To diversify its fuel use and ensure stable plant operation, Arabian Cement Co introduced alternative fuels (AFs) on Line 2 at its plant in Suez, Egypt. Following its initial success, the company decided to lift its thermal substitution rate (TSR) by installing a hotdisc AF system on Line 1 as it aims to raise its TSR to 20 per cent by 2020. By Saeed Abou Hussein, Arabian Cement Co, Egypt.
Arabian Cement Co (ACC) was first established in 1997 by a group of Egyptian entrepreneurs, who aimed to create a leading Egyptian cement company. In 2004 Spain-based Group Cementos La Union acquired the majority of shares in ACC and set the company on a path towards success with its main cement brand, ‘Al Mosalah’, being one of Egypt’s leading brands. In 2014 the company was listed on the Egyptian stock exchange.
Located in Egypt’s Suez governorate, ACC’s cement plant operates two production lines with a clinker capacity of 4.2Mta and a cement capacity of 5Mta. Its present fuel use is coal, petcoke, diesel and alternative fuels (AFs).
First steps to AF use at ACC
To alleviate the impact of a natural gas shortage following the country’s energy crisis in 2011, ACC launched an ambitious plan in 2012 to fully convert fuel use at its production facilities from natural gas to a range of solid fuels – mainly coal and AFs. These fuel mix changes (see Figure 1) would help ensure reliable and stable plant operation.
By the end of the year, the company had started the construction of the first AF system, which included a shredder, storage and dosing facility to feed shredded AFs into the precalciner of Line 2.
With a capacity of 12tph, the system has been designed to achieve a thermal substitution rate (TSR) of up to 10 per cent of Line 2 fuel requirements and is equivalent to a TSR of five per cent in terms of total plant fuel requirements.
The hotdisc system
Following the successful introduction of AFs on Line 2, the cement producer decided to expand the use of AFs to Line 1. Therefore, in 2013 ACC signed a further contract for the engineering and supply of the plant’s second AF system. Construction work on the hotdisc project started in 2014.
The hotdisc installed in ACC is the first in the Middle East-North Africa region and at the time of construction was considered to be the largest installed hotdisc in the world. It has a design capacity of 31tph and can achieve a TSR of up to 40 per cent. The system comprises of two feeding points for bulk solid fuels and pulverised solid fuels, two dosing sytems for each type, a system of conveyors to the feeding point and the hotdisc reactor which is attached to the precalciner of Line 1.
The main benefit of the hotdisc installation compared to other AF installations is its flexibility to burn solid AFs in a range of sizes and specifications. This is made possible by the variable speed of the rotating disc, which provides the ability to adjust the AF residence time on the disc from a few minutes to 45min, ensuring increased combustion efficiency compared to conventional calciner firing.
AF selection
When sourcing AFs for use in a cement plant, the price per heat unit is a key factor. However, there are other parameters that need to be taken into account to achieve an optimal fuel mix. A further important factor is fuel quality. This includes physical properties such as dimensions and moisture, which determine safe storage and on-site handling, as well as chemical properties, net heat value (NHV), chloride content, ash content, etc, all of which can impact on the kiln system and clinker quality. Additional factors are the availability of the AFs throughout the year as well as their uniformity and consistency of quality over time.
In terms of the types of AF used by ACC at its Suez facility, more than 95 per cent of the plant’s fuel mix consists of four kinds of AF that are used on a regular basis (see Figure 2).
Refuse-derived fuel (RDF) represents nearly half of the fuel mix. The RDF is transported from municipal solid waste treatment plants in bulk or pre-shredded form. While it is bought at relatively good prices and is available throughout the year, its quality can vary significantly between different sources due to different treatment technologies used and the location of sites (eg, proximity to major cities).
Biomass represents an extra 39 per cent of the ACC fuel mix. Most agricultural waste, such as rice straw and tree trimmings, arrive at the plant as bulk or pre-shredded material. Compared to other types of solid AF, their main advantage is their stable quality. However, they are only available during certain times of the year, depending on the source.
In addition, the cement producer also uses tyre-derived fuels (TDFs), in particular the shredded variety as the plant’s conveying system is not designed for whole tyres. While its high NHV and consistent quality make it the most economic and convenient fuel in terms of kiln operation, available volumes are very limited.
ACC’s fuel mix is also complemented by dried sewage sludge (DSS), which is a fine material and therefore, requires a separate conveying and dosing system when compared with other fuel types. It is supplied by sewage treatment plants and has a very stable quality. However, DSS volumes are low.
While other AFs such as shredded plastics and industrial wastes are available, their volumes are generally insufficient for large-scale use at the plant. As a result they represent less than five per cent of the ACC fuel mix.
Towards 20 by 2020
Since its commissioning in May 2015, the hotdisc has burned close to 200,000t of AFs, supporting a rise in TSR at the Suez works from four per cent in 2013 to 14 per cent in 2018 – a significant step towards the plant’s target of 20 per cent by the end of 2020 (see Figure 3).
This article was first published in International Cement Review, February 2019.
