PTQ Q3 2022 Issue

New graphical procedure to design reactor supports used in industry Two reactor models used in gas recovery demonstrate a new design strategy that can lead to significant savings in material cost and engineering design time

Osama Bedair Consultant

C hemical reactors are used extensively in hydrocar- bon extractions and gas recovery processes. Rapid expansion in the petrochemical industry has acceler- ated the development of various reactor models. In gas cool- ing (or condensing) operations, for example, vertical vessels are often used to facilitate the contact of hot gas with cooling liquid. Water is used for cooling or condensing processes. The structural design of the support system requires knowledge of reactor operation and maintenance procedures to define the applied loading. Engineering planning that includes pipe routing and tie-in details must be developed for detailed installation of the reactor on the supporting system. A design interface between process, mechanical, electrical, instrumentation, and civil engineering disciplines is required to examine all engineering aspects prior to execution. Much of the published work 1-9 has focused on the process design aspects of chemical reactors. Very few structural guidelines are available in engineering design codes of prac- tice and industry standards dealing with structural aspects. Over the past few years, industry leaders have made exten- sive efforts to develop economic procedures in mega projects that overlooked critical structural design issues. Against this backdrop, a new strategy to design the con- crete supports of reactors can be used in the refinery and petrochemical processing industry. The procedure is effective and leads to significant savings in material cost and engineer - ing design time. The finite element method is used to idealise the load transfer from the reactor to the attached supports and to simulate structure-soil interaction. The procedure is demonstrated in the design of two reactor models used in gas recovery units. Design space concept Chemical reactors vary significantly in size and weight in the hydrocarbon industry. It helps to examine an effective design spectrum that can be utilised by various engineering disci- plines to design industrial reactors of multiple sizes. Consider a typical reactor shown in Figure 1 with a diam- eter (D R ) and height (H z ) measured from the top of the base plate. The reactor is connected to a circular skirt with an internal diameter (D Sk ) to reduce heat transmission to the neighbouring structures. The skirt is welded to a base plate of thickness (t P ). External heat exchangers are connected in some cases to the reactor valves to regulate feedstock inlet temperatures.

Cylindrical skirt

D S K

See Fig.2

Anchor bolt

t P

Base plate

D P1

D P

Octagonal pedestal

t F

Void form

Figure 1 Typical vertical reactor

Anchor rods are installed on the octagonal concrete pedestal around the skirt perimeter. Void form (or cushions) is used on the lower surface of the pile cap to resist the up-heave pressure. The concrete pedestal is projected by distance (D P ) measured from the top surface of the pile cap. The exposed length (D p1 ) is determined by piping requirements. Figure 2 shows Section (B-B) of the reactor support sys- tem to identify the parameters used in the graphical concept. The reactor footprint is identified by the long dashed cen - tral circle in light blue. Pile-cap dimension is denoted by (L F ) x(B F )x(t F ). The octagonal pedestal geometry is defined by the parameters ( β ) and ( α ). The long side is denoted by ( β ) and the short side by ( α ). The pedestal cross-sectional area is denoted by (A P ). The small blue circles identify pile locations. The number of rows and columns are denoted by (m) and (n), as shown in the top left corner. Nominal pile diameter is

PTQ Q3 2022