On April 1, 2021, according to contract No. I / 03 for the inspection of the object "Solid and liquid waste incinerators", the specialists of Wellons.RU LLC carried out a visual inspection of the existing refractory lining of the furnace No. 1. Inspection results are shown in this report.

Inspection of the lining, was carried out with the aim of determining the technical parameters of the facility, collecting initial data for the design of a new refractory lining of the furnace / waste incineration furnaces.

1. WASTE COMBUSTION FURNACE # 1: the oven is designed to incinerate various solid / liquid types of waste, including: various types of polyester, fiber polypropylene, polyester sludge, including ethylene glycol, various types of paper waste, solid activated carbon waste, oil waste, and also wood waste. This waste (solid) is loaded into a receiving chute and fed into the oven using a hydraulic pusher. Waste is fed into the furnace at regular intervals. Ash is removed into ash containers using a hydraulic pusher (periodically), and the flue gases undergo multi-stage cleaning in wet scrubbers. The furnace is ignited, the required combustion is maintained and the afterburning of the sublimation products is carried out using two gas burners. The furnace has two combustion chambers (primary and secondary), lined with heat-insulating and refractory materials.

 

 

1.1 PRIMARY CHAMBER / COMBUSTION CHAMBER.

Furnace hearth lining: the hearth structure is a kind of frame made of fire-resistant concrete on top of the metal body (bottom) of the furnace, which has special slot-like slots for supplying combustion air. At present, fireclay refractory bricks with hand-cut slots along the end, installed inside the "concrete frame", are used as grates. The photographs show the design of the "grate" of the furnace No. 2, made at the time of cleaning and carrying out routine maintenance. In our opinion, the presented grate design does not correspond to the original ones, since the cut holes, due to the small free cross-section of the grates, do not provide the passage of the required amount of air of the required pressure to ensure the normal combustion of the fuel. This assumption is confirmed when analyzing the state of the grate in furnace No. 1 (see photo on the right). We see that the holes in the grates in furnace # 1 are completely absent, clogged with slag / ash. The access of combustion air of the grate blast is completely blocked, due to the ingress of ash into the sawn slots of grate bricks / stones. The ash removal process also has a negative impact, which is carried out due to the movement of the hydraulic pusher, which even more "ramps" the ash in the small slots of the grate, thereby reducing the free section of the grate to its complete overlap. The pressure of the grate blast, for the normal operation of the grate, at the moment, is clearly not enough.

Solution! To ensure the normal operation of the grate, in order to supply a sufficient amount of air for fuel combustion, in the process of replacing the refractory lining or in the process of modernizing the furnace, the following solutions can be envisaged:

• Design and manufacture grate stones with the required free area (under factory conditions), sufficient for the passage of the required volume of combustion air with the required pressure, preventing the ingress of ash particles into the openings of the grate and their overlap in the ash removal process, respectively. With a possible overlap of the free area of the grate, the openings of the grates can be easily cleaned without dismantling them, in the process of carrying out routine maintenance.
• Reconstruction under the furnace, with the device of a heat-insulating layer and the supply of combustion air directly to the fuel combustion zone through the lateral tuyere holes. In this case, the risk of clogging the tuyere holes during the ash removal process will be excluded.

Wall lining: the original lining design provides for a two-layer lining, the working layer of which is made of aluminosilicate refractory concrete and an insulating layer of calcium silicate board. Shotcrete was used as a working layer. The thickness of the refractory concrete of the working layer is 105 mm, the thickness of the heat-insulating layer is 75 mm, the total thickness of the lining is 180 mm (on average).

The main defect in the lining of the walls is the presence of a large number of cracks with a sufficiently large opening of 5–10 mm or more, as well as a small number of lining chips, for example, in the area of the burner or the loading part. Cracks are located throughout the entire area of the lining of the walls in a chaotic manner and of varying concentration (somewhere there are more cracks, for example, in the area of the burner and the front wall - the section of transition to the secondary afterburner; somewhere to a lesser extent).

