On April 25, 2024, specialists from Wellons.RU LLC conducted a technical inspection of the refractory lining of KTVm-5000 No. 1 and No. 2 hot water boilers at the customer's boiler house. The results of the technical inspection are presented in this technical report below.
It should be noted that in October-November 2019, Wellons.RU LLC, under the terms of the EPC contract (including project development, supply of refractory and thermal insulation products, as well as lining works), completed a project for the complete replacement of the refractory lining of boiler No. 2. The following year, after a successful heating season and confirmation of the correctness of the technical solutions used in the project to replace the lining of boiler No. 2, the customer decided to completely replace the refractory lining of boiler No. 1. This repair was carried out by Wellons.RU LLC in August 2020. During 5 years of operation of the lining of boiler No. 2, and, accordingly, 4 years of operation of boiler No. 1, there were no downtimes or any problems associated with the refractory lining of the boilers. A description of the technical condition and proposed measures to maintain the lining in working order is shown in the relevant sections of this report..
1. WATER HEATING BOILER #1.
1.1 Lining of vertical boiler walls – made of aluminosilicate refractory bricks with an Al2O3 content of> 35%. The condition of the refractory lining of all the walls of the furnace, including the side and end walls of both the fuel combustion zone (grate zone) and the end walls of the transition sections (combustion products afterburning zone) are in good technical condition, namely: there are no chips in the refractory bricks, no peeling of the lining from the design position, no cracks that have a negative impact on the structural strength of the lining, no areas with loose lining, etc. Directly in the fuel combustion zone, there are small ash deposits on the walls of the furnace, which do not have a negative impact on either the lining or the technological process. But, despite this, in order to prevent a further increase in the amount of ash deposits, it is advisable to carefully clean the surface of the walls with scrapers or a hard brush (non-impact method).
1.2 Technological hatches and doors, fuel chute - the lining of these units is made of monolithic refractory - refractory concrete with an Al2O3 content of> 55%. The condition of the refractory lining of the process hatches, their frames, as well as the lining of the outlet part of the boiler loading chute is in good technical condition, there are no lining defects that pose a risk to further operation of the boiler as a whole.
Photos of the technical condition of the lining of the walls of boiler No. 1:
Recommendations for restoration of the lining of the furnace walls: no measures are required to carry out restoration work on the refractory lining of the furnace walls, with the exception of cleaning ash deposits on the walls of the boiler furnace.
1.3 Arched vaults of the boiler - shaped brick with Al2O3>40% content is used as a refractory material for the vault. The boiler has three vaults located on top of each other, according to the design of the boiler equipment manufacturer. A description of the technical condition of the lining of each of them is shown in the relevant sections below.
Arch No. 1 – the lower arch directly above the grate zone - the arch is in normal / good technical condition. There are no significant defects that affect the structural strength of the arch structure (such as arch sagging, arch opening, refractory chips and cracks, etc.). The exception is the first / outermost row of the arch, which is the edge of the arch and is located directly in the combustion zone. This row is primarily subject to various technological impacts that occur during boiler operation, for example, when the quality characteristics of the fuel change, when the boiler thermal load changes (increase / decrease in boiler productivity), cooling / heating when the boiler is stopped during its operation. As a result, this row / arched segment of the arch structure is subject to increased thermal loads and, due to the occurrence of sharp variable thermal loads, has chips and cracks in the brick.
Despite the existing defects (chips, transverse cracks in the brick), this row has the required strength - it does not sag or wobble. Moreover, even the collapse of this row, during further operation of the boiler, will not lead to a disruption of the technological process of fuel combustion or boiler productivity - i.e. there is no risk of stopping the boiler for this reason (possible collapse of the first row of vault No. 1).
Recommendations for restoration of the lining of arch vault No. 1 – during the restoration work on vault No. 2 (see below), it is recommended to restore the first row / arch segment of the vault, as well as to carry out local wedging of the arch segments if necessary.
Arch No. 2 – has a satisfactory technical condition, for example, in the fuel combustion zone and for ~ 2/3 of the total length of the arch does not have any significant defects - the arch is smooth, without openings, chips, etc. The final part of ~ 1/3 of the length has a visible opening of the arch outward, which is quite strange, since usually the arch is prone to sagging, due to the expansion of the walls of metal structures, and in this case everything is the opposite, as if the metal frame was compressed, although the walls (as was said above) do not have visible violations of the geometry of the walls, the lining is not squeezed inward. This opening outward can be explained by the effect of high temperatures in the afterburning zone of combustion products on the edge of the second arch and, accordingly, the occurrence of increased stresses directly inside the arched segment. This end section of the arch is primarily subject to various technological effects arising during fuel combustion and is subject to increased variable thermal loads. As a result of these loads, the three outer rows of vault No. 2 collapsed, as well as a visible opening of the vault (see description above) by ~ 1/3 of the length of the arched vault.
