Crimson Engineering Associates, LLC by Zy2C9BH4

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									Crimson Engineering Associates, LLC                                                                                                                       0




   Contents
   Executive Summary ........................................................................................................................ 1

   Background ..................................................................................................................................... 2

   Safety, Environment and Transportation Regulations .................................................................... 2

      Hydrogen Sulfide ........................................................................................................................ 2
      Sulfur Dioxide............................................................................................................................. 4
      Sulfur Powder Handling ............................................................................................................. 5
   Storage Tank Analysis .................................................................................................................... 5

   Option B Economics ....................................................................................................................... 7

   Accuracy ......................................................................................................................................... 8

   Concluding Recommendations ....................................................................................................... 8

   References ....................................................................................................................................... 9

   Appendix ....................................................................................................................................... 10

      Sample Calculations.................................................................................................................. 10
Crimson Engineering Associates, LLC                                                                     1




   Executive Summary
           Crimson Engineering Associates, LLC received a proposal from IRI to analyze
   alterations to a diesel processing plant in order to accommodate new regulations on sulfur
   content in diesel fuel. The total fixed capital investment for the project will be $9,232,000,
   which correlates to an increase in diesel of $0.13/bbl, compared to $0.14/bbl without a Claus unit
   for desulfurization. The rate of sulfur production was estimated to be 12.8tons/day with the
   recommended smallest powder size as 500 µm for safety reasons. Due to its proximity to a
   hydrocarbon storage area, the existing sulphur storage tank is not safe in the event of a
   hydrocarbon fire; therefore, CEA’s recommendation is that a new tank be constructed in a less
   volatile area.

           The chemicals analyzed for this project are hydrogen sulfide and sulfur dioxide.
   Hydrogen sulfide is highly toxic and flammable gas. It must be stored in secure and well
   ventilated areas. The containers it is stored in must meet Class 1 National Electric Codes for
   highly flammable materials. On the other hand, sulfur dioxide is life threatening when the
   concentration is above 100ppm. It is flammable and poisonous in certain concentrations. Low
   levels of sulfur dioxide can harm plant life. It must be stored in well ventilated areas and at
   proper temperature and pressure. Sulfur dioxide should be transported using proper handling
   devices and storage.
Crimson Engineering Associates, LLC                                                                        2




   Background
           IRI operates a refinery that processes 24 106 bbl/calendar year. Fifteen percent of its
   production is diesel fuel. As a result of environmental regulations, IRI has built a catalytic hydro-
   desulfurization unit that will reduce the content of sulfur in diesel from 0.95% wt to 0.1% wt.
   Diesel fuel is premixed with a stream of lighter hydrocarbons and hydrogen before it goes
   through a catalytic reactor. The reactor then transforms the sulfur content of the diesel stream to
   H2S. Flash separations separate H2S from the diesel and the gaseous product goes through an
   absorption tower, where the H2S is recovered. This unit has a capacity to desulfurize 500,000
   metric tons/year of diesel fuel.

   Problem Statement
           IRI is currently investigating the desulfurization of their diesel production to lower the
   sulfur content. They want to know the safety concerns and cost of handling H2S. There are two
   options of handling H2S, which are:
   Option A: Burn H2S in the refinery furnaces for heat generation. The sulfur dioxide that will be
              produced will be released to the atmosphere through a chimney.
   Option B: Build a Claus unit, in which all the sulfur will be recovered, and pass the stream
              through it. IRI wants to know whether to produce and store sulfur in a powder form.


   Safety, Environment and Transportation Regulations
   Hydrogen Sulfide
   Safety
          Hydrogen sulfide is a highly toxic and flammable gas. Hydrogen sulfide is also an
   odorant with a characteristic smell of rotten eggs at concentrations higher than .02 ppm. After
   300-350 ppm, this gas can seem odorless to the senses. Since it is heavier then air, it has a
   tendency to sink low in poorly vented spaces. Hydrogen sulfide is deadly in the fact that it forms
   a complex bond with iron in the mitochondrial cytochrome enzymes, blocking oxygen from
   binding and thus stopping cellular respiration. Low levels of this gas are not harmful to humans;
   however, hydrogen sulfide is harmful to humans in certain concentrations. These concentrations
   along with their symptoms are shown in table below:

