CN105426577A - Figure simulation method for unsteady-state heat transfer process of large-sized crude oil floating-roof tank - Google Patents

Abstract

The present invention relates to a figure simulation method for an unsteady-state heat transfer process of a large-sized crude oil floating-roof tank, which solves the problem that existing figure simulation researches cannot comprehensively reflect an influential rule of related factors on a large-sized floating-roof oil tank temperature field. A mathematical model, which is established by particularly adopting a grid generation technology, of an oil product heat transfer process in a large-sized floating-roof crude oil tank can ensure that a figure simulation process coincides with an actual woking condition to the largest extent; and the model is solved by using an iteration method. The method has the characteristics of simplicity, flexibility and high versatility, and is easy to be implemented on the computer; and not only can computing efficiency be ensured, but also time is saved.

Description

A kind of large-scale crude oil floating roof tank unsteady-state heat transfer numerical simulation method

Technical field

The present invention relates to a kind of method for numerical simulation, particularly one large-scale crude oil floating roof tank unsteady-state heat transfer numerical simulation method.

Background technology

Along with the increase of crude stockpile demand, large floating roof oil tank has become the first-selected oil storage facility of extensive crude oil storage because of its technology and advantage economically.Oil tank in production run, when crude oil temperature in tank is lower than wax precipitation piont, waxy crude oil can because of analyse wax surround at the bottom of floating roof, tank skin and tank in along formation certain thickness and the solidifying oil reservoir of intensity, may the accidents such as solidifying tank be there is time serious.Therefore, for guaranteeing that storage tank is kept the safety in production, the Changing Pattern of crude oil temperature field in tank accurately must be grasped.Research method both at home and abroad for storage tank oil product temperature field mainly concentrates on numerical simulation, on-the-spot test two aspects.Adopt on-the-spot test, more reliable result can be obtained to specific engineering problem, but it can only use when condition is identical, has larger limitation, and apply heat transfer theory to oil tank and carry out numerical simulation, then can make up that this is not enough preferably.

The Changing Pattern in application Numerical Method Study oil tank temperature field, the software simulation calculated now by traditional experimental formula solves, and Physics-mathematics model and the actual oil tank of foundation are more and more pressed close to, and correspondingly numerical solution process also becomes increasingly complex.When adopting empirical formula method to calculate crude oil temperature field Changing Pattern in tank, method with empirical value is often taked to the setting of border heat transfer coefficient, crude oil temperature in tank is regarded as an entirety to calculate, though computation process is simple and convenient, but actual conditions have been carried out over-simplification, cause computational solution precision limited, can only use as reference in Practical Project.Existing business software, as the CFD numerical simulation softwares such as Fluent may be used for the numerical simulation of crude oil storage tank unsteady-state heat transfer process, it has abundant physical model, advanced numerical method and powerful pre-process and post-process function, but calculate consuming time more, only can temperature drop feature in reflection object shorter a period of time, not easily be applied to engineering practice, and this kind of software can not obtain the Changing Pattern of bulk temperature field.

In sum, at present for large-scale crude oil floating roof tank unsteady-state heat transfer numerical simulation research, all there is certain limitation, cannot reflect that correlative factor is to large floating roof oil tank temperature profile effect rule comprehensively.

Summary of the invention

In order to overcome the above-mentioned shortcoming of prior art, the invention provides a kind of large-scale crude oil floating roof tank unsteady-state heat transfer numerical simulation method.

The technical solution adopted for the present invention to solve the technical problems is: a kind of large-scale crude oil floating roof tank unsteady-state heat transfer numerical simulation method, comprises following content:

Step one: cross the section of axis with crude oil storage tank for research object, sets up storage tank two dimensional unsteady heat transfer numerical model;

Step 2: use method of finite difference logarithm value model area to carry out discrete, obtain the unstable state discrete equation of outside angle point, boundary node and internal node, and according to the stability of discrete equation, determine spatial mesh size and time step;

Step 3: according to the boundary condition at the bottom of tank deck, tank skin and tank, set up the corresponding relation of crude oil property parameter, border heat transfer coefficient and temperature, described border heat transfer coefficient comprises heat transfer coefficient at the bottom of tank deck heat transfer coefficient, tank skin heat transfer coefficient and tank, specifically carries out according to following steps:

(1) suppose tank deck temperature, and the mean value between oil product temperature is qualitative temperature, then calculates the physical parameter of oil product under this qualitative temperature: relative density, viscosity, coefficient of heat conductivity, specific heat capacity and coefficient of volumetric expansion;

(2) according to Grashof and Prandtl criterion, determine middle coefficient and value, then calculate inner coefficient of heat emission, outside coefficient of heat emission and radiant heat-transfer coefficient, if double plate floating roof tank, also need to calculate coefficient of heat emission in deliver from vault according to buoyancy module qualitative temperature;

(3) calculate tank deck heat transfer coefficient, check according to heat balance principle; If meet precision, then think that the medial temperature of supposition is accurately; If do not met, should assumed average temperature again, then calculate tank deck heat transfer coefficient, in like manner can obtain heat transfer coefficient at the bottom of tank skin heat transfer coefficient and tank;

Step 4: assignment is carried out to crude oil initial temperature in tank, use method of interpolation by the crude oil property parameter under relevant temperature and border heat transfer coefficient, be updated in outside angle point, boundary node and internal node discrete equation, then iteration carries out the calculating of next time step, draw crude oil temperature field distribution in tank, terminate until whole simulation process calculates, draw the Changing Pattern of crude oil temperature field in tank.

