From Grinding to Green Energy: Pursuit of Net-Zero Emissions in Cement Production ^†

Abstract

In an age of heightened environmental awareness and the pressing need for net-zero emissions, concerns over rising energy consumption in cement production, responsible for 5–8% of global CO₂ emissions, have intensified. This paper proposes a novel pioneering framework that integrates Shannon’s entropy and Multi-Criteria Decision Making (MCDM) methods to steer the cement industry towards sustainability and net-zero emissions. Utilizing Shannon’s entropy, the research impartially determines the significance of multiple criteria, reducing biases in decision-making for energy efficiency in cement production. Four MCDM methods (TOPSIS, VIKOR, ELECTRE, WSM) are applied to rank energy efficiency alternatives, providing a nuanced analysis of options for the cement industry. The study integrates sensitivity analysis to evaluate the robustness of MCDM methods under varying conditions, assessing the impact of changes in criteria weights on the ranking of energy efficiency alternatives and showcasing the adaptability of the proposed framework. Examining six diverse scenarios reveals the framework’s adaptability and the versatility of the Horizontal Roller Mill (HRM), with the Vertical Roller Mill (VRM) emerging as a cost-effective emission reduction alternative. This interdisciplinary approach, integrating information theory, decision science, and environmental engineering, extends beyond industry relevance, providing valuable insights aligned with global sustainability goals. Harmonizing economic viability with ecological responsibility, this report offers an instructive guide, propelling the cement industry toward a more sustainable future.

1. Introduction

About 12–15% of all industrial energy use is accounted for by energy use in the energy-intensive cement industry [1]; as a result, the pursuit of energy efficiency and environmental sustainability is paramount. This study delves into the critical realm of energy-saving measures in finish grinding, a key aspect of cement production. MCDM methods are being employed to assess and prioritize energy-saving alternatives effectively. Specifically, the TOPSIS, VIKOR, ELECTRE, and WSM approaches are applied to assess and rank these options according to a critical set of standards. The study explores energy-saving measures, including improved grinding media, vertical roller mills (VRMs), high-pressure (hydraulic) roller presses, horizontal roller mills, and high-efficiency classifiers [2]. These measures are evaluated against criteria encompassing energy/fuel savings, electric savings, cost considerations, emission reductions, and payback periods.

1.1. Cement Manufacturing Process

Cement production involves combining limestone, silica, alumina, iron ore, and trace elements, followed by a heat-induced chemical transformation [3]. Raw materials like clay, chalk, and limestone undergo crushing and milling before being heated in pre-heaters, furnaces, and coolers to produce clinker. The clinker is ground, mixed with gypsum, and packaged. Two manufacturing systems exist: dry and wet processes. Figure 1 illustrates the energy-intensive wet cement manufacturing system.

1.2. Breakdown of Energy Use

In cement manufacturing, electrical energy is predominantly consumed in grinding and crushing processes. Figure 2 illustrates the energy distribution, with clinker grinding accounting for 38% of total electrical power, while raw material crushing utilizes 33%. Additional energy applications include fuel delivery, air blowers, and motors in kiln systems. Another study supports these findings, indicating that around 60% of energy in cement manufacturing is used for grinding (Figure 2).

1.3. Objectives

Considering the above-outlined challenges in energy efficiency, especially in grinding processes, this study aims to answer the following key research questions (RQs):

RQ1: What criteria should be effectively employed to evaluate and enhance energy efficiency in cement manufacturing, specifically within grinding processes?

RQ2: How can the cement industry strategically prioritize various energy efficiency alternatives in grinding processes based on meticulously selected criteria?

RQ3: How adaptable and robust is the proposed framework for prioritizing energy efficiency measures in diverse grinding process scenarios emphasizing various criteria?

