Study on Curing Effect and the Waste Heat Recovering Equipment Design of Flue Gas of Bulk Curing Barn

Dashuang LlU，Zenghan XU，Zemin SONG，Ye YANG，Jianbin MA，Zhenjie XlAO，Ruifeng LlU，Yongqin GE，Minjie ZOU

1.China Tobacco Hebei Industrial Limited Company，Shijiazhuang，050051，China；

2.Research Center of Tobacco and Health，University of Science and Technology of China，Hefei 230052，China；

3.Qiannan Branch of Guizhou Tobacco Company，Duyun 558000，China

Study on Curing Effect and the Waste Heat Recovering Equipment Design of Flue Gas of Bulk Curing Barn

Dashuang LlU1，Zenghan XU2*，Zemin SONG3，Ye YANG1，Jianbin MA，Zhenjie XlAO1，Ruifeng LlU3，Yongqin GE3，Minjie ZOU3

1.China Tobacco Hebei Industrial Limited Company，Shijiazhuang，050051，China；

2.Research Center of Tobacco and Health，University of Science and Technology of China，Hefei 230052，China；

3.Qiannan Branch of Guizhou Tobacco Company，Duyun 558000，China

In order to realize tobacco curing with energy saving and emission reducing and lower cost，the waste heat recovering equipment was designed and built on blowing-upward type bulk curing barn.The comparative experiment of tobacco leaf curing was conducted between a bulk curing barn with waste heat of flue gas and conventional bulk curing barn.The results showed that the effect of saving coal in bulk curing barn with waste heat of flue gas was obvious than the contrast.The coal consumption quantity was 1.531 kg per kg of dry tobacco leaf.The saving coal in bulk curing barn with use waste heat of flue gas was 0.181 kg per kg of dry tobacco leaf than the contrast and saving coal rate was 10.57%.The electricity consumption quantity was 0.593 kWh per kg of dry tobacco leaf.The saving electricity quantity in bulk curing barn with use waste heat of flue gas was 0.022 kWh/kg and the saving electricity rate was 3.58%than the contrast.The saving curing cost was 0.158 yuan per kg of dry tobacco leaf and saving cost rate 9.09%in bulk curing barn with use waste heat of flue gas than the contrast.The appearance quality，grade structure and primary chemical composition had no significant difference between bulk curing barn with use waste heat of flue gas and the contrast.

Bulk curing barn；Waste heat recovering equipment of flue gas；Tobacco leaf；Curing effect

I n China，tobacco curing in a bulk curing barn traditionally processes on basis of fired coals in a furnace producing heat and smoke that are transported into heating chambers through heat exchangers.The heated airs are then sent into a smoke-loading chamber with a circulating fan to warm tobaccos and promote physiologicalbiochemical changes， chemical changes and physical changes.Finally，the satisfied dry tobaccos can be obtained after yellowing，dewatering and drying.In the heat exchanger，the transferredsmokeswouldentera chimney and be discharged.In practice，however，the smokes still contain lots of heat entering the chimney.The research measured the temperatures of the chimney out of the heating chamber with an infrared thermometer were 108.4-156.7℃，averaging 129.9℃.In general，smoke temperature in the chimney is higher than that of chimney jamb and even as high as 200℃after entering the chimney with heat conductivity coefficient and heat exchange efficiency declined.Currently，it is hardly for smokes from bulk curing barns to be collected and reused in tobacco production domestically，so that the smokes are just wasted.Generally speaking，curing tobacco costs higher for it consumes more coals.What’s worse，toxic gases would produce from coal firing，such as CO2，CO，SO2，NO and H2S. Therefore，it is urgent and necessaryto resolve the issues occurring in tobacco curing，including cost saving and reducing coal consumption and environment pollution.The research collected waste heat from airflow-upward-type bulk curing barn by low-cost method and then heated airs in the barn，which supplied energy for tobacco curing，reducing coal quantity and environment pollution.Such practice increases tobacco farmer's incomes and reduce energy and pollution discharge，with low cost，which is conductive to sustainable development.

