Explosion Accident Simulation for Petrochemical Plant

Explosion accident simulation for Petrochemical plant

Zhao Xiangdi, Yuan Jiwu , Jiang Chunming and Wang Zheng

¹State Key Laboratory of Safety and Control for Chemicals, SINOPEC Safety Engineering Institute, Qingdao, 266071,China

Keywords: Numerical simulation, Explosion, Petrochemical plant, Control room

Abstract. A new method of explosion simulation which based on FLACS software was used for simulating and rebuilding an explosion accident which occurred in a coal gasification company's plant in China. The other two common used method which based on TNT equivalent method and Multi-Energy method were considered to calculated the explosion overpressure too. Simulation results indicate that this new method can calculate all parts of the space after explosion, and can make up for the shortage of traditional assessment techniques and the result is more stable and reasonable when compared with the scene of the accident.

Introduction

The petrochemical plants always have a higher explosion frequency than other facilities because there are many high pressure equipment or devices with lots of material. Once the device of such plants exploded, it may tend to cause large casualties and property losses, such as, Alon big spring refinery(2007),  Guangwei(2008) fire and explosion accidents. The cause of this accident indirectly reflects the lack of explosion protection capability of those device or facilities. It makes sense to make sure or calculate those facility's ability against explosion and determine which class it belongs. Many researchers have formed a special assessment method based on the consequences and risk, and it has been used for design and renovation process of the petrochemical plant^[1,2]. However, studies of this technology lags behind in China, because we still using the traditional assessment technology which based on empirical formula. This method does not consider the actual situation , such as the layer equipment, wind, fire protection system and other condition's effect on the flame acceleration^[3-5].

With the Computational Fluid Dynamics analysis techniques become more sophisticated, the study on the application for explosion based on CFD have increasingly gained wide attention in industry and academia. Herrmann, Hansen et al. using FLACS computational fluid dynamics software studied the consequences of gas cloud which got fire and explosion, then compared the simulation results with experiment, and got a high consistency of results ^[6,7]. Windhors, who using AutoReaGas software to simulate the gas explosion to explore the safe distance between  petrochemical cracker and control room ^[8]. P.Hoorelbeke et al. got a summary analysis for the commonly used in explosion risk assessment techniques, and gave the latest research on risk assessment of explosion using CFD technology ^[9]. However, there is only a little study on numerical simulation model for explosion accidents in China. Therefore, assessment on explosion accident by using FLACS are performed in the work.

Explosion accident and Simulate model

Explosion accident. The scene of the explosion accident with the insulation layer damaged is shown in Fig.1.

 

(a)F2012,F2013, F2014                               (b) T2101,R2103

Fig.1 The scene of the explosion accident with the insulation layer damaged

The key equipment in this unit for simulation is shown in Table 1.

Table 1.  Information for the key equipment

Number	Name	Size(m)	Number	Name	Size(m)
F2102	Gas-liquid separator	µg4.2°Á13.4	R2103	Converter	µg4.9°Á13.8
F2103	Gas-liquid separator	µg3.7°Á11.6	R2104	Converter	µg4.9°Á11.7
F2104	Gas-liquid separator	µg3.7°Á15.6	Control room		15.0°Á46.8°Á4
T2101	Regulate tower	µg3.2°Á26.0	Office building		15°Á46.8°Á19.5

Simulate model. Simulate model which based on the factory's actual situation we used for assessment is shown in Fig.1. This model is a carbon monoxide shift unit of one coal gasification plant. The total size of simulation is 100m °Á 80m °Á 40m. The ignition position is in the center of the carbon monoxide. The distance from ignition position to the control room is approximately 65m. Shapes of the equipment were modified according to the need for simulation. We set different monitor points for the key equipments in the unit as shown in Fig.2.

                         

   (a)Top view                                                        (b) Isometric view

Fig.2 Three dimensional model for simulation

Results and discussion

Leak and dispersion.  The material which flowed in the pipeline is hydrogen with the loss rate of contain is  562kNm3/h. The wind speed is about 3m/s  with the direction is NE when the accident occurred.

 

Fig.3  The fuel size in this unit after dispersion (10m°Á13m°Á7m)

Explosion.  The calculation assumes that the hydrogen and air is in a mixture concentration with equivalence ratio. The TNT equivalent method, Multi-Energy method and FLACS calculation method were used for this assessment and the hydrogen gas cloud explosion impact to the facilities was simulated. However, the TNT equivalent method is simple and does not consider the effect of actual situation on the explosion consequence. Although the Multi-Energy method improvements to consider the impact of the explosion strength, but it did not consider a reflection of complex equipment and did not predict the effect of water spray system also.