To address these inquiries and contribute towards enhancing the understanding of grinding energy within the cement industry, six distinct types of grinding processes, namely improved ball mill internals, vertical roller mills (VRMs), high-pressure grinding rolls (HPGRs), horizontal/ring roller mills, high-efficiency separators (HESs), and process control and management in grinding mills, will be thoroughly examined. The examination focuses on the roles and impacts of each component, with the aim of improving heat efficiency for more sustainable practices in the cement sector.

2. Literature Review

The literature reviews encompass a comprehensive analysis of various aspects, ranging from cement manufacturing methods and energy-saving measures to barriers in green cement production and advancements in grinding technologies (

Table 1. Overview of studies on cement industry practices and efficiency.

Scheme	Focus of Study	Findings	Reference
1	Evaluation of cement manufacturing methods using MCDA	The dry method is ranked as the best for its low carbon dioxide emissions, fuel consumption, production cost, and processing time. Semi-dry, semi-wet, and wet methods ranked accordingly.	[5]
2	Prioritization and alleviation of barriers in green cement production using the Best–Worst Method (BWM)	The lack of a conducive corporate environment is a significant barrier. Cost-effective environmental research and training are suggested for improvement.	[6]
3	Review of energy-saving measures, carbon dioxide emission reductions, and technologies in the cement industry	Enhancing energy efficiency and curbing emissions involves optimizing the clinker production process, particularly through the implementation of waste heat recovery systems, high-efficiency classifiers, and grinding aids.	[7]
4	Thermodynamic and exert economic analysis of a cement factory	Supplying hot gas and reducing moisture rates decrease specific exergy costs, resulting in cost savings.	[8]
5	Use of waste powders in geopolymers	Multi-criteria decision support methods help optimize geopolymer design.	[9]
6	Analysis of energy efficiency in cement finish grinding	Specific energy is dependent on parameters; additional compounds improve efficiency. Optimal parameters for maximizing energy efficiency factor are determined.	[10]
7	Exploration of efficient energy-saving cement grinding technology	Advantages of the joint grinding system include high productivity, low energy consumption, and low noise. Development prospects are broad.	[11]
8	Comparison of cement grinding systems	Specific energy consumption and cement setting times vary among grinding systems. High-pressure roll mill grinding is superior in strength development. Temperature difference affects gypsum dehydration.	[12]
9	Exploring energy conservation in Taiwan’s cement industry	Presented energy conservation technologies such as advanced mills, waste heat recovery, and process control.	[13]
10	Quantitative analysis of energy conservation in China’s cement industry	Energy saving potential of 19.06% and 33.69% with medium and high energy efficiency, respectively.	[14]
11	Aimed at minimizing power consumption and enhancing productivity in the cement industry, emphasizing the advantages of vertical roller mills (VRMs) over ball mills and the impact of VRM parameters on performance	VRMs are favored for their low power consumption, increased capacity, and process simplification. However, sensitivity to vibrations can affect productivity. Using problem-solving tools to address vibration causes and process deterioration can enhance VRM productivity and reduce energy consumption	[15]

).

3. Evaluation Criteria

The evaluation of integrating energy into cement manufacturing considers three main dimensions: financial, technical, and environmental. Financial analysis examines investment costs. Technical evaluation focuses on power generation efficiency and technology maturity. In the environmental dimension, scrutiny involves potential negative impacts and reducing emissions (CO₂ per tonne of cement).

Table 2. The selected criteria.

Criteria	Sub-Criteria	Unit	Criteria Type	Description
Environmental	Emissions reduction	kgCO2/tonne	Cost	The carbon footprint throughout the lifespan of the technology is quantified as equivalent CO2 emissions.
Technical	Energy/fuel saving	G.J./tonne	Benefit	Energy/fuel saving per tonne of cement produced.
Technical	Electricity saving	kWh/tonne	Benefit	Electric savings per tonne of cement produced.
Financial	Cost	USD/tonne	Cost	The cost of producing one tonne of cement.
Financial	Payback period	years	Benefit	Payback periods, or the amount of time needed to recoup the initial expenditure, are determined solely by energy savings.

outlines selected criteria, and initial data for energy savings in finish grinding are provided in

Table 3. Initial data for energy savings in finish grinding [1].

