On September 28, 2022, Wellons.RU LLC completed a project to replace the refractory lining of the flat roof of the boiler as part of the modernization project for the furnace of steam boiler No. 1 at a mini-CHP. These works were carried out under the terms of the EPC contract, including engineering, selection and supply of materials, as well as work on breaking out the existing (old) lining and lining work on the installation of a new refractory lining of the flat roof of the boiler.
ENGINEERING.
The main goal of the flat roof replacement project of the boiler is to find a technical solution based on the analysis of the existing situation of permanent failure of various monolithic refractory lining cards in different areas of the flat roof of the boiler. The situation of failure of refractory lining cards occurs with a certain frequency and is inherent in both furnaces of mini-CHP boilers. Thus, the goal of engineering and the project as a whole is to find a constructive solution that should solve the existing problems and ensure trouble-free operation of the boiler plant for a long time (up to 5 years or more of normal operation of the boiler roof lining). The proposed solution should also take into account the loads from the lining on the metal structures of the ceiling and walls of the boiler - they should not exceed the existing total loads from the lining of the boiler roof.
In order to study the current situation with the loss of the boiler vault maps, Wellons.RU specialists carried out a technical inspection of the boiler to visually inspect the technical condition of the refractory lining of the boiler vault, as well as the lining of the walls and the arched vault. The results of the inspection are presented separately and are part of the explanatory note of the project.
Based on the results of the inspection, as well as on the basis of a drawing of a general view of the lining from the manufacturer, the specialists of Wellons.RU LLC completed a working project for replacing the lining of the flat roof of the boiler, which includes: an explanatory note to the project, a graphic part of the project (working blueprints); work organization project (POW),
The selection of refractory and heat-insulating materials is based on the normal operating conditions of the boiler furnace operating on wood waste, with a temperature in the boiler furnace not exceeding 1050–1100 ° C, taking into account the technological features of the combustion process of wood fuel, its humidity, the impact of ash and slag particles, and also according to technical characteristics of refractories recommended for use by the manufacturer. The design of the lining takes into account the thermal conductivity of the materials used in order to achieve the minimum temperature of the outer shell of the boiler.
The project provides for the construction of a lining made of multilayer lining, the working layer of which is made of refractory monolithic concrete (aluminosilicate) with a thickness of 185–200 mm. As well as a heat-insulating layer of heat-insulating boards (based on kaolin fibers). The thickness of the heat-insulating layer is 200 mm. A system of ceramic and metal anchors is used to fasten the refractory to the metal structures of the boiler ceiling (I-beam). The lining consists of independent concrete cards with a thermal seam / seams formed from rolled thermal insulation material. The formation of an expansion joint is done in order to reduce internal thermal stresses between concrete maps by compensating for the thermal expansion of concrete, and preventing the formation of open cracks and chips. To reduce radial loads from inclined vaults, calipers are provided for the Bullnose transition section. The maximum detail of the design of the vault is shown in the "Graphic part" of the project.
The design of the lining provides for the preservation of the total thickness of the wall of the roof and other geometric dimensions, the preservation of the geometry of the furnace, to ensure the invariance of the internal volume of the furnace and to ensure the operation parameters provided by the manufacturer.
In the process of carrying out repair work to replace the lining of the flat roof of the boiler, design changes were found that were made by the manufacturer, not shown in the drawing of the general view of the lining, the solutions for which are described in detail in the relevant sections of this report.
REFRACTORY BREAKING
We thank the management engineering staff of the mini-CHP plant, who, knowing the technical condition of the lining of the flat roof, strongly recommended breaking out the monolithic refractory of the roof from the outside, due to repeated unpredictable collapse of concrete blocks weighing 350 kg, on average, due to breakage of the anchor bolts for fastening the cards. Indeed, during further work, we found a significant number of broken metal screw anchors along the upper border of the ceramic anchor. These cards were actually kept in a thrust, wedging each other. With little effort, during the period of dismantling, some of the cards collapsed under their own weight. In the presented photo, it can be seen that two anchors were broken even before the work on breaking out the refractory was carried out. And this is not an isolated case. Moreover, a number of broken metal fasteners of ceramic anchors were found not in the zone of primary collapse of two maps of the horizontal section, which led to the shutdown of the steam boiler (May 17, 2022). It can be assumed that the entire row of refractory concrete maps on the horizontal section of the boiler roof could collapse at any time during its operation, causing significant damage to the grate and lining of the arched roof of the steam boiler furnace. The breakage of two fasteners on one side of the card (four anchors in total per card) multiplies the load on the remaining two anchors of the card and, accordingly, increases the load on adjacent anchors due to the card catching on the other row through the Z-shaped expansion joint, thereby increasing the risk breakage of the screw fastening of ceramic anchors of neighboring cards. The further process of destroying maps could only progress. The number of broken screw metal fasteners of ceramic anchors was at least 30–35% on the horizontal section of the flat vault of the boiler furnace.
