1 Introduction
At the end of a two-year planning and construction period, SPZ recommissioned its comprehensively modernised kiln system in spring 2011. With the installation of the world’s first “Low-Dust” Selective Catalytic Reduction (SCR) denitrification system downstream of a cement plant’s preheater tower, the modification of the rotary kiln and replacement of the old planetary cooler with an IKN grate cooler, the Rohrdorf kiln system is now one of the most modern in the world. A special feature of technological alliance is a heat transfer system that transports waste heat from the clinker cooler to the exhaust gas catalytic reactor (Fig. 1).
This new plant technology has been subsidised under the Environmental Innovation Programme of the BMU and as a demonstration project to set the trend for the entire cement industry. Parallel to this project, further thermal utilisation systems – in particular a steam power plant using steam produced from waste heat – are presently under construction.
2 Project profile
Client: Südbayerisches Portland Zementwerk Gebrüder Wiesböck & Co. GmbH (SPZ)
General plant engineering and construction contractor: IKN GmbH
Contract award: 14.01.2010
Main erection period: 03.01.2011 to 27.02.2011 (55 days)
Commissioning: 11.03.2011
Scope of order: Engineering, supply and installation
IKN services:
– Replacing the planetary cooler with an IKN grate cooler
– Construction of a new kiln hood with kiln outlet section
– Construction of a new cooler building
– Construction of the mid-air and exhaust air ducts
– Construction of a new dedusting cyclone
– Installation of the heat transfer system
– Installation of the air-air heat exchanger
– Installation of the bag filter
– Construction of new mid-air and exhaust air fans
– Construction of a new stack
Parallel to the work described above, SPZ carried out an extensive kiln reconstruction programme. This consisted of replacing the kiln tyre and the supporting rollers of pier II and installing a new kiln drive system including girth gear and gear unit at pier I. Furthermore, extensive concrete refurbishment work was executed and a new main burner was installed with its peripheral area having been optimized.
3 System concept
Clinker cooler with a range of options for heat recovery
The reconstruction concept was intented not only to achieve the usual energy savings through installation of the new IKN grate cooler but also to enable various options for the utilisation of the available heat (Fig. 2).
In the conventional cement manufacturing process the grate cooler recuperates approximately 75 % of the heat from the clinker leaving the kiln. The largest portion of the recovered heat is used to preheat the combustion air: as secondary air for the main burner and as tertiary air for the the calciner. In Rohrdorf, the kiln hood was dimensioned to permit extraction of tertiary air from the hood in the event of a future kiln system modification to operation with a precalciner. The prepared openings have been initially closed off with blanking plates. To cool the clinker to 65 °C, more air is required than can be extracted for the pyroprocess. Usually, the surplus air is drawn from the clinker cooler as exhaust air and, with a high percentage of waste heat, cooled and released into the atmosphere via a filter.
To reduce the heat loss through the cooler exhaust air, the so-called mid-air is first extracted from the Rohrdorf clinker cooler. This involves removing the air, at a temperature of more than 400 °C, from the first half of the cooler and using it elsewhere in the process chain. In other plants this hot exhaust air is generally taken for drying various raw materials needed for the cement manufacture, e.g. slag. In the development and demonstration project realised at SPZ, a different and exergetic approach was chosen for the energy utilisation of this air stream, which nevertheless corresponds to a heat flow of 6 MWtherm (Fig. 3). The air coming from the mid-air extraction point at a temperature of approximately 450 °C is initially dedusted in a double cyclone and then passed through an air-oil heat exchanger operated with thermal oil. This is part of the heat transfer system which heats the catalytic reactor in the SCR exhaust gas purification plant. The stream of exhaust gas is cooled to 260 °C and then flows through an air-water heat exchanger. This serves as a feed water preheater for a steam turbine. Once cooled to 110 °C, the air is subsequently delivered by a mid-air fan, together with the remaining cooler exhaust air, to a bag filter. As a safety precaution, an air-air heat exchanger is installed upstream of the filter to prevent the bags from being burnt in the event of any exceptional operational conditions.
