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7/29/2019 bechtle engineering
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Upstream Process Engineering Course Prepared by Genesis Oil and Gas Consultants Ltd Product and Discharge Specifications1
Upstream Process
Engineering Course
2. Product and Discharge
Specifications
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Upstream Process Engineering Course Prepared by Genesis Oil and Gas Consultants Ltd Product and Discharge Specifications2
Contents
Crude Oil Product Specifications
RVP Specification
Gas Sales
Water Content of Natural Gas Wobbe Index
Gas Transportation
LPG Specification
Quality Tests for LPG
Valuation of Crude Oil
Crude Yields
Value Adjustment
Brent Blend
Crude Oil Contaminants
Metal Contaminants
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Upstream Process Engineering Course Prepared by Genesis Oil and Gas Consultants Ltd Product and Discharge Specifications3
Crude Oil Product Specifications
Crude oil is usually exported to market by tanker or by pipeline. Road and
rail shipments are sometimes used for smaller volumes.
For safe handling of crude, the vapour pressure and maximum delivery
temperature are specified.
For storage in tanks and transport by ship/road/rail, the True VapourPressure (TVP) must be less than 1 bara to prevent vapour loss in transit.
Pipeline TVP is set in conjunction with the operating parameters of the
system. TVP will be less than the lowest system pressure to prevent
vapour breakout.
The TVP of the export oil is controlled by the exporting plant operating
conditions, e.g. pressure and temperature of the final stage of separation.
Water and salt content also need to meet specified values to suit
downstream processing requirements.
The lighter ends of the
crude (shaded area) areremoved to meet the TVP
specification of the export
system
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Upstream Process Engineering Course Prepared by Genesis Oil and Gas Consultants Ltd Product and Discharge Specifications4
Crude Oil Product Specifications
For pipeline transmission other variables require to be controlled. These are
fixed by the sales requirement, the following are typical values
Water content: 2-5 wt %
Salt content: 70 - 200 mg per litre Note, higher water contents reduce the pipeline or storage capacity and crude
sales value
For tanker transport, a more stringent water specification is often specified:
BS&W (Basic Sediment and Water) Content: 0.5 vol% maximum
Pour point and/or viscosity may be considered for pipeline capacity and
storage problems but in general facilities are designed to accept the product
rather than vice versa
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Upstream Process Engineering Course Prepared by Genesis Oil and Gas Consultants Ltd Product and Discharge Specifications5
RVP Specification
TVP cannot be measured directly, so instead
an experimental method measures the Reid
Vapour Pressure (RVP). The TVP is then
calculated using a correction factor.
RVP is determined experimentally as follows.
The sample is placed in a standard cell
one fifth oil four fifths air. The RVP is
the pressure of the vapour in the cell at
100 F
Typical RVP spec is 0.7 bara (10 psia) at 38 C.
Nomograph for estimating the RVP of crude oil
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Upstream Process Engineering Course Prepared by Genesis Oil and Gas Consultants Ltd Product and Discharge Specifications6
Gas Sales Specifications
In order to condition gas for sales distribution a range of quality specificationsrequire to be achieved. These vary from country to country, common featuresare hydrocarbon and water dewpoint, temperature, pressure and compositione.g. H2S and CO2
Water dewpoint limits are required to avoid corrosion and hydrate formation,and depend on typical ambient conditions. May be stated as a dewpoint (e.g. -10 deg C at 69 barg) or as a water content (e.g 2lbs/ mmscf).
Temperature - A maximum temperature at the delivery point may be specified,usually around 30-50 C
Pressure - The maximum gas pressure will be decided by the design pressure ofthe system and the allowable back pressure on other system entrants. Nominalgas pressure is the normal entry pressure to the pipeline, typically 70 - 140 Bar
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Upstream Process Engineering Course Prepared by Genesis Oil and Gas Consultants Ltd Product and Discharge Specifications7
Gas Sales
Hydrocarbon Dewpoint Control
To prevent hydrocarbon condensation, with the
consequences of the pipeline flowing two-phase,
the pipeline operator often sets a limit on the gas
cricondenbar. The significance of the cricondenbar
is evident from the phase envelope - providedsystem pressures are higher than the cricondenbar
then a single phase will always exist irrespective
of temperature. A typical cricondenbar
specification is 105-110 bara maximum.
An alternative to cricondenbar control a
hydrocarbon dewpoint or a liquid loading
maximum value may be given
Solids: Free of particulates in amounts
detrimental to transmission and
utilisation equipment
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Upstream Process Engineering Course Prepared by Genesis Oil and Gas Consultants Ltd Product and Discharge Specifications8
Gas Sales
The sales gas specification will be subject to a pricing agreement
which is likely to include the following:
Gross Calorific Value (GCV) or Higher Heating Value (HHV)
The total heat produced by combustion of the fuel
Net Calorific Value (NCV) or Lower Heating Value (LHV)
The total heat produced by combustion of the fuel minus the latent heatcontained in the water vapour discharged as fuel gas, NCV represents the
available heat
Wobbe Index (WI)
Wobbe Index is used to compare fuel quality for different gases it
characterises flame stability
WI is the ratio of GCV to the square root of the gas s.g. - units are MJ/Sm3
This may be estimated from the molecular weight of the gas and corrected
for N2 and CO2
Impurities
Inert gases, usually N2/Ar, are removed to improve the gross calorific
value of the gas
Sulphur Content
Sulphur content is controlled for safety reasons, to prevent pipeline
corrosion and improve the sales value of the gas
Gas
GCV of dry
gas at 15 C
& 101.325
kPa (MJ/m3
)Methane 37.69
Ethane 66.03
Propane 93.97
i-B ut ane 121.43
n-But ane 121. 78
i-Pentane 149.32
n-Pentane 149.65
Hexane 177.56
Hept ane 205.43
CO2 0
H2S 23.79
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Upstream Process Engineering Course Prepared by Genesis Oil and Gas Consultants Ltd Product and Discharge Specifications9
Sales Gas Specifications
Units Continental Sales Gas UK Sales Gas (Transco) US
Gross Calorific Value MJ/Nm3 38 - 43.6 38.9 - 44.6 35 - 45
Wobbe Index MJ/Nm3 46.6 - 52.1 48.2 - 51.2
Hydrocarbon Dew Point@ 2 - 70 bara C -3.0 -1.0 45 F @ 400 psig
Water Dew Point
@ 69 bara C -8.0 -10.0 7lb/MMSCF
Impurities
Oxygen mol % 0.50 0.001 0.2
Carbon Dioxide mol % 2.50 2.0 - 4.0 2
Nitrogen mol % 1.00 7.00 1 - 2
Hydrogen Sulphide ppm 5.00 1.00 4.00
Total Sulphur ppm 15.00 15.00Mercury mg/Nm3 5.00
Delivery Temperature 5 - 30 C 1 - 38 C 120 F (max)
Delivery Pressure Bara 51.00 69.00
Sales Gas Specifications
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Upstream Process Engineering Course Prepared by Genesis Oil and Gas Consultants Ltd Product and Discharge Specifications10
Water Content of Natural Gas
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Upstream Process Engineering Course Prepared by Genesis Oil and Gas Consultants Ltd Product and Discharge Specifications11
Wobbe Index
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Upstream Process Engineering Course Prepared by Genesis Oil and Gas Consultants Ltd Product and Discharge Specifications12
Gas Transportation
For some applications gas may be transported from a remote facility to a
conditioning terminal - St Fergus - prior to gas sales. In this instance the gas
need only be partially processed for transportation between the remote site and
the terminal.
The degree of processing will be application specific but is likely to include
Water dewpointing
Hydrocarbon dewpointing
Acid gas treatment
An alternative to water dewpointing is continuous addition of hydrate
suppressant and corrosion inhibitor. This is used in some SNS fields.
