Product Blending Calculation

CHM 3602 Petroleum Refining Process Product Blending Refinery operations - basic intermediate stream Can be blended to produce • a variety of on-specification finished products • operating flexibility • profits Blending One of the final operations in refining, in which two or more different components are mixed together to obtain the desired range of properties in the finished product Objectives : To allocate the available blending component To meet product demands and specification To produce incremental products To maximise overall profits Maintenance Computer-controlled in-line blending for blending gasoline + high-volume products Inventories, cost and physical properties data

Stream Analysers To ensure blended streams meet the desired specifications • Boiling point (C4 – 193°C) • Specific gravity • Reid Vapour Pressure (RVP) • Research and Motor octane (RON and MON)

Reid Vapour Pressure (RVP) Preliminary cost evalution : Calculations are not at intermediates changes. Blending stocks – boiling ranges within the product specification, control criteria and octane requirement Measure of the vapour pressure of a sample at 38 °C in a volume of air four times the liquid volume As indication of the vapour-lock tendency of a motor gasoline, as well as explosion and evaporation hazards Carried out in the USA : ASTM Method D 323 n-butane (RVP 358 kPa), isobutane (RVP 490 kPa) n-butane is preferred for blending into gasoline to regulate vapour pressure Calculation of RVP The desired RVP of a gasoline is obtained by blending n-butane with C5-193 °C naphtha The amount of n-butane required to give the needed RVP

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CHM 3602 Petroleum Refining Process Mt(RVP)t = ∑ Mi (RVP)iMt = total moles blended product (RVP)t = specification RVP for product, psi or kPa Mi = moles of component i (RVP)i = RVP of component i, psi or kPa Example n-butane : MW = 58, RVP = 52 Calculate the flow rate (BPD) for a 10 psi RVP blend Butane requirement : (2,179) (5.38) + M (52.0)= (2179 + M) (10)

Calculation of RVPblend Estimation of the average molecular weight of a refinery stream using vapour pressure blending indices (VPBI) (by Chevron) Approximately by the sum of all products of the volume fraction (v) multiply by the VPBI for each component (RVP)blend = ∑ vi (VPBI)i(RVP)blend = specification RVP for product vi = volume fraction of component i (VPBI)i = RVP of component I Volume of the butane to be blended for a given RVP is desired: A(VPBI)a + B(VPBI)b + ----- + W(VPBI)w = (Y + W)(VPBI)m A = bbl of component a, etc. W = bbl of n-butane (w) Y = A + B + C + ---- (all compounds except n-butane) w = subscript indicating n-butane (VPBI)m = VPBI corresponding to the desired RVP of mixture Example Calculate the flow rate (BPD) of n-butane for a 10 psi RVP For 10 psi RVP, (VPBI)m = 17.8 Butane requirement : 17.8 (21,000 + W) = 174,070 + 138W

Terminologies Barrels = 42 gallons BPCD (Barrels Per Calendar Day) Average flow rates based on operating days per year BPSD (Barrels Per Stream Day) Flow rates based on actual on stream time of a unit or group of units. PBI (Pour Blending Index) An empirical quantity related to pour point ASTM (American Society for Testing and Materials) WHSV (Weight Hourly Space Velocity) Weight of feed per hour per weight of catalyst LHSV (Liquid Hourly Space Velocity) Volume of liquid feed per hour per volume of catalyst 2 Dr Basyar Rahman

CHM 3602 Petroleum Refining Process GHSV (Gas Hourly Space Velocity) Volume of gas feed per hour per volume of catalyst Space Velocity : The volume (or weight) of gas/liquid passing through a given catalyst or reactor space unit time, divided by the volume of catalyst through which the fluid passes. High space velocities correspond to short reaction times. Octane blending Based on volumetric Using the blending octane numbers of the components (true octane number do not blend linearly) True Octane Number : octane number obtained using a Combined Feed Ration (CFR) test engine (ratio of total feed including recycle to fresh feed) Bt(ON)t = ∑ Bi (ON)iBt = total gasoline blended, bbl (ON)t = desired octane of blend Bi = bbl of component i (ON)i = blending octane number of component i Octane Scale Used to rate the octane no. of gasoline Numbered from 0 – 120.3 (arbitrary number) The scale is defined by 3 difference materials: 1. n-heptane assigned to 0 2. Isooctane (2,2,4-trimethylpentane) 3. Mixture of isooctane and tetraethyl lead (6 ml of TEL per gallon in isooctane is assingned to 120.3) Tetraethyl Lead (TEL) Used to increase the octane of the blend ; Necessary to calculate the amount that must be added to produce the desired leaded-product octane Effectiveness Decreases with concentration Calculate the quantity of TEL needed (special graph) Pb(OC2H5)4 = antiknock agent Blending for other properties Estimating the physical properties Substitute for the value of the inspection to be blended another value which has the property of blending approximately linear Types of blending factors (or index numbers) : 1. Viscosity 2. Flash point 3. Aniline point 4. Vapour pressures Blending Method Applied to bulk batch or in-line mixing of two or more crude or process stocks to form a composite intermediate or finished product 3 Dr Basyar Rahman

CHM 3602 Petroleum Refining Process

Batch Blending In small refineries (limited variety of blends) Accomplished in tanks by circulation or in-tank mixers Circulation Blending High capacity centrifugal pump takes suction from tank the and returns the liquid through one or more nozzles at high velocity. The nozzles enter the tank at an angle of 7 to 12 degree from the tank diameter to produce a swirling motion throughout the liquid In-tank Mixing Blending Three blade propellers are placed within the tank with motors and controls mounted outside the shell. The propellers are placed near the bottom of the tank, at an angle of 7 to 12 degree from the tank diameter, and in a position to induce a clockwise rotation of the liquid in the tank. The propeller blades not only direct the flow axially but also set up a rotary or spiral motion within the stream Partial In-line Blending Adding together product components simultaneously in a pipeline at approx. the desired ratio w/out obtaining a finished specification product Final adjustment and additions are required, based ontest Mixing is required (only for final adjustment) Most suitable for moderate-sized refineries Continuous In-line Blending Provides continuous proportioning and mixing of components Applying the close control loop theory (continuous metering each stream, comparing the signal with the established condition, adjusting the rate if does not match) All streams stay in proper ratios to each other and with the end-product Larger refineries (several grades product)

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