ENERGY EFFICIENCY IMPROVEMENT IN THE CEMENT INDUSTRY THROUGH ENERGY MANAGEMENT

By: Adriana J. Gonzlez, Rosaura Castrilln, Enrique C. Quispe

Grupo de Investigacin en Energas, GIEN, Universidad Autnoma de Occidente Cali, Colombia

ABSTRACT

The technology of energy management called "Sistema de Gestin Integral de la Energa, SGIE was proposed in Colombia in 2007 as a result of a research project funded by the Colombian government. The SGIE technology consists of statistical and monitoring tools, energy efficiency indicators and conforms to the requirements of the Standard ISO 50001. This technology allows the measurement of energy efficiency on industrial processes. Since 2007, the SGIE technology has been used in diverse industrial sectors and between the years 2009 and 2010, it was applied to the cement production industry.

This paper presents the results of a pilot application of the SGIE technology in a cement plant with a wet process, in order to improve its energy efficiency. The results have shown a reduction of 4.6% of the electric energy consumption in this plant; achieved without investing in new equipment, but with only the innovation of the processes through applying the SGIE technologies to the energy management of the plant processes.

The implementation of the SGIE has contributed to the adoption of a culture of energy efficient management and continuous improvement of the processes with impact on productivity and competitiveness of the company.

Keyword cement production, energy efficiency, energy management, energy efficiency indicators, SGIE.

INTRODUCTION Industrial companies can achieve energy savings of up to 40%, some of it without capital investment, through the application of methods of energy management [1]. An energy management technology, called SGIE, was developed by the Universidad Autnoma de Occidente and by the Universidad del Atlntico as part of a project funded by the Administrative Department of Science, Technology and Innovation, Colciencias, and the Ministry of Mines and Energy of Colombia. The final product of this research was a model for the implementation of energy management systems which utilizes stages and steps for its implementation as an integrated management system. SGIE also provides a system for tracking the results and recording the processes used. [1], [2].

The cement industry is an industry that uses electricity intensively and the electricity costs are approximately 20% of total production costs. This highlights the importance of implementing an Energy Management System that will identify and recover the electricity savings potential and will increase the efficiency of the process, by using management tools that dont require high capital investments. The SGIE allows for implementing a method for the efficient management of energy resources that will also be understood by all the members of an organization; this way, in a short period of time and with the least investment risk, the objectives set and the continuous improvement of the system will be achieve. This paper presents the results of the implementation of an Integrated Energy Management System for a cement production plant utilizing wet process.

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METHODOLOGY The methodology employed for the implementation of the Integrated Energy Management System in the cement industry is divided into three stages, as proposed by the guide for implementing the Integrated Energy Management System [3]: Strategic Decision, Implementation of the SGIE in the company and Operation of the System.

The first stage is a preparatory stage in which the current state of energy management of the company is assessed, and the goals and achievable savings activities are defined. The second stage refers to the implementation of the energy management system within the company, taking into account indicators of management, control variables, definition of a monitoring system, energy assessment and a training plan. The final stage is about how to operate the system and make it sustainable, resulting in continuous improvement. Below, the results achieved in the implementation of stages one and two in a cement plant are presented.

First Stage: Strategic Decision

As a starting point of the implementation and operation of an Energy Management System, preparatory activities are required that ensure a potential for cost-effectiveness of the system, as a result of implementing the activities proposed by this model. In this initial phase, the current state of the companys energy structure, the level of energy management and the quantification of potential for saving energy are identified.

1) Identification of the current state of the energy structure of the company

The general understanding of the production schemes and the energy consumption and production data are an initial requirement for the development of this stage. Developing an energy/production diagram showing the contribution of each energy source in the production process is essential for this activity.

Cement production by wet process is a process with an intensive consumption of electricity which includes four main phases: mining and crushing of raw materials, homogenization, production of clinker, and cement milling. [4] Fig. 1 illustrates the energy - production diagram of the process.

Figure 1. Energy production diagram in a typical production process of cement by wet method

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Analyzing energy consumption data in the stages of each production process identifies the main energy consuming areas. By this activity, the average consumption at the defined Energy Cost Centers, ECC, is quantified through historical data collected by energy meters.

Table 1 summarizes the average distribution of the electricity consumption in the cement factory for the seven established Energy Cost Centers.