Cross the section of axis for research object with crude oil storage tank in said method described in step one, set up storage tank two dimensional unsteady heat transfer numerical model, this numerical model is:

$\frac{\∂}{\∂x}\left(\mathrm{\λ}\frac{\∂t(x,y)}{\∂x}\right)+\frac{\∂}{\∂y}\left(\mathrm{\λ}\frac{\∂t(x,y)}{\∂y}\right)=\mathrm{\ρ}c\frac{\∂t(x,y)}{\∂\mathrm{\τ}}.$

Utilization method of finite difference logarithm value model area in said method described in step 2 carries out discrete, and obtain the unstable state discrete equation of outside angle point, the bottom corner point equation in the unstable state discrete equation of its peripheral angle point is:

$\begin{array}{c}{t}_{(1,1)}^{i+1}=2{\mathrm{Fo}}_x{t}_{(2,1)}^i+2{\mathrm{Fo}}_y{t}_{(1,2)}^i+2{\mathrm{Fo}}_x\×{\mathrm{Bi}}_x{t}_f\\ +2{\mathrm{Fo}}_y\×{\mathrm{Bi}}_{ydi}{t}_{tu}+\left(\begin{array}{c}1-2F{o}_x-2F{o}_y-2F{o}_x\\ \×{\mathrm{Bi}}_x-2{\mathrm{Fo}}_y\×{\mathrm{Bi}}_{ydi}\end{array}\right)t_{(1,1)}^i\end{array}$

In formula: Fo _x, Bi _xbe respectively grid Fourier number on x direction, grid finishes wet number, Fo _yfor grid Fourier number, Bi on y direction _ydifor on y direction, bottom, grid finishes wet number;

Top corner point equation in the unstable state discrete equation of its peripheral angle point is:

$\begin{array}{c}{t}_{(M,N)}^{i+1}=2{\mathrm{Fo}}_y{t}_{(M,N-1)}^i+2\left(\begin{array}{c}F{o}_x\×B{i}_x\\ +{\mathrm{Fo}}_y\×{\mathrm{Bi}}_{yding}\end{array}\right)t_f\\ +2{\mathrm{Fo}}_x{t}_{(M-1,N)}^i+\left(\begin{array}{c}1-2{\mathrm{Fo}}_y-2{\mathrm{Fo}}_x-\\ 2{\mathrm{Fo}}_x\×{\mathrm{Bi}}_x-2{\mathrm{Fo}}_y\×{\mathrm{Bi}}_{yding}\end{array}\right)t_{(M,N)}^i\end{array}$

In formula: Bi _ydingfor on y direction, top, grid finishes wet number, K _dingfor tank deck heat transfer coefficient, W/ (m ²dEG C).

Utilization method of finite difference logarithm value model area in said method described in step 2 carries out discrete, obtain the unstable state discrete equation of boundary node, vertical boundary node wherein is mainly subject to the impact of tank skin heat transfer and adjacent three some temperature, and on it, the discrete equation of any node is:

$\begin{array}{c}{t}_{(1,b)}^{i+1}={\mathrm{Fo}}_y{t}_{(1,b-1)}^i+{\mathrm{Fo}}_y{t}_{(1,b+1)}^i+2{\mathrm{Fo}}_x{t}_{(2,b)}^i+\\ 2{\mathrm{Fo}}_x\×{\mathrm{Bi}}_x{t}_f+(1-2{\mathrm{Fo}}_x-2{\mathrm{Fo}}_y-2{\mathrm{Fo}}_x\×{\mathrm{Bi}}_x)t_{(1,b)}^i\end{array}$

Straight boundary node is wherein mainly by the impact of heat transfer and adjacent three some temperature at the bottom of tank deck or tank, and the discrete equation of arbitrary coboundary node E (a, N) in straight boundary node is:

$\begin{array}{c}{t}_{(a,N)}^{i+1}={\mathrm{Fo}}_x{t}_{(a-1,N)}^i+{\mathrm{Fo}}_x{t}_{(a+1,N)}^i+2{\mathrm{Fo}}_y{t}_{(a,N-1)}^i\\ +2{\mathrm{Fo}}_y\×{\mathrm{Bi}}_{yding}{t}_f+(1-2{\mathrm{Fo}}_x-2{\mathrm{Fo}}_y-2{\mathrm{Fo}}_y\×{\mathrm{Bi}}_{yding})t_{(a,N)}^i\end{array}$

The discrete equation of the arbitrary lower boundary node F (d, 1) in straight boundary node is:

$\begin{array}{c}{t}_{(d,1)}^{i+1}={\mathrm{Fo}}_x{t}_{(d-1,1)}^i+{\mathrm{Fo}}_x{t}_{(d+1,1)}^i+2{\mathrm{Fo}}_y{t}_{(d,2)}^i\\ +2{\mathrm{Fo}}_y\×{\mathrm{Bi}}_{ydi}{t}_{tu}+(1-2{\mathrm{Fo}}_x-2{\mathrm{Fo}}_y-2{\mathrm{Fo}}_y\×{\mathrm{Bi}}_{ydi})t_{(d,1)}^i\end{array}$

Utilization method of finite difference logarithm value model area in said method described in step 2 carries out discrete, and the unstable state discrete equation obtaining inner any node H (m, n) is:

$t_{(m,n)}^{i+1}={\mathrm{Fo}}_x{t}_{(m-1,n)}^i+{\mathrm{Fo}}_x{t}_{(m+1,n)}^i+{\mathrm{Fo}}_y{t}_{(m,n-1)}^i+{\mathrm{Fo}}_y{t}_{(m,n+1)}^i+\left(1-2{\mathrm{Fo}}_x-2{\mathrm{Fo}}_y\right)t_{(m,n)}^i$

Compared with prior art, the invention has the beneficial effects as follows: based on varied property model, in the large-scale floating roof crude oil storage tank adopting grid generation technique to set up, the mathematical model of oil product diabatic process, can ensure that numerical simulation and actual condition match to greatest extent; And using the method for iteration to solve this model, it has simply, flexibly and the feature of highly versatile, method is convenient to realize, and can ensure counting yield, can save time again.

