DG Khan's cement plant at Chakwal, Pakistan, is one of the largest cement plants in Asia. With the support of Vecoplan FuelTrack it is successfully using alternative fuels.
Cement demand in Pakistan is strongly correlated with gross domestic product (GDP). For a few years, however, the growth rate of the GDP has stagnated in the south Asian republic. The rising cost of fuels such as oil, diesel and coal on the international markets (now and in the future) represents a serious threat to the economy. It is therefore logical for Pakistani cement manufacturers to substitute their primary fuels with alternative fuels to a very high proportion in the medium term. DG Khan is a pioneer in this field in the Pakistani cement market.
Founded in 1978, DG Khan has belonged to the Nishat Group, which has been active in diversified markets since 1992. Since September of that year the company has also been listed on the stock market. It is currently Pakistan's largest cement manufacturer with a capacity of 14,000t/day (4.2Mt/yr). The company operates three plants, two in Dera Ghazi Khan and another one in Khairpur District in Chakwal.
In November 2009 DG Khan Cement and the parent company of Vecoplan FuelTrack, Vecoplan AG, signed a contract for an extensive system for the handling of alternative fuels at the Chakwal plant.
With the experience gained by the German company from its decades in the field of alternative fuel preparation, storage and promotion, Vecoplan AG is a technology leader in this area today. With this knowledge it was possible to realise a future-oriented project for Pakistan.
As early as 2008, immediately after commissioning of the new kiln line, DG Khan began to plan the targeted use of alternative fuels, the first cement plant to do so in the country. The company had earlier developed its own experiences with the use of rice straw before it turned to an experienced supplier.
Stage 1 of the plant at DG Khan was commissioned in August 2010. Since then 20t/hr of alternative fuels have been employed. The concept of a future-oriented system was designed so that it is possible for the operator to use all available (solid) fuels on the market. In the present operation, biomass consisting of agricultural waste and a pre-treated light fraction from a municipal waste processor are used. The system was designed in a modular fashion so that it can be expanded without interrupting the flow of material at any time.
The core element of the system is the Vecoplan storage system, which is fed through a common line in the first stage. Before the material is received by one of (currently) three loading and unloading conveyors, a shredder downsizes it to the desired particle size (See Figure 1). A modern Vecoplan shredder type VAZ 2000 MF T is used for this application. The rotor is driven by a patented, energy-efficient 203kW high-torque motor.
This shredder also has a built-in protection mechanism that reduces the susceptibility of the cutters to undesired interaction with hard parts of the fuel and impurities that could not be removed (despite pre-treatment of the material). This is a 'must-have' in view of the quality of the RDF that is currently available.
The pre-selected fraction of the household waste is fed either separately or in combination with the waste from agricultural biomass and shredded to <70mm in the Vecoplan shredder.
The high level of sophistication of the materials to be delivered (in terms of their density, moisture and the calorific value) require an intelligent and flexible form of storage. The loading and unloading conveyor from the company Vecoplan AG, which has demonstrated success worldwide, exactly matches these requirements. The storage system has already proven itself hundreds of times in the past and has been successfully used for many years for alternative fuels in cement plants. The loading and unloading conveyor, like the storage systems, is also suitable for ATEX protection areas.
In this storage system, the material is spread by a huge drag chain conveyor that hangs via steel wires from the ceiling (See Figure 2). In this way the material is spread and delivered from above. This results in a layer-wise storage of the fuel. Due to self-compression of the RDF, a high storage volume can be obtained.
During discharge of the material with the scraper, the upper layers of material can be easily removed, as the material is released in the above-supported layers. The fuel slips over the angle of repose that was produced during the entry in separate intermediate bins. From there, the material is dosed with type DFS 400 frequency-controlled double screws in a collecting conveyor.
The whole process is fully automatic and can be altered at any time from the central console. The different material streams are mixed together from all boxes according to the calorific properties of the flow-streams.
DG Khan's plant was planned in a modular fashion to keep the investment costs low at the beginning of stage 1. In the first stage three storage boxes are installed, (See Figure 3), to store various types of fuels.
Due to the modular design it is possible, at a later date, to expand the storage capacity without disruption of the current material flow. The number of storage boxes can theoretically be as high as desired.
As a further conveying enhancement, an inexpensive and low-maintenance closed conveying system was required to feed the calciner. For this purpose, the efficient Vecoplan transport system VecoBelt type VFR 800 was used. This is, as illustrated in Figure 4, a completely closed tube in which the conveyor belt slides on an air cushion. Fans, which are mounted at regular intervals along the conveyor path, feed a constant air flow under the belt so that this slides, almost without friction. Due to the low friction, large flows can be transported over long distances.
Thanks to the lack of casters, which are needed in conventional conveyor belts, there are, in theory, no maintenance catwalks required. In addition to financial savings the visually sleek compact conveyor system makes a positive visual impact at the plant. The alternative fuel is taken to the preheater, weighed and fed to the calciner. DG Khan now has the latest technology for the use of alternative fuels in the cement manufacturing process.
Looking ahead
Even during the early stages, DG Khan planned, with the help of Vecoplan engineers, to not only expand the alternative fuels facility, but also to establish a separate alternative fuel processing line. This would give the company the possibility to have an influence on the quality of the waste fuel from the available waste streams.
Meanwhile, Vecoplan FuelTrack, the joint venture of ThyssenKrupp and Vecoplpan AG, dedicated to serve the cement industry with engineering and equipment for refuse-derived fuels, took over the further project development for DG Kahn and is realising the alternative fuel processing line.
The structure of the processing line started in the second quarter of 2011. The second and third stages were mounted on this ground and have been in full operation since January 2012.
Further updates from this ongoing project will be presented in future issues of Global Cement Magazine.