Chemical & Process Technology

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Mixing of liquid in vapor using spraying nozzle is commonly used in reactor, column, mixing tank, etc. Mixing efficiency and effectiveness subject to liquid droplet size and contact time between droplet and vapor. In order to promote mixing efficiency and effectiveness, spraying nozzle is used to create small droplet size, well distribution of droplet and better spraying angle. Spraying liquid can be done hydraulically (high pressure liquid acting on a special design nozzle), gas assisted (gas kinetic energy acting on liquid for break-up) and rotary spraying (hydraulic pressure acting on moving device and results breakage of liquid).

Spray pattern videos now available include examples of the following nozzles:

• Spiral
• Axial Whirl
• Tangential Whirl
• Fan
• Misting
• Air Atomizing
• Tank Washing

This useful tool is the newest component of BETE Fog Nozzle, Inc.'s efforts to provide customers with solutions specially tailored to their unique spray challenges. BETE Fog Nozzle, utilizing our engineering resources and state-of-the-art Spray Laboratory, is fully prepared to collaborate with customers to supply nozzles that meet their most demanding industrial process conditions.

Following are 5 typical spraying videos.

• Pump Pressure Versus Head
• Why Centrifugal pump NPSH required increases with flow ?
• Tips for Centrifugal Pump
• Rule-of-thumb For Minimum Flow Recycle
• Basis & Tips on Setting Centrifugal Pump "Warming" Recycle Flow
• Potential Problem associate with Double NRV in Series within a Line

Labels: Droplet, Hydraulic

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A pump with capacity of 100 m3/h and pump head of 75 m, base on suction drum elevation, fluid condition and suction piping condition, the calculated available Net Positive Suction Head (NPSHa) is 2m. This NPSHa shall be verified with NPSH required (NPSHr) by selected pump.

N_ss : Suction Specific speed
Q : Flow rate (gpm) at the Best Efficiency Point
N : Pump rotational speed (rpm) *
NPSHr : Net Positive Suction Head required (ft)

Labels: Pump

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Rupture disc (RD) is one of the non-reclosable type pressure relief device for vessel overpressure protection. It has been used in many application due to it uniqueness and special characteristic as covered in "Why Rupture (RD) Upstream of Pressure Relief Valve (PRV) ?". In some application, two RDs are placed in series to minimize inventory lost cause by premature opening of RD. Premature opening of RD may be cause by RD quality during manufacturing. Besides, premature opening of RD may be caused by wrong handling and installation of RDs.

Elfab, a RD manufacturer offer a few RD installation videos which could very useful for most operator. you may download from the following links or visit Elfab.

• Conventional Domed (CD)
• Domed Composite (DC)
• Flat Composite (FC)
• Opti-Gard (OP)
• Opti-Gard SoLo (OPS)
• Safe-Gard (SG)
• Universal Arma-Gard (AGS)

Related Post

• Why Two Rupture Discs in Series ?
• Why Rupture (RD) Upstream of Pressure Relief Valve (PRV) ?
• Tube Rupture : Pressure Relief Valve (PSV) or Rupture Disk (RD) ?
• Criteria for Requirement of Pressure Relief Device for Tube Rupture
• Some Comments on Providing External Insulation as Protective Measure against FIRE
• Protective Measures against FIRE other than Pressure Relief Device (PRD)
• PSV for Shell-and-Tube HEX Tube Side Overpressure Protection against External Fire Attack ?

Labels: Overpressure Protection, Pressure Relief Device

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Earlier post "Relationship between NPSHa & NPSHr", Process engineer must always ensure the operating pressure along the pump (from suction to discharge) always higher than fluid vapor pressure. Net positive suction head (NPSH) is used to check if cavitation will occur. Process engineer must always ensure available Net positive suction head (NPSHa) is always higher than pump required Net positive suction head (NPSHr). In recent discussion with some engineers, there was some doubt or confusion on a simple statement. Should pump still cavitate eventhough Net Positive Suction Head available (NPSHa) higher than Net Positive Suction Head required (NPSHr) ?

Yes. Cavitation can exist eventhough NPSHa is above the NPSHr of a centrifugal pump. Based on Hydraulic institute definition of NPSHr, a NPSHr of a pump is the level of NPSHa that three percent (3%) reduction in total discharge head of the pump caused by flow blockage from cavitation vapor in the impeller eye. Pump manufacturers design their pumps based on this definition. There is still situation where head drop is below 3%. Nevertheless, it is believe this definition was based suction energy sufficient low (below 3% head drop) and will not results cavitation which is detrimental to pump internal i.e. impeller.

