CN105975439B - Coupling calculation for the technological design of Ethylene vapor pyrolysis furnace and operation optimization - Google Patents
Coupling calculation for the technological design of Ethylene vapor pyrolysis furnace and operation optimization Download PDFInfo
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Abstract
The present invention discloses a kind of coupling calculation of Ethylene vapor pyrolysis furnace, and the technological design and operation optimization for pyrolysis furnace calculate.The calculating of pyrolysis furnace is divided into convection section computing module, radiant section computing module and waste heat boiler computing module by this method.Radiant section computing module itself includes burner hearth computational submodule and boiler tube computational submodule.Convection section computing module is used to calculate flowing, phase transformation and the heat transfer of fluid in heat transfer and the pipe row between flue gas and convection section tube row；Burner hearth computational submodule is used to calculate the heat transfer between the burning of fuel, the flowing of flue gas, flue gas and boiler tube；Boiler tube computational submodule is used to calculate free radical cracking reaction and the heat transfer in boiler tube；Waste heat boiler computing module is used to calculate the heat transfer in rapid-cooling heat exchanger between cracking gas and boiler feedwater.By iteratively solving above-mentioned modules, the global solution of available cracking furnace system, for determining the optimal operational parameters of pyrolysis furnace and the operating status of Accurate Prediction pyrolysis furnace.
Description
Technical field
The present invention relates to a kind of coupling calculation for Ethylene vapor pyrolysis furnace, this method can be used for industrial ethylene steaming
The technological design of vapour pyrolysis furnace and operation optimization.
Background technique
Ethylene is a kind of highly important industrial chemicals, and the yield of ethylene, the scale of list covering device and technical level are weighing apparatuses
Measure the important symbol of a National Petrochemical Industry Development Level.Currently, the steam thermal cracking of hydro carbons is still the most main of production ethylene
Want method, and faucet of the ethane cracking furnace as entire cracker, the reasonability of technological design and operating status it is good
It is bad directly to determine the quality of product, the stability of device and energy consumption level.
Fig. 1 is the process flow chart of a typical ethane cracking furnace.It should be pointed out that there are many not for ethane cracking furnace
Same structure, Fig. 1 only illustrate one of possible structure.In general, ethane cracking furnace generally includes three parts, it is respectively
Convection section, radiant section and waste heat boiler.(1) convection section is mainly used for recycling the heat in high-temperature flue gas, this partial heat can be with
For heating cracking stock and dilution steam generation, preheating superpressure boiler water supply, overheat extra high pressure steam；(2) radiant section is hydro carbons
Cracking reaction occurs for raw material to generate the place of cracking product, since cracking reaction is strong endothermic reaction, it is therefore desirable to pass through
A large amount of fuel burn to provide heat；(3) waste heat boiler is made of rapid-cooling heat exchanger and drum, passes through recovered flue gas and cracking
Heat in gas generates extra high pressure steam.
Cracking stock initially enters tentatively to be heated in two sections of one section of raw material preheating and raw material preheating, then with process
The dilution steam generation of dilution steam generation preheating section heating mixes.Mixed cracking stock and dilution steam generation enter raw material and dilution is steamed
After vapour preheated one-section and two sections of further heating, cracking reaction occurs by entering in the radiant coil in radiant section across pipe.
Bottom Nozzle Used (referred to as: burning at bottom) and burner on sidewall (referred to as: burning side) are provided in some radiant sections simultaneously to mention for cracking reaction
For institute's calorific requirement, Bottom Nozzle Used also is provided only in some radiant sections.Pintsch process gas after reaction is needed in rapid-cooling heat exchanger
It is middle to be cooled down rapidly, to reduce side reaction bring adverse effect to greatest extent.Pintsch process gas is in rapid-cooling heat exchanger
The heat being recovered enters one section and two sections further mistakes of extra high pressure steam for generating extra high pressure steam, and after drum extraction
Heat.The temperature of the extra high pressure steam of final output ethane cracking furnace can be adjusted and be controlled by attemperator, super to meet
The requirement of high pressure steam line and steam user.In addition, the superpressure boiler water supply into drum needs to be introduced into economizer
In preheated, so as to the heat in recovered flue gas as much as possible, to improve the thermal efficiency of pyrolysis furnace.
" technological design of ethane cracking furnace " of this patent meaning, is meant that: according to the property of cracking stock, to target
The requirement of product yield and requirement etc. to cracking furnace thermal efficiency, designed from the angle of process flow one it is new, simultaneously
And structure ethane cracking furnace as reasonable as possible.
" operation optimization of ethane cracking furnace " of this patent meaning, is meant that: in existing ethane cracking furnace
On the basis of, by adjusting cracking stock distribution, or by adjusting the process operation parameter of pyrolysis furnace, to improve as much as possible
The thermal efficiency of pyrolysis furnace, the comprehensive yield for improving target product etc..
The process design and calculation of ethane cracking furnace is sufficiently complex, it is necessary to while considering several factors and restrictive condition.Below
Only list part of factor that must be taken into consideration:
(1) when designing the structure of convection section, it is necessary to the physical property of cracking stock is fully considered, to guarantee that cracking stock exists
Phase, temperature and pressure drop in each section of raw material preheating pipe row are all satisfied requirement；Fluid temperature (F.T.) across pipe is (that is, across temperature
Degree) it must within a reasonable range, to meet the requirement of cracking reaction；Extra high pressure steam superheat section pipe arranges structure
Design must satisfy the requirement of steam pipe network and steam user；Exhaust gas temperature must be excessively high to drop within a zone of reasonableness
The thermal efficiency of low pyrolysis furnace, it is too low, dew point corrosion can occur.
(2) the steam heat scission reaction of hydro carbons is a highly endothermic process, and the cracking severity of raw material, target product
Yield and the length in operation cycle it is very sensitive to reaction temperature.Therefore, when designing the structure of radiant section, it is necessary to
Fully consider the corresponding cracking reaction characteristic of cracking stock, rationally design radiation chamber overall dimensions (including length etc.),
The quantity and arrangement etc. of the dimensional structure of radiant tube row, burner make the Heat release mode of fuel combustion, the flue gas in burner hearth as far as possible
The heat absorption mode that flow pattern, pipe are arranged is optimal matching.
(3) when designing the structure of waste heat boiler, it is necessary to the structure of rapid-cooling heat exchanger is rationally designed, to make Pintsch process
Gas fast cooling as much as possible will avoid that coking occurs in rapid-cooling heat exchanger as far as possible to a reasonable temperature；It must be rationally
The circulating ratio that boiler feedwater between drum and rapid-cooling heat exchanger forms Natural Circulation convection current is set, the occurrence quantity of steam and steady is made
It is qualitative to be all satisfied requirement.
Different from process design and calculation, the operation optimization of ethane cracking furnace calculates the size for not needing to redesign pyrolysis furnace
Structure, but by change cracking stock distribution or adjust pyrolysis furnace operating parameter come the yield of object observing product,
How the whole thermal efficiency, operation cycle and the stability of pyrolysis furnace change, so that it is determined that more optimized pyrolysis furnace runs item
Part.In general, the difficulty of " process design and calculation " is larger.In addition, the method for meeting " process design and calculation " can be with
The requirement for meeting " operation optimization calculating ", this is because the core calculations model of the two is identical.
Currently, the pyrolysis furnace calculation method and model of domestic-developed are primarily present following problems:
(1) Most models and method are both for operation optimization, few technological design meters for new pyrolysis furnace
Calculate, many model parameters therein must be fitted recurrences by actual industry park plan data, the applicability of model with
Extrapolation is not high.