Materials and Methods

Materials

The testwas carried outin Fuquan City，Guizhou Province in 2013.The two airflow-upward-type barns are both equipped with a temperature and humidity controller. What’s more，one is equipped with a flue-gas waste-heat utilization equipment（T）［1-2］and the other is a control without the equipment（CK）.The test material was K326 ripe cutters.Tobaccos were strung onto tobacco sticks and hung from three tier-poles in every curing barn，totaling 360 poles.

Methods

Curing method Tobaccos were cured by the specific method of the controller in a bulk curing barn，with alternations upon tobacco changes.The curing method and time based on waste heat is the same as those in the control.

Measurements on chemical components of tobacco leaves The mixed samples in middle position were collected for chemicalcomponent analysis and all dried at 40℃，followed by grinding with a universal high-speed smashing machine and well mixing.

Besides，contents of total sugar，reducing sugar，nicotine，total nitrogen，protein，Cl-and K+were measured with a continuous flow analyzer（BRAN+ LUEBBE AA3）［2］.

Design and Construction of Flue-gasWaste-heatUtilization Equipment in the bulk Curing Barn

The design of the use installation of smoke waste heat

The flue-gas waste-heat utilization equipment is located above the top cap of the heating chamber，including a chimney，a heat exchange chamber，a smoke-collection chamber，and a connection chamber.The chimney is on one side of the heat exchange chamber，and the stack nozzle is above top ofthe heatexchange chamber.The other side of the heat exchange chamber is designed with a smoke-collection chamber.The smoke baffle plate is installed within the chimney which connects the smokecollection chamber，upper or down，with metallic conduits in order to promote circulation of high temperature flue gas and heat dissipation.Besides，hot airs can be guided into heating room of curing barns by connecting exit of heat exchange chamber and air intake of curing barns（Fig.1）.

Construction of flue-gas waste-heat utilization equipment

At building roof（1）and chimney（2）of a curing barn，a front opening should be remained on down part of the right wall of the chimney and a smoke-return chamber（8）should be constructed on the other side of the roof.The wall thickness of the chimney and smoke-return chamber should be 13 cm，based on standard bricks and the walls are then whitewashed with cement mortar.The size of the smokereturn chamber was length at 24 cm，width at 24 cm and height at 56 cm. One end of a weathering resistant steel tube （10）with outer diameter of 18 cm and tube wall of 4 mm is then inserted in down part of the chimney（2）and the height to roof is kept at 10 cm. The other end is inserted into the down part of smoke-return room（8）with the height to roof of 10 cm to guarantee the tuber entering smoke-return room through left walls.Subsequently，the chimney （2）was sealed with a fireproofing board （6）with thickness of 8 cm along the weathering resistant steel tube （10）.Then，for the other steel tube（9）with outer diameter of 18 cm and tube wall of 4 mm，one end is inserted in the opening of right wall of the chimney（2）and the other is inserted in upper part of left wall of the smoke-return room（8）to complete the smoke circuit.Two metal tubes are arranged from top to bottom with interval distance of 10 cm and the chimney walland smoke-return room are sealed.In addition，a door of smokereturn chamber（7）is designed on right wall of the smoke-return room （8）for cleaning dusts in chimney，with threshold height of 6 cm，door height of 56 cm，width of 32 cm and thickness of 6 cm.It is notable that the door（7）is made of fireproofing rock wool-basedcolor plates and the door is only opened at cleaning dusts.A heat exchange chamber（3）is built on the top of heating chamber （17）to encircle down part of the chimney （9），metal tubes（10）and smoke-return chamber（8）.For the heat exchange chamber，the wall thickness is 20 cm on basis of standard bricks，whitewashed with cement mortar and the top is reinforced concrete member with thickness of 10 cm（Fig.1）.

