Automated crude oil
tank cleaning
The benefits of Life Cycle Cost (LCC) analysis to automated tank cleaning are
discussed. Examples of tank cleaning in practice are provided by independent tank
cleaning service providers who use automated non-man entry tank cleaning methods
Carlos Legorreta
Oreco A/S
F
or many, the cleaning of aboveground oil storage tanks is seen as
a nuisance. However, tank cleaning
should be thought of as an integrated part
of the business cycle/revamp schedule
and subjected to the same assessments.
Doing so will reveal that automated
tank cleaning offers several advantages
over conventional manual cleaning. It
can greatly improve safety and the work
environment, as well as have an impact
on the overall economy of operation.
Potential profit areas include reduced
downtime and oil recovery. And when
companies include these advantages in
their overall considerations, effectively
applying a Life Cycle Cost (LCC)
approach to the cleaning process, they
may well adopt new habits.
Cleaning allows for safe and full
access to tanks for maintenance and
repairs, greatly improving safety.
However, the tank cleaning process itself
can be hazardous to both humans and
the environment when conducted
manually, but these hazards are
eliminated by automated cleaning.
such as corrosion and settlement. If the
tank deteriorates beyond a defined limit,
extensive repairs are required to keep it
in operation.
Cleaning is a vital part of tank
maintenance and can help prolong its
useful life. The process does, of course,
require that the tank be taken out of
operation, and this downtime is costly
for the tank farm manager. However,
automated tank cleaning can reduce
downtime by up to 80% compared to
manual cleaning, immediately adding
value to the overall operation.
Legislation prompts new
cleaning approaches
Manual cleaning:
a hazard to workers
Health, safety and environment (HSE)
issues are a growing concern within the
oil and gas industry. Legislation is
becoming stricter with great regularity,
new codes and policies are being issued,
and refineries and tank farms are
introducing new guidelines of their own
volition. Everyone agrees that these
initiatives protect human health,
promote safety and help prevent
negative impacts on the environment,
but many assume they also entail
considerably higher costs. That
assumption is likely to be proven false
when you consider the wider picture, as
will be addressed in the LCC section.
Maximising the lifetime of storage
tanks has been a priority in the
petrochemical industries for some time.
However, long lifetimes can only be
assured through sufficient maintenance
to counteract degradation mechanisms
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“Automated tank cleaning
can greatly improve safety
and the work environment,
as well as have an impact
on the overall economy of
operation”
When conducted manually, tank
cleaning involves hazardous conditions
for workers, imposing strict requirements
on safety measures. Accidents still
happen, though, mostly due to human
error, and sometimes with dire
consequences for employees and
companies alike. It can be difficult to
assess the potential cost of such
accidents, but the value of totally
avoiding them should not be
underestimated.
So when it comes to HSE, what exactly
should be considered? Most agree that
the safety practices for tank cleaning
should match those for the rest of the
processing or storage facilities. To ensure
they do, this checklist may be useful, as
it essentially constitutes an HSE
assessment of crude oil tank cleaning:
Health issues
— All personnel should undergo
thorough and comprehensive training
on the process chosen and the safety
procedures associated with it
— All personnel should undergo
thorough training on working in
potentially explosive and hazardous
environments. Full theoretical and
practical understanding of the hazards
of dangerous gases, liquids and solids
should be ensured through tests and
simulations
— Cleaning-related pollution that could
cause health hazards for neighbouring
areas should be eliminated
— LEL and H2S measuring devices
should be positioned in areas where
personnel may be exposed to
hydrocarbon vapours.