Recommendations on restoration of the lining of the arch vault No. 2 - due to the important technological component of this vault in the process of fuel combustion, namely, preventing the "direct passage" of the gas flow into the convective part of the boiler, in the event of its complete destruction, it is recommended to completely restore this arch vault according to the project. We recommend that the restoration be carried out as follows: clean and blow out the entire outer surface of the arch vault to a clean brick surface; blow out all the "openings" of the vault, install a circle under the corresponding segments that have an opening of the vault, remove the key brick, settle the bricks "in place", install the key bricks, wedge the vault with metal plates 2 mm thick. Restore three destroyed rows of the vault using the appropriate shaped products (according to the design layout of the brick of the arched segment of the vault). To prevent the opening of the end section of the arched vault, it is possible to consider the possibility of installing a concrete screed made of monolithic refractory concrete, on top of the arched structure, 75-100 mm thick.
Arch No. 3 – the upper vault is in good technical condition. There are no defects that could affect the structural strength of the vault structure (such as vault sagging, vault opening, refractory chips and cracks, etc.).
Recommendations on the lining of arch vault No. 3 – restoration work on this vault is not required. It is recommended to clean the vault surface from ash deposits and clean the ash in the transition chamber to the convective part of the boiler.
RESUME:
Based on the results of the technical inspection of the refractory lining of boiler No. 1, it can be concluded that more than 95% of the refractory, after 4 years of boiler operation since the last lining replacement (August 2020), is in good condition. The exception is the second arch, namely its end section ~ 1/3 of the length of the entire arch. In this section, the arch is opening and the three outer arched rows have collapsed. In this section, we recommend carrying out restorative repairs to ensure safe operation of the boiler until the next major repairs. Implementation of the recommended measures will extend the lining work campaign for at least the next 2-3 years.
2. WATER HEATING BOILER #2.
The boiler lining is generally in good technical condition - all the main elements of the lining, such as: horizontal and vertical walls, process hatches and openings, as well as the monolithic lining of the fuel trough, do not have significant defects that could lead to the boiler shutdown due to the destruction of the lining during the heating season. This also applies to the arched vault structures of the boiler. Unfortunately, the boiler was not completely cleaned for inspection, and this conclusion is based on an incomplete inspection of the boiler. After cleaning it, we ask the boiler specialists to independently inspect the second and third vaults from the side of the upper process hatch and send us photographs of the inspection.
Photos of the technical condition of the lining of the walls of boiler No. 2:
Recommendations:
1. Technology - Please note that in the fuel combustion zone in the area of the tuyere holes and directly on the front end wall there is a significant amount of molten ash drips. This factor indicates a significant increase in temperature in the boiler furnace, directly in this combustion zone. This can be caused by various factors from the quality characteristics of wood fuel to problems with monitoring or conducting the technological process and managing the hot water boiler as a whole. We recommend that boiler room specialists and operators pay attention to compliance with the technological regulations for controlling the boiler and the technological process of fuel combustion, including the control values of thermocouples and the correctness of their operation.
2. Lining – please note that the first arched row of vault No. 1 has brick chips and one of them has fallen out halfway. The brick of the first row also has transverse cracks (the description of the reasons for possible destruction is similar to those described in section “1. Hot water boiler No. 1”).
Despite the fact that this row is in the design position and has a strong structure, we recommend replacing this row in parallel with the planned work on restoring the lining in boiler No. 1. At the same time, the structures of all three vaults, after cleaning the boiler, should be strengthened if necessary and, if possible, by additional wedging with metal plates..
RESUME:
Based on the results of the technical inspection of the refractory lining of boiler No. 2, it can be concluded that almost all the refractory, after 5 years of boiler operation since the last lining replacement (November 2019), is in good condition. No restoration work of the refractory lining of the hot water boiler is required, with the exception of the recommendations described above. The decision on the installation of an additional belt of monolithic refractory at the end section of the second arch (in order to avoid a repeat of the situation on boiler No. 1) is made after a complete cleaning of the boiler, during the general restoration repair work on hot water boilers No. 1, No. 2.
