COMPARATIVE ANALYSIS OF VERSIONS OF OPERATION OF UNITS FOR OBTAINING ULTRAHIGH-PURITY CRYOGENIC PRODUCTS

摘要

In [1], we proposed a procedure that allows the production of ultrahigh-purity cryogenic products in air separation plants to be analyzed from the economic and technical point of view. This procedure was used to analyze how units for obtaining ultrahigh-purity nitrogen, argon, and oxygen function under various conditions. The conditions assumed for the calculations were: 1. the ultrahigh-purity nitrogen (UPN) unit consists of one rectification column for removing oxygen (residual impurity concentration 1 ppb, flowrate G_(UPN) = 1000 m~3/h); 2. the ultrahigh-purity argon (UPA) unit consists of two rectification columns for removing oxygen and nitrogen (residual impurity concentration 100 ppb, flowrate G_(UPA) = 100 m~3/h); 3. the ultrahigh-purity oxygen (UPO) unit consists of two rectification columns for removing argon and methane (residual impurity concentration 10 ppb, flowrate G_(UPO) = 100 m~3/h); 4. the thermodynamic parameters of rectification column operation are assumed to be the same as in [1]; and 5. the remaining initial data necessary for a technical and economic analysis are given in Tables 1-3. The results of the calculations are given in Figs. 1-3, which show the costs vs the relative reflux-to-product ratio βr at various values of thermal head ΔT in condensers (evaporators) of rectification columns, the overhead coefficient E_o, and the electricity rate C_(el). Taking the mixture separation into account, we used column packing as the contact device for UPAr and plates for UPN. Fin-plate condensers and evaporators were chosen, since in contrast to the coil type they ensure a minimal thermal head (at a level of 1 K). The calculations were done in U.S. dollars (means of calculation generally accepted in the world economy). A payback coefficient of 0.167 corresponds to the actual standard payback period (6 yr) and the value 0.25 was chosen with allowance for present-day tendency in the Russian economy to cut the payback period (4 yr). The electricity rate of 0.025 $/kWh is the weighted mean rate in the Russian economy and 0.065 $/kWh is the weighted mean rate in the West.