(2) most models and method be in order to reduce difficulty and calculation amount takes simplified processing, such as pipe row
Detailed construction, which is passed through, carries out approximation frequently with " cold-smoothing face ", thus is unable to satisfy design-calculated required precision.In addition some are modeled
Method uses the means that computational fluid dynamics is simulated in order to pursue higher accuracy, but due to the meter of this method
Calculation amount is excessive, the calculating overlong time of single operating condition, therefore is not used to that the process design and calculation of a large amount of operating conditions must be taken into consideration.
(3) domestic at present that convection section, radiant section and Waste Heat System are not still combined into modeling progress technology Calculation
Method.Most methods are limited only to the process design and calculation of radiant section and operation optimization calculates, therefore these models and side
The result that method obtains is only possible to be local optimum, is unable to satisfy the high-precision technology Calculation and operation optimization of whole pyrolysis furnace.
In conclusion in view of the above-mentioned problems, developing a set of joint for covering convection section, radiant section and Waste Heat System
Calculation method, technological design and operation optimization for ethane cracking furnace, can be greatly improved the design of China's ethane cracking furnace
Technical level, and the operating status of existing ethane cracking furnace can be improved.
Summary of the invention
The present invention provides a kind of coupling calculation of Ethylene vapor pyrolysis furnace, and this method has both very high accuracy and very
High operation efficiency both can be used for the process design and calculation of new pyrolysis furnace, can be used for the operation optimization of existing pyrolysis furnace
It calculates.
In order to achieve the above objectives, the present invention provides a kind of coupling calculations of Ethylene vapor pyrolysis furnace, according to ethylene
The calculating of entire pyrolysis furnace is divided into three modules by the practical structures and process flow of pyrolysis furnace, is that convection section calculates mould respectively
Block, radiant section computing module and waste heat boiler computing module obtain cracking furnace system by iteratively solving above three module
Global solution, method includes the following steps:
(1) convection section computing module governing equation group is established, is specifically included:
(1) the convective heat transfer model between convection section coil pipe and high-temperature flue gas is established
The characteristics of according to the staggered sawtooth finned tube of convection section use, between convection section coil pipe and high-temperature flue gas
Convective heat-transfer coefficient calculated using ESCOA method, calculation formula is as follows:
Ao=d+2nbh formula 3
C1=0.091Re-0.25Formula 4
C3=0.35+0.65e-0.17h/sFormula 5
Fin efficiency η11It is calculated using following formula:
At=Af+ π d (1-nb) formula 9
m11=[2ho(b+ws)/Km/b/ws]0.5Formula 11
AfAnd AtIt is the fin area and the gross area under unit boiler tube length, m respectively2/m；
KmIt is the thermal coefficient of fin, W/ (m K)；
Ws is the width of fin, m；
(2) Pressure Drop Model between convection section coil pipe and high-temperature flue gas is established
Pressure drop when high-temperature flue gas flows between convection section tube row is calculated using following formula:
C2=0.75+1.85Re-0.3Formula 16
(3) the single-phase heat transfer model of fluid in heating tube in section of convection chamber is established
Convective heat-transfer coefficient in heating tube in section of convection chamber between monophasic fluid and boiler tube inner wall is calculated using following formula:
(4) Pressure Drop Model of monophasic fluid in heating tube in section of convection chamber is established
Along the pressure drop expression formula of heating tube in section of convection chamber are as follows:
For smooth straight pipe, the calculation expression of Fanning friction factor is as follows:
For smooth bend loss, the calculation expression of Fanning friction factor is as follows:
(5) the two-phase heat transfer model of fluid in heating tube in section of convection chamber is established
The case where for undergoing phase transition in boiler tube, judges stream when fluid flows in pipe using the flow pattern of Baker
Type, the convective heat-transfer coefficient in heating tube in section of convection chamber between fluid and boiler tube inner wall are calculated using following formula:
htc=α τthn+htFormula 24
τt=-10.08547+3.43598 (lnRet)2+0.01038(lnRet)3Formula 26
(2) radiant section computing module governing equation group is established, is specifically included:
(1) the field method radiation heat-transfer model in burner hearth between high-temperature flue gas and radiant tube row is established
The thinking of field method is: radiant section first (a) is divided into a series of surface districts and flue gas area according to certain requirement,
Middle surface district is divided into burner hearth inner surface section and outer surface of furnace tube area again, and assumes that the temperature inside each region is uniform；(b)
The Direct Exchange Areas between each region is calculated on the basis of assuming that all surface is black matrix；(c) assuming that all
Surface is the total transfer area calculated on the basis of ideal grey body between each region；(d) assuming that burner hearth flue gas it is black
Degree can use the orientation flow area calculated between each region on the basis of a transparent gas and several ideal grey gas；(e)
Energy conservation equation is established to each region, and numerical solution is carried out to it, to obtain the temperature of each region；
Direct Exchange Areas between (1-a) surface district and surface district, surface district and gas zone, gas zone and gas zone by
Following formula is calculated:
(1-b) seeks total transfer area on the basis of Direct Exchange Areas, establishes radiation energy levelling to each surface district
Weigh equation, obtains following equation group:
After arranging, following equation group is obtained:
The coefficient matrix that the left side of above-mentioned formula is made of Direct Exchange Areas, surface area and reflectivity, the right side of equation
The column matrix that side is then made of the blackness and Direct Exchange Areas on surface.Above-mentioned equation group is solved using the method that numerical value calculates
It can be obtained than reflection heat flow density, then find out the total transfer area between surface district according to the following formula:
(1-c) establishes radiant flux equilibrium equation to all gas zones, obtains following equation group:
After arranging, following equation group is obtained:
The coefficient matrix that the left side of above-mentioned formula is made of Direct Exchange Areas, surface area and reflectivity, the right side of equation
The column matrix that side is then made of Direct Exchange Areas.Solving above-mentioned equation group using the method that numerical value calculates can be obtained than anti-
Heat flow density is penetrated, then obtains the total transfer area between gas zone and surface district according to the following formula:
Total transfer area between gas zone and surface district can be calculated using following formula:
Total transfer area between gas zone and gas zone can then be calculated using following formula:
(1-d) calculates orientation flow area, and wherein the blackness of burner hearth flue gas is added using a transparent gas and several grey body gas
It weighs and comes approximate characterization, the blackness ε of flue gasgWith absorptivity αgIt may be expressed as:
Orientation flow area is calculated according to following formula:
(1-e) establishes energy-balance equation to all areas
First to furnace wall inner surface section WSiEstablish energy-balance equation:
Secondly, to boiler tube inner surface section TSiEstablish energy-balance equation:
Finally, to gas zone GiEstablish energy-balance equation:
Equation quantity in the energy equation finally established is equal to the quantity of all areas, and equation group is non-thread
Property equation group, is solved using Newton-Raphson method；
(2) the free radical cracking reaction model in radiating furnace tube is established
Reaction, heat transfer and the flow process in radiating furnace tube are characterized using one-dimensional plug flow model, and radiating furnace tube is built
Vertical quality, energy and momentum conservation equation:
1. mass-conservation equation
In reaction tube infinitesimal dz, the mass-conservation equation of certain component i is as follows:
2. energy conservation equation
In reaction tube infinitesimal dz, energy conservation equation is as follows:
3. momentum conservation equation
The momentum conservation equation of radiating furnace tube is consistent with heating tube in section of convection chamber, using formula 20~23.
