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Cement production is a highly energy-intensive process, and the rotary kiln is the most important part of the process. Having a comprehensive model of the kiln in order to reduce manufacturing costs, better performance can be created. In this paper, the influence processes in a simulated cement rotary kiln and operating parameters on the output of the study were to develop and validate the systems using the same batch. The followings were examined: solid phase, gas and coating temperature change in a rotary kiln.

In today’s world, powering along the supply of raw materials, cement production is the most important factor. Cement production process is extremely time-consuming [

A simple system for cement rotary kiln is shown in

During kiln mainly on how long it takes until the temperature of the raw material clinker temperature of about 1370˚C is, it depends. The modern design of the plant, a cyclone preheater to increase the temperature of the solid input materials are used to shorten the length of the kiln.

Raw materials to the kiln consist of calcium carbonate (CaCO_{3}), silica (SiO_{2}), shale (Al_{2}O_{3}) and iron oxide (Fe_{2}O_{3}) feeds. These compounds are very fine powder and mixed with cement to form [

For the balance of power in the rotary kiln, the average temperature of the walls was used in this model. The following equations for the gas, and solid walls, respectively [

According to the equation:

where _{pi} (i specific heat capacity in kJ/(kg・˚C)), ΔT_{i} (i temperature change according to ˚C), Q (heat in kJ) is, and ṁ_{i} replaced by the following equation:

That ρ_{i} (i density in kg・m^{3}), v_{i} (i speed in m/s), A_{i} (i surface area in m^{2}). Therefore the temperature in the gas phase transport equations are:

where T_{w} (wall temperature by ˚C), T_{g} (gas temperature in ˚C), T_{s} (solid temperature in ˚C), β_{1} (heat transfer coefficient between the wall and the gas in W/˚C), β_{2} (transfer coefficient between the solid and the gas temperature in W/˚C), Q_{comb} (combustion heat in W), v_{g} (gas velocity in m/s), ρ_{g} (average gas density of 0.85 kg/m^{3}), ∂T_{g}/∂z (gas temperature changeover the elements in ˚C /m), C_{pg}_{ }(gas specific heat capacity of 1173.8 kJ/kg/˚C) and A_{g} (of gas per m^{2}) and v_{g} obtained from the following equations:

That

That r_{1} (radius of the kiln according tom) and p (surrounded by a solid angle 3π/2) and the solid phase are:

That β_{3} (heat transfer coefficient between the wall and solid in terms of W/˚C), Q_{c} (heat of reaction in terms of W), v_{s} (solid velocity in m/s), ρ_{s} (solid density of 890 kg/m^{3}), ∂T_{s}/∂z (solid temperature changes over the elements in ˚C/m), C_{ps} (specific heat capacity of solid 1089.97 kJ/kg/˚C) is, A_{s} (solid surface in m^{2}) and v_{s} calcu-

lated from the following equations:

Wall:

That β_{4} (heat transfer coefficient between the wall and the environment in terms of W/˚C) and to calculate the heat of reaction is:

where ω (initial value water/CaO), ξ (initial value kg CaCO_{3}/kg CaO), α (initial value kg C_{3}S/kg CaO), β (quantity kg C_{2}S/kg CaO), A_{i} (initial value kg Al_{2}O_{3}/kg CaO), F_{i} (initial value kg Fe_{2}O_{3}/kg CaO), S_{i} (initial value kg SiO_{2}/kg CaO) and C (the initial value of CaO) is.

And A_{w} (wall surfaceinm^{2}) of Equation (11) is calculated as:

where r_{2} (external beam kiln in m) is, β_{1}, β_{2}, β_{3} and β_{4} linear function of temperature, and radiation heat transfer coefficient and geometry that can Equations (12) to (16) is calculated as:

h_{o} fraction of the radiation 0.0757, f_{1} (conductivity gas to the wall), f_{2} (conductivity solid to gas), f_{3} (conductivity wall of the gas), ε_{w} = 0.9, ε_{s} = 0.8, ε_{g} = 0.1, respectively coefficient gas, solid wall and h (radiation coefficient between solid and wall W/m^{2}/˚C) is calculated from the following equation:

That f_{4} (conductivity of the wall) and f_{1} = f_{2} = f_{3} = f_{4} = 22.71 W/m^{2}/˚C is. To calculate the heat transfer coefficient between the wall and the environment (external air), Spang of Equation (16) is used. This is a perfect description of the heat transfer coefficients between the shell and the environment. Since ƒ_{4} the kiln was fixed, β_{4}_{ }not sensitive to the conditions in the longitudinal direction. To increase the accuracy of the model, the heat transfer coefficient of the outer shell of the total displacement

That Re (Reynolds number), Gr (Grashof number), k_{a} (air conductivity), Pr (Prandtl number), D (shell diameter in meters) is:

where C in Equation (18) is obtained as follows:

where T_{a} (ambient temperature on ˚C), T_{sh} (shell temperatures in ˚C) and ε_{sh} = 0.5 (emission shell) and σ = 5.6697 ´ 10^{−8} W/m^{2}・˚C^{4}. As to the equation (16) deduced

To calculate the film temperature (T_{f} according ˚C) fluid inside the kiln elements are considered in the following equation can be used [

In each of the elements considered by the kiln shell surface temperature T_{sh} in ˚C, T_{a} is the ambient temperature in ˚C. So much

where Nu_{forced} (Nusselt forced displacement) and:

where μ (kinematic viscosity in terms of kg/m・s), ρ (density in kg/m^{3}), u (velocity in m/s), d (diameter in m), g (acceleration due to gravity in m/s^{2} times with 9.8), T_{surf} (depending on the surface temperature ˚C), T_{a} (depending on the ambient temperature ˚C), L (characteristic length in m), J (dynamic viscosity in m^{2}/s), k_{a} (air conductivity in W/m・˚C), β (coefficient of gas expansion in 1/˚C) [

where Nu_{free} (free convection Nusselt number) and Ra (Riley number) [

Plug flow of cement rotary kiln flame model is used [

The number of sections is calculated as follows:

Flame length overall, F_{L}, the equation Beer is obtained:

The AF^{*} (stoichiometric air-fuel ratio), ρ_{e} (equivalent to gas density), ρ_{cp} (density of combustion products), ρ_{se} (solid density published), d_{0} (equivalent diameter of the burner) is. Gorog, cement kiln burner Coaxial type equipped [

The

G_{F} and also G_{Pa} in Equation (26) to the flow rate of fuel and primary air. Now Q_{comb} in Equation (3) is calculated by the following expression:

where T_{sa} (depending on the secondary air temperature ˚C), LHV (lower heating value fuel in J/kg), T_{pa} (primary air temperature in ˚C), T_{ref} (adjusted reference temperature ˚C) is.

Rates of chemical reactions rotary kiln using Arrhenius equation can be expressed as follows [

The solid temperature T_{s} by ˚C, and R = 8.314 J/mol・˚C gas constant, A_{i} (i based on the frequency factor 1/h) and E_{i} (i activation energy in J/k mol) and k_{i} (Arrhenius constant reaction i by 1/h) is.

In which:

And by chemical reactions in cement rotary kiln, we have:

In these expressions M_{i} (i molecular mass in kg/m^{3}) and R_{i} (kinetic rates i), C_{i} (level i) is.

Mass imbalances, Equations (30) and (31) for 10 solid compound involved in the reactions occurring in cement kilns and other gas (CO_{2}) is written:

with: i: H_{2}O, CaCO_{3}, SiO_{2}, Al_{2}O_{3}, Fe_{2}O_{3}, CaO, C_{3}S, C_{2}S, C_{3}A, C_{4}AF

and j: CO_{2}.

R_{i} (kinetic rates of the solid phase) and R_{j} (gas phase kinetic rates) are presented in the previous section. Kinetic parameters are presented in the following

These assumptions are as follows:

E_{i} (J/kmol) | A_{i} (1/h) | Reaction Rate |
---|---|---|

42.08 × 10^{6} | 1.94 × 10^{4} | |

805.8 × 10^{6} | 4.55 × 10^{31} | |

256.19 × 10^{6} | 1.33 × 10^{5} | |

193.31 × 10^{6} | 4.11 × 10^{5} | |

185.16 × 10^{6} | 8.33 × 10^{8} | |

194.10 × 10^{6} | 8.33 × 10^{6} |

・ Internal and external diameter of the kiln is assumed.

・ The specific and reaction heat were independent of temperature and they were constant along the axial direction.

・ Conduction in gases and solids in the axial direction of the wall was ignored.

