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10ЭНЕРГЕТИКА И ЭКОЛОГИЯ
ENERGY AND ECOLOGY
Статья поступила в редакцию 06.02.10. Ред. рег. № 712 The article has entered in publishing office 06.02.10. Ed. reg. No. 712
УДК 691.421
ОПТИМИЗИРОВАНИЕ ПРОЦЕССА ПРОИЗВОДСТВА И СУШКИ КИРПИЧА
М. Саиди, М. Хамиане, А. Бенмаунах, Б. Сафи
Отдел материалов, научно-инженерный факультет, Лаборатория минералов и композитных материалов, Университет Бумердес Бумердес 35000, Алжир Тел./факс: (213)(24)816408; E-mail: saidimouh@yahoo.fr
Заключение совета рецензентов: 26.02.10 Заключение совета экспертов: 08.03.10 Принято к публикации: 15.03.10
Строительные материалы играют важную роль в экономике страны. Эта промышленность включает в себя разнообразный диапазон изделий от простого глиняного горшка и строительного кирпича до технической керамики и промышленных цементов.
Рост этой промышленности важен, поскольку создание производственных предприятий становится ежедневной реальностью. Создание завода зависит от наличия качественного сырья, средств производства, хорошей базы знаний и условий работы, позволяющих осуществить отличный контроль за процессом производства. Таким образом, строительные материалы, строительный кирпич в частности, играют огромную роль в развитии экономики страны.
Мы заинтересовались изучением производства кирпича в Будуау (восток Алжира) с технологической, тепловой и экономической точки зрения; серьезные исследования были проведены с точки зрения использования тепла, целью которых было рассчитать приемлемый режим производства кирпича и горения газа.
Исследование теплового баланса позволяет понять схему расчетов и узнать потребление энергии, используемой в печи.
Эта работа позволила сократить использование газа на 63,5 м3/ч и получить энергетическую прибыль в 266,37 кДж/кг продукта и использовать сушку и печь с максимально возможной тепловой эффективностью.
Ключевые слова: тепловой баланс, обжиг, материалы, оптимизация, процесс, сушка.
OPTIMIZATION OF THE PROCESS OF COOKING AND DRYING OF BRICK
M. Saidi, M. Hamiane, A. Benmounah, B. Safi
Department of Material Engineering, Faculty of Science and Engineering,
Materials Minerals and Composite Laboratory, University of Boumerdes Boumerdes 35000, Algeria; Tel/Fax: (213)(24)816408; E-mail: saidimouh@yahoo.fr
Referred: 26.02.10 Expertise: 08.03.10 Accepted: 15.03.10
The construction materials play an enormous part in the economy of the country; this industry comprises a very varied range of products going of simple pottery passing by brick of construction until the technical porcelain and the industry of cements.
As, this production takes a so important rise as the realization of manufacturing plant becomes a daily reality. This realization of quite quantitative factory that qualitative depends on the availability of a raw material of quality, means of production in good knowledge and operating condition to make allowing a perfect control of the process. Considering, the enormous part which plays the construction materials in particular the bricks of construction in the economy of the country.
We were interested to make a study concerning the production unit of bricks of Boudouaou (east of Algeria) on the technological, thermal and economic level since the essential study is made on the thermal part in order to calculate the acceptable mode of cooking and to calculate the combustion of gas.
The study of the heat balance enables us to know how calculations can be carried out and of knowing how and the energies brought to the furnace spent are consumed.
This study enabled us to make a saving in gas in the order of 63.5 m3/h and to make a profit of energy of 266.37 kJ/kg of product and to obtain a better use of the drier and furnace with a possible maximum thermal efficiency.
Key words: heat balance, cooking, materials, optimization, process, drying.
Introduction
The use of clay for the manufacture of construction materials goes back to the oldest times of the history of the man, become of a share an art and in addition an industry.
The construction materials play a very important part in the economy of the country, this industry comprises a very varied range of products. As, this production takes a so important rise as the realization of manufacturing plant becomes a daily reality. This realization of quite quantitative factory that qualitative depends on the availability of a raw material of quality, means of production in good state of operation and aknowledge to make allowing a control of the process.
Our study consists in optimizing the processes of drying and cooking which remain the largest consumers of energy. In order to decrease the quantity of heat and gas, we were interested in calculations of the various heat balances and the acceptable curve of cooking which remain the most important stages in the manufacture of
Список и List
bricks. This study is made on the basis of experimental data of the production unit of bricks "Colonel Amirouche" of Boudouaou.
Experimental
In the first part, we took all the experimental data necessary to calculations of the various heat balances. This production unit uses two types of clay whose proportions and flows of production are summarized in Table 1.
