haccp oil refining
DESCRIPTION
Risk assement and process analysis Edible Oil Refining, canola refining, palm olein refiningTRANSCRIPT
ICheaP10 8-11 May 2011 - Florence, Italy
Hazards assessment of
vegetable oil storage and
processing plants
G. Landucci1, B. Nucci2, M. Pierini1, G. Pannocchia1, L. Pelagagge2, C. Nicolella1*
UNIVERSITA DI PISAICheaP10 8-11 May 2011 - Florence, Italy
ICheaP10 8-11 May 2011 - Florence, Italy
Introduction (1)
The major part of the global vegetable oil production
derives from extraction processes
The process is based on the selective oil extraction
usually carried out with a volatile organic solvent,
typically hexane. After separation from solvent the oil
phase is processed in chemical refining
The vegetable crude oil usually presents a low content
of residual solvent
• SAFETY ISSUES
• PROCESS ISSUES
ICheaP10 8-11 May 2011 - Florence, Italy
Introduction (2)
Source Year Country Location Operation Fatalities Injuries Abstract
(A) 1975 The Netherlands harbour/port/dock Maintenance (cleaning) >1
during cleaning of a tank on tanker
after unloading cocosoil, some hexane
vapours caused at least 1 casualty
(A) 1976 The Netherlands factory Processing 4
wear of pumpseal caused hexane
release under the space of building,
ignition, explosion and 4 casualties
(A) 1977 Germany factory Processing fire in extractor of soya factory
(A) 1979 The Netherlands Inland navigation Maintenance 1 vapour cloud explosion on vessel in
locks caused fire and 1 casualty
(A) 1980 Denmark Factory Processing 27
hexane release at extraction plant for
soya bean caused evacuation of the
plant & after switch off (un)loaded
power supply line an explosion
occurred causing 27 casualties
(A) 1983 Argentina storage/depot Storage 1 >1
a fire in an elevator ignited gas from
sunflower pellets in silo setting of an
explosion causing more than 2
casualties
(A) 1983 Germany Factory Processing 2 11 explosion and fire at oil extraction plant
(A) 1984 The Netherlands Factory Processing 2
while working in the cooker without
the required permit flash fire injured 2
workers
(A) 1991 Japan Factory Maintenance >8
A combustible gas-air mixture was
generated in an extractor by residual
hexane content. Ventilation was not
sufficient. Explosion occurred due to
static electricity when the repair work
started in the extractor.
(A) 1994 USA factory-yard Processing (application) 11 hexane leak caused heavy fire
(B) 2006 Italy Factory (refinery) Maintenance (storage) 4 - Welding operation inside a pomace oil
tank
(C) 2007 Spain Factory (refinery) Maintenance (storage) 1 1 Welding operation inside a pomace oil
tank
Accidents involving veg. oil –
hexane (FACTS, TNO 2007)
ICheaP10 8-11 May 2011 - Florence, Italy
Introduction (3)
Spoleto, 2006
A catastrophic accident occurred in a vegetable oil refinery in
Italy in 2006.
During maintenance operations, an explosion occurred in a
pomace olive oil- storage tank, causing 4 fatalities among
personnel and damaging the surrounding equipment.
The cause of the explosion was the accidental ignition of the
residual solvent vapour during welding operations
An accident with similar features occurred in Spain only few
months later
The residual solvent may accumulate in the vapour
phase, mixing with air and forming flammable
mixtures which could result in the confined
explosion of the storage vessel in presence of
ignition.
ICheaP10 8-11 May 2011 - Florence, Italy
Introduction (4)
Loss of efficiency in high
temperature vacuum
operations (such as the
drying and bleaching).