Table 1 Comparisons between coal consumption and electricity consumption of dry tobacco per unit

The size of the heat exchange chamber（3）is as follows:length at 180 cm，width at 220 cm，and height at 70 cm.Two cold air intakes（5）are designed on upper position of the thermally insulated wall（11），with height of 40 cm and width of 50 cm；the interval distance is 80 cm and the distance between the bottom margin and roof is 20 cm.For every cold air intake（5），inside wall is fixed with 2-3 folded plastic films and four sides of films should be 10 cm larger than those of the intake （5），which prevents heat from diffusion and allows air entering according to curing process.Besides，a hot air outlet of heat exchange chamber（12）should be designed on the center of the walls above cold air intake （14）with height of 40 cm and width of 90 cm，and bottom side of 10 cm away from roof.Then，a connection chamber （13）should be built above circulating fan platform to encircle heat exchange chamber，hot air outlet of heat exchange chamber and air intake.The wall thickness of the connection chamber is 20 cm base on standard bricks and whitewashed with cement mortar.The roof is constructed with reinforced concrete with thickness of 10 cm，and the inner size is as follows:length of 40 cm，width of 120 cm and height of 150 cm.The walls of the connection chamber（13）facing air intake （14）could be designed with a window （15）for convenience of inspection on the door with height of 80 cm，width of 90 cm and thickness of 4 cm.

Because of a clapboard （6）designed in the chimney，the smokes with higher temperature in below position could only enter smoke-return chamber（8）through the down-metal tube（10）and then be discharged with the chimney （2）through backflow in up-metal tube （9）.In the process，the metal tube would be heated with the smokes，based on which the airs in the heat exchange chamber（3）would be heated，so that the heated airs would enter a heating chamber（17）of the curing barn through the connection chamber（13）for auxiliary heating by a circulating fan to reduce coal consumption，save energy，reduce discharge and costs.

Table 2 Grading results of cured tobaccos

Analysis on Curing Effects

Energy-saving effects by using waste heat from smokes

The objective of using waste heat is to minimize consumption on coal and electricity and reduce costs provided tobacco quality guaranteed.The research conducted two contrast tests on basis of waste heats of tobaccos picked at the same time from the same parts with the same load （Table 1）. Specifically，coal consumption was in 1.476-1.586 kg for curing 1 kg tobaccos in T，with an average of 1.531 kg and in 1.691-1.733 kg in CK，with an average of 1.712 kg.It can be concluded that 0.181 kg/kg coal could be saved in T，and the average saving rate reached 10.57%.As for power consumption，T kept in the range of 0.578-0.608 kWh，with an average of 0.593 kWh and 0.599-0.631 kWh in CK，with an average of 0.615 kWh.It is obvious that 0.022 kWh/kg could be saved with saving rate of 3.58%.In addition，assuming coal price at 800 yuan/t and electricity price at 0.60 yuan/kWh，0.158 yuan/kg costs can be saved in T compared with CK and the saving rate reached 9.09.

Appearance quality and grade structure of cured tobaccos

Appearance quality of cured tobaccos For cured tobaccos，appearance quality basically kept similar in T and CK，showing insignificant differences. Specifically，tobacco leaf color was dominated by orange，supplemented by lemon yellow.Besides，the tobaccos also contained some variegated tobacco and the tobacco with green veins.Most tobaccos were ripe，and few were mature or overripe.The leafstructure was dominated by open，and most tobaccos maintained moderate body.In addition to that，most tobaccos contained oily and color intensity kept from moderate to strong.

Table 3 Primary chemical components in middle-part leaves of cured tobaccos

Grade structure As shown in Table 2，tobaccos were graded as per Standard of Flue-cured Tobacco Grading（GB2635-92）.The averaged proportion of higher-grade tobacco advanced 0.6 percent points in T compared with CK，but the proportion of mid-grade tobacco lowered 0.3 percent points.In general，grade structure of tobaccos is not declined by using waste heats.

Primary chemical components of cured tobaccos

The contents of chemical components and proportions in tobaccos decide tobacco quality and the research conducted detection on primary chemical components of cutters of cured tobaccos in T1（Table 3）.

It can be concluded from Table 3 that total sugar and reducing sugar contents of cured tobaccos kept higher in T1；nicotine and K2O contents were lower；total nigrogen，protein，Cl-and pH value showed little differences between T1 and CK1.These indicated that curing tobacco with waste heat has none adverse effects on tobacco quality.

