Net zero from the ground up

The drive towards net-zero cement production is having an impact on all parts of the supply chain, including raw material extraction. For Nuh Çimento it was a rallying call to make mining operations more sustainable, starting with its excavators. By Halim Tekkesin, Ahmet Gitmez, Sami Zengin, Yusuf Mentes and Sabri Karabay, Nuh Çimento, Turkey

The steep rise in energy prices seen in 2021 has accelerated efforts towards decarbonising energy-intensive industries such as the cement, mining, iron and steel sectors. In addition to global net-zero carbon emissions targets set by several international agreements, the ever-deteriorating economics of fossil fuels strongly dictates eliminating their consumption. Heavily reliant on fuels such as diesel, the mining sector is expected to significantly benefit from a move away from fossil fuel usage.

However, there are numerous reports and projections by prestigious institutions, government bodies and universities that aim to predict the number of years required and the amount of incentives necessary for each industry to reach net-zero carbon emissions. The most optimistic estimate for net-zero carbon emissions is no earlier than 2030 and the necessary incentives are no less than billions of US dollars.
Both cement production and the mining operations employed to supply raw materials for the process are leading sources of carbon emissions globally.

Nuh Çimento: reducing emissions from mining operations

Çimnak Co, a wholly-owned subsidiary of Turkey-based producer Nuh Çimento, is responsible for the extraction of 3.7Mta of marl and 3.3Mta of limestone from Nuh Çimento’s licenced mining areas.
To reduce carbon emissions from its mining operations, since 2016 Nuh Çimento’s technical team has been actively working on eliminating the consumption of diesel. Its design philosophy involves:
1. the total replacement of diesel with all-green electricity
2. economic viability without any government incentives or grants, ie a short payback period
3. full conformity with the existing daily mining routine of marl production.

Grid electricity is as green as the types of fuel used to produce it and different countries have different proportions of renewables in their grid fuel mix. In Nuh Çimento’s case the electricity consumed by its mining equipment has been generated by the company’s waste heat recovery plant since 2013.
Due to the high investment costs of electricity conversion, the transition to a new mode of operation is prohibitively expensive. This prepares the ground for a slow pace of conversion and the urgent need for government incentives or grants in the form of tax cuts, rebates, etc.

Nuh Çimento’s starting point was to consider the electricity conversion of its mining equipment as a standalone, self-financing investment project so that all conversion costs would be reimbursed in a few years without any tax cuts, rebates or grants from the government or non-profit organisations.

An additional obstacle that had to be addressed was avoiding any drastic changes to the existing mode of operation. Nuh Çimento’s primary function is to produce and sell ~5Mta of cement. Changes to the daily routine have the potential to impact on this main goal. Therefore, any conversion had to be completely in line with existing daily mining practices.

Grid-connected versus battery operation

There are several technological solutions available for the green conversion of mining equipment, namely:
• grid-connected operation
• battery operation, mostly Li-ion
• proton exchange membrane (PEM) fuel cell consuming H2 gas
• internal combustion engine burning H2 gas.
H2 gas produced from renewables is not yet on price parity with diesel fuel. Additionally, the refuelling infrastructure is yet to be established. As a result, any technological solution employing H2 gas was discarded by Nuh Çimento.
Moreover, a battery-based electric conversion was deemed to have the following drawbacks:
• expensive due to the high initial purchasing cost of Li-ion batteries
• The guaranteed lifespan of batteries is not long enough to redeem the initial high purchasing cost
• Cycle efficiency is lower than grid-connected machinery due to losses incurred at the battery and inverters.

Consequently, the technical solution that fulfilled the criteria set by Nuh Çimento’s design philosophy proved to be a grid-connected electric conversion. Over the last two years, issues related to grid-connected electric conversions have been addressed and solved (as detailed in ICR February 2021).

Phases of the conversion project

Phase I – conversion of large excavators

The term “large excavators” refers to loading shovels or excavators with an operating weight of 120t or higher.

For the sole purpose of a quick return on investment, excavators with higher diesel fuel consumption rates were prioritised for the grid-connected electricity conversion project. Since 2018 three large loading shovels have been converted to grid-connected operation.

Despite the psychological barrier to modifying the primary mining equipment of a 5Mta cement plant, three years of operational experience have proven that the large excavator conversion solution chosen is the most rewarding, bears the shortest payback period and is the easiest to implement in the quarry.

Phase II – conversion of medium- sized excavators

After successfully completing the large excavator conversion at the marl quarry, Nuh Çimento decided to apply the experiences gained to medium-sized excavators loading 3.3Mta of limestone at the limestone quarry. “Medium-sized excavators” refer to excavators that have an operating weight of 45-90t.

The medium-sized excavator conversion proved to be more difficult than large excavators due to a range of factors including:
• Medium-voltage electrical equipment occupies a considerable amount of space within the engine compartment, making the conversion and operation very tight
• Due to tight spacing between the tracks, the cable reel installation proved to be difficult at the lower frame of the excavator
• since medium-sized excavators move more frequently and more rapidly compared to large excavators, the cable reel had difficulty matching the speed of the excavator, risking cable breakage
• the slip ring that transfers the electric current from a stationary lower frame to a rotating upper frame has to have a robust design to prevent any dangerous arc formation or current failure.

Moreover, the limestone quarry occupies a large area and the excavators have to move from one loading location to another in a single shift. To match the mobility criteria of the quarry management, a modular power distribution solution was developed called the ‘e-House’ . The primary function of the e-House, which moves freely on a skid, is to feed six excavators simultaneously.

As of October 2021, three large shovels and six medium-sized excavators are operating as grid-connected electric machinery, consuming all-green electricity. The diesel fuel savings have added up to 1.5Ml and continue to increase every day (see Figure 1).

Feedback from partners

The team responsible for designing and implementing the conversion project strongly believes in energy efficiency and the virtues of a circular economy. Therefore, every piece of hard-earned experience has been generously shared with interested parties such as some leading excavator manufacturers, electrical equipment suppliers, cement plant operators and mining companies, to name a few. Design engineers and managers, general managers, chief technical officers and even board members, including one company chairman, have taken the time to visit the site to observe the all-electric equipment operational at the quarry.

Furthermore, in recognition of its efforts, Cimnak Co received the “Low Carbon Hero” award at the VII Istanbul Carbon e-Summit in September 2021.

Lessons learned

Lessons learned by Nuh Çimento along this conversion journey include:
• Many years of in-depth work and field data proved that a grid-connected electric conversion would be the most rewarding and practical solution compared to other available conversion alternatives.
• The short payback period of the total conversion investment is not a far-fetched dream and is attainable without government subsidies or grants.
• Large excavators (>120t) are the easiest and most feasible to convert.
• Medium-sized excavators require more careful mine site planning and the applicability of low-voltage conversion (400V) has to be explored to ensure easy daily operations.
• Apart from diesel fuel savings and a reduction in carbon emissions, the conversion of second-hand excavators presents another avenue for savings and waste reduction. This is not only in terms of reduced purchasing costs for mining equipment but also the rejuvenation of scrap machinery that would otherwise be wasted.

The next level

All the lessons learned have paved the way for the next level of grid-connected electric mining equipment design: design version 4.0. The new design version will apply to both excavators and drilling equipment, and possibly to wheel loaders. The conversion of 100t dump trucks is at the design stage and is waiting to be implemented in the coming months.

After investing millions of US dollars and thousands of engineering hours into the ambition of net-zero carbon emissions in mining operations, Nuh Çimento’s design team is confident of reaching its net-zero carbon emissions target for mining in the near future without any subsidies.

This article was first published in the January 2022 issue of International Cement Review.