The sintering brick production line of a factory adopts a hanging flat roof tunnel kiln with a width of 4.6m and a length of 130m. Each kiln can accommodate 30 kiln cars, which can better meet the production scale of 60million standard bricks per year. At the same time, the brick quality is well guaranteed. The fire-resistant concrete ceiling of the tunnel kiln is made of aluminate cement, and the fire-resistant aggregate is prefabricated in the formwork. The main specification is 720mm × 720mm top plate is lifted and leveled, and the strength of the plate is high after curing at room temperature. After that, the fire-resistant hoist and the heat-resistant steel hook shall be assembled and installed in the four reserved holes of the fire-resistant concrete ceiling. During the construction of the tunnel kiln, the hanging flat roof is suspended and combined into the kiln roof of the tunnel kiln through H steel main beam, l steel secondary beam and steel hook. In order to ensure the flatness of the ceiling plate in the tunnel kiln, the gap between the plates is filled with ceramic fiber blanket. During the six-year production process of the plant, the tunnel kiln's fire-resistant concrete hanging flat roof fell off due to temperature changes, erosion of harmful gases, quality differences of precast slabs and defects in the kiln drying system. Especially in the 9-14 parking spaces in the transition section between the tunnel kiln's pre heating zone and the high-temperature roasting zone, the ceiling fell off seriously.

Failure mode of refractory concrete ceiling slab

The 4.6m, 130m long suspended flat roof tunnel kiln can accommodate 30 kiln cars. Except for one parking space preparation room at the entrance end, the cast-in-place concrete top plate is adopted, and the whole kiln length adopts fire-resistant concrete ceiling plate. According to the distribution of the preheating zone, high temperature zone and cooling zone of the tunnel kiln, the brick billet gradually rises from the room temperature at the incoming end to the maximum roasting temperature of 1050 ℃, and then gradually cools down to obtain the finished brick. Corresponding to the firing temperature curve and kiln car parking lot, the damage of fire-resistant concrete ceiling slab is concentrated in the interval between 9 and 14 parking lots with the temperature range of 800 ~ 980 ℃, and the damage of ceiling slab in other intervals is less. The damage of fire-resistant concrete ceiling slab is mainly manifested in the following forms.

(1) At the fire-resistant hoist at the four corners of the ceiling plate, one or two corners were broken, causing the ceiling plate to fall.

(2) The surface of ceiling board is loose and peeled.

(3) The ceiling board is cracked as a whole, and the ceiling board falls.

(4) The surface of the heat-resistant steel is corroded and peeled, the strength decreases, and the ceiling plate sinks.

Selection of repair scheme

The damage of the fire-resistant concrete hanging flat roof of the tunnel kiln in the plant is mainly concentrated in 10 ~ 14 parking spaces. After removal, two schemes are considered for the repair of ceiling slab, one is to still use fire-resistant concrete ceiling slab, and the other is to use ceramic fiber module. Due to the short time required for the enterprise to resume production, such as the use of fire-resistant concrete ceiling slab, the prefabrication of ceiling slab, the procurement and construction of fire-resistant hoist, the total repair time is too long. After comparison, it is decided to use ceramic fiber module to repair the hanging flat roof of tunnel kiln.

Implementation and effect of restoration scheme

Ceramic fiber module, 304 stainless steel screw bolt anchor, thermal insulation cotton and other materials are used, and the original H steel main beam and l steel secondary beam are used to realize the repair of the hanging flat roof of the 4.6m tunnel kiln. The repair length is 10 ~ 14 parking spaces, and the length is 22.5m. See Table 1 for main materials.

The original l-steel secondary beam is suspended with fire-resistant concrete ceiling slab. During the repair construction, heat-resistant steel anchors are welded on the l-steel secondary beam at a spacing of 306mm. Seven pieces are welded at one section and eight pieces are welded at one section. Then ceramic fiber modules are installed on 304 stainless steel anchors. The two sections are combined to obtain 15 fiber modules in the direction of 4.6m kiln width, with a combined length of 4590mm. Two sections of L steel secondary beams with 15 fiber modules are respectively suspended on four l steel secondary beams through screws, and the four l steel secondary beams are installed on the H steel main beam on the original tunnel kiln. The ceramic fiber blanket is fixed between each row of ceramic fiber modules by U-nails, and the ceramic fiber blanket is covered above the ceramic fiber modules.

Table 1 main materials for repair

Serial number

Name and specification

Company

quantity

remarks

one

Ceramic fiber module

300mm × 300mm × 300mm

block

one thousand and thirty-five

15 pieces per row

69 rows in total

two

304 stainless steel screw bolt

M6-150mm

set

one thousand and thirty-five

three

ceramic fiber blanket 

kg

four hundred and eighty-eight

four

Ordinary ceramic fiber blanket

kg

five hundred and thirty

five

304 stainless steel anchor

set

one thousand and thirty-five

six

curing agent

kg

two hundred and seven

seven

U-shaped nail

individual

eight hundred and twenty-eight

For the coal feeding hole on the kiln surface, a 120mm hole is rotationally cut on the ceramic fiber module through a self-made circular knife, cast iron pipes are installed, and curing agent is used to fix the fiber.

After the ceramic fiber module and other materials arrive at the site, the repair period of lifting the flat roof is about 5 days.

The ceramic fiber module is used to repair the flat roof of the 4.6m tunnel kiln crane. There are 5 parking spaces with a length of 22.5m. The material cost and freight are 80000 yuan in total. The total material cost is about 92000 yuan when the cost of the used l steel secondary beam and screw bolts are included.

The cost of repairing the ceramic fiber module hanging flat roof of 4.6m tunnel kiln is 4100 yuan /m (excluding labor cost).

After the kiln was ignited and put into operation, the sealing performance of the kiln surface was improved, there was no smoke leakage in the ceramic fiber module repair section, and there was no fiber felt falling off the kiln car and brick stack surface. The thermal system of tunnel kiln is not affected, and the quality of sintered brick products is improved.

The practice and operation results of repairing the hanging flat roof of 4.6m tunnel kiln with ceramic fiber module show that this method is feasible and reliable.