Detailed Storage Tank Sizing

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Mody and Marchildon:Chemical Engineering Process DesignChapter 11 BULK TRANSPORT AND STORAGE P:/CEPDtxt/CEPDtxtCh11

STORAGE

11.1. Choose The Phase Of The Material To Be Stored:

The phase (liquid, gas, solid) of the material to be stored is usually dictated by the form ittakes at ambient pressures and temperatures; in some cases it may make economicalsense to convert the material to another state for storage. For instance, in the case wherelarge quantities of gases are to be stored (greater than about 1500 std cu M), liquefactionof the gas may become economical. Liquefaction of gases (in cryogenic storage) ofteninvolves allowing a portion of the liquid to boil off to maintain temperature and pressurein the tank. Thus, losses from this type of storage system can make the system

environmentally or economically less desirable.

Other phases such as absorption onto solids, dissolving into a liquid, or conversion tosolids via chemical reaction may be considered.

11.2. Choose The Volume Of Storage Required:

Large use plants may utilize pipelines with minimal or no storage to supply the process.Railcars may be temporarily used to store chemicals, thus reducing or eliminating onsitestorage. Hazardous chemicals may be enough of a safety liability that minimal storage is

preferred or possibly on-site or in-situ production of the material can be used. Extremelyhazardous chemicals may require a secondary deinventory storage tank in the event aproblem develops in the primary storage system. However, for average materials thefollowing guidelines may be used to determine storage requirements.

Raw Material Storage is provided to ensure the plant never (or rarely) shuts downbecause the raw materials are unavailable. Thus, the reliability of the supply system mustbe examined. Baasel (ref 1) presents the following guidelines:

Amount of feedstock that should be kept onsite= (date delivered date ordered )* feedrate

Storage Size = Max amount that COULD be present when delivery arrives + AmountOrdered


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Example:A plant requires 20,000 lb of feedstock per day. The supplier will guarantee shipping theorder in 15 days of order receipt. The time to ship the material is anywhere between 2and 5 days. The mode of transport is 36,000 gal jumbo rail cars. The specific gravity ofthe material is 0.85.

Solution:Examine the two possibilities (no delays and maximum delay)

Maximum Delay:

Our plant takes 3 days to process our order (over a long weekend)

The supplier ships 15 days after receipt of the order

The shipping takes 5 days to travel to site

Thus the amount of feed stock that should be on site when the order is placed should be:(3 days + 15 days + 5 days ) * 20,000 lb/day = 460,000 lb

No delays:

A jumbo rail car (36,000 gal) could arrive in 2 days

If the railcar arrives in 2 days, when we had 460,000 lb of material onsite at the time oforder then the amount of storage we need on site is:

460,000 lb 2 days transit * 20,000 lb/day + 36,000 gal (0.85 * 62.4 lb/ft3 / 7.48 gal/ft3)= 676,000 lb of storage (34 days)

The logistics of when a second railcar must be ordered is left to the reader.

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11.3. Choosing A Design Pressure

In the situation where a liquid is to be stored, there are two ways to approach the choiceof design pressure: first by determining the maximum expected pressure in the tank due

to fluid thermal cycling which minimizes looses, or secondly by arbitrarily choosing adesign pressure for a standard tank and then dealing with the loses in some other way.

The normal day to night thermal cycling of a tank causes the pressure in the tank to riseand fall. If the tank were open to atmosphere, the increased pressure is dissipated by thegases (rich with the fluid being stored) in the tank escaping. As the tank cools, thepressure drops and air is drawn in to maintain atmospheric pressure. In a freely ventedtank, the factors that affect how much gas is expelled through the vent are: 1) the changein the temperature in the vapour space, 2) the change in the vapour pressure of the fluid(thus the change in the stored fluid temperature, which is likely different than the vapourspace temperature), and 3) the change in liquid level due to the change in the stored fluid

temperature/density. A tank can be provided with a pressure and vacuum vent system(often called a conservation vent). If the designer chooses a large enough differencebetween the pressure and vacuum set pressure, all thermal cycling losses can beeliminated.

