Detailed Storage Tank Sizing

Mody and Marchildon: Chemical Engineering Process Design Chapter 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 it takes at ambient pressures and temperatures; in some cases it may make economical sense to convert the material to another state for storage. For instance, in the case where large quantities of gases are to be stored (greater than about 1500 std cu M), liquefaction of the gas may become economical. Liquefaction of gases (in cryogenic storage) often involves allowing a portion of the liquid to boil off to maintain temperature and pressure in 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 to solids 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 onsite storage. 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. Extremely hazardous chemicals may require a secondary ‘deinventory’ storage tank in the event a problem develops in the primary storage system. However, for average materials the following guidelines may be used to determine storage requirements. Raw Material Storage is provided to ensure the plant never (or rarely) shuts down because the raw materials are unavailable. Thus, the reliability of the supply system must be examined. Baasel (ref 1) presents the following guidelines: Amount of feedstock that should be kept onsite= (date delivered – date ordered )* feed rate Storage Size = Max amount that COULD be present when delivery arrives + Amount Ordered

Example: A plant requires 20,000 lb of feedstock per day. The supplier will guarantee shipping the order in 15 days of order receipt. The time to ship the material is anywhere between 2 and 5 days. The mode of transport is 36,000 gal jumbo rail cars. The specific gravity of the 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 of order 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 choice of 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 a design 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 rise and fall. If the tank were open to atmosphere, the increased pressure is dissipated by the gases (rich with the fluid being stored) in the tank escaping. As the tank cools, the pressure drops and air is drawn in to maintain atmospheric pressure. In a freely vented tank, the factors that affect how much gas is expelled through the vent are: 1) the change in 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 vapour space 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 difference between the pressure and vacuum set pressure, all thermal cycling losses can be eliminated. By selecting an initial pressure to begin with (typically a small value consistent with the low vacuum capabilities of a storage tank), you can use these factors to determine the maximum expected operating pressure. If a design pressure in excess of the max operating 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 the amount of material to be stored. The reader is cautioned that there is sometimes confusion in stating whether a container is x volume as determined by its dimensions or by volume as determined by the amount of fluid (ie. gas at high pressure) that can be stored in the container. For instance, a container 2 ft in diameter and 20 ft long has a dimensional volume of about 1.8 cu M, but can 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 of the container.

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11.5. Gas Storage Comparison of Tanks for Storage of Gases Situation Typical Possible Occurrence Equipment Gas Storage

Selection Criteria & Alternatives

Small For low quantities (0 to pressure Tank 1000 cu M) or drums can be used.

High Pressure Bottles ‘Bullet Tanks’

ASME VIII vessels can be designed and fabricated by approved pressure vessel shops Generally ASME Section VIII vessels are used. Choice of container size depends on consumption rates. Section VIII Code allows design pressures up to 3000 psig and for vessels above 10,000 psig.

Up to 35000 cu Meters

ASME Spheres / Spheroids

Mid to large storage

Consider liquefied

Suppliers

Spheroids are typically for 30 psig or less. Spheres (typically between 32 to 120 ft dia) have typical design pressure up to about 200 psig

For integrated supply of gases and storage (i.e. by tube trailer)Air Liquide, Air Products, Praxair, etc.

Chicago Bridge and Iron Works www.cbiepc.com

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Situation

Typical Occurrence

Possible Equipment

capacities Very Large Quantities

storage. Caverns

For very high consumption rates or gases with hazardous properties

Conversion to other compounds or states Consider onsite generation

Selection Criteria & Alternatives

Suppliers

Caverns may be economical in situations where natural geography allows. Refer to Gas Processors Suppliers Association – Engineering Data Book

Select on-site generation by economic analysis Select on-site generation when process hazards analysis indicates risk is too great.

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

ASME VIII Vessels Spheres Vapour Floating Pressure Roof API ULC API Tanks

Caverns / Undergroun d Size

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Comparison of Tanks for Storage of Liquids Situation Typical Possible Selection Criteria & Alternatives Occurrence Equipment Liquid Long-term -ULC tanks Determine the tank volume requirements first. Storage storage (in excess of 1 -API type tanks Determine type of tank based on fluid vapour pressure or day), Tank (cone roof), tank working pressure. Farms, or storage -Floating roof external to tanks, Fluid vapour pressures less than atmospheric the process unit. -Spheres ULC Storage Tanks

Suppliers

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

-Underground Storage

Typically found in ‘gas station’ type applications these tanks can be provided with double wall construction thus eliminating the need for dikes.

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Situation Typical Possible Occurrence Equipment

Selection Criteria & Alternatives

Suppliers

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 head space . Tank designs are generally for working pressures < 2.5 inches water gauge (0.09 psi) positive pressure and 0.5 oz/in2 (0.86 in H20 , 0.03 psi) vacuum, but can be designed for pressures up to about 15 psig for smaller tanks. The US EPA organization requires that a vapour recovery system be provided when storing more than 40,000 us gal of a fluid that has a vapour pressure in excess of 1.5 psia when stored in a cone roof tank. For fluids with vapour pressures between 1.5 and 11.1 psia a floating roof tank can be used without a vapour recovery system. Designs are according to API 650 or 620. See table below for a selection of different sizes.

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Situation Typical Possible Occurrence Equipment

Selection Criteria & Alternatives

Suppliers

Floating Roof Tanks

have no headspace, the roof of the tank floats on top of the liquid and rises and falls as the liquid level changes. The lack of headspace ensures there are no ‘breathing’ losses from the tank. A seal (of which there are a variety of different types) ensures neglible evaporation of the liquid even with fluids that have close to atmospheric boiling points. This type of tank design is required in the US (as stated by EPA stds) for fluids with vapour pressures greater than 1.5 psia and less than 11.1 psia. Designs are according to API 650 or API 620.

