A quick and simple approach for reactor—emergency relief system design—for runaway chemical reactions is presented. A cookbook for system sizing with all main characteristic dimensions and parameters is shown on one realistic example from process industry. System design was done based on existing theories, standards, and correlations obtained from the literature, which were implemented for presented case. A simple and effective method for emergency relief system is shown, which may serve as an example for similar systems design. Obtained results may contribute to better understanding of blow down system frequently used in industrial plants, for increasing safety, decreasing explosion damage, and alleviating the ecological problems together with environmental pollution in case of industrial accidents.
In process industry, raw materials are converted into various commercial products using different techniques. One frequently used method is their conversion by exothermic chemical reactions which can lead to a reactor thermal runaway if the heat generation rate exceeds the heat removal rate during process [
In present study, a detailed design of emergency relief system is shown based on Design Method for Emergency Relief Systems (DIERSs). It incorporates the stateoftheart knowledge obtained from mechanical, electrical, and process engineering based on a long year experiences in the process industries all over the world. All components were designed based on API RP 520 and API STD 526 standards [
The purpose of present study is to
show the main mechanical, electrical, and process fundamentals for this system,
design emergency relief system with corresponding scrubber, absorption column, and corresponding connections.
Designed emergency relief system is presented in Figure
Emergency relief system.
Based on the reaction runaway the emergency relief system design was made in stages from plant vent system, blow down tank, and scrubber with corresponding heat exchangers and absorption column.
Pressure relief devices design was made according to API RP 520 standard [
Calculated system dimensions and characteristics for vent area, horizontal and vertical heat exchanger, blow down and scrubber tank, absorption column, and outflow chimney.
Parameter  Unit  Value  




°C  13  Designed 

°C  26  Designed 

°C  24  Designed 

m^{3}·h^{−1}  700  Designed 



A  130  Designed 

V  380  Designed 

kW  50  Designed 



W 

Calculated from ( 

W 

Calculated from ( 
Energy released data  Set condition  Peak condition  


Pa 


Obtained from literature Fauske (1988) [ 

K  394.6  396.7  Obtained from literature Fauske (1988) [ 

K·min^{−1}  15  20  Obtained from literature Fauske (1988) [ 

J·kg^{−1}·K^{−1}  2930.8  Obtained from literature Fauske (1988) [  

°C  124.3  Obtained from literature Fauske (1988) [  

°C  121.2  Obtained from literature Fauske (1988) [ 
Parameter  Unit  Value  


J·g^{−1}·K^{−1}  4.183  Obtained from literature Perry and Green (2007) [ 

J·g^{−1}·K^{−1}  2.9281  Obtained from literature Perry and Green (2007) [ 



m^{3}  30  Designed 

m^{3}  60  Calculated from ( 

Pa 

Calculated from ( 

kg·s^{−1}  346  Calculated from ( 

Pa 

Obtained from literature Fauske (1988) [ 

Pa 

Calculated from ( 

/  0.24  Calculated from ( 

kg·s^{−1}  82  Calculated from ( 

m 

Designed 
MAWP  Pa 

Designed 


DN  m  0.65  Designed 

Pa 

Designed 



J·kg^{−1}  846  Calculated from (6) 

kg·m^{−2}·s^{−1}  2124  Calculated from ( 

m^{2}  0.326  Calculated from ( 

m  0.65  Calculated from (5) 



mm  5000  Designed 

W·m^{−2}·K^{−1} 

Obtained from literature Perry and Green (2007) [ 

W·m^{−1}·K^{−1}  16.2  Obtained from literature Perry and Green (2007) [ 

W  585711  Calculated from ( 

W  366125  Calculated from ( 

°C  80  Calculated from ( 
LMTD  °C  76.16  Calculated from ( 

/  6.83  Obtained from literature Richardson et al. (2009) [ 

/  0.0594  Obtained from literature Richardson et al. (2009) [ 

/  0.96  Obtained from literature Richardson et al. (2009) [ 

°C  73.11  Calculated from ( 

m^{2}  54  Calculated from ( 

/  85  Calculated from ( 



mm  50.8  BWG 16 Perry and Green (2007) [ 

mm  46.732  
Wall thickness  mm  2.034  

mm  63.5  Calculated from ( 

mm  689.1  Calculated from ( 
BDC  mm  93  Obtained from diagrams Richardson et al. (2009) [ 