Safety issues
— The tank cleaning process should
comply with the same regulations as the
rest of the facility (refinery or tank
farm). These include regional or local
standards such as ATEX in the European
Union, UL in the US and CSA in
Canada
— All process equipment and piping
with a high-temperature surface must be
properly insulated
— The use of fire-protective clothing,
helmet, gloves, antistatic footwear and
safety glasses must be enforced without
exception
— All moving parts should be protected
by mechanical covers that cannot be
opened without tools
— Always carry out tank blanketing
with inert gas to reduce oxygen levels
below 8%. This prevents the risk of
explosion (e.g. from static electricity
build-up). Proven sources of accidents
include liquid jet streams, turbulence on
liquid surfaces and high velocities of
fluids in piping
— Like other production facilities, the
cleaning system should be equipped
with continuous process monitoring
and automatic shutdown in the event of
danger
— Electrical grounding must be used
for all external piping and process
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cleaning far more costly than manual
cleaning? No, if you consider the LCC of
non-man entry tank cleaning, it will
prove to be more cost-efficient.
LCC analysis
Figure 1 More than 300 tanks worldwide have been cleaned by the Blabo system
equipment to eliminate sparks. All
should be grounded to the same point as
the tank to ensure the tank and cleaning
equipment have the same electrical
potential at all times.
Environmental issues
— Contamination due to the venting
of oil tanks should be eliminated or
reduced to the greatest possible extent.
For example, vent tanks only when the
hydrocarbon concentration is low
— Contamination of soil, air and
underground water caused by the
extraction and disposal of oily sludge
should be eliminated or minimised by
separating hydrocarbons and inorganic
matter. This reduces the environmental
impact and the costs of final disposal
— Contamination by polluted, oily
water should be eliminated or minimised
by removing the hydrocarbons. Water
recycling will reduce the total water
volumes used during tank cleaning
— Hydrocarbons should be recovered.
Furthermore, the recovered hydrocarbons
must not cause technical disturbances
when introduced to the processing plants.
The recovered hydrocarbons should be
evaluated with regard to BS&W and any
added chemicals.
Observing all these points can be
very demanding, particularly when
using traditional manual cleaning.
However, automated, non-man entry
tank cleaning systems can take them all
into account.
Non-man entry tank cleaning
Obviously, the best way to promote
health and safety in connection with
tank cleaning is to make sure no-one
enters the tank. The Blabo technology
developed and produced by Oreco
eliminates the need for man entry,
increases safety and ensures the recovery
of valuable hydrocarbons. The procedure
carries out desludging, cleaning and oil
recovery in a single, integrated process
by means of automated systems. The
potential polluting streams are also
greatly reduced, as more than 95% of
the hydrocarbons present in the sludge
are recovered.
At present, more than 300 tanks
worldwide have been cleaned using the
Blabo technology. The process complies
with the most demanding safety
regulations in the world, including
ATEX in Europe, UL in the US and CSA
in Canada, and other standards can be
met upon request. But is non-man entry
Factors to consider when taking a LCC approach to automated tank cleaning
— Cost of the cleaning process itself
— Cost of downtime
— Cost of waste disposal
— Value of recovered product
— Savings from accident prevention
— Savings on staff
— Value of extended tank life
— Value of improved environmental profile
— Value of improved working environment profile
Table 1
LCC analysis, which considers all costs
from inception to disposal, has gained
prominence within business communities
of all descriptions. Industries are currently
elevating procurement policies based on
LCC analyses from recommendation
status to prescriptive requirements.
Similar steps are being taken within
the cleaning of oil storage tanks, but the
approach has yet to become standard.
Also, even among those who do take a
LCC approach, the calculations do not
always include all the elements that
should be considered. LCC analysis is
complex, but in essence is a mindset. It
considers intangible as well as tangible
elements and looks far beyond the
immediate contractors’ costs.
It is particularly challenging to perform
proper LCC calculations for processes
such as automated tank cleaning. Most
LCC calculations are made for specific
products and focus on the reliability of
the different choices to determine the net
present value (NPV) of each option. Being
a process rather than a product, automated
tank cleaning requires a slightly different
approach. Even so, this can bring added
value to all who require tank cleaning
and highlight the less apparent benefits
of automated cleaning. Table 1 lists some
of the factors that should be considered.
Most of these points are self-explanatory
and will be looked at briefly in the
following two case studies.