Table 1. Requirements of electricity for the Energy Cost Centers defined in the plant

Energy cost center Electricity Consumption [kWh/ton cement]Cement milling 46 Clinker burning + cooling 35 Primary grinding 17 Secondary grinding 5 Homogenization and transportation 5 Crushing 1 Bagging and shipping 1 Other 4

TOTAL 114

Through the development of a Pareto chart (Fig. 2) showing the process areas, it is possible to identify 20% of those which have an impact on 80% of the electricity consumption in the process. These are: milling of cement, clinker burning + cooling and primary grinding. This allows the plant to focus efforts and initiate actions of energy management in these areas.

Figure 2. Pareto chart of electric energy consumption by areas of process

2) Assessment of energy management and administration levels in the company

Once the energy management level of a process is identified, considering the technical point of view through analysis of production and its associated energy consumption for each phase of the process, all areas of the company are evaluated, including the non-productive areas, by a series of surveys performed by key staff selected in each area.

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The staff selected for the survey represents each area of the organization and they must answer questions to classify the energy management level of the company in a quantitative way and according to their knowledge in a range from 1 to 5.

Specialized software is used [5] and the quantitative results allow the company to assess its own levels with regard to energy management and organizational structure. As a final result, the company obtained an average classification of 3.2 which indicates a medium level of energy management. The following was identified:

- There are no leaders or teams responsible for the analysis of monitored data, operational decision-making, evaluating results of variables or, identification of new potential for increasing energy efficiency.

- There is a lack of policies and written procedures and indicators, in all areas, aimed to the control energy costs.

- A culture among the staff is lacking with regard to the reduction of energy costs and energy efficiency in all areas of the company.

3) Evaluation of potential savings by operational variability

The potential for energy savings can be found within the so-called energy non-associated to production Enap. Fig. 3 shows a scatter diagram of energy vs. production for a process and the non-associated energy is the value of the intercept on the Y axis of the best fit line to the dispersal of data, also known as Energy Baseline.

The relationship between production and energy consumption is linear for most industries. This indicates that reciprocity between the points in a scatter diagram of energy consumption vs. production can be represented approximately by a straight line and, in general, expressed by a linear as (1):

napE mP E += (1)

Provided that the relationship between the analyzed variables is appropriate, equation 1 is considered as the Energy Baseline.

Figure 3. Scatter diagram of energy consumption versus production and estimation of the energy baseline for a productive process

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The measure of the strength relationship between energy consumption and production variables is measured by the Coefficient of Correlation "r". The value of this coefficient can range from - 1 to 1, indicating that the closer the value of the correlation coefficient is to 1, the stronger the linear association is between the two variables. [6]

The potential for savings by operational variability means, as demonstrated in the graph consumption vs. production (scatter diagram E vs. P), that savings can be achieved by analyzing and stabilizing the operation; since, for the same production, there are different energy consumptions. The idea is to standardize the operation values of the variables with the days of maximum efficiency for different work intervals and try to stabilize the process on these points through good practices in energy or actions for saving energy.

To calculate the savings potential by operational variability, it is necessary to establish a "target line" (Fig. 4), which goes through the center of the data related to the lower consumption, corresponding to the best efficiency operational practices in the process.

This target line is drawn using the same value of the slope "m" of the baseline, since it is assumed, at this time, that there are no technological changes to the equipment, areas, or processes on which the analysis is performed.

Figure 4. Estimated Energy target line in a scatter diagram of energy consumption vs. production

As a final activity of Stage 1, the savings potential of electricity by operational variability is quantified by estimating the energy base and target lines created using the daily data set of energy consumptions and production of the selected base period for the year 2008.[7]

In each of the established energy cost centers the savings potential of energy by reducing the operational variability were quantified. They were calculated using (2).

)nap(targetnap(base) EE[kWh]potentialsSaving = (2)

Table 2 summarizes the maximum estimated savings potential by operational variability in each of the analyzed areas.

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Table 2. Estimated energy savings potential by reducing operational variability

Energy cost center Potential of saving[kWh/ton cement]

Cement milling 2.3 Clinker burning+ cooling 2.8 Primary grinding 1.4 Secondary grinding 0.2 Homogenization and transportation 0.1 Crushing 0.2

TOTAL 7.0

The estimated savings potential which can be recovered by operational variability was 7.0 kWh/ton cement, equivalent to 6% of the total consumption of electricity.

Second Stage: SGIE Implementation

Stage II corresponds to the implementation of an Energy Management System, which is constructed from the evaluation of the initial state of energy consumption and production, defining achievable goals and savings activities. In this regard, this second stage includes actions which will be incorporated in the daily operational life of the process, allowing the integral management of the energy resource.

