Visual analysis and calculation method for waste heat boiler heat recovery and utilization scheme based on T-Q diagram
Technical Field
The invention belongs to the technical field of energy-saving and environment-friendly engineering, and particularly relates to a visual analysis and calculation method for a waste heat boiler heat recovery and utilization scheme based on a T-Q diagram.
Background
The waste heat and smoke resources are widely used in the industries of steel, petroleum, chemical industry, building materials, light industry and the like. With the continuous rising of energy price and the continuous improvement of unit GDP energy consumption reduction requirement, the problem of waste heat utilization is paid high attention. The waste heat boiler is a main technical approach for utilizing waste heat flue gas resources, and heat energy carried by the waste heat flue gas is transferred to working media such as steam and water through a heating surface so as to be used for power generation or directly utilized. The heat recovery and utilization scheme for scientifically analyzing the waste heat flue gas and optimizing the design of the waste heat boiler has very important practical significance.
The research aiming at the problem of recovering waste heat and smoke heat energy by adopting a waste heat boiler can be divided into two layers: the first level is a general scheme level, namely aiming at waste heat and flue gas resources under specific conditions, selecting the number of working medium paths of the waste heat boiler on the premise of considering various engineering restriction conditions and aiming at the best target of waste heat recovery economy, analyzing and determining the thermodynamic parameters (pressure, inlet and outlet temperature and the like) of each path of working medium and the heating surface series and arrangement sequence of the waste heat boiler, and calculating to obtain the heat transfer quantity, the evaporation quantity and the like of each level of heating surface; the second layer is a component layer and mainly optimizes the specific geometric structure parameters of each heating surface of the waste heat boiler, such as the length, pitch, pipe diameter, row number, pipe arrangement mode and the like of the pipe sections of the heating surfaces. The invention mainly aims at the technical problem of the first layer.
Aiming at the problem of the heat recovery and utilization scheme of the waste heat boiler, the genetic algorithm is adopted to optimize the design parameters of the waste heat boiler and optimize the layout problem of the heating surface in the multi-pressure waste heat boiler; the Qinghua university deeply analyzes and calculates the thermodynamic performance of the waste heat boiler of the gas-steam combined cycle power station, and obtains the influence of parameters under different pressure levels on the heat balance calculation of the waste heat boiler. At present, waste heat resource conditions of various industries and enterprises are various, specific requirements for recovering waste heat flue gas heat energy by using waste heat boilers are different, a heat recovery scheme of the waste heat boilers correspondingly has various optimization selection problems of different working medium circuits, different working medium parameters, different heating surface arrangement and the like, and a quick and visual method for analyzing and comparing the heat recovery utilization scheme of the waste heat boilers is urgently needed.
Disclosure of Invention
Aiming at the problems, the invention provides a visualized analysis and calculation method of a waste heat boiler heat recovery and utilization scheme based on a T-Q diagram.
In order to achieve the purpose, the invention discloses a visualized analysis and calculation method of a waste heat boiler heat recovery and utilization scheme based on a T-Q diagram, which comprises the following steps:
(1) selecting a waste heat utilization scheme as a first waste heat utilization scheme according to waste heat resources, and drawing a first T-Q graph of each heating surface in the waste heat utilization scheme by taking heat Q as an abscissa and temperature T as an ordinate; moving a working medium process line corresponding to the heating surface and adjusting a vertical coordinate T of an end point of the working medium process line, and respectively finishing the adjustment of the arrangement of the heating surface and the adjustment of the boundary temperature between the multi-stage heating surfaces to obtain a second T-Q diagram representing a second waste heat utilization scheme;
(2) obtaining a first waste heat recycling scheme meeting the conditions according to the narrow point temperature difference and the flue gas acid dew point temperature by combining the first T-Q diagram; a second waste heat recycling scheme meeting the conditions is obtained according to the narrow point temperature difference and the acid dew point temperature of the flue gas by combining a second T-Q diagram,
(3) and determining an optimal waste heat utilization scheme according to the fire loss for the waste heat boiler in the first waste heat recovery utilization scheme and the second waste heat recovery utilization scheme which meet the conditions.