Case study 1
UK refinery
The choice between manual and
automated tank cleaning does not always
appear clear cut, and sometimes a process
of trial and error is to be expected. The
Fawley refinery in the UK, an Esso facility,
was having problems with its catalytic
fines sludge tanks. Over time, the tanks
stratified as catalytic fines gathered in
the bottom strata and consolidated
sediments at the bottom. The refinery
first used manual cleaning to clean one
of the tanks, but the results were not
entirely successful. The manual cleaning
led to considerable waste, very high costs
for disposing of that waste and the entire
process took a long time, which further
added to the total cost. All this prompted
the refinery to try automated tank
cleaning for the other tank.
The automated tank cleaning process
will vary according to several parameters:
the type of tank involved, its size, its
contents, the recovery requirements
stipulated by the tank owner or operator,
and more. As previously described, the
tank at Fawley was used for catalytic
slurry, had a fixed roof, a flat bottom and
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was fitted with internal steam coils. It
had a diameter of 39.5m and a height of
14.5m, and minimal downtime was a
key consideration.
In a typical automated tank cleaning
process, the initial mobilisation includes
nozzles being installed in the roof of the
tank. Known as Single Nozzle Sweepers,
these will handle the actual cleaning,
using recirculated oil as the primary
cleaning media, which is distributed in
far-reaching, low-pressure yet highimpact jets. The nozzles are positioned
according to an indexed washing pattern
to cover the entire tank.
Naturally, the plant safety check list is
completed and all work permits obtained
before the cleaning process begins. The
tank is then blanketed with nitrogen to
provide a safe atmosphere for the
cleaning, which is the final preparation
prior to desludging. The oxygen volume
is also reduced to the 8% value required
to eliminate the risk of explosion.
Desludging is the first stage of the
cleaning process, where most of the oily
sludge from the tank is removed. Nozzles
are operated one at a time, eventually
covering the entire tank. During the
next stage, the actual cleaning, the
nozzles perform an oil wash. At the
Fawley refinery, heated LCO (light cycle
oil) was used as the recirculating
medium. The entire process can be
Product, m3
Sludge, m3
-AR
-AR
-AR
-AR
-AR
-AR
!PR
!PR
Figure 2 Sludge and product levels fell dramatically over a cleaning period of just 15 days
remote controlled so that problem areas
can be addressed without anyone
entering the tank. Once this stage is
complete, the tank is clean.
At Fawley, no final water wash was
necessary once the hot LCO washing was
complete. The tank was opened, and
ejectors degassed the tank and raised the
oxygen concentration above 20%. At this
point, the Blabo system was dismantled
and the tank handed over to the customer.
After 15 days of operation, the tank was
inspected and declared ready to be put
back in operation (Figure 2).
Jorge Oteiza, Managing Director of
STS Tank Cleaning Services, which
carried out the automated cleaning at
Fawley, concluded: “The Blabo non-man
entry closed loop system lets us offer
cleaning options that minimise costs
through shorter downtime, waste
reduction and better safety. Our task was
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Figure 3 The Blabo system mobilised at the MOL refinery, Hungary
The MOL refinery/C&S partnership in brief
Location
Contractors
Tanks cleaned with Blabo
Tank size
Tank content
Roof
Sludge content
Typical cleaning schedule
— Mobilisation
— Desludging
— Demobilisation
Százhalombatta MOL refinery, Hungary
C&S International Services and Euroclean
24 tanks
Variable: up to 80 000 m3
Variable: crude oil, fuel, catalyst
Fixed or floating roof
Variable: typically 500 m3
18 days
4 days
10 days
4 days
Table 2
to clean the tank with a minimum of
downtime and a minimum of waste
generated; both factors that would
directly affect costs.
“The Fawley refinery was very pleased
to have its tank back in operation just 15
days after we started the sludge reduction
process. Managers and supervisors were
surprised after the tank opening; they
had never before seen a slurry tank like
that in their entire professional lives
with Esso. And, of course, they were
pleased that the safer option also ended
up saving them money.”
