SIL grading method of associated overpressure interlock protection circuit considering flare load risk

doi:10.11949/0438-1157.20201224

Abstract

Abstract:

The current international standards for the SIL rating of safety interlocking circuits are only for a single scenario and cannot consider the impact of risk coupling between multiple associated scenarios. When designing the risk distribution and reduction plan of multiple overpressure protection SIF circuits for large-scale combined equipment, it is necessary to consider the risk of flare system overload when the initial event causes multiple devices to discharge at the same time. Based on the situation, the traditional LOPA grading method of the protective layer is improved by the simultaneous discharge superposition method of multiple discharge sources, and a quantitative load calculation method is proposed to determine the safety integrity level of multiple overpressure interlocking protection circuits that affect each other: Reversely realize the check of the safety integrity level of the upstream overpressure interlock by the quantitative data and allowable risk level of the associated release risk of flare system. The case shows that by calculating the frequency of an overpressure accident of the flare system during a power outage, the safety integrity level of multiple overpressure interlocking protection SIF circuits coupled with risk can be recalculated, thereby completing the correction of the traditional LOPA rating results.

Key words: risk coupling, safety integrity level, safety interlock system, safety, instrumentation, optimization

摘要：

现行国际标准对安全联锁回路的SIL定级只针对单一场景而无法考虑多个关联场景之间的风险耦合影响。而设计大型联合装置多个超压保护SIF回路的风险分配与降低方案时，需要考虑同一初始事件导致多个装置同时泄放情形下的火炬负荷超载风险。基于上述现状，使用多泄放源同时泄放叠加方法对传统保护层LOPA定级方法进行改进，提出一种定量负荷计算方法来确定多个相互影响的超压联锁保护回路的安全完整性等级（SIL）：依据关联泄放时火炬风险量化数据及允许风险等级，逆向实现上游超压联锁的SIL等级校核。案例表明，通过计算停电时火炬系统超压事故的频率，实现对风险耦合的多个超压联锁保护SIF回路SIL等级的重新核算，从而完成对传统LOPA定级结果的修正。

关键词: 风险耦合, 安全完整性等级, 安全联锁系统, 安全, 仪表, 优化

CLC Number:

P 624.8

LIU Yin, WANG Haiqing, XU Xiaolin, LIU Meichen. SIL grading method of associated overpressure interlock protection circuit considering flare load risk[J]. CIESC Journal, 2021, 72(5): 2754-2762.

刘荫, 王海清, 许小林, 刘美晨. 考虑火炬负荷风险的关联联锁回路SIL定级方法[J]. 化工学报, 2021, 72(5): 2754-2762.

Figures/Tables 12

Fig.1 Example of a group of relief devices protected by multiple SIF circuit

Fig.2 Example diagram of the discharge path and the probability of the discharge path

Table 1 Risk reduction factor and SIL level correspondence table

SIL等级	所需风险降低因子（RRF）	需求时目标平均失效概率
1	$101 ~ 102$	$10 - 1 ~ 10 - 2$
2	$102 ~ 103$	$10 - 2 ~ 10 - 3$
3	$103 ~ 104$	$10 - 3 ~ 10 - 4$
4	$104$ ~ $105$	$10 - 4 ~ 10 - 5$

Table 1 Risk reduction factor and SIL level correspondence table

SIL等级	所需风险降低因子（RRF）	需求时目标平均失效概率
1	$101 ~ 102$	$10 - 1 ~ 10 - 2$
2	$102 ~ 103$	$10 - 2 ~ 10 - 3$
3	$103 ~ 104$	$10 - 3 ~ 10 - 4$
4	$104$ ~ $105$	$10 - 4 ~ 10 - 5$

Fig.3 Flow chart of SIL grading method considering associated release

Fig.4 Flow chart of flare system in a factory

Table 2 Safety valve parameter

安全阀编号	最大允许压力/bar	允许背压/bar	阀口面积/mm	安全阀类型	停电工况最大泄放量/(kg/h)
1	7.616	3.808	70.968	平衡波纹管式	27000
2	7.616	3.808	70.968	平衡波纹管式	25600
3	8.0	4	61.935	平衡波纹管式	23000
4	8.0	4	126.452	平衡波纹管式	40770
5	8.0	4	61.935	平衡波纹管式	19680

Table 3 SIL level of equipment overpressure SIF circuit determined by LOPA method

SIF回路编号	风险降低因子（RRF）	SIL等级
回路C	22	SIL1
回路D	28	SIL1
回路E	24	SIL1

Table 4 Release probability of rectification tower C, D, E

设备编号	安全阀失效概率	SIF回路编号	SIF回路失效概率	设备泄放概率
精馏塔C	0.085	SIF回路C	0.034	$2.890 × 10 - 3$
精馏塔D	0.112	SIF回路D	0.026	$2.912 × 10 - 3$
精馏塔E	0.096	SIF回路E	0.0078	$7.488 × 10 - 4$

Table 4 Release probability of rectification tower C, D, E

设备编号	安全阀失效概率	SIF回路编号	SIF回路失效概率	设备泄放概率
精馏塔C	0.085	SIF回路C	0.034	$2.890 × 10 - 3$
精馏塔D	0.112	SIF回路D	0.026	$2.912 × 10 - 3$
精馏塔E	0.096	SIF回路E	0.0078	$7.488 × 10 - 4$

