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Contents

Installation technology of air ducts of sewage treatment plants

1. Split the axis of the main duct

2. Arrangement of pits - pits

3. Installation of supports - racks

4. Installation (welding) of duct pipes

5. Laying of air duct on supports

6. Duct test

Literature

Installation technology of air ducts of sewage treatment plants

Work on the installation of the air duct begins after the main construction work on the construction of the aerotank, at the same time support cushions for the air duct and on the brackets of steel or reinforced concrete remote platforms for the installation of gate valves on the branches of the air duct to the aerators laid along the bottom of the sections are installed in the structure of the transition bridges.

Installation openings shall be left for installation of distribution air ducts laid on transition bridges and air duct lowers to aerators, as well as for installation of other equipment in section walls.

The sequence of installation of the external air duct of the aerotank is similar to the installation of the above-ground gas pipeline laid on supports - struts and brackets:

1. Layout of main duct axis and elevation of supports installation places.

2. Pits for the installation of supports - racks are dug up with a pit;

3. Metal or reinforced concrete posts with embedded in consoles for sliding supports are installed in pits - pits for crushed stone preparation. In this design, the supports are accepted as metal pipes with a diameter of 100 mm.

4. After installation of supports, M 100 grade concrete is poured into pits

5. Installation (welding) of air duct pipes with installation of shaped parts is carried out in close proximity to the place of supports installation. Installation (welding) of branch and lowering sections is performed along separation air ducts along longitudinal walls of extreme sections.

6. The installed sections are laid with the help of a pipe-laying crane or a crane equipped with a boom up to 20 m long.

7. The main air duct shall be laid on the supports - struts after concrete strength is not less than 50%.

8. Air duct is tested by air pressure (1.25 working pressure) in the area from the blower to the mating flanges of the valves at the lowering

9. After the test, the welded joints of the duct shall be painted.

Split the axis of the main duct

The transfer to the area of ​ ​ the position of the duct axis is carried out by a geodetic tool with reference to the axis to permanent landmarks - already erected structures, in this case an aerotank. This work is carried out by the surveyor of the construction organization and accepted by act by the master of the installation organization.

At the same time, the place of installation of supports - posts is marked along the axis, their position is fixed by metal pins.

Arrangement of pits - pits

The pits are drilled by means of a crane rig mounted on a wheeled tractor. The dimensions of the pit are determined by calculation - the diameter and depth of the support, according to these data, a drill is strengthened on the installation.

Installation of supports - racks

A 150 mm thick layer of crushed stone falls into dug pits. Metal supports are installed in the pits of the crane installation - posts on the lower end of which steel support heels measuring 500x500mm are welded with a thickness of 5 mm, and on the upper end, made of channel No. 4 and angle 50x50mm, support structures for sliding supports of the air duct. The height of the racks shall ensure the position of the duct according to elevation + 0.7 m above ground level (red elevation - layout). The struts come from the procurement workshop painted - the upper part with oil paint or enamel, and the lower part with bitumen mastic.

After the rack is installed in the pits for crushed stone preparation and their verticality is checked by the plumb, M 100 concrete is poured into the pits. Before laying on the air duct racks, concrete must gain a strength of at least 50%, that is, a time of about 5-7 days is necessary.

Installation (welding) of duct pipes

Pipes and shaped parts come to the mounting platform painted, with the exception of the end part (welding place) with a length of 250-300 mm.

Before welding works start, end faces shall be inspected and checked for ellipsicity, dents and nicks by the value exceeding GOST tolerance for these pipes. The difference in pipe wall thickness shall not exceed the permissible standard.

The ends and adjacent internal and external surfaces are cleaned to metallic gloss with special brushes or an electric cleaning machine.

Given the large diameter of the duct pipes, especially its main part,

pipes are pre-connected by electric welding on grips with length of 6080mm, at the same time, since pipes of electric welding their seams must be displaced by at least 100mm.

Prior to assembly of pipes as a whole, sliding supports are welded to them at the calculated length value; when assembling pipes, the conditions of strict alignment of the latter should be observed. Shaped parts (tees, crosses and taps) should be installed, fulfilling the requirements of their assembly according to the installation diagram of the duct and its positions on the support structures (posts, bridges, platforms).

Laying of air duct on supports

The installed section of the duct is laid by the crane-pipe laying or autocrane using a crossbeam, if the length of the crossbeam is not enough to lift the section (the permissible length for pipes with a diameter of up to 500 mm - 15 m), then two cranes are used. The crossbeam with the pipe is directly connected using soft (tarpaulin) towels fixed on rope loops. Lifting of duct section shall be performed smoothly without jerks, as well as smoothly and descend to supports. It is not allowed to shift pipes along supports in longitudinal direction without lifting.

Welded joints connecting sections to each other shall be located from supports not closer than 200 mm

Installation of gate valves is performed after laying of duct sections on supports.

Duct test

Test of the installed air duct is performed by pneumatic method with pressure equal to 1.25 of the working one from the blower outlet flange to the mating flange behind the gate valves installed on the air duct drops to the aerators. Gate valves are designed for pressure much higher than the working air duct, so it is not rational to replace them for the test period with "coils." Test time - 2 hours from the moment of pressure rise.

The duct shall pass the test if the pressure drop does not exceed 441 Pa.

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