Simulation Model of the Temperature Inside an Intermittent ... · The kiln used to develop the project has 6.83 meters in diameter, 2.2 meters in height from the ground up to the

Simulation Model of the Temperature Inside an Intermittent Kiln of the Red Ceramic Industry

Lima, Y.R.S1*;Morais, A.S.C1;Ferreira, C.N.1;Souza, B.L.1 1 Federal Fluminense Institute

Dr. Siqueira Street, 273 – Parque Dom Bosco, Campos dos Goytacazes – RJ

*[email protected]

Abstract The ceramic industry in Brazil is characterized by the low level of automation

applied in its production process and by the cheap and low-skilled workforce. Among

the obstacles observed for the implementation of automation in Brazilian ceramics, it

is worth mentioning its high cost and the low qualification of the workforce at the

operational level. A simplified and low-cost Feed Control System (FCS) for

intermittent kilns is proposed so that the firing is more homogeneous, consumes less

fuel and, consequently, produces fewer environmental impacts. Therefore, the

objective of this paper is to demonstrate the development of the simulation and the

behavior of the FCS system. The simulation is done using the hardware-in-the-loop

technique, where the system plan and its interaction are recreated in the Simulink of

Matlab Software through blocks diagrams and the control system is executed in a

PLC through control logic. The results (burn curve) of the simulation allow to state

that the system behaves in a more stable way and the fuel expense decreases

considerably when compared to the real system. The process of system simulation is

very important to the industries, especially of red ceramics, so that it is possible to

know how the system will behave before being literally executed and then avoid

unnecessary expenses.

Keywords: Simulation, clayey ceramics, temperature, energy efficiency, intermittent

kiln.

7th International Congress on Ceramics & 62º Congresso Brasileiro de CerâmicaJune 17-21, 2018, Foz do Iguaçu - PR - Brazil

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Introduction

The ceramic industry activity is one of the main industrial activities in Brazil, that

is the 2nd largest producer of ceramic coating as well as the 2nd largest consumer

market in the world, only spotted behind China. In addition to that, in recent years,

Brazil has surpassed important markets such as Italy and Spain [1].

In order to implement new technologies in the industry, it is necessary to break

down some barriers that prevent the development. Due to small and medium-sized

companies, for the most part their production process is quite artisanal and

exceeded, without controlling the main variables in an automatic way, where the

whole process is manually managed based on the experience of the labor force [2].

This way, the quality of the final product can be affected by the linearity of the

conditions in the production process stages, so the production of batches of parts

can differ significantly and not match the technical requirements standard defined.

These difficulties can also be found in the ceramist pole located in Campos

dos Goytacazes, north of Rio de Janeiro state. Most of the cities in this region have

the capacity for innovation, both in terms of product and process. The main factors

for this, are mainly the lack of professionalization of the labor force, as already

mentioned, besides the lack of innovative vision by the owners, once their processes

have been working that way for years [3].

In order for these difficulties to be overcome, there are some actions that need

to be taken by the ceramists, as an improvement of the production process by

establishing the automation and control of the system. Such measures require time

and financial resources. So, the steps of the production process that directly interfere

the final product should be prioritized, as well as considering low-cost alternatives for

the implementation of the control.

The stage of the productive process that can be considered as critical and

then prioritized, once it is about controlling, is the burning stage. It is on this process

that technical and static capabilities are conferred to the product, through sintering,

that generates the physical-chemical transformation in the ceramic material [4].

Due to this fact and with all financial and structural impasses faced by the

ceramic sector, the critical stage of the process has to be prioritized and the use of

alternatives to improve the productive process in intermediate levels of automation


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has to be considered. These options are simple, easy to implement, maintain, and

result in a direct improvement related to the productive process.

Materials and methods This section of the research demonstrates in 3 phases of the materials and

methods used to elaborate the project. In the first one, it is exposed the

characteristics of the kiln where the project was conceived. In the second, the control

system is detailed, clarifying its interaction with the system. Finally, it is shown how

the system simulation is done, detailing from the part of the communication between

the softwares and hardware used in the project to all the algorithms and diagrams

made during its execution.

The object of study on this research is an intermittent domed kiln located at

Arte Cerâmica Sardinha, in the district of São Sebastião, municipality of Campos dos

Goytacazes.