mm  782  Calculated from ( 

mm  313  Calculated from ( 

m^{2}  0.04895  Calculated from ( 

kg·s^{−1}·m^{−2}  1986  Calculated from ( 

mm  36.07  Calculated from ( 

/  65127  Calculated from ( 

/  7.48  Calculated from ( 

/  323  Calculated from ( 

W·m^{−2}·K^{−1}  5490  Calculated from ( 

mm  875  Calculated from ( 

Pa  53800  Calculated from ( 

/  85  Calculated from ( 

kg·m^{−2}·s^{−1}  7971  Calculated from ( 

m·s^{−1}  2596  Calculated from ( 
Re_{tube} 

30390  Calculated from ( 
Pr_{tube} 

0.575  Calculated from ( 

W·m^{−2}·K^{−1}  0.044  Calculated from ( 

W·m^{−2}·K^{−1}  0.022  Calculated from ( 

W·m^{−2}·K^{−1}  1957  Calculated from ( 

Pa  91500  Calculated from ( 


Recycle  h^{−1}  22.22  Calculated from ( 
Total heat vertical  kW  23553  Calculated from ( 
Heat per recycle  kW  145.4  Calculated from ( 

°C  80  Calculated from ( 

m^{2}  5  Calculated from ( 

°C  40  Calculated from ( 

°C  15  Calculated from ( 

°C  24  Calculated from ( 



mm  2500  Designed 

mm  50.8 
BWG 16 Perry and Green (2007) [ 

mm  46.732  
Wall thickness  mm  2.034  

mm  63.5  Calculated from ( 

mm  286.7  Calculated from ( 
BDC  mm  88  Obtained from diagrams Richardson et al. (2009) [ 

mm  388  Calculated from ( 

mm  155.2  Calculated from ( 

m^{2}  0.012043  Calculated from ( 

kg·s^{−1}·m^{−2}  8072  Calculated from ( 

mm  36.07  Calculated from ( 
Re_{shell}  /  264718  Calculated from ( 
Pr_{shell}  /  7.48  Calculated from ( 
Nu_{shell}  /  2547  Calculated from ( 

W·m^{−2}·K^{−1}  43435  Calculated from ( 

mm  437.5  Calculated from ( 

Pa  82000  Calculated from ( 

/  13  Calculated from ( 

kg·m^{−2}·s^{−1}  6196  Calculated from ( 

m·s^{−1}  2018  Calculated from ( 

/  23545  Calculated from ( 

/  0.575  Calculated from ( 

Pa  128000  Calculated from ( 

W·m^{−2}·K^{−1}  0.036  Calculated from ( 

W·m^{−2}·K^{−1}  0.01867  Calculated from ( 

W·m^{−2}·K^{−1}  5617  Calculated from ( 
LMTD  °C  38.44  Calculated from ( 

/  4.44  Obtained from literature Richardson et al. (2009) [ 

/  0.1385  Obtained from literature Richardson et al. (2009) [ 

/  0.96  Obtained from literature Richardson et al. (2009) [ 

°C  36.7  Calculated from ( 

m^{2}  5  Calculated from ( 

/  13  Calculated from ( 





kg·s^{−1}  42.21  Calculated from reaction stoichiometry 
Recycle  h^{−1}  22.22  Calculated from ( 

m^{3}  4.5  Calculated from ( 

m 

Designed 
MAWP  Pa 

Designed 



/  0.023  Calculated ratio 

/  1.8  Obtained from correlations proposed in literature Seader et al. (2010) [ 

kg·m^{−2}·s^{−1}  49  Calculated from obtained factor 

m^{2}  1.68  Calculated from ( 

m  1.46  Calculated from ( 

m  0.3048  Obtained from literature Seader et al. (2010) [ 
No foaming factor 
/  1  Obtained from literature Seader et al. (2010) [ 

/  12  Obtained from literature Seader et al. (2010) [ 
IMTP packing  mm  88.9  Obtained from literature Seader et al. (2010) [ 

/  1.66  Obtained from literature Seader et al. (2010) [ 
HETP  m  1.83  Obtained from literature Seader et al. (2010) [ 

m  3  Obtained from literature Seader et al. (2010) [ 

12  Obtained from literature Seader et al. (2010) [  

m^{3}/h 
59.9  Obtained from literature Seader et al. (2010) [ 

m 

Designed 
MAWP  Pa 

Designed 



kJ·mol^{−1}  22.32  Calculated from literature data Perry and Green (2007) [ 

kW  7.1  Calculated from ( 



m^{3}·h^{−1}  100  Calculated from reaction stochiometry 

Pa  400000  Designed 



Pa  500  Calculated from ( 

m^{3} 
72000  Calculated from ( 

m 
230  Calculated from ( 

RPM  2920  Calculated from ( 

kW  34  Calculated from ( 

mm  1460  Calculated from ( 



mm  6000  Obtained from literature diagrams Bleier (1987) [ 

mm  500  Obtained from literature diagrams Bleier (1987) [ 




DN_{pipes}  
Blow down tankhorizontal heat exchanger  mm  400  Calculated from ( 
Horizontal heat exchangerabsorber  mm  400  Calculated from ( 


