CN105975439A - Coupling calculation method used for process design and operation optimization of ethylene steam cracking furnace - Google Patents
Coupling calculation method used for process design and operation optimization of ethylene steam cracking furnace Download PDFInfo
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Abstract
The invention discloses a coupling calculation method for an ethylene steam cracking furnace, which is used for process design and operation optimization calculation of the cracking furnace. According to the method, calculation modules for the cracking furnace include a convection section calculation module, a radiation section calculation module and a waste heat boiler calculation module. The radiation section calculation module comprises a furnace chamber calculation sub-module and a furnace pipe calculation sub-module. The convection section calculation module is used for calculating heat transfer between flue gas and a convection section pipe row as well as flowing, phase change and heat transfer of a fluid in the pipe row; the furnace chamber calculation sub-module is used for calculating combustion of fuel, flowing of flue gas and heat transfer between the flue gas and a furnace pipe; the furnace pipe calculation sub-module is used for calculating a free radical cracking reaction and heat transfer in the furnace pipe; and the waste heat boiler calculation module is used for calculating heat transfer between cracking gas in a quench heat exchanger and boiler supply water. By iteratively solving the modules, a global solution of a cracking furnace system can be obtained and used for determining an optimal operation parameter of the cracking furnace and accurately predicting a running state of the cracking furnace.
Description
Technical field
The present invention relates to a kind of coupling calculation for Ethylene vapor pyrolysis furnace, the method can be used for industrial ethylene and steams
The technological design of vapour pyrolysis furnace and operation optimization.
Background technology
Ethylene is a kind of highly important industrial chemicals, and the yield of ethylene, the scale of single covering device and technical merit are weighing apparatuses
The important symbol of one National Petrochemical Industry Development Level of amount.At present, the steam heat cracking of hydro carbons is still and produces the most main of ethylene
Want method, and ethane cracking furnace is as the tap of whole cracker, the reasonability of its technological design and running status good
Badly directly determine the quality of product, the stability of device and energy consumption level.
Fig. 1 is the process chart of a typical ethane cracking furnace.It is pointed out that ethane cracking furnace have multiple not
Same structure, Fig. 1 has been diagrammatically only by the structure that one of which is possible.It is said that 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 in reclaiming the heat in high-temperature flue gas, and this partial heat is permissible
It is used for heating cracking stock and dilution steam generation, the feedwater of preheating superpressure boiler, overheated extra high pressure steam；(2) radiant section is hydro carbons
Raw material generation cracking reaction thus generate cracking product place, owing to cracking reaction is strong endothermic reaction, it is therefore desirable to pass through
Burn a large amount of fuel to provide heat；(3) waste heat boiler is made up of rapid-cooling heat exchanger and drum, by recovered flue gas and cracking
Heat in gas produces extra high pressure steam.
Cracking stock initially enters and tentatively heats, then with process in the middle of raw material preheating one section and raw material preheating two-stage nitration
The dilution steam generation of dilution steam generation preheating section heating mixes mutually.Mixed cracking stock and dilution steam generation enter raw material and steam with dilution
After vapour preheated one-section and two-stage nitration heat further, in enter the radiant coil in radiant section across pipe, there is cracking reaction.
It is provided with Bottom Nozzle Used (being called for short: the end burns) in some radiant section simultaneously and burner on sidewall (being called for short: side is burnt) carries for cracking reaction
For institute's calorific requirement, also it is provided only with Bottom Nozzle Used in some radiant section.Reacted Pintsch process gas needs at rapid-cooling heat exchanger
Middle lowered the temperature rapidly, thus reduced the adverse effect that side reaction brings to greatest extent.Pintsch process gas is in rapid-cooling heat exchanger
The heat being recovered for generating extra high pressure steam, and from drum draw laggard enter extra high pressure steam one section and the further mistake of two-stage nitration
Heat.The temperature of the extra high pressure steam of final output ethane cracking furnace can be adjusted by attemperator and control, super to meet
High pressure steam line and the requirement of steam user.It addition, the superpressure boiler feedwater entering drum needs to be introduced into economizer
In preheat, such that it is able 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 indication, it is meant that: according to the character of cracking stock, to target
The requirement of product yield and the requirement etc. to cracking furnace thermal efficiency, from the angle of technological process design one new and
And structure as far as possible reasonably ethane cracking furnace.
" operation optimization of ethane cracking furnace " of this patent indication, it is meant that: at an existing ethane cracking furnace
On the basis of, distribute by adjusting cracking stock, or by adjusting the process operation parameter of pyrolysis furnace, thus improve as much as possible
The thermal efficiency of pyrolysis furnace, the comprehensive yield etc. of raising target product.
The process design and calculation of ethane cracking furnace is sufficiently complex, it is necessary to consider several factors and restrictive condition simultaneously.Below
Only list the wherein factor that must take into of part:
(1) when designing the structure of convection section, it is necessary to take into full account the physical property of cracking stock, thus ensure that cracking stock exists
Phase, temperature and pressure fall in each section of raw material preheating bank of tubes are satisfied by requirement；Across the fluid temperature (F.T.) of pipe (that is, across temperature
Degree) must one reasonably within the scope of, thus meet the requirement of cracking reaction；Extra high pressure steam superheat section bank of tubes structure
Design must is fulfilled for steam pipe system and the requirement of steam user；Exhaust gas temperature too high can must drop within a zone of reasonableness
The thermal efficiency of low pyrolysis furnace, too low, dew point corrosion can occur.
(2) the steam heat cracking 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 all the most sensitive to reaction temperature.Therefore, when designing the structure of radiant section, it is necessary to
Take into full account the cracking reaction characteristic that cracking stock is corresponding, the overall dimensions (including length etc.) of appropriate design radiation chamber,
The radiation dimensional structure of bank of tubes, the quantity of burner and arrangement etc., make the flue gas in the Heat release mode of fuel combustion, burner hearth as far as possible
Flow pattern, the heat absorption pattern of bank of tubes reach Optimum Matching.
(3) when designing the structure of waste heat boiler, it is necessary to the structure of appropriate design rapid-cooling heat exchanger, so that Pintsch process
To a reasonable temperature, in avoiding rapid-cooling heat exchanger, there is coking in gas fast cooling as much as possible simultaneously as far as possible；Must be rationally
Boiler feedwater between drum and rapid-cooling heat exchanger is set and forms the circulating ratio of Natural Circulation convection current, make the generating capacity of steam with steady
Qualitative it is satisfied by requirement.