(3) waste heat boiler computing module governing equation group is established
The overall heat-transfer coefficient K of quenching boiler11It is calculated according to following formula:
The heat transfer coefficient α of cracking gas in heat exchanger tubeiIt is calculated according to following formula:
The boiling heat transfer coefficient α of the outer high pressure boiler water supply of heat exchanger tubeoIt is calculated according to following formula:
Total heat exchange amount of linear rapid-cooling heat exchanger is calculated according to following formula:
Q=K11*F*ΔtmFormula 50
(4) solution is iterated to above three module until convergence, specifically includes:
Step 1: the detailed construction dimensional parameters of input convection section in cracking furnace and radiant section, including length, width and height, pipe row structure,
Burner structure and arrangement；
Step 2: input initial operational parameters: the physical property and flow of cracking stock, thinner ratio, fuel gas composition and flow,
Air composition and coefficient of excess, wall with flues temperature, the distribution of radiant coil outside wall temperature；
Step 3: convection section computing module and waste heat boiler computing module are solved, until convergence, specifically includes:
Step 3.1: inputting the flow of initial superpressure boiler water supply and extra high pressure steam；
Step 3.2: convection section computing module is solved, until convergence；
Step 3.2: the flow of economizer exit temperature and extra high pressure steam that convection section computing module is exported substitutes into useless
Heat boiler computing module, until convergence；
Step 3.3: the flow of the superpressure boiler water supply and extra high pressure steam of comparing the output of waste heat boiler computing module is
It is no to have restrained；If convergence, terminates to calculate；Otherwise, by the flow generation of new superpressure boiler water supply and extra high pressure steam
Enter convection section computing module to iterate to calculate again；
Step 4: the variate-value across temperature that convection section computing module is exported substitutes into radiant section computing module and counts
It calculates, until convergence, specifically includes:
Step 4.1: input prompt radiation coil metal outside wall temperature distribution；
Step 4.2: burner hearth computational submodule is solved, until convergence；
Step 4.3: the radiant coil metal outer wall heat flux distribution that burner hearth computational submodule is exported substitutes into boiler tube and calculates
Submodule is calculated, until convergence；
Step 4.4: whether the radiant coil metal outer wall Temperature Distribution for comparing the output of boiler tube computational submodule has restrained.
If restrained, terminate to calculate；Otherwise, new radiant coil metal outer wall Temperature Distribution is re-entered into burner hearth and calculates son
Module is calculated；
Step 5: whether judging the variate-value of the new wall with flues temperature and flue gas flow of radiant section computing module output
Convergence, if restrained, terminates to calculate and exports final calculation result；Otherwise, by new wall with flues temperature and flue gas flow
Variate-value substitute into convection section and waste heat boiler computing module and re-start calculating.
Further, the convergence criterion of whole system and modules is made of the threshold value of a certain series of preset, when
Front and back twice calculated result difference be less than corresponding threshold value, then whole system and modules convergence.
Carry out pyrolysis furnace process design and calculation and operation optimization calculate when, convection section, radiant section and waste heat boiler this
The calculating of three big modules is consumingly coupled: (1) diabatic process of convection section will affect across temperature；(2) across
Temperature then will affect cracking reaction, fuel consumption and wall with flues temperature in radiant section；(3) fuel consumption and wall with flues temperature are anti-
Come over and will affect the temperature of fluid and final exhaust gas temperature in each section of pipe row of convection section；(4) cracking reaction temperature can shadow
The occurrence quantity of extra high pressure steam is rung, and the occurrence quantity of extra high pressure steam also will affect the operating condition of convection section.
The complication system being coupled for above-mentioned this multiple module heights, it is necessary to by modules according to certain
Logical order, which organizes together, to be iterated solution and restrains, and the global solution of whole system can be just obtained.On the contrary, if only by it
In some module individually split out and solved, can only obtain local solution, and this local solution may seriously partially
From global solution, therefore the true operating status of pyrolysis furnace can not be represented.
The global solution of cracking of ethylene furnace system is solved present invention employs nested coupling calculation.This method is according to second
The calculating of entire pyrolysis furnace is divided into three modules, is convection section meter respectively by the practical structures and process flow of alkene pyrolysis furnace
Calculate module, radiant section computing module and waste heat boiler computing module.Wherein, radiant section computing module itself contains two sons again
Module is burner hearth computational submodule and boiler tube computational submodule respectively.Convection section computing module be used to calculate high-temperature flue gas with it is right
Flow flowing, phase transformation and heat transfer that interior fluid is arranged in heat transfer and pipe between section pipe row；Burner hearth computational submodule is used to calculate fuel
Radiation and convective heat transfer between combustion heat release, the flowing of high-temperature flue gas, high-temperature flue gas and radiant tube row；Boiler tube computational submodule
For calculating free radical cracking reaction and diabatic process complicated in radiating furnace tube；Waste heat boiler computing module is used to calculate chilling
Heat transfer in heat exchanger between cracking gas and boiler feedwater.The global solution of the available cracking furnace system of the calculation method, rather than
Local solution, so as to the true operating status of accurate description pyrolysis furnace.
Nested coupling calculation in the present invention has the following characteristics that
1, the practical structures and process flow of ethane cracking furnace have been fully considered, can completely describe convection section in cracking furnace,
Coupling correlation between radiant section and waste heat boiler, therefore, by this method be calculated the result is that entire pyrolysis furnace
The global solution of system, rather than local solution, can be with the true operating status of accurate description pyrolysis furnace.
2, follow-on field method has been used in burner hearth computational submodule, and radiant tube row is no longer visualized as " a cold-smoothing
Face ", but fully considered the practical three-dimensional structure of radiant tube row, by the independent progress subregion calculating of each boiler tube.Its
Secondary, user can targetedly carry out region division according to the practical structures of burner hearth and boiler tube, very flexibly and easily.It is this
Follow-on field method really reflects the practical three-dimensional structure and size of pyrolysis furnace, both can guarantee the accuracy of calculated result,
Calculation amount can be maintained in a reasonable range again simultaneously.
3, boiler tube computational submodule has used one-dimensional piston flow reactor model, and establishes quality, momentum and energy and keep
Permanent equation；Furnace tube model can be according to the macroscopic properties of cracking stock, including PONA value, distillation curve, average molecular weight peace
Equal density etc., the molecular composition for obtaining cracking stock using the method that numerical value calculates is (certain to need compared with weight molecule using virtual group
Part replaces), and the input condition as cracking reaction；Accurately to describe the steam hot tearing of hydro carbons using radical reaction network
Solution preocess, radical reaction network include 100 various ingredients and more than 2000 a radical reactions, can accurately obtain turning for raw material
A series of important parameters such as rate, distribution, endothermic heat of reaction amount and the coking state for cracking product.Due to using above-mentioned model,
Boiler tube computational submodule can describe the flowing, heat transfer and reaction of furnace tube fluid with high accuracy.
4, convection section computing module has fully considered the structure of practical pipe row, length, internal diameter including pipe, wall thickness, wing
Arranged opposite etc. between piece pattern, fin height and thickness, pipe, can be with the biography between accurate description high-temperature flue gas and pipe row
Thermal process.
5, waste heat boiler computing module uses rapid-cooling heat exchanger and the true three-dimension structure of drum carries out Modeling Calculation, can
Pass through rapid-cooling heat exchanger with the circulating ratio of Accurate Prediction Natural Circulation convection current, the occurrence quantity of extra high pressure steam and cracking gas
Temperature etc. afterwards.