By selecting an initial pressure to begin with (typically a small value consistent with thelow vacuum capabilities of a storage tank), you can use these factors to determine themaximum expected operating pressure. If a design pressure in excess of the maxoperating pressure is used, you will have eliminated losses due to thermal cycling.

11.4. Selecting A Tank Type

The choice of tank depends partly on the required design pressure and partly on theamount of material to be stored.

The reader is cautioned that there is sometimes confusion in stating whether a container isx volume as determined by its dimensions or by volume as determined by the amount offluid (ie. gas at high pressure) that can be stored in the container. For instance, acontainer 2 ft in diameter and 20 ft long has a dimensional volume of about 1.8 cu M, butcan store 300 std. cu M of gas when filled to a pressure of 2450 psig. In the table below,the dimensional volume is used to state the capacity of the containers.

Gases, due to their low density, tend to be stored under pressure to minimize the cost ofthe container.

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11.5. Gas Storage

Comparison of Tanks for Storage of Gases

Situation TypicalOccurrence

PossibleEquipment

SelectionCriteria &

Alternatives

Suppliers

Gas Storage Smallquantities (0 to1000 cu M)

For lowpressure Tankor drums canbe used.

High PressureBottles

Bullet Tanks

GenerallyASME SectionVIII vessels

are used.

Choice ofcontainer sizedepends onconsumptionrates. SectionVIII Codeallows designpressures up to3000 psig and

for vesselsabove 10,000psig.

ASME VIIIvessels can bedesigned andfabricated byapprovedpressure vesselshops

For integratedsupply of gases

and storage (i.e.by tube trailer)-Air Liquide, AirProducts,Praxair, etc.

Up to 35000cu Meters

ASMESpheres /Spheroids

Spheroids aretypically for30 psig or less.Spheres(typically

between 32 to120 ft dia)have typicaldesignpressure up toabout 200 psig

Chicago Bridgeand Iron Workswww.cbiepc.com

Mid to largestorage

Considerliquefied

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PossibleEquipment

SelectionCriteria &Alternatives

Suppliers

capacities storage.

Very Large

Quantities

Caverns

Conversion toothercompounds orstates

Caverns may

be economicalin situationswhere naturalgeographyallows. Referto GasProcessorsSuppliersAssociation EngineeringData Book

For very highconsumptionrates or gaseswithhazardous

properties

Consider on-site generation

Select on-sitegeneration byeconomicanalysis

Select on-sitegenerationwhen processhazardsanalysisindicates riskis too great.

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11.6. Liquid Storage:

The combination of tank operating pressures (as dictated by the vapour pressure ofthe fluid) and required storage volume drives the selection process.

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Size

VapourPressure

APITanks

ASME VIIIVessels

FloatingRoof API

Caverns /UndergrounSpheres

ULC


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Comparison of Tanks for Storage of Liquids


PossibleEquipment

Selection Criteria & Alternatives Suppliers

LiquidStorage

Long-termstorage (inexcess of 1day), Tank

Farms, orstorageexternal tothe processunit.

-ULC tanks

-API type tanks(cone roof),

-Floating rooftanks,

-Spheres

-UndergroundStorage

Determine the tank volume requirements first.

Determine type of tank based on fluid vapour pressure ortank working pressure.

Fluid vapour pressures less than atmospheric

ULC Storage Tanks

Typically found in gas station type applications thesetanks can be provided with double wall construction thuseliminating the need for dikes.

ULC:http://www.g.t.machineandfab.com/

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PossibleEquipment


Cone Roof Tanks (API)

are used with fluids that have very low vapour pressures(usually less than 1.5 psia) and have air in the headspace . Tank designs are generally for working pressures< 2.5 inches water gauge (0.09 psi) positive pressure and0.5 oz/in2 (0.86 in H20 , 0.03 psi) vacuum, but can bedesigned for pressures up to about 15 psig for smallertanks.

