Storage Tanks Selection and Sizing CBE 497 1

Storage Tanks Selection and Sizing CBE 497 1 Oct 02 richardhaw@sympatico. ca

Dow Chemical - LOPC • LOPC stands for Loss of Primary Containment. • Considerable effort goes into preventing loss of product from storage tanks and vessels. • LOPC generally leads to fires and explosions with loss of life and loss of investment. • LOC at Phillips in Houston in Oct 89 killed 23, injured 130 and cost over $750 million. • LOC at Union Carbide’s plant in Bhopal, India killed over 4000 people and cost UC well over $500 million. • This is why LOPC is so important.

Job 1 at Dow

NIOSH Data • NIOSH stands for National Institute for Occupational Safety and Health. • Lookup your chemical on the NIOSH Pocket Guide to Chemical Hazards. • http: //www. cdc. gov/niosh/npg. html • As soon as you know you have a certain chemical, extract the following NIOSH data:

NIOSH Exposure Limits • Ca. Any substance that NIOSH considers to be an occupational carcinogen is designated by the notation – Ca. • REL – Recommended Exposure Limit based on a 10 hour workday during a 40 hour work week. • A ceiling REL is designated by a “C” preceding the value. The ceiling value should not be exceeded at any time.

NIOSH STEL • Short term exposure limit (STEL) is a 15 minute time weighted average (TWA) exposure limit that should not be exceeded at any time during a workday.

NIOSH Gives OSHA Limits • NIOSH also presents Occupational Safety and Health Act data (OSHA). • OSHA uses PEL for permissible exposure limits.

NIOSH Gives ACGIH Limits • The American Conference of Governmental Industrial Hygiene (ACGIH). • ACGIH uses Threshold Limit Values (TLV) which are 8 hour TWA concentrations • ACGIH A 1 is a confirmed carcinogen. • ACGIH A 2 is a suspected carcinogen. • ST is a 15 minute TWA value for a STEL.

NIOSH IDLH • IDLH stands for Immediately dangerous to life and health. • IDLH represents the maximum concentration from which, in the case of respirator failure, one could escape within 30 minutes without a respirator and without experiencing any escapeimpairing or irreversible effects.

NIOSH Flammability • LEL = Lower Explosive Limit aka LFL for Lower Flammable Limit in vol% in air at room temperature. • UEL = Upper Explosive Limit aka UFL for Upper flammable Limit in vol% in air at room temperature. • Flash Point (Fl. P. ) using either closed cup (cc) or open cup (op) methods.

NIOSH Other Important Data • NIOSH gives the Auto Ignition Temperature (AIT), if it is known. • Boiling Point (BP) at 1 atmosphere. • Freezing Point (FRZ) temperature. • Solubility in water (sol) as % by weight. • Specific gravity (Sp. Gr. ).

NIOSH Incompatibilities • NIOSH give the important hazardous incompatibilities or reactivities of each substance. • This is where I would look for polymerization potential and the need to take special preventative action should a polymerization reaction start to generate high heat of reaction.

OSHA Classification of Flammables • Class 1 A flammable liquid. Fl. P. below 73 F and BP below 100 F. • Class 1 B flammable liquid. Fl. P. below 73 F and BP above 100 F. • Class 1 C flammable liquid. Fl. P. at or above 73 F and below 100 F.

MSDS Information • MSDS stands for Material Safety Data Sheets. A repeat of NIOSH data. • Most large companies publish their MSDS on the internet. • Often six different MSDS sets of one chemical are compared and a consensus is taken to resolve differences in toxic and flammability data – particularly auto ignition. (NH 3 as an example).

Vapor Pressure Data • Generate your own Antoine Constants over your temperature range including summer to winter ambient temperatures. • The typical Antoine equation is: Log 10(P) = A + B/(t+C) where P is in psia, t is in deg C and A, B, C are the Antoine Constants. • 3 sets of (P, t) data required to solve for A, B, C in 3 equations.

Antoine Constants for EO

Vapor Pressure Plot for EO

Vapor Pressure Info • Look to see where VP is at lowest ambient temperature. • If the VP is below atmospheric pressure of 14. 7 psia, and if the chemical is a flammable chemical, air will leak into the vessel creating an extremely hazardous situation. • Static electricity created by falling liquid into the vessel can set off an explosion.

Pad – Depad with an Inert gas • To prevent air from leaking into a flammable vessel under sub atmospheric pressure, add nitrogen as a pad gas to maintain the pressure above 14. 7 psia. • As the vessel requires venting during filling, de-pad the inert gas & hydrocarbon to a flare or to a recovery system. • As an alternative, heat the tank to bring the vapor pressure above 14. 7 psia.

Pad – Depad Sketch

The Enthalpy Chart

The Enthalpy Chart Cont’d • It provides a roadmap for your process. • Try to find an enthalpy chart for your single component chemicals. • If one is not available, you can construct your own from HYSIS. • The enthalpy chart tells you about the need for pre-heaters, vaporizers, superheaters, knock-out pots, pumps, compressors.

MIACC or RMP? • Check to see if your chemical is listed on the Major Industrial Accident Coordinating Committee List. • Check to see if your chemical is listed on the U. S. Risk Management Plan List. • These lists tell you whether or not you need to take toxic or flammable preventative measures in your design.

U. S. RMP • The U. S. RMP method is now favored in Canada over the CDN MIACC method. • If your chemical is on the list and if your quantity exceeds the specified threshold quantity, you must run the RMP program to determine the environmental impact on the public and file the results with the EPA. • The EPA will approve your plant design if you have developed a suitable emergency response plan with the public.