Alternative		Criteria					Remarks
		Energy/Fuel Saving (G.J./Tonne)	Electric Saving (kWh/Tonne)	Cost (USD/Tonne)	Emissions Reduction (kgCO2/Tonne)	Payback Period (Years)
Improved Grinding Media	A1	0.068	6.1	1.11	6.27	8	Based on energy savings alone, payback periods are calculated
Vertical Roller Mill	A2	0.2	17	5	8.82	3
High Pressure (Hydraulic) Roller Press	A3	0.31	25	4	4.05	10
Horizontal Roller Mill	A4	0.3	27.78	4	4.33	3
High-Efficiency Classifiers	A5	0.3	2.778	2.5	0.48	10
Process Control and Management in Grinding Mills	A6	0.04	3.24	0.5	1.68	1.5

.

4. A Concise Overview of the Primary MCDM Approach

This study employs entropy and MCDM methods to rank energy efficiency measures in cement manufacturing for achieving net-zero emissions and reducing greenhouse gas (GHG) emissions. Shannon’s entropy is used to calculate the relative importance of evaluation criteria, reducing decision-making bias. Four MCDM techniques are then applied to rank energy efficiency choices, providing a comprehensive examination of possibilities. The study concludes with guidelines for the cement sector to promote efficient and sustainable production methods. Figure 3 displays the study framework.

4.1. The Calculation of Criteria Weight

Two methods for weight calculation exist: subjective and objective. The entropy weight method, based on Shannon’s entropy, provides objective weights derived from real data, promoting objectivity and reducing the influence of subjective opinions in decision-making. The calculation of Shannon’s entropy weight is conducted as in [16].

4.2. MCDM Methods

In this segment, we provide succinct remarks on four MCDM techniques used to rank energy savings in finish grinding. Kabir et al. [17] have previously addressed a broad overview of MCDM for Infrastructure Management (IM) and its applications.

• Weighted sum method (WSM) [18], TOPSIS [19], VIKOR [20], ELECTRE [21]

The combination of these methods (

Table 4. Summary of MCDM techniques and characteristics.

Method	Description
TOPSIS	Ideal for selecting alternatives closest to positive ideals and farthest from negative ideals.
VIKOR	Focuses on compromise solutions for conflicting criteria.
ELECTRE	Ranks alternatives based on outranking relations, considering both concordance and discordance of criteria.
WSM	Effective for equally important criteria, utilizing a simple additive weighting method.

), along with a rigorous approach to criteria weighting, contributes to the study’s credibility and replicability, offering a comprehensive framework for guiding the cement industry towards sustainable practices and net-zero emissions.

Additionally, a sensitivity analysis is conducted to assess the robustness of the MCDM methods under varying conditions, demonstrating their adaptability and consistent results despite changes in criteria weights.

5. Result of MCDM

Shannon’s entropy was employed to assess the relative significance of each criterion based on the initial data presented in Table 3. The application of Shannon’s entropy to Table 3 resulted in the derivation of

Table 5. Shannon’s entropy weight.

Criteria	k = 1/Ln (m), m Alternatives as Sample Size	Ej (Entropy)	Dj	Wj	Rank
Energy/Fuel saving (G.J./tonne)	0.558	0.898	0.102	0.167	5
Electric saving (kWh/tonne)		0.832	0.168	0.273	1
Cost (USD/tonne)		0.893	0.107	0.174	3
Emissions reduction (kgCO2/tonne)		0.869	0.131	0.214	2
Payback period (years)		0.893	0.107	0.173	4

, which enumerates the weights and corresponding rankings for each criterion. Notably, the analysis reveals that electric savings (kWh/tonne) emerge as the most crucial factor for cement businesses, as indicated by the data presented in Table 5. The relevant criteria include energy/fuel savings (G.J./tonne), payback period (years), cost (USD/tonne), and emissions reduction (kgCO₂/tonne).

Moreover, the ranking of energy savings in finish grinding is presented in Table 5, where various methods are assessed through TOPSIS, VIKOR, ELETRE, and WSM methodologies. The rankings in

Table 6. The ranking of energy savings in finish grinding in different methods.

Alternative	Short Code		Rank	TOPSIS	VIKOR	ELETRE	WSM
Improved Grinding Media	A1	IGM	1	A4	A4	A4	A4
Vertical Roller Mill	A2	VRM	2	A2	A2	A2	A2
High-Pressure (Hydraulic) Roller Press	A3	HPRP	3	A3	A3	A3	A3
Horizontal Roller Mill	A4	HRM	4	A1	A1	A1	A1
High-Efficiency Classifiers	A5	HEC	5	A6	A6	A5	A5
Process Control and Management in Grinding Mills	A6	PCMG	6	A5	A5	A6	A6

and Figure 4 are determined using the weights derived from Shannon’s entropy.

6. Sensitivity Analysis

The sensitivity analysis, conducted through varied weight assignments in six scenarios outlined in

Table 7. Criteria weights under different cases.

Criteria	Scenario 1 (Equal Weight)	Scenario 2 (Energy/Fuel Saving)	Scenario 3 (Electric Saving)	Scenario 4 (Cost)	Scenario 5 (Emissions Reduction)	Scenario 6 (Payback Period)
Energy/Fuel Saving	0.2	0.5	0.125	0.125	0.125	0.125
Electric Saving	0.2	0.125	0.5	0.125	0.125	0.125
Cost	0.2	0.125	0.125	0.5	0.125	0.125
Emission reduction	0.2	0.125	0.125	0.125	0.5	0.125
Payback period	0.2	0.125	0.125	0.125	0.125	0.5

, reveals the impact of changing criterion weights on method rankings. This exploration emphasizes the pivotal role of criterion weightings in shaping decision outcomes.

Table 8. Ranking of aggregate in different scenarios (among alternatives).

Rank	Scenario 1	Scenario 2	Scenario 3	Scenario 4	Scenario 5	Scenario 6
	(Equal-Weight)	(Energy/Fuel Saving)	(Electricity Saving)	(Cost)	(Emissions Reduction)	(Payback Period)
1	HRM	HRM	HRM	VRM	VRM	HRM
2	VRM	VRM	VRM	PCMG	HRM	VRM
3	IGM	IGM	HPRP	HRM	IGM	HPRP
4	HPRP	HPRP	IGM	IGM	PCMG	PCMG
5	PCMG	PCMG	HEC	HPRP	HPRP	IGM
6	HEC	HEC	PCMG	HEC	HEC	HEC

presents rankings under distinct scenarios, each characterized by unique weightings detailed in Table 7.

In decision-making, the aggregation method is employed to incorporate individual preferences, viewpoints, or assessments into a final decision. According to Mohd and Abdullah [22], each alternative is ranked and given points, with the option receiving the most points deemed the best. This approach, used in MCDM, helps identify the optimal alternative by assigning points based on ranking. If there are k options, the first option earns k points, the second k-1 points, and so on, with the greatest option being the one with the most points.

7. Discussions

This study uses a unique fusion of Shannon’s entropy and MCDM techniques to provide useful insights into the cement industry’s desire to achieve net-zero emissions. An objective examination of the criteria using entropy offers a strong foundation, and the application of four MCDM approaches results in more sophisticated assessments of energy-efficient solutions.

Table 9. Integrated assessment of cement production alternatives.