Different from process design and calculation, the operation optimization of ethane cracking furnace calculates the size that need not redesign pyrolysis furnace
Structure, but by change cracking stock distribution or adjust pyrolysis furnace operating parameter come object observing product yield,
How overall thermal efficiency, operation cycle and the stability of pyrolysis furnace change, so that it is determined that the pyrolysis furnace more optimized runs bar
Part.It is said that in general, the difficulty of " process design and calculation " is some larger.It addition, the method meeting " process design and calculation " is the most permissible
Meet the requirement of " operation optimization calculating ", this is because the core calculations model of the two is identical.
At present, the pyrolysis furnace computational methods of domestic-developed and model are primarily present problems with:
(1) Most models and method are both for operation optimization, seldom have the technological design meter for new pyrolysis furnace
Calculate, a lot of model parameters therein must rely on reality industry park plan data be fitted return, the suitability of model and
Extrapolation is the highest.
(2) most models and method all take simplification and process to reduce difficulty and amount of calculation, such as bank of tubes
Detailed construction is through approximating frequently with " cold-smoothing face ", thus cannot meet design-calculated required precision.Additionally some modeling
Method have employed the means of computational fluid dynamics simulation to pursue higher degree of accuracy, but due to the meter of this method
Calculation amount is excessive, the calculating overlong time of single operating mode, is therefore not used to must take into the process design and calculation of a large amount of operating mode.
(3) the most domestic the most convection section, radiant section and Waste Heat System are not combined modeling carry out technology Calculation
Method.Overwhelming majority method is limited only to process design and calculation and operation optimization calculating, therefore these models and the side of radiant section
The result that method obtains is only possible to be local optimum, it is impossible to meet high accuracy technology Calculation and the operation optimization of whole pyrolysis furnace.
In sum, for the problems referred to above, develop a set of associating containing convection section, radiant section and Waste Heat System
Computational methods, for technological design and the operation optimization of ethane cracking furnace, can be greatly improved the design of China's ethane cracking furnace
Technical merit, and the running status of existing ethane cracking furnace can be improved.
Summary of the invention
The present invention provides the coupling calculation of a kind of Ethylene vapor pyrolysis furnace, and the method has both the highest accuracy and very
High operation efficiency, both may be used for the process design and calculation of new pyrolysis furnace, it is also possible to for the operation optimization of existing pyrolysis furnace
Calculate.
For reaching above-mentioned purpose, the invention provides the coupling calculation of a kind of Ethylene vapor pyrolysis furnace, according to ethylene
The practical structures of pyrolysis furnace and technological process, be divided into three modules by the calculating of whole pyrolysis furnace, is that convection section calculates mould respectively
Block, radiant section computing module and waste heat boiler computing module, by iterative above three module, obtain cracking furnace system
Global solution, the method comprises the following steps:
(1) set up convection section computing module governing equation group, specifically include:
(1) the convection heat transfer' heat-transfer by convection model between convection section coil pipe and high-temperature flue gas is set up
According to the feature of the staggered sawtooth finned tube that convection section uses, between convection section coil pipe and high-temperature flue gas
Convective heat-transfer coefficient use ESCOA method calculate, computing 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 η uses equation below to calculate:
At=Af+ π d (1-nb) formula 9
M=[2ho(b+ws)/Km/b/ws]0.5Formula 11
AfAnd AtIt is the fin area under unit boiler tube length and the gross area, m respectively2/m；
KmIt is the heat conductivity 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 set up
Pressure drop when high-temperature flue gas flows between convection section bank of tubes uses equation below to calculate:
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 set up
In heating tube in section of convection chamber, the convective heat-transfer coefficient between monophasic fluid and boiler tube inwall uses equation below to calculate:
(4) Pressure Drop Model of monophasic fluid in heating tube in section of convection chamber is set up
Pressure drop expression formula along heating tube in section of convection chamber is:
For smooth straight length, 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 biphase heat transfer model of fluid in heating tube in section of convection chamber is set up
When undergoing phase transition in boiler tube, the flow pattern of Baker is used to judge the fluid stream when Bottomhole pressure
Type, in heating tube in section of convection chamber, the convective heat-transfer coefficient between fluid and boiler tube inwall uses equation below to calculate:
htc=α τthn+htFormula 24
τt=-10.08547+3.43598 (lnRet)2+0.01038(lnRet)3Formula 26
(2) set up radiant section computing module governing equation group, specifically include:
(1) the field method radiation heat-transfer model between high-temperature flue gas and radiation bank of tubes in burner hearth is set up
The thinking of field method is: radiant section is first divided into a series of surface district and flue gas district according to certain requirement by (a), its
Middle surface district is divided into again burner hearth inner surface section and outer surface of furnace tube district, and assumes that the temperature of each intra-zone is uniform；(b)
The Direct Exchange Areas between each region is calculated on the basis of hypothesis all surface is black matrix；C () is assuming own
Surface calculates the total transfer area between each region on the basis of being preferable grey body；D () is assuming the black of burner hearth flue gas
Degree can calculate the oriented flow area between each region on the basis of a transparent gas and several preferable ash gas；(e)
Each region is set up energy conservation equation, and it is carried out numerical solution, thus obtain the temperature of regional；
(1-a) Direct Exchange Areas between surface district and surface district, surface district and gas zone, gas zone and gas zone by
Equation below calculates:
(1-b) on the basis of Direct Exchange Areas, ask for total transfer area, each surface district is set up radiant flux and puts down
Weighing apparatus equation, obtains below equation group:
After arranging, obtain equation below group:
The coefficient matrix that the left side of above-mentioned formula is made up of Direct Exchange Areas, surface area and reflectance, the right side of equation
The column matrix that limit is then made up of blackness and the Direct Exchange Areas on surface.The method using numerical computations solves above-mentioned equation group
I.e. can obtain ratio reflection heat flow density, then according to following equation obtains the total transfer area between the district of surface:
(1-c) all of gas zones is set up radiant flux equilibrium equation, obtains below equation group:
After arranging, obtain equation below group:
The coefficient matrix that the left side of above-mentioned formula is made up of Direct Exchange Areas, surface area and reflectance, the right side of equation
The column matrix that limit is then made up of Direct Exchange Areas.The method using numerical computations solves above-mentioned equation group and i.e. can obtain ratio instead
Penetrate heat flow density, then according to following equation draws the total transfer area between gas zone and surface district:
Total transfer area between gas zone and surface district can use following formula to calculate:
Total transfer area between gas zone and gas zone then can use following formula to calculate:
(1-d) calculating oriented flow area, wherein the blackness of burner hearth flue gas uses a transparent gas and several ash bromhidrosis to add
Power approximates sign, the blackness ε of flue gasgWith absorbance αgIt is represented by:
Oriented flow area calculates according to following formula:
(1-e) energy-balance equation is set up in all regions
First to furnace wall inner surface section WSiSet up energy-balance equation:
Secondly, to boiler tube inner surface section TSiSet up energy-balance equation:
Finally, to gas zone GiSet up energy-balance equation:
Equation quantity in the final energy equation set up is equal to the quantity in all regions, and equation group is non-thread
Property equation group, use Newton-Raphson method solve；
(2) the free radical cracking reaction model in radiating furnace tube is set up
Use one-dimensional plug flow model to the reaction characterizing in radiating furnace tube, heat transfer and flow process, 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, uses formula 20～23.