The main objective of this phase is to create processes to operate the system by defining a system of indicators which become the basis for monitoring and strategic energy analysis, analysis and control of energy variability and operating conditions; such as the structure of generation and validation of the plans of action for continuous process improvement. The methodology and results of the main activities developed in this stage are described below.

1) Establishing indicators of efficiency for the SGIE

It is important to introduce a system of indicators to measure energy performance that allows for analyzing the result of actions taken or the lack of action. For this reason, the system is based on the understanding of the relationship between energy and production.

The base information for structuring the indicators corresponds to the data obtained during the energy characterization, (Stage I) and were raised in the scatter diagrams "Energy vs. Production" of the established Energy Cost Centers.

The proposed energy efficiency indicators to be implemented within the Integrated Energy Management System are: Energy Consumption Indicator (IC), Percent Energy Efficiency Indicator (PEEI) and Cumulative Sum Control Indicator and Chart CUSUM.

Energy Consumption Indicator (IC)

The specific energy consumption indicator is defined as the ratio between consumed energy and the value of the production obtained with this energy (3). Given that this indicator provides information of the unitary energy requirement for a process, it is possible to make comparisons with regard to national or international standards for the same products or uses, areas or equipment. Also, it can be the basis for the development of optimization and improvement of energy programs.

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][ton Production[kWh]n ConsumptioEnergy IC = (3)

Replacing (1) (calculation of the base line) in (3), the base consumption indicator is obtained (4).

][ton Production[kWh] E m.P

IC napBase+

= (4)

From this point of view, in a production process where an energy characterization has been performed, the characteristic equations of each process can be obtained and the base or characteristic consumption indicator (IC) for reference can be defined as (5):

PE

m nap+=BaseIC (5)

The above equation represents a Base Consumption indicator, consisting of a constant term (m) and a

term that is in function of the production variable (PEnap ). As can be seen in Fig. 5, the reference

Consumption Indicator is an inverse function of the production variable. Having the base equation for the Consumption Indicator (IC) the characteristic value of the base energy performance can be obtained for each level of production, as Fig. 5 shows. This suggests that it is possible to compare the measured energy performance for any level of production, with an updated base reference value on recent energy performance.

Figure 5. Variation of the Base Consumption Indicator (IC) with regard to the production

Percent Energy Efficiency Indicator (PEEI)

The Percent Energy Efficiency Indicator is a management tool of the energy sector, which allows comparing the behavior of the energy consumption results measured in a process during an operating period, with respect to the values of the base or trend energy consumption of the same period, taking as reference of compliance a non-dimensional value of 100 [8], mathematically is defined as (6):

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100EE

PEEImeasured

Trend = (6)

This indicator is calculated from data of production and energy for a given period of analysis and the equation or baseline of energy established during the energy characterization. The use of the Percent Energy Efficiency Indicator can be understood in terms of three trends or conditions. As a result, the calculation between the trend energy and the measured energy can be found within three numeric ranges, < 100, > 100 and = 100. The following paragraph explains each of the cases and presents the corresponding diagram.

In the first case, if the indicator is higher than 100, it means that the energy consumption of the analyzed period was lower than it should be according to the trend estimated from the base equation and, therefore, is located in the area of efficiency in the diagram (Fig. 6). For the second case, if the indicator is lower than 100 it means that in the analyzed period more energy was consumed than should be according to the trend and it is in the area of inefficiency. In the last case, when the indicator is equal to 100 this represents stable consumption (it hasnt consumed more or less energy than necessary) and it is within the consumption trend.

Figure 6. Percent Energy Efficiency Indicator

In conclusion, the PEEI is a tool that generates warnings about positive and/or negative variations in the processes efficiency, facilitating the analysis and generation of plans based on the best energy practices, which allow analytical interactions between production and energy consumption in order to achieve continuous improvement.

Cumulative Sum Control Indicator and Chart CUSUM

This indicator and its chart are used to monitor the trend of the company, area or equipment regarding the variation of energy consumption, with respect to a given base period. By using the CUSUM, the amount of the energy consumed in excess or that wasnt consumed until the moment of its updating can be quantitatively determined.

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( )1ITRENDREALITRENDREAL )E(E)E(ECUSUM += (7)

Fig. 7 Graphic indicator of trend or cumulative sums CUSUM

In Fig. 7 it can be seen that a negative cumulative value represents a trend toward process efficiency, given that the cumulative sum of energy consumption with respect to the established base is lower, it results in a saving or reduction of energy consumption.