Conclusion and Discussion

Significant reduction on discharge and cost by using waste heat

The curing barns with waste heat proved much economical，for example，coal and electricity saving rates were average 10.57%and 3.58%，and curing costs was average saving 9.09%. In other words，0.158 yuan could be saved for 1 kg cured tobacco.Assuming every 550 kg tobaccos can be produced from a barn and curing processes 7 times，608.3 yuan could be saved for one bulk in a season based on waste heats.The bulk using waste heats improves innertemperature and the flue-gas waste-heat utilization equipmentfunctions wellin heat preservation，preventing heat diffusion and reducing coal consumption.

Less effects on appearance quality and grade structure of cured tobaccos by using waste heats

The research proved that appearance quality of tobaccos changed was little between T and CK.Furthermore，averaged proportion of higher-grade advanced 0.6 percent points in T compared with CK，but the proportion of mid-grade tobacco lowered 0.3 percent points，showing insignificant differences.

Using waste heat conductive to guaranteeing quality of cured tobaccos

Theprimarychemicalcomponents of cured tobaccos are much similar in T and CK.For instance，except of total sugar and reducing sugar，nicotine，total nitrogen，protein，Cl-content and pH value all keep proper，which incorporates thatusing waste heat would not lower tobacco quality，because waste heats are just used for curing tobaccos instead of changing curing techniques.In practice，flue-gas waste-heat utilization equipment functions well in heat preservation，slowing down temperature decreasing，which would just benefit quality of cured tobacco.

［1］XU ZH（徐增汉），ZHU GC（朱贵川），SONG ZM（宋泽民），et al.The flue-gas waste-heat utilization equipment of tobacco in bulk curing barns（烟叶密集烤房烟气余热利用装置）［P］.ZL 201320096091.4

［2］GENG FQ（耿富卿），LIU MJ（刘明竞），YANG X（杨相），et al.Study on curing effects of flue-cured tobacco curing ways（不同烤烟烘烤方式的烘烤效应研究）［J］.Guangdong Agricultural Sciences（广东农业科学），2012（4）:29-31.

Responsible editor：Xiaoxue WANG

Responsible proofreader：Xiaoyan WU

密集烤房烟气余热利用及烘烤效果的研究

刘大双1，徐增汉2*，宋泽民3，杨晔1，马建彬1，肖振杰1，刘瑞峰3，葛永琴3，邹敏杰3（1.河北中烟工业有限责任公司，河北石家庄050051；2.中国科学技术大学，安徽合肥230052；3.贵州省烟草公司黔南州公司，贵州都匀 558000）

为了节能减排、降低烘烤成本，在气流上升式密集烤房上面设计建造了烟气余热利用装置，并对利用烟气余热的密集烤房和对照密集烤房进行了烟叶烘烤对比试验。结果表明，利用烟气余热的密集烤房节煤效果明显，平均1 kg干烟叶的耗煤量为1.531 kg，比对照烤房节省0.181 kg，节煤率为10.57%；平均1 kg干烟叶耗电量为0.593 kWh，比对照烤房节省0.022 kWh/kg，节电率为3.58%；平均节约烘烤成本0.158元/kg（干烟），节本率为9.09%。利用烟气余热的密集烤房的烤后烟叶的外观质量、等级结构和主要化学成分与对照密集烤房的没有明显差异。

密集烤房；烟气余热利用装置；烟叶；烘烤效果

河北中烟工业有限责任公司“河北中烟福泉基地‘钻石’品牌导向的原料生产体系研发”（111201315524）；贵州省烟草公司黔南州公司“烟叶密集烘烤问答研编”｛黔南烟办［2012］17号｝。

刘大双（1981-），男，河南获嘉人，硕士，农艺师，主要从事烟草栽培生理及烟叶质量评价研究，E-mail：dashuangliu@126.com。

2015-10-03

Supported by Hebei Industrial Co.，LTD.of China Tobacco （111201315524）；Qiannan Co.LTD.Of Guizhou Industrial Co.，LTD.，China Tobacco（［2012］17）.

*Corresponding author.E-mail:xuzh0707@ustc.edu.cn

Received:October 3，2015 Accepted:November 15，2015

*通讯作者，E-mail：xuzh0707@ustc.edu.cn。

修回日期 2015-11-15