(44u) 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

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.

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

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