                         Table 1: Concentrations of Hydrogen Sulfide and Symptoms
                 Concentration        Symptoms
                 10-20 ppm            Conjunctival irritation
                 50-100 ppm           Serious eye damage
                 150-250 ppm          Paralyzes olfactory perception
                 320-530 ppm          Pulmonary edema with possibility of death
                 530-1000 ppm         Lead to breathing loss
                 800 ppm              Lethal
                 1000 ppm             Immediate collapse with single breath
Crimson Engineering Associates, LLC                                                                      3



           In order to protect against such hazards, personal working around such chemical should
   carry hydrogen sulfide detectors that will warn the worker before levels come into the toxic
   level. In the area of containers, atmosphere detection monitors can be used to tell the occupants
   around the container’s contents of the atmosphere in that container.

   Environmental
            Hydrogen sulfide is regulated by the EPA in the areas of exposure to the air and water. It
   is also regulated in the work place by OSHA. The EPA requires any company to report
   quantities of hydrogen sulfide 100 lbs or more under the Comprehensive Environmental
   Response, Compensation, and Liability Act of 1990. It is also listed as a extremely hazardous
   substance under the Superfund Amendment and Reauthorization Act with a threshold planning
   quality of 500 lbs in Sections 302/304. In addition it is report as hazardous chemical reporting
   under Sections 311/312 as immediate health, pressure, reactive, and fire hazards. In the SARA
   Title III Act, it is also needed to be reported in toxic chemical release reporting.
   Under the Clean Air Act in Section 112, hydrogen sulfide is listed as a regulated substance with
   threshold planning quantity of 10,000 lbs. It is also listed in the Toxic Substances Control Act.
   As an aquatic toxin, hydrogen sulfide has threshold limits as follows:




                                       Table 2: Aquatic Toxicity
                   Type                                      Quantity
                   TLm (assellussp) 96 hours                 .111 mg/L
                   TLm (Cranfgonyx) 96 hours                 1.07 mg/L
                   TLm (Gammarrus) 96 hours                  .84 mg/L
                   LC50 (fly inhalation) 960 minutes         380 mg/m3
                   LC50 (fly inhalation) 7 minutes           1500 mg/m3
                   TLm (bluegill sunfish) 96 hours           .0478 mg/L
                   TLm (fathead minnow) 96 hours             .0071-.55 mg/L
                   TLm (brook trout) 96 hours                .0216-.038 mg/L

          Hydrogen sulfide is not mobile in soil. In addition, it converts to elemental sulfur upon
   standing in water. These restrictions are also measured by the EPA.

   Transportation
           Hydrogen sulfide must be stored in well ventilated, secure area, protected from the
   weather. They must be stored upright will valve seals and caps in place. It should be kept away
   from an ignition source. All containers must meet Class 1 in National Electric Codes for highly
   flammable materials. Must not be within 20 feet of oxygen with well posted no smoking or open
   flames signs around it. When moving, be sure to not drag, roll, slide, or drop cylinders. All
   containers must be labeled with flammable gas and toxic gas. In addition, only certified hand
   truck should be used to move cylinders of hydrogen sulfide.
Crimson Engineering Associates, LLC                                                                       4




   Sulfur Dioxide
   Safety
           Sulfur Dioxide can be a flammable/poisonous gas in certain concentrations. Short term
   exposure to high levels of hydrogen sulfide can be life threatening when concentration is above
   100 ppm in atmosphere. It can cause burning of the nose and throat, breathing difficulties, and
   severe airway obstructions. Persistent levels can affect the functions of the lungs when exposed
   to .4-3.0 ppm for 20 years or more. In addition, asthmatics are sensitive to the respiratory effects
   of concentrations of sulfur dioxide as low as .25 ppm.
   OSHA regulates sulfur dioxide in the workplace to range from no more than 0-5 ppm. During a
   40- hour work week, concentrations of sulfur dioxide cannot exceed 5 ppm. Sulfur dioxide must
   be measured on a regular basis in areas where workers are. Monitors for monitoring these
   conditions can be set up in such areas, and engineering principles can be put into place in order
   to keep these areas of high sulfur concentration well ventilated. Full face ventilators are
   recommended in areas of highest concentration to prevent long term effects.

