Specific features pertinent to calculation of a condenser with inclined tubes

Abstract

622The cellulose production process entails emissions of sulfurous compounds, substances polluting the atmospheric air. A soda recovery boiler unit (SRBU) and a fusion cake dissolving tank (FCDT), which is part of the SRBU are among the main sources of such emissions. The steam-gas emissions discharged from the SRBU fusion cake dissolving tank have the follow ing composition under normal conditions of its oper ation: steam (1.87 kg/m 3 ), fusion cake dust particles (19 g/m 3 ), hydrogen sulfide (0.25 g/m 3 ), sulfurous anhydride (0.18 g/m 3 ), and air (from 5 to 25 vol %). Dust particles consist of sodium carbonate, sodium sulfide, sodium sulfate, and insoluble inclusions. The temperature of steam-gas emissions is within the range 85-125°С. On the average, the amount of steam-gas emissions from the FCDT is 226 m 3 per ton of produced cellulose.In practice, various methods for preventing emis sions of harmful substances into the atmosphere are used: single stage schemes for recovering heat or removing fusion cake dust particles and sulfur con taining gases, and two stage schemes, in which the first stage serves for recovering heat, and the second stage serves for removing pollutants. However, none of them covers the entire scope of problems that have to be solved in purifying the emissions from the SRBU fusion cake dissolving tank; in addition, it was found that two stage schemes have rather low efficiency and reliability during long term operation [1].One way in which dust laden emissions with a high content of moisture discharged from the SRBU fusion cake dissolving tank can be purified consists of using the condensation method that was developed by the authors of this paper and which has been put in use at a number of production facilities. A description of this method can be found in [2,3]. The condenser, which consists of an inclined bundle of tubes placed at an angle of 15°-30° to the horizon, is installed upstream of the exhaust pipe and performs a few functions:(i) It condenses steam from steam-gas flow and essentially slows down its velocity in the exhaust pipe.(ii) It decreases the temperature of steam-gas flow.(iii) It captures dust particles.(iv) It absorbs sulfur containing admixtures by the condensed liquid.(v) It recovers the energy released during steam condensation.The use of the condensation method makes it pos sible to solve environment protection problems with out introducing additional chemical agents into the technological process, without increasing the expen diture of energy resources, without disturbing the technological parameters of the main process, and with returning the chemicals captured from steamgas mixture into the FCDT. Water cooling the con denser may be heated, as it passes through its tubes, to a temperature sufficient for using in the subsequent technological process.Calculation of the gas purification condenser con sists in determining the cooling surface area required for reduction of steam-gas flow velocity, efficient cap ture of dust and absorption of sulfur containing ad...