(3) waste heat boiler computing module governing equation group is set up
Overall heat-transfer coefficient K of quenching boiler calculates according to equation below:
The heat transfer coefficient α of cracking gas in heat exchanger tubeiCalculate according to equation below:
The boiling heat transfer coefficient α of the outer high pressure boiler water supply of heat exchanger tubeoCalculate according to equation below:
Total heat exchange amount of linear rapid-cooling heat exchanger calculates according to equation below:
Q=K*F* Δ tmFormula 50
(4) being iterated solving above three module until restraining, specifically including:
Step 1: input convection section in cracking furnace and the detailed construction dimensional parameters of radiant section, including length, width and height, bank of tubes structure,
Burner structure and arrangement；
Step 2: input initial operational parameters: the physical property of cracking stock and flow, 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: solve convection section computing module and waste heat boiler computing module, until convergence, specifically includes:
Step 3.1: input the feedwater of initial superpressure boiler and the flow of extra high pressure steam；
Step 3.2: solve convection section computing module, until convergence；
Step 3.2: the economizer exit temperature exported by convection section computing module and the flow of extra high pressure steam substitute into useless
Heat boiler computing module, until convergence；
Step 3.3: the flow of the superpressure boiler feedwater and extra high pressure steam of comparing the output of waste heat boiler computing module is
No restrain；If convergence, then terminate to calculate；Otherwise, by new superpressure boiler feedwater and the flow generation of extra high pressure steam
Enter convection section computing module iterative computation again；
Step 4: the variate-value across temperature exported by convection section computing module substitutes into radiant section computing module and counts
Calculate, until convergence, specifically include:
Step 4.1: input prompt radiation coil metal outside wall temperature distribution；
Step 4.2: solve burner hearth calculating sub module, until convergence；
Step 4.3: radiant coil metal outer wall heat flux distribution burner hearth calculating sub module exported substitutes into boiler tube and calculates
Submodule calculates, until convergence；
Step 4.4: the radiant coil metal outer wall Temperature Distribution comparing the output of boiler tube calculating sub module has restrained.
If restrained, then terminate to calculate；Otherwise, new radiant coil metal outer wall Temperature Distribution is re-entered burner hearth and calculates son
Module calculates；
Step 5: judged the variate-value of new wall with flues temperature that radiant section computing module exports and flue gas flow the most
Convergence, if restrained, then terminates calculate and export 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 up of the threshold value of a certain series of preset, when
Front and back the difference of twice result of calculation is less than corresponding threshold value, then whole system and modules convergence.
When carrying out the process design and calculation of pyrolysis furnace and operation optimization calculates, convection section, radiant section and waste heat boiler this
The calculating of three big modules is coupled consumingly: the diabatic process of (1) convection section can affect across temperature；(2) across
Temperature then can affect the cracking reaction in radiant section, Fuel Consumption and wall with flues temperature；(3) Fuel Consumption and wall with flues temperature are anti-
Come over and the temperature of fluid in each section of bank of tubes of convection section and final exhaust gas temperature can be affected；(4) cracking reaction temperature can shadow
Ring the generating capacity of extra high pressure steam, and the generating capacity of extra high pressure steam also can affect the operating condition of convection section.
The complication system that above-mentioned this multiple module height are coupled, it is necessary to by modules according to certain
Logical order organizes together and is iterated solving and restraining, and just can obtain the global solution of whole system.On the contrary, if only by it
In some module individually split out and solve, can only obtain local solution, and this local solution may be the most inclined
From global solution, the true running status of pyrolysis furnace therefore cannot be represented.
Present invention employs nested coupling calculation to solve the global solution of cracking of ethylene furnace system.The method is according to second
The practical structures of alkene pyrolysis furnace and technological process, divide into three modules by the calculating of whole pyrolysis furnace, is convection section meter respectively
Calculate module, radiant section computing module and waste heat boiler computing module.Wherein, radiant section computing module itself contains again two
Submodule, is burner hearth calculating sub module and boiler tube calculating sub module respectively.Convection section computing module be used for calculate high-temperature flue gas with
The flowing of fluid, phase transformation and heat transfer in heat transfer between convection section bank of tubes and bank of tubes；Burner hearth calculating sub module is used for calculating fuel
Combustion heat release, the flowing of high-temperature flue gas, high-temperature flue gas and radiation bank of tubes between radiation and convection heat transfer' heat-transfer by convection；Boiler tube calculates submodule
Block is used for calculating complicated free radical cracking reaction and diabatic process in radiating furnace tube；Waste heat boiler computing module is used for calculating urgency
Heat transfer between cracking gas and boiler feedwater in cold heat exchanger.These computational methods can obtain the global solution of cracking furnace system, and
Non local solution, such that it is able to the real running status of accurate description pyrolysis furnace.
Nested coupling calculation in the present invention has the following characteristics that
1, taken into full account practical structures and the technological process of ethane cracking furnace, can completely describe convection section in cracking furnace,
Coupling correlation between radiant section and waste heat boiler, therefore, is whole pyrolysis furnace by the calculated result of the method
The global solution of system, rather than local solution, can be with the real running status of accurate description pyrolysis furnace.
2, burner hearth calculating sub module employs follow-on field method, no longer radiation bank of tubes is visualized as " a cold-smoothing
Face ", but taken into full account the actual three dimensional structure of radiation bank of tubes, carry out subregion calculating by independent for each boiler tube.Its
Secondary, user can carry out region division targetedly, the most flexibly and easily according to the practical structures of burner hearth and boiler tube.This
Follow-on field method truly reflects actual three dimensional structure and the size of pyrolysis furnace, both can guarantee that the degree of accuracy of result of calculation,
Amount of calculation can be maintained at again simultaneously one reasonably in the range of.
3, boiler tube calculating sub module employs 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, mean molecule quantity peace
All density etc., the method for employing numerical computations obtains the molecular composition of cracking stock, and (some relatively weight molecule needs to use virtual group
Part replaces), and as the initial conditions of cracking reaction；Have employed radical reaction network and accurately describe the steam hot tearing of hydro carbons
Solution preocess, radical reaction network includes 100 various ingredients and more than 2000 radical reaction, can accurately obtain turning of raw material
A series of important parameters such as rate, the cracking distribution of product, endothermic heat of reaction amount and coking state.Owing to have employed above-mentioned model,
Boiler tube calculating sub module can be exactly accurate describe stove tube fluid flowing, conduct heat and react.