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Upstream Process Engineering Course Prepared by Genesis Oil and Gas Consultants Ltd Product and Discharge Specifications13
Commercial Propane Commercial Butane Commercial B-P Mixtures
Composition
Predominantly
propanes and/or
propylenes
Predominantly
butanes and/or
butylenes
Predominantly mixtures
of butanes and/or
butylenes with propane
and/or propylene
Vapour Pressure
@ 100 F, max. 208 70 208@ 37.8 C, max. 1434 483 1434
Volatile Residue
temperature @ 95% evaporation,
F, max -37 36 36
C, max -38.3 2.2 2.2
butane and heavier, liquid vol %, max. 2.5 - -
pentane and heavier, liquid vol %, max. - 2 2
Residual Matter
residue on evaporation of 100 cm3, max 0.05 cm3 - -
oil stain observation pass (*) - -Corrosion, copper strip, max. No. 1 No. 1 No. 1
Total sulphur, mg/kg 185 140 140
Moisure content pass - -
Free water content - none none
Product Characteristics
Product Designation
LPG Specification
(*) An acceptable product shall not yield a persistent oil ring when 0.3 cm3 of solvent residue mixture
is added to a filter paper in 0.1 increments and examined in daylight as described in ASTM D-2158
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Upstream Process Engineering Course Prepared by Genesis Oil and Gas Consultants Ltd Product and Discharge Specifications14
Quality Tests for LPG
The standard test for corrosivity (H2S) is the Copper Corrosion Test (ASTM D-1838)
A polished copper strip is immersed in the sample for 1 hour at 38C
The test strip is then rated according to the following standards:
No. 1 Slight tarnish (light to dark orange)
No. 2 Moderate tarnish (red, lavender, brassy gold)
No. 3 Dark tarnish (magenta, red, green)
No. 4 Corrosion (black, dark grey, brown)
There are several methods of determining the acceptable levels of moisture in propane
The Cobalt Bromide Test The cobalt bromide is supported on white cotton wadding and exposed to a stream of propane vapour, chilled to 0 C
The colour of cobalt bromide changes from green to lavender at about 30% relative humidity indicating wet gas
The Valve-Freeze Method
A specially constructed and calibrated orifice designed to simulate expansion of propane through a pressure
regulator
A liquid sample is passed through the valve at a pre-set flowrate and the time taken for the valve to freeze and
interrupt flow determines whether or not the propane is commercially dry
The Bureau of Mines Dew Point Test
A simple field test designed to use calculate moisture content of natural gases
Not recommended as the accuracy is dependant on temperature and pressure which are difficult to control
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Upstream Process Engineering Course Prepared by Genesis Oil and Gas Consultants Ltd Product and Discharge Specifications15
Valuation of Crude Oil
When evaluating the value of a crude produced from a new field, it will be compared to the benchmark
crude, which for the North Sea is usually Brent Blend
This takes into account the impact on the refinery of processing and any unusual qualities in the crude, for
example product yields and qualities
Blend ( or Grade) US$/bblFri. 31/01/03
US$/bblFri. 22/09/06
OPEC Basket 30.58 57.55
Dubai Fateh 29.13 57.94
Bonny Light 33.07 62.15
N. Sea Brent 32.50 60.49
Urals/ Mediterranean 31.45 57.48
W. Texas Intermediate 33.53 54.46
World Average - 56.38
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Upstream Process Engineering Course Prepared by Genesis Oil and Gas Consultants Ltd Product and Discharge Specifications16
Valuation of Crude Oil
When evaluating the value of a crude produced from a new field, it will be compared to
the benchmark crude, which for the North Sea is usually Brent Blend
This takes into account the impact on the refinery of processing and any unusual
qualities in the crude, for example product yields and qualities
Any new crude is likely to be de-valued in order for a refinery to take the risk of
processing an unknown feed, this discount may be in the range of $0.10 to $1.00 per
barrel
As the refineries experience handling the crude and market acceptance grows, these
discounts may be moderated
The method of loading the crude oil can also affect its initial market value, the
perceived or actual risks of offshore loading such as delays due to the weather could
de-value a crude compared with pipeline delivery which is assumed to be more reliable
Pre-production assay samples of all the wells to be produced are blended in the
appropriate production ratios to generate data for the valuation analysis
Crude is separated into three key distillation cuts, Naphtha, Middle Distillate and
Residue as a basis for valuation.
