Method and system for evaluating feasibility of waste heat recovery of coal-fired power plant

Abstract

The invention belongs to the technical field of waste heat recovery, and discloses a coal-fired power plant waste heat recovery feasibility assessment method and system.The coal-fired power plant waste heat recovery feasibility assessment method and system can accurately identify the type and the recoverable amount of coal-fired power plant waste heat, formulate a reasonable waste heat recovery scheme, effectively improve the energy utilization efficiency and reduce energy waste through the links of pre-assessment and the like of the system; and a remarkable energy-saving effect is achieved. The LCA analysis can comprehensively quantify various influences of the waste heat recovery scheme on the environment, and a scientific basis is provided for evaluating the environmental protection property of the scheme. By optimizing the scheme, carbon emission and emission of other pollutants can be effectively reduced, a good environmental protection effect is achieved, and related environmental protection standard requirements are met. The TEA analysis can comprehensively consider the profit amount of the waste heat recovery scheme and the output amount brought by the environmental protection benefit, and evaluates the economic feasibility of the scheme based on various economic indexes. According to the method, a scientific and reasonable basis is provided for decision-making of a waste heat recovery project of the coal-fired power plant, and coordinated development and sustainable development of energy, environment and economy are achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of waste heat recovery, and particularly relates to a method and system for evaluating the feasibility of waste heat recovery in a coal-fired power plant. BACKGROUND

[0002] During the operation of a coal-fired power plant, a large amount of waste heat is generated. If this waste heat is not effectively recovered and utilized, it not only causes energy waste, but also increases carbon emissions and has a negative impact on the environment. At the same time, with the growth of energy demand and the improvement of environmental protection requirements, how to efficiently recover waste heat from coal-fired power plants to achieve energy saving and emission reduction and obtain good economic benefits has become an important problem in the current energy field. At present, there are relevant waste heat recovery standards, but the scales of coal-fired power plants around the world are not the same. The existing various standards only have good applicability for waste heat recovery of some power plants, and lack a systematic and comprehensive waste heat recovery evaluation and scheme design method for the actual situation of all kinds of different coal-fired power plants to scientifically and reasonably determine and evaluate whether to recover waste heat and how to recover it.

[0003] In the prior art, a relatively close method is a coal-fired power plant flue gas waste heat and water recovery system, such as an existing utility model patent. The system generally includes a boiler, an air preheater, a dust collector, a desulfurization tower, a chimney, a steam turbine and its cooling waste heat device, and a waste heat recovery system is additionally provided between the air preheater and the dust collector, and a water recovery system is configured between the desulfurization tower and the chimney to realize the recovery and utilization of flue gas waste heat and water. This technical route has played a certain role in improving energy utilization.

[0004] However, the above-mentioned prior art mainly focuses on the structural design of the waste heat recovery device and its process flow, and still lacks several key links: firstly, there is a lack of quantifiable pre-evaluation model in the evaluation stage, which cannot systematically judge the recovery potential of different waste heat sources (such as flue gas, circulating water, furnace body, slag, etc.); secondly, a multi-objective comprehensive analysis framework has not been established in the scheme selection and optimization stage, especially the energy saving, environmental benefits and economy have not been uniformly included in the life cycle evaluation, technical and economic analysis and weight balancing system, so a complete "evaluation-optimization-decision" closed loop logic has not been formed. This makes it difficult for the existing technology to achieve single-point or multi-point recovery of waste heat and water, but there are still obvious deficiencies in systematization, evaluation depth and comprehensive decision-making ability.

[0005] In addition, in the existing literature and patent layout, there are also some schemes involving the simultaneous recovery of multiple waste heat. For example, the application number CN201911070897.4 of a power plant waste heat recovery system capable of double-effect operation can recover two types of waste heat at the same time; for example, the application number CN202411879048.4 of a power plant waste heat recovery system and recovery method realizes the collaborative recovery of four types of waste heat. This kind of technical scheme has made certain progress in multi-source waste heat recovery, but still cannot break through the limitations of the lack of evaluation system and comprehensive optimization method. SUMMARY

[0006] In view of the problems existing in the prior art, the present application provides an evaluation method for the feasibility of waste heat recovery in a coal-fired power plant.

[0007] The present application is implemented as follows: an evaluation method for the feasibility of waste heat recovery in a coal-fired power plant, comprising the following steps:

[0008] Step one, determine the evaluation basis, determine the waste heat recovery evaluation requirements through national standards, industry specifications and local regulations;

[0009] Step two, perform pre-evaluation, calculate the recoverable waste heat and waste heat types according to the installed capacity, coal quality, energy consumption and equipment operating parameters of the coal-fired power plant, and determine whether the waste heat recovery pre-evaluation requirements are met;

[0010] Step three, develop a scheme, determine the waste heat recovery sub-scheme for flue gas, circulating water, furnace body and slag for the coal-fired power plant that meets the pre-evaluation requirements, and compile a preliminary comprehensive scheme;

[0011] Step four, analysis and optimization, perform energy saving analysis, life cycle assessment analysis and technical and economic analysis on the preliminary comprehensive scheme, and optimize the energy saving, environmental protection and economy according to the analysis results;

[0012] Step five, trade-off analysis, perform multi-objective weight analysis on energy saving, environmental protection and economy, and form a trade-off result;

[0013] Step six, determine the final scheme, determine the comprehensive weight according to the trade-off result, and output the final waste heat recovery scheme.

[0014] Further, step one compares national standards, industry specifications and local regulations to establish a basic database for waste heat recovery evaluation, and provides a unified evaluation criterion for subsequent evaluation.

[0015] Further, step two calculates the flue gas waste heat, circulating water waste heat, furnace body waste heat and slag waste heat by establishing a quantitative model, and uses threshold to judge the waste heat recovery potential.

[0016] Further, in step three, for the flue gas waste heat part, the recovery object is the flue gas waste heat after passing through the coal economizer and the air preheater, i.e., before entering the chimney, the flue gas temperature is generally in the range of 100-200 DEG C, which is suitable for high-efficiency recovery by using the absorption heat pump scheme; for the circulating water waste heat part, it is appropriate to use the heat exchanger scheme to realize heat transfer; for the furnace body waste heat part, the surface waste heat recovery device scheme is adopted; for the slag waste heat part, the dry slag discharge waste heat recovery device scheme is adopted, and the operability of each sub-scheme is evaluated.

[0017] Further, in step four, the energy-saving analysis is performed by comparing the total waste heat under the non-recovery condition and the total recovery amount after adopting the recovery scheme, and then calculating the waste heat recovery potential; the life cycle assessment analysis evaluates the environmental impact according to the global warming potential, the ozone layer depletion potential, the acidification potential and the eutrophication potential; the technical and economic analysis calculates the economic indicators according to the total investment, the energy-saving benefits and the policy subsidies, and performs the sensitivity analysis.