The kiln used to develop the project has 6.83 meters in diameter, 2.2 meters in

height from the ground up to the load and 3.3 meters from the ground to the center of

the dome, in addition it has 4 furnaces and two doors of 1.84 meters each one, the

width of the kiln wall is 1.20 meters. In figure 1, one of the doors and two of its four

furnaces can be seen.

Figure 1 – Intermittent domed kiln

The kiln operates in 3 phases; the first one is the heating of internal atmosphere

to the desired temperature, after reaching that temperature, the furnace supply is

decreased in order to maintain the constant value for a determined period of time and

finally the kiln is cooled so that the load can be handled.


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The proposed feed control system (FCS) focuses on the temperature control

of the internal atmosphere of the kiln. In order for this to be possible, the temperature

is measured through thermocouples placed inside the kiln. There are 6 type K

thermocouples installed, they were placed as shown in figure 2.

Figure 2 – Thermocouples placed on the kiln

These thermocouples send information about temperature to a Programmable

Logic Controller (P.L.C.) that has the control logic. In order to be manipulated by the

P.L.C, these temperature data are pre-purchased by a Phoenix Contact Mini MCR-

SL-TC-UI-NC thermocouple module that performs the reception, noise treatment,

reference joint compensation and scanning through a 12-bit analog-to-digital

converter, sending to the Arduino the temperature values with a resolution of 0.25° C.

Considering the values of the temperature the process control can be

automatic or manual. Automatically, any increase of the temperature and control in a

certain value is processed automatically through the control logic implemented in the

P.L.C. Manually, the set-point related to the temperature and the "output" value of the

frequency inverter for the sawdust and air-blower machine are defined by the

operator, remaining on this value while the operator judge it is necessary.

In automatic mode, the P.L.C. acts in the process through the addition or not

of fuel in the furnaces besides the addition of oxidizer (air). The fuel used in the

studied kiln is the sawdust. This fuel is sent to the interior of the furnace through a

sawdust feeding machine that has a motor that rotates a kind of toothed gearing

responsible for throwing the fuel into the furnace. This way you can control the

rotation speed and consequently the amount of sawdust that will feed the furnace,


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through its connection to a frequency inverter that regulates the frequency will reach

the machine.

According to the temperature information that comes from the thermocouples

and with the interaction of these data in the control logic, the P.L.C. will have the

motor rotating faster or slower and this way more or less sawdust in the furnaces.The

same goes for adding air to the interior of the furnace. The relationship between fuel

and oxidizer is described in the control logic.

There are 4 fuel-blowers, each one for a furnace and two oxidizer-blowers.

These machines are connected to frequency inverters that receive the information

coming from the P.L.C. of how much it should be blown into the furnace. In figure 3 it

is possible to see one of the sawdust machines.

Figure 3 – Sawdust machine

The FCS operating in automatic mode does not require an operator to change

the set-point temperature because it changes value according to the control logic.

The only human intervention in the process is the need to keep the sawdust reservoir

full so that there will never be an error or lack of fuel when it is necessary to add it to

the interior of the furnace. The schematic model of the system can be seen in figure

4.


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Figure 4 –FCS model

In order to simulate the process, a series of steps must be taken to ensure that

it is faithful to the actual process. The first step to be developed is the integration

between the software and the hardware used. The software chosen for the simulation

was the Matlab, with the use of the Simulink tool, the InTouch where the operator

supervision and interaction screen was developed and the PC Worx Express where

the control programming was developed. The hardware used was the Phoenix

Contact P.L.C. - model ILC 150 ITH.

The Communication between InTouch and Simulink is done through a protocol

called Dynamic Data Exchange (DDE) that performs information exchange between

Windows applications. The communication between the Phoenix P.L.C. and the

Simulink is done through the communication protocol called O.P.C. (OLE for Process

Control) developed by Microsoft to connect or integrate documents and other objects.

It is important to highlight that there is no direct communication between the InTouch

and the P.L.C.

The control logic developed to the FCS was developed in the programming

language called Ladder and elaborated according to the instruction of professionals

that have experience in the ceramic industry. It was established that when it is

running automatically the set-point temperature would increase by 30ºC every 2


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hours until reaching the maximum temperature selected by the operator, being the

Top Thermocouple (T9) defined as a parameter to increase the temperature.

The burning time varies according to the maximum temperature set by the

operator what will affect the amount of increments the temperature will suffer.