We also draw your attention (in addition to a small number of anchors - 4 pieces per plate of the available size and weight) to the structure of the metal of the cast screw fastening of the ceramic anchor in the place of its destruction - the presence of micropores, a large granular structure of heat-resistant casting (see the corresponding photo).
During the dismantling of the inclined section No. 1, two cards in the area of the “tooth” transition section (bullnose), which had a “peeling” of up to 100 mm, without direct impact of pneumatic jackhammers, but only from vibration during the dismantling of neighboring cards, collapsed without direct impact on them impact. All this confirms the correctness of the decision to replace the refractory lining of the flat roof of the boiler top as a whole.
Before the start of dismantling work on the inclined sections of the flat vault, the arched vault of the boiler furnace was protected with a wooden deck to prevent its possible destruction.
The breakout of the refractory of the flat roof of the boiler is shown in maximum detail in the video “LINING OF THE FLAT BOILER ROOM. DISMANTLING WORKS".
LINING WORKS.
The implementation of this project was carried out under the terms of the EPC contract. To do this, the specialists of Wellons.RU LLC developed their own project for laying refractory lining (a set of working documentation) based on a general view drawing of the lining from the manufacturer, selected heat-insulating and refractory materials; design and manufacture of anchor products; carrying out all work within the framework of this project was within the scope of responsibility of Wellons.RU LLC. The main features of the work are shown in the relevant sections of this report below.
1. LINING OF THE HORIZONTAL SECTION OF THE FLAT COVER OF THE BOILER FURNACE:
Preparation of ceramic anchors: prior to the start of work on the installation of the lining of the cards of the boiler furnace roof, it is necessary to prepare the ceramic anchors for installation by applying bituminous mastic in one layer (mastic layer thickness up to 1 mm). A layer of mastic is applied to the working surface of the anchor, i.e. to the height of immersion of the anchor in the working layer of refractory with a small margin. In our case, ~ 250 mm. This work must be done in advance, to ensure the hardening of this layer, before the installation of anchors in place.
This bituminous layer acts as a thermal seam between the body of the ceramic anchor and the layer of refractory concrete. This layer is necessary to compensate for various thermal expansions of the anchor and concrete, as have different chemical composition and, accordingly, different coefficients of thermal expansion.
Installation of anchor products: marking and installation of anchors (ceramic and metal) is carried out in accordance with the project drawing No. VB39.01-02-01.
At the stage of installation of anchor products, it is necessary to pay attention to the fastening of ceramic anchors. After suspension of ceramic anchors in the design position, they must be unfastened with wedges, which, after laying the refractory of the working layer, removing the formwork, are removed without fail. These wedges are recommended to be fixed with a tie wire to prevent weakening of the structure when working with a vibrator at the time of laying the concrete of the working layer. Suspension elements must be tied with steel wire to ensure that these elements are held in the desired position. The wire (on suspension elements) remains and is not dismantled during further work.
Due to the presence of longitudinal load-bearing beams of the ceiling of the boiler furnace, part of the fastenings of the ceramic anchors of the side cards (the first row from the central axis of the furnace) are installed by welding (one side of the suspension elements), in order to avoid cutting the supporting structures and, accordingly, a possible decrease in the bearing capacity floor beam data. These forced forces do not adversely affect the design of the flat roof lining as a whole.
Metal hanging anchors are installed on metal hangers Ø25 mm, according to the project documentation. Due to the presence of longitudinal load-bearing beams of the ceiling of the boiler furnace during the installation of anchors, it was decided to add one metal anchor (4x30x350 mm) on the side maps of the horizontal section. Installing an additional anchor makes it possible to increase the reliability of fixing the concrete card and increase the number of attachment points to 9 pcs (against 4 pcs provided by the original design), reducing the specific load on the card anchor.