   Environmental
           Sulfur dioxide is mostly regulated in its environmental effects by the EPA in standards of
   air quality. Even low concentrations of sulfur dioxide can harm plants and trees, but even higher
   levels can form acid rain deposits and affect land and water ecosystems. Most of the sulfur
   dioxide released in the atmosphere is absorbed by soils and plants. The air limits for sulfur
   dioxide are found in the Clean Air Act and fall in the following ranges:

                                  Table 3: Clean Air Act Limits
                                Time periods               Limits
                                Annual arithmetic mean .03 ppm
                                24 hour                    .14 ppm
                                3 hour                     .50 ppm

          Sulfur dioxide is not as highly regulated as some other chemicals due to its inherent
   presence already in the atmosphere. It can become dangerous in the above limits to not only
   humans but to all plant and animal life around the world.


   Transportation
          Sulfur Dioxide must be used in well-ventilated areas with valve protection caps in place
   to secure that no excess gas escapes. Do not drag or roll cylinders for chance of explosion.
   While moving cylinders of sulfur dioxide, be sure to keep in well-ventilated areas. This gas can
   corrode metals if it isn’t stored at the proper temperature and pressure. These containers should
   be marked as flammable with nonhazardous electrical classification on each cylinder. In
   addition, these containers should be moved with only approved trucks with proper holding
   devices and storage.
Crimson Engineering Associates, LLC                                                                        5


   Sulfur Powder Handling
          Dusts clouds in general can cause rapid combustion when mixed at the right air
   concentration. Ways to resist this possible explosion is to:
          prevent ignition
          limit the effects of the explosion
          restrict formation of hazardous atmosphere
           The first can be used be done by limiting contact within a 25 foot radius with possible
   high oxygen content areas or possible spark able areas. The second can be done by building
   containment units that are capable of taking on high pressures from explosion without being
   exploding themselves. Another way to do this is to have some sort of blast doors that let out
   extra pressure from such high pressure explosive containers. The third way to prevent dust
   explosion is to limit the combustible atmosphere. This can be done by using inert gases to keep
   combustible gases from setting off expositions, ventilating the areas of possible dust buildup, or
   proper cleanup and maintenance of the area keeping dust buildup to a minimum. The best way
   to keep buildup down is limit the particle size to well above 500 µm, the maximum size of
   particle mixture for dust.


   Storage Tank Analysis
           Assessing the viability of the Claus unit includes the storage facilities where the final
   product will be held. The subsequent study revealed that the current storage tank is insufficient
   in the event of a hydrocarbon fire in the adjacent storage facility. Some form of remediation is
   necessary before the tank can be used.

           The existing storage tank is cylindrical with a capacity of 22,500 gal and a base diameter
   of 15 ft. The maximum allowable tank pressure is 80 inches of water (gauge). The tank contains
   a vent with a surface area of 0.5 ft2. The product of the Claus process is a liquid sulfur stream
   which is deposited to the tank for storage. Due to its proximity to the plant’s hydrocarbon
   storage tanks, the structural integrity of the tank is critical in the event of a plant fire. As fire
   engulfs the storage tank, the molten sulfur will begin to vaporize increasing the pressure in the
   storage tank. When the pressure inside the tank exceeds its design specification it will rupture,
   releasing toxic sulfur gas and endangering employees and the surrounding community.

           In order to determine whether such a scenario would occur, it was necessary to assess
   several factors in the event of a hydrocarbon fire. Empirical studies have shown that the
   temperatures produced in such a fire are generally near 2200˚F. The heat transferred into the
   tank will be the sum of convective and radiant transfer. Existing data demonstrates that the
   convective heat transfer coefficients for such a situation are generally between 1 and 2 BTU/(hr
   ft2 ˚R). For the sake of added safety, the higher value of 2 will be chosen. Before the quantity of
   heat transferred due to convection can be determined, a few assumptions are necessary. First, it
   can be assumed that the tank contains no insulation and the thermal resistance of the tank wall is
   negligible. Secondly, the convective heat transfer coefficient of the liquid sulfur is very large,
   indicating minimal resistance to heat transfer. This is reasonable considering the high
Crimson Engineering Associates, LLC                                                                         6


   temperature of the fluid and the presence of turbulent mixing in the tank. These assumptions
   imply that the temperature of the outside surface of the tank is the same as that of the liquid
   sulfur in the tank. This permits simplification of the important heat transfer equations as follows:

                                                                                                 (1)

            Where Q is the heat transferred, A is the effective heat transfer area, T fire is the
   temperature of the hydrocarbon fire, and Tliquid is the temperature of the liquid sulfur. For a
   measure of added safety, it will be assumed that the temperature of the liquid sulfur is already at
   its boiling point of 832.5˚F. As the fire surrounds the vertical walls of the tank, the heat transfer
   to the bottom and top of the tank is negligible, and the effective heat transfer area can be taken as
   the cylinder walls. Evaluating equation 1 at these conditions gives a value of 2.68 x 106 BTU/hr
   of convective heat transfer.