Simulation results of explosion overpressure in the position 48m from the ignition point using the three method are shown in table 2. It can be seen in the table that TNT equivalent method and Multi-Energy method can only take into account the overpressure in two-dimensional. For example, the overpressure calculation results in the position 48m from the center of explosion is 5.2 kPa using TNT equivalent method, however, the results increase to 7.5 kPa when we use the Multi-Energy method. But ,simulation results calculated by FLACS is different , it's results is reasonable and accurate, it can predict the overpressure in the three-dimensional space, as for the different with the traditional method, it can give the overpressure in the position 48m from the ignition point with different height above the ground, overpressure with 10m above ground is 6.7 kPa, and the result with 19m above ground is 4.7 kPa. FLACS method can simulate the decrease of the overpressure intensity with spray system start also shows in Table 2.

Table 2. Results of explosion overpressure using different methods.

		Overpressure in the different position  from the ignition point (kPa)
		48m	65m(control room)	74m
TNT equivalent method		5.2	3.48	2.95
Multi-Energy (blast strength 5~10)		7.9 ~ 24.7	5 ~ 16	5.1 ~ 13.4
FLACS method the height above ground(m)	1m	7.8	6.5	3.9
	10m	6.7	-	3.6
	19m	4.7	-	1.9

The overpressure of explosion in the different monitor points(as shown in Fig.1.) we set for assessment equipments are shown in Fig. 4. The overpressure intensity with spray system decrease significantly, the maximum explosion overpressure in carbon monoxide shift unit is about 62 kPa, as well as, the overpressure is about 6.5kPa near the control room.

Fig.4. Overpressure of explosion in the different monitor points

Explosion overpressure wave change and expand process and impact on the building around the facilities during the hydrogen cloud explosion without water spray system are shown in Fig. 5. As soon as the explosion start, a strong shock wave (a), causing major damage to the surrounding equipment, overpressure wave will gradually expanding then, and began to weaken (b-c) and subsequently affect the control room and other key structures (d).

(a) 0.15s after ignition       (b) 0.19s                        (c) 0.21s                           (d) 0.28s

Fig. 5. Explosion overpressure wave change and expand process without water spray system

(5-50 kPa)

Conclusions

As for the shortage of traditional assessment techniques can't predict the explosion effects with the water spray system. A method of explosion simulation which based on FLACS software for Petrochemical plant with water spray were introduced in this paper. The results shows as follows:

This method can calculate all parts of the space after explosion, and can make up for the shortage of traditional assessment techniques. The overpressure simulation results using this method is between the results calculated by TNT equivalent method and Multi-Energy method. The result is more stable and reasonable when compared with the scene of the accident.

Acknowledgements

This work was financially supported by the National Basic Research Program (NO.2012CB724210).

References

[1] D.Bjerketvedt, J.R.Bakke and K. Wingerden: Journal of Hazardous Materials Vol.52(1997), p.1-150.

[2] S.B. Dorofeev: International Journal of Hydrogen Energy. Vol.32(2007),p.2118-2124.

[3] B.H.Hjertager, I.Moen, J.H.S.Lee, R.k.Eckhoff, k.Fuhre, O. krest: CM1 Report No. 803403-2, Chr. Michelsen  Institute, Bergen, Norway (1981).

[4]Guidelines for chemical process quantitative risk analysis. American institute of chemical engineers, NY,2000.

[5] A.C. van den Berg: Journal of Hazardous Materials, Vol.12(1985),p.1-10.

[6] Herrmann, D.D. International Conference and Workshop on Modeling the Consequence of Accidental Releases of Hazardous Materials. CCPS/AIChE, Sep. 28 (1999),p.479-494.

[7] Hansen, O.R., Talberg, O. and Bakke, J.R.: International Conference and Workshop on Modeling the Consequence of Accidental Releases of Hazardous Materials. CCPS/AIChE, Sep. 28, (1999),p. 457-477.

[8] Windhorst, J.C.A..: International Conference and Workshop on Modeling the Consequence of Accidental Releases of Hazardous Materials. CCPS/AIChE, Sep. 28, (1999),p. 495-514.

[9] P.Hoorelbeke, C.Izatt, J.R.Bakke, J.Renoult, R.W.Brewerton: American Society of Safety Engineers Middle East Chapter 7th Professional Development Conference& Exhibition kingdom of Bahrain. March 18-22,(2006),p.1-15.