02 P&d Specs

Upstream Process Engineering Course 2. Product and Discharge Specifications

Upstream Process Engineering Course

Prepared by Genesis Oil and Gas Consultants Ltd

Product and Discharge Specifications

1

Contents • • • • • • •

Crude Oil Product Specifications RVP Specification Gas Sales Water Content of Natural Gas Wobbe Index Gas Transportation LPG Specification

Upstream Process Engineering Course

• • • • • • •

Quality Tests for LPG Valuation of Crude Oil Crude Yields Value Adjustment Brent Blend Crude Oil Contaminants Metal Contaminants

Prepared by Genesis Oil and Gas Consultants Ltd

Product and Discharge Specifications

2

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 Vapour Pressure (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.

Upstream Process Engineering Course

Prepared by Genesis Oil and Gas Consultants Ltd

The lighter ends of the crude (shaded area) are removed to meet the TVP specification of the export system

Product and Discharge Specifications

3

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: – Salt content:

• •

2-5 wt % 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

Upstream Process Engineering Course

Prepared by Genesis Oil and Gas Consultants Ltd

Product and Discharge Specifications

4

RVP Specification Nomograph for estimating the RVP of crude oil

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 ºF Typical RVP spec is 0.7 bara (10 psia) at 38 ºC.

Upstream Process Engineering Course

Prepared by Genesis Oil and Gas Consultants Ltd

Product and Discharge Specifications

5

Gas Sales Specifications •

In order to condition gas for sales distribution a range of quality specifications require to be achieved. These vary from country to country, common features are hydrocarbon and water dewpoint, temperature, pressure and composition e.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 ºC

•

Pressure - The maximum gas pressure will be decided by the design pressure of the system and the allowable back pressure on other system entrants. Nominal gas pressure is the normal entry pressure to the pipeline, typically 70 - 140 Bar

Upstream Process Engineering Course

Prepared by Genesis Oil and Gas Consultants Ltd

Product and Discharge Specifications

6

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 - provided system 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

Upstream Process Engineering Course

Prepared by Genesis Oil and Gas Consultants Ltd

Product and Discharge Specifications

7

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) •

–

Net Calorific Value (NCV) or Lower Heating Value (LHV) •

–

• •

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 •

–

The total heat produced by combustion of the fuel minus the latent heat contained in the water vapour discharged as fuel gas, NCV represents the available heat

Wobbe Index (WI) •

–

The total heat produced by combustion of the fuel

Inert gases, usually N2/Ar, are removed to improve the gross calorific value of the gas

GCV of dry gas at 15 ºC & 101.325 Gas kPa (MJ/m 3) Methane 37.69 Ethane 66.03 Propane 93.97 i-Butane 121.43 n-Butane 121.78 i-Pentane 149.32 n-Pentane 149.65 Hexane 177.56 Heptane 205.43 CO2 0 H2S

23.79

Sulphur Content •

Sulphur content is controlled for safety reasons, to prevent pipeline corrosion and improve the sales value of the gas

Upstream Process Engineering Course

Prepared by Genesis Oil and Gas Consultants Ltd

Product and Discharge Specifications

8

Sales Gas Specifications Sales Gas Specifications Units MJ/Nm3 MJ/Nm3

Gross Calorific Value Wobbe Index Hydrocarbon Dew Point @ 2 - 70 bara ºC Water Dew Point @ 69 bara ºC Impurities Oxygen mol % Carbon Dioxide mol % Nitrogen mol % Hydrogen Sulphide ppm Total Sulphur ppm Mercury mg/Nm3 Delivery Temperature Delivery Pressure Bara

Upstream Process Engineering Course

Continental Sales Gas UK Sales Gas (Transco) 38 - 43.6 38.9 - 44.6 46.6 - 52.1 48.2 - 51.2

US 35 - 45

-3.0

-1.0

45 ºF @ 400 psig

-8.0

-10.0

7lb/MMSCF

0.50 2.50 1.00 5.00 15.00 5.00 5 - 30 ºC 51.00

0.001 2.0 - 4.0 7.00 1.00 15.00

0.2 2 1-2 4.00

1 - 38 ºC 69.00

120 ºF (max)

Prepared by Genesis Oil and Gas Consultants Ltd

Product and Discharge Specifications

9

Water Content of Natural Gas

Upstream Process Engineering Course

Prepared by Genesis Oil and Gas Consultants Ltd

Product and Discharge Specifications

10

Wobbe Index

Upstream Process Engineering Course

Prepared by Genesis Oil and Gas Consultants Ltd

Product and Discharge Specifications

11

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.