4, convection section computing module has taken into full account the structure of actual bank of tubes, including the length of pipe, internal diameter, wall thickness, wing
Arranged opposite etc. between sheet pattern, fin height and thickness, pipe, can be with the biography between accurate description high-temperature flue gas and bank of tubes
Thermal process.
5, waste heat boiler computing module have employed the true three-dimension structure of rapid-cooling heat exchanger and drum and is modeled calculating, can
With the circulating ratio of Accurate Prediction Natural Circulation convection current, the generating capacity of extra high pressure steam and cracking gas through rapid-cooling heat exchanger
After temperature etc..
6, the method has the most different computation schemas, the most flexible and practical.For example, it is possible to setting fuel gas
The conversion ratio of cracking stock, the cracking yield of product, exhaust gas temperature, gas production etc. is calculated with the flow of cracking stock；Also may be used
The fuel tolerance etc. of needs is calculated with the conversion ratio of the yield of target setting product cracking stock alive；Sensitivity can also be passed through
The mode analyzed determines the correlation degree between each variable, thus help user determine optimal product distribution scheme and
Optimum operating parameter Assembled lamp.
The present invention has taken into full account the coupling between ethane cracking furnace convection section, radiant section and waste heat boiler these three module
Correlation, initially sets up the governing equation group of modules oneself, is then iterated according to the logical relation between module
Calculate, the final global solution obtaining cracking of ethylene furnace system.This invention possesses the highest accuracy and operation efficiency, may be used for
The process design and calculation of pyrolysis furnace and operation optimization calculate.This method suitability is relatively broad, can be used for different types of cracking
Raw material and hydrocarbons steam cracking furnace.
Accompanying drawing explanation
Fig. 1 is the process 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 convection section computing module and the detailed logic frame of waste heat boiler computing module of one embodiment of the invention
Figure；
Fig. 5 is the detailed logic block diagram of the radiant section computing module of one embodiment of the invention；
Fig. 6 be one embodiment of the invention field method between surface district and surface district direct interchange areas signal
Figure；
Fig. 7 be one embodiment of the invention field method between flue gas district and surface district direct interchange areas signal
Figure；
Fig. 8 be one embodiment of the invention field method between flue gas district and flue gas district direct interchange areas signal
Figure.
Detailed description of the invention
Calculated examples below in conjunction with certain industrial naphthas steam cracking furnace illustrates:
The pyrolysis furnace structure that calculated examples uses is as shown in Figure 1.Convection section bank of tubes is followed successively by raw material preheating one from top to bottom
Section, economizer, raw material preheating two-stage nitration, raw material and dilution steam generation preheated one-section, dilution steam generation preheating section, extra high pressure steam are overheated by one
Section, the overheated two-stage nitration of extra high pressure steam, raw material preheat two-stage nitration with dilution steam generation.At the outlet of dilution steam generation preheating section and raw material preheating two
Section exit arranges blender.Between extra high pressure steam overheated one section and two-stage nitration, attemperator is set.The end, is only set in radiant section
Portion's burner.The Waste Heat System arranging rapid-cooling heat exchanger and drum composition is lowered the temperature to cracking gas and produces extra high pressure steam.
1, convection section computing module governing equation group is set up
(1) the convection heat transfer' heat-transfer by convection model between convection section coil pipe and high-temperature flue gas
In this calculated examples, convection section have employed staggered sawtooth finned tube to strengthen convection heat transfer' heat-transfer by convection effect, convection current
Convective heat-transfer coefficient between section coil pipe and high-temperature flue gas uses famous ESCOA method to calculate, and computing 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 the bank of tubes obstruction area to flue gas, m2/m
CpIt 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)
K is the heat conductivity of flue gas, W/ (m K)
μ is the viscosity of flue gas, kg/ (m s)
(need to use average flue-gas temperature when calculating flue gas physical property.)
TgAnd TfIt is the temperature of flue gas and fin respectively, K
G is the mass flux of flue gas, kg/ (m2s)
D is the external diameter of heating tube in section of convection chamber, m
NwIt it is the radical of every grate furnace pipe
NdIt it is bank of tubes number
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 respectively, m
Re is the Reynolds number of flue gas
Fin efficiency η uses equation below to calculate:
At=Af+ π d (1-nb) formula 9
M=[2ho(b+ws)/Km/b/ws]0.5Formula 11
AfAnd AtIt is the fin area under unit boiler tube length and the gross area, m respectively2/m
KmIt is the heat conductivity 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 bank of tubes uses equation below to calculate:
C2=0.75+1.85Re-0.3Formula 16
ΔPgIt is pressure drop, mm wc
ρgIt is flue gas density under mean temperature, kg/m3
(3) the single-phase heat transfer model of fluid in heating tube in section of convection chamber
In heating tube in section of convection chamber, the convective heat-transfer coefficient between monophasic fluid and boiler tube inwall uses equation below to calculate:
hcIt is the convective heat-transfer coefficient between tube fluid and boiler tube inwall, 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)
K is the heat conductivity 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
Pressure drop expression formula along heating tube in section of convection chamber is:
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 length, 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 angle of bend of bend pipe, rad
(5) the biphase heat transfer model of fluid in heating tube in section of convection chamber
When undergoing phase transition in boiler tube, the flow pattern of Baker is used to judge the fluid stream when Bottomhole pressure
Type, in heating tube in section of convection chamber, the convective heat-transfer coefficient between fluid and boiler tube inwall uses equation below to calculate:
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 the nucleate boiling heat transfer coefficient correction factor relevant with flow pattern, can read from correlation graph
hnIt is nucleate boiling heat transfer coefficient, W/ (m2K)
htIt is biphase forced convection heat transfer coefficient, W/ (m2K)
τtIt it is biphase forced convertion nuclear boiling interference coefficient
kLIt is the heat conductivity of liquid medium, kcal/ (m hr K)
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 and fluid with T, DEG C
PWAnd PSIt is medium vapour pressure under wall and saturation temperature, kg/cm2
RetIt it 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 computational methods refer to Baker flow pattern
2, radiant section computing module governing equation group is set up
(1) in burner hearth high-temperature flue gas and radiation bank of tubes between field method radiation heat-transfer model
The core thinking of field method is: radiant section is first divided into a series of surface district and flue gas according to certain requirement by (a)
District, wherein surface district is divided into again burner hearth inner surface section and outer surface of furnace tube district, and assumes that the temperature of each intra-zone is uniform
's；B () calculates the Direct Exchange Areas between each region on the basis of hypothesis all surface is black matrix；C () is in vacation
If all surface calculates the total transfer area between each region on the basis of being preferable grey body；D () is assuming burner hearth cigarette
The blackness of gas can calculate the orientation stream interface between each region on the basis of a transparent gas and several preferable ash gas
Long-pending；E energy conservation equation is set up in each region by (), and it is carried out numerical solution, thus obtains the temperature etc. of regional.