6, this method has many different calculating modes, very flexible and convenient and practical.For example, fuel gas can be set
The conversion ratio of cracking stock, the yield, exhaust gas temperature, the gas production that crack product etc. are calculated with the flow of cracking stock；It can also
The conversion ratio of yield cracking stock living to set target product is come the fuel tolerance etc. that calculates needs；Sensitivity can also be passed through
The mode of analysis determines the correlation degree between each variable, thus help user determine optimal product distribution scheme and
Optimal operating parameter Assembled lamp.
The present invention has fully considered the coupling between these three modules of ethane cracking furnace convection section, radiant section and waste heat boiler
Correlation initially sets up the governing equation group of modules oneself, is then iterated according to the logical relation between module
It calculates, the final global solution for obtaining cracking of ethylene furnace system.The invention has very high accuracy and operation efficiency, can be used for
The process design and calculation and operation optimization of pyrolysis furnace calculate.This method applicability is relatively broad, can be used for different types of cracking
Raw material and hydrocarbons steam cracking furnace.
Detailed description of the invention
Fig. 1 is the process flow chart of typical ethane cracking furnace；
Fig. 2 is the concept logic block diagram of the nested coupling calculation of one embodiment of the invention；
Fig. 3 is the detailed logic block diagram of the nested coupling calculation of one embodiment of the invention；
Fig. 4 is the convection section computing module of one embodiment of the invention and the detailed logic frame of waste heat boiler computing module
Figure；
Fig. 5 is the detailed logic block diagram of the radiant section computing module of one embodiment of the invention；
Fig. 6 is that direct interchange areas is illustrated between surface district and surface district in the field method of one embodiment of the invention
Figure；
Fig. 7 is that direct interchange areas is illustrated between flue gas area and surface district in the field method of one embodiment of the invention
Figure；
Fig. 8 is that direct interchange areas is illustrated between flue gas area and flue gas area in the field method of one embodiment of the invention
Figure.
Specific embodiment
It is illustrated below with reference to the calculated examples of certain industrial naphthas steam cracking furnace:
The cracking furnace structure that calculated examples use is as shown in Figure 1.Convection section tube row is followed successively by raw material preheating one from top to bottom
Section, economizer, two sections of raw material preheating, raw material and dilution steam generation preheated one-section, dilution steam generation preheating section, extra high pressure steam overheat one
Section, two sections of extra high pressure steam overheat, raw material and dilution steam generation preheat two sections.In the outlet of dilution steam generation preheating section and raw material preheating two
Mixer is arranged in section exit.It is overheated in extra high pressure steam and attemperator is set between one section and two sections.Bottom is only set in radiant section
Portion's burner.The Waste Heat System of rapid-cooling heat exchanger and drum composition is set to cool down to cracking gas and generate extra high pressure steam.
1, convection section computing module governing equation group is established
(1) the convective heat transfer model between convection section coil pipe and high-temperature flue gas
Convection section uses staggered sawtooth finned tube to enhance convective heat transfer effect, convection current in this calculated examples
Convective heat-transfer coefficient between section coil pipe and high-temperature flue gas is calculated using famous ESCOA method, and calculation formula is as follows:
Ao=d+2nbh formula 3
C1=0.091Re-0.25Formula 4
C3=0.35+0.65e-0.17h/sFormula 5
AoIt is obstructed area of the pipe row to flue gas, m2/m
Cp11It is the specific heat of flue gas, J/ (kg K)
hcIt is the convective heat-transfer coefficient between convection section coil pipe and flue gas, W/ (m2K)
k12It is the thermal coefficient of flue gas, W/ (m K)
μ11It is the viscosity of flue gas, kg/ (m s)
It (is needed when calculating flue gas physical property using average flue-gas temperature.)
TgAnd TfIt is the temperature of flue gas and fin, K respectively
G is the mass flux of flue gas, kg/ (m2s)
D is the outer diameter of heating tube in section of convection chamber, m
NwIt is the radical of every grate furnace pipe
NdIt is pipe number of rows
L is the effective length of boiler tube, m
H is the height of fin, m
B is the thickness of fin, m
N is the density of fin, fin number/m
WgIt is the flow rate of flue gas, kg/s
STAnd SLIt is spacing horizontal and vertical between heating tube in section of convection chamber, m respectively
Re is the Reynolds number of flue gas
Fin efficiency η11It is calculated using following formula:
At=Af+ π d (1-nb) formula 9
m11=[2ho(b+ws)/Km/b/ws]0.5Formula 11
AfAnd AtIt is the fin area and the gross area under unit boiler tube length, m respectively2/m
KmIt is the thermal coefficient of fin, W/ (m K)
Ws is the width of fin, m
(2) Pressure Drop Model between convection section coil pipe and high-temperature flue gas
Pressure drop when high-temperature flue gas flows between convection section tube row is calculated using following formula:
C2=0.75+1.85Re-0.3Formula 16
ΔPgIt is pressure drop
ρgIt is density of the flue gas under mean temperature, kg/m3
(3) in heating tube in section of convection chamber fluid single-phase heat transfer model
Convective heat-transfer coefficient in heating tube in section of convection chamber between monophasic fluid and boiler tube inner wall is calculated using following formula:
hc11It is the convective heat-transfer coefficient between tube fluid and boiler tube inner wall, W/ (m2K)
W is the mass flowrate in single boiler tube, kg/s
CpIt is the specific heat of fluid, J/ (kg K)
μ is the viscosity of fluid, kg/ (m s)
k11It is the thermal coefficient of fluid, W/ (m K)
diIt is the internal diameter of boiler tube, m
(4) in heating tube in section of convection chamber monophasic fluid Pressure Drop Model
Along the pressure drop expression formula of heating tube in section of convection chamber are as follows:
PtFor stagnation pressure, Pa
α is conversion coefficient
rbFor the radius of pipe bent position, m
F is Fanning friction factor
ξ is alunite carat rope husband's coefficient of elbow
For smooth straight pipe, the calculation expression of Fanning friction factor is as follows:
For smooth bend loss, the calculation expression of Fanning friction factor is as follows:
K is the bending angle of bend pipe, rad
(5) in heating tube in section of convection chamber fluid two-phase heat transfer model
The case where for undergoing phase transition in boiler tube, judges stream when fluid flows in pipe using the flow pattern of Baker
Type, the convective heat-transfer coefficient in heating tube in section of convection chamber between fluid and boiler tube inner wall are calculated using following formula:
htc=α τthn+htFormula 24
τt=-10.08547+3.43598 (lnRet)2+0.01038(lnRet)3Formula 26
htcIt is the comprehensive convective heat-transfer coefficient of two phase flow, W/ (m2K)
α is nucleate boiling heat transfer coefficient correction factor related with flow pattern, can be read from correlation graph
hnIt is nucleate boiling heat transfer coefficient, W/ (m2K)
htIt is two-phase forced convection heat transfer coefficient, W/ (m2K)
τtIt is two-phase forced convertion nuclear boiling interference coefficient
kLIt is the thermal coefficient of liquid medium
cLIt is the specific heat at constant pressure of liquid medium, kcal/ (kg K)
ρLIt is the density of liquid medium, kg/m3
ρVIt is the density of gas medium, kg/m3
σLIt is the surface tension of liquid medium, dyn/cm
μLIt is the viscosity of liquid medium, cP
H is the evaporation latent heat of liquid medium, kcal/kg
TWIt is the temperature of wall surface and fluid with T, DEG C
PWAnd PSIt is vapour pressure of the medium under wall surface and saturation temperature, kg/cm2
RetIt is the Reynolds number of two phase flow
hLIt is the heat transfer coefficient of liquid phase, kcal/ (m2hr K)
X is Martin's parameter, and calculation method can refer to Baker flow pattern
2, radiant section computing module governing equation group is established
(1) the field method radiation heat-transfer model in burner hearth between high-temperature flue gas and radiant tube row
The core ideas of field method is: radiant section first (a) being divided into a series of surface districts and flue gas according to certain requirement
Area, wherein surface district is divided into burner hearth inner surface section and outer surface of furnace tube area again, and assumes that the temperature inside each region is uniform
's；(b) Direct Exchange Areas between each region is calculated on the basis of assuming that all surface is black matrix；(c) in vacation
If all surface is the total transfer area calculated on the basis of ideal grey body between each region；(d) assuming that burner hearth cigarette
The blackness of gas can use the orientation stream interface calculated between each region on the basis of a transparent gas and several ideal grey gas
Product；(e) energy conservation equation is established to each region, and numerical solution is carried out to it, to obtain the temperature etc. of each region.