[0018] Further, in step five, the analytic hierarchy process is used to calculate the weights of energy-saving, environmental protection and economy, and according to the weights, the scheme parameters are adjusted to maximize the comprehensive benefits.

[0019] The application also provides an evaluation system for the feasibility of waste heat recovery in a coal-fired power plant, comprising:

[0020] A standard reference module is used to obtain the waste heat recovery evaluation requirements.

[0021] A pre-evaluation module is used to calculate the recoverable waste heat and the waste heat type according to the installed capacity, the coal quality, the energy consumption and the equipment operation parameters of the coal-fired power plant, and to determine whether the waste heat recovery pre-evaluation requirements are met.

[0022] A scheme development module is used to determine the waste heat recovery sub-schemes for flue gas, circulating water, furnace body and slag for the coal-fired power plant meeting the pre-evaluation requirements, and to form a preliminary comprehensive scheme.

[0023] An analysis and optimization module is used to perform energy-saving analysis, life cycle assessment analysis and technical and economic analysis on the preliminary comprehensive scheme, and to optimize the energy-saving, environmental protection and economy according to the analysis results.

[0024] A trade-off analysis module is used to perform multi-objective weight analysis on the energy-saving, environmental protection and economy, and to form a trade-off result.

[0025] A final scheme module is used to determine the final scheme, to determine the comprehensive weight according to the trade-off result, and to output the final waste heat recovery scheme.

[0026] The above modules are connected through a data bus and cooperatively output the final waste heat recovery scheme.

[0027] Further, the pre-evaluation module comprises a data acquisition unit and a residual heat amount calculation unit, the data acquisition unit is used for acquiring installed capacity, coal quality, energy consumption and equipment operation parameters, and the residual heat amount calculation unit is used for calculating flue gas residual heat amount, circulating water residual heat amount, furnace body residual heat amount and slag residual heat amount according to the data.

[0028] Further, the analysis optimization module comprises an energy-saving analysis unit, a life cycle assessment unit and a technical economic analysis unit, the energy-saving analysis unit is used for outputting residual heat recovery potential, the life cycle assessment unit is used for outputting environmental impact assessment results, and the technical economic analysis unit is used for outputting economic indicators and providing sensitivity analysis results.

[0029] Further, the trade-off analysis module is used for calculating the weights of energy-saving performance, environmental protection performance and economic performance by using the analytic hierarchy process, and adjusting scheme parameters according to the weights to realize maximum comprehensive benefits.

[0030] In combination with the above technical solutions and the technical problems solved, the technical solutions to be protected by the present application have the following advantages and positive effects:

[0031] Through the pre-evaluation, energy-saving evaluation and other links of the system, the types and recoverable amounts of residual heat of the coal-fired power plant can be accurately identified, a reasonable residual heat recovery scheme can be formulated, energy utilization efficiency can be effectively improved, energy waste can be reduced, and significant energy-saving effects can be realized.

[0032] The LCA analysis can quantitatively evaluate various environmental impacts of the residual heat recovery scheme, including greenhouse gas emissions, resource consumption, toxic substance release and other factors, and provide a scientific basis for evaluating the environmental protection performance of the scheme. Through optimization of the scheme, carbon emissions and other pollutant emissions can be effectively reduced, good environmental protection effects can be achieved, and relevant environmental protection standards can be met.

[0033] The TEA analysis can comprehensively consider the total capital investment of the residual heat recovery scheme, the profit brought by energy-saving benefits and the output brought by environmental protection benefits, and evaluate the economic feasibility of the scheme through various economic indicators. In combination with sensitivity analysis, the scheme can be further optimized to improve economic benefits, so that the residual heat recovery project is optimal in economy.

[0034] The comprehensive evaluation link combines the results of energy, environmental and economic benefits to analyze the weights, can obtain comprehensive and objective comprehensive evaluation results according to the actual situation of the power plant, provides a scientific and reasonable basis for the decision of the residual heat recovery project of the coal-fired power plant, realizes the coordinated development of energy, environment and economy, and promotes the wide application and sustainable development of the residual heat recovery technology of the coal-fired power plant. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 It is the evaluation method flowchart of the feasibility of the residual heat recovery of the coal-fired power plant provided by the embodiment of the present application.

[0036] Figure 2 is the system structure block diagram of the evaluation of the feasibility of waste heat recovery of a coal-fired power plant provided by the embodiment of the present application.

[0037] Figure 3 is the detailed flow chart of the evaluation method of the waste heat recovery scheme of the coal-fired power plant provided by the embodiment of the present application. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0039] At present, there is a problem of inefficient utilization of heat energy in the power generation process of coal-fired power plants, especially a large amount of low-grade waste heat generated in the links of flue gas, circulating water, slag, etc. is not effectively utilized, resulting in low system comprehensive energy efficiency and high carbon emission intensity, which does not meet the requirements of energy efficiency improvement and pollutant co-emission reduction under the "double carbon" target. The existing waste heat recovery design generally lacks systematic and index-based preliminary selection and evaluation mechanism, often based on experience judgment or local economic calculation, lacking comprehensive consideration of energy saving potential, environmental performance and life cycle economic benefit, which is easy to cause technical selection deviation and resource investment waste. Therefore, a systematic and scientific waste heat recovery feasibility evaluation method is urgently needed to improve the precision of technology application and the scientificity of investment decision.

[0040] The evaluation model of the feasibility of waste heat recovery of a coal-fired power plant proposed in the present application solves the key problems of dispersed evaluation process, non-uniform index system and lack of environmental and economic dimensions in the existing waste heat recovery practice through the six-step closed-loop process of "pre-evaluation-scheme design-energy efficiency analysis-LCA-TEA-comprehensive evaluation". In the pre-evaluation link, the data-driven heat loss identification and distribution model is constructed by introducing parameters such as installed capacity, boiler type, low calorific value of coal, ash content and volatile matter of coal fed into the furnace, turbine back pressure level, feed water temperature, deaerator arrangement, etc., to quickly locate the heat nodes with recovery potential.

[0041] In the energy saving evaluation stage, the energy efficiency evaluation method combining the first law of thermodynamics with the second law of thermodynamics is adopted, the calculation model of waste heat recovery rate and equivalent coal consumption reduction rate within the system boundary is constructed, and further consideration is given to the heat exchange efficiency, system pressure drop and temperature and enthalpy value change of the medium after recovery of various heat exchanger arrangement forms (including circulating water heat exchange, low-temperature coal economizer, heat pump heat recovery, etc.), so as to realize the fine energy balance analysis and scheme optimization of the waste heat recovery subsystem.

[0042] In the environmental impact assessment, combined with the life cycle assessment method, the intensity of the comprehensive carbon footprint and pollutant emissions (including sulfur dioxide, nitrogen oxides, inhalable particulate matter) of the "baseline operating condition" and "waste heat recovery operating condition" is quantified and compared under the unified function unit and accounting boundary, and the influence on the environment, human health and resource consumption is further compared and analyzed.