2) Identification of the control variables at the cost centers

This activity is about identifying events that have an impact on energy consumption in each of the energy costs centers set out by the organization. By identifying and implementing measures to stabilize the identified variables to the recommended appropriate values, a significant reduction of the energy consumption is achieved in the process.

For the detection of these variables a methodology [7] based on the use of statistical tools was designed and implemented and, as a starting point, was taken to analyze the relationship of the energy-production variables in a scatter diagram and the established energy baselines. As a result, seven variables were identified as having the highest impact on energy consumption at the critical cost centers of clinker, cement milling, and primary grinding, which are summarized below:

Table 3. Identified control variables and associated savings potential

Energy cost center Identified variable Identified savings potential[kWh/ton cement]

Clinker burning

Excess of air in the chamber of the coolers. 0,42 Height the layer of clinker bed in the coolers Removal of crusts and sudden chills in the kiln. 0,40

Cement milling

Flow of return in cement mills. 0,36

Change of product (preparation times of special cements).

(it depends on the type of cement to produce)

Downtime operation for auxiliary equipment. ----

Primary grinding Proper selection of pumps for the operation of the mills. 0,25

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Through the identification of these variables, it is possible to establish actions to retrieve the identified potential of electricity savings, and thus design procedures to keep the variables controlled to recommended values and ensure their sustainability.

3) Definition of monitoring systems

Monitoring allows identity of all deviations and, if possible, corrects them. Additionally, it can point out if it is necessary to carry out a general improvement to the process. This system of monitoring should facilitate the identification of all deviations and provide methodological tools, such as software for acquisition and management of data, indicators and control diagrams for energy variables, for guiding the plans of action, indicating if it is necessary to perform a general improvement in the process.

For the implementation of the monitoring system, the mentioned methodological tools should be used for developing phases such as: data collection, calculation of energy efficiency indicators, comparison and analysis of the indicators results based on the established target lines, analysis of the causes of deviations, reporting of results, and finally, the modification of target lines.

Therefore, SGIE technology recommends establishing a structure of energy performance indicators at company or process level in the form of an "indicator tree diagram" (see Fig. 8), so that the energy efficiency indicator of the company is structured based on Percent Energy Efficiency Indicator of each of the areas and end-use equipment that compose it. This allows for easily determining the cause, the time and the area or equipment where the indicator of the company or process has deteriorated or improved while reducing the response time for implementing the corresponding corrective or preventive action. The proposed indicator tree for the case of raw materials preparation in cement production is shown in Fig. 8.

Figure 8. Tree for the monitoring and control of energy management indicators

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4) Energy Diagnostic

Energy diagnostic aims to identify opportunities or projects for energy savings in the equipment and key processes of the company. The energy diagnostic carried out focused on three aspects: operational variability in processes, current technology of equipment, and energy culture. As a result the following issues were detected:

- Marked operational variability of processes especially for the areas of clinker and milling of cement. - Equipment operating during downtime. - Motors that are inefficient and obsolete and operating underload. - Use of inefficient lamps in several sections of the factory. - Poor energy management level in all areas of the company.

The energy savings potential associated with the main actions or projects identified within the three areas of study in this diagnosis produced the estimated saving potentials that are summarized in Table 4.

Table 4. Summary of identified savings potential

Identified opportunity Potential of

saving [kWh/ton cement]

Reduction of operational variability of processes.

7.0

Replacement of standard motors for high efficiency motors (< 25 HP).

1.6

Implementation of variable speed systems in 2 motors of fans in Clinker coolers.

0.18

Upgrade the technology in the lighting system.

0.32

TOTAL 9.1

As noted in Table 4, the total savings potential identified with the recommended actions is 9.1 kWh/ton cement corresponding approximately to 8% of the total electricity consumed in the plant.

RESULTS

Reduction of Electrical Energy Consumption in the Plant

Actions performed during the implementation of the SGIE in the plant demanded very low investment and succeeded in reducing the consumption of electricity by 4.6 % which is equivalent to 5.2 kWh/ton cement during a period of twelve months compared to the same level of production and with the trend baseline of the last two years. Fig. 9 shows Cumulative Sum Control Chart CUSUM of the plant for year 2009 showing a downward trend, which means less electrical energy consumption for the same production with regard to the energy consumption trends.