It should be pointed out that when carrying out region division to outer surface of furnace tube, it, cannot will be whole in order to improve accuracy in computation
A pipe row simplification is processed into one " cold-smoothing face ", on the contrary, needing individually to calculate each boiler tube.This calculated examples will be every
Root boiler tube is alongst divided into a surface district every 1 meter or so, and is calculating each outer surface of furnace tube Qu Yuqi
When Direct Exchange Areas between its region, it is necessary to fully consider the mutual masking between boiler tube using the knowledge of solid geometry.
Direct Exchange Areas between (1-a) surface district and surface district, surface district and gas zone, gas zone and gas zone
(see Fig. 7~8) can be calculated by following formula:
WithIt is between surface district and surface district, surface district and gas zone, gas zone and gas zone respectively
Direct Exchange Areas, m2
k22For attenuation coefficient of the flue gas under grey gas hypothesis, 1/m
r22For the distance between region infinitesimal, m
θiAnd θjRelative angle between region, rad
DA and dV is respectively the unit dimension and element of volume of surface district and gas zone, m2And m3
(1-b) is next, seek total transfer area on the basis of Direct Exchange Areas.Each surface district is established and is radiated
Energy mobile equilibrium equation, available following equation group:
After arranging, available following equation group:
The coefficient matrix that the left side of above-mentioned formula is made of Direct Exchange Areas, surface area and reflectivity, the right side of equation
The column matrix that side is then made of the blackness and Direct Exchange Areas on surface.Above-mentioned equation group is solved using the method that numerical value calculates
It can be obtained than reflecting heat flow density, then can find out the total transfer area between surface district according to the following formula.
For surface district SjSurface area, m2
For surface district SjBlackness
For surface district SjReflectivity, it is numerically equal to
For than reflecting heat flow density
(1-c) next, establish radiant flux equilibrium equation to all gas zones, available following equation group:
After arranging, available following equation group:
The coefficient matrix that the left side of above-mentioned formula is made of Direct Exchange Areas, surface area and reflectivity, the right side of equation
The column matrix that side is then made of Direct Exchange Areas.Solving above-mentioned equation group using the method that numerical value calculates can be obtained than anti-
Heat flow density is penetrated, then obtains the total transfer area between gas zone and surface district according to the following formula:
Total transfer area between gas zone and surface district can be calculated using following formula:
Total transfer area between gas zone and gas zone can then be calculated using following formula:
(1-d) next calculates orientation flow area, and the blackness of burner hearth flue gas can be using a transparent gas and several ashes
Body gas, which weights, carrys out approximate characterization.According to above-mentioned viewpoint, the blackness ε of flue gasgWith absorptivity αgIt may be expressed as:
Wherein, ag,n(Tg) and a'g,n(Tg,Ts) it is the weight of n-th of grey gas when calculating flue gas blackness and absorptivity respectively.
Therefrom it will be seen that the weight of blackness is only related with the temperature of flue gas, and the weight of absorptivity both has with the temperature of flue gas
It closes again related with the temperature of surface district of transmitting radiation.k'nIt is the specific damping coefficient of n-th of grey gas, 1/ (atm*m).P is flue gas
Pressure value, atm.L11For the stroke length for radiating heat ray, m.
Therefore, orientation flow area can be calculated according to following formula:
(1-e) next establishes energy-balance equation to all areas
First to furnace wall inner surface section WSiEstablish energy-balance equation:
1st: WSiThe radiant heat from all furnace wall inner surfaces absorbed
2nd: WSiThe radiant heat from all boiler tube inner surfaces absorbed
3rd: WSiThe radiant heat from all gas area absorbed
4th: WSiAll radiant heat launched outward
5th: WSiPass through the heat in the received flue gas area of convective heat transfer mode
6th: WSiCorresponding furnace wall outer wall heat loss value
Secondly, to boiler tube inner surface section TSiEstablish energy-balance equation:
1st: TSiThe radiant heat from all furnace wall inner surfaces absorbed
2nd: TSiThe radiant heat from all boiler tube inner surfaces absorbed
3rd: TSiThe radiant heat from all gas area absorbed
4th: TSiAll radiant heat launched outward
5th: TSiPass through the heat in the received flue gas area of convective heat transfer mode
6th: TSiBy the heat of Absorption of Medium in boiler tube
Finally, to gas zone GiEstablish energy-balance equation:
1st: GiThe radiant heat from all furnace wall inner surfaces absorbed
2nd: GiThe radiant heat from all boiler tube inner surfaces absorbed
3rd: GiThe radiant heat from all gas area absorbed
4th: GiAll radiant heat launched outward
5th: GiThe heat that fuel combustion is discharged
6th: GiBy convective heat transfer model to the heat of surface block transitive
7th: GiThe enthalpy change occurred by the flowing of flue gas
Equation quantity in the energy equation finally established is exactly equal to the quantity of all areas.Equation group is
Nonlinear System of Equations can be solved using Newton-Raphson method.
(2) the free radical cracking reaction model in radiating furnace tube
The heat scission reaction of hydrocarbon raw material is sufficiently complex in radiating furnace tube, and its computational accuracy directly determines that product is received
The accuracy of the key parameters such as rate and endothermic heat of reaction amount.Currently, to the simulation of cracking process, there are mainly three types of different models:
The first is empirical model.It directly adopt Empirical Equation to cracking product yield and reaction condition parameter into
Row association, and regression fit is carried out to the parameter in Empirical Equation according to a large amount of actual industry park plan data.Empirical Mode
Type simple, intuitive, it is very practical in a certain range.But better than it be empirical, therefore fundamentally cannot be used exploitation novel furnace and
The process design and calculation of novel furnace prolongs and extrapolates and be all very unreliable in model, and a set of model parameter is often appropriate only to specific
The type of furnace.
Second is molecular model.The model at single virtual component, and will split complicated cracking stock illusion
Solution reaction is simplified to a primary first-order equation and several secondary responses, does not intersect mutually between two reactions.Molecular model ratio
Empirical model has stronger extrapolation and applicability, but for different cracking stocks, cracking condition and cracks furnace structure,
There is still a need for be fitted recurrence to the parameter being related in primary first-order equation.It is being extrapolated to model in application, there is still a need for benefits
Fill suitable experimental data.
The third is free radical model.The model is reappeared in boiler tube as far as possible using the radical reaction of a series of complex
True cracking reaction process, reaction process include chain cause, take by force H, free radical addition, free radical decomposition, free radical isomerization,
The processes such as chain termination.The model has very strong versatility and very high precision.