Таблица 1
Производительность установки
Table 1
Productivity of the unit
Matter Gray Clay 66,67 % Yellow Clay 33,33% Water Drying Cooking
Flow, T/h 14,45 7,23 3,31 12,95 8,59
Таблица 2
[ых данных
Table 2
e data
Source data for calculation Measuring unit Value
Ph: time productivity of the tunnel kiln kg/h 8 856,768
Pci: lower calorific value of fuel kJ/m3 37 136,18
Vai prat: quantity of air practically necessary to combustion M3/m3 18,97
Trai: temperature of the ambient air brought in the circuit of combustion °C 20
Cair: specific heat of the air to this temperature kJ/m3 °C 1,304
Tin: initial temperature of the parts at the entry °C 60
Cin: specific heat of the parts (heat-storage capacity) kJ/kg °C 0,847
Pf: loss on the ignition % 16
Mbriq: mass brickwork of coach - firebrick Ml - porous firebrick m2 kg kg/wag kg/wag 6 615 3 780 2 835
Cbriq: heat-storage capacity of brickwork kJ/kg °C 0,842
Mmet: mass of metal part coach kg 1 748,38
Cmet: heat-storage capacity of metal kJ/kg °C 0,481
Nh: number of coach entering the furnace Wag/h 0,611
Ceau: Heat of evaporation of 1 kg of water kJ/kgH2O 2 500
h: relative humidity of the part % 4,76
Tp: temperature of cooking °C 900
Cpin: heat-storage capacity of the part with Tp Kj/kg °C 1.1
QAl2O3: Quantity of heat absorptive by dissociation of the kaolinite brought back 1 kg from Al203 Kj/kg Al2O3 2 100
Al2O3 %: content of Al2O3 of the dry ceramic masses % 12
International Scientific Journal for Alternative Energy and Ecology № 5 (85) 2010
© Scientific Technical Centre «TATA», 2010
М. Саиди, М. Хамиане, А. Бенмаунах, Б. Сафи. Оптимизирование процесса производства и сушки кирпича
Vf: quantity of smoke coming from the furnace m3/m3 20,42
tf: temperature of smoke °C 150
Tim: average temperature of the accumulation of the firebrick °C 170
Cbrl: heat-storage capacity of brick kJ/kg °C 1,02
T2m: average temperature of the accumulation of heat of porous firebrick °C 270
Cbr2: heat-storage capacity of the porous firebrick kJ/kg °C 0,908
Tmet: average temperature of the heat accumulator of part metal of the coach °C 100
Cmet: heat-storage capacity of metal part kJ/kg °C 0,49
Fwag: surface coach: - width b1 - length 11 m2 m M 18,9 4,2 4,5
Ts: average temperature of surface coach °C 20
Cair: capacie calorific of the cooling air kJ/m3 °C 1,304
T'air: temperature of the recovered air °C 200
C'air: heat-storage capacity of exit of furnace kJ/m3 °C 1,31
Tps: temperature of the parts on the outlet side of the furnace °C 70
Cf: heat-storage capacity of the parts at this temperature kJ/kg °C 0,85
Tf: temperature of garnishing on the outlet side of the furnace °C 100
C'br: heat-storage capacity of the brickwork at this temperature. kJ/kg °C 0,86
C'met: heat-storage capacity of the metal part at this temperature kJ/kg °C 0.5
Psec: dry mass kg/h 12948
Win: initial moisture at the entrance of drier % 23
Wf: final moisture on the outlet side of the drier % 5
Te: temperature of the wet products °C 20
Ts: temperature of the dry products °C 45
Tin: temperature of the surrounding air °C 20
Tf: temperature of the preheated air °C 120
T': temperature of the evacuated air °C 35
He: moisture of the evacuated air % 80
W: quantity of evaporated water kg of water/h 3026,8
L: quantity of air necessary kg of dry air/h 131600
x0,x2: moisture content of the fresh air and the air on the outlet side of the drier kg of water/kg of dry air 0,007; 0,03
H0,H1;H2: enthalpy of the fresh air, hot air and of the evacuated air kJ/kg of dry air 37,9; 139,8; 112,3
Results and discussions
Curve practices cooking The shape of the practical curve represents an increase and a reduction in the temperature during cooking. This curve shows that the matter undergoes a thermal cycle of three principal phases [1, 2]:
1 - A rise of the temperature which is done by hot gases in circulation in pre-heating.
2 - Obtaining the maximum temperature and its constant maintenance for a certain length of time (stage).
3 - A reduction in the maximum temperature by an ambient air flow which crosses the products and thus causes a cooling.