Table 5 Discharge combination and discharge path

泄放组合	泄放路径编号	泄放路径
ABC	M1	100%A+100%B+100%C
ABD	M2	100%A+100%B+100%D
ABE	M3	100%A+100%B+100%E
ABCD	M4	100%A+100%B+100%C+50%D
ABCD	M5	100%A+100%B+100%D+50%C
ABCE	M6	100%A+100%B+100%C+50%E
ABCE	M7	100%A+100%B+100%E+50%C
ABDE	M8	100%A+100%B+100%D+50%E
ABDE	M9	100%A+100%B+100%E+50%D
ABCDE	M10	100%A+100%B+100%C+50%D+50%E
	M11	100%A+100%B+100%D+50%C+50%E
	M12	100%A+100%B+100%E+50%C+50%D

Table 6 The discharge volume of the device and occurrence probability under each discharge path

泄放路径编号	设备A泄放量/ (kg/h)	设备B泄放量/ (kg/h)	装置C泄放量/ (kg/h)	装置D泄放量/ (kg/h)	装置E泄放量/ (kg/h)	泄放路径出现概率 $P D i$
M1	27000	25600	23000	0	0	$2.890 × 10 - 3$
M2	27000	25600	0	40770	0	$2.912 × 10 - 3$
M3	27000	25600	0	0	19680	$7.488 × 10 - 4$
M4	27000	25600	23000	20385	0	4.20 $8 × 10 - 6$
M5	27000	25600	11500	40770	0	4.20 $8 × 10 - 6$
M6	27000	25600	23000	0	9840	$1.082 × 10 - 6$
M7	27000	25600	11500	0	19680	$1.082 × 10 - 6$
M8	27000	25600	0	40770	9840	1.09 $0 × 10 - 6$
M9	27000	25600	0	20385	19680	1.09 $0 × 10 - 6$
M10	27000	25600	23000	20385	9840	2.10 $1 × 10 - 9$
M11	27000	25600	11500	40770	9840	2.10 $1 × 10 - 9$
M12	27000	25600	11500	20385	19680	2.10 $1 × 10 - 9$

Table 6 The discharge volume of the device and occurrence probability under each discharge path

泄放路径编号	设备A泄放量/ (kg/h)	设备B泄放量/ (kg/h)	装置C泄放量/ (kg/h)	装置D泄放量/ (kg/h)	装置E泄放量/ (kg/h)	泄放路径出现概率 $P D i$
M1	27000	25600	23000	0	0	$2.890 × 10 - 3$
M2	27000	25600	0	40770	0	$2.912 × 10 - 3$
M3	27000	25600	0	0	19680	$7.488 × 10 - 4$
M4	27000	25600	23000	20385	0	4.20 $8 × 10 - 6$
M5	27000	25600	11500	40770	0	4.20 $8 × 10 - 6$
M6	27000	25600	23000	0	9840	$1.082 × 10 - 6$
M7	27000	25600	11500	0	19680	$1.082 × 10 - 6$
M8	27000	25600	0	40770	9840	1.09 $0 × 10 - 6$
M9	27000	25600	0	20385	19680	1.09 $0 × 10 - 6$
M10	27000	25600	23000	20385	9840	2.10 $1 × 10 - 9$
M11	27000	25600	11500	40770	9840	2.10 $1 × 10 - 9$
M12	27000	25600	11500	20385	19680	2.10 $1 × 10 - 9$

Table 7 Overpressure relief path parameters

泄放路径编号	安全阀1/bar	安全阀2/bar	安全阀3/bar	安全阀4/bar	安全阀5/bar
M1	4.02	4.02	3.20	1.58	1.58
M2	3.60	3.60	2.49	2.86	2.17
M3	3.45	3.45	2.26	1.68	1.90
M4	4.095	4.096	3.298	2.184	1.979
M5	3.893	3.894	2.932	2.982	2.331
M6	4.044	4.045	3.233	1.749	1.805
M7	3.738	3.738	2.714	1.829	2.030
M8	3.688	3.688	2.628	3.101	2.506
M9	3.592	3.592	2.485	2.411	2.391
M10	4.161	4.162	3.381	2.435	2.293
M11	3.986	3.987	3.058	3.227	2.664
M12	3.887	3.888	2.924	2.554	2.536

Table 8 Overpressure relief path and occurrence probability of distillation column C without SIS system protection

泄放路径编号	泄放路径	泄放路径出现概率P_d_i
M1	100%A+100%B+100%C	$8.500 × 10 - 2$
M4	100%A+100%B+100%C+50%D	1.238 $× 10 - 4$
M5	100%A+100%B+100%D+50%C	1.238 $× 10 - 4$
M6	100%A+100%B+100%C+50%E	3.182 $× 10 - 5$
M10	100%A+100%B+100%C+50%D+50%E	6.178 $× 10 - 8$
M11	100%A+100%B+100%D+50%C+50%E	6.178 $× 10 - 8$
M12	100%A+100%B+100%E+50%C+50%D	6.178 $× 10 - 8$

Table 8 Overpressure relief path and occurrence probability of distillation column C without SIS system protection

泄放路径编号	泄放路径	泄放路径出现概率P_d_i
M1	100%A+100%B+100%C	$8.500 × 10 - 2$
M4	100%A+100%B+100%C+50%D	1.238 $× 10 - 4$
M5	100%A+100%B+100%D+50%C	1.238 $× 10 - 4$
M6	100%A+100%B+100%C+50%E	3.182 $× 10 - 5$
M10	100%A+100%B+100%C+50%D+50%E	6.178 $× 10 - 8$
M11	100%A+100%B+100%D+50%C+50%E	6.178 $× 10 - 8$
M12	100%A+100%B+100%E+50%C+50%D	6.178 $× 10 - 8$

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