ICheaP10 8-11 May 2011 - Florence, Italy
Aims of the work:
Development of an approach able to
quantitatively evaluate the hazards due to the
residual solvent
Safety issues related to storage – formation of
flammable mixtures inside the tanks
Processing of vegetable oils – determination of
residual solvent accumulation among refining
process
ICheaP10 8-11 May 2011 - Florence, Italy
Methodological approach
Estimation of liquid
phase composition
Thermodynamic model
for the estimation of
vapor phase
composition
Model validation
against available
experimental data
1
2
3
Definition and
evaluation of case-
studies
4a
Determination of
hazard indexes5a
Safety issues in storage tanks
Definition of critical
sections for hexane
accumulation
4b
Control and restoring
measures5b
Safety issues in oil refining
ICheaP10 8-11 May 2011 - Florence, Italy
Model set up (1)
Liquid phase characterization:
• Triglycerides mixture
(depending on oil type and
origin)
• Free fatty acids (0.5-1 up to few
percent)
• Residual solvent
Schematization:
one reference triglyceride, namely LLP (constituted by two Linoleic
groups and one Palmitic group)
one free fatty acid, namely oleic acid
Thecnical hexane assumed a reference solvent and assimilated as pure
n-hexane
Crude vegetable oil inside the
storage tank
ICheaP10 8-11 May 2011 - Florence, Italy
Model set up (2)
A well mixed air-hexane vapour phase is assumed in the top space of the vessel, due to open vent on the tank roof.
Stratification is not considered in the present work, which assesses possible formation of flammable mixtures, without accounting for possible sources of ignition and the consequent effects following the ignition
The analysis is referred to normal operation, the presence of oil sludge (sediment solids) is not considered in model.
ICheaP10 8-11 May 2011 - Florence, Italy
Model set up (3)
Equilibrium relationship: c
SAT
i
SAT
iiii NiTPTxPy ,1
Where: 1
iy : molar fraction of the i-th component in vapour phase; 2
P : operative pressure (Pa); 3
i : activity coefficient of the i-th component; 4
ix : molar fraction of the i-th component in liquid phase; 5
SAT
i : fugacity coefficient of the pure i-th component; 6
SAT
iP : vapour pressure of the pure i-th component; 7
T : operative temperature (K) 8
cN : total number of components. 9
A modified version of the UNIFAC (UNIversal Functional
Activity Coefficient) model was used to assess the activity
coefficient
ICheaP10 8-11 May 2011 - Florence, Italy
Model validation
In order to test the validity of the model, a comparison with available experimental data was carried out.
Available data ONLY at high hexane concentration (Extraction studies)
The only available data for diluted solutions are reported by Smith & Wechter (J. of the American Oil Chemists’ Society 28, 381-382, 1951).
RSC = 1.32%
RSC = 1.08%
RSC = 0.85%
RSC = 0.62%
RSC = 0.41%
RSC = 0.20%
0
5
10
15
20
25
30
15 30 45 60 75 90 105 120
Temperature (°C)
He
xa
ne
pa
rtia
l p
res
su
re (
kP
a)
Model estimates
Experimental values
Extrapolation
Temperature (°C)
ICheaP10 8-11 May 2011 - Florence, Italy
Analysis of vegetable oil storage (1)
The model was applied to the analysis of an industrial storage plant.
The refinery processes sunflower, olive, peanut and corn oil with a maximum residual solvent content RSC of 0.1% by weight
Higher RSC values were taken into account (e.g., 0.38% and 0.75% by weight).
The tank farm is equipped with a heating system which prevents the vessel cooling to temperatures lower than about 18°C in presence of cold weather.
For temperatures higher than 18°C the operative temperature can be assumed equal to the average ambient temperature.
Typical weather conditions of the zone of the oil refinery were considered in the study
•Vegetable oil refinery of SALOV
S.p.A., located in Massarosa (Italy)
•The tank farm of the plant
comprises 28 vessels with volumes
ranging between 85 and 750 m3,
with a total capacity of about 8500
tons.
ICheaP10 8-11 May 2011 - Florence, Italy
Analysis of vegetable oil storage (2)
Estimation of
vapor pressure in
the tank
according to
external meteo
conditions
Possibility of
having flammable
mixtures for high
RSC
ICheaP10 8-11 May 2011 - Florence, Italy
Analysis of vegetable oil refining (1)
Typical refining process conditions: purification of a sunflower oil assuming a free fatty acid content (FFAC) of 4 %wt. to be reduced up to 0.04 %wt.
