On October 22, 2020, according to an agreement for a visual inspection of the state of the existing refractory lining of 4 cells of the Wellons boiler, "Wellons.RU" specialists carried out a technical inspection, the results of which are given below.
1. BOILER’s HEARTH REFRACTORY (BURNING AREA):
The lining of the bottom of the boiler and the necks of the cells (the outlet of cells to the boiler) is in a satisfactory condition. There are no significant lining defects that require immediate action. The adjoining of the boiler hearth liner (refractory fireclay tiles) with refractory concrete has a satisfactory condition. The collectors of the side and front screens have no significant visible damages. The lining of the walls of the water screens is in a good condition. The "retaining" wall of the front screen is slightly overwhelmed outward, but its integrity is preserved.
The uneven thickness of the monolithic lining of the necks of the boiler furnaces is observed - the thickness is from 230 mm to 130 mm. The state of the lining of these units must be additionally monitored at each technological scheduled shutdown of the boiler for routine maintenance. Taking into account the technical condition of the lining inside the furnaces (see description below), this deviation is not critical. With a high degree of probability, a deviation in the thickness of the furnace neck lining could be obtained during its installation (in the process of direct formation of the furnace throats). If this deviation in size is of an actual nature and during the further operation of the boiler, increased wear of the lining will be noticeable in these areas, it is necessary to provide for a number of technical measures during the period of the subsequent planned shutdown of the boiler. In general, the boiler hearth lining is in a satisfactory condition.
The pipe part of the boiler (front, rear and side screens, collector) is in good condition. Insignificant ash deposits on the walls of the screen pipes can be removed with the help of improvised means (scraper, brush) manually or mechanically. Ash deposits in the corners of the bottom of the boiler - in the dead zone, as well as on the collectors of water screens, require periodic cleaning to prevent their sintering.
2. CELLS’ REFRACTORY:
The furnace lining has been in operation since 2008, and after the boiler was put into operation for 12 years, it has not undergone significant refurbishment. Despite the long term and "heavy" operating mode of the boiler in the incinerators’ mode, in order to utilize production wastes with a high degree of contamination like (sand and other impurities) and high average fuel moisture up to 65% and more, the boiler furnace lining is in a satisfactory condition. Because of disposal of contaminated fuel in the cells, ash deposits are present on the walls of the furnaces. To assess the degree of wear of the boiler furnace walls, numerous measurements of the internal diameter of the furnaces were carried out at different heights. The measurement results were compared with the design internal diameter of a 9-foot cell, which is 2740 mm, and the design wall thickness of 230 mm. Detailed information on measurements and the general technical condition of the lining, for each of the furnaces, presented below:
Cell №1 – technical inspection: almost 1/3 of the furnace circumference has significant ash and slag deposits (especially in the lower part), which partially or completely overlap the sections of the tuyere openings, carrying a negative effect on the combustion process (incorrect distribution of air supply to the fuel combustion zones). Cleaning of furnaces from these depositions must be carried out carefully, so that the refractory of the furnaces does not break off along with ash and slag build-ups, while maintaining the design thickness of the walls of the refractory.
As mentioned above, to determine the thickness of the walls of the refractory lining of the furnace, a number of measurements were carried out in two or three diametrical perpendicular directions (cross to cross), in places previously cleaned from ash and slag deposits, namely:
According to the results of measurements, we see that the deviation in measuring the internal diameter of the furnace from the design value (2740 mm) is from 10 to 80 mm. Thus, the decrease in the thickness of the refractory wall in the furnace No. 1 is from 5 to 40 mm per side. Even taking into account the possible measurement error (possible non-observance of the perpendicularity when measuring the internal diameter of the furnace), it can be stated that the wear of the refractory, over 12 years of heavy boiler operation, is minimal.
After cleaning the boiler furnaces from ash and slag deposits, it may be necessary to carry out refurbishment of the lining of the fuel chute (satisfactory condition), as well as the lining of the lower belt in the area of the grate shafts.
Cell №2 – technical inspection: the situation with the presence of ash and slag deposits is similar to the situation described in the section on cell No. 1. The main ash and slag build-ups are observed in the fuel combustion zone, in the zone of fuel pile formation in the furnace.
After cleaning the boiler cells from ash and slag deposits, it may be necessary to carry out refurbishment of the lining of the fuel chute (satisfactory condition), as well as the lining of the lower belt in the area of the grates.
Measurements of the internal diameters of the furnace showed the following results:
The dimensions are smaller than the design ones, probably due to two possible reasons - the first reason is non-compliance with the design dimensions during the installation of the lining (which was good thing afterall); the second reason is a slight deviation from the center line when taking measurements of the inner diameter. Despite this, it can be stated that the wear of the refractory monolithic lining of the furnace No. 2 is minimal. The wall thickness is close to design. This is confirmed by additional auxiliary measurements of the lengths of the tuyere holes - they are actually equal to the lengths of the tuyere holes in the furnace No. 1 and are: in the furnace No. 1 - 210 mm, in the furnace No. 2 - 220 mm. The uniform length of the tuyere holes characterizes the uniform wear of the refractory lining of the boiler walls. According to calculations, the wall thickness of the refractory of the furnace No. 2 is at least 190-200 mm. We see that the use of a highly refractory and wear-resistant refractory material (analogue of WELL-PLAST P85) allows achieving minimum wear in 12 years.
Cell №3 – technical inspection: it should be noted that there is a significantly smaller amount of ash and slag deposits in this furnace. Inner diameter measurements showed the following results:
We also see the dimensions of the diameters less than the design one, equal to 2740 mm. After analyzing additionally, the geometry of the walls of the furnaces, from the elevation of the boiler bottom, we can speak with a high degree of confidence about the deviation in the thickness of the refractory at the time of its installation in the furnaces of the boiler (the thickness in fact was somewhat larger than the design one). We see from above that the walls are even, without visible critical blockages of the lining inside, or violation of the geometry of the lining. Thus, we can also say that the thickness of the lining is within the project (plus / minus) and is 200-230 mm.
Cell №4 – technical inspection: it is necessary to pay attention to the photograph of the neck of the furnace No. 4 - it is clearly seen that the thickness of the lining at the outlet of the boiler is not uniformly made and has a significant thickness, which confirms the assumptions made above (the possibility of laying the lining at the installation stage of greater thickness than indicated in the project 230 mm). Measurements of the inner diameter showed the following results:
Taking into account the auxiliary measurements of the lengths of the tuyere holes (on average 220 mm) it can be assumed that the thickness of the refractory wall is at least 200-210 mm.
After cleaning the boiler furnaces from ash and slag deposits, it may be necessary to carry out refurbishment of the lining of the fuel chute (satisfactory condition), as well as the lining of the lower belt in the area of the grate shafts.
The main attention shall be paid to the presence of open transverse cracks in the lining (see photo on the right). If they are present (this is true for all boiler furnaces), it is necessary to provide measures for their restoration (a description of the recommended solution is shown below). Transverse cracks that do not open do not need to be treated. Cracks with a small opening angle are repaired according to the procedure described below.
3. GENERAL RECOMMENDATIONS FOR CRACKS REPAIR:
1. Repair of cracks with a small opening angle or chips:
2. Reconstruction of open through cracks:
TOTAL: a visual inspection of the Wellons boiler furnace refractory lining showed the possibility of further operation of the boiler furnace lining, subject to the lining recommendations described in this report. Due to the recommended service life of the refractory lining by the manufacturer (WELLONS) equal to 8-10 years, it is necessary to constantly monitor possible changes and, if necessary, plan refurbishment, and if it is impossible, plan a complete replacement of the boiler furnace refractory.
