Modernization of a kiln line within shortest shut-down period

In line with the overall trend in Swiss cement industry, Vigier Cement AG, of Péry (Canton of Berne, Fig. 1) took a decision to invest in the modernization of its existing kiln line in June 2007. The target for Project 880 RO3 was primarily that of increasing the production capacity of the plant, which had been in operation for forty-five-years, from 1800 t/d to 2400 t/d of clinker, allowing the usage of new alternative fuels and thus increasing the thermal substitution rate of alternative fuels used. In order to achieve this objective it was necessary to enlarge all four cyclone stages and respective riser ducts, integrate a precalciner with an additional calcining chamber and tertiary air duct into the system, and replace the kiln hood.

Particular importance is attached in such projects to the technical and administrative planning of the installation work, in addition to that of the process-engineering arrangements, complete with the appurtenant dimensioning and design of the plant ­sections and static analysis and modification of the existing ­support structures. Specification of a maximum kiln downtime of seven weeks by the client thus necessitated, for example, ­
performance of as much of the work as possible prior to the “fire off” period, and accurate day-by-day planning of the team’s ­activities during the intensive conversion phase. It was also necessary, ­simultaneously, to map the boundary conditions imposed by the existing load-bearing structures, or to modify them by means of supplementary structures in such a way that the optimum balance between practicality and the ­saving of working time during the kiln “fire off” phase could be achieved, with a view to optimizing the level of preassembly of system components. The essential work  involved in implementation of the project, and the experience gained from these procedures, are described below.

The central element of the 1964 kiln line consists of a 68 m long three-tire rotary kiln with a design diameter of 4.4 m.
A four-stage preheater was installed in a 71 m high steel structure at the kiln inlet (Fig. 2). The cyclones had diameters of 3.9 m, 5.6 m and (in two cases) 6.65 m. The cylindrical height of the cyclones varied between 4.6 m (Double Cyclone 1) and 3 m. A total of seven main platform structures, their surfaces each consisting of a 20 cm thick concrete slab, were created in the preheater tower. The maximum load permissible on these slabs was restricted to 5 kN per individual load and 5 kN/m²,
due to the slabs‘ extremely low reinforcement content.

The two electrostatic precipitators were installed in the filter tower added to the side of the kiln, with a total height of 56 m. After conversion work in 2004, these filters were removed and the use of the building discontinued.

The kiln hood was positioned on a reinforced concrete burner platform. Two binding beams with a distance of 6 m apart were responsible for bearing the imposed loads, including axial movement of the kiln hood. This structure simultaneously defined the boundary conditions for the geometry of the new kiln hood.

The maximum fuel feed to the kiln by means of main burner is limited by the volume of the kiln. With the given kiln dimensions, further input of thermal energy, and an increase in production capacity, could be achieved only by means of a second exothermic reaction. For this purpose, a separate calcining chamber and an approx. 85 m long calciner channel, extending the retention time of the raw meal by around five to six seconds, were installed in the preheater tower (Fig. 3).

Both the noble fossil fuel, coal and also alternative fuels can be fed into the calcining chamber. At the prevailing high temperatures, these energy sources can be burned without residue and, on the other hand, it is possible to reduce the percentage of expensive primary energy sources used. Hot air which is necessary for combustion process is routed from the clinker cooler by means of an additional tertiary air duct parallel to the kiln into the separate calcining chamber.

Connection of the new tertiary air duct and the planned increase in clinker production necessitated the installation of a new kiln hood. It was also necessary to select larger dimensions for the cyclones, the riser ducts and the material discharge chutes, to take account of the new process parameters. It proved possible, despite the concomitant increase in radiant surface area, to reduce energy consumption from 3600 to 3400 kJ/kg clinker. This was achieved primarily thanks to more efficient heat transfer within the system components, as a result of lower flow velocities.

The project was carried through between September 2008 and August 2009, and was split into four phases. All the preparatory work was performed during the first two phases, including, in particular, setting-up and equipping of the site, installation of the new plant elements which were independent of the existing kiln line, preassembly of the other components, and reinforcement and modification of the support structures. Phase 3 was the period of kiln shut-down. One essential aim of the project was that of keeping this phase, in particular, limited to only ­seven weeks, and thus restricting interruption of production, and the thus necessary purchase of clinker from outside suppliers, to a minimum. All project elements not essential for operation of the plant were completed in the final, fourth, phase.

Of the large range of activities undertaken for equipping of the site, two were of particular importance: the selection and positioning of the most suitable crane type, and the decision to use a large work tent for preassembly of the components.

