Design Paste.docx

1.1

Design of reaction Furnace

Here the equipment called muffle furnace is actually a plug flow reactor provided with refractory linings to avoid material damage on the account of liberation of high exothermic heats of reaction and combustion. In this thermal reactor we treat acid gas with air to produce sulfur dioxide which then reacts in the claus three stage reactors to produce elemental sulfur. As we are oxidizing or burning hydrogen sulfide in the presence of air, the reaction will be highly exothermic, thus liberating high heat contents, so we named it a furnace. Design is totally on reactor base calculations. The basic design steps included are (keeping in mind that due to absence of kinetic data the reactor has to be designed based upon the concept of residence time): Step-1: Estimation of Residence time (ԏ) Step-2: Calculation of volumetric flowrate (u) Step-3: Calculation of volume of reactor (v) Step-4: calculation of length of reactor (L)

Step-5: Selection of refractory material Step-6: Calculation of internal diameter of reactor (Di) Step-7: Calculation of thickness of reactor (t) Step-8: Calculation of outer diameter (Do) Step-9: Calculation of the volume of steel required (Vs) Step-10: Calculation of the mass of steel required (Ms) Step-11: Calculation of pressure drop (∆P) The assumptions are taken before coming to the actual design are: Plug flow Steady state Constant density Constant tube diameter No mixing in axial direction Complete mixing in axial direction A uniform velocity profile across the radius Step-1: Estimation of residence time (ԏ) Residence time (ԏ) = Volume of reactor (V) / Volumetric flowrate (u) The residence time is actually based upon the results obtained from the information and calculations of the kinetics of reactions involved. Since kinetic data is not available we have to take help from literature. The residence time is taken as 2.5 seconds. Residence time (ԏ) = 2.5 sec Step-2: Calculation of volumetric flowrate (u) For the calculations of volumetric flow rate we proceeds as: Ɛ = (Uo – Ui) / Ui Whereas: Ɛ = Expansivity (dimensionless) Uo = outlet volumetric flow rate (m3/hr) Ui = inlet volumetric flow rate (m3/hr)

Now: Inlet volumetric flow rate (Ui) = Inlet mass feed flow rate (mi) ÷ density of inlet steam (ῥ) Inlet mass feed flow rate (mi) = Mass flow rate of stream-01 ÷ mass flow rate of stream-2 For the calculations of the mass flow rate of both streams we must know the average molecular weight of both streams. Stream-01 Composition Component Mole fractions Molecular wt. (kg/kgmol) H2S 0.523 34.0 CO2 0.376 44.0 CH4 0.004 16.0 H2O 0.010 18.0 C2H6 0.0008 30.0 C3H8 0.0001 44.0 Average molecular wt. of stream-01 = (0523 × 34.0) + (0.376 × 44.0) + (0.004 × 16.0 ) + (0.10 × 18.0) + (0.0008 × 30.0) + (0.0001 + 44.0) = 34.60 kg/kgmol Similarly: Stream-02 compositions component O2 N2

Mole fraction 0.210 0.790

Molecular wt. (kh/kgmol) 32.0 28.0

Average molecular wt. of stream-02 = (0.210 × 32.0) + ( 0.790 × 28.0) = 28.84 kg/kgmol Now: Mass flow rate of stream-01 = 198.80 kgmol 34.60 kg Hr 1 kgmol = 7490.0 kg/hr

Inlet mass feed flow rate (mi) = 6878.50 + 7490 kg/hr = 14368.50 kg/hr Now we are to calculate the density of the inlet stream (Di). We know general eqn. of gas PV = nRT OR PV = M(RT) / (M.W) M/V =ῥi= P(M.W) / RT For the calculations of molecular wt. of the gas we proceed as follows: The composition of the stream formed after the mixing of stream-01 and stream02 is as follows: Mixed stream compositions components Flow rate (kgmol/hr) H2S 104.03 CO2 74.83 CH4 0.95 H2O 18.8 C2H6 0.16 C3H8 0.02 O2 54.54 N2 205.2

Mole fraction 0.226 0.163 0.002 0.041 0.0003 0.00004 0.119 0.447

Molecular weight (kg/kgmol) 34.0 44.0 16.0 18.0 30.0 44.0 32.0 28.0

Molecular wt. of the mixed stream = (0.226 × 34.0) + (0.163 × 44.0) + (0.002 × 16.0) + (0.041 + 18.0) + (0.0003 × 30.0) + (0.00004 ×44.0) + (0.119 × 32.0) + (0.447 × 28.0) = 32.10 kg/kgmol Now: Density = (1 atm) (32.10 kg/kgmo) ÷ (0.0821) (416.2 k) = 0.94 kg/m3 Now from eqn. Inlet vol. flow rate (ui) = 14368.50 kg/hr ÷ 0.94 kg/m3 = 15285.60 m3/hr