Scenarios	Best Alternative	Explanation of Potential Causes
Scenario 1—four dimensions are considered equally crucial	HRM	In this case, all factors, such as energy efficiency, cost-effectiveness, and emissions reduction, are considered equally important. The Horizontal Roller Mill (HRM) was chosen as the best alternative due to its overall performance in terms of energy efficiency, cost-effectiveness, and emissions reduction.
Scenario 2—Energy/Fuel Saving is the most crucial	HRM	This scenario prioritizes reducing energy or fuel consumption. HRM is the preferred choice because it offers significant energy savings during the cement production process.
Scenario 3—Electricity Saving is the most crucial	HRM	Here, the emphasis is on reducing electricity usage. HRM is chosen as the best alternative, suggesting that it may be more efficient in terms of electricity consumption.
Scenario 4—Cost is the most crucial	VRM	This scenario focuses on cost-effectiveness. The Vertical Roller Mill (VRM) is selected as the best alternative, indicating that it might offer the most cost-effective solution for cement production.
Scenario 5—Emissions reduction is the most crucial	VRM	In this scenario, the goal is to minimize emissions. The Vertical Roller Mill (VRM) is chosen as the best alternative, suggesting that it might be more effective in reducing emissions during cement production.
Scenario 6—The payback period is the most crucial	HRM	This scenario considers the time it takes for an investment to pay off. HRM is selected as the best alternative, indicating that it might offer a shorter payback period.

outlines the integrated assessment of cement production alternatives across various scenarios.

In addition to solving industry problems, governments can promote the adoption of energy-efficient grinding technologies through incentives, subsidies, or regulations to reduce energy consumption and emissions in cement production. Additionally, industry associations and research institutions can collaborate in sharing best practices and conducting studies on the effectiveness of these technologies.

8. Conclusions

Integrating entropy and MCDM, this study guides the cement industry towards sustainable practices and achieving net-zero emissions. The innovative framework employs Shannon’s entropy for unbiased criteria significance determination and four MCDM methods to rank energy-efficient alternatives. The analysis of six scenarios showcases the framework’s adaptability, emphasizing the versatility of the Horizontal Roller Mill (HRM) and highlighting the Vertical Roller Mill (VRM) for its cost-effectiveness and emission reduction capabilities.

This interdisciplinary approach contributes valuable insights globally, aligning with sustainability goals and promoting economic viability alongside ecological responsibility. The study effectively aligns with global sustainability goals by guiding the cement industry towards net-zero emissions, emphasizing economic viability alongside environmental sustainability. However, a deeper analysis beyond CO₂ reduction is needed to consider impacts on resource conservation, biodiversity, and the broader ecological footprint. The interdisciplinary approach offers insights beyond the cement sector, potentially influencing policy-making and environmental standards. Future research should focus on lifecycle analyses, scalability, and long-term environmental benefits for a comprehensive understanding of sustainable practices in the industry. This study helps as the cement industry grapples with the need to implement more environmentally friendly practices. In order to ensure a future that prioritizes environmental sustainability, the cement industry needs to strike a balance between economic viability and ecological responsibility, and this study offers an example of guidance on how to do so.

To pave the way for a more sustainable future in the cement industry, several practical strategies are recommended: Firstly, stakeholders should prioritize the adoption of Horizontal Roller Mills (HRMs) and Vertical Roller Mills (VRMs) for their proven effectiveness in enhancing energy efficiency and reducing emissions. Secondly, to incentivize the widespread adoption of these technologies, it is essential for government bodies and industry associations to provide incentives such as subsidies or regulatory support. Thirdly, fostering collaborative efforts between industry stakeholders and research institutions is crucial. By sharing best practices and conducting joint studies on the efficacy of energy-saving technologies, the industry can accelerate its transition towards sustainability. Lastly, it is imperative for the cement industry to strike a balance between economic viability and ecological responsibility. This entails making decisions that not only yield financial returns but also minimize environmental impact, ensuring long-term sustainability. By implementing these recommendations, the cement industry can progress towards sustainable practices and achieve net-zero emissions, addressing the urgent need for environmentally friendly solutions while upholding economic viability.