Equipment: R: reactor; P: pump; CS: centrifugal separator; E: heat exchanger; S: flash separator;
EJ : steam ejector; F: filter; C: column. Material streams : S_MP: medium pressure steam; S_LP:
low pressure steam; EA: earths & activated carbons; W: water; SH: sodium hydroxide; HP:
phosphoric acid; FO: feedstock oil; SW: soaps & waxes; SE: spent earths; FFA: free fatty acids;
RO: refined oil.
ICheaP10 8-11 May 2011 - Florence, Italy
Analysis of vegetable oil refining (2)
Process
section
Operative
temperature
( C)
Operative
pressure
(mbar)
Process description
Neutralization 20 1000 Adding sodium hydroxide to reach an
intermediate grade of acidity
Degumming 20 1000 adding phosphoric acid and subsequently
oil is sent to centrifugal separation to split
the oil fraction from the solid waste.
Washing 90 1000 The oil is washed with water
Dehydration 90 50 Oil is dehydrated in a flash separator under
vacuum conditions
Discoloration 95 60 Adding bleaching earth and activated
carbon in a stirred vessel under vacuum
conditions, then oil filtered
Deodorization 230 2 “physical” neutralization with water steam at
high temperature under vacuum conditions.
The FFAC is stripped and condensed in a
direct contact condenser, while steam with
non condensable vapor are sent to the
ejectors section.
ICheaP10 8-11 May 2011 - Florence, Italy
Simulation of vegetable oil refining (1)
Process simulations were performed using HYSYS V7.1
(by ASPEN Tech, Cambridge MA) simulation software.
• The crude vegetable oil, including FFAC and hexane,
was schematized according to the described
thermodynamic model
• A residual hexane content of 0.1%wt. was considered
as process input.
• The aim of the process simulation was to “trace” the
hexane flow through each part of the process, with
particular attention to units working at high
temperature and low pressure, in which hexane
vaporization is favoured (thus issuing safety
problems in shut down and maintenance operations)
ICheaP10 8-11 May 2011 - Florence, Italy
Simulation of vegetable oil refining (2)
Sankey diagram identifying the critical nodes in which the accumulation of hexane is predicted
The analysis evidenced the need to focus on the operative problems related to dehydration, discoloration and deodorization
The vacuum conditions are kept in these units by steam
ejectors. The steam ejector model was set up on the basis of
actual plant field data, based on typical operative conditions
ICheaP10 8-11 May 2011 - Florence, Italy
Sensitivity analysis
Determine the effect of the variation of a process variable to the refining process performance.
Increasing content of hexane in feedstock oil was analyzed (up to 0.5%)
Effect on the ejector system aimed at keeping low pressures in high temperature units.
The process performance was analyzed through the dehydration efficiency
0,000 0,001 0,002 0,003 0,004 0,0050,70
0,75
0,80
0,85
0,90
0,95
1,00
Dehydra
tion
effic
ency
Hexane weight fraction (w/w)
Potential decrease of 30% in process efficiency related to ejectors, thus evidencing the criticality of the residual solvent content in input feedstock.
ICheaP10 8-11 May 2011 - Florence, Italy
Conclusions
A quantitative methodology for the evaluation of residual
volatile solvent content effect on storage and processing of
edible extracted oils.
A thermodynamic model was implemented and validated in
order to reproduce the liquid-vapor equilibrium of crude
vegetable oil - residual solvent system.
Application to industrial case studies:
• Identification of potential hazards due to formation of flammable
mixtures inside the storage tanks
• The critical nodes of solvent accumulation were identified among
the process, evaluating the influence on the global efficiency.
Acknowledgments
This research has received funding from Regione Toscana
(Bando Unico R&S n.2009DUA/526090469/1)
ICheaP10 8-11 May 2011 - Florence, Italy
Thank you….
Maintenance operations on a
crude vegetable oil tank