[0043] In the economic evaluation aspect, the technical and economic analysis model is adopted, the initial investment, operation and maintenance cost, system life, annual saved standard coal quantity and unit coal price of the scheme are introduced into the calculation formula of net present value, investment recovery period and internal rate of return, and the carbon price factor is introduced at the same time, additional income under the influence of carbon trading mechanism is simulated, and therefore the timeliness and adaptability of the economic evaluation of the scheme are improved.

[0044] Finally, in the comprehensive evaluation stage, a three-dimensional matrix scoring system is proposed, the energy saving index (i.e. energy efficiency improvement rate), environmental index (i.e. carbon dioxide emission reduction equivalent) and economic index (i.e. net present value and internal rate of return) are normalized and weighted to calculate a comprehensive optimization index, and a multi-objective decision method (such as TOPSIS or AHP) is used to realize the sorting and screening of the alternative schemes, so that the evaluation result has the decision guidance value of engineering landing.

[0045] The evaluation model and method not only consider the three attributes of engineering technology, environmental impact and economic benefit, but also form a universal waste heat recovery decision tool suitable for multiple types of coal-fired units through the standardized evaluation process and parameter model nesting, which significantly improves the scientificity and systematicness of the existing waste heat recovery design, and effectively solves the actual problems of unclear technical path, resource waste and large evaluation deviation in the energy saving reconstruction practice of coal-fired power plants.

[0046] As shown in Figure 1 , Figure 3 The evaluation method for the waste heat recovery feasibility of the coal-fired power plant provided by the embodiment of the present application comprises the following steps:

[0047] S101, determining the evaluation basis, determining the waste heat recovery evaluation requirements through national standards, industry specifications and local regulations;

[0048] S102, performing pre-evaluation, calculating the recoverable waste heat and waste heat types according to the installed capacity, coal quality, energy consumption and equipment operation parameters of the coal-fired power plant, and judging whether the pre-evaluation requirements of waste heat recovery are met;

[0049] S103, formulating a scheme, determining waste heat recovery sub-schemes for flue gas, circulating water, furnace body and slag for the coal-fired power plant meeting the pre-evaluation requirements, and collecting and forming a preliminary comprehensive scheme;

[0050] S104, analysis and optimization, energy-saving analysis, life cycle assessment analysis and technical and economic analysis are carried out on the preliminary comprehensive scheme, and the energy-saving, environmental protection and economy are optimized according to the analysis results;

[0051] S105, trade-off analysis, multi-objective weight analysis is carried out on energy-saving, environmental protection and economy, and trade-off results are formed;

[0052] S106, determine the final scheme, determine the comprehensive weight according to the trade-off result, and output the final waste heat recovery scheme.

[0053] The S102 provided by the embodiment of the present application calculates the flue gas waste heat, the circulating water waste heat, the furnace body waste heat and the slag waste heat by establishing a quantitative model, and uses a threshold to judge the waste heat recovery potential.

[0054] The S103 provided by the embodiment of the present application is for the flue gas waste heat part, the recovery object is the flue gas waste heat after passing through the coal economizer and the air preheater, that is, before entering the chimney, the flue gas temperature is generally in the range of 100-200℃, which is suitable for using the absorption heat pump scheme for efficient recovery; for the circulating water waste heat part, it is appropriate to use the heat exchanger scheme to realize heat transfer; for the furnace body waste heat part, the surface waste heat recovery device scheme is still used; for the slag waste heat part, the dry slag discharge waste heat recovery device scheme is used, and the operability of each sub-scheme is evaluated.

[0055] The energy-saving analysis in S104 provided by the embodiment of the present application calculates the waste heat recovery potential by comparing the total waste heat under the condition of not recovering with the total recovery amount after adopting the recovery scheme; the life cycle assessment analysis evaluates the environmental impact according to the global warming potential, the ozone layer depletion potential, the acidification potential and the eutrophication potential; the technical and economic analysis calculates the economic indicators according to the total investment, energy-saving benefits and policy subsidies and performs sensitivity analysis.

[0056] The S105 provided by the embodiment of the present application uses the analytic hierarchy process to calculate the weights of energy-saving, environmental protection and economy, and adjusts the scheme parameters according to the weights to maximize the comprehensive benefits.

[0057] The S105 provided by the embodiment of the present application uses the analytic hierarchy process to calculate the weights of energy-saving, environmental protection and economy, and adjusts the scheme parameters according to the weights to maximize the comprehensive benefits.

[0058] (1) Calculate each type of waste heat without waste heat recovery scheme, and sum them up;

[0059] 1) Flue gas residual heat quantity calculation

[0060] Boiler input heat quantity Q in Calculation formula: Q in = B x Q net,ar , wherein B is annual fuel consumption (kg), Q net,ar is fuel received-based high calorific value (kJ / kg);

[0061] Flue gas heat loss q2 calculation formula (calculated according to boiler heat balance): wherein I py is flue gas enthalpy (kJ / kg), a py is excess air coefficient at flue gas, I lk is cold air enthalpy (kJ / kg);

[0062] Flue gas residual heat quantity Q yq Calculation formula: (yearly flue gas residual heat quantity, unit: kJ / year), if conversion to GJ / year is needed, Q yq (GJ) = Q yq (kJ) ÷ 10 6 ;

[0063] 2) Circulating water residual heat quantity calculation

[0064] Circulating water taken heat quantity Q xs Calculation formula: Q xs = G x c x At, wherein G is circulating water mass flow (kg / s), c is specific heat capacity of water (4.1868 kJ / (kg·℃)), and At is circulating water inlet and outlet temperature difference (℃);

[0065] Annual circulating water residual heat quantity Q xs,year Calculation formula: Q xs,yea r = Q xs x 3600 x t, wherein t is annual operation time (h); Q xs,year (GJ) = Q xs,year (kJ) ÷ 10 6 ;

[0066] 3) Furnace body residual heat quantity calculation

[0067] Furnace body surface heat loss q5 calculation formula (calculated according to boiler heat balance): wherein Q5 is furnace body surface heat loss heat quantity (kJ / kg fuel);

[0068] Furnace body residual heat quantity Q lt Calculation formula: (yearly furnace body residual heat quantity, unit: kJ / year), Q lt (GJ) = Q lt (kJ) ÷ 106 ;

[0069] 4) Slag heat recovery amount calculation

[0070] Heat taken away by slag Q lz Calculation formula: Where A ar is the fuel received-based ash content (%), C lz is the combustible content in slag (%), ΔH lz is the heat of combustion of combustible in slag (kJ / kg);

[0071] Annual slag heat recovery amount Q lz,year Calculation formula: (B year is the annual fuel consumption, kg), Q lz,year (GJ) = Q lz,year (kJ) ÷ 10 6 ;