4 Planning in 3D
At a very early stage in the project planning, during the quotation phase, it quickly became apparent that space limitations in the existing plant in Rohrdorf would make classical 2D design almost impossible, or would at least be unsuitable to guarantee the degree of safety and reliability required required when planning such a complex system.
At the start of detail engineering, a 3D laser scan of the existing kiln system and the adjacent areas affected by the planning was carried out. The data obtained was compared with already available 3D measurements made by SPZ in order to establish a common database (Fig. 4).
The CAD system, Autodesk Inventor, is used as a standard tool by both SPZ and IKN. However, construction engineering was carried out using Allplan and Bocad. As no satisfactory conversion tools were available at that time, data exchange tended to be a specific challenge.
The amount of work involved in the constant maintenance of a consistent, continuously growing data model of the overall project was considerable. The demands imposed by the software on the PC workstations of the planning staff constantly increased – up to the point where hardware and software had to be upgraded twice in the course of the project: Windows XP – Vista – Windows 7 were the milestones here.
Nevertheless, due to effective teamwork and a regu-lar exchange of information, the construction engineers, system planners and general planners achieved a satisfactory solution (Fig. 5).
5 Special concepts
5.1 Clinker cooler
Modernisation projects to replace planetary coolers with grate coolers are usually characterised by very restricted space conditions. The new cooler had to be set up between kiln foundations #3 and #4 of the existing kiln system and connected to the existing clinker conveying equipment in order to minimise the time needed for conversion work. Dimensions of grate coolers installed in this way are usually outside the normal length to width ratio. In Rohrdorf the grate is 5.6 m wide, and is dimensioned for a maximum future production rate of 4000 t/d. Fortunately, the existing planetary cooler was installed relatively high, so that only a small amount of excavation work was to be done for the new grate cooler. The housing of this cooler stands directly on new foundation strips. Two flat parallel tube chain conveyors were installed between the foundations. It was therefore possible to carry out all necessary excavation and foundation construction work without interrupting the kiln system operation.
The other essential peripheral conditions for the engineering and design of the clinker cooler were defined by the required heat utilisation possibilities: secondary air for the kiln inlet burner, tertiary air for the future precalcination system, mid-air for the heat transfer system and feed water preheating, as well as achieving an exhaust air temperature that is as low as possible. In the cooler, one movable heat shield was installed above the grate to separate the different hot zones and permit regulation of the air flow rates to the individual extraction points.
5.2 Air suction duct
As the cement plant is situated close to the village of Rohrdorf, high priority was placed in the planning phase on minimising noise emission. Prior to starting the project SPZ carried out a survey in order to ensure that the planned modernisation reduced noise emission levels to the absolute minimum. To meet this objective and to avoid unnecessary duct penetration through the cooler building, a common air suction duct fitted with a silencer was planned in co-operation with Reitz GmbH for the fans on the west side of the cooler (Fig. 6). The suction port for this duct was integrated into the passage between cooler and filter building. After three months of operation it can be stated that practically no noise emissions from the fans can be heard outside the cooler building. Furthermore, as the duct is suspended beneath the burner platform and there was no need to install silencers at the individual fans, accessibility to the cooler has been significantly improved. This suction concept has the additional benefit that clean, dust free air is always drawn in.
5.3 Stack
The original plan envisaged erecting a stack with a diameter of 2700 mm preceded by a silencer in the duct. However, in the course of planning it became apparent that the existing stack of the oil furnace burner in the immediate vicinity of the cooler was in urgent need of repair. In keeping with the solution-oriented project philosophy it was decided that the old stack should be demolished and replaced by an additional tube in the new exhaust air stack. During project planning it also became clear that in the future an additional heat exchanger between the exhaust air fan and the stack would be desirable. To allow for this possibility, the silencer was not mounted in the duct but integrated into the stack. The installed stack had a final diameter of 3200 mm and includes a baffle-type silencer and a DN400 stainless steel tube.