The practical speed of cooking is determined by:
vpractic (°C/h) = (AT)/i.
Таблица 3
Практическая скорость обжига
Table 3
Practical speed of cooking
Interval of T (°C) Duration (H) Speed (°C/H) Observations
120-300 6,5 27,65 Leaving residual water and zeolitic
300-700 7,5 53,33 Oxidation of the organic matters, departure of combined water and destruction of argillaceous minerals
700-900 3,0 66,67 Transformation of aluminosilicates
900 bearing 5,5 -- Profound change of texture
900-700 2,0 100 Vitrification
700-300 6,5 61,54 Solidification, quartz effect
300-50 5,0 50,00 Stabilization
Total duration of cooking = 36 hours
Рис. 1. Кривая обжига в зависимости от времени и длины печи
Fig. 1. Curve of cooking practices according to the time and according to the length of the furnace
a: Thermal Coefficient of conductibility (m /H); K: Coefficient which depends on the form and the density of the part (K = 0.2-0.5); E: Thickness to heat part (m); X: Thermal conductibility (w/m°C); p: apparent bulk density of the part; p =200 kgm3; C: Specific heat (kJ/kg°C). After calculation, we end to the following results:
Таблица 4
Приемлемая температура обжига
Table 4
Acceptable temperature of cooking
T (°C) 0-100 100-700 700-900 Bearing 900 900-100
Time of cooking 2,89 2,66 1,39 1,22 3,30
Total duration of cooking = 11.46 hours
1000 800 600 400 200 0
О
2,89 5,32 6,94
8,16 11,46 Time (h)
Calculation of the acceptable curve The essential parameter of the choice of the rational mode of cooking is the acceptable speed of heating and cooling of the parts [3, 4]. It is calculated by the following formula:
(°C/h) = with a = 3.6A/pC
T^ acceptable gradient of T° determined by experiment, it depends on the physical quality of clay;
Рис. 2. Приемлемая кривая обжига в зависимости от времени Fig. 2. Acceptable curve of cooking according to time
Heat balances of the furnace and the drier It is important to establish the heat balance of the furnace and the drier in order to detect the losses of heat and to calculate the flow of fuel necessary [6, 7]. Type of furnace: tunnel kiln. Type of drier: drier with room.
International Scientific Journal for Alternative Energy and Ecology № 5 (85) 2010
© Scientific Technical Centre «TATA», 2010
0
M. Саиди, M. Хамиане, А. Бенмаунах, Б. Сафи. Оптимизирование процесса производства и сушки кирпича
Heat balance of the furnace Zone pre-heating and of cooking
2 Qf = 2 Q^ = 19.336-106 kj/h.
X: volume of gas necessary for the burners (m3/H)
X = 493.34 m2/h. Specific natural gas consumption
X 439.34 0 0557 m3gas
q =— =-= 0.0557-.
gas Ph 8856.768 kg of product
Heat rate
q = qgasPc. = 0.0557 • 37136.18 = 2068.485 kJ/kg . Thermal efficiency of the furnace
heat
Rf = Use ful-
totalheat spent
(1.317 + 8.768 + 2.657)i06 19.336 •iO6
= 65.9%.
The useful heat represents the sum of the quantities of heat necessary to the water evaporation of the parts and heat necessary to the heating of the parts until the temperature of stage TP as well as the heat absorptive by the endothermic reaction of dissociation of kaolinite [7].
Quantity of air necessary to combustion
Vmr = Va,r praX = 18.97493.34 = 9358.66 m3/h.
3.3.2. Heat balance of the drier
X QEny = X Qx« = 18.951-106 kJ/h.
The output of the drier is calculated by: Rc = qth/q. With
q: quantity of specific heat provided by the hot blast stove;
qth: quantity of specific heat theoretical.
q = 4427.11 kJ/kg of evaporated water qth = 2500 kJ/kg of evaporated water
Потребление тепла и газа с
Consumption of heat and gas
Thus Rc = 56.47%
The correction of mode of cooking is done by experiment by taking account of the various physical and chemical phenomena during cooking (effect quartz withdrawal) [5].
The enormous difference in time of cooking between the acceptable and real curve (24.54 H) rises from the real phenomena which occur in the various zones which require a slow speed [5, 7].
The results show us that:
- The thermal efficiency of the furnace is approximately 66% thus the losses are estimated at 34%, the loss is distributed as follows:
- Waste heat with the conveyer.
- Waste heat through the walls.
- Waste heat by smoke from the furnace.
