On February 25, 2020, specialists of LLC Wellons.RU performed internal inspection of the technical condition of the refractory lining of the boiler KVT-4000 E. The results of the inspection of the lining are shown in this report.
External inspection of the boiler did not reveal any visible defects in the casing of the boiler body, there are no obvious burnouts of the shell or deformation of the boiler body as a result of a possible increased temperature effect on the body (for example, in case of boiler overheating, collapse of the lining of the boiler walls, etc.)
Internal inspection of the lining of the boiler (two-arch design of the lining): due to the fact that the boiler is new and has been in operation for less than 2 years, the general condition of the lining should have been much better than that of boiler No. 1. Unfortunately, the existing number of reasons carries significant risks that affect the structural strength of the lining and the reliable trouble-free operation of the boiler as a whole.
Lining of the grate zone of the boiler: Lining of the fuel gutter, lining of the walls, condition of the tuyere holes, technological manholes and viewing windows, especially in the under-arch zone of the boiler, are in normal technical condition. There are no cracks, chips that have a negative effect on the process or on the lining resistance. Moreover, it can be argued that the temperature in the under-arch space is quite low - the existing metal parts of the boiler in the open state in the fuel combustion zone do not have traces of temperature effects. This fact may indicate a violation of the technological process, namely, it shows a shift in the main process of burning fuel to the loading part of the boiler, i.e. to the fuel trench, as evidenced by the following factors (see below).
Lining of the fuel supply zone / transition shaft to the boiler afterburning zone: in the lower grate of the boiler in this section there are large ash and slag deposits on the walls of the boiler, which go into the vitreous phase above, in the area of the second roof. This indicates that the temperature in this zone of the boiler reaches periodically or permanently, up to 1100-1180 ° С. This temperature leads to the melting of the ash with the formation of a glassy phase, which enters into a chemical reaction with aluminates of refractory bricks. As a result of the reaction, chemical corrosion (alkaline) of the refractory brick occurs, and it gradually breaks down.
This process is very clearly visible in the photographs given. The glassy melt flows down the arch and the walls and primarily destroys the brick in the seams of fire persistent masonry. The destruction of the brick in the vertical joints of the masonry reaches 25-30 mm. This suggests that this process is a constant or at least often repeated process. Almost the entire upper part of the walls of the transitional shaft looks like pavers, i.e. It has pronounced defects in masonry joints (vertical and horizontal). It makes sense to pay attention to algo the rhythm of the boiler control system as a whole. When breaking off this glassy phase in the lower part of the walls - pieces of slag break off together with the surface layer of brickThis process is very clearly visible in the photographs given. The glassy melt flows down the arch and the walls and primarily destroys the brick in the seams of fire persistent masonry. The destruction of the brick in the vertical joints of the masonry reaches 25-30 mm. This suggests that this process is a constant or at least often repeated process. Almost the entire upper part of the walls of the transitional shaft looks like pavers, i.e. It has pronounced defects in masonry joints (vertical and horizontal). It makes sense to pay attention to the algorithm of the boiler control system as a whole. When breaking off this glassy phase in the lower part of the walls - pieces of slag break off together with the surface layer of brick.
Please note that the refractory brick of the arched part of the transitional shaft of the boiler has a huge number of thin cracks - there is not a single whole brick, alt-hough the integrity of the structure of the whole is not violated. This type of brick destruction is also a conse-quence of local overheating of the lining and the occur-rence of internal thermal stresses arising from the ther-mal expansion of the refractory material and the ab-sence of mechanisms for its compensation. Further operation of the boiler, with increased temperature conditions, can lead to the destruction of the lining of the vault structure in this area.
Lining of the lower boiler furnace vault: the first half of the vault on the side of the boiler’s loading part has been replaced due to collapse or wear due to the effect of maximum temperatures from fuel combustion in this section, as well as due to the design features of the boiler vault described in detail in parts of boiler inspection No. 1. We consider it necessary to once again draw attention to the fact that the main structural feature of the existing arch is a gentle arch with a large radius of curvature. The design of such a vault does not provide the proper strength of the vault, especially at sufficiently frequent stops of technological equipment. Due to residual temperature deformations generated by the pressure of the arch on the walls of the lining and the metal walls of the boiler body, respectively, the “opening” of the arch occurs, i.e. subsidence of the central dome with the formation of large open cracks. On this vault there is a pronounced disclosure of the vault along its entire length. The width of the disclosure of the masonry is on average 10-15 mm. In these plac-es, the failure of the vault segments is already visible, which will only be aggravated in the process of further operation of the boiler. Taking into account the short period of operation of the boiler (less than 2 years from the moment of start-up), the presence of these defects on the roof looks more than strange, and apart from constructive solutions of the arch, as well as possible violations of the technological regime of fuel combustion, the appearance of these defects cannot be explained
lining of vertical walls, lining of the process hatch, lin-ing of the vault design do not have significant defects that could adversely affect the overall service life of the lining. It should be noted that all the walls and the arch of the boiler afterburning zone are covered with signifi-cant slag deposits, which characterizes the presence of significant temperatures. These slag deposits are quite strong and, when removed, break off together with the brick surface, this is especially clearly seen at the junc-tion of the lower arch with the vertical walls of the boiler at the transitional mine. Despite the fact that there is no visible opening of the upper arch (at least they are not visible, it may be due to slag deposits), but when examining the boiler input shaft into the fire tube, it can be seen that the arch in the transition section sagged with the formation of a large open crack at the junction brick and refractory concrete head shah. How much will this problem pro-gress will be shown by further operation of the boiler.
We also draw your attention to the large deposition of ash particles on the tube sheet of the fire tube boiler. The thickness of ash and slag deposits reaches 50 mm or more, formed as a result of the above technological problems.
TOTAL: despite the fact that most of the lining is in normal technical condition, there are a number of significant reasons that do not allow us to conclude that this lining will work reliably in the next 1-3 years without repairs. Taking into account the above-mentioned facts, as well as the lines for which these problems arose (operation of the boiler No. 3 for less than two years), it is practically impossible to predict how quickly (or whether) these or other de-tected defects will progress - this depends on many factors, primarily from the technological parameters of the operation mode of the boiler, start / stop cycles and other factors. The main problem areas: the lower arch of the boiler furnace and the transition shaft to the afterburning zone boiler (fuel supply zone). These two zones carry the maximum thermal load and are most exposed to temperature influences. At the moment, these zones have significant defects, which can affect the overall durability of the lining and the reliable operation of the boiler as a whole.
As possible measures to prepare for the repair of refractory lining, we recommend that you consider the fol-lowing development options, namely:
When choosing the option of periodically replacing / repairing the lining of a particular section, it is difficult to achieve reliable operation of the equipment of the boiler for a long period of time. In fact, you will have to deal with expensive repairs immediately after or before each heating season, having the risk of collapse of the lining of a particular site in the heating season. Choosing the option of completely replacing the lining, you, at lower comparative total costs, will get the most reliable boiler with trouble-free operation for a long period (5-7 years minimum).
To estimate the budget of possible costs for lining works, we made an approximate calculation, which is based on the measurements made during the technical inspection, as well as on the basis of the sketch drawing shown in the boiler passport. Unfortunately, detailed technical documentation, namely detailed lining drawings for these boilers, is missing. The calculations are based on the terms of the EPC contract and include the follow-ing work: engineering; selection, manufacture and supply of refractory and insulation materials; necessary anchor products; transport services; lining work (work on breaking the existing refractory is not included in the cost of work). The cost of replacing the refractory lining of the boiler is shown in the table:
