Study on influence of inclination of coils on melting process of waxy crude oil in a floating roof tank

doi:10.11949/0438-1157.20191431

Abstract

Abstract:

Heating by coils are the most common used way for heating and melting waxy crude oil in a floating roof tank. And optimizing the layout of coils in the tank helps to improve the melting efficiency and reduce production cost. For this purpose, deep investigation on the temperature increase and melting processes of waxy crude oil by coil heating is necessary. This research establishes a physical and mathematical model describing the processes based on a comprehensive consideration of structure and rheological changes of the oil as well as the influence of turbulent flow during melting. Considering the irregularity of the oil domain and the regularity of other parts of the tank, immersed boundary method is employed to realize integrated calculation on structured grids over the whole computational domain. Results in literatures are used for model validation. Then the temperature increase and melting processes of waxy crude oil are simulated under three projects of coil layout. Taking an actual 1000 m³ floating roof oil tank as an example, the melting law of waxy crude oil in the tank is studied, and the influence of the inclination angle on the melting process is analyzed.

Key words: floating roof tank, waxy crude oil, melting, turbulent flow, non-Newtonian fluid, immersed boundary method

摘要：

利用盘管组来加热融化浮顶油罐内含蜡原油是油罐加热融化的主要方式之一。而优化盘管组的布置方式对提高罐内含蜡原油的融化效率、降低生产成本具有重要的意义。基于此，在考虑含蜡原油融化过程中形态和流变性变化的基础上，建立了盘管组加热的浮顶油罐内含蜡原油湍流融化物理数学模型。考虑到罐顶空气层、钢板层、保温层的规则性以及罐内含蜡原油区域的非规则性，利用浸入边界法在结构化网格上处理罐内含蜡原油与盘管组之间的耦合问题。利用文献结果对模型进行验证。以实际1000 m³浮顶油罐为例，对罐内含蜡原油的融化规律进行研究，并对倾角对融化过程的影响进行分析。

关键词: 浮顶油罐, 含蜡原油, 融化, 湍流, 非牛顿流体, 浸入边界法

CLC Number:

TE 821

Min WANG, Qianqian SHAO, Xiaofan YANG, Jingfa LI. Study on influence of inclination of coils on melting process of waxy crude oil in a floating roof tank[J]. CIESC Journal, 2020, 71(5): 2035-2048.

王敏, 邵倩倩, 杨晓帆, 李敬法. 盘管组倾角对浮顶油罐内含蜡原油融化过程的影响研究[J]. 化工学报, 2020, 71(5): 2035-2048.

Figures/Tables 13

Fig.1 Physical model of melting of waxy crude oil in a floating roof tank heated by coils

Fig.2 Flow chart of this research

Table 1 Three inclinations of heating coils at tank bottom

算例	盘管数	p3		δr / m	θ /(°)	r₀ / m	T₀ /℃
算例	盘管数	x₃ / m	r₃ / m	δr / m	θ /(°)	r₀ / m	T₀ /℃
1	5	0.6	3.0	0.6	-5.71	0.1	80
2	5	0.6	3.0	0.6	0	0.1	80
3	5	0.6	3.0	0.6	5.71	0.1	80

Table 2 Physical properties of waxy crude oil, air layer, wax crystal, steel layer, soil and insulating layer

材料	ρ /(kg/m³)	c_p/(J/(kg·℃) )	λ /(W/(m·℃) )	β /℃^-1	μ /(Pa·s)	L/(J/kg)
含蜡原油	869	2100	0.14	7.53×10^-4	式（14）	2.0×10⁵
空气	1.25	1009	0.025	3.7×10^-3	1.77×10^-5	—
蜡晶	869	2100	0.14	—	+∞	2.0×10⁵
钢板	7860	475	46	—	+∞	—
土壤	1700	753	1.6	—	+∞	—
保温层	55	1880	0.02	—	+∞	—

Fig.3 Comparison of simulated and measured longitudinal average oil temperature at gauge hatch

Table 3 Steady heat flux of heating coil in a square cavity heated with constant temperature

Ra	项目	稳态热流量/J
Ra	项目	r/l=0.1	r/l=0.2	r/l=0.3
1.0×10⁴	本文计算结果	2.074	3.156	5.242
	Ref. [23]	2.051	3.161	5.303
	Ref. [31]	2.071	3.331	5.826
1.0×10⁵	本文计算结果	3.701	4.861	6.119
	Ref. [23]	3.704	4.836	6.171
	Ref. [31]	3.825	5.080	6.212
1.0×10⁶	本文计算结果	6.403	9.459	11.892
	Ref. [23]	5.944	8.546	11.857
	Ref. [31]	6.107	9.374	11.620

Fig.4 Variation of average oil temperature inside tank along with time

Fig.5 Initial fields for melting process of floating roof tank

Fig. 6 Temperature and velocity fields in tank during melting process of case 1

Fig.8 Temperature and velocity fields in tank during melting process of case 3

Fig.7 Temperature and velocity fields in tank during melting process of case 2

Fig.9 Melting characteristic of waxy crude oil in floating roof tank

Fig.10 Variations of heat flux of coils along with time

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