Following the buy-out of all remaining Lafarge Romania shares in Medgidia Cement in August 2015 by Irish building materials group CRH, the Romanian cement producer has started a new chapter in its 65-year history. The installation of a new alternative fuel (AF) co-processing facility marks the company’s continued drive towards sustainable cement production.
Medgidia’s AF project
In 2014 the 4000tpd Medgidia cement works in southeastern Romania decided to reduce its carbon footprint by including municipal solid waste (MSW) in its fuel mix and thus reach 16tph of solid shredded waste usage. Following a RON15.71m (US$1.8m) government grant – representing half of the project cost – Medgidia Cement in September 2014 awarded the contract for equipment procurement, mechanical erection and commissioning services to IMSAT, part of the France-based SNEF Group.
The order involved the construction of a new co-processing facility with storage capacity and transport for solid shredded waste (SSW). In addition, a new chlorine bypass would enable the works to handle the higher chloride content resulting from the burning of alternative fuels. Using its own funds the Medgidia plant also implemented a project that allows the dosing, transport and injection of alternative fuel into the precalciner, effectively developing the existing AF installation to help reach its TSR target.
SSW co-processing facility
To increase AF use, Medgidia will co-process SSW, which is expected to consist of MSW and Industrial Solid Waste with a moisture content of 30-40 per cent.
The industrial waste is sourced from the textile industry and includes materials such as plastics, tyres without embedded metal, wood wastes such as pallets, furniture and tree bark, paper and leather wastes.
The SSW is delivered to the plant’s new handling platform by truck or railway in closed or covered vehicles. To comply with European legislation in terms of monitoring the quantity of AF used, a truck weighing system has been installed on the concrete platform.
In addition, a dedicated SSW storage building has been constructed, a longitudinal side of which will be left open to allow truck access for the unloading of waste. This storage hall has four compartments: three for the raw SSW and one for mechanical waste shredding systems. The storage hall is further equipped with a grab crane bridge to load SSW onto the feeding chute of the waste shredder.
The shredder combines the latest generation knife technology with a heavyduty separator and drum screen to yield an output of 33tph, depending on the mixing of AF and related moisture. It shreds 50-60 per cent of the SSW to 0-70mm in size. MSW output is expected to reach 40tph.
Shredded material is then transported by a conveyor system (which consists of enclosed belt conveyors, a drag chain conveyor and a 145m long pipe conveyor), to the shredded storage compartment of the storage building. The shredded material can then be transported on one of two routes:
1. It can bypass the screen separator to a new drag chain conveyor that distributes the material to the two storage compartments in the storage hall.
2. The 0-30mm-sized particles from the screen separator are delivered to the storage silos via existing transport to the kiln burner. Material with a grain size of 30-70mm is sent through a double gate and drag chain conveyor to the new storage compartment for shredded SSW.
Subsequent material extraction and homogenisation from the storage compartments is carried out by two drag chain conveyors and two screw conveyors. The material is then sent to the dosing installation for the calciner. Based on material heat and kiln operational requirements, the AF is dosed at a specific flow rate and sent towards the preheater via a 135m-long pipe belt conveyor.
Chlorine bypass installation
The second part of the Medgidia project involved the installation of a chlorine bypass system to accommodate the higher chlorine content from increased AF use.
The project consisted of five components:
- chlorine bypass station
- bypass dust storage and dosing to cement mills
- bypass dust transport from the chlorine bypass to the dust station
- raw meal storage, dosing and transport to the chlorine bypass station
- clean gases exhausting from chlorine bypass station to the grate cooler.
In terms of the process, bypass gases are drawn from the kiln inlet and cooled by fresh air. The core of the bypass is in the mixing chamber, where efficient mixing of fresh air and kiln gases takes place. The gases require rapid cooling to avoid the formation of dioxins. Bypass gases are then dedusted and specific volumes of dust can be added to the cement mill, provided the cement’s chlorine content remains below 0.1 per cent.
Located inside the preheater building, the bypass station is designed to handle gases at a rate of 5000Nm3/h and at a temperature of 1150˚C. To enable gas sampling, a suction chute is mounted at the kiln inlet so the gases will have a low (1.5m/s) speed, which helps ensure a small dust volume. The gases are then rapidly cooled by introducing atmospheric air via a cooling fan. Bypass gas flow resulting from the mixture is ~90,000m3/h and the temperature is 150˚C. The gases are cleaned by passing through the bag filter surface of 1600m2. The concentration of dust on the clean gases will be below 20mg/Nm3.
If the chlorine concentration is above 4.5 per cent, a dilution of kiln dust is foreseen with raw meal. In this respect a new ~1m3 meal bunker is located under the meal silo. The meal will be sampled by extraction, through a new airslide and pneumatically into the bypass hot gas duct which goes to the bypass filter.
A maximum of 2tph of meal will be introduced to the hot gas duct. Dust is collected from the bag filter and deposited into a bunker, from where it is extracted by a screw conveyor and sent to the pneumatic screw pump at a rate of 12tph. From there, it is transported to a 350m3 dust storage silo near the cement grinding department.
A discharge screw in the silo then directs the dust to two dosing systems where pneumatic transport injects the dust into the cement mill separator.
The dedusted gases from the bypass filter are transported to the grate cooler and diverted to three cooler fans. In case the bypass installation is not working, a control valve is installed on each gas duct along with a shut-off valve on the main duct.
Driving AF utilisation
The new AF installation enables Medgidia Cement to increase its TSR and meet the company’s sustainability targets as well as improve cement production at the site. ■
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