DN_{pipes}  
Pipes from scrubber via pump  mm  125  Calculated from literature data Fauske (1986), Richardson et al. (2009) [ 


DN_{pipes}  
Main cooling water pipes  mm  300  Calculated from literature data Fauske (1986), Richardson et al. (2009) [ 
Cooling water pipes after crossing  mm  200  Calculated from literature data Fauske (1986), Richardson et al. (2009) [ 
The analytical vent sizing equation for homogeneous vessel venting is [
Physicalchemical parameters use for blow down system design:
The purpose of the blow down tank is to capture the two phase material flow from reactor and to decrease the pressure of outflow material [
Various procedures for heat exchanger design may be found in the available literature [
Assume pipe diameter, length, inside, and outside fouling factor.
For the pipe construction, an INOX AISI 316 was used with corresponding characteristics presented in Table
Corresponding energetic balances for horizontal and vertical heat exchanger were written as
The Log Mean Temperature Difference (LMTD) for countercurrent flow was calculated by
Based on the experiences and literature data, divided flow shell and even tube passes were assumed for both condensers. Following the procedure proposed by Richardson et al. [
Overall heat transfer coefficients were assumed from the data reported in the literature [
Equations used for horizontal and vertical heat exchanger design are as follows:
The heat transfer coefficient
The overall heat transfer factor was calculated on “
The overall heat transfer factor was calculated on “
The tubeside pressure drop was calculated:
For the vertical heat exchanger design, exactly the same procedure as proposed for the horizontal heat exchanger was used. Firstly, the amount of condensed vapor was calculated from the ratio of vapor pressures at reactor release in the blow down tank and after the volumetric expansion:
All calculated parameters are presented in Table
Since the reaction enthalpy for the neutralization reaction of phenol acid with sodium hydroxide cannot be found in the available literature it was calculated from formation enthalpies and was 22.32 kJ/mol [
Neutralization reaction gives the stoichiometric ratio of phenolic acid versus sodium hydroxide and enables the calculation of the amount of neutralization medium needed for neutralization. The necessary 50 wt.% neutralization liquid flow rate was calculated from the reaction and was 42.3 kg/s. To decrease the necessary volume of used sodium hydroxide, its recycling was assumed. The recycle flow was calculated using
Before outflow gas from blow down system was left into surrounding air, it was neutralized by sodium hydroxide in counterflow absorption column. A lot of literature for absorption column design can be found in available literature [
The vapor gas coming out from absorption column is mainly composed of different phenolic vapors which are heavier than air; therefore, a ventilator fan needs to be inserted into outflow chimney. The role of the fan is to suck the vapor gas coming out from absorption column and to blow it out via chimney into surrounding air. Equations used for the fan design are presented as follows [
Design equations for ventilator fan design in outflow chimney.
Pressure of ventilator:
Gas vapor velocity:
Ventilator motor power:
Axial fan velocity:
The fan pressure and the fan capacity were designed based on capacity of 82.3 kg · s^{−1} of outcoming gas by (
Electrical connections for pump and fan motor.
Rupture disc and safety relief valve connection to reactor.
Blow down equipment is connected using thick wall pipes made of INOX AISI 316 due to highly corrosive medium, high fluid velocities, and large pressures at reaction runaway. For the vent size pipes, diameter design at reaction runaway frequently used technique proposed by Bleier [
Neutralization process characteristics demand 100 m^{3}·h^{−1} of 50 wt.% sodium hydroxide. For this, a corresponding pump with 5.5 kW electrical motor and capacity of 120 m^{3}
It needs to be mentioned that reaction mixture which appears at reaction runaway is very viscous, which may result in appearance of plug in designed pipes, equipment, and huge pressure drops. This problem will be avoided by decreasing the connection pipe length without reductions and low pipe elbow number. Horizontal heat exchanger which is located above the blow down tank decreases the fluid temperature which results in fluid condensation, that is why lower amount of gas need to be neutralized in absorption column. Less required gas for neutralization results in lower NaOH consumption which decreases operational costs of designed system. Additionally, horizontal heat exchanger produces huge pressure drop which results in lower gas velocities and higher gas/liquid mass transfer coefficients which increases the efficiency of absorption columns [