Accompanying drawing explanation

Fig. 1 is the iterative numerical calculation flow chart of the present invention's large-scale crude oil floating roof tank unsteady-state heat transfer process.

Fig. 2 is the floating roof tank area of space discrete model schematic diagram that the present invention adopts.

Fig. 3 is the floating roof tank time zone discrete model schematic diagram that the present invention adopts.

Fig. 4 is the comparison diagram of numerical simulation result of the present invention and actual measurement.

Embodiment

Also will be described the inventive method with reference to accompanying drawing by specific embodiment below:

A kind of large-scale crude oil floating roof tank unsteady-state heat transfer numerical simulation method, comprises following content:

Step one: cross the section of axis with crude oil storage tank for research object, sets up the foundation of storage tank two dimensional unsteady heat transfer numerical model for the ease of mathematical model, makes following necessary simplification:

1. ignore the component between upper and lower floating plate, be one and be communicated with air section;

2. ignore oil product inside and analyse wax phase transition process;

3. the initial temperature uniformity of oil product cooling in tank is supposed.

Crude oil storage tank two dimensional unsteady heat transfer numerical model:

$\frac{\∂}{\∂x}\left(\mathrm{\λ}\frac{\∂t(x,y)}{\∂x}\right)+\frac{\∂}{\∂y}\left(\mathrm{\λ}\frac{\∂t(x,y)}{\∂y}\right)=\mathrm{\ρ}c\frac{\∂t(x,y)}{\∂\mathrm{\τ}}$

Step 2: use method of finite difference logarithm value model area to carry out discrete, obtain the unstable state discrete equation of outside angle point, boundary node and internal node, and according to the stability of discrete equation, determine spatial mesh size and time step

One, method of finite difference logarithm value model area is used to carry out discrete, set up the discrete model as Fig. 2, obtain M × N number of space nodes, each node can regard the representative of a zonule centered by it as, be referred to as first body, the step-length between adjacent two nodes is Δ x, Δ y.A ~ D is outside angle point, and each point represents 1/4th first bodies; E ~ H is the node in straight boundary, and each point represents 1/2nd first bodies; I is interior nodes, represents whole first body.On the basis that area of space is discrete, carry out discrete to time zone, as shown in Figure 3.Divide the region on time coordinate into i equal portions, obtain i+1 timing node, the interval delta τ of adjacent two time horizons is time step, and corresponding temperature is designated as

Two, discrete equation:

(1) the unstable state discrete equation of outside angle point

1. outside angle point mainly by the bottom of tank, the impact of tank skin heat transfer and adjacent 2 temperature, the bottom angle point that its mid point D (1,1) is storage tank model, use law of conservation of energy to obtain to first body representated by it:

$\begin{array}{c}{t}_{(1,1)}^{i+1}=\frac{2a\mathrm{\Δ}\mathrm{\τ}}{{\mathrm{\Δx}}^2}{t}_{(2,1)}^i+\frac{2a\mathrm{\Δ}\mathrm{\τ}}{{\mathrm{\Δy}}^2}{t}_{(1,2)}^i+\frac{2K_{bi}\mathrm{\Δ}\mathrm{\τ}}{\mathrm{\ρ}c\mathrm{\Δ}x}{t}_f+\frac{2K_{di}\mathrm{\Δ}\mathrm{\τ}}{\mathrm{\ρ}c\mathrm{\Δ}y}{t}_{tu}\\ +\left(1-\frac{2a\mathrm{\Δ}\mathrm{\τ}}{{\mathrm{\Δx}}^2}-\frac{2a\mathrm{\Δ}\mathrm{\τ}}{{\mathrm{\Δy}}^2}-\frac{2K_{bi}\mathrm{\Δ}\mathrm{\τ}}{\mathrm{\ρ}c\mathrm{\Δ}x}-\frac{2K_d\mathrm{\Δ}\mathrm{\τ}}{\mathrm{\ρ}c\mathrm{\Δ}y}\right)t_{(1,1)}^i\end{array}$

Wherein, a=λ/(ρ c), can obtain after arrangement formula:

In formula, λ is the coefficient of heat conductivity of oil product, W/ (m DEG C); K _bifor tank skin heat transfer coefficient, W/ (m ²dEG C); K _difor heat transfer coefficient at the bottom of tank, W/ (m ²dEG C); ρ is the density of oil product, kg/m ³; C is the specific heat capacity of oil product, kJ/ (kg DEG C);

Wherein, the grid Fourier number that is characteristic length with Δ x, Δ y respectively, then can obtain after arrangement:

$\frac{K_{bi}\mathrm{\Δ}\mathrm{\τ}}{\mathrm{\ρ}c\mathrm{\Δ}x}=\frac{\mathrm{\λ}}{\mathrm{\ρ}c}\frac{\mathrm{\Δ}\mathrm{\τ}}{{\mathrm{\Δx}}^2}\frac{K_{bi}\mathrm{\Δ}x}{\mathrm{\λ}}=\frac{a\mathrm{\Δ}\mathrm{\τ}}{{\mathrm{\Δx}}^2}\frac{K_{bi}\mathrm{\Δ}x}{\mathrm{\λ}}={\mathrm{Fo}}_x{\mathrm{Bi}}_x$

$\frac{K_{di}\mathrm{\Δ}\mathrm{\τ}}{\mathrm{\ρ}c\mathrm{\Δ}y}=\frac{\mathrm{\λ}}{\mathrm{\ρ}c}\frac{\mathrm{\Δ}\mathrm{\τ}}{{\mathrm{\Δy}}^2}\frac{K_{di}\mathrm{\Δ}y}{\mathrm{\λ}}=\frac{a\mathrm{\Δ}\mathrm{\τ}}{{\mathrm{\Δy}}^2}\frac{K_{di}\mathrm{\Δ}y}{\mathrm{\λ}}={\mathrm{Fo}}_y{\mathrm{Bi}}_{ydi}$