Before the formwork is installed, a gasket made of heat-insulating rolled material 5–10 mm thick is glued to the end part of the ceramic anchors to prevent concrete from getting between the anchor and the formwork. The end part of the ceramic anchor must remain clean, without a layer of concrete. This measure is necessary to prevent possible chipping due to possible thermal expansion of the ceramic anchor.
After the formwork is completed, the pre-prepared concrete mass BORTCAST-55W is poured into the formwork. An immersion vibrator is used to compact the concrete mass. To form expansion joints, the side surfaces of the cards are glued with rolled heat-insulating material.
The lining process continues along the entire horizontal section of the flat roof of the boiler according to the procedure described above.
After the pouring of the refractory concrete of the working layer, the laying of heat-insulating plates, the material of the heat-insulating layer, is started. The plates are cut to size and stacked as tightly as possible, the seams are clogged with rolled heat-insulating material. The subsequent layer is laid with an offset, with overlapping seams.
2. BULLNOSE TRANSITION LINING.
In parallel with the work on the installation of the lining of the horizontal section of the flat roof, work is underway on the transitional section to ensure the scope of work on the installation of the lining of the inclined sections of the flat roof (to optimize working time and reduce the time for repairs).
Installation of the T-beam for fastening anchors: During the execution of works, namely, works on the lining of the transition section of the "tooth" (Bullnose) of the boiler, a deviation in the metal structure of this section from the design documentation was found. In fact, the inner metal lining of the sloping sections of the roof forms an acute angle, and the lining, among other things, was made with a deviation from the project, based on the drawing of a general view of the boiler lining from the manufacturer. In order to minimize the financial and, most importantly, time costs for the plant associated with the dismantling / installation of metal structures for the casing of the inclined sections of the boiler roof, the specialists of Wellons.RU LLC decided to install a T-beam of the transition section of the “tooth” of the boiler (“Bullnose” ) in place, with welding of the beam to the existing metal structures of the roof. A detailed description and solution of the current situation is shown in the “explanatory note on the arrangement of the “tooth” and the inclined section of the furnace roof of steam boiler No. 1” under the number “No. Wellons.RU-01/22-09-2022”
Installation of anchor products: before the process of installation of anchor products and further actions for the installation of refractory lining, two rows of supports are installed, according to drawing No. VB39.01-02-01. These supports provide a reduction in the load from the lining of the inclined sections of the roof of the boiler on the transition section.
Anchors 3x30x150 mm are welded to the installed calipers of the first and second row. As a result, the design of the Bullnose section has three rows of anchors: the central row is ceramic anchors with fastening through suspension elements to the T-beam; two side rows - metal anchors with fastening by welding to the installed calipers. This anchoring system forms the most optimal fastening system within the existing metal structure of the boiler roof, without its global reconstruction, and ensures a long service life of the refractory.
Fastening of ceramic anchors is similar to the procedure described above, except that plastic wedges are used to open the anchors, which melt during the heating process and provide thermal expansion of the refractory and ceramic anchor.
Formwork installation, laying of refractory concrete mass, expansion joints are completely identical to those described in section “1. LINING OF THE HORIZONTAL SECTION OF THE FLAT ROOM OF THE BOILER FURNACE".
3. LINING OF THE INCLINED SECTION No. 1 OF THE FLAT ROOM OF THE BOILER FURNACE.
As it was mentioned earlier in section 2 (lining of the transition section), in the course of work, a deviation was found in the metal structure of the inclined sections of the flat roof of the boiler from the design documentation.
For example, sloping vaults have an internal fixed skin welded to the boiler's load-bearing beams. Those. the design of these inclined sections differs from the design of the horizontal section of the boiler roof, which has removable elements to provide access to the lining at its stage in the "explanatory note on the arrangement of the "tooth" and the inclined section of the furnace roof of steam boiler No. 1" under the number "No. Wellons.RU -01/22-09-2022. In the process of installing anchor products, in order to maintain a smooth transition from the “Bullnose” section to the horizontal section of the arch (on the inclined section No. 1), tee elements for fastening ceramic anchors of variable height are used on two rows of cards (from the section of the transitional “tooth”). These changes do not have a negative impact on the structural strength of the refractory lining of the flat roof of the boiler as a whole. The last row (border of the transition to the horizontal section) of ceramic anchors was installed in the design position by hooking the suspension elements of the ceramic anchor to the transverse I-beam of the boiler. To ensure engagement, at the places where the suspension elements were installed, holes were cut in the inner metal lining of the roof into which the suspension elements of the anchor were inserted. To ensure a strong fastening of the ceramic anchor, the suspension elements were fixed by welding in the desired position. The anchor was wedged with plastic wedges. Metal anchors were welded to the inner metal sheathing 5 mm thick.