RMP Computer Program • RMP Worst Case Scenario tells you the impact distance from your storage tank to the public for either a toxic or flammable chemical. • Free download at http: //www. epa. gov/ceppo/tools/rmp-comp/rmpcomp. html • Download it on to your hard disc. • It’s very simple to use. • If you don’t know your storage quantity yet, run the threshold quantity to see how big a problem you may have. You may decide to store less.

Design Tools Needed • • The Ideal Gas Law, P 1 V 1/T 1 = P 2 V 2/T 2 Dalton’s law of Additive Pressure. Dew Point calculation. Bubble Point calculation. Flash % calculation. Equation of state PV = (Z)(n)(R)(T) The Antoine Vapor Pressure equation.

API Storage Tanks • API – Low pressure storage, DP < 15 psig

Pressure Vessels, DP>15 psig • High pressure where DP > 15 psig.

Codes for API Tanks • • API-12 B – bolted tanks API-12 D – field welded tanks API-12 F – shop welded tanks API-620 – large welded, low pressure tanks • API-650 – welded steel tanks for oil storage.

Codes for Pressure Vessels • ASME VIII - Pressure Vessel Code • B 51 -M 1981 – Canadian Standards Association – Code for the Construction and Inspection of Boilers and Pressure Vessels.

Codes for Piping • American National Standards Institute (ANSI) – B 31. 1 – Power Piping – B 31. 2 - Fuel Gas Piping – B 31. 3 - Chem Plant & pet Plant Piping. – B 31. 4 Liquid petroleum Transportation Piping – B 31. 4 – 1974 Refrigeration Piping – B 31. 8 – gas Transmission Piping

Fire Protection • National Fire protection Association (NFPA) • No. 30 – Flammable & Combustible Liquids Code • No. 58 Liquified Petroleum Gases, Stg & Hdlg. • No. 59 Liquified Petroleum Gases at Utility Gas Plants. • PSV Design – NFPA – 30 • PSV Design – API-520 & API-521

Drainage • NFPA 30 - 2 -3. 3 Control Of Spillage From Aboveground Tanks (see PSV Size & Cost V 3. 7)

Dyking • Dyke Dimensions on CD-ROM

EO Storage

UC MIC Storage Area

Sizing API Tanks • • • Need Liquid Density, lb/cf Need a Soil Bearing reading in lb/sf. Maximum allowable Ht of liquid = HL Max HL = lb/sf / lb/cf = ft. of liquid Need storage time in hours, days or weeks. Need average flow rate, cu. Ft / hr Volume = (cu. Ft. / hr )(hours). Never fill more than 90%. Diameter, D = [ cu. Ft. /. 785 / HL ]^0. 5

Selection of API Tanks • API 650 Tanks on CD-ROM. • Select tanks from large data base that meet volume and maximum height limits. • Select options • • • Length of pipe rack Painting Insulation thickness Dyke type – concrete or earthen Year for escalation of cost in database.

Calculate Heat Loss • Heat Loss From Vessels on CD-ROM • May have to add re-circulating pumps and heat exchangers. • Basic goal is to save energy at DCFRRAT of 20% or better.

Determine Breathing Losses • Storage Tank Venting folder on CDROM • Read Design Methods for Storage Tank Venting. • BLOSS program on CR-ROM for breathing losses due to ambient temperature changes and pump in / pump out changes. • Make changes in process to lower losses.

Sizing Pressure Vessels • • Pressure Vessels V 1. 5 on CD-ROM Need volume, cf, by (lb/hr)(hrs) / (lb/cf) Use a safety factor of 40%. Select diameter, D, and length, L, so that L/D = 4 to 5 or thereabouts. • Select Design Pressure, DP, and Design Temperature, DT, to safely cover all upset conditions.

Sizing PV Cont’d • Select Corrosion Allowance – ca, usually 1/16 inch for inside. • May have to allow 1/16 inch for outside corrosive atmospheres – near Cl 2 plant. • Select materials from data base. • Select Joint Efficiency, E, = 0. 85 or 1. 0 • Select flange rating = 150 lb, 300 lb or ?

Flange Data

Sizing Cont’d • Cylindrical Shell thickness = t where t = (P)(R) / [(S)(E) - (0. 6)(P)] • P = Design Pressure, psig, aka MAWP for Maximum allowable Working pressure. • R = Vessel radius, inches • S = Stress value of material, lb/sq. inch • E = Joint Efficiency = 0. 85 or 1. 0 • P = (S)(E)(t) / [R + (0. 6)(t)]

Sizing Con’d • 2: 1 Ellipsoidal head • t = (P)(D) / [(2)(S)(E) - (0. 2)(P)] • Final tf = [t + ca] rounded to next thickness • P = (2)(S)(E)(tf) / [(D) + (0. 2)(tf)] where P is now the back-calculated Design Pressure • Units same as above.

Final Design Conditions • Design thickness is selected on the basis of the maximum of: • Longitudinal seam of cylindrical shell • Head type – ellipsoidal or ASME • Flange rating

Mechanical Results & Cost

Results Cont’d

Other Storage Tank Issues • Cold Insulation to prevent dew point forming on external surfaces. • Complete Hazard Analysis. • Mini- Quantitative Risk Analysis (QRA). • Spheres • Floating Roof API tanks. • Pressure Safety Valve (PSV) design.

End of Presentation • Good luck with your storage tank designs. • Any questions? • If you have questions later, email me at richardhaw@sympatico. ca