In formula, Fo _x, Bi _xbe respectively grid Fourier number on x direction, grid finishes wet number, Fo _yfor grid Fourier number, Bi on y direction _ydifor on y direction, bottom, grid finishes wet number, then the unstable state discrete equation of bottom angle point can be write as again:

$\begin{array}{c}{t}_{(1,1)}^{i+1}=2{\mathrm{Fo}}_x{t}_{(2,1)}^i+2{\mathrm{Fo}}_y{t}_{(1,2)}^i+2{\mathrm{Fo}}_x\×{\mathrm{Bi}}_x{t}_f\\ +2{\mathrm{Fo}}_y\×{\mathrm{Bi}}_{ydi}{t}_{tu}+\left(\begin{array}{c}1-2F{o}_x-2F{o}_y-2F{o}_x\\ \×{\mathrm{Bi}}_x-2{\mathrm{Fo}}_y\×{\mathrm{Bi}}_{ydi}\end{array}\right)t_{(1,1)}^i\end{array}$

2. for top angle point B (M, N), have:

$\begin{array}{c}{t}_{(M,N)}^{i+1}=2{\mathrm{Fo}}_y{t}_{(M,N-1)}^i+2\left(\begin{array}{c}F{o}_x\×B{i}_x\\ +{\mathrm{Fo}}_y\×{\mathrm{Bi}}_{yding}\end{array}\right)t_f\\ +2{\mathrm{Fo}}_x{t}_{(M-1,N)}^i+\left(\begin{array}{c}1-2{\mathrm{Fo}}_y-2{\mathrm{Fo}}_x-\\ 2{\mathrm{Fo}}_x\×{\mathrm{Bi}}_x-2{\mathrm{Fo}}_y\×{\mathrm{Bi}}_{yding}\end{array}\right)t_{(M,N)}^i\end{array}$

In formula, Bi _ydingfor on y direction, top, grid finishes wet number, K _dingfor tank deck heat transfer coefficient, W/ (m ²dEG C).

(2) boundary node equation

1. vertically boundary node mainly by the impact of tank skin heat transfer and adjacent three some temperature, any node G on it (1, discrete equation b) is:

$\begin{array}{c}{t}_{(1,b)}^{i+1}={\mathrm{Fo}}_y{t}_{(1,b-1)}^i+{\mathrm{Fo}}_y{t}_{(1,b+1)}^i+2{\mathrm{Fo}}_x{t}_{(2,b)}^i+\\ 2{\mathrm{Fo}}_x\×{\mathrm{Bi}}_x{t}_f+(1-2{\mathrm{Fo}}_x-2{\mathrm{Fo}}_y-2{\mathrm{Fo}}_x\×{\mathrm{Bi}}_x)t_{(1,b)}^i\end{array}$

2. straight boundary node is mainly by the impact of heat transfer and adjacent three some temperature at the bottom of tank deck or tank.The discrete equation of coboundary node E (a, N) is:

$\begin{array}{c}{t}_{(a,N)}^{i+1}={\mathrm{Fo}}_x{t}_{(a-1,N)}^i+{\mathrm{Fo}}_x{t}_{(a+1,N)}^i+2{\mathrm{Fo}}_y{t}_{(a,N-1)}^i\\ +2{\mathrm{Fo}}_y\×{\mathrm{Bi}}_{yding}{t}_f+(1-2{\mathrm{Fo}}_x-2{\mathrm{Fo}}_y-2{\mathrm{Fo}}_y\×{\mathrm{Bi}}_{yding})t_{(a,N)}^i\end{array}$

3. the discrete equation of lower boundary node F (d, 1) is:

$\begin{array}{c}{t}_{(d,1)}^{i+1}={\mathrm{Fo}}_x{t}_{(d-1,1)}^i+{\mathrm{Fo}}_x{t}_{(d+1,1)}^i+2{\mathrm{Fo}}_y{t}_{(d,2)}^i\\ +2{\mathrm{Fo}}_y\×{\mathrm{Bi}}_{ydi}{t}_{tu}+(1-2{\mathrm{Fo}}_x-2{\mathrm{Fo}}_y-2{\mathrm{Fo}}_y\×{\mathrm{Bi}}_{ydi})t_{(d,1)}^i\end{array}$

(3) internal node equation

Internal node mainly affects by the temperature of its four spatially adjacent points, and the discrete equation of inner any point H (m, n) is:

$t_{(m,n)}^{i+1}={\mathrm{Fo}}_x{t}_{(m-1,n)}^i+{\mathrm{Fo}}_x{t}_{(m+1,n)}^i+{\mathrm{Fo}}_y{t}_{(m,n-1)}^i+{\mathrm{Fo}}_y{t}_{(m,n+1)}^i+(1-2{\mathrm{Fo}}_x-2{\mathrm{Fo}}_y)t_{(m,n)}^i$

Three, spatial mesh size and time step is determined

The relation of spatial mesh size Δ x, Δ y and time step Δ τ is subject to the impact of discrete equation stability, in discrete equation front coefficient must be more than or equal to zero.Due to top angle point front coefficient is minimum, as its value is more than or equal to zero, then can ensure the stability of all discrete equations.