           Previous observations have demonstrated that the thermal radiation produced during
   similar hydrocarbon fires is on the order of 30000 BTU/(hr ft2). However, the absorbing body
   will reradiate a fraction of that energy. The quantity reradiated can be determined by use of the
   Stefan-Boltzmann law, given below:

                                                                                                 (2)

           Where Q is the radiant heat transferred, A is the effective heat transfer area,  is a
   proportionality constant, and T is the temperature of the radiating body (taken to be the
   temperature of the liquid). Evaluation of equation 2 gives 8.06 x 105 BTU/hr of heat reradiated
   for a net radiant heat transfer of 2.86 x 107 BTU/hr. The total heat transferred to the liquid may
   be found by summing the contributions from the convective and radiant heat transfer yielding
   2.73 x 107 BTU/hr.

          Determination of the heat transferred to the storage fluid enables calculation of its rate of
   vaporization through the following relation:


                                                                                                 (3)

           Where m is the vaporization rate, Hvap is the heat of vaporization of sulfur, and Q is the
   net heat transfer rate. Solving equation 3 gives a value of 86,500 kg/hr of sulfur vaporized. In
   order to determine whether the tank will overpressure in this situation, it is useful to calculate the
   flow of vapor through the conservation vent. Because the vent is open to the air, it is at
   atmospheric pressure. The pressure drop across the vent will be equal to the absolute pressure
   inside the tank minus atmospheric pressure. As pressure inside the tank approaches its design
   maximum, the pressure drop across the vent will approach 80 inches of water. By comparing the
   flow through the vent at the designated pressure drop to the rate of vaporization in the tank, it
   can be determined whether the tank will rupture.
Crimson Engineering Associates, LLC                                                                          7


          A correlation is necessary to relate the flow rate of material through the vent to the
   pressure drop across it. No such correlations are immediately available for a conservation vent.
   However, the vent can instead be modeled as an orifice meter. This assumption is reasonable
   considering the constriction in area through which the gas travels. Peters, Timmerhaus, and
   West provide the following relation in Plant Design and Economics for Chemical Engineers:


                                                                                                  (4)

           Where mv is the volumetric flow rate of material through the orifice, Cd is the coefficient
   of discharge, Y is the expansion factor, Ac is the minimum cross-sectional area of the orifice, p1
   is the pressure at the orifice entry, p2 is the pressure at the orifice outlet, is the fluid density,
   and  is the ratio of the throat diameter to the pipe diameter. The expansion factor, Y, can be
   calculated using the physical properties of the gas and equation 12-48 in Peters, Timmerhaus,
   and West. Evaluation of equation 4 and subsequent unit conversion revealed a flow rate of 0.18
   kg/s through the vent at the critical tank pressure.

           The calculated rate of vaporization is several orders of magnitude higher than the flow
   rate through the vent at the maximum design pressure. Therefore, the storage tank will fail
   catastrophically in the event of a hydrocarbon fire. The preferred solution would be to construct
   a new storage tank in a less volatile area of the plant. However, if such an option were not
   feasible, the existing tank could be reinforced to withstand the pressure created by a fire, and a
   water deluge system could be added to cool the shell of the tank.