The work tent was used in Phases 1 and 2 for the delivery and storage under covered conditions of components, the size of which was limited due to transport restrictions, and for the efficient performance, using the shielded-arc process, of a major portion of the necessary welds (Fig. 4). Without this protection, it would not have been possible to meet the tight schedule at this time of the year. It was necessary at the planning stage to ensure that both access for a telescopic handler and lifting out of the preassembled components using the site crane would be possible. For this purpose, scaffolding elements were used to create a U-shaped wall structure; this was cable-braced from the outside. The roof structure consisted of two independent elements made up of truss girders, which could be easily detached and removed using the crane.

A level luffing crane was selected for this work, on the basis of experience from previously completed projects (Fig. 5). This type permits significantly larger loads for short and medium reaches compared to conventional revolving tower cranes, due to the reduction of the moment resulting from the deadweight of the boom during its movement. In our case, maximum load for a radius of 21 m was no less than twelve tonnes. This limiting weight was, in fact, exactly equivalent to the weight of the upper section of the calcining channel, with the benefit that it was possible to weld this element in its entirety in the tent and then place it with only minimal effort in its final position.

The advantage of an existing support structure in the form of the filter tower, which by this time was of no further importance for the production process, was exploited in the design of the new system, and the calcining channel positioned in this building. This decision allowed complete assembly and refractory lining of this component during Phases 1 and 2, with the exception of the elements leading to the preheater tower. Thanks to the large deadweights and effective loads of the electrostatic precipitators – 960 t each – assumed for the original design of the filter tower, modifications of the support structure remained restricted to local reinforcements of individual girders and of the roof structure and existing bracing systems. Chronological coordination of the work on the structural steel and on the calcining channel, combined with stage-by-stage lifting in of all the appurtenant components via the already completed opening in the roof, assured an efficient installation sequence.

One of the essential questions in the planning of the installation work was that of movement of materials out of and into the preheater tower during Phase 3, the actual modification period. The idea of temporary removal of the roof structure, including the bifurcation and, possibly, the upper platform structures, in order to allow vertical access to the plant elements, was quickly discarded, due to the amount of work which would have been necessary, and the time required for it. There thus remained only the alternative of lateral inward and outward movement of the material via the only unclad Axis A of the preheater tower. This concept, however, necessitated an auxiliary structure which would permit „parking“ of the ­elements in front of the preheater tower at the ­corresponding platform levels, and access to all levels for operation. The stepped installation platforms developed for
this purpose (Fig. 6) were dimensioned for all payloads of twice 5 t acting simultaneously at any position and an additional 500 kg/m² distributed load, in order that the material could be temporarily positioned during the dismantling and installation work, and that the working operations could be made largely independent of crane availability.

A further milestone during Phase 2 was the installation and masonry lining of the tertiary air duct between the position selected for the new calcining chamber and the old kiln hood (Fig. 7). For this purpose, the steel pipes were welded together to form elements of between 14 and 18 m in length and, after installation of the lightweight insulation, lifted in five sections into their ultimate position. Lining with refractory bricks was accomplished in this final position, the necessary material being brought into the duct from both ends.

The preassembly of the components of the preheater tower consisted essentially of the positioning and welding of the cylindrical and conical shells to create elements of around 4 m in height, and a projection of up to 8 m. These dimensions were limited primarily by the triangular openings in Axis A of the preheater tower, since it was not possible to remove the diagonals in this axis even temporarily. The discharge chutes and the top air duct (connection of the tertiary air duct to the top of the calcining chamber) – with the exception of the transition pieces and the conical lower sections of Cyclones 2 and 3 – were, in addition, also concrete lined. Finally, the orderly and recorded temporary storage of a major portion of the new components around 500 m to the north of the preheater tower ultimately assured adequate space for maneuver and a storage area during the dismantling phase, and systematic delivery of the necessary elements during reconstruction.

Not only installation of the working platforms, but also the major portion of the modification work on the structural steel, were also performed during Phase 2. The focus here was on modification of the wall of Axis 1 to the filter tower, which needed to be significantly altered, due to the necessary penetration for the calciner channel, the creation of all the new floor penetrations, and the modification and reinforcement of the entire planking system. It was ascertained in the course of the static calculation that uniform load transmission of the cyclone loads, in particular, at four points had been taken as the basis for the original dimensioning. This assumption is not realistic when the differing stiffnesses of the girders and the tolerances for their production and installation are taken into account, and could have resulted in serious damage. For this project, all girders were therefore dimensioned for primary load transmission at only two opposing points. Achievement of the optimum static solution of three-point support was not possible, due to the reuse of the support elements.

The demanding time schedule for Phase 3 was reason enough to seek methods of achieving rapid cooling of the kiln line. For this purpose, the large double doors above the kiln inlet chamber were opened and cold air drawn in from both directions (rotary kiln and cyclones) using the fan of the clinker-cooler dedusting system and the kiln ID fan. Flame cutting of holes in the roofs of the cyclones and in the riser ducts was started only
24 h later. Thanks to this concept, the cooling-down process had progressed sufficiently within 48 h to permit the commencement of modification work on a 24/7 basis.

