Modeling of the synthesis plant of 55% formalin solution, calculation of the material balance and thermal loads of devices

The paper presents the modeling of an industrial plant for producing a 55% formalin solution with a capacity of 180 000 t/y in Aspen Plus. The model is based on the oxidative dehydrogenation of methanol over an iron-molybdenum catalyst (Formox process) and corresponds to the operating parameters of the KF-3 unit. A calculation model includes feed preparation units, a stoichiometric synthesis reactor, a contact-gas cooling system, and an absorption column. The gas-phase stage was described using the Peng – Robinson equation of state, while the absorption column was modeled with the combined NRTL-RK method. To correctly account for the behavior of formaldehyde in an aqueous medium, a user-defined component representing its hydrated form was created; an auxiliary block was also introduced to convert methylene glycol to an equivalent mixture of formaldehyde and water for material balance. A material balance was calculated for the main process components, and equality between inlet and outlet streams was confirmed. Specific consumptions of methanol, water and air per unit of formalin solution produced were determined. A thermal analysis of the plant was performed, showing that the main contribution to the overall heat duty arises from the reaction stage and the contact gas cooling stage. The obtained results can be used for equipment selection and for evaluating the energy parameters of the process.