A few interesting facts about NPSHa and NPSHr

• Cavitation occur when NPSHa is above NPSHr, however it is not reach detrimental level
  
• Possible achieve 100% head when NPSHa = 1.05 to 2.5 times NPSHr
• Zero cavitation when NPSHa = 2 to 20 times HPSHr, subject to suction energy, present of air, erosive & abrasive material, etc however
• Common Zero cavitation when NPSHa = 4 times NPSHr
• NPSHa in the range of 1.1-1.3 of NPSHr for low suction energy pump design
• NPSHa in the range of 1.3-2.5 of NPSHr for high suction energy pump design
• Minimum one (1) meter NPSHa above NPSHr
  

Above may be used as guildeline in determining margin between NPSHa and NPSHr. However, higher margin shall be included if air and abrasive material is present in the pumping fluid.

Related Topic

• Protect Pump for Longer Operation
• Basis & Tips on Setting Centrifugal Pump "Warming" Recycle Flow
• Flow-Delta P Protection Strategy
• Centrifugal Pump Minimum Flow Control Strategies
• Quick Check Pump Performance Using Motor Data and Field Measure Current
• Is PumpSmart Right Solution for You ?
• Vortex Breaker to Avoid Vapor Entrainment

Labels: Hydraulic, Pump

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Restriction orifice (RO) is widely used to in Oil and Gas, Refinery and Petrochemical chemical plant. Simple search on internet lead you to plenty of articles related to functionality, calculation and specification of restriction orifice. "Restrcition Orifice Used in Many Applications in Different Manners" brought out a few applications of RO in the industries. Earlier post "A refresh to Process Engineer on few phenomenons in restriction orifice" has summarized a few concepts that a process engineer may needs to understand for restriction orifice :

• Restriction orifice is used to limit flow to required or expected flowrate with the available differential pressure across.
• Vena contracta (VC) present just short distance downstream of restriction orifice
• Maximum velocity and minimum pressure at vena contracta (VC)
• Choked flow occurred when velocity at vena contracta (VC) reach sonic velocity (Ma=1). The corresponding downstream pressure (P2) at choked condition called critical pressure (Pc).
• Increase in upstream pressure (P1) will increase mass flow passing the restriction orifice but velocity at VC still maintaining at Ma=1

1. composition ( k, MW, ...)
2. driving force (Differential pressure) across RO (P1-P2)
3. density (function of P1, MW, z, T1)
   

1. composition (and therefore k, MW...) remain unchanged
2. reducing P2 lead to higher P1-P2 which will result higher mass flow passing RO. Mass flow increase will continue until until P2 reach critical pressure of fluid (Pc). Sonic velocity (Mach no =1) occurred at vena contrata, some distance downstream of RO. When P2 lower than Pc, further reduction of P2 will not result any mass flow increase.
3. reduce upstream temperature (T1) will results higher density and higher mass flow passing RO.
   

• A refresh to Process Engineer on few phenomenons in restriction orifice
• How to determine if a restriction orifice will experience cavitation ?
• Restrcition Orifice Used in Many Applications in Different Manners
• Bug in ASPENTECH HYSYS 2006 Dynamic Depressuring Fisher Valve model
• Controlled and Non-controlled Type Depressuring
• How to apply valve equation in HYSYS Depressuring ?
• Why Restriction Orifice is some distance from Blowdown valve ?

Labels: Fluid Flow, hydrualic

Labels: E-Doc, Education, Learning

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Minimum oxygen concentration (MOC) is minimum quantity of oxygen required present in hydrocarbon mixture so that a fire can be initiated and propagated. Below this limit, a fire will not form. More discussion in "Minimum Oxygen Concentration (MOC) for Flare Purge". A mixture is combustible / flammable if and only if the hydrocarbon composition is within mixture LFL/LEL and UFL/UEL as discussed in "Estimate Mixture Flammability & Explosivity At Reference P & T One shall remember, as the operating pressure (P) and temperature (T) change (from reference P & T, the mixture LFL/LEL and UFL/UEL at P & T will change accordingly. This post will discuss the relationship between MOC with LFL/LEL.

LFL Relate to MOC
LFL is minimum hydrocarbon (HC) concentration in air which a mixture will burn when an ignition source is present. LFL can be written as follow

MOC is minimum oxygen present in hydrcarbon mixture which a mixture will burn. MOC can be written as follow



Combining [1] & [2],




Combustion of Hydrocarbon



Above equation may be used to estimate MOC if you know the LFL of hydrocarbon.

Example
1) A Ethane (C₂) having LFL of 3.0 vol% (Refer to "Estimate Mixture Flammability & Explosivity At Reference P & T". Estimate MOC of Ethane.