Upstream Process Engineering Course

Prepared by Genesis Oil and Gas Consultants Ltd

Product and Discharge Specifications

12

LPG Specification Product Characteristics

Composition Vapour Pressure @ 100 ºF, max. @ 37.8 ºC, max. Volatile Residue temperature @ 95% evaporation, ºF, max ºC, max butane and heavier, liquid vol %, max. pentane and heavier, liquid vol %, max. Residual Matter residue on evaporation of 100 cm 3, max oil stain observation Corrosion, copper strip, max. Total sulphur, mg/kg Moisure content Free water content

Commercial Propane Predominantly propanes and/or propylenes

Product Designation Commercial Butane Commercial B-P Mixtures Predominantly mixtures Predominantly of butanes and/or butanes and/or butylenes with propane butylenes and/or propylene

208 1434

70 483

208 1434

-37 -38.3 2.5 -

36 2.2 2

36 2.2 2

0.05 cm3 pass (*) No. 1 185 pass -

o N.1 140 none

o N.1 140 none

(*) 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 Upstream Process Engineering Course

Prepared by Genesis Oil and Gas Consultants Ltd

Product and Discharge Specifications

13

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 38ºC The test strip is then rated according to the following standards: • • • •

•

No. 1 No. 2 No. 3 No. 4

Slight tarnish (light to dark orange) Moderate tarnish (red, lavender, brassy gold) Dark tarnish (magenta, red, green) Corrosion (black, dark grey, brown)

There are several methods of determining the acceptable levels of moisture in propane –

The Cobalt Bromide Test • •

–

The Valve-Freeze Method • •

–

The cobalt bromide is supported on white cotton wadding and exposed to a stream of propane vapour, chilled to 0 ºC The colour of cobalt bromide changes from green to lavender at about 30% relative humidity indicating wet gas

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

Upstream Process Engineering Course

Prepared by Genesis Oil and Gas Consultants Ltd

Product and Discharge Specifications

14

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$/bbl Fri. 31/01/03

US$/bbl Fri. 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

-

56.38

World Average Upstream Process Engineering Course

Prepared by Genesis Oil and Gas Consultants Ltd

Product and Discharge Specifications

15

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.

Upstream Process Engineering Course

Prepared by Genesis Oil and Gas Consultants Ltd

Product and Discharge Specifications

16

Crude Yields • Naphtha – Light naphtha (C5 - 95ºC) – Medium Naphtha (95 - 150ºC) – Heavy Naphtha (150 - 180ºC)

• Middle Distillate – Kerosene (180 - 260ºC) – Gas Oil (260 - 327ºC) – Heavy Distillate (327 - 370ºC)

• Residue – Vacuum Gasoil (350 - 565ºC) – Vacuum Residue (565+ ºC)

Upstream Process Engineering Course

• Approximate values March 2006 follows (US$ per metric tonne): – C4 – Naphtha – Middle Distillate

$435-490/ te $506-514 / te $530-540/ te

• Gas Oil Specific Gravity – The European oil retail market is volume based – To ensure consistency, cargo's are sold using the internationally agreed specific gravity of 0.845 – For example, if the sales price is $300/tonne and the actual gravity is 0.85, the actual sales price is: 0.845/0.850  300 = $298.24

Prepared by Genesis Oil and Gas Consultants Ltd

Product and Discharge Specifications

17

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 ºC – no correction

•

Gas Oil 165-350 ºC – s.g. adjustments made

•

Vacuum Gas Oil 350 - 550 ºC – s.g., sulphur and viscosity adjustments

•

Fuel Oil 550+ ºC –

s.g., sulphur and viscosity adjustments

Upstream Process Engineering Course

Prepared by Genesis Oil and Gas Consultants Ltd

Product and Discharge Specifications

18

Brent Blend •

The properties of the North Sea benchmark crude are as follows: – – – –

•

38.5 0.36 0 0.05

Crude Distillation Yields (wt %) – – – –

•

Gravity ºAPI Sulphur, wt % Pour Point, ºC Acid Number, mgKOH/g

C1 - C4 Naphtha (C5 - 180ºC) Middle Distillate (180 - 370 ºC) Residue (370+ ºC)

2.7 26.1 34.4 36.9

Middle Distillate Properties – – – –

Kerosene smoke point, mm Gasoil cetane index Gasoil density @ 15ºC Gasoil sulphur content, wt%

Upstream Process Engineering Course

22.8 51.7 0.848 0.22

Prepared by Genesis Oil and Gas Consultants Ltd

Product and Discharge Specifications

19

Crude Oil Contaminants/Adjustments Quality

Typical Limit Attracting Penalties

Basis of Penalty Blending, shipping and Acidity 0.3 mg KOH/g working capital costs Logarithmic relationship of fuel oil prices at different sulphur Sulphur Continuous levels Catalyst costs in conversion Metals 3 ppm (Ni + V) process Conradson Carbon 5.7 wt% Loss of throughput Nitrogen 1000 ppm in Vac. Gas Oil Yield Loss Gas Oil S.G. Continuous Weight/volume relationship Market prices for fuel oil and Fuel Oil Viscosity Continuous gas 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 Upstream Process Engineering Course

Prepared by Genesis Oil and Gas Consultants Ltd

Product and Discharge Specifications

20

Metal Contaminants • •

Metals in crude oil (specifically; nickel, vanadium and sodium) are considered for three distinct reasons Catalyst Poison – – –

•

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 (560ºC + residue) of less than 400 ppm nickel plus vanadium

Fuel Oil Specification – –

•

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

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

Upstream Process Engineering Course

Prepared by Genesis Oil and Gas Consultants Ltd

Product and Discharge Specifications

21