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Situation Typical Possible Occurrence Equipment

Selection Criteria & Alternatives

Suppliers

http://www.superiortank.com/

Variations on the standard floating head tank include a hybrid cone/floating roof that ensures rain and snow are kept away from the tank contents. Consideration to venting this secondary headspace may be required to eliminate flammability issues. Bolted Tanks Suitable for fluids with low vapour pressures bolted tanks are transported in segments and bolted together at site. Tanks can be erected by hand and easily transported later.

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Situation Typical Possible Occurrence Equipment

Selection Criteria & Alternatives

Suppliers

Spheres: Chicago Bridge and Iron Company (www.cbiepc.com)

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Situation Typical Possible Occurrence Equipment

Selection Criteria & Alternatives

Suppliers

Fluid vapour pressures greater than atmospheric Spheres and Spheroids

for operating pressures from 15 psig, but up to 250 psig are 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 for pressures up to 3000 psig are covered by ASME Section VIII Div 1. Asme Section VIII, Div 3 covers designs for tanks greater than 10,000 psig. Underground storage is particularly useful for high vapour pressure fluids and large volumes of liquid. No formal standards for design exit, refer to GPSA handbook for further information.

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Situation Typical Possible Occurrence Equipment

In plant ‘day’ storage. Waste Storage

Selection Criteria & Alternatives

Suppliers

3.1.1. Alternatives Consider cooling the liquid to reduce vapour pressure and utilize a less expensive tank tank. See above selection, but typically a horizontal or vertical drum (Bullet tank) is used.

Generally smaller tanks, where costs are less sensitive to the tank design Lined Ponds Used for the disposal and evaporation of fluids

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The API standard has listed some typical tank sizes. Tank Diameter ft m 15 4.6 20 6.1 25 7.6 25 7.6 30 9.1 35 10.7 45 13.7 70 21.3 100 30.5 120 36.6 200 61.0

A Selection of Typical API Field Constructed Tanks Tank Approx Capacity Height L/D Total Volume gal/ft m3/m ft m US Gal US Barrels 1320 16.4 18 5.5 1.2 23800 567 2350 29.2 18 5.5 0.9 42300 1007 3670 45.6 18 5.5 0.7 66100 1574 3670 45.6 24 7.3 1.0 88100 2098 5290 65.7 24 7.3 0.8 127000 3024 7190 89.3 30 9.1 0.9 216000 5143 11900 147.8 36 11.0 0.8 428000 10190 28800 357.6 54 16.5 0.8 1550000 36905 58700 728.8 36 11.0 0.4 2110000 50238 84500 1,049.2 30 9.1 0.3 2540000 60476 190000 2,359.1 18 5.5 0.1 4230000 100714

cu M 90 160 250 333 481 818 1620 5867 7987 9615 16012

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11.7. Solids Storage Solid storage is typically done either by piling on the ground (possibly inside a building i.e. in the case of hydroscopic materials), or in bins or silos. Baasel suggests: 1. It’s 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 conveyors 3. 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 the distribution of particle sizes in a mixture, the greater the tendency to compact and to resist flow. 5. To ensure materials freely flow out the bottom of a bin (to avoid bridging), make the bottom an eccentric cone with one straight vertical side. This Author’s 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 on flat 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), seek advice from experts such as Jennike and Johanson (http://www.jenike.com) or Jerry Johanson (http://www.jrjohanson.com). References (section 3.1) 1. Baasel, William D ‘ Preliminary Chemical Engineering Plant Design’ Elsevier North Holland, 1980, ISBN 0-444-00152-2. 2. Amrouche, Dave, Gursahani, Lee and Montemayor; ‘General Rules for Aboveground Storage Tank Design and Operation’; Chem Eng Progress (Dec. 2002) pp 54-58. 3. Gas Processors Supplies Association; ‘Engineering Data Book’; 11th 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 of the 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 4x the 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 kg and 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 handling containers, 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 distances o 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 bulk solids 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 built double walled tankers (Conoco) have a capacity of 727,100 barrels (about 98 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 due to the use of natural gas instead, but can be economical in certain situations. 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 about 3.1E-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 other forms of transportation. 11.16. On-site Generation Although not really a mode of transport this is commonly grouped with transportation methods for comparison purposes. o On site generation of standard gases (nitrogen, oxygen ) can provide for significantly larger consumption rates.: oxygen plants of 100 to 135,000 std ft3/hr (72,000 to 100 million std ft3 /month) and typical nitrogen plant sizes are 5000 to 160,000 std ft3/hr. A comparison of transportation methods by capacity Truck Containers Rail Ship Pipeline Conveyor OnSite Generation Notes: 1 2 3 4 5 6

Gases unit capacity 1500 cu M/truck (1)

usually liqified 3.50E+07 kg/day (5) n/a

yearly (millions)

12,775 million kg/yr

Liquids/Solids unit capacity yearly (millions) 30,000 kg/truck 110 million kg/yr (2) 30,000 kg/container 120,000 kg/car 624 million kg/yr 3) 98,000,000 kg/ship 5,100 million kg/yr (4) 2,600,000 kg/hr (6) 22,800 million kg/yr 750,000 kg/hr 6,600 million kg/yr

at 2450 psig Assume 10 trucks per day Assume 2 trains, composed of 50 cars per week Assume 1 ship / wk Not necessarily typical of all pipelines liq, 4 ft/sec, SG=0.9, 36 in dia

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