# Theoretical calculation models

Many production and storage operations using VOC in the industry can be source of atmospheric emissions. However, in many cases installation don't have canalised outputs with a real throughput (only simple atmospheric vents). Then, emissions can only be determined using theoritical models (no realistic measurement can be done).

In order to evaluate total VOC air emissions during an industrial process, we can concider the process as several succesive unit operations. Therefore the total emissions are equal to the sum of theoretical calculated emissions on unit operations.

For example, a making process consisting in loading a solvent in a vessel, heating it and then transfering it to another vessel, can be split in three successive unit operations : loading, heating, transfering.
A loading model can be used to calculate emissions during loading and transfering unit operations and a heating model for the heating unit operation.

Envmodels theoretical models working with single or multi solvents can be used to calculate air emissions during the following unit operations:

All models are either "standard" models from various references (EPA, chemical handbooks, various scientific publications), or "specific" models (new models or slightly modified standard models) developped by Envmodels in order to take consideration of specific installations (immiscible products, installation with condenser, etc).

In the case of models using "miscible multi-solvents", mixing are considered as perfect solutions : Raoult's law is applicable and activity coefficients are negligible.

Environmental Models