[0072] Total heat Q without taking the heat recovery scheme total,no-recovery Calculation formula: Q total,no-recovery = Q yq + Q xs,year + Q lt + Q lz,year (unit: GJ / year)

[0073] (2) According to the scheme determined in 3, the amount of each kind of heat recovery is calculated in detail, and summed up;

[0074] 1) Flue gas heat recovery amount Q yq,recovery Calculation

[0075] If low-temperature economizer technology is adopted, according to the heat exchanger efficiency η yq and the flue gas heat Q yq , the calculation is: Q yq,recovery = Q yq × η yq (unit: GJ / year)

[0076] 2) Circulating water heat recovery amount Q xs,recovery Calculation

[0077] If heat pump technology is adopted, according to the heat pump performance coefficient COP and the circulating water heat Q xs,year , the recoverable heat (heat extracted from circulating water by heat pump) is calculated: (unit: GJ / year)

[0078] 3) Furnace body heat recovery amount Q lt,recovery Calculation

[0079] If the furnace body surface is equipped with a heat recovery device, according to the recovery device efficiency ηlt and the furnace body residual heat amount Q lt Calculation: Q lt,recovery = Q t x η lt (unit: GJ / year)

[0080] 4) Slag residual heat recovery amount Q lz,recovery Calculation

[0081] If the slag dry slagging machine residual heat recovery technology is used, according to the recovery efficiency η lz and the slag residual heat amount Q lz,year Calculation: Q lz,recovery = Q lz,year x η lz (unit: GJ / year)

[0082] Total recovery amount Q when the residual heat recovery scheme is adopted total,recovery Calculation formula: Q total,recovery = Q yq,recovery + Q xs,recovery + Q lt,recovery + Q lz,recovery (unit: GJ / year)

[0083] (3) Residual heat recovery potential: the value of (1) minus the value of (2);

[0084] Residual heat recovery potential Q potential Calculation formula Q potential = Q total,no-recovery - Q total,recovery (unit: GJ / year)

[0085] (4) According to the residual heat recovery potential, whether energy saving is evaluated, and whether optimization is possible; if the residual heat recovery scheme is optimized under the premise that the scheme is feasible;

[0086] (5) The energy saving evaluation result is proposed.

[0087] The final scheme provided by the embodiment of the present application is determined: for the power plant through pre-evaluation, further determine the corresponding residual heat recovery scheme (each scheme is according to the residual heat type and recovery target, such as used for heating or used for power generation; heat transfer or heat work, etc. Different angles, etc.), and the following work is done:

[0088] (1) Flue gas residual heat recovery scheme

[0089] (2) Circulating water residual heat recovery scheme

[0090] (3) Furnace body residual heat recovery scheme

[0091] (4) Slag residual heat recovery scheme

[0092] (5) Evaluate the operability of each scheme, determine whether it is feasible in practical application. Unfeasible further optimization scheme. Feasible into energy saving evaluation link.

[0093] The analysis and optimization provided by the embodiments of the present application:

[0094] 1) Target and scope determination: including analysis target, functional unit, accounting boundary, data quality requirements;

[0095] 2) Inventory analysis

[0096] 3) Impact assessment (completed by SimaPro, OpenLCA and other software)

[0097] Quantify the impact of factors such as greenhouse gas emissions, resource consumption, toxic substance release, etc. on the environment and human health, such as global warming potential (GWP), ozone depletion potential (ODP), acidification potential (AP), eutrophication potential (EP), etc.

[0098] Measure the severity of specific environmental problems in combination with each impact category. Characterization of evaluation results (Characterization) by using specific models and category indicators, various emissions and resource consumption are converted into common measurement units under corresponding impact categories. For example, carbon dioxide, methane and other greenhouse gases can be converted into carbon dioxide equivalents to measure their contribution to global warming), normalization (Normalization provides a reference benchmark so that the results between different impact categories can be compared. Usually, the impact of each category is compared with the total annual impact of a certain region (such as Europe or the world).

[0099] Summarize environmental impact: Interpretation (Interpretation) According to the collected and analyzed data, draw conclusions and provide suggestions.

[0100] 4) Sensitivity analysis, uncertainty analysis, result interpretation, report preparation.

[0101] 5) According to the relevant environmental protection standards, determine whether it meets the requirements, and analyze whether the scheme can be further optimized.

[0102] 6) Propose environmental assessment results;

[0103] The TEA analysis

[0104] According to the determined waste heat recovery scheme, calculate the total capital investment;

[0105] According to the energy saving benefit, convert the profit brought by the energy saving potential;

[0106] According to the environmental protection benefit, combined with relevant government subsidies, green credit, etc., convert the corresponding output;

[0107] Make various (according to the needs of selection, such as static evaluation, dynamic evaluation, investment recovery period, net present value and the like) economic index evaluation;

[0108] Combined with sensitivity analysis, check whether the economic benefit can be further improved through scheme optimization.

[0109] Propose economic evaluation results.

[0110] The comprehensive evaluation provided by the embodiment of the present application combines the results of energy benefit, environmental benefit and economic benefit, does weight analysis, and determines the comprehensive evaluation result according to the actual power plant.

[0111] The ISO 14040 series standards establish a complete system for life cycle assessment (LCA) research. First, ISO 14040:2006, as a programmatic document, clearly defines the basic concepts, principles and four main stages of LCA, namely, target and scope definition, inventory analysis, impact assessment and result interpretation. This framework ensures that researchers can start with a unified logic in different situations, so that different studies are comparable and consistent.

[0112] Second, ISO 14044:2006 refines the framework of 14040 and specifies the specific operation requirements of each stage. It not only puts forward requirements for the definition of target and scope, the setting of functional unit and system boundary, but also gives systematic guidelines for data collection and allocation of inventory analysis, methods and indicators of impact assessment, and report and decision support of result interpretation, so that LCA research has clear operability.

[0113] At the same time, ISO / TR 14047:2003 and ISO / TR 14049:2012 provide supplementary instructions for example and case study. The former shows how to apply ISO 14040 and 14044 standards through actual cases in different industries, helping researchers intuitively understand the operation process of LCA; the latter focuses on the definition of target and scope and the inventory analysis of two key stages, and shows how to reasonably determine the research boundary and data processing method through examples, providing practice-oriented reference for actual research.

[0114] In addition, ISO 14071:2014 specifies the process of key review and the ability requirements of reviewers for quality assurance of research. Through systematic review of target and scope, data quality, impact assessment method and result interpretation, the scientificity and credibility of research results are guaranteed, and method bias and conclusion distortion are avoided. This standard strengthens the credibility of LCA.