5.4 Swivel loader
In addition to the “normal” demands imposed by process and plant assembly on the structural design, the “Paus” swivel loader used by SPZ also had to be regarded in the planning stage. This type of swivel loader was originally designed for the mining industry, but is mainly used by SPZ for work on the refractory brick lining of the kiln. First, the large vertical loads imposed by this machine had to be taken into account in the structural dimensioning of the burner platform. Second, the possibility of a vehicle impact had to be considered. To ensure optimum planning and trouble-free construction, a customized concept was developed at an early stage and agreed with the inspecting structural engineer. The fundamental point was to prevent a collision of the vehicle with the building supports and consequent failure of the structure. To achieve this, latticework was installed in the working area of the loader to act as a crumple zone in the case of a collision and to reduce the impact energy to an acceptable level (Fig. 7).
As the loader is to be used for transporting refractory bricks from the burner platform into the kiln, a suitable design for a kiln hood bridge became also necessary. In view of the large loads it was evident that a standard solution could not be applied. IKN therefore designed a steel bridge being dismantable. It has guide wheels and railings and can be easily installed and removed with the aid of the burner carriage. The bridge was manufactured by a local company on the basis of IKN workshop drawings.
5.5 Refractory lining concept
The refractory lining concept had two main objectives:
a) A top-quality solution and
b) the shortest-possible installation time.
The concept developed also demonstrated the close and forward looking working relationship between SPZ and IKN. As early as February 2010, IKN invited selected suppliers to technical discussions at SPZ. On the basis of this exchange of experience and the subsequent evaluations, the order was quickly awarded to Refratechnik GmbH of Göttingen. In further discussions between SPZ, IKN and Refratechnik the final solution described here was developed. .
The side walls of the cooler were delivered by the steel fabricator directly to the refractory lining installation company, where they were completely casted under workshop conditions. This had two advantages, it achieved an outstanding lining quality and also significantly reduced onsite work in Rohrdorf. Completed panels were delivered there shortly before the assembly date reducing their storage time on site. The cooler banquets were refractory lined by the jetcast process after the cooler housing had been assembled. The ceiling lining is a conventional system brick solution.
The hot gas ducts were refractory lined as far as possible during preassembly on the construction site, so that it was only necessary to line the butt joint zones after installation. Whereas it was possible to install the refractory lining in the double cyclones while they were lying on the ground, for weight reason lining of the kiln hood by means of jetcasting had to wait until the hood had been installed in its final location.
6 Manufacturing
Construction projects in the cement industry are typified by intense cost pressure, resulting in plant engineering firms being forced to have their components manufactured in low-wage countries. Although SPZ was fully aware of this situation and imposed the same cost pressure, the contracts for this project expressly excluded manufacture in such countries as the company did not want to make any compromises regarding the quality of the supplied equipment.
IKN accepted this challenge. Since the plant design had already been completed in 3D systems, it was a logical step to design the individual parts in 3D as well. This provided an opportunity to utilise advanced manufacturing methods applied in the German automobile sector. Instead of using the classical method of manufacturing components by cutting and welding steel sections and plates, parts were laser-cut from steel plate and folded in a largely automated process. In this pilot project, said advanced manufacturing methods have produced high-quality components at competitive prices.
7 Assembly
7.1 General
IKN were required to dismount the existing components and assemble the new equipment within a period of 55 days. This ambitious target demanded not only precise planning, but also excellent co-operation between all the companies and people involved (Fig. 8). The assembly concept was based on the principle of maximising the degree of completion during preassembly in order to minimise the amount of work required during the plant stoppage.
7.2 Initial situation
The Rohrdorfer cement plant is bounded to the south and west by mountain slopes and has expanded naturally during the preceding decades. As a result, the plant is not a classical cement production line with a straight flow of material from the quarry through the raw mill to the kiln and on to the clinker silo. The flow of material meanders through the plant entails a high building density on the site. For this reason it was not possible to use the frequent method of preassembling the clinker cooler parallel to its final installation position and later shifting it into place.