It can be seen that some time ago the lining was "repaired" by applying a thin layer of shotcrete to protect the lining from further destruction and cracking. Unfortunately, this method did not bring a significant positive effect, due to the too thin layer of the applied material - up to 15–20 mm. The thickness of this protective layer is very small and does not allow ensuring the mechanical strength of this layer. The material of this layer also has numerous cracks and in the process of operation began to peel off from the main working layer of the lining. This is very clearly seen in the photograph of the vault of the primary combustion chamber of furnace # 2.
The method of applying a thin layer of shotcrete over the main refractory of the working layer can only be used as a short-term solution in critical cases, as an "emergency" solution for hot repairs.
We would also like to draw your attention to the thickness of the existing shotcrete layer in the waste loading zone in kiln # 2. It can be seen that the thickness of the working layer on the refractory cleavage is no more than 20–40 mm, which is much less than the design thickness of the lining (90–105 mm). Due to the fact that the technology of refractory laying in furnaces No. 1,2 is the same, this fact can also be observed in furnace No. 1, even if the internal dimensions of the chambers are kept to the design dimensions.

The main reason for the formation of cracks is the violation of the technology of laying the refractory of the working layer of the lining. Regardless of what type of material and the method of laying it is chosen: gunning or casting, the working layer of a monolithic lining is always laid with cards with expansion joints (usually 10-13 mm thick). Expansion joints are filled with rolled thermal insulation material to compensate different thermal expansions of the furnace lining and body, respectively. The optimal size of concrete cards is 750x750 mm. The dimensions of the cards may vary upwards, depending on the design features of the equipment (selected individually).

In the existing lining of the walls and vault of the furnace chambers, there is no device for expansion joints in principle. As a result of thermal expansion of the lining, despite the small thickness of the working layer of the lining (90–105 mm), cracks form randomly and uncontrollably. Their concentration depends on the thickness and strength of the lining in different places. The operation of the furnace, associated with periodic loading of waste for incineration, also carries a negative factor of impact on the lining. The lining receives additional thermal shocks during heating / cooling of the lining, which leads to internal stresses in the lining, as a result of which cracks are formed. Unfortunately, their large number negatively affects the operation of the lining and equipment as a whole. Cracks progress, form chips, and the lining does not provide the necessary requirements for thermal protection and "tightness" of the lining from the penetration of aggressive combustion products of various types of waste to the furnace body, which will eventually lead to corrosion and burnout of the furnace body.

At the moment, during the reconstruction of the furnace, a complete replacement of the lining of the primary / combustion chamber of the furnace will be required.

Solution! Regardless of which type of refractory (monolithic / refractory concrete or molded / refractory brick) will be chosen as a replacement for the existing one, and regardless of which method of laying this refractory will be proposed (gunning / casting for monolithic lining), the design of the lining device should include obligatory arrangement of expansion joints in the working layer of the refractory. The device of expansion joints is necessary for any type of refractory, including a refractory molded brick lining (example in the photo), but for a monolithic lining it is simply a must!

1.2 SECONDARY CHAMBER / AFTERBURNER CHAMBER.

Wall lining: the original lining design provides for a two-layer lining, the working layer of which is made of aluminosilicate refractory concrete and an insulating layer of calcium silicate plate. Shotcrete was used as a working layer. The thickness of the refractory concrete of the working layer is 105 mm, the thickness of the heat-insulating layer is 75 mm, the total thickness of the lining is 180 mm (on average).

The main defects of the walls of the horizontal section of the afterburner, defects of the end walls are of a similar nature to the defects described in the section "wall lining" for the primary chamber / combustion chamber. The walls have numerous cracks, chips, are located chaotically, due to the lack of the necessary expansion joints. The combustion air supply tuyeres both in the end wall where the gas burner is located and the tangential air supply tuyeres (for mixing air with combustion products) are in a satisfactory condition.

We would like to draw your attention to the thickness of the existing shotcrete layer in the transition zone of the afterburner and the chimney (in the junction zone of the horizontal and vertical sections). It can be seen that the thickness of the working layer on the refractory cleavage is no more than 20–30 mm, which is much less than the design thickness of the lining (90–105 mm). This fact once again confirms that the technology of laying the lining, its design is the same for two furnaces. The shotcrete of the working layer, in the waste loading zone in the kiln No. 2, has the same thickness of the working layer (20–40 mm). Based on these two facts, it can be assumed that the lining of the entire furnace is thinner than the original design. The small thickness of the lining of the working layer can be one of the reasons for the increased formation of cracks in the absence of expansion joints.

At the moment, when carrying out the reconstruction of the furnace, we recommend that you completely replace the lining of the secondary / afterburner of the furnace, in order to solve the problems described above.