This calculated examples uses the steam thermal cracking processes that radical reaction network accurately to describe hydro carbons, the free radical
Reaction network includes a radical reaction more than 100 various ingredients and 2000, the weight such as pre-exponential factor and activation energy of each reaction
It wants parameter to determine by stringent theory deduction with a large amount of experiment and industry park plan data, can accurately obtain naphtha
Conversion ratio of the raw material under various different pipes row structures, distribution, endothermic heat of reaction amount and the coking state for cracking product etc. are a series of
Important parameter.
In addition, the macroscopic properties of naphtha mainly include averag density, average molecular weight, PONA value and D86 distillation curve,
Therefore, it before using radical reaction network, first has to obtain stone brain using the molecular composition reconstruction model of cracking stock
Input of the molecular composition of oil as reaction network.The library of molecules of complete set is contained in molecular composition reconstruction model, wherein
Store the physical property of all candidate molecules.Meanwhile it being also associated between naphtha macroscopic properties and Molecuar matter and determining in model
Magnitude relation formula.The model utilizes these quantitative relation formulas and information entropy maximization using oil product macroscopic properties as input condition
Principle obtains the molecular composition of oil product.
Reaction, heat transfer and the flow process in radiating furnace tube can be characterized using one-dimensional plug flow model, it is necessary to it
Establish quality, energy and momentum conservation equation.
1. mass-conservation equation
In reaction tube infinitesimal dz, the mass-conservation equation of certain component i is as follows:
FiFor the molar flow rate of component i, kmol/s
rkTo react k1Reaction rate, kmol/m3/s
vkiTo react k1The reaction stoichiometric coefficient of middle component i
n11For the reaction number in reaction network
d11For the internal diameter of reaction boiler tube
2. energy conservation equation
In reaction tube infinitesimal dz, energy conservation equation is as follows:
ω is the perimeter of boiler tube, m
Q is the heat flux that burner hearth is passed to boiler tube, kJ/m2/s
T is the temperature of fluid, K
CpiFor specific heat of the component i in temperature T, kJ/kmol/K
For the standard molar formation enthalpy of component k, kJ/kmol
RkFor the net generating rate of component k, kmol/m3/s
3. momentum conservation equation
The momentum conservation equation of radiating furnace tube is consistent with heating tube in section of convection chamber, can use formula 20~23.
3, waste heat boiler computing module governing equation group is established
The major function of waste heat boiler computing module is the outlet temperature for calculating cracking gas and the production gas of extra high pressure steam
Amount, wherein the calculated result of gas production directly will affect the Calculation of Heat Transfer of convection section.This calculated examples uses linear chilling and changes
Hot device, can be by cracking gas fast cooling, and can reduce the coking tendency of cracking gas to the greatest extent, extends the operation cycle.
The overall heat-transfer coefficient K of quenching boiler11It is calculated according to following formula:
K11It is overall heat-transfer coefficient, W/ (m2K)
αiIt is the heat transfer coefficient of cracking gas in heat exchanger tube, W/ (m2K)
αoIt is the boiling heat transfer coefficient of water supply in the outer pressure cooker of heat exchanger tube, W/ (m2K)
doAnd diIt is the outer diameter and inner diameter of heat exchanger tube, m respectively
dcIt is the internal diameter of focus layer, m
λwIt is the thermal coefficient of heat exchanger tube, W/ (m K)
λcIt is the thermal coefficient of focus layer, W/ (m K)
RoAnd RiIt is the dirtiness resistance of on the outside of heat exchanger tube and inside, W/ (m respectively2K)
The heat transfer coefficient α of cracking gas in heat exchanger tubeiIt is calculated according to following formula:
λgIt is the mean coefficient of heat conductivity of cracking gas, W/ (m K)
Re11It is Reynolds number when cracking gas flows in heat exchanger tube
ρ is the density of cracking gas, kg/m3
μgAnd μwIt is viscosity of the cracking gas in pipe under mean temperature and under wall temperature, kg/ (m s) respectively
Pr is Prandtl number
The boiling heat transfer coefficient α of the outer high pressure boiler water supply of heat exchanger tubeoIt is calculated according to following formula:
Q is mean heat flux, W/m2；
psIt is the absolute pressure of boiler feedwater, MPa；
Total heat exchange amount of linear rapid-cooling heat exchanger is calculated according to following formula:
Q=K11*F*ΔtmFormula 50
F is total heat exchange area of heat exchanger tube, m2；
ΔtmFor logarithm heat transfer temperature difference, DEG C；
The gas production of extra high pressure steam is calculated according to following formula:
D is steam production；
η is the radiation loss rate of rapid-cooling heat exchanger；
R is the latent heat of vaporization of boiler feedwater, kJ/kg；
4, solution is iterated to all modules until convergence
After the governing equation group of convection section, radiant section and waste heat boiler computing module is established, according to being patrolled described in Fig. 3
The relationship of collecting is iterated solution to these modules until restraining, and the actual operation parameters of pyrolysis furnace under specified criteria can be obtained,
Yield, furnace tube temperature and heat flux distribution, wall with flues temperature, the convection section smoke evacuation temperature of cracking severity, target product including raw material
Degree, convection section each pipe row temperature, extra high pressure steam yield, cracking gas leave rapid-cooling heat exchanger temperature and some other very
Important operating parameter.
The iterative calculation of whole system is sufficiently complex, and following methods can be improved the constringency performance of this method:
(1) it is particularly significant that reasonable initial value is set；
(2) in order to improve the convergence capabilities of calculation method, one relaxation factor can be set for each module, reduces intermediate
The impact strength of parameters value in calculating process；
(3) maximum concussion section and the concussion step-length of each parameter are set；
(4) all parameter values that can first force to fix some module again open the module after the convergence of other modules.
Finally, it should be noted that the above embodiments are merely illustrative of the technical solutions of the present invention, rather than its limitations；Although
Present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that: it still may be used
To modify to technical solution documented by previous embodiment or equivalent replacement of some of the technical features；And
These are modified or replaceed, the spirit and model of technical solution of the embodiment of the present invention that it does not separate the essence of the corresponding technical solution
It encloses.