Figure 9 illustrates the initial situation in the direct vicinity of the future clinker cooler. It shows the old planetary cooler (a), the blending bed hall (b) and the coarse material conveyor belt (c). The coarse material conveyor belt runs right through the planned new building and had to remain in operation during the conversion work, which presented a particular challenge.
7.3 Construction site logistics
Due to the restricted space conditions in the immediate vicinity of the installation area, preassembly was, to a great degree, carried out south of the production plant. Special vehicles had to be used in some cases for transporting the preassembled components to the actual construction site (Fig. 10). Only the grate cooler substructure was preassembled next to the clinker crusher so that it could be hoisted into place as a complete unit (Fig. 11).
To implement this concept, a 350 t crawler crane was positioned west of the existing planetary cooler. Transportation to or from site of components to be hoisted took place in the corridor between the clinker silo and the rotary kiln. In the phase prior to plant stoppage, the crane was equipped with a 24 m main jib and a 42 m articulated jib to permit assembly of parts weighing up to 18 t in the area of the filter building. Before plant stoppage, the crane was converted to an articulated jib of 24 m, to ensure that sufficient hoisting capacity was available for the disassembly and installation of heavy plant components. After the upper part of the cooler building had been completed, further assembly work proceeded with the aid of mobile cranes.
7.4 Work prior to plant stoppage
Demolition of the burner platform and coal loading equipment
SPZ had already started with this work as early as May 2010, meaning about 7 months before the planned stoppage. The first step was the demolition of the existing burner platform together with roof, annex and the coal loading station.
Foundation work for the filter and cooler buildings
Parallel to the demolition work, approximately 130 micropiles were driven as a foundation for the cooler and filter buildings. Part of this work was carried out underneath the rotating planetary cooler, demanding special measures for the safety and cooling of the equipment used.
Erection of the filter building
Due to a combination of cast-in-place concrete supports, semi-precast wall sections and preassembled ceilings, the filter building could be constructed quickly. It was possible to hand over on time the three-storey structure to IKN in mid-October 2010.
Preassembly of the plant components and steel structures
Delivery of the first plant components and their preassembly commenced in September 2010. The sizes and weights of the parts were limited by the restricted space conditions on the installation site. The following work was carried out:
Kiln shell end section – assembly of the outlet segments and mounting parts
Kiln hood – assembly of the four sections and installation of the refractory anchors
Ducts and piping – assembly in sections of maximum hoisting size, lining with refractory materials
Cyclones – assembly and installation of the refractory lining
Air-air heat exchanger – assembly in sections of maximum hoisting size
Bag filter – assembly in sections of maximum hoisting size
Assembly of plant components
From the middle of October 2010, plant components in
the area of the filter building were assembled. The initial step in this phase meant to build in the completely assembled troughs under the air-air heat exchanger (AAHE) and the filter. The lower section of the 32 m high stack was erected next. Pipe bundles were then installed in the AAHE and the erection of the completely preassembled filter housing took place (Fig. 12). Afterwards the upper section of the stack was hoisted into place. Upon the exhaust air ducts had been positioned on the 2nd floor, the double-flow exhaust fan was installed.
Erection of the eastern section of the cooler building
Parallel to the work on the filter building, the steel structure for the cooler building was erected between the rotating planetary cooler and the existing coal mill building. The distance between the cooler tubes and the erected steel structure measured 300 mm only. After completion of the floor levels, the prefabricated concrete floor slabs were installed, so that all levels of the building were accessible. Subsequently, the preassembled and prelined dedusting cyclones were hoisted into their prepared supporting frames. At the same time the exhaust air duct between cooler building and AAHE was laid. In addition to a significant reduction in the amount of work involved in the main assembly, these activities, carried out under extremely restricted space conditions, provided valuable experience that led to additional time savings during the production stoppage.
Preassembly of the grate cooler
At the same time, foundations for the grate cooler were constructed beneath the planetary cooler, the tube dust extractor was assembled and the compartment partition walls were installed into the lower cooler housing. Alongside the existing bucket elevator for clinker, the movable and static sub-structures of the grate cooler were completely assembled and aligned within hoisting distance to its final place of installation. At this point the grate plates were installed, aligned and removed again in packages of three rows. The fixed inlet section of the cooler was mounted at the preassembly area. Remaining components, such as the crusher, hydraulic power pack and housing had already been delivered fully assembled to the construction site, so that no further preassemblies were required on site.
