a decision tree for technology selection of nitrogen production plants

nitrogen is produced mainly from its most abundant source, the air, using three processes: membrane, pressure swing adsorption (psa) and cryogenic. the most common method for evaluating a process is using the selection diagrams based on feasibility studies. since the selection diagrams are presented by different companies, they are biased, and provide unsimilar and even controversial results. in order to provide an impartial evaluation means and getting an integrated and reliable selection method, all existing diagrams have been reviewed in this paper and integrated into a single diagram. with the help of proposed selection diagram and considering the operating conditions, flow rate and purity of nitrogen, the most economic technology for separation of nitrogen from the air can be chosen. of course for some values of purity and flow rate, more than one technology can be selected. in these ranges, other parameters such as economic value of by-products phase of delivered product fluid (liquid or gaseous) and the product applications should be taken into account. in order to provide an engineering tool for selecting the most economic technology of nitrogen production, a decision tree is proposed. with this decision tree one can choose the most suitable technology for its production. heuristic rules along with literature data are implemented within the decision tree and it has been validated and updated with domestic nitrogen producing companies. generally for high capacity of nitrogen production, the cryogenic process is the most economical alternative and for medium and low capacities, psa and membrane systems are the best choices, respectively. finally, a computer program is proposed to find out the most suitable technology for nitrogen production.