In summary, the key factors behind
the choice of automated tank cleaning
at Fawley included:
— Manual tank cleaning had been tried
and proved expensive due to downtime
and waste disposal
— Automated tank cleaning provided
shortened downtime, minimal waste
and improved safety.
Case study 2
Hungarian refinery
For the MOL refinery in Hungary, the
choice of automated tank cleaning was
chiefly based on a concern for safety. In
2000, the refinery decided to increase
safety by no longer having personnel
enter its tanks. This decision made it one
of the first to explore automated tank
cleaning in Hungary and across Eastern
Europe.
The commitment to safety did not
mean cost could be ignored. However,
the refinery essentially took an LCC
64 REVAMPS 2008
approach when making its choice and
saw how the added cost of automated
cleaning would be comfortably offset
by other factors. As Marc Schindler, CEO
of C&S International Service, which has
now supplied non-man entry tank
cleaning to the MOL refinery for five
years, says: “The MOL refinery was, of
course, aware that traditional tank
cleaning, performed manually by people,
was more competitive in terms of
immediate investment costs. However,
it was also aware that safer processes
save money on intangible aspects such
as accident prevention.
“A more easily quantifiable factor
concerns the value of recovered oil;
automated tank cleaning allows users to
recover vast quantities of oil that would
otherwise have gone to waste, and to
impose specific requirements on the
quality of that oil.”
Over
the
five-year
working
relationship, C&S has cleaned a total of
24 tanks in Hungary. The tanks cleaned
so far have been both large and small,
with floating or fixed roofs, double or
simple decks, crude oil tanks, fuel oil
tanks, asphaltene and catalyst tanks.
The variety of tasks to be solved is one of
the key reasons behind C&S’s choice of
the Blabo system for its automated tank
cleaning services.
While Blabo technology was not the
client’s first experience with non-man
entry tank cleaning, it decided to adopt
the system in 2003 due to additional
advantages specific to the system:
— Opportunities for improving the
quality of the recovered product thanks
to the integrated separation unit, which
can separate the sludge into clean oil,
solids and water during the desludging
stage. The recovered oil is analysed by
MOL before being approved for use
elsewhere
— Versatility of the system facilities
cleaning of many different types of tank.
The Blabo system (Figure 3) lets C&S
and Euroclean, its contracting partner,
customise services to MOL’s requirements,
handling all tank types, sizes and
products (Table 2). Recently, C&S and
Euroclean also began cleaning 80 000 m3
tanks belonging to the Hungarian
government’s storage company, KT RT,
which is clear proof that the thoughts
inherent in the LCC approach are
becoming increasingly widespread.
In summary, the key factors behind
the choice of automated tank cleaning
at the MOL refinery included:
— Manual tank cleaning rejected due
to safety concerns
— Automated tank cleaning provided
better safety, the opportunity to specify
and improve the quality of the recovered
product, a system applicable to a wide
variety of tanks and added value from
accident
prevention
and
other
intangibles.
Automation adds value
In conclusion, automated tank cleaning
can clearly add value to tank owners. As
the price of crude oil and oil products has
reached record levels in 2008, efficient
tank capacity is becoming increasingly
important. Quite simply, storage has
become a source of value in itself.
Automated tank cleaning has several
advantages such as oil recovery and
minimised tank downtime, and more
intangible benefits such as accident and
personnel injuries and damages
prevention. These aspects should be
taken into consideration when comparing
manual and automated tank cleaning
options, as well as the more immediately
obvious HSE issues. When one takes an
LCC approach to automated tank
cleaning, considering its full impact
and the value it adds, the choice
becomes clear.
Blabo (BLABO) is a mark of Oreco A/S.
Carlos Legorreta is Sales Director, Oreco
A/S in Vaerloese, Denmark. He is a
graduated mechanical engineer with
specialisation in thermal processes and
fluid mechanics. He has more than 30
years’ experience of industrial processing
plants involving water treatment, heat
transfer and separation technologies.
Email: [email protected]
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