Aslan Çimento has been part of OYAK Group since 2009. OYAK Group, one of Turkey’s major cement producers, has over 17.5Mt/yr of cement production capacity across six geographically well-positioned cement plants. The Aslan Çimento plant in Kocaeli has 1.25Mt/yr of clinker and 2Mt/yr of cement production capacity. Here, Neslihan Akgün and Özlem Başaran, Environment, Health and Safety Manager and Production Engineer, respectively, from Aslan Çimento describe the results of recent environmental upgrades, including the new solid-recovered fuel (SRF) unit and the waste heat recovery (WHR) system.
Introduction
Aslan Çimento is recognised as the corner stone of the Turkish cement manufacturing industry. The company was established in 1910 as the first private equity of the Ottoman Empire and started operations in 1911 with 20,000t/yr of cement production capacity. It is Turkey’s first and oldest cement plant. The plant, together with its quarry and production and harbour facilities, is located by the sea, some 30km from Istanbul. The production base and capacity has been upgraded and expanded as cement manufacturing processes and technology has evolved in the years since the plant’s inception.
Newly-introduced environmental laws, regulations and rules have imposed notable restrictions on cement producers in Turkey, which have prompted equipment and process adaptations and modernisations by the entire industry, particularly with regards to emissions controls and waste management. While those restrictions have created an unusually difficult manufacturing environment in all of the heavy industries, particularly during the transition period, waste management issues have highlighted the topic of alternative fuel use in the cement industry. Additionally, fossil fuel based energy has continued to become increasingly expensive at the same time.
Aslan Çimento saw the change in regulations as an important opportunity and recognised alternative fuels as a sustainable lever for cost management. In addition, to further manage its costs, day-to-day process optimisations became a much higher priority. As such, a waste heat recovery (WHR) project to reuse heat from the rotary kiln was invested in. The heat energy of the excess kiln gas, which had previously been emitted to the atmosphere, is now used to produce electricity by a turbine generator.
Alternative fuel use at Aslan Çimento
Fossil fuels such as coal, petcoke and natural gas provide most of the energy needs of the cement world today. Coal and natural gas are used in their natural forms, but petcoke and other fossil fuels such as shale and bituminous sands require distillation and refinement to provide usable fuels. These fuels exist as solids, liquids and gases. The finite nature of global fossil fuel resources, high prices and their damaging effect on the environment underscores the need to develop alternative fuels for many industrial systems that rely on fossil fuels. Increased use of renewable and alternative fuels can extend fossil fuel supplies and help resolve air pollution problems associated with the use of conventional fuels.
Coal is the primary fuel burned in cement kilns throughout the world. However, the use of alternative fuels in cement kilns is common and increasing. The range of alternative fuels is extremely wide. They are usually available as gases, liquids and solids. In order to consume alternative fuels, there are three main steps to fulfil (Figure 2):
- The acceptance of alternative fuels;
- The mechanical processing of waste;
- The storage and feeding to burners from silos.
Aslan Çimento only uses solid wastes such as tyres, paper wastes, oil/solvent contaminated textiles, dried sludge, refused-derived fuel (RDF) and plastic residues. The use of these low-grade alternative fuels in precalciners is a viable option because combustion in a precalciner vessel takes place at a lower temperature. In precalciners where kiln exhaust gases pass through, the NOx emissions are reduced due to re-burn reactions. There is an increased net reduction in CO2 emissions when the waste is combusted in cement kiln systems as opposed to dedicated incinerators, resulting in a reduction in CO2 penalties. Since alternative fuels are often cheaper than conventional fossil fuels, the possibility of a competitive edge is also generated.
Besides the reduction in consumption of natural resources and the positive effect on the environment regarding waste disposal, other benefits of using alternative fuels include providing employment and helping to consume the waste of approximately 300 companies from other industries near the Aslan Çimento plant.
In 2011, a solid recovered fuel (SRF) unit was established at the Aslan Çimento plant in order to improve its environmental impact, increase its sustainability and reduce its production costs (Figure 3). The SRF unit has 10t/hr of shredding capacity. Outsourced SRF, pre-shredded and ready for consumption, is also supplied.
Since its installation, the benefits of the SRF unit have increased every year and fossil fuel consumption has fallen accordingly (Figure 4). The plant’s target for 2015 was 30%. According to the Turkish Cement Manufacturers’ Association Benchmark Report in 2014, the plant has the highest alternative fuel substitution rate in Turkey. The average substitution rate of the 50 cement plants in the country is 3.7%. After awareness about Aslan Çimento’s use of alternative fuels spread, more cement plants have turned to alternative fuels to minimise costs and meet environmental targets.
Waste heat recovery (WHR) from the rotary kiln excess gas
OYAK Group has installed waste heat recovery (WHR) units at two of its cement plants; Aslan Çimento and Bolu Çimento. Its four other cement plants do not have WHR systems as the process conditions required for electricity production are absent.
In the rotary kiln system at Aslan Çimento, approximately 270,000Nm3/hr of air comes from the cooler fans that cool the clinker to 80 - 100°C. In addition, the CO2 gas that separates from the raw meal produced during the calcination reaction adds to this air. All of the gas is used in the mills for drying and transporting the raw meal to the silos from the mills. At the end of the process, the excess gas, around 260,000Nm3/hr, is emitted to the atmosphere after being cooled by the cooling tower.
To recover this loss, Aslan Çimento invested in a waste heat recovery (WHR) unit, which started operations in the last quarter of 2014. The installed electricity production capacity is 7500kWh when 260,000Nm3/hr of excess hot air at 380°C is supplied from the rotary kiln (Table 1). The 7500kWh is equal to around 26 - 27% of the plant’s energy consumption. Aslan Çimento’s electricity production in the first 10 months of 2015 is shown in Table 2.
Installed capacity (MW) | 7 |
Annual operation duration (hr) | 7612 |
Annual gross power generation (kWh) | 52063982 |
Estimated annual net power supply (kWh) | 46138279 |
Above - Table 1: The parameters of the WHR system installed at Aslan Çimento.
Average production (kWh) | Total production (kWh) | |
January | 7291 | 4463802 |
February | 7591 | 4069548 |
March | 6993 | 4246452 |
April | 7554 | 5262327 |
May | 7307 | 5142501 |
June | 7653 | 1332450 |
July | 5222 | 1558542 |
August | 6796 | 4455864 |
September | 6740 | 4726116 |
Total | 7016 | 35257332 |
Above - Table 2: Electricity production by Aslan Çimento’s WHR system in 2015.
The waste heat carried by the stack gas is turned into electricity within the steam power cycle system (Figure 5). An ACQ boiler and a pre-heater (PH) boiler were installed at the existing facility system. The boilers heat the gas to the required temperatures and turn the water into steam via heat exchange. The steam runs the condensing impulse turbine by the low pressure-low temperature flow principle. While the mechanical work turns into electrical energy, the ‘dead steam’ is turned into water via the condenser and sent to the steam boilers to restart the cycle.
The WHR unit is expected to reduce 3% of total CO2 emissions from the calcination process and the combustion reactions from cement production at Aslan Çimento. Electricity production via the WHR unit is one of the most important methods for reducing the plant’s energy consumption from traditional fuels.
Summary
The importance of using energy resources efficiently is emphasised by OYAK Group Managers at every opportunity, such as in meetings and seminars. Studies to minimise the impact on the environment and decrease the consumption of resources through continuous improvement activities are ongoing at all of OYAK Group’s cement plants. Every employee is aware of the importance of sustainability in the cement industry.