| There is not only no recovery of high grade waste heat in the old acetone recovery process of cellulose acetate tow production, but also electrical power consumptionfor circulating cooling water what is used for condensation and cooling of the acetone-steam gas mixture. In recent years, there are projects of waste heat recovery, but both single segmental baffle shell-and-tube exchanger technology and stuffing absorbing tower technology did not achieve the ideal effect. Single segmental baffle shell-and-tube heat exchanger is with bad pressure drop performance while packed absorption tower needs middle media, heat temperature difference gradually become smaller, what leads to low heat exchange efficiency.This paper do a further study on the non-steady state, non-analytical steam continuous flow of in the case of less than20KPa of the shell side pressure drop in orderto recover waste heat continuously in a high efficiency. The main research includes:⑴According to multi component with phase transition characteristics, the total heat exchanged during peak condition of the acetone-steam gas mixture is calculated by stagesand checked by energy and mass conservation mode, as a result, the deviation is about7.56%.Complete the design of heat exchanger tube part: shell diameter900mm, length6m, pipe number482, heat exchange surface227m2.⑵In the condition of the acetone-steam gas mixture, studying the relation between the baffle or operating parameters such as baffle cut-fraction, baffle spacing, spiral angle, flow rate and the shell-sideperformance including heat transfer coefficient, pressure drop of single helix baffle shell-and-tube exchanger and single segmental baffle shell-and-tube heat exchanger by using HTRI software. Conclusions are drawn as bellow:Flow rate of tube side is inversely proportional to resistance of shell side slightlywhile is proportional to heat transfer coefficient. It should be taken a comprehensiveconsideration of benefit of waste heat recovery and energy consumption of the pump to determinate flow rate of tube side. Flow rate of shell side is inversely proportionalto resistance of shell side. However, the effect of flow rate of shell side on pressuredrop of single helix baffle shell-and-tube exchanger is much fewer than that of singlesegmental baffle shell-and-tube heat exchanger, thus, helix baffle is very suitable forthe non-continuous and variable flow condition. Shell side resistance of helix baffle isabove36%of that of single segmental baffle. The heat transfer coefficient of helixbaffle is slightly lower than that of single segmental baffle, but it is not obvious whe n the helix angle less than15degrees. Taking the heat transfer coefficient of unit pressure drop as a comprehensive performance measurement, the helical baffle heat exchanger is better than the single segmental baffle heat exchanger when the helix angle isabout15degrees. As the spacing of the single segmental baffle increases, the resistance decreases rapidly and the heat transfer coefficient decreases slowly, while as the spacing of the helical baffle increases, resistance does not change significantly, when the space is about500mm, the heat transfer coefficient achieves the optimal effect, buthave no significant difference with other spaces.According to the result of design, a1/4type single helix baffle shell-and-tube exchanger had been produced and applicator in the waste heat recovery system, and thenthe operation effect had been calculation. In the summer the average temperature ofbrine water at the inlet is30.6℃, while at the outlet of heat recovery system, the average temperature is risked to61.42℃.It brings adsorption systems about600mmwater column, namely of6kpa pressure drop, in less than15kpa of which is expected in design because of the heat recovery system. According to the theoretical calculation, the energy saving benefits throughout the year is about1.27million yuan becauseof the operation of the waste heat recovery system. |
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