It is pointed out that when outer surface of furnace tube being carried out region and dividing, in order to improve accuracy in computation, it is impossible to by whole
The simplification of individual bank of tubes is processed in one " cold-smoothing face ", on the contrary, needs individually to calculate each boiler tube.This calculated examples will be every
Root boiler tube is alongst divided into surface district every about 1 meter, and calculate each outer surface of furnace tube district and its
During Direct Exchange Areas between its region, it is necessary to utilize the knowledge of solid geometry to take into full account mutually covering between boiler tube.
(1-a) Direct Exchange Areas between surface district and surface district, surface district and gas zone, gas zone and gas zone
(see Fig. 7～8) can be calculated by equation below:
WithIt is between surface district and surface district, surface district and gas zone, gas zone and gas zone respectively
Direct Exchange Areas, m2
K is flue gas attenuation quotient under ash gas is assumed, 1/m
R is the distance between the infinitesimal of region, m
θiAnd θjFor the relative angle between region, rad
DA and dV is respectively surface district and the unit dimension of gas zone and element of volume, m2And m3
(1-b) it follows that ask for total transfer area on the basis of Direct Exchange Areas.Each surface district is set up radiation
Can mobile equilibrium equation, can obtain below equation group:
After arranging, equation below group can be obtained:
The coefficient matrix that the left side of above-mentioned formula is made up of Direct Exchange Areas, surface area and reflectance, the right side of equation
The column matrix that limit is then made up of blackness and the Direct Exchange Areas on surface.The method using numerical computations solves above-mentioned equation group
I.e. can obtain ratio reflection heat flow density, then according to following equation just can obtain the total transfer area between the district of surface.
For surface district SjSurface area, m2
For surface district SjBlackness
For surface district SjReflectance, it is numerically equal to
For than reflection heat flow density
(1-c) it follows that all of gas zones is set up radiant flux equilibrium equation, below equation group can be obtained:
After arranging, equation below group can be obtained:
The coefficient matrix that the left side of above-mentioned formula is made up of Direct Exchange Areas, surface area and reflectance, the right side of equation
The column matrix that limit is then made up of Direct Exchange Areas.The method using numerical computations solves above-mentioned equation group and i.e. can obtain ratio instead
Penetrate heat flow density, then according to following equation draws the total transfer area between gas zone and surface district:
Total transfer area between gas zone and surface district can use following formula to calculate:
Total transfer area between gas zone and gas zone then can use following formula to calculate:
(1-d) next calculating oriented flow area, the blackness of burner hearth flue gas can use a transparent gas and several ashes
Bromhidrosis weighting approximates sign.According to above-mentioned viewpoint, the blackness ε of flue gasgWith absorbance αgIt is represented by:
Wherein, ag,n(Tg) and a'g,n(Tg,Ts) it is to calculate flue gas blackness and during absorbance respectively, the weights of the n-th ash gas.
Therefrom it will be seen that the weights of blackness are only the most relevant with the temperature of flue gas, and the weights of absorbance both temperature with flue gas have
Close again relevant with the temperature in the surface district launching radiation.k'nIt is the specific damping coefficient of the n-th ash gas, 1/ (atm*m).P is flue gas
Force value, atm.L is the haul distance of radiant heat ray, m.
Therefore, oriented flow area can calculate according to following formula:
(1-e) next energy-balance equation is set up in all regions
First to furnace wall inner surface section WSiSet up energy-balance equation:
1st: WSiThe radiant heat coming from all furnace wall inner surfacies absorbed
2nd: WSiThe radiant heat coming from all boiler tube inner surfacies absorbed
3rd: WSiThe radiant heat coming from all gas district absorbed
4th: WSiTo all radiant heat of emission
5th: WSiBy the heat in the flue gas district that convection heat transfer' heat-transfer by convection pattern receives
6th: WSiCorresponding furnace wall outer wall heat loss value
Secondly, to boiler tube inner surface section TSiSet up energy-balance equation:
1st: TSiThe radiant heat coming from all furnace wall inner surfacies absorbed
2nd: TSiThe radiant heat coming from all boiler tube inner surfacies absorbed
3rd: TSiThe radiant heat coming from all gas district absorbed
4th: TSiTo all radiant heat of emission
5th: TSiBy the heat in the flue gas district that convection heat transfer' heat-transfer by convection pattern receives
6th: TSiBy the heat of Absorption of Medium in boiler tube
Finally, to gas zone GiSet up energy-balance equation:
1st: GiThe radiant heat coming from all furnace wall inner surfacies absorbed
2nd: GiThe radiant heat coming from all boiler tube inner surfacies absorbed
3rd: GiThe radiant heat coming from all gas district absorbed
4th: GiTo all radiant heat of emission
5th: GiThe heat that fuel combustion is discharged
6th: GiBy convection heat transfer' heat-transfer by convection model to the heat of surface block transitive
7th: GiThe enthalpy change occurred due to the flowing of flue gas
Equation quantity in the final energy equation set up is exactly equal to the quantity in all regions.Equation group is
Nonlinear System of Equations, can use Newton-Raphson method to solve.
(2) the free radical cracking reaction model in radiating furnace tube
In radiating furnace tube, the heat scission reaction of hydrocarbon raw material is sufficiently complex, and its computational accuracy directly determines product and receives
The accuracy of the key parameters such as rate and endothermic heat of reaction amount.At present, the simulation to cracking process mainly has three kinds of different models:
The first is empirical model.It directly uses Empirical Equation to enter the yield of cracking product with reaction condition parameter
Row association, and according to the industry park plan data of substantial amounts of reality, the parameter in Empirical Equation is carried out regression fit.Empirical Mode
Type simple, intuitive, the most practical.But it is experimental for being better than it, therefore fundamentally cannot be used exploitation novel furnace and
The process design and calculation of novel furnace, prolongs in model and extrapolates the most unreliable, and a set of model parameter is often appropriate only to specific
The type of furnace.
The second is molecular model.Complicated cracking stock illusion is become single virtual component by this model, and will split
Solve reaction and be simplified to a primary first-order equation and several secondary responses, mutually do not intersect between two reactions.Molecular model ratio
Empirical model has higher extrapolation and the suitability, but for different cracking stocks, cracking condition and pyrolysis furnace structure,
Remain a need for being fitted the parameter related in primary first-order equation returning.When model being carried out extrapolation application, it is still desirable to mend
Fill appropriate experimental data.
The third is free radical model.This model uses the radical reaction of series of complex to reappear as far as possible in boiler tube
Real cracking reaction process, course of reaction includes that chain causes, takes H, free radical addition, free radical decomposition, free radical isomery by force
The processes such as change, chain termination.This model has the strongest versatility and the highest precision.
