An evaluation of cement manufacture options for sustainable infrastructure

An evaluation of cement manufacture options for sustainable infrastructure

Sustainable production and use of cement, including limiting additional environmental protection costs, efficiently producing cement and minimising natural resources used, are significant global industrial objectives. One of the major challenges facing the cement manufacturing industry is that ordinary Portland cement production emits approximately 5% of the world’s carbon dioxide, and each kilogram of Portland cement produces 0.85 kg of carbon dioxide. High energy levels are also needed to produce cement, which requires heavy carbon dioxide emissions and accelerates the consumption of natural resources, which in turn affects climate change. One solution is to mix a certain amount of supplementary cementitious materials within ordinary Portland cement production. This outcome alleviates energy intensive production, reduces carbon dioxide emissions and slows natural resource consumption as well as decreasing production facility investment. Geopolymer based cement manufacturing is an alternative solution to improving this situation, as there is no carbonate content in the raw materials and less energy is required for production, which minimises carbon dioxide emission. Therefore, this is another method used to reduce the carbon footprint. In addition, fly ash is a by product of coal fired power stations and is now one of the major raw materials used to make fly ash based geopolymer cement, which slows abiotic depletion.

The goal of this research is to optimise the three areas of maximising profit in manufacturing cement, minimising natural resources depletion and reducing carbon dioxide emissions in the manufacturing process. Selecting the right tools to measure these factors was achieved by using the proposed advanced framework, which integrated tools such as linear programming with the simplex method, and used traditional mathematical and spreadsheet based methods to seek optimal results.

Six scenario based studies covered ordinary Portland cement; ordinary Portland cement with supplementary cementitious materials and fly ash based geopolymer cement in production under the same manufacturing conditions and the same boundaries in terms of the manufacturing process, seeking optimal solutions by using the linear programming equation method:

 Scenario 1 maximised the profit of mixed production ordinary Portland cement and ordinary Portland cement with supplementary cementitious materials.
 Scenario 2 maximised the profit of mixed production geopolymer based cement, including fly ash based and metakaolin based geopolymer cement.
 Scenario 3 maximised the profit of fly ash based geopolymer and ordinary Portland cement.
 Scenario 4 minimised carbon dioxide emissions from transport using the Carbon Dioxide Equivalent method.
 Scenario 5 minimised carbon dioxide emissions from transport using the Australian National Greenhouse Accounts Factors method (2014 to 2016).
 Scenario 6 made optimal use of raw materials for cement using abiotic depletion for ordinary Portland cement production.

Further, the linear programming equations consisted of ‘subject to function’ and ‘subject to constraints’, which played the vital roles in the scenario based studies. The sources of developing the ‘subject to function’ equations are found in Chapter 3 Methodology. For example, the Australian National Greenhouse Accounts Factors method (2014 to 2016) and the Carbon Dioxide Equivalent method acted as ‘subject to function’ to minimise carbon dioxide emissions from transport and to compare the benefits of the two methods. Optimal use of natural resources depletion was based on an abiotic depletion equation. The optimal mix production equation was derived from a typical cement plant operation, such as kiln, grinding, mix, machines hours, labour hours and so on. The ‘subject to constraint’ equations for scenario based studies were derived from the primary and secondary data. The primary data were collected based on well constructed interviews and questionnaire with assistance of a supplementary electronics survey if necessary. In addition, secondary data came from the literature, the annual financial reports of the target companies (2015), the Australian Bureau of Statistics (2014 to 2016), the Cement Industry Federation (2012 to 2013) and more.

To solve tailor made, complex linear programming equation problems, traditional mathematical methods were used involving graphical and Gaussian Jordan Elimination methods and spreadsheet based methods with the assistance of the Solver®, which can produce answers, sensitivity analyses and limit reports to deliver optimal solutions. Here, one of the most important outcome of the research was a sensitivity analysis report, which reflected cement factory efficiency and profit performances.

By adding to the analysis, the additional constraint that the supply of fly ash was likely to be reduced because of scheduled power station closures in Australia by 2022, it was found that the cost of the raw materials for fly ash based geopolymer cement could then be 17% higher than for ordinary Portland cement. Metakaolin or ground granulate blast slag based geopolymer cement, both of which would positively affect carbon dioxide emissions in production, could pose potential solutions to this shortage.

To probe further domestic material consumption in Australia, the time series for the regression model were developed using statistical methods, including ratio indices tools and XLminer Analysis ToolPak® to calculate raw materials consumption and forecast cement production. It also examined the status of further raw material reserves based on Chapter 3’s assigned equation. However, this equation needed to carefully analyse curve characteristics based on the trend of domestic material consumption in Australia in the outcome of results. The solution in this study was the polynomial equation, including the linear equation, instead of the original exponential equation used in the French region. Here, one of the results was that the calcium carbonate and sand would be in short supply within five to 10 years based on 9.1 to 11.1 million tonnes cement production each year.

The whole life cycle method based on 20 years of producing fly ash based geopolymer cement, ordinary Portland cement and ordinary Portland cement with supplementary cementitious materials was also used to intensively examine each raw material’s abiotic depletion and reserve status. These outcomes would send earlier messages to cement entrepreneurs organising cement manufacturing for sustainable infrastructure and provide them with optimal solutions as a result of expert, validated knowledge and opinion and optimisation of the proposed methodology.