After the stage of installation of anchor products, the stage of arranging a heat-insulating layer from heat-insulating plates was carried out. The plates are cut to size and stacked as tightly as possible, the seams are clogged with rolled heat-insulating material. The subsequent layer is laid with an offset, with overlapping seams.
Formwork installation, laying of refractory concrete mass, expansion joints are completely identical to those described in section “1. LINING OF THE HORIZONTAL SECTION OF THE FLAT ROOM OF THE BOILER FURNACE".
4. LINING OF INCLINED SECTION No. 2 OF THE FLAT ROOM OF THE BOILER FURNACE.
All changes associated with the presence of the internal metal cladding of the metal structures of the boiler floor are also inherent in this section of the roof.
To ensure engagement, at the places where the suspension elements were installed, holes were cut in the inner metal lining of the roof into which the suspension elements of the anchor were inserted. To ensure a strong fastening of the ceramic anchor, the suspension elements were fixed by welding in the desired position. When the anchor fastening hit the supporting longitudinal beam, the suspension elements fell in place. The anchor was wedged with plastic wedges. Metal anchors were welded to the inner metal sheathing 5 mm thick.
In the course of work, a number of changes were made in relation to the project in order to improve the design of the lining and its reliable operation, namely:
Formwork installation, laying of refractory concrete mass, expansion joints are completely identical to those described in section “1. LINING OF THE HORIZONTAL SECTION OF THE FLAT ROOM OF THE BOILER FURNACE".
5. RESTORATION REPAIR OF THE BOILER ARCH.
During the period of operation, with repeated collapse of the maps of the flat vault (as a result of the fall of maps weighing ~ 350 kg) directly in the zone of the arched vault, the two extreme rows of the straight section of the arched vault were destroyed
At the request of the specialists of the plant for the repair of this section, we studied the possibility of its restoration from the remnants of refractory materials left as a reserve from the main supply of refractory products during the construction of boilers. Based on the results of the analysis of the range of available refractory products, the following conclusions can be drawn:
As an alternative, an action plan was proposed to prevent further possible destruction of the arched vault of the boiler, namely, the installation of a reinforcing layer of refractory concrete, similar to the installation of a protective layer of concrete over a stepped inclined arched vault. This event will ensure the normal operation of the steam boiler until the main restoration work of the arched vault of the furnace is carried out. The corresponding photographs show the process of arranging the reinforcing layer of the arched vault.
6. RESTORATION REPAIR OF THE ARCHED BEAM OF THE TECHNOLOGICAL HATCH COVERING.
During the operation of the boiler furnace, the concrete frame of the technological hatch (the first on the right side of the boiler furnace loading device) had significant wear on the side walls and floor beams. If the presence of chips on the vertical side walls is not critical and does not have a critical impact on the operation of the boiler plant as a whole, the upper beam had to be changed. This beam had a through open (up to 20 mm) crack, large chips. Thus, this beam did not provide a bearing function, which is confirmed by the presence of “weak” masonry above the opening of the technological hatch.
It was decided to replace the existing beam with the one available from stock. The following works have been carried out:
7. PROJECT SUMMARY:
In our opinion, the main goal of the project of replacing the lining of the flat roof of the boiler, as well as increasing the service life of the refractory lining through the use of appropriate technical solutions, has been achieved. The main technical solution to increase the service life of the refractory lining and prevent periodic dropout of concrete maps is:
Due to the use of highly qualified lining specialists, as well as the help of the plant's specialists in solving organizational issues, all this made it possible to implement the project of replacing the lining of the flat vault of boiler No. , as well as the installation of the fan and the outer casing of the horizontal section of the boiler roof / the upper platform for servicing the equipment). The work was completed six days earlier than the planned date of work.
8. PORTFOLIO OF FINISHED WORKS TO REPLACE THE BOILER FLAT BOILER LINING.