Step 3, according to the boundary condition at the bottom of tank deck, tank skin and tank, set up the corresponding relation of crude oil property parameter, border heat transfer coefficient and temperature

Oil product in floating roof tank is mainly through three kinds of approach outwardly environment transferring heat at the bottom of tank deck, tank skin and tank, physical parameter and its temperature one_to_one corresponding such as viscosity and density of oil product in diabatic process, in order to avoid choosing due to the improper of temperature, the error of calculation is constantly amplified, the method of main employing segmentation tentative calculation calculates, and concrete steps are as follows:

(1) tank deck medial temperature t is supposed _ding, with oil product temperature t _ybetween mean value be qualitative temperature t, be calculated as follows:

$t=\frac{1}{2}(t_y+t_{ding})$

Then oil density temperature coefficient ξ, relative density under this qualitative temperature is calculated viscosity coefficient of heat conductivity specific heat capacity and table look-up according to the relative density of oil product under qualitative temperature and draw the volume expansivity β of oil product;

1. density temperature coefficient: ξ=0.002876-0.003984d _t+ 0.001632*d _t ²

2. relative density: $d_y^t=d_t-\mathrm{\ξ}(t-t_1)$

In formula, d _tfor oil product is at t ₁time oil product relative density;

3. viscosity, m2/s: (wherein )

In formula, υ _t1for oil product is at t ₁time kinematic viscosity, m ²/ s; υ _t2for oil product is at t ₂time kinematic viscosity, m ²/ s;

4. coefficient of heat conductivity, W/ (m ²dEG C):

5. specific heat capacity, kJ/ (kg DEG C):

Work as d _t>0.7 (mink cell focus) $C_y^t=2.018+0.00322(t-100)$

Work as d _t<0.7 (lightweight oil) $C_y^t=\frac{4.1868}{\sqrt{d_t}}(0.403+0.810\&times;{10}^{-3}t)$

6. oil volume expansion coefficient β

(2) oil product to the heat transfer of tank deck inside mainly based on infinite space natural convection, oil product natural convection accurate number Gr and the accurate number Pr of oil property is calculated according to Grashof and Prandtl criterion, then the product according to Gr and Pr is followed, table look-up and can obtain coefficient ε and n value, calculate oil product thus to the inner coefficient of heat emission α of tank deck _1ding:

The accurate number of oil product natural convection (g=9.8)

In formula, h is oil product liquid level in storage tank, m;

The accurate number of oil property $\mathrm{Pr}=\frac{{\mathrm{\&upsi;}}_y^t{C}_y^t{d}_y^t\&times;{10}^3\&times;{10}^3}{{\mathrm{\&lambda;}}_y^t}$

ε, n is obtained by (Gr, Pr)

Coefficient ε, n value is as following table:

Oil product to the inner coefficient of heat emission of oil tank, W/ (m ²dEG C):

Forced-convection heat transfer and the environmental radiation heat release towards periphery of tank deck are mainly skimmed in tank deck to the heat transfer of surrounding environment with air, obtain the coefficient of heat conductivity λ of air under qualitative temperature by tabling look-up _qiand viscosity υ _qi, calculate Reynolds number, and obtain the Prandtl number Pr of air by tabling look-up _qi, calculate the outside coefficient of heat emission α of tank deck thus _2dingand radiant heat-transfer coefficient α _3ding:

Air conduction coefficient, viscosity are by t _qilook into following table and obtain air conduction coefficient lambda _qi, W/ (m DEG C) and air viscosity υ _qi, m ²/ s

The dry air physical constant of following table to be atmospheric pressure be 760 mm Hg

Reynolds number

In formula, D is tank diameter, m; W _qifor mean wind speed, m/s

Table look-up and can obtain air Pr _qinumber

The outside coefficient of heat emission of tank deck, W/ (m ²dEG C):

Blackbody coefficient, C ₀=5.67W/ (m ²h DEG C ⁴)

Tank deck radiant heat-transfer coefficient, W/ (m ²dEG C): ${\mathrm{\&alpha;}}_{3ding}={\mathrm{\&epsiv;C}}_0\frac{{\left(\frac{t_{ding}+273}{100}\right)}^4-{\left(\frac{t_{qi}+273}{100}\right)}^4}{t_{ding}-t_{qi}}$

In formula, t _qifor ambient temperature, DEG C; ε is tank skin coating blackness.

If double plate floating roof tank, coefficient of heat emission h in the cabin that also should calculate buoyancy module _qi, the major way of its heat transfer is finite space natural convection, and when natural convection occurs in buoyancy module, the motion of fluid is subject to the restriction of cabin body, and heating and the carrying out while of cooling in cavity of fluid, therefore buoyancy module wall is divided into high temperature t _h(its value is similar to oil product liquid level temperature), low temperature t _c(its value is similar to ambient temperature) two parts.The temperature difference in Gr number and Newtonian Cooling formula is taken as t _h-t _c, the qualitative temperature of fluid is (t _h+ t _c)/2, characteristic length gets the distance δ between hot and cold.The Gr number that it is characteristic length that flowing in cold and hot interlayer depends primarily on thickness of interlayer δ:

The accurate number of oil product natural convection, (due to fluid inherently air, so expansion coefficient β gets 1)

Convection heat transfer intensity number:

When 1.0 × 10 ⁴≤ Gr _δ≤ 4.6 × 10 ⁵time: Nu=0.212 (Gr _δpr) ^1/4

Work as Gr _δ> 4.6 × 10 ⁵time: Nu=0.061 (Gr _δpr) ^1/3,

The inner electronic equipment of buoyancy module,

(3) tank deck Coefficient K is calculated according to above parameter _ding:

Single-deck floating roof tank: $K_{ding}=\frac{1}{\frac{1}{{\mathrm{\&alpha;}}_{1ding}}+\frac{{\mathrm{\&delta;}}_{iding}}{{\mathrm{\&lambda;}}_{iding}}+\frac{1}{{\mathrm{\&alpha;}}_{2ding}+{\mathrm{\&alpha;}}_{3ding}}}$

Double plate floating roof tank: $K_{ding}=\frac{1}{\frac{1}{{\mathrm{\&alpha;}}_{1ding}}+\frac{{\mathrm{\&delta;}}_{iding}}{{\mathrm{\&lambda;}}_{iding}}+\frac{h_{ding}}{h_{qi}}+\frac{1}{{\mathrm{\&alpha;}}_{2ding}+{\mathrm{\&alpha;}}_{3ding}}}$

In formula, h _dingfor floating roof height, m; δ _idingfor tank deck thickness of deposits, m; λ _idingfor tank deck sediment coefficient of heat conductivity, W/ (m DEG C).