[0115] Finally, ISO / TS 14072:2014 sets forth requirements and guidelines for information exchange, emphasizing that research findings should be presented in a clear, transparent, and standardized manner when reported and disseminated. It not only standardizes the content, format, and visualization of reports but also emphasizes effective communication with stakeholders, ensuring that LCA results are correctly understood and applied, providing solid support for policy-making, industry decision-making, and environmental management. In the aforementioned TEA (Technology-Economic Analysis) process, the total capital investment is first calculated based on the waste heat recovery scheme, and then the potential profit from energy-saving benefits is converted into the actual profit. Simultaneously, environmental benefits are combined with relevant policy support, including government subsidies and green credits, and converted into corresponding outputs. By comparing the energy and environmental benefits with the total investment, the basic data for economic benefit evaluation is formed.

[0116] Furthermore, appropriate economic evaluation methods are selected based on different needs, such as static evaluation, dynamic evaluation, investment payback period, net present value, and other indicators. Sensitivity analysis is then combined to examine the impact of changes in key parameters on the results, so as to test the stability and feasibility of the scheme under different operating conditions, thereby providing a basis for scheme optimization and risk control.

[0117] Finally, a weighted analysis of the energy, environmental, and economic benefits is conducted, and a comprehensive evaluation conclusion is drawn by considering the specific operating conditions and actual circumstances of the power plant. This conclusion can provide scientific decision-making support for power plants in the selection and implementation of waste heat recovery technologies, ensuring that the solution achieves both energy conservation and emission reduction effects and reasonable investment.

[0118] In the aforementioned TEA (Technology and Economic Analysis) process, the total capital investment is first calculated based on the waste heat recovery scheme, and then the potential profit from energy-saving benefits is calculated accordingly. Simultaneously, environmental benefits are combined with relevant policy support, including government subsidies and green credit, and converted into corresponding output. By comparing the energy and environmental benefits with the total investment, the basic data for economic benefit evaluation is formed. Appropriate economic evaluation methods are selected based on different needs, such as static evaluation, dynamic evaluation, investment payback period, and net present value indicators. Sensitivity analysis is combined to examine the impact of changes in key parameters on the results, verifying the stability and feasibility of the scheme under different operating conditions, thus providing a basis for scheme optimization and risk control. The results of energy benefits, environmental benefits, and economic benefits are weighted and analyzed, combined with the specific operating conditions and actual situation of the power plant, to arrive at a comprehensive evaluation conclusion. This conclusion can provide scientific decision-making support for power plants in the selection and implementation of waste heat recovery technology, ensuring that the scheme has both energy-saving and emission-reduction effects and investment rationality.

[0119] like Figure 2 As shown in the embodiment of the present invention, a feasibility assessment system for waste heat recovery from coal-fired power plants includes:

[0120] a standard reference module for obtaining waste heat recovery evaluation requirements;

[0121] a pre-evaluation module for calculating recoverable waste heat and waste heat types according to the installed capacity, coal quality, energy consumption and equipment operation parameters of the coal-fired power plant, and judging whether the pre-evaluation requirements are met;

[0122] a scheme development module for determining waste heat recovery sub-schemes for flue gas, circulating water, furnace body and slag of the coal-fired power plant meeting the pre-evaluation requirements, and summarizing the preliminary comprehensive scheme;

[0123] an analysis and optimization module for performing energy saving analysis, life cycle assessment analysis and technical and economic analysis on the preliminary comprehensive scheme, and optimizing the energy saving, environmental protection and economy according to the analysis results;

[0124] a trade-off analysis module for performing multi-objective weight analysis on the energy saving, environmental protection and economy, and forming a trade-off result;

[0125] a final scheme module for determining a final scheme, determining a comprehensive weight according to the trade-off result, and outputting a final waste heat recovery scheme;

[0126] The above modules are connected through a data bus and cooperatively output the final waste heat recovery scheme.

[0127] Further, the pre-evaluation module includes a data acquisition unit and a waste heat quantity calculation unit, the data acquisition unit is used to acquire the installed capacity, coal quality, energy consumption and equipment operation parameters, and the waste heat quantity calculation unit is used to calculate the flue gas waste heat quantity, circulating water waste heat quantity, furnace body waste heat quantity and slag waste heat quantity according to the data.

[0128] The evaluation system for the feasibility of waste heat recovery of the coal-fired power plant proposed in the embodiment adopts modular design in architecture, different modules are independent in function, but realize logical cooperation through the data bus, and ensure the complete closed loop from the acquisition of evaluation basis, quantitative calculation of waste heat quantity to generation, optimization and trade-off of the comprehensive scheme. The system emphasizes standardization, scalability and compatibility in the design process, and can adapt to coal-fired power plants of different scales, different coal qualities and operating conditions.

[0129] In specific functions, the standard reference module undertakes the import function of normative constraints, and combines policy compliance with engineering evaluation by analyzing national standards, industry specifications and local management requirements. The module not only provides the basic judgment criteria for waste heat recovery, but also provides parameter boundary conditions for subsequent model calculation, so that the evaluation system has consistency and authority.

[0130] The pre-evaluation module is composed of a data acquisition unit and a residual heat amount calculation unit. The data acquisition unit can extract the installed capacity, coal quality composition, energy consumption level and operation parameters of main equipment from the operation monitoring system of the power plant. The residual heat amount calculation unit calculates the potential residual heat amounts of flue gas, circulating water, furnace heat dissipation and slag sensible heat based on thermodynamic formulas and energy balance models, forming a multi-dimensional energy database. Through a threshold judgment mechanism, this module can quickly screen out residual heat sources with recycling value, providing quantitative basis for scheme development.

[0131] After obtaining the recoverable potential of various residual heat sources, the scheme development module matches suitable recycling technology paths according to different residual heat characteristics. The system can automatically generate multiple sub-schemes including low-temperature coal economizer, heat pump recovery, furnace heat exchange device and dry slag discharge device, and integrate them into a preliminary comprehensive scheme. This module not only supports independent evaluation of single process path, but also can combine and compare multiple schemes to ensure the comprehensiveness and technical adaptability of the scheme.

[0132] The analysis and optimization module is further refined into an energy-saving analysis unit, a life cycle assessment unit and a technical and economic analysis unit. The energy-saving analysis unit outputs the residual heat recovery potential by comparing the energy efficiency changes under different schemes; the life cycle assessment unit calculates environmental indicators such as global warming potential, acidification potential and eutrophication potential based on the ISO 14040 series standards; the technical and economic analysis unit outputs core economic indicators such as net present value and investment recovery period by combining investment cost, operating income, subsidy policy and sensitivity parameters, providing quantitative support for final decision-making.

[0133] The trade-off analysis module converts energy-saving, environmental protection and economy into comparable weight factors based on the analytic hierarchy process, forming a multi-objective comprehensive evaluation matrix. The system can dynamically adjust the weight proportion of each index according to the energy price, environmental constraints and policy orientation of the power plant location, and give the optimal trade-off result on this basis. This process ensures that the final scheme not only meets the goal of improving energy utilization efficiency, but also takes into account environmental and economic constraints, and has the implementability of industrial application.