1.3 EXHAUST PIPE.

Wall lining: The chimney lining is divided into two sections: the upper section has a single-layer refractory lining made of 125 mm thick shotcrete; the lower section provides for a two-layer lining, the working layer of which is made of aluminosilicate refractory shotcrete (layer thickness 75 mm) and an insulating layer of calcium silicate plate (layer thickness 50 mm).

A visual inspection of the lining of the chimney and the elbow of the gas duct going to the system of scrubbers for cooling and cleaning flue gases makes it possible to conclude that the lining of these sections is in normal technical condition. There are no cracks, lining chips, in contrast to the lining of the primary and secondary chambers of the furnace.

The presented photograph shows the cardinal difference between the lining device, in relation to the lining of the furnace walls, with correctly formed maps and expansion joints between them. Lining with monolithic refractory cards, and the formation of seams between them, respectively, allows you to avoid increased internal stress in concrete when it is heated. These joints allow to compensate for the linear elongation / expansion of concrete when it is heated, maintaining its strength and preventing the occurrence of cracks and chips. Provide normal operation of monolithic refractory lining in this area as a whole.

At the moment, during the reconstruction of the furnace, there is no need to carry out any repair or replacement of the chimney lining, the chimney lining is in a satisfactory condition.

TOTAL:

Based on the results of visual inspection of the refractory lining of the "Solid and liquid waste incineration furnace", it is possible to draw a preliminary conclusion about the presence of a significant number of defects in the form of numerous cracks and chips of the lining, as well as the inconsistency of the furnace hearth in terms of the design of the used grate stones, which do not provide normal air supply for combustion of fuel waste. Possible reasons for the formation of defects, in our opinion, may be the following reasons:

• Violation of the technology of laying the refractory of the working layer of the lining - increased formation of cracks. Regardless of what type of material and the method of laying it is chosen: gunning or casting, the working layer of a monolithic lining is always laid using cards with expansion joints (usually 10–13 mm thick). As a positive example, you can use a lining device for the exhaust pipe from the secondary / afterburner chamber, which has a minimum number of cracks, chips and other lining defects, is in normal technical condition after long-term operation of the equipment.
• Thickness of the working layer lining - perhaps it does not correspond to the project. In the process of inspecting the lining, namely the existing chips in the fuel / waste loading zone of the furnace No. 2, and in the transition zone of the secondary chamber and exhaust pipe of the furnace No. 1, a deviation of the thickness of the working layer from the design was found. The project provides for a working layer thickness of 90–105 mm, in fact, we see a thickness of no more than 30–40 mm. These lining thicknesses have been found at various locations in the equipment and, moreover, on various production lines. If we take into account that a given thickness of the working layer lining can be in the entire furnace, this also explains the increased number of cracks in the working layer lining in the first and second furnace chambers.
• After a visual inspection of the first chamber of kiln # 2, we see similar defects described in this report for kiln # 1. The results of the inspection of furnace No. 1, as well as the recommendations issued on the lining of the furnace No. 1, in our opinion, can be applied to the furnace No. 2 in full.

GENERAL RECOMMENDATIONS:

At the moment, when carrying out the reconstruction of the furnace, we recommend that you completely replace the lining of the primary chamber (combustion chamber) and the secondary chamber (afterburner), in order to solve the problems described above. Repair or replacement of the chimney lining is not required due to its satisfactory condition.

We draw your attention to the following important factors in the formation of the technical specification for the lining device:

• no matter what type of refractory (monolithic / refractory concrete or molded / refractory brick) will be chosen as a replacement for the existing one, and no matter what method of laying this refractory will be proposed (gunning / casting for monolithic lining), the design of the lining device should include itself an obligatory arrangement of expansion joints in the working layer of the refractory. The device of expansion joints is necessary for any type of refractory, including refractory molded brick lining, but for a monolithic lining it is simply a must!
• Compliance with the minimum thickness of the working layer of the lining provided for by the project. We recommend increasing the thickness of the working layer of the lining to 115–120 mm (not less) to ensure the normal structural strength of the lining (chambers 1, 2).

All the photographs presented, as well as photographs that were not included in this report, but which allow assessing the technical condition of the refractory lining of furnaces for incineration of solid and liquid wastes No. 1, 2, were transferred on electronic media together with this report.