Check according to heat balance principle, if time, then think that the medial temperature of supposition is accurately; If do not met, should the t of assumed average temperature again _y, then calculate tank deck Coefficient K _ding.

Oil product to the inside heat release of tank skin and tank skin to the radiation heat release of surrounding environment and tank deck similar, therefore its inner coefficient of heat emission α _1biwith radiant heat-transfer coefficient α _3biall can by the coefficient of heat emission α of tank deck _1dingand α _3dingformulae discovery, tank deck temperature is wherein made into tank wall temperature.Tank skin to the convection heat transfer of surrounding environment should skim over the forced-convection heat transfer formulae discovery of pipe by air; Calculate the Re number of tank skin according to method provided above, table look-up and obtain obtaining coefficient C, n

The outside coefficient of heat emission of tank skin, W/ (m ²dEG C):

Tank skin heat transfer coefficient, W/ (m ²dEG C):

In formula, δ _baofor tank skin insulation layer thickness, m; λ _baofor tank skin insulation material coefficient of heat conductivity, W/m DEG C.

At the bottom of tank then main based on oil product to the infinite space heat transfer free convection of pot bottom and to thermal conduction of soil.Inside heat release at the bottom of oil product to tank considers it is use riser heat release formula instead transverse slat heat release, and heat delivery surface causes heating strength to weaken to some extent downwards, therefore the result required by oil product to the inner coefficient of heat emission of oil tank is reduced by 30%.

Oil product to tank bottom coefficient of heat emission, W/ (m ²dEG C):

Heat transfer coefficient at the bottom of tank: (π gets 3.14)

In formula, δ _idifor bottom settlings thing thickness, m; λ _idifor bottom settlings thing coefficient of heat conductivity, W/m DEG C; λ _tufor soil thermal conductivity, W/m DEG C.

Check similar to tank deck heat transfer coefficient, the heat transfer coefficient at the bottom of tank skin and tank is checked, if meet accuracy requirement, thinking that the tank skin of supposition, temperature at the bottom of tank are accurate, if do not met, then needing to re-start checking computations.

According to the corresponding relation of above method establishment crude oil property parameter, border heat transfer coefficient and temperature.

Step 4: assignment is carried out to oil product initial temperature in tank, use method of interpolation by the crude oil property parameter under relevant temperature, border heat transfer coefficient, be updated in outside angle point, boundary node and internal node discrete equation, then the calculating of next time step is carried out, terminate until whole simulation process calculates, concrete iterative numerical flow process is shown in accompanying drawing 1.

Embodiment 1

For making foregoing of the present invention become apparent, below using Daqing oil field storage tank as research object, to crude oil temperature unsteady-state heat transfer process simulation in its tank, be described in detail below:

Daqing oil field oil depot 10 × 104 double plate floating roof tank, diameter at the bottom of tank is 80m, tank skin height 21m, oil product liquid level height 8.2m in tank, and ambient temperature is 18 DEG C, and wind speed is 5m/s, the density 980kg/m of oil product 20 DEG C time ³, viscosity is 8.4 × 10-6m ²/ s, the viscosity of oil product 15 DEG C time is 10.53 × 10-6m ²/ s, tank skin insulation material thickness 0.08m, coefficient of heat conductivity 0.035W/m DEG C, in tank, the initial temperature of Tempreture Decrease for Oil Product is 42.5 DEG C, and the temperature drop time is 15 days, as follows to crude oil temperature simulation process in tank:

Step one: according to given known conditions, the section of axis is crossed for research object with crude oil storage tank, be based upon the unsteady-state heat transfer numerical value two-dimensional mathematical model under rectangular coordinate system, be 80m according to tank diameter determination numerical model region horizontal ordinate, be approximately 8m according to oil product liquid level determination ordinate in tank.

Step 2: use method of finite difference logarithm value model area to carry out discrete, obtain outside angle point (0,0), (80,0), (0,8), (80,8), boundary node (1,0) ~ (79,0), (0,1) ~ (0,7), (1,8) ~ (79,8), (80,1) ~ (80,7), internal node (1,1) the unstable state discrete equation of ~ (79,7), according to the stability of discrete equation, determine that the spatial mesh size on transverse and longitudinal coordinate is 1m, time step is 3600s.

Step 3: (1) supposition tank deck temperature t _dingwith oil product temperature t _ybetween mean value be qualitative temperature t, then calculate oil density temperature coefficient ξ, relative density under this qualitative temperature viscosity coefficient of heat conductivity specific heat capacity and table look-up according to the relative density of oil product under qualitative temperature and draw the volume expansivity β of oil product.

(2) calculate oil product natural convection accurate number Gr and the accurate number Pr of oil property according to Grashof and Prandtl criterion, then follow the product according to Gr and Pr, table look-up and can obtain coefficient ε and n value, calculate oil product thus to the inner coefficient of heat emission α of tank deck _1ding:

The coefficient of heat conductivity λ of air under qualitative temperature is obtained by tabling look-up _qiand viscosity υ _qi, calculate Reynolds number, and obtain the Prandtl number Pr of air by tabling look-up _qi, calculate the outside coefficient of heat emission α of tank deck thus _2dingand radiant heat-transfer coefficient α _3ding:

According to the accurate number Gr of temperature computation oil product natural convection of buoyancy module in floating plate _δ, convection heat transfer intensity number Nu, obtains the inner electronic equipment h of buoyancy module thus _qi.