Designed results of this study demonstrate that proposed method can be used for emergency relief system design. Based on calculated data the following conclusions were made.
Emergency relief system for exothermic reaction for reactor volume up to 30 m^{3} was designed. A 60 m^{3} blow down tank, with 700 m^{3}·h^{−1} of 13°C/26°C cooling water, and two condensers—horizontal and vertical—with cooling area of 54 m^{2} and 5 m^{2} are proposed. An absorber column with diameter of 1.5 m and 3.0 m height, 4.5 m^{3} scrubber tank, and corresponding outflow chimney were designed. All other system parameters are presented in Table
Length (m)
Thermal conductivity (
Specific heat of cold medium (
Specific heat of hot medium (
Specific heat of cooling water (
Heat transfer (W)
Temperature of hot medium (°C)
Reactor charge (kg)
Area (m^{2})
Reactor volume (m^{3})
Density (kg·m^{−3})
Heat release per unit mass cold medium (
Heat release per unit mass hot medium (
Discharge mass flow rate per unit area (
Pressure (Pa)
Temperature (K)
Self heat rate in runaway reactions (
Energy release rate (
Heat of hot medium (W)
Heat of cold medium (W)
Temperature of hot medium (°C)
Log mean temperature difference (°C)
Parameter for temperature correction factor prediction
Parameter for temperature correction factor prediction
Temperature correction factor
Mean temperature difference (°C)
Overall heat transfer coefficient (
Average provisional area (
Number of tubes
Pipe diameter (mm)
Ration
Mass flow (
Friction factor
Pressure drop on the shell side (Pa)
Pressure drop on the tube side (Pa)
Bundle diameter clearance (mm)
Wall thickness (mm)
Tube pitch (mm)
Bundle diameter (mm)
Shell diameter (mm)
Baffle spacing (mm)
Area for crossflow (
Shellside mass velocity (
Shell equivalent diameter (mm)
Reynolds number
Prandtl number
Nusselt number
Shellside heat transfer coefficient (
Shellside heat transfer factor
Baffle spacing (mm)
Number of tubes per pass
Tubeside mass velocity (
Tubeside velocity (
Inside tube Reynolds number
Inside tube Prandtl number
Inside tube Nusselt number
Shell side friction factor
Inside heat transfer coefficient (
Overall heat transfer factor for inside tubes flow (
Overall heat transfer factor for outside tubes flow (
Average heat transfer factor (
IMTP packing factor
NaOH flow (
Recycle of NaOH in absorber (
Volume of scrubber tank (
Absorber area (
Absorber diameter (m)
Pressure drop on absorber tray (Pa)
IMTP packing factor
Mark of absorber fill
Number of theoretical plates or trays
Height equivalent to the theoretical plate (m)
Height of absorption column (m)
Blow down volume (
Maximal tank volume (
Heat release per unit mass at reaction runaway (
Specific heat of material (
Self heat rate at temperature turn around or maximal over pressure defined by API RP 520 during run away (
Self heat rate at set pressure of pressure relief devices (
Temperature of reactant correlates to the temperature turn around or maximum over pressure defined by API RP 520 during runaway (K)
Temperature of reactant correlates to set pressure of pressure relief devices (K)
Temperature difference (K)
Time (s)
Viscosity (
Kinematic viscosity (
Volume (
diameter (m)
Density (
Flow reduction factor
Voltage (V)
Current (A)
Power supply (W)
Gas rate (
Liquid rate (
Liquid concentration (
Gas concentration (
liquid rate to tank volume (
Ventilator fan flow (
Axial fan velocity (
Ventilator fan pressure (Pa)
Ventilator motor power (W)
Rotational velocity of ventilator fan (RPM)
Ventilator area (
Fan diameter (mm)
Height of outflow chimney (mm)
Gravity acceleration (
Outflow vapor gas velocity (
Flow reduction factor
Reaction enthalpy (
Gas flux (
Inner diameter (m)
Blow down
Pressure turnaround, mean
Maximal value
Relief set conditions, shell
Initial conditions
Cold in
Cold out
Absorber
Vent
Birmingham Wire Gauge
Coatings of dirt on the in and out site of pipe
Wall
Tube side
Shell side
Refers to tube and shell side
Specific heat
Refers to position
Saturated pressure at position 1 and 2
Horizontal
Hot in
Hot out
Out site
Unit in time
Equivalent
IMTP packing type
Cold
Hot
Pitch
Bundle
Heat
Friction
Inside
Outside
Absorber
Theoretical
3.14
Set point
Electrically grounded
Electro phases
Electro phases
Electro phases
Electro phases
Electro phases
Neutral phase
Switch 1
Position in switch and correction
Fusion 1
Analog current
Contactor
Motor
Three phase electro motor
Maximal allowed working pressure.