The US EPA organization requires that a vapour recovery

system be provided when storing more than 40,000 us galof a fluid that has a vapour pressure in excess of 1.5 psiawhen stored in a cone roof tank. For fluids with vapourpressures between 1.5 and 11.1 psia a floating roof tankcan be used without a vapour recovery system.

Designs are according to API 650 or 620. See tablebelow for a selection of different sizes.

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PossibleEquipment


Floating Roof Tanks

have no headspace, the roof of the tank floats on top ofthe liquid and rises and falls as the liquid level changes.The lack of headspace ensures there are no breathinglosses from the tank. A seal (of which there are a varietyof different types) ensures neglible evaporation of theliquid even with fluids that have close to atmosphericboiling points. This type of tank design is required in theUS (as stated by EPA stds) for fluids with vapourpressures greater than 1.5 psia and less than 11.1 psia.Designs are according to API 650 or API 620.

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PossibleEquipment


Variations on the standard floating head tank include ahybrid cone/floating roof that ensures rain and snow arekept away from the tank contents. Consideration toventing this secondary headspace may be required toeliminate flammability issues.

Bolted Tanks

Suitable for fluids with low vapour pressures bolted tanksare transported in segments and bolted together at site.

Tanks can be erected by hand and easily transported later.

http://www.superiortank.com/

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PossibleEquipment


Spheres: Chicago Bridge and Iron

Company (www.cbiepc.com)

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PossibleEquipment


Fluid vapour pressures greater than atmospheric

Spheresand Spheroids

for operating pressures from 15 psig, but up to 250 psigare technically possible.Designs are generally to ASME Section VIII Div 1

Drums (a.ka. Bullet Tanks)

Cylindrical with torispherical heads these thanks are

suitable for high pressure applications. Standars forpressures up to 3000 psig are covered by ASME SectionVIII Div 1. Asme Section VIII, Div 3 covers designs fortanks greater than 10,000 psig.

Underground storage

is particularly useful for high vapour pressure fluids andlarge volumes of liquid. No formal standards for designexit, refer to GPSA handbook for further information.

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PossibleEquipment


3.1.1. AlternativesConsider cooling the liquid to reduce vapour pressure andutilize a less expensive tank tank.

In plant

daystorage.

Generally

smaller tanks,where costs areless sensitive tothe tank design

See above selection, but typically a horizontal or vertical

drum (Bullet tank) is used.

WasteStorage

Lined Ponds Used for the disposal and evaporation of fluids

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The API standard has listed some typical tank sizes.A Selection of Typical API Field Constructed Tanks

TankDiameter Approx Capacity

TankHeight L / D Total Volume

ft m gal/ft m3/m ft m US Gal US Barrels cu M

15 4.6 1320 16.4 18 5.5 1.2 23800 567 90

20 6.1 2350 29.2 18 5.5 0.9 42300 1007 160

25 7.6 3670 45.6 18 5.5 0.7 66100 1574 250

25 7.6 3670 45.6 24 7.3 1.0 88100 2098 33330 9.1 5290 65.7 24 7.3 0.8 127000 3024 481

35 10.7 7190 89.3 30 9.1 0.9 216000 5143 818

45 13.7 11900 147.8 36 11.0 0.8 428000 10190 1620

70 21.3 28800 357.6 54 16.5 0.8 1550000 36905 5867

100 30.5 58700 728.8 36 11.0 0.4 2110000 50238 7987

120 36.6 84500 1,049.2 30 9.1 0.3 2540000 60476 9615

200 61.0 190000 2,359.1 18 5.5 0.1 4230000 100714 16012

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11.7. Solids Storage

Solid storage is typically done either by piling on the ground (possibly inside abuilding i.e. in the case of hydroscopic materials), or in bins or silos.