Claims (2)
1. a kind of coupling calculation of Ethylene vapor pyrolysis furnace, which is characterized in that according to the practical structures of ethane cracking furnace and
The calculating of entire pyrolysis furnace is divided into three modules by process flow, be respectively convection section computing module, radiant section computing module and
Waste heat boiler computing module obtains the global solution of cracking furnace system by iteratively solving above three module, this method include with
Lower step:
(1) convection section computing module governing equation group is established, is specifically included:
(1) the convective heat transfer model between convection section coil pipe and high-temperature flue gas is established
The characteristics of according to the staggered sawtooth finned tube of convection section use, pair between convection section coil pipe and high-temperature flue gas
Stream heat transfer coefficient is calculated using ESCOA method, and calculation formula is as follows:
Ao=d+2nbh formula 3
C1=0.091Re-0.25Formula 4
C3=0.35+0.65e-0.17h/sFormula 5
AoIt is obstructed area of the pipe row to flue gas, m2/m；
Cp11It is the specific heat of flue gas, J/ (kg K)；
hcIt is the convective heat-transfer coefficient between convection section coil pipe and flue gas, W/ (m2K)；
k12It is the thermal coefficient of flue gas, W/ (m K)；
μ11It is the viscosity of flue gas, kg/ (m s)；
TgAnd TfIt is the temperature of flue gas and fin, K respectively；
G is the mass flux of flue gas, kg/ (m2s)；
D is the outer diameter of heating tube in section of convection chamber, m；
NwIt is the radical of every grate furnace pipe；
NdIt is pipe number of rows；
L is the effective length of boiler tube, m；
H is the height of fin, m；
B is the thickness of fin, m；
N is the density of fin, fin number/m；
WgIt is the flow rate of flue gas, kg/s；
STAnd SLIt is spacing horizontal and vertical between heating tube in section of convection chamber, m respectively；
Re is the Reynolds number of flue gas；
Fin efficiency η11It is calculated using following formula:
At=Af+ π d (1-nb) formula 9
m11=[2ho(b+ws)/Km/b/ws]0.5Formula 11
AfAnd AtIt is the fin area and the gross area under unit boiler tube length, m respectively2/m；
KmIt is the thermal coefficient of fin, W/ (m K)；
Ws is the width of fin, m；
(2) Pressure Drop Model between convection section coil pipe and high-temperature flue gas is established
Pressure drop when high-temperature flue gas flows between convection section tube row is calculated using following formula:
C2=0.75+1.85Re-0.3Formula 16
ΔPgIt is pressure drop；
ρgIt is density of the flue gas under mean temperature, kg/m3；
(3) the single-phase heat transfer model of fluid in heating tube in section of convection chamber is established
Convective heat-transfer coefficient in heating tube in section of convection chamber between monophasic fluid and boiler tube inner wall is calculated using following formula:
hc11It is the convective heat-transfer coefficient between tube fluid and boiler tube inner wall, W/ (m2K)；
W is the mass flowrate in single boiler tube, kg/s；
CpIt is the specific heat of fluid, J/ (kg K)；
μ is the viscosity of fluid, kg/ (m s)；
k11It is the thermal coefficient of fluid, W/ (m K)；
diIt is the internal diameter of boiler tube, m；
(4) Pressure Drop Model of monophasic fluid in heating tube in section of convection chamber is established
Along the pressure drop expression formula of heating tube in section of convection chamber are as follows:
PtFor stagnation pressure, Pa；
α is conversion coefficient；
rbFor the radius of pipe bent position, m；
F is Fanning friction factor；
ξ is alunite carat rope husband's coefficient of elbow；
For smooth straight pipe, the calculation expression of Fanning friction factor is as follows:
For smooth bend loss, the calculation expression of Fanning friction factor is as follows:
K is the bending angle of bend pipe, rad；
(5) the two-phase heat transfer model of fluid in heating tube in section of convection chamber is established
The case where for undergoing phase transition in boiler tube, judges flow pattern when fluid flows in pipe using the flow pattern of Baker, right
Convective heat-transfer coefficient between stream section furnace tube fluid and boiler tube inner wall is calculated using following formula:
htc=α τthn+htFormula 24
τt=-10.08547+3.43598 (lnRet)2+0.01038(lnRet)3Formula 26
htcIt is the comprehensive convective heat-transfer coefficient of two phase flow, W/ (m2K)；
α is nucleate boiling heat transfer coefficient correction factor related with flow pattern, can be read from correlation graph；
hnIt is nucleate boiling heat transfer coefficient, W/ (m2K)；
htIt is two-phase forced convection heat transfer coefficient, W/ (m2K)；
τtIt is two-phase forced convertion nuclear boiling interference coefficient；
kLIt is the thermal coefficient of liquid medium；
cLIt is the specific heat at constant pressure of liquid medium, kcal/ (kg K)；
ρLIt is the density of liquid medium, kg/m3；
ρVIt is the density of gas medium, kg/m3；
σLIt is the surface tension of liquid medium, dyn/cm；
μLIt is the viscosity of liquid medium, cP；
H is the evaporation latent heat of liquid medium, kcal/kg；
TWIt is the temperature of wall surface and fluid with T, DEG C；
PWAnd PSIt is vapour pressure of the medium under wall surface and saturation temperature, kg/cm2；
RetIt is the Reynolds number of two phase flow；
hLIt is the heat transfer coefficient of liquid phase, kcal/ (m2hr K)；
X is Martin's parameter, and calculation method can refer to Baker flow pattern；
(2) radiant section computing module governing equation group is established, is specifically included:
(1) the field method radiation heat-transfer model in burner hearth between high-temperature flue gas and radiant tube row is established
The thinking of field method is: radiant section first (a) being divided into a series of surface districts and flue gas area according to certain requirement, wherein table
Face area is divided into burner hearth inner surface section and outer surface of furnace tube area again, and assumes that the temperature inside each region is uniform；(b) in vacation
If all surface is the Direct Exchange Areas calculated on the basis of black matrix between each region；(c) assuming that all surface
It is the total transfer area calculated on the basis of ideal grey body between each region；(d) assuming that the blackness of burner hearth flue gas can
With with the orientation flow area calculated on the basis of a transparent gas and several ideal grey gas between each region；(e) to every
Energy conservation equation is established in a region, and carries out numerical solution to it, to obtain the temperature of each region；
Direct Exchange Areas between (1-a) surface district and surface district, surface district and gas zone, gas zone and gas zone is by as follows
Formula is calculated:
WithIt is straight between surface district and surface district, surface district and gas zone, gas zone and gas zone respectively
Meet exchange area, m2；
k22For attenuation coefficient of the flue gas under grey gas hypothesis, 1/m；
r22For the distance between region infinitesimal, m；
θiAnd θjRelative angle between region, rad；
DA and dV is respectively the unit dimension and element of volume of surface district and gas zone, m2And m3；
(1-b) seeks total transfer area on the basis of Direct Exchange Areas, establishes radiant flux balance side to each surface district
Journey obtains following equation group:
After arranging, following equation group is obtained:
The coefficient matrix that the left side of above-mentioned formula is made of Direct Exchange Areas, surface area and reflectivity, the right of equation is then
The column matrix being made of the blackness and Direct Exchange Areas on surface；Above-mentioned equation group is solved using the method that numerical value calculates
It obtains then finding out the total transfer area between surface district according to the following formula than reflection heat flow density:
For surface district SjSurface area, m2；
For surface district SjBlackness；
For surface district SjReflectivity, it is numerically equal to
For than reflecting heat flow density；
(1-c) establishes radiant flux equilibrium equation to all gas zones, obtains following equation group:
After arranging, following equation group is obtained:
The coefficient matrix that the left side of above-mentioned formula is made of Direct Exchange Areas, surface area and reflectivity, the right of equation is then
The column matrix being made of Direct Exchange Areas；It solves above-mentioned equation group using the method that numerical value calculates and can be obtained and compare reflective thermal
Then current density obtains the total transfer area between gas zone and surface district according to the following formula:
Total transfer area between gas zone and surface district can be calculated using following formula:
Total transfer area between gas zone and gas zone can then be calculated using following formula:
(1-d) calculate orientation flow area, wherein the blackness of burner hearth flue gas using a transparent gas and several grey body gas weighting come