Further, the specific steps of obtaining the waste heat utilization scheme meeting the conditions are as follows:
(1) giving the flue gas temperature, components, flue gas quantity and working medium parameters, determining the segmented position and the arrangement sequence of the heating surface of the waste heat boiler,
(2) setting the minimum temperature difference delta T between the outlet working medium of each heating surface and the corresponding flue gasminIDetermining the flue gas inlet temperature T of the heating surface I by using a narrow point temperature difference method in heat balance calculationgIiAnd working medium outlet temperature TsIoTemperature difference DeltaT ofIWill Δ TIAnd a minimum temperature difference Δ TminIMaking a comparison if Δ TIGreater than or equal to the temperature difference DeltaTminIObtaining a waste heat recycling scheme meeting the conditions;
if Δ TILess than delta T of temperature differenceminIThen readjust the minimum temperature difference to make the minimum temperature difference be Δ TIThen, the heat balance calculation is carried out to obtain the exhaust gas temperature TpyAccording to the SO in the composition of the flue gas3The content and the volume percentage content of the water vapor are checked to obtain the dew point temperature T of the acid of the flue gasacidAnd the temperature T of the exhaust gaspyComparing with the acid dew point temperature of the flue gas if TpyGreater than or equal to TacidObtaining a waste heat recycling scheme meeting the conditions; if TpyLess than TacidThen, the heat balance calculation is carried out again to obtain a new exhaust gas temperature until TpyGreater than or equal to Tacid。
Furthermore, the first T-Q diagram and the second T-Q diagram respectively comprise a smoke side process line and a working medium side process line, and the projection length of each segmented process line of the working medium side process line on the transverse heat Q coordinate axis represents the heat exchange quantity Q of the corresponding heat exchangeri(ii) a The slope of the process line at the working medium side represents the steam flow M flowing through the heat exchangers of different pressure stagessISince the steam flows in the heat exchanger sections of the same pressure stage are the same, the process line slopes shown on the T-Q diagram, i.e., of the same pressure stage, are the same.
Further, in the case of Δ TIAnd a minimum temperature difference Δ TminIWhen compared, the minimum temperature difference delta T in the T-Q diagram isminIThe temperature difference delta T between the flue gas side and the working medium side of each heating surface is judgedIAnd if the temperature difference exceeds the threshold value, readjusting the heat exchange temperature difference.
According to the visualized analysis and calculation method of the waste heat boiler heat recovery scheme based on the T-Q diagram, for any waste heat resource, different and reasonable waste heat utilization schemes can be obtained quickly by changing the process lines corresponding to the heat exchangers on the T-Q diagram according to the law of thermodynamics and production experience according to actual production requirements, different heat utilization schemes are analyzed and compared, the required optimal calculation result of the waste heat boiler is selected, convenience and rapidness are achieved, the calculation visualized calculation result is accurate, and the visualized analysis and calculation method is suitable for arrangement of various heat exchangers, particularly for optimal calculation of heat balance of a multi-pressure waste heat boiler with complicated heat exchanger arrangement.
Drawings
FIG. 1 is a flow chart of a waste heat boiler thermodynamic performance calculation operation;
FIG. 2 is a flow chart of a dual pressure exhaust heat boiler structure;
FIG. 3 is a T-Q diagram corresponding to a dual pressure exhaust heat boiler;
FIG. 4 is a flow chart of a structure of a dual-pressure waste heat boiler after the arrangement of heating surfaces is changed;
FIG. 5 is a T-Q diagram corresponding to the dual pressure waste heat boiler after the arrangement of the heating surfaces is changed.
Detailed Description
The invention is further described with reference to the accompanying drawings.
Example 1
With reference to fig. 2 to 5, the present embodiment provides a visual analysis and calculation method for waste heat boiler recycling based on T-Q diagram, which includes the following steps: (1) selecting a waste heat utilization scheme as a first waste heat utilization scheme according to waste heat resources, and drawing a first T-Q graph of each heating surface in the waste heat utilization scheme by taking heat Q as an abscissa and temperature T as an ordinate; moving a working medium process line corresponding to the heating surface and adjusting a vertical coordinate T of an end point of the working medium process line, and respectively finishing the adjustment of the arrangement of the heating surface and the adjustment of the boundary temperature between the multi-stage heating surfaces to obtain a second T-Q diagram representing a second waste heat utilization scheme;
(2) obtaining a first waste heat recycling scheme meeting the conditions according to the narrow point temperature difference and the flue gas acid dew point temperature by combining the first T-Q diagram; a second waste heat recycling scheme meeting the conditions is obtained according to the narrow point temperature difference and the acid dew point temperature of the flue gas by combining a second T-Q diagram,
(3) and determining an optimal waste heat utilization scheme according to the fire loss for the waste heat boiler in the first waste heat recovery utilization scheme and the second waste heat recovery utilization scheme which meet the conditions.