[0134] The final scheme module outputs the optimal residual heat recovery scheme based on the results of the aforementioned trade-off analysis, and generates a complete decision support report. This report covers energy-saving benefit prediction, environmental benefit evaluation and economic return analysis, and can also provide parameterized reference for engineering implementation. To realize the automatic operation of the whole process, the present application also proposes a computer readable storage medium having a executable program stored thereon, which can execute the method steps in sequence when run on a processor; at the same time, the present application also provides an electronic device comprising a processor, a memory and the above computer readable storage medium, which can complete the whole set of residual heat recovery evaluation process in a hardware environment, thereby realizing the complete landing of the method to the system.

[0135] Embodiment

[0136] A certain coal-fired power plant has a installed capacity of 600 MW, and the annual operating time is about 5500 hours. The current energy consumption and emission indicators are relatively high. In response to the energy saving and emission reduction policy, and to improve energy utilization efficiency, the above technical solution is used to evaluate and design the waste heat recovery of the power plant.

[0137] Implementation steps and effects

[0138] 1. Determine the pre-evaluation requirements

[0139] According to the relevant waste heat recovery standards of the state and local, such as "Industrial Waste Heat Resource Evaluation Method" (GB / T1028-2018), the calculation method and evaluation standard of each index of energy saving potential, environmental protection effect and economic benefit in pre-evaluation are determined. For example, the energy saving potential is measured by the proportion of recoverable waste heat to total energy consumption; the environmental protection effect is measured by the carbon dioxide emission reduction per unit of electricity generation; and the economic benefit is measured by the static rate of return, net present value, investment recovery period and other indicators.

[0140] 2. Pre-evaluation

[0141] Data collection: Collect the installed capacity (600 MW) of the power plant, coal quality parameters (received base low heat 21 MJ / kg, received base ash 25%, received base moisture 10% and other parameters), energy consumption parameters (auxiliary power rate 7%, power supply coal consumption 320 gce / kWh) and equipment parameters (boiler efficiency 90%, steam turbine efficiency 42% and other parameters).

[0142] Energy saving potential calculation:

[0143] Flue gas waste heat: Through heat balance calculation, it is estimated that the recoverable amount of flue gas waste heat accounts for about 8% of the total input heat of the boiler, and the annual recoverable heat is about [total input heat of the boiler (calculated according to annual power generation) × 8%]. Assuming that the annual fuel consumption of the boiler is a certain value, the annual recoverable flue gas waste heat is about 1.2×10 6 GJ.

[0144] Circulating water waste heat: According to the circulating water flow and the temperature difference between the inlet and outlet, it is estimated that the recoverable amount of circulating water waste heat accounts for about 15% of the steam turbine exhaust waste heat, and the annual recoverable heat is about 0.5×10 6 GJ.

[0145] Furnace body waste heat: The heat loss of the furnace body surface accounts for about 3% of the total input heat of the boiler, and the annual recoverable heat is about 0.4×10 6 GJ.

[0146] Slag waste heat: The heat carried away by the slag accounts for about 1% of the total input heat of the boiler, and the annual recoverable heat is about 0.1×10 6 GJ.

[0147] Recovery difficulty assessment: flue gas waste heat recovery needs to consider the impact of flue gas composition (sulfur, dust, etc.) on heat exchange equipment, recovery difficulty is relatively large; circulating water waste heat recovery is relatively simple, but water quality treatment needs to be considered; furnace body waste heat recovery is limited by furnace structure and insulation measures; slag waste heat recovery needs to solve the problems of slag conveying and heat exchange efficiency.

[0148] Environmental effect assessment: if all the above waste heat is recovered, it is calculated that about 500,000 tons of carbon dioxide can be reduced per year (according to the waste heat recovery amount converted into standard coal, and then calculated according to the standard coal carbon emission coefficient).

[0149] Economic benefit assessment:

[0150] Static income rate: preliminary estimate of total investment of about 80 million yuan, annual energy saving benefit of about 15 million yuan (converted into fuel cost saved according to waste heat recovery amount), static income rate of about 18.75%.

[0151] Net present value: assuming a discount rate of 8% and a project life of 15 years, the calculated net present value is about 30 million yuan.

[0152] Investment recovery period: the investment recovery period is about 5.3 years.

[0153] According to the pre-evaluation results, the power plant has great waste heat recovery potential, and the economic and environmental benefits are considerable, so it is decided to design a waste heat recovery scheme for the power plant.

[0154] 3. Determine the waste heat recovery scheme

[0155] Flue gas waste heat recovery scheme: low-temperature economizer technology is adopted, low-temperature economizer is installed at the tail of the boiler, flue gas waste heat is recovered to heat circulating water, boiler feed water temperature is increased, and exhaust gas temperature is reduced.

[0156] Circulating water waste heat recovery scheme: heat pump technology is adopted to extract waste heat from circulating cooling water for heating or hot water preparation.

[0157] Furnace body waste heat recovery scheme: insulation materials are installed on the surface of the furnace body to reduce heat loss, and waste heat recovery devices are installed to recover part of the lost heat for preheating combustion air.

[0158] Slag waste heat recovery scheme: dry slag discharging machine is adopted to recover slag waste heat during slag discharging for heating desalted water.

[0159] Scheme operability assessment:

[0160] Flue gas waste heat recovery scheme: low-temperature economizer technology is mature, but flue gas corrosion and wear problems need to be considered, the scheme is feasible through selection of appropriate materials and optimization design.

[0161] Circulating water waste heat recovery scheme: Heat pump technology is widely used in this field, and the technology is mature and the scheme is feasible.

[0162] Furnace body waste heat recovery scheme: The technology of adding insulation materials and waste heat recovery devices is feasible, but the furnace structure needs to be modified, and the scheme is feasible.

[0163] Slag waste heat recovery scheme: Dry slagging machine technology is mature, and waste heat recovery device can be integrated with slagging machine, and the scheme is feasible.

[0164] Each scheme is feasible and enters the energy saving evaluation link.

[0165] 4. Energy saving evaluation

[0166] Waste heat calculation when not taking waste heat recovery scheme: Detailed calculation of various heat losses of boiler, steam turbine and other equipment shows that the annual total waste heat is about 2.2×10 6 GJ.

[0167] Waste heat recovery amount calculation after taking the scheme:

[0168] Flue gas waste heat recovery amount: After detailed calculation, about 1.1×10 6 GJ of flue gas waste heat can be recovered annually.

[0169] Circulating water waste heat recovery amount: About 0.45×10 6 GJ of circulating water waste heat can be recovered annually.

[0170] Furnace body waste heat recovery amount: About 0.35×10 6 GJ of furnace body waste heat can be recovered annually.

[0171] Slag waste heat recovery amount: About 0.1×10 6 GJ of slag waste heat can be recovered annually.

[0172] The total recovery amount is about 2.0×10 6 GJ.

[0173] Waste heat recovery potential: 2.2×10 6 GJ-2.0×10 6 GJ=0.2×10 6 GJ.