Approximation characterization, the blackness ε of flue gasgWith absorptivity αgIt may be expressed as:
Wherein, ag,n(Tg) and a'g,n(Tg,Ts) it is the weight of n-th of grey gas when calculating flue gas blackness and absorptivity, k' respectivelynIt is
The specific damping coefficient of n-th of grey gas, 1/ (atm*m)；P is the pressure value of flue gas, atm；L11For radiate heat ray stroke length,
m；
Orientation flow area is calculated according to following formula:
(1-e) establishes energy-balance equation to all areas
First to furnace wall inner surface section WSiEstablish energy-balance equation:
1st: WSiThe radiant heat from all furnace wall inner surfaces absorbed；
2nd: WSiThe radiant heat from all boiler tube inner surfaces absorbed；
3rd: WSiThe radiant heat from all gas area absorbed；
4th: WSiAll radiant heat launched outward；
5th: WSiPass through the heat in the received flue gas area of convective heat transfer mode；
6th: WSiCorresponding furnace wall outer wall heat loss value；
Secondly, to boiler tube inner surface section TSiEstablish energy-balance equation:
1st: TSiThe radiant heat from all furnace wall inner surfaces absorbed；
2nd: TSiThe radiant heat from all boiler tube inner surfaces absorbed；
3rd: TSiThe radiant heat from all gas area absorbed；
4th: TSiAll radiant heat launched outward；
5th: TSiPass through the heat in the received flue gas area of convective heat transfer mode；
6th: TSiBy the heat of Absorption of Medium in boiler tube；
Finally, to gas zone GiEstablish energy-balance equation:
1st: GiThe radiant heat from all furnace wall inner surfaces absorbed；
2nd: GiThe radiant heat from all boiler tube inner surfaces absorbed；
3rd: GiThe radiant heat from all gas area absorbed；
4th: GiAll radiant heat launched outward；
5th: GiThe heat that fuel combustion is discharged；
6th: GiBy convective heat transfer model to the heat of surface block transitive；
7th: GiThe enthalpy change occurred by the flowing of flue gas；
Equation quantity in the energy equation finally established is equal to the quantity of all areas, and equation group is non-linear side
Journey group, is solved using Newton-Raphson method；
(2) the free radical cracking reaction model in radiating furnace tube is established
Reaction, heat transfer and the flow process in radiating furnace tube are characterized using one-dimensional plug flow model, and matter is established to radiating furnace tube
Amount, energy and momentum conservation equation:
1. mass-conservation equation
In reaction tube infinitesimal dz, the mass-conservation equation of certain component i is as follows:
FiFor the molar flow rate of component i, kmol/s；
rkTo react k1Reaction rate, kmol/m3/s；
vkiTo react k1The reaction stoichiometric coefficient of middle component i；
n11For the reaction number in reaction network；
d11For the internal diameter of reaction boiler tube；
2. energy conservation equation
In reaction tube infinitesimal dz, energy conservation equation is as follows:
ω is the perimeter of boiler tube, m；
Q is the heat flux that burner hearth is passed to boiler tube, kJ/m2/s；
T is the temperature of fluid, K；
CpiFor specific heat of the component i in temperature T, kJ/kmol/K；
For the standard molar formation enthalpy of component k, kJ/kmol；
RkFor the net generating rate of component k, kmol/m3/s；
3. momentum conservation equation
The momentum conservation equation of radiating furnace tube is consistent with heating tube in section of convection chamber, using formula 20~23；
(3) waste heat boiler computing module governing equation group is established
The overall heat-transfer coefficient K of quenching boiler11It is calculated according to following formula:
K11It is overall heat-transfer coefficient, W/ (m2K)；
αiIt is the heat transfer coefficient of cracking gas in heat exchanger tube, W/ (m2K)；
αoIt is the boiling heat transfer coefficient of water supply in the outer pressure cooker of heat exchanger tube, W/ (m2K)；
doAnd diIt is the outer diameter and inner diameter of heat exchanger tube, m respectively；
dcIt is the internal diameter of focus layer, m；
λwIt is the thermal coefficient of heat exchanger tube, W/ (m K)；
λcIt is the thermal coefficient of focus layer, W/ (m K)；
RoAnd RiIt is the dirtiness resistance of on the outside of heat exchanger tube and inside, W/ (m respectively2K)；
The heat transfer coefficient α of cracking gas in heat exchanger tubeiIt is calculated according to following formula:
λgIt is the mean coefficient of heat conductivity of cracking gas, W/ (m K)；
Re11It is Reynolds number when cracking gas flows in heat exchanger tube；
ρ is the density of cracking gas, kg/m3；
μgAnd μwIt is viscosity of the cracking gas in pipe under mean temperature and under wall temperature, kg/ (m s) respectively；
Pr is Prandtl number；
The boiling heat transfer coefficient α of the outer high pressure boiler water supply of heat exchanger tubeoIt is calculated according to following formula:
Q is mean heat flux, W/m2；
psIt is the absolute pressure of boiler feedwater, MPa；
Total heat exchange amount of linear rapid-cooling heat exchanger is calculated according to following formula:
Q=K11*F*ΔtmFormula 50
F is total heat exchange area of heat exchanger tube, m2；
ΔtmFor logarithm heat transfer temperature difference, DEG C；
The gas production of extra high pressure steam is calculated according to following formula:
D is steam production；
η is the radiation loss rate of rapid-cooling heat exchanger；
R is the latent heat of vaporization of boiler feedwater, kJ/kg；
(4) solution is iterated to above three module until convergence, specifically includes:
Step 1: the detailed construction dimensional parameters of input convection section in cracking furnace and radiant section, including length, width and height, pipe row structure, burning
Device structure and arrangement；
Step 2: input initial operational parameters: the physical property and flow of cracking stock, thinner ratio, fuel gas forms and flow, air
Composition and coefficient of excess, wall with flues temperature, the distribution of radiant coil outside wall temperature；
Step 3: convection section computing module and waste heat boiler computing module are solved, until convergence, specifically includes:
Step 3.1: inputting the flow of initial superpressure boiler water supply and extra high pressure steam；
Step 3.2: convection section computing module is solved, until convergence；
Step 3.2: the flow of economizer exit temperature and extra high pressure steam that convection section computing module is exported substitutes into waste heat boiler
Furnace computing module, until convergence；
Step 3.3: whether the flow of the superpressure boiler water supply and extra high pressure steam of comparing the output of waste heat boiler computing module
Through restraining；If convergence, terminates to calculate；Otherwise, by the substitution pair of the flow of new superpressure boiler water supply and extra high pressure steam
Stream section computing module iterates to calculate again；
Step 4: the variate-value across temperature that convection section computing module is exported substitutes into radiant section computing module and calculates, directly
To convergence, specifically include:
Step 4.1: input prompt radiation coil metal outside wall temperature distribution；
Step 4.2: burner hearth computational submodule is solved, until convergence；
Step 4.3: the radiant coil metal outer wall heat flux distribution that burner hearth computational submodule is exported substitutes into boiler tube and calculates submodule
Block is calculated, until convergence；
Step 4.4: whether the radiant coil metal outer wall Temperature Distribution for comparing the output of boiler tube computational submodule has restrained；If
It has been restrained that, then terminate to calculate；Otherwise, new radiant coil metal outer wall Temperature Distribution is re-entered into burner hearth computational submodule
It is calculated；
Step 5: judge whether the variate-value of the new wall with flues temperature and flue gas flow of radiant section computing module output has restrained,
If restrained, terminates to calculate and export final calculation result；Otherwise, by the variable of new wall with flues temperature and flue gas flow
Value substitutes into convection section and waste heat boiler computing module re-starts calculating.
2. coupling calculation according to claim 1, which is characterized in that the convergence of whole system and modules is sentenced
It is constituted according to the threshold value by a certain series of preset, when the difference of front and back calculated result twice is less than corresponding threshold value, then entire system
System and modules convergence.
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| CN103992813A (en) * | 2014-05-28 | 2014-08-20 | 惠生工程（中国）有限公司 | Ethylene cracking furnace |
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| CN103992813A (en) * | 2014-05-28 | 2014-08-20 | 惠生工程（中国）有限公司 | Ethylene cracking furnace |
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