In this embodiment, the first and second T-Q diagrams respectively include a flue gas side process line and a working medium side process line, and the projection length of each segment process line of the working medium side process line on the transverse heat Q coordinate axis represents the heat exchange amount Q of the corresponding heat exchangeri(ii) a Working mediumThe slope of the side process line represents the steam flow M through the heat exchangers of different pressure stagessISince the steam flows in the heat exchanger sections of the same pressure stage are the same, the process line slopes shown on the T-Q diagram, i.e., of the same pressure stage, are the same.
When multiple paths of heat recovery working media exist, the process lines of all the paths of working media are represented by different line shapes or colors. The method specifically comprises the steps of simultaneously displaying T-Q graphs of a plurality of waste heat recovery schemes through different line shapes in the same graph and comparing the T-Q graphs.
Wherein, in the T-Q diagram, the positions of engineering restriction conditions such as heat transfer narrow point temperature difference, flue gas acid dew point and the like are displayed by highlighted marks. For any pressure level waste heat boiler, the types of heating surfaces contained in the waste heat boiler mainly include three types: an economizer E, an evaporator B and a superheater S; the reheat section, if any, also includes a heat exchanger RH, LP for low pressure, IP for medium pressure, and HP for high pressure.
Because the minimum temperature difference of all the heating surfaces is different, the segmentation and arrangement sequence of the heating surfaces of the waste heat boiler is changed at will, the number of the heating surfaces and the arrangement sequence thereof are changed, and the position of the narrow point temperature difference in the heat balance calculation can also be changed, thereby causing the change of the maximum high-pressure evaporation capacity, the smoke exhaust temperature and the like.
Specifically, in the case of Δ TIAnd a minimum temperature difference Δ TminIWhen compared, the minimum temperature difference delta T in the T-Q diagram isminIThe temperature difference delta T between the flue gas side and the working medium side of each heating surface is judgedIAnd if the temperature difference exceeds the threshold value, readjusting the heat exchange temperature difference.
Embodiment 2, with reference to fig. 1, as a specific scheme of embodiment 1, in this embodiment, specific steps of obtaining a waste heat utilization scheme satisfying the conditions are as follows:
(1) giving the flue gas temperature, components, flue gas quantity and working medium parameters, determining the segmented position and the arrangement sequence of the heating surface of the waste heat boiler,
(2) setting the minimum temperature difference delta T between the outlet working medium of each heating surface and the corresponding flue gasminIDetermining the flue gas inlet temperature T of the heating surface I by using a narrow point temperature difference method in heat balance calculationgIiAnd working medium outlet temperature TsIoTemperature difference DeltaT ofIWill Δ TIAnd a minimum temperature difference Δ TminIMaking a comparison if Δ TIGreater than or equal to the temperature difference DeltaTminIObtaining a waste heat recycling scheme meeting the conditions;
if Δ TILess than delta T of temperature differenceminIThen readjust the minimum temperature difference to make the minimum temperature difference be Δ TIThen, the heat balance calculation is carried out to obtain the exhaust gas temperature TpyAccording to the SO in the composition of the flue gas3The content and the volume percentage content of the water vapor are checked to obtain the dew point temperature T of the acid of the flue gasacidAnd the temperature T of the exhaust gaspyComparing with the acid dew point temperature of the flue gas if TpyGreater than or equal to TacidObtaining a waste heat recycling scheme meeting the conditions; if TpyLess than TacidThen, the heat balance calculation is carried out again to obtain a new exhaust gas temperature until TpyGreater than or equal to Tacid。
The invention relates to a visual analysis and calculation method of a waste heat boiler heat recovery utilization scheme based on a T-Q diagram, which has multiple choices of waste heat utilization schemes for given waste heat resources.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are also included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope defined by the claims.