The following procedure was selected for dismantling and removal of the components: The discharge chutes were firstly removed, and chutes were fixed to the cone outlets of the cyclones and used to transfer the refractory material into hoppers of 4 m³ capacity, which were then used to transport the material away. Climbing experts then removed the encrustations on the cyclone walls, riser ducts and roof linings. Subsequent dismantling and removal of the components, alternating with breaking out of the refractory lining and cutting of the steel shell into smaller pieces, then progressed downward, and was completed within a period of nine days (Fig. 9).

Installation work in the preheater tower comprised the creation of five cyclone housings (with Cyclone Stage 1 in the form of a double cyclone) above the reused support elements, renewal of the outlets of Cyclones 2 and 3, the installation of three riser ducts, and of the discharge chutes, the installation of the calcining chamber, including connection of the tertiary air duct, installation of the missing elements of the calcining channel, and the not yet accomplished modifications to the support structure (Figs. 8 and 10). Particular attention was devoted in the planning and execution of these activities to stage-by-stage completion of the individual elements, since only an early start and virtually continuous performance of the refractory work would allow on-time installation of the 240 t of insulation concrete and 750 t
refractory concrete.

The integration of the new tertiary air duct into the system also necessitated reconstruction of the kiln hood. This installation task was performed by another contractor, independently of the activities taking place in the preheater tower. Removal of the old kiln hood took three days, while installation of its replacement, after repair of the refractory lining in the rotary kiln, was accomplished in three prepared segments in a total of five days. The kiln hood seal was installed and the tertiary air duct connected simultaneously to the refractory lining work.

After weighing up the advantages and disadvantages, VIGIER CEMENT AG decided to install ceramic dip tubes manufactured by HASLE/Denmark, in Cyclones 3 and 4. Assessment of the condition of these elements under the prevailing operating conditions, and thus the efficiency of this investment, will be the subject of the upcoming inspections. As far as their installation is concerned, the around 1,200 bricks were installed without complications by four men working under the instructions of a supervisor in just sixteen hours.

All project work not absolutely necessary for the production process, such as the completion of the service platforms, repair of the surfaces on the main platforms, and concluding reinforcement work on the support structure, was performed in Phase 4. Commissioning of the new burner was also completed on schedule two weeks from starting of the kiln. This procedure made it possible to meet the requirement of a maximum interruption to production of sixty days. Work on and close to hot plant components did, however, impose significant extra burdens on the persons performing this work.

Project 880 RO3 demonstrated that, with detailed planning of all work and construction phases, assignment of all work not relevant to the production process to a preparatory and a completion phase, the assistance of highly capable partners and flexible conduct by all those involved, a kiln line can be modified with an extremely short kiln downtime (Fig. 11). The quality of the work performed is reflected, inter alia, in the production quantities and process data achieved since the restart. A figure of 1800 tonnes clinker/day (equal to the previous production capacity) was achieved, for example, after only seven days of renewed operation, and 90  % of the target of 2400 tonnes of clinker/day within twenty-nine days. At this point, energy consumption was already below the guaranteed figure.

It should be noted in conclusion, that the Clinker-silo bucket conveyor dedusting system” were also completed alongside Project 880 RO3, with around two hundred and twenty external workers, and the annual inspection also performed. Despite in some cases difficult logistical problems, all tasks were completed successfully and on time, thanks to supra-project planning and extremely good communication between the project managers.

Steel content of newly installed components

Cyclones, riser ducts and raw material discharge

chutes 150 t

Calcining chamber 21 t

Tertiary air duct, including support structures 99 t

Calcining channel 117 t

Kiln hood 51 t

Service platforms 34 t

Weight of refractory lining installed (all phases)

Refractory bricks 900 t

Insulation concrete 340 t

Fireclay bricks 113 t

Ceramic anchors 78 t

Structural steel

Modification of steel structures for the

preheater and filter towers 208 t

Flooring plates in the preheater and filter towers 62 t

Installation platforms, inc. flooring plates 51 t

Client:

VIGIER CEMENT AG, CH-2603 Péry, Switzerland

Planning and fabrication of components:

PSP Engineering a.s., CZ-750 53 Prerov, Czech Republic

Planning of structural steel modification and reinforcement, structural steel and plant-engineering project management:

Bau Ing AG, CH-5312 Döttingen, Switzerland

Installation of structural steel and components, Phase 1:

BFE AG, CH-8488 Turbenthal, Switzerland

Installation of structural steel and components, Phases 2 to 4:

ZMOP spol. s r.o., SK-900 02 Modra, Slovakia

Kiln hood installation:

TEUTRINE GmbH, D-59302 Oelde-Stromberg, Germany

Supply and installation of refractory lining:

CALDERYS France SAS, F-92446 Issy les Moulineaux Cedex, France