However, from expert information the average burning time determined on the

simulation was 100 hours, with 50 hours for heating to the maximum temperature of

900ºC and 50h controlling this value. After this, the process goes into natural cooling

and the automatic control system is switched off.

For the simulation to occur, it is necessary to implement a block diagram in

Simulink that lists all the system variables with the transfer function that correctly

relates the input and output of the process.

The control strategy chosen was the feedback control, simply known as

"feedback", where only the information of the Thermocouple is used to compare with

the reference value of the temperature that generates an error and then causes an

action of control that interacts with the system plant, returning a value that will be

read back by the sensor and sent for comparison [5].

According to the idea of how a feedback control system behaves, it was

necessary to obtain the transfer function that relates the amount of fuel to the

temperature. This way, an experiment was performed where the initial temperature of

the system with 0% of fuel was measured. After this, the fuel machine and the air-

blower with maximum load were placed to verify at which temperature it would

stabilize. It is important to note that the procedure was performed with load inside the

kiln.

By analyzing the system behavior, it can be verified that it behaves like a

system of order 1. It is known that a first order system behaves according to equation

A. 𝐶𝐶(𝑠𝑠)𝑅𝑅(𝑆𝑆) =

𝐾𝐾𝑇𝑇𝑆𝑆+ 1

(A)

This way, in order to find the time constant T, it is necessary to check in the

graph the moment when the system reaches 63.2% of the final value. So, we used

Matlab. The values were placed in a matrix and plotted on a graph. By knowing that

the final value of the temperature is 200 ° C and the initial value is 130 ° C, the value

corresponding to 63.2% in that temperature range is 174.2 ° C. The time the system


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reaches this temperature is approximately 2880s. In this way the transfer function

obtained can be seen in equation B. 𝐶𝐶(𝑠𝑠)𝑅𝑅(𝑆𝑆) =

702880𝑆𝑆 + 1

(B)

For comparison of the actual system with the transfer function, the behavior of

the real system and the response to a step-type input of the transfer function was

plotted on a graph. Figure 5 shows the comparison of the transfer function with the

current burning of the kiln and a very similar behavior can be checked.

Figure 5 - Comparison transfer function x Real temperature

After acquiring the transfer function, the block diagram was assembled in

Simulink, showing how each variable interacts in the proposed control system

(feedback). Knowing how such a control operates the main block diagram of the

system can be seen in figure 6 and 7.

Figure 6- Main diagram block

Figure 7- ICT diagram blocks


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Figure 8 - HMI from the FCS

Figure 9- Temperature behavior during FCS simulation

In order to allow an interaction between the operator and the control system by

changing the values of Kp, Ki, Kd and visualization of the current and set-point

temperature, a Human Machine Interface (HMI) was developed. The implemented

HMI illustrates, in a simple way, the control system implemented. Figure 8 shows the

HMI of the control system.

Results and discussion For the FCS, the simulation was executed and the results of the temperature

behavior plus the fuel values were compared to the current burning.

It is important to mention that the simulation time was established as 1 hour,

due to software limitations, so each minute elapsed in the simulation is equivalent to

2 hours in real time.

In the simulation the parameters of the controller were adjusted in Kp = 7.5; Ki =

0.006; Kd = 1.22.

From parameters choice, the simulation was started in automatic mode and at

the end of the simulation the kiln temperature behaved according to figure 9.


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Analyzing the figure 9, it is possible to observe that the burning process occurs

in two phases predominantly, one phase of rising temperature (30ºC every 2 hours)

and another phase of constant burning at 900ºC. It is worth to mention that after

100h, a temperature drop begins and initiates the cooling inside the kiln. An

important observation is that due to the limitation of the simulation time, it is not

possible to verify the cooling behavior of the system.

Based on the behavior of the temperature with the use of the FCS, a

comparison was made with the current burning of the furnace (the one without using

the control system), to verify the difference in performance between them. This

difference can be seen in figure 10.

Figure 10 – Comparison Temperature using FCS x Current burning 1

Analyzing the behavior of the FCS it is possible to notice that it controls the

temperature to remain in the specified value and that the implemented control logic is

quite precise with the chosen parameters. During the temperature rise step it is

raised smoothly and within the time considered as ideal based on the literature.

During the control of the maximum temperature, the system does not generate any

type of error and keeps the temperature constant.