(3) according to above formulae discovery result, tank deck Coefficient K is drawn _ding, check according to heat balance principle, if time, then think that the medial temperature of supposition is accurately; If do not met, should the t of assumed average temperature again _y, then calculate tank deck Coefficient K _ding;

The inner coefficient of heat emission α of tank skin _1biwith radiant heat-transfer coefficient α _3biby the coefficient of heat emission α of tank deck _1dingand α _3dingformulae discovery, tank deck temperature is wherein made into tank wall temperature.Tank skin is to the convection transfer rate α of surrounding environment _2biskim over the forced-convection heat transfer formulae discovery of pipe by air, obtain tank skin Coefficient K thus _bi;

By calculating oil product to tank bottom coefficient of heat emission α _1di, obtain the Coefficient K at the bottom of tank _di, heat transfer coefficient at the bottom of tank skin tank is checked, then thinking that supposition temperature is suitable as met accuracy requirement, recalculating if do not met then needs.

Finally obtain the corresponding relation of crude oil property parameter, border heat transfer coefficient and the temperature that it is as shown in the table.

Step 4: carrying out assignment to oil product initial temperature in tank is 42.5 DEG C, use method of interpolation by the crude oil property parameter at its temperature, border heat transfer coefficient, be updated to outside angle point, in boundary node and internal node discrete equation, then the calculating of next time step 3600s is carried out, until the total number of days of temperature drop reaches 15 number of days, obtain the numerical simulation result of crude oil temperature field in tank as shown in Figure 4, as can be seen from the figure, As time goes on, in tank, oil product temperature reduces gradually, the temperature difference between oil product and environment is diminished gradually, temperature drop rate also reduces thereupon.

In order to verify the accuracy of above-mentioned numerical simulation result, on-the-spot crude oil storage tank temperature measured data and analog result is utilized to contrast.On-the-spot thermometric adopts VITOMTT system, and temperature element adopts PT100 platinum resistance, and temperature measurement accuracy≤± 0.1 DEG C, Measurement Resolution is 0.01 DEG C.On storage tank guidepost, point for measuring temperature is specifically arranged as shown in the table.

Tank temperature numerical result and observed temperature data contrast as shown in Figure 4, and numerical simulation temperature distribution history and observed temperature distribution curve coincide better, and maximum relative error is 1.9%, and analog result accurately and reliably.On the basis of this analog result, further can also study the Changing Pattern of crude oil temperature field in tank by changing the factors such as environment temperature, oil storage liquid level, tank volume, its result can be the storage process design optimizing large-scale floating roof tank, ensures that oil storage safety economical production is run and provides important technical support.

Claims (5)

1. a large-scale crude oil floating roof tank unsteady-state heat transfer numerical simulation method, comprises following content:

Step one: cross the section of axis with crude oil storage tank for research object, sets up storage tank two dimensional unsteady heat transfer numerical model;

Step 2: use method of finite difference logarithm value model area to carry out discrete, obtain the unstable state discrete equation of outside angle point, boundary node and internal node, and according to the stability of discrete equation, determine spatial mesh size and time step;

Step 3: according to the boundary condition at the bottom of tank deck, tank skin and tank, set up the corresponding relation of crude oil property parameter, border heat transfer coefficient and temperature, described border heat transfer coefficient comprises heat transfer coefficient at the bottom of tank deck heat transfer coefficient, tank skin heat transfer coefficient and tank, specifically carries out according to following steps:

(1) suppose tank deck temperature, and the mean value between oil product temperature is qualitative temperature, then calculates the physical parameter of oil product under this qualitative temperature: relative density, viscosity, coefficient of heat conductivity, specific heat capacity and coefficient of volumetric expansion;

(2) according to Grashof and Prandtl criterion, determine middle coefficient and value, then calculate inner coefficient of heat emission, outside coefficient of heat emission and radiant heat-transfer coefficient, if double plate floating roof tank, also need to calculate coefficient of heat emission in deliver from vault according to buoyancy module qualitative temperature;

(3) calculate tank deck heat transfer coefficient, check according to heat balance principle; If meet precision, then think that the medial temperature of supposition is accurately; If do not met, should assumed average temperature again, then calculate tank deck heat transfer coefficient, in like manner can obtain heat transfer coefficient at the bottom of tank skin heat transfer coefficient and tank;

Step 4: assignment is carried out to crude oil initial temperature in tank, use method of interpolation by the crude oil property parameter under relevant temperature and border heat transfer coefficient, be updated in outside angle point, boundary node and internal node discrete equation, then iteration carries out the calculating of next time step, draw crude oil temperature field distribution in tank, terminate until whole simulation process calculates, draw the Changing Pattern of crude oil temperature field in tank.

2. large-scale crude oil floating roof tank unsteady-state heat transfer numerical simulation method according to claim 1, it is characterized in that: described in step one, cross the section of axis for research object with crude oil storage tank, set up storage tank two dimensional unsteady heat transfer numerical model, this numerical model is:

$\frac{\&part;}{\&part;x}\left(\mathrm{\&lambda;}\frac{\&part;t(x,y)}{\&part;x}\right)+\frac{\&part;}{\&part;y}\left(\mathrm{\&lambda;}\frac{\&part;t(x,y)}{\&part;y}\right)=\mathrm{\&rho;}c\frac{\&part;t(x,y)}{\&part;\mathrm{\&tau;}}.$

3. large-scale crude oil floating roof tank unsteady-state heat transfer numerical simulation method according to claim 1, it is characterized in that: the utilization method of finite difference logarithm value model area described in step 2 carries out discrete, obtain the unstable state discrete equation of outside angle point, its mid point D (1,1) be the bottom angle point of storage tank model, the bottom corner point equation in the unstable state discrete equation of outside angle point is:

$\begin{array}{c}{t}_{\left(1,1\right)}^{i+1}=2{\mathrm{Fo}}_x{t}_{\left(2,1\right)}^i+2{\mathrm{Fo}}_y{t}_{\left(2,1\right)}^i+2{\mathrm{Fo}}_x\&times;{\mathrm{Bi}}_x{t}_f\\ +2{\mathrm{Fo}}_y\&times;{\mathrm{Bi}}_{ydi}{t}_{tu}+\left(\begin{array}{c}1-2{\mathrm{Fo}}_x-2{\mathrm{Fo}}_y-2{\mathrm{Fo}}_x\\ \&times;{\mathrm{Bi}}_x-2{\mathrm{Fo}}_y\&times;{\mathrm{Bi}}_{ydi}\end{array}\right)t_{\left(1,1\right)}^i\end{array}$

In formula: Fo _x, Bi _xbe respectively grid Fourier number on x direction, grid finishes wet number, Fo _yfor grid Fourier number, Bi on y direction _ydifor on y direction, bottom, grid finishes wet number;

Wherein: for top angle point B (M, N), the top corner point equation in the unstable state discrete equation of outside angle point is:

$\begin{array}{c}{t}_{\left(M,N\right)}^{i+1}=2{\mathrm{Fo}}_y{t}_{\left(M,N-1\right)}^i+2\left(\begin{array}{c}{\mathrm{Fo}}_x\&times;{\mathrm{Bi}}_x\\ +{\mathrm{Fo}}_y\&times;{\mathrm{Bi}}_{yding}\end{array}\right)t_f\\ +2{\mathrm{Fo}}_x{t}_{\left(M-1,N\right)}^i+\left(\begin{array}{c}1-2{\mathrm{Fo}}_y-2{\mathrm{Fo}}_x-\\ 2{\mathrm{Fo}}_x\&times;{\mathrm{Bi}}_x-2{\mathrm{Fo}}_y\&times;{\mathrm{Bi}}_{yding}\end{array}\right)t_{\left(M,N\right)}^i\end{array}$

In formula: Bi _ydingfor on y direction, top, grid finishes wet number, K _dingfor tank deck heat transfer coefficient, W/ (m ²dEG C).

4. large-scale crude oil floating roof tank unsteady-state heat transfer numerical simulation method according to claim 1, it is characterized in that: the utilization method of finite difference logarithm value model area described in step 2 carries out discrete, obtain the unstable state discrete equation of boundary node, vertical boundary node wherein is mainly subject to the impact of tank skin heat transfer and adjacent three some temperature, any node G on it (1, discrete equation b) is:

$\begin{array}{c}{t}_{\left(1,b\right)}^{i+1}={\mathrm{Fo}}_y{t}_{\left(1,b-1\right)}^i+{\mathrm{Fo}}_y{t}_{\left(1,b+1\right)}^i+2{\mathrm{Fo}}_x{t}_{\left(2,b\right)}^i+\\ 2{\mathrm{Fo}}_x\&times;{\mathrm{Bi}}_x{t}_y+\left(1-2{\mathrm{Fo}}_x-2{\mathrm{Fo}}_y-2{\mathrm{Fo}}_x\&times;{\mathrm{Bi}}_x\right)t_{\left(1,b\right)}^i\end{array}$

Straight boundary node is wherein mainly by the impact of heat transfer and adjacent three some temperature at the bottom of tank deck or tank, and the discrete equation of arbitrary coboundary node E (a, N) in straight boundary node is:

$\begin{array}{c}{t}_{\left(a,N\right)}^{i+1}={\mathrm{Fo}}_x{t}_{\left(a-1,N\right)}^i+{\mathrm{Fo}}_x{t}_{\left(a+1,N\right)}^i+2{\mathrm{Fo}}_y{t}_{\left(a,N-1\right)}^i\\ +2{\mathrm{Fo}}_y\&times;{\mathrm{Bi}}_{yding}{t}_f+\left(1-2{\mathrm{Fo}}_x-2{\mathrm{Fo}}_y-2{\mathrm{Fo}}_y\&times;{\mathrm{Bi}}_{yding}\right)t_{\left(a,N\right)}^i\end{array}$

The discrete equation of the arbitrary lower boundary node F (d, 1) in straight boundary node is:

$\begin{array}{c}{t}_{\left(d,1\right)}^{i+1}={\mathrm{Fo}}_x{t}_{\left(d-1,1\right)}^i+{\mathrm{Fo}}_x{t}_{\left(d+1,1\right)}^i+2{\mathrm{Fo}}_y{t}_{\left(d,2\right)}^i\\ +2{\mathrm{Fo}}_y\&times;{\mathrm{Bi}}_{ydi}{t}_{tu}+\left(1-2{\mathrm{Fo}}_x-2{\mathrm{Fo}}_y-2{\mathrm{Fo}}_y\&times;{\mathrm{Bi}}_{ydi}\right)t_{\left(d,1\right)}^i\end{array}.$

5. large-scale crude oil floating roof tank unsteady-state heat transfer numerical simulation method according to claim 1, it is characterized in that: the utilization method of finite difference logarithm value model area described in step 2 carries out discrete, the unstable state discrete equation obtaining inner any node H (m, n) is:

$t_{(m,n)}^{i+1}={\mathrm{Fo}}_x{t}_{(m-1,n)}^i+{\mathrm{Fo}}_x{t}_{(m+1,n)}^i+{\mathrm{Fo}}_y{t}_{(m,n-1)}^i+{\mathrm{Fo}}_y{t}_{(m,n+1)}^i+(1-2{\mathrm{Fo}}_x-2{\mathrm{Fo}}_y)t_{(m,n)}^i.$