Baasel suggests:1. Its cheapest to build bins with a cylindrical cross section.2. Provide one large bin wherever possible rather than multiple small bins to save on

supports, materials, fabrication costs and conveyors3. Bins larger in diameter than 11 ft 6 in are difficult to transport by road and should

thus be avoided if possible. A practical length is about 30 ft.4. Coarse, uniform-particle size materials flow easily (i.e. plastic pellets). Fine,

relatively uniform materials are almost fluid (i.e. kitchen starch). The greater thedistribution of particle sizes in a mixture, the greater the tendency to compact andto resist flow.

5. To ensure materials freely flow out the bottom of a bin (to avoid bridging), makethe bottom an eccentric cone with one straight vertical side.

This Authors experience:6. The cone angle should always be the greater of the angle of slide, or the angle

of repose.

Angle of Slide This is determined by a simple test whereby the material is place onflat plate made from the materials and same finish the bin is to be constructed from.The plate is tipped up, and the point at which the material begins to slide is noted.

Angle of Repose - The angle of the pile when material is poured onto a flat surface.

7. For materials that may be hydroscopic, sticky, or fuses together (i.e. ice), seekadvice from experts such as Jennike and Johanson (http://www.jenike.com) orJerry Johanson (http://www.jrjohanson.com).

References (section 3.1)1. Baasel, William D Preliminary Chemical Engineering Plant Design Elsevier NorthHolland, 1980, ISBN 0-444-00152-2.

2. Amrouche, Dave, Gursahani, Lee and Montemayor; General Rules for AbovegroundStorage Tank Design and Operation; Chem Eng Progress (Dec. 2002) pp 54-58.

3. Gas Processors Supplies Association; Engineering Data Book; 11 th Edition(http://www.gasprocessors.com/); Vol 1 pp 6-1 to 6-26.

4. Steve E Sizing up the Storage Bin Chemical Engineering (July 2000) pp 84 88.

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BULK SHIPPING

The ideal transportation method for materials and chemicals is dependant upon:- the volume of material to be used on a weekly or monthly basis- the pressure required (for gases)

- the state of the material to be used (i.e. if liquid nitrogen is required for freezing,then vapour delivery is of little use)

- Proximity to existing pipelines, proximity to rail, water or roads and suppliers ofthe material.

The common bulk shipping methods for Gases, Liquids and Solids are:

11.8. Cylinder

o Usually transported by truck, cylinders provide a convenient method of

moving small volumes of gases (up to 10 m3 per cylinder).o Where slightly larger volumes of gases are required, liquefied gas

transported in dewars (insulated vessels) is utilized (nitrogen liquid has 4xthe density of nitrogen gas at 2450 psig, hydrogen a factor of 5x ).

11.9 Container

o Although not a mode of shipment, containers may be shipped by road,

rail or water.o There are a series of standardized sizes for containers, but all containers

are 8 ft wide. The most widely used containers are the general purpose(dry cargo) containers having a nominal length and height of 20' x 8.5', 40'x 8.5', and 40' x 9.5'.

o The capacity of a 20' dry cargo container is 24,000 kg (52,900 lbs.), and a

40' is 30,480 kg (67,200 lbs.). The containers themselves weigh 2400 kgand 3900 kg respectively.

o Containers are available for carrying bulk gases, liquids, bulk solids, and

refrigerated products.

11.10. Truck

o Generally, a transit distance within 1,000 kilometers using road freight is

competitive compared to rail and air freight.o Maximum weight allowable on Canadian roads is a complex calculation

based upon tire widths, axel distances, number of tires, and time of year.

However the weight is generally in the 18,000 to 34,000 kg range.o Bulk Gases delivered by tank truck (usually hydrogen or helium) are

utilized when consumption rates are 25,000 to 150,000 std ft3 / month.o Liquefied gases may be transported where higher volumes of gas must be

handled (usage rates 30,000 to several million std ft3 / month).