[0174] Energy saving evaluation: The relatively small waste heat recovery potential indicates that the current scheme is relatively efficient in waste heat recovery, but it can still be further optimized, such as optimizing the heat exchange area and arrangement of low-temperature economizer to improve the efficiency of flue gas waste heat recovery.

[0175] Energy saving evaluation result: This waste heat recovery scheme has good energy saving effect, but there is still room for optimization.

[0176] 5. LCA analysis

[0177] Objective and scope:

[0178] Analysis objective: To evaluate the environmental impact of the waste heat recovery scheme for a coal-fired power plant and determine whether the scheme meets environmental requirements.

[0179] Functional unit: The annual power generation of the plant is 3.3 billion kWh.

[0180] Accounting boundary: The "cradle-to-gate" accounting boundary is adopted, which includes the entire process from raw material extraction, transportation to waste heat recovery equipment manufacturing, installation and operation.

[0181] Data quality requirements: The data sources should be reliable, including actual enterprise data, industry statistics and literature, etc., and the data precision should meet the analysis requirements.

[0182] Inventory analysis: Collect the energy consumption, material input and pollutant emission data of the waste heat recovery scheme in the processes of raw material extraction, transportation, equipment manufacturing, installation and operation, etc., and establish the inventory table.

[0183] Impact assessment: Quantify the impact of various factors on the environment, resources and human health by using SimaPro software or empirical formula calculation. This example is based on formula calculation.

[0184] Global warming potential (GWP): The calculated GWP of the scheme's entire life cycle is about 4.8×10 5 kg CO2-eq.

[0185] Ozone depletion potential (ODP): The ODP is close to 0, indicating that the scheme has no significant impact on the ozone layer.

[0186] Acidification potential (AP): The AP is about 1.2×10 4 kg SO2-eq.

[0187] Eutrophication potential (EP): The EP is about 800 kg PO43--eq.

[0188] Characterization and normalization: Convert various emissions and resource consumption into common units of measurement under corresponding impact categories, and compare with the total annual impact globally or regionally. For example, the GWP of the scheme accounts for a small proportion of the global annual GWP, indicating its relatively limited contribution to global warming.

[0189] Summary of environmental impact: The waste heat recovery scheme can significantly reduce greenhouse gas emissions such as carbon dioxide, has no impact on the ozone layer, but will produce certain acidification and eutrophication impacts. Overall, the scheme has good environmental effects.

[0190] Sensitivity analysis, uncertainty analysis, result interpretation, report compilation: sensitivity analysis is performed on key parameters such as energy price, pollutant emission factor, etc. to evaluate their impact on the environmental impact assessment results. Uncertainty analysis is performed to determine the reliability of the assessment results. Based on the analysis results, a detailed LCA report is compiled and improvement suggestions are proposed.

[0191] Environmental assessment results: the waste heat recovery scheme meets the requirements of relevant environmental standards and has good environmental performance, but further measures such as optimizing equipment manufacturing process and improving energy utilization efficiency can be taken to further reduce environmental impact.

[0192] 6. TEA analysis

[0193] Total capital investment calculation: the total investment of the project is about 80 million yuan, including equipment purchase cost, installation cost, commissioning cost, etc.

[0194] Energy saving benefit profit conversion: annual energy saving benefit is about 15 million yuan (converted from waste heat recovery amount to saved fuel cost).

[0195] Environmental benefit output conversion: according to the local government subsidy policy, 50 yuan of subsidy can be obtained for each ton of carbon dioxide emission reduction, and about 25 million yuan of subsidy can be obtained annually (0.5 million tons x 50 yuan / ton). At the same time, green credit can be applied for to reduce financing cost, and the additional benefit brought by green credit is estimated to be about 2 million yuan / year. Therefore, the environmental benefit output is about 27 million yuan / year.

[0196] Economic indicator evaluation:

[0197] Static evaluation: the static benefit rate is about (1500+2700) / 8000x100%=52.5%.

[0198] Dynamic evaluation: assuming the discount rate is 8% and the project life is 15 years, the calculated net present value is about 120 million yuan.

[0199] Investment recovery period: the investment recovery period is about 2.2 years.

[0200] Sensitivity analysis: sensitivity analysis is performed on key parameters such as energy saving benefit, environmental benefit, investment cost, etc. It is found that energy saving benefit and environmental benefit have greater impact on project economic benefit. When energy saving benefit decreases by 10%, the investment recovery period is extended to 2.5 years; when environmental benefit decreases by 10%, the investment recovery period is extended to 2.4 years.

[0201] Economic evaluation results: the waste heat recovery scheme has significant economic benefit and certain risk resistance ability. Further optimization of the scheme can be made to improve energy saving and environmental benefit and further enhance economic benefit.

[0202] 7. Comprehensive evaluation

[0203] Weight analysis: According to the actual situation of the power plant, the weights of energy benefit, environmental benefit and economic benefit are determined as 0.3, 0.3 and 0.4 respectively.

[0204] Comprehensive evaluation result: According to the results of energy saving evaluation, LCA analysis and TEA analysis, the comprehensive score is calculated. The energy benefit score is 80 (the energy saving effect is good, but there is optimization space), the environmental benefit score is 85 (it meets the environmental protection standard and has good environmental protection), and the economic benefit score is 90 (the economic benefit is significant). Comprehensive score = 80x0.3+85x0.3+90x0.4 = 85.5 points. The comprehensive evaluation result shows that the waste heat recovery scheme of the coal-fired power plant has high feasibility and can be implemented in the power plant.

[0205] As can be seen from the above examples, the technical scheme can systematically and comprehensively evaluate and design the waste heat recovery of the coal-fired power plant, effectively improve the energy utilization efficiency, reduce environmental pollution, and obtain good economic benefit.

[0206] To solve the technical problems existing in the prior art, the method provided by the embodiments of the present application first takes the national standards, industry specifications and local policies as the evaluation basis, establishes a unified waste heat recovery access and comparison system, and makes the evaluation process have policy compliance and operability. By constructing a waste heat quantity calculation model taking installed capacity, coal quality parameters, boiler flue gas temperature, circulating water temperature difference and slag sensible heat as input, various waste heat potential indicators can be quantitatively output, and whether the power plant has engineering value for recovery is judged by using a set threshold. This process converts the technical link that depends on experience into a data-driven criterion, improving the comparability and transparency in industrial application.

[0207] In the scheme design link, special recovery process paths are proposed for different waste heat sources, such as reducing the flue gas temperature by using a low-temperature economizer to recover the sensible heat of flue gas, using a heat pump to improve the waste heat quality of circulating cooling water, capturing the heat loss of the furnace body through a heat exchange device, and obtaining the waste heat of slag by using a dry slag discharge device. The proposal of these sub-schemes is not isolated, but is part of the overall comprehensive scheme. The applicability of the process under specific unit operating conditions is verified through operability analysis, thereby solving the technical bottleneck of previous single waste heat source without overall coordination.