According to the diagram of RAMZINE of the humid
air [6], we can deduce that the humid air used for drying undergoes several changes of states:
State 0: fresh air t0 = 20 °C;
H0 = 37.89 kJ/kg of dry air;
X0 = 0.007 kg of water/kg of dry air
State 1: hot air t: = 120 °C;
H = 139.80 kJ/kg; X = X0
State 2: air evacuated t2 = 35 °C;
H2 = 112.26 kJ/kg; X2 = 0.03 kg/kg
We evaluate the losses of heat in the drier with 43,53% of the total heat provided by the generator is 2725.44 kJ per kg of evaporated water.
To obtain a better use of the furnace, one thought of decreasing the losses and the need for reducing in important proposals consumption of gas, and that by using the hot air coming from recovery on the one hand, and on the other hand by cooling the arch of the furnace by a current circulating between a double vault. The energy conveyed by this air will be recovered and used like air for combustion [7].
The temperature of the recovered hot air of the zone of recovery is estimated at 100 °C and that of the cooling air recovered of the double vault is about 200 °C. The computation results of combustion are registered in Table 5.
восстановлением воздухом by using the air of recovery
Таблица 5 Table 5
Parameter Furnace of the unit Recovery of hot air Furnace to double vault
Temperature of the hot air of combustion 20 °C 100 °C 200 °C
Fuel used natural gas natural gas natural gas
Lower calorific value of the gas [kJ/m3] 37 136,18 37 136,18 37 136,18
Coefficient of excess of air 1,9 2,0 2,15
Rate per hour of gas X [m3/h] 493,34 465,48 429,8
Specific consumption of the gas [m3/kg] 0,0557 0,0525 0,0485
Specific consumption of heat [kJ/kg] 2 o68,48 1951,74 1 802,11
Thermal efficiency of the furnace % 65,9 66,1 66,53
According to Fig. 3, one can say that an improvement was noted as regards the consumption of heat and gas.
2100
2000
1900
e a.
(Ü
1800
200
T (°C)
200
Рис. 3. Удельное потребление газа и тепла Fig. 3. Specific consumption of the gas and heat
(pressing), recycling of a certain quantity of evacuated air and the reduction in the temperature of the preheated air.
The consumption of the furnace of 354.22 megacals per tons of is cooked. The quantity of heat taken of the furnace for the drying of 222.35 megacals per ton is cooked. This quantity of recovered heat is distributed as follows:
- 30% for the tunnel kiln;
- 40% for the drier with room.
The modern tunnel kilns understand many fixed particular equipment in its various zones which give the main advantage compared to the other furnaces. The only disadvantage which the tunnel kiln presents is the heterogeneity of the temperature according to the height of the tunnel; the hot gases tend to circulate partly higher disadvantaging the exchanges in foot. The more important the height of the channel of the furnace is, the more it is difficult to organize a homogeneous gas circulation in the section of stacking. For that, it is recommended to decrease the height of the tunnel, while preserving the productivity. In order to decrease the masses of the latter.
This study allowed us on the one hand, to make a saving in gas of about 63.54 m3/h and a profit of energy of 266.37 kJ/kg in the case of use of the air of the double vault and 27.86 m3/h of gas and 116.74 kJ/kg in the case of the air of recovery and on the other hand to reduce the quantity of the polluting smoke rejected into the atmosphere.
In conclusion, a profit of energy can be carried out while following all the stages of manufacture and the various stations energy consumers.
Conclusion
The specific consumption of the drier of this brickyard is too important and was evaluated with 472.35 megacals per ton of cooked. The distribution of the various quantities of heat shows that:
1. The loss constitutes a proportion of 43.53% of provided heat.
2. The heat brought by the products, moisture as well as the accessories constitute a relatively weak station.
3. The taken heat of the furnace is appreciable and was estimated at 28.5% of the total heat of drying.
The energy optimization of the process of drying results in the reduction in the quantity of water contained in the worked part (1 kg per part) by mechanical way
References
1. Chabat P. La brique et la terre cuite. Paris, 1886.
2. Jouenne C.A. Traité de céramique et matériaux minéraux. Paris, 1990.
3. Kornmann M. Matériaux de construction en terre cuite, fabrication et propriétés. Paris: Septima, 2007.
4. Plumridge A., Meulankamp W. Brickwork. Architecture and design. Londres Seven Dials, 2000.
5. Sigg J. Les produits de la terre cuite. Paris, 1991.
6. Krause E.B. Le séchage en céramique, principes et techniques. Paris: Septima, 1977.
7. Krause E.B. Principes et techniques de cuisson et de construction de four céramique. Paris: Septima, 1977.
International Scientific Journal for Alternative Energy and Ecology № 5 (85) 2010
© Scientific Technical Centre «TATA», 2010