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11.11. Rail

o Rail Cars are typically 40 to 89 ft long and each car is limited to a weight

of 120 metric tons (typical range 60 to 120 metric tons). When handlingcontainers, a typical 50 car train can haul 3 million kg.

o Hopper cars have typical volume capacities of 4750 to 5150 cu ft.o General information about rail transportation can be found at the CN

website at http://www.cn.ca/en_index.shtml.o The guidelines for transportation of dangerous goods can be found at the

transport Canada web site http://www.tc.gc.ca/tdg/menu.htm.o Rail Cars can be insulated (for liquefied gases) and they may have

pressure ratings for pressurized gases.

11.12. Ship

o Suitable where easy access to water is available

o Suitable for large volumes and especially heavy cargo

o Economical for large distanceso Ships commonly utilize containers (approximately 100 million, 20 ft long

containers, are handled by the worlds ports every year)

Containers are available for carrying bulk gases, liquids, and bulksolids

o Ships are generally limited to 900 ft in length and 105 ft in width (to fit the

panama canal).o Essentially there are no weight restrictions. Size restrictions apply to

shipments using containers (see section below) however, recently builtdouble walled tankers (Conoco) have a capacity of 727,100 barrels (about98 million kg).

11.13. Pipeline

o Commonly used method of delivering fluids and gases (i.e. tap water or

natural gas to houses).o Provides the lowest cost per lb transportation charge for large capacities

o Where an existing pipeline infrastructure is nearby, economic and inherent

safety (minimal site inventory) advantages exist.o Pipelines exist for water, natural gas, oil, oxygen, nitrogen, hydrogen (the

later three in the gulf coast area).o For instance, natural gas pipelines send gas to central Canada at a rate of

2,362 million std. cu ft of gas per day.o

Steam distribution from central heating centers is less common today dueto the use of natural gas instead, but can be economical in certainsituations.

o Liquid pipelines are designed with velocities up to 10 ft/sec and maximum

pressures to 1000 psig. Gas pipelines have higher velocities.

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11.14. Conveyor Belt

o Conveyor belts are typically used in mining applications where large

masses of material must be transported over reasonable distances.

o Conveying Distances of 8 to 20 km have been commercially proven.o Example : 750 metric tons / hr over 6 km distances, energy use = 0.4 kW/

metric ton / hr (0.68 BTU/lb), at a electrical cost (0.07 $/kW hr) of about3.1E-5 $/kg of material.

o See http://www.conveyor-dynamics.com/

11.15. Air

o Air freighters like the Boeing 747-400F can carry loads weighing up to

110.67 metric tons. It can carry 30 standard air containers (dimension 96"x 125" x 118") and 32 smaller Type 8 containers (lower deck container,dimension is 60.4" x 61.5" x 64").

o Generally, air freight is perceived as being expensive as compared to otherforms of transportation.

11.16. On-site Generation

Although not really a mode of transport this is commonly grouped with transportationmethods for comparison purposes.

o On site generation of standard gases (nitrogen, oxygen ) can provide for

significantly larger consumption rates.: oxygen plants of 100 to 135,000std ft3/hr (72,000 to 100 million std ft3 /month) and typical nitrogen plantsizes are 5000 to 160,000 std ft3/hr.

A comparison of transportation methods by capacityGases Liquids/Solids

unit capacity yearly (millions) unit capacity yearly (millions)

Truck 1500 cu M/truck (1) 30,000 kg/truck 110 million kg/yr (2)

Containers 30,000 kg/container

Rail 120,000 kg/car 624 million kg/yr 3)

Ship usually liqified 98,000,000 kg/ship 5,100 million kg/yr (4)

Pipeline 3.50E+07 kg/day (5) 12,775 million kg/yr 2,600,000 kg/hr (6) 22,800 mill ion kg/yr

Conveyor n/a 750,000 kg/hr 6,600 million kg/yr

OnSite Generation

Notes:

1 at 2450 psig

2 Assume 10 trucks per day

3 Assume 2 trains, composed of 50 cars per week

4 Assume 1 ship / wk

5 Not necessarily typical of all pipelines

6 liq, 4 ft/sec, SG=0.9, 36 in dia

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Detailed Storage Tank Sizing

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