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Figure 9. Cumulative Sum Control Chart for the consumption of electrical energy of the factory in 2009

CO2 Emission Reduction

3.33 kg of CO2 per ton of cement produced annually were stopped from being released into the atmosphere in year 2009 due to a 4.6% reduction in the electrical energy consumed by the cement plant, ensuring a positive environmental impact.

At the Operational Level

At the operational level, good operational practices focused on increasing energy efficiency were accepted. New indicators of Energy Management were implemented in the companys information system (Percent Energy Efficiency Indicator and the Cumulative Sum Control Indicator and Chart CUSUM); these two indicators allow for analysis of the energy efficiency of the production process and critical equipment depending on the conditions and variables of operation that have an impact on consumption. Procedures at the operational level for control and monitoring of indicators, and work-related instructions aimed at lowering energy consumption were developed.

At the Strategic Level

At the strategic level, the company adopted the creation of an Energy Committee, which is responsible for energy information management and coordination with all other components of the organization. The head of this committee is the chief of energy management and includes coordinators of the higher energy consumption systems. Through this Committee, policies and guidelines for sustainability of continuous improvements are proposed. The committee also contributes to the change in the energy culture from the top management level to the operational level, makes monitoring and validation of management indicators, proposes innovations on processes and equipment for increasing energy efficiency with impact on productivity and performs technological monitoring through information exchange networks.

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CONCLUSIONS

In the implementation of Stage 1 of the SGIE technology, savings potential of up to 6% of the energy consumption have been detected and can be achieved with management actions of very little or no investment; such as the identification and stabilization of the energy control variables in the operation of the processes.

The implementation of the Integrated Energy Management System as a pilot project in the cement production by wet process industry increased the energy efficiency of its processes, achieving a reduction of 4.6% of electricity consumption and 3.33 kg CO2/ton of cement produced was stopped from being released into the atmosphere during the year of implementation.

A methodology to identify control variables was developed; it was applied to three critical stages of the process and seven variables of higher impact on the electricity consumption in the stages of Clinker, Cement Milling and Primary Crushing were identified.

For the improvement of the indicators of efficiency and productivity, fundamental changes, both in the organizational culture and the processes and production, procedures are required. These should be discussed and implemented appropriately.

For the implementation and sustainability of the SGIE in a company, it requires the commitment of the companys top management to achieve institutional changes, the responsibilities and functions within the organizational structure of the company must be clearly defined; and, the changes should also positively affect the work environment and working conditions in ways that contribute to achieving the goals of energy efficient management.

REFERENCES

[1] J. Campos, E. Quispe, Y. Castrillon, E. Lora. Proyecto: Programa de Gestin Integral de la Energa para el Sector Productivo Nacional. Informe parcial del Proyecto UPME-COLCIENCIAS - U del Atlntico - U Autnoma de Occidente. Nmero 1116-06-17871. Colombia, Julio 2006.

[2] J. Campos, E. Quispe, O. Prias, R. Vidal, E. Lora. EL MGIE, un modelo de gestin energtica para el sector productivo nacional. El hombre y la maquina, Ao XX, No 30, pp. 18-31. 2008.

[3] J. Campos, E. Quispe, O. Prias, R. Vidal, E. Lora. Sistema de Gestin Integral de la Energa. Gua para la implementacin. Publicado por UPME-Colciencias, Colombia, 2008.

[4] Universidad Autnoma de Occidente, Universidad del Atlntico. Ahorro de Energa en la industria del cemento Colombia 2008. Disponible en: http://www.si3ea.gov.co/Portals/0/Gie/Procesos/cemento.pdf

[5] UPME. Herramientas Virtuales Calificador de Niveles de gestin energtica. Colombia 2008. Disponible en: http://www.upme.gov.co/Index4.htm.

[6] M. Zoran and G. Dusan. Applied industrial energy and environmental management. Great Britain, Wiley, 2008, pp. 88-109.

[7] R. Castrilln, A. Gonzlez, D. Fandio, E. Quispe. Informe Proyecto: Implementacin del SGIE en la Industria del Cemento. Proyecto I+D No. 08INTER-102. Universidad Autnoma de Occidente, Cali Colombia, 2011.

[8] J. Campos, E. Quispe, E. Lora. Nueva herramienta para la medicin y el control de la eficiencia energtica en la gestin de procesos empresariales. Memorias de XI Semana Tcnica de Ingeniera, Universidad del Atlntico, pp. 76-86. Colombia 2009.

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