・ Displacement and diffusion coefficients are independent of temperature and location.

・ Height and speed of the solids in the kiln section is assumed.

・ solid material conveyed by the exhaust gas flow is not included in the model

・ Arrhenius reaction rate specified by law.

・ Average amount of coating conductivity 0.74 W/m^{2}/˚C was considered.

・ The conductivity of the refractory could be estimated by Equation (32) which was correlated from the experimental data, given by the refractory manufacturer for the magnetite-fried brick type is:

・ Conductivity of the metallic shell 45 W/m^{2}/˚C is considered close to the alloy carbon steel.

・ Since conductivity changes during the refractory lining is not possible, the starting amount was fixed. This assumption can be a source of grave error in the prediction model.

・ The numbers of points scanned shell temperature kiln for a full rotation every 40 elements. At any point in the calculation of the axial position of an average value of all points in between.

Length, diameter and outdoor cement kiln 70, respectively, 4.1 and 4.5 meters. Average thickness of 15 cm refractory magnetite, which can be considered to be uniform throughout the cooking area. Tilt cylinder to facilitate axial displacement of the solid bed, moving toward the discharge end in a state where the hot gases circulating in the opposite direction, was 4%.

In

Mass and energy equations are integrated with a set of differential equations and algebraic models are flame by software MATLAB R2014a (ver. 8.3) is solved. Equations for the particular type of cooking area Hlknndh ODE15S are used. After solving the model, the wall temperature profile to the application submitted by Hlknndh ODE is solved. To solve the model equations, ODE during kiln divided into 70 elements. The size of each element of the program was considered a meter. The generated two-dimensional matrix, the temperature of the gas

phase, solid coating in the oven during the show. Resistance between the wall and the surface layer is shown in

Heat flow in cylindrical coordinates (without heat) as follows [

For one-dimensional mode with the following assumptions, Equation (33) can be simplified:

1) Steady-state heat transfer through the layers of the wall of the kiln (Steady-State) was considered.

2) The heat conductivity in the z direction was ignored.

Thus, according to

Coating layer:

Refractory layer:

Shel layer:

Therefore, the above equation with boundary conditions (34), the following equation is obtained:

At each stage (ΔZ), in the inner wall of the kiln temperature (T_{w}) to find. Equations (1) to (28) are solved simultaneously in the program. Then, using Equations (38), (37) and (36), Q_{pass}, T_{b}, T_{c}, respectively, can be calculated. The simulation code, both inside the kiln wall temperature (T_{w}) and the temperature of the kiln shell (T_{sh}) as a two-dimensional matrix in terms of the length of the kiln is considered. We can conclude that the thermal

resistance Equation (35) to (38) can be used to adapt the matrix elements, developed. Therefore, the heat loss from the body of the kiln is calculated (see

Now using equations results in mind, we can change the temperature of the solid phases, gas and coating in a rotary kiln were investigated (

Also according to the model equations, we can obtain the amount of waste in the rotary kiln (

Since the temperature changes of the gas phase, solid coating of cement kilns was essential; therefore, an integrated model was developed in the cement kiln. First, a mathematical model of steady state (Steady-State) to estimate the inner wall surface of the rotary kiln temperature profiles was formulated. Then, by calculating the

20 | Ambient air temperature (˚C) |
---|---|

5 | Air velocity (m/s) |

1000 | Secondary air inlet temperature (˚C) |

44,856 | Secondary air flow rate (m^{3}/h) |

5479 | Gas flow rate (m^{3}/h) |

205 | Feed rate (ton/h) |

2.8 | Kiln rotation speed (rpm) |

temperature profile in the kiln and temperature profiles measured by the outside, the heat dissipation of body heat transfer resistance in the adjacent layers of the cylinder was estimated by the model. A comparison of model and data was collected from an industrial kiln, confirming that the feature is good for heat dissipation body temperature changes and the different phases. In addition, it is concluded that the heat loss from the body in the rotary kiln sintering temperature is greater than the thickness of the coating layer of the coating material, which does not create a problem.

Hereby, Mr. Doctor Yavari at Ghadir engineering companies in preparing this article appreciate their assistance and I appreciate it.

Hamid RezaGoshayeshi,Fariba KerdarPoor, (2016) Modeling of Rotary Kiln in Cement Industry. Energy and Power Engineering,08,23-33. doi: 10.4236/epe.2016.81003