   Option B Economics
   Cost Analysis
           The total fixed capital investment for the desulfurization unit was $8,650,000, with an
   additional $582,000 for the Claus unit. The desulfurization unit FCI was found using Figure 1
   from the problem statement based on 10,400 BPSD of diesel to be treated and then adjusting this
   amount to 2008 dollars. The FCI of the Claus unit was found by getting the equipment cost from
   Figure 2 based on 12.8 tons/day of sulfur removed from the diesel stream and adjusting to 2008
   dollars. The equipment cost was then related to the FCI using Table 6-9 from Plant Design and
   Economics for Chemical Engineers. With desulfurization alone, the price of diesel would have
   to be raised by $0.14/bbl. For the desulfurization unit with the Claus unit, the increase in price
   of diesel would have to be $0.13/bbl. These numbers were obtained by first solving the
   following formula for R:
Crimson Engineering Associates, LLC                                                                       8


          In this equation, ROI is the minimum return on investment, which is 8% for IRI. D is the
   depreciation, which is assumed to be straight line, with $0 assumed for the salvage value of the
   unit. d is 0.1, based on straight line depreciation for 10 years. The FCI is as listed above. t is
   assumed to be 35%. TCI is the total capital investment, which is found by the formula:



           The revenue, R, is then added to the labor costs, which are assumed to be $174,000 for
   both processes, based on the amount of material processed. This number is divided by the total
   number of barrels of diesel which will be processed over the 10 year lifetime of the project. For
   the Claus unit (Option b) the sulfur is sold at $130/ton, which accounts for its smaller increase in
   price from just desulfurization.


   Accuracy
   There is a certain amount of error in the economic analysis due to:
      1. Error associated with reading numbers off of a graph.
      2. Uncertainties of the future economics of crude price, market value of sulphur, etc.
      3. Age of publications used for economics.
   Despite these error sources, Crimson Engineering Associates believes that our conclusions have
   a total error of less than ten percent.

          The safety analysis of the storage tank will have a considerable amount of error. Several
   assumptions were necessary to reduce the actual conditions of a hydrocarbon fire surrounding a
   storage tank to a system which can be approached analytically. However, all assumptions were
   conservative and designed to err on the side of safety. As a result, CEA’s recommendations
   provide a significant margin of safety in the event of such a scenario.



   Concluding Recommendations
            In conclusion, Crimson Engineering Associates recommends that Independent Refineries
   build the Claus unit to produce powdered sulphur. The cost of diesel production actually
   decreases due to the fact that the sulphur can be sold. We also recommend that IRI not use the
   current storage tank for storage of powdered sulphur due to fire hazards. Building a new tank is
   the safest option available. Please visit our website for a brief summary of our findings at
   http://faculty-staff.ou.edu/B/Clay.A.Buie-1/.
Crimson Engineering Associates, LLC                                                           9




   References
   Hydrogen sulfide
   Safety and Transport
   http://msds.chem.ox.ac.uk/HY/hydrogen_sulfide.html
   http://www.cdc.gov/niosh/idlh/7783064.html
   Environmental
   http://www.epa.gov/compliance/resources/agreements/caa/cafo-fcsht-0501.html
   http://www.cdc.gov/niosh/idlh/7783064.html
   Sulfur Dioxide
   Environmental
   http://www.eia.doe.gov/cneaf/electricity/clean_air_upd97/exec_sum.html
   Safety and Transport
   http://msds.chem.ox.ac.uk/SU/sulfur_dioxide.html
   http://www.cdc.gov/niosh/idlh/7446095.html
   Powder Size
   Perry's Chemical Engineering Handbook, 7th edition Chapter 26
   Economic Analysis
   Plant Design and Economics for Chemical Engineers, 5th Edition
   Storage Tank Analysis
   Welty, James R. et al. Fundamentals of Momentum, Heat, and Mass Transfer. 17th Ed. John
   Wiley and Sons, Inc. New York: 1984.
   Peters, Timmerhaus, and West. Plant Design and Economics for Chemical Engineers, 5th Ed.
Crimson Engineering Associates, LLC                                              10


   Appendix
   Sample Calculations

   Desulfurization Unit

           From Figure 1 in the lab manual,
                 2004 FCI for 10,400 BPSD: $7,000,000
                 2008 FCI:




                           needed to make up for FCI over 10 years
   Labor
         $20/hr*(25 man-hours/day)*(347 operating days per year) = $174,000/yr
   Added Price per Barrel of Diesel




   Desulfurization with Claus Unit
           Sulfur production: 12.835 ton/day
           From Figure 2 in the lab manual,
                   2004 Claus Equipment Cost: $110,000
                   2008 Cost:


           Total FCI HDS and Claus:
           Total TCI:



                             needed to make up for FCI over 10 years
   Profit from Sale of Sulfur
           Sulfur Price: $130/ton


   Added Price per Barrel of Diesel
Crimson Engineering Associates, LLC   11




      =$0.13/bbl

								
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