This calculated examples have employed radical reaction network and accurately describes the steam heat cracking process of hydro carbons, this free radical
Reaction network includes 100 various ingredients and more than 2000 radical reaction, the weight such as the pre-exponential factor of each reaction and activation energy
Want parameter all to be determined with substantial amounts of experiment and industry park plan data by strict theoretical derivation, can accurately obtain Petroleum
Raw material conversion ratio, the cracking distribution of product, endothermic heat of reaction amount and coking states etc. under various different bank of tubes structures are a series of
Important parameter.
It addition, the macroscopic properties of Petroleum mainly includes average density, mean molecule quantity, PONA value and D86 distillation curve,
Therefore, before using radical reaction network, first have to use the molecular composition reconstruction model of cracking stock to obtain stone brain
The molecular composition of oil is as the input of reaction network.Molecular composition reconstruction model contains the molecular library of complete set, wherein
Store the physical property of all candidate molecules.Meanwhile, model is also associated with determining between Petroleum macroscopic properties and Molecuar matter
Magnitude relation formula.Oil product macroscopic properties as initial conditions, and is utilized these quantitative relation formulas and comentropy to maximize by this model
Principle obtains the molecular composition of oil product.
One-dimensional plug flow model can be used to the reaction characterizing in radiating furnace tube, heat transfer and flow process, it is necessary to it
Set up 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
rkFor reacting the reaction rate of k, kmol/m3/s
vkiFor the reaction stoichiometric coefficient of component i in reaction k
N is the reaction number in reaction network
D is 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 girth of boiler tube, m
Q is the heat flux of the incoming boiler tube of burner hearth, kJ/m2/s
T is the temperature of fluid, K
CpiFor the component i specific heat when temperature T, kJ/kmol/K
For the standard molar formation enthalpy of component k, kJ/kmol
RkFor the clean 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 set up
The major function of waste heat boiler computing module is to calculate outlet temperature and the aerogenesis of extra high pressure steam of cracking gas
Amount, wherein the result of calculation of gas production directly can affect the Calculation of Heat Transfer of convection section.This calculated examples have employed linear chilling and changes
Hot device, can by cracking gas fast cooling, and can reduce as far as possible cracking gas coking tendency, extend the operation cycle.
Overall heat-transfer coefficient K of quenching boiler calculates according to equation below:
K is overall heat-transfer coefficient, W/ (m2K)
αiIt is the heat transfer coefficient of cracking gas, W/ (m in heat exchanger tube2K)
αoIt is the boiling heat transfer coefficient of feedwater, W/ (m in the outer pressure cooker of heat exchanger tube2K)
doAnd diIt is external diameter and the internal diameter of heat exchanger tube respectively, m
dcIt is the internal diameter of focus layer, m
λwIt is the heat conductivity of heat exchanger tube, W/ (m K)
λcIt is the heat conductivity of focus layer, W/ (m K)
RoAnd RiIt is outside heat exchanger tube respectively and the dirtiness resistance of inner side, W/ (m2K)
The heat transfer coefficient α of cracking gas in heat exchanger tubeiCalculate according to equation below:
λgIt is the mean coefficient of heat conductivity of cracking gas, W/ (m K)
Re is the cracking gas Reynolds number when heat exchange Bottomhole pressure
ρ is the density of cracking gas, kg/m3
μgAnd μwIt is cracking gas viscosity in pipe under mean temperature and under wall temperature respectively, kg/ (m s)
Pr is Prandtl number
The boiling heat transfer coefficient α of the outer high pressure boiler water supply of heat exchanger tubeoCalculate according to equation below:
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 calculates according to equation below:
Q=K*F* Δ tmFormula 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 calculates according to equation below:
D is steam production, kg/hr
η is the radiation loss rate of rapid-cooling heat exchanger；
R is the latent heat of vaporization of boiler feedwater, kJ/kg；
4, it is iterated solving all modules until restraining
The governing equation of convection section, radiant section and waste heat boiler computing module is set up after standing, according to patrolling described in Fig. 3
These modules are iterated solving until restraining by the relation of collecting, and i.e. can get the actual operation parameters of pyrolysis furnace under specified criteria,
Including cracking severity, the yield of target product, furnace tube temperature and the heat flux distribution of raw material, wall with flues temperature, convection section smoke evacuation temperature
Degree, convection section each bank of tubes temperature, extra high pressure steam yield, cracking gas leave the temperature of rapid-cooling heat exchanger, and some other is very
Important operating parameter.
The iterative computation of whole system is sufficiently complex, and following methods can improve the constringency performance of the method:
(1) it is particularly significant that rational initial value is set；
(2) in order to improve the convergence capabilities of computational methods, can be that each module arranges a relaxation factor, reduce middle
The impact strength of parameters value during calculating；
(3) maximum concussion interval and the concussion step-length of each parameter are set；
(4) can first force to fix all parameter values of certain module, again this module be opened after other module restrains.
Last it is noted that above example is only in order to illustrate technical scheme, it is not intended to limit；Although
With reference to previous embodiment, the present invention is described in detail, it will be understood by those within the art that: it still may be used
So that the technical scheme described in previous embodiment to be modified, or wherein portion of techniques feature is carried out equivalent；And
These amendments or replacement, do not make the essence of appropriate technical solution depart from spirit and the model of embodiment of the present invention technical scheme
Enclose.