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Upstream Process Engineering Course Prepared by Genesis Oil and Gas Consultants Ltd Product and Discharge Specifications17
Crude Yields
Naphtha
Light naphtha (C5 - 95C)
Medium Naphtha (95 - 150C)
Heavy Naphtha (150 - 180C)
Middle Distillate
Kerosene (180 - 260C)
Gas Oil (260 - 327C)
Heavy Distillate (327 - 370C)
Residue
Vacuum Gasoil (350 - 565C)
Vacuum Residue (565+ C)
Approximate values March 2006follows (US$ per metric tonne):
C4 $435-490/ te
Naphtha $506-514 / te
Middle Distillate $530-540/ te
Gas Oil Specific Gravity
The European oil retail market isvolume based
To ensure consistency, cargo's are
sold using the internationally agreedspecific gravity of 0.845
For example, if the sales price is$300/tonne and the actual gravity is0.85, the actual sales price is:
0.845/0.850 300 = $298.24
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Upstream Process Engineering Course Prepared by Genesis Oil and Gas Consultants Ltd Product and Discharge Specifications18
Value Adjustment
Specific crude values are adjusted to take account of variations in the
physical properties and compositional properties of the distillation cuts
Naphtha C5-165 C
no correction
Gas Oil 165-350 C
s.g. adjustments made
Vacuum Gas Oil 350 - 550 C
s.g., sulphur and viscosity adjustments
Fuel Oil 550+ C
s.g., sulphur and viscosity adjustments
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Upstream Process Engineering Course Prepared by Genesis Oil and Gas Consultants Ltd Product and Discharge Specifications19
Brent Blend
The properties of the North Sea benchmark crude are as follows:
Gravity API 38.5
Sulphur, wt % 0.36
Pour Point, C 0
Acid Number, mgKOH/g 0.05
Crude Distillation Yields (wt %)
C1 - C4 2.7
Naphtha (C5 - 180C) 26.1
Middle Distillate (180 - 370 C) 34.4
Residue (370+ C) 36.9
Middle Distillate Properties
Kerosene smoke point, mm 22.8
Gasoil cetane index 51.7
Gasoil density @ 15C 0.848
Gasoil sulphur content, wt% 0.22
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Upstream Process Engineering Course Prepared by Genesis Oil and Gas Consultants Ltd Product and Discharge Specifications20
Crude Oil Contaminants/Adjustments
Quality
Typical Limit Attracting
Penalties Basis of Penalty
Acidity 0.3 mg KOH/g
Blending, shipping and
working capital costs
Sulphur Continuous
Logarithmic relationship of fueloil prices at different sulphur
levels
Metals 3 ppm (Ni + V)
Catalyst costs in conversion
process
onradson Carbo 5.7 wt% Loss of throughput
Nitrogen 1000 ppm in Vac. Gas Oil Yield Loss
Gas Oil S.G. Continuous Weight/volume relationship
Fuel Oil Viscosity ContinuousMarket prices for fuel oil andgas oil
Conradson Carbon - A measurement of hydrocarbon mixtures tendency to leave carbon deposits (coke) when burned as fuel or subjected to intense
heat in a processing unit such as a catalytic cracker. The ConCarbon test involves destructive distillation -subjection to high temperature which causes
cracking, coking, and drives off any volatile hydrocarbons produced--and weighing the residue which remains. A somewhat similar test, Ramsbottom
carbon, also measures mixtures tendency to form coke. For reasons of laboratory convenience, analysts ordinarily restrict the Ramsbottom method to
hydrocarbons which flow 90 C. To obtain a useful indication of carbon residue formation by light distillates, such as high-speed diesel, the industry
often measures coke formation by the last 10 percent of the material to boil. This technique goes by names such as "ConCarbon residue on 10 percent
bottoms
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Upstream Process Engineering Course Prepared by Genesis Oil and Gas Consultants Ltd Product and Discharge Specifications21
Metal Contaminants
Metals in crude oil (specifically; nickel, vanadium and sodium) are considered for three
distinct reasons
Catalyst Poison
In fluid catalytic cracking, nickel and vanadium act as a catalyst poison resulting in an
increased yield of hydrogen and coke at the expense of more valuable products The refiner can deal with this problem by either increasing the catalyst replacement rates or
blending feedstocks
The absolute limits on metals are very site specific and range from 1-2 ppm for a conventional
VGO (Vacuum Gas Oil) cracker to 60 ppm for a state of the art residue cracker
Residue Specification
Anode grade coke for use in aluminium smelting commands a premium, the metals
specification is stricter of these grades of coke and consequently requires a feedstock (560C +residue) of less than 400 ppm nickel plus vanadium
Fuel Oil Specification
Residual fuel oil has both a sodium and vanadium specification which refiners must meet
For most of Europe this specification is 300 ppm vanadium, 150 ppm sodium
Refiners will generally blend feedstocks to achieve this specification