It can be observed that in the real system, in each burning the temperature

behaves in a way with different rise times and control of the final temperature with

variations that can cause problems in the structure of the ceramic material. It

happens because there is no automatic temperature control implemented.

To analyze the fuel spending, the average value sent by the frequency inverter

to the sawdust machine and the air blower was used. This way, it is possible to know

0100200300400500600700800900

1000

0 10 14 18 22 26 30 34 38 42 46 50 54 58 62 66 70 74 78 82 86 90 94 98 102

106

Tem

pera

tura

(°C)

Tempo (h)Queima 1 Simulação 1


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the amount of sawdust that will be required to burn completely using the feed control

system.

In the simulation a value range from 0 to 100% output of the frequency inverter

equivalent to 3Hz and 60Hz were used, which are the minimum and maximum

frequency values that are sent to the motor and to the blower for speed control. The

minimum value of 3Hz was used so that the outputs did not stop spinning and

blowing and when they were going out of inertia they would require a high current,

"expending" more energy for it.

This way, with the data analysis it was seen that the average output of the

frequency inverter during the temperature rise stage remained on average at 45%,

28.6 Hz for the motor and 34.38 Hz for the blower, values almost half of the 60Hz

which is the standard provided by the electric supplier companies and currently used

by equipments. In the heavy-load fire stage where the constant temperature is

maintained at 900 ° C, the inverter output remains constant at 11% generating an

inverter output frequency of 9.3 Hz for the motor and 11 Hz for the fuel blower.

Regarding to the fuel, in burnings without the control system it is used an

average of 12200 kg of sawdust per burn, with an average mass flow rate of 100 kg /

h. Data obtained through kiln measurements. With the use of the FCS, the flow rate

is reduced to approximately 40 kg / h on average, as the frequency inverter

decreases the motor rotation speed and the blower blow by reducing the working

frequency of the equipment to values that will control the system at the required

temperature. Considering this new value of flow, the fuel expense decreases even

more, reaching 4000 kg of sawdust.

As each bag of sawdust has 12 kg and the average bag price is R$ 1.80, there

is an economy of fuel up to R$ 600.00 per burning with the use of the FCS. For a low

value-added product, such reductions in cost look quite considerable.

Conclusions In this research, it was proposed the development and simulation of a feed

control system (FCS), in which the current burning behavior was compared with the

use of the FCS. The results show that by using the FCS, the combustion occurs

without variations and abrupt changes in temperatures, what is different from the

current burning process.


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During the simulation of the FCS, the parameters for the PID controller were

defined and it behaved with a very satisfactory temperature control, because, as it

can be seen in figures 12 and 13, the temperature increase is carried out in a non-

abrupt manner, within the time required to acquire structural and aesthetic properties,

reducing the chances of structural deformities and increasing the standardization of

the final product at each burn. During the stage of heavy-load fire, the temperature

remains constant at 900ºC without variations.

The FCS is able to provide to the burning process, a reduction of fuel and

consequently a reduction of production cost that can reach R$ 600 per burn.

References [1] ANICER, - Associação Nacional da Industrial Cerâmica. Recovered from http://portal.anicer.com.br/setor/, 2016. [2] BRAGA, W. A.; SANTOS, M. W. L. C.; SALES, J. C. Qualidade na Indústria de Cerâmica Vermelha: Medidas e Alternativas para o Controle Dimensional. Cerâmica Industrial, 21(5–6), p. 40–43, 2016. [3] ROCHA, A. F.; PALMA, M. A. M. Gestão da inovação e capacidade competitiva: uma análise não paramétrica no setor cerâmico de Campos dos Goytacazes, RJ. Cerâmica, 58(346), p. 244–252, 2012 [4] PAIVA FILHO, E.; AGOSTINHO, R.; JÚNIOR, J.; BEZERRA, F.; AQUINO, P.Cooperação Internacional E Desenvolvimento Tecnológico: Controle Do Processo De Queima Em Fornos Hoffmann Para Cerâmica Vermelha. Presented at the Brazilian Congress of Engineering Education, Brasília, 2004. [5] OGATA, K. Engenharia de controle moderno. 4o ed. São Paulo: Pearson Prentice Hall, 2007.s


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Simulation Model of the Temperature Inside an Intermittent ... · The kiln used to develop the project has 6.83 meters in diameter, 2.2 meters in height from the ground up to the