Sustainability through Optimization

Introduction

Background

To achieve global decarbonization targets, there are two main approaches: replacing carbon-intensive energy sources with carbon-free alternatives, or reducing and optimizing the current specific energy consumption (both thermal and electrical).

This paper examines two cases from a cement plant where we worked to optimize processes with the objective of reducing CO2 emissions by lowering specific energy consumption. The first case involves a VRM (Vertical Roller Mill) that experienced increase in power consumption due to system defects and operational issues. The second case focuses on optimizing the specific heat consumption of one kiln.

Sustainability Vision

ASEC approach to problem solving stems from our responsibility toward the environment and our clients. By focusing on optimization, we aim to achieve cost optimization while contributing to the production of green cement.

Optimization shifts the priority from maintain to produce to become maintain to reduce CO2 emission. It involves working within existing system limits to achieve emission reductions. By optimizing, companies can save on operational costs and minimize the need for large investments in CO2 reduction technologies.

Investigation strategy

To achieve optimization, the first step is to identify bottlenecks and key points within each system. Conducting intensive and comprehensive audits is essential for evaluating system performance. These audits assess the operational status (on/off) of equipment and include both process and mechanical evaluations. Key elements of these audits typically involve:

1. False air mapping.

2. Airflow measurements.

3. Gas Speed assessments.

4. Heat & Mass Balance

5. Cooler efficiency assessment.

6. Radiation assessment.

7. Visual inspection.

8. Mechanical assessment & review design.

Case (#1) VRM

It is important to note that the increase in power consumption directly translates to higher electricity usage, resulting in increased CO2 emissions. At ASEC, we believe that optimization is the key starting point for effective decarbonization.

An investigation was conducted by ASEC's Technical Center, involving both the process and mechanical teams. A comprehensive audit was carried out, leading to the following findings:

1. Very fine material as input to mill, which has 78% passing mesh 1 mm versus reference (max 10% pass mesh 1 mm).

2. High false air in mill, which reached 70% Vs Best Practice 17% (Including mill, Cyclones and Fan).

3. Very low air nozzle area of mill which reached 1.86 m2 Vs design 4 m2 which reflected in very high gas speed which reached 80 m/sec – reference is 50 m/sec.

4. Worn out in top seal of separator (Pic#1) and guide vanes (pic#2).

Defected Top seal (pic#1)                           

worn out guide vanes (pic#2)

Recommended actions applied as the following:

1. Controlled feed size at mill input.

2. Closed all false air points.

3. Enlarged air nozzle area.

4. Adjusted all control valves of the hydraulic circuit.

5. Complete repair of top seal and vanes of separator.

6. Enlarged motors pulleys of 3 air lift blowers.

Results

1. Increase flow rate of air lift blowers by 24.5%.

2. Vibration issue solved.

3. Mill productivity recovered.

The estimated CO2 reduction achieved is as follows:

For Scope 2 emissions related to specific power consumption, CO2 emissions were reduced from 37 kg CO2/ton of cement (before optimization) to 29 kg CO2/ton of cement (after optimization). This represents a total reduction of approximately 9,030 tons of CO2, equating to a decrease of 21.6%.

Case (#2) KILN 

The kiln in this case is 77 meters in length and 4.75 meters in diameter, equipped with a 5-stage preheater, an inline calciner, and a modulated cooler. Initially, kiln operation was stable, but performance began to deteriorate, leading to increase specific power and specific heat consumption. We recognized that optimizing these parameters would positively affect CO2 reduction. Below is a comparison of the kiln's design versus its actual performance figures during period before optimization.

ASEC Technical Center conducted a comprehensive audit, including a detailed heat balance analysis within the system boundary, to pinpoint the sources of energy losses. The audit revealed that the primary losses were from the cooler, which accounted for 196 kcal/kg of clinker. Based on this finding, the ASEC team focused on optimizing the cooler, as outlined in the following cooler balance:

The process measurements revealed the following key findings:

1. Cooler losses were around 196 kcal/kg of clinker, compared to the reference value of 100 kcal/kg.

2. Secondary and tertiary air temperatures were low, measured at 870°C and 885°C, while the benchmark temperature is around 1000°C or more.

3. Clinker temperature was high at 130°C, compared to the reference value of 100°C.

4. Cooler efficiency was very low, reached only 54%, while the reference efficiency is between 70% and 75%.

5. The absolute airflow of the cooler fans was found to be lower than the design and PGT figures.

6. Visual inspections revealed: 

1. Blockages in the pathways of the cooler fan flow and buildup on the cooler modules, restricting fan airflow. (pic #3)

2. Malfunctions in the airflow controllers inside the cooler. (Pic #4)

                               Pic #3                                       Pic #4

The following actions were taken to address the issues:

1. All pathways for the fans and cooler modules were thoroughly cleaned.

2. All cooler airflow controllers were adjusted to ensure proper functioning.

Results

1. The airflow of the cooler fans increased by 5% to 13%.

2. Both tertiary and secondary air temperatures increased by 25%.

3. Specific heat consumption decreased from 854 kcal/kg of clinker to 785 kcal/kg of clinker.

The impact of this optimization on CO2 reduction, which is the core objective of this investigation, is as follows:

Conclusion

After thoroughly analyzing the previous two cases involving the VRM and kiln, it is clear that optimization can lead to significant CO2 reduction. To conclude the performance optimization in relation to CO2 reduction, we can observe the following outcomes:

By the end of the case, it becomes evident that investing in carbon reduction is essential. However, achieving this while maintaining a budget surplus through optimization is even more advantageous. By working within defined constraints and focusing on operational efficiency, significant cost savings can be achieved. These savings can then be reinvested in additional decarbonization projects, amplifying the impact.