Combustion of C₂H₆,

C₂H₆ + d.O₂ ==> 2CO₂ + 3H₂O

a = 2
b = 6
c = 0
d = 2 + 6 /4 - 0/2 = 3.5

MOC = 3.5 x 3.0 = 10.5 Vol%, close to 11.2 vol% in literature.


2) A n-butane (nC₄) having LFL of 1.86 vol% (Refer to "Estimate Mixture Flammability & Explosivity At Reference P & T". Estimate MOC of n-butane.

Combustion of C₄H₁₀,

C₄H₁₀ + d.O₂ ==> 4CO₂ + 5H₂O

a = 4
b = 10
c = 0
d = 4 + 10 /4 - 0/2 = 6.5

MOC = 6.5 x 1.86 = 12.1 Vol%. Close to 12.3 vol% in literature.

Related Topic

• Estimate Mixture Flammability & Explosivity At Operating P & T
• Estimate Mixture Flammability & Explosivity At Reference P & T
• Inert Gas or Fuel Gas For Flare Purge ?
• Nitrogen Purging - What are the factors you need to consider ?
• Fire related topics...
• Flare related topics...

Labels: Fire, Safety

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Earlier post "Estimate Mixture Flammability & Explosivity At Reference P & T" discussed about the Lower flammable limit (LFL) or Lower Explosive Limit (LEL) and Upper flammable limit (UFL) or Upper Explosive Limit (UEL) for single component fluid and mixture at reference pressure (P_ref) and temperature (T_ref). This post will discuss the way to correlate the LFL/LEL and UFL/UEL at P_ref and T_ref and operating pressure (P) and temperature (T) .

Temperature & Pressure Corrected LFL/LEL & UFL/UEL
Below are two equations may be used to correlate the LFL/LEL and UFL/UEL at P_ref and T_ref and operating pressure (P) and temperature (T).

One shall take note that these equations are used for single component. For a mixtures, the LFL/LEL and UFL/UEL at operating pressure (P) and temperature (T) will be calculated using following equation (as discussed in "Estimate Mixture Flammability & Explosivity At Reference P & T":

Calculation Steps
2 steps in determining mixtures LFL/LEL and UFL/UEL at operating pressure (P) and temperature (T) .
(i) Estimate LFL/LEL and UFL/UEL at operating pressure (P) and temperature (T) for every component in a mixture
(ii) Estimate mixture LFL/LEL and UFL/UEL

Example
A mixture contains of Methane, Ethane and Propane with volume% of 20%, 20% and 60%. Estimate UEL at (i) 20 degC & 101.325 Pa, (ii) 70 degC & 3 MPa.

Data
Methane (C1)
UEL_C1,20C,1ATM = 15.0%, E_{C1,combustion} = 212.79 kcal/mole

Ethane (C2)
UEL_C2,20C,1ATM = 12.4%, E_{C2,combustion} = 372.81 kcal/mole

Propane (C3)
UEL_C3,20C,1ATM = 10.1%, E_{C3,combustion} = 526.74 kcal/mole

Output
(i) UEL_Mix at 20 degC & 101.325 Pa

UEL_Mix = 1 / [ 0.2/15 + 0.2 /12.4 + 0.6 / 10.1 ]

UEL_Mix = 11.25 vol% at 20 degC & 101.325 kPaA

(ii) UEL_Mix at 70 degC & 3 MPa
UEL_C1,7oC,3MPa
= 15 x [1+0.75(70-20)/212.79]
+ 20.6 x [Log10(3)+1]
= 48.07 vol%

UEL_C2,7oC,3MPa
= 12.4 x [1+0.75(70-20)/372.81]
+ 20.6 x [Log10(3)+1]
= 44.08 vol%

UEL_{C3,7oC, 3MPa}
= 10.1 x [1+0.75(70-20)/526.74]
+ 20.6 x [Log10(3)+1]
= 41.25 vol%

UEL_Mix,70C,3MPa = 1 / [ 0.2/48.07 + 0.2 /44.08 + 0.6 / 41.25 ]

UEL_Mix,70C,3MPa = 43.02 vol% at 70 degC & 3 MPaA

Related Topic

• Estimate Mixture Flammability & Explosivity At Reference P & T
• Inert Gas or Fuel Gas For Flare Purge ?
• Nitrogen Purging - What are the factors you need to consider ?
• Personnel Exposure Time For Heat Radiation
• Heat Radiation For Pain & Blistering Threshold
• Fire related topics...
• Flare related topics...

Labels: Fire, Safety