Claims (2)
1. the coupling calculation of an Ethylene vapor pyrolysis furnace, it is characterised in that according to the practical structures of ethane cracking furnace and
Technological process, is divided into three modules by the calculating of whole pyrolysis furnace, be respectively convection section computing module, radiant section computing module and
Waste heat boiler computing module, by iterative above three module, obtains the global solution of cracking furnace system, the method include with
Lower step:
(1) set up convection section computing module governing equation group, specifically include:
(1) the convection heat transfer' heat-transfer by convection model between convection section coil pipe and high-temperature flue gas is set up
The feature of staggered sawtooth finned tube used according to convection section, right between convection section coil pipe and high-temperature flue gas
Stream heat transfer coefficient uses ESCOA method to calculate, and computing 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 the bank of tubes obstruction area to flue gas, m2/m；
CpIt 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)；
K is the heat conductivity of flue gas, W/ (m K)；
μ is the viscosity of flue gas, kg/ (m s)；
TgAnd TfIt is the temperature of flue gas and fin respectively, K；
G is the mass flux of flue gas, kg/ (m2s)；
D is the external diameter of heating tube in section of convection chamber, m；
NwIt it is the radical of every grate furnace pipe；
NdIt it is bank of tubes number；
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 respectively, m；
Re is the Reynolds number of flue gas；
Fin efficiency η uses equation below to calculate:
At=Af+ π d (1-nb) formula 9
M=[2ho(b+ws)/Km/b/ws]0.5Formula 11
AfAnd AtIt is the fin area under unit boiler tube length and the gross area, m respectively2/m；
KmIt is the heat conductivity 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 set up
Pressure drop when high-temperature flue gas flows between convection section bank of tubes uses equation below to calculate:
C2=0.75+1.85Re-0.3Formula 16
ΔPgIt is pressure drop, mm wc；
ρgIt is flue gas density under mean temperature, kg/m3；
(3) the single-phase heat transfer model of fluid in heating tube in section of convection chamber is set up
In heating tube in section of convection chamber, the convective heat-transfer coefficient between monophasic fluid and boiler tube inwall uses equation below to calculate:
hcIt is the convective heat-transfer coefficient between tube fluid and boiler tube inwall, 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)；
K is the heat conductivity 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 set up
Pressure drop expression formula along heating tube in section of convection chamber is:
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 length, 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 angle of bend of bend pipe, rad；
(5) the biphase heat transfer model of fluid in heating tube in section of convection chamber is set up
When undergoing phase transition in boiler tube, the flow pattern of Baker is used to judge the fluid flow pattern when Bottomhole pressure, right
Convective heat-transfer coefficient between stream section stove tube fluid and boiler tube inwall uses equation below to calculate:
htc=α τthn+htFormula 24
τt=-10.08547+3.43598 (ln Ret)2+0.01038(ln Ret)3Formula 26
htcIt is the comprehensive convective heat-transfer coefficient of two phase flow, W/ (m2K)；
α is the nucleate boiling heat transfer coefficient correction factor relevant with flow pattern, can read from correlation graph；
hnIt is nucleate boiling heat transfer coefficient, W/ (m2K)；
htIt is biphase forced convection heat transfer coefficient, W/ (m2K)；
τtIt it is biphase forced convertion nuclear boiling interference coefficient；
kLIt is the heat conductivity of liquid medium, kcal/ (m hr K)；
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 and fluid with T, DEG C；
PWAnd PSIt is medium vapour pressure under wall and saturation temperature, kg/cm2；
RetIt it 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 its computational methods refer to Baker flow pattern；
(2) set up radiant section computing module governing equation group, specifically include:
(1) the field method radiation heat-transfer model between high-temperature flue gas and radiation bank of tubes in burner hearth is set up
The thinking of field method is: radiant section is first divided into a series of surface district and flue gas district, Qi Zhongbiao according to certain requirement by (a)
Face district is divided into again burner hearth inner surface section and outer surface of furnace tube district, and assumes that the temperature of each intra-zone is uniform；B () exists
Assume that all surface calculates the Direct Exchange Areas between each region on the basis of being black matrix；C () is assuming all tables
Face calculates the total transfer area between each region on the basis of being preferable grey body；D () is assuming the blackness of burner hearth flue gas
The oriented flow area between each region can be calculated on the basis of a transparent gas and several preferable ash gas；E () is right
Energy conservation equation is set up in each region, and it is carried out numerical solution, thus obtains the temperature of regional；
(1-a) Direct Exchange Areas between surface district and surface district, surface district and gas zone, gas zone and gas zone is by as follows
Formula calculates:
WithIt is straight between surface district and surface district, surface district and gas zone, gas zone and gas zone respectively
Meet exchange area, m2；
K is flue gas attenuation quotient under ash gas is assumed, 1/m；
R is the distance between the infinitesimal of region, m；
θiAnd θjFor the relative angle between region, rad；
DA and dV is respectively surface district and the unit dimension of gas zone and element of volume, m2And m3；
(1-b) on the basis of Direct Exchange Areas, ask for total transfer area, each surface district is set up radiant flux balance side
Journey, obtains below equation group:
After arranging, obtain equation below group:
The coefficient matrix that the left side of above-mentioned formula is made up of Direct Exchange Areas, surface area and reflectance, the right of equation is then
The column matrix being made up of blackness and the Direct Exchange Areas on surface.The method using numerical computations solves above-mentioned equation group
Obtain ratio reflection heat flow density, then according to following equation obtains the total transfer area between the district of surface:
For surface district SjSurface area, m2；
For surface district SjBlackness；
For surface district SjReflectance, it is numerically equal to
For than reflection heat flow density；
(1-c) all of gas zones is set up radiant flux equilibrium equation, obtains below equation group:
After arranging, obtain equation below group:
The coefficient matrix that the left side of above-mentioned formula is made up of Direct Exchange Areas, surface area and reflectance, the right of equation is then
The column matrix being made up of Direct Exchange Areas.The method using numerical computations solves above-mentioned equation group and i.e. can obtain than reflection heat
Current density, then according to following equation draws the total transfer area between gas zone and surface district:
Total transfer area between gas zone and surface district can use following formula to calculate:
Total transfer area between gas zone and gas zone then can use following formula to calculate:
(1-d) calculating oriented flow area, wherein the blackness of burner hearth flue gas uses a transparent gas and several ash bromhidrosis weightings
Approximation characterizes, the blackness ε of flue gasgWith absorbance αgIt is represented by:
Wherein, ag,n(Tg) and a'g,n(Tg,Ts) it is to calculate flue gas blackness and during absorbance respectively, the weights of the n-th ash gas, k'nIt is
The specific damping coefficient of the n-th ash gas, 1/ (atm*m)；P is the force value of flue gas, atm.L is the haul distance of radiant heat ray,
m；
Oriented flow area calculates according to following formula:
(1-e) energy-balance equation is set up in all regions
First to furnace wall inner surface section WSiSet up energy-balance equation:
1st: WSiThe radiant heat coming from all furnace wall inner surfacies absorbed；
2nd: WSiThe radiant heat coming from all boiler tube inner surfacies absorbed；
3rd: WSiThe radiant heat coming from all gas district absorbed；
4th: WSiTo all radiant heat of emission；
5th: WSiBy the heat in the flue gas district that convection heat transfer' heat-transfer by convection pattern receives；
6th: WSiCorresponding furnace wall outer wall heat loss value；
Secondly, to boiler tube inner surface section TSiSet up energy-balance equation:
1st: TSiThe radiant heat coming from all furnace wall inner surfacies absorbed；
2nd: TSiThe radiant heat coming from all boiler tube inner surfacies absorbed；
3rd: TSiThe radiant heat coming from all gas district absorbed；
4th: TSiTo all radiant heat of emission；
5th: TSiBy the heat in the flue gas district that convection heat transfer' heat-transfer by convection pattern receives；
6th: TSiBy the heat of Absorption of Medium in boiler tube；
Finally, to gas zone GiSet up energy-balance equation:
1st: GiThe radiant heat coming from all furnace wall inner surfacies absorbed；
2nd: GiThe radiant heat coming from all boiler tube inner surfacies absorbed；
3rd: GiThe radiant heat coming from all gas district absorbed；
4th: GiTo all radiant heat of emission；
5th: GiThe heat that fuel combustion is discharged；
6th: GiBy convection heat transfer' heat-transfer by convection model to the heat of surface block transitive；
7th: GiThe enthalpy change occurred due to the flowing of flue gas；
Equation quantity in the final energy equation set up is equal to the quantity in all regions, and equation group is non-linear side
Journey group, uses Newton-Raphson method to solve；
(2) the free radical cracking reaction model in radiating furnace tube is set up
Use one-dimensional plug flow model to the reaction characterizing in radiating furnace tube, heat transfer and flow process, radiating furnace tube is set up matter
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；
rkFor reacting the reaction rate of k, kmol/m3/s；
vkiFor the reaction stoichiometric coefficient of component i in reaction k；
N is the reaction number in reaction network；
D is 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 girth of boiler tube, m；
Q is the heat flux of the incoming boiler tube of burner hearth, kJ/m2/s；
T is the temperature of fluid, K；
CpiFor the component i specific heat when temperature T, kJ/kmol/K；
For the standard molar formation enthalpy of component k, kJ/kmol；
RkFor the clean 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, uses formula 20～23.
