| Introduction |
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| Final cooling of coke gas is intended for reduction of its temperature after sulfate branch from 55 - 57 °Ñ to 25 - 30 °Ñ, which is favourable for benzene hydrocarbon absorption , and its purifying from naphthalene and tar materials. According to classical technology plantable or shelfable devices are used for final cooling of coke gas, in which gas and coolling water move in different directions, but the heatexchange occurs during the direct contact between them. Water warmed up to 35 - 37 °Ñ is coolled by air in special cooler down to 23 - 25 °Ñ and againe pumped into a gas cooler (the open water cycle). When cooling gas in a cooler the condensation of the vapours of naphthalene occurs, which stands out in the form of small crystals and speeds away together with coolling water. Before presenting of this water into special cooler the naphthalene is separated in settlers or extracted by the coal tar in plantable device, which is placed in the lower part of a cooler. |
| Methods for solving problem of harmful releases in the open water cycle |
| The disadvantage of such a scheme of final coke gas cooling is that during the contact with gas the water is saturated by cyanic hydrogen, hydrogen sulfide, naphthalene, benzene hydrocarbons and other harmful components, the majority of which during water cooling process in special cooler are standed out into atmosphere. The practice of coke-chemical enterprises work shows that special coolers for cooling of circulating water of final gas cooler are the largest source of harmful releases in catching department of chemical coking products . As for the Ukrainian coke-chemical plants research data the releases of harmful components into atmosphere from special coolers of final cooling are in gram per ton of gross coke: cyanic hydrogen - 180; the hydrogen sulfide - 60, ammonia - 30, benzene - 250, naphthalene - 210, phenols - 20. |
| The analysis of this problem shows two possible ways of its decision: |
| - to make the cycle of circulating water in the final gas cooler (FGC) closed that is to cool water not in a special cooler, but in plate or spiral heatexchangers with technical water; |
| - to cool coke gas by technical water in cooler, excluding direct contact of the phases that is to use separating walls. |
| The experience of FGC usages with closed water cycle has found the serious disadvantages of such a scheme, as follows: |
| - a quick efficiency drop of water cooler operation because of sediment of naphthalene and tar materials in them that requires the frequent soaring or washing by hot coal oil; |
| - an accumulation in circulating water cyanides, rodanides and the other salts, causing escalated corrosion of the equipment; |
| - a deterioration of quality of absorbtion oil in benzene branch because of raised concentrations of cyanic hydrogen in gas; |
| - an increase the consuption of the soda and amount of the ballast salts in sulphuric-cleaning department. |
| For eliminating these defects different methods of extraction of cyanic hydrogen from circulating water FGC are offered , including by blowing the domain and inverse coke gas, water steam under vacuum, by means of sulphuric ferric, formaldehyde and other reagents. However these methods require the significant additional expenseses associated with formation of difficult utilized wastes and so have not got the practical application. |
| The second way of problem decision of atmosphere contamination in branch of final cooling of coke gas that is gas cooling in coolers of surrface type, introduces more simple and efficient. In 70-th years of past century for this purpose at the factory in Niyuporte (England) gas cooler with horizontal pipes was installed . There is also more late experience of gas cooler with horizontal pipes on Mariupoliskiy coke – chemical plant. For removing the naphthalene scales on pipes the between-pipe space of such coolers is irrigated by oil or tar. The disadvantages of such devices are crockhood, big amount of trumpet lattice and water-divide lids, difficulty of the service. |
| The company "Alpha Laval" designed and manufactured on order of Avdeevskiy coke-chemical plant the spiral heatexchanger for final cooling of coke gas on type of devices, used on some coke-chemical plants as deflegmators and capacitors in benzene branches. In this device water moves on spiral channel by height beside 2 m and width 15 mms from periphery to the centre of the device, but gas moves in cross direction between wall of the spiral water channel from top to bottom. At present time the adjustment of working cooler operation and estimation of its efficiency is produced . Because danger to pollute the water spirals by hard scales which are inaccessible for cleaning, the scrub-up water coolling from weighted admixtures is required. |
| Final gas cooler’ development and calculations |
| From the theoretical standpoint the highest intensity of heatexchange between coke gas and water can be provided in pipe-like device under transverse pipes washing by gas, providing strong turbulization of gas flow, and water motion in pipe at the speed of around 1 m/sec, preventing contamination scales in them. |
| We designed a final gas cooler, consisting of standard heatexchangers, located horizontally one above others and united consecutively for gas and water flow. For removing the naphtalene scales the irrigation of beetwen-pipe space by water-tar emulsion is provided . In accordance with calculation for cooling the 120000 m3/hour of gas from 55 to 30 °C it is required 2300 m2 surface of heatexchange which corresponds to 9 heatexchangers Ø 1200 mms with length of pipes 4 m and Ø 25*2 mms, separated on 3 parallel sections on 3 heatexchangers, united consecutively, in each. On the other variant the use of standard capacitors-coolers with pipes Ø 38*2 mms and length 4 m is provided. For cooling the given volume of gas heatexchange with the surface 2800 m2, corresponding to 2 parallel sections on 2 heatexchangers in each is required . |
| The offered scheme of final cooling of coke gas allows us completely to exclude the releases of HCN and other harmful components into atmosphere, requires less capital and working expenditures. |
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