[0208] In the analysis optimization stage, the method introduces three means of energy-saving analysis, life cycle assessment and technical and economic analysis. Energy-saving analysis determines the size of the recovery potential through the comparison of the total residual heat and the recovery amount; life cycle assessment quantitatively presents the external benefits of the recovery scheme in the environmental aspect by means of global warming potential and acidification potential; technical and economic analysis further converts investment cost, energy-saving benefit and subsidy policy into economic indicators such as net present value and investment payback period, and investigates the stability of the results under the fluctuation of key parameters through sensitivity analysis. This process realizes the cross-verification from the three dimensions of energy, environment and economy, so that the technical scheme not only stays in the theoretical feasibility, but also has the engineering rationality of industrial promotion.

[0209] In the multi-objective trade-off link, the analytic hierarchy process is used to convert the energy-saving, environmental and economic indicators into weight factors, realizing the quantitative balance between different evaluation dimensions. Through weight adjustment, the configuration parameters of the final scheme can be flexibly optimized according to the energy price, policy orientation and environmental protection constraints in the region where the power plant is located, ensuring the maximization of comprehensive benefits. This mechanism solves the problem of lacking unified decision-making tools and relying on artificial experience in the prior art, making the scheme selection objective and scientific.

[0210] The evaluation system solidifies the above method into a modular structure, covering functional modules such as standard reference, pre-evaluation, scheme development, analysis optimization, trade-off analysis and final output, and realizes collaborative work through a data bus. The whole working principle is to drive the complete closed-loop process from quantitative evaluation to process design, and then to multi-dimensional optimization and decision output, by data collection and model calculation. This technical path solves the problem of lacking systematic evaluation and scientific decision-making in the industrial application of coal-fired power plant waste heat utilization, ensuring that the scheme meets the engineering goal of improving energy utilization efficiency, and also meets the industrial demand of environmental sustainable development and economic affordability.

[0211] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any modification, equivalent replacement and improvement made by those skilled in the art within the technical scope disclosed by the present application, which is within the spirit and principles of the present application, should be covered within the protection scope of the present application.

Claims

1. A method for evaluating the feasibility of waste heat recovery in a coal-fired power plant, characterized in that, Comprising the following steps: Step one, determine the evaluation basis, through the national standard, industry standard and local regulations to determine the waste heat recovery evaluation requirements; Step two, perform pre-evaluation, according to the installed capacity of coal-fired power plants, coal quality, energy consumption and equipment operation parameters to calculate the recoverable waste heat and waste heat type, and judge whether it meets the pre-evaluation requirements of waste heat recovery; Step three, develop a program, for the coal-fired power plants that meet the pre-evaluation requirements, determine the waste heat recovery sub-scheme for flue gas, circulating water, furnace and slag, and form the preliminary comprehensive scheme; Step four, analysis and optimization, energy saving analysis, life cycle assessment analysis and technical and economic analysis are carried out on the preliminary comprehensive scheme, and the energy saving, environmental protection and economy are optimized according to the analysis results; Step five, trade-off analysis, multi-objective weight analysis is carried out on energy saving, environmental protection and economy, and the trade-off result is formed; Step six, determine the final scheme, determine the comprehensive weight according to the trade-off result, and output the final waste heat recovery scheme.

2. The method of claim 1, wherein, Step one, by comparing the national standard, industry standard and local regulations, establish the basic database of waste heat recovery evaluation, and provide unified evaluation criteria for subsequent evaluation.

3. The method of claim 1, wherein, Step two, by establishing quantitative model to calculate flue gas waste heat, circulating water waste heat, furnace waste heat and slag waste heat, and using threshold to judge waste heat recovery potential.

4. The method of claim 1, wherein, Step three, for flue gas waste heat, low-temperature economizer scheme is adopted, for circulating water waste heat, heat pump scheme is adopted, for furnace waste heat, surface waste heat recovery device scheme is adopted, for slag waste heat, dry slag discharge waste heat recovery device scheme is adopted, and the operability of each sub-scheme is evaluated.

5. The method of claim 1, wherein, Step four, energy saving analysis is carried out by comparing the total waste heat under the condition of no recovery with the total recovery after adopting the recovery scheme to calculate the waste heat recovery potential; life cycle assessment analysis evaluates environmental impact according to global warming potential, ozone layer depletion potential, acidification potential and eutrophication potential; Technical and economic analysis calculates economic indicators according to total investment, energy saving benefit and policy subsidy and carries out sensitivity analysis.

6. The method of claim 1, wherein, Step five, the weights of energy saving, environmental protection and economy are calculated by using AHP, and the scheme parameters are adjusted according to the weights to maximize the comprehensive benefit.

7. A system for assessing the feasibility of waste heat recovery in a coal-fired power plant, characterized by, Comprising: Standard reference module, used to obtain waste heat recovery evaluation requirements; Pre-evaluation module, used to calculate the recoverable waste heat and waste heat type according to the installed capacity of coal-fired power plants, coal quality, energy consumption and equipment operation parameters, and judge whether it meets the pre-evaluation requirements of waste heat recovery; Scheme development module, used to determine the waste heat recovery sub-scheme for flue gas, circulating water, furnace and slag for the coal-fired power plants that meet the pre-evaluation requirements, and form the preliminary comprehensive scheme; Analysis and optimization module, used to carry out energy saving analysis, life cycle assessment analysis and technical and economic analysis on the preliminary comprehensive scheme, and optimize the energy saving, environmental protection and economy according to the analysis results; Trade-off analysis module, used to carry out multi-objective weight analysis on energy saving, environmental protection and economy, and form the trade-off result; Final scheme module, used to determine the final scheme, determine the comprehensive weight according to the trade-off result, and output the final waste heat recovery scheme; The above modules are connected through data bus and cooperatively output the final waste heat recovery scheme.

8. The system of claim 7, wherein, The pre-evaluation module comprises a data acquisition unit and a residual heat amount calculation unit, the data acquisition unit is used for acquiring installed capacity, coal quality, energy consumption and equipment operation parameters, and the residual heat amount calculation unit is used for calculating flue gas residual heat amount, circulating water residual heat amount, furnace body residual heat amount and slag residual heat amount according to the data.

9. The system of claim 7, wherein, The analysis optimization module comprises an energy saving analysis unit, a life cycle assessment unit and a technical and economic analysis unit, the energy saving analysis unit is used for outputting residual heat recovery potential, the life cycle assessment unit is used for outputting environmental impact assessment results, and the technical and economic analysis unit is used for outputting economic indicators and providing sensitivity analysis results.

10. The system of claim 7, wherein, The trade-off analysis module is used for calculating weights of energy saving, environmental protection and economy by using analytic hierarchy process, and adjusting scheme parameters according to the weights to realize maximum comprehensive benefits.

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