Mechanical design for height of a formaldehyde fixed bed reactor

Height of Fixed Bed Reactor for Formaldehyde Production

The production of formaldehyde through the oxidation of methanol is a crucial process in the chemical industry. A fixed bed reactor filled with a silver catalyst is commonly used for this process. To ensure safe and efficient operation, a mechanical design is required for the construction of the reactor.

Process Design Parameters

The following process design parameters have been developed by process design engineers:

- Catalyst: Silver

- Reactor length: 5 m

- Reactor diameter: 2.4 m

- Catalyst form: Crystalline granular form

- Tube height: 4 m

- Inlet stream temperature and pressure: 149.6 °C and 28.0 psi

- Outlet stream temperature and pressure: 343 °C and 25.0 psi

- Material of construction: Carbon steel

Mechanical Design Considerations

The mechanical design of the reactor must take into account various safety parameters, structural supports, and other considerations, including:

- Corrosion allowance: The shell thickness will be increased to provide a corrosion allowance.

- Pressure shocks: The head section will be designed to withstand pressure fluctuations.

- Structural supports: The reactor will be designed with adequate structural supports to ensure stability and safety.

- Manhole provisions: The reactor will be equipped with manhole provisions for easy access and maintenance.

- Flange fittings: The reactor will be designed with flange fittings to facilitate connections to other equipment.

Mechanical Design Calculations

The mechanical design solver will calculate the following:

- Height of the reactor

- Head thickness

- Shell thickness

- Crown radius and knuckle radius for the ellipsoidal head

The mechanical design of the fixed bed reactor for formaldehyde production is a critical step in ensuring safe and efficient operation. By considering various safety parameters, structural supports, and other considerations, the reactor can be designed to meet the required process conditions and ensure reliable operation.

 

Mechanical design of fixed bed reactor model

 

Inner Diameter of the reactor Di = 2.4 m

Radius of the reactor r = 1.2m

Minimum thickness of reactor t = PDi

                                                     2fj – P

Where P is the design pressure = 3.5* 10⁵ N/m²

           f is the design stress       = 95*10⁶ N/m²

           Thickness of the reactor =    3.5*10⁵*2.4             

                                                        2*0.85*95*10⁶ – (3.5*10⁵)       

                                                = 5mm

  Assume Corrosion allowance as t = 3mm

     T = 5mm+ 3mm

         = 8mm

Outer Diameter of the reactor Do = Di + 2T

                                                      = 2400mm + 2*8

                                                      =2416mm

                                                 Do = 2.416m

Crown Radius Ro = 0.82Do

                              = 1.98m

Knuckle Radius r_o = 0.148Do

                              = 0.357m

Outside height of the ellipsoidal head:

     ho = Ro - [ (Ro-0.5D_o)(Ro+0.5D_o-2r_o)]

            =   1.98-[(1.98-(0.5*2.416))(1.98+(0.5*2.416)-(2*0.357)]

         =0.19m

Total height of the reactor H = h + 2ho

Where h = height of the reactor = 5m

                       H = 5 + 2*0.19

                           = 5.5m

Fixed bed reactor model