Large Volume Inorganic Chemicals - Ammonia ... - ammk-rks.net

Chapter 3Achieved environmental benefits• tail gas levels of 40 – 50 ppm NO x (82 – 103 mg NO x /m 3 ) are technically feasible(15 bar, production of a typical low strength nitric acid, completely optimisedabsorption columns)• the combination of technical and economic viability of a new absorption column,combined with the high absorption pressure, can result in values of 100 – 150 ppm(210 – 308 mg NO x /m 3 ).The existing absorber column design limits the achievability of these figures, as absorptioncolumns need to be retrofitted or replaced by a more modern design.Cross-media effects• high absorption pressures can reduced steam export• extended absorption with an adjusted form of cooling can be expected to use more energy.Cooling systems are necessary to reach the lower temperatures, hence heat losses to theenvironment may increase, discharge of warm water may have negative effect on receivingwater bodies• H/H systems show a lower NO yield and generate more N 2 O.Operational dataSee description.ApplicabilityHigh pressure systems. In existing plants, the pressure in the absorption unit can be raisedwithin certain technical limits. Generally applicable for new plants, usually designed as an M/Hplant.Extended absorption can be applied to existing and new plants. In existing plants, retrofitapplications involve adding a second absorption column in series with an existing column, orreplacing the old column(s) by a new design absorption column. New plants are generallydesigned with a single large column that is an integral component of the new plant design. Theextended absorption abatement using a different form of cooling is only practical in nitric acidplants operating with an absorber pressure above 9 bar. Also refrigeration equipment andassociated pipework will need additional expenditure. Haifa Chemicals Ltd. added a secondabsorption column to the existing set-up (7 bar).The HEA column can be applied both in existing and new nitric acid plants. In existing plants,the HEA column can be placed in series with an existing absorption tower.ZAK, Tarnow decided to replace its existing eight production lines by one M/H line (5/15 bar)of 700 tonne HNO 3 /day. The Instytut Nawozow Sztucznych (INS) – which is an academicinstitute that is working for this plant – developed a computer program to optimise the design ofthis new absorption column. This program could also simulate the performance of theabsorption column. Table 3.11 shows the results of the high absorption pressure and theoptimum design (structure of the sieve plates, distance between the sieve plates, size of thecolumn).Large Volume Inorganic Chemicals – Ammonia, Acids and Fertilisers 119