(3) waste heat boiler computing module governing equation group is set up
Overall heat-transfer coefficient K of quenching boiler calculates according to equation below:
K is overall heat-transfer coefficient, W/ (m2K)；
αiIt is the heat transfer coefficient of cracking gas, W/ (m in heat exchanger tube2K)；
αoIt is the boiling heat transfer coefficient of feedwater, W/ (m in the outer pressure cooker of heat exchanger tube2K)；
doAnd diIt is external diameter and the internal diameter of heat exchanger tube respectively, m；
dcIt is the internal diameter of focus layer, m；
λwIt is the heat conductivity of heat exchanger tube, W/ (m K)；
λcIt is the heat conductivity of focus layer, W/ (m K)；
RoAnd RiIt is outside heat exchanger tube respectively and the dirtiness resistance of inner side, W/ (m2K)；
The heat transfer coefficient α of cracking gas in heat exchanger tubeiCalculate according to equation below:
λgIt is the mean coefficient of heat conductivity of cracking gas, W/ (m K)；
Re is the cracking gas Reynolds number when heat exchange Bottomhole pressure；
ρ is the density of cracking gas, kg/m3；
μgAnd μwIt is cracking gas viscosity in pipe under mean temperature and under wall temperature respectively, kg/ (m s)；
Pr is Prandtl number；
The boiling heat transfer coefficient α of the outer high pressure boiler water supply of heat exchanger tubeoCalculate according to equation below:
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 calculates according to equation below:
Q=K*F* Δ tmFormula 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 calculates according to equation below:
D is steam production, kg/hr；
η is the radiation loss rate of rapid-cooling heat exchanger；
R is the latent heat of vaporization of boiler feedwater, kJ/kg；
(4) being iterated solving above three module until restraining, specifically including:
Step 1: input convection section in cracking furnace and the detailed construction dimensional parameters of radiant section, including length, width and height, bank of tubes structure, combustion
Burner structure and arrangement；
Step 2: input initial operational parameters: the physical property of cracking stock and flow, 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: solve convection section computing module and waste heat boiler computing module, until convergence, specifically includes:
Step 3.1: input the feedwater of initial superpressure boiler and the flow of extra high pressure steam；
Step 3.2: solve convection section computing module, until convergence；
Step 3.2: the economizer exit temperature exported by convection section computing module and the flow of extra high pressure steam substitute into waste heat boiler
Stove computing module, until convergence；
Step 3.3: the superpressure boiler comparing the output of waste heat boiler computing module has fed water the flow with extra high pressure steam the most
Through convergence；If convergence, then terminate to calculate；Otherwise, the flow substitution by new superpressure boiler feedwater and extra high pressure steam is right
Stream section computing module iterative computation again；
Step 4: the variate-value across temperature exported by convection section computing module 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: solve burner hearth calculating sub module, until convergence；
Step 4.3: radiant coil metal outer wall heat flux distribution burner hearth calculating sub module exported substitutes into boiler tube and calculates submodule
Block calculates, until convergence；
Step 4.4: the radiant coil metal outer wall Temperature Distribution comparing the output of boiler tube calculating sub module has restrained.If
Restrain, then terminated to calculate；Otherwise, new radiant coil metal outer wall Temperature Distribution is re-entered burner hearth calculating sub module
Calculate；
Step 5: judge that the variate-value of new wall with flues temperature that radiant section computing module exports and flue gas flow has been restrained,
If restrained, then terminate calculate and export final calculation result；Otherwise, by new wall with flues temperature and the variable of flue gas flow
Value substitutes into convection section and waste heat boiler computing module re-starts calculating.
Coupling calculation the most according to claim 1, it is characterised in that the convergence of whole system and modules is sentenced
Constitute according to by the threshold value of a certain series of preset, when the difference of twice result of calculation of front and back is less than corresponding threshold value, the most whole system
System and modules are restrained.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN109214113A (en) * | 2018-09-30 | 2019-01-15 | 西安交通大学 | A kind of new model depression of order method for solving of architectural exterior-protecting construction dynamic heat transfer |
| CN111032831A (en) * | 2017-06-16 | 2020-04-17 | 法国德西尼布 | Cracking furnace system and process for cracking hydrocarbon feedstock therein |
| CN113958947A (en) * | 2021-11-10 | 2022-01-21 | 西安热工研究院有限公司 | Method for determining key size of 1000 MW-grade east-west high-sodium coal boiler furnace |
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| CN103310123A (en) * | 2013-07-10 | 2013-09-18 | 华东理工大学 | Coupling modeling method for verifying and optimizing design of industrial ethylene steam cracking furnace |
| CN103992813B (en) * | 2014-05-28 | 2016-04-06 | 惠生工程（中国）有限公司 | Ethane cracking furnace |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111032831A (en) * | 2017-06-16 | 2020-04-17 | 法国德西尼布 | Cracking furnace system and process for cracking hydrocarbon feedstock therein |
| CN109214113A (en) * | 2018-09-30 | 2019-01-15 | 西安交通大学 | A kind of new model depression of order method for solving of architectural exterior-protecting construction dynamic heat transfer |
| CN113958947A (en) * | 2021-11-10 | 2022-01-21 | 西安热工研究院有限公司 | Method for determining key size of 1000 MW-grade east-west high-sodium coal boiler furnace |
| CN113958947B (en) * | 2021-11-10 | 2024-04-19 | 西安热工研究院有限公司 | Method for determining critical dimension of 1000 MW-level quasi-east high-sodium coal boiler furnace |
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