement and the number of tube rows in the flue gas travel direction, respectively, for the convective heat transfer coefficient h. and These are the correction factors for the tube bundle geometry arrangement and the number of tube rows in the flue gas travel direction, respectively, for the pressure drop Δp. During the simulation, the Reynolds number Re ranges from... This range can cover the Reynolds number of flue gas flow in marine auxiliary boilers; the number of tubes varies from 1 to 15.

[0029] Next, the constraints and external requirements are determined in the "External Constraints and Requirements Input Module". The constraints mainly consider the safety requirements of the classification society and the requirements of the marine auxiliary boiler industry standards. The convection tube bundle design should first meet the safety requirements of the CCS classification society. For pressure-bearing components with a metal temperature greater than 50°C, the allowable stress [σ] is calculated by the following formula, and the smaller value is taken:

[0030]

[0031] In the formula, This refers to the tensile strength of the material at ambient temperature. The yield point or specified non-proportional elongation stress of a material at the metallic temperature of a component; For the material at the component metal temperature Mean breaking stress. From this, the design pressure can be determined. Minimum wall thickness of lower convection tube bundle According to the formula:

[0032]

[0033] Furthermore, regardless of the calculation result above, the minimum pipe wall thickness must not be less than 3 mm. The pipe outer diameter D ranges from 32 to 219 mm; the pipe wall thickness s ≥ 3 mm; the needle fin diameter d ranges from 4 to 8 mm; and the needle fin length l ≤ 60 mm. The external requirements in this example include: thermal efficiency η ≥ 80% in methanol mode; boiler volume remains unchanged after modification (V = V0); boiler weight after modification (M ≤ M0); flue gas resistance after modification (Δp ≤ p0); cost is calculated based on the weight of the needle tube material, with the lowest possible cost; cost is determined as the primary requirement, and all others are secondary requirements.

[0034] Then, a performance verification program library for a methanol dual-fuel auxiliary boiler was established. Since methanol is also a carbon-based fuel, this library integrates industry-standard methods for thermal calculation, hydrodynamic calculation, and flue gas resistance calculation, as well as a strength calculation program based on classification society specifications. After establishing the boiler design calculation program, the dimensionless thermal calculation correlation formula for the needle tube bundle was incorporated into the boiler's thermal calculation program and flue gas resistance calculation program. The boiler volume is determined by the furnace volume and the arrangement of the convection tube bundles. Due to the furnace volume heat load limitations, no modifications were made to the furnace side; therefore, the height of the convection tube bundles was determined. The volume on the convective side remains unchanged. From the transverse pitch of the tube bundle Longitudinal pitch Number of horizontal pipe rows The number of longitudinal tube rows N is determined by, i.e.

[0035]

[0036] For the boiler weight, since only the convection tube bundle changes, it is only necessary to calculate the weight change ΔM on the convection side, the value of which is determined by the following formula:

[0037]

[0038] In the formula, This refers to the total length of the needle-shaped tubes in the convection tube bundle; This represents the total weight of the convection tube bundle before modification. The modification cost W is calculated using the following formula:

[0039]

[0040] In the formula, The cost of modifying the unit weight of needle tubes.

[0041] Finally, the constraints and external requirements are input into the "structural parameter optimization module" to determine the multi-objective optimization problem as follows: The parameters are: pipe outer diameter D, pipe length, needle fin diameter d, needle fin length l, needle fin spacing t, number of needle fin rows n, needle fin circumferential angle a, and lateral pitch. Longitudinal pitch Horizontal row number Number of longitudinal rows N, total pipe length As variables; with wall thickness s≥3 mm and s≥smin, 4 mm≤fin diameter d≤8 mm, and fin length l≤60 mm as constraints; with thermal efficiency η≥80% in methanol mode, and volume = Weight ΔM≤0, flue gas resistance Δp≤p0, hydrodynamic and strength calculations passed. The objective function is used. Constraint methods are used to solve the above multi-objective optimization problem. If the primary objective is to set the others as secondary objectives, then the problem can be transformed into a single-objective optimization problem as follows:

[0042]

[0043]

[0044] The above single-objective optimization problem is solved using an open-source genetic algorithm program. When calculating the function response, a performance verification program library for a methanol dual-fuel auxiliary boiler is called to obtain a convection tube bundle structure that meets the requirements. If the calculation result is an empty set, the volume and weight constraints can be appropriately relaxed, and the solution can be repeated until a reasonable result is obtained.