Preparatory work for disassembly of the planetary cooler
The kiln system was shut down on 17.12.2010 and SPZ personnel removed the entire refractory lining of the kiln and dismounted the tube bends of the planetary cooler. This work was finished in time for the Christmas break.
7.5 Work during plant stoppage
Disassembly of the planetary cooler
Disassembly work recommenced on 03.01.2011. The initial step was to remove the 10 planetary tubes. After the kiln shell had been cut along its length and transversely between tyres 3 and 4, the upper shell halves were dismantled in two hoisting operations. Subsequently, the burner tunnel and the lower shells halves of the kiln were removed. The planetary cooler was completely disassembled in 7 days.
Assembly of the grate cooler
After the preassembled substructure of the grate cooler had been positioned in a single hoisting operation, the grate plate packages were hoisted in. As the grate plates had been aligned during preassembly, only fine adjustment remained to be done. At the same time, the fixed inlet section (KIDS) was positioned and the lower cooler housing installed, followed by the installation of the cooling fans including the air suction duct (Fig. 13).
Erection of steel structures and assembly of plant components
After the cooler housing, fans, etc. had been mounted, the various sections of the next level of the building were completed. While SPZ was finishing demolition of the kiln foundation in the rear section and the cooler roof was being mounted in the middle section, the preassembled kiln hood was installed in the front section. During this stage, the concept of using prefabricated concrete roof sections proved to be very advantageous, enabling quick assembly and immediate accessibility to the respective levels.
As one support and the tension station of the belt conveyor between the filter and the cooler building was located in the new cooler building, the support got integrated into the new building. This resulted in the tension station being relocated to the blending bed hall situated to the east of the cooler building. The existing belt conveyor was supported by a structure to be modified with the aid of a bridge between the filter and the cooler building. The design of this bridge allowed operation of the belt conveyor even while it was temporarily secured. On conclusion of the plant installation work, the final support was set in place and the temporary solution removed. After completion of the cyclone platform, the supporting frames for the heat transfer system were installed, including the associated ducts and platforms. It was then possible to hoist the thermal oil heat exchanger, being the connecting link to the SCR system. Moreover, a “place holder” was built in for the feed water preheater system of the power station (Fig. 14).
Assembly of the kiln end section
Parallel to the activities in the area of the grate cooler, SPZ also installed a new intermediate kiln shell section and tyre support shell section while IKN mounted the kiln end section. After careful preparation and coordination, these closely linked work tasks were carried out according to schedule.
Electrical systems and cold commissioning
Wherever possible, the electrical system installation was carried out by SPZ simultaneously to the mechanical work. On completion, the equipment was connected to the power supply system and control room. System testing could be carried out during the last two weeks of February 2011 and was co-ordinated with the progress of mechanical installation. Thanks to the comprehensive electrotechnical planning carried out in advance by SPZ, trial runs of individual machine units at the respective manufacturer’s works and the use of modular applications, no unexpected problems were encountered on site. During commissioning the engineers and technicians could concentrate fully on the performance of individual drives and the kiln line control and signalling of the complete kiln system in the control room.
8 Commissioning of the kiln line
During the assembly stage, the necessary steps for system commissioning were coordinated and prepared. After a grate cooler assembly period of 55 days, the kiln was recommissioned on 11th March 2011. Although the conversion work had affected the core components of the production plant, full production capacity was achieved within a few days and the agreed performance data were attained or surpassed. The performance test was successfully carried out on 7th April 2011. The SCR section was put in operation 14 days later than the kiln.The heat transfer system has fulfilled the expectations to the complete satisfaction of SPZ.
Note of thanks
The heat transfer system is part of the SCR plant. This demonstration project received funding from the Environmental Innovation Programme of the BMU, financed by the KfW.
