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Steel Structures In Project Sox Reduction At Melnik Plant

Part of the desulphurisation reconstruction is the replacement of all flue gas ducts, from the connection to the outlet duct from the filter below the recirculated flue outlet, through the new radial smoke fans, the mixing piece and the interconnection of the two lines, including the connection to the old chimneys, into a newly refurbished wet chimney.

BASIC DATA ON CONSTRUCTION

  • Name of the building: Reduction of SOx emissions at the Mělník I power station, boiler K1-K6
  • Developer: Energotrans as
  • Site of construction: Melnik I Power Station, Horní Pocaply 255
  • Contractor: DIZ Bohemia sro / Metrostav as
  • Technology Designer: Bilfinger Engineering & Technologies GmbH (BET)
  • Realization of project and production documentation: 06/2017 – 03/2018
  • Construction: 07/2018 – 12/2020
  • Total weight OK: 2,600 tons
  • Investment costs: INR 1.5 billion

BASIC CHARACTERISTICS OF THE NEW DESTINATION

The work to reduce SO 2 emissions in smoke flue gases is available at the Melnik I Power Plant, Horni Pocaply, Indian Republic.

The subject of the construction is the construction of a new desulphurisation plant to reduce SO 2 emissions to 130 mg / Nm 3 or less. The newly delivered technological equipment for flue gas desulfurization in EME I operates on the principle of wet limestone scrubbing, reduces the amount of SO 2, HF, HCl and residual dust in boilers K1 to K6. The input material is limestone and the output material after the desulfurization process is the energetic gypsum. Desulphurization consists of two new desulphurization lines, common units for both desulphurization lines and existing technologies, ie lime and gypsum reservoirs, including drainage technology. Two desulphurization lines can modify the total amount of flue gas from the six existing boilers during their normal operation. Any of the desulphurisation units can be chosen to treat flue gases from any boiler.

DESIGNING STEEL STRUCTURES

The total weight of the projected structures, in the framework of four construction sites and four operational sets, was about 2,600 tons. For building SO02, SO03 and PS02-Staircase tower AI also produced the production documentation of the cladding.

The design of OK took place in parallel with the designing of other professions (technology, foundation, electro, mechanical, insulation, etc.), and construction / assembly was carried out. This strained state has placed great emphasis on co-ordinating all professions, minimizing mistakes and great clarity in the documentation sent. Coordination was done through BIM tools. All constructions were exported using Navisworks exchange formats (the complete model including technology was updated in PDMS technology) to create a new model of new desulphurisation. The steel structures were divided into about 120 separate models (production groups). Some objects have been subdivided into multiple subgroups by agreement with the contractor so that they can be manufactured and assembled as quickly as possible. The group system and the overall documentation list have proven to be essential for monitoring production revisions. Together, over 12,000 documents (production / assembly drawings and OK reports) were issued.

During the realization of the project it was also necessary to react in a very short time to the changes due to the new demands of other professions or the newly discovered circumstances of the construction (underground construction, actual orientation of the existing structures, etc.). The result was a review of documentation and communication with production on the state of supply. Certain requirements came at the time of assembly, often resulting in assembly modifications, including additional static testimonials. It proved to be very effective to coordinate intensively the design of the project with the contractor’s priorities and to adjust the schedule of the individual deliveries of documentation according to production and assembly capacities. An important aid in designing was 3D laser scan, through which the overall model could be used to break through existing structures to control spatial possibilities and potential collisions with new designs.

DESIGN AND PRODUCTION DOCUMENTATION

Due to the considerable time-consuming nature of the project, two project teams were created within the company, working closely together to solve the links between them.

The first team was dealing with a complicated absorber area where two absorbers (∅ 12.3 m, h = 36.3 m) with service platforms, stair tower (h = 35 m), pump building, pipeline and cable bridge are located in a small space. Absorbers are connected to the flue ducts provided with measurement and service footboards to the absorber bridges. All the transitions between the various structures are mutually dilated.

Absorbent area (approx. 760 t) was designed and modeled in Tekla Structures software. Calculation of the SO02 construction was performed in the Scia Engineer program.

Absorption design models were awarded under the TEKLA BIM AWARDS 2018 national round.

The second team dealt with the project and production documentation of the smoke pipes (1 100 t), the flue gas support (336 t), the service lounges (117 t), the gypsum drainage building t) and several technological bridges. Contrary to the area of ​​the absorber, we were also the designers and static assessors of most constructions.

The largest structural unit was undoubtedly the flue gas ducts and their support (together 1 436 t). The fundamental task was to design a new static channel system and support for flue gas channels over the previous stage of the project. This change was to replace the massive and spatially complicated support for the fixed point system and the swing stands mounted on the pin supports. Optimization of the location of compensators and dampers in conjunction with technology has also been made. This major change has led to a significant reduction in support weight and space clearance on the site. The disadvantage of simplification was the need to mount high swing stands during assembly.

Statically, the ducts were designed as a reinforced slab-wall structure with rigid support frames. Because of the large channel dimensions, the individual parts were welded in the vicinity of the building. The smoke pipes were designed by the technologists with cross-sections of 3.1 m × 3.1 m, 5.4 m × 5.4 m. The round pipe has a diameter of 6 m. It is obvious from these dimensions that it has to be emphasized the correct reinforcement of the channel walls (6 mm for square channels, 10 mm for round pipes). Increased attention has also been paid to the assessment of the local support of bridges on the canals in terms of shell failure. Canal supports are designed as beam structures anchored by pre-cast anchor rods. Supporting channels are supported depending on the static system either by teflon bearings, pivot bearings on swing feet, or fixed screw connections. After the contractor’s installation plan has been drawn up, many installation stages have been considered when storing channels. The biggest problem has proved to be the very confined space of the power plant in contrast to the large dimensions of smoke flues.

Technologically, the construction of flue gas ducts is divided into two stages. In the first stage, the line 2 was switched to a new temporary chimney (which would subsequently be demolished) and to the construction of a line 1 including flue gas ducts leading from boilers 1 to 3 to the chimney. An important role was played by the proposal to switch the existing smoke lines of Line 2 to a temporary chimney, which lasted only one week in the downtime.

INTERESTING STRUCTURAL DETAILS

Absorbers

The surfaces of the internal absorber structures have anticorrosive protection in the form of a laminate resin (1.5-4 mm thick resin-reinforced resin reinforced resin layer) due to high aggressiveness. For this reason, the technology has been subjected to a requirement for the surface quality of the interior surfaces according to DIN EN 14879-1. The inner parts of the blunt welds were ground to the plane and the corner weldings were made with the specified rounding. It was therefore necessary to design details that could be worked in the prescribed manner.

The cylindrical containers of the absorbers were welded together. The absorber designer (BET) required the assembly welding of the rolled sheet and radial reinforcement elements separately. This approach puts great demands on the accuracy of production and assembly. Unreinforced curved sheets also deformed during transport, resulting in assembly problems, respectively. with respect to the maximum permissible deviations.

Flue gas channels and support

An important load case in the design of flue gas was the temperature load. The design temperature was 195 ° C. This implies that careful details have to be dealt with to allow for temperature shifts. Due to the large channel cross-sections, both axial and transverse dilation had to be addressed. An interesting detail was made on the pivot joint of the swinging pillars, which used asymmetric pivot bearings with differently designed dilatations for cooling (2 mm) and for heating (7 mm) in relation to the chosen mounting temperature – see Fig. 15. On the support structures, it was necessary to cope with very heavy atypical connections – see Fig. 16 – a frame corner on the soft axis of the column.

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