[0045] The above description is merely a specific embodiment of the present invention, used to fully illustrate the technical solution and practical application process of the present invention. Any adjustments, modifications, or replacements to the system modules made for different boiler models, fuel types, enhanced heat exchange tube forms, or application requirements without departing from the principles of the present invention should be considered to fall within the protection scope of the claims of the present invention.

Claims

1. A design platform for convection tube bundles in marine auxiliary boilers, characterized in that, It includes a tube bundle thermal performance acquisition module, used to obtain the thermal performance correlation of the enhanced heat transfer tube bundle; and an external constraint and demand input module, used to determine the constraint conditions and objective function for optimization calculation; The boiler performance calculation module is used to verify various performance parameters of the auxiliary boiler when using enhanced heat exchange tube bundles with specific structural parameters. And a structural parameter optimization module, used to calculate the optimal structural parameters of the enhanced heat exchange tube bundle based on the thermal performance correlation, constraints and objective function.

2. The marine auxiliary boiler convection tube bundle design platform according to claim 1, characterized in that, The tube bundle thermal performance acquisition module includes: a tube bundle simulation unit, used to establish and correct the simulation model of the enhanced heat transfer tube bundle, and perform large-scale simulation calculations to obtain convective heat transfer coefficient and pressure drop data; and a correlation fitting calculation unit, used to obtain the dimensionless correlation of convective heat transfer and drag pressure drop of the enhanced heat transfer tube bundle based on the convective heat transfer coefficient and pressure drop data through a multiple linear regression method.

3. The marine auxiliary boiler convection tube bundle design platform according to claim 2, characterized in that: The tube bundle thermal performance acquisition module also acquires data through a tube bundle thermal performance testing device; the testing device is used to measure the heat transfer and pressure drop of an enhanced heat transfer tube bundle with fixed structural parameters but varying number of tube rows at different Reynolds numbers, in order to correct the simulation model established by the tube bundle simulation unit.

4. The marine auxiliary boiler convection tube bundle design platform according to claim 1, characterized in that: In the external constraint and demand input module, the constraint conditions include strengthening the structural parameter range constraint of the heat exchange tube, and the objective function includes one or more indicators based on boiler performance.

5. The marine auxiliary boiler convection tube bundle design platform according to claim 4, characterized in that: The structural parameter range constraints include the specified ranges for pipe wall thickness, pipe diameter, and fin size.

6. The marine auxiliary boiler convection tube bundle design platform according to claim 4, characterized in that: The objective function includes at least one of boiler efficiency, weight, volume, and manufacturing cost; wherein, when there are multiple objective functions, the module is configured to identify one as the primary objective function and convert the remaining objective functions into constraints.

7. The marine auxiliary boiler convection tube bundle design platform according to claim 1, characterized in that: The boiler performance calculation module is used to verify performance parameters including at least one of the following: thermal efficiency, flue gas resistance, volume, weight, and manufacturing cost of the convective heating surface.

8. The marine auxiliary boiler convection tube bundle design platform according to claim 7, characterized in that: The performance parameters verified by the boiler performance calculation module correspond to the objective function set in the external constraints and demand input module.

9. The marine auxiliary boiler convection tube bundle design platform according to claim 1, characterized in that: The structural parameter optimization module is configured to perform the following operations: transform the multi-objective optimization problem into a single-objective optimization problem, wherein a primary objective function from the external constraint and demand input module is used as the optimization objective, and the remaining secondary objective functions are used as constraints; and call an optimization algorithm to solve the single-objective optimization problem to obtain the optimal structural parameters of the enhanced heat exchange tube bundle.

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